Capacity theorems for multi-functioning radios

We consider in this paper a system with multi-functioning radios: communication between nodes involve transmissions of both messages and source sequences. For point-to-point systems, this amounts to a simple trade-off between message transmission and source transmission: an optimal strategy is to split total capacity into two components, one for message transmission and one for source transmission as long as the message and the source sequence are independent of each other. For the multi-user case, we show that this is no longer the case by examining the simple problem of sending a common source sequence and two independent messages through a Gaussian broadcast channel.