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iqimbal

Apply I/Q imbalance to input signal

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Syntax

y = iqimbal(x,A)
y = iqimbal(x,A,P)

Description

example

y= iqimbal(x,A)applies I/Q amplitude imbalanceAto input signalx.

example

y= iqimbal(x,A,P)applies I/Q amplitude imbalanceAand phase imbalancePto input signalx.

Examples

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Open Live Script

Generate a 16-QAM signal. Display the scatter plot.

x = qammod(randi([0 15],1000,1),16); h = scatterplot(x); holdon

图散点图包含an axes object. The axes object with title Scatter plot contains an object of type line. This object represents Channel 1.

Apply a 10 dB amplitude imbalance. A positive amplitude imbalance causes horizontal stretching of the constellation.

y = iqimbal(x,10); scatterplot(y,1,0,'ro',h)

图散点图包含an axes object. The axes object with title Scatter plot contains 2 objects of type line. This object represents Channel 1.

Apply a -10 dB amplitude imbalance. A negative amplitude imbalance causes vertical stretching of the constellation.

z = iqimbal(x,-10); scatterplot(z,1,0,'k*',h) holdoff

图散点图包含an axes object. The axes object with title Scatter plot contains 3 objects of type line. This object represents Channel 1.

Open Live Script

Generate a 16-QAM signal having two channels.

x = qammod(randi([0 15],1000,2),16);

Apply a 3 dB amplitude imbalance and a 10 degree phase imbalance to the first channel. Apply a –5 dB amplitude imbalance and a –15 degree phase imbalance to the second channel.

y = iqimbal(x,[3 -5],[10 -15]);

Plot the constellation diagram of both channels of the impaired signal.

h = scatterplot(y(:,1),1,0,'b*'); holdonscatterplot(y(:,2),1,0,'ro',h) holdoff

图散点图包含an axes object. The axes object with title Scatter plot contains 2 objects of type line. This object represents Channel 1.

The first channel is stretched horizontally, and the second channel is stretched vertically.

Open Script

Apply a 1 dB, 5 degree I/Q imbalance to a QPSK signal. Then apply a DC offset. Visualize the offset using a spectrum analyzer.

Generate a QPSK sequence.

x = pskmod(randi([0 3],1e4,1),4,pi/4);

Apply a 1 dB amplitude imbalance and 5 degree phase imbalance to a QPSK signal. Apply a 0.5 + 0.3i DC offset.

y = iqimbal(x,1,5); z = y + complex(0.5,0.3);

Plot the spectrum of the impaired signal.

sa = dsp.SpectrumAnalyzer('SampleRate',1000,'YLimits',[-50 30]); sa(z)

Display the corresponding scatter plot.

scatterplot(z) grid

The effect of the I/Q imbalance and the DC offset is observable.

Open Script

Generate random data and apply 8-PSK modulation.

data = randi([0 7],2000,1); txSig = pskmod(data,8,pi/8);

Pass the transmitted signal through an AWGN channel. Apply an I/Q imbalance.

noisySig = awgn(txSig,20); rxSig = iqimbal(noisySig,2,20);

Create a constellation diagram object that displays only the last 1000 symbols. Plot the constellation diagram of the impaired signal.

cd = comm.ConstellationDiagram('ReferenceConstellation',pskmod(0:7,8,pi/8),...'SymbolsToDisplaySource','Property','SymbolsToDisplay',1000); cd(rxSig)

Correct for the I/Q imbalance by using acomm.IQImbalanceCompensatorobject. Plot the constellation diagram of the signal after compensation.

iqComp = comm.IQImbalanceCompensator('StepSize',1e-3); compSig = iqComp(rxSig); cd(compSig)

The compensator removes the I/Q imbalance.

Input Arguments

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Input signal, specified as a column vector or matrix. The function supports multichannel operations, where the number of columns corresponds to the number of channels.

Example:pskmod(randi([0 3],100,1),4,pi/4)

Data Types:single|double
Complex Number Support:Yes

Amplitude imbalance in dB, specified as a real scalar or row vector.

  • IfAis a scalar, the function applies the same amplitude imbalance to each channel.

  • IfAis a vector, then each element specifies the amplitude imbalance that is applied to the corresponding column (channel) of the input signal. The number of elements inA必须等于列数x.

Example:3

Example:[0 5]

Data Types:single|double

Phase imbalance in degrees, specified as a real scalar or row vector.

  • IfPis omitted, a phase imbalance of zero degrees is used.

  • IfPis a scalar, the function applies the same phase imbalance to each channel.

  • IfPis a vector, then each element specifies the phase imbalance that is applied to the corresponding column (channel) of the input signal. The number of elements inP必须等于列数x.

Example:10

Example:[2.5 7]

Data Types:single|double

Output Arguments

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Output signal, returned as a vector or matrix having the same dimensions asx. The number of columns inycorresponds to the number of channels.

Data Types:single|double
Complex Number Support:Yes

Algorithms

Theiqimbalfunction applies an I/Q amplitude and phase imbalance to an input signal.

Given amplitude imbalanceIain dB, the gain,g, resulting from the imbalance is defined as

g ≜ g r + i g i = [ 10 0.5 I a 20 ] + i [ 10 − 0.5 I a 20 ] .

Applying the I/Q imbalance to input signalxresults in output signalysuch that

y = Re ( x ) ⋅ g r e − i 0.5 I p ( π / 180 ) + i Im ( x ) ⋅ g i e i 0.5 I p ( π / 180 ) ,

wheregis the imbalance gain andIpis the phase imbalance in degrees.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2016b

See Also

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