codegen.m

GPS的matlab程序

function [ca_used]=codegen(svnum,offset);
%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
% svnum: satellite number

g2s=[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=g2s(svnum,1);
 % generate G1 code
 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
 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;
 % from single sample c/a code by multiplying g1 and g2 
 ss_ca=g1.*g2;
 ca_used=-ss_ca;
 
 %shift left
 %ca_temp(1,1:offset)=ca_used(1,1:offset);
 %ca_used(1,1:1023-offset)=ca_used(1,offset+1:1023);
 %ca_used(1,1023-offset+1:1023)=ca_temp(1,1:offset);
 
 %shift right
 ca_temp(1,1:offset)=ca_used(1,1023-offset+1:1023);
 ca_used(1,offset+1:1023)=ca_used(1,1:1023-offset);
 ca_used(1,1:offset)=ca_temp(1,1:offset);