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US 2019/0296832 A1Published application
System and method for adaptive channel equalization in a time varying channel
AssigneeHuawei Technologies Co., Ltd.
InventorsNASH'AT ABUGHALIEH, ZHUHONG ZHANG
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Abstract
Systems and methods are provided for adaptive equalization, for example for use with coherent optical reception. The equalizer has a loop for updating taps of an adaptive linear filter forming part of the equalizer. In the loop, an error calculator calculates an error, a gradient calculator calculates a gradient of the error or filtered error. One or more gradient filters are used to filter the gradient, and the filtered gradient is used to update the taps of the adaptive linear filter. A reduction in self oscillation in the equalizer is achieved by separating the frequencies with channel features that change with time and scaling them up to speed up convergence of the equalizer.
Claims20
An adaptive equalizer comprising:
- an adaptive linear filter having a plurality of taps configured to process an input to produce an equalizer output;
- a plurality of components, the adaptive linear filter and the plurality of the components connected in a loop configuration to update taps of the adaptive linear filter, the plurality of functional components comprising:
- an error calculator configured to calculate an error using an error constraint function based on the equalizer output;
- a gradient calculator configured to calculate a gradient, wherein the gradient is a gradient of the error or a gradient of a filtered error with respect to taps of the adaptive linear filter;
- at least one gradient filter configured to perform a filtering operation on the gradient to produce a filtered gradient, wherein each gradient filter is a bandpass filter having a passband that isolates a respective frequency band of the gradient;
- and
- an overall gain adjusted filtered gradient calculator configured to apply a gain factor to the gradient to produce a gain adjusted gradient and to apply a respective gain factor to each of the corresponding filtered gradients produced by the at least one gradient filter to produce corresponding gain adjusted filtered gradients, and to sum the gain adjusted gradient and the corresponding gain adjusted filtered gradients to produce the overall gain adjusted filterer gradient;
- a filter tap updater configured to calculate updated taps for the adaptive linear filter phase based on the overall gain adjusted filtered gradient.
5 more elements
A coherent receiver comprising:
- a receiver for receiving a signal over a channel;
- an analog to digital to converter;
- a front end digital to signal processor;
- an adaptive equalizer comprising:
- an adaptive linear filter having a plurality of taps configured to process an input to produce an equalizer output;
- a plurality of components, the adaptive linear filter and the plurality of the components connected in a loop configuration to update taps of the adaptive linear filter, the plurality of functional components comprising:
- an error calculator configured to calculate an error using an error constraint function based on the equalizer output;
- a gradient calculator configured to calculate a gradient, wherein the gradient is a gradient of the error or a gradient of a filtered error with respect to taps of the adaptive linear filter;
- at least one gradient filter configured to perform a filtering operation on the gradient to produce a filtered gradient, wherein each gradient filter is a bandpass filter having a passband that isolates a respective frequency band of the gradient;
- and
- an overall gain adjusted filtered gradient calculator configured to apply a gain factor to the gradient to produce a gain adjusted gradient and to apply a respective gain factor to each of the corresponding filtered gradients produced by the at least one gradient filter to produce corresponding gain adjusted filtered gradients, and to sum the gain adjusted gradient and the corresponding gain adjusted filtered gradients to produce the overall gain adjusted filterer gradient;
- a filter tap updater configured to calculate updated taps for the adaptive linear filter phase based on the overall gain adjusted filtered gradient.
9 more elements
A method of adaptive equalization, the method comprising:
- processing an input with an adaptive linear filter having a plurality of taps to produce an equalizer output;
- calculating at least one error using an error constraint function based on the equalizer output;
- calculating at least one gradient, wherein each of the at least one gradient is a gradient of a respective one of the at least one error or a gradient of a respective filtered one of the at least one error with respect to taps of the adaptive linear filter;
- filtering the at least one gradient to produce at least one filtered gradient;
- and
- updating taps for the adaptive linear filter phase based on the at least one filtered gradient;
- wherein said filtering the at least one gradient filter is configured to improve adaptive filter convergence at specific frequencies that suffer from more time variations by filtering the specific frequencies and giving them higher loop gain than other frequencies.
4 more elements
Dependencies are inferred from the claim text.