Energy cooperation for reciprocally-benefited spectrum access in cognitive radio networks

In this paper, we develop an energy cooperation scheme for secondary users´ (SU) spectrum access in the hybrid energy supply primary system, which will improve both energy efficiency and spectral efficiency. Specifically, the cooperation is implemented into two stages. In the first stage, the secondary system is allowed to access the licensed for secondary transmission. Simultaneously, the primary system harvests energy from the secondary radio-frequency signals. In the second stage, the primary system employs the energy from the energy harvester and the constant energy source for primary transmission in the remaining slot. Both the primary and secondary systems will benefit from our proposed energy cooperation scheme. The secondary system is allocated to access the spectrum freely and the primary system can harvest energy from SUs´ radio-frequency signals. To analyze the throughput performance of both the primary and secondary systems, we derive the closed-form expressions of the outage probability and ergodic capacity for the delay-limited and delay-tolerant transmission modes, respectively. Simulation results verify the analytical results and demonstrate that compared with direct transmission, the performance of the primary system in terms of throughput improves and the secondary system acquires more spectrum opportunities for the secondary transmission.