Communications Toolbox

fskdemod

Frequency shift keying demodulation

Syntax

z = fskdemod(y,M,freq_sep,nsamp) z = fskdemod(y,M,freq_sep,nsamp,Fs) z = fskdemod(y,M,freq_sep,nsamp,Fs,symbol_order)

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, then 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 will use a natural binary-coded ordering. If symbol_order is set to 'gray', it will use 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; N = Fs;
nsamp = 17; freqsep = 8;
msg = randint(5000,1,M); % Random signal
txsig = fskmod(msg,M,freqsep,nsamp,Fs); % Modulate.
msg_rx  = awgn(txsig,EbNo+10*log10(k)-10*log10(N),...
   'measured',[],'dB'); % AWGN channel
msg_rrx = fskdemod(msg_rx,M,freqsep,nsamp,Fs);  % Demodulate
[num,SER] = symerr(msg,msg_rrx); % Symbol error rate
BER = SER*(M/2)/(M-1) % Bit error rate
BER_theory = berawgn(EbNo,'fsk',M,'noncoherent') % Theoretical BER

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

BER =

    0.1006


BER_theory =

    0.1029

fskdemod

Syntax

Description

Examples

See Also