A Tutorial on Chirp Spread Spectrum Modulation for LoRaWAN: Basics and Key Advances

Chirp spread spectrum (CSS) signal is the heart of long-range (LoRa) modulation, also known as CSS modulation, and is used in long-range wide area network (LoRaWAN) in Internet of things (IoT) scenarios. CSS modulation has drawn much attention from the research and industry communities in recent years. However, to the best of our knowledge, a comprehensive tutorial, investigating the mathematical foundations of CSS modulation in the LoRaWAN application, is missing in the literature. Therefore, in the first part of this paper, we provide a thorough analysis and tutorial of CSS modulation as the physical (PHY) layer of LoRaWAN, discussing various aspects such as signal generation, detection, error performance, and spectral characteristics. Moreover, a summary of key recent advances in the context of CSS modulation modifications and applications in IoT networks is presented in the second part of this paper under four main categories, i.e., transceiver configuration and design, data rate improvement, interference modeling, and synchronization algorithms. Finally, future research directions are also provided to discuss the potential issues and solutions for improving the performance of CSS modulation in LoRaWAN.