Cooperative Wireless Communication Research Articles

Impact of Co-Channel Interference and Vehicles as Obstacles on Full-Duplex V2V Cooperative Wireless Network

Vehicular communications, with their promise to provide drivers and passengers with a wide range of applications, are attracting significant attention from both research and industry. In this paper, we study the performance of full duplex amplify and forward (AF) relaying-based vehicle-to-vehicle (V2V) cooperative wireless communications over Nakagami- $m$ fading channels. In such systems, in practical scenarios, the communication link inevitably suffers from co-channel interference, residual self-interference, and blockage from other vehicles on the road. In this context, we consider independent and not necessarily identically distributed (i.n.i.d) Nakagami- $m$ fading channels and derive novel exact and asymptotic outage probabilities of the exact equivalent and approximated signal-to-interference-plus-noise ratio (SINR), respectively. Building on this, the end-to-end exact and asymptotic outage probabilities are expressed in terms of the blockage probability and then used to evaluate the throughput of the proposed system. In addition, a lower bound to the symbol error rate of the considered system is also derived. Monte-Carlo simulation results are provided to demonstrate the accuracy of the proposed analytical expressions. The results demonstrate the significant impact of the considered interference and blockage on the system performance. Precisely, it is shown that the system performance is degraded when the average height of the obstacles is increased. This highlights the importance of taking into account these phenomena in the performance evaluation in order to assess the practical limit of V2V cooperative wireless communications.

Bit error rate performance analysis of AC-MAP in multiple input single output wireless relay network

In this paper, we propose a joint decoding scheme called AC-MAP decoder for multiple input single output (MISO) wireless cooperative communication network that consists of single source, single relay, and single destination. The proposed scheme is based on both Alamouti combining (AC) scheme and maximum a posteriori (MAP) decoder and is used to estimate the data at the destination. The AC-MAP decoder is optimal in the sense that it minimizes the end-to-end bit error rate (BER). In order to analyze performance of the proposed decoder, we derive a closed form expression for the upper bound (UB) on the end-to-end error probability. Distances between system nodes, transmit energy, and channel noise and fading effects are considered in the derivation of the UB. Numerical results show that the closed form UB is very tight and it almost coincides with the exact BER results obtained from simulations. Therefore, we use the derived UB expression to study the effects of the relay position on the BER performance and to find the optimal location of the relay node.

Ergodic Capacity Analysis of Full Duplex Relaying in the Presence of Co-Channel Interference in V2V Communications.

We analyze the ergodic capacity of a dual-hop full duplex amplify-and-forward (AF) vehicle-to-vehicle (V2V) cooperative relaying system over Nakagami-m fading channels. In this context, the impacts of self-interference (SI) at the relay and co-channel interference (CCI) at the destination are taken into account in this analysis. Precisely, based on the analysis of the moment generating function (MGF) of the signal-to-interference-plus-noise ratio (SINR), new exact and lower bound expressions for the ergodic capacity are derived. The ergodic capacity upper bound is also derived based on the asymptotic outage probability of the approximated SINR. Monte-Carlo simulation results are presented to corroborate the derived analytical results. Our results show the significant impact of the considered interferences on the system performance. It is shown that the ergodic capacity is degraded when the average SI at the relay and/or the average CCI at the destination is increased. This highlights the importance of taking these phenomena into account in the performance evaluation in order to assess the practical limit of full duplex relaying (FDR) cooperative wireless communications. Interestingly, it is also observed that FDR with SI and CCI still shows a higher ergodic capacity than the interference-free half duplex relaying, especially at medium to high signal-to-noise ratios (SNRs).

Uniquely Decodable Codes for Physical-Layer Network Coding in Wireless Cooperative Communications

Physical-layer network coding (PNC) has received much attention, both from academia and industry lately, since it takes advantages of multiple-access signals. Because of a reduced number of time slots (TSs), PNC is capable of improving throughput significantly, especially for a typical 3-node network consisting of 2 user terminals and 1 relay node. However, a network with $M$ nodes ( $M>3$ ) and without adopting additional techniques needs $(2M-2)$ TSs to realize information exchange among all the nodes, since network coding is unable to distinguish between users at the relay node. This paper proposes uniquely decodable codes (UDCs) for PNC in wireless cooperative communications. The proposed UDC requires only two TSs for information exchange irrespective of the number of nodes in the network. This paper also investigates the amplify-and-forward and decode-and-forward modes for UDC-based PNC. The bit error rate and throughput of the proposed schemes are analyzed in this paper. Using simulation results, we demonstrate that our theoretical results align well with the simulation results.

Delay-Optimal Cooperation Policy in a Slotted Aloha Full-Duplex Wireless Network: Static Approach

We consider a cooperative wireless communication network comprising two full-duplex (FD) nodes transmitting to a common destination based on slotted Aloha protocol. Each node has exogenous arrivals and also may relay some of the unsuccessfully transmitted packets of the other node. In this article, we find the optimal static policies of nodes in order to minimize the sum of the average transmission delays, while the average transmission delay of each node is constrained. The static policy of each node specifies the probability of accepting an unsuccessfully transmitted packet of the other node and how the node prioritizes its transmissions. We show that in the optimal policies, just the node with the better link to destination may relay the packets of the other node. We derive optimal acceptance probability of the relaying node in closed form, and show that it should transmit the packets of the other node first. Moreover, we prove that the noncooperation policy is optimal if the ratio of successful transmission rates of nodes does not exceed the Golden ratio. We also show that FD capability of nodes is helpful only when full-acceptance is the optimal policy. Efficiency of the attained optimal policy is illustrated by numerical results.

A comprehensive methodology to evaluate the performance of a cooperative wireless network

Performance evaluation of a cooperative wireless communication network depends on several parameters. Many of the studies, in fact, take a limited number of performance metrics individually to reach a conclusion about the performance of a network. Besides, in general, some performance metrics might be in conflict. Thus, ignoring the combined effect of all performance criteria in the network may lead to an incorrect conception of the overall communication performance of the network. Therefore, in this study, a comprehensive evaluation methodology in terms of various metrics is proposed to calculate the performance of a cooperative wireless communication network deployment using a real terrain map. The proposed methodology, based on desirability functions, is discussed in terms of signal quality, signal quality with hopping, average number of hopping, hopping duty, and deployment altitude. In addition to individual scores for each performance criterion, an overall performance score is also obtained. Furthermore, the effects of the desirability function's ambition factor, terrain characteristics, and connectivity requirement rate on the score are also presented. The simulation results show that the desirability function-based performance evaluation approach could support a flexible evaluation as well as provide an agreement on the conflicting performance metrics.

Performance analysis of bi-directional relay selection strategy for wireless cooperative communications

This paper proposes a new two-way double-relay selection strategy for wireless cooperative communication systems with its bit error rate (BER) performance analysis. In this work, two relays are first chosen to maximize the overall system performance in terms of BER. Then, either the two-phase or three-phase protocol is performed to achieve two-directional communications between the communicating terminals through the selected relay nodes that apply orthogonal space-time coding (STC) scheme in a distributed fashion to improve the overall system performance with linear decoding complexity. In other words, the proposed strategy offers an improvement in the reliability of the system and enjoys very low decoding complexity by enabling a symbol-wise decoder. On the other hand, another improvement in the performance at the communication terminals is achieved by performing a network coding method at the selected relay nodes. Furthermore, we offer also analytical approximation of the BER performance for the proposed strategy where the simulation results match perfectly the analytical ones. From the simulation results section, the proposed strategy shows a substantially improved BER performance as compared to the current ones.

Performance analysis of multiple access relay channels for non-coherent modulations

One of the most important applications of network coding is the Multiple Access Relay Channel (MARC) technique in which source terminals transmit independent data blocks over one or more relay terminals to a common destination terminal. In recent years, MARC has become one of the vital network coding applications in the area of innovative wireless cooperative communications for enhancing spectral efficiency. In this paper, non-coherent binary frequency shift keying (BFSK) modulation and differential binary phase shift keying (DPSK) modulation techniques are applied to the decode-and-forward (DF)-based MARC model and the average bit error rate (BER) of the proposed system is derived theoretically by using the maximum likelihood (ML) decision rule. The simulation results show that the BER performance of DPSK modulation is better than the non-coherent BFSK and full diversity gain is achieved in both modulation techniques. We also propose a power allocation scheme for the proposed system model which optimizes the power allocated to the source and relay transmissions. Depending on the location of the relay, performance gains up to 1.25 dB are achieved with the proposed optimum power allocation (OPA) scheme. Also, the mathematical derivations are verified through Monte-Carlo simulations and the superior performance of the OPA over equal power allocation (EPA) is observed.

Exact error rate analysis of two-hop AF Rayleigh fading cooperative systems with variable amplification gain

A careful exploration of literature confirms that exact symbol-error-rate (SER) performance of amplify-and-forward (AF) wireless cooperative communication systems with variable amplification gain has not been analyzed before; even for simple models with single relay (i.e, two-hop systems) and Rayleigh fading channels. The main source of this mathematical intractability is the appearance of the modified Bessel function of the second type Kν(·) in the statistics of these systems end-to-end SNR. Here, however, we aim at filling this literature gap by proposing a novel theoretical method that helps in examining, for the first time, the exact SER performance of two-hop AF systems, where, as a case study, we assume Rayleigh quasi-static fading environment with perfect channel estimation. Specifically, we derive two new exact expressions for the system’s SER performance, which involve rapidly convergent infinite summation(s) and efficiently computable special functions. Furthermore, for the same system, we obtain new approximate closed-form SER expression, which outperforms its literature counterpart. The obtained analytical results are useful to gain insight about the actual error performance of variable gain AF systems. The presented methodologies can form a generic framework for exact SER performance evaluation of other variable gain AF cooperative system models.

Optimized Polar Coded Selective Relay Cooperation With Iterative Threshold Decision of Pseudo Posterior Probability

This paper proposes an optimized polar coded selective relay cooperation with an iterative threshold decision of pseudo posterior probability to solve the excessive redundancy of received signals and the high decoding complexity in a selective decode-and-forward (SDF) relay scheme. By sharing antennas of a relay node, a polar coded cooperation scheme is illustrated in a three-node relay transmission model, accompanied by an SDF protocol. Simultaneously, the SDF protocol is completed according to the channel status information at the relay node. In the logarithmic belief propagation algorithm, an expression of pseudo posterior probability-based stopping iteration threshold with independent and variable signal-to-noise ratios is derived to decide convergence condition and thus timely stop the iterations for low decoding complexity. And an extrinsic information transfer chart is also used to verify the completion of the iterative process. In addition, an information detection factor is introduced to check decoded bits correctly by the change of it, thereby reducing the average number of decoding iterations. It also accelerates the convergence speed of the BP algorithm by setting threshold and prejudgment, thereby improving the decoding efficiency. Simulation results show that the proposed polar coded relay cooperation scheme obtains over 2 dB performance gain, when the bit error rate (BER) is lower than 10 -3 , compared with the existing low-density parity-check codes related schemes. It also reduces the complexity of the BP algorithm by stopping the iteration of high-reliability nodes at the cost of performance loss within 0.5 dB. Therefore, the proposed scheme obtains both good BER performance and low complexity, which endows its good applications in cooperative wireless communications.

Analysis and Enhancement of Joint Security and Reliability in Cooperative Networks

In this study, we deal with a cooperative wireless communications system of security constraints in which there is no knowledge about channel state information (CSI) of the eavesdropper. In order to improve the tradeoff between security and reliability, we opportunistically employ relays via an incremental and selective cooperation with respect to the CSI of the main link. In this cooperation, named as opportunistic cooperative transmission (OCT), the first priority is communication through the direct link as far as possible. However, a relay that has the best link to the main destination is employed for retransmitting the source information when the direct link is so weak which cannot provide a specific quality. In fact, since improving the reliability of the favorable communications by use of the relays increases the risk of successful interception by the eavesdropper at the same time, the OCT scheme tries to avoid excess of rebroadcasting the secret information by the relays whenever the direct link is strong enough; otherwise it employs an opportunistically selected relayed link. Hence, it can improve the security for a specific level of reliability and vice versa. We derive closed-form expressions for the security-reliability tradeoff (SRT) and secrecy outage probability (SOP) of the OCT scheme. Moreover, we provide asymptotic analyses which are illustrative on the security behavior of the proposed scheme. Finally, simulation results are presented which confirm validity of the analysis and reveal the desired performance of OCT in terms of both SRT and SOP.

A Novel Hybrid RSS and TOA Positioning Algorithm for Multi-Objective Cooperative Wireless Sensor Networks

Due to the significance of positioning in complicated electromagnetic environment of its variety of applications, wireless localization techniques have attracted significant research interests with the trends moving toward boosting the capabilities of multi-objective cooperative networks. This paper addresses the problem of locating multiple targets in 3-D cooperative wireless sensor network. A novel hybrid received signal strength (RSS) and time-of-arrival (TOA) positioning scheme is proposed. Employing RSS and TOA measurements, four valuable expressions are drawn. The TOA and RSS technologies are combined with path loss difference variable being introduced. Based on the weighted least squares criterion, the rough solutions of multiple targets positions are derived. Finally, the locations of obtained targets are optimized by cooperative wireless communication between the target and another target. The location accuracy of the proposed estimation algorithm is analyzed and compared with the conventional RSS and TOA estimation algorithms through simulation experiments. The simulation result demonstrates that the proposed hybrid RSS and TOA localization algorithm for multi-objective cooperative wireless networks outperforms traditional approaches.

Analysis of time-switching and power-splitting protocols in wireless-powered cooperative communication system

SWIPT techniques combined with wireless cooperative communication provides a sustainable solution to extend the lifetime of the communication networks. It prolongs the battery life of wireless low-powered devices and enables additional efficiency in terms of power in wireless communications. This paper explores performance difference of two simultaneous wireless information and power transfer (SWIPT) protocols named Time-Switching (TS) and Power-Splitting (PS). Two identical decode-and-forward relaying communication networks with multiple relays are considered, where energy constrained relay nodes harvest energy from the received Radio Frequency (RF) and use harvested energy to assist information transmission between the source and the destination. All relay nodes in one network use TS protocol while the relay nodes in the other network use PS protocol. In particular, we evaluate throughput and outage probability of maximal ratio combiner (MRC) output at the destination node of both systems. In order to evaluate throughput, outage probability is derived for delay-limited transmission mode. The numerical results provide practical insight into the performance difference in various system parameters for both TS and PS protocols. Simulation results obtained depict that the TS protocol is superior to PS protocol in performance parameters, BER, Outage probability and throughput in low transmission rate. However, in higher transmission rates PS becomes superior to TS protocol, though overall performance reduce compare to lower transmission rate.

Energy-Efficient Path Selection Using SNR Correlation for Wireless Multi-Hop Cooperative Communications

In this paper, we consider partial path selection (PPS) for a multi-hop decode-and-forward cooperative system with limited channel state information (CSI) feedback, where the PPS utilizes local CSI only for a subset of hops on each of all independent paths between a source and a destination to reduce the energy consumption for CSI feedback. To enhance the end-to-end performance of the PPS, we propose a novel PPS method with local CSI chosen by the correlation between the end-to-end signal-to-noise ratios (SNRs) based on global and local CSI under Nakagami-m fading channels. For each path, we pick a subset of hops to report CSI with the highest correlation for a given CSI feedback overhead requirement, which can achieve the similar end-to-end outage probability to the best path selection with global CSI. We provide an exact and closed-form expression for the SNR correlation coefficient and present an impact of the SNR correlation on the end-to-end outage probability.

Lyapunov-Optimized Two-Way Relay Networks With Stochastic Energy Harvesting

Energy harvesting wireless cooperative communications have become more and more popular in recent years. In this paper, we consider a two-way relay cooperative network, where the relay is an energy harvesting node and uses decode-and-forward (DF) or amplify-and-forward (AF) cooperation protocol. We formulate the energy management problem in such a network as an optimization problem, which minimizes the long-term average outages with a long-term average battery constraint. We then apply Lyapunov optimization to transform the long-term optimization problem into the drift-plus-penalty. We also conduct theoretic analysis of the proposed energy management strategy. Specifically, we prove that the long-term average battery constraint can be guaranteed with the proposed strategy and derive an upper bound of the average outages with the proposed strategy. Furthermore, we analyze theoretically the diversity order and energy harvesting gain of the proposed strategy with the DF and AF protocols. Finally, simulation results using real-solar irradiance data measured by the solar site in Elizabeth City University show that the outage performance and the diversity order of our algorithms are better than the existing MDP-based method.

Multi‐level construction of polar‐coded single carrier‐FDMA based on MIMO antennas for coded cooperative wireless communication

A multi-level construction of polar-coded single carrier frequency division multiple access (SC-FDMA) with multiple input multiple output (MIMO) antennas scheme is proposed and its bit error rate performance over frequency selective Rayleigh fading channels has been evaluated. The existence of a parallel split in the design of multi-level construction of polar code has enabled the authors to effectively extend the proposed scheme in coded cooperative scenarios. As in coded cooperation communication, the relay plays a crucial role in the design of communication system; therefore, an efficient selection criterion for reinforcing the bad channels has been adopted at the relay node. Moreover, the joint successive cancellation decoding is employed at the destination node. To check the efficacy in the performance of the proposed coded cooperative scheme, the authors have also upgraded the traditional nested polar-coded cooperative scheme in the context of SC-FDMA with MIMO antennas as a useful benchmark. Monte Carlo simulated results revealed that the proposed coded cooperative scheme have triumphed the conventional nested polar coded cooperative scheme based on SC-FDMA system by gain of 0.5 dB under identical conditions. Moreover, the proposed cooperative schemes outperform their corresponding non-cooperative counterpart schemes by the gain of 1 dB under identical conditions.

A statistical channel model for a decode-and-forward based dual hop mixed RF/FSO relay network

In this paper, we have considered a dual branch with dual hop wireless cooperative communication system which comprises direct radio frequency path as well as indirect path with RF links and a free space optics (FSO) link through a Relay node (R) in between source (S) to destination (D). The faded channel for RF link is modelled with Nakagami-m distribution and the FSO link is modelled using double generalized Gamma fading. This proposed communication system uses the intensity modulation and direct detection technique for optical signal transmission and reception purpose, respectively in the FSO link. Further, we have employed selection combining diversity technique at the receiver during the use of both branches. Moreover, we have also derived probability density function and cummulative distribution function of the proposed communication system which is used to compute the performance metrics such as the outage probability and average bit error rate.

Lyapunov Optimized Cooperative Communications With Stochastic Energy Harvesting Relay

Energy harvesting (EH) wireless communications have become more and more popular due to its capability of effectively reducing the battery replacement time. In this paper, we focus on decode-and-forward-based cooperative wireless communications with an EH relay. The stochastic characteristics of the harvestable energy and the wireless channel make it difficult to optimally manage the energy harvested at the relay for better communication performance. We formulate such a problem as an optimization by minimizing the long-term average symbol error rate (SER) subject to a battery constraint. Based on the Lyapunov optimization theory, we utilize the virtual queue technique and transform the optimization problem into a drift-plus-penalty minimization. Then, we conduct theoretic analysis of the optimal energy strategy derived by the proposed scheme. Specifically, we show the convexity of the drift-plus-penalty minimization problem, and prove that the virtual queue is bounded and the battery constraint is always satisfied. We also show that the proposed optimal energy management strategy is limited by an upper bound that is independent of the operation time index, derive the closed-form expression for the asymptotical average SER, and analyze the corresponding diversity order and EH gain. Finally, simulation results using the real solar irradiance data show that the proposed algorithm can achieve much better performance in terms of both average SER and diversity order, compared with the Markov decision process-based method.

Ultra-Reliable Cooperative Short-Packet Communications With Wireless Energy Transfer

We analyze a cooperative wireless communication system with finite block length and finite battery energy, under quasi-static Rayleigh fading. Source and relay nodes are powered by a wireless energy transfer process, while using the harvested energy to feed their circuits, send pilot signals to estimate channels at receivers, and for wireless information transmission. Other power consumption sources beyond data transmission power are considered. The error probability is investigated under perfect/imperfect channel state information, while reaching accurate closed-form approximations in ideal direct communication system setups. We consider ultra-reliable communication (URC) scenarios under discussion for the next fifth-generation (5G) of wireless systems. The numerical results show the existence of an optimum pilot transmit power for channel estimation, which increases with the harvested energy. We also show the importance of cooperation, even taking into account the multiplexing loss, in order to meet the error and latency constraints of the URC systems.

Sequential Closed-Form Semiblind Receiver for Space-Time Coded Multihop Relaying Systems

In this letter, we present a sequential closed-form semi-blind receiver for a one-way multi-hop amplify-and-forward (AF) relaying system. Assuming Khatri-Rao space-time (KRST) coding at each relay, it is shown that the system with K relays can be modeled by means of a generalized nested PARAFAC model. Decomposing this model into K +1 third-order PARAFAC models, we develop a closed-form semi-blind receiver for jointly estimating the information symbols and the individual channels, at the destination node. Each step consists of a Khatri-Rao factorization. Parameter identifiability conditions are given, and simulation results are provided to illustrate the effectiveness of the proposed semi-blind receiver. Index Terms—Multi-hop relaying, sequential closed-form semi-blind receiver, space time (ST) coding, amplify-and-forward, generalized nested PARAFAC model. I. INTRODUCTION Relay nodes will play an important role in 5G communication systems. In such systems, the high-capacity wireless backhaul offers operators an alternative solution to conventional backhauling using multi-hop short-distance communications [1]–[4]. Tensor decompositions have been widely exploited for point-to-point wireless communication systems. The practical motivation for tensor modeling comes from the fact that one can simultaneously benefit from multiple (more than two) signal diversities, like space, time and frequency diversities, for instance. In the context of cooperative wireless communications, few results have been published on tensor-based receivers, and most of them are limited to a single relay scenario. In previous works [5]–[8], the problem of channel estimation for multiple input multiple output (MIMO) relaying systems was considered under a supervised approach. The works [5]–[7] considered one-way two-hop systems, while [8] addressed two-way MIMO relaying systems. In [9] and [10], three-hop relaying systems were studied. Recent works proposed semi-blind receivers for joint symbol and channel estimation. For instance, one can cite the PARAFAC-PARATUCK [11] and the nested PARAFAC receivers [12], [13]. However, the generalization of tensor-based semi-blind receivers to the multi-hop relaying scenario has not been addressed so far to the best of authors' knowledge.