A Comparative Analysis of MU-NOMA IRS- and Relay-Assisted Symbiotic Radio IoT Networks

This work analyzes the energy-efficiency (EE) performance of two types of energy harvesting secondary networks (SN) in a symbiotic radio network (SRN) relationship with a multi-user non-orthogonal multi-access primary network. The first SN type comprises of a multiple secondary transmitters semi-passive (i.e., equipped with sensing capabilities) intelligent reflective surface using backscatter technology to communicate with a secondary receiver. While the second SN type consists of multiple multi-antenna decode-and-forward relaying sensors communicating with an SRN. Closed-form expressions are derived for the achievable EE, which correlate exactly with Monte Carlo simulations. In addition, the IRS-enabled SRN shows higher EE compared to the relay-enabled SRN due to lower power consumption and higher reflective surface spatial diversity.