The rapid growth of Internet-of-Things (IoT) devices demands communication systems that are both spectrally efficient and energy frugal. Backscatter communication (BackCom) is an attractive low-power paradigm, but its spectral efficiency declines in dense deployments. This paper presents an uplink BackCom design that integrates non-orthogonal multiple access (NOMA) and maximizes system energy efficiency (EE). In a bistatic network where multiple backscatter nodes (BNs) harvest RF energy and alternate between sleep and active modes, we formulate a fractional program with coupled time, power, and reflection variables and develop a Dinkelbach-based alternating optimization (AO) algorithm with closed-form updates. Analysis reveals two operating modes depending on power availability, circuit demands and propagation conditions. Simulations show the proposed design adapts the time allocation, achieving up to 8% higher EE than fixed-power and 68% than no-sleep baselines, and delivering up to 127% EE gains over orthogonal multiple access (OMA). These results establish NOMA-enabled BackCom as a scalable, energy efficient solution for large-scale IoT deployments.

翻译：物联网设备的快速增长要求通信系统兼具频谱高效与能量节约的特性。反向散射通信是一种极具吸引力的低功耗范式，但在密集部署中其频谱效率会下降。本文提出一种上行链路反向散射通信设计，该设计集成了非正交多址接入技术，并最大化系统能量效率。在一个多路反向散射节点采集射频能量并在睡眠与活跃模式间切换的双站网络中，我们构建了一个耦合时间、功率与反射系数的分式规划问题，并开发了一种基于Dinkelbach方法的交替优化算法，该算法具有闭式更新步骤。分析揭示了两种运行模式，其选择取决于功率可用性、电路需求与传播条件。仿真表明，所提设计能够自适应调整时间分配，相较于固定功率基准方案实现高达8%的能量效率提升，相较于无睡眠基准方案提升68%，并且相比正交多址接入方案带来高达127%的能量效率增益。这些结果确立了NOMA使能的反向散射通信作为大规模物联网部署的可扩展、高能效解决方案。