acquisition.m

This a framework to test new ideas in transmission technology. Actual development is a LDPC-coder in

function acquisition( filename, offset )

%clear all
%close all
%
toto = get_visual_data( filename );
%

load satCAcodes
fchip = 1.023e6;
nchip = 1023;
nsat  = 37;
%
% Choose some of the parameters
noisesdt   = sqrt(0);
fsample    = 100e6/24; %4*fchip; %2^12*1e3; %5e6 % Hz
nsample    = ceil(1*nchip/fchip*fsample)
maxdoppler = 6e3;
stepdoppler= 500;
%offset=70000+1*nsample
rxsig = toto(1+offset:nsample+offset).';
%clear toto,
tic
%
% Aquisition
fd=[-maxdoppler:stepdoppler:+maxdoppler];
ctime  = [0:nsample-1]./fsample;
dtime  = floor(ctime*fchip)+1;
cormmm = zeros(nsat,3);
for sat=1:nsat
    cacode = satCAcodes(sat,:);
    cacode = cacode(dtime);
    cacode = conj(fft(cacode));
    mmm = zeros(1,length(fd));
    ppp = zeros(1,length(fd));
    for col=1:length(fd)
        cor = ifft(fft(rxsig.*exp(-j*(2*pi*fd(col)*ctime))).*cacode);
        [a,b] = max(abs(cor));
        mmm(col) = a; % max{cor} wrt delay for fixed doppler
        ppp(col) = b; % position of max{cor} wrt delay for fixed doppler
    end
    [a,b] = max(mmm);
    cormmm(sat,1) = a;       % max{cor} wrt delay AND doppler
    cormmm(sat,2) = fd(b);   % doppler at which `max{cor} wrt delay AND doppler`occurs
    cormmm(sat,3) = ppp(b)-2;% delay at which `max{cor} wrt delay AND doppler`occurs
end
cor1 = cormmm;
%
[a,b] = sortrows(cor1,1);
b     = sort(b(end-3:end))', cor1(b,:)
figure;
plot([1:nsat],cor1(:,1),'*')
grid on
%
toc