A Simplified Sphere Decoding-Based Detector for Generalized SCMA Codebooks

Sparse code multiple access (SCMA) is one of the promising schemes to meet high connectivity and spectral efficiency in future wireless networks. The iterative detectors, for example message passing algorithm (MPA), can provide near optimal multiuser detection (MUD) performance but becomes infeasible when codebook size large or overloading factor high. Recently, sphere decoding (SD) has been considered MUD SCMA by rewriting generalized transmission into a linear system. In this work, we first review state-of-the-art SD-based detectors SCMA: (SD-SCMA) SD-SCMA (GSD-SCMA). We not only explain comprehensive way, also exploit sorted QR decomposition Schnorr-Euchner enumeration accelerate tree search. Although GSD-SCMA overcomes constraint SD-SCMA, its computational complexity extremely sensitive factor. To satisfy trade-off between performance, propose two pruning algorithms, PRUN1 PRUN2, introduce simplified (SGSD-SCMA). paper, error probabilities proposed algorithms are derived. Simulation results show that detector outperforms moderate large.