Viterbi IP Core User Guide

ID 683280
Date 11/06/2017
Public
Document Table of Contents

3.3.5. Trellis Initialization

The parallel decoder always starts its trellis from state zero for a new block.

However, the hybrid decoder allows you to set the initial state (usually zero) with bm_init_state. This signal ranges from 0 to 2 (L – 1) – 1, which are the trellis states. The bm_init_value signal initializes the state metric of the state indicated by bm_init_state. The decoder initializes all other states with zero. The appropriate value for this port is approximately 2(bmgwide – 2) or any value between 2(N + softbits) to 2(bmgwide – 1). Continuous decoders never reset the state metrics, which creates a possible difference if the same block of data is sent several times. Initially, the decoder sets the state metrics so that the state metric for state 0 is 0, and all others infinity. For any subsequent blocks, the state metrics contain whatever they have when the previous block ends.