Cooperative spectrum sharing with energy harvesting best secondary user selection and non-orthogonal multiple access

We propose two novel cooperative spectrum sharing (CSS) protocols by using time-switching and power-splitting based energy harvesting (EH), namely CSS-TSP and CSS-PSP, respectively. The considered system consists of a set of energy constrained secondary transmitters (STs) that cooperate with the primary user to forward its symbol. All STs rely on the harvested energy from the source signal to forward the primary symbol. In exchange of cooperation, one of the STs behaving as the best EH decode-and-forward relay (ST
_br
) gets channel access simultaneously with the primary user according to the non-orthogonal multiple access. Two ST
_br
selection strategies, namely ST
_br
selection based on harvested energy in current block of time and ST
_br
selection based on harvested energy from current plus previous blocks of time, have been proposed. The distributed nature of the ST
_br
selection in the proposed schemes to forward the primary symbol increases the network lifetime. We have investigated the achievable sum data rate/throughput of both CSS-TSP and CSS-PSP. Moreover, the optimal EH ratio that maximizes the sum data rate of both protocols is also investigated numerically.