Enhancing Spectral Efficiency in CSS Modulation via Cumulative Encoding

Conventional Chirp Spread Spectrum (CSS) modulation typically transmits one data symbol per chirp, resulting in low spectral efficiency. In this paper, we propose a novel concurrent transmission scheme, termed Cumulative Encoding-CSS (CE-CSS), that enhances spectral efficiency by allowing multiple symbols to be transmitted within a single chirp duration. In the proposed scheme, the input bit stream is first segmented into symbols and then cumulatively encoded into groups. Within each group, every cumulative sum is mapped to a distinct chirp signal, and these chirps are superimposed and transmitted concurrently. At the receiver, dechirping followed by FFT-based peak detection and differential decoding enables the recovery of multiple symbols from a single composite chirp. Simulation results demonstrate that CE-CSS can significantly improve spectral efficiency while retaining the inherent robustness and low-power advantages of traditional CSS modulation.