IRS-Assistance with Outdated CSI: Element subset selection for secrecy performance enhancement

TL;DR

This paper examines how outdated channel information affects secrecy in IRS-assisted systems and proposes an element subset selection method to optimize secrecy performance.

Contribution

It introduces a novel element subset selection approach that improves secrecy performance under outdated CSI conditions in IRS-assisted systems.

Findings

Outdated CSI significantly impacts secrecy performance.

The proposed subset selection reduces secrecy outage probability.

Closed-form expressions determine the optimal number of IRS elements.

Abstract

In this work, we investigate the secrecy performance in an intelligent reflecting surface (IRS)-assisted downlink system. In particular, we consider a base station (BS)-side IRS and as such, the BS-IRS channel is assumed to be known perfectly. Of more importance, we consider the case, in which only outdated channel state information (CSI) of the IRS-user channel is available. We study the impact of outdated CSI on the secrecy performance numerically and analytically. Furthermore, we propose an element subset selection (ESS) method in order to improve the secrecy performance. A key observation is that minimal secrecy outage probability (SOP) can be achieved using a subset of the IRS, and the optimal number of selected reflecting elements can be effectively found by closed-form expressions.