carrier_x4c.m

本文件内包含了QPSKandQAM256的系统仿真

% QPSK Demod Test

load c:\qpsk\lecroy_1.dir\sc1002.dat;
offset=1;
size=1024*4;
wave=sc1002';
fs=1e9;

% Display wave form

plot(wave(1:100));
grid
title('IF Signal');
%%%%pause;

data_fft=10*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      (wave(offset:offset+size-1))))));
   data_fft=data_fft-max(data_fft);
   nnnn=size;
   ff=-nnnn/2:nnnn/2-1;
   ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
	title(' IF Data Spectrum Before Filtering ');
	axis([400e6, 500e6 -50 0]);
	grid;
	xlabel('FREQUENCY (HZ)');
	ylabel('MAGNITUDE (dB) ');
   %pause;
   
   % generate local carrier
   
   f_lo=(480-50)*1e6;   % carrier
   t=[0:length(wave)-1]/fs;
	carrier_a=sin(2*pi*f_lo*t); 	% carrier sine;

	if_data=wave.*carrier_a;	% down converting

%	% plot spectrum;
data=if_data;
data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
		 data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
	title(' I Data Spectrum After Down Converting');
	grid;
   %pause;
   
   axis([0 100e6 -10 30]);
   %pause;
   
      
   %************************************
   %		Design A Low-Pass Filter 		*
   %************************************
   
   f_lowpass=[   0,    65/500,   80/500 ,    1.     ];
        m=   [   1.,   1.0 ,       1e-5,       1e-5   ];

n1=80;
b=firls(n1, f_lowpass, m);

a=1;
moduc=2^(-23);
%b=round(b/moduc/max(b))*moduc;
[amp,freq]=freqz(b,a,4096,fs);
amp=20*log10(  (abs(amp)+1e-8)  /  (max(abs(amp)) +1e-8)  );
plot(freq,amp);
grid
%pause  
axis([0e6 100e6 -50 0]);
title('N1=100 taps FIR low pass filter.');
%pause;

if_data=filter(b,a,if_data);



   %***************************
   %	Plot Spectrum				*
   %***************************
   data=if_data;
   offset=100;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
	title(' IF Data Spectrum After Low-Pass Filter');
	grid;
   %pause;
   axis([0e6 100e6 -50 30]);
	%pause;
   
   %***************************
   %		Times 2					*
   %***************************
   
   if2_data=if_data.*if_data;
   
   %***************************
   %	Plot Spectrum				*
   %***************************
   offset=100;
   data=if2_data;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      		data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
   axis([0e6 250e6 -50 30]);
	title(' IF Data Spectrum After X2');
	grid;
   %pause;
   
   %***************************
   %		Times 4					*
   %***************************
   
   if4_data=if2_data.*if2_data;
   
   %***************************
   %	Plot Spectrum				*
   %***************************
   offset=100;
   data=if4_data;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      		data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
   axis([200e6 250e6 -100 -30]);
	title(' IF Data Spectrum After X4');
	grid;
   %pause;
   

   
   
   %*********************************
   %		Design A Low-Pass Filter	*
   %*********************************
      b=fir1(100,[210/500 220/500]);

   a=1;
moduc=2^(-23);
%b=round(b/moduc/max(b))*moduc;
[amp,freq]=freqz(b,a,4096,fs);
amp=20*log10(  (abs(amp)+1e-8)  /  (max(abs(amp)) +1e-8)  );
plot(freq,amp);
title(' Band-Pass Filter After X2');
axis([200e6 250e6 -50 0]);
grid
%pause  

if4_data=filter(b,a,if4_data);

plot(if4_data(1000:3100));
grid;
title('IF Waveform X4');
%pause;


	%***************************
   %		sign  					*
   %***************************
   
   if4_data=sign(if4_data);
   
   %***************************
   %	Plot Spectrum				*
   %***************************
   offset=100;
   data=if4_data;
   data_fft=20*log10(abs(fftshift(fft(kaiser(size,11.)'.*...
      		data(offset:offset+size-1)))));
	ff=-nnnn/2:nnnn/2-1;
	ff=ff/nnnn*2*fs/2;
   plot(ff,data_fft);
   %axis([200e6 250e6 -100 -30]);
	title(' IF Data Spectrum After X4');
	grid;
   %pause;
   

   
   
if4_data=filter(b,a,if4_data);

plot(if4_data);
grid;
title('IF Waveform X4');
%pause;

%***********************
% count cycle
%***********************

carrier_ref=if4_data(100:5000-100);
length_ref=length(carrier_ref);
cycle_count=0;
for i=1:length_ref-1;
   if carrier_ref(i)*carrier_ref(i+1) <=0
      cycle_count=cycle_count+1;
   end
end

carrier_cycle=(length_ref-1)/fs/cycle_count*2;
carrier_frequency=1/carrier_cycle;

%*******************
%	Generate LO	   *
%*******************
length_if=length(if4_data);
t=[0:length_if-1]/fs;
sin_lo=sin(2*pi*carrier_frequency*t);

plot(if4_data(1000:1100));
hold on;
aaa=-1;
plot(sin_lo(1000+aaa:1100+aaa),'r');
hold off;
grid;
title('Carrier Waveform ');
%pause

true_carrier_frequency=f_lo+carrier_frequency/4;

   %*******************
	%	Generate LO	   *
   %*******************
   
   length_wave=length(wave);
   t=[0:length_wave-1]/fs;
   phase_offset=0;
   lo_cos=cos(2*pi*true_carrier_frequency*t+phase_offset);
   lo_sin=sin(2*pi*true_carrier_frequency*t+phase_offset);
   
   %************************
   %	Check Carrier Phase
   %***********************
   
   for i=1:100
     step=30;
	plot(wave(1+(i-1)*step:i*step)*5);
	hold on;
	aaa=-1;
   plot(lo_sin(1+aaa+(i-1)*step:i*step+aaa),'r');
   plot(lo_cos(1+aaa+(i-1)*step:i*step+aaa),'g');
	hold off;
	grid;
	title('***** Check Carrier Phase ***** ');
	pause
	end

   
   
   %****************
   %	Down Convert LO
   %***************
   
   i_data=wave.*lo_cos;
   q_data=wave.*lo_sin;
   
   
   %*********************************
   %		Design A Low-Pass Filter	*
   %*********************************
      b=fir1(100,25/500);

   a=1;
moduc=2^(-23);
%b=round(b/moduc/max(b))*moduc;
[amp,freq]=freqz(b,a,4096,fs);
amp=20*log10(  (abs(amp)+1e-8)  /  (max(abs(amp)) +1e-8)  );
plot(freq,amp);
title(' Low Pass Filter');
%axis([200e6 250e6 -50 0]);
grid
%pause  

i_data=filter(b,a,i_data);
q_data=filter(b,a,q_data);



%plot(i_data(1:2000));
%hold on;
%plot(q_data(1:2000),'r');
%hold off;
%grid;
%title(' Demod I Data');
%axis([1 2000 -.2 .2]);
%pause;

sample_i_data=reshape(i_data(1+500:4000+500),20,200);
sample_q_data=reshape(q_data(1+500:4000+500),20,200);

for ii=1:20
   
   i_out=sample_i_data(ii,:);
   q_out=sample_q_data(ii,:);
   
   iq=i_out+1i*q_out;
   
   plot(iq,'*');
   grid;
   pause
end