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In this paper, we present a relaying scheme which combines the spectral efficiency of successive opportunistic relaying with the robustness of single-link selection. More specifically, we propose the min − power scheme that minimizes the total energy expenditure per time slot under an inter-relay interference (IRI) cancellation scheme. It is the first time that interference cancellation is combined with buffer-aided relays and power adaptation to mitigate the IRI and minimize the energy expenditure.The new relay selection policy is analyzed in terms of outage probability and diversity by modeling the evolution of the relay buffers as a Markov Chain. We construct the state transition matrix of the I. Krikidis is with the ECE Department, University of Cyprus, Nicosia 1678 (E-mail: krikidis@ucy.ac.cy).Preliminary results of this work have been published in [1]. This paper extends the work further through detailed algorithm description, discussion on channel state information schemes, outage probability and diversity analysis, extra illustrative examples and performance evaluation scenarios based on various system parameters.

In this work, we present a buffer-aided successive opportunistic relaying scheme that aims at improving the average capacity of the network when inter-relay interference arises between relays that are selected for simultaneous transmission and reception. We propose a relay selection policy that, by exploiting the benefits of buffering at the relays, decouples the receiving relay at the previous time slot to be the transmitting relay at the next slot. Furthermore, we impose an interference cancellation threshold allowing the relay that is selected for reception to decode and subtract the inter-relay interference. The proposed relaying scheme selects the relaying pair that maximises the average capacity of the relay network. Its performance is evaluated through simulations and comparisons with other state-of-the-art half-duplex and full-duplex relay selection schemes, in terms of outage probability, average capacity and average delay. The results reveal that a trade-off has to be made between improving the outage at the cost of reduced capacity and increased delay and vice versa. Finally, conclusions are drawn and future directions are discussed, including the need for a hybrid scheme incorporating both half-duplex and full-duplex characteristics.

Abstract-In this paper we consider a simple cooperative network consisting of a source, a destination and a cluster of decode-and-forward relays characterized by the half-duplex constraint. At each time-slot the source and (possibly) one of the relays transmit a packet to another relay and the destination, respectively. When the source and a relay transmit simultaneously, inter-relay interference is introduced at the receiving relay. In this work, with the aid of buffers at the relays, we mitigate the detrimental effect of inter-relay interference through either interference cancellation or mitigation. More specifically, we propose the min − power opportunistic relaying protocol that minimizes the total energy expenditure per time slot under an inter-relay interference cancellation scheme. The min − power relay-pair selection scheme, apart from minimizing the energy expenditure, also provides better throughput and lower outage probability than existing works in the literature. The performance of the proposed scheme is demonstrated via illustrative examples and simulations in terms of outage probability and average throughput. I. INTRODUCTIONRelaying cooperation is an efficient technique to combat fading and path-loss effects in wireless systems. It enables multiple nodes to create virtual multiple-input multiple-output (MIMO) configurations in order to provide transmit and/or receive spatial diversity to single-antenna destinations [1]. Traditional cooperative systems are characterized by the halfduplex constraint and thus relay nodes cannot receive and transmit data simultaneously resulting in bandwidth loss. In order to overcome this limitation, several techniques have been proposed in the literature [2]. Among them, the successive relaying scheme in [3] incorporates two relays and proposes a transmission overlap (source-relay (SR), relay-destination (RD)) which mimics full-duplex transmission. On the other hand, for networks with multiple relay nodes, relay selection has been introduced as a promising solution that exploits the available channel diversity degrees by keeping the implementation complexity low. In earlier works, relays were assumed to lack data buffers and selection was based on the maxmin criterion and its variations (see, for example, [4]-[6] and references therein). As a result, the relay that received the

In this work, we propose a buffer-aided successive opportunistic relay scheme where each time a relay-pair is selected with the target of rate maximization. Due to overlapping transmissions by the source and the relay which transmits to the destination, inter-relay interference arises. The efficient mitigation of inter-relay interference either through cancellation or avoidance, requires increased channel state information. Thus, in order to reduce the implementation complexity induced by centralized selection, distributed switch-and-stay combining is combined with buffer-aided successive opportunistic relaying. In this way, by applying a rate threshold we can avoid increased relay-pair switching and channel state information acquisition. The efficiency of the proposed scheme is demonstrated through simulations and comparisons with other state-of-the-art relay selection policies.

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