prn_gen.m

GPS PRN产生器,输入卫星号,输出GPS PRN序列.

function [PRN_out] = PRNgen(prn_num)
% Generates PRN sequence for satellite number prn_num
  
switch prn_num
case 1
   tap1 = 2; tap2 = 6;
case 2
   tap1 = 3; tap2 = 7;
case 3
   tap1 = 4; tap2 = 8;
case 4 
   tap1 = 5; tap2 = 9;
case 5
   tap1 = 1; tap2 = 9;
case 6
   tap1 = 2; tap2 = 10;
case 7
   tap1 = 1; tap2 = 8;
case 8
   tap1 = 2; tap2 = 9;
case 9
   tap1 = 3; tap2 = 10;
case 10
   tap1 = 2; tap2 = 3;
case 11
   tap1 = 3; tap2 = 4;
case 12
   tap1 = 5; tap2 = 6;
case 13
   tap1 = 6; tap2 = 7;
case 14 
   tap1 = 7; tap2 = 8;
case 15
   tap1 = 8; tap2 = 9;
case 16
   tap1 = 9; tap2 = 10;
case 17
   tap1 = 1; tap2 = 4;
case 18
   tap1 = 2; tap2 = 5;
case 19
   tap1 = 3; tap2 = 6;
case 20
   tap1 = 4; tap2 = 7;
case 21
   tap1 = 5; tap2 = 8;
case 22
   tap1 = 6; tap2 = 9;
case 23
   tap1 = 1; tap2 = 3;
case 24 
   tap1 = 4; tap2 = 6;
case 25
   tap1 = 5; tap2 = 7;
case 26
   tap1 = 6; tap2 = 8;
case 27
   tap1 = 7; tap2 = 9;
case 28
   tap1 = 8; tap2 = 10;
case 29
   tap1 = 1; tap2 = 6;
case 30
   tap1 = 2; tap2 = 7;
case 31
   tap1 = 3; tap2 = 8;
case 32
   tap1 = 4; tap2 = 9;
otherwise
   PRN = 0;
   disp([' Error: not valid PRN number (1 - 32)'])
   return
end

% ***** Initialize variables ***** 
register1 = ones(1,10);
register2 = ones(1,10);
check = zeros(1,10);
count = 0;

% ***** Run loop until all ones are found in the register *****
while sum(check) ~= 10
   
   % ***** add counter *****
   count = count + 1;
   
   % ***** Check XOR logic circuit on first register *****
   o1 = xor(register1(3), register1(10));
   
   % ***** check XOR logic circuit on second register *****
   o2 = xor(register2(2),xor(register2(3),xor(register2(6),xor(register2(8),xor(register2(9),register2(10))))));
   
   PRN(count,:) = xor(register1(10), xor(register2(tap1), register2(tap2)));
      
   % ***** Shift values *****
   for i = 9:-1:1
      register1(i+1) = register1(i);
      register2(i+1) = register2(i);
   end
   register1(1) = o1;
   register2(1) = o2;
   
   check = register2;
end

% ***** Change values to 1's and -1's *****
for i=1:length(PRN)
    if PRN(i)==0
        PRN_out(i)=-1;    
    else
        PRN_out(i)=1;      
    end
end