Reverse tracing of forward state metric in Log-Map and MAX-Log-MAP decoders

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