Solutions for the MIMO Gaussian Wiretap Channel with a Cooperative Jammer

TL;DR

This paper derives a closed-form solution for the optimal artificial noise covariance in a MIMO Gaussian wiretap channel with a cooperative jammer, enhancing secrecy capacity without null space restrictions.

Contribution

It provides the first general MIMO solution for artificial noise design in wiretap channels with a helper, extending beyond SISO and MISO cases.

Findings

Closed-form expression for artificial noise covariance matrix.

Method to achieve good secrecy rates without null space constraints.

Applicable to general MIMO wiretap channels.

Abstract

We study the Gaussian MIMO wiretap channel with a transmitter, a legitimate receiver, an eavesdropper and an external helper, each equipped with multiple antennas. The transmitter sends confidential messages to its intended receiver, while the helper transmits jamming signals independent of the source message to confuse the eavesdropper. The jamming signal is assumed to be treated as noise at both the intended receiver and the eavesdropper. We obtain a closed-form expression for the structure of the artificial noise covariance matrix that guarantees no decrease in the secrecy capacity of the wiretap channel. We also describe how to find specific realizations of this covariance matrix expression that provide good secrecy rate performance, even when there is no non-trivial null space between the helper and the intended receiver. Unlike prior work, our approach considers the general MIMO case, and is not restricted to SISO or MISO scenarios.