奇偶校驗
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];
h2=[011101100011111001101001];
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,
      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;