Relay-Based Spectrum Sharing With Secondary Users Powered by Wireless Energy Harvesting

Spectrum sharing and energy harvesting are promising techniques to improve the bandwidth and energy efficiencies to meet the ever-growing demand of wireless data transmissions. In this paper, we propose an efficient relay-based spectrum sharing protocol in the cognitive radio network, where the secondary user (SU) can implicitly harvest the radio frequency (RF) energy from the primary user (PU) transmissions. Using the harvested energy, the SU can assist the PU transmission to exchange for the opportunity of spectrum access. Both the Alamouti coding and the superposition coding techniques are adopted by the transmitters to facilitate the primary data relaying and the secondary data transmission simultaneously. The joint decoding and the interference cancelation techniques are adopted by the receivers to retrieve the desired signals. The more power allocated for the primary data relaying, the higher throughput can be achieved for the PU, while the less throughput is available for the SU with less energy remained. The optimal power allocation is numerically determined by maximizing the SU throughput while guaranteeing the PU throughput. Numerical results show that our protocol can greatly improve the system throughput and the impacts of various system settings are revealed for the network deployment.