On Generalized Signal Waveforms for Satellite Navigation (797942), страница 9
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Original formulasare proposed to calculate the SSC between any two arbitrary signals.o Assessment of the effect of non-random codes and data on the SpectralSeparation Coefficients. Particular examples for Galileo and GPS signals areprovided and the consequences are discussed.o Overview of the most representative multiplexing schemes in satellitenavigation with special emphasis on those modulations that GPS, Galileo andpotentially other navigation systems will use in the future.
Furthermore, thepossibility to use the above described multiplexing schemes to accommodatethe generalized signal waveforms is also discussed in this thesis.1.3Thesis OutlineThis thesis focuses on the derivation of general analytical expressions that can describe all thecurrent signal waveforms, modulations and multiplexing schemes today or that could beimplemented in the future. Furthermore, given the importance that the Spectral SeparationCoefficient plays in the design of any Satellite Navigation System’s signal plan, specialattention is paid to this figure.
The thesis concludes discussing existing and new theory onmultiplexing. In order to provide a comprehensive overview, this thesis has been divided inthe following chapters:••Chapter 1 gives and introduction to the semantics and to the scope of this thesis,giving a brief overview of the current situation and expectations on the futuredevelopment of satellite navigation in the next decades.Chapter 2 concentrates on giving a detailed overview of all the current and plannedSatellite Navigation Systems, summarizing the main constellation parameters andenvisioned signal and frequency plans.
The chapter begins with a brief discussion onthe direction in which GNSS could evolve in the coming years. Then, the AmericanGlobal Positioning System (GPS) is presented, followed by the European Galileo, theRussian GLONASS and the Chinese Compass system. After summarizing the maincharacteristics of these four systems, additional regional and augmentation satellitesystems are introduced and their main figures are briefly outlined. To conclude thechapter, actual information on other augmentation systems that are not based onsatellite technology is also provided.5Introduction••••••Chapter 3 makes a review of the evolution of the Galileo’s Signal and FrequencyPlan since it was officially announced that Europe would also pursue to have its ownGlobal Navigation Satellite System.
The chapter begins with the description of thefirst signal plan back in the late 1990´s and concludes with the newly adopted MBOCmodulation. In recognition of the difficulty that the signal design represents, thischapter tries to provide the technical arguments that were used to justify each of thesignal waveform that form today’s signal plan. Furthermore a brief description of thenavigation services that Galileo will offer is equally provided.Chapter 4 presents the theory on generalized signal waveforms, setting up a completetheory framework with which all of the signals used today for satellite navigation canbe described mathematically. The chapter begins defining the main spectral and timecharacteristics of any signal waveform, introducing then the generic Multi-CodedSymbol (MCS) modulation.
After that, general and particular analytical expressionsare derived and compared with the well known expressions that can be found in theliterature. Generalized waveforms are further introduced concluding the chapter withthe recently adopted MBOC modulation and an assessment of its performance fordifferent receiver configurations.Chapter 5 is dedicated to the derivation of analytical expressions for the SpectralSeparation Coefficients (SSC) using the theory presented in chapter 4. The chapterbegins deriving generic expression for the SSCs between any two generic BCS signalswith infinite bandwidth.
It concludes giving general expressions for the power in theband and for different efficiency parameters of interest. Analytical results andnumerical computations are compared to show the validity of the model.Chapter 6 concentrates on assessing the validity of the expressions derived in chapter5 under more realistic scenarios. The effect of non-random codes and data is furtherexamined and different signal waveforms are further investigated regarding theirspectral properties as seen in the receiver.Chapter 7 deals with signal multiplex techniques for GNSS. After giving a quickreview of all the techniques that are relevant for satellite navigation, the most relevantones are investigated in detailed. The chapter begins with a brief discussion on theneed of multiplexing and the requirement on constant envelope to justify the differentsolutions that will be later studied.
Beginning with non-constant envelope, the chaptergoes through more flexible techniques such as Interplex and its generalization to anynumber of sub-carriers, to finally conclude with new multiplexing schemes. Toconclude, this chapter presents a brief discussion on CDMA and FDMA stressing itsimportance on the modernization of GLONASS.Annexes A to N derive the analytical expressions for the Power Spectral Densities,Spectral Separation Coefficients, Multiplexing schemes and interference models thatare presented in the previous chapters.6Global Navigation Satellite Systems2.
Global Navigation Satellite Systems (GNSS)2.1GNSS – Thinking globalThe USA entered the global navigation satellite system (GNSS) era with the GlobalPositioning System as the result of efforts that began in the late 1960s. The Russians followedsoon afterwards with GLONASS. Both systems are now undergoing extensive modernization.Moreover, the European Galileo system is joining the GNSS club, and China is now planningits own version called Compass.In the meantime lots of augmentation and regional systems have been developed or arecurrently under consideration. From military to civil signals, from Medium Earth Orbit(MEO) to Geostationary Earth Orbit (GEO) and Inclined GeoSynchronous Orbits (IGSO), thepalette of systems and offered services is considerably wide.It is time to pause and think for a moment about where we want GNSS to move. It is alreadytime to really think global and to coordinate and harmonize all the existing and projectednavigation satellite systems.
Indeed the question naturally arises: what should the GlobalNavigation Satellite System of Systems look like?This chapter describes the world of GNSS in which we will live around the year 2020 if allthe currently modernizing and planned new systems come into reality. The word coordinationwill be the key since, if things are well done, it will give the users the possibility to profitfrom all the navigation systems as if they were only one. After all, GNSS users should notcare about whether one of the signals comes from GPS, the other from Galileo, the third fromGLONASS and the fourth from Compass as long as the GNSS receiver works well.2.2Scenes from the PresentToday only GPS is fully operational.
Nevertheless, Russia hopes to return GLONASS to fulloperation capability (FOC) with a completed constellation by 2009, and Galileo’s FOC is nowexpected end of 2013. Compass has also ambitious plans and in spite of the fact that Chinahas still a long way to go and lengthy negotiations will be needed, a scenario of four globalcoverage satellite systems seems to be very likely in a future not so far away from today.From the experience with Galileo, we know how important the roles of interoperability andcompatibility with GPS were from the very beginning. Unfortunately, major differencesbetween those two systems using the Code Division Multiple Access (CDMA) andGLONASS using the Frequency Division Multiple Access (FDMA) approach still exist today.However, GLONASS seems to have made first movement into adopting CDMA as will beshown in chapter 2.5.
It seems that Compass will use CDMA too.7Global Navigation Satellite SystemsOn the GPS/GLONASS side, work for reaching real interoperability continues. During theGPS/GLONASS Working Group 1 meeting in December 2006 both sides emphasized thebenefit to the user community that a common approach concerning FDMA/CDMA will bringin terms of interoperability. The Russian side announced that they would come to a decisionby the end of 2007 [US-Russia Statement, 2006] but it was not until April 2008 that the finaldecision was taken. GLONASS seems to plan now CDMA signals in L1 and L5 as we willshow in chapter 2.5.In fact, if the need of standardization was always there, it seems that the concept is gaining ininterest the more systems come into play. But before dreaming with our ideal GNSS, let usfirst look more closely into what the current reality is and the plans for new GNSS systems.If we take a look at the signal structure, we can recognize that all the present GNSS systemsare based on the Direct Sequence Spread Spectrum (DSSS) technique which is a particularcase of the more general Spread Spectrum (SS) method.
Moreover, Code Division MultipleAccess (CDMA), Frequency Division Multiple Access (FDMA) and Time Division MultipleAccess (TDMA) are particular cases of DSSS. The overall constellation parameters of thefour global GNSSes are shown in Table 2.1 next.Table 2.1. Space Constellation ParametersParameterGalileoGPSConstellationWalker MEO(27/3/1) plus 3non-active sparesMEO (24/6)including 3active sparesGLONASSCompassMEO (24/3)GEO (5),MEO (27),IGSO (3)GEO Longitudes---58.75°, 80°,110.5°, 140° and160° EGSO EquatorialCrossing---118°Eccentricity0000GSO Inclination---55°MEO Inclination56°55°64.8°55°Semi-major axis29,601.297 km26,559.7 km25,440 kmMEO 27,878 kmIGSO 42,146 kmAs we know, in spread spectrum communications a higher-frequency signal is injected into abaseband signal bandwidth.
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