Joint power and sensing optimization for hybrid cognitive radios with limited CSIT

The problem of optimal Power Policy (PP) design for hybrid interweave/underlay Cognitive Radio (CR) systems is investigated, in the presence of imperfect Spectrum Sensing (SS). A limited Channel State Information at the Transmitter (CSIT) scenario is considered, that has never been studied before, where the Secondary Transmitter (STx) uses combined instantaneous and statistical CSIT. Given such CSIT, the optimal PP with the aim of maximizing the average transmission rate of the CR system, subject to a constraint on the average interference caused by STx transmission to the primary system, is found. The derived PP is then exploited for the development of an iterative framework for the problem of jointly optimizing the sensing time and the applied PP. By means of simulations, it is shown that the proposed joint SS and PP optimization framework offers a clear gain in terms of the achievable rate of the CR system, with respect to conventional underlay and interweave CR systems, especially for intermediate values of the average interference constraint and also for different primary user activity regimes.