Enhanced Group-Based Chirp Spread Spectrum Modulation: Design and Performance Analysis

LoRa is one of the most prominent low power wide area network (LPWAN) technologies for Internet of Things (IoT) applications. As the core technique of LoRa physical (PHY) layer, chirp spread spectrum (CSS) modulation is employed to support low power and long range communications. Although it provides a compelling trade-off between coverage and data rate, the relatively low spectral efficiency (SE) is still a limiting factor for its extensive applications. In this paper, we propose two enhanced group-based CSS modulation schemes, named IQ-GCSS (in-phase and quadrature group-based CSS) and TDM-GCSS (time domain multiplexed group-based CSS), which can achieve much higher SE than the conventional LoRa modulation. The transmitter architectures of our proposed modulation schemes are presented along with both coherent and non-coherent detection methods. Moreover, an overall performance analysis of our proposed schemes is provided in terms of bit error rate (BER) and computational complexity. Numerical results not only validate the accuracy of our theoretical analysis but also demonstrate substantial performance improvements of our proposed schemes in terms of effective throughput compared to the classical counterparts.