On the capacity of the symmetric interference channel with a cognitive relay at high SNR

The capacity of the Interference Channel with a Cognitive Relay, a channel model which generalizes the broadcast, interference and cognitive interference channels, is still an open question. Towards understanding this complex channel, we first consider the binary linear deterministic model that approximates the Gaussian channel at high SNR. We consider symmetric channel gains and show achievability of a tightened version of a previously known outer bound for almost all channel parameters. Of particular interest in this channel model is how the cognitive relay may be used to simultaneously relay as well as cancel/neutralize interference at the two receivers. The achievability schemes used to prove capacity use combinations of three main strategies at the cognitive relay that we term bit cancellation, bit sharing, and bit (self)cleaning. We highlight the capacity achieving schemes in the different regimes, pointing out some of the interesting new behaviors seen at the cognitive relay.