VLR Radinavigation Dissertation DissertationPelgrum

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New Potential of Low-Frequency Radionavigation in the 21st Century Cover illustration:3D representation of H-field measurements of local propagation phenomena around the Sunshine Skyway Bridge, Tampa Bay, Florida, USA New Potential of Low-Frequency Radionavigation in the 21st Century Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof. dr. ir. J.T. Fokkema, voorzitter van het College van Promoties, in het openbaar te verdedigen op dinsdag 28 november 2006 om 10:00 uur door Wouter Johan PELGRUM elektrotechnisch ingenieur geboren te Bussum. Dit proefschrift is goedgekeurd door de promotor: Prof. dr. ir. L.P. Ligthart Samenstelling promotiecommissie: Rector Magnificus,voorzitter Prof. dr. ir. L.P. Ligthart,Technische Universiteit Delft, promotor Prof. dr. ir. D. van Willigen,Technische Universiteit Delft Prof. dr. ir. F. van Graas,Ohio University Prof. dr. J.D. Last,University College of North Wales Prof. dr. B. Forssell,Norwegian University of Science and Technology Prof. dr. A.G. Tijhuis,Technische Universiteit Eindhoven Prof. ir. J.A. Spaans,Koninklijk Instituut voor de Marine Prof. ir. P. Hoogenboom,Technische Universiteit Delft, reservelid ISBN 978-90-811198-1-8 Copyright 2006 by W.J. Pelgrum Allrightsreserved.Nopartofthismaterialmaybereproducedorutilizedinanyformorbyanymeans, electronic or mechanical, including photocopying, recording or by any other information storage and retrieval system, without permission from the author. v Summary GPS(GlobalPositioningSystem)hasenabledaccurate,affordable,andalmostubiquitous positioningandtiming.Thishasnotonlyresultedinitswidespreadusage,increased popularity,andnumerousnewapplications,butithasalsoresultedinanincreased dependencyoftheGlobalNavigationSatelliteSystems.Theever-improvingperformanceof GPS has long fueled the thought that GPS and GPS alone was to be the designated future ofradiopositioningandtiming.The2001Volpestudy,andlaterthe2004proposedERNP (EuropeanRadioNavigationPlan),statedotherwise:althoughveryaccurate,GPSandother satellitenavigationsystemsarenotconsideredreliableenoughtobeusedasthesole-means forsafety,environmental,and/oreconomicallycriticalapplications.Thosecritical applicationsneedabackupsystemwithdissimilarfailuremodes.Thesolutionsuggestedby theVolpe-reportandbytheERNP-proposalisperhapsrathersurprisinglyanoldand almostforgottenradionavigationsystem:Loran-C.Thissystemwithitshigh-energy,low-frequency pulses is largely dissimilar to GPS. The combination of Loran-C and GPS, therefore, has the potential to be far more robust than either system individually. However, the official performanceofthe1958 Loran-Csystemisnomatchfor thestringentrequirementsofmost modern applications. Fortunately, this Loran performance reflects the capabilities of outdated technologyratherthanthefoundationsoflow-frequencyradionavigation.Thefollowing question now arises: What are the fundamental limits of low-frequency radionavigation and how do they affect potential applications? Loran-Ciscurrentlytheonlyoperationalandpubliclyavailablelow-frequency radionavigation system with regional coverage. This dissertation, therefore, primarily focuses onLoran-Calthoughmostresultswillalsobeapplicabletootherlow-frequency radionavigation systems. Chapter 2 introduces the system details of Loran-C. Thesearchforthefundamentallimitsbeginsbyidentifyingthepotentialerrorsources. Chapter 3containsathoroughsystemanalysis,startingwiththetransmitter,andcovering propagation, antenna, receiver algorithms, and concluding with calculated position and time. Low-frequencygroundwavesexperiencedelaysasafunctionofgroundconductivity, topography,seasons,andweather.Thesepropagationdelayscancausesignificantposition errorsifleftuncompensated.Chapter4discussestheuseofadifferentialreferencestationto compensateforthetemporalfluctuationsinpropagation.Aspatialcorrectionmapfurther reducesthepropagationrelatedpositioningerrors.Theresultingpositingaccuracyis potentiallysufficientforsuchsituationsas thestringent 20meter,95% accuracyrequirement of the maritime Harbor Entrance and Approach procedure. vi Chapter5paysspecialattentiontotheH-fieldantenna;thechapterdiscusseserrorsources suchasnoise,E-fieldsusceptibility,tuning,andcrosstalkthoroughly,aswellasnovel mitigation techniques and their successful implementation. Chapter6discussesvariousmeasurementcampaignsthatbringthepresentedtheoryinto practice. Throughout the Ph.D. research, the author of this work developed a highly accurate measurementsystem.TheReeuwijkmeasurementsshowthefirststepwithprecisedual-differencemeasurements;boththetemporaldomainandthespatialdomainreveallocal propagationeffects.Theland-mobilemeasurementcampaigninBostonexpandsthe measurement setup further. Simultaneous measurement of both E-field and H-field took place there allowing unprecedented analysis of re-radiation and an assessment of the applicability of low-frequency radionavigation in a land-mobile environment. The introduction of differential correctionsandH-fieldantennacalibrationfortheTampaBaycampaignresultedinan unprecedentedmeasurementperformance.Chapter6alsoshowstheeffectofbridgeson positioningperformancequantitatively,andpresentsthesuccessfulresultsofaunique re-radiationdetectionalgorithm.Thisalgorithmenablesdetectionoflocaldisturbances allowingatimelywarningofpotentialerroneouspositioninformation.Finally,Chapter6 showstheachievementofapositioningperformanceofbetterthan10meterswith95% confidence during a realistic Harbor Entrance and Approach (HEA) scenario. Thisdissertationconcludeswithanassessmentofthepotentialoflow-frequency radionavigation,basedontheresultsoftheauthorsPh.D.researchcombinedwithhis personal views. Wouter J. Pelgrum Delft, November 2006 Contents Summary..................................................................................................................................... v1Introduction ....................................................................................................................... 1 1.1 GNSS: almost perfect............................................................................................................. 21.2 LF radionavigation in the 21st century............................................................................... 41.3 Research question................................................................................................................. 61.4 Outline of dissertation......................................................................................................... 61.5 References .............................................................................................................................. 72Loran System Description................................................................................................ 9 2.1 Loran history ....................................................................................................................... 102.2 eLoran................................................................................................................................... 112.3 Loran System Characteristics ........................................................................................... 112.3.1 Loran-C system performance ............................................................................................ 122.3.2 eLoran system performance............................................................................................... 122.3.3 Coverage ................................................................................................................................. 132.4 Loran-C Signal in Space definition................................................................................... 142.4.1 Pulse shape ............................................................................................................................. 142.4.2 System timing........................................................................................................................ 162.4.3 Positioning ............................................................................................................................. 172.4.4 Data communication........................................................................................................... 172.5 Transmitter .......................................................................................................................... 182.6 Propagation.......................................................................................................................... 202.7 Noise and interference ....................................................................................................... 212.8 Receiver ................................................................................................................................ 222.9 References ............................................................................................................................ 233Loran-C Error Model ....................................................................................................... 25 3.1 From pseudorange to position ......................................................................................... 263.1.1 Geometry................................................................................................................................ 263.1.2 Repeatable accuracy............................................................................................................. 273.1.3 Absolute accuracy ................................................................................................................ 273.2 Overview of error model................................................................................................... 283.3 Transmitter timing ............................................