Code covered by the BSD License

# Contemporary Communications Systems Matlab Files

### Omar Ruiz (view profile)

Matlab Files in this book

[pb,ps]=cm_sm32(snr_in_dB)
```function [pb,ps]=cm_sm32(snr_in_dB)
% [pb,ps]=cm_sm32(snr_in_dB)
%		CM_SM32  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
% 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;			  	% 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 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```