Design and Analysis of Chirp-Layered Superposition Coding for LoRa

2026-04-07

AI Summary

This work proposes a chirp-based layered superposition coding scheme to enhance the spectral efficiency of LoRa systems without compromising standard demodulation performance. Specifically, a high spreading factor (e.g., SF12) BPSK data stream is linearly superimposed onto a primary signal employing a lower spreading factor (e.g., SF7). The design maintains compatibility with conventional LoRa receivers by leveraging dechirping followed by DFT-based demodulation and exploiting the hierarchical structure of spreading factors, thereby enabling additional data transmission while minimally affecting the original link performance. Analytical bit error rate expressions for both signal layers are derived and validated through Monte Carlo simulations. The approach achieves significant gains in spectral efficiency under a simple transceiver architecture.

Abstract

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.

Problem

• LoRa
• superposition coding
• spectral efficiency
• chirp waveform
• demodulation interference

Innovation

• chirp-layered superposition coding
• LoRa
• spreading factor
• spectral efficiency
• BPSK