www.gusucode.com > GPS仿真Matlab编程源码程序 > GPS仿真Matlab编程源码程序/tracking.m
function [trackResults, channel]= tracking(fid, channel, settings) % Performs code and carrier tracking for all channels. % %[trackResults, channel] = tracking(fid, channel, settings) % % Inputs: % fid - file identifier of the signal record. % channel - PRN, carrier frequencies and code phases of all % satellites to be tracked (prepared by preRum.m from % acquisition results). % settings - receiver settings. % Outputs: % trackResults - tracking results (structure array). Contains % in-phase prompt outputs and absolute starting % positions of spreading codes, together with other % observation data from the tracking loops. All are % saved every millisecond. %-------------------------------------------------------------------------- % SoftGNSS v3.0 % % Copyright (C) Dennis M. Akos % Written by Darius Plausinaitis and Dennis M. Akos % Based on code by DMAkos Oct-1999 %-------------------------------------------------------------------------- %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: tracking.m,v 1.14.2.32 2007/01/30 09:45:12 dpl Exp $ %% Initialize result structure ============================================ % Channel status trackResults.status = '-'; % No tracked signal, or lost lock % The absolute sample in the record of the C/A code start: trackResults.absoluteSample = zeros(1, settings.msToProcess); % Freq of the C/A code: trackResults.codeFreq = inf(1, settings.msToProcess); % Frequency of the tracked carrier wave: trackResults.carrFreq = inf(1, settings.msToProcess); % Outputs from the correlators (In-phase): trackResults.I_P = zeros(1, settings.msToProcess); trackResults.I_E = zeros(1, settings.msToProcess); trackResults.I_L = zeros(1, settings.msToProcess); % Outputs from the correlators (Quadrature-phase): trackResults.Q_E = zeros(1, settings.msToProcess); trackResults.Q_P = zeros(1, settings.msToProcess); trackResults.Q_L = zeros(1, settings.msToProcess); % Loop discriminators trackResults.dllDiscr = inf(1, settings.msToProcess); trackResults.dllDiscrFilt = inf(1, settings.msToProcess); trackResults.pllDiscr = inf(1, settings.msToProcess); trackResults.pllDiscrFilt = inf(1, settings.msToProcess); %--- Copy initial settings for all channels ------------------------------- trackResults = repmat(trackResults, 1, settings.numberOfChannels); %% Initialize tracking variables ========================================== codePeriods = settings.msToProcess; % For GPS one C/A code is one ms %--- DLL variables -------------------------------------------------------- % Define early-late offset (in chips) earlyLateSpc = settings.dllCorrelatorSpacing; % Summation interval PDIcode = 0.001; % Calculate filter coefficient values [tau1code, tau2code] = calcLoopCoef(settings.dllNoiseBandwidth, ... settings.dllDampingRatio, ... 1.0); %--- PLL variables -------------------------------------------------------- % Summation interval PDIcarr = 0.001; % Calculate filter coefficient values [tau1carr, tau2carr] = calcLoopCoef(settings.pllNoiseBandwidth, ... settings.pllDampingRatio, ... 0.25); hwb = waitbar(0,'Tracking...'); %% Start processing channels ============================================== for channelNr = 1:settings.numberOfChannels % Only process if PRN is non zero (acquisition was successful) if (channel(channelNr).PRN ~= 0) % Save additional information - each channel's tracked PRN trackResults(channelNr).PRN = channel(channelNr).PRN; % Move the starting point of processing. Can be used to start the % signal processing at any point in the data record (e.g. for long % records). In addition skip through that data file to start at the % appropriate sample (corresponding to code phase). Assumes sample % type is schar (or 1 byte per sample) fseek(fid, ... settings.skipNumberOfBytes + channel(channelNr).codePhase-1, ... 'bof'); % Get a vector with the C/A code sampled 1x/chip caCode = generateCAcode(channel(channelNr).PRN); % Then make it possible to do early and late versions caCode = [caCode(1023) caCode caCode(1)]; %--- Perform various initializations ------------------------------ % define initial code frequency basis of NCO codeFreq = settings.codeFreqBasis; % define residual code phase (in chips) remCodePhase = 0.0; % define carrier frequency which is used over whole tracking period carrFreq = channel(channelNr).acquiredFreq; carrFreqBasis = channel(channelNr).acquiredFreq; % define residual carrier phase remCarrPhase = 0.0; %code tracking loop parameters oldCodeNco = 0.0; oldCodeError = 0.0; %carrier/Costas loop parameters oldCarrNco = 0.0; oldCarrError = 0.0; %=== Process the number of specified code periods ================= for loopCnt = 1:codePeriods %% GUI update ------------------------------------------------------------- % The GUI is updated every 50ms. This way Matlab GUI is still % responsive enough. At the same time Matlab is not occupied % all the time with GUI task. if (rem(loopCnt, 50) == 0) try waitbar(loopCnt/codePeriods, ... hwb, ... ['Tracking: Ch ', int2str(channelNr), ... ' of ', int2str(settings.numberOfChannels), ... '; PRN#', int2str(channel(channelNr).PRN), ... '; Completed ',int2str(loopCnt), ... ' of ', int2str(codePeriods), ' msec']); catch % The progress bar was closed. It is used as a signal % to stop, "cancel" processing. Exit. disp('Progress bar closed, exiting...'); return end end %% Read next block of data ------------------------------------------------ % Find the size of a "block" or code period in whole samples % Update the phasestep based on code freq (variable) and % sampling frequency (fixed) codePhaseStep = codeFreq / settings.samplingFreq; blksize = ceil((settings.codeLength-remCodePhase) / codePhaseStep); % Read in the appropriate number of samples to process this % interation [rawSignal, samplesRead] = fread(fid, blksize, settings.dataType); %% for bupt if data %rawSignal =rawSignal.'; rawSignal =rawSignal >0; rawSignal = 2*rawSignal-1; rawSignal =rawSignal.'; % If did not read in enough samples, then could be out of % data - better exit if (samplesRead ~= blksize) disp('Not able to read the specified number of samples for tracking, exiting!') fclose(fid); return end %% Set up all the code phase tracking information ------------------------- % Define index into early code vector tcode = (remCodePhase-earlyLateSpc) : ... codePhaseStep : ... ((blksize-1)*codePhaseStep+remCodePhase-earlyLateSpc); tcode2 = ceil(tcode) + 1; earlyCode = caCode(tcode2); % Define index into late code vector tcode = (remCodePhase+earlyLateSpc) : ... codePhaseStep : ... ((blksize-1)*codePhaseStep+remCodePhase+earlyLateSpc); tcode2 = ceil(tcode) + 1; lateCode = caCode(tcode2); % Define index into prompt code vector tcode = remCodePhase : ... codePhaseStep : ... ((blksize-1)*codePhaseStep+remCodePhase); tcode2 = ceil(tcode) + 1; promptCode = caCode(tcode2); remCodePhase = (tcode(blksize) + codePhaseStep) - 1023.0; %% Generate the carrier frequency to mix the signal to baseband ----------- time = (0:blksize) ./ settings.samplingFreq; % Get the argument to sin/cos functions trigarg = ((carrFreq * 2.0 * pi) .* time) + remCarrPhase; remCarrPhase = rem(trigarg(blksize+1), (2 * pi)); % Finally compute the signal to mix the collected data to bandband carrCos = cos(trigarg(1:blksize)); carrSin = sin(trigarg(1:blksize)); %% Generate the six standard accumulated values --------------------------- % First mix to baseband qBasebandSignal = carrCos .* rawSignal; iBasebandSignal = carrSin .* rawSignal; % Now get early, late, and prompt values for each I_E = sum(earlyCode .* iBasebandSignal); Q_E = sum(earlyCode .* qBasebandSignal); I_P = sum(promptCode .* iBasebandSignal); Q_P = sum(promptCode .* qBasebandSignal); I_L = sum(lateCode .* iBasebandSignal); Q_L = sum(lateCode .* qBasebandSignal); %% Find PLL error and update carrier NCO ---------------------------------- % Implement carrier loop discriminator (phase detector) carrError = atan(Q_P / I_P) / (2.0 * pi); % Implement carrier loop filter and generate NCO command carrNco = oldCarrNco + (tau2carr/tau1carr) * ... (carrError - oldCarrError) + carrError * (PDIcarr/tau1carr); oldCarrNco = carrNco; oldCarrError = carrError; % Modify carrier freq based on NCO command carrFreq = carrFreqBasis + carrNco; trackResults(channelNr).carrFreq(loopCnt) = carrFreq; %% Find DLL error and update code NCO ------------------------------------- codeError = (sqrt(I_E * I_E + Q_E * Q_E) - sqrt(I_L * I_L + Q_L * Q_L)) / ... (sqrt(I_E * I_E + Q_E * Q_E) + sqrt(I_L * I_L + Q_L * Q_L)); % Implement code loop filter and generate NCO command codeNco = oldCodeNco + (tau2code/tau1code) * ... (codeError - oldCodeError) + codeError * (PDIcode/tau1code); oldCodeNco = codeNco; oldCodeError = codeError; % Modify code freq based on NCO command codeFreq = settings.codeFreqBasis - codeNco; trackResults(channelNr).codeFreq(loopCnt) = codeFreq; %% Record various measures to show in postprocessing ---------------------- % Record sample number (based on 8bit samples) trackResults(channelNr).absoluteSample(loopCnt) = ftell(fid); trackResults(channelNr).dllDiscr(loopCnt) = codeError; trackResults(channelNr).dllDiscrFilt(loopCnt) = codeNco; trackResults(channelNr).pllDiscr(loopCnt) = carrError; trackResults(channelNr).pllDiscrFilt(loopCnt) = carrNco; trackResults(channelNr).I_E(loopCnt) = I_E; trackResults(channelNr).I_P(loopCnt) = I_P; trackResults(channelNr).I_L(loopCnt) = I_L; trackResults(channelNr).Q_E(loopCnt) = Q_E; trackResults(channelNr).Q_P(loopCnt) = Q_P; trackResults(channelNr).Q_L(loopCnt) = Q_L; % samplesPerCode = round(settings.samplingFreq / (settings.codeFreqBasis / settings.codeLength)); % % %--- For all channels in the list ... % % for channelNr = channelList % % %--- Compute the travel times ----------------------------------------- % travelTime(channelNr) = trackResults(channelNr).absoluteSample(msOfTheSignal(channelNr)) / samplesPerCode; % end end % for loopCnt % If we got so far, this means that the tracking was successful % Now we only copy status, but it can be update by a lock detector % if implemented trackResults(channelNr).status = channel(channelNr).status; end % if a PRN is assigned % samplesPerCode = round(settings.samplingFreq / ... % (settings.codeFreqBasis / settings.codeLength)); % travelTime(channelNr) = ... % trackResults(channelNr).absoluteSample(msOfTheSignal(channelNr)) / samplesPerCode; end % for channelNr % Close the waitbar close(hwb)