Capacity of cognitive radio under outage constraint with partial channel knowledge

This paper considers a cognitive radio network where a secondary user (SU) shares the same narrow spectrum band that is originally licensed to the primary user (PU) as long as the interference caused by the SU to the latter is below a prescribed threshold. At the SU, channel state information (CSI) is used to regulate the SU transmit power to limit the interference. In this respect, we assume only partial CSI is available to the SU, and investigate the SU ergodic capacity under the PU outage loss constraint as well as the peak/average transmit power constraint in Rayleigh fading channels. In particular, we derive the optimal power allocation to achieve the SU ergodic capacity, and further obtain closed-form expressions for the ergodic capacity. Numerical simulations are also given to corroborate our theoretical results.