Performance analysis of SC-RA coded IDMA systems with segmented interleavers

This paper considers spatially coupled repeat-accumulate (SC-RA) coded interleave-division multiple-access (IDMA) systems with segmented interleavers. Each user employs an SC-RA encoder and a spreader followed by user-specific segmented interleavers. Each segment corresponds with a parity variable node in the SC-RA code's protograph. Since all the users' parity bits at the ends of the coupling positions are synchronously superimposed in segments, the extrinsic messages to the sum node are totally enhanced in the iterative decoding. Density evolution (DE) with Gaussian approximation (GA) shows that the belief propagation threshold of the proposed system approaches closer to the Shannon limit than systems without segmentation and the conventional RA-IDMA systems.