Outage-constrained power control in spectrum sharing systems with partial primary CSI

Due to limited cooperation between the primary users and the secondary users (SUs), the SUs only have partial channel state information related to the primary receiver. Under such an assumption, this paper investigates power allocation strategies for the SUs in spectrum sharing systems subject to an outage probability constraint on the primary transmission and a peak transmit power constraint on the secondary transmission. The challenge lies in the non-convexity of the outage probability constraint. We investigate two methods to solve the non-convex optimization problem. First, strong duality is shown to be satisfied. Since the Karush-Kuhn-Tucker (KKT) conditions are then necessary but not sufficient for optimality, we derive the KKT solutions and address the optimality issue of the solutions. Alternatively, the non-convex constraint is replaced by a stricter convex constraint. A more conservative suboptimal solution is thus obtained, which corresponds to the solution of the problem with the conventional interference temperature constraint. Simulation results show that both proposed strategies outperform constant-power transmission. The superiority of the optimal strategy over the suboptimal one is also verified.