M-Ary Direct Modulation Chirp Spread Spectrum for Spectrally Efficient Communications

Spread spectrum techniques, such as the Chirp Spectrum (CSS) used by LoRa technology, are important for machine-to-machine communication in context of Internet Things. They offer high processing gain, reliable over long ranges, robustness to interference and noise harsh environments, etc. However, these features compromised their poor spectral efficiency, resulting a very low data transmission rate. This paper deals with spectrally efficient variant CSS. The system uses M-ary phase keying modulate exploits CSS’s properties transmit modulated symbols overlapping chirps. chirp signals may affect performance due inter-symbol interference. Therefore, we analyse relationship between number overlaps effect (ISI), also determine BER expression function overlaps. Finally, derive optimal that corresponds minimum error probability.