This paper investigates the design of chirp-layered superposition coding for LoRa, where an additional waveform is linearly superposed on a standard LoRa transmission with minimal impact on the LoRa demodulation process. We first show that any non-zero superposed signal perturbs the output of the standard dechirp-and-DFT demodulator, and then characterize the class of superposed waveforms that minimize this degradation under a given power budget. In particular, we show that a high spreading factor (high-SF) LoRa waveform superposed on a low-SF signal (e.g., SF12 on SF7) can be designed so that its impact on the standard LoRa demodulation remains small. As a result, within each low-SF symbol interval, the high-SF segment can be treated as a quasi-narrowband carrier that conveys an additional BPSK stream. We derive analytical error-rate expressions for both the low-SF LoRa layer and the superposed high-SF layer, and validate them through Monte Carlo simulations. The proposed chirp-layered superposition coding scheme improves the spectral efficiency of LoRa-based links and uses a relatively simple transceiver architecture.

翻译：本文研究了 LoRa 的啁啾分层叠加编码设计，其中一种附加波形与标准 LoRa 传输进行线性叠加，且对 LoRa 解调过程的影响最小。我们首先证明，任何非零的叠加信号都会扰动标准解啁啾-DFT 解调器的输出，然后刻画了在给定功率预算下能够最小化这种退化的叠加波形类别。具体而言，我们证明，将高扩频因子（高SF）LoRa 波形叠加在低SF信号（例如，在 SF7 上叠加 SF12）上可以设计为使其对标准 LoRa 解调的影响保持较小。因此，在每个低SF符号间隔内，高SF段可以被视为一个准窄带载波，传输额外的 BPSK 数据流。我们推导了低SF LoRa 层和叠加的高SF层的解析误码率表达式，并通过蒙特卡洛仿真进行了验证。所提出的啁啾分层叠加编码方案提高了基于 LoRa 链路的频谱效率，并采用了相对简单的收发器架构。