satellite Internet of things, sparse code multiple access, multi-user detection, message passing algorithm, state position information, Information technology, T58.5-58.64, Management information systems, T58.6-58.62

Satellite-based Internet of Things is critical to realize the intelligent connection of all things in 6G. However, the dual constraints of spectrum resources and onboard payload capabilities present significant challenges in enhancing access efficiency for a massive number of users. To deal with the problem of low multi-user detection efficiency in satellite-borne receivers utilizing sparse code multiple access (SCMA), a state position information based log message passing algorithm (SPI-Log-MPA) by taking the variability of the transmission probability of codewords during the iterative process into account was proposed. Through reducing unreliable codewords, decoding stable users in advance, and implementing a reward and penalty mechanism for unstable users, the proposed algorithm significantly improves detection efficiency. In addition, a two-phase improved algorithm was also proposed by optimizing both the phase setting and state position information matrices, which further accelerates the algorithm convergence. Complexity analysis and simulation results demonstrate that the proposed two algorithms can achieve lower computational complexities while maintaining the bit error rate (BER) performance.