Tail-Biting Viterbi Decoding Using Circular State Traceback
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Solution Overview
Problem
Conventional Viterbi decoding techniques are inappropriate for decoding tail-biting convolutional encoded signals in the mobile WiMAX standard, where the initial and final states of the encoded signals are unknown.
Innovation Solution
A decoder and method that performs a traceback operation on portions of the total code block, using a circular state as the traceback starting state, reduces memory requirements and facilitates decoding by selectively executing bit decisions for subsequent portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional Viterbi decoding techniques are used, then decoding can be performed when initial and final states are known, but the technique is inappropriate for tail-biting convolutional encoded signals where initial and final states are unknown
Solution Approach 1:
The total code block is divided into multiple portions (first portion, second portion, third portion) with different traceback operations applied to each. The first portion performs full traceback to determine the circular state, the second portion uses the circular state as starting point, and the third portion performs selective bit decisions. This segmentation allows the decoder to handle unknown initial and final states while reducing overall complexity.
Solution Approach 2:
The decoder performs a preliminary traceback operation on the first portion of the code block to determine the circular state before processing the remaining portions. This preliminary action establishes the correct starting state for subsequent decoding operations, enabling accurate decoding of tail-biting signals where the initial state is unknown.
2Reliability
If traceback operation is performed on the entire total code block, then complete decoding is achieved, but the required memory for storing state metric information is significantly increased
Solution Approach 1:
The code block is segmented into multiple portions with different processing strategies. Only the first portion requires complete traceback and full state metric storage, while subsequent portions use the determined circular state as a starting point and perform selective bit decisions. This segmentation maintains decoding accuracy for the entire block while significantly reducing the memory required for state metric information in the second and third portions.
Solution Approach 2:
Instead of performing full traceback operations on the entire code block, the decoder performs partial traceback only on the first portion to establish the circular state. For the second and third portions, selective bit decisions are made based on the circular state without complete traceback, achieving sufficient decoding reliability with reduced memory consumption.
Data Source
AI summary
A decoder and method for decoding a tail-biting convolutional encoded signal using Viterbi decoding scheme performs a traceback operation for a first portion of a total code block, which includes a code block of the tail-biting convolutional encoded signal and a padded block. During the traceback operation for the first portion, a particular state at a predefined position within the first portion is stored as a circular state. The circular state is used as a traceback starting state for at least one subsequent portion of the total code block to produce a decoded signal of the code block.