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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