experiment5_7.m

Simon Haykin的《Communication Systems》(《通信系统》)的配套MATLAB源代码。包括脉冲调制、随机过程、和差错编码等。

% Experiment 5, CSBOOK: Haykin
% Timing (clock) recovery
% Measured S-curve of the 
% NDA-ELD loop, Noise added, E/N=10dB


clear all

% time slot

T=1/8000;deltaT=T/50;

%Nyquest pulse

t=[-3*T/2+deltaT/2:deltaT:3*T/2-deltaT/2];

h=sinc(2*t./T).*(cos(pi*t./T)./(1-2*t./T).^2);

% Generating QPSK signals

no_of_bits=2000;

b=round(rand(no_of_bits,1));

bits=2*b-1;

bitsi=bits(1:2:length(bits)-1);

bitsq=bits(2:2:length(bits));

amp=(bitsi+i*bitsq)/sqrt(2);

amp=conj(amp');

% signal to noise ratios 
 
SNRdB =[30];
 
snr = 10^(SNRdB/10);
 
S_curvef=0;
 

for trial=1:100

% Add AWGN with STD equal to std_value
       
wn = (randn(length(amp),1)+i*randn(length(amp),1))/sqrt(2)/sqrt(snr);
        
s_n=amp+wn';

%FIR filtering
  
s_i=upfirdn(real(s_n),h,50,1);
  
s_q=upfirdn(imag(s_n),h,50,1);
  
s=s_i+i*s_q;
 
x=s(1: length(s)-15);


  
      % FIR filtering
         y_i=upfirdn(real(x),h,50,1);
         y_q=upfirdn(imag(x),h,50,1);
         y=(y_i+y_q);


	%Timing error prediction
	tau=15;tauerror=-50:50;tauhat=tau-tauerror;
		for k=1:990
     			tp(k,:)=y(75+50*k+48+tauhat)-y(75+50*k+3+tauhat);
		 	tq(k,:)=y(75+50*k+25+tauhat);
     			tqconj(k,:)=conj(tq(k,:));
     			e(k,:)=real(tqconj(k,:).*tp(k,:));		
		end

	%Accumulate S_curve
	for k=1:length(tauerror)
  		S_curve(k)=mean(e(:,k));
	end

      S_curvef=S_curvef+S_curve;

end
 
S_curvef=S_curvef/trial;
 
plot(-0.48:1/50:0.5, S_curvef(51:100))
ylabel('S-curve')
xlabel('Normalized timing offset, \delta/T')