Secrecy in Cooperative Relay Broadcast Channels
The authors investigate the effects of user cooperation on the secrecy of broadcast channels by considering a cooperative relay broadcast channel. They show that user cooperation can increase the achievable secrecy region. They propose an achievable scheme that combines Marton's coding scheme for broadcast channels and Cover and El Gamal's compress-and-forward scheme for relay channels. They derive outer bounds for the rate-equivocation region using auxiliary random variables for single-letterization. Finally, they consider a Gaussian channel and show that both users can have positive secrecy rates, which is not possible for scalar Gaussian broadcast channels without cooperation.