An Optimality-Robustness Tradeoff in the Compress-and-Forward Relay Scheme

The compress-and-forward relay scheme developed by (Cover and El Gamal, 1979) is modified by realizing that it is not necessary for the destination to decode the compressed observation of the relay; and even if the compressed observation is to be decoded, it can be more easily done by joint decoding with the original message, rather than in a successive way. This modification introduces flexibility in choosing the compression rate at the relay, which improves the robustness of the compress-and-forward relay scheme in the application to uncertain networks. Nevertheless, it is also shown that this flexibility is associated with a penalty on the achievable rate, and higher than necessary compression rates will incur suboptimal achievable rates.