jist
Intro
What is FEC
Problem Statemnet
Scope
Literature Survey
Why error control
Convolutional codes
Principle
Functional Block
Properties of CC
Wimax
About
What is WImAX
Comparison with Wifi
Viterbi Decoder
Principle
Need for AVD in 802.16e
3 VITERBI Decoder and AVD
3.1 Introduction
Conventional Viterbi Decoding is considered to be the best decoding algorithm for linear block codes. Convolution codes along with the Viterbi decoding gives the maximum performance. Viterbi Decoding uses the concept of tracing the least cost path based on the minimum distance obtained between the received sequence and branch output. Viterbi decoding is one of two types of decoding algorithms used with convolutional encoding-the other type is sequential decoding. Sequential decoding has the advantage that it can perform very well with long-constraint-length convolutional codes, but it has a variable decoding time. Viterbi decoding has the advantage that it has a fixed decoding time. It is well suited to hardware decoder implementation. But its computational requirements grow exponentially as a function of the constraint length, so it is usually limited in practice to constraint lengths of K = 7 or less. For years, convolutional coding with Viterbi decoding has been the predominant FEC technique used in space communications.
Design
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3.2 DECODING TYPES
Convolution codes can be decoded by means of Viterbi algorithm.
There are two types of Viterbi Algorithm:
- Hard-Decision decoding algorithms.
- Soft-Decision decoding algorithms.
3.2.1 Hard-Decision decoding algorithms:
- Calculating the Hamming distance
3.2.2 Soft-Decision decoding algorithms:
- Calculating the Euclidean distance
In this system we have implemented the hard decision Viterbi Algorithm.
Implementation Details
System design
ENCODING
Significance of CONSTRAINT LENGTH
Generation of encoder output
Decoding
Path construction
Traceback
Pruning
Perfromance Analysis
