Folded Chirp-Rate Shift Keying Modulation for LEO Satellite IoT

In the low earth orbit (LEO) satellite Internet of Things (IoT), the IoT devices can be distributed in remote areas (e.g., desert, ocean, and forest) for some special applications, where they are unable to have direct terrestrial network accesses and can only be covered by satellite. But in the LEO satellite scenario, it has to face the effects of high doppler and fast doppler rate, due to satellite movement at high speed and utilization of higher frequency bands. So fine frequency synchronization and frequency track are necessary to be done, even for LORA. In this paper, we propose a folded chirp-rate shift keying (FCrSK) modulation with strong immunity to doppler effect. Its data information is mapped to different folded chirp-rate waveforms, which have an advantage of the consistency of bandwidth and symbol length among chirp-rates compared to traditional chirp-rate shift keying system. Moreover, we analyze the optimal non-coherent receiver in case of the doppler channel, whose optimal decision depends on signal energy focusability in frequency spectrum after dechirp, so frequency peak average rate adopts as a decision criterion. Furthermore, system parameters' setting is discussed so as to maximize system modulation efficiency with the minimum interference among chirp-rate. Finally, some simulations are provided to analyze robustness to doppler shift and doppler-rate in the system. And based on universal software radio platform (USRP), some experimental measurements are made to validate its feasibility under the realistic wireless environment and doppler environment.