Message-Cognizant Assistance and Feedback for the Gaussian Channel

A formula is derived for the capacity of the Gaus-sian channel with a message-cognizant rate-limited helper that provides a noncausal description of the noise to the encoder and the decoder. This capacity is strictly larger than when the helper is message oblivious. It is shown that, in this setup, a feedback link from the receiver to the encoder does not increase capacity. However, in the presence of such a link, said capacity can be achieved even if the helper is oblivious to the transmitted message.