Statistical Delay QoS Protection for Primary Users in Cooperative Cognitive Radio Networks

In cooperative cognitive radio networks, where secondary users (SU) can relay the signal of primary user (PU) in exchange for PU´s licensed spectrum, most existing works employ deterministic quality-of-service (QoS) guarantee in terms of minimum required transmission rate for PU´s protection. In this letter, we adopt the statistical QoS requirement characterized by queue-length bound violation probability for PU´s delay QoS provisioning. By applying the effective capacity theory, we further convert PU´s queue-length bound violation probability requirement to the equivalent effective capacity constraint and formulate the corresponding SU´s throughput maximization problem. Then, we obtain the optimal joint time-slot allocation scheme, where the time-slot division adapts to both channel conditions and PU´s delay QoS requirements, such that not only PU´s statistical delay QoS requirement can be well guaranteed, but also SU´s throughput can be optimized. Moreover, we also develop a fixed time-slot allocation scheme that only varies with PU´s delay QoS requirements. Simulation results show that both the optimal and fixed allocation schemes can flexibly perform time-slot divisions according to the delay QoS requirements of PU´s traffic, but the developed optimal scheme outperforms the fixed time-slot allocation scheme.