function [pb,ps,a]=Awgn_channel(snr_in_dB)
E=1; % energy per symbol
snr=10^(snr_in_dB/10); % signal to noise ratio
sgma=sqrt(E/snr)/2; % noise variance
s00=[1 0]; s01=[0 1]; s11=[-1 0]; s10=[0 -1]; % signal mapping
% generation of the data source
N=1;
%numofsymbolerror=0; %simulated symbol error rates, zero clearing.
numofbiterror=0; %simulated bit error rates, zero clearing.
while(numofbiterror<=1000),
temp=rand; % a uniform random variable between 0 and 1
if (temp<0.25), % with probability 1/4, source output is "00"
dsource1=0; dsource2=0;
elseif (temp<0.5), % with probability 1/4, source output is "01"
dsource1=0; dsource2=1;
elseif (temp<0.75), % with probability 1/4, source output is "10"
dsource1=1; dsource2=0;
else % with probability 1/4, source output is "11"
dsource1=1; dsource2=1;
end;
n=sgma*randn(1,2); % 2 normal distributed r.v with 0, variance sgma
if ((dsource1==0) && (dsource2==0)),
r=s00+n;
elseif ((dsource1==0) && (dsource2==1)),
r=s01+n;
elseif ((dsource1==1) && (dsource2==0)),
r=s10+n;
else
r=s11+n;
end;
% The correlation metrics are computed below
c00=dot(r,s00); c01=dot(r,s01); c10=dot(r,s10); c11=dot(r,s11);
% The decision on the ith symbol is made next
c_max=max([c00,c01,c10,c11]);
if (c00==c_max), decis1=0; decis2=0;
elseif (c01==c_max), decis1=0; decis2=1;
elseif (c10==c_max), decis1=1; decis2=0;
else decis1=1; decis2=1;
end;
% Increment the error counter, if the decision is not correct
%symbolerror=0;
if (decis1~=dsource1), numofbiterror=numofbiterror+1; %symbolerror=1;
end;
if (decis2~=dsource2), numofbiterror=numofbiterror+1; %symbolerror=1;
end;
%if (symbolerror==1), numofsymbolerror=numofsymbolerror+1;
%end;
N=N+1;
end;
pb=numofbiterror/(2*N) % since 2N bits are transmitted
ps=numofbiterror/N % since there are totally N symbols
a=N
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