Reverse tracing of forward state metric in Log-MAP and MAX-Log-MAP decoders with fixed point precision

Abstract

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.