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Frequency shift keying modulation


y = fskmod(x,M,freq_sep,nsamp) outputs the complex envelope y of the modulation of the message signal x using frequency shift keying modulation.

y = fskmod(x,M,freq_sep,nsamp,Fs) specifies the sampling rate of y.


y = fskmod(x,M,freq_sep,nsamp,Fs,phase_cont) specifies the phase continuity.

y = fskmod(x,M,freq_sep,nsamp,Fs,phase_cont,symorder) specifies how the function assigns binary words to corresponding integers.


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Generate an FSK modulated signal and display its spectral characteristics.

Set the function parameters.

M = 4; % Modulation order
freqsep = 8; % Frequency separation (Hz)
nsamp = 8; % Number of samples per symbol
Fs = 32; % Sample rate (Hz)

Generate random M-ary symbols.

x = randi([0 M-1],1000,1);

Apply FSK modulation.

y = fskmod(x,M,freqsep,nsamp,Fs);

Create a spectrum analyzer System object™ and call it to display a plot of the signal spectrum.

specAnal = dsp.SpectrumAnalyzer('SampleRate',Fs);

Figure Spectrum Analyzer contains an axes object and other objects of type uiflowcontainer, uimenu, uitoolbar. The axes object contains an object of type line. This object represents Channel 1.

Input Arguments

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Input signal, specified as a vector or matrix of positive integers. The elements of x must have values in the range of [0, M – 1]. If x is a matrix, fskmod processes the columns independently.

Example: randi([0 3],100,1)

Data Types: double

Modulation order, specified as an integer power of two.

Example: 2 | 4 | 16

Data Types: double

Symbol order, specified as 'bin' or 'gray'. This argument specifies how the function assigns binary vectors to corresponding integers.

  • If symorder is 'bin', the function uses a natural binary-coded ordering.

  • If symorder is 'gray', the function uses a Gray-coded ordering.

Data Types: char

Desired separation between frequencies, specified in Hz. By the Nyquist sampling theorem, freq_sep and M must satisfy (M-1)*freq_sep <= 1.

Data Types: double

Number of samples per output symbol, specified as a positive scalar greater than 1.

Data Types: double

Sample rate, specified as a positive scalar.

Data Types: double

Phase continuity, specified as either 'cont' or 'discont'. Set phase_cont to 'cont' to force phase continuity across symbol boundaries in y, or 'discont' to avoid forcing phase continuity.

Data Types: char

Output Arguments

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Complex baseband representation of a FSK-modulated signal, returned as vector or matrix of complex values. The columns of y represent independent channels.

Data Types: double | single
Complex Number Support: Yes


[1] Sklar, Bernard. Digital Communications: Fundamentals and Applications. Upper Saddle River, NJ: Prentice-Hall, 2001.

Version History

Introduced before R2006a