Achievable rates in three-user interference channels with one cognitive transmitter

In this paper, we derive a lower bound on the capacity of a three-user interference channel with one cognitive transmitter. The cognitive transmitter is assumed to have noncausal knowledge of the messages of the other senders. The receivers of the non-cognitive users are allowed to decode a part (called public information) of the message from the cognitive transmitter, while the receiver of the cognitive user cannot decode any message from the non-pairing senders. We consider first a discrete memoryless version of the channel and derive a set of achievable rates, by employing a combination of Cover´s superposition coding technique and Gel´fand-Pinsker´s binning technique used to code for channels with random parameters. We then consider the Gaussian channel model to numerically evaluate and plot the achievable rate region. Results demonstrate that, with noncausal message sharing, more rate triples are achievable on the three-user cognitive channel than the classical three-user interference channel. This work is a sequel of the results for the three-user cognitive radio channels, where the authors introduced two ways of noncausal unidirectional message-sharing mechanism, namely cumulative message sharing (CMS) and primary-only message sharing (PMS).