Secure Degrees of Freedom of the Gaussian MIMO Wiretap and MIMO Broadcast Channels with Unknown Eavesdroppers

TL;DR

This paper determines the maximum secure communication rates (SDoF) for Gaussian MIMO wiretap and broadcast channels with unknown eavesdroppers, showing that cooperative jamming achieves optimal security without eavesdropper channel information.

Contribution

It provides the exact sum SDoF for MIMO wiretap and broadcast channels with unknown eavesdroppers, introducing a new upper bound and demonstrating the optimality of cooperative jamming.

Findings

Exact sum SDoF characterized for the system.

A new upper bound on SDoF derived.

Cooperative jamming is optimal even without eavesdropper CSI.

Abstract

We investigate the secure degrees of freedom (SDoF) of the wiretap and the K user Gaussian broadcast channels with multiple antennas at the transmitter, the legitimate receivers and an unknown number of eavesdroppers each with a number of antennas less than or equal to a known value NE. The channel matrices between the legitimate transmitter and the receivers are available everywhere, while the legitimate pair have no information about the eavesdroppers' channels. We provide the exact sum SDoF for the considered system. A new comprehensive upperbound is deduced and a new achievable scheme based on utilizing jamming is exploited. We prove that cooperative jamming is SDoF optimal even without the eavesdropper CSI available at the transmitters.