Effects of primary user interference and channel estimation errors on ergodic capacity of secondary user

This paper studies the impact of primary user interference and imperfect estimation of channel between secondary transmitter and primary receiver on the ergodic capacity of secondary user in a spectrum sharing environment under an average received-power constraint, in presence of Rayleigh fading. We consider that a secondary user is allowed to access the spectral band allocated to a primary user as long as the average interference caused by the secondary user to the latter is below a predetermined threshold. The secondary user performs minimum mean square error (MMSE) estimation of the channel gain between its transmitter and the receiver of the primary user. We analyze the ergodic capacity, outage probability as well as the optimal power allocation strategy of the secondary user. Further we derive a closed-form expression for ergodic capacity considering the effects of primary user interference and imperfect channel information, which is validated by a simulation model in MATLAB. The results indicate that both the primary user interference and channel estimation error significantly degrade the ergodic capacity of the secondary user.