CHANNEL EQUALIZATION by NAVEEN TOKAS follow me on: https://www.facebook.com/engineernaveen.tokas

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Equalization is the process of adjusting the balance between
frequency components.
It is use to mitigate the effect of ISI (inter symbol
interference), Co-Channel Interference
and Adjacent Channel Interference that occurred in the signal
from input to output.

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INTER SYMBOL INTERFERENCE
•It is a form of distortion of a signal in which one symbol
interface with subsequent signals.
•It causes the errors at decision making device.
•ISI arrises when the data is transmitted through the channel
is dispersive in which each
•Received pulse is affected by the adjacent pulses and due to
which interference occurs in the transmitted signals.

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CO-CHANNEL INTERFERENCE
and
ADJACENT CHANNEL INTERFERENCE
•These interferences occur in communication systems
due to multiple access techniques using space,
frequency and time.
•CCI occurs in cellular radio and dual polarized
microwave radio for efficient utilization of the allocated
channels frequencies by receiving the frequency in
different cells.

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It is used to remove the effects of ISI and noise effect from the channel.

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Those equalizers where frequency response characteristics are unknown but time
variant and the parameters of a equalizer are adjustable. If the parameters are once
adjusted it will be fixed during the transmission of data.
Those equalizers that can update their parameters on a periodic basis during the
transmission of data.

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n = 100; % FIR filter order
fp = 20; % passband frequency
fs = 96; % sampling frequency
rp = 0.01; %Corresponds to 0.01 dB peak-to-peak ripple passband
rst = 20; % stopband attenuation
num = firceqrip(n,fp/(fs/2),[rp rst]);
% num = vector of coeffs(used to design n order filter)
fvtool(num,'Fs',fs) % Visualize filter

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Equalizing a signal using Communications System Toolbox software involves these
steps:
1.Create an equalizer object that describes the equalizer class and the adaptive
algorithm that you want to use.
2.An equalizer object is a type of MATLAB variable that contains information about
the equalizer, such as the name of the equalizer class, the name of the adaptive
algorithm, and the values of the weights.
2.Adjust properties of the equalizer object, if necessary, to tailor it to your needs. For
example, you can change the number of weights or the values of the weights.
3.Apply the equalizer object to the signal you want to equalize, using the equalize
method of the equalizer object.

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% Build a set of test data.
hMod = comm.BPSKModulator; % BPSKModulator System object
x = step(hMod,randi([0 1],1000,1)); % BPSK symbols
rxsig = conv(x,[1 0.8 0.3]); % Received signal
% Create an equalizer object.
= lineareq(8,lms(0.03));
% Change the reference tap index in the equalizer.
eqlms.RefTap = 4; % Apply the equalizer object to a signal.
= equalize(eqlms,rxsig,x(1:200));