Secure Transmission with Artificial Noise over Fading Channels: Achievable Rate and Optimal Power Allocation

TL;DR

This paper analyzes secure multi-antenna transmission over fading channels, deriving achievable secrecy rates, optimizing power allocation between signals and artificial noise, and examining effects of eavesdropper collusion and imperfect channel information.

Contribution

It provides a closed-form expression for secrecy rate, optimal power allocation strategies, and insights into artificial noise use under various eavesdropper scenarios and channel knowledge conditions.

Findings

Equal power allocation is near optimal for non-colluding eavesdroppers.

More artificial noise power benefits colluding eavesdroppers.

An SNR upper bound ensures positive secrecy rate at low SNR.

Abstract

We consider the problem of secure communication with multi-antenna transmission in fading channels. The transmitter simultaneously transmits an information bearing signal to the intended receiver and artificial noise to the eavesdroppers. We obtain an analytical closed-form expression of an achievable secrecy rate, and use it as the objective function to optimize the transmit power allocation between the information signal and the artificial noise. Our analytical and numerical results show that equal power allocation is a simple yet near optimal strategy for the case of non-colluding eavesdroppers. When the number of colluding eavesdroppers increases, more power should be used to generate the artificial noise. We also provide an upper bound on the signal-to-noise ratio (SNR) above which the achievable secrecy rate is positive and show that the bound is tight at low SNR. Furthermore, we consider the impact of imperfect channel state information (CSI) at both the transmitter and the receiver and find that it is wise to create more artificial noise to confuse the eavesdroppers than to increase the signal strength for the intended receiver if the CSI is not accurately obtained.