y = modulate(x,fc,fs)
modulates the real message signal x with a carrier frequency
fc and sample rate fs. If x is a
matrix, the modulated signal is computed independently for each column and stored in the
corresponding column of y.

[y,t] = modulate(x,fc,fs)
also returns the internal time vector t.

[___] = modulate(x,fc,fs,method)
modulates the real message signal using the modulation technique specified by
method. You can use these inputs with either of the previous output
syntaxes.

Generate two sinusoidal signals frequencies of 10 Hz and 20 Hz, sampled at a rate of 200 Hz for 1 second. Embed the sinusoids in white Gaussian noise of variance 0.01.

fs = 200;
t = 0:1/fs:1;
i = sin(2*pi*10*t) + randn(size(t))/10;
q = sin(2*pi*20*t) + randn(size(t))/10;

Create a quadrature amplitude modulated signal from signals i and q using a carrier frequency of 70 Hz. Compute the Welch power spectral density estimates of the original and modulated sequences. Use a 100-sample Hamming window with 80 samples of overlap. Specify an FFT length of 1024.

y = modulate(i,70,fs,'qam',q);
pwelch([i;q;y]',hamming(100),80,1024,fs,'centered')
legend('In-phase signal','Quadrature signal','Modulated signal')

amdsb-sc or am — Amplitude modulation,
double sideband, suppressed carrier. Multiplies x by a sinusoid
of frequency fc.

y = x.*cos(2*pi*fc*t)

amdsb-tc — Amplitude modulation, double sideband,
transmitted carrier. Subtracts scalar opt from
x and multiplies the result by a sinusoid of frequency
fc.

y = (x-opt).*cos(2*pi*fc*t)

If you do not specify the opt parameter,
modulate uses a default of min(min(x)) so
that the message signal (x-opt) is entirely nonnegative and has
a minimum value of 0.

amssb — Amplitude modulation, single sideband. Multiplies
x by a sinusoid of frequency fc and adds
the result to the Hilbert transform of x multiplied by a
phase-shifted sinusoid of frequency fc.

y = x.*cos(2*pi*fc*t)+imag(hilbert(x)).*sin(2*pi*fc*t)

This effectively removes the upper sideband.

fm — Frequency modulation. Creates a sinusoid with
instantaneous frequency that varies with the message signal
x.

y=cos(2*pi*fc*t + opt*cumsum(x))

cumsum is a rectangular approximation of the integral of
x. modulate uses opt as
the constant of frequency modulation. If you do not specify the
opt parameter, modulate uses a default of
opt = (fc/fs)*2*pi/(max(max(x))) so the maximum
frequency excursion from fc is
fc Hz.

pm — Phase modulation. Creates a sinusoid of frequency
fc whose phase varies with the message signal
x.

y=cos(2*pi*fc*t + opt*x)

modulate uses opt as the constant of phase
modulation. If you do not specify the opt parameter,
modulate uses a default of
opt = pi/(max(max(x))) so the maximum phase
excursion is π radians.

pwm — Pulse-width modulation. Creates a pulse-width
modulated signal from the pulse widths in x. The elements of
x must be between 0 and 1, specifying the width of each pulse
in fractions of a period. The pulses start at the beginning of each period, that
is, they are left justified. modulate(x,fc,fs,'pwm','centered')
yields pulses centered at the beginning of each period. The length of
y is length(x)*fs/fc.

ppm — Pulse-position modulation. Creates a pulse-position
modulated signal from the pulse positions in x. The elements of
x must be between 0 and 1, specifying the left edge of each
pulse in fractions of a period. opt is a scalar between 0 and 1
that specifies the length of each pulse in fractions of a period. The default for
opt is 0.1. The length of
y is length(x)*fs/fc.

qam— Quadrature amplitude modulation. Creates a quadrature
amplitude modulated signal from signals x and
opt.

y=x.*cos(2*pi*fc*t) + opt.*sin(2*pi*fc*t)

The input argument opt must be the same size as
x.

opt — Optional input for some methods real vector

Optional input, specified for some methods. Refer to method for
more details on how to use opt.

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