DSP56300 datasheet(41/108 Pages) FREESCALE

Part #	DSP56300

Description	Implementing Viterbi Decoders Using the VSL Instruction on DSP Families

PDF	108 Pages

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Manufacturer	FREESCALE [Freescale Semiconductor, Inc]

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Expanding the Viterbi Algorithm

Traceback: Obtaining the Decoder Output

Viterbi Decoder Implementation

3-13

For other codes that do not use this assumption, traceback can either begin at state 0

anyway (relying on the convergence of paths to give the correct output at the traceback

depth) or the decoder can search for the state with the maximum path metric to begin

the traceback.

3.6

TRACEBACK: OBTAINING THE DECODER OUTPUT

This section presents the code needed to obtain the decoder output from the stored path

data. For this example, we have data organized in blocks of 168 bits. Because the encoder

is flushed to the zero state at the end, and the data for all 168 bits is stored, the traceback

can obtain the entire block at once. The most complicated portion of this code is the need

to obtain the pointer to the next previous state from the current path data.

The code listings for storage and traceback appear in Example 3-3 and Example 3-4,

respectively.

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DSP56300 Datasheet(PDF) 41 Page - Freescale Semiconductor, Inc