The Effects of Limited Channel Knowledge on Cognitive Radio System Capacity

We examine the impact of limited channel knowledge on the secondary user (SU) in a cognitive radio system. Under a minimum signal-to-interference-and-noise ratio (SINR) constraint for the primary user (PU) receiver, we determine the SU capacity under five channel knowledge scenarios. We derive analytical expressions for the capacity cumulative distribution functions and the probability of SU blocking as a function of allowable interference. We show that imperfect knowledge of the PU-PU channel gain by the SU-Tx often prohibits SU transmission or necessitates a high interference level at the PU. We also show that errored knowledge of the PU-PU channel is more beneficial than statistical channel knowledge and imperfect knowledge of the SU-Tx to PU-Rx link has a limited impact on SU capacity.