Skip to content Skip to navigation Skip to collection information

OpenStax-CNX

You are here: Home » Content » Digital Signal Processing: A User's Guide » Adaptive Equalization

Navigation

Table of Contents

Lenses

What is a lens?

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

This content is ...

In these lenses

  • Lens for Engineering

    This module is included inLens: Lens for Engineering
    By: Sidney Burrus

    Click the "Lens for Engineering" link to see all content selected in this lens.

  • SigProc display tagshide tags

    This module is included inLens: Signal Processing
    By: Daniel McKennaAs a part of collection: "Fundamentals of Signal Processing"

    Click the "SigProc" link to see all content selected in this lens.

    Click the tag icon tag icon to display tags associated with this content.

  • richb's DSP display tagshide tags

    This module is included inLens: richb's DSP resources
    By: Richard BaraniukAs a part of collection: "Adaptive Filters"

    Comments:

    "A good introduction in adaptive filters, a major DSP application."

    Click the "richb's DSP" link to see all content selected in this lens.

    Click the tag icon tag icon to display tags associated with this content.

Recently Viewed

This feature requires Javascript to be enabled.

Tags

(What is a tag?)

These tags come from the endorsement, affiliation, and other lenses that include this content.
 

Adaptive Equalization

Module by: Douglas L. Jones. E-mail the author

goal:

Design an approximate inverse filter to cancel out as much distortion as possible.
Figure 1
Figure 1 (fig1AdaptiveEqual.png)
In principle, WH z - Δ W H z - Δ , or W z - Δ H W z - Δ H , so that the overall response of the top path is approximately δnΔ δ n Δ . However, limitations on the form of WW (FIR) and the presence of noise cause the equalization to be imperfect.

Important Application

Channel equalization in a digital communication system.

Figure 2
Figure 2 (fig2AdaptiveEqual.png)
If the channel distorts the pulse shape, the matched filter will no longer be matched, intersymbol interference may increase, and the system performance will degrade.

An adaptive filter is often inserted in front of the matched filter to compensate for the channel.

Figure 3
Figure 3 (fig3AdaptiveEqual.png)
This is, of course, unrealizable, since we do not have access to the original transmitted signal, s k s k .

There are two common solutions to this problem:

  1. Periodically broadcast a known training signal. The adaptation is switched on only when the training signal is being broadcast and thus s k s k is known.
  2. Decision-directed feedback: If the overall system is working well, then the output s^ k - Δ 0 s k - Δ 0 should almost always equal s k - Δ 0 s k - Δ 0 . We can thus use our received digital communication signal as the desired signal, since it has been cleaned of noise (we hope) by the nonlinear threshold device!
    Figure 4
    Decision-directed equalizer
    Decision-directed equalizer (fig4AdaptiveEqual.png)
    As long as the error rate in s^k s k is not too high (say 75% 75% ), this method works. Otherwise, d k d k is so inaccurate that the adaptive filter can never find the Wiener solution. This method is widely used in the telephone system and other digital communication networks.

Collection Navigation

Content actions

Download:

Collection as:

PDF | EPUB (?)

What is an EPUB file?

EPUB is an electronic book format that can be read on a variety of mobile devices.

Downloading to a reading device

For detailed instructions on how to download this content's EPUB to your specific device, click the "(?)" link.

| More downloads ...

Module as:

PDF | More downloads ...

Add:

Collection to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks

Module to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks