frequencyOffset
Description
Y = frequencyOffset(X,samplerate,offset)X.
Examples
Display a rectangular 16-QAM signal frame that has a frequency offset.
Define simulation parameters and create a constellation diagram object to plot the signals.
M = 16; % 16-QAM spf = 1e3; % Number of symbols per frame fs = 1e5; % Sample rate (Hz) fOffset = 50; % Frequency offset (Hz) refQAM = qammod(0:M-1,M,UnitAveragePower=true); cd = comm.ConstellationDiagram( ... ReferenceConstellation={refQAM}, ... ShowLegend=true, ... ChannelNames={'Frequency offset signal'});
Generate a frame of random data and apply 16-QAM modulation.
data = randi([0 M-1],spf,1); modSignal = qammod(data,M,UnitAveragePower=true);
Apply the frequency offset to the modulated signal and plot the constellation diagram. The frequency offset causes the constellation points to rotate tracing circles at the symbol magnitudes.
y = frequencyOffset(modSignal,fs,fOffset); cd(y)
Define parameters to configure the signal and spectrum analyzer.
fc = 1e6; % Carrier frequency (Hz) fs = 4e6; % Sample rate (Hz) Nspf = 100e3; % Number of samples per frame freqSpan = 400e3; % Frequency span for spectrum computation (Hz)
Create sine wave and spectrum analyzer objects with the specified parameter values.
sinewave = dsp.SineWave(Amplitude=1, ... Frequency=fc, ... SampleRate=fs, ... SamplesPerFrame=Nspf, ... ComplexOutput=true); sascope = spectrumAnalyzer( ... SampleRate=fs, ... FrequencySpan="Span and center frequency", ... CenterFrequency=fc, ... Span=freqSpan, ... SpectrumType="Power density", ... SpectrumUnits="dBW/Hz", ... ShowLegend=true, ... ChannelNames=["Input sine wave","Frequency-offset sine wave"], ... YLimits=[-50 10]);
Generate a sine wave signal.
x = sinewave();
Apply a frequency offset of 100 kHz to the signal.
offset = 100e3; y = frequencyOffset(x,fs,offset);
Display the input and frequency-shifted signals by using the spectrum analyzer.
sascope(x,y)
When adding frequency offset to the signal, batch mode processing allows you to process input data with a batch dimension.
Initialize simulation parameters and preallocate arrays.
M = 16; % 16-QAM spf = 1000; % Number of symbols per frame fs = 10000; % Sample rate (Hz) fOffset = [500,200,750]; % Frequency offset (Hz) numFrames = 1e4; % Number of frames modSig = zeros(spf,3,numFrames); offsetSig = zeros(spf,3,numFrames); [timeDim,channelDim,batchDim] = size(modSig)
timeDim = 1000
channelDim = 3
batchDim = 10000
Frame Mode Processing
Simulate frame mode processing in a for-loop and display the total run time.
tic for k = 1:numFrames data = randi([0 M-1],spf,3); modSig(:,:,k) = qammod(data,M,UnitAveragePower=true); offsetSig(:,:,k) = frequencyOffset(modSig(:,:,k),fs,fOffset); end frameModeTime = seconds(toc)
frameModeTime = duration
2.8527 sec
Batch Mode Processing
Simulate batch mode simulation processing and display the total run time.
tic data = randi([0 M-1],spf,3,numFrames); modSigB = qammod(data,M,UnitAveragePower=true); offsetSigB = frequencyOffset(modSigB,fs,fOffset); batchModeTime = seconds(toc)
batchModeTime = duration
1.0364 sec
