Power allocation for cognitive radio with hybrid energy supplies

In this paper, we investigate the power allocation problem for a point-to-point cognitive radio (CR) with the secondary user (SU) powered by both the renewable energy and the conventional energy. In particular, the transmission of the SU is assumed to be divided into time slots, and a transmission outage constraint is proposed to provide a satisfactory quality of service (QoS) to the SU by restricting the number of slots whose rate is lower than the target rate. Meanwhile, an interference outage constraint is proposed to guarantee the QoS of the primary user (PU) by restricting the number of slots whose interference power is higher than the predefined interference power threshold. Under the proposed transmission outage and interference outage constraints together with the energy causality constraint, the power allocation problem to minimize the total conventional energy consumption of the SU is investigated and a heuristic scheme is proposed. We show that the proposed power allocation scheme greatly outperforms the reference random scheme. We also show that relaxing the transmission outage constraint is more effective in reducing the conventional energy consumption of the SU than relaxing the interference outage constraint.