codegen.m

MATLAB编写的GPS 信号的产生捕获程序

% codegen.m generates one of the 32 C/A codes

function [ca_used]=codegen(svnum);
% ca used : a vector containing the desired output sequence
% the g2s vector holds the appropriate shift of the g2 code to generate
% the C/A code (ex. for SV#19 - use a G2 shift of g2s(19)=471)
% svnum: Satellite number

gs2=[5;6;7;8;17;18;139;140;141;251;252;254;255;256;257;258;469;470;471; ... 
    472;473;474;509;512;513;514;515;516;859;860;861;862];

g2shift=gs2(svnum,1);
% ***** Generate G1 code *****

% load shift register
reg=-1*ones(1,10);
for i=1:1023,
    g1(i)=reg(10);
    save1=reg(3)*reg(10);
    reg(1,2:10)=reg(1:1:9);
    reg(1)=save1;
end

% ***** Generate G2 code *****
% load shift register
 
reg=-1*ones(1,10);
for i=1:1023,
    g2(i)=reg(10);
    save2=reg(2)*reg(3)*reg(6)*reg(8)*reg(9)*reg(10);
    reg(1,2:10)=reg(1:1:9);
    reg(1)=save2;
end

% ***** Shift G2 code *****
g2tmp(1,1:g2shift)=g2(1,1023-g2shift+1:1023);
g2tmp(1,g2shift+1:1023)=g2(1,1:1023-g2shift);
g2=g2tmp;

% ***** Form single sample C/A code by multiplying G1 and G2
ss_ca=g1.*g2;
ca_used=-ss_ca;