# Relay-Pair Selection in Buffer-Aided Successive Opportunistic Relaying using a Multi-Antenna Source

## TL;DR

This paper proposes relay-pair selection strategies in buffer-aided, multi-antenna source cooperative networks to mitigate inter-relay interference, enhancing throughput and outage performance through precoding and phase alignment techniques.

## Contribution

It introduces novel relay-pair selection policies that leverage precoding and phase alignment to reduce inter-relay interference in buffer-aided cooperative networks.

## Key findings

- Precoding at the source can fully cancel inter-relay interference with global CSI.
- Phase alignment reduces IRI when only CSIR is available.
- Proposed policies outperform existing schemes in throughput and outage metrics.

## Abstract

We study a cooperative network with a buffer-aided multi-antenna source, multiple half-duplex (HD) buffer-aided relays and a single destination. Such a setup could represent a cellular downlink scenario, in which the source can be a more powerful wireless device with a buffer and multiple antennas, while a set of intermediate less powerful devices are used as relays to reach the destination. The main target is to recover the multiplexing loss of the network by having the source and a relay to simultaneously transmit their information to another relay and the destination, respectively. Successive transmissions in such a cooperative network, however, cause inter-relay interference (IRI). First, by assuming global channel state information (CSI), we show that the detrimental effect of IRI can be alleviated by precoding at the source, mitigating or even fully cancelling the interference. A cooperative relaying policy is proposed that employs a joint precoding design and relay-pair selection. Note that both fixed rate and adaptive rate transmissions can be considered. For the case when channel state information is only available at the receiver side (CSIR), we propose a relay selection policy that employs a phase alignment technique to reduce the IRI. The performance of the two proposed relay pair selection policies are evaluated and compared with other state-of-the-art relaying schemes in terms of outage and throughput. The results show that the use of a powerful source can provide considerable performance improvements.