SCMA Multiple Access Technology in Satellite Internet of Things System

The satellite communication technology is suitable as a supplement to the ground communication network. It can be applied in the Internet of things (IoT) system to form a satellite IoT system. However, the satellite IoT system has its inherent disadvantages that need to be solved urgently. Therefore, how to improve the spectrum utilization rate of the satellite IoT system while maintaining good error performance has become a key research issue. In this paper, we propose to apply SCMA technology to the satellite IoT system. SCMA technology is a code domain non-orthogonal multiple access technology. Its basic idea is to map user bits into high-dimensional complex digital codewords according to a predetermined codebook set at the transmitting end, and then all users multiplex their codewords on the same time–frequency resource according to a factor graph (or mapping matrix). When the received signal, channel information and codebooks are known, the receiving end can use the message passing algorithm (MPA) to perform correct decoding. The simulation results show that the error performance of the SCMA system is affected by the number of iterations of the decoding algorithm. When the appropriate number of iterations is selected, the SCMA system can improve the spectrum utilization rate while maintaining good system error performance. This feature makes SCMA technology have important advantages in improving the spectrum utilization rate of satellite communication system and supporting large-scale machine-connected communication.