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Delay-QoS-Driven Secrecy Power Allocation in Underlay Secure Cognitive Radio System

In this paper, we investigate the power allocation policy for an underlay secure cognitive radio (CR) system with statistical delay quality-of-service (QoS) guarantees. The objective is to maximize the secure effective capacity of the secondary user (SU) in CR system, which represents the maximum secrecy constant arrival rate with delay QoS requirements for the secrecy system. The constrains include the average transmission power of the SU and the interference power to the PU. Both the average interference power and the peak interference power are taken into account in the problem formulation. A closed-form power allocation scheme is derived via employing the Lagrangian dual method and the Karush-Kuhn-Tucker optimization conditions. It is shown that the fading states of the wiretap channel and the peak interference power to the PU have significant impacts on the QoS driven power adaptation. Simulation results demonstrate that our proposed power policy outperforms other policies in improving the system throughput with delay QoS guarantees, especially when the delay QoS requirement is strict.