Efficient Design of Chirp Spread Spectrum Modulation for Low-Power Wide-Area Networks

LoRa is an abbreviation for low power and long range and it refers to a communication technology developed for low-power wide-area networks (LPWANs). Based on the principle of chirp spread spectrum (CSS), LoRa technology is very attractive to provide low bit-rate wireless connections over an extended communication range and under very low power consumption. While the medium access control (MAC) layer of LoRa specifications is open for developers, the physical layer is not. In particular, LoRa modulation and demodulation techniques are patented by Semtech and have not been mathematically described in detail. This paper presents novel approaches to modulate and demodulate LoRa signals with very high implementation efficiency, great flexibility, and excellent performance. In particular, compared to the commercially available receiver made by Semtech, the proposed design is shown to yield a saving of transmitted power from 0.9 to 2.5 dB over the spreading factor (SF) range of 6-12. Moreover, this paper suggests a method to exploit the phase information of CSS signals to encode extra information bits, leading to throughput improvement over the conventional CSS system, for example, by 33%, 25%, 20%, and 17% for SFs of 6, 8, 10, and 12, respectively.