STARS aided NOMA ambient backscatter communications

Simultaneously transmitting and reflecting surface (STARS) has emerged as a revolutionary technology to enable full spatial coverage. This paper investigates the application of STARS into non-orthogonal multiple access based ambient backscatter communication (NOMA-AmBC) networks, where the backscatter signals are separately reflected and transmitted to user n and user f with the help of STARS. Specifically, we derive new exact and approximate expressions of outage probability and ergodic rate for backscatter signals and a pair of users. Based on the asymptotic analytical results, the diversity order and multiplexing gain are provided for STARS-NOMA-AmBC networks. For the purpose of comparison, we further deduce the exact expressions of outage probability and ergodic rate for STARS aided orthogonal multiple access AmBC (STARS-OMA-AmBC) networks. The numerical results confirm our analysis and show that: (i) The outage behaviors of STARS-NOMA-AmBC are superior to that of STARS-OMA-AmBC; (ii) As the number of reconfigurable elements and backscatter coefficients increases, the backscatter signal has ability to acquire the greater performance gains; and (iii) The ergodic performance of STARS-NOMA-AmBC networks is better than that of reconfigurable intelligent surface assisted AmBC networks.