codegen.m

GPS中的伪随机码产生程序,用matlab仿真生成伪随机码序列,用于测距

%codegen.m generates one of the 32 C/A codes written by D.Akos modified by J.Tsui
function [ca_used] = codegen(svnum);
%ca_used:a vector containing the desired output sequence
%the g2s vector holds the appropriates 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_sat = g1.*g2;
ca_used = -ss_sat;