Minimum Throughput Maximization for Peer-Assisted NOMA-Plus-TDMA Symbiotic Radio Networks

This letter studies a symbiotic radio network (SRN) with multiple backscatter devices (BDs) coexisting with a primary receiver. A hybrid peer-assisted non-orthogonal-multiple-access (NOMA)-plus-dynamic-time-division-multiple-access (TDMA) scheme is proposed. Under this scheme, BDs are categorized into different clusters, and only one cluster is allowed to transmit in each time slot. Within each cluster, NOMA is adopted. The latter cluster can harvest energy from previous clusters using peer assistance. We maximize the minimum throughput among all BDs by jointly optimizing the BS’s power allocation, BDs’ power reflection coefficients and the time allocation under practical constraints. Particularly, a practical energy causality constraint is considered, and the effect of imperfect successive interference cancellation (SIC) of NOMA is also studied. Numerical results show that the peer-assisted NOMA-plus-TDMA scheme achieves satisfactory throughput gain over conventional schemes. It is also shown that peer assistance does help in terms of improving the system throughput and fairness.