www.gusucode.com > GPS仿真Matlab编程源码程序 > GPS仿真Matlab编程源码程序/include1/generateCAcode.m

    function CAcode = generateCAcode(PRN)
% generateCAcode.m generates one of the 32 GPS satellite C/A codes.
%
% CAcode = generateCAcode(PRN)
%
%   Inputs:
%       PRN         - PRN number of the sequence.
%
%   Outputs:
%       CAcode      - a vector containing the desired C/A code sequence 
%                   (chips).  

%--------------------------------------------------------------------------
%                           SoftGNSS v3.0
% 
% Copyright (C) Darius Plausinaitis
% Written by Darius Plausinaitis
% Based on Dennis M. Akos, Peter Rinder and Nicolaj Bertelsen
%--------------------------------------------------------------------------
%This program is free software; you can redistribute it and/or
%modify it under the terms of the GNU General Public License
%as published by the Free Software Foundation; either version 2
%of the License, or (at your option) any later version.
%
%This program is distributed in the hope that it will be useful,
%but WITHOUT ANY WARRANTY; without even the implied warranty of
%MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%GNU General Public License for more details.
%
%You should have received a copy of the GNU General Public License
%along with this program; if not, write to the Free Software
%Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
%USA.
%--------------------------------------------------------------------------

%CVS record:
%$Id: generateCAcode.m,v 1.1.2.5 2006/08/14 11:38:22 dpl Exp $

%--- Make the code shift array. The shift depends on the PRN number -------
% 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)
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 ... end of shifts for GPS satellites 
       ... Shifts for the ground GPS transmitter are not included
       ... Shifts for EGNOS and WAAS satellites (true_PRN = PRN + 87)
                 145, 175,  52,  21, 237, 235, 886, 657, ...
       634, 762, 355, 1012, 176, 603, 130, 359, 595, 68, ...
       386];

%--- Pick right shift for the given PRN number ----------------------------
g2shift = g2s(PRN);

%--- Generate G1 code -----------------------------------------------------

%--- Initialize g1 output to speed up the function ---
g1 = zeros(1, 1023);
%--- Load shift register ---
reg = -1*ones(1, 10);

%--- Generate all G1 signal chips based on the G1 feedback polynomial -----
for i=1:1023
    g1(i)       = reg(10);
    saveBit     = reg(3)*reg(10);
    reg(2:10)   = reg(1:9);
    reg(1)      = saveBit;
end

%--- Generate G2 code -----------------------------------------------------

%--- Initialize g2 output to speed up the function ---
g2 = zeros(1, 1023);
%--- Load shift register ---
reg = -1*ones(1, 10);

%--- Generate all G2 signal chips based on the G2 feedback polynomial -----
for i=1:1023
    g2(i)       = reg(10);
    saveBit     = reg(2)*reg(3)*reg(6)*reg(8)*reg(9)*reg(10);
    reg(2:10)   = reg(1:9);
    reg(1)      = saveBit;
end

%--- Shift G2 code --------------------------------------------------------
%The idea: g2 = concatenate[ g2_right_part, g2_left_part ];
g2 = [g2(1023-g2shift+1 : 1023), g2(1 : 1023-g2shift)];

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