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背向散射（LB）通信系统因其低成本与低功耗特性，可被视为超低功耗广域网（LPWAN）的潜在候选方案。本文从时域、频谱及差错性能特征等多个维度全面分析了LB调制技术。首先，我们提出了一种考虑标签中有限负载数量的LB信号模型；其次，研究了LB信号的频谱特性，获得了功率谱的闭式表达式；最后，在加性高斯白噪声（AWGN）信道和双Nakagami-m衰落信道下，推导了采用最大似然（ML）译码器和快速傅里叶变换（FFT）译码器两种方案时的符号差错率（SER）。频谱分析表明，仅当负载数量相对较大时，LB的带外发射方能满足欧洲电信标准协会（ETSI）的规定。在差错性能方面，与传统LoRa不同，FFT译码器并非最优方案；然而，采用中等负载数量时，ML译码器可实现与传统LoRa相似的性能。