Optimal Number of Transmit Antennas for Secrecy Enhancement in Massive MIMOME Channels

TL;DR

This paper analyzes how selecting an optimal number of transmit antennas in massive MIMO wiretap channels can maximize secrecy throughput, revealing that too many antennas can harm security performance.

Contribution

It introduces an analytical method to determine the optimal number of transmit antennas for secrecy enhancement in massive MIMO systems using large-system approximations.

Findings

Optimal antenna number maximizes secrecy throughput.

Increasing antennas beyond the optimal point reduces security.

Analytical results match simulations well.

Abstract

This paper studies the impact of transmit antenna selection on the secrecy performance of massive MIMO wiretap channels. We consider a scenario in which a multi-antenna transmitter selects a subset of transmit antennas with the strongest channel gains. Confidential messages are then transmitted to a multi-antenna legitimate receiver while the channel is being overheard by a multi-antenna eavesdropper. For this setup, we approximate the distribution of the instantaneous secrecy rate in the large-system limit. The approximation enables us to investigate the optimal number of selected antennas which maximizes the asymptotic secrecy throughput of the system. We show that increasing the number of selected antennas enhances the secrecy performance of the system up to some optimal value, and that further growth in the number of selected antennas has a destructive effect. Using the large-system approximation, we obtain the optimal number of selected antennas analytically for various scenarios. Our numerical investigations show an accurate match between simulations and the analytic results even for not so large dimensions.