demod - Demodulation for communications simulation

Syntax

Description

demod performs demodulation, that is, it obtains the original signal from a modulated version of the signal. demod undoes the operation performed by modulate.

x = demod(y,fc,fs,'method') and

x = demod(y,fc,fs,'method',opt) demodulate the real carrier signal y 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.)

Note   Use demod and modulate in the Signal Processing Toolbox™ with real-valued signals to obtain real-valued outputs. demod and modulate are not intended to accept complex-valued inputs or produce complex-valued outputs.

Method	Description
amdsb-sc or am	Amplitude demodulation, double sideband, suppressed carrier. Multiplies y by a sinusoid of frequency fc and applies a fifth-order Butterworth lowpass filter using filtfilt. x = y.*cos(2*pi*fc*t); [b,a] = butter(5,fc*2/fs); x = filtfilt(b,a,x);
amdsb-tc	Amplitude demodulation, double sideband, transmitted carrier. Multiplies y by a sinusoid of frequency fc, and applies a fifth-order Butterworth lowpass filter using filtfilt. x = y.*cos(2*pi*fc*t); [b,a] = butter(5,fc*2/fs); x = filtfilt(b,a,x); If you specify opt, demod subtracts scalar opt from x. The default value for opt is 0.
amssb	Amplitude demodulation, single sideband. Multiplies y by a sinusoid of frequency fc and applies a fifth-order Butterworth lowpass filter using filtfilt. x = y.*cos(2*pi*fc*t); [b,a] = butter(5,fc*2/fs); x = filtfilt(b,a,x);
fm	Frequency demodulation. Demodulates the FM waveform by modulating the Hilbert transform of y by a complex exponential of frequency -fc Hz and obtains the instantaneous frequency of the result.
pm	Phase demodulation. Demodulates the PM waveform by modulating the Hilbert transform of y by a complex exponential of frequency -fc Hz and obtains the instantaneous phase of the result.
ppm	Pulse-position demodulation. Finds the pulse positions of a pulse-position modulated signal y. For correct demodulation, the pulses cannot overlap. x is length length(t)*fc/fs.
pwm	Pulse-width demodulation. Finds the pulse widths of a pulse-width modulated signal y. demod returns in x a vector whose elements specify the width of each pulse in fractions of a period. The pulses in y should start at the beginning of each carrier period, that is, they should be left justified.
qam	Quadrature amplitude demodulation. [x1,x2] = demod(y,fc,fs,'qam') multiplies y by a cosine and a sine of frequency fc and applies a fifth-order Butterworth lowpass filter using filtfilt. x1 = y.*cos(2*pi*fc*t); x2 = y.*sin(2*pi*fc*t); [b,a] = butter(5,fc*2/fs); x1 = filtfilt(b,a,x1); x2 = filtfilt(b,a,x2);

The default method is 'am'. In all cases except 'ppm' and 'pwm', x is the same size as y.

If y is a matrix, demod demodulates its columns.

x = demod(y,fc,fs,'pwm','centered') finds the pulse widths assuming they are centered at the beginning of each period. x is length length(y)*fc/fs.

See Also

fskdemod | genqamdemod | modulate | mskdemod | pamdemod | pmdemod | qamdemod | vco

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