In this paper, we investigate relay selection for cooperative multiple-antenna systems that are equipped with buffers, which increase the reliability of wireless links. In particular, we present a novel relay selection technique based on switching and the selection of the best link, that is named Switched Max-Link. We also introduce a novel relay selection criterion based on the Maximum Likelihood (ML) principle and the Pairwise Error Probability (PEP) denoted Maximum Minimum Distance (MMD) that is incorporated into the proposed Switched Max-Link protocol. We compare the proposed MMD to the existing Quadratic Norm (QN), in terms of PEP and computational complexity. Simulations are then employed to evaluate the performance of the proposed and existing techniques.
In this paper, we propose a relay selection scheme for buffer-aided cooperative relay networks. The proposed scheme exploits the channel state information and the buffer state information to minimize the outage probability. To achieve that, it constantly seeks to maintain the states of the buffers by balancing the arrival and departure rates at each relay's buffer. More specifically, the half-full buffer state is used as a reference to monitor the state of balance, where a relay's buffer is considered balanced if its arrival and departure rates are equal. In each time slot, among all links that are available for selection, the one that can enhance the balance status of the most unbalanced buffer is selected. The outage probability performances in independent and identically distributed and independent and nonidentically distributed Rayleigh fading channels are investigated. In terms of outage probability, simulation results show that the proposed scheme significantly outperforms the max-link scheme and achieves some improvement compared to the buffer-state-based scheme. Relays receive and retransmit signals between one or more sources and one or more destinations. Cooperative relaying is a novel technique for wireless communications that increases throughput and extends the coverage of networks. The task of relay selection serves as a building block to realize cooperative relaying. Recently, relays with buffers have been incorporated into cooperative relaying providing extra degrees of freedom in selection, thus improving various performance metrics, such as outage probability, power reduction, and throughput, at the expense of tolerating an increase in packet delay. In this survey, we review and classify various buffer-aided relay selection policies and discuss their importance through applications. The classification is mainly based on the following aspects: 1) duplexing capabilities, 2) channel state information (CSI), 3) transmission strategies, 4) relay mode, and 5) performance metrics. Relay selection policies for enhanced physical-layer security and cognitive communications with reduced interference are also discussed. Then, a framework for modeling such algorithms is presented based on Markov Chain theory. In addition, performance evaluation is conducted for various buffer-aided relay selection algorithms. To provide a broad perspective on the role of buffer-aided relay selection, various issues relevant to fifth-generation (5G) networks are discussed. Finally, we draw conclusion and discuss current challenges, possible future directions, and emerging technologies. We consider a wireless relay network that consists of a source, half-duplex decode-and-forward buffer-aided relays and a destination. While the majority of previous works on relay selection assume no direct transmission between source and destination in such a setting, we lift this assumption and propose a link selection policy that exploits both the buffering ability and the opportunity for successful reception of a packet directly from the source. The proposed relay selection scheme incorporates the instantaneous strength of the wireless links and adapts the relay selection decision based on the strongest available link. The evolution of the network as a whole is modeled by means of a Markov chain and thus, the outage probability is associated with the steady state of the Markov chain. It is deduced that even if the link between the source and the destination is in principle a very unreliable link, it is always beneficial for the source to multicast a packet to both the relay with the strongest available link and the destination. In this paper, we propose novel relay selection policies that aim at reducing the average delay by incorporating the buffer size of the relay nodes into the relay selection process. More specifically, we propose two delay-aware protocols that are based on the max — link relay selection protocol. First, a delay-aware only approach while it reduces the delays considerably it starves the buffers and increases the outage probability of the system. Towards this end, we propose a delay- and diversity-aware buffer-aided relay selection policy that aims at reducing the average delay considerably and at the same time maintaining good diversity. The protocols are analyzed by means of Markov Chains and expressions for the outage, throughput and delay are derived. The performance and use of our proposed algorithms is demonstrated via extensive simulations and comparisons. In this paper, we propose a new relaying scheme, referred to as priority-based max-link relay selection, for buffer-aided decode-and-forward cooperative networks. We give the first priority to the relay buffers having status full, the second priority to the relay buffers having status empty, and the third priority to the relay buffers having status neither full nor empty. The best relay node is selected corresponding to the link having the highest channel gain among the links within a priority class. By adopting a Markov chain approach to analyze the state transition matrix that models the evolution of the buffers status, we derive analytical expressions for the outage probability and the average bit error rate. Analytical expressions for the steady-state probability vector are also obtained, and through these expressions, it is shown that states with the same probabilities can be grouped, thus reducing the size of the state transition matrix. We propose a general state-grouping-based method to obtain the reduced state transition matrix, which in turn reduces the computational complexity in obtaining the steady-state distribution. Our analytical and simulation results demonstrate that the proposed relaying scheme has better performance gain over the conventional max-link scheme. This paper investigates the buffer-aided relay selection problem for a decode-and-forward cooperative wireless network with @math relays. We propose a new relay selection scheme that incorporates the status of the relay buffers and the instantaneous strength of the wireless links. Specifically, each link is assigned with a weight related to the buffer status; then, the best relay is selected with the largest weight among all the qualified source–relay and relay–destination links. We derive the closed-form expression for the outage probability and the diversity gain by introducing several Markov chains (MCs) to model the evolution of the buffer status. The analysis shows that the proposed scheme can achieve the optimal diversity gain @math for a small @math (i.e., @math ), an improvement in comparison with the existing max-link scheme that achieves the optimal diversity gain only when @math is sufficiently large, where @math denotes the buffer size of each relay. The provided theoretical and numerical results confirm the performance gain of the proposed relay selection scheme over the existing max-link scheme.