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(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 non-negative 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`.
`ptm`	Pulse time modulation. Creates a pulse time modulated signal from the pulse times 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.

`demod`	Demodulation for communications simulation.
`vco`	Voltage controlled oscillator.