On Secure Communication over Multiple Access Wiretap Channels under Channel Uncertainty

The problem of secure communication over a multiple access wiretap channel (MAWC) is studied. Here, two transmitters send confidential messages to a legitimate receiver while keeping a non-legitimate eavesdropper ignorant of them. In this paper, this communication scenario is studied for compound channels, for which it is only known to the users that the actual channel realization is fixed and belongs to a known set of possible channels. The criterion of strong secrecy is analyzed and its impact on the decoding performance of the eavesdropper is specified. It is shown that the average decoding error at the eavesdropper approaches one exponentially fast regardless of the applied decoding strategy. Furthermore, an achievable strong secrecy rate region is presented and a multi-letter outer bound is derived. Both together establish a multi-letter description of the strong secrecy capacity region.