function [pb,ps]=cm_sm32(snr_in_dB)
% [pb,ps]=cm_sm32(snr_in_dB)
%                CM_SM3 finds the probability of bit error and symbol error for 
%                the given value of snr_in_dB, signal to noise ratio in dB.
N=10000;
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
for i=1:N,
    temp=rand;                                  % a uniform random variable between 0 and 1
    if (temp<0.25),                             % with probability 1/4, source output is "00"
        dsource1(i)=0; dsource2(i)=0;
    elseif (temp<0.5),                          % with probability 1/4, source output is "01"
        dsource1(i)=0; dsource2(i)=1;
    elseif (temp<0.75),                         % with probability 1/4, source output is "10"
        dsource1(i)=1; dsource2(i)=0;
    else                                        % with probability 1/4, source output is "11"
        dsource1(i)=1; dsource2(i)=1;
    end;
end;
% detection and the probability of error calculation
numofsymbolerror=0;
numofbiterror=0;
for i=1:N,
    % the received signal at the detection, for the ith symbol,is:
    n=sgma*randn(1,2);                          % 2 normal distributed r.v with 0, variance sgma
    if ((dsource1(i)==0) & (dsource2(i)==0)), 
        r=s00+n;
    elseif ((dsource1(i)==0) & (dsource2(i)==1)), 
        r=s01+n;
    elseif ((dsource1(i)==1) & (dsource2(i)==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(i)), numofbiterror=numofbiterror+1; symbolerror=1; 
    end;
    if (decis2~=dsource2(i)), numofbiterror=numofbiterror+1; symbolerror=1; 
    end;
    if (symbolerror==1), numofsymbolerror=numofsymbolerror+1; 
    end;
end;
ps=numofsymbolerror/N;                          % since there are totally N symbols
pb=numofbiterror/(2*N);                         % since 2N bits are transmitted