Node Selection for Belief Propagation Based Channel Equalization

Mitsuyoshi HAGIWARA  Toshihiko NISHIMURA  Takeo OHGANE  Yasutaka OGAWA  

IEICE TRANSACTIONS on Communications   Vol.E100-B    No.8    pp.1285-1292
Publication Date: 2017/08/01
Publicized: 2017/02/08
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2016FGP0015
Type of Manuscript: Special Section PAPER (Special Section on Radio Access Technologies for 5G Mobile Communications System)
Category: Wireless Communication Technologies
belief propagation algorithm,  log-likelihood ratio,  interference canceller,  equalization,  

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Recently, much progress has been made in the study of belief propagation (BP) based signal detection with large-scale factor graphs. When we apply the BP algorithm to equalization in a SISO multipath channel, the corresponding factor graph has many short loops and patterns in an edge connection/strength. Thus, proper convergence may not be achieved. In general, the log-likelihood ratio (LLR) oscillates in ill-converged cases. Therefore, LLR oscillation avoidance is important for BP-based equalization. In this paper, we propose applying node selection (NS) to prevent the LLR from oscillating. The NS extends the loop length virtually by a serial LLR update. Thus, some performance improvement is expected. Simulation results show that the error floor is significantly reduced by NS in the uncoded case and that the NS works very well in the coded case.