在“万物互联”的愿景下，物联网技术的应用领域和物联网系统的覆盖范围都在迅速扩张。随着物联网终端设备数量的增长，设备的功耗问题得到了广泛的关注。功耗水平在很大程度上决定了物联网设备的使用寿命，较短的使用寿命意味着频繁的设备维护或更换，在海量终端设备的基数下带来了不可忽视的成本。因此，低功耗技术是物联网的重要研究领域之一。 无线通信模块是物联网设备的重要功能模块，其消耗的能量相当可观，并且难以通过集成电路等技术进行优化。近年来，反向散射技术由于其低功耗特性得到了大量的研究和应用。这是一种利用外界电磁波进行通信，节省用于生成本地载波的能量，从而大幅降低设备功耗的技术。一些工作将低功耗广域网技术与反向散射相结合，设计出的LoRa反向散射系统能够以微瓦级别的功耗实现上千米的反向散射上行通信。然而，当前的反向散射系统具有较高的下行通信功耗，这阻碍了系统总体功耗的进一步降低。 本文针对反向散射系统中低功耗下行通信的需求，提出了一种适用于LoRa反向散射系统的低功耗下行通信设计。该设计构建了一条从LoRa设备向反向散射设备发送数据的下行通信链路，利用低频载波的优良特性降低了接收端的能量消耗，并且无需对发送端设备做任何硬件修改。本文详细描述了该设计的通信协议、硬件架构以及算法实现，解决了下行通信信号幅度控制难、载波信号放大难和解码功耗高的挑战，并着重分析了该设计在接收灵敏度、抗干扰能力和接收端功耗方面的优势。本文在商用LoRa设备和印刷电路板（PCB）上实现了该设计的原型系统，并通过实验验证了系统的可行性和性能。实验结果表明，系统具有-47dBm的接收灵敏度和-3dB的信噪比要求，以及15.57μW的接收端平均功耗。 综上所述，本文面向反向散射系统的功耗瓶颈，提出了一种具有极低接收端功耗，并适用于LoRa反向散射系统的下行通信设计。本文实现了该设计的原型系统，并对其进行了可行性和性能的测试。本文的设计能够降低反向散射设备的总体功耗，优化反向散射系统的下行通信性能，为反向散射系统的无线部署、网络管理、数据安全等功能提供下行通信的技术基础，提升反向散射系统的可靠性。

In the vision of ＂Internet of Everything＂, both the application areas of IoT （the Internet of Things） technology and the coverage of IoT systems are expanding rapidly. With the growing number of IoT terminal devices, the issue of device power consumption has received widespread attention. The power consumption level largely determines the lifespan of IoT devices. A shorter lifespan implies frequent device maintenance or replacement, leading to significant costs, especially given the massive number of terminal devices. Therefore, low-power consumption technology is one of the important research areas in the field of IoT. The wireless communication module is a module with critical function of IoT devices, consuming considerable energy and being difficult to optimize through technologies such as integrated circuits. In recent years, backscatter technology has garnered significant research and application attention due to its low-power characteristics. It utilizes external electromagnetic waves for communication, saving energy used for generating local carriers, thus significantly reducing device power consumption. Some research combines low-power wide-area network （LPWAN） technology with backscatter, the designed LoRa backscatter systems can achieve thousands of meters of backscatter uplink communication with microwatt-level power consumption. However, current backscatter systems have relatively high power consumption for downlink communication, hindering further reduction of overall system power consumption. This paper addresses the demand for low-power downlink communication in backscatter systems and proposes a low-power downlink communication design suitable for LoRa backscatter systems. The design constructs downlink communication from LoRa devices to backscatter devices, leveraging the excellent characteristics of low-frequency carriers to reduce energy consumption of the receiver, without requiring any hardware modifications to the transmitter. This paper provides detailed descriptions of the communication protocol, hardware architecture, and algorithm implementation of this design, addressing challenges such as difficulty in controlling signal amplitude, signal amplification of carrier signals, and high decoding power consumption. This paper emphasizes the advantages of the design in terms of receiving sensitivity, anti-interference capability, and power consumption of receiver. The prototype system of this design is implemented on commercial LoRa devices and printed circuit boards （PCBs）, and its feasibility and performance are verified through experiments. Experimental results demonstrate a receiving sensitivity of -47dBm, a signal-to-noise ratio （SNR） requirement of -3dB, and an average receiver power consumption of 15.57μW. In conclusion, this paper proposes a low-power downlink communication design tailored to the power consumption bottleneck in backscatter systems and suitable for LoRa backscatter systems. The prototype system of this design is implemented and tested for feasibility and performance. This design can reduce the overall power consumption of backscatter devices, optimize the downlink communication performance of backscatter systems, provide downlink communication technology for wireless deployment, network management, data security and other functions of backscatter systems, and enhance the reliability of backscatter systems.