Low-complexity CSMA communication system for satellite IoT environments based on non-orthogonal sparse codebooks

This paper proposes a low-complexity compressive sensing multiple access (CSMA) communication system based on non-orthogonal sparse codebooks in sparse code multiple access (SCMA) for the special environments of satellite Internet of Things (IoT) communications. At the transmitter (Tx), a measurement matrix constructed from multi-user codebooks measures multi-user data, replacing linear traditional SCMA encoding. At the receiver (Rx), leveraging the sparse characteristic of active satellite IoT users, the smoothed L0 (SL0) algorithm is used instead of the traditional message passing algorithm (MPA) and logarithmic-message passing algorithm (Log-MPA), significantly reducing the number of multiplication operations and, in turn, greatly lowering computational complexity. The proposed scheme has been experimentally validated in a W-band wireless communication system with a transmission distance of 6 meters and 12 meters, achieving 4.5 Gb/s. For input optical power (IOP) ranging from -3 dBm to 3 dBm, whether in the case of 1/6 or 1/3 user activity, the bit error rate (BER) performance of the SL0 algorithm outperforms that of the MPA and Log-MPA. Furthermore, in terms of computational cost, the SL0 algorithm can achieve a maximum 85.7% and 72.8% in computational complexity reduction rate (CCRR) compared to the MPA and Log-MPA, respectively. These results indicate that the proposed scheme has significant potential for application in satellite IoT communication scenarios.