Abstract: LoRa (Long Range Radio) system is in a relatively leading position in the currently developing LPWAN (Low Power Wide Area Network). Its MAC layer adopts an ALOHA-based access protocol. Although this access mechanism is simple and easy to implement, it can also easily aggravate the occurrence of conflicts and collisions, degrading the communication performance of the whole system. Therefore, it is necessary to study the mutual interference when multiple terminals occupy the channel resources at the same time. For an LoRa signal, its SF (Spreading Factor) determines the communication coverage of the signal. Thus, the effect of an interference signal on the demodulation performance of a transmitting signal was analyzed when the SF of the interfering signal was the same as or different from the SF of the transmitting signal. Experimental results show that the interference effect between the same SF signals is relatively large. When the SF used for the interference signal is different from that of the transmitting signal, the effect of interference is relatively small. The SIR (Signal-to-Interference Ratio) required for correct demodulation at the receiver side was obtained through theoretical analyses. It can be seen that LoRa signals with different SFs can be viewed as pseudo-orthogonal.

Key words: LPWAN (Low Power Wide Area Network), LoRa, SF (Spreading Factor), interference analysis, performance research

摘要： LoRa（Long Range Radio）系统在当前不断发展的低功率广域网（LPWAN）中处于相对领先地位。它的MAC层采用的是基于ALOHA 的接入协议。该接入机制虽然简单易实现，但同时也容易加剧冲突和碰撞的发生，降低整个系统的通信性能。因此，需要研究多个终端同时占用信道资源时的相互干扰情况，而LoRa信号的扩频因子（SF）将决定信号的通信覆盖范围。因此，分析了干扰信号的SF与发送信号的SF相同以及不同时，干扰信号对发送信号解调性能的影响。实验结果表明，相同SF信号间的干扰影响相对较大，而干扰信号使用的SF与发送信号不同时，干扰的影响相对较小。通过理论分析，获得了接收端正确解调时所要求的信干比（SIR）。可见，不同SF的LoRa信号可看作伪正交。

关键词: 低功率广域网, LoRa, 扩频因子, 干扰分析, 性能研究