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1-4

Viterbi Decoder Implementation

Introduction

Manual Organization

1.3

MANUAL ORGANIZATION

Section 2

of this manual covers many basics of the Viterbi algorithm and introduces

much of the terminology used in this application note. Those already acquainted with

the algorithm may wish to proceed directly to Section 3.

Section 3

shows how to develop assembly language routines for the Viterbi algorithm.

This is done by means of an example, taking a set of encoding polynomials from the

wireless interim standard IS-136 and developing the assembly routines needed to

implement the corresponding decoder using the Viterbi algorithm.

Section 4

discusses some code modifications that are useful for generalizing and

optimizing the example code. The code-to-cover generalized branch metrics is extended,

and an efficient method for normalizing the path metrics is introduced. In addition, two

additional sets of code are given for more efficient processing of data periodically forced

through a known state.

Section 5

summarizes the application report and presents interesting data and statistics

arrived at by comparing the basic Viterbi algorithm code of Section 2 with that of the

modified program code presented in Section 3 and Section 4.

Appendix A

contains the complete program listing for Section 3.

Appendix B

contains the complete program listing for Section 4.

Appendix C

contains the complete 24-bit program listing for Section 4.

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