Reverse Tracing of Forward State Metric in Log-MAP and MAX-Log-MAP Decoders with Fixed Point Precision

Jaeyoung KWAK  Sook Min PARK  Kwyro LEE  

IEICE TRANSACTIONS on Communications   Vol.E86-B    No.1    pp.451-455
Publication Date: 2003/01/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: LETTER
Category: Fundamental Theories
turbo code,  state metric,  Log-MAP,  MAX-Log-MAP,  reverse tracing,  

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Serious BER performance degradation due to finite numeric precision in VLSI implementation of Log-MAP and MAX-Log-MAP decoders where forward state metric is calculated using reverse tracing method, is analyzed, and two methods are proposed to overcome this problem, the loser storing method for MAX-Log-MAP and the periodic storing method for Log-MAP and MAX-Log-MAP. Both methods can reduce memory storage size effectively by half, but with additional circuit overhead. Our VLSI implementation examples show that, compared with original method, both methods give about 15% improvement in area and power consumption with identical BER performance.