Soft-Decision Viterbi Equalizer with Limited Trellis Stages
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Solution Overview
Problem
Existing Viterbi Algorithm implementations in communication systems are limited by the inner Viterbi Algorithm block producing only hard decisions, leading to reduced performance of the outer block and introducing unacceptably long time delays due to long paths that often do not merge, necessitating a system that generates soft decisions with a limited number of stages.
Innovation Solution
A Viterbi Equalizer with a limited number of stages, such as four, that produces soft decisions and provides reliability information, calculated based on path convergence and branch metrics, allowing for improved performance and integration in hardware or software without requiring all paths to converge on a final decision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Viterbi Algorithm block is used with long paths to ensure convergence, then reliability of final decision is improved, but time delay becomes unacceptably long
Solution Approach 1:
The patent applies partial action by using a limited number of stages (e.g., four stages) instead of requiring full convergence of all paths. The equalizer produces reliable soft decisions with a limited path history, accepting that not all paths converge but providing sufficient reliability for the application through the calculated soft decisions based on the limited stages.
2Device complexity
If the inner Viterbi Algorithm block produces hard decisions, then device complexity is reduced, but performance of the outer block deteriorates
Solution Approach 1:
The patent changes the parameter of the decision output from hard decisions (binary) to soft decisions (multi-level reliability information). The inner Viterbi Algorithm block outputs not just the final decision but also reliability information indicating the confidence level, which is then used by the outer block to improve overall system performance through more informed error correction.
3Productivity
If a limited number of stages is used in the Viterbi Equalizer, then productivity is improved, but measurement precision of path convergence deteriorates
Solution Approach 1:
The patent introduces reliability information as an intermediary that bridges the gap between limited stage convergence and decision accuracy. This reliability metric serves as a mediator that quantifies the confidence level of the final decision even when paths haven't fully converged, allowing the system to maintain high productivity while compensating for reduced convergence precision through the reliability indicator.
Data Source
AI summary
A Viterbi Equalizer having a limited number of stages is disclosed. In some embodiments, the Viterbi Equalizer may have only four stages. The Viterbi Equalizer produces soft decisions, which comprise a final decision and reliability information related to that final decision. The Viterbi Equalizer is able to provide reliability information even if all paths do not converge on the final decision at the last stage. The reliability information is calculated based on if and when the paths in the trellis converge on a final decision. This reliability information can be used downstream, such as by another Viterbi Algorithm block to perform forward error correction. The use of soft decision provides gains of up to several dB in performance. Additionally, the Viterbi Equalizer is low cost and readily implemented in hardware or software.