DSP56300 datasheet(19/108 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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The Viterbi Algorithm

Viterbi Decoder

Viterbi Decoder Implementation

2-5

Figure 2-2

shows a prototype for one state of the state tree for this decoder. Figure 2-3

shows the entire tree used by the decoder to track the first five input pairs. The state of

the recreated encoder appears in the box. Along each arrow (a state transition) appears a

number pair showing the corresponding encoder output bit pair for that state transition

(the output produced immediately before the state changes). This figure is ordered so

that transitions corresponding to an input 0 are always the upper path and transitions

corresponding to an input 1 are always the lower path. To determine the encoder output

for a given transition, load the encoder with the state and use a 0 or 1 for the input bit,

according to the transition chosen. The encoder polynomials then determine the encoder

output, as shown in Figure 2-1.

Figure 2-2

Single State of Prototype Encoder Tree Diagram

State

Transition

Encoder Output

Branch Metric

Path Metric State

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DSP56300 Datasheet(PDF) 19 Page - Freescale Semiconductor, Inc