On adaptive modulation and power control for cognitive radios with primary user outage constraint

We study power and rate adaptation for cognitive radios in fading channels, with the objective to maximize the average spectral efficiency of the secondary user (SU) transmitter. The average transmit power and bit error rate (BER) constraints of the SU is considered, together with either the short-term or the long-term outage constraint over the channel state of the primary user (PU). In each case, the optimal power and rate solutions are derived. Unlike previous works on power and rate adaptation for cognitive radios, in this work the cochannel interferences between the SU and PU are explicitly modeled and related to their respective average BER and outage requirements, as well as their respective power and rate variables. Numerical results are presented to provide insights into the dynamics of the power and rate solutions.