A Novel Symbiotic Backscatter-NOMA System

Abstract

This article proposes a symbiotic backscatter non-orthogonal multiple access (backscatter-NOMA) system, where a backscatter device (BD) conveys its own information $c(n)$ to two users by riding on the NOMA downlink signal. Notably, different from the conventional backscatter-NOMA, the BD adaptively adjusts its reflection coefficient to guarantee the successful decoding of the NOMA downlink signal and the backscatter signal $c(n)$ at the two users, relying on the decoding requirement of $c(n)$ at the two users. To depict the overall transmission robustness of the concurrent NOMA downlink and the backscatter link, we introduce a metric of coexistence outage probability (COP) and develop its tight upper bound. Also, asymptotic analysis shows that, unlike the conventional backscatter-NOMA, the COP of the proposed symbiotic system obeys the scaling law of $\frac{\ln (P_{s})}{P_{s}}$ , which eliminates the error floor of the conventional solution. In addition, for different decoding requirements of $c(n)$ , it is shown that the optimal power allocations of the NOMA signal depend on different system parameters.