%***********************************************************************
% cm_sm32.m
% 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.
% Programmed by Liu Dejian
% Dtat:2008-3-8
%***********************************************************************
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.
% (cm_sm32求出以dB为单位的给定信噪比的比特误码率和符号误码率)(p276/p324)
N=10000; % 在不同信噪比Eb/N0下发送10000符号进行蒙特卡罗仿真
E=1; % energy per symbol（这里E=Es=2Eb）
snr=10^(snr_in_dB/10); % signal-to-noise ratio
sgma=sqrt(E/(3*2*snr)); % noise variance
% the signal mapping
s000=[1 0];
s001=[cos(pi/4) sin(pi/4)];
s011=[0 1];
s010=[cos(3*pi/4) sin(3*pi/4)];
s110=[-1 0];
s111=[cos(5*pi/4) sin(5*pi/4)];
s101=[0 -1];
s100=[cos(7*pi/4) sin(7*pi/4)];
% generation of the data source
for i=1:N,
temp=rand; % a uniform random variable between 0 and 1
if(temp<0.125), % With probability 1/8, source output is "000."
dsource1(i)=0;
dsource2(i)=0;
dsource3(i)=0;
elseif(temp<0.25), % With probability 1/8, source output is "001."
dsource1(i)=0;
dsource2(i)=0;
dsource3(i)=1;
elseif(temp<0.375), % With probability 1/8, source output is "010."
dsource1(i)=0;
dsource2(i)=1;
dsource3(i)=0;
elseif(temp<0.5), % With probability 1/8, source output is "011."
dsource1(i)=0;
dsource2(i)=1;
dsource3(i)=1;
elseif(temp<0.625), % With probability 1/8, source output is "100."
dsource1(i)=1;
dsource2(i)=0;
dsource3(i)=0;
elseif(temp<0.75), % With probability 1/8, source output is "101."
dsource1(i)=1;
dsource2(i)=0;
dsource3(i)=1;
elseif(temp<0.875), % With probability 1/8, source output is "110."
dsource1(i)=1;
dsource2(i)=1;
dsource3(i)=0;
else % With probability 1/8, source output is "111."
dsource1(i)=1;
dsource2(i)=1;
dsource3(i)=1;
end;
end;
% detection and the probability of error calculation（判决误码率的计算）
numofsymbolerror=0;
numofbiterror=0;
for i=1:N,
% The received signal at the detector, for the ith symbol, is:
% （在判决器处的接收信号，对于第i个符号为：）
n(1)=gngauss(sgma);
n(2)=gngauss(sgma);
if((dsource1(i)==0)&(dsource2(i)==0)&(dsource3(i)==0)),
r=s000+n;
elseif((dsource1(i)==0)&(dsource2(i)==0)&(dsource3(i)==1)),
r=s001+n;
elseif((dsource1(i)==0)&(dsource2(i)==1)&(dsource3(i)==0)),
r=s010+n;
elseif((dsource1(i)==0)&(dsource2(i)==1)&(dsource3(i)==1)),
r=s011+n;
elseif((dsource1(i)==1)&(dsource2(i)==0)&(dsource3(i)==0)),
r=s100+n;
elseif((dsource1(i)==1)&(dsource2(i)==0)&(dsource3(i)==1)),
r=s101+n;
elseif((dsource1(i)==1)&(dsource2(i)==1)&(dsource3(i)==0)),
r=s110+n;
else
r=s111+n;
end;
% The correlation metrics are computed below.
% （以下为计算互相关量度）
c000=dot(r,s000);
c001=dot(r,s001);
c010=dot(r,s010);
c011=dot(r,s011);
c100=dot(r,s100);
c101=dot(r,s101);
c110=dot(r,s110);
c111=dot(r,s111);
% The decision on the ith symbol is made next.
% （第i个符号的判决按如下方式进行）
c_max=max([c000 c001 c010 c011 c100 c101 c110 c111]);
if(c000==c_max),
decis1=0;decis2=0;decis3=0;
elseif(c001==c_max),
decis1=0;decis2=0;decis3=1;
elseif(c010==c_max),
decis1=0;decis2=1;decis3=0;
elseif(c011==c_max),
decis1=0;decis2=1;decis3=1;
elseif(c100==c_max),
decis1=1;decis2=0;decis3=0;
elseif(c101==c_max),
decis1=1;decis2=0;decis3=1;
elseif(c110==c_max),
decis1=1;decis2=1;decis3=0;
else
decis1=1;decis2=1;decis3=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(decis3~=dsource3(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/(3*N); % since 3N bits are transmitted
