SCMA Joint Coding and Decoding Algorithm Based on Code Reliability

The wide application of the Internet of Things (IoT), large-scale satellite clusters and drone clusters requires multiple access capabilities for massive devices. In order to meet the high-capacity and low-latency access requirements in application scenarios such as the IoT, this paper proposes to apply sparse code multiple access (SCMA) technology to the massive terminal access of the IoT, focusing on the study of SCMA decoding algorithm. Aiming at the high complexity of its traditional decoding algorithm, a decoding algorithm based on codeword reliability is proposed. The algorithm reduces the number of codeword iterations with higher reliability by setting a threshold to reduce the algorithm complexity. The simulation results show that the algorithm reduces the complexity of the algorithm while the loss of bit error rate performance is very small. Then, aiming at the poor bit error rate performance of SCMA technology under the condition of low signal-to-noise ratio, a joint coding and decoding simulation link based on soft input and soft output Turbo code and SCMA technology is proposed. The simulation results prove that Turbo codes can speed up the convergence speed of the decoding algorithm. When the SNR is 4 dB, the bit error rate of the joint system has been reduced to below 10e-3, which has obvious advantages compared with the SCMA system without Turbo coding. Therefore, the two methods proposed in this paper can be used for the high-capacity demand of the IoT communication system.