Decision Feedback Equalizer with Phase Tracker for Multipath Tracking

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Solution Overview

Problem

Adaptive decision feedback equalizers in ATSC DTV receivers face convergence and tracking issues due to multipath interference and low signal-to-noise ratios, leading to error propagation and degraded performance.

Innovation Solution

The use of long traceback trellis decoders with parallel path memory outputs to correct and store equalizer outputs, allowing for reliable symbol decisions and updated tap weights to be determined, thereby improving channel impulse response estimation and equalizer adaptation between training sequences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a standard least mean square (LMS) algorithm with an 8 level slicer is used for adaptive decision feedback equalization, then the equalizer can adapt to channel conditions, but symbol decision errors propagate through the feedback filter degrading performance

Engineering Contradiction:

Improveequalizer adaptation to channel conditionsVSAvoidsymbol decision accuracy

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

A channel impulse response estimator is introduced as an intermediary component that processes the equalizer output before it reaches the slicer. This estimator provides refined channel knowledge that mediates between the equalizer and the decision-making process, reducing the impact of error propagation while maintaining adaptation capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements a feedback mechanism where the channel impulse response estimator continuously updates its knowledge based on equalizer outputs and feeds this information back to improve subsequent decisions. This feedback loop allows the system to learn from past decisions and correct for error propagation effects.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If the field sync segment is used as a training sequence for equalizer convergence, then the equalizer can be adapted to channel conditions, but the total convergence time becomes quite long due to infrequent transmission

Engineering Contradiction:

Improvechannel condition estimation accuracyVSAvoidequalizer convergence time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The channel impulse response estimator operates continuously between training sequences, continuously refining its knowledge of the channel based on incoming signals. This continuous operation eliminates the idle periods that occur with periodic training only, maintaining adaptation capability throughout the entire reception process.

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The system performs preliminary channel estimation using the field sync segment training sequence, then uses this preliminary knowledge to guide subsequent continuous estimation. This preliminary action provides a head start that reduces the overall time needed to achieve accurate channel knowledge.

Inventive Principle:

Principle #10Preliminary action

3Speed

If symbol decisions are made frequently to track channel variations between training sequences, then tracking performance improves, but more symbol decision errors are fed to the feedback filter causing error propagation

Engineering Contradiction:

Improvechannel variation tracking speedVSAvoiderror propagation

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The channel impulse response estimator serves as a buffer and mediator between frequent symbol decisions and the feedback filter. It processes multiple decisions through its estimation algorithm, which inherently filters out some errors, before updating the feedback information. This mediation reduces the direct impact of individual symbol errors on the feedback loop.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7382828B2Channel impulse response (CIR) estimating decision feedback equalizer with phase tracker

Publication Date: 2008.06.03 ZENITH ELECTRONICS CORPORATION

AI summary

An equalizer system includes an equalizer, first and second decoders, and a tap weight controller. The equalizer equalizes a received signal to provide an equalizer output. The first decoder is characterized by a first parallel output, and the first decoder decodes the equalizer output to provide first symbol decisions having a first accuracy. The second decoder is characterized by a second parallel output, the second decoder receives the first parallel output and decodes the equalizer output to provide second symbol decisions having a second accuracy, the first accuracy is greater than the second accuracy, and the second decoder applies the second parallel output to the equalizer. The tap weight controller determines tap weights based on the first symbol decisions and supplies the tap weights to the equalizer.