MATLAB implements the modulation and demodulation of the QPSK signal and calculate the code rate BER

tags: matlab Digital communications C language

Insert a clear all here;
clc ;
fc=1e8;fs=1e9;Band=1e8;M=4;T=2e-4;
%%
ts=1/fs;%time interval 
L=T*Band;
pskbit1 = randi([0,M-1],1,L);%Generate PSKL -mapping symbols (0-3）
pskbit1=pskbit1';%Converted to a column vector
txSig1 = pskmod(pskbit1,M,pi/M);%MPSK modulation 
   txSig1 = awgn(txSig1,10,'measured'); % Add AWGN
%%
%Surge
rolloff = .2; %  Rolling factor
span = 20 ; %  Cutting length
sps = 10;  % Samples per symbol
rrcFilter=rcosdesign(rolloff,span,sps,'sqrt'); 
upsam_sig = upfirdn(txSig1, rrcFilter, sps); 

%%
%The transmitting end 
%Frequency conversion
N=length(upsam_sig);
n = (0:ts:(N-1)*ts)';
waveform_fc_ref  = real(upsam_sig).*cos(2.*pi.*fc.*(n)) + imag(upsam_sig).*sin(2.*pi.*fc.*(n));%MP
%%
%Receiving end 
%Lower frequency conversion
 waveform_fc_ref = awgn(waveform_fc_ref,20,'measured'); % Add AWGN
I=waveform_fc_ref.*cos(2.*pi.*fc.*(n)) ;
Q=waveform_fc_ref.*sin(2.*pi.*fc.*(n));
IQ=I+1j*Q;
%%
%Reverse Filter (Sample Sample)
dowmsam_sig=upfirdn(IQ, rrcFilter, 1, sps);
dowmsam_sig=dowmsam_sig(span+1:end-span); %Go to the end
pskbit_demod=pskdemod(dowmsam_sig,4,pi/M);
 h=scatterplot(dowmsam_sig);%Drawing
 hold on 
 scatterplot(txSig1);
 hold off


%%
  err=biterr(pskbit_demod,pskbit1);%Number of mistakes, not the number of errors
 err1=err/L;%Coding rate%
%%
%  Turn the decomposition code into bit
hIntToBit = comm.IntegerToBit(log2(M));
Rx_bit = step(hIntToBit, pskbit_demod);%trainlen+1:end
Tx_bit = step(hIntToBit, pskbit1);%trainlen+1:end
berVec = step(comm.ErrorRate,Rx_bit,Tx_bit);
brate = berVec(1);%Coding rate
bnum = berVec(2);%Number of codes

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