GPS Software Receivers - Fundamentals of Global Positioning System Receivers: A Software Approach - page 212

%p92.m This program checks the parity code

function [pt, navd]=matchsubf(navd);

nsat = size(navd,1);

pt = zeros(nsat);

pt = findsf1(navd)';
dlen = (floor(size(navd,2) / 30) - 1) * 30;

h1=[111011000111110011010010];
% from GPS Theory & App p.131
h2=[011101100011111001101001];%by
B.W. Parkinson & J.J. spilker
h3=[101110110001111100110100];
h4=[010111011000111110011010];
h5=[101011101100011111001101];
h6=[001011011110101000100111];
H = [h1; h2; h3; h4; h5; h6];

for m=1:nsat;
if pt(m)>0
for pnt=pt(m):30:dlen, %for different initial pts
D29 = navd(m, pnt-2);
D30 = navd(m, pnt-1);
navd(m, pnt:pnt+23) = D30 * navd(m, pnt:pnt+23);
d = navd(m, pnt:pnt+23);
Df = [D29 D30 D29 D30 D30 D29];
for k = 1:6,
temp = H(k,:) .* d;
p(k) = prod([Df(k) temp(find(temp))]);

end
if p = navd(m, pnt+24:pnt+29),

disp('Parity check failed!')

∼

end
end

end

end
ind=find(pt

∼

=0);

pt=pt(ind);
navd = -navd;
navd=(navd+1)./2;