cacode.m

几个BOC 信号的分析例程

%A.1 C/A Code Generator
function CA = cacode(n, chiprate, fs, n_samples,coph)
% The funtion
% CA = cacode(n, chiprate, fs, n_samples)
% returns the Gold code for GPS satellite ID n
% n = 1..32
% chiprate = number of chips per second.
% fs = sampling freqeuncy
% n_samples = number of samples
% The code is represented at levels : -1 for bit = 0
% 1 for bit = 1
% phase assignments
phase=[2 6; 3 7; 4 8; 5 9; 1 9; 2 10; 1 8; 2 9; 3 10;
2 3; 3 4; 5 6; 6 7; 7 8; 8 9; 9 10; 1 4; 2 5;
3 6; 4 7; 5 8; 6 9; 1 3; 4 6; 5 7; 6 8; 7 9;
8 10; 1 6; 2 7; 3 8; 4 9];
% Intial state - all ones
G1 = -1*ones(1,10);
G2 = G1;
% Select taps for G2 delay
s1 = phase(n,1);
s2 = phase(n,2);
tmp=0;
for i=1:1023;
% Gold-code
G(i)=G2(s1)*G2(s2)*G1(10);
% Generator 1 - shift reg 1
tmp=G1(1);
G1(1)=G1(3)*G1(10);
G1(2:10)=[tmp G1(2:9)];

% Generator 2 - shift reg 2
tmp=G2(1);
G2(1)=G2(2)*G2(3)*G2(6)*G2(8)*G2(9)*G2(10);
G2(2:10)=[tmp G2(2:9)];
end;
G
G=[G G G G G];
G=[G G G G G];
% Resample - doesn't work for (i*chiprate/fs)>1023
% but replica chiprate is constant in this
% implementation
i=1:n_samples;
CA(i) = G(ceil((i/fs+coph)*chiprate)+1023);