Acquisition of GPS C/A Code Signals - Fundamentals of Global Positioning System Receivers: A Software Approach - page 157

[mamp mrw] = max(mfrq1); % find highest peak
mfrq=cfrq+200*(mrw-2);
fr=mfrq; % medium freq

% ******* find fine freq *******
zb5=za5 .* exp(j*2*pi*fr*ts*[0:5*n-1]); % one DFT component
zc5=diff(-angle(sum(reshape(zb5,n,5)))); % find difference
angle
zc5fix=zc5;

%******* Adjust phase and take out possible phase shift
*******
threshold=2.3*pi \ 5;

for i=1:4;
if abs(zc5(i))>threshold;% for angle adjustment
zc5(i)=zc5fix(i)-2*pi;
if abs(zc5(i))>threshold;
zc5(i)=zc5fix(i)+2*pi; % end
if abs(zc5(i))>2.2*pi \ 5; %for pi phase shift

correction
zc5(i)=zc5fix(i)-pi;
if abs(zc5(i))>threshold;
zc5(i)=zc5fix(i)-3*pi;
if abs(zc5(i))>threshold;
zc5(i)=zc5fix(i)+pi; %end

end

end

end

end

end
end

dfrq=mean(zc5)*1000/(2*pi);
frr=fr+dfrq;% fine freq

plot(abs(yy(crw,1:n)))
title(['GPS = ' num2str(svnum) ' max at '

num2str(pt init)])
figure
plot(abs(yy(:,ccn)),'*')
% title(['GPS = ' num2str(svnum) '

Freq = ' num2str(frr)])

format
pt init
format long e
frr