Differential Phase Shift Keying-Aided Multi-Mode Chirp Spread Spectrum Modulation

Long-range (LoRa) radio technology is one of the most prominent choices for the low-power wide area networks (LPWANs) applications. The LoRa technology enables long-range communications while effectively minimizing energy consumption and costs. However, the existing LoRa schemes suffer from low spectral efficiency and show a degraded bit-error-rate (BER) performance. To tackle this issue, in this letter, we propose a differential phase shift keying-aided multi-mode chirp spread spectrum (DPSK-MM-CSS) scheme. The proposed DPSK-MM-CSS scheme allows for information transmission not only by the frequency shifts of the multiple multiplexed chirp signals but also by the DPSK symbols, thereby significantly improving the spectral efficiency. Furthermore, we propose a low-complexity non-coherent detection algorithm for the DPSK-MM-CSS scheme. We also compare the spectral efficiency and BER performance of DPSK-MM-CSS with that of benchmark schemes. Comparison results indicate that the proposed DPSK-MM-CSS scheme, without requiring channel state information (CSI), can achieve a comparable BER performance and significantly higher spectral efficiency compared to the existing benchmark schemes.