Distributed Power Control Based on Linear Quadratic Optimal Controller for Cognitive Radio Network

We propose a distributed closed-loop power control scheme for a cognitive radio network (CRN) based on our developed state space model of the CRN. The whole power control process is separated into outer control loop and inner control loop in order to solve different problem. In outer loop, the interference temperature (IT) constraint is transformed to a performance index minimized by a state feedback controller to obtain an appropriate target signal to interference plus noise ratio (SINR) of secondary user (SU). For ideal channel model and random time varying channel model, our designed controller is a linear quadratic regulator (LQR) and a linear quadratic Gaussian (LQG) regulator respectively. While in inner loop, SU controls its transmit power to make the instantaneous SINR track the corresponding target and ensure the IT constraint under the limited threshold. The closed-loop stability of the CRN is proved and the performance of proposed control scheme is presented by computer simulations, which shows that this scheme can effectively guarantee both the requirement of SINR and IT constraint for all SUs.