Secrecy Sum-Rates for the Multiple-Access Wire-Tap Channel with Ergodic Block Fading

We consider a two-user multiple-access wiretap channel that undergoes ergodic block fading. In this scenario, there are two users are communicating with a base station in the presence of an eavesdropper, who has access to the communications through a multiple-access channel. We assume independent fading for each block, and that the fading process is ergodic. We also assume that the channel gains are measured accurately and are available to each transmitter and the eavesdropper in advance. We find the sum-rate maximizing power allocations for this case, and compare this to the instantaneous power control sum-rate. We also give a numerical solution when we incorporate cooperative jamming, where a user is allowed to use part of its power to jam the eavesdropper. In addition, we present an outer bound to the general multiple-access wire-tap channel, which is shown to be tight only for the degraded case.