A Novel Symbiotic Backscatter-NOMA System

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 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.