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;
