The cognitive radio in TV white space with coexistence constraint

In this paper we investigate the rate region of the cognitive radio (CR) systems sharing the geographically used or unused spectrum in TV white space to accommodate the operation in real environment. That is, the primary user (PU) is a TV multi-casting system with one transmitter and several receivers; the secondary user (SU) is a Gaussian broadcast channel. In addition, the coexistence constraint which requires that PUs´ coding schemes and rates are not changed with the emergence of SU, should be satisfied. All transmitters and receivers are equipped with single antenna. To investigate the performance of the considered model, we formulate a power allocation problem to optimize the rate region of the CR system while not degrade any TV receivers. Then we use the uplink-downlink duality and the convexity of the dual problem to solve this optimization problem. Numerical results show that the considered CR system outperforms those purely using interference avoidance mode, especially when the probability of PU being active is high.