Outage and SEP of secondary user with imperfect channel estimation and primary user interference

Spectrum sharing in a cognitive radio network aims to improve the spectrum efficiency where a secondary user (SU) shares the spectrum band licensed to the primary user causing a limited interference to the PU. However, the performance of a SU will be affected by interference from the PU. In this paper we investigate the impact of PU interference on symbol error probability (SEP) and outage probability of SU under constraint of PU outage. The channel state information (CSI) available at SU 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 (P_m) during the absence of PU. A power control scheme based on a scaling factor is proposed for SU so as to maintain a desired outage constraint on PU even in case of imperfect CSI. A closed form expression for outage probability of SU under PU interference is developed. A simulation test bed has been developed in MATLAB to assess the performance of SU in terms of SEP and outage probability with imperfect CSI in presence of PU interference. 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.