Optimal Power Control over Fading Cognitive Radio Channels by Exploiting Primary User CSI

This paper is concerned with spectrum sharing cognitive radio networks, where a secondary user (SU) or cognitive radio link communicates simultaneously over the same frequency band with an existing primary user (PU) link. It is assumed that the SU transmitter has the perfect channel state information (CSI) on the fading channels from SU transmitter to both PU and SU receivers (as usually assumed in the literature), as well as the fading channel from PU transmitter to PU receiver (a new assumption). With the additional PU CSI, we study the optimal power control for the SU over different fading states to maximize the SU ergodic capacity subject to a new proposed constraint to protect the PU transmission, which limits the maximum ergodic capacity loss of the PU resulted from the SU transmission. It is shown that the proposed SU power-control policy is superior over the conventional policy under the constraint on the maximum tolerable interference power/interperferecne temperature at the PU receiver, in terms of the achievable ergodic capacities of both PU and SU. Index Terms Cognitive radio, ergodic capacity, fading channel, power control, spectrum sharing.