Relay Selection Protocol Research Articles

The Role of Delay and Connectivity in Throughput Reduction of Cooperative Decentralized Wireless Networks

We proposed a multiple relay selection protocol for decentralized wireless networks. The proposed relays selection protocol aims to address three issues: (1) selecting relays within the coverage area of the source and destination to ensure that the relays are positioned one hop away from the destination, (2) ensuring that the best node (best relays with less distance and attenuation from the destination) access the channel first, and (3) ensuring that the proposed relays selection is collision-free. Our analysis also considers three important characteristics of decentralized wireless networks that are directly affected by cooperation: delay, connectivity, and throughput. The main goal of this paper is to demonstrate that improving connectivity and increasing number of relays reduce the throughput of cooperative decentralized wireless networks; consequently, a trade-off equation has been derived.

Link quality estimation in VANETs for multi-hop alert messages dissemination

Reception of alert messages by endangered vehicles at time of an emergency event e.g., a traffic accident is a prime objective of alert messaging protocols in vehicular ad hoc networks VANETs. This work proposes a new bi-directional stable communication BDSC protocol for relay nodes selection in multi-hop alert messages propagation in VANETs. The BDSC protocol is based on a dynamic link quality estimation algorithm. The proposed protocol is evaluated by assessing the alert messages reachability in varying network size and traffic densities. Results obtained from extensive simulation experiments favour the performance of the proposed protocol with a large margin of reachability improvement compared to conventional furthest distance relay selection protocols. In a multi-lane road segment with dense traffic scenario, reachability improvement of approximately 25% is noticed over the furthest distance protocols. This reachability improvement is achieved with comparable end-to-end communication delays to those exhibited by furthest distance-based solutions.

On relay selection and power allocation in cooperative free-space optical networks

Drawing increasing attention, free-space optics (FSO) is a cost-effective technology to support data intensive communications. Cooperative diversity is considered to be an effective means for combating weather turbulence in FSO networks. In this paper, we consider the challenging problem of joint relay selection and power allocation in FSO networks. The objective was to maximize the FSO network-wide throughput under constraints of a given power budget and a limited number of FSO transceivers. The problem is formulated as a mixed integer nonlinear programming (MINLP) problem, which is NP-hard. We first adopt the reformulation-linearization technique (RLT) to derive an upper bound for the original MINLP problem. Due to the relaxation, the solutions obtained from RLT are infeasible. We then propose both centralized and distributed algorithms using bipartite matching and convex optimization to obtain highly competitive solutions. The proposed algorithms are shown to outperform the noncooperative scheme and an existing relay selection protocol with considerable gains through simulations.

Partial Relay Selection with Feedback Delay and Cochannel Interference: Performance Analysis and Power Optimization

The performance of a dual-hop amplify-and-forward (AF) relay system is studied with the kth worst partial relay selection (PRS) protocol under the joint impact of feedback delay and multiple cochannel interference (CCI) at the relay nodes. In our analysis, the closed-form and asymptotic expressions of the outage probability are derived and the achievable coding gain and diversity gain of the system are accurately revealed. Further, based on the asymptotic analysis we propose a power allocation scheme, which can lead to SNR performance gains of more than 1 dB compared to the equal power allocation scheme. Finally, Monte-Carlo simulation results are presented to verify the validity of our theoretical analysis.

Distributed switch and stay combining with partial relay selection and signal space diversity

Spatial diversity schemes are often used to extract additional performance from wireless communication systems. Incorporating the partial relay selection (PRS) protocol into a distributed switch-and-stay combining (DSSC) cooperative communication network gives the benefit of diversity while simplifying hardware, processing and feedback requirements. Because only a single relay is ever active, the destination employs no combiner; the best relay is chosen based on first-hop relay conditions. However, achieved performance is worse than other distributed protocols, such as distributed selection combining (DSC). In this study, signal space diversity (SSD) is added to the DSSC–PRS system to provide further diversity and error performance gains, at the expense of necessitating a maximum-likelihood detector with increased complexity at the receiver. Analytical results are presented in the form of a lower bound based on the minimum distance lower bound for SSD systems and are verified with simulation. The DSSC–PRS–SSD system shows an improvement of 5 dB at a symbol error rate of 10 − 4 as well as a clear diversity order improvement. Spectral efficiency of the new system with SSD is slightly decreased at low signal-to-noise ratios, but is still an improvement over other distributed schemes, such as DSC.

Impact of Correlated Log-Normal Shadowing on Two-Way Network Coded Cooperative Wireless Networks

In this letter, we provide a novel theoretical framework for studying the effects of correlated shadowing, in the number of relays that are capable of helping two nodes (sources) to exchange their messages. The relays use network coding to simultaneously transmit the received messages to the sources. We prove theoretically and verify by means of simulations that the average number of relays that are capable of forwarding the network coded message, is independent from any correlation between the links from one source to the relays. Finally, we apply this framework, to compute the network outage probability. The presented results are essential for the theoretical study of medium access control and relay selection protocols designed for network coded cooperative communications.

A Dynamic Paradigm for Spectrally Efficient Half-Duplex Multi-Antenna Relaying

This paper presents a spectrally efficient protocol for half-duplex multi-relay systems in block fading channels where a direct source-destination link is unavailable. The proposed protocol adaptively selects either successive interference cancelation (SIC) or joint decoding according to the causal decoding status of each relay. We also adopt dynamic refreshing that restarts the protocol whenever it is advantageous to do so, even if the relay decoding set (the set of relays that are able to decode the message) is not empty. The achievable diversity-multiplexing tradeoff (DMT) of the proposed protocol with m-antenna nodes is analyzed via a Markov chain whose states are related to the cardinality of a decoding set. This protocol strictly improves the DMT of the existing DF half-duplex relay-selection protocols without decoding delay, and in the low multiplexing gain region is able to meet the DMT upper bound. The main contributions of the paper are the state-dependent decoding strategies in DF multi-relay systems and also the dynamic refresh for the flushing of residual interferences in the system, concepts that may find usefulness beyond the gains in the high-SNR regime.

Optimal power‐aware relay placement for cooperative wireless sensor networks

SUMMARYWe study the problem of optimizing the symbol error probability (SEP) performance of cluster‐based cooperative wireless sensor networks. Recent studies in literature show that an efficient relay selection protocol based on simple geographical information of the nodes to execute cooperative diversity can significantly improve the SEP performance at the destination of such networks. As well, similar line of research on optimal power allocation (for the source and relay nodes) can be found in literature. However, to achieve the best SEP performance at the destination of a cooperative wireless sensor network, joint optimization of power allocation and relay placement should be accomplished. To this aim, we reformulate the SEP of a multi‐hop cooperative communication in a general form and optimize transmitted power level and relay placement simultaneously. This analysis is developed for both amplify‐and‐forward and decode‐and‐forward relaying protocols. Simulation results demonstrate that the proposed joint optimization can effectively improve the SEP performance of the network. Copyright © 2013 John Wiley & Sons, Ltd.

Outage Probability and Ergodic Capacity Analysis for Two-Way Relaying System with Different Relay Selection Protocols

The outage probability and ergodic capacity analysis for decode-and-forward two-way relaying system is investigated in this paper. First, the exact expressions (or bounds) of outage probability, ergodic capacity and average bidirectional ergodic capacity (ABEC) for max---min relay selection, random relay selection and direct transmission protocols are derived through theoretic analysis, and performance comparisons among different relay selection protocols are developed. Then a novel maximum average bidirectional mutual information (MABM) relay selection protocol is proposed and analyzed. Simulation results demonstrate that the derived analytical results fit well with Monte-Carlo simulations. The proposed MABM protocol can always achieve larger ABEC than other protocols while keeping low outage probability, and the MABM and max---min protocols in this paper can always achieve better performance than the max---min selection and max-sum selection in Krikidis (IEEE Trans Veh Technol 59(9):4620---4628, 2010). In addition, outage probability, ergodic capacity and ABEC performance of the proposed protocol become worse while distance becomes larger.

One-Bit CSI Feedback Selection Schemes for Energy-Efficient Multiuser and Multirelay Systems

A new approach to relay and user selection is proposed using threshold-based transmission to reduce outage probability and save transmit power. By exploiting properties of dual-hop transmission using amplify-and-forward (AF) relaying, new threshold-based relay and user (TRU) selection protocols that employ one-bit channel state information (CSI) feedback are proposed for multiple-relay, multiple-user systems. These new protocols have the advantages of (1) economical feedback, and (2) optional adaptive power-saving transmission. Centralized selection (CS) and distributed selection (DS) policies as well as lower-complexity suboptimal selection schemes are investigated for downlink transmission. Exact expressions for outage probability, outage diversity and feedback requirement are provided to quantify the complexity/performance trade-offs. The analysis shows that selection threshold(s) can be chosen such that transmission is interrupted when system outage is certain, which allows power saving without impairing outage performance. These protocols are compared in terms of performance, energy-efficiency and system requirement to others that trade outage performance for additional energy saving and/or reduced complexity.

Jointing Adaptive Modulation Relay Selection Protocols for Two-Way Opportunistic Relaying Systems with Amplify-and-Forward Policy

Two novel best-relay selection protocols, the jointing adaptive modulation max---min (AM-MM) protocol and the jointing adaptive modulation maximum harmonic mean (AM-MHM) protocol, are proposed for ...

Relay Selection Protocols for Relay-Assisted Free-Space Optical Systems

We investigate transmission protocols for relay-assisted free-space optical (FSO) systems, when multiple parallel relays are employed and there is no direct link between the source and the destination. As alternatives to all-active FSO relaying, where all the available relays transmit concurrently, we propose schemes that select only a single relay to participate in the communication between the source and the destination in each transmission slot. The selection is based on the channel state information obtained either from all or from the last used FSO links. Thus, the need for synchronization of the relays’ transmissions is avoided, while the slowly varying nature of the atmospheric channel is exploited. For the considered relay selection and all-active relaying schemes, novel closed-form expressions for the outage performance are derived, assuming the versatile Gamma–Gamma channel model. In addition, based on the derived analytical results, the problem of optimizing the optical power resources of the FSO links is addressed. Optimal and more computationally attractive suboptimal solutions are proposed that lead to a power efficient system design. Numerical results for equal and non-equal length FSO links illustrate the merits of the proposed relay selection protocols compared to the all-active scheme and demonstrate the significant power savings offered by the proposed power allocation schemes.

Performance Analysis of an Opportunistic Relay Selection Protocol for Multi-Hop Networks

We analyze the performance of an interference-aware opportunistic relay selection protocol for multi-hop line networks which is based on the following simple rule: a node always transmits if it has a packet, except when its successive node on the line is transmitting. We derive analytically the saturation throughput and the end-to-end delay for two and three hop networks, and present simulation results for higher numbers of hops. In the case of three hops, we determine the throughput-optimal relay positions.

Packet Delivery Performance of Simple Cooperative Relaying in Real-World Car-to-Car Communications

We evaluate the packet delivery performance of low-complex cooperative relaying in car-to-car communications by real-world measurements. The ratio and temporal correlation of packet delivery are evaluated for suburban and highway environments using three cars equipped with programmable radios and serving as sender, relay, and destination. We compare the relaying performance to that of pure time diversity and show how temporal autocorrelation of packet delivery is a key factor in whether or not relaying exhibits benefits. Results are relevant in the design of relay selection protocols, as they give guidelines for the affordable selection delay.

A Threshold-Based Relay Switching Protocol for Enhanced Capacity and Resource Efficiency

This letter deals with the issue of inefficient use of radio resources due to frequent relay switchings in overhead constrained cooperative relay networks. A threshold-based relay switching protocol is proposed for enhanced achievable capacity and efficient resource management while preventing frequent switchings. We derive the achievable capacity under fading channels based on switching probability and ergodic capacity analysis. Also, the optimal threshold value is obtained from a convex optimization problem. Numerical and simulation results reveal the advantage of the proposed protocol over the conventional opportunistic relay selection protocols.

Optimized Relay Selection Strategy Based on GF(2p) for Adaptive Network Coded Cooperation

Adaptive network coded cooperation (ANCC) scheme may have excellent performance for data transmission from a large collection of terminals to a common destination in wireless networks. However, the random relay selection strategy for ANCC protocol may generate the distributed low-density parity-check (LDPC) codes with many short cycles which may cause error floor and performance degradation. In this paper, an optimized relay selection strategy for ANCC is proposed. Before data communication, by exploiting low-cost information interaction between the destination and terminals, the proposed method generates good assembles of distributed LDPC codes and its storage requirement reduces dramatically. Simulation results demonstrate that the proposed relay selection protocol significantly outperforms the random relay selection strategy.

Errata [on "LR-AKE-Based AAA for Network Mobility (NEMO) Over Wireless Links" (Sep 09 1725-1737)

In the above mentioned paper, the authors proposed an incremental transmission relay selection (ITRS) protocol, whose diversity-multiplexing-tradeoff performance was illustrated and compared with existing alternatives in Fig. 3 (R. Tannious et al., Oct, 2008). However, in our opinion, these comparisons are unfair and a curve depicted in Fig. 3 is wrong. We discuss the full detail of our comment in this paper.

Comments on "Spectrally-efficient relay selection with limited feedback"

In the above mentioned paper, the authors proposed an incremental transmission relay selection (ITRS) protocol, whose diversity-multiplexing-tradeoff performance was illustrated and compared with existing alternatives in Fig. 3 (R. Tannious et al., Oct, 2008). However, in our opinion, these comparisons are unfair and a curve depicted in Fig. 3 is wrong. We discuss the full detail of our comment in this paper.

Building blocks of cooperative relaying in wireless systems

The concept of cooperative relaying promises gains in robustness and energy efficiency in wireless networks. This survey gives an introduction and overview of promising methods that can be used for cooperative relaying: relay selection protocols, cooperative channel and network coding, and physical layer aspects such as cooperative modulation. The particular methods can be seen as building blocks that can be configured and optionally used for designing a system. They offer a large number of design options for relaying systems. Based on available hardware features, expected environment, and required services an efficient system needs to be tailored using the right subset of available methods.

The Impact of Channel Feedback on Opportunistic Relay Selection for Hybrid-ARQ in Wireless Networks

This paper presents a decentralized relay selection protocol for a dense wireless network and describes channel feedback strategies that improve its performance. The proposed selection protocol supports hybrid automatic repeat request transmission where relays forward parity information to the destination in the event of a decoding error. Channel feedback is employed for refining the relay selection process and to select an appropriate transmission mode in a proposed adaptive modulation transmission framework. An approximation of the throughput of the proposed adaptive modulation strategy is presented, and the dependence of the throughput on system parameters such as the relay contention probability and the adaptive modulation switching point is illustrated via maximization of this approximation. Simulations show that the throughput of the proposed selection strategy is comparable with that yielded by a centralized selection approach that relies on geographic information.