Power control for cognitive radio networks under channel uncertainty

Cognitive radio (CR) networks can re-use the RF spectrum licensed to a primary user (PU) network, provided that the interference inflicted to the PUs is carefully controlled. However, due to lack of explicit cooperation between CR and PU systems, it is often difficult for CRs to acquire CR-to-PU channels accurately. In fact, if the PU receivers are off, the sensing algorithms cannot obtain the channels for the PU receivers, although they have to be protected nevertheless. In order to achieve aggressive spectrum re-use even in such challenging scenarios, power control algorithms that take channel uncertainty into account are developed. Both log-normal shadowing and small-scale fading effects are considered through suitable approximations. Accounting for the latter, centralized network utility maximization (NUM) problems are formulated, and their Karush-Kuhn-Tucker points are obtained via sequential geometric programming. For the case where CR-to-CR channels are also uncertain, a novel outage probability-based NUM formulation is proposed, and its solution method developed in a unified fashion. Numerical tests verify the performance merits of the novel design.