A new achievable ergodic secrecy rate region for the fading multiple access wiretap channel

We give a new achievable ergodic secrecy rate region for the two-user fading multiple access wiretap channel. Our scheme creates a vector channel between the two transmitters and the intended receiver that has full-rank and creates another vector channel between the two transmitters and the eavesdropper whose rank is 1. In this sense, our scheme removes interference from the main receiver multiple access channel by introducing an extra dimension in this channel, while sustaining the interference in the eavesdropper multiple access channel by keeping the rank of this channel equal to one. We show that the secrecy sum rate achieved by our scheme scales with SNR. In particular, we show that a total number of 1/2 secure degrees of freedom is achievable for the two users. Moreover, we compare our scheme with the Gaussian signaling scheme with cooperative jamming which improves significantly over the plain Gaussian signaling scheme. Our proposed scheme outperforms Gaussian signaling schemes (with or without cooperative jamming) at high signal-to-noise ratios (SNR). In particular, we show that Gaussian signaling schemes with or without cooperative jamming achieve zero secure degrees of freedom, while our proposed scheme achieves 1/2 total secure degrees of freedom.