Power Control of Cognitive Radio System in Rayleigh Fading

An adaptive power control scheme for cognitive radio system (CRS) in Rayleigh fading channel is proposed. The transmit power of a secondary user (SU) is adjusted in Rayleigh fading to maximize the constant output signal-to-noise ratio (SNR) at an SU receiver while keeping the interference to a primary user (PU) under given constraints. To calculate the maximum constant output SNR at the SU receiver under the interference constraints of the PUs, we develop an analytical model for the distribution of the interference to PUs while considering the detection performance at the SUs. The analytical model takes into account of the use of multiple antennas and includes a single antenna scenario as a special case. The proposed scheme is compared with a straightforward fixed power control scheme for the CRS in terms of bit-error-rate (BER). Results show that the proposed adaptive power control scheme outperforms the fixed power control scheme. For example, when the BER is 10 3 the adaptive power control scheme with two transmit antennas and two receive antennas has a 3-dB improvement in SNR as compared with the fixed power control scheme.