LR-FHSS Transceiver for Direct-to-Satellite IoT Communications: Design, Implementation, and Verification

This paper proposes a long range-frequency hopping spread spectrum (LR-FHSS) transceiver design for the Direct-to-Satellite Internet of Things (DtS-IoT) communication system. The DtS-IoT system has recently attracted attention as a promising non-terrestrial network (NTN) solution to provide high-traffic and delay-tolerant data transfer services, such as wide-area situational awareness (WASA) in smart grids and car share management in automotive applications, to IoT devices in global coverage. In particular, this study provides guidelines for the overall DtS-IoT system architecture and design details that conform to the Long Range Wide-Area Network (LoRaWAN). Furthermore, we also detail various DtS-IoT use cases. Considering low-Earth orbit (LEO) satellites, we develop the LR-FHSS transceiver to improve system efficiency, which is a leading attempt to build practical satellite communication systems using LR-FHSS, excluding commercial products. Moreover, we apply a robust synchronization scheme against the Doppler effect and co-channel interference (CCI) caused by LEO satellite channel environments, including signal detection for the simultaneous reception of numerous frequency hopping signals and an enhanced soft-output-Viterbi-algorithm (SOVA) for the header and payload receptions. Lastly, we present proof-of-concept implementation and testbeds using an application-specific integrated circuit (ASIC) chipset and a field-programmable gate array (FPGA) that verify the performance of the proposed LR-FHSS transceiver design of DtS-IoT communication systems. The laboratory test results reveal that the proposed LR-FHSS-based framework with the robust synchronization technique can provide wide coverage, seamless connectivity, and high-throughput communication links for the realization of future satellite communication networks.