نبذة مختصرة : International audience ; In this paper, we investigate the secrecy energy-efficiency of a multi-user downlink non-orthogonal multiple access (NOMA) system with ambient backscatter communication in the presence of a passive eavesdropper. We formulate the optimization problem as a trade-off between secrecy sum-rate and total power consumption, which is inherently non-convex due to interference and variable coupling. A closed-form solution for the optimal reflection coefficient is derived, transforming the optimization problem into a convex power allocation that has been recently solved in a closed form. The solution can also be utilized to efficiently maximize the ratio between the secrecy sum-rate and power consumption, requiring only a line search. Simulation results show that the proposed approach outperforms conventional NOMA and orthogonal multiple access (OMA) schemes, with or without backscatter, in terms of secrecy energy-efficiency.
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