Joint Overlay and Underlay Power Allocation Scheme for OFDM-Based Cognitive Radio Systems

In this paper, we investigate joint overlay and underlay power allocation for OFDM-based cognitive radio (CR) systems. Unlike existing work in literature where power is allocated in either overlay only or underlay fashion, we propose schemes which perform a joint allocation. Specifically, the total capacity of CR is maximized while maintaining a total power budget and keeping the interference introduced to the primary user (PU) band below a threshold. As the complexity of optimal scheme can be high, a suboptimal scheme has also been proposed. Presented simulation results show that a significant gain in transmission capacity is achieved by using joint overlay and underlay allocation scheme as compared to either overlay or underlay only scheme. Further, numerical results show that even our proposed suboptimal scheme outperforms either overlay or underlay only scheme.