Optimal power allocation under QoS constraints in cognitive radio systems

Cognitive radio technology aims at the efficient utilization of the limited radio resources and the improvement of flexibility of spectrum usage in wireless networks. The main idea of this technology is the development of intelligent networks where the unlicensed secondary users may coexist with the licensed primary users, always limited by the obligation not to affect their communication. In this paper, we consider a spectrum underlay cognitive radio system operating in fading environment. Guaranteeing that the average interference limit constraint to primary users is satisfied, we propose a quality of service (QoS)-driven power allocation scheme, with a view to maximizing the effective capacity of the secondary users. The proposed scheme takes into consideration the interference of primary user to the secondary user, in order to accomplish the optimal allocation more realistically. Finally, the proposed allocation scheme has been evaluated through numerical simulations that confirm the presented theoretical analysis.