cm_sm32.m

matlab通信仿真

function [pb,ps]=cm_sm32(snr_in_dB)

% find the probability of bit error and symbol error for the giben value of
% snr_in_dB.

N=10000;
E=1;
snr=10^(snr_in_dB/10);
sgma=sqrt(E/snr)/2;

% the signal mapping
s00=[1 0];
s01=[0 1];
s11=[-1 0];
s10=[0 -1];

% generation of the data source
for i=1:N
    temp=rand;
    if(temp<0.25)
        dsource1(i)=0;
        dsource2(i)=0;
    elseif (temp<0.5)
        dsource1(i)=0;
        dsource2(i)=1;
    elseif(temp<0.75)
        dsource1(i)=1;
        dsource2(i)=0;
    else
        dsource1(i)=1;
        dsource2(i)=1;
    end
end

%detection and probability of error calculation
numofsymbolerror=0;
numofbiterror=0;

for i=1:N
    % the received signal at the detector , for the ith symbol, is:
    n(1)=gngauss(sgma);
    n(2)=gngauss(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