Relay Selection for Two-way Relaying with Amplify-and-Forward Protocols

TL;DR

This paper introduces a relay selection protocol for bi-directional relay networks using amplify-and-forward, optimizing relay choice based on SER to enhance performance with lower complexity.

Contribution

It proposes a simple Min-Max relay selection criterion and derives asymptotic SER expressions, improving relay selection efficiency and system performance in two-way relay networks.

Findings

Min-Max relay selection achieves near-optimal performance.

Asymptotic SER expressions match simulation results.

Optimal power allocation significantly improves system performance.

Abstract

In this paper, we propose a relay selection amplify-and-forward (RS-AF) protocol in general bi-directional relay networks with two sources and $N$ relays. In the proposed scheme, the two sources first transmit to all the relays simultaneously, and then a single relay with a minimum sum symbol error rate (SER) will be selected to broadcast the received signals back to both sources. To facilitate the selection process, we propose a simple sub-optimal Min-Max criterion for relay selection, where a single relay which minimizes the maximum SER of two source nodes will be selected. Simulation results show that the proposed Min-Max selection has almost the same performance as the optimal selection with lower complexity. We also present a simple asymptotic SER expression and make comparison with the conventional all-participate amplify-and-forward (AP-AF) relaying scheme. The analytical results are verified through simulations. To improve the system performance, optimum power allocation (OPA) between the sources and the relay is determined based on the asymptotic SER. Simulation results indicate that the proposed RS-AF scheme with OPA yields considerable performance improvement over an equal power allocation (EPA) scheme, specially with large number of relay nodes.