PROJECT TITLE :

Performance Improvement of Iterative Multiuser Detection for Large Sparsely Spread CDMA Systems by Spatial Coupling

ABSTRACT:

Kudekar et al. proved that the belief-propagation (BP) performance for low-density parity check codes will be boosted up to the maximum a posteriori (MAP) performance by spatial coupling. During this paper, spatial coupling is applied to sparsely spread code-division multiple-access systems to boost the performance of iterative multiuser detection primarily based on BP. 2 iterative receivers based on BP are thought-about: one) one receiver is predicated on actual BP and 2) the opposite on an approximate BP with Gaussian approximation. The performance of the 2 BP receivers is evaluated via density evolution (DE) within the dense limit once taking the big-system limit, in which the quantity of users and the spreading factor tend to infinity whereas their ratio is kept constant. The two BP receivers are shown to achieve the same performance as each alternative in these limits. Furthermore, taking a continuum limit for the obtained DE equations implies that the performance of the two BP receivers can be improved up to the performance achieved by the symbol-wise MAP detection, called individually optimal detection, via spatial coupling. Numerical simulations show that spatial coupling can give a significant improvement in bit-error rate for finite-sized systems especially in the region of high system hundreds.