Ranked successive detection and decoding method and receiver based on sparse code multiple access

A R-SDD receiver based on SCMA, comprising:

• an SCMA detector;
• a channel decoder;
• and
• a decoding order controller;
• wherein the SCMA detector is configured to perform, based on a received signal superimposed by transmissions from a plurality of users and an initialized posteriori log-likelihood ratio of each user or a first posteriori log-likelihood ratio of each user, message passing iterative detection for each user or for each unsuccessfully decoded user, and correspondingly determine a first priori log-likelihood ratio for each user or a second priori log-likelihood ratio for each unsuccessfully decoded user;
• the channel decoder is configured to perform decoding and decoding verification based on each first priori log-likelihood ratio or each second priori log-likelihood ratio;
• determine the first posteriori log-likelihood ratio for each user or the second posteriori log-likelihood ratio for each unsuccessfully decoded user;
• update and determine a successfully decoded user or an unsuccessfully decoded user, update an external iteration count according to the first posteriori log-likelihood ratio or the second posteriori log-likelihood ratio;
• and determine whether there is the unsuccessfully decoded user and whether the external iteration count reaches an external iteration threshold;
• and when it is determined that there is no unsuccessfully decoded user or that the external iteration count reaches the external iteration threshold, output a decoded bit sequence consisting of decoded bits of each user;
• and
• the decoding order controller is configured to determine a real-time confidence order using a real-time confidence level corresponding to each first priori log-likelihood ratio;
• or, if there is the unsuccessfully decoded user and the external iteration count does not reach the external iteration threshold, determine a real-time confidence order using a real-time confidence level corresponding to each second priori log-likelihood ratio of each unsuccessfully decoded user;
• and control, according to the real-time confidence order, the SCMA detector and the channel decoder to successively perform external iterations of message passing iterative detection, decoding, and decoding verification.