fskdemod - Frequency shift keying demodulation

Syntax

Description

z = fskdemod(y,M,freq_sep,nsamp) noncoherently demodulates the complex envelope y of a signal using the frequency shift key method. M is the alphabet size and must be an integer power of 2. freq_sep is the frequency separation between successive frequencies in Hz. nsamp is the required number of samples per symbol and must be a positive integer greater than 1. The sampling frequency is 1 Hz. If y is a matrix with multiple rows and columns, the function processes the columns independently.

z = fskdemod(y,M,freq_sep,nsamp,Fs) specifies the sampling frequency in Hz.

z = fskdemod(y,M,freq_sep,nsamp,Fs,symbol_order) specifies how the function assigns binary words to corresponding integers. If symbol_order is set to 'bin' (default), the function uses a natural binary-coded ordering. If symbol_order is set to 'gray', it uses a Gray-coded ordering.

Examples

The example below illustrates FSK modulation and demodulation over an AWGN channel.

M = 2; k = log2(M);
EbNo = 5;
Fs = 16; nsamp = 17; freqsep = 8;
msg = randi([0 M-1],5000,1); % Random signal
txsig = fskmod(msg,M,freqsep,nsamp,Fs); % Modulate.
msg_rx  = awgn(txsig,EbNo+10*log10(k)-10*log10(nsamp),...
    'measured',[],'dB'); % AWGN channel
msg_rrx = fskdemod(msg_rx,M,freqsep,nsamp,Fs);  % Demodulate
[num,BER] = biterr(msg,msg_rrx) % Bit error rate
BER_theory = berawgn(EbNo,'fsk',M,'noncoherent') % Theoretical BER

The output is shown below. Your BER value might vary because the example uses random numbers.

BER =

    0.1086

BER_theory =

    0.1029

See Also

fskmod | pskdemod | pskmod

How To

• Digital Modulation

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