modulate (Signal Processing Toolbox)

Modulation for communications simulation

Syntax

y = modulate(x,fc,fs,'method')
y = modulate(x,fc,fs,'method',opt)
[y,t] = modulate(x,fc,fs)

Description

y = modulate(x,fc,fs,'method') and

y = modulate(x,fc,fs,'method',opt) modulate the real message signal x with a carrier frequency fc and sampling frequency fs, using one of the options listed below for 'method'. Note that some methods accept an option, opt.

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 the opt parameter is not present, 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 to the integral of x. modulate uses opt as the constant of frequency modulation. If opt is not present, 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 opt is not present, modulate uses a default of
opt = pi/(max(max(x)))
so the maximum phase excursion is 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. y is length 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. y is length 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)
opt must be the same size as x.

`amdsb-sc` or `am`	Amplitude modulation, double sideband, suppressed carrier. Multiplies `x` by a sinusoid of frequency `fc`. `y = x.cos(2pifct)`
`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(2pifct)` If the `opt` parameter is not present, `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(2pifct)+imag(hilbert(x)).sin(2pifct)` This effectively removes the upper sideband.
`fm`	Frequency modulation. Creates a sinusoid with instantaneous frequency that varies with the message signal `x`. `y = cos(2pifct + optcumsum(x))` `cumsum` is a rectangular approximation to the integral of `x`. `modulate` uses `opt` as the constant of frequency modulation. If `opt` is not present, `modulate` uses a default of `opt = (fc/fs)2pi/(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(2pifct + optx)` `modulate` uses `opt` as the constant of phase modulation. If `opt` is not present, `modulate` uses a default of `opt = pi/(max(max(x)))` so the maximum phase excursion is 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. `y` is length `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`. `y` is length `length(x)`*`fs/fc`.
`qam`	Quadrature amplitude modulation. Creates a quadrature amplitude modulated signal from signals `x` and `opt`. `y = x.cos(2pifct) + opt.sin(2pifct)` `opt` must be the same size as `x`.

If you do not specify 'method', then modulate assumes am. Except for the pwm and ptm cases, y is the same size as x.

If x is an array, modulate modulates its columns.

[y,t] = modulate(x,fc,fs) returns the internal time vector t that modulate uses in its computations.

See Also

demod, vco

medfilt1 nuttallwin