Large-Scale MIMO Relaying Techniques for Physical Layer Security: AF or DF?

TL;DR

This paper analyzes the secrecy performance of large-scale MIMO relaying systems using AF and DF techniques, showing AF's superiority at high power levels and identifying an optimal transmit power for maximizing secrecy capacity.

Contribution

It provides a comparative analysis of AF and DF relaying methods in LS-MIMO systems under practical assumptions, including imperfect CSI and no eavesdropper CSI.

Findings

AF outperforms DF at high transmit powers in secrecy performance.

An optimal transmit power exists that maximizes secrecy outage capacity.

Asymptotic analysis offers insights into system behavior at large scales.

Abstract

In this paper, we consider a large scale multiple input multiple output (LS-MIMO) relaying system, where an information source sends the message to its intended destination aided by an LS-MIMO relay, while a passive eavesdropper tries to intercept the information forwarded by the relay. The advantage of a large scale antenna array is exploited to improve spectral efficiency and enhance wireless security. In particular, the challenging issue incurred by short-distance interception is well addressed. Under very practical assumptions, i.e., no eavesdropper channel state information (CSI) and imperfect legitimate CSI at the relay, this paper gives a thorough secrecy performance analysis and comparison of two classic relaying techniques, i.e., amplify-and-forward (AF) and decode-and-forward (DF). Furthermore, asymptotical analysis is carried out to provide clear insights on the secrecy performance for such an LS-MIMO relaying system. We show that under large transmit powers, AF is a better choice than DF from the perspectives of both secrecy performance and implementation complexity, and prove that there exits an optimal transmit power at medium regime that maximizes the secrecy outage capacity.