Outer Bounds for the Symmetric Gaussian Cognitive Radio Channel with DPC Encoded Cognitive Transmitter

We present new outer bounds to the individual rates and the conditions under which these bounds become tight for the symmetric Gaussian cognitive radio (CR) channel in the low interference gain regime. The CR transmitter is assumed to use dirty paper coding while deriving the outer bounds. The capacity of the CR channel in the low interference scenario is known when the CR employs “polite” approach by devoting some portion of its power to transmit primary user’s (PU’s) message. However, this approach does not guarantee any quality of service for the CR users. Hence, we focus on the scenario when the CR goes for the “rude” approach, does not relay PU’s message and tries to maximize its own rates only. It is shown that when both CR and the PU operate in low interference gain regime, then treating interference as additive noise at the PU receiver and doing dirty paper coding at the CR is nearly optimal.