Outage and SEP Performance of Secondary User in Spectrum Sharing with Imperfect Channel Estimation

Cognitive radio (CR) has evolved as a promising technique to increase spectrum utilization by allowing secondary user (SU) to coexist with primary user (PU) satisfying the interference constraint imposed by PU in terms of an acceptable level of primary outage. In this paper we evaluate the performance of a secondary user (SU) in terms of outage probability and symbol error probability (SEP) where the SU adapts its transmit power based on an activity model of PU and estimation of channel between the SU transmitter and the PU receiver which is assumed to be Rayleigh faded. During the presence of PU, imperfect channel state information (CSI) available at SU transmitter is used to estimate the instantaneous transmit power of SU under an acceptable outage constraint of PU, while the SU transmits at the maximum power level (Pm) during the absence of PU. A power control with a scaling factor has been proposed for SU to maintain the interference constraint on PU in terms of maximum allowable outage. A simulation test bed is developed in MATLAB to assess the performance of SU. The impact of PU interference threshold, imperfection in CSI, primary user outage constraint, and the maximum level of transmit power on SU performance is investigated. We also highlight the effects of imperfection in CSI on primary outage. Further the effects of constellation size (M) of the transmitted MPSK signal of SU is indicated on the outage and SEP performance of SU.