An Index-Modulated FSCM Systems with Low Complexity Algorithm and Enhanced Data Rate

Frequency-Shift Chirp Modulation (FSCM) also known as LoRa modulation, enables long-distance transmission with low power consumption for Internet of Things (IOT), but has a limited transmission rate. Frequency-shift chirp spread spectrum system with index modulation (FSCSS_IM) introduces index modulation to improve the transmission rate of FSCM at the cost of high demodulation complexity. This letter propose an improved FSCSS_IM scheme to further improve the transmission rate of FSCM by adding indexes with equal values to the codebook. And then we design a low complexity demodulation algorithm which employs index matching to replace the index search matching algorithm in FSCSS_IM. Finally, we derive the approximate BER expression of the proposed scheme. The analysis and simulation results show that the transmission rate of the proposed scheme is up to 91.7% higher than that of the FSCM and 8.3% higher than that of the existing FSCSS_IM scheme, and the demodulation algorithm has the almost the same computational complexity as the FSCM and much lower than that of FSCSS_IM.