Outage Performance for NOMA-Based FSO-RF Systems With a Dual Energy Harvesting Mode

Energy harvesting (EH) is an effective approach that can not only extend the service life for those energy-constraint devices but also reduce the carbon footprint for wireless communication. Unlike the commonly used single EH scheme adopted in existing works, in this considered free-space optical-radio frequency (FSO-RF) system, a dual EH mode is considered, in which an EH relay is capable of harvesting energy from both the ambient RF signal in the environment and the direct-current component separated from the FSO signal simultaneously. In addition, in this considered system, a source node plans to communicate with two users equipped with multiple antennas via an EH relay on a non-orthogonal multiple access (NOMA) basis, and all the harvested energy of the relay is used to transmit the signal to both NOMA users. Moreover, assuming a selection-combining scheme is adopted at the user side, both the analytical and asymptotic expressions of outage probability for each NOMA user are presented, and the system performance with various atmospheric turbulence, detection technique, as well as pointing error is investigated. Finally, numerical results show that our proposed dual EH mode can lead to better outage performance than that with the single EH one.