Cross-layer based power allocation over cognitive wireless relay link with statistical delay QoS guarantees

In this paper, we propose a cross-layer based power allocation scheme with statistical delay QoS guarantees for the cognitive (secondary) amplify-and-forward relay link, which coexists with one primary link by sharing particular portion of the spectrum. Specifically, our derived power allocation scheme aims at maximizing the effective capacity of the cognitive relay link, which can be seen as the maximum arrival rate supported by the system under given QoS constraints. In our work, not only the average total transmit power and average interference power constraints are considered, but also the impact of the interference from the primary link to the cognitive relay link is taken into consideration. Simulation results show that the effective capacity of the cognitive relay link varies with the statistical QoS constraints. In particular, the stringent QoS constraint will cause low effective capacity. Moreover, we observe that the average total transmit power and average interference power are two important parameters, which will obviously impact the performance of the cognitive relay link. In addition, we find that the transmission of the primary link will significantly affect the performance of the cognitive relay link, such that a larger transmit power of the primary link will cause the performance degradation of the cognitive relay link.