fsk modulator and demodulator
조회 수: 6 (최근 30일)
이전 댓글 표시
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
댓글 수: 0
채택된 답변
Rob Graessle
2011년 4월 22일
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
추가 답변 (1개)
Walter Roberson
2011년 4월 21일
You calculate v=sqrt(G1.^2+G2.^2) where G1 and G2 are 1 x n. You then take v(2) and throw away the rest of v. What is the point of doing all of that, when you could just do
A = sqrt(randn^2+randn^2);
This hints that you are doing something wrong. As does the fact that you use only noise(3) when noise is 1 x n .
You need to check out the magnitude of noise(3) and compare it to the magnitude of A*exp(j*theta)*txsig -- if noise(3) is very small then it would be as if you had not added the noise, merely phase-shifted the signal.
참고 항목
카테고리
Help Center 및 File Exchange에서 FSK에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!