Equalizer Adaptation Using Unclipped Samples in Clipped Signals
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Solution Overview
Problem
Traditional adaptive equalization techniques for communications signals fail to maintain optimal performance when signals are severely clipped or compressed, leading to incorrect equalizer tap values and increased bit-error-rate due to loss of soft information.
Innovation Solution
The solution involves selectively using only unclipped or minimally compressed input samples for equalizer adaptation, and applying adaptive techniques that adjust coefficients based on clipping rates to prevent corruption of tap values, thereby improving equalization performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If traditional adaptive equalization techniques are used on clipped or compressed signals, then equalizer adaptation can be performed, but the equalizer tap values become corrupted and bit-error-rate increases
Solution Approach 1:
The patent segments the input signal samples into clipped samples and unclipped samples based on a determined clipping level. By separating these samples, the system can selectively use only unclipped samples for equalizer adaptation, preventing corruption of tap values while maintaining automated adaptation functionality.
Solution Approach 2:
The patent performs preliminary determination of a clipping level before the equalizer adaptation process. This preliminary action identifies which samples are clipped and which are unclipped, allowing the system to pre-select appropriate samples for adaptation and avoid using corrupted clipped samples.
2Productivity
If all input samples are used for equalizer adaptation, then adaptation speed is maintained, but corrupted tap values result from clipped samples
Solution Approach 1:
The patent segments the sample set used for adaptation by determining a clipping level and identifying unclipped samples. This segmentation ensures that only accurate unclipped samples contribute to tap coefficient updates, maintaining precision while preserving adaptation functionality through efficient use of valid samples.
Solution Approach 2:
The patent applies local quality by treating different samples differently based on their clipping status. Unclipped samples are used for adaptation while clipped samples are excluded, allowing the system to maintain high tap coefficient accuracy by using only high-quality (unclipped) samples for the adaptation process.
3Reliability
If clipping is avoided in the transmission signal, then signal quality is maintained, but peak-to-average power ratio increases requiring more complex modulation
Solution Approach 1:
The patent converts the harmful effect of clipping into a beneficial filtering mechanism. By determining a clipping level and using it to identify unclipped samples for adaptation, the system transforms the presence of clipped samples from a problem into a useful criterion for selecting high-quality training samples, improving equalizer performance without requiring complex modulation schemes.
Data Source
AI summary
Apparatus and methods generate equalizer coefficients for an equalizer of a receiver. In a high-speed receiver, received symbols can be subject to inter-symbol-interference (ISI). An equalizer can compensate for ISI and improve a bit error rate (BER). However, traditional adaptive techniques to generate coefficients for equalization can generate corrupted coefficients when equalized samples used for adaptation are based on clipped or heavily compressed signals. In certain situations, the clipping rate can be relatively high, such as over 20%. Equalizer performance is improved when the equalized symbols used directly or indirectly for adaptation are selected such that equalized symbols based on clipped input samples are not used for adaptation.