Joint Power Allocation for Energy Harvesting and Power Superposition Coding in Cooperative Spectrum Sharing

In this paper, a decode-and-forward type cooperative spectrum sharing scheme exploiting energy harvesting and power superposition coding is proposed. The secondary transmitter (ST) acting as a relay harvests energy in the first phase of every two phases from the radio frequency signal transmitted by the primary transmitter (PT) of the primary network (PN) and uses it in the second phase for transmitting power superposed codes of primary signal of the PN and secrecy signal of the secondary network (SN). The ST splits the received primary signal with adjustable power splitting ratio for decoding the primary signal and charging the battery. The harvested energy in addition to internal energy from the battery of the ST is used for power superposition coding with variable power sharing coefficient. Our main concern here is to know the impact of the two power parameters on outage performances (probabilities) of the PN and the SN. Impact of the other system parameters on outage performances is also considered to provide more comprehensive view of system operation. Analytical or mathematical expressions of the outage probabilities of the PN and the SN are derived in terms of the power parameters, location of the ST, channel gain, and other system related parameters. Jointly optimal power splitting ratio and power sharing coefficient achieving target outage probabilities of the PN and the SN are found from the expressions.