Improvement of BP-Based CDMA Multiuser Detection by Spatial Coupling
Kudekar et al. proved that the Belief-Propagation (BP) threshold for low-density parity-check codes can be boosted up to the Maximum-A-Posteriori (MAP) threshold by spatial coupling. In this paper, spatial coupling is applied to randomly spread Code-Division Multiple-Access (CDMA) systems in order to improve the performance of BP-based Multi User Detection (MUD). Spatially-coupled CDMA systems can be regarded as multi-code CDMA systems with two transmission phases. The large-system analysis shows that spatial coupling can improve the BP performance, while there is a gap between the BP performance and the Individually-Optimal (IO) performance.