On cooperative downlink transmission with frequency reuse

We study a three-node Gaussian relay channel with interference which is non-causally known at the source. It is assumed that the interference affects only the relay-destination link. This model is motivated by a downlink scenario, where the source (base station), communicates with two destinations. We present several transmission strategies for this class of relay channels. Our proposed relaying schemes can be divided into two main categories: instantaneous relaying and causal relaying. In the former, the relay functionality is restricted to a memoryless, symbol-by-symbol mapping (linear as well as non-linear). While in the latter, the relay has an infinite memory and utilizes past received blocks to cooperate in the present block. For causal relaying, we investigate decode-and-forward (DF), compress-and-forward (CF), and combined DF and CF. To utilize the knowledge of the interference at the source, superposition coding at the source and Costa encoding at the relay are employed. One interesting observation is that instantaneous relaying can achieve higher rates than those achieved with causal relaying.