Low-Complexity Detectors for Uplink SCMA: Symbol Flipping and Dynamic Partial Marginalization-Based MPA

In this paper, two low-complexity detectors for uplink sparse code multiple access (SCMA) systems are proposed. The first, called symbol flipping algorithm (SFA), is an analogy of the bit-flipping decoding algorithm in the low-density parity check code field. Specifically, the local hard-decision detection is first performed at each resource node, and the decided signal in the least reliable resource node is flipped. The second is an improved partial marginalization (PM)- based message passing algorithm (MPA). Based on the reliability definition introduced in SFA, the variable nodes to be marginalized are determined dynamically during the MPA iteration procedure, and the resulted detector is termed as dynamic PM-based MPA. Simulation results show that the proposed hard-decision SFA can achieve a numerous complexity reduction and the proposed dynamic PM-based MPA has better performance than the conventional PM-based MPA.