% 注意這里和cm_sm32程序的區別是信號在信道上只考慮了加性白噪聲
 % 沒有瑞利衰落; 其他的都是一樣的;

 function [pb1,ps1]=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=100;
E=1;  % energy per symbol                                           
snr=10^(snr_in_dB/10);  % signal to noise ratio
sgma=sqrt(E/snr)/2;     % noise variance
% signal mapping
s00=[1 0]; s01=[0 1]; s11=[-1 0]; s10=[0 -1];  
% generation of the data source
numofsymbolerror=0;
numofbiterror=0;
counter=0;
while(numofbiterror<100)
for i=1:N
    % a uniform random variable between 0 and 1
    temp=rand;  
    % with probability 1/4, source output is "00"
    if (temp<0.25) 
        dsource1(i)=0; dsource2(i)=0;
        % with probability 1/4, source output is "01"
    elseif (temp<0.5)
        dsource1(i)=0; dsource2(i)=1;
         % with probability 1/4, source output is "10"
    elseif (temp<0.75)                        
        dsource1(i)=1; dsource2(i)=0;
        % with probability 1/4, source output is "11"
    else  
        dsource1(i)=1; dsource2(i)=1;
    end;
end;
% detection and the probability of error calculation

for i=1:N
    % the received signal at the detection, 
    % for the ith symbol,is:
    % 2 normal distributed r.v with 0, variance sgma
    
    % 注意這里和cm_sm32程序的區別是信號在信道上只考慮了加性白噪聲
    % 沒有瑞利衰落;
    n=sgma*randn(1,2);
    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;
counter=counter+1;
end;
% since there are totally N symbols
ps1=numofsymbolerror/(N*counter); 
% since 2N bits are transmitted 
pb1=numofbiterror/(2*N*counter);