Advanced global navigation satellite system receiver design (797918), страница 33
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141- 146, 1951[Lyons 2004]Lyons R.G., “Understanding Digital Signal Processing, 2nd Edition”, PrenticeHall, pp. 32-35, April 2004[Martin et al 2003]Martin N., Leblond V. Guillotel G., Heiries V., “BOC(x,y) signal acquisitiontechniques and performances” Proceedings of ION GPS 2003, Portland,Oregon, September 2003[Mattos 2005]Mattos P., “Acquisition of the Galileo OAS L1b/c signal for the mass-marketreceiver”, Proceedings of ION GPS 2005, Long Beach, California,September 2005[Mitel 1996]Mitel Semiconductor, “GP2000 GPS Chipset – Designers Guide”, Availableat: http://www.datasheetarchive.com/ Accessed in December 2006[Nemerix 2005]Nemerix, “NJ1006A GPS Receiver RF Front End IC”, Revision 1.5,September 2005, Available at:http://www.nemerix.com/products/rf_rec_ics.php , Accessed in December2006[Park and Miller 1988]Park S.K.
and Miller K.W., "Random Number Generators: Good Ones AreHard To Find", Communications of the ACM, pp. 1192-1201, October 1988[Parkinson and Spilker1996]Parkinson B.W., Spilker Jr J. J., “Global Positioning System: Theory andApplications Volume I”, Progress in Astronautics and Aeronautics, Vol. 163,pp. 374, 1996.[Purivigraipong et al2000]Purivigraipong S., Unwin M. J.
and Hashida Y., “Demonstrating GPSAttitude Determination from UoSat-12 Flight Data”, Proceedings of IONGPS 2000, Salt Lake City, Utah, September 2000[Pratt and Owen 2003]Pratt A.R., Owen J., “BOC Modulation Waveforms”, Proceedings of IONGPS 2003, Portland, Oregon, September 2003[Pratt et al 2004]Pratt A. R., Powe M., Owen J. R., “Concatenated Sequential CodesPerformance Attributes and Applications for Galileo” Proceedings of IONNational Technical Meeting, San Diego, California, January 2004[Psiaki et al 2006]Psiaki M. et al, “ Searching for Galileo”, Proceedings of ION GNSS 2006,Fort Worth Texas, September 2006.[Rebeyrol et al 2005]Rebeyrol E., Macabiau C., Lestarquit L., Ries L., Issler J.-L., Boucheret M.L., Bousquet M., “BOC Power Spectrum Densities”, Proceedings of ION2005 National Technical Meeting, San Diego, California, January 2005[Research and Markets2006]Research and Markets, “World Global Positioning Systems Market Forecast(2006-2008)”, Available at:http://www.researchandmarkets.com/reports/312517/ Accessed in December2006225References[Ries et al 2002]Ries L., Lestarquit L., Armengou-Miret E., Legrand F., Vigneau W, BourgaC., Erhard P., Issler J.-L., “A Software Simulation Tool for GNSS2 BOCSignals Analysis”, Proceedings of ION GPS 2002, Portland, Oregon,September 2002[Ries et al 2003]Ries L., Legrand F., Lestarquit L., Vigneau W., Issler J.-L., “Tracking andMultipath Performance Assessments of BOC Signals Using a Bit-LevelSignal Processing Simulator” Proceedings of ION GPS 2003, Portland,Oregon, September 2003[Rooney et al 2007]Rooney E., Unwin M., Taylor B., Gatti G., “Giove-A Navigation andExperimental Payload Design and Operation in Orbit”, Proceedings of IONNTM 2007, San Diego, California, Jan 2007[SiRF 2005]SiRF, “SiRFstarIIA GPS System on Chip Chipset for Telematics and VehicleNavigation”, 2005, Available at: http://www.sirf.com/about_sirf/index.html,Accessed in December 2006[Sklar 1988]Sklar B., “Digital Communications: Fundamentals and Applications”,Prentice Hall International, pp.
695 – 757, 1988.[SSTL 2007]GPS receiver datasheets, Available at: http://www.sstl.co.uk/, Accessed inMay 2007[Steenwijk et al 2006]de Vos van Steenwijk R., Unwin M., Hashida Y., Blunt P., Weiler R.,“Development of a GPS Receiver for MEO/GEO and Initial Results of InOrbit Testing On Board the Giove-A Spacecraft”, Proceedings of Navitech2006, Noordwijk, Netherlands, December 2006.[Teunissen et al 2002]Teunissen P., Joosten P., Tiberius C., “A Comparison of TCAR, CIR andLAMBDA GNSS ambiguity resolution”, Proceedings of ION GPS 2002,Portland, Oregon, September 2002[Unwin 1995]Unwin M.J., “The Design and Implementation of a Small SatelliteNavigation Unit Based on a Global Positioning System Receiver”, PhDDissertation, University of Surrey, 1995.[Van Nee and Coenen1991]Van Nee D.
J. R., Coenen A. J. R. M. “New fast GPS Code-AcquisitionTechnique using FFT”, Electronics Letters,Vol. 27, January 1991[Ward 2003]Ward P.W., “A Design Technique to Remove the Correlation Ambiguity inBinary Offset Carrier (BOC) Spread Spectrum Signals”, ION 59th AnnualMeeting / CIGTF 22nd Guidance Test Symposium, Albuquerque, NewMexico, June 2003[Xilinx 2005]Xilinx, “Virtex 5 data sheet” DS202, v2.1, October 2006, Available at:http://www.xilinx.com/products/silicon_solutions/fpgas/virtex/virtex5/index.htm, Accessed in December 2006[Zarlink 1999]Zarlink Semiconductor, “GPS Receiver Hardware DesignApplication Note”, AN4855, Issue 2.0, October 1999, Available at:http://www.zarlink.com/, Accessed in December 2006[Zarlink 2001]Zarlink Semiconductor, “GPS 12-Channel Correlator”, DS4077, Issue 3.2,April 2001, Available at: http://www.zarlink.com/, Accessed in December2006[Zarlink 2005]Zarlink Semiconductor, “GP2015 GPS Receiver RF Front End”, May 2005,Available at : http://products.zarlink.com/product_profiles/GP2015.htm,Accessed in December 2006226ATiered codes for GPS modernisation and GalileoConceived initially for the new GPS L5 signal, tiered codes are to be broadcast byboth GPS modernised and Galileo signals.
A tiered system overlays the fast changingPRN sequence, which is denoted the primary code, with a secondary code whose bitperiod is equal to one primary code epoch. The secondary code length is then chosensuch that the secondary code period is equal to one symbol period of the navigationaldata stream (Figure A-1).
The aim is to rapidly eliminate the ambiguity that initiallyexists in locating the PRN code epoch relative to the longer length data transitions.GNSS receivers can detect 180˚ phase shifts of the incoming carrier due to asecondary code or navigational data bit flip.
The secondary code is known andtherefore, its bit pattern can be searched for. Once detected, this sequence can be usedto accurately predict the navigational data transitions and true PLL discriminatorsused in the tracking loops.Primary code(N chips long)N chips × tCSecondary code(M chips long)M × (N chips × tC)Navigationaldata (K sps)Symbol period= (1 / K) secFigure A-1, Tiered code hierarchical structureThe secondary codes are typically less than 100 bits long, in order to maintain anacceptable data rate and therefore can have significant cross correlation magnitudes.To minimise this they are chosen from families of codes that have goodsynchronisation properties, meaning, the absolute value of their cross-correlation issmall. For short secondary codes, up to 13 bits long, the unique Barker or Willardcodes can be used. However, for long sequences, up to 100 bits long, Newman /Hofman sequences are used.In general terms, a tiered code can be writtenA-1Tiered codes for GPS modernisation and GalileoaT (t ) = ∑ a P (t − nt P )∑ a S (t − mt S )nA-1mwhere aP(t) is the primary code repeating every t P = N × t C sec, and aS(t) is thesecondary code repeating every t S = M × t P sec, as follows.j=Na P (t ) =∑aPp P (t − jt C )A-2p S (t − kt P )A-3j =1k =Ma S (t ) =∑aSk =1a P ∈ (−1,+1) is the primary code PRN sequence counting over 1 ≤ j ≤ N ,a S ∈ (−1,+1) is the secondary sequence counting over 1 ≤ k ≤ M , p P (t ) andp S (t ) are ideal rectangular pulses of width t C and t P , respectively.A-2BMathcad simulations of PSK and BOCA number of software packages are currently available for theoretical modelling andevaluation of GNSS algorithms.
The Mathworks Matlab package is generallyfavoured for analysis and plotting of sampled data, and was used to generate plots ofthe data generated by the receiver. However, during this research the MathsoftMathcad package was favoured for modelling and comparative analysis of the variousGNSS receiver algorithms. This powerful tool provides a see-at-a-glanceenvironment to the designer where all the operations of a representative GNSSreceiver can be displayed on a single console screen.B.1Received signal representationsConsistent with the theory given in Chapter 5, received PSK signals down-convertedto a suitable IF frequency were modelled as follows.u PSK (t ) = A × cos(ω0t + φ ) × a (t − τ ) × d + v(t )B-1A is the amplitude of the signal, ω 0 is the centre frequency of the IF signal, a(t) is thePRN code sequence and d is the navigational data.
τ is the time delay of the code, φ isa general phase shift and v(t) is additive white Gaussian noise. In Appendix C, DrHodgart provides the necessary theory to set v(t) in order to vary the carrier to noisedensity of the incoming signal and loop parameters of the simulation.A single multipath PSK interferer was modelled using a addition of the received directand multipath signal, which can be written as follows.u PSK (t ) = A × cos(ωC t + φ ) × a (t − τ ) × dB-2+ α × [ A × cos(ωC t + φ ) × a (t − τ − δ ) × d ]α is the coefficient of reflection, which in all analysis presented here is assumed to beα = 0.5.
δ is time delay of the multipath signal with respect to the direct signal.B-1Mathcad simulations of PSK and BOCSimilarly a single received BOC signal was modelled as follows.u BOC (t ) = A × cos(ω0t + φ ) × s (t − τ ) × a (t − τ ) × d + v(t )B-3s(t) is the BOC sub-carrier waveform. The multipath BOC model is thenu BOC (t ) = A × cos(ωC t + φ ) × s (t − τ ) × a (t − τ ) × dB-4+ α × [ A × cos(ωC t + φ ) × s (t − τ − δ ) × a (t − τ − δ ) × d ]Simulation of multiple interfering signals was also modelled, again simply using thelinear addition of signals.B.2Example simulationIn order to demonstrate the format of the simulations and the flow in Mathcad we usethe PSK model.
The extensions to BOC and the various tracking schemes given inChapters 5 and 6 are then elementary as they follow the same simulation flow. In thefollowing PSK example a 15 chip PRN code spreading sequence is used to reduce thesimulation time. Full-length code simulations were carried out for all techniquespresented in this thesis. However, using a shorter codes allows rapid initial evaluationof receiver algorithms provided noise levels and loop bandwidths are adjustedaccordingly.The sampling rate of the simulations was generally set to be much greater thanrequired in order to remove any sampling dependant effects.
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