acquisitionconvolution.m

gps捕获源码

function [codephase,frequency] = acquisitionConvolution(svnum)
% Performs acquisition on collected data
% Searches for the satellite with number svnum
% Returns the code phase and the coarse frequency of the signal

% ***** initial conditions *****
load data.mat
x=double(data');

fs=11.999e6;	% sampling freq
ts=1/fs;	% sampling time
n=fs/1000;	% data pt in l ms
nn=[0:n-1];	% total no. of pts
fc0=3.563e6;	% center freq without Doppler

% ***** Reads code with 1024 different phases
filename=sprintf('gold%i.mat',svnum);
load(filename);
code=double(code(1,:));

% ***** DFT of C/A code
codefreq = conj(fft(code));

for i=1:41
  fc(i) = fc0 + 0.0005e6*(i-21);
  expfreq=exp(j*2*pi*fc(i)*ts*nn);
  sine= imag(expfreq);		% generate local sine
  cosine= real(expfreq);	% generate local cosine 
  I = sine.*x;
  Q = cosine.*x;
  IQfreq = fft(I+j*Q);
  convcodeIQ = IQfreq .* codefreq;
  result(i,:) = abs(ifft(convcodeIQ)).^2;
end

[peak codephase]=max(max(result));
[peak frequency]=max(max(result'));

frequency = fc(frequency);

codephaseChips = round(1023 - (codephase/11999)*1023)
gold_rate = 1.023e6;			% Gold code clock rate in Hz
ts=1/fs;
tc=1/gold_rate;
b=[1:n];
c=ceil((ts*b)/tc);

figure(1)
x_axis=c;
y_axis=fc/1e6;
s=surf(x_axis,y_axis,result);
set(s,'EdgeColor','none','Facecolor','interp');
axis([min(x_axis) max(x_axis) min(y_axis) max(y_axis) min(min(result)) max(max(result))]);
caxis([0 max(max(result))]);
xlabel('Code Phase [chips]');
ylabel('Frequency [MHz]');
zlabel('Magnitude');
text=sprintf('SVN %i',svnum);
title(text);