Improving User Capacity of Satellite Internet of Things via Joint User Grouping and Multi-Beam Processing

We explore a satellite internet of things (SIoT) system, wherein multiple IoT users are allowed to access the SIoT in a grant-free manner. Such a manner may incur the severe co-frequency interference (CFI), and decease the user capacity in terms of the number IoT users successfully accessing the SIoT. To this end, we first design two beam preprocessing oriented user grouping methods, called user distribution based user grouping (UDUG) and user position based user grouping (UPUG), respectively. With respect to the UDUG, we propose the regional statistical channel state information based multi-beam processing (RsCSI-MBP). For the UPUG, we conceive the user statistical channel state information with position error based MBP (UsCSIPe-MBP). Both the RsCSI-MBP and the UsCSIPe-MBP schemes can mitigate inter-beam CFI relying on MBP, wherein the optimized beamforming vectors are obtained by using generalized Rayleigh quotient. Furthermore, the user capacity, preamble collision probability and packet loss probability are analyzed for the RsCSI-MBP and UsCSIPe-MBP schemes. Numerical results demonstrate that the UsCSIPe-MBP scheme outperforms the RsCSI-MBP and the conventional seven-color frequency-reuse multibeam schemes in terms of a higher user capacity and a lower packet loss probability, even considering the satellite mobility, phase and amplitude inconsistence of the antenna array used.