Cooperative Diversity Systems Research Articles

Performance analysis of dual‐hop dual‐branch amplify‐and‐forward relaying cooperative diversity system using best‐path selection technique over Nakagami‐m fading channels

AbstractOne of the promising technologies for achieving virtual diversity gains is cooperative relaying. This study considers a dual‐hop dual‐branch cooperative diversity system with an amplify‐and‐forward mechanism where the hop count here means the total number of relays between source and destination which equals two. Utilizing the best‐path selection combining technique, a closed‐form formula for the average bit error rate and outage probability is obtained. Furthermore, between the nodes in the two branches, we consider independent non‐identical Nakagami‐m slow flat fading channels. The Monte Carlo simulation results are confirmed with the analytical ones.

Performance Analysis of Dual-Hop THz Transmission Systems Over α-μ Fading Channels With Pointing Errors

In this article, the performance of a dual-hop relaying terahertz (THz) wireless communication system is investigated. In particular, the behaviors of the two THz hops are determined by three factors, such as the deterministic path loss, fading effects, and pointing errors. Assuming that both THz links are subject to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> fading with pointing errors, we derive exact expressions for the cumulative distribution function (CDF) and probability density function (PDF) of the end-to-end signal-to-noise ratio (SNR). With these statistical expressions, some important performance metrics are evaluated, such as the outage probability (OP), average bit error rate (BER), and average channel capacity (ACC). Moreover, the asymptotic analyses are presented to obtain more insights. The results show that the dual-hop relaying scheme has better performance than the single THz link. Furthermore, the system diversity order depends on the fading parameters and pointing errors of both THz links. In addition, we extend the analysis to a multirelay cooperative diversity system and derive the asymptotic symbol error rate (SER) expressions. Finally, the derived analytical expressions are verified by the Monte Carlo simulation.

Impact of Co-channel Interference on the Performance of Cooperative Diversity Systems over α–μ Fading Channels

This paper investigates the impact of the co-channel interference on the performance of cooperative diversity networks. Selection combination technique is applied to the paths from multiple relay branches with no link directly connects the source and destination nodes. In addition, we derive the statistical characteristics of the upper bound of the SINR under the α–μ fading channel model, which then were used to derived the outage (P_{out}) and error (P_b(e)) probabilities for the cooperative network.

Full Euclidean Distance Based Selection Combining for SSK DF Cooperative Diversity Systems

Space Shift Keying (SSK) is a multiple-input multiple-output technique that has drawn more attention in recent years because of its low complex transceiver design. In this paper, an investigation on the Symbol Error Probability (SEP) performance of SSK in a Decode-and-Forward (DF) cooperative relaying system is done. The DF cooperative relaying scenario considers an origin node, an intermediate node and an end node with a direct link between origin and end node, and an indirect link between origin to the intermediate node and intermediate to end node. The SSK modulation is considered at the origin and intermediate nodes with Full Euclidean Distance based Selection Combining (FED-SC) employed at the end node for SSK symbol detection. The SEP expression of the SSK FED-SC in the DF cooperative relaying scheme is derived using the Order Statistics Approach (OSA). Further, a closed-form SEP expression is obtained using a Combined Order Statistics Approach (COSA) considering the number of receive antennas at the intermediate node is equal to the number of receive antennas at the end node. In addition, the closed-form asymptotic SEP expression is presented to evaluate the diversity order of the system. The SEP expressions derived through OSA and COSA are verified using the Monte Carlo simulations. The simulation results revealed that the proposed SSK FED-SC outperforms all the existing SSK DF cooperative selection combining schemes.

Research on Cooperative Communication Technology to Improve Capacity and Reliability of Integrated Energy System

The integrated energy system makes full use of renewable resources such as local photovoltaics, fully considers the difference and complementarity of load types in the region, and realizes the efficient, economic and clean utilization of regional energy from the dimensions of time and space. The existing communication system of the integrated energy system has become a constraint on business development. First, the communication rate is low and the system capacity is limited. After the terminal collects various energy information, a large amount of data needs to be uploaded, which puts huge pressure on the communication bandwidth. The second is poor reliability and high operation and maintenance costs. The current communication technology is single, equipment and networking costs are high. Aiming at the abovementioned pain points, an opportunistic relay cooperation technology and scheme based on signaling measurement is proposed. Theoretical analysis and simulation results show that the above scheme can improve the performance of the cooperative diversity system while reducing conflicts.

Performance evaluation of decode and forward cooperative diversity systems over nakagami-m fading channels with non-identical interferers

The deficiencies of regular cooperative relaying schemes were the main reason behind the development of Incremental Relaying (IR). Fixed relaying is one of the regular cooperative relaying schemes and it relies on using the relay node to help in transmitting the signal of the source towards the destination despite the channel’s condition. However, adaptive relaying methods allocate the channel resources efficiently; thus, such methods have drawn the attention of researchers in recent years. In this study, we analyze a two-hop Decode-and-Forward (DF) IR system’s performance via Nakagami-m fading channels with the existence of the several L distinguishable interferers placed close to the destination which diminishes the overall performance of the system due to the co-channel interference. Tight formulas for the Bit Error Rate (BER) and the Outage Probability (OP) are drawn. The assumptions are consolidated by numerical calculations.

Comparative performance analysis of cooperative and multi dual‐hop relay networks using MGF approach

SummaryIn this paper, we analyzed and compared the performance of cooperative diversity systems such as cooperative and multi dual‐hop networks with non‐regenerative relay nodes. The contributions of this study are twofolds. Firstly, analytical expressions of outage probability Pout and average symbol error rate ASER are derived using moment generating function (MGF) analysis of the received SNR with the assumption that the channel experiences Weibull fading and the best relay selection is used. Then, using the analytical results, comparative performance evaluation of cooperative and multi dual‐hop relay networks is done for varying number of relay nodes and different receive diversity schemes such as maximal ratio combining (MRC) and selection combining (SC). The results show that the cooperative relay network has better performance than a multi dual‐hop relay network in terms of Pout and ASER. The results also show that the multi dual‐hop network can achieve the same performance as the cooperative network with the requirement that it needs the deployment of three times more relay nodes.

Performance of cooperative full‐duplex AF relay networks with generalised relay selection

In this work, a full-duplex (FD) variable gain amplify-and-forward multi-relay cooperative-diversity system with(out) a direct path (DP) between the source and destination is studied over independent identically (non-identically) distributed slow Rayleigh fading channels. Generalised relay selection, i.e. generalised selection transmission (GST) over relays is investigated for two extreme cases; single relay selection (RS) and use of all relays, i.e. maximum ratio transmission (MRT). By developing an equivalent link, the approximated probability density function (PDF) and cumulative distribution function (CDF) of a dual-hop link with FD relay are obtained, thereafter, the adopted approximated PDF and CDF are offered. Then, approximated and asymptotic expressions for outage probability, moment generating function, and symbol error rate (SER) of GST with(out) DP are derived. Additionally, approximated ergodic capacity expressions are also obtained. All theoretical results validated by Manto Carlo simulation technique show that the proposed approximations of dual-hop link with FD relay are robust and thus can be used to analyse such systems with FD relay, RS and MRT provide close performance which is significantly better than single relay. Additionally, for equal rates, substantial reduction in SER can be obtained by FD transmission as compared to half-duplex one.

Performance of relay‐based decode‐and‐forward cooperative diversity systems over Rayleigh fading channels with non‐identical interferers

Incremental relaying was initially presented so as to adjust for the shortages or limitations related to the usual cooperative methods, specifically, the fixed relaying methods in which the relay node assists the source node in transmitting the signals belonging to the destination independent of the channel status. Matter of fact, the adaptive relaying methods related to the cooperative diversity networks have attracted current researchers’ attention as of being capable of offering an efficient way in assigning the channel expedients when required. In this study, a two-hop decode-and-forward incremental relaying over Rayleigh fading channels is assessed taking into account the existence of multiple non-identical interferers close to the destination. Interestingly, investigating the non-identical interferers case instead of identical ones, like what are published in the literature, is extremely challenging as it refers to a more generalised case. Interestingly, the performance of the system is degraded due to co-channel interference. To this end, tight closed-form expressions of the bit error rate and outage probability are ultimately obtained. Analytical and simulation results are introduced to consolidate the assumptions considered.

Physical Layer Security for Cooperative Relaying Over Generalized-$K$ Fading Channels

In this letter, we analyze the secrecy performance for a cooperative diversity system with amplify-and-forward over generalized- ${K}$ fading channels. More specifically, some lower bounds on the secrecy performance, such as secure outage probability, average secrecy capacity, and strictly positive secrecy capacity, are derived in closed-form. Finally, we provide simulation results to verify the accuracy of our analytical results.

Performance Analysis of Joint Relay and Transmit–Receive Antenna Selection for Low Density Parity Check-Asynchronous Distributed Space Time Block Coded Cooperative Diversity System

In this work we propose a joint relay and transmit–receive antenna selection method for amplify and forward asynchronous distributed space time block coded (ADSTBC) system. To the LDPC coded signal received from the source at the relays, we apply linear dispersion codes which are optimized over the delay profile of the system to produce the ADSTBC. Selection of the best transmit–receive antenna pair between source and selected relays, and that of between the selected relays and destination is done on the basis of instantaneous signal to noise ratio (SNR) of the respective paths. The relays and transmit-receive antenna pairs are selected by maximizing the end-to-end instantaneous SNR. Performance analysis of the system is done on the basis of pair wise error probability and outage probability (Pout).

Alamouti-OSTBC Wireless Cooperative Networks With Mobile Nodes and Imperfect CSI Estimation

This paper is concerned with investigating the impact of both nodes mobility and imperfect channel-state-information (CSI) estimation on the symbol-error-probability (SEP) performance of a multiple-relay amplify-and-forward cooperative diversity system employing Alamouti-type orthogonal-space-time-block-code transmission at the source and classical Alamouti's space-time-decoder (ALD) at the destination. Due to nodes mobility, the system's links are characterized by time-selective fading channels, which are modeled by the first-order-autoregressive (AR1) process, and due to imperfect CSI estimation, the estimated channel gains are assumed to be corrupted by Gaussian errors. For such a system model, an approach is proposed to derive a tight approximate expression for the system's conditional SEP. This approach is based on utilizing the AR1 model to derive exact expressions for the signal-to-interference-plus-noise ratios of the ALD decoder's decision variables, and on benefiting from the central limit theorem to approximate some of the non-Gaussian interference and noise terms. The obtained conditional SEP expression is function of both the fading channel correlation parameters and the estimation error variances, and thus, it is valid for mobile as well as static nodes for imperfect as well as perfect CSI estimation processes. The system's average SEP is evaluated semianalytically using the obtained conditional SEP expression. Numerical results along with Monte Carlo link-level simulations are provided to validate the accuracy of the presented analyses and to demonstrate the system performance under several realistic scenarios.

A new error analysis technique for cooperative 5G systems

Deployment of cooperative techniques on 5G cellular networks has been a subject of recent interest to researchers. A cooperative diversity relay system has a root terminal, an intermediate terminal and an end terminal is presented. The intermediate terminal detects the root terminal’s information through the decode and forward protocol and forwards it to the end terminal. The authors have proposed a new switched diversity scheme for the above system and have done a mathematical investigation of its performance. In the flat Rayleigh fading environment with phase shift keying modulation, the symbol error probability has been derived for a cooperative diversity system. The proposed scheme has been compared against other competing schemes seen in literature. The numerical results have revealed a better performance of the proposed system than the existing system.

Threshold-based selection combining for relay networks

A wireless system model which typically consists of a beginning node, multiple relays, and an ending node, has been considered. The conventional selection combining schemes are not suitable for cooperative diversity systems due to its inherent detection errors. The relays forward beginning node’s information through a decode and forward protocol. The detection errors can be minimized by having a threshold at the relay. The relays participate in the cooperation process only if the instantaneous signal-to-noise ratio (SNR) of the beginning node to relay node is more than a fixed threshold. We derive the end-to-end symbol error probability of this scheme for M-ary phase-shift keying using paired error method for relay networks in the presence of flat Rayleigh fading. We numerically find the optimum value of relay-threshold. Numerical results show that the relay-threshold selection combining outperforms the conventional selection combining in terms of SNR gain.

Relay-Assisted OFDM for Ultraviolet Communications: Performance Analysis and Optimization

Ultraviolet (UV) communication enables non-line-of-sight (NLOS) outdoor wireless connectivity and is particularly desirable to relax or eliminate pointing and tracking requirements of infrared links. In comparison to infrared counterparts, UV links are subject to relatively higher path loss as well as intersymbol interference resulting from frequency selective nature of the channel. In this paper, we propose the powerful combination of relay-assisted transmission and multi-carrier architecture based on orthogonal frequency division multiplexing (OFDM). Specifically, we consider a cooperative diversity system with orthogonal cooperation protocol and use DC-biased optical OFDM as the underlying physical layer. We consider both amplify-and-forward (AF) and detect-and-forward (DF) relaying. We investigate the error rate performance of the proposed relay-assisted OFDM UV system under consideration and demonstrate performance gains over point-to-point OFDM UV systems. We further determine optimal power allocation schemes to improve the performance. We also propose a variable-rate UV OFDM system and improve system throughput via bit loading.

Joint Antenna and Relay Selection Strategies for Decode-and-Forward Relay Networks

Cooperative diversity systems with optimal and suboptimal antenna and relay selection have been paid significant attention for more than half a decade. However, optimal antenna and relay selection strategies require global channel state information (CSI), which is a cumbersome process. In this paper, we propose a diversity-optimal and three suboptimal transmit–receive antenna and relay selection strategies, named S1, S2, and S3, for decode-and-forward cooperative relaying systems, equipped with $N_{t}$ and $N_{r}$ antennas at the source (S) and the destination (D), respectively, and considering a multirelay scenario. Furthermore, we study the symbol error probability (SEP) for these strategies, assuming $M$ -ary phase-shift keying signaling over Rayleigh fading channels. In addition, we perform diversity order analysis through closed-form asymptotic SEP expressions. Since the proposed suboptimal strategies, i.e., S2 and S3, involve the so-called switch-and-examine combining scheme, we compare the complexity of S1, S2, and S3 in terms of the average number of CSI required at D to select the best transmit–receive antenna pair and relay. From the derived SEP expressions, it can be concluded that all three suboptimal strategies achieve the same diversity order of $N_{t}N_{r}+N$ , where $N$ is the number of relays, except for the case when the switching threshold signal-to-noise ratio (SNR) is much lower than the average SNR in S2 and S3. Finally, the diversity-optimal strategy achieves full diversity order of $N_{t}N_{r}+N\min(N_{t},N_{r})$ .

Joint-Design of Link-Adaptive Modulation and Coding with Adaptive ARQ for Cooperative Amplify and Forward Relaying System

This paper analyzes the efficiency of a joint-design of an adaptive modulation and coding (AMC) at the physical (PHY) layer with an adaptive R max -truncated selective-repeat automatic repeat request (ARQ) protocol at the medium access control (MAC) layer to maximize the throughput of cooperative nonregenerative relay networks under prescribed delay and/or error performance constraints. Particularly, we generalize the existing design model/results for cross-layer combining of AMC along with truncated ARQ in non-cooperative diversity networks in three-folds: (i) extension of the cross-layer PHY/MAC design or optimization to cooperative diversity systems; (ii) generalization/unification of analytical expressions for various network performance metrics to generalized block fading channels with independent but nonidentically distributed (i.n.d) fading statistics among the spatially distributed nodes; (iii) analysis of the effectiveness of joint-adaptation of the maximum retransmission limit R max of ARQ protocol and cooperative diversity order N for delay-insensitive applications. Our insightful numerical results reveal that the average throughput can be increased significantly by judiciously combining two additional degrees of freedom (N and R max ) that are available in cooperative amplify-and-forward (CAF) relay networks besides employing AMC at the PHY layer, especially in the most challenging low signal-to-noise ratio (SNR) regime.

Performance Comparison of Selection Combining With Full CSI and Switch-and-Examine Combining With and Without Post-Selection

Selection combining (SC) with full channel state information (CSI) achieves full diversity order in a decode-and-forward (DF) relaying system. However, the estimation of CSI of all the links is a cumbersome process. As an alternative, switched-diversity techniques have been proposed in the literature, in which CSI of all the links are not simultaneously required. In this paper, we compare the variants of the switched-diversity and full-CSI SC schemes through a paired error approach for a multi-DF-relaying-based cooperative diversity system. We derive the exact symbol error probability (SEP) expressions for the full-CSI SC, switch-and-examine combining (SEC), and SEC with post-selection (SECps) schemes, considering $M$ -ary phase-shift keying (MPSK) signaling over slow, flat, independent, and nonidentical Nakagami- $m$ fading channels. It is to be noted that the derived SEP expressions are valid for integer values of fading severity parameter $m$ . In addition, we also present the closed-form asymptotic SEP expressions for MPSK signaling to evaluate the diversity order. Concisely, from the numerical results, it is observed that the SECps scheme is able to offer the same performance as that of the full-CSI SC scheme. Furthermore, the SECps scheme outperforms the SEC scheme with more CSI.

Performance of an Improved Energy Detector in Multihop Cognitive Radio Networks

Cooperative spectrum sensing in a multihop cognitive radio (CR) network based on multiple antennas using an improved energy detector is studied in this paper. The improved energy detector uses the $p$ th power of the absolute value of samples of primary user's (PU's) signals. We replace the conventional energy detector by an improved energy detector to enhance the performance of CR. Analytical expressions of the probability of false alarm and missed detection in each CR are derived. Furthermore, we extend our study to a multihop cooperative diversity system containing multiple multihop secondary transmission paths between the PU and the fusion center. Performance analysis of multihop cooperative diversity is discussed using an improved energy detector. We introduce a framework to derive a closed-form expression of the optimal number of multihop cooperative diversity branches by minimizing the total error rate. An efficient quick spectrum sensing algorithm is proposed, which requires fewer than the total number of cooperative multihop diversity branches. It is shown, through various numerical examples, that by using the optimal number of secondary transmission paths, it is possible to perform quick spectrum sensing while satisfying an upper bound on the total error rate.

Improved error performance ZFSTD for high mobility relay‐based cooperative systems

An Alamouti-type orthogonal space–time-block-code transmission over a relay-based cooperative-diversity system under the influence of the cooperating nodes’ mobility is considered. It is shown that the high nodes' mobility destroys the optimality of the conventional Alamouit's decoder (ALD) employed at the system's destination, which causes severely degraded error performance. A zero-forcing-space–time-decoder is proposed, to be applied instead of the ALD, and its capability of mitigating this severe impact of the nodes' mobility is shown.