Achievable Rates for Embedded Bidirectional Relaying in a Cellular Downlink

In this work we provide an achievable rate region for the cellular downlink with three users where two users want to communicate with each other. Due to the side information from the prior uplink, gains are achievable by combining bidirectional and classical broadcast channel coding strategies. A coding theorem for the bidirectional broadcast channel with random state non-causally known at the encoder is generalized to continuous alphabets and applied to Gaussian channels with an average power constraint. The single-user capacities are achievable if one decoder additionally knows the channel state. Accordingly, we see that a more comprehensive view on the information flow in a multi-user network can lead to a larger achievable rate region.