Multi-access edge computing (MEC) enhances users’ computing capabilities. However, it still faces the queue instability challenge due to the conflict between limited communication-computation resources and the massive access of users. In this paper, we invoke a multiple one-to-one queuing system in a non-orthogonal multiple access (NOMA)-MEC network, where NOMA enables massive access, and study its network stability and queuing delay control mechanisms. Meanwhile, we jointly consider the many-to-one queuing system. We formulate two network power minimization stochastic problems, each subject to the stability of the multiple one-to-one/many-to-one queuing system. We propose Lyapunov-based algorithms to solve these problems analytically and achieve a computational complexity of approximatelyO(N)withNusers. We further investigate the queuing-delay control mechanism in the multiple one-to-one queuing system-based NOMA-MEC network. Numerical results show that the proposed algorithms converge efficiently, effectively stabilize queuing systems, satisfy the queuing-delay requirement, and further demonstrate that: 1) the proposed multiple one-to-one queuing system-based NOMA-MEC exhibits a better balanced load distribution between users and the MEC server compared to orthogonal multiple access (OMA)-MEC; 2) we obtain a more efficient tradeoff between network power consumption and queue backlog compared to the many-to-one queuing system; and 3) we obtain superior queue stabilization capacity under bursty data and network power suppression conditions. This also validates NOMA’s high spectral efficiency and fine-grained remote execution control at the MEC server.

The emergence of the Metaverse brings new opportunities for enhancing productivity and creativity through real time updates and personalized content. However, it also leads to the generation of massive volumes of dynamic information, placing unprecedented demands on existing communication networks. Current bit-oriented communication systems are not designed to cope with such high levels of semantic complexity and data volume, ultimately limiting the responsiveness and interactivity of Metaverse applications. To address this research gap, we propose a goal-oriented semantic communication framework enabled by generative AI and optimal transport for Metaverse construction (GSC). The proposed GSC framework includes an hourglass network-based (HgNet) encoder to extract semantic information of objects in the Metaverse and a semantic decoder to construct the Metaverse content after wireless transmission,enabling efficient communication and real-time object behaviour updates to the scenery for the Metaverse construction task. To overcome the wireless channel noise at the receiver, we design an optimal transport (OT)-enabled semantic denoiser, which enhances the accuracy of the Metaverse scenery through wireless communication. The results of our computer experiments demonstrate that compared to the conventional Metaverse construction, our proposed GSC framework significantly reduces wireless Metaverse construction latency by 92.6%, while improving the Metaverse object status accuracy and viewing experience by45.6% and 44.7%, respectively.

Using ambient magnetic for indoor localization has been a research focus in recent years. However, intricate magnetic feature patterns in complicated indoor ambiance, with particular emphasis on the multi-scale dynamics arising from diverse user motion states, further hinder localization accuracy and universality. To address these challenges, this paper originally proposes a novel mixed-frequency magnetic data representation learning-based framework (MixLoc) for accurate and universal localization. Our core idea is to systematically model the multi-scale dynamics-affected pedestrian indoor localization as a location-semantic learning problem based on mixed-frequency magnetic data. First, we propose a data augmentation method to automatically construct a mixed-frequency magnetic dataset. Then, we propose a novel encoder to learn temporal and spatial representations from these data and extract subtle differences among multi-scale sequences. Finally, a novel localization model is proposed to accurately infer locations by capturing significant global and local features from both temporal and spatial representations. The evaluation results based on comprehensive experiments show that the accuracy of MixLoc increases about 42% compared to other state-of-the-art approaches.

With the emergence of the metaverse and its role in enabling real-time simulation and analysis of real-world counterparts, an increasing number of personalized metaverse scenarios are being created to influence entertainment experiences and social behaviors. However, compared to traditional image and video entertainment applications, the exact transmission of the vast amount of metaverse-associated information significantly challenges the capacity of existing bit-oriented communication networks. Moreover, the current metaverse also witnesses a growing goal shift for transmitting the meaning behind custom-designed content, such as user-designed buildings and avatars, rather than exact copies of physical objects. To meet this growing goal shift and bandwidth challenge, this paper proposes a goal-oriented semantic communication framework for metaverse application (GSCM) to explore and define semantic information through the goal levels. Specifically, we first analyze the traditional image communication framework in metaverse construction and then detail our proposed semantic information along with the end-to-end wireless communication. We then describe the designed modules of the GSCM framework, including goal-oriented semantic information extraction, base knowledge definition, and neural radiance field (NeRF) based metaverse construction. Finally, numerous experiments have been conducted to demonstrate that, compared to image communication, our proposed GSCM framework decreases transmission latency by up to 92.6% and enhances the virtual object operation accuracy and metaverse construction clearance by up to 45.6% and 44.7%, respectively.

In this paper, the problem of energy-efficient uncrewed aerial vehicle (UAV)-assisted multi-access task offloading is investigated. In the studied system, several UAVs are deployed as edge servers to cooperatively aid task executions for several energy-limited computation-scarce terrestrial user equipments (UEs). An expected energy efficiency maximization problem is then formulated to jointly optimize UAV trajectories, UE local central processing unit (CPU) clock speeds, UAV-UE associations, time slot slicing, and UE offloading powers. This optimization is subject to practical constraints, including UAV mobility, local computing capabilities, mixed-integer UAV-UE pairing indicators, time slot division, UE transmit power, UAV computational capacities, and information causality. To tackle the multi-dimensional optimization problem under consideration, the duo-staggered perturbed actor-critic with modular networks (DSPAC-MN) solution in a multi-agent deep reinforcement learning (MADRL) setup, is proposed and tailored, after mapping the original problem into a stochastic (Markov) game. Time complexity and communication overhead are analyzed, while convergence performance is discussed. Compared to representative benchmarks, e.g., multi-agent deep deterministic policy gradient (MADDPG) and multi-agent twin-delayed DDPG (MATD3), the proposed DSPAC-MN is validated to be able to achieve the optimal performance of average energy efficiency, while ensuring 100% safe flights.

In this paper, the problem of energy-efficient unmanned aerial vehicle (UAV)-assisted computation offloading over the Terahertz (THz) spectrum is investigated. In the studied system, several UAVs are deployed as edge servers to aid task executions for multiple energy-limited computation-scarce terrestrial user equipments (UEs). Then, an expected energy efficiency maximization problem is formulated, aiming to jointly optimize UAVs’ trajectories, UEs’ local central processing unit (CPU) clock speeds, UAV-UE associations, time slot slicing, and UEs’ offloading powers. To tackle the considered multi-dimensional optimization problem, the duo-staggered perturbed actor-critic with modular networks (DSPAC-MN) solution in a multi-agent deep reinforcement learning (MADRL) setup, is proposed and tailored, after mapping the original problem into a stochastic (Markov) game. Compared to representative benchmarks in simulations, e.g., multi-agent deep deterministic policy gradient (MADDPG) and multi-agent twin-delayed DDPG (MATD3), the proposed DSPAC-MN can achieve the optimal performance of average energy efficiency, while ensuring 100% safe flights.

With the emergence of the metaverse and its applications in representing humans and intelligent entities in social and related augmented reality (AR) applications. The current bit-oriented network faces challenges in supporting real-time updates for the vast amount of associated information, which hinders development. Thus, a critical revolution in the sixth generation (6G) networks is envisioned through the joint exploitation of information context and its importance to the goal, leading to a communication paradigm shift towards semantic and effectiveness levels. However, current research has not yet proposed any explicit and systematic communication framework for AR applications that incorporate these two levels. To fill this research gap, this paper presents a goal-oriented semantic communication framework for augmented reality (GSAR) to enhance communication efficiency and effectiveness in 6G. Specifically, we first analyse the traditional wireless AR point cloud communication framework and then summarize our proposed semantic information along with the end-to-end wireless communication. We then detail the design blocks of the GSAR framework, covering both semantic and effectiveness levels. Finally, numerous experiments have been conducted to demonstrate that, compared to the traditional point cloud communication framework, our proposed GSAR significantly reduces wireless AR application transmission latency by 95.6%, while improving communication effectiveness in geometry and color aspects by up to 82.4% and 20.4%, respectively.

Network slicing technology promises to be a critical enabler of fifth-generation (5G) and sixth-generation (6G) wireless networks, allowing the infrastructure to be divided into several virtual slices. Mobile network operators are focused on developing novel solutions to implement various slices to address diverse use cases and guarantee key performance indicators (KPIs) such as latency, resource utilization, and energy efficiency. Energy efficiency (EE) KPIs are particularly important during slice deployments to ensure a reduced carbon footprint. However, deploying slices with high energy efficiency presents significant challenges. This paper proposes an energy-aware design policy for deploying slices by optimizing energy consumption and deployment capacity. A deep reinforcement learning (DRL) approach is employed, utilizing an actor-critic architecture to train a learning network modeled with a pointer network structure and an attention mechanism. A search strategy is also proposed to refine learning parameters and determine the final design policy. Compared to two existing approaches, the proposed algorithms demonstrate improved performance in terms of energy efficiency and cumulative acceptance ratio. Specifically, the EE KPI achieved by the proposed approach is enhanced to 69.7%.

The ultra-reliable and low-latency communication (URLLC) service of the fifth-generation (5G) mobile communication network struggles to support safe robot operation. Nowadays, the sixth-generation (6G) mobile communication network is proposed to provide hyper-reliable and low-latency communication to enable safer control for robots. However, current 5G/ 6G research mainly focused on improving communication performance, while the robotics community mostly assumed communication to be ideal. To jointly consider communication and robotic control with a focus on the specific robotic task, we propose goal-oriented semantic communication in robotic control (GSRC) to exploit the context of data and its importance in achieving the task at both transmitter and receiver. At the transmitter, we propose a deep reinforcement learning algorithm to generate optimal control and command (C&C) data and a proactive repetition scheme (DeepPro) to increase the successful transmission probability. At the receiver, we design the value of information (VoI) and age of information (AoI) based queue ordering mechanism (VA-QOM) to rank the queue based on the semantic information extracted from AoI and VoI. The simulation results validate that our proposed GSRC framework achieves a 91.5% improvement in the mean square error compared to the traditional unmanned aerial vehicle control framework.

In this paper, we investigate a cellular-connected unmanned aerial vehicle (UAV) network, where multiple UAVs receive messages from base stations (BSs) in the down-link, and in the meantime, BSs serve their paired ground user equipments (UEs). To effectively manage inter-cell interferences (ICIs) among UEs due to intense reuse of time-frequency resource block (RB) resource, a first p-tier based RB coordination criterion is adopted. Then, to enhance wireless transmission quality for UAVs while protecting terrestrial UEs from being interfered by ground-to-air (G2A) transmissions, a radio resource management (RRM) problem of joint dynamic RB coordination and time-varying beamforming design is formulated to minimize UAV's ergodic outage duration (EOD). To cope with conventional optimization techniques' inefficiency in solving the formulated RRM problem, a deep reinforcement learning (DRL)-aided solution is proposed, where deep double duelling Q network (D3QN) and twin delayed deep deterministic policy gradient (TD3) are invoked to deal with RB coordination in the discrete action domain and beamforming design in the continuous action regime, respectively. Numerical results illustrate the effectiveness of the proposed hybrid D3QNTD3 algorithm, compared to representative baselines.

In this paper, physical layer security issue for a down-link wireless communication system is examined, composed of an unmanned aerial vehicle (UAV), a legitimate receiver and a passive eavesdropper. The destination is equipped with two antennas and applies the full-duplex (FD) Bob-based jamming (FD-BBJ) strategy to achieve secure transmission. Considering that practical air-to-ground (A2G) channels experience Nakagami-m fading and the FD legitimate receiver is affected by self-interference (SI), closed-form expressions of approximate ergodic achievable secrecy rate (EASR) with help of Gauss-Laguerre Quadrature (GLQ) and compact secrecy outage probability (SOP) expression are derived, respectively. To gain more insights, asymptotic secrecy performance is analysed in the case of extreme total system transmit power, via deriving closed-form expression for asymptotic EASR and compact expression for asymptotic SOP. Numerical results have verified the correctness of our theoretical analysis and proved that the FD-BBJ strategy applied in the UAV-aided wireless communication system can help achieve considerable secrecy performance gain.

This article proposes a novel mathematical model for teleoperation over communication networks. For teleoperation over a communication network, a high packet rate can result in inefficient data transmission and cross-traffic problems, leading to extra delay and jitter. This article proposes an long short-term memory (LSTM)-based mathematical model which focuses on kinesthetic data reduction without loss of transparency during the transmission process through joint training combined with haptic data and perceptual deadband. Since the LSTM network can deal with a time series of haptic data, we further test the system performance through practically collected data. We investigate the packet rate and perceptual transparency of the proposed mathematical model by comparing with the conventional deadband. Additionally, we compare the proposed mathematical model with the perceptual deadband-based codecs. Simulation results show that the proposed solution further reduces the packet rate when dealing with haptic data without noticeable distortion. Also, comparing with the current just noticeable difference perceptual threshold, the proposed mathematical model helps improve the practicality of the bilateral teleoperation system without losing transparency.

Reinforcement learning (RL) is a widely investigated intelligent algorithm and proved to be useful in the wireless communication area. However, for optimization problems in large-scale multi-cell networks whose dimension increases exponentially, it is unrealistic to employ a conventional centralized RL algorithm and make decisions for the entire network. Multi-agent RL, which allows distribute decision-making, is expected to solve the scalability problem but with performance issues due to the unknown global information, i.e., non-stationary environment. In this paper, we propose a parameter-sharing multi-agent RL for grouping decisions of coordinated multi-point in a large-scale network, where agents jointly serve users to enhance the cell-edge service. By sharing information via parameters, our theoretical and simulation results show that parameter sharing can largely benefit the multi-agent algorithm with convergence proof and convergence speed analysis. To reduce the effect of biased local heterogeneous experience, we also propose a transfer learning method for the parameter sharing process, whose performance of transfer learning algorithms is verified by the simulation results.

Integrating unmanned aerial vehicles (UAVs) into existing cellular networks encounters lots of challenges, among which one of the most striking concerns is how to achieve harmonious coexistence of aerial transceivers, inter alia, UAVs, and terrestrial user equipments (UEs). In this paper, a cellular-connected UAV network is focused, where multiple UAVs receive messages from base stations (BSs) in the down-link, while BSs are serving ground UEs in their cells. For effectively managing inter-cell interferences (ICIs) among UEs due to intense reuse of time-frequency resource block (RB) resource, a first$p$-tier based RB coordination criterion is proposed and adopted. Then, to enhance wireless transmission quality for UAVs while protecting terrestrial UEs from being interfered by ground-to-air (G2A) transmissions, a radio resource management (RRM) problem of joint dynamic RB coordination and time-varying beamforming design minimizing UAV’s ergodic outage duration (EOD) is investigated. To cope with conventional optimization techniques’ inefficiency in solving the formulated RRM problem, a deep reinforcement learning (DRL)-aided solution is initiated, where deep double duelling Q network (D3QN) and twin delayed deep deterministic policy gradient (TD3) are invoked to deal with RB coordination in discrete action domain and beamforming design in continuous action regime, respectively. The hybrid D3QN-TD3 solution is trained via interacting with the considered outer and inner environments in an online centralized manner so that it can then help achieve the suboptimal EOD minimization performance during its offline decentralized exploitation. Simulation results have illustrated the effectiveness of the proposed hybrid D3QN-TD3 algorithm, compared to several representative baselines.

Reinforcement learning (RL) is a efficient intelligent algorithm when solving radio resource management problems in the wireless communication network. However, for large-scale networks with limited centralization (i.e., high latency connection to center-server or capacity-limited backbone), it is not realistic to employ a centralized RL algorithm to perform joint real-time decision-making for the entire network, which calls for scalable algorithm designs. Multi-agent RL, which allows separate local execution of policy, has been applied to large-scale wireless communication areas. However, it has performance issue which largely varies with different system settings. In this paper, we study a multi-agent algorithm for a coordinate multipoint (CoMP) scenario, which requires cooperation between base stations. We show that the common settings of user distribution, the design of reward, and episodic in the environment can significantly ease the learning of the algorithm and obtain beautiful converge results. However, these settings are not realistic in wireless communication. By validating the performance difference between these settings with our algorithm in a coordinate multipoint (CoMP) scenario, we introduce several possible solutions and highlight the necessity of further study in this area.

Despite the massive increase in network capacities and devices capabilities, intra-domain TE problems have remained a challenge due to high traffic demand in dynamic network settings. In this paper, we fundamentally adopt and construct the use of Deep Reinforcement Learning (DRL) algorithm to improve end-to-end delay and maximum link utilisation (MLU) in a wireless All-IP access network. In an experimental pseudo setting, we propose a routing method DRL-MPR (Multi-Plane Routing) within a Dueling Deep Q-Network (DDQN) framework as a controller in which by simultaneously allocating multiple robust IP sessions, each session will take the near optimal path/plane. We first revisit Multi-Plane Routing Protocol (MPR) to configure a set of routing paths/Routing Planes (RP) from a physical topology as pre-condition ahead of the traffic injection. We compare our decision making scheme results with some traditional routing methodologies such as OSPF and standard Multi-Plane Routing (MPR). Our simulation results show that DRL obtains lower maximum link utilisation (MLU) and end-to-end delay. For example, in the 19 nodes and 41 links topology, a small traffic load results in 60% maximum link utilisation for DRL-MPR, whereas those of OSPF and MPR are 100% and 94% respectively. In this simulation environment, the traffic demand in the IP access network is gradually increasing to the point of saturated network link utilisation.

In the presence of Warden’s detection, a maximization problem on transmission throughput from unmanned aerial vehicle (UAV) to legitimate nodes is considered and solved via UAV trajectory design, subject to covert, velocity and mobility constraints. With the building-distribution-based pathloss model and the Warden’s uncertain location model, the formulated optimization problem is challenging to be tackled through standard offline optimization methods. Alternatively, a twin delayed deep deterministic policy gradient (TD3) approach enhanced by multi-step learning and prioritized experience replay (PER) techniques, termed as multi-step TD3-PER, is proposed to help the UAV adaptively select velocity from continuous action space. Numerical results demonstrate the effectiveness of the proposed multi-step TD3-PER solution and showcase the corresponding superiorities against provided baselines.

In cellular-connected unmanned aerial vehicle (UAV) network, a minimization problem on the weighted sum of time cost and expected outage duration is considered. Taking advantage of UAV’s adjustable mobility, an intelligent UAV navigation approach is formulated to achieve the aforementioned optimization goal. Specifically, after mapping the navigation task into a Markov decision process (MDP), a deep reinforcement learning (DRL) solution with novel quantum-inspired experience replay (QiER) framework is proposed to help the UAV find the optimal flying direction within each time slot. Via relating experienced transition’s importance to its associated quantum bit (qubit) and applying Grover-iteration-based amplitude amplification technique, the proposed DRL-QiER solution commits a better trade-off between sampling priority and diversity. Compared to several representative baselines, the effectiveness and supremacy of the proposed DRL-QiER solution are demonstrated and validated in numerical results.

Wireless access networks are ever-changing their setup, topologies and provisions of coverage. Forthcoming deployment trends include densification of cells and convergence of the ‘native IP’ with cellular access networks with more than best-effort expectations. Greater meshing in networks due to practical deployment requirements is inevitable and needed. This paper proposes a routing protocol to address the “randomness” of topology interconnections, routing paths and sizes in emerging IP access networks. Termed as Minimum Set Cover (MSC) approach, it is a generalization of the NP and NP complete mathematical problem. The offline component of the MSC multiplies intra-domain routing installations, called Routing Planes (RPs) modelled as graphs, to suitably cover the whole routing topology prior to the traffic injections in the online component. We introduce novel offline optimization features using a dynamic cost function that plans availability of capacities and correlation of routing paths via the chosen set of RPs. Our simulations verify effective path diversity using MSC with its modest protocol overhead and a heuristic used for RPs selection. For randomly constructed access network topologies with 7, 18 and 33 routers and various meshing levels, our results show convincing suitability and key performances gains compared with rival routing solutions.

Connected Cars (CCs) and vehicle-to-everything (V2X) use cases require stringent reliability for safety and non-safety uses. With increasing network softwarisation, it has become easier to use multiple, redundant connectivity options instead of relying on a single network connectivity. But where should these redundant connections be managed? Is it at a network provider’s core network - i.e., supply side managed (SSM) - or at the CC - i.e., demand side managed (DSM)? In our work, we investigate the use of SSM and DSM for CCs on four separate days and across 800 kilometers of major / minor roads in South East England. For Day 1, we captured performance indicators, and determined hypothetical multi-operator configurations for four U.K. providers and a global Universal SIM. For Day 2, 3 & 4, we built and deployed a test-bed to actually implement network switching and understand performance (incl. for TCP & UDP) either on the road or in a stationary location. Based on our results, we make three contributions. First, we show that DSM can deliver superior performance for CCs more than any individual network (up to 28 percentage points in a hypothetical scenario), or SSM which had up to 4.8x longer page load times. Second, unlike other smartphone-only studies, our system-level study demonstrates that improvements of at least 12% can be obtained in a practical DSM field implementation for a CC. Third, we confirm that the advantage of DSM in a field implementation is higher for UDP traffic (23% better latency) compared to TCP (13%).

End-to-End network slicing is an emerging technology with huge potential to carry flexible resource provisioning for the next generation of mobile networks (5G). With the powerful SDN and NFV technologies, multiple and logical network slices of various services can be deployed to the same underlying infrastructure. Physical resources are flexibly configured for different use cases. Therefore, it is necessary to explore how to guide the implementation of network slices via a general design policy. In this paper, we propose a service-aware network slicing design policy for 5G use cases, not only to satisfy various service requirements for different applications but also to enhance resource efficiency with fluctuated traffic demands. Firstly, multiple design objectives of slices are presented to guarantee different services in diverse use cases. Then we formulate a deterministic optimization model of the network slicing design problem and further extend it into a robust version considering uncertain traffic demands. Besides, a heuristic algorithm is proposed to obtain a promising network slicing design policy with the low computational effort, which is inspired by the multiple-objective particle swarm optimization (MOPSO) algorithm. The effectiveness of the present formulations and algorithms is verified by a series of simulations.

With the stringent requirement of receiving video from the unmanned aerial vehicle (UAV) from anywhere in the stadium of sports events and the significant-high per-cell throughput for video transmission to virtual reality (VR) users, a promising solution is a cell-free multi-group broadcast (CF-MB) network with cooperative reception and broadcast access-points (AP). To explore the benefit of broadcasting user-correlated decode-dependent video resources to spatially correlated VR users, the network should dynamically schedule the video and cluster APs into virtual cells for a different group of VR users with overlapped video requests. By decomposing the problem into scheduling and association sub-problems, we first introduce the conventional non-learning-based scheduling and association algorithms, and a centralized deep reinforcement learning (DRL) association approach based on the rainbow agent with a convolutional neural network (CNN) to generate decisions from observation. To reduce its complexity, we then decompose the association problem into multiple sub-problems, resulting in a networked-distributed Partially Observable Markov decision process (ND-POMDP). To solve it, we propose a multi-agent deep DRL algorithm. To jointly solve the coupled association and scheduling problems, we further develop a hierarchical federated DRL algorithm with scheduler as meta-controller, and association as the controller. Our simulation results show that our CF-MB network can effectively handle real-time video transmission from UAVs to VR users. Our proposed learning architecture is effective and scalable for a high-dimensional cooperative association problem with increasing APs and VR users. Also, our proposed algorithms outperform non-learning based methods with significant performance improvement.

In cellular-connected unmanned aerial vehicle (UAV) network, a minimization problem on the weighted sum of time cost and expected outage duration is considered. Taking advantage of UAV’s adjustable mobility, a UAV navigation approach is formulated to achieve the aforementioned optimization goal. Conventional offline optimization techniques suffer from inefficiency in accomplishing the formulated UAV navigation task due to the practical consideration of local building distribution and directional antenna radiation pattern. Alternatively, after mapping the navigation task into a Markov decision process (MDP), a deep reinforcement learning (DRL)-aided solution is proposed to help the UAV find the optimal flying direction within each time slot, and thus the designed trajectory towards the destination can be generated. To help the DRL agent commit a better trade-off between sampling priority and diversity, a novel quantum-inspired experience replay (QiER) framework is proposed, via relating experienced transition’s importance to its associated quantum bit (qubit) and applying Grover iteration based amplitude amplification technique. Compared to several representative DRL-related and non-learning baselines, the effectiveness and supremacy of the proposed DRL-QiER solution are demonstrated and validated in numerical results.

With the stringent requirement of receiving video from unmanned aerial vehicle (UAV) from anywhere in the stadium of sports events and the significant-high per-cell throughput for video transmission to virtual reality (VR) users, a promising solution is a cell-free multi-group broadcast (CF-MB) network with cooperative reception and broadcast access points (AP). To explore the benefit of broadcasting user-correlated decode-dependent video resources to spatially correlated VR users, the network should dynamically cluster APs into virtual cells for a different group of VR users with overlapped video requests. We first introduce the conventional non-learning-based association algorithms. We then formulate the association problem into a networked-distributed Partially Observable Markov decision process (ND-POMDP). To solve it, we propose a multi-agent deep DRL algorithm based on the rainbow agent with a convolutional neural network (CNN) to generate decisions from observation. Our simulation results shown that our CF-MB network can effectively handle real-time video transmission from UAVs to VR users. Our proposed learning architectures is effective and scalable for a high-dimensional cooperative association problem with increasing APs and VR users. Also, our proposed algorithms outperform non-learning based methods with significant performance improvement.

Smartphone-based indoor localization has attracted considerable attentions in both research and industrial areas. However, the localization accuracy and robustness are still challenging problems due to low-cost noisy devices, especially in those complicated localization environments. Considering that pedestrian dead-reckoning (PDR) devices are widely equipped in recent smartphones, we propose a novel indoor localization fusing algorithm that integrates both wireless fidelity (WiFi) features and PDR features. By formulating the fusing indoor localization as a recursive function approximation problem, a sliding-window-based displacement scheme is designed to generate a time-series-based feature data set. We further apply the long short-term memory (LSTM) network for data fusion and localization on this data set by taking advantage of its benefits in time-series prediction and characterization. To evaluate the performance of the proposed algorithm, we compare it with state-of-the-art filter-based localization algorithms in three typical movements and three postures of holding smartphones. Extensive experiment results demonstrate the accuracy and robustness of the proposed algorithm in indoor localization, even in some extreme environments.

In this work, we develop a novel channel estimation method using recurrent neural networks (RNNs) for massive multiple-input multiple-output (MIMO) systems. The proposed framework alleviates the need for channel-state-information (CSI) feedback and pilot assignment through exploiting the inherent time and frequency correlations in practical propagation environments. We carry out the analysis using empirical MIMO channel measurements between a 64T64R active antenna system and a state-of-the-art multi-antenna scanner for both mobile and stationary use-cases. We also capture and analyze similar MIMO channel data from a legacy 2T2R base station (BS) for comparison purposes. Our findings confirm the applicability of utilising the proposed RNN-based massive MIMO channel acquisition scheme particularly for channels with long time coherence and hardening effects. In our practical setup, the proposed method reduced the number of pilots used by 25%.

Network Slicing is regarded as a promising tech-nology to provide required services for different application scenarios by means of supporting multiple slices to embed the underlying physical network. However, it is still a challenging task to design network slicing aiming at providing specific services for different types of tenants while making efficient use of physical resources. Thus, the paper attempts to tackle the problem by proposing a novel end-to-end network slicing design policy. We start from modeling the mathematical model of the physical network and network slicing requests by using the Formal Concept Analysis methodology. Then, multiple design objectives for various use cases are defined, and the relevant resource constraints are also provided. Moreover, we propose a meta-heuristic algorithm based on the Multi-Objective Particle Swarm Optimization for the network slicing design problem. Extensive simulations illustrate that the resource efficiency of our proposed algorithm is better than the existing algorithms in terms of both node and link resources utilization.

The exploding volumes of mobile video traffic call for deploying content caches inside mobile operator networks. With in-network caching, users' requests for popular content can be served from a content cache deployed at mobile gateways in vicinity to the end user. This inherently reduces the load on the content servers and the backbone of operator's network. In light of the increasing trend in virtualization of network functions, we propose a cost-effective caching as a service (CaaS) framework for virtual video caching in 5G mobile networks. In order to evaluate the pros and cons of our CaaS approach, we formulate two virtual caching problems, namely maximum return on investment(MRI) and maximum offloaded traffic (MOT). MRI aims at maximizing return on caching investment by finding the best trade-off between the cost of cache storage and bandwidth savings from caching video contents in the mobile network operator (MNO)'s cloud. Likewise, MOT aims to maximize the traffic offloaded from the MNO's core and backhaul within given budget constraints. More specifically, taking the popularity and size of video contents into account, MRI and MOT aim to find the optimal caching tables which maximize the ratio of transmission bandwidth cost to storage cost and the offloaded traffic for a given budget, respectively. We reduce the complexity of the proposed problem formulated as a binary-integer programming (BIP) by using canonical duality theory (CDT). Experimental results obtained using the invasive weed optimization (IWO) have shown significant performance enhancement of the proposed system in terms of return on investment, quality, offloaded traffic, and storage efficiency.

To enhance transmission performance, privacy level, and energy manipulating efficiency of wireless networks, this article initiates a novel simultaneous wireless information and power transfer (SWIPT) full-duplex (FD) relaying protocol, named harvest-and-opportunistically-relay (HOR). Due to the FD characteristics, the dynamic fluctuation of relay's residual energy is difficult to quantify and track. To solve this problem, the Markov Chain (MC) theory is invoked. Furthermore, to improve the privacy level of the proposed HOR relaying system, covert transmission performance analysis is performed, where closed-form expressions of the optimal detection threshold and minimum detection error probability are derived. Last but not least, with the aid of stationary distribution of the MC, closed-form expression of transmission outage probability is calculated, based on which transmission outage performance is analyzed. Numerical results have validated the correctness of analyses on transmission outage and covertness. The impacts of key system parameters on the performance of transmission outage and covertness are given and discussed. Based on mathematical analysis and numerical results, we showcase that the proposed HOR model can not only reliably enhance the transmission performance via smartly managing residual energy but also efficiently improve the privacy level of the legitimate transmission party via dynamically adjusting the optimal detection threshold.

In this work, a deep learning-based symbol detection method is developed for multi-user multiple-input multiple-output (MIMO) systems. We demonstrate that the linear threshold-based detection methods, which were designed for AWGN channels, are suboptimal in the context of MIMO fading channels. Furthermore, we propose a MIMO detection framework which replaces the linear thresholds with decision boundaries trained with neural network (NN) classifiers. The symbol error rate (SER) performance of the proposed detection model is compared against conventional methods under state-of-the-art system parameters. Here, we report to up to a 2 dB gain in SER performance using the proposed NN classifiers, allowing for exploiting higher-order modulation schemes, or transmitting with reduced power. The underlying gain in performance may be further enhanced from improvements to the NN architecture and hyper-parameter optimization.

This paper studies the physical (PHY)-layer security performance in full-duplex (FD) multiple- input multiple-output (MIMO) small-cell networks. Here, we take into account (i) residual self- interference (SI) over Rician fading channels, and (ii) mutual-interference (MI) under successive interference cancellation (SIC) mechanism. Considering linear zero-forcing (ZF) beamforming, the downlink (DL) and uplink (UL) average secrecy rates under both scenarios of passive and colluding eavesdropping are derived. Our findings indicate that the FD functionality can provide substantial improvements in the PHY-layer security performance, especially with the aid of MIMO communications and interference cancellation solutions.

The expected variable nature of future access network structures calls for network providers to adapt accordingly in order to facilitate loss free networks supported with the developing IP infrastructure. To this end, a routing optimization mechanism applicable to randomly shaped all-IP access networks must be developed. In this paper, Multi-Plane Routing (MPR) that consolidates various aspects in all-IP infrastructure as a whole is redesigned and reformulated to provide a comprehensive solution in consideration of the randomness of future access networks. We prove the offline Routing Plane (RP) construction problem as being the generalization of the Minimum Set Cover (MSC) problem which is NP and also NP-complete. To this end, we propose a novel MSC-based paths-diverse offline TE algorithm which is comprehensively applicable to random wireless access network structures. Our simulation results demonstrate the constructed RPs for complex random networks of different sizes and sparseness (i.e. meshing). Hence, the comprehensive applicability of our novel approach is verified. Moreover, we propose a new optimization framework along with a dynamic cost function (considering capacity and correlation of paths) that formally describe our novel offline TE mechanism for future randomly shaped wireless IP access networks.

The tremendous growth of mobile multimedia applications leads to increased traffic as well as energy consumption in cellular mobile communications. Hence, further improvements in resource allocation are essential. Wireless communication systems are aimed at providing higher capacity, improved, and continuous connectivity and minimizing energy consumption to support data-intensive multimedia applications. The main contribution of this paper is toward the maximization of the spectrum and power efficiencies of such networks through intelligent Q-learning-based control algorithms in the Downlink. The model in this paper considers a two-tier HetNet with Cognitive Open Access femtocell, which is designed using stochastic geometry tool. Furthermore, we analyzed and evaluated the Rate Coverage performance for macrocell and femtocell users over the Rayleigh Fading environment in the Downlink. The MonteCarlo simulations results that have been obtained and validated showed that the proposed method achieved an increased overall capacity while guaranteeing the primary user service level. Moreover, Rate Coverage signifies the user population meeting their target threshold. These factors cumulatively enhanced the overall network capacity.

As a new way to design, deploy, and manage network services, network functions virtualization (NFV) decouples the network functions, from one or more physical network infrastructures and black boxes so they can run in software. It therefore comes as no surprise that NFV originated from service providers, who were looking to improve the deployment of new network services to support their revenue and growth objectives. Within the NFV ecosystem, high availability, and low latency are one of the key quality of service (QoS) benefits that service providers can expect from the 5G Cloud and the NFV networks to make delay-critical services such as remote surgery a reality. Therefore, network services should be placed, chained, and routed through the network considering users/tenants stringent QoS and service-level agreement requirements. To this end, routing and placement optimization plays a major role in improving network performance and the overall network cost. In this paper, we study the problem of virtual network functions (VNFs) placement and routing across the physical hosts to minimize overall latency defined as the queuing delay within the edge clouds and in network links. In that respect, this paper takes a holistic view by considering not only VNFs chaining and placement problem but also considering the flows routing aspect since these two problems are inter-related and have a major impact on network latency.

We provide a theoretical study of physical (PHY)-layer security performance in full-duplex (FD) small-cell networks. Here, the multi-antenna base stations (BSs) and user equipments (UEs) follow from the homogeneous Poisson point process-based abstraction model. To facilitate FD communications, we take into account: 1) successive interference cancellation capability at the UE side via guard regions of arbitrary radii and 2) residual self-interference at the BS side using Rician fading distribution with arbitrary statistics. We investigate the small-cell network PHY-layer security performance in the presence of a Poisson field of eavesdroppers, under the different scenarios of passive and colluding eavesdropping. Considering linear zero-forcing beamforming, we characterize the downlink and the uplink ergodic secrecy rates and derive closed-form expressions for the different useful and interference signals statistics. In certain special cases of interest, we apply non-linear curve-fitting techniques to large sets of (exact) theoretical data in order to obtain closed-form approximations for the different ergodic rates and ergodic secrecy rates under consideration. Our findings indicate that the FD functionality, in addition to enhancing the spectral efficiency, can significantly improve the PHY-layer security performance, especially with the aid of multi-antenna communications and interference cancellation schemes.

With the expected surge in the global IP traffic, service providers would need to adapt accordingly to operate disruption and loss free networks supported with the developing IP infrastructure. With the disposal of the hierarchical network structure, radio access networks are moving towards a flat-IP architecture and novel topological set-ups in the backhaul. Hence, a routing paradigm that employs suitable Traffic Engineering (TE) techniques aligned with the developing nature of future access networks must be applied. It becomes imminent that the routing considerations for IP access networks converge with the ones found in conventional intra-domain routing. In this paper, Multi-Plane Routing (MPR) that consolidates various aspects in all-IP infrastructure is extensively studied in access network structures. We propose a MPR-based TE approach considering two different scenarios to reflect the evolution in the architectural design of access network structures under a realistic traffic scenario with a varying range of internal/external traffic. Moreover, a new optimization framework for the offline and online TE mechanisms of MPR have been formulated. Accordingly, a practical performance evaluation testing the validity of the aforementioned scenarios is presented. Our simulation results demonstrate extensive analysis in terms of several performance criteria in networks. It is convincingly shown that for ranges of topologies, MPR's utilization of whole topology in building path diversity in networks, allows for significant improvement of networks capacity, performance, and support for meshing.

In this paper, motivated by recent developments in physical layer (PHY) security, we study the achievable secrecy rate of a multi-power level cognitive radio network (CRN) based on stochastic geometry distribution. We consider a realistic transmission scheme with multiple levels of transmission power. Additionally, having multi-level power strategy can help improve security as eavesdroppers will find it more difficult to recognize the exact power level of the legitimate users. We derive the achievable secrecy rate in an additive white Gaussian noise channel for a cognitive radio model. Furthermore, the cumulative distribution function of the achievable secrecy rate between the primary transmitter and receiver is studied. Finally, we investigate the outage probability of secrecy capacity of the legitimate user from a secure communication graph point of view.

Traditional cellular networks are moving towards heterogenous cellular networks (HetNets) to satisfy the stringent demand for data rates and capacity. To enable the new applications in 5G, such as haptic communications, we face new challenges of achieving high availability with low latency in HetNets. In this paper, we introduce coordinated multi-point (CoMP) and carrier aggregation (CA) techniques in HetNets to guarantee the availability of all UEs, where CoMP improves the single-path availability, and CA enhances availability via multi carrier gain combining. To characterize the availability, we first derive an exact closed-form expression for the availability of a random UE in a CoMP&CA-enabled HetNets. To achieve the maximum UE availability, we formulate a max-min optimization problem. To solve it, we then propose a joint two-step optimization algorithm (JTOA), and our results showcase the effective of our proposed JTOA, and the effective of CoMP in availability improvement in HetNets.

In this work, we investigate the physical layer security (PHYLS) performance of full-duplex (FD) cellular networks, where the downlink (DL) and uplink (UL) occur over the same radio-frequency (RF) resources. Here, the locations of the base stations (BSs) and mobile terminals (MTs) are drawn from stationary Poisson point processes (PPPs). Moreover, the eavesdroppers (EDs) locations are unknown to the network, and are thus modeled from an independent PPP. We characterize the signal-to-interference-plus-noise ratio (SINR) distributions at the reference BS, MT, and most malicious EDs. Accordingly, we develop explicit expressions for the secrecy rates in both UL and DL of the FD cellular network under consideration. Our finding show that the choice of FD versus HD operation, in addition to improving the spectral efficiency, can enhance the secrecy rate, particularly for ultra-dense deployments.

Traditional cellular networks are moving toward heterogeneous cellular networks (HetNets) to satisfy the stringent demand for data rates and capacity. To enable the new applications in 5G, such as haptic communications, we face new challenges of achieving high availability with low latency in HetNets. In this paper, we introduce coordinated multi-point (CoMP) and carrier aggregation (CA) techniques in HetNets to guarantee the availability of all user equipment (UE), where the CoMP improves the single-path availability, and the CA enhances availability via multi-carrier gain combining. To characterize the availability, we first derive an exact closed-form expression for the availability of a random UE in a CoMP and CA-enabled HetNets. To achieve the maximum UE availability, we formulate a max-min optimization problem. To solve it, we then propose a two-step optimization algorithm (TSOA) and a joint (JTOA). The TSOA is based on heuristic algorithm for the optimal subcarrier assignment and UE association, and based on the Lagrangian dual method for the power allocation. The JTOA is based on genetic algorithm to achieve the interaction between the first step and the second step. Our results showcase the effective of our proposed JTOA, and the effective of the CoMP in availability improvement in HetNets.

Spectrum aggregation provides a promising approach to improve the network capacity for Cognitive Radio Ad-Hoc Networks (CRAHNs). Resource allocation for spectrum aggregation-based CRAHNs has become one of the main issues. In this paper, we propose a cross-layer optimization for CRAHNs with the spectrum aggregation. The main objective of our paper is to maximize the network throughput under the network resource constraints. In this regard, we investigate the joint optimization for channel allocation, power control and routing under signal-to-interference-and- noise ratio (SINR) model. This cross-layer optimization problem is decomposed into two sub-problems: a resource allocation at the physical (PHY) layer, and a throughput optimization at the network layer. At the PHY layer, the particle swarm optimization algorithm is proposed to find the suboptimal solution, then at the network layer, linear programming is applied to evaluate the particle's fitness value for throughput maximization. The simulation results demonstrate that the joint optimization of channel allocation and power control is an effective way to improve network throughput, especially when the network has sufficient power supply.

The exponential growth in data traffic and dramatic capacity demand in fifth generation (5G) has inspired the move from traditional single-tier cellular networks towards heterogeneous cellular networks (HetNets). To face the coming trend in 5G, the high availability requirement in new applications, needs to be satisfied to achieve low latency service. In this work, we present a tractable multi-tier multi-band availability model to examine the high availability in carrier aggregation (CA)-enabled HetNets. We first derive a closed-form expression for the availability in CA- enabled HetNets based on the signal-to-interference- plus-noise model. By doing so, we formulate the joint subcarrier and power allocation problem, to maximize the availability under the power constraint. The optimization problem is non-convex problem, which is challenging to solve. To cope with it, the genetic algorithm (GA) is proposed to optimize availability through joint subcarrier and power allocation. The average availability in CA-enabled HetNets improves with decreasing the number of UEs, and increasing the power budget ratio interestingly.

The exploding volumes of mobile video traffic call for deploying content caches inside mobile operators network. With in-network caching, users' requests for popular content can be served from a content cache deployed at mobile gateways in vicinity to the end user, therefore considerably reducing the load on the content servers and the backbone of operator's network. In practice, content caches can be installed at multiple levels inside an operator's network (e.g., serving gateway, packet data network gateway, RAN, etc.), leading to an idea of hierarchical in-network video caching. In order to evaluate the pros and cons of hierarchical caching, in this paper we formulate a cache provisioning problem which aims to find the best tradeoff between the cost of cache storage and bandwidth savings from hierarchical caching. More specifically, we aim to find the optimal size of video caches at different layers of a hierarchical in-network caching architecture which minimizes the ratio of transmission bandwidth cost to storage cost. We overcome the complexity of our problem which is formulated as a binary-integer programming (BIP) by using canonical duality theory (CDT). Numerical results obtained using the invasive weed optimization (IWO) show that important gains can be achieved, with benefit-cost ratio and cost efficiency improvements of more than 43% and 38%, respectively.

There has been a rapid rise in the IP traffic throughout the Internet which takes advantage of the already established widespread IP infrastructure. Different suggestions are being explored to facilitate the next-generation access networks via IP mechanisms, with a growing trend towards a flat-IP structure and novel topological set-ups in the backhaul. Aligned with this evolution, there are increasingly more user applications flooding the Internet that calls for a consistent routing strategy to minimize loss in data transmission. In this paper, Multi-Plane Routing (MPR), which incorporates various aspects in all-IP infrastructure will be studied under the new access network structure. MPR is based on Multi-Topology Open Shortest Path First (MT-OSPF) principle and divides the physical network topology into several logical Routing Planes (RPs). The offline Traffic Engineering (TE) strategy for MPR has been optimized using a heuristic hop-constraint solution that suits the “flattened” network realized through the incorporation of direct communication between Aggregation Routers. With our approach, despite of a higher number of Ingress —Egress pairs for traffic in the access network, the number of RPs has been kept to the desirable level whilst the reliability indicator and the path diversity index ratio have increased up to 47% and 33% respectively. Our proposed MPR-based offline approach has also shown improvement compared with the Multi-Protocol Label Switching (MPLS) offline approach.

In this paper, we consider a multi-level power allocation scheme for cognitive users in the cognitive radio networks. The proposed system uses a new frame structure to improve overall throughput of the cognitive radio systems. We propose a strategy in which, the licensed user can transmit with multiple levels of power which seems to be more realistic and practical. In this work, the proposed strategy also allows cognitive users to choose different power levels according to their receiving energy. The optimal achievable rate under the constraints of average transmit power at the cognitive users and average interference temperature to the licensed users is investigated. Simulation results indicate the enhancement in the throughput of the system compared to conventional strategy.

In this paper, we develop a tractable model for joint downlink (DL) and uplink (UL) transmission of K -tier heterogeneous cellular networks (HCNs) with simultaneous wireless information and power transfer (SWIPT) for efficient spectrum and energy utilization. In the DL, the mobile users (MUs) with power splitting receiver architecture decode information and harvest energy based on SWIPT. While in the UL, the MUs use the harvested energy for information transmission. Since cell association greatly affects the energy harvesting in the DL and the performance of wireless powered HCNs in the UL, we compare the DL and UL performance of a random MU in HCNs with nearest base station (NBS) cell association to that with maximum received power (MRP) cell association. We first derive the DL average received power for the MU with the NBS and the MRP cell associations. To evaluate the system performance, we then derive the outage probability and the average ergodic rate in the DL and UL of a random MU in HCNs with the NBS and MRP cell associations. Our results show that increasing the small cell base station (BS) density, the BS transmit power, the time allocation factor, and the energy conversion efficiency, weakly affects the DL and UL performance of both the cell associations. However, the UL performance of both the cell associations can be improved by increasing the fraction of the DL received power used for energy harvesting.

In this paper we investigate power-efficient resource allocation for transmission of perceptual quality guaranteed video over LTE downlink under delay quality of service (QoS) constraints. We formulate the resource allocation problem as the minimization of sum power in the downlink under user perceived quality and statistical delay QoS provisioning. We solve the problem using dual decomposition and employ the ellipsoid method to update dual variables. Experimental results have shown significant performance enhancement of the proposed system in terms of power efficiency while satisfying the statistical delay-bounded QoS and perceptual quality requirements.

Reducing the queue length and queuing delay in the buffer which in turn reduces congestion and latency in the network are of great importance for real-time video services. In this paper, we propose a perceptual quality-aware queue management mechanism to shorten the queue length and waiting time of video traffic in a finite buffer. Our proposed approach prioritizes video layers in a stream in accordance with their hierarchical structure and selectively drops packets from different layers under a target user perceived quality constraint. This in turn reduces network load and latency and increases the capacity to serve more concurrent streams while satisfying users' perceptual quality requirements. We develop a statistical queuing model to express the delay requirements of video layers with an equivalent cross-layer constraint We then formulate the queue management problem as a minimization of queuing delay using a selective packet drop approach under perceptual quality and queue expiry time provisioning. Numerical results show that our proposed approach outperforms the widely deployed random early detection (RED) and tail drop (ID) queue management schemes in terms of reducing queuing delay and queue length in the buffer, while increasing the fraction of perceived quality-satisfied users.

Machine-to-machine (M2M) communications enables networked devices to exchange information among each other as well as with business application servers and therefore creates what is known as the Internet-of-Things (IoT). The research community has a consensus for the need of a standardized protocol stack for M2M communications. On the other hand, cognitive radio technology is very promising for M2M communications due to a number of factors. It is expected that cognitive M2M communications will be indispensable in order to realize the vision of IoT. However cognitive M2M communications requires a cognitive radio-enabled protocol stack in addition to the fundamental requirements of energy efficiency, reliability, and Internet connectivity. The main objective of this paper is to provide the state of the art in cognitive M2M communications from a protocol stack perspective. This paper covers the emerging standardization efforts and the latest developments on protocols for cognitive M2M networks. In addition, this paper also presents the authors' recent work in this area, which includes a centralized cognitive medium access control (MAC) protocol, a distributed cognitive MAC protocol, and a specially designed routing protocol for cognitive M2M networks. These protocols explicitly account for the peculiarities of cognitive radio environments. Performance evaluation demonstrates that the proposed protocols not only ensure protection to the primary users (PUs) but also fulfil the utility requirements of the secondary M2M networks.

Cooperative routing and spectrum aggregation are two promising techniques for Cognitive Radio Ad-Hoc Networks (CRAHNs). In this paper, we propose a spectrum aggregation-based cooperative routing protocol, termed as SACRP, for CRAHNs. To the best of our knowledge, this is the first contribution on spectrum aggregation-based cooperative routing for CRAHNs. The primary objective of SACRP is to provide higher energy efficiency, improve throughput, and reduce network delay for CRAHNs. In this regard, we design the MAC and Physical (PHY) layer, and proposed different spectrum aggregation algorithms for cognitive radio (CR) users. We propose two different classes of routing protocols;Class Afor achieving higher energy efficiency and throughput, andClass Bfor reducing end-to-end latency. Based on stochastic geometry approach, we build a comprehensive analytical model for the proposed protocol. Besides, the proposed protocol is compared with the state of the art cooperative and non-cooperative routing algorithms with spectrum aggregation. Performance evaluation demonstrates the effectiveness of SACRP in terms of energy efficiency, throughput, and end-to-end delay.

In this paper, we investigate power efficient resource allocation for the uplink of LTE networks under delay Quality-of-Service (QoS) constraints. We formulate the resource allocation problem as the minimization of sum power in the uplink under statistical delay QoS provisioning, which is complicated due to the specific constraints of SC-FDMA (uplink air interface in LTE networks). We solve the problem using Canonical duality theory. Numerical results which are obtained using the Invasive Weed Optimization algorithm, show that the proposed resource allocation algorithm not only outperforms classical algorithms in terms of power efficiency while satisfying the QoS requirements, but also performs closer to the optimal solution.

Mobile data offloading on smaller cells such as Wi-Fi comes as a natural solution to boost cellular networks capacity and keep up with the rapid increase of mobile data traffic demand. In this paper, we propose an offloading mechanism through the abstraction of Software-defined Networking (SDN) in the mobile backhaul to provide programmable offloading policy derivation that are aware of users and applications as well as the condition of wireless network. The proposed mechanism considers the real-time network condition to derive the offloading policies and efficiently accommodate the traffic in both LTE and Wi-Fi networks. Numerical results prove that the proposed approach can significantly improves dropping rate of the incoming traffic with using more real-time and dynamic decisions for offloading.

It is expected that cognitive Machine-to-Machine (M2M) communication will be indispensable in near future. Moreover, M2M networks must be Internet Protocol (IP) enabled for ubiquitous connectivity. Recently, IETF has standardized RPL (Routing Protocol for Low Power and Lossy Networks), which is expected to be the standard routing protocol for majority of M2M applications. Our objective in this paper is to enhance RPL for cognitive radio enabled M2M networks. Our enhanced protocol provides novel modifications to RPL in order to address the routing challenges in cognitive radio environments along with protecting the primary users as well as meeting the utility requirements of secondary network. The proposed protocol is evaluated through system level simulation studies.

Increasing the cell edge user throughput in the Long Term Evolution (LTE) systems is a relatively new arising research area. The requirement for higher data rates especially at cell edges is becoming ever more pressing as the advantages could help satisfy better Quality of Service (QoS) on an enduser level and mean higher profitability on the operator side. Therefore developing algorithms and techniques to mitigate the inherently increased inter-cell interference (ICI) and reduced signal to interference and noise ratio (SINR) in the cell edge is a challenge with high potential benefits and rewards. To serve the above objective, we study the downlink (DL) packet scheduling and resource allocation of an LTE system under proportional fairness (PF) with an innovated utility function and a frequency reuse factor of one. We present our joint ICI-avoiding cooperative packet scheduling algorithm and show through simulations, cell edge throughput improvements of about 40% as an exchange for a 16% decrease in cooperating cells' throughput in comparison to the results obtained under no cooperation between the evolved Node Bs (eNB).

This paper investigates energy and interference aware Cooperative Routing algorithms in Cognitive Radio Ad-Hoc Networks. Two routing algorithms have been proposed. In Algorithm I, we propose to minimize transmission power based on the rate required, and investigate the total transmission power consumption of the shortest path from source to destination whereby each link on the path is given the option of selecting a relay to further reduce transmission power. In Algorithm II, we consider Primary User (PU) receiver protection by reducing the fractional overlap area of each secondary node with the primary coverage area, and use the average interference probability to optimize route choice again allowing a cooperative relay to be chosen for each link on each possible path. Simulation results show that the proposed Algorithm I can achieve a transmission power saving of up to 30%, while Algorithm II can reduce interference probability for PU receivers by up to 6%.

Recently, energy efficiency in wireless networks has become an important objective. Aside from the growing proliferation of smartphones and other high-end devices in conventional human-to-human (H2H) communication, the introduction of machine-to-machine (M2M) communication or machine-type communication into cellular networks is another contributing factor. In this paper, we investigate quality-of-service (QoS)-driven energy-efficient design for the uplink of long term evolution (LTE) networks in M2M/H2H co-existence scenarios. We formulate the resource allocation problem as a maximization of effective capacity-based bits-per-joule capacity under statistical QoS provisioning. The specific constraints of single carrier frequency division multiple access (uplink air interface in LTE networks) pertaining to power and resource block allocation not only complicate the resource allocation problem, but also render the standard Lagrangian duality techniques inapplicable. We overcome the analytical and computational intractability by first transforming the original problem into a mixed integer programming (MIP) problem and then formulating its dual problem using the canonical duality theory. The proposed energy-efficient design is compared with the spectral efficient design along with round robin (RR) and best channel quality indicator (BCQI) algorithms. Numerical results, which are obtained using the invasive weed optimization (IWO) algorithm, show that the proposed energy-efficient uplink design not only outperforms other algorithms in terms of energy efficiency while satisfying the QoS requirements, but also performs closer to the optimal design.

The use of cognitive radio technology for M2M communications is expected to be indispensable in near future. In the meanwhile, the unique features of M2M communications create various challenges, especially at the MAC layer. We aim to design a cognitive MAC protocol for generic M2M communications that sufficiently fulfils the service requirements of M2M devices. For this purpose, we propose PRMA, carry out its feasibility study, adapt, and significantly enhance it with modifications especially tailored for M2M communications. By combining PRMA and cognitive radio technology, a frame structure is developed for supporting co-existence of cognitive M2M network with the primary network. This frame structure is further optimized considering different tradeoffs. The proposed protocol is evaluated using both analytical and simulation results.

M2M communications enables devices with an ability to communicate autonomously and thus acts as the enabling technology for Internet-of-Things. It is expected that a multitude of connected devices will exist in near future. In order to avoid any spectrum scarcity issues, there is a need to explore alternate spectrum opportunities. Thus the need of cognitive radio technology for M2M communications will be indispensable. On the other hand, the unique features of M2M communications create a number of challenges for existing communication networks, especially at the MAC layer. We aim to design a MAC protocol for generic M2M communications that uses cognitive radio technology at the physical layer. For this purpose, we propose PRMA, carry out its feasibility study, adapt and significantly enhance it with modifications especially tailored for M2M communications. Analytical and simulation results show a promising combination for application in practical M2M scenarios.

In this paper, cooperative physical layer network coding (CPLNC) is introduced as an energy efficient transmission strategy for future wireless networks. Implementation framework for CPLNC is presented and its performance is analyzed in Rayleigh fading channels. To demonstrate the effectiveness of the proposed scheme in saving energy, we incorporate CPLNC in two major energy-efficient routing algorithms. Simulation results demonstrate the effectiveness of the proposed algorithms in reducing energy consumption.

This paper introduces a transmit beamforming strategy taking into account the positions of primary, secondary victim and intended secondary receivers, to achieve underlay secondary access in multihop cognitive radio networking. The transmit beamforming strategy defines a novel path optimization scheme that deviates from a preselected path given by the routing module, based on local information and according to a relay selection metric. This metric is designed to improve both coexistence with primary/secondary victim receivers and performance of the secondary cognitive network. Simulations compare the proposed strategy with a baseline solution that does not adopt beamforming, and with a strategy that applies beamforming on each hop without modifying the original path. Results show that the proposed strategy is capable of improving coexistence with primary/secondary victims, and highlight that a trade-off exists between the meeting of coexistence constraints and maximisation of secondary network performance.

This paper's central aim is to address the issue of resource management at the Local Mobility Anchors (LMA) in the Proxy Mobile IPv6 (PMIPv6) networks. A class-based admission control is proposed to improve the bottleneck effect caused by triangular routing in PMIPv6, where resource units are rationed amongst different classes of traffic according to their QoS requirements. The PMIPv6 network is modeled as an M/M/m/m tandem queuing network with two types (classes) of arrival process and an analytical model is presented. Performance of our proposed admission control scheme is evaluated through simulation and results are compared to the case where no distinction in terms of resource unit allocation between classes of traffic was considered.

In this paper a novel fuzzy non-dominance routing and path ordering algorithm is presented for quality-of-service (QoS) routing for networks with inaccurate information. As one of the essential characteristic of both mobile wireless and fixed networks, the information available for decision making of QoS routing is always inaccurate[1][2]. Typically the link state information is collected by a decision maker as a result of dynamic traffic demand, channel quality, mobility, routing aggregation, out of date routing updates as well as any combination of the above factors. Therefore it is very difficult to model an exact cost for individual QoS path across the network. In this paper, we consider that network link weight is naturally uncertain due to inaccurate information. We define the routing problem in a fuzzy weighted graph. A novel concept of fuzzy shortest path and non-dominated multi-path will be introduced into network routing. A combination of fuzzy controller, link-state fuzzy shortest path routing and path ordering algorithm is developed for finding QoS paths through the network with inaccurate information. It supports a better network QoS with less computational and management cost. We examine our fuzzy non-dominance routing scheme under a rate-based service model in[3]. Under such circumstance the available bandwidth is considered as a main parameter to guarantee the network QoS. We develop the simulation on OPNET Modeler and demonstrate our results based on randomized partial meshed mobile access networks. However this is easy to extend to other type of networks with different key metrics.

In spectrum bands where spectrum sharing is allowed by national regulators, radio access technology recognition is an important technique for reducing interference and facilitating cooperation among cognitive radios. Unlicensed users (secondaries) need to be able to differentiate between transmissions of licensed users (primaries) and other unlicensed users. Furthermore, secondaries should only free a band when the licensed primary user starts to transmit. In this regard, secondary users' transmission technology classification will have a vital role for coexistence/cooperation purposes in such shared spectrum bands. For the purpose of this work, a practical testbed made up of software defined radio transceivers and a set of computing units was put together. A classification neural network was trained in a supervised learning method. Testbed results demonstrate the efficiency of the classification in differentiating among different radio access transmissions.

Helicopter radio links via satellite are limited in performance when the antenna is located below the main rotor. The fuselage may obstruct the line-of-sight signal and the rotating blades not only periodically block it but also generate reflections which cause periodic ripples in the signal complex envelope. This paper presents receive diversity and transmit space time coding with up to three antennas combined with variable high order modulation and coding techniques in order to overcome these problems allowing unprecedented bandwidth efficiencies in helicopter links for existing and future satellite systems. As a satellite system example, the Inmarsat enhanced Broadband Global Access Network (BGAN) is considered operating over the Alphasat satellite to be launched in 2013 over the European airspace by Inmarsat and ESA. With the proposed techniques and radio upgrades, bandwidth efficiency approaching 5 b/s/Hz may be achievable to/from helicopters and at the same time the reliability of the link and service area increases.

This paper investigates the green or energy efficient operation of cellular access networks through dynamic spectrum and traffic load management techniques. Different energy saving techniques are discussed along with applications in realistic multi-cellular scenarios. The use of base station cooperation is discussed. The outage probability analysis is also discussed for different energy saving techniques in order to satisfy a particular Quality-of-Service (QoS) threshold for different services. The analysis is supported by different base station power consumption models, traffic models, and realistic statistics of different base stations in London, UK. Results show a considerable power saving potential of up to 65% or more in base station power.

The introduction of Machine-to-Machine (M2M) communications in cellular networks creates a whole new set of challenges due to the unique service requirements and features of M2M devices. One such challenge is the radio resource management, particularly on the uplink. The requirements of high energy efficiency coupled with diverse QoS requirements of M2M devices and conventional Human-to-Human (H2H) users complicate the resource allocation problem. In this paper, we address the issue of energy efficient radio resource allocation for M2M/H2H co-existence scenarios in LTE networks, while meeting the QoS requirements for different users. Our proposed algorithm shows encouraging performance in achieving the desired objectives, compared to existing algorithms in literature.

The rapidly increasing demand for mobile data services urges operators to explore alternative technologies to handle the voluminous data traffic on their networks. In this regard, mobile data offloading is expected to become a key industry segment in near future. In this paper, we propose a policy based offloading framework for cellular network which is based on a cost function approach. We discuss user centric, network centric and hybrid policies where the decision making is shared between the user and the network. We also present a novel mechanism for the decision sharing between user and network which is based on principles of autonomic networking and where policies are chosen dynamically according to the variation of network conditions and the operator strategies. Detailed simulation studies are conducted to validate the effectiveness of these policies in real networks.

Receiver-based MAC (RB-MAC) is a preamble-sampling MAC protocol for WSNs in which a receiver node is dynamically elected, among potential neighbors of the sender node, based on current channel conditions. In this paper, we evaluate the performance of RB-MAC and compare it with a senderbased preamble-sampling MAC protocol by using analytical methods, and implementation in real sensor nodes. We have used Configurable MAC (C-MAC), which is a framework to develop different MAC protocols in WSNs. This framework is realized as a component architecture that can produce application-specific communication protocols. The experimental results presented in the paper corroborate with the analytical and numerical results showing how RB-MAC outperforms sender-based MAC protocols in terms of transmission delay, and energy consumption.

In this paper, we focus on energy efficient routing in wireless ad hoc networks. We exploit modulo combining of continuous-time signals arriving at a receiving node from a number of synchronized transmitting nodes and introduce a cooperative physical layer network coding (CPLNC) scheme. To demonstrate the effectiveness of the proposed scheme in reducing energy consumption, we propose two routing algorithms that utilize CPLNC as a basic building block. Through analysis, we show that with sufficiently long packets, the proposed algorithms can achieve energy saving gains of up to 37% and 62% with respect to the conventional shortest-path routing algorithm in regular line and grid networks, respectively, using less number of hops. We incorporate CPLNC into two major energy efficient routing algorithms and derive threshold distances that enable the current node to intelligently decide whether it should use CPLNC or point to point transmission to the next hop. Simulation results confirm that the proposed and the modified algorithms based on CPLNC outperform their conventional counterparts in terms of achieving significant energy saving gains in networks of randomly distributed nodes.

In this paper, we focus on energy efficient routing in wireless ad hoc networks. We exploit modulo combining of continuous-time signals arriving at a receiving node from a number of synchronized transmitting nodes and introduce a cooperative physical layer network coding (CPLNC) scheme. To demonstrate the effectiveness of the proposed scheme in saving energy, we incorporate CPLNC in two major energy-efficient routing algorithms. In the resulting modified algorithms, we derive threshold distances that enable the current node to intelligently decide whether it should use CPLNC or point to point transmission for the next hop. Simulation results confirm that the energy saving gains of the proposed new algorithms significantly outperform that of the baseline energy-efficient routing algorithms.

With the increasing interest in continuous media streaming applications such as audio and video, quality of service (QoS) is becoming more and more important. Providing QoS guarantees in packet access networks gives rise to several challenging issues. There are several aspects of QoS to be considered. For example, to support video communication high throughput is required and therefore, high bandwidth guarantees will have to be made. Audio communication, in contrast, does not usually require high bandwidth. End-to-end delay and delay variations are other factors that must be taking into account for time-critical traffic such as VoIP. In this paper, we propose a new mechanism using Multi-Plane Routing (MPR) principle based on multi-topology OSPF (MT-OSPF). Our approach, Q-MPR, leverages multiple alternate routing planes through a network for enabling maximum path diversity, and then maps traffic flows onto specific planes, using a multi-constrained cost function, respecting QoS requirements and improving quality of experience seen from end users. A maximum gain of 55%, 91% and 82% in throughput, packet loss and one-way packet delay can be achieved using our approach.

This paper investigates the energy savings a cellular operator can achieve in the access network by dynamically offloading users or traffic loads to Wi-Fi networks. The method used to analyze energy savings is presented, followed by detailed simulations using different traffic types. Results show that significant savings of up to 65-70% can be achieved by opportunistically powering down cellular radio network equipment as facilitated by the offloading of users to Wi-Fi.

In this paper, we focus on energy efficient cooperative routing in wireless mesh networks of cellular base stations. Our aim is to design a cooperative routing algorithm which is sensitive to both, the power consumed in transmitting the message between the base stations and the power consumed in operating the radio electronics. We introduce the concept of supernode with improved power efficiency and propose a power aware cooperative routing algorithm. Simulation results show a significant performance improvement over well known power saving routing schemes.

It becomes more and more recognized that using IP as the underlying foundation for the next-generation of wireless networks makes strong economic sense. This is evident in installation and operation, and technical aspects as it takes advantage of the ubiquitous installed IP infrastructure. Because of that, a resilient, efficient and easy implementable routing paradigm is needed. Multi-Plane Routing (MPR) is a routing technique, using the recent multi-topology approach, that leverages multiple alternative paths (from each source-destination pair) through a network. In this paper, we introduce MPR for wireless access networks and show that, with an optimal link weight assignment, it can reduce the maximum link utilization by up to 40% and end-to-end delay by up to 90%. MPR also increases the overall network performance by maximizing path diversity across the routing planes and splitting traffic using a branching factor. Finally, our experiments show that our nascent approach can achieve high performance in next-generation all-IP wireless access networks with a moderate number of routing planes.

Hierarchical Mobile IPv6 (HMIPv6) was proposed by Internet Engineering Task Force (IETF) to reduce signalling cost by localising the mobility signalling traffic of Mobile Nodes (MNs). However, certain MNs still generate excessive signalling overhead, due to their ping pong movement at borders of different Mobility Anchor Point (MAP) domains. In this paper, an algorithm is proposed, to effectively reduce the handover signalling overhead in the network. A cost function was developed and allocated to Access Routers (ARs) in then network, by taking into account several parameters. The proposed algorithm spreads the domain of each MAP to its adjacent MAP(s) domains by selecting boundary ARs one by one, based on their cost values, and creating overlapping regions between the domains. The performance in the new network structure created by the proposed algorithm is evaluated against a single MAP per domain HMIPv6 access network. A comparison simulation study illustrates a significant improved performance in the network is obtained, in terms of average rate of inter-area handover, whilst balance in terms of bandwidth utilisation among MAPs is maintained.

Delay-sensitive video transmission over IEEE 802.11 wireless local area networks (WLANs) is analyzed in a cross-layer optimization framework. The effect of delay constraint on the quality of received packets is studied by analyzing “expired-time packet discard rate”. Three analytical models are examined and it is shown that M/M/1 model is quite an adequate model for analyzing delay-limited applications such as live video transmission over WLAN. The optimal MAC retry limit corresponding to the minimum “total packet loss rate” is derived by exploiting both mathematical analysis and NS-2 simulations. We have shown that there is an interaction between "packet overflow drop" and "expired-time packet discard" processes in the queue. Subsequently, by introducing the concept of virtual buffer size, we will obtain the optimal buffer size in order to avoid "packet overflow drop". We finally introduced a simple and yet effective real-time algorithm for retry-limit adaptation over IEEE 802.11 MAC in order to maintain a loss protection for delay-critical video traffic transmission, and showed that the average link-layer throughput can be improved by using our adaptive scheme.

Various algorithms have recently been proposed to enhance the Quality of Service (QoS) in Wireless Mesh Networks (WMNs). In this respect, we investigate joint Call Admission Control (CAC) and routing in order to provide quality of service (QoS) in wireless mesh networks. Joint association of each mesh client with a mesh access point and multi-hop backhaul routing to the Gateway, determine the availability of resources as to admit or reject a flow.We formulate a joint optimization problem, which maximizes the total revenue from all the carried connections in the network while taking into account the bandwidth constraints of access and backhaul links. In this regard, firstly we derive an optimal pricing policy that considers the complexity of the problem and the connection dropping probability. Then a CAC algorithm is presented using the pricing model. Due to its complexity, the proposed problem cannot be dealt with using the exact methods; therefore a sub-optimal solution is presented through incorporating the meta-heuristic search algorithm i.e batch based simulated annealing to the CAC algorithm.

Dynamic load and spectrum usage management techniques can significantly improve the energy efficiency of mobile communications systems. This paper considers: (i) the opportunistic reallocation of traffic loads between bands to allow radio network equipment in the bands that the traffic is originated from to be powered down, and (ii) the opportunistic selection of more appropriate spectrum based on propagation characteristics to minimize necessary transmission power through improving propagation and/or reducing power leaking into co-channel cells in frequency reuse cases. This paper addresses the simulation of video, FTP and HTTP (web browsing) traffic sources for configurations representing LTE and HSDPA telecommunications networks, and shows that the opportunistic reallocation of users between bands to power down radio equipment achieves a significant saving of 50% or more in from-the-socket power. Furthermore, it shows that the opportunistic reallocation of users/links to minimize transmission power through using more appropriate propagation spectrum leads to a further modest reduction in from-the-socket power consumption.

Various facets of cognitive radio technology have been studied in recent years. However, one possibility that is only thus-far marginally investigated is the ability to perform secondary access at the same time, band and location as ongoing primary transmissions through beamforming to secondary users. Clearly one reason why this has not been at the forefront of research is that it could imply a significant interference to primary users. This paper, however, demonstrates that such an approach is not only feasible, but derives an optimisation problem to constrain interference to primary users while keeping the received signal-to- interference-plus-noise ratio at the secondary users to above a threshold to maintain an acceptable level of quality of service, even taking into account positioning errors. It analyses the described concept and shows good performance against effective beam width increases in secondary transmissions, enacted to improve coverage to account for angular positioning error.

Existing power-aware routing algorithms are fixed and unaware of channel fading dynamics. They are suitable for interconnection of base station subsystem in large cellular networks, where the impact of fading is negligible. However, the height of base station towers could be reduced as the cell size shrinks. In such scenarios, and, in particular, in urban areas, the impact of fading cannot be ignored due to possibility of multipath reflections. Thus, when deployed in real world scenarios, these algorithms suffer from severe performance degradation in terms of power consumption. In this paper, we propose a routing algorithm that takes into account the real channel conditions such as multipath fading. The algorithm is optimised based on location knowledge of nodes and dynamic variation of the channel localised to each node. The results show a power saving gain of around 35% over the baseline scheme.

Provision of ubiquitous services is considered as an important source of revenue generation for future telecommunication operators. However, these services must be adaptable to a large variety of users within administrative networks. The request of such adaptations will be processed by various Adaptation Mechanisms (ADME) located in different parts of the administrative network; therefore ADMEs' selection strategy is a vital task. This paper presents a joint pricing and ADME's selection strategy taking into account the capacity constraints of ADMEs in order to minimize the total administrative network cost. In this respect, we first formulate a joint optimization problem, which minimizes the network cost and finds the solution using the exact methods. We then carry on tackling the problem by applying a heuristic method, which can be used in future in order to provide results for a complex scenario and achieves a satisfying near-optimal solution.

Abstract Proxy Mobile IPv6 is a network based mobility management solution and was proposed to address the shortcomings of the existing set of mobility management protocols. The presence of local mobility anchors (LMA) in PMIPv6 networks can lead constrained routing and create areas of bottleneck. This is due to all traffic to the mobile nodes (MNs) in the PMIPv6 domain having to flow to and from the LMA. Future IP networks will support a wide variety of sessions ranging for high QoS Video conferencing to FTP and P2P download. Providing the same level of mobility support for all of these sessions can lead to the resources of LMA being drained. To avoid this, we propose the QoS aware Dynamic Route Optimization scheme where the network identifies the lower QoS sessions and establishes a binding update with the correspondant node (CN) rather than with the LMA. To achieve this a flow based binding approach is followed. The level of congestion in the network is also considered as part of the mechanism. To ensure optimal performance of the proposed mechanism, routing policies are proposed. Simulation results show considerable benefit to the network in terms of reduction in blocking probability as well as reduction in tunnelling overhead cost in comparisons to no route optimization (RO) and adaptive route optimization (ARO) being deployed in the PMIPv6 networks. Copyright © 2009 John Wiley & Sons, Ltd.

Abstract-In this paper, we propose a dynamic OFDMA based subcarrier/power allocation scheme, which aims to balance the aggregate rate and the achieved TCP throughput of competing TCP flows. The proposed allocation utilizes the theoretical TCP throughput which can be accomplished in the end-to-end path. In doing so, the TCP aware scheme attempts to minimize the gap between the allocated rate and the theoretical upper bound under the system constraints. Such a technique can be of significant importance since due to its popularity, TCP is commonly used for streaming video or other ultimedia applications. Numerical investigations reveal that the proposed approach, provides more balance towards the TCP throughput, and under some considerations significantly increase the fairness among competing TCP flows over end-to-end paths of different characteristics. In addition to that, it also manages to avoid starvation of TCP flows with poor channel conditions.

As the amount of information in particular multimedia contents and services increases over networks, and in conjunction with the increases in the number of end user devices, it is becoming more and more inefficient for content and service providers to prepare their content in advance. An Adaptation Management Framework (AMF) has been proposed to provide a dynamic adaptation mechanism that allows Content/Service to be automatically adapted to a user's current capabilities, i.e. device and environment capabilities and their individual preferences. This work forms part of the Mobile VCE Ubiquitous Service program. In this paper, we investigate one of the major complexities involved in the design of the AMF, that is to select and combine appropriate adaptation operations as well as their concrete implementations once adaptation tasks are given. We proposed the use of a selection algorithm for selecting among multiple content Adaptation Mechanisms when multimedia content must be adapted to a user's context and device characteristics. The performance of such an algorithm is evaluated with respect to effectiveness and efficiency.

The performance of multi-hop multiple-input, multiple-output (MIMO) communication scenarios is evaluated for space time block coded (STBC) and the proposed distributed cyclic delay diversity (CDD) technique. By increasing the frequency selectivity, multi-stage CDD with low complexity implementation yields significant performance improvement as relaying network. Both diversity techniques based on frequency-correlated MC-CDMA subcarriers networks are investigated by using the moment generating function (MGF) over correlated Nakagami-m fading channels .The system performance evaluation is provided for the exact average symbol error rate (SER) and the end-to-end bit error rate (BER). In order to maximize the end-to-end throughput [bits/s/Hz], explicit allocations strategies are derived and analyzed. Simulation results are also presented which show excellent agreement with the analytical framework.

A plethora of modifications to transmission control protocol (TCP) have recently been proposed, a major aim being to improve its performance over wireless links. Two schools of thought have emerged: the first investigates changes to the transport-layer protocol, whereas the second explores the potential to enhance the characteristics of lower layers to improve the end-to-end performance of TCP. This study focuses on the latter, and, in contrast to most research in this area, which thus-far has concentrated on a single TCP flavour, examines the case where different TCP flavours are competing over a wireless link. To this end, the authors present and assess a cross-layer solution to adapt the coding rate at the link-layer based on the detected TCP flavour, to maximise fairness among TCP flows. Through both analysis and simulation, the authors show that the proposed scheme considerably improves the fairness among different TCP flavours that compete over a wireless link. Furthermore, the proposed approach has minimal detrimental effect on the aggregate throughput of TCP flows.

In fixed worldwide interoperability for microwave access (WiMAX), radio and network planning can be optimised by tuning a cost/revenue function which incorporates the cost of building and maintaining the infrastructure and the effect of the available resources on revenues. Supported throughput typically decreases with larger cells because of the implied greater average distance of users from the base station, although the use of sub-channelisation can keep throughput steady up to a larger radius. Sectorisation can improve the throughput of the cell by facilitating the use of higher order modulation and coding schemes; besides, sectorisation equipment is more expensive, and there is the need for three times more spectrum bandwidth, increasing costs while increasing system capacity by a factor of 3. On a multi-cell level, system capacity is determined by the chosen frequency reuse pattern, K. In this study, under the assumption of a revenue per Mbyte of information transfer somewhere between 0.0025 euro and 0.010 euro, the choice of K=3 or 4 with sectorial cells is preferable to the use of omnidirectional cells with K=7. This study also concludes that a cell radius in the range 1000–1500 m is preferable, corresponding to profit in percentage terms of near the achievable maximum, while keeping costs acceptable.

To minimize the large handover delays associated with mobile IPv6 numerous micro-mobility protocols were proposed. In this paper, we consider the mobility agent (MA) based family of micro-mobility protocols such as hierarchical mobile IPv6 and proxy mobile IPv6 and focus on the issue of the bottlenecks that MAs can lead up to under high network load. We propose a Dynamic QoS aware route optimization with the aim of reducing the bottlenecks around MAs. We exploit the fact that not all classes of IP traffic require low handover latency support; for example, P2P traffic, web browsing, etc. do not require high QoS and are delay tolerant. Hence, such traffic classes can be forced to establish a direct connection with the CN and the routing policies at edge routers can ensure these traffic classes bypass the MA. The number of traffic classes that are to bypass the MA increases dynamically according to the congestion of the network. Results show that by implementing the dynamic route optimization the network utilization increases and the average packet delay in the network are reduced.

Cognitive radio is presently being researched as a means to greatly improve spectrum usage efficiency, connectivity and QoS among wireless devices and systems. In parallel, efficient and fair resource allocation strategies are being studied in order to address the requirements of future wireless technologies. In this paper, we assess a novel resource allocation scheme for OFDM systems which aims to maximize performance while limiting received interference at each user to below a defined threshold. We show that our scheme is relevant to cognitive radio, and demonstrate that through our approach, significant power savings can be achieved in wireless systems.

Distributed Cooperative Cyclic Delay Diversity (DCCDD) multi-hop relay network is shown to yield superior performance over traditional link network. The benefits provided by increased frequency selectivity caused by the cyclic delays are evaluated through the explicit closed-form BER expressions and maximum achievable throughput [bits/s/Hz]. Towards that end resource allocation strategies in terms of fractional frame duration and transmission power are assigned. By using the moment generating function (MGF) of the correlated Nakagami-m random variable and considering a realistic case of frequency-correlated multicarrier code division multiple-access (MC-CDMA) system, allocation strategies are derived and analyzed in order to maximize the end-to-end throughput. Monte-Carlo simulations are used to numerically verify the analytical framework with maximum ratio combining (MRC) detection technique.

In this paper, the performance of a cooperative relaying scheme with cyclic delay diversity (CDD) for an orthogonal frequency division multiplexing (OFDM) system is investigated. The system under consideration consists of multiple single-antenna terminals acting as relays and cooperating to provide spatial diversity. Cyclic shift is introduced at each relay and thus increase the frequency selectivity of relay channels. To exploit a highly selective channel, convolutional code is employed together with OFDM. Simulations demonstrate the bit error performance of the proposed scheme with different numbers of relays as well as performance in flat and frequency selective fading channels. The performance of the system is also compared to conventional multiple-input multiple-output (MIMO) with CDD and a conventional amplify-and-forward (AF) relay system. The results indicate that the proposed scheme provides enhanced performance under various considerations.

The IEEE 802.15.4 specification has generated a lot of interest in recent times, especially within the Wireless Sensor Network (WSN) research community, primarily because energy efficiency is one of the specifications' design cornerstone. As this specification is relatively new, it is incumbent that its operational mechanisms are well understood, to allow for efficient cross layer interactions between the different processes that make up the specification and existing or new higher layer protocols. In this paper, we present a deterministic Petri-Net model of the IEEE 802.15.4 CSMA-CA process, that is timer driven and operates within the bounds of the contention access period (CAP). Using this model, we are able to analyze the performance characteristics of the CSMA-CA process, especially in terms of channel throughput and energy consumption. We also verify the extracted system indices by comparing them to those gotten from a full model of the specification, implemented using the OPNET network simulation platform.

All-IP mobile networks require a mechanism for enabling seamless handovers between different access technologies. For real-time services, such as voice and video, the Session Initiation Protocol (SIP) is becoming the leading signalling protocol in IP networks and has already been accepted as the signalling standard in 3G wireless systems. However, existing proposals for supporting mobility with SIP suffer from undesirable delay in multimedia applications. The IEEE 802.21 Media Independent Handover (MIH) group has proposed a new layer called layer 2.5 (L2.5) or MIH layer that offers advanced services for handover such as event notification, L2 handover commands and information on available networks. In this paper, we combine the 802.21 MIH smart triggers with SIP mechanism to provide a fast handover solution. We also modelled this combination using OPNET network simulation tools and show how the event triggers could improve the handover initiation time.

This paper describes the architecture of a self-configuring multi-hop mobile network and analyse the performance of the ad-hoc routing protocols. A testbed is deployed to analyse the performance of the ad-hoc routing protocols in a self-configuring multi-hop environment. The testbed comprises of a set of mobile nodes and an Internet gateway. The mobility of the nodes and the resulting network topology are emulated. During the experiments, the mobile node move virtually around a specified area and communicated with the gateway by sending UDP packets. The routing between the MNs and the Internet gateway is established by the ad-hoc routing protocols namely AODV and OLSR. Based on the measurements obtained during the experiments, some of the well known performance metrics are calculated.

In this paper we develop a framework for resource allocation in a secondary spectrum access scenario, where a group of cognitive radios (CR) access the resources of a primary system. We assume the primary system is a cellular OFDM-based network operating in uplink. We develop an optimum resource allocation strategy, using cooperative game theory, which guarantees the primary's required QoS and allocates an achievable rate at a given bit error rate for the secondary, when possible. The proposed cognitive radio game (CRG) is a network-assisted resource management method, where users (both primary and secondary) inform the primary system's BS of their channel state information and power limitation and the base station calculates the optimum sub-channel and power allocation for all users. Using Game theoretic axiom of fairness, i.e., Nash Bargaining Solutions (NBS), we develop an alternative efficient and fair resource allocation and compare its performance with the proposed CRG method. We use Sequential Quadratic Programming (SQP) to solve the proposed non-linearly constrained CRG optimization problem.

We propose a technique for enhancing the achievable spectral efficiency of multiuser direct-sequence code-division multiple-access (DS-CDMA) fading channels in the presence of additive white Gaussian noise (AWGN) and multiple access interference (MAI). The proposed scheme involves the joint optimization of outer loop power control (OLPC) and rate control using variable spreading factors (VSFs). The optimality is in the sense of average spectral efficiency maximization. The optimum outer loop target signal-to-noise ratio (SNR-target) and the corresponding spreading factor are derived jointly, in terms of the number of active users. Along with transmit power adaptation in the inner loop, this leads to maximized average spectral efficiency. Total and truncated channel inversion strategies are used in the inner loop. The average spectral efficiency of the joint optimization scheme is derived for the conventional matched-filter and the multiuser decorrelating detectors. Average transmit power and instantaneous bit error rate (BER) constraints are considered and the performance is evaluated over Nakagami-m flat-fading channels. In low SNRs, the proposed scheme can provide a considerable gain in bits/s/Hz for either of the detectors, compared to a VSF-assisted system that does not exploit OLPC and thus the optimum SNR-target.

A significant body of recent research has analyzed the problematic behavior of TCP over wireless links, and a plethora of modifications to TCP have been proposed in order to increase its performance in such contexts. Two schools of thought have emerged: the first proposes changes to the end-to- end protocol, while the second explores the potential to enhance lower layers as a means to improve the end-to-end performance of TCP. This paper focuses on the latter, and in contrast to most research in this area, which thus-far has concentrated on a single TCP flavor, examines the case where different TCP flavors are competing over a wireless link. To this end, we present and assess a cross-layer solution that involves the adaptation of lower layer characteristics (i.e., the coding rate) based on the detected TCP flavor, in order to maximize the fairness among TCP flows. Through extensive numerical investigations, we show that the proposed scheme considerably improves the fairness over wireless links among different TCP flavors. Our approach also has a minimal effect on the aggregate throughput of the TCP flows, and in cases where the packet error rate is very low, has a small positive effect on throughput.

In this paper we develop a framework for resource allocation in a secondary spectrum access scenario where a group of cognitive radios (CR) access the resources of a primary system. We assume the primary system is a cellular OFDM-based network. We develop the optimum resource allocation strategies which guarantee a level of QoS, defined by minimum rate and the target bit error rate (BER), for the primary system. Using the game theoretic axiom of fairness, i.e., Nash bargaining solutions (NBS), we show that by allocating a priority factor to all players an efficient and fair resource allocation can be achieved. We show how the priority factors are assigned in this scheme and outline a method to select the users who are allowed to share a specific sub-channel.

Ubiquitous multimedia services are formed by coalescing wireless communication into distributed multimedia systems. Content and service provisioning becomes problematic as many of the access devices are restricted in terms of processing, information display and network data rates, therefore, content must be suited to the user's preferences, usage context, device capabilities and network conditions. Since content may have to be converted into several intermediate forms to get into its final desired adapted form, content adaptation becomes multi-step process involving a number of services each performing a specific adaptation operation.

In this paper we develop a cellular cognitive radio network based on MC-CDMA, which is able to coexist with a number of legacy RANs in a shared band. Using the simple-to-obtain knowledge of RF environment, namely the bandwidth and frequency location of each legacy system, the cognitive MC-CDMA transmitter mitigates the interference in the corresponding receivers by adaptive transmission. We will develop an algorithm for calculating the adaptive transmission parameters and elaborate on error performance of this approach analytically and numerically.

In mobile communication environments, traditional routing protocols designed for static wireless sensor networks may fail to deliver data timely. The aim of this work is to identify improvements that can be obtained considering mobility and to recognize its research challenges. We briefly describe different levels of mobility in wireless sensor networks (WSNs) and highlight the efficiency of routing in the presence of the mobility.

A range of flavors of TCP are already in existence, and further flavors are being introduced in order to, for example, cope with the packet loss characteristics of wireless links. Moreover, the proliferation new wireless standards and the relative performance differences among them have been mushrooming in recent years. Given the increasingly heterogeneous nature of the Internet, mechanisms do not usually exist for a server to specifically select an appropriate TCP flavor for each individual download. In this paper, we therefore present and assess a cross-layer solution for a node (e.g. a base-station) to quickly adapt lower-layer characteristics (the coding rate and local ARQ retransmissions threshold) based on the detected TCP flavor, in order to optimize the end-to-end performance of the download for that utilized flavor. We demonstrate that the proposed scheme has considerable potential to improve the overall download throughput, while placing no burden on the server and requiring no changes to existing TCP implementations.

From a network perspective, the major challenge in providing seamless connectivity whilst maintaining the required level of QoS to users results from the negative interactions that occur between mobility and QoS. These interactions, particularly those of mobility and QoS, have been the subject of much research. In this paper, we discuss the various approaches that have already been taken to combine QoS and mobility mechanisms, and present a new framework to combine such mechanisms with the aim of reducing the negative interactions that might arise between them. We propose the concept of enhanced nodes which is a special IP router with an extra sub-layer of mobility, QoS and security features. Our framework is illustrated with an example of a QoS-based mobility selection mechanism.

With the advent of various access technologies and increasing number of applications, a set of challenges concerning efficient delivery of ubiquitous services to heterogeneous users and devices have been posed. One of the important challenges is to integrate quality of service (QoS), security and mobility support in heterogeneous networks. To facilitate the interworking of these mechanisms we propose the concept of enhanced node (EN) in this paper. The EN is an intelligent entity with a network sub-layer, which integrates QoS, security and mobility management (MM). ENs are located in the access network and they communicate with each other via signalling. In this paper, the functionalities of the ENs are described and the framework with ENs to integrate QoS, security and MM in IP-based networks is presented. The mechanisms to provide the authenticated and authorized access control and to enhance the secured QoS combined fast handovers are also proposed.

Battery-powered wireless sensor networks (WSNs) are highly constrained in energy. In order to maximize the node and network lifetime, the energy usage has to be optimized. In this paper, we analyze the sources of energy consumption in p-persistent CSMA for non-saturated conditions, showing that maximum efficiency is achieved for a narrow range of traffic load. Furthermore, the optimum traffic load is a function of the consumption characteristics of the node and it does not guarantee maximum system throughput. Our analytical framework can be applied in various CSMA variants, thus aiding in the design of Medium Access Control (MAC) protocols for WSNs.

The main goal of this article is to show a context-aware PAA multi-agent system (CAPMAS) framework and how it conveys context-aware computing and agent technologies into ubiquitous system. We use context-awareness to provide computing environments with the ability to usefully adapt the services or information they provide. The dasiaagent technologiespsila take into account of different service solutions, which form the ultimate link to the context aware computing. In this article, we shall explore some of the basic agent technologies that lead us to develop our context awareness personal assistant agent (PAA) based systems and concepts.

Spectrum sharing methods, such as secondary spectrum access, are powerful candidates to improve spectrum utilization and efficiency. In this paper, we develop a novel resource allocation scheme for WiMAX networks, which is designed to maximize performance while limiting the received interference at each user. By defining different interference tolerances for different sets of users, the proposed allocation scheme can be exploited in a secondary spectrum access scenario where two WiMAX operators, one as the primary operator and the other one as the secondary operator, are using a shared band. The primary system benefits either by charging the secondary system for the use of its resources, or by some form of reciprocal arrangement allowing it to use the secondary system's licensed bands when needed. Numerical results show our resource allocation approach to achieve an excellent fairness, while incurring only a slight reduction in system throughput compared with the theoretical upper limit of opportunistic scheduling.

Sensor networks as cooperative spatial diversity (CSD) is implemented and analyzed for cyclic delay diversity (CDD) distributed MC-CDMA system. In such as cooperative system, it is proposed a distributed SISO analysis employing CDD to simplify the system evaluation in terms of probability of errors and maximum achievable throughput [bits/s/Hz]. Furthermore, the moment generating function (MGF) of the correlated Nakagami-m random variable is used and considered for the realistic case of frequency-correlated MC-CDMA subcarries. To this end, an explicit allocation strategy for the distributed diversity is deducted. Simulation results are also presented which show excellent agreement with the analytical framework.

A novel hierarchical QoS routing (HQoSR) protocol is proposed to perform adaptive area re-partition in wireless access networks. In its core, a re-partition algorithm is invoked either when traffic concentrated by the area borders cause excessive inter area handover rate or when the load imbalance between neighboring areas cause congestion and inefficient resource management. Simulations illustrate that the adaptive HQoSR mitigate both routing and mobility overhead suggesting better network performance.

Distributed cyclic delay diversity (DCDD) multistage MC-CDMA system communication system is shown to yield superior performance over traditional link network. The benefits provided by increased frequency selectivity caused by the cyclic delays are evaluated through explicit closed-form formulas for the exact average symbol error rate (SER) of M-ary signals. By using the moment generating function (MGF) of the correlated Nakagami-m random variable and considering a realistic case of frequency-correlated MC-CDMA subcarriers, allocation strategies are derived and analysed in order to maximise the end-to-end throughput. Furthermore, the application of CDD is presented for equal subchannel gains. Monte-Carlo simulations are used to numerically verify the analytical framework, which show excellent agreement.

In this survey paper, we investigate some of the challenges to be addressed before a practical real-time secondary market for spectrum can be developed. We differentiate the methods of dynamic spectrum allocation as coordinated usage of resources, interworking solutions, integration solutions and secondary access of spectrum. Secondary spectrum access approaches are generally classified as real-time and non-real-time secondary access. However, the focus of this work is on real-time secondary spectrum utilization which can follow a negotiated or opportunistic access strategy. While different solutions for increasing spectrum utilization and efficiency are under investigation, many aspects of spectrum sharing technologies are still open questions. After an extensive literature survey, the major challenges and open questions of real-time secondary usage of spectrum are addressed here. We also provide some insights on potentially important design considerations and requirements when developing successful spectrum management schemes to realize real-time secondary spectrum usage.

Efficient and fair resource allocation strategies are being extensively studied in current research in order to address the requirements of future wireless applications. A novel resource allocation scheme is developed for orthogonal frequency-division multiplexing (OFDM) networks designed to maximise performance while limiting the received interference at each user. This received interference is in essence used as a fairness metric; moreover, by defining different interference tolerances for different sets of users, the proposed allocation scheme can be exploited in various cognitive radio scenarios. As applied to the scheme, the authors investigate a scenario where two cellular OFDM-based networks operate as primary and secondary systems in the same band, and the secondary system benefits by accessing the unused resources of the primary system if additional capacity is required. The primary system benefits either by charging the secondary system for the use of its resources or by some form of reciprocal arrangement allowing it to use the secondary system's licenced bands in a similar manner, when needed. Numerical results show our interference-limited scheduling approach to achieve excellent levels of efficiency and fairness by allocating resources more intelligently than proportional fair scheduling. A further important contribution is the application of sequential quadratic programming to solve the non-convex optimisation problems which arise in such scenarios.

Aiming to generate ultra wideband (UWB) pulses based on wavelet packets, four different circuits are proposed. It has been shown that the wavelet packets are quasi-orthogonal and have almost identical time duration, and therefore appear to be valuable candidates for UWB pulse shape modulation systems. However, as with any technology, circuitry is an important challenge to solve before a theoretical application can live up to its full potential. The four proposed circuits are based on different interpretations of the equation defining the wavelet packets and their performance is investigated by computer simulation. The research also illustrates the characteristics and the consequent implementation advantages or issues afferent to each circuit.

In this paper, we propose a cognitive cellular system based on DS MC-CDMA to coexist with a number of narrow-band legacy systems in the same frequency range. If the bandwidth and the frequency location of each narrow-band system are known to this cognitive MC-CDMA, it is possible to mitigate their interfering effect in the cognitive receivers by adaptive transmission. We will develop an algorithm for calculating the adaptive transmission parameters and show that it combats interference in the channel effectively.

Many existing communication protocols fail to perform efficiently when groups of users move in unison and at high velocity. A classic example is the Mobile IP protocol, which, as it stands, leads to storms of binding updates at every IP handover, but is resolved by the NEMO basic support protocol. However, a problem of similar nature is also existent in Quality of Service protocols, which again tend to produce signalling storms at handover, leading to, somewhat paradoxically, surges of congestion within the access network. While QoS aggregation improves protocol scalability by maintaining a single QoS state for potentially the entire moving network rather than for each individual node, the act of having to constantly maintain this state when sessions are frequently created and terminated undermines its benefit. We therefore propose a dynamic cost-driven QoS aggregation policy, which aims at minimising network operator costs for each aggregation cycle. Simulations of the cost-driven policy show that costs are reduced by up to 6.5% relative to other QoS aggregation policies, with expected user waiting times prior to session establishment increasing by a only a fraction of a second.

The rise in the number of mobile wireless devices accessing IP based communication networks has fuelled the need for efficient mobility support for seamless communication. As a consequence a profusion of mobility protocols were proposed. The mobility agent based family of protocols have risen in popularity due to the simplicity in implementing them compared to per host based protocols. The mobility agents located within wireless access networks hide the movement of the mobile nodes by acting as an anchor point through which all the packets traverses to and from the mobile node. The presence of these mobility agents will result in bottlenecks of high congestion within the access network. This paper provides a formal definition to study this effect of mobility agents on wireless access networks. Using maximum concurrent flow problem we model the access network as a multicommodity flow problem and study the throughput of the network with and without the presence of the mobility agents. From the results it can be confidently concluded that by implementing local mobility solutions based on agents, the wireless access network capacity is reduced and the number and location of the agents within the access network have direct impact on the loss.

This paper focuses on the problem mobile terminals face when different protocols operate for providing the same service between visited access networks. Examples of such services are mobility management and QoS signaling. This plethora of protocols can restrict a mobile terminal from using the offered service since it might not be equipped with the appropriate software. This problem can be solved with the use of software reconfiguration. We present a framework for constructing mobile terminal architectures capable of dynamically reconfiguring between protocols that offer the same service. Then we employ the framework to construct two architectures; one capable of adapting to the offered mobility protocol and one capable of adapting to the offered QoS signaling protocol. Finally, we present an implementation of the emerged architectures and estimate through experiments their reconfiguration time.

This paper presents a mobile terminal architecture that can dynamically reconfigure between different mobility management protocols. Our main goal is to design an architecture that minimizes the required changes in its operation. This is achieved through the development of a generic mobility component, a composite entity capable of modeling the analyzed mobility protocols. When reconfiguring to a new mobility protocol only distinct functional parts of the generic mobility component are modified; functional parts that are common are not affected. The reconfiguration procedure is coordinated by another functional entity, the generic mobility component manager. Further, we compare the reconfigurable architecture's performance in terms of received application data and terminal protocol processing delay against of-the-shelf mobility protocol implementations, including mobile IPv6 and BCMPv1.

This paper proposes a positioning routing algorithm for UWB ad hoc networks. The algorithm is deployed in two main scenarios: Multi-Coordinate System (MCS) and Unique Coordinate System (UCS). A Packet Forwarding Zone (PFZ) is proposed to investigate the performance where a limited forwarding region is used. New ideas have been included in the routing algorithm, such as the use of the Davidon-Fletcher-Powell (DFP) algorithm to estimate the position of the locally available beacon nodes, and the Reference Group (RG) concept as formed by suitable nodes with the Reference Group Master (RGM) chosen as elected by the nodes in the RG. The RG group characteristics particularly apply in the UCS case. In addition, the performance of Direct Method (DM) and DFP position estimation algorithms are also analyzed.

This paper deals with the problem mobile terminals face when different QoS signaling protocols, than the one installed in the mobile terminal, operates in visited access networks. We present a framework for construction of mobile terminals architectures that can dynamically reconfigure among protocols that offer similar services. Further, we employ the framework to develop an architecture that can dynamically change its operation in order to adapt to the offered QoS signaling protocol. Experiments are also presented so as to estimate the architecture's reconfiguration and processing time.

In this paper, we discuss the development of a Software Download Management (SDM) module, envisioned to handle the implications and associated operations of downloads for mobile terminal reconfiguration. We highlight the SDM operations in the pre-, during-, and post-download phases, and some emphasis is also placed on the transport-layer decision making capabilities of the SDM. An important emerging capability is mass-reconfiguration, involving the alteration of common functionalities in many terminals concurrently. Relevant scenarios here might include the adaptation of a protocol or codec, an upgrade of an operating system capability, or indeed a change in network configuration which requires a large number of terminals to be adapted accordingly. A particular emphasis is also therefore on one-to-many download functionalities.

Transmission control protocol (TCP), the almost universally used reliable transport protocol in the Internet, has been engineered to perform well in wired networks where packet loss is mainly due to congestion. TCP throughput, however, degrades over wireless links, which are characterized by a high and greatly varying bit error rate and by intermittent connectivity. Over such wireless links, the performance achieved by TCP can be improved through the use of cross-layer algorithms at the link-level, which interact with the TCP state machine. In this paper, a TCP-aware dynamic ARQ algorithm is therefore proposed, which utilizes TCP timing information to prioritize ARQ packet retransmissions. Numerical investigation of the proposed algorithm demonstrates the performance improvements that can be attained through this approach, in comparison with TCP-agnostic link-layer approaches.

The problem of multi-rate power-controlled collision-free scheduling in spatial time division multiple access (STDMA) wireless mesh networks is formulated as a mathematical program utilising cross layer information. As these mixed integer linear programs are intractable (${\cal NP}$-hard problems), optimal collision-free schedules can be found only for topologies consisting of a few nodes. To this end, approximation algorithms that are based on linear programming relaxation and randomised rounding are studied. The proposed framework, which aims to maximise the spatial timeslot reuse under predefined signal-to-interference noise ratio thresholds, is suitable for providing centralised scheduling in the mesh mode of the IEEE 802.16 standard. Performance aspects of the approximation algorithms under different scenarios are investigated.

Mobile ad hoc networks (MANETs) are unpredictable by nature. Providing any kind of reliability for quality of service (QoS) in such networks is challenging. Quantifying available resources accurately, avoiding interference with ongoing QoS traffic and adapting to QoS violations caused by nodes' mobility are the main concerns for the design of an efficient admission control protocol in MANETs. Adaptive admission control (AAC), a novel admission control protocol which uses robust and accurate resource estimation and prediction techniques for relevant admission decisions has been proposed. Furthermore, AAC uses statistical QoS provision to counteract the QoS threatening mobility. Through simulations, we show that our proposed scheme outperforms existing approaches in terms of correctness and overall performance.

Over-the-air software download is a key enabler for many aspects related to the reconfiguration of terminals based on software-defined radio (SDR). Different mechanisms for advertising the availability of software enhancements to a group of SDR terminals in universal mobile telecommunication system networks are evaluated. In order to exploit efficiencies in terms of transmission and processing, addressing strategies that allow the subsequent download to be performed in a multicast fashion are considered. A novel scheme for advertising software to only those terminals that are targeted by the download is introduced. On the basis of cost analysis, it is shown that the proposed scheme performs favourably compared with other viable schemes for performing software upgrade announcements.

In this paper, we address the issue of co-existence of Bluetooth (BT) and Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)-based Wireless Local Area Networks (WLANs) in the license free 2.4 GHz band. Specifically, the probabilistic treatment presented in the following investigates the effect of the slotted p-persistent CSMA/CA system on a co-existing BT piconet. A closed-form expression for packet error probability (PEP) in BT as a function of CSMA/CA parameters such as the persistence probability, probability of packet generation and the number of users is derived. The analytical model entails different BT packet types, frequency hopping guard time, and different traffic models in the BT piconet.

Providing Quality of Service in Mobile Ad Hoc Networks (MANET) is a challenging task due to the unreliability of the wireless medium and mobility. QoS routing is used to find QoS available paths that map QoS requirements, based on network information acquired during the route discovery process, and/ or using periodic monitoring. If the QoS demand goes beyond the network capacity, the call admission procedure generally rejects any incoming QoS request, thus, avoiding quality deterioration of existing QoS flows. However, channel conditions are likely to change and might threaten the QoS provision at any time. Therefore, a strategy is needed to reinstate QoS guarantees when at risk. Whenever Best-Effort traffic deterioration is not applicable or useless, a QoS flow has to be sacrificed for the sake of others. The selection of the victim QoS flow expresses a need for conflict resolution policies. This paper proposes and analyses different conflict resolution policies and their impact on QoS provision in Ad Hoc networks.

This paper describes the evaluation of a flexible reconfigurable IP-based terminal architecture, supporting interoperation among macro and micro mobility management protocols. It is a generic component architecture that can intelligently change at runtime the operating mobility protocol, according to the available access networks. Further, it can transparently combine multiple protocols, for micro and macro mobility cooperation. This paper describes the performance evaluation results when operating the flexible reconfigurable terminal with combined macro mobility, mobile IPv6, together with micro mobility, hierarchical mobile IPv6 or BCMPv6

Cognitive radio is certain to transform our traditional radio resource allocation regimes. Through cognitive radio, better spectrum efficiency can be leveraged by radios intelligently altering their radio resource usages dependent on locally available information about radio conditions. A significant challenge for cognitive radio, however, is awareness of these local radio conditions. One crude solution is for the radio to periodically scan the complete spectrum band over which cognition in radio resource usages can apply. Such an operation would be time-consuming and wasteful of power, and ultimately would be entirely impractical. In this paper, we therefore propose the concept of a resource awareness channel (RAC)-a single universally available channel on a fixed frequency, on which information about resource usage is conveyed by all radios using the cognitive radio spectrum band. This allows cognitive radios that want to alter their transmission resources to make an informed decision about the practicality or these prospective changes in terms or interference for the system as a whole, simply by listening to the RAC. We analyse the performance or this proposed RAC concept, and show it to be practical even in areas that are highly populated by radios

This paper proposes a dynamic frequency subband and code channel assignment method for multicast band division multicarrier CDMA systems. The proposed method introduces multiple channel multicast transmissions, where the multicast transmission is divided into two channels; one is for all users in the multicast group, and the other is for a part of the multicast users. The base stations individually assign the frequency subbands and code channels to these two multicast channels. The optimum and suboptimum solutions are proposed for the two-layered frequency subband and code channel assignment. The evaluation results show that the proposed method has superior throughput performance to the single channel multicast systems

This paper presents the design and evaluation of a reconfigurable mobile terminal focusing on IP mobility protocols. The presented terminal architecture is capable of dynamically modifying its operation so as to employ the mobility services offered from the visited access networks. The fundamental concept in the architecture is that mobility protocols terminal operation can be modeled with a certain group of functional abstractions. As a consequence, only a few particular functional parts of the architecture need to be modified so as to implement a new mobility protocol. Evaluation results show that the terminal performance complies with the expected behavior and, further, that the reconfiguration process is accomplished within a few milliseconds.

Orthogonal space-time block codes allow utilising the diversity provided by multiple-input-multiple-output communication channels, thereby decreasing the error probability for a given communication rate. The contribution of this paper is the derivation of closed-form expressions of the symbol error probability of distributed codes deployed over Nakagami flat fading channels with different channel gains and fading parameters

In this paper, a family of integer linear programs is formulated for performing collision free scheduling in Spatial-TDMA wireless mesh networks. We extend previous formulations for power aware STDMA scheduling to include discrete power transmission and multi-rate support via adaptive constellation selection. Despite the theoretical attractiveness of these (mixed) integer linear programs, STDMA scheduling problems are in general intractable (NP-hard problems). Thus, the practicality of providing optimal solutions is rather limited. To this end, we study approximation algorithms that are based on linear programming relaxation and randomized rounding. Based on these approximation algorithms we focus our study on the trade-off between optimality of the solution and feasibility. Conducted numerical investigations aim to vindicate the claim regarding the strength of randomized algorithms. In that respect the performance of the approximation algorithms under different scenarios, such as the number of active links and number of nodes in the mesh network, is investigated.

When an ad hoc network is connected to the Internet, it is important for the mobile nodes to detect available gateways providing access to the Internet. We discuss the problem of interworking and integration between the ad hoc and radio access networks. Furthermore, we propose a signalling mechanism to discover and select the optimum gateway when more than one gateway is available. A gateway is considered to be optimum if the path via this gateway provides better quality of service such as total path bandwidth or overall delay. An optimum gateway selection scheme should consider both the ad hoc and radio access networks to provide better QoS support. To achieve this selection, QoS information from both sides of the network needs to be communicated across the network. Further research is required to adapt the proposed mechanism to be applied for wireless sensor networks

The performance of a space-time block coded (STBC) multicarrier code division multiple-access (MC- CDMA) system operating in Nakagami-m fading channel with correlated subcarriers is investigated. Independency among MC-CDMA subcarriers is often assumed in literature which leads to idealistic performance bounds. The contribution of this paper is the derivation of closed-form expressions of the symbol error probabilities. We use the moment generating function (MGF) of the correlated Nakagami-m random variable (RV) to calculate the closed-form average symbol error rates (SERs) of binary and M-QAM signals with maximum ratio combining detection technique. Both, numerical and simulation results are presented, showing an excellent agreement.

This paper presents the exact bit error rate (BER) analysis of a cyclic delay diversity (CDD) multicarrier code division multiple-access (MC-CDMA) system. By using the moment generating function (MGF) of the correlated Nakagami-mrandom variable and considering the realistic case of frequency-correlated MC-CDMA subcarriers (which is often ignored in literature), closed-form BER expressions are obtained with maximum ratio combining (MRC) detection technique for both uplink and downlink scenarios. Simulation results are also presented which show excellent agreement with the analytical framework.

Media Independent Handover (MIH) is a technique proposed by the emerging IEEE 802.21 standard that provides solutions for seamless handover across heterogeneous networks. The IEEE standard provides link layer intelligence information to upper layer to optimize handover between networks of the same type as well as handover between different network types. Session Initiation Protocol (SIP) is becoming the leading protocol for multimedia call control in IP networks and is expected to be widely deployed in the near future. The existing SIP infrastructures and signalling could be optimized to provide a good solution for mobility support. In this paper we introduce the concept of MIH and propose a solution for vertical handover of a multimedia session based on SIP with the triggers being provided by MIH for efficient terminal mobility management in a SIP environment.

In this paper, we study the capacity of space time block codes (STBCs) over correlated Rayleigh flat-fading MIMO channels combined with adaptive transmitting techniques. We study three adaptive schemes known as optimal power and rate allocation (opra), optimal rate allocation (ora), total channel inversion with fixed rate policy (cifr) and its truncated variant (tifr). We obtain closed form capacity expressions of STBCs combined with these adaptive schemes, taking into account the effect of channel correlation, hence avoiding numerical integrations or Monte-Carlo simulations

Due to the unreliable nature of the wireless medium as well as risks of route failure (mobility), supporting quality of service (QoS) in ad hoc networks is a rather challenging task. In this paper, we propose AQuoS, an exclusive framework which provides and ensures QoS in mobile ad hoc networks (MANETs). Compared to existing work, to our knowledge, AQuoS is the only framework which assume different node capacity limits along with considering multi-hopping and carrier sensing interferences for admission control. To extend our contribution, we also developed a new approach which deals with unexpected lost of QoS guarantees. The low complexity of our scheme along with its flexibility makes it highly scalable for MANETs. Through simulations, we show that AQuoS outperforms SWAN protocol, especially when congestion arises

Random access MAC protocols for radio environments are prone to collisions without offering a way to successfully avoid or identify them and thus fail to achieve the performance required by a multitude of applications. However, in some cases it is possible to use collision detection in order to reduce the time spent on collisions and improve the system efficiency. In this paper we provide an analytical framework for WCSMA/CD with a finite user population. The expected channel throughput is then derived for different design parameters and compared against p-persistent CSMA/CA.

This paper proposes a new common radio resource management (CRRM) methodology which allows increasing the capacity of heterogeneous CDMA/TDMA. This is achieved by controlling the effective cell radius of the CDMA-based system (i.e. a network-controlled cell-breathing) through appropriate initial RAT selection and vertical handover strategies, so that the interference level in the CDMA-based RAT is reduced while at the same time the target coverage area is assured by means of the cooperation of the FDMA/TDMA based RATs. The proposed approach is evaluated by means of system level simulations in a detailed scenario including UTRAN and GERAN as examples of CDMA and FDMA/TDMA-based access technologies. Results reveal that throughput improvements up to 24% can be achieved with respect to other CRRM strategies based on load balancing principles

To facilitate upgrades to software, firmware, or FPGA functionality in terminals, over-the-air downloads can provide in-the-field solutions. For mobile terminals, over-the-air downloads provide a security-conscious option due to the ubiquitous availability of the radio interface as they guarantee that the upgrade will be performed if the terminal is to be allowed to use the operator's network. Ensuring system stability through urgent upgrades, this provides a degree of certainty which has hitherto not been present in other forms of downloads. In this paper, we concentrate on mass-upgrades, as might apply to an OS, codec, or urgent security upgrade in a number of terminals concurrently. We investigate relative performances of a range of one-to-many reliable data transfer techniques. Based on these performances, we introduce a unified protocol, able to dynamically switch between the one-to-many download methods many-unicast, multicast, and broadcast during a file download, thereby achieving enhanced performance of the mass-upgrade download from both user and system perspectives, as well as from the perspectives of other users in the network which have to share the same resources as the one-to-many download.

Abstract ‘Always Best Connected’ (ABC) is considered one of the main requirements for next generation networks. The ABC concept allows a person to have access to applications using the devices and network technologies that best suits his or her needs or profile at any time. Clearly, this requires the combination of a set of existing and new technologies, at all levels of the protocol stack, into one integrated system. In this paper, a considerable set of the technologies, that are expected to play a key role towards the ABC vision, are presented. Starting from a reference architecture, the paper describes the required enhancements at certain levels of a traditional protocol stack, as well as technologies for mobility and end‐to‐end Quality of Service (QoS) support. The paper concludes with a case study that reveals the advantages of the ABC concept. This article replaces a previously published version (Wireless Communications and Mobile Computing; 5(2): 175‐191. [DOI: 10.1002/wcm.207]). Retraction notice DOI: 10.1002/wcm.426 . Copyright © 2006 John Wiley & Sons, Ltd.

A number of methods have been suggested for reducing the risk of feedback implosion in reliable multicast. In tandem with the use of negative acknowledgements (NAKs), one of the most effective of these is the router-assist function of feedback aggregation. Feedback aggregation has hitherto only applied to conventional per-packet NAKs; however, it would be far more efficient if used in conjunction with bitmapped feedback. Hence in this paper, we describe a scheme for aggregation of bitmapped NAK feedback packets, and we show its simplicity, practicality and interoperability with basic router functions. We present some useful analysis of the scheme, which might also apply to NAK aggregation in general under certain circumstances. Finally, we perform simulations showing the benefits of the scheme to uplink traffic load.

In this paper, we study the effect of channel estimation error on transmitter design in a multiple input multiple output (MIMO) channel. We assume that only knowledge of either the channel correlation or mean is available at the transmitter and find the transmitting strategy. Under covariance feedback, at the transmitter the channel is modelled as a matrix of zero mean circularly symmetric complex Gaussian (ZMCSCG) random variables with known covariances. We assume that only rows of channel matrix are correlated. Under mean feedback the covariance of channel is modelled as white. We determine the necessary and sufficient conditions under which a unit rank input covariance matrix, i.e. eigen-beamforming, can achieve capacity lower bound. Numerical simulations are conducted to corroborate theoretical results.

Over-the-air software download is a key enabler for many aspects related to the reconfiguration of terminals based on software-defined radio (SDK). In this contribution, mechanisms for advertising the availability of a software upgrade to a group of SDR terminals are evaluated. In order to exploit efficiencies in terms of transmission and processing, addressing strategies that allow the subsequent download to be performed in a multicast fashion are considered. A novel scheme for advertising a software download to only those terminals that are targeted by the download is introduced. Based on a cost analysis, it is shown that the proposed scheme performs favourably compared with other viable schemes for performing software upgrade announcements.

A novel approach is proposed and analysed in this paper, where the micro-cell utilises the same frequency band as the macro-cell to transmit non-real time data. The main idea is that, whenever the macro-cell interference falls below a given threshold, the micro-cell schedules data with a transmission rate dependent on the micro-cell signal strength and the macro-cell interference level. We prove analytically that utilizing the hence created micro-cell transmission scheme non-real time data can be transmitted at micro-cells. We also derive the average duration and the frequency of transmit event for non-real time data transmission at micro-cells, all of which is verified by means of a dynamic CDMA system level simulator

The Universal Mobile Telecommunications System (UMTS) is already realizing its ability to provide a rich tapestry of media to mobile users, including audio, video, data, and a combination of these termed `multimedia'. The high speed downlink packet access (HSDPA) solution within UMTS can greatly enhance bit rates on the downlink; however, given HSDPA using a shared channel, carefully considered scheduling of packet transmissions at HSDPA-enabled base stations is important. Hence in this paper, we present an effective inter-user and inter-class multimedia packet scheduling algorithm for HSDPA. We optimize the traffic class weightings that are central to the packet prioritization approach of the scheduling algorithm. Finally, we show our optimized algorithm to perform well through simulations of complex multimedia sessions being concurrently transmitted to users over the HSDPA link in a single cell

In the B3G system considered, which is based on the 3GPP UMTS architecture, the initial hypothesis made in this paper, is that the QoS management of the IP access network is taken in charge by a bandwidth broker. A pre-handover signalling for QaS-aware path selection is investigated with the goal of achieving the "always best connected" paradigm. Furthermore, the scalability of the proposed scheme is analysed taking into account the overhead due to IP micromobility, QoS routing, CRRM and bandwidth broker

The paper presents a detailed analysis of the properties of the cost function vital to WCDMA radio network optimization. The cost function for the downlink is carefully selected and analyzed numerically for three representative small network layouts and antenna orientation parameters (azimuth and tilt). The analysis includes local minima search, their distribution and their attraction regions. Based on obtained results, several notable conclusions about optimal solutions for network configuration are made as well as some directives for proper optimization algorithm design suggested

We investigate the performance of parity-based reliable multicast in third-generation networks in terms of residual packet error rate, throughput and delay. For multicast over the CDMA air interface, we distinguish between the use of point-to-multipoint (PTM) channels that are broadcast over the entire cell or separate point-to-point (PTP) channels that are transmitted to individual users of the group. As a first step, the residual packet error rates of the radio link control (RLC) layer using PTM and PTP channels for multicast are established, assuming that the RLC layer is not fully reliable. Subsequently, these results are used to determine the performance of the end-to-end reliable multicast mechanism operating on top of the RLC layer. Our results provide insight into the throughput and packet delay trade-off of using a single PTM or separate PTP channels for reliable multicast in third-generation mobile networks

The paper presents a brief survey of the methods for solving systems of linear equations (linear solvers), which could be useful in application to WCDMA network optimization. The methods are scored with respect to their computational cost when base stations are equipped with traditional antennas as well as with smart antennas. Preconditioning in the conjugate gradient square (CGS) method is discussed. We also analyze the technique, which without any loss of accuracy, may reduce dimensions of the power control problem in a multi-service network but is limited only to traditional antennas the smart antenna case must be solved with conventional solver. Theoretical considerations are confirmed experimentally.

A link adaptation schemes is proposed to improve the efficiency to support DiffServ traffic over CDMA air interface. To differentiate the resource allocation between DiffServ PHBs and between the in/out profile packets within each AF class, two-level differentiation is done in the proposed scheme: inter-class differentiation and infra-class differentiation. Through this interaction between the two levels, a better QoS balance between classes is achieved and therefore a higher capacity is gained as shown by our numerical evaluation.

The paper presents a generic algorithm for supervisory control of periodical updates by monitoring mobility and traffic load in ad hoc networks. We discuss the specifications of a proposed mobility metric for mobile ad hoc network protocol evaluation that captures both longevity and rate of link changes. We apply our proposed mobility metric in conjunction with traffic load information as input parameters to design a generic algorithm that controls the rate of wireless link state updates to improve the efficiency of proactive protocols. We describe the application of the proposed controller to improve the efficiency of proactive routing and Internet gateway discovery protocols.

An increasingly popular paradigm for beyond 3G (B3G) telecommunications considers clusters of co-operating networks, which offer the user seamless access through a range of technologies such as GPRS, UMTS, WLAN or DVB. We introduce a digital video broadcast (DVB) technology from the perspective of B3G interworked services, providing an overview of the technology and an introduction to the MobileVCE Core III project and our IoN (interworking of networks) UMTS-DVB interworked architecture. We present and analyse three original proposals for providing mobile terminal (MT) location discovery in an efficient manner across the interworked network and conclude that our proposed 'hybrid' UMTS plus DVB paging scheme offers promise for efficient MT discovery. Furthermore, we briefly introduce other aspects of research that must be addressed in order that our architecture proposal can function effectively.

We propose an efficient uplink media access control (MAC) protocol for a variable spreading gain interference-limited wideband CDMA system. It can, with high spectral efficiency, support both real-time traffic like speech and video and also nonreal-time data traffic based on packet transmission. The schemes for power allocation, joint scheduling, and transmission rate adaptation for nonreal time data traffic are designed as integrated parts of the MAC, working together to improve the system performance in terms of capacity and delay. With these associated resource management mechanisms, the performances of the MAC protocol with two different channel-allocation methods for real-time traffic are numerically compared. One is demanding channel allocation, and the other is reserve channel allocation, in which a certain bandwidth is reserved for concurrent real-time traffic.

Information theoretical optimization problems related to the resource allocation of wireless cellular and ad hoc networks are not solvable in closed form due to the nonlinear logarithmic representation of the Shannon capacity. This paper introduces functional approximations to the MIMO capacity over flat Rayleigh fading channels, which allow for analytical solutions to network resource optimization problems. The precision of the suggested approximations is assessed and is shown to provide a very close match to the exact capacity expression.

Abstract With IP technology being in the epicenter of future wireless networks, IP‐centric resource management is currently receiving an increasing research attention. In this paper, a power and rate adaptation semantic is proposed that integrates quality of service (QoS) information from the IP layer of the differentiated services (DiffServ) architecture together with lower layer criteria in order to optimize packet transmission over the wireless interface. An optimization problem is formulated based on the output of a time sliding window three color marker (TSWtcm) of the ingress DiffServ node in the radio access network (RAN), where color aware power and rate control are performed. The critical impetus of the proposed approach besides minimization of the transmitted power is mainly twofold. Firstly, to achieve the required per‐class aggregate data rate, while prioritizing and ensuring QoS of in‐profile packets and secondly, to increase aggregate power gains by penalizing out‐of‐profile packets. The seminal aspect of the proposed scheme is that tangible power gains can be achieved by differentiating transmission of conformant and non‐conformant packets while at the same time the power gains within each AF classes can be utilized to enhance the performance of in‐profile traffic. To buttress the case, both theoretical and simulation results are meticulously presented that depict architectural and performance related aspects of the proposed scheme. Copyright © 2005 John Wiley & Sons, Ltd.

Mobile Internet Protocol version 6 (MIPv6) is a proposal for handling the routing of IPv6 packets to mobile nodes in a foreign network. There are two methods for routing of IPv6 packets from the correspondent node (CN) to the mobile node (MN): triangular routing (TR) and route optimisation (RO). With MIPv6 RO, the CN uses the care-of address (CoA) as the destination address to transfer packets to the MN. Hence the MIPv6 module of the CN adds the mobility routing header (MRH) to store the home address of the MN. This increases packet sizes and may result in fragmentation. Fragmentation degrades transmission control protocol (TCP) performance over MIPv6. The paper discusses the cost of fragmentation and innovative fragmentation avoidance techniques. The cost of fragmentation is studied by carrying out experiments in a real IPv6 backbone (6Bone) where it is found that improved performance can be obtained by implementing innovative fragmentation avoidance techniques in the TCP/MIPv6 protocol stack of the Kame software. The efficiency of fragmentation avoidance techniques is also calculated. The paper also illustrates the impact of MIPv6 TR on TCP performance. A performance comparison between TR and RO is discussed. Based on this performance comparison, a generic adoptive routing technique is proposed.

The convergence of multimedia applications with telecommunications networks has resulted in the need to create source traffic models for these new applications. These models are required for network performance evaluation purposes. A framework to model multimedia applications is outlined. By analyzing existing and prospective multimedia applications, it is possible to categorize multimedia applications as being made up of three basic components: block, transaction and streaming traffic. These three components are integrated to build a model for the multimedia traffic source. The framework outlined is versatile and allows modelers to build source traffic models for a large number of multimedia applications.

Ultra wideband (UWB) systems have attracted a lot of research interest lately, owing to their appealing features in short-range mobile communications. These features include low power peer-to-peer transmissions, multiple access communications, high data rates, and precise positioning capabilities. Space-time coding (STC) techniques, such as the block coding scheme, or the trellis coding scheme, are known to be simple and practical ways to increase the spectral efficiency in wireless communications. We aim to combine a pulse position modulation (PPM) impulse radio multiple access (IRMA) system with two different space-time coding techniques. Thus, we developed a space-time block code scheme and adapted a space-time trellis code scheme to UWB signalling, relying on the channel state information (CSI) at the receiver side. Then the added diversity produced by these techniques is exploited to enhance the performance of UWB systems. Analysis is conducted in a typical UWB environment, with fractionally-spaced (FS) coherent RAKE detection.

This work presents a performance analysis that minimises the possibility of experiencing a handover delay when a user or a group of mobile nodes (MN) initiate a handover request to a heterogeneous overlay network. More specifically this refers to a handover from a boundary cell of Universal Mobile Telecommunication System (UMTS) network; towards an overlaying digital video broadcast-satellite (DVB-S) cell.

Distributed multi-hop communication systems have been introduced recently which allow the application of multiple-input-multiple-output (MIMO) capacity enhancement techniques over spatially separated relaying mobile terminals. They were shown to yield significant capacity gains over direct communication or non-distributed single-input-single-output (SlSO) relaying networks. The contribution of This work is the derivation of throughput-maximising resource allocation strategies in terms of fractional frame duration and transmission power. It is assumed that distributed terminals cooperate at each relaying stage and that the detection of packets is performed at each relaying stage.

We investigate the impact of power control on the performance of a multi-hop CSMA/CA system, also taking into account the additional traffic generated due to multi-hop transmissions. An analytical model is presented with emphasis on the influence of power, more specifically the number of nodes dwelling in the area covered by this power, on the number of hops and, consequently, on the end-to-end throughput. Unlike other works, a closed form solution is derived for the throughput performance of a multi-hop CSMA/CA system, as a function of the offered load, the nodes density and transmission power.

Mobile ad-hoc networks (MANETs) potentially satisfy a long-standing dream of mobile users: networking without limitations. A significant challenge in MANETs is radio resource allocation, where it is assumed that the available unregulated bandwidth over which such systems can operate is limited, hence resource allocation should be efficient and dynamically reactive to resource clashes due to node mobility. Subject to this consideration, we propose a novel hierarchical radio resource allocation scheme to operate in MANETs, able to distribute resources between nodes using a number of radio access technologies acting in parallel. The use of a hierarchy is shown to assist in the allocation of radio access functions in constituent parts (e.g. FDMA, TDMA, CDMA etc), and to help provide efficient operation of resource allocation schemes by aiding functions such as frequency reuse.

The impact of handover blocking on the control load, capacity, and coverage of the W-CDMA downlink is studied using a dynamic system level simulator. The handover control mechanism, as defined by the 3GPP, was simulated in detail for a sectorized macro cell layout scenario. The results show that handover blocking increases the average holding time of a connection and the number of handover requests. The results also show that higher transmission power is required per channel to provide the desired coverage in both soft and hard handover cases, whereas the capacity is not reduced in the case of soft handover unless the blocking probability exceeds 0.8. The dynamic range required for transmission power control is also discussed.

Mobility tracking yields efficient network resource management and enables very useful additional services, provided that accurate online estimations of both the location and the velocity of a mobile user are performed. We present a novel method for tracing a mobile user by subsequently estimating his/her position through a single base station positioning (SBSP) method designed for microcellular and third generation (3G) wireless communications systems. Raw data about user position are then smoothed through a linear regression setup which adaptively varies its inertia on the basis of the previous observations. This results in a tracking method which is able to estimate both the location and the velocity of a user with high accuracy, as proven by numerical results obtained in different microcellular scenarios.

In WCDMA, data transfer to a group may either take place on multiple point-to-point (FTP) channels transmitted to individual group members separately or on a single point-to-multipoint (PTM) channel that is broadcast over the entire cell. We evaluate the capacity of both channel selection strategies for one-to-many multicast over the WCDMA air interface in terms of outage probability. We study the capacity of both schemes by first deriving suitable outage probability expressions and then calculating the overall capacity, i.e., the number of multicast users that can be supported by both schemes. Particular attention is paid to the impact of code orthogonality, power control error and the activity factor of the multicast source on the capacity of both schemes for multicast transmissions.

When an ad hoc network is connected to the Internet, it is important for the mobile nodes to detect the available gateways providing access to the Internet. Therefore, a gateway discovery mechanism is required. The two main approaches for discovering Internet gateways are the reactive and the proactive one. This paper compares the performance of these approaches in various scenarios by means of simulation. We show that the proactive approach performs better in the simulated scenario.

In this paper, we focus on resource reservation protocol (RSVP)-based quality-of-service (QoS) provisioning schemes under Internet protocol (IP) micromobility. We consider QoS provisioning mechanisms for on-going RSVP flows during handoff. First, the rerouting of RSVP branch path at a crossover router (CR) at every handoff event can minimize resource reservation delays and signaling overheads, and in turn the handoff service degradation can be minimized. We show that RSVP branch path rerouting scheme could give a good tradeoff between the resource reservation cost and the link usage. Second, the new RSVP reservation can be made along the branch path toward the CR via a new base station in advance, while the existing reservation path is maintained, and in turn the on-going flow can be kept with the guaranteed QoS. We also show that seamless switching of RSVP branch path could provide the QoS guarantee by adaptively adjusting the pilot signal threshold values. Third, during RSVP resource reservation over wireless link, dynamic resource allocation scheme is used to give a statistical guarantee on the handoff success of on-going flows. We finally obtain the forced termination probability of guaranteed service flows, the average system time of best effort flows by using a transition rate matrix approach.

Digital radiology places very high demands on the networking and digital storage infrastructure of hospitals. In addition to having quite stringent requirements on the quality of the images displayed to the radiologist, much of the technical challenge resides in the necessity of displaying desired images as rapidly as possible. We present an infrastructure for progressive transmission and compression of medical images, which can refine an initial image by increasing the detail information not only in scale-space, but also in coefficient precision. The approach is based on the embedded zerotree wavelet (EZW) algorithm. This algorithm offers a tremendous amount of flexibility in meeting the bandwidth and image quality constraints in a radiological imaging environment. We propose an application of the EZW algorithm in progressive medical image transmission in which it can specify and control both the resolution constraint and rate constraint. The presented method can provide a framework for lossy image compression, with performance far superior to those provided by the standard JPEG algorithm. Also due to the flexibility of the method we will show how any region of interest of an image can be sent progressively.

An approximate but explicit fractional bandwidth and power allocation algorithm for orthogonal regenerative frequency-division multiple-access-based multihop communication systems over ergodic flat-fading channels is presented. The exposed algorithm is assessed for a two-hop scenario, where it is shown to operate within 10% of the optimum resource allocation. The achieved end-to-end capacity is up to 45% higher if compared to a trivial allocation strategy with equal resources.

This paper presents the results of the development and evaluation of the IP mobility protocol BRAIN candidate mobility management protocol (BCMP) using a real IPv6 network environment. BCMP is an intra domain mobility protocol i.e. it handles user mobility within an administrative domain. The protocol setup is based on a focal point in the network, called anchor point, from whereon dynamic tunnel establishment to MH's points-of-attachment is deployed. We show all protocol stages and their impact during the communication phases of MHs in the network including the logins, packet transfers and handovers. The work presented in this paper is part of the research conducted in the EU sponsored project MIND.

OFDM is regarded as a viable solution to combat the impact of frequency selective fading; however, the channel does not have flat amplitude over the entire bandwidth, thus channel equalization is still required at the receiver. Radial basis function (RBF) neural networks have been widely considered for channel equalization, since they offer certain advantages over conventional equalizer structures. In this paper, a novel RBF channel equalizer structure, which performs Bayesian estimation, is proposed for OFDM communication systems. The proposed equalizer structure is shown to outperform existing equalizers; it can therefore be considered as a better practical alternative for OFDM channel equalization.

We propose a new multicast protocol for UMTS networks. Our scheme relies on establishing multicast tunnels throughout the network that allow multicast packets to be transferred in an optimal manner on shared links towards multiple destinations. We describe the mechanisms of our scheme in establishing the multicast tunnels and performing group management. We show that our scheme performs particularly well when multicast subscribers are densely populated throughout the network. Given a dense multicast subscriber population, our scheme requires fewer multicast packet transmissions than comparable broadcast or one-to-many unicast schemes.

In a macrocell network, there will remain some geographical areas within the cell coverage where mobile stations require further services. These are mainly in terms of downloading data, in particular in temporary or permanent hotspot areas, such as exhibitions, conference centers, etc. The objective of this study is to obtain extra capacity for W-CDMA systems by adding hotspot base stations to an already present continuous macrocell layer. IP-based services are offered to local mobile stations, using packet switched transmission without additional bandwidth; i.e. using the same frequency band in both the hotspot and macrocell. In order to maximize the hotspot base station throughput, and at the same time, to minimize the interlayer interference from hotspot to macrocell, a new link quality control scheme is designed. Downlink system level simulations are also carried out to prove the feasibility of the idea and to show the effect of required E/sub b//(I/sub o/ + N/sub o/) for macrocell users, on the hotspot data throughput.

In this paper novel prolate spheroidal wave functions are proposed as pulse shapes for use in impulse radio (ultra-wideband) communications. These classes of functions yields orthogonal pulses and have a constant pulse width regardless of the pulse order. This is an important property since it eliminates inter-symbol interference. An M-ary communications system is considered that employs these pulses, and the generation of these pulses using the eigenfunction form of a self-adjoint operator is proposed. It is also shown that these pulses are suitable for use in pulse position modulation (PPM) ultra wideband (UWB) communication systems.

Mesh connectivity is traditionally dealt with at IP-layer, where packets are relayed to adjacent network nodes according to prior specified rules. Recently, the concept of data relaying at PHY-layer has gained widespread interest, where regenerative and transparent relaying are feasible M. O. Hasna, M-S. Alouini (2002). In parallel, investigations into MIMO systems have become mature. The current paper introduces a generalised concept of data relaying at PHY layer, where relaying is combined with MIMO technology. The thus created distributed PHY-layer mesh network is a natural generalisation of previously introduced virtual antenna arrays.

This paper addresses the connectivity between ad hoc networks and IP based fixed networks. This connection can be achieved through an Internet gateway, which in this paper is assumed to be a router at the edge of the fixed network. We investigate issues on Internet gateway discovery, addressing and QoS support for interconnecting ad hoc networks and the Internet. We compare different approaches regarding addressing and micro-mobility management. Our simulation results show the performance of an ad hoc routing protocol while connecting to the Internet.

The interaction between layers in multilayer cellular systems can be in terms of directing the traffic overflow from the lower layer to the overlaying layer (overflow sensitive cell-layer selection strategy), and/or of classifying the users based on their speed (speed sensitive cell-layer selection strategy). In this paper, we study a hybrid speed/overflow sensitive micro/macro cell-layer selection strategy for two-layer CDMA cellular systems. It is shown that the speed threshold has a major impact on the capacity and the handover rate in such systems. Therefore, here we propose a handover rate control scheme where the speed threshold can be dynamically adjusted according to the handover and blocking rate feedbacks. Simulation results show that the proposed scheme can control the handover rate even when the speed distribution of mobile stations changes with time.

A high gain, ultra wideband and low noise SiGe/BiCMOS distributed amplifier for a 4G multiband, multimode mobile terminal is presented. The proposed SiGe/BiCMOS cascaded single stage distributed amplifier (CSSDA) has shown 21 dB power gain with power flatness of /spl plusmn/ 0.5 dB and return loss less than -10 dB for both input and output over the frequency range from 300 KHz to 15 GHz. This is the first SiGe/BiCOMS HBT based-CSSDA, which combines the active load loss compensation algorithm to achieve the ultra-high gain over one decade of bandwidth using commercially available SiGe/BiCMOS technology.

In OFDM transmission, a loss of sub-carrier orthogonality due to Doppler-spread of the channel leads to inter-carrier interference (ICI). We have proposed a method to reduce the ICI caused by the Doppler spread of the channel. The transmission channel is modeled by a combination of multiple Doppler-shifted propagation paths, and their parameters such as attenuation, relative delay and Doppler-shift are estimated using scattered pilot symbols. The ICI is canceled by multiplying the inverse matrix of the estimated channel matrix with the received OFDM symbol vector. However, the ICI canceller causes enhancement of noise component, so it can't improve the bit error rate characteristics sufficiently. In this paper, we propose the new ICI canceller based on MMSE, which does not cause enhancement of noise component. As the result of computer simulation, it was confirmed that the ICI canceller based on MMSE could reduce the bit error rate more than ICI canceller based on zero-forcing under the Doppler-spread channel.

In this paper, we explore code division multiple access (CDMA) systems with multiple transmit and receive antennas combined with space-time trellis codes over a frequency selective channel. The conventional multi-user minimum mean square error (MMSE) detector is generalized to deal with multiple antennas and multiple paths and, then, extended to include the turbo principle in an iterative fashion, allowing interference regeneration and cancellation at the receiver. Iterative multi-user MMSE receivers employing chip level and symbol level detectors are derived and their equivalence is demonstrated. Computer simulations show that the proposed iterative MMSE equalizer completely remote the interference of the other users and transmit antennas in the system, providing a significant improvement compared to the conventional non-iterative multi-user MMSE detector and effectively achieving the single-user performance, even in a fully loaded system.

An analytical model is developed to investigate integrated packet-switching/circuit-switching service CDMA cellular systems. Due to the defer-first-transmission mode, link-level congestion control is essential for packet-data transmission. With congestion control, the intra-cell and inter-cell interference interact each other. To reflect this interaction closely, a recursive model is used to derive the inter-cell interference in this paper. With this model, the performances of a CDMA system are numerically evaluated in terms of voice capacity, data delay, and data blocking probability.

We propose a wireless resource allocation scheme considering mobility for providing quality of service (QoS) under IT micro mobility domain with differentiated services (DiffServ). In this scheme, each base station provides infinite waiting queue for both assured forwarding (AF) and best effort (BE) handoff flows and guard channels for expedited forwarding (EF) handoff flows. This scheme also allows BE flows to overflow over the region reserved for EF flows with the risk of being preempted by the newly arriving EF flows. If there is no idle channel bandwidth in a new cell after a handoff in heavily crowded area, the EF handoff request is just dropped. Hence, it is required to give a statistical guarantee on the EF handoff success in this wireless mobile environment. The remaining channel bandwidth except for the regions reserved for EF flows in a cell is dedicated to both AF and BE flows. The BE flows preempted by the newly arriving EF flows in a cell are queued, and AF handoff flows has preemptive priority over BE flows existing in dedicated region. We derive the dropping probabilities of both EF and AF flows, and the average system time of BE flows by using a transition rate matrix approach. We also obtain the forced termination probability of EF flow and bandwidth utilization.

The paper proposes a viable technique for performing software upgrades of reconfigurable user terminals across the entire public land mobile network (PLMN) of an IMT-2000/UMTS network. The proposed solution utilizes over-the-air software downloads in conjunction with IP multicast as the enabling technology. The paper describes in detail the interaction required between logical network elements within the PLMN in order to perform the software upgrade on a set of targeted terminals. The limitations of the proposed technique are outlined and the paper addresses possible schemes for facilitating the presented solution and improving its scalability to large networks.

General Packet Radio Service (GPRS) is a system for efficient data packet radio transmission services which is used in conjunction with the Global System for Mobile Communications (GSM) system. The three mobile station (MS) states idle, ready, and standby are defined for efficient management of radio resources and signaling networks. The MS state transition behavior is modeled and the steady state probability of the MS states is derived using a semi-Markov process approach. The effect of various input parameters on the steady state probability is investigated. These results can be used in analyzing the effect of the input parameters on the tradeoff between location update and paging signaling, and thus, providing guidelines for proper selection of GPRS system parameters.

Universal Mobile Telecommunication System (UMTS) is a third generation system for efficient data packet radio transmission services. The three mobility management (MM) states PMM detached, PMM connected, and PMM idle are defined for efficient management of radio resources and signaling networks. In addition, two radio resource control (RRC) states idle and connected are introduced for the management of more detailed location information. The connected state is further divided into cell connected and URA connected states. These MM state models and RRC state models are combined together. The user equipment (UE) state transition behavior is modeled and the steady state probability of the UE states is derived using a semi-Markov process approach. The effect of various input parameters on the steady state probability is investigated.

A novel telecommunication system, termed virtual antenna arrays, was previously presented that allows the application of multiple-input-multiple-output (MIMO) capacity enhancement techniques to mobile terminals with a limited number of antenna elements. This paper introduces a novel approach extending the possible applicability of the space-time block codes (STBC) to such virtual antenna arrays. The main idea is to emulate the (2 transmit antennas, 2 receive antennas) diversity scheme developed by Alamouti (1998). This approach successfully deals with the problem of just one receiving antenna in a handset. Simulations results indicate an improvement in error performance over the simple (2,1) Alamouti scheme.

A dynamic radio network simulator is implemented for studying WCDMA based hierarchical cell structures. The simulator allows estimation of capacity and quality of service related issues in a two-layer network (microcells and macrocells). The input to the simulator is base station and mobile station information and its output is presented as the blocking and dropping probabilities, handoff rate and capacity of the assumed network. Both uplink and downlink are considered. As an example, the impact of between-layer handover on the capacity is investigated. The whole simulator is based entirely on visual C++ software.

The objective of the IST project MIND (Mobile IP based network developments) is to facilitate IP-based broadband services for mobile users in various operating environments. Activities within MIND concentrate on the development, optimisation and harmonisation of the appropriate layers involved. The physical (PHY) layer was chosen to base on the high performance radio local area network type 2 standard (HIPERLAN/2). The work presented here demonstrates the applicability of HIPERLAN/2 to scenarios with increased mobility. Initially, HIPERLAN/2 was designed for rather static environments providing hot spot data rates of up to 54 Mbps. Mitigation techniques to overcome the drawbacks of a fast fading environment are thus studied within IST-MIND. The extracted transceiver structures allow the deployment of HIPERLAN/2 in almost any environments currently envisaged. Particularly, the system deployment of HIPERLAN/2 to a vehicle-to-vehicle communication scenario is studied and preliminary system level performance results presented.

The paper examines the performance of a new dynamic resource allocation (DRA) strategy for a 3G hierarchical cellular structure (HCS). With rising demands on wireless communication systems there is a need to improve the resource utilisation of mobile networks. This can be achieved with the implementation of HCS along with a suitable self-adaptive DRA strategy. The main focus of attention is to evaluate the ability of the new DRA strategy to deal with multimedia traffic. Simulation results confirm that the modified DDRA (distributed DRA) performs adequately in the HCS under multimedia traffic conditions.

In the OFDM SFN (single frequency network) system, where the received signal from the main broadcast station is rebroadcast at the relay station, the area where the delay spread of the received signal is longer than the guard interval length increases as compared to the SFN system where the signals are transmitted at the same time both from the main station and from the relay station. If the channel delay spread is longer than the guard interval length, inter-symbol interference (ISI) and inter-carrier interference (ICI) are generated at the receiver and the bit error rate (BER) characteristics are much degraded. Therefore, the service area of the OFDM SFN system where the signal is re-broadcast at the relay station is narrower that that of the OFDM system where the signals are broadcast at the same time from both stations. In order to improve this problem, an SFN system that rebroadcasts the received signal from the main station after adding an appropriate delay is proposed. We propose an array antenna receiver using a maximum ratio combining technique for the SFN system, where additive delay is inserted to the signal at the relay station. By theoretical analyses and computer simulations, better BER characteristics than the conventional system are confirmed.

A novel method for improving the spectrum efficiency of multi-layer cellular systems, by means of prioritisation based on the user mobility behaviour and service application has been proposed. The proposed system is shown to have a higher efficiency over a wider range of offered traffic, in comparison to the conventional FIFO queuing. Computational results suggest that using this new scheme, the system capacity for handover voice calls at 2% dropping rate can be improved by as much as 27% compared with FIFO. This benefit came at the expense of some increase in the dropping rate of the low priority calls. The improvement in capacity also reduces with service priority.

RSVP (resource reservation protocol) is an attempt to provide a real-time service through the use of virtual circuits in the Internet. It is designed for the integrated services (IntServ) model, and allows Internet real-time applications to reserve resources before they start transmitting data. We consider a cellular system with two-level hierarchy, where RSVP resource reservation is made newly over the two-hop link between the macro-level base station and the mobile host during a handoff. For wireless access networks, we propose a dynamic resource allocation scheme that adapts to variations in handoff attempts, where a macrocell provides bandwidth channels for the GS (guarantee service) handoff flows overflowing from the underlying micro-cells. We derive the average system time of BE (best effort) flows. We also obtain the forced termination probability of GS flow and other performance measures.

In OFDM transmission, a loss of sub-carrier orthogonality due to Doppler-spread of the channel leads to intercarrier interference (ICI), especially under mobile reception environments. ICI causes significant degradation of bit error rate characteristics and this influence becomes larger as the carrier frequency or moving velocity of the receiver increases. In this paper, a method to reduce the ICI caused by Doppler-spread of the channel is proposed. In the proposed method, the transmission channel is modeled by a combination of multiple Doppler-shifted propagation paths and their parameters such as attenuation, relative delay and Doppler-shift are estimated using scattered pilot symbols. Then, ICI is canceled by multiplying the inverse matrix of the estimated channel matrix to the received OFDM symbol vector. As the result of computer simulation, it is confirmed that the proposed method can improve the bit error rate characteristics under Doppler-spread channel.

We propose a modified BLAST architecture which employs space-time trellis codes at each layer as constituent codes, and an iterative parallel interference canceller (PIC) at the receiver. The PIC performs both interference regeneration and cancellation; and furthermore, the scheme employs maximum-likelihood soft-output decoders, based on the Viterbi algorithm. These decoders calculate the a posteriori probabilities of the codewords in order to produce a soft output. Comparisons are drawn against the original BLAST architecture and simulation results are obtained. A significant gain is achieved in the case of Horizontal BLAST and a similar gain for the case of Diagonal BLAST, at a reduced computational complexity.

One of the major areas of interest in software radio technology is the envisaged ability to adapt the functionality of a given terminal by downloading software over the wireless link and subsequently installing the software on the device, thereby achieving over-the-air reconfiguration. Downloading modules or functional blocks, from end-user applications to protocol entities, gives users, network operators as well as terminal manufacturers the ability to reconfigure terminals as required in any given situation. This paper proposes a suitable traffic model for a single-source traffic download over the wireless link by describing the statistics of the reconfiguration data as well as the reconfiguration process itself. The proposed model is then extended to encompass the packet-based transmission nature of the transmission service.

Welcome to the second issue of Volume 2 of Wireless Communications and Mobile Computing/ (WCMC). We have been receiving a large number of great articles and we would like to assure you that we are grateful for your contributions. Our fast review process and publication turnaround has caught the attention of our authors and readers. We are working hard with the John Wiley staff to make the review process more efficient by introducing a new system soon. Once that is implemented, we will be able to process more manuscripts in a short span of time. In the meantime, we appreciate receiving your quality manuscripts and would like to invite you to sit back and enjoy reading the articles in this issue. As always, we welcome your contributions, whether by submitting manuscripts and/or special issues. We also appreciate any comments/feedback you have regarding WCMC. Send your comments to any of the editors and/or to the Wiley office. Multicast protocols in mobile ad-hoc networks have been an area of active research for the past couple of years. In the first paper, Papavassiliou and An discuss the issues, challenges, and protocols related to multicasting in mobile ad-hoc wireless networks. They survey several existing multicasting protocols in mobile ad-hoc networks and summarize the activities of recent advances in the field. A qualitative comparison of these protocol characteristics according to several distinct features and performance parameters is presented. Finally, they present an overview of research and development efforts in the area of group mobility modeling in mobile ad-hoc networks. Next, Cui and Bassiouni present an analysis of hierarchical cellular networks with mobile base stations, termed as totally mobile wireless networks (TMWNs). Their performance evaluation concentrated on comparing the results of a two-tier system's throughput, handoff blocking rate and new call success rate with those obtained by a one-tier model. Under all load conditions, their results show that the two-tier system outperforms the one-tier system if the number of channels is kept the same. Other conditions have been studied and results have been presented. An analytical model to compute the new call and handoff blocking probabilities in TMWN is given and evaluated. Extensive results are presented. In the third article, a software architecture for GPRS session management (SM) is presented by Haung and Lin. This software architecture is designed to accommodate 3G wireless networks. It is compatible, modular, and flexible. The aim of the architecture is to support a GPRS support node. In a situation where single-band and dual-band PCS handsets co-exist, the channel assignment becomes a concern. In the fourth article, Chang and Li propose load-balancing channel assignment schemes to improve the system performance. To further improve the system capacity, a channel reassignment scheme is also presented. Modeling and simulation results are carried out. The results indicate that both load-balancing and channel re-assignment techniques significantly increase the system capacity as the percentage of dual-band handsets increases. Furthermore, the load-balancing with channel re-assignment scheme that combines both techniques achieves the best system performance, even when the percentage of dual-band handsets is as low as 25%. To reduce the peak-to-average power ratio (PAR) of an orthogonal frequency division multiplexing (OFDM) signal, a set of fixed permutations are used by Jayalath and Tellambura. This set of permutations is applied on K − 1 interleavers are used to produce K − 1 permuted sequences from the same information sequence. To reduce the technique's complexity, an adaptive approach is adapted. Simulation results show that random interleavers and odd-even symmetric interleavers are performing equally well in reducing the PAR. Other results for the out-of-band radiation and the bit error rate performance of interleaved OFDM (IOFDM) and conventional OFDM are also presented and discussed. In the sixth paper, Liu and Li propose a new modulation scheme to improve the performance of DS-CDMA systems in fast time-dispersive fading channels called differential space–time modulation for DS-CDMA (DST-CDMA). They study three different types of receivers using this new scheme. Then, they compare the three types under different design combinations. Finally, Sheikh and Shah present an application of LMS algorithm with optimum step size (µopt-LMS) for fading channel estimation. The expression for optimum step size of the LMS algorithm is modified for use in the fading channel estimation problem. The robustness of the proposed µopt-LMS algorithm is demonstrated via simulation in different channel conditions. Thanks to all the authors and the reviewers. We appreciate your support and hope that you continue your dedication to WCMC.

Welcome to the fourth issue of the second volume of Wireless Communications and Mobile Computing (WCMC). Our Journal has been getting a lot of attention from many experts in the field and therefore many new subscriptions but we still need your continuous support as always. Even though we have enough submissions and special issues to fill all the slots for next year, we would like to encourage all readers to send us their Special Issue proposals and manuscripts in their fields of expertise to enrich the rest of the community of their new findings. I extend a special invitation to all members of the editorial board to step in and contribute at this junction, now that we are ready to take WCMC to the next level of excellence. I would like to extend special thanks to the authors who have worked hard to produce the fine articles you are about to read in this issue. Thanks also to those who have contributed whether running a special issue or publishing a regular manuscript. Of course, the continuous help from the staff of John Wiley is always very much appreciated. We welcome any comments/feedback you have regarding WCMC. Send your comments to any of the editors and/or to the Wiley office. The first article by Mähönen et al. reviews and analyzes the standards currently available and describes the European two-layer trial system developed in 1996–2000. The authors show why further development towards IP-based LMDS is useful in the future. Most of their recommendations are based on results derived from the European Union supported research project CABSINET. It had the aim of demonstrating the viability of a 40 GHz cellular digital television system with a return channel to offer interactive services. Two systems were tested: a line of sight link using QPSK, and a non-line of sight with COFDM modulation scheme. Then, they present the architectures of the transmitters, nomadic terminals, and the design of the IF/RF subsystems for both types of modulations. The discussion is focused on system engineering and selections required in order to build a full two-layer LMDS system. Jaseemuddin et al., in the second article, present a study of profiled handoff for DiffServ-based mobile nodes. They investigate the effects of handoff on service quality of mobile nodes. Several experiments are conducted using various packet metering and marking schemes with or without transferring profiles to the new router. Results indicate the relative instability period following handoff, loss of packets and delay encountered by packets in profiled or un-profiled handoffs, leading to determining suitable mix of metering and marking schemes with or without context transfer. The third and fourth articles are two parts of the same topic prepared by Nassar et al. The first part (third article) is entitled ‘Multi-carrier platform for wireless communications: High-performance, high-throughput TDMA and DS-CDMA via multi-carrier implementations.’ In part I, the authors demonstrate how a multi-carrier platform can be adopted by TDMA and DS-CDMA systems. Then, they show how, in both systems, the proposed multi-carrier platform is able to: (1) outperform existing time-based-processing receiver structures in multipath fading channels, due to better exploitation of the channel diversity and a minimization of the MAI (multi-access interference); (2) achieve increases in network capacities (measured by numbers of users or, equivalently, throughput per user); and (3) reduce receiver complexity. In part II, OFDM and MC-CDMA systems with high-performance, high-throughput via innovations in spreading, the authors demonstrate how the CI (carrier interferometry), which brought far reaching benefits to TDMA and DS-CDMA, is also able to enhance existing multi-carrier systems, namely existing OFDM and MC-CDMA architectures. By application of the CI approach to these systems, they demonstrate significant performance benefits (measured in terms of probability of error performance) and notable network capacity gains (measured by numbers of users or throughput per user). Moreover, in the case of OFDM, the CI approach eliminates the PAPR (peak to average power ratio) problem, and in the case of MC-CDMA, a simple procedure is available to resolve all PAPR concerns. Combining the results of part I and part II, the authors succeeded in presenting a common multi-carrier platform for the most popular architectures in use today. Hence, by use of the CI approach, a simple software code will switch a CI processor from one mode to another, where modes include CI/TDMA, CI/DS-CDMA, CI/MC-CDMA, and CI/OFDM. Each mode demonstrates improved performances and network capacities relative to its traditional counterpart. Next, Al-Hussaini et al. propose and analyze parallel co-channel interferers (CCI) multistage cancellation by combining RAKE and selection diversity. In order to account for channel variations, adaptive implementation of decision thresholds at the RAKE output is suggested. It is shown to provide significant improvement over either hard or soft decision techniques especially in the near-far situation. Investigation of the system robustness to imperfect channel parameter estimation is also presented. The communication channel is modeled as slowly varying Rayleigh fading discrete multipath channel. Finally, Annamalai and Srivastava outline a general numerical procedure for computing the probability of outage of a cellular mobile radio system that is equipped with a smart antenna to suppress a few strongest co-channel interferers (CCI) out of a total of NI active interferers by adaptive null-steering. Aside from the interference-limited case, refined outage criterion that either treat receiver noise as CCI or consider a minimum detectable receiver signal threshold are studied. Exact closed-form expressions for both the basic and refined outage criterion are also derived by assuming that all the CCI signals are subject to Nakagami-m fading with a positive integer fading severity index. Selected numerical examples are provided to illustrate the application of the theory which includes the investigation into the effects of fade distribution of the CCI signals and traffic loading on the outage probability, and also the study of spectrum utilization efficiency improvement using a selective co-channel interference cancellation technique.

TCP is a reliable connection-oriented transport protocol that performs well in traditional networks. However, in networks with wireless and other lossy links the protocol suffers from losses and delays due to frequent handoffs like in wireless networks running mobile IP. Many micromobility protocols have been proposed to reduce handoff latency and the load on the network when a mobile host moves among small wireless cells. In this paper, the performance of several TCP and UDP schemes over one of these protocols, MMP (multicast for mobility protocol), is compared and improvements to TCP in a multiple handoff network are proposed. The simulation results are presented using the Network Simulator-ns2 and different metrics for comparison. Our results show that the number of UDP packets lost is reduced when using MMP instead of mobile IP in a micromobility environment and that TCP provides better throughput performance for a traditional scheme like Tahoe TCP when it is adapted to the conditions of the network.

It is expected that the main service that will exist on 3G mobile systems, besides voice, will be World Wide Web (WWW) based services. 3G systems (e.g. UMTS) will be based on W-CDMA. We present an approximate analysis of the Erlang capacity of the reverse link of such a system. We compare our analysis with a simulation. Our results show that the Gaussian approximation is quite accurate at high traffic intensities but underestimates the outage probability at low traffic intensities. Using this approximation, it was found that Web page traffic can have a significant impact on the voice Erlang capacity. It was also found that the higher the bit rate of the Web traffic, the lower was the Web traffic Erlang capacity, for the same voice traffic and outage probability.

Welcome to the fourth issue of the journal Wireless Communications and Mobile Computing (WCMC). We have been fortunate so far that we are able to attract quality papers and also meet all our publication deadlines. I am sure that you have been enjoying reading the fine articles in the previous three issues and hope that you continue to do so in the future ones. Special thanks to the authors who worked hard to produce the fine articles that we present to you in this issue. Thanks to those who have contacted us praising the efforts and quality of this publication. We welcome any comments/feedback you have regarding WCMC. Please send your comments to any of the editors and/or to the Wiley office. The first article in this issue reviews mobility management for the third-generation mobile networks. The authors, Y-B. Lin, Y-R. Haung, Y-K. Chen, and I. Chlamtac, focus on the evolution from General Packet Radio Service (GPRS) to Universal Mobile Telecommunication System (UMTS). In this evolution, the radio access network UTRAN has been introduced, and radio-related management is moved from the core network to UTRAN. They elaborate on how this architecture change affects the mobility management functionality, including the attach and detach procedures, location update, serving radio network controller relocation and intersystem change between GPRS and UMTS. Existing research in ad hoc mobile networks is mainly concerned with unicast routing. There is a growing interest in supporting multicast communication in an ad hoc mobile environment. C-K. Toh and S. Bunchua present an ad hoc mobile multicast routing using the concept of long-lived routes. They propose a new routing protocol called ABAM (associativity-based ad hoc multicast) routing protocol. They show that ABAM has many advantages in route reconstruction. Then, they demonstrate that ABAM is robust since the repair can be triggered by a node in the tree or by the migrated node itself. They also show that ABAM is capable of handling multicast group dynamics when mobile hosts decide to join and leave an existing multicast group. Their simulation results reveal that under different mobility scenarios and multicast group size, ABAM has low communication overhead and yields better throughput performance. Next, A. Andreadis, G. Benelli, G. Giambene, and B. Marzucchi discuss the analysis of the WAP protocol over SMS in GSM networks based on the PALIO Project within the fifth Research Framework of the European Commission. This deals with an information tourist service accessible through mobile phones by means of the Wireless Application Protocol (WAP). They considered a Global System for Mobile communications (GSM) network where the WAP traffic is transported by the Short Message Service (SMS) on a logical channel that also conveys signaling messages. Suitable models have been considered for both WAP browsing traffic and signaling traffic. Analytical predictions have been validated through comparisons with simulation results. Quality of Service (QoS) requirements in terms of the maximum transmission delay that is guaranteed in 95 per cent of cases was also considered. They concluded that this study proves the feasibility for the envisaged mobile service based on WAP and it also allows dimensioning WAP pages so that each user experiences reasonable browsing delays. A review of reduced-trellis equalization using the M-BCJR Algorithm is presented by C. Fragouli, N. Seshadri, and W. Turin. They review the complexity of channel equalization using the BCJR algorithm and how it grows exponentially with the channel memory. They also discuss how the M-BCJR algorithm provides a method for reduced-trellis channel equalization, but its performance varies significantly with the distribution of a channel energy to its taps. Then, they use the implementation of the BCJR algorithm in the logarithmic domain to propose a variation of the M-algorithm, which (they show) can offer robust performance. They discuss how the designer can make decision regarding delay, maximum and minimum phase transformation, and selection of states. Simulation is carried out to demonstrate the effect of different parameters on the proposed algorithm's performance. The broadcast nature of WDM star couplers makes the handoff scheme easier and reduces the number of reconnections. This is needed as the radio cells becomes gradually smaller and smaller, the procedures for mobile terminals call setup and control become complicated due to the high handoff frequency. H-C. Chao, R-C. Wang, and J-Y. Hong propose a channel allocation algorithm, called pre-empted assigned offset (PAO) scheme, for the WDM- and SCM/WDM-based personal communication network architectures. The main idea is to keep the offset conflict probability lower. Simulation results are provided to show that the proposed scheme outperforms those previously introduced schemes, especially in offset conflict probability under a moderate roaming rate for WDM and even under heavy roaming situations for SCM/WDM. Finally, A. Annamalai, Jr. discusses the effect of Gaussian error in Selection Diversity Combiners (SDC). SDC is one of the simplest and most commonly implemented diversity mechanisms for mitigating the detrimental effects of deep fades experienced on wireless channels. SDC main advantage is the reduction of the probability of deep fades. The effect of Gaussian errors in the branch gain estimates on the SDC receiver performance is investigated by deriving new closed-form expressions for the probability density function, cumulative distribution function and the moment generating function of the combiner output SNR statistic. Mathematical expressions for quantifying the degradation in the mean combined SNR, outage probability and the average symbol error rate of a broad class of binary and multilevel modulation schemes owing to imperfect branch SNR estimates in Rayleigh fading are also derived. The author then shows that combiner errors affect the mean combined SNR negligibly in comparison to their effect on the deep fades.

This is the first issue of the new journal Wireless Communications and Mobile Computing (WCMC) published by John Wiley & Sons, Ltd. WCMC promises to bring its readers outstanding published work that will enrich their horizons in their areas of expertise related to all aspects of wireless systems. It also promises authors speedy publication under the guidance of an international Advisory Board and Editorial Board drawn from academia and industry. The objective and strategy of WCMC is to carry high calibre survey papers, and a rapid publication time with a strong focus on new trends, developments, emerging technologies and industrial standards. We realize that we have a long way to go in order to attain these goals and objectives, but we have already made an excellent start. We are very proud of the highly qualified individuals who have joined our Advisory and Editorial Boards. They represent an international panel of well-known experts from around the world. In addition, we have instituted three region editors, under the leadership of a Senior Editor, in order to minimize workloads and encourage speedy manuscript processing. We have already reached a wide range of audiences around the world who have submitted and/or are in the process of submitting manuscripts to WCMC. We at WCMC are aware of the number of fine publications already in this field and the tight competition to attract the best manuscripts. Nevertheless, we feel that WCMC will target a different pool of contributions. The focus of WCMC will be towards running more special issues on hot topics that describe industry projects/standards, publishing at least one review/tutorial paper in each issue, and bridging the gap between wireless communications and mobile computing. This fresh approach to international publication will enlarge the pool of quality publications, rather than draw from the existing pool. WCMC's publication process will be fully electronic, administered by dedicated editors, which we firmly believe will contribute to a speedy review process and reduce the waiting time for authors. Finally, we would like to offer special thanks to all of those who have encouraged and contributed in the initial stages of this project, in particular the staff at John Wiley & Sons, Ltd. We also would like to thank those authors who have already sent their contributions to WCMC that you will read in this issue and in the next two issues. Furthermore, we welcome all authors and readers of WCMC and ask for their involvement and participation by submitting their manuscripts and welcome their personal subscriptions and that of their libraries. At the outset it was our priority to make sure both personal and institutional subscriptions to WCMC are affordable. For more details about the topics and how to make your electronic submission/subscription, we invite you to visit the WCMC web site at: www.interscience.wiley.com/jpages/1530-8669/ We also welcome any comments to any of the four editors listed below. Again, we welcome all of you to contribute and encourage your colleagues and libraries to subscribe to this fine publication.

This is the second issue of Wireless Communications and Mobile Computing (WCMC) published by John Wiley & Sons, Ltd. The first issue was published ahead of time and presented some excellent review papers from experts in the field. We received great feedback from a number of colleagues about its content and we promise to continue producing excellent issues in the future. If you did not receive your sample copy of the inaugural issue, please let me or any of the regional editors know to arrange to send you a copy. We have selected seven papers to appear in this second issue. These papers span a good range of topics in the area. The first is a review paper by Ralph and Aghvami. They discuss the Wireless Application Protocol (WAP) architecture and characteristics. Then, they investigate the devices that are supported by WAP as well as the drivers and services. These services include quality of service, security, billing, interoperability, and performance engineering. The variety of media types combined with the diversity of Internet connection characteristics raises momentous challenges to the achievement of ubiquitous access to Internet multimedia content. The second paper, by Margaritidis and Polyzos, addresses issues related to this topic. They identify the importance of adaptation to this category. Then, they examine several important factors that influence the design and optimization of the adaptation architecture. In conclusion, they describe current commercial solutions and future trends in application adaptation in conjunction with recent developments towards wireless access to the Internet. The third paper, by Havinga and Smit, discusses also wireless multimedia networking, but focuses more on energy efficiency. The authors identify three key problems and provide possible solutions to overcome them. The efficient management of power-controlled cellular wireless systems is necessary for their deployment success. Power control can be used as a platform for radio resource management and is important for channel fading as well as providing QoS to individual users. Xiao, Shroff and Chong review the developments of distributed power control and related resource management problems in cellular wireless systems. The discussion is concentrated on achieving high efficiency for a power-controlled system while preventing the system from failure. They then review power and rate control schemes proposed for wireless data, and present a framework for utility-based power control as a possible candidate for distributed power control of multimedia wireless systems. In the fifth paper, Arslan and Bottomley review commonly used approaches to channel estimation. This is necessary in adaptive receiver designs used in narrowband and wireless digital communication systems. They consider both time-invariant and time-varying channels in their discussion. They also provide a number of applications that will make use of this standard. On the other hand, Tepedelenliolu, Abdi, Giannakis and Kaveh talk about estimation of Doppler spread and signal strength in wireless systems. They concentrate on estimating the received signal strength, mobile velocity, and other related statistical channel parameters that apply to handoff and adaptive transmission. They provide comparison of the presented schemes based on their modeling and simulation results. Finally, Annamalai and Tellambura present a research paper discussing three new exponential-type bounds derived using the Cauchy–Schwarz bounding technique. They show that these new bounds are found to be tight and useful for a number of applications. They compare these bounds to other well-known exponential type bounds and prove that these perform at least comparable or tighter. We hope that you will enjoy reading this issue and welcome any comments to any of the four editors listed below. Again, we welcome all of you to contribute and encourage your colleagues and libraries to subscribe to this fine publication.

Abstract Wireless application protocol (WAP) is being heralded as the standard for communication of mobile Internet services to smart phone and personal digital assistant devices. The protocol utilises the low bandwidth, short battery power, quality of service and limited display facilities which are characteristic of current types of mobile device. This paper will examine the WAP architecture and the drivers and issues surrounding the development of services for this environment including the requirements for addressing, quality of service, security, billing, interoperability and performance engineering. Copyright © 2001 John Wiley & Sons, Ltd.

This paper contains a design description for an IP-mobility protocol called multicast for mobility protocol (MMP). The protocol is intended to provide fast and efficient location management and routing for mobile hosts in internet networks. The general configuration of the protocol which is divided into two parts: global and local, or macro and micro mobility, makes it an optimal and attractive solution for the emerging internet-based mobility-enabled stub networks, referred to as IP access networks. This version of MMP contains various enhancements to the initial version such as the introduction of a new control message MMP instruct and protocol mechanisms for handling new protocol issues such as: paging, support for mobile sources, advance registrations, implementation adaptations. However, the initial main concepts of mobile IP-controlled macro mobility and micro mobility enabled by a sparse mode multicast protocol called core based trees (CBT) are still the main characteristics of the protocol.

This paper presents an accessing and allocation scheme for a Global Pilot and Download Channel (GPDCH) on which all broadcast, signalling messages and downloading of re-configuration data are conducted between the base station and mobile software terminals. The performance of this proposed scheme is investigated by means of computer simulation to estimate the delay in the registration and downloading processes when a software terminal reconfigures itself over-the-air to a new air interface standard. Different downloading scenarios are also identified and analysed.

Performance (QoS and capacity) improvement by use of interference cancellation detection is examined for an uplink W-CDMA system with imperfect power control. Link- and system-level simulation results are given along with analytical expressions to investigate the case.

Distributed call admission control has been proposed for wireless/mobile high-speed networks. Preliminary studies showed that the proposal has better performance results when compared to the trunk reservation method. The primary assumption is that the traffic simulated is of uniform nature. In reality, such is not the case. Multimedia applications are expanding and future wireless/mobile networks should be designed to take into account the different traffic classes, and guarantee their quality-of-services (QoS) requirements, such as handover dropping probability and new call blocking probability that are essential as they measure the performance of a wireless network. We considered different traffic classes in a multimedia environment and their impact on QoS metrics. User mobility is also another important factor that will affect the performance of our wireless/mobile network.

Usually, when combining two or more services (each having their own QoS requirements), it is difficult to achieve a common operation point for all the services, When we satisfy the highest QoS requirement, the other services will be operating at "unnecessary high quality". In this case, a lot of bandwidth is wasted due to a low traffic load. To solve this problem and to achieve higher spectral efficiency, a "QoS balance" method is developed in this paper to optimise the allocation of transmission power and evaluated in a wide-band DS-CDMA environment integrated with video and voice services. Our simulation results demonstrate that the capacity of the network or spectral efficiency is improved significantly, by this optimal power allocation scheme.

This paper presents an overview of current research and published work on the performance of multi-layer cellular architectures and the handover performance in such networks. In a multi-layer cellular network, macrocells with a large coverage area, overlay microcells or picocells with smaller coverage areas. This network architecture, if well engineered, can provide improved QoS and higher capacity over the traditional single-tier cellular network under the same resource constraints. The small coverage of microcells/picocells, and the consequent multipath and shadow fading characteristics, mean that handover events in future systems will occur at a much higher rate. Therefore efficient handover algorithms are a cost-effective way of enhancing the capacity and QoS of cellular systems. This paper describes several methods that can be used for the evaluation of handover-related system performance.

The performance of an array of antennas combined with a RAKE receiver at the base station of a wideband code division multiple access system with quaternary phase shift keying modulation is investigated for single-user reception. This receiver structure is also known as a multidimensional RAKE receiver. Expressions for the interference correlation matrix are derived, and subsequently, an analysis of the error probability is provided. With regard to antenna weights, the optimum combining linear receiver, which takes into account the spatial distribution of all the users in the system, is compared with the suboptimum combining receiver (SOC), which exploits knowledge of the desired user array vector only. It is shown how the two receivers, ideal in the sense that perfect channel estimation is assumed, achieve very similar performances under realistic conditions. Consequently, the investigated pilot assisted combining receiver, which estimates the channel based on limited overhead, calculates weights according to the SOC strategy by a very simple algorithm.

The impact of imperfect amplitude estimation on interference cancellation is addressed in this study. Several parameters are discussed such as position of training sequence, influence of Doppler frequency and symbol rate. It is shown that, when using linear interpolation, the idea of splitting the training sequence into 3 parts as a pre-/ mid-/ post-amble allows the evolution of the channel to be followed with greater accuracy than in the case of mid-amble only. In addition, for fast fading rate channels, the idea of processing the estimates in two different lines is introduced and improves estimation. The conclusion is that linear interpolation can offer a solution for the channel estimation required by interference cancellation, combining very low complexity and very good channel tracking capability even at relative high vehicular speeds.

Different receiver structures that enable digitally modulated signals to be received in the presence of a number of similarly modulated cochannel interfering signals, which may additionally be dispersed in time owing to the influence of the channel, were investigated. Simplified MLSE techniques using decision feedback are analyzed mathematically and simulated. The performance of the different receivers in terms of complexity, channel estimation requirements and BER performance variation, are compared. These performances are obtained in the presence of AWGN and Rayleigh fading conditions.

In this paper the performance of feed-forward amplitude gain estimator techniques for orthogonal frequency division multiplexing (OFDM) utilising multilevel modulation is considered. Based on the split-symbol algorithm and the nonlinearity algorithm, the techniques operate on a number of frequency domain symbols in one OFDM symbol to estimate short term amplitude gain. Application of these techniques results in a efficient bandwidth transmission, reduced complexity system and, due to its feed-forward feature, a fast estimation period. The performance evaluation has been carried out by computer simulation over a frequency selective channel with AWGN, and compared for several estimation symbol lengths.

In this paper the application of a linear-quadratic processor is proposed for detection of each user's signal in a direct sequence code division multiple access system. In this method, some statistical knowledge of interfering transmitters' signals is used to detect the desired user's signal without needing exact "a priori" knowledge of the interfering signal parameters such as spreading sequences and signal powers. Parameters of the proposed processor can be obtained by solving a system of linear equations for which many effective techniques exist. A model for this detection procedure is developed and it is shown that a good compromise between complexity and quality of performance can be achieved. Finally, the problem of interference cancellation is also treated from an estimation point-of-view in which a different linear-quadratic processor is used to estimate the interference for further cancellation. Estimated error and probability of error are derived as measures of estimation performance.

This study assesses the performance of the decorrelating detector for DS-CDMA systems over multipath Rayleigh fading channels with AWGN. The decorrelating detector applies the inverse of the correlation matrix to decorrelate the matched filter outputs. The drawback of the decorrelating detector is that it enhances noise and that the inverse of the correlation matrix not always exists. The theoretical performance of the decorrelating detector is presented and the problem of inversion of the correlation matrix is discussed. This article also considers the case when the inverse of a smaller correlation matrix can be used for decorrelating the received data. The performance of the decorrelating detector is compared with other multi-user detectors proposed for DS-CDMA.

The use of high level trellis-coded modulation such as TCM 16-QAM, with equalization, diversity, interleaving and slow frequency hopping is investigated for wideband mobile communications. The symbol error rate (SER) performance of those systems in presence of intersymbol interference (ISI) and Rayleigh fading is evaluated by theoretical analysis and computer simulation. Several schemes of combining equalizers with diversity are evaluated by computer simulations. It shows that by choosing a proper interleaving size, number of the frequency hopping and the combining scheme of equalization and space diversity, the proposed system gives considerable performance improvement and can cope with the frequency selective multipath fading in wideband mobile communication systems.

The need for wireless ATM networks is motivated by an anticipated demand for wireless extension of integrated multimedia services. This wireless extension gives the mobile access part of a backbone ATM-based broadband services fixed network (B-ISDN) for future integrated communications. One of the major mobility-related functions, is connection hand-off when a mobile terminal roams between radio cells. Using the virtual connection tree already proposed for high-speed cellular radio networks based on an ATM backbone, this paper presents an implementation of the Quality of Service (QoS) and overload concepts in a wireless ATM system. Simulation results are presented for a voice and multimedia scenario.

Multidimensional packet reservation multiple access (MD PRMA) is proposed as a medium access strategy for the UMTS uplink channel. It embraces both code division PRMA (CDPRMA) and frequency division PRMA (FDPRMA) and is suitable for several air interface candidates for third generation mobile communications systems. In MD PRMA slots are defined not only in the time domain, but also in the frequency or "code domain", to increase the total number of slots per frame and thereby the multiplexing efficiency /spl eta//sub max/. This is particularly important when only a limited number of slots per frame are available, for instance 8 as in GSM, where /spl eta//sub max/ for voice-only traffic is only 0.67 with conventional PRMA on a single carrier, but 0.85 with 4 carriers and 0.90 with 8 carriers pooled together for FDPRMA operation. An adapted pseudo Bayesian algorithm is introduced to stabilise the protocol and simulation results are presented for FDPRMA with various sets of design parameters.

In this paper an analysis is carried out on the propagation mechanisms which cause polarisation changes of the electromagnetic field in a simplified microcellular environment. For this purpose a street surrounded by buildings is studied adopting a four-ray model and using the Fresnel equations for the reflections of the electrical field. The gain which can be achieved when exploiting polarisation diversity is determined with respect to a system receiving only the vertically polarised field. The linear combining techniques used to process the signal received on the two orthogonally polarised antennas were switching, equal gain combining, and maximal ratio combining. For a 10 per cent outage probability the average gain observed was 8 dB.

A complete traffic model and analysis for microcellular mobile systems with handoff using fixed channel allocation (FCA) is described. Only the new call arrival rate is supposed to be known and a method of assessing the hand-off arrival rate in each cell for any kind of traffic is derived. The analytical method is validated with a real non-uniform traffic distribution and is verified by simulations. An extension to the nonuniform compact pattern allocation algorithm is presented as an application of this analysis. Based on this extended concept, we propose a modified version of a dynamic channel allocation (DCA) strategy called compact pattern with maximised channel borrowing (CPMCB). It is shown that CPMCB is now a self-adaptive prioritised hand-off DCA strategy with enhanced performance that can be exploited in a PCS environment. The effect of user mobility on the grade of service is also considered by CPMCB.

Different channel estimation algorithms for direct-sequence code-division multiple-access (DS/CDMA) communications systems using binary phase-shift-keying (BPSK) modulation and a RAKE receiver are evaluated under fading multipath conditions. Two strategies are considered: the transmission of a pilot signal in the downlink and the block organization of the data in the uplink. The performance degradation of the system is due mainly to inaccurate estimation of the complex amplitudes rather than the delays; it remains low when using pilot signals with averaging filters or combining preamble information with symbol estimation.

In frequency selective channels, the delay-lock loop, and tracking systems derived from it are not ideal candidates for PN code tracking. This is because they are primarily designed for the AWGN channel. A tracking system designed specifically for use in frequency selective channels is presented. It is shown that with the knowledge of the channel response of the first few resolvable paths, an extended Kalman filter can be used to generate estimates of the PN code delay from the output of baseband inphase and quadrature early-late detectors, similar to those used in delay-lock loops. From computer simulation results of a practical model of the tracking system, it is shown that the tracking system is quite robust to errors in the parameters used to describe the PN code timing process. It is also shown that a simple channel noise estimation system can be used to provide the extended Kalman algorithm with reliable estimates of the channel noise. The performance of the tracking system in PN code clock drift situations is also presented.

A joint code-division multiple-access/packet-reservation multiple-access (CDMA/PRMA) technique is proposed and investigated as a candidate for an uplink protocol for third generation mobile communication systems. Access to the radio channel is controlled such that compared to random access CDMA, interference variance is reduced and throughput increased. Mixed voice/data traffic is investigated for an isolated cell only, whereas voice-only traffic is also investigated in a cellular environment with a regular hexagonal cell structure. Intercell interference is assumed to be Gaussian, and only the average interference level is considered.

This paper deals with the new reshuffle strategy for channel allocation algorithms. The need for a reshuffle strategy arises when the normal channel allocation algorithm wants to block a new call arrival or handover. It removes the congestion, frees channels and allocates them, so in some cases the blocking probability decreases by over 50%. The allocation algorithms are simulated in a cellular mobile network. The results obtained are compared with those achieved by channel allocation algorithms without the reshuffle technique and a new theoretical performance limit of blocking probability is derived.

This paper describes work carried out on examining the effects of spectral shaping on the performance of the RAKE receivers, in the presence of multipath propagation. Modelling techniques are used to simulate frequency-selective fading on DS modulated spread spectrum signals. RAKE receiver performance is examined with several pulse shaping filters. The filters range from ideal rectangular to Gaussian, covering the extreme performance bounds. The effect of pulse shaping is studied for several different signalling bandwidths, examining the benefits of frequency diversity and increased path diversity resolution on the filter performance. To enable the pass-band study of such systems, a static frequency-sensitive geometrical propagation channel model is used. The channel model provides information such as frequency and impulse response, delay power spectrum and the spaced-frequency correlation function of the channel. Based on the channel model output, signalling bandwidth and pulse shape, the output of RAKE receivers are categorised in terms of fade-depth statistics. The results indicate that pulse shape influence the RAKE receiver performance considerably. Depending on the filter type, there can be up to 7 dB improvement on the fade-depth at the receiver output. Results show that trade-off between the pulse width and side-lobe interference, favours the later. So filters such as Chebyshev, that result in pulses with narrow main-lobe but high side-lobes provide better performance than filters with larger main lobe, but low and rapidly decaying side-lobes, such as raised-cosine and Gaussian.

The two major requirements of future cellular mobile and personal communication systems are: the support of multi-rate services and operation in multi-cell environments. This paper is concerned with the identification and development of efficient and flexible methods of mapping logical traffic and control channels onto physical channels at the air interface for future multi-rate CDMA systems. We also address how a GSM 900/DCS 1800 fixed network may be evolved to support such systems.

In this paper the performance of an indoor wireless communication system is investigated. Adaptive decision feedback equalisers (DFE) are used to mitigate the intersymbol interference (ISI) caused by multipath propagation in the indoor radio channel. The system can be described as follows. It is a 16 quadrature amplitude modulation (16-QAM) system with raised cosine matched filtering with a roll-off factor of 0.50. A realistic channel model is used in the simulations by interpreting complex measured impulse responses of indoor radio channels. The measurements used were done in different types of rooms, and for line-of-sight (LOS) and obstructed (OBS) situations at the frequency of 2.4 GHz. After the signals have gone through the multipath channel additive white Gaussian noise (AWGN) was added. Symbol error rate (SER) performance simulations were done for different signal-to-noise ratios (SNR) and different data rates. On the average the SER performance was a few orders of magnitude (2-4) better than was the case without adaptive equalisation, depending on the SNR.

After a brief review of previous studies of dynamic channel allocation (DCA), the concept and the operation principles of distributed control channel allocation (DCCA) is described. This system can adapt to local traffic density and has good potential to reduce the number of call handovers in a microcellular system. It is shown by computer simulations that significant reductions in the number of handovers and forced terminations of calls can be achieved, in comparison to autonomous DCA techniques.

The paper describes analysis carried on frequency-selective channels to establish and quantify the performance improvements offered by broadband channels. The work focuses on the two types of diversity, frequency and path, which are offered only by wideband communications systems. For this reason a geometric propagation channel model is developed enabling the performance study of frequency-selective channels to be carried out at their operating frequencies; i.e. at bandpass. The channel model provides the transfer function and parameters such as coherence bandwidth and multipath spread of broadband channels. Based on these transfer functions the time responses of communication channels, separated by one or more signalling bandwidths, are compared and statistically quantified. The results indicate that, depending on the channel bandwidth, there is considerable correlation between broadband communications which are centred at different carrier frequencies. The high correlation between the different broadband channels can be used for propagation path-loss estimation for transmission power control applications in DS and hybrid CDMA systems.

The paper presents a new reduced-state soft decision feedback Viterbi equalizer (RSSDFVE) with a channel estimator and predictor. A multi-ray Rayleigh fading channel model with a Doppler frequency shift is used in the simulation. For fast convergence, a channel estimator with fast start-up is proposed. The channel estimator obtains the sampled channel impulse response (CIR) from the training sequence and updates the RSSDFVE during the bursts in order to track the changes of the channel. According to the simulation results, the proposed RSSDFVE gives much better performance than the DFE for severe Rayleigh multipath fading channels with much less implementation complexity than MLSE. The fast start-up (FS) channel estimator gives a faster convergence than a Kalman channel estimator and can achieve the same performance as the Kalman estimator with a shorter training sequence.>

This paper presents the performance of a matched filter acquisition scheme in nonselective and frequency-selective Rayleigh fading channels. This acquisition scheme employs a reference filter to estimate the variance of the interference at the output of the detecting matched filter. Expressions for probability of detection and probability of false alarm are derived and the mean acquisition time is evaluated for various channel and system parameters. The results presented show the relationship between channel and system parameters and the system performance.>

Channel outage probabilities for QPSK and pi /4-DQPSK are evaluated in a Gaussian profiled multipath fading channel with additive white noise by computer simulation. Assuming a minimum acceptable bit error rate of 10/sup -5/, it is found that even with a very small normalised delay spread d'=0.05, the channel outage probability is greater than 10/sup -3/. Using 4-branch switched diversity this can be reduced such that channel outage is less than 10/sup -5/ with d'>

The authors discuss the possibility of transmitting synchronous digital hierarchy (SDH) signals through two-link nonlinear satellite channels. Transmitting such high bit rate signals through a standard 54 MHz or 36 MHz transponder bandwidth requires the use of high-level modulation schemes. The techniques and technologies needed to make the use of 16-ary quadrature amplitude modulation (QAM) and 64-ary QAM transmissions feasible for future satellite communication systems are examined. It is shown that it is possible to transmit a synchronous transport module-level 1 (STM-1) signal through a standard 54 or 36 MHz transponder bandwidth using 16-ary QAM or 64-ary QAM transmission, respectively, for the 6/4 GHz band. However, for higher frequency bands, due to high fade margins needed to achieve the high availability and performance for SDH systems, is not practical to transmit the STM-1 signal through such standard transponder bandwidths.>