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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 use its step method to display a plot of the signal spectrum.

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

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.

Introduced before R2006a