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% Script postProcessing.m processes the raw signal from the specified data
% file (in settings) operating on blocks of 37 seconds of data.
%
% First it runs acquisition code identifying the satellites in the file,
% then the code and carrier for each of the satellites are tracked, storing
% the 1msec accumulations. After processing all satellites in the 37 sec
% data block, then postNavigation is called. It calculates pseudoranges
% and attempts a position solutions. At the end plots are made for that
% block of data.
%--------------------------------------------------------------------------
% SoftGNSS v3.0
%
% Copyright (C) Darius Plausinaitis
% Written by Darius Plausinaitis, Dennis M. Akos
% Some ideas by Dennis M. Akos
%--------------------------------------------------------------------------
%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.
%--------------------------------------------------------------------------
% THE SCRIPT "RECIPE"
%
% The purpose of this script is to combine all parts of the software
% receiver.
%
% 1.1) Open the data file for the processing and seek to desired point.
%
% 2.1) Acquire satellites
%
% 3.1) Initialize channels (preRun.m).
% 3.2) Pass the channel structure and the file identifier to the tracking
% function. It will read and process the data. The tracking results are
% stored in the trackResults structure. The results can be accessed this
% way (the results are stored each millisecond):
% trackResults(channelNumber).XXX(fromMillisecond : toMillisecond), where
% XXX is a field name of the result (e.g. I_P, codePhase etc.)
%
% 4) Pass tracking results to the navigation solution function. It will
% decode navigation messages, find satellite positions, measure
% pseudoranges and find receiver position.
%
% 5) Plot the results.
%% Initialization =========================================================
disp ('Starting processing...');
[fid, message] = fopen(settings.fileName, 'rb');
%If success, then process the data
if (fid > 0)
% Move the starting point of processing. Can be used to start the
% signal processing at any point in the data record (e.g. good for long
% records or for signal processing in blocks).
fseek(fid, settings.skipNumberOfBytes, 'bof');
%% Acquisition ============================================================
% Do acquisition if it is not disabled in settings or if the variable
% acqResults does not exist.
if ((settings.skipAcquisition == 0) || ~exist('acqResults', 'var'))
% Find number of samples per spreading code
samplesPerCode = round(settings.samplingFreq / ...
(settings.codeFreqBasis / settings.codeLength));
% Read data for acquisition. 11ms of signal are needed for the fine
% frequency estimation
data = fread(fid, 11*samplesPerCode, settings.dataType)';
%--- Do the acquisition -------------------------------------------
disp (' Acquiring satellites...');
acqResults = acquisition(data, settings);
plotAcquisition(acqResults);
end
%% Initialize channels and prepare for the run ============================
% Start further processing only if a GNSS signal was acquired (the
% field FREQUENCY will be set to 0 for all not acquired signals)
if (any(acqResults.carrFreq))
channel = preRun(acqResults, settings);
showChannelStatus(channel, settings);
else
% No satellites to track, exit
disp('No GNSS signals detected, signal processing finished.');
trackResults = [];
return;
end
%% Track the signal =======================================================
startTime = now;
disp ([' Tracking started at ', datestr(startTime)]);
% Process all channels for given data block
[trackResults, channel] = tracking(fid, channel, settings);
% Close the data file
%fclose(fid);
disp([' Tracking is over (elapsed time ', ...
datestr(now - startTime, 13), ')'])
% Auto save the acquisition & tracking results to a file to allow
% running the positioning solution afterwards.
disp(' Saving Acq & Tracking results to file "trackingResults.mat"')
save('trackingResults', ...
'trackResults', 'settings', 'acqResults', 'channel');
%% Calculate navigation solutions =========================================
disp(' Calculating navigation solutions...');
navSolutions = postNavigation(trackResults, settings);
disp(' Processing is complete for this data block');
%% Plot all results ===================================================
disp (' Ploting results...');
if settings.plotTracking
plotTracking(1:settings.numberOfChannels, trackResults, settings);
end
plotNavigation(navSolutions, settings);
disp('Post processing of the signal is over.');
else
% Error while opening the data file.
error('Unable to read file %s: %s.', settings.fileName, message);
end % if (fid > 0)