cm_sm32.m

对衰落以及AGWN信道进行仿真

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;
%RayleighFading calculation
%******************************************************

    fd= 3500;  
    no=6;
    tstp=0.5*1.0e-6;
    counter=1000;  nsamp=1;
    ac0 = sqrt(1.0 ./ (2.0.*(no + 1)));   % power normalized constant(ich)
    as0 = sqrt(1.0 ./ (2.0.*no));         % power normalized constant(qch)
    ic0 = counter;                        % fading counter
 
    pai = 3.14159265;   
    wm = 2.0.*pai.*fd;
    n = 4.*no + 2;
    ts = tstp;
    wmts = wm.*ts;
    paino = pai./no;                        

    xc=zeros(1,nsamp);
    xs=zeros(1,nsamp);
    ic=[1:nsamp]+ic0;

  for nn = 1: no
	  cwn = cos( cos(2.0.*pai.*nn./n).*ic.*wmts );
	  xc = xc + cos(paino.*nn).*cwn;
	  xs = xs + sin(paino.*nn).*cwn;
  end

  cwmt = sqrt(2.0).*cos(ic.*wmts);
  xc = (2.0.*xc + cwmt).*ac0;
  xs = 2.0.*xs.*as0;
  
  R=sqrt(xc.^2+xs.^2);   

% ***********************************************************
% 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*R+n;
    elseif ((dsource1(i)==0) & (dsource2(i)==1)), 
        r=s01*R+n;
    elseif ((dsource1(i)==1) & (dsource2(i)==0)), 
        r=s10*R+n;
    else 
        r=s11*R+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