Optimal Power Allocation for OFDM-Based Cognitive Radios with Imperfect Channel Sensing

Opportunistic spectrum access in Cognitive Radio (CR) systems significantly improves spectrum efficiency by allowing secondary users (SUs) to opportunistically use licensed spectrum without causing harmful interference to primary users (PUs). However, as a prevailing transmission scheme, OFDM introduces unwanted interference to the primary user due to its side-lobe leakage. Meanwhile, miss detection and false alarm caused by imperfect sensing of SUs inevitably degrade PU´s performance to a certain extent. In this paper, we propose an efficient power allocation algorithm for an OFDM-based CR system taking into account the interference resulted from both side-lobe leakage and imperfect channel sensing, simultaneously. The algorithm we propose maximizes the downlink transmission capacity of the CR users, while keep the Co-channel Interference (CCI) and the Side-lobe Interference (SLI) introduced by the CR users under a tolerable level. Based on the convex optimization theory, we leverage the dual decomposition method (DDM) to solve the problem of the optimal power allocation. Simulation results demonstrate the effectiveness of this approach in context of protecting PU´s transmission.