快速变化信道上的LoRa调制：较高的扩频因子是否必然更稳健？
The LoRa Modulation Over Rapidly-Varying Channels: Are the Higher Spreading Factors Necessarily More Robust?
摘要：
长距离（LoRa）通信技术的物理层采用线性调频扩频（CSS）调制方案。在本文中，我们研究了CSS在时变信道上的性能，这些信道的增益在接收LoRa帧期间可能会发生变化。这与文献中通常采用的模型相反，该模型假设信道增益在整个帧中是恒定的。具体而言，我们调查指数相关的瑞利衰落的CSS接收机的误帧率的影响，其中信道增益估计在每帧的开始。我们的主要观察结果是，在快速变化的信道中，随着有效载荷大小的增加，较大扩频因子的鲁棒性优势趋于消失。这一观察结果与较高的扩频因子必然提供更大的抗噪声能力的普遍看法相反，突出了在为可靠和节能的LoRa通信分配扩频因子时考虑信道特性和有效载荷大小的必要性。
英文摘要：
The chirp spread spectrum (CSS) modulation scheme is employed by the physical layer of the Long Range (LoRa) communication technology. In this paper, we examine the performance of CSS over time-varying channels whose gain may change during the reception of a LoRa frame. This is in contrast to the usually employed model in the literature, which assumes the channel gain to be constant throughout a frame. Specifically, we investigate the effects of exponentially correlated Rayleigh fading on the frame-error rate of a CSS receiver in which the channel gain is estimated at the beginning of each frame. Our primary observation is that over rapidly-varying channels, the robustness benefits of the larger spreading factors tend to disappear as the payload size grows. This observation, which is contrary to the common perception that higher spreading factors necessarily provide greater immunity against noise, highlights the need to consider channel characteristics and payload sizes in allocating the spreading factor for reliable and energy-efficient LoRa communications.
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