LoRa backscatter (LB) communication systems can be considered as a potential candidate for ultra low power wide area networks (LPWAN) because of their low cost and low power consumption. In this paper, we comprehensively analyze LB modulation from various aspects, i.e., temporal, spectral, and error performance characteristics. First, we propose a signal model for LB signals that accounts for the limited number of loads in the tag. Then, we investigate the spectral properties of LB signals, obtaining a closed-form expression for the power spectrum. Finally, we derived the symbol error rate (SER) of LB with two decoders, i.e., the maximum likelihood (ML) and fast Fourier transform (FFT) decoders, in both additive white Gaussian noise (AWGN) and double Nakagami-m fading channels. The spectral analysis shows that out-of-band emissions for LB satisfy the European Telecommunications Standards Institute (ETSI) regulation only when considering a relatively large number of loads. For the error performance, unlike conventional LoRa, the FFT decoder is not optimal. Nevertheless, the ML decoder can achieve a performance similar to conventional LoRa with a moderate number of loads.

翻译：LoRa反向散射（LB）通信系统因其低成本和低功耗特性，可作为超低功耗广域网（LPWAN）的潜在候选方案。本文从时域、频谱和误码性能等多个维度对LB调制进行全面分析。首先，我们提出了考虑标签负载数量受限的LB信号模型；其次，研究了LB信号的频谱特性，推导出功率谱的闭式表达式；最后，推导了采用最大似然（ML）译码器和快速傅里叶变换（FFT）译码器两种方案时LB系统在加性高斯白噪声（AWGN）信道和双Nakagami-m衰落信道中的符号误码率（SER）。频谱分析表明，仅当标签负载数量较大时，LB的带外发射才能满足欧洲电信标准协会（ETSI）规范要求。在误码性能方面，与传统LoRa不同，FFT译码器并非最优方案，但ML译码器在中等负载数量下可实现与传统LoRa相近的性能。