MATLAB: FSK and MSK mod

fskmodmskmod

Hello, i have a question about fskmod and mskmod, when I tried to use these functions, it can only run when my bipolar bitstream. When I use unipolar, then the code can't compile.

ms = 2*randi([0 1],1000,1) -1;
msk = mskmod(ms,8,[],pi/2);

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 >> help mskmod
 [...] The elements of X must be 0 or 1.
 >> help fskmod
 [...] M is the alphabet size and must be an integer power of 2. The message signal must consist of integers between 0 and M-1.

Your ms is -1 and +1, which is against the requirement that the values must be 0 or 1. Neither function accepts bipolar signals.

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MATLAB: FSK and Adalm-Pluto

Hi Andrea,

The error can be solved when the variable data passed to fskDemod is type casted to double. Update the following in the code:

demodSignal=fskDemod(double(data))

The purpose of this update is due the different type provided by capture, based on the input length. Here are more details about what the data type of data would be while using the capture function of Pluto. https://www.mathworks.com/help/supportpkg/plutoradio/ref/plutoradio.sdrrxpluto.capture.html#mw_2dd7d96d-66cc-4e3d-a19a-8bcf004cf4c2 (Go through output arguments sections)

Regarding the dimensions of modSignals and data. The property 'SamplesPerSymbol' of FSKModulator decides it. The defult value is 17. So, the output length is the product of SamplesPerSymbol and length of input, i.e. 17*5 = 85. For more derails on the usage of object, go through https://www.mathworks.com/help/comm/ref/comm.fskmodulator-system-object.html

Hope this helps.

Regards,

Sriram

MATLAB: Fsk modulator and demodulator

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

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MATLAB: FSK and Adalm-Pluto

MATLAB: Fsk modulator and demodulator

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