On Joint Power Control and Adaptive Modulation for Cognitive Radios

We study joint power control and adaptive modulation for cognitive radios in an interference channel with multiple primary users (PUs) and multiple secondary users (SUs). By exploiting the PU channel (in terms of signal-to-interference-plus-noise-ratio (SINR)) and the PU interference to SUs, two iterative power control algorithms are proposed to optimize the total throughput performance of CR systems, subject to the tolerable interference limits at the PUs. In the proposed Algorithm 1, we show that for optimal throughput performance, in addition to the channel gains from the SU transmitters to the PU and SU receivers (as commonly assumed in the literature), the SU transmitters also need to know the PU interference to the SU receivers, as well as the SINRs at the PU receivers. In the proposed Algorithm 2, the SU transmitters need to know only the PU interference to the SU receivers, in addition to the channel gains from the SU transmitters to the PU and SU receivers, but not require to know the PU channels.