On Secrecy Rate of the Generalized Artificial-Noise Assisted Secure Beamforming for Wiretap Channels

TL;DR

This paper proposes a generalized artificial-noise beamforming scheme for secure wireless communication, improving secrecy rates by optimally injecting noise in the main channel, especially when the legitimate channel quality is poor.

Contribution

It introduces a novel AN-assisted beamforming method that injects noise into the message direction, optimizing secrecy rate under partial eavesdropper channel knowledge.

Findings

Outperforms previous schemes, especially with poor legitimate channels.

Enlarges the regime of non-zero secrecy rate.

Provides an efficient algorithm for power allocation.

Abstract

In this paper we consider the secure transmission in fast Rayleigh fading channels with full knowledge of the main channel and only the statistics of the eavesdropper's channel state information at the transmitter. For the multiple-input, single-output, single-antenna eavesdropper systems, we generalize Goel and Negi's celebrated artificial-noise (AN) assisted beamforming, which just selects the directions to transmit AN heuristically. Our scheme may inject AN to the direction of the message, which outperforms Goel and Negi's scheme where AN is only injected in the directions orthogonal to the main channel. The ergodic secrecy rate of the proposed AN scheme can be represented by a highly simplified power allocation problem. To attain it, we prove that the optimal transmission scheme for the message bearing signal is a beamformer, which is aligned to the direction of the legitimate channel. After characterizing the optimal eigenvectors of the covariance matrices of signal and AN, we also provide the necessary condition for transmitting AN in the main channel to be optimal. Since the resulting secrecy rate is a non-convex power allocation problem, we develop an algorithm to efficiently solve it. Simulation results show that our generalized AN scheme outperforms Goel and Negi's, especially when the quality of legitimate channel is much worse than that of eavesdropper's. In particular, the regime with non-zero secrecy rate is enlarged, which can significantly improve the connectivity of the secure network when the proposed AN assisted beamforming is applied.