In light of the revolutionary requirements of the sixth generation (6G) and beyond wireless networks, reconfigurable intelligent surface (RIS) and rate-splitting multiple access (RSMA) have emerged as pivotal technologies due to their potential for improving spectral efficiency, user fairness, and interference management. This survey explores the theoretical foundations, architectural frameworks, and design strategies of RIS-assisted RSMA, emphasizing the combined adaptability of RIS’s wireless propagation control and RSMA’s multi-user flexibility for dynamic spectrum management. The article first discusses the fundamental concepts of RSMA and RIS technologies. Then, we investigate various enabling technologies for RIS-RSMA networks, highlighting key advancements in interference mitigation, energy efficiency, and security for future networks. Subsequently, some optimization techniques crucial for enhancing RIS-RSMA network performance are presented. Additionally, we examine advanced machine learning (ML) approaches that enable RIS configurations to dynamically adapt to changing network requirements. Techniques such as deep reinforcement learning support real-time adjustments, creating more scalable and resilient RIS-RSMA architectures. Finally, we discuss open research directions for advancing RIS-assisted RSMA in emerging 6G applications. We also consider the potential of advanced ML techniques, including quantum-based ML and large language models, to handle the complexities of large-scale network optimization. This comprehensive survey addresses critical challenges and current advancements. It offers a roadmap for future research in RIS-assisted RSMA networks, paving the way for robust, intelligent, and adaptive 6G wireless communication systems.

Ultra-reliable low-latency communication (URLLC) has been considered as a major use case for the fifth generation (5G) wireless networks. Therefore, the Third Generation Partnership Project (3GPP) has targeted the support of URLLC in the new radio (NR) air interface by introducing several technologies such as short transmission time intervals (sTTIs) and puncturing scheduling. However, scheduling URLLC without impacting the quality-of-service (QoS) of enhanced mobile broadband (eMBB) traffic is a challenging task. In this paper, we optimize the resource allocation and scheduling process of URLLC puncturing eMBB transmissions by considering the QoS of eMBB and the transmission errors associated with the finite blocklength coding of the URLLC traffic. In addition, we propose a deep supervised learning approach to predict the optimized resource allocation in a computationally efficient manner to be practically used in real-time operation. The numerical results show that by adjusting the model parameters, we can increase the accuracy of the lowcomplexity predictions for an efficient scheduling scheme with superior performance as compared to other techniques.

Shortened transmission time interval (sTTI) is considered one of the most significant enhancements to evolve the current Long-Term Evolution (LTE) networks to fulfill the 5G requirement of supporting critical machine-type communications (cMTC). However, scheduling the sporadic cMTC and the data-intensive human-type communications (HTC) on different scales of transmission duration is a challenging task. In addition, the finite blocklength coding of the small-size packets of cMTC makes the process more challenging. In this paper, we address the scheduling problem of cMTC coexistent with HTC in LTE. In this regard, we formulate the processes as optimization problems that maximize the system utility while providing guarantees for the different quality-of-service (QoS) of both types of traffic. Moreover, we propose computationally-efficient algorithms that utilize the matching theory and analyze them from a practical perspective to prove that they can be used as practical schemes. The simulation results show a close-to-optimal performance for the proposed scheme and its superiority to conventional algorithms.

This paper investigates the physical layer security of inband underlay Device-to-Device (D2D) communication, where there is no direct link between D2D users. In this respect, optimal relay selection is utilized to secure the D2D transmission. The eavesdropper uses either maximal-ratio combining or selection combining to improve the wiretapped signals. The D2D secrecy performance analysis is performed regarding the secrecy out-age probability (SOP) and the probability of non-zero secrecy capacity, and closed-form expressions are provided. To validate the correctness of our analysis, numerical and simulation results are presented. Furthermore, the asymptotic analysis of the SOP is provided, where new insights into the system parameters are revealed.

This paper investigates physical layer security and data transmission in cellular networks with inband underlay Device-to-Device (D2D) communication, where there is no direct links between D2D users. We propose the use of full-duplex (FD) transmission and dual antenna selection at the relay node. Thanks to the FD transmission, the relay node can simultaneously act as a jammer to enhance the cellular network secrecy performance, while improving the D2D communication data transmission. This describes a practical attractive scheme, where spectrum sharing is beneficial for both the D2D and cellular networks in terms of throughput enhancement and security provisioning, respectively. We analyze the secrecy performance of the cellular network and derive closed-form expressions for the secrecy outage probability (SOP) and the probability of non-zero secrecy capacity. We also derive a closed-form expression of the D2D outage probability. Furthermore, asymptotic analysis for SOP is performed. Simulation and numerical results are provided to verify the efficiency of the proposed scheme and to validate the accuracy of the derived expressions.

Cellular systems present one of the most suitable wireless technologies to efficiently serve critical machine‐type communications (MTC) that require strict quality‐of‐service (QoS) guarantees. Therefore, ultra‐reliable and low‐latency communications is a target use case in the design of the upcoming generations of cellular networks. From the radio resource management perspective, guaranteeing such stringent QoS requirements in long term evolution (LTE) networks is a challenging task, especially in the case of the coexistence of MTC with the human‐type communications (HTC). In this study, the authors address the resource allocation and scheduling problem of critical MTC that coexist with HTC in LTE. The optimisation problem is formulated such that the overall system utility is maximised while fulfilling the different QoS demands of the two sets of users. Utilising the effective bandwidth and effective capacity theories, a cross‐layer design is developed to guarantee the QoS requirements of the critical MTC. For a computationally‐efficient solution of the problem, they formulate it as a two‐sided matching process that can be used as a practical scheduling scheme. To this end, they analyse the convergence, stability, and computational complexity of the proposed methods. Results reveal the close‐to‐optimal performance of the matching‐based scheduling scheme and its superiority to other existing techniques.

In this article, we analyze the performance of the long-term evolution random access procedure with the Third Generation Partnership Project's access class barring (ACB) mechanism in an energy harvesting (EH) machine-to-machine (M2M) scenario. To circumvent the state-space explosion in the conventional Markov-chain-based analysis due to time-dependent traffic pattern and data and energy buffer status, we develop an analytical model that combines mean-value analysis with the Markov-based analysis. Based on the analytical model, the random access success probability, the access delay of the network, and the average time duration between two successive successful transmissions are derived. Our analysis suggests that in the EH scenario, despite the lower number of the contending nodes in comparison with the non-EH scenario, the ACB parameters must be chosen in a more conservative way to avoid excessive collisions. The ACB parameters include access barring rate and mean barring duration. We also study an energy threshold-based activation policy and investigate the joint effects of this policy and the ACB mechanism on the random access success probability. The extensive simulations were conducted to evaluate the accuracy of the analytical model.

We consider uplink transmission using a single carrier frequency division multiple access (SC-FDMA) scheme in a cellular network with human-to-human (H2H) and machine-to-machine (M2M) communications. The M2M traffic is relayed through energy harvesting (EH) gateways. An optimization framework is developed to minimize the data dropping in the EH gateways caused by delay constraint violation of the M2M traffic while taking into account the rate requirements of the H2H communication, the data and energy causality constraints as well as the SC-FDMA transmission constraints. By introducing two transforms, the original problem is expressed in a linearly separable form in terms of its discrete and continuous variables with the convexified continuous part. Then, Generalized Benders Decomposition is applied to solve the problem by decomposing it into primal and master problems. Due to the NP-hardness of the optimal solution, a low-complexity method is proposed by combining the solution of the primal problem with a heuristic resource block allocation algorithm. Simulation results show that the proposed heuristic method performs better than two alternative heuristic methods when applied to small scale and large scale networks.

This paper studies the physical layer security (PLS) of underlay multihop device-to-device (D2D) relaying. New closed-form expressions on the lower bound of the outage probability, the secrecy outage probability (SOP), and the probability of non-zero secrecy capacity are derived. Hence, new insights into the secrecy performance of the underlay multihop D2D relaying are revealed. The obtained analysis is validated through Mont-Carlo simulations.

In this paper, we consider multiple-input single-output multi-eavesdropper cognitive radio networks (MISOME-CRNs), where a secondary user (SU) aims to transmit confidential information to a legitimate SU receiver in the presence of a primary user (PU) and a multi-antenna passive eavesdropper in fast fading environments. For this system setting, we study beamforming with artificial noise (AN) for the SU to achieve confidential communications. We consider designing an AN-assisted optimal beamforming scheme, denoted cognitive beamforming (CB), which maximizes the ergodic secrecy rate. Moreover, we propose two suboptimal beamforming schemes, namely, scaled beamforming (SB) and projected beamforming (PB). We develop an analytical framework to assess the performance of the proposed schemes in a unified manner. First, we analyze the achievable ergodic secrecy rate of the three schemes. Second, we derive the optimal power allocation for the information and AN signals that maximizes the achievable ergodic secrecy rate in the large-antenna regime. Third, we study the performance of the three schemes in terms of the secrecy outage probability. Using numerical simulations, we validate our analytical results and show that CB achieves the best performance among the three proposed schemes. In addition, we provide insights into the effect of various system parameters on the secrecy performance. In particular, we show that the interference threshold at the PU plays an important role in the beamforming design.

Network coding is an effective idea to boost the capacity of wireless networks, and a variety of studies have explored its advantages in different scenarios. However, there is not much analytical study on throughput and end-to-end delay of network coding in multi-hop wireless networks considering the specifications of IEEE 802.11 Distributed Coordination Function. In this paper, we utilize queuing theory to propose an analytical framework for bidirectional unicast flows in multi-hop wireless mesh networks. We study the throughput and end-to-end delay of inter-flow network coding under the IEEE 802.11 standard with CSMA/CA random access and exponential back-off time considering clock freezing and virtual carrier sensing, and formulate several parameters such as the probability of successful transmission in terms of bit error rate and collision probability, waiting time of packets at nodes, and retransmission mechanism. Our model uses a multi-class queuing network with stable queues, where coded packets have a nonpreemptive higher priority over native packets, and forwarding of native packets is not delayed if no coding opportunities are available. Finally, we use computer simulations to verify the accuracy of our analytical model.

In this paper, we consider the power allocation (PA) problem in cognitive radio networks (CRNs) employing nonorthogonal multiple access (NOMA) technique. Specifically, we aim to maximize the number of admitted secondary users (SUs) and their throughput, without violating the interference tolerance threshold of the primary users (PUs). This problem is divided into a two-phase PA process: a) maximizing the number of admitted SUs; b) maximizing the minimum throughput among the admitted SUs. To address the first phase, we apply a sequential and iterative PA algorithm, which fully exploits the characteristics of the NOMA-based system. Following this, the second phase is shown to be quasiconvex and is optimally solved via the bisection method. Furthermore, we prove the existence of a unique solution for the second phase and propose another PA algorithm, which is also optimal and significantly reduces the complexity in contrast with the bisection method. Simulation results verify the effectiveness of the proposed two-phase PA scheme.

In this paper, we investigate the detection problem of binary faster-than-Nyquist (FTN) signaling and propose a novel sequence estimation technique that exploits its special structure. In particular, the proposed sequence estimation technique is based on sphere decoding (SD) and exploits the following two characteristics about the FTN detection problem: 1) the correlation between the noise samples after the receiver matched filter, and 2) the structure of the intersymbol interference (ISI) matrix. Simulation results show that the proposed SD-based sequence estimation (SDSE) achieves the optimal performance of the maximum likelihood sequence estimation (MLSE) at reduced computational complexity. This paper demonstrates that FTN signaling has the great potential of increasing the data rate and spectral efficiency substantially, when compared to Nyquist signaling, for the same bit-error-rate (BER) and signal-to-noise ratio (SNR).

Proactive caching is a promising technique used to minimize peak traffic rates by storing popular data, in advance, at different nodes in the network. We study a cellular network with one base station (BS) communicating with multiple mobile units (MUs). The BS has a number of cached files to be delivered to the MUs upon demand, and the popularities of these files are changing over time. We show that proactively and constantly updating the MU finite caches and jointly encoding the delivery of different demanded files to the MUs over different time slots minimize the delivery sum rate. We propose two different schemes for a two different scenarios, where the file popularities over time can be either arbitrary increasing or decreasing for the first scheme and decreases with demand for the second scheme. Numerical results show the benefits of the proposed schemes, over conventional caching schemes, in terms of reducing the delivery sum rate.

Using Unmanned Aerial Vehicles (UAVs) or drones in Vehicular Ad-hoc Networks (VANETs) has started to attract attention. This paper proposes a mathematical framework to determine the minimum drone density (maximum separation distance between two adjacent drones) that stochastically limits the worst case for the vehicle-to-drone packet delivery delay. In addition, it proposes a drones-active service (DAS) that is added to the location service in a VANET to obtain the required number of active drones based on the current vehicular density while satisfying a probabilistic requirement for vehicle-to-drone packet delivery delay. Our goal is boosting VANET communications using infrastructure drones to achieve the minimum vehicle-to-drone packet delivery delay. We are interested in two-way highway VANET networks with low vehicular density. The simulation results show the accuracy of our mathematical framework and reflect the relation between the vehicle-to-drone packet delivery delay and the drone density.

In this paper, we propose a novel joint routing and medium access control (MAC) protocol with traffic differentiation, based on quality of service (QoS) for wireless sensor networks (WSNs). This is referred to as joint routing and MAC (JRM) protocol. By leveraging the classical layered approach and combining routing and MAC layer functions, the proposed JRM protocol achieves a solution for energy efficiency in WSNs. JRM also ensures low latency for prioritized traffic. There are three major advantages of the proposed protocol. Firstly, the instantaneous network information (e.g., estimated time to destination, and node's unavailability to forward additional packet) is piggy-backed with the control packets acknowledgement and clear- to-send of the MAC frame. Based on the updated network knowledge and the objective of the required performance metrics (e.g., energy and latency), the next hop neighbor is chosen dynamically with reduced control overhead. Secondly, the JRM protocol introduces an approach for finding the constrained shortest path for forwarding packets, which results in load balancing in WSNs. Finally, routers (nodes) in JRM require very little forwarding and routing table information, which is compatible with the resource constraints in WSNs. The efficiency of the proposed protocol is shown through simulation results.

In recent years, a significant amount of research has been conducted to explore the benefits of network coding in different scenarios, from both theoretical and simulation perspectives. In this paper, we utilize queueing theory to propose an analytical framework for bidirectional unicast flows in multi-hop wireless mesh networks, and study throughput of inter-flow network coding. We analytically determine performance metrics such as the probability of successful transmission in terms of collision probability, and feedback mechanism and retransmission. Regarding the coding process, our model uses a multi-class queueing network where coded packets are separated from native packets and have a non-preemptive higher priority over native packets, and both queues are in a stable state. Finally, we use simulations to verify the accuracy of our analytical model.

In this paper, the power allocation (PA) problem is investigated in cognitive radio networks (CRNs), employing non-orthogonal multiple access (NOMA) technique. In such a framework, the quality of service (QoS) requirements for both the primary users (PUs) and secondary users (SUs) should be met. We propose a novel PA algorithm, which fully exploits the characteristics of NOMA-based system. The QoS requirements for PUs are guaranteed through the setup of the overall power for SUs. In addition, it provides PA in a descending order, according to SUs' channel gains. It is validated that the proposed algorithm is optimal. To show its effectiveness, it is compared with one of the most efficient PA algorithms, namely fractional transmit power control (FTPC). The superiority of the proposed algorithm is thoroughly verified by simulation results. Additionally, the computational complexity of our proposed algorithm is only linear, i.e., O(N).

In this paper, the resource allocation problem is considered in the context of spectrum underlay in cognitive radio (CR) networks. In such a framework, the quality of service (QoS) requirements for both primary users (PUs) and secondary users (SUs) need to be satisfied. Admission control based on removal algorithms is used jointly with power control such that the QoS requirements of all admitted SUs are satisfied, while no excessive interference is caused to PUs. For the first time in the literature, we introduce the min-weight load-balancing problem based on weighted bipartite graphs, while combining it with power control and user removal. Simulation results show that the combined algorithm achieves improved results when compared with merely using power control and user removal algorithms.

For a wide range of wireless channels, symmetric alpha-stable (SαS) is shown to be applicable to model the noise and/or the interference. However, the ongoing research of the optimal detection of the cooperative diversity in alpha-stable noise is limited to few closed-form expressions for special values of the characteristic exponent due to the unavailability of the probability density function of the noise. This limits the performance analysis of such networks. In this paper, to overcome this difficulty, we use the compound property of the SαS distribution to derive an approximate analytical expression for the error probability. This facilitates the calculation of the error performance of the cooperative amplify-and-forward diversity with optimal detection of binary signals in SαS noise for any value of . Computer simulations are used to verify the correctness and accuracy of the derived analytical error results. Our mathematical modeling and simulations prove that asymptotic maximum diversity order is achievable.

For structural health monitoring (SHM), mode shape calculation is an important task that needs to be performed accurately and reliably. The use of wireless sensor networks (WSNs) for SHM is a very effective and a promising solution. However, WSNs experience synchronization errors among the sensor nodes, which can affect the accuracy of the mode shape calculation. In this paper, we study the impact of time synchronization error (TSE) on the mode shape calculation in a semi-local manner using frequency domain decomposition (FDD) implemented in a semi-local manner. In order to decrease the size of the transmitted data by the sensor nodes and reduce the processing load and needed storage capacity on the central unit, we adopt a semi-local processing approach where each node partially processes the measured data. Then, sensor nodes send the partially-processed data to a central unit for further processing and mode shape calculation. Numerical results prove that the time synchronization error has a significant impact on the accuracy of the mode shape calculation. Furthermore, results show that semi-local processing is more sensitive to TSE compared with centralized processing.

In this paper, we adopt a multiobjective optimization for the bit and power allocation problem in order to meet the requirements of emerging wireless systems, i.e., achieving higher throughput without considerably increasing the transmit power. More specifically, we propose to simultaneously maximize the throughput and minimize the transmit power of an OFDM system subject to average bit error rate (BER), power budget, and maximum allocated number of bits per subcarrier constraints. The formulated optimization problem is not convex and we use an evolutionary algorithm, i.e., genetic algorithm, in order to obtain the solution. We study the structure of the problem and the obtained solution and notice that the constraint on the average BER can be replaced by a BER per subcarrier constraint. As such, we propose an approximate non-convex optimization problem. We further exploit the structure of the approximate optimization problem and notice that the BER constraint per subcarrier (i.e., the source of the non-convexity) must be satisfied with an equality sign and can be substituted; this leads to an equivalent convex optimization problem where the global optimality of the Pareto solutions is guaranteed. Closed-form expressions are obtained for the bit and power allocations with reduced complexity. Simulation results show that the proposed multiobjective optimization approach provides significant performance improvements over single objective optimization techniques presented in the literature, without incurring additional complexity.

Multi-hop relaying is an efficient transmission technique that splits the communication link between the source and the destination into several, possibly shorter, hops for extended coverage, improved reliability, and less power consumption. Previous works on multi-hop communications use the assumption of frequency-flat and quasi-static fading, which can be justified only for narrowband systems in stationary or quasi-static channels. In this paper, we extend multi-hop relaying into vehicular communication in highways.We propose a precoded transmission over multi-hop vehicle-to-vehicle links with time- and frequency-selective fading in highways. We investigate the performance gains where traveling vehicles are allowed to relay signals via neighboring vehicles to the final destination. With the aid of the precoded transmission and best-relaying vehicular selection, we succeeded to extract the rich diversity gains that are inherited in these types of doubly selective fading channels, through time, frequency, and space dimensions. We developed a mathematical model and derived a tight upper-bound expression for the pairwise error probability for future studies and analysis. Computer simulations are used to verify the correctness and accuracy of the derived analytical error.

In recent years, network coding has emerged as an innovative method that helps wireless network approaches its maximum capacity, by combining multiple unicasts in one broadcast. However, the majority of research conducted in this area is yet to fully utilize the broadcasting nature of wireless networks, and still assumes fixed route between the source and destination that every packet should travel through. This assumption not only limits coding opportunities, but can also cause buffer overflow in some specific intermediate nodes. Although some studies considered scattering of the flows dynamically in the network, they still face some limitations. This paper explains pros and cons of some prominent research in network coding and proposes FlexONC (Flexible and Opportunistic Network Coding) as a solution to such issues. The performance results show that FlexONC outperforms previous methods especially in worse quality networks, by better utilizing redundant packets spread in the network.

This paper studies the optimal placement problem in structural health monitoring (SHM) using wireless sensor networks (WSN). This problem is formulated as a refined multi-objective optimization problem with various constraints of connectivity and flow conservation conditions, while minimizing the energy consumption and maximizing the information quality are the objectives. To perform the multi-objective optimization, we modify the heuristic single objective power-aware sensor placement using the effective independence model (p-SPEM) algorithm introduced in [1]. In this paper, we design and analyze a multi-objective p-SPEM (mop-SPEM) algorithm for sensor node placement. The multi-objective formulation adds more flexibility because the energy consumption and the information quality can be easily traded-off. The mop-SPEM is simulated and compared with p-SPEM for a nine-storey building. Results show that mop-SPEM is able to trade-off the energy with the information quality by adjusting the relative weights of the objective functions.

Wireless sensor networks (WSNs) have shown to be an efficient solution for physical parameters monitoring and activity detection. WSNs are usually designed using single optimization by optimizing one objective function such as energy consumption taking some constraints into consideration. In multi-objective optimization (MOPT) multiple and often conflicting objectives need to be optimized while satisfying some constraints. This paper proposes MOPT-based routing and flow rate assignment methodologies for WSNs. The first methodology employs Karush-Kuhn-Tucker (KKT) conditions to find the optimal solution, while the second one is based on genetic algorithms (GA). A new formulation is introduced jointly minimize the energy and the delay. Performance metrics such as the average end-to-end delay and energy consumption are evaluated and compared with those of previous work, namely the hybrid geographical routing (HGR) algorithm. The proposed work helps network designers to address design procedures efficiently and increase the flexibility in the energy delay tradeoff for communications in WSNs.

In cognitive radio (CR) networks, secondary users (SUs) are allowed to opportunistically access the primary users (PUs) spectrum to improve the spectrum utilization; however, this increases the interference levels at the PUs. In this paper, we consider an orthogonal frequency division multiplexing OFDM-based CR network and investigate the tradeoff between increasing the SU transmission rate (hence improving the spectrum utilization) and reducing the interference levels at the PUs. We formulate a new multiobjective optimization (MOOP) problem that jointly maximizes the SU transmission rate and minimizes its transmit power, while imposing interference thresholds to the PUs. Further, we propose an algorithm to strike a balance between the SU transmission rate and the interference levels to the PUs. The proposed algorithm considers the practical scenario of knowing partial channel state information (CSI) of the links between the SU transmitter and the PUs receivers. Simulation results illustrate the performance of the proposed algorithm and its superiority when compared to the work in the literature.

A joint channel assignment and power allocation algorithm is presented for cognitive wireless networks, where primary and secondary users operate over the same frequency band at the same time. In this study, we take into consideration a constraint on the interference from secondary users towards primary users, as well as a constraint on the QoS of secondary users. The problem is formulated as a constrained utility maximization problem, for which we prove the existence and the uniqueness of the global optimum solution. Since the problem is NP-hard, we provide a novel heuristic algorithm that operates in two phases. Firstly, it admits all the incoming secondary users and allocates the available channels through a distributed and dynamic procedure, taking into account the interference constraint. Secondly, an iterative power control, which considers both constraints, is applied. In each iteration, a user removal algorithm is employed to reduce the number of admitted secondary users until a steady state is reached. The performance of the joint resource allocation algorithm is investigated in terms of the total number of admitted secondary users for several network parameters, such as the minimum QoS requirements and the interference constraint.

In this paper, the power loading problem for orthogonal frequency division multiplexing (OFDM) with imperfect channel estimation is investigated considering the trade-off between energy efficiency (EE) and spectral efficiency (SE). Unlike traditional research that uses the EE as an objective function and imposes constraints either on the SE or the achievable rate, we propound a multiobjective optimization approach that can flexibly switch between the EE and the SE functions or change the priority level of each function using a trade-off parameter. Our dynamic approach is more tractable than conventional approaches and more convenient to realistic communication applications and scenarios. The system model considers the path loss and shadowing effect in modeling the EE and SE metrics, in addition to taking the channel estimation error into account. We first solve the marginal problems of maximizing the EE and the SE individuality, and then prove that the multiobjective optimization of the EE and the SE is equivalent to a simple problem that maximizes the capacity and minimizes the total power consumption. Finally, we use numerical results to discuss the choice of the trade-off parameter and study the effect of the estimation error, transmission power budget and channel-to-noise ratio on the multiobjective optimization.

This paper adopts a multiobjective optimization (MOOP) approach to investigate the optimal link adaptation problem of orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems, where secondary users (SUs) can opportunistically access the spectrum of primary users (PUs). For such a scenario, we solve the problem of jointly maximizing the CR system throughput and minimizing its transmit power, subject to constraints on both SU and PUs. The optimization problem imposes predefined interference thresholds for the PUs, guarantees the SU quality of service in terms of a maximum bit-error-rate (BER), and satisfies a transmit power budget and a maximum number of allocated bits per subcarrier. Unlike most of the work in the literature that considers perfect SU spectrum sensing capabilities, the problem formulation takes into account errors due to imperfect sensing of the PUs bands. Closed-form expressions are obtained for the optimal bit and power allocations per SU subcarrier. Simulation results illustrate the performance of the proposed algorithm and demonstrate the superiority of the MOOP approach when compared to single optimization approaches presented in the literature, without additional complexity. Furthermore, results show that the interference thresholds at the PUs receivers can be severely exceeded due to the perfect spectrum sensing assumption or due to partial channel information on links between the SU and the PUs receivers. Additionally, the results show that the performance of the proposed algorithm approaches that of an exhaustive search for the discrete optimal allocations with a significantly reduced computational effort.

In this paper, we adopt a multiobjective optimization approach to jointly optimize the rate and power in OFDM-based cognitive radio (CR) systems. We propose a novel algorithm that jointly maximizes the OFDM-based CR system throughput and minimizes its transmit power, while guaranteeing a target bit error rate per subcarrier and a total transmit power threshold for the secondary user (SU), and restricting both co-channel and adjacent channel interferences to existing primary users (PUs) in a statistical manner. Since the interference constraints are met statistically, the SU transmitter does not require perfect channel-state-information (CSI) feedback from the PUs receivers. Closed-form expressions are derived for bit and power allocations per subcarrier. Simulation results illustrate the performance of the proposed algorithm and compare it to the case of perfect CSI. Further, the results show that the performance of the proposed algorithm approaches that of an exhaustive search for the discrete global optimal allocations with significantly reduced computational complexity.

This paper discusses the receiver design of a destination node supporting multiple antennas for an alternate-relaying decode-and-forward (DF) cooperative communication system. We exploit the structure of the received signal to develop an optimal data detection algorithm at the destination. It is shown that the optimal algorithm can be implemented by parallel detectors, each based on a family of Bahl, Cocke, Jelinek and Raviv (BCJR) algorithms. The proposed optimal algorithm requires to receive and store all packets before performing data detection. To avoid this, a sub-optimal algorithm is also proposed. Unlike the optimal algorithm, the sub-optimal one exploits two consecutive received packets to detect one packet. It turns out that the sub-optimal algorithm has less reduced delay, complexity, memory size and bandwidth loss with a slight increase of the bit-error-rate. The detection performance of the proposed algorithms is evaluated via Monte Carlo simulations, and the results demonstrate their effectiveness.

In this paper, we investigate the resource allocation problem (joint bit and power loading) of secondary users sharing the radio spectrum with primary users in cognitive radio networks. We consider the co-existence scenario where a secondary user is allowed to access the shared spectrum while guaranteeing tolerable interference to primary users. For such a scenario, we formulate and solve an optimization problem that jointly maximizes the secondary user throughput and minimizes its transmit power while satisfying target bit error rate per subcarrier and certain limits of co-channel and adjacent channel interferences to existing primary users. Simulation results are described that illustrate the performance of the proposed algorithm, and show its closeness to that of an exhaustive search for the equivalent discrete formulation.

This paper studies the joint rate and power allocation problem for OFDM-based cognitive radio systems where secondary users (SUs) can opportunistically access the spectrum of primary users (PUs). We propose a novel algorithm that jointly maximizes the OFDM-based cognitive radio system throughput and minimizes its transmit power, while guaranteeing a target bit error rate per subcarrier and restricting both co-channel interference (CCI) and adjacent channel interference (ACI) to existing primary users. Since estimating the instantaneous channel gains on the links between the SU transmitter and the PUs receivers is impractical, we assume only knowledge of the path loss on these links. Closed-form expressions are derived for the close-to-optimal bit and power distributions. Simulation results are described that illustrate the performance of the proposed scheme and show its closeness to that of an exhaustive search for the discrete optimal allocations. Further, the results quantify the violation ratio of both the CCI and ACI constraints at the PUs receivers due to the partial channel information. The effect of adding a fading margin to reduce the violation ratio is also studied.

This paper shows that the unwanted In-phase/quadrature (IQ) imbalance can be exploited to achieve a diversity gain for Alamouti space-time coding orthogonal frequency division multiplexing (AL-OFDM) systems. In addition, we propose a novel iterative algorithm to jointly estimate the channel impulse response (CIR) and IQ imbalance occurring at both the transmitter and receiver. A pilot sequence is employed for initial estimation and detection. Then, soft information is exchanged between the detector and the estimator iteratively in order to enhance the system performance. Simulation results confirm the effectiveness of the proposed algorithms.

Transmission collision is one of the main reasons of performance degradation in dense wireless sensor networks (WSNs). Transmission collision can cause throughput reduction, excessive delay and packet loss. One of the methods to minimize the probability of packet collision is the reduction of the collision area (area around sending nodes where collision may take place). In this study we investigate the problem of collision probability minimization through the use of cooperative transmissions and optimal power allocation in WSNs. We formulate the problem as a constrained optimization problem subject to an outage probability constraint. We determine the optimal transmission power of the source and the relay nodes which minimizes the collision area. Results show that the proposed technique significantly reduces the collision area while keeping the outage performance below the targeted value. Results also show that the proposed technique outperforms the direct transmission system as well as the cooperative system with equal transmission power.

A key issue in the full‐rate alternate‐relaying cooperative communication systems is the interference which is caused by the simultaneous transmission of the source and one of the relays. In this study, the authors propose maximum‐likelihood (ML) detectors to mitigate the interference in such systems. Unlike previous work in which interference cancellation is required at the destination, the authors exploit the interference signal as a beneficial resource to develop an optimal detector. It is shown that the optimal detector can be implemented by parallel Viterbi algorithms. The major drawback of the proposed optimal detector is the delay because the destination has to receive and store the entire frame before performing data detection. Owing to the inevitable delay restriction, a sub‐optimal detector is developed. In contrast with the optimal detector, the sub‐optimal detector exploits two consecutive received packets to decode one packet. It turns out that the sub‐optimal detector significantly reduces the required delay, memory size and bandwidth loss, with a slight increase of the bit‐error‐rate and the computational complexity. Extensive simulation results have been presented to demonstrate the effectiveness of the proposed detectors.

This paper proposes a novel low complexity joint bit and power suboptimal allocation algorithm for multicarrier systems operating in fading environments. The algorithm jointly maximizes the throughput and minimizes the transmitted power, while guaranteeing a target bit error rate (BER) per subcarrier and meeting a constraint on the total transmit power. Simulation results are described that illustrate the performance of the proposed scheme and demonstrate its superiority when compared to the algorithm in [4] with similar or reduced computational complexity. Furthermore, the results show that the performance of the proposed suboptimal algorithm approaches that of an optimal exhaustive search with significantly lower computational complexity.

In this paper, a novel joint bit and power loading algorithm is proposed for orthogonal frequency division multiplexing (OFDM) systems operating in fading environments. The algorithm jointly maximizes the throughput and minimizes the transmitted power, while guaranteeing a target average bit error rate (BER) and meeting a constraint on the total transmit power. Simulation results are described that illustrate the performance of the proposed scheme and demonstrate its superiority when compared to the algorithm in [1].

In this paper, a novel low complexity bit and power loading algorithm is formulated for orthogonal frequency division multiplexing (OFDM) systems operating in fading environments and in the presence of unknown interference. The proposed non-iterative algorithm jointly maximizes the throughput and minimizes the transmitted power, while guaranteeing a target bit error rate (BER) per subcarrier. Closed-form expressions are derived for the optimal bit and power distributions per subcarrier. The performance of the proposed algorithm is investigated through extensive simulations. A performance comparison with the algorithm shows the superiority of the proposed algorithm with reduced computational effort.

In this paper, we propose the use of bit-interleaved coded modulation iterative decoding (BICM-ID) in the full-rate decode and forward cooperative communication systems. At the destination, we exploit the interference signal to develop the optimal detector. It is shown that the proposed detector is implemented by parallel concatenating maximum a posteriori (MAP) algorithms and dampers to the decoders. The detector exchanges soft information between decoders and MAP algorithms in an iterative way, thus, improving communication reliability. Due to the inevitable delay restriction of the optimal detector, a sub-optimal detector is developed. Extensive simulation results are presented to demonstrate the effectiveness of proposed detectors. Results indicate that the proposed detectors outperform conventional relaying detectors in terms of their bit error rate.

This paper proposes a novel joint bit and power allocation algorithm for multicarrier systems operating in fading environments. The algorithm jointly maximizes the throughput and minimizes the transmitted power, while guaranteeing a target average bit error rate (BER). Simulation results are described and they illustrate the performance of the proposed scheme and demonstrate its superiority with respect to existing schemes.

In this paper, we consider a network-coded cooperative wireless network, where users mutually pair among themselves to realize network coding. We consider a multi-user environment, where users transmit to a common destination in the absence of dedicated relays. Two nodes constituting a pair periodically swap the roles of the source and relay to mutually achieve spatial diversity. As such, conditioned on the successful detection of the source''s packet, a networkcoded packet is formed at the relay by a linear combination of its own packet and the source''s packet. A single transmission of this network-coded packet therefore helps both nodes to achieve diversity gain. In this work, we address the important problem of the mutual pairing of users, which directly governs the overall network performance. We first propose an optimal user pairing algorithm in order to maximize the total network capacity. To simplify the pairing process, we subsequently propose computationally simpler, heuristic user pairing schemes. In particular, we propose max-max pairing to maximize the network capacity, and max-min pairing to minimize the outage probability. Performance analysis of the proposed optimal and heuristic user pairing schemes is performed in terms of the average capacity, average outage probability, and user-fairness.

In this paper, we propose maximum likelihood (ML) detectors to mitigate the influence of the interference signal for the two-relays full- rate cooperative systems. At the relays, the proposed ML detector is employed by averaging out the interference signal. Furthermore, at the destination, we exploit the interference signal to develop the ML detector. It is shown that the optimal detector is implemented by parallel Viterbi algorithms. The major drawback of the proposed optimal detector is the delay, i.e a destination has to receive and store the whole received packets before performing data detection. Due to the inevitable delay restriction, sub-optimal detector is developed. In contrast with the optimal detector, the sub-optimal detector exploits two consecutive received packets to decode one packet. It turns out that the sub-optimal detector outperforms the optimal detector in terms of the required delay, memory size, bandwidth loss, and computational complexity. Extensive simulation results have been presented to demonstrate the effectiveness of the proposed detectors. Results indicate that the proposed detectors outperform conventional relaying detectors in terms of their bit error rate and packet error rate.

A key issue in the full-rate two-relay cooperative communication systems is the interference which is caused by the simultaneous transmission of the source and one of the relays at any time. In this paper, we exploit the interference signal at the destination to develop a maximum likelihood (ML) detector for decode and forward full-rate cooperative systems. It is shown that the Viterbi algorithm can be employed to find the ML solution. To reduce the complexity of the proposed ML detector, a sub-optimal detector is also introduced. Further, we propose a ML interference cancellation scheme at the relays. The performance of the proposed schemes is evaluated through Monte Carlo simulations. Results indicate that the proposed schemes outperform direct transmission and conventional relaying schemes in terms of their bit error rate.

The transport reliability is a very important feature in Wireless Sensor Networks (WSN), particularly in some critical applications such as forest fire detection. In this paper, we propose reliability enhancement mechanisms in order to improve the reliability of three MAC protocols we proposed in for forest fire detection. We evaluate the reliability performance analytically and by simulation. Results show that a significant enhancement in the transport reliability is achieved due to the proposed mechanisms. Furthermore, we show that the reliability enhancement is achieved with a very slight increase in the energy consumption and packet delay.

Cooperative diversity is achieved by utilizing neighboring terminals as relays. These relays can forward copies of the same signal to the destination using independent paths to provide spatial diversity. One of the main challenges of cooperative diversity is the throughput loss due to the extra resources needed for relaying. Adaptive modulation can be used to convert the Signal-to-Noise Ratio (SNR) gain (from the cooperative diversity) to throughput enhancement in order to compensate for the throughput loss. The availability of accurate Channel State Information (CSI) is essential for cooperative-diversity systems. However, perfect CSI is not always available in wireless systems. In this paper, we determine analytically the average throughput and bit error rate (BER) of cooperative-diversity systems with adaptive modulation and imperfect CSI over Rayleigh fading channel. Simulation results are also used for verification. Results show that imperfect CSI slightly lowers the throughput gain of the cooperative-diversity system. However, the cooperative-diversity system with imperfect CSI still outperforms the direct transmission.

Cooperative-diversity has recently been proposed as an efficient technique to form virtual antenna arrays without using collocated multiple antennas at the transmitters or receivers. Cooperative-diversity networks use the neighbour nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative-diversity networks make an inefficient use of the channels because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental-relaying cooperative-diversity has been proposed to save the channels by restricting the relaying process to the bad channel conditions only. Incremental-relaying cooperative-diversity networks exploit limited feedback from the destination terminal, for example, a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback, in this case only, the relay retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the relay. In this study, the authors study the end-to-end performance of un-coded incremental-relaying cooperative-diversity networks using decode-and-forward and amplify-and-forward relaying over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate, the signal-to-noise ratio (SNR) outage probability and average achievable rate are determined. Results show that the un-coded incremental-relaying cooperative-diversity can achieve the maximum possible diversity, compared with the regular cooperative-diversity networks, with higher channel utilisation.

In this study, the performances analysis of cooperative-diversity networks using adaptive decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels is investigated. The authors derive exact and approximate closed-form expressions for the error probability, outage probability and average channel capacity, and analyse their dependence on the channel parameters. In adaptive DF relaying, among M relays that can participate, only C relays (C≤M), with good channels to the source, DF (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using maximum ratio combining technique. The authors derive a closed-form expression for the the moment generating function of the total signal-to-noise ratio (SNR) at the destination node. Then, the authors find an exact closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the exact closed-form expressions of the performance metrics. Such closed-form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Since exact expressions are complicated, the authors have introduced simple approximate expressions for the error and outage probabilities where these expressions explicitly show the diversity order. Computer simulations are used to validate our analytical results. Results show the significant performance improvement because of the use of the adaptive DF cooperative diversity. Also, results indicate that increasing the number of relays will not always decrease the outage probability.

In this paper, we introduce a comprehensive analysis of the incremental-best-relay cooperative diversity, in which we exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the best relay among M available relays retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the best relay. Furthermore, we study the end-to-end performance of the incremental-best-relay cooperative-diversity networks using decode-and-forward and amplify-and-forward relaying over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate, the outage probability and average channel capacity are determined. Results show that the incremental-best-relay cooperative diversity can achieve the maximum possible diversity order, compared with the regular cooperative-diversity networks, with higher channel utilization. In particular, the incremental-best-relay technique can achieve M+1 diversity order at low signal-to noise ratio (SNR) and considerable virtual array gain at high SNR.

Performance analysis of cooperative multiple-input multiple-output (MIMO) relaying system with a single relay is discussed in this paper. The MIMO scheme is based on Alamouti space-time block coding (STBC) over Rayleigh flat fading channels. The source node, equipped with two transmit antennas, simply broadcasts each STBC code to the relay and the destination nodes. Then, the relay node, equipped with multiple antennas, amplifies-and-forwards (AF) the received STBC codes. Finally, the destination node uses maximum ratio combining (MRC) and exploits the diversity gain obtained through the direct and the indirect links simultaneously. Lower bounds of the symbol error probability (SEP) and the outage probability are derived using the moment generating function (MGF) of the total signal-to-noise ratio (SNR) for a particular signal of M-ary-quadrature-amplitude modulation (M-QAM). Subsequently, simulation results are provided to verify the validity of the analytical results.

Outage analysis of cooperative space-time block coding (STBC) multiple-input multiple-output (MIMO) relaying system with a single relay is discussed in this paper. The source node, equipped with two transmit antennas, broadcasts each STBC code to the relay and the destination nodes. Then, the relay node also equipped with multiple antennas, amplifies-and-forwards (AF) the received STBC codes. Finally, the destination node uses maximum ratio combining (MRC) and exploits the diversity gain obtained through the direct and the indirect links simultaneously. Lower bounds of the outage probability is derived using the moment generating function (MGF) of the total signal-to-noise ratio (SNR) for a particular signal of M-ary-quadrature-amplitude modulation (M-QAM). Simulation results are provided to verify the validity of the analytical results.

This paper analyzes the performance of Proportional Fair (PF) scheduling in Orthogonal Frequency Division Multiple Access (OFDMA) wireless systems. OFDMA represents a promising multiple access scheme for high-data-rate transmission over wireless channels as it combines the Orthogonal Frequency Division Multiplexing (OFDM) modulation and subcarrier allocation. On the other hand, the PF scheduling is an efficient resource allocation scheme with good fairness characteristics. Consequently, OFDMA with PF scheduling represents an attractive solution to deliver high data rate services to multiple users simultaneously with a high degree of fairness. We investigate a two dimensional (time slot and frequency subcarrier) PF scheduling algorithm for OFDMA systems, and evaluate its performance analytically and by simulation. We derive closed-form expressions for the average throughput and throughput fairness index. Computer simulations are used for verification. The analytical results agree well with the results from simulations, which verifies the correctness and accuracy of the analytical expressions.

In this paper, the use of adaptive source transmission with amplify-and-forward best relaying selection scheme is proposed. Three different adaptive techniques are considered: (i) optimal simultaneous power and rate adaptation; (ii) constant power with optimal rate adaptation; (iii) channel inversion with fixed rate. The capacity upper bounds of these adaptive protocols are derived for the relay-selection amplify-and-forward cooperative network over independent and identical (i.i.d) and independent and non-identical (i.n.d) Rayleigh fading channels. The capacity analysis is based on an upper bound on the effective received signal-to-noise ratio (SNR). It is shown that at high SNR the optimal simultaneous power and rate adaptation and the optimal rate adaptation with constant power provide roughly the same capacity. Channel inversion is shown to suffer from a deterioration in capacity relative to the other adaptive techniques.

We consider adaptive decode-and-forward (DF) cooperative-diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). In this paper, we analyze the system where N multiple relays that have the strongest signal strength at the destination are selected out of M relays and forward their received data from the source node to the destination node. We derive closed-form expressions for the average symbol error probability, the outage probability and the average channel capacity. In particular, closed-form expression for the moment generating function of the SNR at the destination node is determined. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Simulation results are also given to verify the analytical results.

Cooperative diversity is a relatively new technique that can be used to improve the performance of the wireless networks. The main advantage of this technique is that the diversity gain can be achieved without the need to install multiple antennas at the transmitter or the receiver. In this paper, we investigate the performance of the best-relay selection scheme where the "best" relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the number of relays (M). The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio at the destination node. A general mathematical probability model is developed to study the outage performance of the best-relay selection adaptive decode-and-forward cooperative networks. In particular, closed-form expressions for the outage probability and average channel capacity are derived. Results show that the best-relay selection not only reduces the amount of required resources but also can maintain a full diversity order.

In this letter, we consider the adaptive decode-and-forward (DF) and amplify-and-forward (AF) cooperative-diversity systems with the Nthbest-relay selection scheme. In the best-relay selection scheme, from the set of M relays the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the Nth best relay. We derive closed-form expressions for the symbol error probability, outage probability and asymptotic error probability. In particular, we derive a closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function (MGF) of the output SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. All these expressions are derived over identical and non-identical Rayleigh fading channels. Results show that with the Nthbest relay the diversity order is equal to (M - N + 2) where M is the number of relays.

Cooperative-diversity networks have recently been proposed as an effective technique to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider the adaptive decode-and-forward (DF) cooperative-diversity system with the Nth best-relay selection scheme. In the best-relay selection scheme, from the set of M relays the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the Nth best relay. We derive closed-form expressions for the symbol error probability, outage probability and channel capacity. In particular, we derive a closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function (MGF) of the output SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. Results show that with the Nth best relay the diversity order is equal to (M - N + 2) where M is the number of relays. Simulation results are also given to verify the analytical results.

We consider power allocation (PA) and relay positioning in a dual-hop decode-and-forward relaying system over Nakagami-m fading channels. We investigate adaptive power allocation (PA) with fixed relay location, optimal relay location with fixed power allocation and joint optimization of the PA and relay location under transmit power constraint in order to minimize outage probability and average error probability upper bound. Results show that the analyzed adaptive algorithms outperform uniform algorithms and direct transmission. It is also found that as the source destination channel is getting better, the less power will be needed to allocate to the relay node in order to satisfy the optimization criteria. Numerical results are presented to verify our analysis.

In this paper, we investigate amplify-and-forward (AF) incremental-best-relay cooperative diversity to make efficient use of the channel spectrum by exploiting a limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the best relay among M available relays retransmits the source signal in an attempt to exploit spatial diversity by combining the signals received at the destination from the source and the best relay. Closed-form expressions for the bit error rate, the outage probability and average channel capacity are determined over independent non-identical Rayleigh fading channels. Results show that the AF incremental-best-relay cooperative diversity can achieve the maximum possible diversity order, compared with the conventional cooperative-diversity networks, with higher channel utilization. In particular, the AF incremental-best-relay technique can achieve M + 1 diversity order at low signal-to noise ratio (SNR) and and exhibits a 20 to 30 dB gain relative to direct transmission, assuming single-antenna terminals at high SNR.

We investigate the incremental relaying protocol in conjunction with relay-selection cooperative diversity networks with an aim to make efficient use of the degrees of freedom of the channels by exploiting a limited feedback signal from the destination. In particular, whenever the direct link from the source to the destination is not favorable to decoding, the destination will request the help from the best relay. The performance of the incremental-relay-selection decode-and-forward technique over independent non-identical Rayleigh fading channels is derived in terms of average bit error probability, outage probability and average channel capacity. The analytic results show that the system assisted by the selection relaying can achieve full diversity at low SNR regime and exhibits a 20 to 30 dB gain relative to direct transmission, assuming single-antenna terminals.

Cooperative-diversity networks have been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider the amplify-and-forward cooperative-diversity system with theNthbest-relay selection scheme. In the best-relay selection scheme, the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally theNthbest relay. We derive closed-form expressions for the symbol error probability, outage probability and channel capacity. In particular, we derive a closed-form expression for the probability density function of the signal-to-noise ratio of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function of the total SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. Results show that with theNthbest relay the diversity order is equal to (M-N+ 2) whereMis the number of relays. Simulation results are also given to verify the analytical results.

We consider an amplify-and-forward (AF) cooperative-diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays), in this paper, we analyze the system where N multiple relays that have the strongest signal strength at the destination are selected out of M relays and forward their received data from the source node to the destination node. We derive closed-form expressions for the average symbol error probability, the outage probability, the average channel capacity, the average signal-to-noise ratio (SNR), the amount of fading, and the SNR moments. In particular, closed-form expression for the moment generating function of the SNR at the destination node is determined. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Simulation results are also given to verify the analytical results. Results show that increasing N will slightly improves the error performance and degrade the outage probability and average channel capacity. In particular, N = M gives the best performance in terms of error performance and N = 1 (the best relay) gives the best performance in terms of outage probability and average channel capacity.

In this paper, the performances analysis of cooperative-diversity networks using adaptive decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels is investigated. We derive closed-form expressions for the error probability, outage probability and average channel capacity, and analyze their dependence on the channel parameters. In adaptive DF relaying, among M relays that can participate, only C relays (C les M), with good channels to the source, decode and forward (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using maximum ratio combining (MRC) technique. We derive a closed-form expression for the the moment generating function (MGF) of the total signal-to-noise ratio (SNR) at the destination node. Then, we find a closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the closed-form expressions of the performance metrics. Computer simulations are used to validate our analytical results. Results show the significant performance improvement due to the use of the adaptive DF cooperative diversity. Also, results indicate that increasing the number of relays will not always decrease the outage probability.

Cooperative-diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. Cooperative-diversity networks use the neighbor nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative-diversity networks make an inefficient use of the channel resources because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental relaying cooperative diversity has been proposed to save the channel resources by restricting the relaying process to the bad channel conditions only. Incremental relaying cooperative relaying networks exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the relay retransmits in an attempt to exploit spatial diversity by combining the signals that the destination receives from the source and the relay. In this paper, we study the end-to-end performance of incremental relaying cooperative-diversity networks using decode-and-forward relays over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate and the signal-to-noise ratio (SNR) outage probability are determined. Results show that the incremental relaying cooperative diversity can achieve the maximum possible diversity, compared with the regular cooperative-diversity networks, with higher throughput.

Cooperative diversity is a promising technology for future wireless networks. In this paper, we derive the average bit error rate (BER) and outage probability (Pout) for differential equal gain combining (EGC) in cooperative diversity networks. The considered network uses adaptive decode-and-forward (DF) relaying over independent non-identical Nakagami-m fading channels. In adaptive DF relaying among M relays, that can participate, only C relays (C les M), with good channels to the source, decode and then forward (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using differential EGC. We first derive a simple exact expression for the equivalent SNR at the destination. Second, we derive the expressions of the PDF and the MGF of this equivalent total SNR at the destination. Then the MGF is used to determine the error and outage probabilities of adaptive DF with an arbitrary number of relays. Furthermore, we found (in terms of MGF) the SNR moments, the average signal-to-noise ratio (SNR) and the amount of fading. Computer simulations are used to validate our analytical results. Results show the significant performance improvement due to the use of the adaptive DF cooperative diversity. Also, results show that the performance of the adaptive DF differential EGC is comparable to the adaptive DF maximum ratio combining (MRC) performance.

In this paper, we present closed form expressions for tight lower bounds of the performance of dual-hop non- regenerative relaying over independent non-identical Weibull fading channels. Since it is hard to find a closed form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) for the Weibull fading distribution, we use an approximate value instead. Novel closed form expressions for the PDF, outage probability and the moments of the approximate value of the SNR at the destination are derived. Also, the average SNR and amount of fading are determined. Moreover, closed form expressions (in terms of the tabulated Meijer's G-function) are found for the average symbol error probability (for several modulations schemes) as well as the Shannon capacity. It should be noted that the Meijer's G-function is widely available in many scientific software packages, such as MATHEMATICAL and MAPLEreg. Finally, simulations results are also shown to verify the analytical results.

Link adaptation techniques aim to maximise the quality of service and resource utilisation in wireless networks. However, fairness must be taken into consideration, particularly, in low-mobility environments where the channel dynamic variation is small. The authors propose and analyse three link adaptation techniques [using joint power control (PC) and adaptive coding and modulation (ACM)] for fairness enhancement. In the first technique, called aggregate throughput maximisation with fairness constraint, the authors formulate the fairness problem as a constrained optimisation problem where the authors try to maximise the aggregate throughput subject to the throughput fairness constraint. In order to solve the optimisation problem, the authors convert the constrained optimisation problem to an unconstrained optimisation one using the penalty method. Then, the unconstrained optimisation problem is solved using the steepest descent technique. The second techniques, called individual throughput balancing, tries to equalise the individual throughput by using a higher throughput level for disadvantaged users and using a lower throughput level for advantaged users. Finally, the third technique, called adaptive virtual maximum power constraint, uses virtual maximum power cap, which is lower than the real maximum power cap. The virtual maximum power cap of each user is variable and it adapts based on the user's individual throughput to compensate disadvantaged users. The authors analyse the three proposed techniques in terms of the throughput fairness and the throughput efficiency and compare them with three basic link adaptation techniques (PC, ACM, and joint PC and ACM). The three proposed techniques are shown to be able to enhance the fairness with different degrees and with different levels of aggregate throughput degradation.

Cooperative diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider adaptive decode-and-forward cooperative diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). In this letter, we investigate the performance of the best-relay selection scheme where the best relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the total number of relays. The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio at the destination node. We developed a general analytical model to analyze the performance of the adaptive decode-and-forward cooperative networks with best-relay selection. In particular, exact closed-form expressions for the error probability and Shannon capacity are derived over independent and nonidentical Rayleigh fading channels. Results show that the best-relay selection not only reduces the number of required channels but also can maintain a full diversity order.

Cooperative diversity is a promising technology for future wireless networks. In this paper, we derive exact closed-form expressions for the average bit error rate (BER) and outage probability (Pout) for differential equal gain combining (EGC) in cooperative diversity networks. The considered network uses amplify-and-forward relaying over independent non-identical Nakagami-m fading channels. The performance metrics (BER and Pout) are derived using the moment generating function (MGF) method. Furthermore, we found (in terms of MGF) the SNR moments, the average signal-to-noise ratio (SNR) and amount of fading. Numerical results show that the differential EGC can benefit from the path-loss reduction and outperform the traditional multiple-input single output (MISO) system. Also, numerical results show that the performance of the differential EGC is comparable to the maximum ratio combining (MRC) performance.

Cooperative diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. Cooperative diversity networks use the neighbor nodes to assist the source by sending the source information to the destination for achieving spatial diversity. Regular cooperative diversity networks make an inefficient use of the channel resources because relays forward the source signal to the destination every time regardless of the channel conditions. Incremental relaying cooperative diversity has been proposed to save the channel resources by restricting the relaying process to the bad channel conditions only [1]. Incremental relaying cooperative relaying networks exploit limited feedback from the destination terminal, e.g., a single bit indicating the success or failure of the direct transmission. If the destination provides a negative acknowledgment via feedback; in this case only, the relay retransmits in an attempt to exploit spatial diversity by combining the signals that the destination receives from the source and the relay. In this paper, we study the end-to-end performance of incremental relaying cooperative diversity networks using amplify-and-forward relays over independent non-identical Rayleigh fading channels. Closed-form expressions for the bit error rate and the signal-to-noise ratio (SNR) outage probability are determined. Results show that the incremental relaying cooperative diversity can achieve the maximum possible diversity, compared with the regular cooperative diversity networks, with higher channel utilization.

In multihop cellular networks (MCN), the user nodes can act as relays and forward other nodes' traffic to/from base stations. There are several advantages of MCN such as the improved signal quality and higher coverage. However, it is known that multihop relaying networks require extra radio resources. Therefore the performance of MCN depends to a great extent on the availability of adequate radio resources. The performance of a time division multiple access (TDMA)-based multihop fixed cellular network is analysed with highlighting the dependence of the system performance on the amount of available radio resources, namely, the number of frequency carriers. Results show that in a fixed cellular network, the multihop architecture significantly outperforms the traditional single-hop architecture in terms of the outage probability and throughput if an adequate amount of frequency carriers is available in the network. Otherwise, the multihop fixed cellular networks architecture loses its superiority and might even lead to performance degradation, particularly at high loading levels.

In this paper, we present closed form expressions for tight lower bounds of the performance of dual-hop non- regenerative relaying over independent non-identical generalized gamma fading channels. The generalized gamma distribution is very versatile and accurately approximates many of the commonly used channel models for multi-path, shadow, and composite fading. Since it is hard to find a closed form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) for the generalized gamma distribution, we use an approximate value instead. Novel closed form expressions for the PDF, outage probability and the moments of the approximate value of the SNR at the destination are derived. Also, the average SNR and amount of fading are determined. Moreover, closed form expressions (in terms of the tabulated Meijer's G-function) are found for the average symbol error probability (for several modulations schemes) as well as the Shannon capacity. It should be noted that the Meijer's G-function is widely available in many scientific software packages, such as MATHEMATICAreg and MAPLEreg. Finally, simulations results are also shown to verify the analytical results.

This paper analyzes the end-to-end bit error rate performance of cooperative diversity networks using decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels. We derive a closed-form expression for the error rate and analyze its dependence on the channel parameters. In DF cooperative diversity, a relay detects the received signal and then relays the signal to the destination. The destination combines the two signals received from the source and relay. We assume here that the relay decides independently (based on the received signal quality at the relay) whether or not to forward the signal to the destination. Computer simulations are used to validate our analytical results. Results show the significant performance improvement due to the use of the DF cooperative diversity. Also, results indicate that the source-relay channel has the most influence on the error performance.

Cooperative diversity is a promising technology for future wireless networks. In this paper, based on the moment generating function (MGF), we derive exact closed-form expressions for the average bit error rate (BER), the amount of fading (AF), and outage probability (Pout) for cooperative diversity networks withamplify-and-forwardrelaying overRayleigh-fading channel using differentially- non-coherent equal gain combining (EGC) technique. We show that this scheme (differentially-non-coherent EGC) achieves a diversity order of 2 at highSNR. The main advantage of this scheme is that it does not need channel state. information of the transmission links at the relay and destination nodes. This feature reduces the design and implementation complexity. Furthermore, we study in this paper the impact of the relay location on the system performance.

Maximizing the aggregate throughput of wireless cellular networks using link adaptation techniques (e.g. adaptive modulation and power control) has got a great deal of attention (e.g., [5]). However, the fairness of individual throughput allocation has not been well addressed yet. The fairness problem of link adaptation techniques has recently attracted some attention (e.g., [6, 9]) but the problem still needs deeper analysis and more efficient solutions. This paper proposes a new scheme that finds the optimal power and modulation level that maximizes the aggregate throughput while taking the individual throughput fairness into consideration. The problem is formulated as a constrained optimization problem and then converted to an unconstrained optimization one by including the constraint as a penalty term in the objective function. The unconstrained optimization problem is solved using the steepest descent technique. Results show that the proposed scheme is always able to achieve the fairness requirements with high aggregate throughput.

Abstract This paper proposes a transmission‐scheduling algorithm for interference management in broadband wireless access networks. The algorithm aims to minimize the cochannel interference using basestation coordination while still maintaining the other quality of service (QoS) requirements such as packet delay, throughput and packet loss. The interference reduction is achieved by avoiding (or minimizing) concurrent transmission of potential dominant interferers. Dynamic slot allocation based on traffic information in other cells/sectors is employed. In order to implement the algorithm in a distributed manner, basestations (BSs) have to exchange traffic information. Both real‐time and non‐real‐time services are considered in this work. Results show that significant reduction in the packet error rate can be achieved without increasing the packet delay at low to medium loading values and with a higher but acceptable packet delay at high loading values. Since ARQ schemes can also be used for packet error rate reduction, we compare the performance of the proposed scheme with that of ARQ. Results indicate that although ARQ is more effective in reducing packet error rate, the proposed algorithm incurs much less packet delay particularly at medium to high loading. Copyright © 2006 John Wiley & Sons, Ltd.

In this paper, we present a novel transmission scheduling scheme for fixed broadband wireless access (FBWA) networks. In order to mitigate high co-channel interference resulting from dense reuse of frequency, scheduling schemes often consider interference management issues as an essential part. To that end, a series of literature has been published recently, where a group of base stations form an interference group, and scheduling scheme deployed in the group allows only one base station to transmit at a time. As a result of time orthogonality in transmissions, the co-channel interference and hence the packet error rate can be reduced. However, prohibiting concurrent transmissions in these orthogonal schemes introduces higher end-to-end packet delay which might not be desirable for real-time traffic such as voice and video. Our proposed scheme aims to improve delay performance as well as to ensure better resource utilization in such schemes in several ways, most notably by introducing opportunistic non-orthogonality in transmissions, incorporating channel state based scheduling decisions, and employing adaptive modulation and coding.

Call admission control (CAC) is essential to guarantee the signal quality in CDMA systems. Signal-to-interference-and-noise ratio (SINR) is used as the criterion for user admission by comparing the SINR with a predefined threshold value (SINR/sub th/). Lowering this threshold level is desirable to reduce the blocking rate. However, a lower bound of SINR/sub th/ is vital to keep the outage probability (P/sub out/) below a maximum value. In this paper, we derive this lower bound of SINRth (SINR/sub th-lb/) for multi-class CDMA systems with imperfect power control. SINR/sub th-lb/ of class i (SINR/sub th-lb/(i), i=1, 2,...., L) is determined by finding the relationship between P/sub out/(i) (i=1, 2,...., L) and SINR/sub th/(i) (i=1, 2,...., L) where L is the number of classes. Then, SINR/sub th-lb/(i) is determined as the lowest value of SINR/sub th/(i) that keeps the outage probability of all classes below the corresponding maximum values.

This work analyzes the impact of having more than one frequency channel on outage probability and node throughput in TDMA-based broadband fixed cellular multihop networks. The scenario considered is a low node density, start-up network with inadequate single-hop coverage. In this scenario the user terminals themselves act as relays, therefore, there are no additional relays deployed by the service provider: besides, no separate relaying channels are used (this scenario ensures a fair comparison between the multihop cellular network considered here and the traditional single-hop cellular network). In a situation where there is outage with a single-hop due to poor coverage, a suitable multihop route with minimum number of hops is sought. It is observed that as the number of available channels increases the coverage is enhanced remarkably; in addition, the average node throughput is increased as well although no explicit attempt for throughput maximization is made during the search for the multihop routes.

This paper proposes a joint adaptive rate selection and power control algorithm for broadband TDMA/TDM wireless networks. The proposed algorithm is a modified, enhanced, and more robust version of the selective power control with active link protection (SPC-ALP) algorithm proposed for adaptive transmission rate and power control in CDMA networks [R.Jantti and S. Kim, 2000]. Unlike SPC-ALP, the proposed algorithm uses adaptive coding and modulation (instead of variable spreading gain) for transmission rate control. In addition, the proposed algorithm is different in two aspects; the first one is the inclusion of the cochannel interferer assistance mode, while the second one is the use of the signal quality as a criterion for user removal. Results show that the proposed algorithm outperforms SPC-ALP in terms of the net throughput and signal quality measures such as the outage probability and frame error rate. Channel reallocation is also studied and found to be very effective in enhancing the system performance particularly at low to medium loading.

The system capacity of TDMA systems can be enhanced by utilizing the slow frequency hopping feature. More capacity gain can be achieved if interference reduction techniques such as smart antennas and discontinuous transmission are used. This paper addresses the capacity gain in the downlink due to the use of smart antennas in an FH-TDMA cellular system. We estimate the system capacity analytically and by simulation. Multiple switched beam smart antennas are utilized in the study. Perfect power control and discontinuous transmission (using voice activity) are assumed in the simulation and in theoretical analysis. The TDMA system is assumed to be GSM-like. However the analysis is valid for any TDMA system.