function [p]=cm_sm34(snr_in_dB)% [p]=cm_sm34(snr_in_dB)%		CM_SM34  finds the probability of error for the given%   		value of snr_in_dB, signal to noise ratio in dB.N=10000;E=1;				  	% energy per symbolsnr=10^(snr_in_dB/10);	 	  	% signal to noise ratiosgma=sqrt(E/(4*snr));	  	  	% noise variance% generation of the data source followsfor i=1:2*N,	  temp=rand;			  	% a uniform random variable between 0 and 1  if (temp<0.5),		      dsource(i)=0;		  	% with probability 1/2, source output is "0"  else    dsource(i)=1;		  	% with probability 1/2, source output is "1"  end;end;% Differential encoding of the data source followsmapping=[0 1 3 2];M=4;[diff_enc_output] = cm_dpske(E,M,mapping,dsource);% received signal is thenfor i=1:N,  [n(1) n(2)]=gngauss(sgma);  r(i,:)=diff_enc_output(i,:)+n;end;% detection and the probability of error calculationnumoferr=0;prev_theta=0;for i=1:N,  theta=angle(r(i,1)+j*r(i,2));  delta_theta=mod(theta-prev_theta,2*pi);  if ((delta_theta<pi/4) | (delta_theta>7*pi/4)),    decis=[0 0];  elseif (delta_theta<3*pi/4),    decis=[0 1];  elseif (delta_theta<5*pi/4)    decis=[1 1];  else    decis=[1 0];  end;  prev_theta=theta;  % increase the error counter, if the decision is not correct  if ((decis(1)~=dsource(2*i-1)) | (decis(2)~=dsource(2*i))),    numoferr=numoferr+1;  end;end;p=numoferr/N;