Autonomous exploration in unknown environments is a fundamental capability for intelligent mobile IoT systems, especially in scenarios where prior environmental information is unavailable. In such settings, mobile IoT devices are required to achieve safe and efficient full-area coverage based solely on onboard sensing and limited computational resources. However, the unpredictable and continuously changing nature of unknown environments poses significant challenges to adaptive and collision-free exploration, particularly for resource-constrained mobile IoT devices. To address these challenges, we propose an autonomous full-area exploration algorithm for mobile IoT devices based on reward strategy cloning. Specifically, a state representation method using color mapping is designed to improve the information intensity of input state in full-area coverage exploration missions. Simultaneously, to address the issue of sparse rewards in full-area exploration missions, we construct an intensive reward shaping function that integrates exploration rewards, collision penalties, and incentives for exploring frontier trends. Furthermore, a lightweight exploration model that maps state to action reward is designed for mobile IoT devices with limited computing power and storage resources. Moreover, we propose a reward-sensitive dynamic ϵ-greedy strategy that adaptively balances exploration and exploitation based on real-time performance trends. Finally, empirical results demonstrate the robustness of the proposed algorithm in exploring various complexities and dynamic environments. In particular, the computational complexity of the proposed exploration model is significantly reduced compared to other models.

The advent of the 5G RedCap, the upcoming 6G and the proliferation of the Internet of Things (IoT) have catalyzed the rapid advancement of unmanned aerial vehicle (UAV) technology while also promoting UAVs' widespread application. In IoT-enabled environments where the global positioning system (GPS) signals are compromised, visual simultaneous localization and mapping (V-SLAM) technology has emerged as an effective positioning solution, valued for its reliability. However, the presence of dynamic elements in complex environments, such as pedestrians and vehicles, poses challenges to the positioning accuracy of UAVs employing V-SLAM for navigation. This paper proposes a dynamic feature filtering-based SLAM (DFF-SLAM) approach to eliminate the impact of dynamic factors in dynamic environments, thereby enhancing the positioning accuracy of UAVs in IoT-enabled complex environments. Firstly, a semantic detection thread is designed to identify semantic information in the scene and acquire prior dynamic targets, facilitating the filtering of prior dynamic feature points. Secondly, optical flow tracking conducted at each level of the image pyramid facilitates feature point matching across consecutive images. Finally, the epipolar geometry constraint is utilized to determine the motion status of remaining feature points, further filtering out dynamic feature points. Simulation results demonstrate that compared to traditional visual SLAM systems, the UAV equipped with the DFF-SLAM system achieves more accurate positioning and meets real-time positioning requirements when navigating through IoT enabled complex environments

Radio-based simultaneous localization and mapping (SLAM) facilitates unmanned systems to fulfill self-localization and navigation in complex environments. However, the existing studies overlooked communication between devices, which may lead to low efficiency and high costs when performing SLAM tasks. Reconfigurable intelligent surface (RIS) can satisfy the growing demands of users and improve SLAM accuracy in dynamic and complex environments. This paper proposes a RIS enabled simultaneous radio communication, localization, and mapping (SCLAM) system, where an unmanned aerial vehicle (UAV) can perform concurrent communication and SLAM with the help of RIS by utilizing communication signals from base station (BS). The proposed method enables the UAV to simultaneously accomplish SLAM and ensure communication with the BS, while also enhancing the spectrum utilization efficiency. We derive the Bayesian Fisher information matrix (BFIM) for joint SLAM and symbol detection of the proposed system, in which the trade-off between the BFIM of SLAM and the upper bound of the ergodic mutual information is illustrated. Then, a weighted factor based BFIM is presented to further achieve a performance trade-off between SLAM and communication. We formulate an optimization problem of joint BS active beamforming and RIS passive beamforming to maximize the log determinant of weighted BFIM. Numerical results verify the superiority of the proposed SCLAM system on position error bound (PEB), mapping error bound (MEB), and spectral efficiency (SE). The performance trade-off between communication and SLAM is also discussed and explored.

Considering the inefficient resource allocation (RA) and high quality of service (QoS) requirement in vehicular communications, this paper proposes two dynamic RA algorithms, spectral clustering based greedy (SCGR) algorithm and multi-agent deep reinforcement learning (DRL) algorithm, to maximize both the sum capacity of the vehicle-to-infrastructure (V2I) uplinks and the total energy efficiency (EE) of the vehicle-to-vehicle (V2V) links by assigning the proper power and resource block (RB) to each V2V link in spatial modulation (SM) multiple-input multiple-output (SM-MIMO) vehicular system. For the SCGR algorithm, the spectral clustering (SC) scheme is first utilized to group the V2V links for the suitable RBs. Then, the optimal power is distributed to each V2V link by the greedy (GR) algorithm. For the DRL algorithm, a decentralized model-free network, improved multi-agent deep Q fully connected neural network (IDQFN), is developed to simultaneously find the best power allocation (PA) and RB assignment (RBA). Moreover, the SM technology is exploited to convey the information through the V2I and V2V links and improve the system capacity. Numerical results reveal that the proposed SCGR and IDQFN RA schemes outperform the typical RA algorithms, and the IDQFN scheme achieves better EE than the SCGR scheme, while the SCGR algorithm obtains the optimal average bit error rate (ABER) performance.

This paper proposes a transmit antenna subset selection (TASS) scheme in the cooperative spatial modulation multiple-input multiple-output (CSM-MIMO) system with decode-and-forward (DF) protocol. Specifically, the relay selects the best TA subset via maximizing the minimum squared Euclidean distance (MSED) for the transmission to the destination. The relay then feedbacks the index of the chosen TA subset to the source. At the destination, the maximum likelihood detection (MLD) is taken. Based on the order statistics and union bounding technique, a closed-form analytical average bit error rate (ABER) of the CSM-MIMO system with the proposed TASS scheme is derived. Numerical results verify that the analytical ABER performance matches the Monte Carlo simulation well. The proposed TASS in the CSM-MIMO system outperforms the existing CSM-MIMO and non-CSM-MIMO (NCSM-MIMO) schemes with more transmit diversity, and achieves superior ABER performance than the typical TASS methods.

The conventional transmitted reference (TR) technique in ultra wide-band (UWB) communications has provided a springboard for a lot of studies, and a TR pulse cluster (TRPC) structure was proved to have robust performance. Most of TR and TRPC related studies hitherto are based on the assumption that the delay lines (DLs) in their schemes are ideal. However, the group delay ripple (GDR) of nonideal DLs triggered by practical imperfect factors at implementation causes an unexpected distortion in both TR and TRPC UWB systems, and there are few studies so far. In this article, we first analyze the impact of the GDR of nonideal DLs on the performance of TR and TRPC UWB systems. Then a new design solution for both TR and TRPC transceivers is proposed, where the GDR information of the nonideal DL at the receiver side is introduced into transmitter side. The performance of the new design solution is analyzed and simulation results prove the robustness and efficiency of this new design method in reducing the impaction caused by nonideal DLs. Moreover, the proposed design solution can also greatly relieve the high design requirement of DLs in both the transmitter and receiver side and therefore offer valuable insight for the practical transceiver design in both TR and TRPC related UWB systems.

In this paper, a spatial-index modulation (SIM) based orthogonal time frequency space (OTFS) system, named SIM-OTFS, is proposed to enhance the effectiveness and the reliability of high mobility vehicular networks in intelligent transportation systems. The SIM-OTFS system adopts a three dimensional index modulation (IM) technique which utilizes the transmit antenna, delay, and Doppler indexes in the space and delay-Doppler domains, respectively, to achieve a higher transmission rate. Considering the characteristics of vehicular networks, we first present the SIM-OTFS system design and the corresponding signal processing. Then, we derive the average bit error rate (ABER) upper bound of the SIM-OTFS system by the union bound theory. Moreover, the diversity, the coding gain, and the complexity of the SIM-OTFS system are further investigated. Numerical results verify the theoretical analysis of the ABER and the diversity of the SIM-OTFS system, which shows the superiority of the SIM-OTFS system in the ABER performance over the multiple-input and multiple-output (MIMO) based OTFS (MIMO-OTFS) system. Meanwhile, the SIM-OTFS system realizes better performance than the spatial modulation (SM) and IM based orthogonal frequency division multiplexing (SM-OFDM-IM) system in high mobility vehicular communication with reasonable complexity sacrifice. Furthermore, the influence of the resolvable multipaths of the channel in vehicular networks on the ABER performance of the SIM-OTFS system is also illustrated.

In this paper, we investigate the joint user association and resource allocation problem in the downlink of cloud radio access networks (CRAN). The central cloud performs the scheduling of spectrum resource across different base stations (BSs) to user equipments (UEs) for the maximal network utility under practical network constraints. Nevertheless, the problem is a combinatorial optimization problem, which is intractable by the traditional exhaustive search when the network size is large. We propose a new scheduling selection method by introducing Markov approximation, which synthesizes algorithm to achieve approximate optimization by forming a reversible continuous-time Markov chain. This method adapts to not only the static network situation but also the dynamic network situation caused by users joining or departure. Besides, this method solves the two network subproblems of user association and resource allocation concurrently, which reduces the computing complexity. Simulation results demonstrate the convergence of Markov approximation and the validity of the proposed algorithm.

Cooperative task offloading has emerged as a compelling computing paradigm for balancing spatially uneven task workloads and computational resources in distributed mobile edge computing (MEC) systems. However, enabling cooperation among multiple MEC nodes inevitably requires extra communication and computational energy overheads which might counteract the cooperation gain without energy-efficient offloading mechanisms. This paper presents an adaptive cooperative task offloading algorithm aiming at maximizing the time-averaged energy efficiency for small cell MEC networks enabled by millimeter-wave backhauls. With the considered network dynamics, the proposed algorithm makes a good tradeoff between the harvested cooperation utility and the total energy consumption in the long term. In addition, our algorithm ensures the network stability and fulfills the task admission rate requirement of each individual user equipment, by making slot-based decisions over time without requiring a-priori knowledge of the network dynamics. Simulation results verify the outstanding performance of the proposed algorithm by comparing with the static cooperative and adaptive non-cooperative schemes.

The cognitive radio-enabled$massive$Internet of Things (CR-$m$IoT) is envisioned to shape the future of densely connected IoT devices in the sixth-generation networks to support the hyperconnected society. In conventional CR networks, secondary users (SUs) sense the whole block of spectrum to find idle channels, which is an energy-consuming, delay-inducing, and processing-intensive task. With the large scale of resource-constrained heterogeneous devices in CR-$m$IoT, the sensing process becomes a major hurdle for CR-$m$IoT devices to achieve efficient utilization of the limited device and network resources. Thus, a novel multiparameter-based flexible scheme is proposed for idle channel prediction and channel ranking, which considers priorities as well as heterogeneity of users. The scheme uses a probabilistic approach and employs multiple parameters simultaneously to evaluate the suitability of a channel before selecting it for transmission. In addition, valid channel obsolescence, a major problem inherent with channel prediction and ranking, is countered by the proposed scheme. The scheme is evaluated under the impact of variable primary and SUs’ arrivals and under multiple channel failures rates and variable sensing and frame time duration. The proposed scheme is also compared with its own modified version that disregards channel failures, and with the random channel selection approach followed by IEEE 802.22. The overall evaluation is conducted under realistic spectrum sensing. Simulation results show that for different parameter values, the proposed scheme improves the collision probability by 11%–55%, reduces sensing time and energy by 60% and 65%, respectively, and enhances throughput by 4%–70%, and spectrum utilization efficiency by 11%–40%.

Ensuring security and privacy in the Internet of Things (IoT) while taking into account the resource-constrained nature of IoT devices is challenging. In smart home (SH) IoT applications, remote users (RUs) need to communicate securely with resource-constrained network entities through the public Internet to procure real-time information. While the 6LoWPAN adaptation-layer standard provides resource-efficient IPv6 compatibility to low-power wireless networks, the basic 6LoWPAN design does not include security and privacy features. A resource-efficient authenticated key exchange (AKE) scheme becomes imperative for 6LoWPAN-based resource-constrained networks to render indecipherable communication functionality. This article presents a lightweight user AKE scheme for 6LoWPAN-based SH networks (LAKE-6SH) to achieve authenticity of RUs and establish private session keys between the users and network entities by employing the SHA-256 hash function, exclusive-OR operation, and a simple authenticated encryption primitive. Informal security validation illustrates that LAKE-6SH is protected against different pernicious security attacks. The security is further validated formally through the random oracle model. Moreover, through Scyther validation, it is demonstrated that LAKE-6SH is secure. In addition, it is demonstrated that LAKE-6SH renders better security features aside from its low communication and computational overheads.

Wireless networks in next generation will provide users ubiquitous computing services with low delay by devices at the network edge, namely mobile edge computing (MEC). The intensive computation tasks can be partially offloaded to the MEC server via the wireless link and then processed through the MEC computation resources to cater for the delay demand. A parallel computation process is formed in the MEC network consists of local computation at MEC users (MUs) and MEC computation at MEC servers. However, the fluctuating wireless channel environment, changeable spatial distribution of MUs and the randomness of MEC servers’ locations make it hard to characterize and guarantee the end-to-end quality of service requirements. In this work, we are devoted to analyze and optimize the overall delay bound for MEC networks under two orthogonal frequency division multiple access (OFDMA) strategies via stochastic network calculus (SNC). Specifically, Poisson cluster process is utilized to capture the randomness of MEC servers’ and users’ spatial locations and to derive the Laplace transform of interference suffered by an MU of interest. The upper bounds for the delay violation probability of two OFDMA strategies are established by exploiting SNC with the Mellin transform of signal-to-interference ratio. Furthermore, we propose an optimal task offloading scheme by minimizing the overall delay, which balances the local computation delay and MEC delay.

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is an extension of the traditional OFDM modulation scheme. Its key idea is to adopt the activated subcarrier index to carry extra information. In this paper, we propose a new optical multi-input multiple-output (MIMO) visible light communication (VLC) system based on OFDM-IM and generalized light-emitting diode (LED) index modulation (GLIM). The proposed scheme utilizes the subcarrier index selection to improve the system flexibility and adopts the LED index modulation to increase the spectral efficiency, which also avoids the Hermitian symmetry processing. Simulation results show that the proposed scheme achieves better bit error rate (BER) performance than the traditional GLIM scheme. Moreover, the proposed scheme can flexibly select the number of the active subcarriers according to the channel condition and ensure better system performance.

In this paper, link adaptation (LA) schemes based on adaptive modulation (AM), where the transmit parameters can be adapted to the varying channel conditions, are investigated for spatial modulation (SM). We propose machine learning (ML) based adaptive spatial modulation (ASM) as the optimal technique for modulation selection (MS) compared with the exhaustive search based ASM scheme. Specifically, two supervised machine learning classifiers (MLCs), K-nearest neighbors (KNN) and support vector machine (SVM), are proposed to design the MS in ASM and make the tradeoff between the system complexity and the bit error rate (BER) performance. The proposed classifiers are employed to solve the MS problem in ASM as a multi-class classification problem and obtain the best modulation selection candidate (MSC) that achieves the maximum minimum Euclidean distance. Simulation results show that, under the same spectral efficiency (SE), the proposed schemes provide considerable system complexity reduction and obtain a sub-optimal BER performance compared with the typical ASM scheme.

Unmanned aerial vehicles (UAV) wireless communications have attracted great interests in 5G networks due to its high mobility, on-demand deployment and low cost. However, it arises new serious concerns about the malicious eavesdropping attacks against UAV communications. In this paper, we study the UAV transmission with a wiretap Rayleigh fading channel, over which UAVs transmit data to a target receiver in an unsafe environment with multiple eavesdroppers. A secure transmission scheme is proposed for satisfying various performance requirements including secrecy and transmission latency, considering the unavailability of wiretappers' instantaneous channel state information (CSI). In particular, secrecy performance is measured by the derivation of secure transmission probability (STP) by physical layer security (PLS) technique. A novel stochastic-network-calculus (SNC) approach is proposed to analyze the service capability of the wiretap channel and as well calculate the latency bounds, whilst obtaining the internal relationship between secrecy and latency. Simulation results verify the theoretical performance bounds, which provide a guidance for designing secure transmission strategies with various performance requirements.

Abstract Energy harvesting (EH) aided Internet of Things (IoT) network is a promising paradigm to librate IoT network from energy deficiency. Dynamic energy and traffic scheduling in such a scenario is challenging due to temporal correlation of energy constraints and delay requirements of IoT applications. In this paper, joint energy management and sampling rate control to explore the tradeoff between network utility and delay performance are studied while maintaining the energy causality constraint. Taking into account the dynamic characteristics of EH process, channel fading and traffic arrivals, a stochastic optimisation problem is formulated to maximise the network utility. Leveraging the Lyapunov optimisation approach, combined with the idea of weight perturbation, a framework is proposed to decompose the stochastic problem into several deterministic sub‐problems that can be solved separately. Based on the framework, an online resource allocation algorithm is developed to achieve two major goals: first, balancing energy consumption and energy harvesting to stabilise their data and energy queues; second, deriving the utility‐delay tradeoff by adjusting the control parameter. The stability of data buffer and energy buffer in the proposed network is theoretical verified with performance analysis.

In this article, we investigate control-aware energy-efficient transmission strategies for wireless control systems with short packets (WCSs), in which remote state estimation error, system stability, transmission energy consumption, and communication packets with finite-length coding are all taken into account. Specifically, we formulate the transmission strategy design problem as a multiobjective optimization problem, which minimizes the remote state estimation error and transmission energy consumption simultaneously under the constraints of system stability and short packet communications. To solve the multiobjective optimization problem, we first introduce a novel objective function that encapsulates two different objective functions into a single one by using weight parameters, and further prove that the solution of the new stochastic optimization problem is a nondominated solution of the original one. Moreover, to solve the new stochastic optimization, we propose a dynamic control-aware energy-efficient transmission (DCET) algorithm that pushes the objective cost close to the optimal with a tradeoff in virtual queue backlogs for constraints. In particular, to tackle the nonconvexity constraint due to short packet communications, we introduce an additional constraint, with which the optimization problem is convex. Finally, simulation results verified the superiority of our proposed transmission strategy as compared with schemes of TDMA and Aloha-RAM multi access.

In this paper, we propose a color space and multi-stream spatial modulation (CS-MSM) based visible light communication (VLC) system to improve both the system spectral efficiency and the symbol error rate (SER), which exploits the color index and also the spatial index of the quad-LED (QLED) to convey information bits. We first take the multi-stream spatial modulation (MSM) scheme to select the QLED indexes based on the channel correlation. Then, spatial modulation (SM) is further employed in the color index selection for each QLED to increase the information bit rate of the VLC system. Finally, an analytical SER upper bound of the proposed CS-MSM scheme is derived. Numerical results and analysis verify that the CS-MSM based VLC system outperforms the other SM based VLC systems significantly. Moreover, the effect of the half-power semi-angle of the QLEDs on the system performance has also been discussed.

In this paper, a single-relay cooperative spatial modulation (SM) system based on color shift keying (CSK) modulation in visible light communication (VLC) has been proposed, which aims to improve the system performance and expand the communication range. For the proposed scheme, only one relay with decode-and-forward (DF) protocol can be activated during a communication process without direct link and the optimal maximum likelihood (ML) detection is employed. The average bit error rate (ABER) of the proposed scheme has been derived based on the system pairwise error probability (PEP). Monte-Carlo simulation results show advantages of the proposed system compared with the non-cooperative SM VLC scheme and the conventional cooperative SM VLC system.

To capture the ubiquitous randomness such as time-varying wireless channel and unpredictable task arrivals in the non-orthogonal multiple access aided multi-access edge computing networks, we formulate a stochastic optimization problem aiming to minimize the time-average cost for Internet of Things devices in this paper. Due to the absence of distribution of random network information, we develop a stochastic gradient descent (SGD) based method to learn the randomness online and minimize the cost asymptotically. The proposed SGD method makes decisions only depending on the observed network information in each time-slot and achieves an [O(ε),O(1/ε)]-tradeoff between the cost-optimality and task queue backlog. To polish this tradeoff, we further propose a momentum-based SGD method by amending SGD iterations with momentum terms, which can efficiently accelerate algorithm convergence while reducing the task queue backlog without loss of cost-optimality. Finally, simulation results confirm the outstanding performance of the proposed methods.

Non-orthogonal multiple access (NOMA) is considered as a potential technique to relieve the congestion due to concurrent access from massive devices in machine-to-machine (M2M) communication system. However, the cochannel interference caused by NOMA, and the energy budget of machine-type devices (MTDs), become the bottleneck to further improve the system performance. Given above issues, we formulate the joint user scheduling and energy management problem as a stochastic optimization problem. Specifically, the goal of the problem is to maximize the long-term average sum rate under the constraint of all MTDs’ quality-of-service (QoS) requirements. For tractability, the stochastic problem is firstly transformed into two static subproblems based on Lyapunov optimization. Then, using successive convex approximation (SCA) method, we design an effective algorithm to deal with the joint user scheduling and power allocation subproblems, which is a mixed integer and non-convex programming (MINCP). Simulation results demonstrate that our proposed algorithm has a good performance in convergence and outperforms other schemes in terms of user satisfaction.

The future 5G wireless network is largely driven by the increasing heavy traffic and spectrum scarcity. Cognitive Radio (CR) techniques provide a potential solution for improving the spectrum efficiency. In this paper, we study the stochastic framework for the CR networks, considering different quality of service (QoS) requirements. To analyze the performance of the CR network, we adopt a poisson point process (PPP) to capture the mobility and randomness of user location. A stochastic-network-calculus (SNC) based approach is proposed to model the wireless transmission and evaluate the network performance. In order to achieve the performance metrics of end-to-end (E2E) delay and backlog in the entire network, we propose a new conception named as effective service process (ESP) which is able to capture the QoS requirements of users. Furthermore, we evaluate the performance in the exponential domain, which can present the E2E analysis more directly. The simulation results verify the theoretical analysis and show that the performance in the CR networks can be derived perfectly with the proposed approach, considering the stochastic traffic arrival and designed service model in our schedule.

In this paper, we consider a mission-critical control system, where a dynamic plant is monitored by a mobile device (MD), and the monitored signal is transmitted to a remote controller via heterogeneous cellular and Wi-Fi networks. We propose an optimal control-aware machine-to-machine (M2M) transmission strategy for mission-critical control applications, in which control performance is measured by remote estimation error and system stability while limited by bandwidth cost. Specifically, the problem of minimizing estimation error, subject to the constraints of cellular usage costs and system stability, is formulated as an infinite-horizon constrained Markov decision process (CMDP), where the MD has options to transmit through Wi-Fi or cellular, or to stay idle. We solve the problem by utilizing the Lagrange multiplier approach, and prove that the optimal strategy is a randomized mixture of two threshold structure strategies. Furthermore, to estimate the structured optimal strategy, we present an algorithm called simultaneous perturbation stochastic approximation (SPSA), in which the complexity is O(IAI) lower than a non-structured one with IAI being the number of the actions.

Long-term evolution (LTE) and wireless local area network (WLAN) are often presented as opposing technologies. Hence, efficient partitioning of the spectrum resources carries critical importance for achieving the coexistence of these on the unlicensed spectrum band. In this paper, we firstly develop an online spectrum partitioning algorithm, which needs little signal transmission and exchange between coordination manager and networks. Then, we focus on the convergence analysis of the online spectrum partitioning algorithm, which is difficult due to the time-varying wireless channels. To overcome this challenge, we model the algorithm and network dynamics as the stochastic differential equations (SDE) and show that the algorithm convergence is equivalent to the stochastic stability of a virtual stochastic dynamic system constructed by the SDEs. Then, we give the sufficient condition about the algorithm convergence and the upper bound on the tracking error of the spectrum partitioning algorithm under exogenous variations of time-varying channel state information (CSI). Based on the insights of the impact of time-varying CSI on algorithm convergence, an online compensative spectrum partitioning algorithm is developed to offset the tracking error caused by the disturbance of time-varying CSI. Through performance evaluation, we show that the coexistence performance efficiency will come at low expense of algorithm complexity and signal overhead.

In this paper, we investigate rate splitting (RS) for an uplink non-orthogonal multiple access (NOMA) system with a pair of near and far users adopting cyclic prefixed single carrier transmissions. Frequency-domain equalization is applied to assist successive interference cancellation at the base-station. Two kinds of RS schemes, namely, fixed RS (FRS) and cognitive RS (CRS) schemes, are proposed to realize RS for uplink NOMA with the aim of improving user fairness and outage performance in delay-limited transmissions. Corresponding to the split data streams, transmit power is allocated in either a fixed or cognitive manner for the FRS and CRS schemes, respectively. Based on achievable rate region analysis, the benefits of applying RS to uplink NOMA for enhancing the user fairness and outage performance are revealed. A modified Jain's index is proposed to measure the user fairness for the considered delay-limited transmissions. Closed-form expressions are derived for the outage probabilities of the paired users, respectively, whereas the preferred system parameters are chosen based on asymptotic outage probability expressions. The enhanced user fairness and superior outage performance of the proposed RS schemes are corroborated by Monte Carlo simulation results.

This paper investigates the resource allocation and user association for time-varying heterogeneous wireless network (HetNet), where the multi-homed user equipment (UE) utilizes multiple access options (AOs) simultaneously. Firstly, a stochastic optimization model is proposed to maximize the long-term energy efficiency (EE), which is defined as the ratio of long-term total throughput to the long-term corresponding energy consumption. A modified fractional programming method is proposed to convert the long-term EE maximize problem into an instance throughput-minus- energy optimization problem, which is proved as a mixed integer nonlinear optimization (MINO). The continuity relaxation and Lagrange dual method are proposed to solve the MINO problem. Then, a utility-based selection algorithm is developed to determine the optimal associated AO sets for each UE. After that, the dynamic EE-based resource allocation algorithm is developed to allocate the AOs radio resource energy efficiently, which depends only on the current network state information. Our simulation results show that the proposed algorithm achieves EE performance improvement compared to other general algorithms.

A multi-relay cooperative quadrature spatial modulation (QSM) system is proposed in this paper. The distinguishable feature of the multi-relay cooperative QSM lies in the enlarged aggregate throughput of the system since extra information bits at the source can be transmitted through the selection of the relays. During the communication process, only one relay is activated which adopts the amplify-and-forward (AF) relaying protocol. Furthermore, a closed-form expression of the average pairwise error probability (APEP) of the proposed multi-relay cooperative QSM system is given and employed to derive the tight upper bound of the average bit error probability (ABEP) over Rayleigh fading channels. Monte-Carlo simulation shows that the proposed multi-relay cooperative QSM system achieves better ABEP performance compared with the traditional multi-relay cooperative spatial modulation (SM) system.

We propose drowsiness detection in real-time surveillance videos by determining if a person’s eyes are open or closed. As a first step, the face of the subject is detected in the image. In the detected face, the eyes are localized and filtered with an extended Sobel operator to detect the curvature of the eyelids. Once the curves are detected, concavity is used to tell whether the eyelids are closed or open. Consequently, a concave upward curve means the eyelid is closed whereas a concave downwards curve means the eye is open. The proposed method is also implemented on hardware in order to be used in real-time scenarios, such as driver drowsiness detection. The evaluation of the proposed method used three image datasets, where images in the first dataset have a uniform background. The proposed method achieved classification accuracy of up to 95% on this dataset. Another benchmark dataset used has significant variations based on face deformations. With this dataset, our method achieved classification accuracy of 70%. A real-time video dataset of people driving the car was also used, where the proposed method achieved 95% accuracy, thus showing its feasibility for use in real-time scenarios.

This paper presents two radio frequency (RF) sensors with different directivities designed and tested for device-free localization (DFL) in an indoor environment. Mostly, in smart homes and smart offices, peoples may be irritated by wearing the device on them all the time. As compared with device-based localization, the proposed sensors can localize both cooperative and non-cooperative targets (intruders and guests etc.) without privacy leakages. Both sensors are tested to detect the change in received signal strength (ΔRSS) due to the presence of an obstacle. RF sensors, i.e., antennas are designed to operate in the ISM band of 2.4–2.5 GHz. Experimental results show that the sensor with higher directivity provides better ΔRSS that helps in improved accuracy to detect a device-free target.

Spectrum sensing is of the utmost importance to the workings of a cognitive radio network (CRN). The spectrum has to be sensed to decide whether the cognitive radio (CR) user can transmit or not. Transmitting on unoccupied spectrum becomes a hard task if energy-constrained networks are considered. CRNs are ad hoc networks, and thus, they are energy-limited, but energy harvesting can ensure that enough energy is available for transmission, thus enabling the CRN to have a theoretically infinite lifetime. The residual energy, along with the sensing decision, determines the action in the current time slot. The transmission decision has to be grounded on the sensing outcome, and thus, a combined sensing–transmission framework for the CRN has to be considered. The sensing–transmission framework forms a Markov decision process (MDP), and solving the MDP problem exhaustively through conventional methods cannot be a plausible solution for ad hoc networks such as a CRN. In this paper, to solve the MDP problem, an actor–critic-algorithm-based solution for optimizing the action taken in a sensing–transmission framework is proposed. The proposed scheme solves an optimization problem on the basis of the actor–critic algorithm, and the action that brings the highest reward is selected. The optimal policy is determined by updating the optimization problem parameters. The reward is calculated by the critic component through interaction with the environment, and the value function for each state is updated, which then updates the policy function. Simulation results show that the proposed scheme closely follows the exhaustive search scheme and outperforms a myopic scheme in terms of average throughput achieved.

In this paper, we investigate a coordinated direct and relay transmission for uplink (CDRT-UL) of a cooperative non-orthogonal multiple access (NOMA) system, in which two users communicate with a base station (BS) with the aid of a decode-and-forward relay. By incorporating both relay links and non-negligible direct links from two users to BS, the CDRTUL scheme forms an orthogonal structure at the BS receiver side, so that the BS receiver applies only linear combinations to recover the desired signals without abusing successive interference cancellation. Outage probability of the paired two users is derived in closed-form under independent but not necessarily identically distributed Nakagami-m fading channels. Asymptotic analysis in the high signal-to-noise ratio regime is also introduced that provides closed-form expressions, which indicates that both two users achieve the same asymptotic outage performance. It is also shown that an improved outage performance and the higher target rate can be achieved by the CDRT-UL scheme over those of the DF relay without direct links. The enhanced system performance achieved by the CDRT-UL scheme is corroborated by Monte Carlo simulations.

In 5G networks, self-organizing network (SON) is envisioned to reduce the network operating complexity and costs by providing SON functions, especially in ultra- dense small cell networks. However, diverse SON functions have different time scales and inconsistent targets, which leads to the operation conflicts and network performance degradation. In this paper, we devise a multiple time-scale coordination management scheme (MTCS) to guarantee efficient and stable network operations for densely deployed SONs, where different SON functions have their own specific time scales. Specifically, we propose a novel analysis model , named M time-scale Markov decision process (MMDP), where SON decisions made in each time-scale considers the impacts of SON decisions in other M-1 time scales on the network. Then the proposed scheme with two functions of mobility load balancing (MLB) and energy saving management (ESM) is evaluated in terms of the designed network utility. Simulation results demonstrate that the proposed SON function coordination scheme significantly improves the network utility, while guaranteeing the stability of cooperative operations in wireless networks.

Small cell networks (SCNs) are envisioned as a promising solution to increase the network capacity and coverage. The densely deployments of SCNs in 5G networks pose new challenges for energy-efficient network management. Energy harvesting technique is put forward as a relatively new energy saving concept. However, due to the opportunistic nature of energy harvesting, the uncertainty and complexity will be introduced in energy harvesting SCNs (EH-SCNs) network management. In this paper, we study the self- organized cell operation management problem with different quality of service (QoS) requirements of users, in which the EH-SCNs needs to perform cell activation operation in a distributed manner with the uncertainty of harvested energy. With the assumption of Markovian energy harvesting process, multi-armed bandit game (MAB) based Thompson Sampling algorithm is developed to solve the small cell activation problem with a self-organized manner in EH-SCNs. Simulation results show that our proposed approach is particularly suitable to manage the large-scale EH-SCNs more efficiently under uncertain environment with incomplete information.

In this paper, we investigate the outage performance of opportunistic relaying for a cooperative small-cell system with M small-cell transmitters and N relays. To enable flexible deployment of ultra dense small-cells, wireless backhauls are applied for connecting a macro-cell base station and M smallcell transmitters. In each transmission block, the transmitter-relay pair achieving the highest end-to-end signal-to-noise ratio is selected to transmit the source signal to the destination. The backhaul reliability is considered for revealing the practical constraints on wireless backhaul-based opportunistic relaying, while cyclic pre-fixed single carrier transmission is employed for mitigating frequency-selective fading. The new closed-form outage probability and asymptotic outage performance limit are derived for the cooperative small-cell system with unreliable backhauls and under frequency-selective fading channels. It is shown that transmitter cooperation and a corresponding back-haul reliability levels exclusively determine asymptotic outage probability, while diversity gain is jointly determined by M, N, and the sum number of multi-path components of frequency-selective fading channels. Link-level simulations are conducted to verify the derived joint impact of backhaul reliability and transmitter-relay cooperation on the outage performance.

In this paper, we investigate the effect of unreliable wireless backhaul links on the outage performance for cognitive full-duplex relay (FDR) networks with best user selection over frequency-selective fading channels. Due to FDR operation, the primary user (PU) is interfered by the selected small-cell transmitter and FDR node simultaneously. Subject to the allowed interference level at the PU, the new analytical outage probability is derived for the cognitive FDR network in terms of the residual self-interference, multiuser scheduling, channel statistics, and wireless backhaul reliability. It is shown that asymptotic outage probability achieved by cognitive FDR network is exclusively determined by multiuser scheduling and wireless backhaul reliability. By employing multiuser scheduling, cognitive FDR network achieves the allowable smallest outage probability with alleviated burden for self-interference cancellation, while its achieved outage capacity doubles that of the cognitive half-duplex relay network in the small and middle interference-to-noise ratio regions. The outage performance of the considered system is verified by simulations and compared to that of cognitive half-duplex relay networks.

In this paper, a hybrid modulation scheme combining quad-LED complex modulation (QCM) and spatial modulation (SM) has been proposed in indoor visible light communication (VLC) system. The SM scheme is firstly used to select one quad-LED (QLED). Then, QCM scheme is further employed by the selected QLED to map the complex modulation symbols. Hence, the hybrid quad-LED complex spatial modulation (QCSM) scheme obtains the advantages of both QCM and SM, and can improve the system performance and the transmission rate simultaneously. Symbol error rate (SER) and bit error rate (BER) of the proposed scheme are studied based on the maximal likelihood (ML) detection. Simulation results and theoretical analysis show the better performance of the proposed QCSM scheme, compared with the SM VLC system. The system performance with different distances of the QLEDs has also been analyzed.

Recently, millimetre‐wave (mmWave) wireless fronthauls have been regarded as an effective solution to deploy remote radio heads with higher flexibility and efficiency in cloud radio access networks (C‐RANs). Different from the traditional fibre fronthauls, in order to maximise the utilisation of the time‐frequency resource, the mmWave wireless fronthauls are more expected to operate in a dynamic allocation manner. In this study, the energy efficient mmWave fronthaul and OFDMA resource optimisation in C‐RANs is investigated. The TDMA‐based fronthaul allocation mechanism is first presented and then the joint resource optimisation is formulated as an energy efficiency (EE) maximisation problem which is in the form of a mixed‐integer non‐linear fractional programming (MINLFP) problem. By taking advantage of the Dinkelbach method, the MINLFP problem is transformed into a subtractive optimisation problem and solved by using the Lagrange dual decomposition theory. Moreover, a maximal weighted bipartite graph matching approach is proposed to determine the optimal resource block allocation. Finally, extensive simulation results are provided to evaluate the EE performance of the proposed algorithm by comparing with several benchmark schemes, and it shows that the proposed algorithm can achieve great EE performance gain over the benchmark schemes.

To enable sustainable wireless networks, though new technologies have been proposed to improve the system spectrum efficiency, the energy efficiency (EE) is also of vital importance due to the increasing users and devices. Active array system (AAS) and heterogeneous networks (HetNets) have been reckoned as an enormous enhancement in spectrum efficiency and EE. In this study, the energy efficient user association and resource allocation problem for preference‐aware multicast service in AAS aided HetNets is investigated, formulated as a mixed‐integer non‐linear fractional programming. By generalised fractional programming theory and Lagrangian dual decomposition, an iterative algorithm is devised to determine user association and resource allocation. Further, an efficient solution is proposed to perform quality of service‐guaranteed user association and resource allocation to maximise the EE. Simulation results demonstrate the convergence performance and potential gain of the proposed algorithms in terms of EE.

In this letter, we investigate the dynamic rate allocation and forwarding strategy adaption scheme for wireless networks with potential selfish nodes. Aided by an incentive mechanism, we develop a stochastic differential equation (SDE) to portray the dynamic node selfishness in terms of node's energy resource and incentives. Then, a stochastic optimization model is employed to maximize the average network utility while bounding the node selfishness. Based on the continuous-time Lyapunov optimization theory, we solve the optimization problem and propose a dynamic rate allocation and forwarding strategy update (DRAF) algorithm to accommodate the dynamic network state. We further analyze the tracking errors between the output of DRFA algorithm and the optimal solution. Then, an adaptive-compensation rate allocation and forwarding strategy update (ACRAF) algorithm is designed, which iterates only once when network state changes. Finally, we provide a sufficient condition that the ACRAF algorithm asymptotically tracks the moving equilibrium point with no tracking errors. Simulation results validate the theoretical analysis.

This paper investigates a cooperative non-orthogonal multiple access system, in which a base station communicates with two far users with the aid of a decode-and-forward (DF) relay. Three cooperative relaying schemes, namely, the fixed relaying (FR), the selective DF with coordinated direct and relay transmission (SDF-CDRT), and the incremental-selective DF (ISDF) relaying are proposed to enhance the outage performance for the two far users by utilizing both the direct and relay links. Taking into account the received signal-to-noise ratio (SNR) events at the relay, the SDF-CDRT scheme adaptively forms an orthogonal transmission branch with respect to the direct link or keeps silent to reduce error propagation. Besides considering the relay detection results, the ISDF scheme further exploits the limited feedback of the received SNR events from two users, so that error propagation can be avoided and unnecessary relaying can be reduced. Analytical expressions for the outage probabilities and average throughputs of the paired users are derived in closed-form for the three cooperative relaying schemes. Asymptotic expressions for the outage probabilities are derived in the high SNR region. It is shown that the FR and SDF-CDRT schemes achieve a diversity order of one for both users, while the ISDF scheme achieves a diversity order of two for both users. The superior system performance achieved by the proposed schemes over those of the existing methods is verified by Monte Carlo simulations.

We investigate a secure multiuser time division multiple access (TDMA) system with statistical delay quality of service (QoS) guarantee in terms of secure effective capacity. An optimal resource allocation policy is proposed to minimize theβ‐fair cost function of the average user power under the individual QoS constraint, which also balances the energy efficiency and fairness among the users. First, convex optimization problems associated with the resource allocation policy are formulated. Then, a subgradient iteration algorithm based on the Lagrangian duality theory and the dual decomposition theory is employed to approach the global optimal solutions. Furthermore, considering the practical channel conditions, we develop a stochastic subgradient iteration algorithm which is capable of dynamically learning the intended wireless channels and acquiring the global optimal solution. It is shown that the proposed optimal resource allocation policy depends on the delay QoS requirement and the channel conditions. The optimal policy can save more power and achieve the balance of the energy efficiency and the fairness compared with the other resource allocation policies.

At each channel use, the complex quadrature spatial modulation (CQSM) transmits two signal symbols drawn from two disjoint modulation sets. The indices of the antennas from which symbols are transmitted also carry information. In the improved CQSM (ICQSM), an additional antenna is used to transmit the second signal symbol only when the indices of the antennas to be used for transmission are equal. Conventionally, the second modulation set is a rotated version of the first, where the rotation angle is optimized such that the average unconditional error probability (AUP) is reduced. In this paper, we propose a low‐complexity method to design the PSK modulation sets based on reducing the AUP. After introducing min‐BER and max‐dmin, two exhaustive search methods, we analytically show that the AUP depends on Euclidean distance between transmitted vectors, which in turn depends on the power of signal symbols, the Euclidean distance between the symbols of each modulation set, and the Euclidean distance between the symbols of the two sets. The optimal rotation angle is analytically derived for any modulation order and the radii of the modulation sets are optimized such that AUP is reduced for a wide range of system configurations. The simulation results show that more than 3 dB of power gain is achieved in the case of 16PSK, where higher gains are achieved for higher modulation orders. These gains are achieved at no computational cost because the optimization does not depend on the channel realization.

In this paper, the high efficient ultra wideband (UWB) spatial modulation (SM) system has been proposed and the maximum ratio combining (MRC) based performance analysis has been presented. Compared with the traditional UWB system, the bit rate of the UWB SM system is improved through the extra information bit transmission based on the selection of the active transmit antenna from multiple antennas. Meanwhile, the high energy efficiency can be obtained in the proposed UWB SM system. The UWB SM system has lower implementation complexity than the multi-antenna UWB system. MRC detection is adopted to separately recover the modulated symbol and the active transmit antenna index in two stages, which leads to lower detection complexity compared with maximum likelihood (ML) detection. Theoretical symbol error rate (SER) of the UWB SM system is derived, and the simulation results and analysis show the efficiency and performance of the proposed UWB SM system.

Based on the distinguishing features of multi-tier millimeter wave (mmWave) networks such as different transmit powers, different directivity gains from directional beamforming alignment and path loss laws for line-of-sight (LOS) and non-line-of-sight (NLOS) links, we introduce a normalization model to simplify the analysis of multi-tier mmWave cellular networks. The highlight of the model is that we convert a multi-tier mmWave cellular network into a single-tier mmWave network, where all the base stations (BSs) have the same normalized transmit power 1 and the densities of BSs scaled by LOS or NLOS scaling factors respectively follow piecewise constant function which has multiple demarcation points. On this basis, expressions for computing the coverage probability are obtained in general case with beamforming alignment errors and the special case with perfect beamforming alignment in the communication. According to corresponding numerical exploration, we conclude that the normalization model for multi-tier mmWave cellular networks fully meets requirements of network performance analysis, and it is simpler and clearer than the untransformed model. Besides, an unexpected but sensible finding is that there is an optimal beam width that maximizes coverage probability in the case with beamforming alignment errors.

In order to improve the utilization of the fading channel of the high-rate IEEE 802.11n wireless networks, an adaptive rate control and frame length adjustment scheme (i.e., ARCLA) is proposed in this paper. In ARCLA, the subframe error rate (SFER) of the aggregate MAC protocol data unit (A-MPDU) is used for the estimation of the link quality, and the channel air time is fairly allocated over the data transmissions based on the channel coherent time to ensure the uniformity of the link quality during one frame transmission. According to that, the data rate and the data frame length are adaptively adjusted in two-dimensions to fit the fluctuant channel condition. Furthermore, an analytical framework based on the semi-Markov process is formulated to evaluate the performance of our scheme. Simulations results verify the theoretical analysis and show the superiority of ARCLA in respect to throughput performance.

In this study, the authors investigate the problem of maximising the mean rate in a multi‐cell coordinated beamforming system considering practical delayed limited feedback and constrained backhaul. To tackle this hard problem, they first derive the analytical expression of the upper bound on the mean rate loss due to the clustered coordination and the imperfect channel feedback. Particularly, this upper bound quantitatively reveals a key tradeoff between decreasing inter‐cell interference with larger base station (BS) cluster and decreasing inter‐user interference with smaller BS cluster but improved channel state information accuracy. In light of this, they jointly optimise the BSs clustering and feedback bits allocation (BCFA) with the objective of minimising the upper bound on mean rate loss, which is equivalent to the problem of maximising the mean rate. Utilising the relaxation‐and‐rounding approach, a BSs clustering and feedback bits allocation algorithm, referred to as BCFA, is designed, which has good performance with low complexity. Finally, extensive simulation results are provided to demonstrate the advantages of the proposed algorithm.

In this study, the authors investigate the delay‐guaranteed resource optimisation in orthogonal frequency division multiple access networks under time‐varying channels and bursty data arrivals. Stochastic optimisation model is employed to minimise the long‐time‐average transmit power consumption (PC) of base station under the constraints of network stability and individual user's delay requirement. They develop a delay‐guaranteed power‐optimal algorithm (DPOA) to obtain the optimal decisions of stochastic optimisation problem. Without prior knowledge of channel statistics and data arrivals, DPOA yields a time‐averaged transmit PC that can arbitrarily approach the theoretical optimum attained by the network with complete knowledge of statistics. Simulations results verify the theoretical analysis on the network performance and show the effectiveness of DPOA.

In this study, the authors investigate the resource allocation for orthogonal frequency‐division multiple access (OFDMA) wireless networks, where the base station is powered by renewable energy and electric grid. To fully exploit the renewable energy, the authors propose an energy‐aware resource allocation (EARA) algorithm to maximise the network utility, which captures the tradeoff between the system throughput and the grid energy consumption. Specifically, the EARA algorithm only has to track the current system states (e.g. channel and queueing conditions) without requiring a relevant priori distribution knowledge, making it applicable for practical OFDMA wireless networks with unpredictable channel dynamics, renewable energy arrivals and stochastic traffics. Moreover, the performance achieved by the EARA algorithm is theoretically characterised. Most importantly, the authors develop an implementation architecture to take the EARA algorithm into practice, and also analyse the low implementation costs (e.g. low computational complexity, trivial signalling overhead etc.). Finally, simulation results verify the theoretical analysis and also demonstrate the advantages of the EARA algorithm.

In this paper, dynamic resource management is investigated for serving on-demand video streaming users in heterogeneous wireless networks (HWNs) with time varying channel conditions. The HWN is equipped with multi-homing capability, simultaneously connecting to different wireless interfaces. In order to take advantage of the time varying nature of wireless channels, we utilize the joint quality selection associated with quality adjustment at application layer and resource allocation associated with power allocation, subcarrier assignment, and time fraction determination at physical layer to perform the dynamic resource management. By using Lyapunov optimization technique, we develop a quality-aware streaming (QAS) algorithm to maximize the network utility, which is the difference of time-averaged users' perceived video quality and time-averaged HWN's transmit power. Simulation results exhibit that the proposed QAS algorithm can significantly improve network utility compared with the state-of-art baselines, which are not specific for on-demand video streaming.

This study investigates relay control for simultaneous wireless information and power transfer in full-duplex relay networks under Nakagami-mfading channels. Unlike previous work, harvest-transmit (HT) and general harvest-transmit-store (HTS) models are respectively considered to maximize average throughput subject to quality of service (QoS) constraints. The end-to-end outage probability of the network in an HT model is presented in an exact integral-form. To prevent outage performance degradation in an HT model, time switching (TS) is designed to maximize average throughput subject to QoS constraints of minimizing outage probability and maintaining a target outage probability, respectively. The optimal TS factors subject to QoS constraints are presented for an HT model. In general, in an HTS model, energy scheduling is performed across different transmission blocks and TS is performed within each block. Compared with the block-based HTS model without TS, the proposed general HTS model can greatly improve outage performance via greedy search (GS). By modeling the relay's energy levels as a Markov chain with a two-stage state transition, the outage probability for the GS implementation of the general HTS model is derived. To demonstrate the practical significance of QoS-constrained relay control, numerical results are presented showing that the proposed relay control achieves substantial improvement of outage performance and successful rate.

In this paper, we present a multiband ultra wideband (UWB) system design to realize the interference suppression and improve the bit transmission rate. With reasonable division of the UWB bandwidth, the multiband UWB scheme can improve the spectrum utilization and also the bit transmission rate through the utilization of the multiple frequency bands to transmit the information bit simultaneously. Meanwhile, we employ the offset-stacking (OS) spreading modulation based orthogonal complementary code (OCC) UWB system with SQRT chirp waveform (CW) to resist the multiple narrowband interferences (NBIs), multiple access interference (MAI), and multipath interference (MI) together. Simulation results and analysis validate the efficiency of the proposed multiband UWB scheme in the improvement of the system performance and transmission rate.

This paper investigates the energy saving of base station (BS) deployed in a 1-D multi-hop vehicular network with sleep scheduling strategy. We consider cooperative BS scheduling strategy where BSs can switch between sleep and active modes to reduce the average energy consumption utilizing the information of vehicular speeds and locations. Assuming a Poisson distribution of vehicles, we derive an appropriate probability distribution function of distance between two adjacent cluster heads, where a cluster is a maximal set of vehicles in which every two adjacent vehicles can communicate directly when their Euclidean distance is less than or equal to a threshold, known as the communication range of vehicles. Furthermore, the expected value of the sojourn time in the sleep mode and energy saving are obtained. The numerical results show that the sleep scheduling strategy significantly reduces the energy consumption of the base stations.

In this paper a novel Geometric Programming based distributed approach is proposed which enables small cell users to optimize their downlink performance by exploiting distributed joint allocation of transmission power and subchannels. The problem is formulated to maximize the system sum capacity, specifically, the time delay is taken into as a constraint to guarantee the quality of service. Consequently, the original problem is modeled as a non-convex NP-hard problem. To solve this problem, Geometric Programming is used to convert the original optimization problem into a convex one, which is further solved to obtain the global optimal solution. What's more, Simulation results show that the proposed approach yields significant performance gains.

In this paper, we address the relay selection problem in the cooperative energy harvesting (EH) network where the optimal mobile terminal will be selected as the relay if it can obtain expected profits. We model the utility as the power difference between the collected energy by using the time switching (TS) EH technique and the consumed energy by relaying signals. This relay selection problem is formulated as a convex optimization problem with nonlinear constraints. An interior point penalty function based method is proposed to approach the global optimal result. The iteration algorithm is described and the simulations are presented. Simulations unveil there is a tradeoff between the optimal TS coefficient and the transmission power of the relay node and conclude that our proposed single relay selection scheme outperform the common random relay selection policies in terms of the energy revenue and system throughput.

In this study, the authors investigate the energy‐aware quality of information (QoI) maximisation problem by jointly optimising the sensor selection, sampling rate, packet‐dropped rate, and transmit power in wireless sensor networks. By introducing the weight parameters, the authors first present a revenue‐cost (RC) function which combines the optimisation objectives of the QoI and energy expenditure into a single objective to capture the tradeoff between them. Then, a stochastic optimisation programming is formulated to maximise the long‐term average RC value subject to the network stability constraint. Using the Lyapunov drift theory, the authors develop a collaborative sensing and transmit power control algorithm that can guarantee the worst‐case delay for each packet. Simulation results demonstrate the advantages of the proposed algorithm.

This work is motivated by the following observation: modern wireless applications such as content prefetching, allow different extent of delay tolerance, thus in practice users may have different time‐averaged data rates during a certain period of time. In this study, the authors consider resource allocation in small cell networks under time‐varying channels while each user has an individual time‐averaged rate requirement. Stochastic optimisation model is employed to minimise the time‐averaged power consumption of small base stations subject to individual user's time‐averaged rate constraint. They develop an online power optimal resource allocation (PORA) algorithm to achieve the optimal power allocation and subcarrier assignment decisions without prior knowledge of channel statistics. Furthermore, considering that the power allocation and subcarrier assignment problem is a nonconvex combinatorial problem, they further develop an iterative heuristic algorithm with polynomial complexity. Simulation results show the effectiveness of PORA and verify the theoretical analysis on the network performance.

In this study, the authors investigate subcarrier and power allocation for point‐to‐point data transmission under imperfect channel state information in multi‐user orthogonal frequency‐division multiple‐access (OFDMA) networks. The resource optimisation problem is formulated to handle inter competition (the resource competition among different users) and intra competition (the resource assignment between channel estimation and data transmission for each individual user). The authors employ the non‐cooperative game with pricing approach to solve the optimisation problem. By analysing optimal relationship between channel estimation cost and total occupied resource for each user, the two‐level resource competition is simplified to the problem including only inter competition, which is modelled as a non‐cooperative subcarrier and power allocation game with subcarrier pricing. In this game, the utility function is defined as the number of received data bits per joule of energy, which is associated with the estimate error and cost, the data transmit power and the number of data‐subcarriers. The authors prove the existence, uniqueness and Pareto efficiency of Nash equilibrium (NE) for the proposed resource allocation game. Furthermore, a distributed resource allocation algorithm is designed to achieve the NE.

In this letter, we investigate the optimal EH-ratio and beamwidth selection in millimeter wave (mmWave) communications. Specifically, users in mmWave communications operate in slotted mode, where each frame consists of three continuous segments-energy harvesting, beam-searching, and data transmissions. In this sense, we propose a joint optimal EH-ratio and beamwidth selection scheme by maximizing the achievable throughput. Simulation results validate the performance superiority of the proposed scheme.

In this paper, we investigate the multiservice delivery between the source-destination pairs in distributed selfish wireless networks (SeWN), where selfish relay nodes (RN) expose their selfish behaviors, i.e., forwarding or dropping multiservices. Owing to the effect of the RNs' node-selfishness on the multiservices, a distributed framework of the node-selfishness management is constructed to manage the RN's node-selfishness information (NSI) in terms of its available resources, the employed incentive mechanism and the quality-of-service (QoS) requirements, and the other RNs' NSI in terms of their historical behaviors. In this framework, the RNs' NSI includes the degree of node-selfishness (DeNS), the degree of intrinsic selfishness (DeIS) and the degree of extrinsic selfishness (DeES). Under the distributed node-selfishness management, a path selection criterion is designed to select the most reliable and shortest path in terms of RNs' DeISs affected by their available resources, and the optimal incentives are determined by the source to stimulate forwarding multiservices of the RNs in the selected path. Our simulation results demonstrate that this framework effectively manages the RNs' NSI, and the optimal strategies of both the path selection and the incentives are determined.

In this paper, we design an adaptive multi-homing resource allocation algorithm for time-varying heterogeneous wireless networks (HetNet), where the algorithm iteration timescale is the same to the network state acquisition timescale. First, the network utility maximization is characterized by a stochastic optimization model. Second, the multi-homing resource allocation (MHRA) algorithm is developed to accommodate the dynamic wireless network states, i.e., time-varying wireless channels between the access points (AP) and mobile terminals and as well the queuing dynamics at the APs. Then, we investigate the tracking error between the MHRA algorithm output and the target optimal resource allocation solution. Based on these results, an adaptive-compensation multi-homing resource allocation (AMRA) algorithm is proposed to offset the tracking error so as to enhance the network utility. Specifically, we give a sufficient condition that the AMRA algorithm asymptotically tracks the moving equilibrium point with no tracking errors. Finally, we derive a tradeoff between network utility and media transmission delay, where the increase of average delay is approximately linear in V and the increase of network utility is at the speed of 1/V with the control parameter V. Simulation results validate the theoretical analysis of our proposed scheme.

In this paper, we investigate the transmission strategy for cognitive radios (CRs), which opportunistically operate on various primary users' channels with the aid of proactive spectrum handoff. In particular, a secondary user (SU) in the CR network proactively predicts the future spectrum status and decides whether to keep idle, or stay in the current channel, or switch to a new channel to resume its transmission. A problem of completing a target data packet size of V bits within a predefined deadline D time slots is formulated as a discrete-time Markov decision process, in which the SU aims at minimizing its expected total cost, i.e., transmission cost, handoff cost, and overtime penalty. We solve the problem using dynamic programming, and propose a general optimal transmission with the proactive spectrum handoff (OTPH) algorithm whose complexity is 2 x |V| x D. Furthermore, we prove that for a convex penalty function, the optimal handoff-aided transmission exhibits a threshold structure. A monotone OTPH algorithm with a complexity of max(|V |, D) is used in this case. Simulation results verify that our proposed scheme achieves both the minimal total cost and the highest data transmission efficiency as compared with the traditional always staying and always changing schemes.

This paper investigates simultaneous wireless information and power transfer (SWIPT) for a decode-and-forward (DF) full-duplex relay (FDR) network. A battery group consisting of two batteries is applied to utilize the relay-harvested energy for FDR transmission. The virtual harvest-use model and the harvest-use-store model are considered, respectively. By switching between two batteries for charging and discharging with the aid of power splitting (PS), concurrent source and relay transmissions can overcome spectral efficiency loss compared with half-duplex relay (HDR)-assisted PS-SWIPT. The outage probability for the virtual harvest-use model is presented in an exact integral form and the optimal PS (OPS) ratio that maximizes the end-to-end signal-to-interference-plus-noise ratio (e-SINR) is characterized in closed form via the cubic formula. The fundamental tradeoff between the e-SINR and recycled self-power is quantified. The OPS ratios and the corresponding outage probabilities in noise-limited and interference-limited environments are also derived. In the harvest-use-store model, a greedy switching (GS) policy is implemented with energy accumulation across transmission blocks. The OPS ratio of the GS policy is presented and the corresponding outage probability is derived by modeling the relay’s energy levels as a Markov chain with a two-stage state transition. Numerical results verify the performance improvement of the proposed scheme over HDR-assisted PS-SWIPT in terms of outage probability and average throughput.

In this paper, we propose a modified nonlinear SQRT chirp function based ultra wideband (UWB) pulse to suppress the narrowband interference (NBI). With the proposed chirp pulse design, the UWB systems can utilize the good characteristics of SQRT function and achieve the requirement of NBI suppression. Furthermore, we employ the sqrt chirp UWB pulse into the offset-stacking (OS) spreading modulation based orthogonal complementary code (OCC) UWB system to realize the flexible data rate and further alleviate the multiple access interference (MAI) and multipath interference (MI). Theoretical and simulation results validate the efficiency of the proposed scheme in the suppression of NBI, MAI and MI.

We consider the dynamic resource management and allocation with respect to users' personalized quality requirements in dynamic orthogonal frequency division multiple access (OFDMA) networks with time varying wireless channels and bursty traffic. We first propose a new performance metric for evaluating the degree of user's satisfaction with respective to its personalized quality requirement. We then develop a quality-oriented joint rate control and resource allocation algorithm (QO_JRCRA) with the aim to maximize the time average satisfaction of all users (SAU). QO_JRCRA can be adaptive to the time varying wireless channels and bursty traffic without knowledge of external data arrivals and channel statistics, yet yields an SAU that can arbitrarily approach the optimal SAU achieved by an algorithm with complete knowledge of future events. Simulations results verify the theoretical analysis on the system performance and show the adaptiveness of the QO_JRCRA.

In this paper, we investigate the resource allocation for orthogonal frequency division multiple access relay networks, where the relay does not have embedded energy supply and needs to first harvest energy from the received signals from the source before forwarding transmission. The relay uses time switching scheme for wireless information and power transfer. We aim to maximize the weighted sum rate under several constraints by varying the source transmission power, the relay transmission power, and the time switching ratio. We formulate the joint resource allocation problem as an optimization problem, which is non-convex. Although it is difficult to solve the non-convex problem, we derive its closed-form solution by exploiting its special structure. We also prove that the closed- form solution is a partial optimum. Finally, simulations verify the proposed closed-form solution is superior to the equal power solution.

In this paper, we design an energy-efficient cross-layer optimization framework for media streaming over time-varying wireless network. The energy efficiency (EE) is characterized by the stochastic optimization model subject to the network stability, which is also used to depict the average media delivery delay. In harmony with the hierarchical architecture of the wireless network, the problem of stochastic optimization of media streaming is decomposed by the Lyapunov drift theory into two subproblems, associated with the flow control in transport layer and the power allocation in physical (PHY) layer. Specifically, the dynamic cross-layer control algorithm for media streaming is developed for adapting to the time-varying network state information, i.e. time-varying channel state information (CSI) of mobile terminal (MT)-access points (AP) links and dynamic queue state information (QSI) at APs. We derive a tradeoff between EE and media streaming delay, where the increase of average delay is approximately linear in V and the increase of EE is at the speed of 1/V with the control parameter V. Simulation results validate the theoretical analysis of our proposed scheme.

In this paper, a hybrid time-division duplex access scheme with confidence factor based weighted cooperative sensing for the femtocells has been proposed in cognitive massive multiple-input multiple- output (massive MIMO) system to improve the detection performance and achieve the high throughput while alleviate the influence to the macrocell users as little as possible. In the cognitive massive MIMO system, femtocell base stations (FBSs) sense the spectrum through cooperative scheme and decide whether to access the channel or not. Firstly, all the FBSs sense the macrocell users in the uplink channel and the macrocell BS in the downlink channel, and make dynamical clustering based on the channel conditions. After the information exchange within each cluster, the FBSs in each cluster update their confidence factors (CFs) and weight factors (WFs) according to the detection results. With consideration of the CFs and WFs, more accurate sensing results would be obtained. Simulation results and theoretical analysis show that the proposed scheme can get more accurate sensing results and better throughput tradeoff for the femtocells.

Summary Digital fountain techniques have received significant academics and industry attention in the past years because of their rateless, robust, and real‐time characteristics used in networks and storage systems such as cloud data storage. Semi‐Random low‐density parity‐check (SR‐LDPC) codes are a kind of digital fountain codes with linear encoding and decoding complexity. In this paper, We propose a novel encoding procedure to realize codes that resemble SR‐LDPC codes (rateless codes for erasure correction) in both structure and performance. For the case of two sources communicating with a single destination via a common relay, the two sources separately encode their own symbols of information using SR‐LDPC codes. The relay then makes Exclusive OR (XOR) for the two sequences received from the two sources. The destination can recover the information bits of the two sources using the sequences received directively from the two sources and the sequence received from the relay. It is shown that the sequences received by the destination are still SR‐LDPC codes. Iterative decoding can be used by the destination using the sequences received from both the relay and the sources and obtain good performance. Copyright © 2014 John Wiley & Sons, Ltd.

Maximising the tag reading rate of a reader is one of the most important design objectives in radio frequency identification (RFID) systems as it is inversely proportional to the time required to completely read all the tags within the reader's radio field. To this end, numerous techniques have been independently suggested so far and they can be broadly categorised into pure advancements in the link‐layer tag anti‐collision protocols and pure advancements in the physical‐layer RF signal reception model. This study shows by rigorous mathematical analysis and Monte‐Carlo simulations that how those two independent approaches can be coupled to maximise the tag reading efficiency in an RFID system, considering a slotted Aloha‐based dynamic link‐layer anti‐collision protocol at tags and a multi‐packet reception capable RF reception model at the reader.

For the TV white space (TVWS) in a wireless regional area network (WRAN), wireless microphone (WM) signals must be detected as primary users. Since the very narrow band of a WM signal, there will be several spectrum fragments after spectrum sensing. In our work, a singular value decomposition (SVD) based approach is presented to detect multiple WM signals and then to select component carriers (CCs) and further implement carrier aggregation (CA) in a wideband Cognitive Radio (CR) network. Simulation results prove the better detection performance over the traditional energy detection, and the proposed CC selection approach works effectively compared to the blindly CC assigning method.

Mobile relay stations (MRSs) which are mounted in a high-speed train (HST) is popular system architecture for high-speed mobile communications. However, sharing spectrums between the macro cell and the MRS cell, interference exists in this hybrid system. In this paper, we investigate the downlink of a multi-cellular decode and forward (DF) relayed orthogonal frequency division multiple access (OFDMA) system and formulate the problem to maximize the system sum rate of all cells subject to a total power constraint and a new proposed time delay constraint. An effective resource allocation scheme combined by greedy sub-carriers allocation and geometric programming (GP) based power allocation algorithm is proposed to optimize subcarrier allocation and power allocation. Particularly, a rigid time delay constraint is introduced to accommodate the high speed mobile environment except for the common power constraint. Numerical experiments verify that the proposed resource allocation scheme outperforms the other traditional approaches and the necessity of introducing the time delay constraint.

Intra-vehicle wireless sensor network, which is also called networked control system (NCS) is a promising new research area. NCS can not only provide part cost, assembly, maintenance savings, and fuel efficiency through the elimination of the wires, but also enable new sensor technologies to be integrated into vehicles. Ultra wideband (UWB) communication is a competitive candidate for the intra-vehicle NCS. In this paper, the performance of cyclic prefixed single carrier with frequency domain equalization (SC-FDE) transmission is investigated over intra-vehicle NCS propagation environment. The error-rate performance and the implementation complexity are compared among impulse based single carrier UWB (SC-UWB), multicarrier UWB (MC-UWB) employing orthogonal frequency-division-multiplexing (OFDM), and CP-SC under the same transmitting data rate conditions. Simulation results demonstrate conclusive performance advantage of the SC-FDE scheme on the communication of two different intra-vehicle NCS scenarios, especially when minimum mean square error method is taken into account.

As a promising technology, Device-to-Device (D2D) communication can bring some advantages such as high bit rates, low delays, low power consumption by reusing frequency band with the cellular user equipments (UEs). While at the same time, inter-cell and intra-cell interference is inevitable. In this paper, we propose an algorithm Stackelberg game based to jointly allocate power and resources when uplink frequency is shared. Specially, we group evolved NodeB (eNB) and D2D UE to form the seller- buyer pair. In the game, eNB sets prices to reduce the interference that it suffers from, meanwhile maximize its revenue. For given specified prices, the D2D users compete the resources to communicate with each other and reach their individual utility maximization. Simulation results prove that satisfying performance can be achieved by using the proposed mechanisms.

Proximate device discovery is a critical function in a device-to-device (D2D) network for LTE-Advanced. In this paper, to tackle the practical issues in device discovery, we study the radio resource allocation and reusing scheme, and the time hopping method in a network coverage scenario. We propose three resources allocation schemes and prove that only two device discovery periods are needed by using the proposed approach. In the dense deployment scenario, we devise an effective resource reusing mechanism to avoid local collisions. Simulations verify that our schemes outperform the traditional methods by considering the discovery ratio and collision probability.

In a Device-to-device (D2D) underlaying cellular system interference cancellation is a key problem. In this paper, based on the practical LTE system, we proposed an eNB-aided interference avoidance mechanism. Firstly, the interference range (IR) is identified and then bad physical resource blocks (BPRBs) which are defined as PRBs with low signal- to-interference-and-noise ratio (SINR) between terminals and the eNB are detected. Based on such knowledge, within the IR, BPRBs are allocated to the D2D transmission but suitable PRBs are used by the cellular users whereas PRBs are shared outside the IR. By doing so, the interference not only between the D2D users and cellular users but also between the eNB and D2D users is avoided effectively. Simulations prove the efficacy of the proposed scheme over the traditional algorithms.

Wireless body area network (WBAN) has been recognized as one of the promising wireless sensor technologies for improving healthcare service, thanks to its capability of seamlessly and continuously exchanging medical information in real time. However, the lack of a clear in-depth defense line in such a new networking paradigm would make its potential users worry about the leakage of their private information, especially to those unauthenticated or even malicious adversaries. In this paper, we present a pair of efficient and light-weight authentication protocols to enable remote WBAN users to anonymously enjoy healthcare service. In particular, our authentication protocols are rooted with a novel certificateless signature (CLS) scheme, which is computational, efficient, and provably secure against existential forgery on adaptively chosen message attack in the random oracle model. Also, our designs ensure that application or service providers have no privilege to disclose the real identities of users. Even the network manager, which serves as private key generator in the authentication protocols, is prevented from impersonating legitimate users. The performance of our designs is evaluated through both theoretic analysis and experimental simulations, and the comparative studies demonstrate that they outperform the existing schemes in terms of better trade-off between desirable security properties and computational overhead, nicely meeting the needs of WBANs.

In order to provide more accurate detection of the primary user's activity in cognitive radio (CR) systems, cooperative spectrum sensing is proposed. The transmit diversity can also be employed by cooperative spectrum sensing to improve the performance of decision reporting. Hence, in the reporting channels between the cognitive users and the base station (BS), space time block code (STBC) scheme is considered in each cluster with time division multiple access (TMDA) method. In this paper, to improve the time efficiency in the case that one cluster makes sensing report, whereas the others do nothing but wait for their orders, we set each cluster with different sensing durations and the clusters will not stop the spectrum sensing until their results are reported. Furthermore, we also adopt the flexible sensing durations to decrease unnecessary energy consumption based on the clusters’ sensing sensitivities. Simulation results and analysis show the better detection performance and time efficiency of the proposed scheme. Copyright © 2012 John Wiley & Sons, Ltd.

This paper proposes a novel method utilizing chirp signals to substitute the traditional ultra-wideband (UWB) pulse waveform. With the application of the effective iterative method and the development of spectrum detection technology, the Conjugate Gradient (CG) algorithm and Cognitive Radio (CR) technology are employed to realize the adaptive filter and narrow-band interference (NBI) suppression. Utilizing the characteristics of the CG algorithm and its corresponding adaptive filter, we realize the NBI suppression and obtain the low cost and more practical UWB pulse design for a kind of optional proposes. Simulation results show that the CG adaptive filter can suppress the NBI effectively and outperforms the conventional method significantly.

We investigate the physical layer security for opportunistic scheduling scheme using transmit antenna selection (TAS) with maximal ratio combining (MRC) at receiver and eavesdropper under a quasi-static Rayleigh fading channel. We assume a scenario composed of a single transmitter, multiple users and a single eavesdropper each equipped with multiple antennas. The transmitter selects best transmit antenna and best user to enhance the secure communication. A theoretical analysis is performed to derive new closed form expressions for probability of positive secrecy and outage probability at a normalized secrecy rate. Furthermore, asymptotic analysis on the outage probability reveals the outage diversity gain and array gain. It is confirmed that number of antennas at eavesdropper impacts on secrecy array gain while the outage diversity gain is determined by the product of number of users and antennas at the transmitter and the user. From numerical results, TAS is verified as a suitable option for secure opportunistic scheduling.

In this paper, an effective resource allocation mechanism aiming to avoid the uplink interference between the macro cell and the mobile relay (MR) cell is proposed. We firstly formulate this problem as a mixed integer nonlinear programming (MINLP). Such an optimization problem is hard to solve, we therefore propose an alternative heuristic scheme by which the bad resource blocks (BRBs) and suitable RBs are allocated separately between these two subsystems and then the optimal power is determined to maximize the system sum throughput. Implementation details are shown in a practical Long Term Evolution (LTE) system and simulations prove the efficacy of our provided approach.

In this paper, a fast content distribution scheme is proposed with QoS provisions and user cooperation in cellular networks. A group of mobile terminals (MTs), which are interested in the same content, can cooperate to reduce the content distribution time (CDT). The Nash bargaining solution was derived to formulate the content distribution problem, where each player of the game can maximize its individual payoff. Simulation results demonstrate that the MTs endowed with cooperative scheme achieve a significant gain in terms of decreasing the CDT compared with those without cooperation.

A window based channel allocation scheme is conceived for two-way AF relay aided OFDMA systems. Two users communicating with each other via a specific relay constitute a user-pair. At most one channel index with its channel gain lying within a window, given the left and the right thresholds, is reported to the relay by each user at a time. If two users of a user-pair send non-identical channel indices, one of them makes a concession to match the channel index sent by its partner. Furthermore, all user-pairs with different QoS requirements can employ the concession process with the aid of scheduling scheme parallelly to attain optimal channel allocation. Simulation results demonstrate that the proposed algorithm with limited feedback of channel state information (CSI) achieves asymptotic system performance compared with the full CSI feedback based scheme.

In this paper, a cell zooming based dynamic base stations (BS) switching scheme is conceived for energy saving in cellular networks. A cell zooming algorithm is developed for leveraging the BS's coverage with inter-cell cooperation and downlink power control. Meanwhile, we design a feasible working strategy for the cell zooming scheme to maximizing the energy saving. Simulations are provided to demonstrate the advantages of the proposed scheme.

We conceive an interference mitigation scheme, for twin-layer networks for protecting the macrocell-users, from the interference imposed by the femtocells as well as for mitigating the interference amongst femtocells. Femtocells are capable of finding the available sub-bands using cognitive radio techniques, where the lowest interference is observed by the nearby macrocell-users. A sub-channel allocation algorithm is developed with the aid of graph-theoretic approaches for optimizing the femtocell throughput in dense femtocells deployment scenarios. The femto-users are grouped into different clusters for suppressing the interference amongst them. Each cluster is assigned a unique sub-channel by using the classic cluster-coloring approach. Adaptive power allocation is performed among the femtocells for further enhancing the system throughput and the attainable performance is quantified.

In this paper, we study the problem of devising distributed bilayer quasi-cyclic Low-Density Parity-Check (QC-LDPC) codes for cooperative relaying communications. One theorem in designing the bilayer QC-LDPC code without small stopping sets and small girth is proposed, which significantly simplifies the bilayer QC-LDPC codes design. Based on the proposed theorem and the two-hop decode-and-forward (DF) relaying protocol, in which the relay node is used to assist the source to transmit extra parity bits to the destination, a new design method for a distributed irregular bilayer QC-LDPC is developed. It is demonstrated that the overall performance can be improved by using the proposed approach in DF-based cooperative relaying communications. Finally, it is shown that the proposed construction method also leads bilayer QC-LDPC codes to have a bigger minimum distance.

Wireless body area network (WBAN) is one of the most promising wireless sensor technologies, significantly enhancing the quality of service of healthcare. But the potential users' worries about privacy leakage impede its wider application. To alleviate such worries, we present a remote anonymous authentication protocol to enable client terminals/application to securely access WBAN services. In particular, our protocol is rooted in a novel certificateless cryptosystem, which has negligible computational cost and a number of security properties that are especially desirable in WBANs. Our protocol ensures that even the application providers (APs) cannot recover the user's real identity given all the session information. Also, the network manager (NM), who plays the role of private key generator (PKG), can be prevented from impersonating any legitimate users. We theoretically validate that our protocol can achieve a better tradeoff than most of existing schemes in terms of essential security properties and computational overhead.

A new relaying scheme with the combination of incremental decode-and-forward (DF) relaying and selective relaying employed hybrid decode-amplify-forward (HDAF), termed incremental HDAF relaying (IHDAF), is proposed and analyzed in this paper. Closed-form expressions of outage probability for the incremental HDAF relaying scheme is derived. Simulation results and analysis show that the incremental HDAF relaying scheme outperforms the incremental DF relaying scheme especially when the relay locates near the destination.

In this paper, we investigate the performance of the orthogonal complementary code (OCC) based direct sequence ultra wideband (DS-UWB) system. OCC has perfect partial autocorrelation and cross-correlation characteristics. With the application of OCC in DS-UWB system, we can offer multiple access interference (MAI) free operation in both synchronous and asynchronous transmissions over MAI-AWGN channel. Theoretical analysis illustrates that multipath interference (MI) as well as MAI can be also mitigated over lognormal multipath fading channels in OCC based DS-UWB system. Our simulation also shows the superiority of the OCC based DS-UWB to unitary code based system.

In this study, from a more practical point of view, the authors develop an improved transmitted reference pulse cluster (iTRPC) scheme. Based on a recently proposed transmitted reference pulse cluster (TRPC) structure, each pulse cluster is broken into reference pulse clusters (RPCs) and data pulse clusters (DPCs). It is observed that by inserting a number of zeros at the end of each RPC and each DPC, inter pulse interference can be dramatically reduced. This also results in more multi-path delayed power being captured for data detection. The performance of the proposed iTRPC scheme is analysed and compared with that of traditional TR and the original TRPC (oTRPC) system. Simulations verify that this iTRPC scheme, with quite low-complexity and not extra energy requirements, achieves more than 7 dB performance improvement over the oTRPC scheme.

A timing synchronisation method for orthogonal frequency division multiplexing (OFDM) using improved cross-correlation (ICC) is proposed in this study. The proposed method is derived in terms of maximum-a-posteriori (MAP) criterion over an additive white Gaussian noise (AWGN) channel. In this way, the proposed ICC method is able to take into consideration the surrounded data signals, which is not considered in the conventional cross-correlation (CCC) method and thus the timing accuracy is improved accordingly. Compared to the CCC method, the ICC method only appends a correction term to the cross-correlator output, which can be easily implemented using an iterative method. Therefore the complexity of the proposed ICC method has no significant increase. Simulation results show that the proposed ICC method significantly outperforms the CCC based timing method.

Abstract In order to alleviate the narrowband interference (NBI) to ultra wideband (UWB) systems, we propose two non‐linear UWB chirp waveforms based on the arctrigonometric and archyperbolic function in this paper. The proposed UWB pulses can obtain good performance in NBI suppression. Both of the two chirp pulses require only the time domain processing because of the inherent relationship between the frequency domain and the time domain. Theoretical analysis and simulation results show that the direct sequence pulse binary amplitude modulation (DS‐BPAM) UWB systems with the proposed chirp waveforms can achieve excellent NBI suppression performance and outperform the linear chirp waveform based UWB system significantly. Copyright © 2010 John Wiley & Sons, Ltd.

Applications of sensor networks in healthcare have undergone major changes in recent times. Implanted wireless sensor devices inside the human body to monitor the activities are a reality now. A new field called the Wireless Body Area Networks (WBAN or BAN) has emerged as a hot research area. To fulfill the needs for a common standard and solve the issues in this emerging field, IEEE has proposed a new task group, the IEEE 802.15.6 TG6. To control the communications from implanted devices in both PHY and MAC point of view is still a major challenge. An efficient MAC protocol can help manage and control the communication. In this paper, we propose one such MAC protocol to control the communication in implant devices. Our method of using wakeup table for normal communication and radio based wakeup for emergency communication is found to be efficient in terms of energy consumption, and delay.

The applications of ultra wideband (UWB) technologies in commercial vehicles wireless networked control systems (NCS) are attracting attention recently. The transmitted reference (TR) signaling, along with an autocorrelation receiver (AcR), is used for UWB intra-vehicle communication systems. In this paper, we analyze the performance of UWB intra-vehicle NCS with TR signaling under different time-bandwidth products and different numbers of transmitted pulses per symbol conditions. The bit-error probability (BEP) performance of this system is estimated based on the Gaussian approximation and the sampling expansion methods. Through Monte Carlo simulations, we investigate the limitation of the validity of the conventional Gaussian approximation and the sampling expansion methods for the intra-vehicle NCS.

An over-booking based dynamic spectrum management (DSM) scheme is conceived for improving the attainable spectral efficiency. All secondary users (SU) will be categorized into different classes and they borrow spectral resource from the primary users (PU) before data transmission. Under the risk-based policy model, the effects of both booking cancellations and 'no-show' reservations are analyzed. Assuming that the booking demands obey an inhomogeneous Poisson process, we derive the optimal number of excess reservations, while minimizing the total compensation costs. Algorithms are developed for determining the capacity allocation dedicated to each class, whilst denying allocation, which would lead to congested bookings.

The average symbol error rate (ASER) for the single-input multiple-output (SIMO) cyclically prefixed single-carrier (CP-SC) system with best terminal selection (BTS) is considered. Using derived closed-form expressions for the ASER and an upper bound on it, an asymptotic diversity gain is derived. Based on this result, it is shown that a QR decomposition (QRD)-based receiver and BTS are both needed to maintain the asymptotic diversity gain. Monte Carlo simulations verify the derived diversity gain analysis.

In this paper, we investigate the ARQ technology based wireless cooperative network, which can improve the spectral efficiency and decrease the collision probability. With the application of channel estimation, the source and the relays in our scheme can decide the best terminal and the optimal cooperation protocol by their timers. Comparing to opportunistic relay selection (ORS), the spectral efficiency and collision probability could be improved. Meanwhile, comparing to Incremental Transmit Relay Selection (ITRS), the new scheme benefits from AF cooperative protocol and obtains more power gains, it is also more robust to the networks topology. Additionally, the complexity in the destination becomes lower.

This paper investigates the power allocation algorithms based on convex theory for multiuser multi-relay amplify-and-forward (AAF) wireless cooperative network. In this system, there are multiple single-antenna users to communicate with one destination with the help of multiple relay nodes at the same time. In order to guarantee the quality-of-service (QoS) for all the users and reduce the power consumption, we propose two relay power allocation strategies, one is to minimize the total relay transmission power and the other is to maximize the minimum signal-to-noise ratio (SNR) among all the users. Simulation results and analysis demonstrate the efficiency and fairness of our proposed strategies.

Wireless Body Area Network (WBAN) is becoming increasingly important for ubiquitous healthcare, consumer electronics, and entertainment applications. WBAN provides unprecedented opportunities to monitor the health status of a patient with real-time updates to the physician. IEEE 802.15.6 is established to develop a wireless communication standard on WBAN. The aim is to optimize low-power in-body/on-body nodes to serve a variety of medical and non-medical applications. In this paper, we present numerical formulas to determine the theoretical throughput and delay limits of IEEE 802.15.6 networks for an ideal channel with no transmission errors. The limits are derived for different frequency bands and data rates. Additionally, to measure the spectral utilization, we analyze the bandwidth efficiency of IEEE 802.15.6 networks. The throughput, delay, and bandwidth efficiency results are presented as a function of payload size. The results of this paper can be used by protocol designers to optimize the packet size and to determine the upper bounds of IEEE 802.15.6 networks for different WBAN applications.

This study deals with signal transmission and reception over a fast-fading wireless environment. Conventional methods usually consider the rapid change of channel to be harmful, which may decrease the performance of existing systems. There are also methods proposed to make use of the cause of degradation in existing systems – Doppler spread – to provide additional diversity, at the cost of folds increased complexity. In this study, the authors focus on exploiting the array gains provided by the fast-fading wireless channel multipath array gain (MAG) and Doppler array gain (DAG). The conceptions of MAG and DAG are straightforward extensions of the conception of array gain in multi-antenna systems. For methods which exploit multipath and Doppler diversities, complex signal processing is required at the receiver side, leading to a great increase in complexity. The MAG and DAG can be easily obtained using simple transmit waveform design. Therefore, no extra computational load is required. Both analytical and simulation results show that, with the same computational complexity, the proposed methods can significantly outperform the conventional ones.

Designing a non-ideal delay line (DL) with phase distortion in a transmitted-reference ultra-wideband system with an autocorrelation receiver is a great technical challenge. Differing from the currently empirical design method of DL, a semi-analytic approach is proposed through Gaussian approximation of the expression for conditional bit error rate (BER), based on investigation on the degradation of average BER caused by a group delay ripple range (GDRR) over independent Nakagami-m fading channels. This GDRR-based design method can directly evaluate its effects on the system performance and determine the acceptable phase distortion level to trade-off the BER performance and system complexity.

In this paper, we propose a distributed adaptive interference coordination algorithm for a practical orthogonal frequency division multiple access (OFDMA)-based mobile cellular systems. The designed algorithm can achieve an efficient frequency reuse for any user distribution and traffic load. Since no a priori frequency planning is required, the minimal coordination between base stations is also achieved. Moreover, the proposed algorithm can adapt to different network interference conditions and is power-saving in some degree. We also develop a way to decompose a multi-cell optimization problem into distributed single-cell optimization problems, which greatly reduces the computational complexity.

In this paper, we investigate a cooperative multiple input multiple output (MIMO) system with multi-antenna relays. In order to minimize the system outage probability, we propose a new relay selection policy for this system based on the opportunistic relaying scheme. The relays are endowed with the ability of channel estimation and the maximal ratio receiver combining (MRRC) technology and beamforming are employed in the first and the second cooperative phase, respectively. Statistical optimal power allocation algorithm, close-form expression of the system outage probability and also the diversity order are presented in detail. Finally, simulation results prove the accuracy of the the theoretical analysis and also the efficiency of the new scheme which can obtain more power gains or wider coverage compared with the opportunistic relaying scheme.

A new pulse for cognitive radio-ultra wideband (CR-UWB) using multiple modified transform domain communication system (M-TDCS) is presented in this paper. Utilizing multiple M-TDCS to sense the electromagnetic environment and UWB as a versatile PHY layer to adapt various wireless channel conditions, this pulse can avoid interference to/from the existing wireless systems or noise. This pulse can be implemented using surface acoustic wave (SAW) devices and some other accessorial devices. The bit error ratio (BER) performance of system using this pulse can be observably improved for UWB systems.

Owing to the extremely high-time resolution of impulse radio ultra-wideband (IR-UWB), time of arrival (TOA) estimation has been an important and tempting issue of this technology ever since its emergence. Conventional TOA estimation (TOAE) schemes require prohibitively high sampling rate and a priori knowledge of the received signal, and hence render a practical implementation rigorous or even infeasible. To tackle these drawbacks, this paper proposes a low-complexity energy detection-based non-coherent TOAE scheme, which is composed of two processing stages: initial signal acquisition (ISA) and fine timing estimation (FTE). In the ISA stage, a linear quadrature optimisation (LQO)-based weighting scheme is proposed to coarsely capture the arrival of the IR-UWB signals. Capitalising on the acquisition of the IR-UWB signal in a relatively short time range, the authors then develop in the FTE stage, a double-threshold test (DTT) tailored for locating the leading edge of the IR-UWB signal. Simulations illustrate that the LQO algorithm yields a considerably increased probability of seizing the arrival of the IR-UWB signals in a blind manner, and the DTT strategy significantly ameliorates the TOAE accuracy in terms of mean absolute error, compared with the conventional energy detection-based TOAE methods.

The authors investigate the symbol error rate (SER) performance of the cooperative decode-and-forward (DF) relaying strategy with orthogonal space–time block coding (OSTBC) applied at all links of source-relay, source-destination and relay-destination. Only when one relay node is able to correctly decode the OSTBC codeword of the source, it will forward source information to the destination with the same OSTBC codeword. The exact SER expressions of DF relaying with OSTBC are presented for M-PSK and M-QAM modulations, respectively, over dissimilar Rayleigh fading channels. By virtue of the multinomial theorem and the law of total probability, the derived expressions are further deduced in closed form. Simulations demonstrate the proposed closed-form analytical results. It is pointed out that such results have seldom appeared in literatures before.

Despite their near-noise power emission, ultra wideband (UWB) radios, particularly direct-sequence ultra wideband (DS-UWB), are still possible to cause harmful interference to legacy radio systems. When they participate in a large dense cognitive radio network (CRN) and transmit simultaneously, their joint power emission would be disastrous if without control. We address this problem by imposing a limit on the aggregate power emission of DS-UWB CRN. The limit is negotiable. It takes effect by letting each transmitter adapt to a spectrum void defined as the area below the limit itself and above the interference temperature experienced instantly by the transmitter. We propose a water-filling algorithm that maximises the sum capacity while enabling each transmitter to fit its power spectral density into, and thus to make the most of, the spectrum void. The algorithm is performed locally at the transmitter with low complexity. Numerical analysis based on a realistic office network shows that the algorithm can bring the aggregate power emission even down below the Federal Communications Commission limit for individual UWB device, but still guarantees a given bit-error performance to nearly 40 active users.

In this paper, we analyze and evaluate the performance of IEEE 802.15.3c MAC standard, especially for high-definition uncompressed video transmission. At first, the improvements of IEEE 802.15.3c MAC, such as aggregation method and block ACK, are discussed. Then the transmission efficiency concerned with superframe size, channel time allocation, ACK policies, and payload size etc. is analyzed. Simulation results show performance of video streaming over MAC under different conditions. Based on these results, we propose some useful suggestions in order to fully exploit the network capacity and perfectly represent such video application.

This paper addresses the performance analysis for orthogonal space-time block coded (STBC) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) systems. As the channel model considers the log-normal fading, the resultant signal to noise ratio (SNR) will be the product of a log-normal distributed variable and a variable of sum of several Gamma- distributed variants. Based on this, the exact expressions for the bit error probability and the outage probability are derived theoretically. And their approximate expressions can be obtained via the Gauss-Hermite and the Gauss- Laguerre quadratures, respectively. Simulation results verify the theoretical solutions.

In this paper, three optimal linear soft fusion schemes for cooperative sensing are proposed on the basis of corresponding optimality criteria, namely Neyman-Pearson (N-P), deflection coefficient maximization (DCM), and linear quadratic optimization (LQO). Multiple cooperative secondary users (SU) in the cognitive radio (CR) network simply serve as relays to provide space diversity for the fusion center (FC) to obtain the global test statistic. After the ideal optimal fusion weights are acquired, iterative weight setting strategies are utilized to implement them in practice. Analysis and simulation results illustrate that the proposed N-P and DCM schemes yield significant improvements on the sensing performance and the iterative weight setting algorithm can effectively approach the ideal performance of these two schemes. As for the LQO scheme which operates on the received signal covariance matrices merely, it is capable of providing satisfactory performance with sufficient cooperative SUs.

Ultra wideband (UWB) is a well known technology in wireless personal area networks (WPANs). Our work analyzes a multiple access code-selected M-ary direct sequence (DS) UWB communication system. The objective is to get a high data rate multiple access M-ary modulation scheme of UWB system. M-ary modulation is obtained by assigning a DS code set to each user, which is different with the traditional M-ary modulation schemes, such as pulse position modulation (PPM) and pulse amplitude modulation (PAM) etc. For this multiple access code-selected M-ary modulation UWB system, with the increase of the modulation level M, we can keep the same number of users, the data transmission rate and the multiple access performance while reduce the required transmitter power. In this paper, the signal processing algorithm is provided and the simulation results prove the efficiency of this multiple access M-ary UWB system.

We study the outage performance for the decode-and-forward (DF) relaying in the Nakagami fading under unequal Nakagami interference. A closed-form expression for the outage probability is derived. Simulations are provided to verify the analytical results.

A novel Gaussian approximation algorithm is proposed for calculating the thresholds of low-density parity- check (LDPC) code ensembles under sum-product decoding. The updating rules of means and error probability are derived. Numerical results show that the thresholds obtained by the proposed algorithm closely coincide with the values computed by density evolution (DE). Moreover, our algorithm can calculate the thresholds of irregular LDPC codes with higher accuracy than the algorithm proposed by Lehmann and Maggio.

In this paper, we propose a scheme to design unequal error protection low-density parity-check (UEP-LDPC) codes based on Gaussian approximation algorithm over AWGN channel. Using this method, we can find effective UEP-LDPC code ensemble which has good overall performance and good UEP property. Simulation results show the superiority of the proposed UEP-LDPC code in improving the quality of reconstructed image in uncompressed image and set partitioning into hierarchical trees (SPIHT) coded image transmission.

This paper proposes an optimal soft fusion scheme for cooperative spectrum sensing in cognitive radio (CR) network. Multiple cooperative secondary users (SUs) simply serve as relay nodes in the network to provide space diversity for spectrum sensing. An optimal soft fusion scheme of the relayed sensing observations is derived in Neyman-Pearson framework, on the basis of maximizing the deflection coefficient of the global test statistic at the fusion center. However, the proposed fusion scheme requires instantaneous measurements of the received PU signal strengths in SUs with high accuracy, which are extremely difficult to obtain in an energy detection based spectrum sensing scenario. An iterative algorithm is therefore proposed to perform the estimation of the received PU signal strengths. Simulation results illustrate that the proposed optimal soft fusion scheme can significantly improve the spectrum sensing performance and the estimate algorithm can effectively approach the ideal performance of the proposed optimal fusion scheme.

The authors investigate the outage performance for decode-and-forward relaying schemes in the presence of dissimilar Nakagami-m interferers under non-identical Nakagami-m fading channels. A closed-form expression for the outage probability is derived under this scenario. Simulation results demonstrate our theoretical solutions.

Conflict free spectrum allocation for secondary users in cognitive networks is a challenging problem, since the accessible spectrum is shared among users. The problem becomes to be especially difficult when it is wanted to get the maximum utility of the system considering access fairness among users. In this paper, a novel method using bipartite graph matching is proposed to approach this target, where users cooperatively optimize spectrum allocation to get the maximal system utility while avoiding interference with its neighbors. An idealized method for centralized cognitive networks is presented; experimental results show that proposed algorithm dramatically maximizes spectrum utilization together with reducing allocation conflictions among users, which minimize the number of starved users during the allocation.

In this paper, an M-ary code selected direct sequence bipolar pulse amplitude modulation (MCSDS-BPAM) ultra wideband system is introduced and the code selection criteria of this system is investigated. The particular DS code sequence used in MCSDS-MPAM scheme is selected by the log2M/2 bits from the DS code set, which offers the system higher data rate without increasing the system bandwidth or changing the pulse shape compared to other M-ary modulation schemes. The system performance can be varied by the selection of DS code set from the common DS code set without any extra expense. The criteria based on four parameters used to evaluate the system performance under different code sets are given over an ideal AWGN channel and correlation receivers.

In this paper, the system performance of M-ary code shift keying (MCSK) impulse modulation is studied in detail and compared to M-ary pulse position modulation (MPPM) under single- and multi-user scenarios. For that, bounds on the semi- analytic symbol-error rate (SER) expressions are derived and simulation studies are conducted. When practical implementations of MCSK and MPPM are considered, it is shown that MCSK can provide about 2 dB performance gain over MPPM as it reduces the effects of multipath delays on the decision variables by randomizing locations of the transmit pulse.

In ultra-wideband impulse radio (UWB-IR) systems, multipath-delayed received pulses may overlap if two consecutive multipaths arrive within less than the pulse duration. This condition makes it nontrivial for the Rake receiver to capture enough multipath energies for reliable communications. In this paper, we study in detail the effects of channel models and Rake receiving process on the performance of UWB-IR systems. Specifically, we consider Tc- and T-spaced channel models and different Rake receiver implementations to maximize the captured signal energy, where we discuss their validity for real system considerations. Also, we show that code shift keying (CSK) impulse modulation can achieve about 1 dB performance gain over conventional pulse position modulation (PPM) when there is pulse overlapping, as it randomizes pulse transmit locations as opposed to fixed pulse transmit locations used by PPM.

In this paper, a novel frequency coded orthogonal UWB pulse design method based on orthogonal carriers and PN (pseudo noise) sequence is presented. The basic idea of the new approach is that the frequency-shifted sub-pulses are used to generate the orthogonal pulses by coding with PN sequence in frequency domain. Because the orthogonal carriers and PN codes are introduced into IR-UWB (impulse radio UWB), the new method not only has the advantages of both the traditional IR-UWB and multi-banded CB-UWB (carrier based UWB), but also improves the efficiency of the instantaneous spectrum and energy of the transmitting UWB signal. Furthermore, the Auto-correlation and cross-correlation characteristic of the proposed pulses are better than those of other conventional pulses. In addition, by the aid of cognitive radio technology, it is can be guaranteed the transmitting signal in accordance with FCC spectral mask and coexistence, interference avoidance with other traditional narrow band system. And simulation result showed that the proposed pulse could reduce the effect of narrow band interference on UWB system with litter complexity.

Fixed guard times considered for the physical layer of the IEEE 802.15.4a standard (low-rate Wireless Personal Area Networks) cause user asynchronism-dependent collisions that affect the instantaneous bit-error-rate (BER) and packet- error-rate (PER) performances in the presence of simultaneously operating piconets (SOPs). Using code shift keying (CSK), the location of the guard times can be randomized yielding the collision event independent of user asynchronism. In this paper, CSK modulation is adopted for the physical layer of the IEEE 802.15.4a standard with a special code design technique, and it is shown that the proposed implementation of CSK stabilizes the instantaneous BER and PER values. Stabilizing the instantaneous BER and PER values prevents worst-case scenarios, where many packets may be lost due to user asynchronism-dependent collisions, and should be carefully considered for real system implementation.

The performance of two direct sequence ultra wideband (DS-UWB) communication systems is investigated. The first system is the classic DS-UWB system. The second is obtained by adding a forward error control codes (FEC), convolutional code. For the two systems, binary pulse amplitude modulation is applied. The performance of these two systems is analyzed in detail under AWGN channel. In our proposed coded scheme, we use soft output Viterbi algorithm (SOVA). The analysis shows that the coded DS-UWB system outperforms the DS-UWB system significantly, or more importantly, at a given bit error rate, the coding scheme increases the number of users by a factor which is logarithmic in the number of pulses used in DS UWB systems. Simulation results on the bit error rate of the proposed system indicates that the system is capable to work in lower SNR's and therefore supports higher data transmission rates compared to the previously proposed UWB communication systems.

Coexisting with many concurrent narrowband services, the performance of UWB systems will be affected considerably by them due to the high power of these narrow-band signals with respect to the UWB signals. Specifically, IEEE 802.11a systems which operate around 5 GHz and overlap the band of UWB signals will interfere with UWB systems significantly. In this paper, a novel narrow-band interferences (NBI) suppression technique based on singular value decomposition (SVD) algorithm for two UWB systems is presented. The two systems are direct sequence ultra-wideband (DS-UWB) system and timing hopping (TH) binary pulse amplitude modulation (PAM) UWB system. SVD is used to approximate the interferences which then are subtracted from the received signals. The proposed technique is simple and robust. Simulation results show that the proposed new technique is very effective.

In this study, we propose an adaptive handoff scheme with dynamic hysteresis value for cellular communications, which is based on distance between the mobile station and the serving base station. Performance is evaluated in terms of the expected number of handoffs, the expected handoff delay, standard deviation of handoff location, and the expected link degradation probability as well. Numerical results and simulations show that the proposed scheme outperforms the handoff schemes with static hysteresis levels. The effect of distance error is also discussed.

In the 3GPP TD-SCDMA standard, a favorable receiver is block equalizer. In fast varying environment, the channel estimation calculated by Midamble sequence has to be used to detect the noisy data far away from the Midamble sequence. This can lead to a high error floor. A new detection method is proposed in this paper. At first, parts of chip data adjacent to Midamble are detected by the channel estimation result obtained by Midamble and detected bits are then applied to do channel estimation to renew the channel impulse response. The renewed channel impulse response result will be used to detect the residual chip data. Simulation results show that the proposed method can dramatically lower the error floor of the conventional block equalizer in fast time-varying channel.

In this letter, we present a unified mathematical expression for the decoding algorithm of space-time block codes (STBC). Based on the unified expression, we make a comparison of the STBC transmit diversity and the maximal-ratio combining MRC receive diversity, and analyze the symbol error probability for the STBC transmissions. The effects of the channel correlation and the number of transmit and receive antennas on the performance of the STBC are discussed.

The enhanced spreading codes with zero correlation duration (ZCD) characteristics and novel interference-cancelled ZCD-UWB (ultra-wideband) systems using PG-corrected ternary ZCD codes are presented in this paper. The ZCD-UWB system could be a very useful solution for a enhanced wireless personal area network (WPAN) system having interference-cancellation property without employing complicated multiuser detection (MUD) or other interference cancellation techniques.

Noncoherent multiuser detection for CDMA systems with M-ary nonlinear modulation was recently studied, and noncoherent optimum, decorrelative, and MMSE detection schemes for this kind of system were proposed and analyzed in previous papers. In this letter we propose a blind adaptive noncoherent decorrelative multiuser prefilter for CDMA systems with M-ary nonlinear modulation over AWGN channel. The proposed multiuser detector uses possibly known signature waveforms of users as much as possible, so it provides better performance compared with previous multiuser detectors for nonlinearly modulated CDMA systems in terms of convergence properties and symbol error rate.

An alternative blind adaptive multiuser detection is investigated based on modified constrained constant modulus (CM) criterion. It is shown that the performance of a CM-based receiver is limited by the received power of the desired user. In this paper, we show that the limitation can be avoided using the noncanonical constraint CM criterion and that in the presence of channel noise the modified CM criterion function is strictly convex by properly selecting some constant. With analyzing the extrema of the cost function, we point out how to select the constant. Moreover, a simple stochastic gradient algorithm for implementing our scheme is presented, and the convergence properties of the algorithm are analyzed. Simulation examples are given to demonstrate the performance of the proposed scheme.

Random multiple access and reservation multiple-access protocols which are currently employed in most satellite communication systems have some merits and demerits according to the type of users and traffic. A modified packet demand assignment multiple access (PDAMA) protocol with better characteristics is proposed and analyzed. Using simulation with approximate analysis, the performance of the modified PDAMA is compared with that of a modified random-access protocol as well as the original PDAMA in terms of delay and throughput. For small packet arrival rate, the performance of the proposed access protocol is shown to be similar to that of the modified random-access protocol, and better than that of the PDAMA protocol. While the packet arrival rate increases, the performance of the proposed access protocol is improved greatly compared with that of the PDAMA protocol.>

In radio communication systems, capture arises due to different locations in transmitters or different times of arrivals of packets onto the receiver and thus improves the overall system performance. In cellular mobile communication systems the transmitted signals may be experienced in serious variations because of shadowing and fading from dense and high-rise buildings. So the receiver of a base station may decode one of many signals due to different power levels or different times of arrival. The authors model and analyze, using a multiband concept, a random access system for cellular radio mobile networks. Mobile stations are assumed uniformly distributed over a cell and the cell is composed of many circularly disjoint bands with equal width from a base station. Then capture may naturally occur from the different bands of different locations. The authors derive the performance of the system, and show that the performance is remarkable as the number of bands increases.>