Achievable transmission rate of the secondary user in underlay cognitive radio networks over a Rayleigh fading channel

In this paper, achievable transmission rate of the secondary user in underlay cognitive radio networks over a Rayleigh fading channel is studied. We assume diversity combing technique is available at the secondary receiver. Under the constraints on average interference power at the receiver of primary user and peak transmit power at the transmitter of secondary user, for a given bit error ratio (BER) target, the optimal transmit power and modulation level of the secondary transmitter are derived with considering the interference generated by the activities of the primary transmitter. Thus, expression of achievable transmission rate can be obtained. Finally, achievable transmission rates are simulated for various power constraints, BER requirements and different number of diversity branches.