A Novel Symbiotic Backscatter-NOMA System
Hancheng Yang, Haiyang Ding, Maged Elkashlan, Haipeng Li, Kewei Xin
Abstract
This article proposes a symbiotic backscatter non-orthogonal multiple access (backscatter-NOMA) system, where a backscatter device (BD) conveys its own information <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$c(n)$</tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$c(n)$</tex-math></inline-formula> at the two users, relying on the decoding requirement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$c(n)$</tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\frac{\ln (P_{s})}{P_{s}}$</tex-math></inline-formula> , which eliminates the error floor of the conventional solution. In addition, for different decoding requirements of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$c(n)$</tex-math></inline-formula> , it is shown that the optimal power allocations of the NOMA signal depend on different system parameters.