acquisition.m

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function [amp,ccn,cfrq]=Acquisition(lpfdata, svnum)


% **************initial parameters****************
fs=4.8e+6;  % the sampling frq;
ts=1/fs;
fc=30e+3;   % the center frq without the Doppler;
Rc=1.023e+6;

AccumPara=1;    % the parameter that divides the 1ms; 16 or 8 or 4
AccumTime=1e-3/AccumPara;   % the accumulation time interval;
CorrelationLength=AccumTime*fs;  % the correlation length for one time;

intodat=2531;   % the initial phase 
% svnum=1;    % the PRN number;

AcquireTime=1;  % the total acquisition time for one time, united by 1ms;


% **** start the acquisiton ******************
% ******* the circular correlation method ***************

%*** input the GPS data that have passed through the down convert****
GPSdata=zeros(1,CorrelationLength);
GPSdata=lpfdata(intodat:intodat+CorrelationLength-1);   % get CorrelationLength points out of the data stream coming from the LPF, 
                                                        %   started at the point of intodat;
% GPSdata = conj(GPSdata);
gf = fft(GPSdata);
gf = conj(gf);
FreqValue = zeros(21, CorrelationLength);
for i=1:21
    fri = fc - 10000 + (i-1)*1000;
    lsi = LocalCarrierCodeGen(svnum, CorrelationLength, fri, 0, 0);
    lf = fft(lsi);
    FreqValue(i,:) = ifft(lf .* gf);
    plot(abs(FreqValue(i,:)))
end

[amp crw] = max(max(abs(FreqValue')));
[amp ccn] = max(max(abs(FreqValue)));
pt_init=ccn; % initial point
cfrq = fc - 10000 + (crw-1)*1000;

plot(abs(FreqValue(crw,:)))
amp
ccn
slew=mod(floor(ccn*Rc/fs),1023*2)
cfrq

% *********************************************************

% ************* the time domain correlation method ************
% AccNumPara = 2;     % the step of slewing, normalized by sampling point
% AccNum = 4800/AccNumPara;   % there are AccNum search bin in the time domain
% CorrValue = zeros(AccNum,AccumPara);    % store the correlator value of every search bin
% FreqValue = zeros(AccNum,32);                   % store the fft result of every search bin
% GPSdata=zeros(1,CorrelationLength);
% 
% % ********* for test ****************************************************
% f=zeros(AccNum,32,AcquireTime);
% % ***********************************************************************
% % fc = 0;   % test in the mode without carrier
% lsdata = LocalCarrierCodeGen(svnum, 96000, fc, 0,0);
% lsi = zeros(1, CorrelationLength);
% 
% for i = 1:AcquireTime
%     for t = 1:AccumPara
%         % obtain 1/AccumPara(ms)'s sampling data
%         GPSdata = lpfdata(intodat+(t-1)*CorrelationLength+4800*(i-1) : intodat+(t-1)*CorrelationLength+4800*(i-1)+CorrelationLength-1);
%         
%         for s = 1:AccNum
%             % generate AccNum's correlator channels' local data
%             lsi = lsdata(1+AccNumPara*(s-1)+(t-1)*CorrelationLength+4800*(i-1) : CorrelationLength+AccNumPara*(s-1)+(t-1)*CorrelationLength+4800*(i-1));
%             CorrValue(s,t) = sum(lsi .* GPSdata);
%         end
%     end
%     f = fft(CorrValue', 32);
%     FreqValue = FreqValue + abs(f');
%     
%     % ********** for test *******************************************
% 
% %     f(:,:,i) = fft(CorrValue', 32);
% %     plot(abs(f(:,:,i)'))
% %     FreqValue = FreqValue + abs(f(:,:,i)');
%     % **************************************************************
%     
% end
% 
% plot(abs(FreqValue))
% [amp ccn] = max(max(abs(FreqValue')));
% [amp crw] = max(max(abs(FreqValue)));
% cfrq = crw;