Full-Duplex Relay Selection in Cognitive Underlay Networks

TL;DR

This paper analyzes the performance of full-duplex relay selection in spectrum-sharing networks, highlighting its potential to improve secondary throughput while managing interference constraints, with detailed theoretical and simulation results.

Contribution

It provides the first exact analysis of opportunistic full-duplex relay selection performance considering residual self-interference and interference constraints in cognitive networks.

Findings

Full-duplex relay selection offers significant diversity gain.

Residual self-interference impacts end-to-end performance.

Relay selection can boost secondary throughput under interference constraints.

Abstract

In this work, we analyze the performance of full-duplex relay selection (FDRS) in spectrum-sharing networks. Contrary to half-duplex relaying, full-duplex relaying (FDR) enables simultaneous listening/forwarding at the secondary relay(s), thereby allowing for a higher spectral efficiency. However, since the source and relay simultaneously transmit in FDR, their superimposed signal at the primary receiver should now satisfy the existing interference constraint, which can considerably limit the secondary network throughput. In this regard, relay selection can offer an adequate solution to boost the secondary throughput while satisfying the imposed interference limit. We first analyze the performance of opportunistic FDRS with residual self-interference (RSI) by deriving the exact cumulative distribution function of its end-to-end signal-to-interference-plus-noise ratio under Nakagami-m fading. We also evaluate the offered diversity gain of relay selection for different full-duplex cooperation schemes in the presence/absence of a direct source-destination link. When the adopted RSI link gain model is sublinear in the relay power, which agrees with recent research findings, we show that remarkable diversity gain can be recovered even in the presence of an interfering direct link. Second, we evaluate the end-to-end performance of FDRS with interference constraints due to the presence of a primary receiver. Finally, the presented exact theoretical findings are verified by numerical simulations.