Viterbi IP Core User Guide

ID 683280
Date 11/06/2017
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3.4.3.2. State Metrics

The Viterbi decoder state metrics are accumulative not Euclidean and are based on maximum metrics rather than minimum metrics.

As the metrics grow, normalize them to avoid overflow. When a normalization occurs the decoder subtracts 2(bmgwide – 1) from all metrics and increases the normalization register by +1. The total metric value for the best path = (number of normalizations) × (2(bmgwide – 1)) + bestmet. The total metric value for the best path, the number of symbols processed, and the number of errors in the BER block indicate the quality of the channel and whether you have a suitable value for softbits. The output bestadd indicates the state that has the best metric.