Open AccessA low complexity detector for downlink SCMA systems
Author(s) -
Tian Lining,
Zhao Minjian,
Zhong Jie,
Xiao Pei,
Wen Lei
Publication year - 2017
Publication title -
iet communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.355
H-Index - 62
eISSN - 1751-8636
pISSN - 1751-8628
DOI - 10.1049/iet-com.2017.0420
Subject(s) - computer science , detector , telecommunications link , superposition principle , computational complexity theory , logarithm , message passing , bit error rate , algorithm , code (set theory) , real time computing , theoretical computer science , parallel computing , mathematics , telecommunications , decoding methods , set (abstract data type) , mathematical analysis , programming language
Sparse code multiple access (SCMA) is a novel non‐orthogonal multiple access scheme for 5G systems, in which the logarithm domain message passing algorithm (Log‐MPA) is applied at the receiver to achieve near‐optimum performance. However, the computational complexity of Log‐MPA detector is still a big challenge for practical implementation, especially for energy‐sensitive user equipments in the downlink scenario. A region‐restricted detector with an improved Log‐MPA (RRL detector) is proposed for downlink SCMA systems, in which the complexity is reduced from two perspectives. To avoid unnecessary calculations when searching the superposition constellation exhaustively, the proposed RRL detector updates the function nodes only within a restricted search region. While constellation points outside the search region are neglected, the performance is well maintained which is verified by simulations. Besides, the original Log‐MPA heavily relies on exponential operations, resulting in high computational complexity. To solve this problem, an improved Log‐MPA is also put forward in this study to make a better compromise between complexity and performance. Simulation results show that the complexity of the RRL detector is reduced considerably while the bit error rate performance degrades unnoticeably.