The General Gaussian Multiple Access and Two-Way Wire-Tap Channels: Achievable Rates and Cooperative Jamming

摘要

The General Gaussian Multiple Access Wire-Tap Channel (GGMAC-WT) and theGaussian Two-Way Wire-Tap Channel (GTW-WT) are considered. In the GGMAC-WT,multiple users communicate with an intended receiver in the presence of aneavesdropper who receives their signals through another GMAC. In the GTW-WT,two users communicate with each other over a common Gaussian channel, with aneavesdropper listening through a GMAC. A secrecy measure that is suitable forthis multi-terminal environment is defined, and achievable secrecy rate regionsare found for both channels. For both cases, the power allocations maximizingthe achievable secrecy sum-rate are determined. It is seen that the optimumpolicy may prevent some terminals from transmission in order to preserve thesecrecy of the system. Inspired by this construct, a new scheme,\ital{cooperative jamming}, is proposed, where users who are prevented fromtransmitting according to the secrecy sum-rate maximizing power allocationpolicy "jam" the eavesdropper, thereby helping the remaining users. This schemeis shown to increase the achievable secrecy sum-rate. Overall, our results showthat in multiple-access scenarios, users can help each other to collectivelyachieve positive secrecy rates. In other words, cooperation among users can beinvaluable for achieving secrecy for the system.