GPS.rar_GPS的MATLAB代码

function [eph, TOW] = ephemeris(bits, D30Star) %Function decodes ephemerides and TOW from the given bit stream. The stream %(array) in the parameter BITS must contain 1500 bits. The first element in %the array must be the first bit of a subframe. The subframe ID of the %first subframe in the array is not important. % %Function does not check parity! % %[eph, TOW] = ephemeris(bits, D30Star) % % Inputs: % bits - bits of the navigation messages (5 subframes). % Type is character array and it must contain only % characters '0' or '1'. % D30Star - The last bit of the previous nav-word. Refer to the % GPS interface control document ICD (IS-GPS-200D) for % more details on the parity checking. Parameter type is % char. It must contain only characters '0' or '1'. % Outputs: % TOW - Time Of Week (TOW) of the first sub-frame in the bit % stream (in seconds) % eph - SV ephemeris %-------------------------------------------------------------------------- % SoftGNSS v3.0 % % Copyright (C) Darius Plausinaitis and Kristin Larson % Written by Darius Plausinaitis and Kristin Larson %-------------------------------------------------------------------------- %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: ephemeris.m,v 1.1.2.7 2006/08/14 11:38:22 dpl Exp $ %% Check if there is enough data ========================================== if length(bits) < 1500 error('The parameter BITS must contain 1500 bits!'); end %% Check if the parameters are strings ==================================== if ~ischar(bits) error('The parameter BITS must be a character array!'); end if ~ischar(D30Star) error('The parameter D30Star must be a char!'); end % Pi used in the GPS coordinate system gpsPi = 3.1415926535898; %% Decode all 5 sub-frames ================================================ for i = 1:5 %--- "Cut" one sub-frame's bits --------------------------------------- subframe = bits(300*(i-1)+1 : 300*i); %--- Correct polarity of the data bits in all 10 words ---------------- for j = 1:10 [subframe(30*(j-1)+1 : 30*j)] = ... checkPhase(subframe(30*(j-1)+1 : 30*j), D30Star); D30Star = subframe(30*j); end %--- Decode the sub-frame id ------------------------------------------ % For more details on sub-frame contents please refer to GPS IS. subframeID = bin2dec(subframe(50:52)); %--- Decode sub-frame based on the sub-frames id ---------------------- % The task is to select the necessary bits and convert them to decimal % numbers. For more details on sub-frame contents please refer to GPS % ICD (IS-GPS-200D). switch subframeID case 1 %--- It is subframe 1 ------------------------------------- % It contains WN, SV clock corrections, health and accuracy eph.weekNumber = bin2dec(subframe(61:70)) + 1024; eph.accuracy = bin2dec(subframe(73:76)); eph.health = bin2dec(subframe(77:82)); eph.T_GD = twosComp2dec(subframe(197:204)) * 2^(-31); eph.IODC = bin2dec([subframe(83:84) subframe(197:204)]); eph.t_oc = bin2dec(subframe(219:234)) * 2^4; eph.a_f2 = twosComp2dec(subframe(241:248)) * 2^(-55); eph.a_f1 = twosComp2dec(subframe(249:264)) * 2^(-43); eph.a_f0 = twosComp2dec(subframe(271:292)) * 2^(-31); case 2 %--- It is subframe 2 ------------------------------------- % It contains first part of ephemeris parameters eph.IODE_sf2 = bin2dec(subframe(61:68)); eph.C_rs = twosComp2dec(subframe(69: 84)) * 2^(-5); eph.deltan = ... twosComp2dec(subframe(91:106)) * 2^(-43) * gpsPi; eph.M_0 = ... twosComp2dec([subframe(107:114) subframe(121:144)]) ... * 2^(-31) * gpsPi; eph.C_uc = twosComp2dec(subframe(151:166)) * 2^(-29); eph.e = ... bin2dec([subframe(167:174) subframe(181:204)]) ... * 2^(-33); eph.C_us = twosComp2dec(subframe(211:226)) * 2^(-29); eph.sqrtA = ... bin2dec([subframe(227:234) subframe(241:264)]) ... * 2^(-19); eph.t_oe = bin2dec(subframe(271:286)) * 2^4; case 3 %--- It is subframe 3 ------------------------------------- % It contains second part of ephemeris parameters eph.C_ic = twosComp2dec(subframe(61:76)) * 2^(-29); eph.omega_0 = ... twosComp2dec([subframe(77:84) subframe(91:114)]) ... * 2^(-31) * gpsPi; eph.C_is = twosComp2dec(subframe(121:136)) * 2^(-29); eph.i_0 = ... twosComp2dec([subframe(137:144) subframe(151:174)]) ... * 2^(-31) * gpsPi; eph.C_rc = twosComp2dec(subframe(181:196)) * 2^(-5); eph.omega = ... twosComp2dec([subframe(197:204) subframe(211:234)]) ... * 2^(-31) * gpsPi; eph.omegaDot = twosComp2dec(subframe(241:264)) * 2^(-43) * gpsPi; eph.IODE_sf3 = bin2dec(subframe(271:278)); eph.iDot = twosComp2dec(subframe(279:292)) * 2^(-43) * gpsPi; case 4 %--- It is subframe 4 ------------------------------------- % Almanac, ionospheric model, UTC parameters. % SV health (PRN: 25-32). % Not decoded at the moment. case 5 %--- It is subframe 5 ------------------------------------- % SV almanac and health (PRN: 1-24). % Almanac reference week number and time. % Not decoded at the moment. end % switch subframeID ... end % for all 5 sub-frames ... %% Compute the time of week (TOW) of the first sub-frames in the array ==== % Also correct the TOW. The transmitted TOW is actual TOW of the next % subframe and we need the TOW of the first subframe in this data block % (the variable subframe at this point contains bits of the last subframe). TOW = bin2dec(subframe(31:47)) * 6 - 30;