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.
The main idea of Max-Link is to select in each time slot the strongest link among all the available SR and RD links (i.e., among @math links) for transmission @cite_28 . For independent and identically distributed (i.i.d.) links and no delay constraints, Max-Link achieves a diversity gain of @math , which is twice the diversity gain of BRS and MMRS. Max-Link has been extended in @cite_40 to account for direct source-destination (SD) connectivity, which provides resiliency in low transmit SNR conditions @cite_28 . In @cite_12 @cite_31 @cite_4 @cite_34 , some buffer-aided relay selection protocols improve the Max-Link performance by: reducing the average packet delay, maintaining a good diversity gain, and or achieving full diversity gain with a smaller buffer size compared to Max-Link. In summary, the previous schemes (MMRS, HRS and Max-Link) only use buffer-aided relay selection for cooperative single-antenna systems.
@cite_4 @cite_28 @cite_40 @cite_31 @cite_34 @cite_12
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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. The performance analysis of optimal decode-and-forward (DF) relay selection for the full-duplex (FD) mode in underlay cognitive radio (CR) networks is studied, with the impact of critical parameters such as the residual self-interference, the distributions of the received signal-to-noise ratio (SNR), and the outage probability, being analyzed. Different from the conventional relay selection schemes with half-duplex (HD) mode, the FD relay suffers from the impact of residual self-interference due to its simultaneous transmission and reception using the same channel. Furthermore, the exact closed-form expressions for the outage probabilities of the proposed FD relay-selection scheme over both independent Nakagami- @math and Rayleigh fading channels are derived, with the validity of the proposed analysis being proven by using simulation. Numerical results show that, in the presence of multiple candidate relays, an optimum relay-selection solution in terms of outage probability can always be achievable within the SNR range of (10 dB, 15 dB). 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. 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.