www.gusucode.com > GPS仿真Matlab编程源码程序 > GPS仿真Matlab编程源码程序/acquisition1.m
function [codePhase,carrFreq,peak]= acquisition1(longSignal, settings, PRN) % function acqResults= acquisition(longSignal, settings, PRN) %Function performs cold start acquisition on the collected "data". It %searches for GPS signals of all satellites, which are listed in field %"acqSatelliteList" in the settings structure. Function saves code phase %and frequency of the detected signals in the "acqResults" structure. % %acqResults = acquisition(longSignal, settings) % % Inputs: % longSignal - 11 ms of raw signal from the front-end % settings - Receiver settings. Provides information about % sampling and intermediate frequencies and other % parameters including the list of the satellites to % be acquired. % Outputs: % acqResults - Function saves code phases and frequencies of the % detected signals in the "acqResults" structure. The % field "carrFreq" is set to 0 if the signal is not % detected for the given PRN number. %-------------------------------------------------------------------------- % SoftGNSS v3.0 % % Copyright (C) Darius Plausinaitis and Dennis M. Akos % Written by Darius Plausinaitis and Dennis M. Akos % Based on 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: acquisition.m,v 1.1.2.12 2006/08/14 12:08:03 dpl Exp $ %% Initialization ================================================ % Find number of samples per spreading code samplesPerCode = round(settings.samplingFreq / ... (settings.codeFreqBasis / settings.codeLength)); % Create two 1msec vectors of data to correlate with and one with zero DC signal1 = longSignal(1 : samplesPerCode); signal2 = longSignal(samplesPerCode+1 : 2*samplesPerCode); signal3 = longSignal(2*samplesPerCode+1 : 3*samplesPerCode); signal4 = longSignal(3*samplesPerCode+1 : 4*samplesPerCode); signal5 = longSignal(4*samplesPerCode+1 : 5*samplesPerCode); signal6 = longSignal(5*samplesPerCode+1 : 6*samplesPerCode); signal0DC = longSignal - mean(longSignal); %-------------------------------------------------------------------------- % Find sampling period ts = 1 / settings.samplingFreq; %-------------------------------------------------------------------------- % Find phase points of the local carrier wave phasePoints = (0 : (samplesPerCode-1)) * 2 * pi * ts; %-------------------------------------------------------------------------- % Number of the frequency bins for the given acquisition band (500Hz steps) numberOfFrqBins = round(settings.acqSearchBand * 2) + 1; %-------------------------------------------------------------------------- % Generate all C/A codes and sample them according to the sampling freq. caCodesTable = makeCaTable1(settings,PRN); %-------------------------------------------------------------------------- % Initialize arrays to speed up the code % Search results of all frequency bins and code shifts (for one satellite) results = zeros(numberOfFrqBins, samplesPerCode); % Carrier frequencies of the frequency bins frqBins = zeros(1, numberOfFrqBins); %-------------------------------------------------------------------------- % Initialize acqResults % Carrier frequencies of detected signals acqResults.carrFreq = zeros(1, 32); %-------------------------------------------------------------------------- % C/A code phases of detected signals acqResults.codePhase = zeros(1, 32); %-------------------------------------------------------------------------- % Correlation peak ratios of the detected signals acqResults.peakMetric = zeros(1, 32); %-------------------------------------------------------------------------- fprintf('('); %-------------------------------------------------------------------------- % Perform search for all listed PRN numbers ... % for PRN = settings.acqSatelliteList %% Correlate signals ============================================= %--- Perform DFT of C/A code ------------------------------------------ caCodeFreqDom = conj(fft(caCodesTable(PRN, :))); %--- Make the correlation for whole frequency band (for all freq. bins) for frqBinIndex = 1:numberOfFrqBins %--- Generate carrier wave frequency grid (0.5kHz step) ----------- frqBins(frqBinIndex) = settings.IF - ... (settings.acqSearchBand/2) * 1000 + ... 0.5e3 * (frqBinIndex - 1); %--- Generate local sine and cosine ------------------------------- sinCarr = sin(frqBins(frqBinIndex) * phasePoints); cosCarr = cos(frqBins(frqBinIndex) * phasePoints); %--- "Remove carrier" from the signal ----------------------------- I1 = sinCarr .* signal1; Q1 = cosCarr .* signal1; I2 = sinCarr .* signal2; Q2 = cosCarr .* signal2; I3 = sinCarr .* signal3; Q3 = cosCarr .* signal3; I4 = sinCarr .* signal4; Q4 = cosCarr .* signal4; I5 = sinCarr .* signal5; Q5 = cosCarr .* signal5; I6 = sinCarr .* signal6; Q6 = cosCarr .* signal6; %--- Convert the baseband signal to frequency domain -------------- IQfreqDom1 = fft(I1 + j*Q1); IQfreqDom2 = fft(I2 + j*Q2); IQfreqDom3 = fft(I3 + j*Q3); IQfreqDom4 = fft(I4 + j*Q4); IQfreqDom5 = fft(I5 + j*Q5); IQfreqDom6 = fft(I6 + j*Q6); %--- Multiplication in the frequency domain (correlation in time domain) convCodeIQ1 = IQfreqDom1 .* caCodeFreqDom; convCodeIQ2 = IQfreqDom2 .* caCodeFreqDom; convCodeIQ3 = IQfreqDom3 .* caCodeFreqDom; convCodeIQ4 = IQfreqDom4 .* caCodeFreqDom; convCodeIQ5 = IQfreqDom5 .* caCodeFreqDom; convCodeIQ6 = IQfreqDom6 .* caCodeFreqDom; %--- Perform inverse DFT and store correlation results ------------ acqRes1 = abs(ifft(convCodeIQ1)) .^ 2; acqRes2 = abs(ifft(convCodeIQ2)) .^ 2; acqRes3 = abs(ifft(convCodeIQ3)) .^ 2; acqRes4 = abs(ifft(convCodeIQ4)) .^ 2; acqRes5 = abs(ifft(convCodeIQ5)) .^ 2; acqRes6 = abs(ifft(convCodeIQ6)) .^ 2; %--- Check which msec had the greater power and save that, will %"blend" 1st and 2nd msec but will correct data bit issues % if (max(acqRes1) > max(acqRes2)) % results(frqBinIndex, :) = acqRes1; % else % results(frqBinIndex, :) = acqRes2; % end results(frqBinIndex, :) = acqRes1+acqRes2+acqRes3+acqRes4+acqRes5;%+acqRes6; end % frqBinIndex = 1:numberOfFrqBins %% Look for correlation peaks in the results ============================== % Find the highest peak and compare it to the second highest peak % The second peak is chosen not closer than 1 chip to the highest peak %--- Find the correlation peak and the carrier frequency -------------- [peakSize frequencyBinIndex] = max(max(results, [], 2)); %--- Find code phase of the same correlation peak --------------------- [peakSize codePhase] = max(max(results)); %--- Find 1 chip wide C/A code phase exclude range around the peak ---- samplesPerCodeChip = round(settings.samplingFreq / settings.codeFreqBasis); excludeRangeIndex1 = codePhase - samplesPerCodeChip; excludeRangeIndex2 = codePhase + samplesPerCodeChip; %--- Correct C/A code phase exclude range if the range includes array %boundaries if excludeRangeIndex1 < 2 codePhaseRange = excludeRangeIndex2 : ... (samplesPerCode + excludeRangeIndex1); elseif excludeRangeIndex2 >= samplesPerCode codePhaseRange = (excludeRangeIndex2 - samplesPerCode) : ... excludeRangeIndex1; else codePhaseRange = [1:excludeRangeIndex1, ... excludeRangeIndex2 : samplesPerCode]; end %--- Find the second highest correlation peak in the same freq. bin --- secondPeakSize = max(results(frequencyBinIndex, codePhaseRange)); %--- Store result ----------------------------------------------------- acqResults.peakMetric(PRN) = peakSize/secondPeakSize; % If the result is above threshold, then there is a signal ... if (peakSize/secondPeakSize) > settings.acqThreshold %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Fine resolution frequency search ============================== %--- Indicate PRN number of the detected signal ------------------- fprintf('%02d ', PRN); %--- Generate 8 msec long C/A codes sequence for given PRN -------- caCode = generateCAcode(PRN); codeValueIndex = floor((ts * (1:8*samplesPerCode)) / ... (1/settings.codeFreqBasis)); longCaCode = caCode((rem(codeValueIndex, 1023) + 1)); %--- Remove C/A code modulation from the original signal ---------- % (Using detected C/A code phase) xCarrier = ... signal0DC(codePhase:(codePhase + 8*samplesPerCode-1)) ... .* longCaCode; %--- Find the next highest power of two and increase by 8x -------- fftNumPts = 8*(2^(nextpow2(length(xCarrier)))); %--- Compute the magnitude of the FFT, find maximum and the %associated carrier frequency fftxc = abs(fft(xCarrier, fftNumPts)); uniqFftPts = ceil((fftNumPts + 1) / 2); [fftMax, fftMaxIndex] = max(fftxc(5 : uniqFftPts-5)); fftFreqBins = (0 : uniqFftPts-1) * settings.samplingFreq/fftNumPts; %--- Save properties of the detected satellite signal ------------- acqResults.carrFreq(PRN) = fftFreqBins(fftMaxIndex); acqResults.codePhase(PRN) = codePhase; % else % %--- No signal with this PRN -------------------------------------- % fprintf('. '); end % if (peakSize/secondPeakSize) > settings.acqThreshold codePhase=acqResults.codePhase(PRN); carrFreq=acqResults.carrFreq(PRN); peak=acqResults.peakMetric(PRN);%peakSize; % end % for PRN = satelliteList %=== Acquisition is over ================================================== fprintf(')\n');