MATLAB: Fsk modulator and demodulator

berbit error ratefskfsk demodulatorfsk modulatorsnr

i have this code and although i added noise to it the bit error rate is still zero.. any clue?!!
%%%%%%%%%%%%%fsk mod and demod%%%%%%%%%%%%%%%%%%%%
M = 2; 
k = log2(M);
EbNo = 5;
Fs = 16; 
nsamp = 17; 
freqsep = 8;
n=100;
msg = randint(n,1,M); % Random signal
txsig = fskmod(msg,M,freqsep,nsamp,Fs); % Modulate.
ab=abs(txsig);
ps=(sum(ab.^2))/n; 
snr=30;
pn=10.^(-0.1.*snr).*ps;
noise= sqrt(pn)*randn(1,n);
G1=randn(1,n); %generation of Gaussian noise
G2=randn(1,n);
v= sqrt(power(G1,2)+ power(G2,2));
A=v(2);
theta=2*pi*rand;
msg_rx  = A*exp(j*theta)*txsig + noise(3); %flat fading
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

Best Answer

Walter is right - when you add noise(3) to the signal you are not actually adding random noise, you're just adding some positive or negative shift. Also, the noise vector you are generating is too short.
You can try out the code below (with the changes commented). When you run it several times, you will see that the BER average is close to the theoretical BER of 0.1029.
M = 2; 
k = log2(M);
EbNo = 5;
Fs = 16; 
nsamp = 17; 
freqsep = 8;
n=100;
msg = randint(n,1,M); 
txsig = fskmod(msg,M,freqsep,nsamp,Fs); 
ab=abs(txsig);
ps=(sum(ab.^2))/n; 
snr=5; % Changed this to match EbNo above
pn=10.^(-0.1.*snr).*ps;
noise= sqrt(pn)*randn(1,n*nsamp); % Changed the length of the noise vector from n to n*nsamp
G1=randn(1,n); % You are not generating noise here, you are generating fading coefficients
G2=randn(1,n);
v= sqrt(power(G1,2)+ power(G2,2));
A=v(2);
theta=2*pi*rand;
% I got rid of fading to make sure code works for AWGN case
msg_rx  = txsig + noise'; % txsig is 1700x1 and noise is 1x1700, so need transpose
msg_rrx = fskdemod(msg_rx,M,freqsep,nsamp,Fs);  
[num,BER] = biterr(msg,msg_rrx) % Bit error rate
BER_theory = berawgn(EbNo,'fsk',M,'noncoherent') % Theoretical BER
Related Question