The increasing demand for high-speed, ultra-reliable and low-latency communications in 5G and beyond networks has led to a significant increase in power consumption, particularly within the Radio Access Network (RAN). This growing energy demand raises operational and sustainability challenges for mobile network operators, requiring novel solutions to enhance energy efficiency while maintaining Quality of Service (QoS). 5G networks are evolving towards disaggregated, programmable, and intelligent architectures, with Open Radio Access Network (O-RAN) spearheaded by the O-RAN Alliance, enabling greater flexibility, interoperability, and cost-effectiveness. However, this disaggregated approach introduces new complexities, especially in terms of power consumption across different network components, including Open Radio Units (RUs), Open Distributed Units (DUs) and Open Central Units (CUs). Understanding the power efficiency of different O-RAN functional splits is crucial for optimising energy consumption and network sustainability. In this paper, we present a comprehensive measurement study of power consumption in RUs, DUs and CUs under varying network loads, specifically analysing the impact of Physical resource block (PRB) utilisation in Split 8 and Split 7.2b. The measurements were conducted on both software-defined radio (SDR)-based RUs and commercial indoor and outdoor RU, as well as their corresponding DU and CU. By evaluating real-world hardware deployments under different operational conditions, this study provides empirical insights into the power efficiency of various O-RAN configurations. The results highlight that power consumption does not scale significantly with network load, suggesting that a large portion of energy consumption remains constant regardless of traffic demand.

The advent of 6G technology demands flexible, scalable wireless architectures to support ultra-low latency, high connectivity, and high device density. The Open Radio Access Network (O-RAN) framework, with its open interfaces and virtualized functions, provides a promising foundation for such architectures. However, traditional fixed base stations alone are not sufficient to fully capitalize on the benefits of O-RAN due to their limited flexibility in responding to dynamic network demands. The integration of Unmanned Aerial Vehicles (UAVs) as mobile RUs within the O-RAN architecture offers a solution by leveraging the flexibility of drones to dynamically extend coverage. However, UAV operating in diverse environments requires frequent retraining, leading to significant energy waste. We proposed transfer learning based on Dueling Double Deep Q network (DDQN) with multi-step learning, which significantly reduces the training time and energy consumption required UAVs to adapt to new environments. We designed simulation environments and conducted ray tracing experiments using Wireless InSite with real-world map data. In the two simulated environments, training energy consumption was reduced by 30.52% and 58.51%, respectively. Furthermore, tests on real-world maps of Ottawa and Rosslyn showed energy reductions of 44.85% and 36.97%, respectively.

Conventional coverage and capacity from a high altitude platform (HAP) over an extended coverage area suffer significantly from inter-cell interference (ICI), antenna beam broadening, and uneven cell loading, which results in poor edge performance. In this paper, we show how a single antenna array on a HAP can be used to mitigate against these and achieve ubiquitous coverage by forming two tiers of a homogeneous contiguous cellular structure. We propose separate algorithms that implement the two-tier architecture with many antenna beams, which are used to form cells, and associate users with an appropriate cell and tier. A user associates with the cell and tier, which offer the best carrier power-to-noise ratio (CNR) and carrier power-to-interference-plus-noise ratio (CINR) respectively. The performance of the architecture, which is evaluated using simulation, is compared with a typical one-tier architecture. The results show that the two-tier architecture achieves over 30% higher user throughput and enhances throughput fairness and edge-of-cell connectivity by centralising as many users as possible within cells compared to the typical one-tier architecture. These benefits are better exploited by ensuring spectrum orthogonality between the two tiers.

This paper presents a lightweight cross-layer protocol relIable Routing with coordInated medium acceSs control (IRIS) which is designed for long-range pipeline Wireless Sensor Networks (WSNs) with extremely low power budget, typically seen in a range of monitoring applications. IRIS includes functions of network discovery, medium access control and routing designed for heavily energy constrained networks. The protocol is able to operate with less than 1% duty cycle, thereby conforming to ISM band spectrum regulations in the 868MHz band. The duty cycle can be flexibly configured to meet other regulations/power budgets as well as to improve the route forming performance. Simulation results show a guaranteed route formation in different network topologies with various protocol configurations. An analytical model is presented to validate the simulation results of route formation time. System robustness against unreliable wireless connections and node failures are also demonstrated by simulations. A network of 71 attenuated LoRa nodes is implemented to evaluate the capability of IRIS. Long-term operation of the network shows consistent performance compare with the simulations.

Machine-type communications (MTC) is considered as one of the promising technologies over the next decade and these MTC devices are continuously increasing. When a large number of MTC devices try to access a cellular base station simultaneously using the existing LTE/LTE-A Random Access Channel (RACH), the collision probability among Machine-to-Machine (M2M) and Human-to-Human (H2H) device increases drastically. Thus the performance of RACH degrades sharply which causes significant blocking and huge access delay. Delay-critical applications, cannot therefore be served using the legacy RACH protocol. The present work aims at solving this delay issue for a specific user group by proposing a Prioritised Dynamic Random Access scheme (PD-RACH) that improves the conventional RA procedure in order to minimize the delay and offer priority to the specific user group. Simulation results show that the proposed scheme can significantly reduce the access delay for the priority user group.

In this paper, the deployment of a High Altitude Platform (HAP) exploiting the mmWave bands to provide broadband infotainment services for vehicular users in rural areas, that, otherwise, would have little or no broadband connectivity is proposed. In this context, an investigation into the use of steerable beam directional antennas to provide performance improvements in terms of Carrier to Noise Ratio (CNR) and high data rates for Line of sight (LOS) HAP beams is undertaken. An analysis of coverage and capacity for clusters of vehicular users utilizing HAP arrays with different numbers of antenna elements is presented. Simulation results indicate the minimum number of clusters that will be required for a given antenna array in order to achieve at least a 95% coverage while simultaneously providing an upper bound of average user capacity of 135 Mbps, and a lower bound of 34 Mbps, as for the 900 antenna element case. Results additionally show that a maximum user capacity of 50 Mbps can be attained by users at the mobile edge utilizing more than 64 array elements despite the increased path loss experienced by these users.

Unmanned aerial vehicles (UAVs) are envisioned to be widely deployed as an integral component in the next generation cellular networks, where spectrum sharing between the aerial and terrestrial communication systems will play an important role. However, there exist significant security and privacy challenges due to the untrusted broadcast features and wireless transmission of the UAV networks. This article endeavors to resolve the security issues through proposing a novel privacy-preserving secure spectrum trading and sharing scheme based on blockchain technology. Specifically, from the operator's perspective, a pricing-based incentive mechanism is first introduced, in which a primary mobile network operator (MNO) leases its owned spectrum to a secondary UAV network in exchange for some revenue from the UAV operators. To address the potential security issues, a spectrum blockchain framework is then proposed to illustrate detailed operations of how the blockchain helps to improve the spectrum trading environment. Under this framework, a Stackelberg game is formulated to jointly maximize the profits of the MNO and the UAV operators considering uniform and nonuniform pricing schemes. Security assessment and numerical results confirm the security and efficiency of our schemes for spectrum sharing in UAV-assisted cellular networks.

In this paper, we propose a scheme for beam-pointing from a high altitude platform (HAP) for contiguous coverage delivery within an extended service area. The scheme, which illuminates cells, considers the broadening of beams on the ground from the HAP-based antenna array. A predetermined degree of overlap is introduced between neighbouring cells to minimize user outages when moving between cells. In order to evaluate the performance of the scheme, users are randomly distributed at a density of λ users/km2over a service area of radius R. We compare the cell overlap, users' carrier-to-noise ratio (CNR), and carrier-to-interference-plus-noise ratio (CINR) with those of other cell-pointing schemes. The results show that cell overlap is better managed using our proposed schemes. In addition, the proposed scheme significantly improves user CNR and CINR, achieving a CINR improvement of 5-15dB compared with the other schemes.

In this paper, we evaluate iterative interference cancellation (IIC) as a method to remove the intrinsic interference terms in filter bank multicarrier - quadrature amplitude modulation (FBMC-QAM) systems. We propose an IIC receiver that separates the received signal into even- and odd-numbered subcarrier components and use the demodulated even- and odd-numbered subcarrier symbols to iteratively remove the effect of interference. Numerical results show that the out-of-band emission performance of the IIC FBMC-QAM system is superior to that of OFDM and conventional FBMC-QAM. Bit error rate (BER) simulation results also indicate that the proposed IIC FBMC-QAM can effectively improve BER performance under different time-varying channels.

In this paper, we focus on reducing the on-grid energy consumption in heterogeneous radio access networks (HetNets) supplied with hybrid power sources (grid and renewables). The energy efficiency problem is analyzed over both short- and long-timescales by means of reactive and proactive management strategies. For short-timescale case, a renewable-energy (RE) aware user equipment-base station association is proposed and analyzed for the cases when no storage infrastructure is available. For long-timescale case, a traffic flow method is proposed for load balancing in RE base stations (BSs), which is combined with a model predictive controller (MPC) to include forecast capabilities of the RE source behavior in order to better exploit a Green HetNet with storage support. The mechanisms are evaluated with data of solar measurements from the region of Valle de Aburrá, Medellín, Colombia and wind estimations from the Moscow region, Russian Federation. Results show how the green association proposal can reduce on-grid energy consumption in a HetNet by up to 34%, while is able to exceed the savings obtained by other methods, including the best-signal level policy by up to 15%, additionally providing high network efficiency and low computational complexity. For the long-timescale case, MPC attainable savings can be up to 22% with respect to the on-grid only Macro-BS approach. Finally, an analysis of our proposals in a common scenario is included, which highlights the relevance of storage management, although emphasizing the importance of combining reactive and proactive methods in a common framework to exploit the best of each approach.

This work investigates the performance of user-centric joint transmission coordinated multipoint (JT-CoMP) clustering in a control/data decoupled cell-less architecture taking radio resource assignment into account. In CoMP networks, a trade-off exists between signal to interference noise ratio (SINR) gain and loss of radio resources. To achieve a balance between SINR gain and loss of radio resources, it is essential to find an optimal power level difference (PLD) value that can identify the number of users that can operate under a CoMP mode. Also, CoMP requires a proper radio resource management approach that can support the resource assignment from multiple base stations (BSs). In this paper, we study the effect of choosing a PLD value on the per-user throughput of CoMP and non-CoMP users. Also, we provide a radio resource management scheme that can support a CoMP cell-less architecture. Simulation results demonstrated that a PLD value of 5 dB can provide a good balance between SINR gain and loss of radio resources. Also, efficient radio resource scheduling improves the throughput of 65% of non-CoMP users and 35% of CoMP users when the PLD value is 5 dB.

This paper discusses a base station selection scheme for handover in a mobility-aware ultra-dense small cell urban vehicular environment. The scheme follows a three step sequence to select future base station (eNB) depending on k-nearest neighbor value (k-value) and azimuth angle. Considering vehicle mobility and severe cross interference in the ultra-dense topology, selection of eNB is an essential factor which affects both latency and data rates. The underlying motivation is to strike a balance between handover frequency and system performance with QoS guarantee. Analyzing the proposed scheme, we found that a unique pattern is associated with every k-value. Pattern recognition scheme will be exploited to implement the proposed scheme in a more complex topology. The simulation results demonstrate a system level performance comparison drawn among different handover approaches using the proposed scheme in order to understand the influence of eNB selection on the quality of service (QoS) at different vehicle speed.

The provision of service-oriented network resource virtualization, commonly known as network slicing, is envisioned as an answer to the increasing diversity of application demands in evolving 5G mobile networks. Network slicing is helpful in isolating a specified amount of resources in order to accommodate diverse services having heterogeneous requirements that may be conflicting. In this paper, we propose a service-oriented network resource slicing scheme for a Time Division Duplex (TDD) network that, for a pre-defined time duration, forms service-specific network slices based on traffic prediction. The aim of the proposed slicing scheme is to enhance the services, Quality of Experience (QoE) and system resource utilization efficiency by introducing a new degree of flexibility upon allocating resources to different tenants. System-level simulation analysis shows that the proposed scheme improves the performance of high priority services and boosts resource utilization at negligible performance loss for low-priority traffic.

This paper introduces promising millimetre wave backhaul deployment options that serve an ultra-dense outdoor radio access network installed on street-level fixtures. A backhaul architecture which is based on either Cloud-RAN (C-RAN) or Distributed-RAN (D-RAN) configuration is introduced. We investigate the advantages and disadvantages of utilising millimetre wave in bands 71-76 and 81-86 GHz and free space optics (FSO) to fronthaul/backhaul links. As an initial study, the proposed architecture based on D-RAN is applied to a dense urban city area where moving vehicles and other users are served mixed traffic, including high resolution on demand and real time video. The analysis shows that the unevenly distributed traffic caused by different user types and mobility requires that the location and number of backhaul links need to be carefully designed to overcome the problems of bottlenecks on the backhaul links.

In this paper, we propose an algorithm for dynamic spectrum access (DSA) in LTE cellular systems-distributed ICIC accelerated Q-learning (DIAQ). It combines distributed reinforcement learning (RL) and standardized inter-cell interference coordination (ICIC) signalling in the LTE downlink, using the framework of heuristically accelerated RL (HARL). Furthermore, we present a novel Bayesian network based approach to theoretical analysis of RL based DSA. It explains a predicted improvement in the convergence behaviour achieved by DIAQ, compared to classical RL. The scheme is also assessed using large scale simulations of a stadium temporary event network. Compared to a typical heuristic ICIC approach, DIAQ provides significantly better quality of service and supports considerably higher network throughput densities. In addition, DIAQ dramatically improves initial performance, speeds up convergence, and improves steady state performance of a state-of-the-art distributed Q-learning algorithm, confirming the theoretical predictions. Finally, our scheme is designed to comply with the current LTE standards. Therefore, it enables easy implementation of robust distributed machine intelligence for full self-organisation in existing commercial networks.

This paper assesses the robustness of the distributed reinforcement learning (RL) approach to dynamic spectrum access (DSA) in cellular systems with asymmetric topologies and non-uniform offered traffic distributions. Large scale simulations of a stadium small cell LTE network, employing a distributed Q-learning based DSA scheme, show that such asymmetries in the network environment cause no degradation of the QoS provided to any part of the network.

This paper investigates the distributed Q-learning approach to secondary LTE spectrum sharing, its autonomously emerging spectrum usage patterns, and their impact on the primary and secondary user quality of service (QoS). Large scale simulations of a stadium temporary event scenario show that it is capable of servicing a dramatic 51-fold increase in offered traffic, but with no need for additional spectrum and with no perceived degradation in the primary user QoS.

This paper studies interoperability concerns arising from coupling energy-aware radio resource and topology management techniques which are developed to minimise the energy consumption of current and future mobile broadband systems. This paper also proposes an Energy-aware Network Management middleware that harmonises the joint operation of energy-aware radio resource and topology management schemes enhancing the system QoS as well as energy efficiency.

This paper presents the concept of the Win-or-Learn-Fast (WoLF) variable learning rate for distributed Q-learning based dynamic spectrum management algorithms. It demonstrates the importance of choosing the learning rate correctly by simulating a large scale stadium temporary event network. The results show that using the WoLF variable learning rate provides a significant improvement in quality of service, in terms of the probabilities of file blocking and interruption, over typical values of fixed learning rates. The results have also demonstrated that it is possible to provide a better and more robust quality of service using distributed Q-learning with a WoLF variable learning rate, than a spectrum sensing based opportunistic spectrum access scheme, but with no spectrum sensing involved.

This paper introduces the concept of virtual cells in Time-Division Long Term Evolution (TD-LTE) systems, which enables users residing in overlapping cells' coverage regions to utilize resources from multiple base stations. The benefits of virtual cells are realized by the efficient resource utilization, via adapting the network resource availability with the traffic demand taking also into account the impact of cross-slot interference. Besides the increased resource flexibility, virtual cells also resolve pseudo congestion, and introduce a customized, user specific, resource utilization. Such a feature enables mobile users to utilize sub-frames from different base stations creating on demand virtual frame. A simulation study elaborates the benefits of our approach, and demonstrates the performance enhancements in comparison with the conventional TD-LTE configurations.

To enhance channel throughput, end to end delay and energy efficiency for wireless networks based on a single-hop topology, this paper proposes a distributed reservation multiple access scheme with adaptive switching requests (DRMA-ASR). The DRMA-ASR scheme uses a repeating frame structure with a reservation period and a data transmission period based on the principles of the ALOHA-reservation scheme. To improve performance, this scheme proposes an adaptive or skipped reservation period with the probability based on a hidden Markov model (HMM). In addition, request packets are transmitted based on a permission probability to increase the probability with which the reservation period can be reduced in duration or skipped, and energy saving is achieved by putting terminals into a low power sleep mode when they are not required to transmit during the data transmission period. The scheme applies a virtual carrier sensing mechanism and does not require physical sensing. Simulation results show that DRMA-ASR provides better performance in terms of channel throughput, end to end delay, and energy efficiency than CSMA/CA with both small and large interference ranges.

In this paper, a novel interference aware, energy efficient resource allocation scheme based on signal to interference plus noise ratio (SINR) rank restrictions is proposed for beyond next generation mobile networks. The relationship between the choice of base stations (when their ranking and selection is based on SINR) and inter-cell interference is examined. It is observed that lower SINR choices result in higher interference in the network and vice versa. Based on the observed relationship, the capability of the proposed scheme to mitigate inter-cell interference and achieve energy saving is evaluated with different SINR based choice restriction policies. The energy efficiency and quality of service (QoS) performance of the proposed scheme is compared with schemes without interference awareness features. The results show that the proposed scheme can achieve up to 65% energy savings at low offered traffic and can also provide significantly higher QoS over a wide range of traffic loads than the schemes without interference awareness.

In this paper, we introduce a novel paradigm of transfer learning for spectrum and topology management in a rapidly deployable opportunistic network for the post disaster and temporary event scenarios. The network architecture is designed to be rapidly changing between different disaster phases, and highly flexible during the temporary event period. Transfer learning is developed to learn the dynamic radio environment from network topologies. This also allows previously learnt information in earlier phases of a deployment to be efficiently used to influence the learning process in later phases of a deployment. A Transfer Learning strategy is designed to change the knowledge base from the most recent phase via multi-agent coordination. We evaluate transfer learning paradigm in a small cell Terrestrial eNB architecture, integrated with Q-Learning and Linear Reinforcement Learning. It is demonstrated that transfer learning significantly improves the initial performance, the convergence speed and the steady state QoS, by exchanging topology information for resource prioritization.

This paper considers designing efficient medium access strategies for secondary users (SUs) to select frequency channels to sense and access in cognitive radio networks. The interaction among the SUs is considered as a learning problem, in which every SU behaves as an intelligent agent. Each SU believes that its competitors alter their future medium access strategies in proportion to its own current strategy change. These beliefs adapt in accordance with limited information exchange. In this way, each SU can obtain the behavior feature of other users through conjecture, optimize the medium access strategy, and finally achieve the goal of reciprocity, based on which two learning algorithms are proposed. We show that the SUs' stochastic behaviors and beliefs converge to a steady state under some conditions. Numerical results are provided to evaluate the performance of the two algorithms, and show that the achieved system performance gain outperforms some existing protocols.

Adding fixed relay nodes (RNs) to wireless access networks requires additional costly infrastructure. Utilising mobile RNs, that is, user terminals that relay signals intended for other users being the destination nodes (DNs), is an appealing cost-effective solution. However, the changing node topology increases the required signalling for relay selection (RS). The signalling overhead consists of control signals that need to be exchanged between the RNs, the source node (SN) and the DN, to achieve the objectives of cooperation. To reduce signalling without penalising performance, the authors propose a three-step approach exploiting statistical knowledge on the likelihood of attaining performance gains by using RNs as a function of the node position (position of DNs and RNs). In the first step only the cell DNs that are likely to gain from relaying request the assistance of RNs. In the second step, for each DN that requests relaying, a limited set of RN candidates is formed. These decisions are made with the aid of thresholds applied to inter-node distances whose values are based on the acquired statistical knowledge. In the final step, RN candidates feed back the relevant channel state information to the SN that performs RS. Furthermore, the authors investigate the attained gains from mobile RNs as a function of the fading environment and they show that mobile RNs can help overcome the effects of severe fading.

This study presents a novel two-stage reinforcement-learning-based algorithm for distributed cognitive radio (CR) spectrum sharing. The traditional reinforcement-learning model is modified in order to be applied in a fully distributed CR scenario. CRs are able to discover the best available resources autonomously by utilising learning, which results in significantly improved performance, while reducing the need for spectrum sensing. Instead of sensing all available spectrum arbitrarily, the scheme is designed to share the spectrum based on an optimal spectrum sharing strategy, which is discovered by the CR agents from their trial-and-error interactions with the wireless communication environment. On the other hand, the inherent exploration against exploitation trade-off seen in reinforcement learning is also examined in the context of CR. A ‘warm-up’ stage is proposed to effectively control the exploration phase of the learning process. A better system performance can be expected by carefully balancing the tradeoff between exploration and exploitation. The benefit of applying a warm-up stage is demonstrated. Comparisons of system performance using different warm-up strategies are also given to illustrate their impact on the spectrum sharing process.

This study introduces two novel approaches, pre-partitioning and weight-driven exploration, to enable an efficient learning process in the context of cognitive radio. Learning efficiency is crucial when applying reinforcement learning to cognitive radio since cognitive radio users will cause a higher level of disturbance in the exploration phase. Careful control of the tradeoff between exploration and exploitation for a learning-enabled cognitive radio in order to efficiently learn from the interactions with a dynamic radio environment is investigated. In the pre-partitioning scheme, the potential action space of cognitive radios is reduced by initially randomly partitioning the spectrum in each cognitive radio. Cognitive radios are therefore able to finish their exploration stage faster than more basic reinforcement learning-based schemes. In the weight-driven exploration scheme, exploitation is merged into exploration by taking into account the knowledge gained in exploration to influence action selection, thereby achieving a more efficient exploration phase. The learning efficiency in a cognitive radio scenario is defined and the learning efficiency of the proposed schemes is investigated. The simulation results show that the exploration of cognitive radio is more efficient by using pre-partitioning and weight-driven exploration and the system performance is improved accordingly.

We propose a new analytical approach to evaluate the average packet error rate (PER) of a conventional packet transmission system over a quasi static fading channel, by presenting an integral inequality lemma. The basic idea of the approach is that, given the PER for the AWGN channel as a function of signal-to-noise ratio (SNR), the average PER over Rayleigh fading channel can be generally upper bounded by a quite simple inequality, i.e.,1 - exp(-wo/γ̅), for both coded and uncoded schemes, where wo, defined by an integral expression, corresponds exactly to the inversion of coding gain; and this bound is tight in the high SNR region or for long packet systems. We further apply the integral inequality to extend our research to more general Nakagami-m fading channel.

The purpose of this paper is to present a modified scheduling algorithm, called Traffic-oriented scheduling algorithm for Aerial platform based Routing and MAC (APRMAC) protocol for Wireless Sensor Networks (WSNs) to maximise throughput. This algorithm keeps the characteristics of APRMAC, which is energy efficient, contention free and inherent routes establishment. The advantages of APRMAC and the novel scheduling algorithm are analysed. A simulation is carried out for both crossing chain and random topologies to validate the scheme and for comparison of performance with the original delay-oriented APRMAC and a well-known schedule-based MAC protocol, TRAMA. The results show that APRMAC offers higher energy efficiency against TRAMA. The results also show that the traffic-oriented scheduling algorithm can provide better throughput performance then the original delay-oriented one.

Despite the very substantial body of research on the performance analysis of cooperative relay systems, most studies focus on either the symbol error ratio (SER) or outage behavior. This paper analyzes the asymptotic average packet error rate (PER) of the packet cooperative relay system for both AF (Amplify-and-Forward) and DF (Decode-and-Forward) schemes in the high signal-to-noise ratio (SNR) region, and studies the effect of packet length on average PER performance. It is shown that the system achieves the same diversity gain in terms of PER as in terms of SER, but with different coding gain depending on packet length. If we consider practical packet lengths, the DF scheme always achieves better performance than the AF scheme; with shorter packet length, the advantage of DF over AF is more significant. For large enough packet length, AF performance approaches that of DF.

In this paper we propose a novel connection admission control scheme named Rate Transition Area assisted Guaranteed Handover Scheme (GHS-RTA), which utilizes the geographical information, rate transition areas and overlap areas to intelligently decide when to block a new call. This scheme helps avoid possible inter-cell and intra-cell handover failures for HAP communications systems with adaptive modulation and coding in the physical layer. Simulation results show that the GHS-RTA can improve the average new call blocking probability greatly (by a minimum of 21.5% for the system model with the parameter values chosen) while maintaining zero inter-cell and intra-cell handover call dropping probabilities compared with Extended Time-based Channel Reservation Algorithm, and that the larger the rate transition area and the overlap area, the better the average new call blocking performance.

Despite the very substantial body of research on the performance analysis of cooperative relay systems, most studies focus on either the symbol error ratio (SER) or outage behavior. This paper first analyzes the asymptotic average packet error probability (PEP) of uncoded packet cooperative relay system for DF (Decode-and-Forward) schemes in the high signal-to-noise ratio (SNR) region. In particular, the effect of packet length on optimum power allocation roptis studied. It is found, with a symmetrical links assumption, the optimum power allocation ratio is in the region of 1/2optoptvalue converges to (3-√3)/2.

This study analyses a cognitive radio scenario based on non-persistent carrier sense multiple access (CSMA) and time division multiple access (TDMA) systems sharing a single-channel wireless network. TDMA users are considered as primary users who can access the channel at any time, and non-persistent CSMA users are considered as secondary users who can share the channel when it is free. New expressions for the individual and aggregate throughput performance of this combined system have been developed, and the system performance is evaluated for a variety of proportions of non-persistent CSMA and TDMA traffic levels. Simulation and analytical results are presented and the ways in which both schemes suffer negative effects as a result of the interaction are shown, primarily caused by increased number of collisions arising from the other scheme.

This paper presents a new family of Interference routing metrics, ILR (interference level routing), ILRk (interference level routing to the power of k) and ILRth(interference level routing with a threshold value) for wireless ad hoc networks. Unlike conventional routing metrics, such as shortest path, these proposed routing metrics have been replaced with weight metrics that take into account the combination of node inward and outward interference. By assigning and adjusting the value of the interference level factor in the metrics, the priority of 'inconvenience' and 'disturbance' can be controlled. The performance of the proposed routing metrics is examined and compared with conventional shortest path routing. The simulation results show that these proposed routing metrics improve load balancing to provide enhanced network capacity and reduced bottlenecks.

This paper shows how channel assignment in multicast terrestrial communication systems with different user populations and distributed channel occupancy detection can be improved using intelligence based on reinforcement learning. The schemes greatly reduce the number of reassignments and improve the dropping probability, at the expense of increased blocking. It is found that compared to detection by single users, detection by multiple users reduces the 'hidden node' problem. Using different minimum quality of service threshold percentages can partly control and improve the performance, in place of the more traditional SINR threshold levels. At the same time, with reinforcement leaning, the ability of find an optimal channel for users is significantly improved, because the channel weighting can help the users avoid the interference.

Cognitive wireless mesh networks have great flexibility to improve the spectrum utilization by opportunistically accessing the authorized frequency bands, within which the secondary users (SUs) should not violate the quality of service (QoS) requirement of the primary users (PUs) while transmitting. In this paper, we consider inter-cluster connection among neighboring clusters under the framework of cognitive wireless mesh networks. Corresponding to the neighboring clusters, all nodes operate in half-duplex mode; hence exchanging control message usually needs four time slots by traditional scheme, which leads to a loss in networking and spectral efficiency especially at the gateway node. A novel scheme based on network coding is proposed, which needs only two time slots. Our simulation experiments reveal the following findings: the performances of traditional inter-cluster connection and network coding based inter-cluster connection are comparable. Next, how to choose optimal signal amplification factor at the gateway node according to the wireless environment is discussed. And we present an intelligent policy based on reinforcement learning to solve the problem. Theoretical analysis and numerical results both show the policy can achieve optimal throughput for the SUs in the long run.

The efficiency of wireless communication systems largely depends on proper understanding of propagation impairments and the design of suitable countermeasures, taking into account physical causes and time-scales of propagation phenomena. The primary focus of this paper is the link between High Altitude Platform (HAP) and a collective mobile terminal onboard high speed train. The paper characterizes the temporal behavior of the propagation channel on this link by means of first- and second-order statistics, presents a QoS framework based on IP architecture, and discusses potential propagation impairment countermeasures from the perspective of their usage in the provision of different services.

This paper investigates the ways of improving the Grade-of-Service (GoS) in a coexistence scenario with different user types in a multiple High Altitude Platforms (HAPs) system with shared coverage area and radio spectrum. It is achieved through the exploitation of HAP diversity. An analytical model based on a two-dimensional state-transition-rate diagram is developed to describe system behaviour of a coexistence scenario containing two user groups, which have full and limited HAP availability. On the basis of the analytical model, a novel restriction mechanism is implemented in order to achieve a fair balance of GoS to the two user groups using connection admission control (CAC). The mechanism restricts access to the channel resource for users with full HAP choice in order to give more chance of access to users with a more limited HAP selection. Different types of restriction function are analysed and the paper shows that a step restriction function is the most suitable mechanism to provide a balanced low blocking probability performance to both user groups simultaneously. Furthermore, the mechanism can potentially provide a certain level of GoS guarantee for the users if adequate flexibility is available within the whole system.

Two spectrum etiquettes are developed for the use on the downlink of coexisting high-altitude platform (HAP) and terrestrial fixed broadband systems that are intended for future application with cognitive radio-based user terminals with directional antennas. The spectrum etiquettes are based on the interference to noise ratio and carrier to interference plus noise ratio levels at the receiver of an incumbent user. Antenna beamwidths and multiple modulation scheme levels determine the parameter settings for coexistence performance. It is shown that coexistence performance can be improved by exploiting the surplus transmitter power of the terrestrial system, thereby enabling the incumbent terrestrial system to accommodate additional interference arising from a newly activated HAP system.

This paper investigates the feasibility of coexistence of co-channel time division synchronous code-division multiple access (TD-SCDMA) and wideband code division multiple access (WCDMA) systems operating in a macro cell environment. A Monte-Carlo simulation is performed for a TD-SCDMA network, a WCDMA network, and the coexistence network comprising both systems for both the uplink and downlink. The impact of eight interference modes is considered. The pole capacity in each case is calculated and compared with each other. From the comparison and analysis, it is found that the combined system can achieve comparable performance to that of the individual systems, and the WCDMA cells and TD-SCDMA cells can effectively share the same spectrum resources.

The effect of user antenna pointing error in multiple high-altitude platform (HAP) systems is examined. A truncated Gaussian distribution is applied to the pointing error. Ranges of different standard deviations and user antenna beamwidth are combined to show different aspects of the system capacity degradation. A concept of virtual points of HAP locations is introduced to give a direct indication of the severity of the pointing error. Optimum user antenna beamwidths are determined as a function of standard deviation of pointing error, for various percentiles of the spectral efficiency, to aid the system designer. The multiple HAP system itself will not jeopardise the system capacity by introducing the user antenna pointing error. It is shown that pointing error reduces the received carrier power with the interference little affected and hence multiple HAP systems are no more susceptible than a single HAP system.

Clustering sizes, power control strategies and antenna beamwidths, and orientations are investigated for quasi-stationary high-altitude platforms (HAPs) or other aerial platforms operating in the millimetre-wave band. It is shown that considering the carrier-to-noise and interference ratios (CNIRs) when optimising antenna beamwidths and directions can lead to significant increases in minimum CNIR levels (e.g. from 8.7 to 16.9 dB) over the coverage area. It is also shown that the optimum antenna configurations and transmit powers are a function of the weather, and should (if possible) be adjusted during periods of cloud cover and rainfall. In more practical situations in which only the transmit powers from the HAP antennas can be adjusted dynamically, it is shown that the loss in performance is <2 dB relative to the optimum scheme with dynamically adjustable antenna beamwidths and orientations over a wide range of rainfall conditions.

A method of significantly improving the capacity of high-altitude platform (HAP) communications networks operating in the millimeter-wave bands is presented. It is shown how constellations of HAPs can share a common frequency allocation by exploiting the directionality of the user antenna. The system capacity of such constellations is critically affected by the minimum angular separation of the HAPs and the sidelobe level of the user antenna. For typical antenna beamwidths of approximately 5/spl deg/ an inter-HAP spacing of 4 km is sufficient to deliver optimum performance. The aggregate bandwidth efficiency is evaluated, both theoretically using the Shannon equation, and using practical modulation and coding schemes, for multiple HAP configurations delivering either single or multiple cells. For the user antenna beamwidths used, it is shown that capacity increases are commensurate with the increase in the number of platforms, up to 10 HAPs. For increases beyond this the choice of constellation strategy becomes increasingly important.

A method for predicting movements in cellular coverage caused by lateral drift of a high-altitude platform (a quasi-stationary platform in the stratosphere) is developed. Cells are produced by spot beams generated by horn-type antennas on the platform. It is shown how the carrier-to-interference ratio (CIR) across these cells varies when the antenna payload is steered to accommodate the lateral movement of the platform. The geometry of the antenna beam footprint on the ground is first developed and then applied to a system of many cochannel beams. Pointing strategies are examined, where the pointing angle is calculated to keep, for example, a center cell or an edge cell in the same nominal position before and after the platform drift, and the CIR distribution is calculated. It is shown that the optimum pointing angle depends on the desired level of CIR across the service area, typically lying between 3/spl plusmn/0.75/spl deg/ for a platform drift of 2 km and corresponding to a cell in the middle ring. It is shown that it is necessary for a significant proportion of users to perform a handover to maintain a given CIR after platform drift. The analysis reveals that there is an optimum pointing angle that minimizes the probability of handover for a particular value of drift and CIR.

The burst targeted demand assignment multiple access (BTDAMA) protocols incorporate an original approach to DAMA, which eliminates the fundamental end-to-end delay bound associated with the traditional DAMA techniques. Whilst they offer significant improvements in the achievable delay/utilisation performance for bursty packet transmission over satellite, they are constrained by the initial build up of packets at the start of traffic bursts. In this paper, we introduce the adaptivity to the uplink frame that enables the proportion of alternative types of capacity allocation to be varied on a dynamic basis. Sufficient demand assigned capacity is assigned to meet the instantaneous user requirements, with spare capacity allocated by an alternative strategy to assist with initial throughput at the start of bursts. Results show that this approach enhances the end-to-end delay distribution and delay jitter performance compared with the conventional static frame BTDAMA schemes.

This paper presents a detailed performance evaluation of the burst targeted demand assignment multiple-access (BTDAMA) schemes, which employ an original approach to implementing demand assignment multiple-access (DAMA), suited to supporting ON/OFF type traffic over a broadband geostationary satellite link. A novel analytical model is introduced which can be used to predict and evaluate the delay performance of rate-based medium access control schemes, and is applied to BTDAMA to investigate the potential performance enhancements offered by introducing free assigned capacity to the scheme. Results show that BTDAMA eliminates the end-to-end delay bound of traditional DAMA techniques, offering significantly superior performance compared with conventional schemes, with free assignment effective in improving the delay performance for a wide range of traffic burst durations.

An investigation is performed into the capacity enhancements achievable from deploying multiple high altitude platforms (HAPs) arranged in different constellations but sharing common frequency bands and serving the same coverage area. Single and multiple cell configurations per HAP are examined. It is shown how overall system capacity may be increased, largely commensurate with the number of extra platforms deployed. This enhanced spectrum utilisation relies upon the fixed users employing a sufficiently directive antenna, pointing to HAPs located in different parts of the sky. Such deployments allow services to be offered to a significantly increased user population density, and facilitate incremental service roll-out.

This paper considers the problem of optimizing the downlink capacity of broadband fixed wireless access systems in two representative scenarios: a non-line-of-sight terrestrial system, and a system operating from a high altitude platform. In each case a packet-based system is considered, with the delay through the system of constant-length packets taken as the metric to evaluate the effectiveness of the resource allocation schemes considered. The joint optimization of adaptive modulation, channel selection scheme and queueing strategies is a complex multidimensional problem and a simulation approach is taken to evaluate the trade-offs. It is shown that good performance can be obtained from a simple resource allocation scheme over a wide range of different operating conditions, that consideration of queueing strategy is important to minimizing packet delay through the systems, and that the capacity of a broadband system using a high-altitude platform can be over three times as great as a terrestrial system of the same bandwidth.

In a wireless communications network served by a high altitude platform (HAP) the cochannel interference is a function of the antenna beamwidth, angular separation and sidelobe level. At the millimeter wave frequencies proposed for HAPs, an array of aperture type antennas on the platform is a practicable solution for serving the cells. We present a method for predicting cochannel interference based on curve-fit approximations for radiation patterns of elliptic beams which illuminate cell edges with optimum power, and a means of estimating optimum beamwidths for each cell of a regular hexagonal layout. The method is then applied to a 121 cell architecture. Where sidelobes are modeled as a flat floor at 40-dB below peak directivity, a cell cluster size of four yields carrier-to-interference ratios (CIRs), which vary from 15 dB at cell edges to 27 dB at cell centers. On adopting a cluster size of seven, these figures increase, respectively, to 19 and 30 dB. On reducing the sidelobe level, the improvement in CIR can be quantified. The method also readily allows for regions of overlapping channel coverage to be shown.

Channel assignment strategies for use with a high altitude platform spot beam architecture are examined. A novel power roll-off approximation is derived to allow terrestrial simulation tools to be used, and simulation performance is compared with a theoretical lower bound derived from the Engset distribution. It is shown that the use of cell overlap considerably enhances the blocking probability performance, in addition to boosting flexibility.

This paper explores the relative performance of the combined free/demand assignment multiple access (CFDAMA) protocol with random access and with packet accompanied request strategies in supporting self-similar traffic over a geostationary satellite link. It Is shown that both request strategies have certain advantages and are suited to different levels of channel loading. A new scheme is proposed, CFDAMA with combined requests (CFDAMA-CR), which combines the two request strategies to gain the benefits of both. Simulation results show that the CFDAMA-CR scheme can achieve better delay/throughput performance for a satellite channel than either of the standard schemes.

This paper introduces the burst targeted demand assignment multiple access scheme with pure demand assigned slots (BTDAMA-PD), which employs a different approach to implementing DAMA, suited to handling long bursts from on-off type data traffic sources. Its delay/throughput performance is compared with a variant of the combined free/demand assignment multiple access (CFDAMA) schemes. Simulation results show that BTDAMA-PD can achieve better delay/throughput performance of geo-stationary satellite channels carrying data traffic, with an excellent distribution of end-to-end delay values and low variation in the end-to-end delay of consecutive packet transmissions.

This paper examines the relative performance of the Combined Free/Demand Assignment Multiple Access (CFDAMA) protocol with different terminal request strategies. A new scheme is proposed employing round robin assignment of request slots (CFDAMA-RR), which is compared with the standard schemes incorporating random, packet accompanied, and Combined Requests (CFDAMA-CR). It is shown that the CFDAMA-RR scheme can offer improved delay/utilisation performance of a satellite channel due to its inherent fairness and contentionless nature. Simulation results are presented with three different source traffic models, Poisson, self-similar (Pareto ON-OFF) and exponential ON-OFF. The results indicate that the ON-OFF nature of a traffic model has a more significant impact on Medium Access Control (MAC) protocol performance than the specific distribution of ON and OFF times.

Methods of substantially reducing call dropping in networks which use distributed dynamic channel assignment (DDCA) schemes are discussed. Interference and received power thresholds coupled with power control are used to maintain performance, without the need for intra-cell handoffs. It is shown that the schemes reduce call dropping and increase capacity compared to those using fixed transmitter power. The schemes are developed with the aid of mathematical analysis and a pictorial model. Results are presented which show that call dropping may be virtually eliminated in shadowing environments with the median transmitter power being reduced by 15 dB. The various call dropping mechanisms are discussed, and it is suggested that the residual level of call dropping is principally a result of multiple additional call arrivals close to an active link. Methods to make further reductions in the call dropping probability are also proposed.

The effects of building geometric placement error have been considered both theoretically and using a two dimensional ray based model. The ray based model implements both reflection and diffraction and operates on a uniform, 1 km square grid of building data. Placement error is modelled by randomly displacing the building coordinates using a truncated Gaussian distribution. It has been found both theoretically and verified with results from a computer testbed that, when reflection predominates, the effect of angular error (rather than spatial error) is most significant as this causes rays to deviate away from their true route. It has been found that close to the transmitter, with an RMS deviation of 2.0 m in the building vertex position, that path loss peaks, caused by reflection, and corresponding path loss "nulls" can be moved up to 50 m.