tryfastacq1.m

faster algorithm for GPS signal Acquistion

%function [yes, f, ph] = acquisition(fid, K, sat_id, fc_lo,step,fc_hi, T)

clear all;
fres=5.714e6/8192;
temp=[0:8191];
iffre=1.422e6;
fs=5.714e6;
padzeros=8192-5714;
Nif=ceil(1.422e6/fres);

fid = fopen('d:\datafiles\fdata33.dat','r'); %file pointer to data
disp('zero padding 8192 fft methode');

data= fscanf(fid,'%f',8192);
fftdata=fft(data);
count=0;
for sn=1:1,
code=digitizg(5714,5.714e6,0,sn);
code2=[code,zeros(1,padzeros)];
codefft=conj(fft(code2'));
% as if multiplifying by carrier IF 
for i=-11:11,
fftdata2=fftdata([Nif-i:8192,1:Nif-i-1]);
corr=abs(ifft(fftdata2.*codefft));
[corrout(i+12)  startpoint(i+12)]=max(abs(corr));
end;
[signalpower(sn) carrier]=max(corrout);
codestart= startpoint(carrier);
cn(sn)=10*log10( signalpower(sn));
if cn(sn)> 27
    count=count+1; 
    %disp('deteted  sateelite ') , sn
    detected(count)=sn
    course_fre=(carrier-12)*fres+iffre
    sn ,    cn(sn),   codestart,  carrier,  
        
else 
    sn
    disp ('not detected') 
    
end;
       
end;

fclose(fid);
fid = fopen('d:\datafiles\fdata33.dat','r'); %file pointer to data
fs= 5.714e6;
d1=fs/1000;
ph=codestart;


% Generate CA code

data3=fscanf(fid,'%f',ph);
sat_id=1;
d2=d1;
%ca = cacode(sat_id, 1.023e6, fs, d1ms);
ca=digitizg(d2,fs,0,sat_id);
disp('c/a code started');
     for i=1:18,
    data4=fscanf(fid,'%f',d2);
    remove_code=ca.*data4';
    figure(i);
   
    r1=remove_code;
    r2=fft(r1);
   plot(abs(fft(r1)));
    value(i)=max((fft(r2)));
    v1=imag(value(i));
    v2=real(value(i));
    pha(i)=atan(v2/v1);
end;
 disp('completed');
   p1=pha(2)-pha(1)
   p2=pha(3)-pha(2)
   p3=pha(4)-pha(3)
   p4=pha(5)-pha(4)
   p5=pha(6)-pha(5)
   p6=pha(7)-pha(6)
   p7=pha(8)-pha(7)
   p8=pha(9)-pha(8)
   p9=pha(10)-pha(9)
   p10=pha(11)-pha(10)
   p11=pha(12)-pha(11)
   p12=pha(13)-pha(12)
   p13=pha(14)-pha(13)
   p14=pha(15)-pha(14)
   p15=pha(16)-pha(15)
   p16=pha(17)-pha(16)
   p17=pha(18)-pha(17)
   
   
   p11=[p1 p2 p3 p4];
   p12=[p5 p6 p7 p8];
   p13=[p9 p10 p11 p12];
   p14=[p13 p14 p15 p16];