A list,

Demodulation of FSK signals can also be incoherent and coherent. FSK signals can be regarded as transmitted by two frequency sources alternately, so the FSK receiver is composed of two ASK receivers in parallel.

(1) Coherent demodulation

Coherent demodulation uses a multiplier to input a reference signal coherent with carrier frequency multiplied by carrier frequency, filter out high-frequency signals through low-pass filtering, and obtain the original signal. FSK can be regarded as two ASK signals after bandpass filtering. The principle of coherent detector composition is shown as follows:

Ii. Source code

% Main function: implementation4FSK modulation % s: sequence of input integers [0- 3】, F0, F1, F2, F3: respectively4Carrier %nSamples, the number of samples for each symbol, must be an even number s= Randint (1.10.4);
f0=1; f1=2; f2=4; f3=8;
nSamples=100;
t=0:2*pi/99:2*pi; % Note that the length of t is consistent with the length of nSamples cp=[]; mod=[]; bit=[];for n=1:length(s)
     if s(n)==0
         cp1=ones(1,nSamples); c=sin(f0*t);
         bit1=zeros(1,nSamples); % 00
     elseif s(n)= =1
         cp1=ones(1,nSamples); c=sin(f1*t);
         bit11=zeros(1,nSamples/2); %01
         bit12=ones(1,nSamples/2);
         bit1=[bit11 bit12];
     elseif s(n)= =2
         cp1=ones(1,nSamples); c=sin(f2*t);
         bit11=ones(1,nSamples/2); %10
         bit12=zeros(1,nSamples/2);
         bit1=[bit11 bit12];
     else s(n)==3
         cp1=ones(1,nSamples); c=sin(f3*t);
         bit11=ones(1,nSamples/2); %11
         bit12=ones(1,nSamples/2);
         bit1=[bit11 bit12];
     end
     
     cp=[cp cp1];
     mod=[mod c];
     bit=[bit bit1];
end
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3. Operation results

Fourth, note

Version: 2014 a