Gibbs Sampling for HMM Equalization Complexity

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Solution Overview

Problem

Forward-backward equalization methods are complex due to their reliance on Hidden Markov Models with extensive state memory, making them computationally intensive for long symbol sequences, which is a challenge in digital communications where efficient signal recovery is needed.

Innovation Solution

An apparatus and method using a sampler to generate subsets of sequences from a statistical distribution, employing Gibbs sampling and error tolerance, with a processor applying functions to these samples to determine the most likely input sequence to a finite state system, and a summing unit normalizing the results to obtain a posteriori distributions, reducing computational complexity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If forward-backward equalization using Hidden Markov Models is applied, then accurate symbol sequence recovery is achieved, but computational complexity increases significantly

Engineering Contradiction:
Improvesymbol sequence recovery accuracyVSAvoidcomputational complexity
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the complex HMM equalization problem into multiple simpler iterations. Instead of computing the full a posteriori distribution in one complex pass, the method performs multiple forward-backward iterations, each computing partial contributions to the distribution. This segmentation reduces the computational burden of each individual pass while maintaining the accuracy of the final result through cumulative refinement.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent introduces dynamic adaptation by allowing the equalization process to iterate multiple times, with each iteration refining the a posteriori distribution based on previously computed results. The system dynamically adjusts the estimation by incorporating feedback from previous iterations, enabling accurate symbol recovery with reduced complexity per iteration compared to a single-pass HMM approach.

Inventive Principle:
Principle #15Dynamics

2Quantity of substance

If the length of transmitted symbol sequence increases, then more information is transmitted, but the complexity of forward-backward equalization increases proportionally

Engineering Contradiction:
Improveinformation transmission capacityVSAvoidequalization complexity
Core Design Contradiction:
Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent segments the long symbol sequence processing into multiple manageable iterations. Each iteration processes the sequence with reduced computational requirements, breaking down the overall complexity into smaller computational tasks that can be executed sequentially. This allows handling of long sequences without proportional increase in per-step complexity.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent applies partial action by performing multiple forward-backward passes that each contribute partially to the final a posteriori distribution. Rather than requiring a single comprehensive pass that processes all sequence information at once, the method accumulates results from multiple partial passes, each with reduced computational demands, thereby handling long sequences efficiently.

Inventive Principle:
Principle #16Partial or excessive action

Data Source

PatentUS8315955B2Method and apparatus for determining inputs to a finite state system
Publication Date: 2012.11.20 MASSACHUSETTS INST OF TECH
  • US8315955B2 patent drawing
  • US8315955B2 patent drawing
  • US8315955B2 patent drawing

AI summary

A method of equalization used to estimate a transmitted signal given a received output is presented herein. The equalization method involves modeling a transmission channel as a Hidden Markov Model (HMM). The HMM channel is evaluated as a finite state machine. A Markov Chain Monte Carlo technique of sampling and computation is then utilized to estimate the transmitted signal.