Cut to the Chase: A Fast-Decoding Scheme for Symbiotic Backscatter Multi-User NOMA Systems

This paper proposes a fast-decoding scheme based on the successive interference cancellation (SIC) framework for symbiotic backscatter multi-user non-orthogonal multiple access (NOMA) systems, which aims to decode the desired primary NOMA signal and the backscatter signal for the end-users in an efficient manner. Under the proposed decoding framework, we derive a closed-form expression of the coexistence outage probability (COP) with perfect SIC for the end-users over Nakagami-m fading channel. More importantly, the diversity order is determined by the bottleneck fading parameter of the two-hop backscatter channels in most general cases, but is dominated by the bottleneck fading parameter of the primary and backscatter channels in a rare special case. Due to the influence of the residual interference, the COP with imperfect SIC would converge to an error floor. Moreover, we formulate the symbiotic constraints to guarantee the minimum decoding times and a shorter decoding time than the conventional solutions, and further derive the corresponding successful fast-decoding probability at high transmit signal-to-noise ratio (SNR). The results show that by keeping a weak primary channel statistics or lowering the threshold to decode the backscatter signal, the proposed fast-decoding scheme outperforms conventional schemes in terms of decoding times.