Advanced global navigation satellite system receiver design (797918), страница 4
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Much of this was inunpublished technical memoranda which duly appear here in the various appendices.I would also like to acknowledge the contribution of my industrial supervisor DrMartin Unwin for his invaluable guidance, practical knowledge and instructionThis research has been supported by the Location and Timing Knowledge TransferNetwork, EPSRC, Surrey Satellite Technology Limited and the Surrey Space Centre.Many individuals from SSTL and SSC have helped and encouraged me during mystudies and my thanks to them all. I am particularly indebted to Michael Meier for hisexpert practical knowledge and teaching.
Also, I would like to thank the members ofthe GNSS team at SSTL for their help and friendship.I thank my family and my extended Finnish family for their love and support over thepast years. Finally my greatest thanks go to Hanna-Leena for inspiring andencouraging me throughout and keeping me somewhat sane.1IntroductionThis chapter introduces the various partnerships that have invested in and contributedto this research project. A brief history of the contributing parties is given to providea context for the project. Following this, a short description of the content in thesubsequent chapters of this report is given.1.1 The CASE PhD studentshipThe CASE PhD studentship was created by the Electrical and Physical SciencesResearch Council (EPSRC) to promote collaboration between industry and academiathrough research with common goals.
EPSRC set up a number of groups, eachdevoted to a specific area of electrical and physical sciences and called these Faradaypartnerships. Each partnership is given funding to develop the interaction betweenindustry and academia through research in its specific area. The Pinpoint Faradaypartnership is devoted to research into the applications of Global Navigation SatelliteSystems (GNSS) and enabled the core funding for this research.The goals of the CASE research are expected to satisfy both industrial and academicpartners.
For this reason the CASE projects tend to contain more practical work thanthe traditional theoretical PhD.The industrial partner of this CASE studentship was Surrey Satellite TechnologyLimited (SSTL). SSTL was formed as a spin-off company from the University ofSurrey in 1985. Since then, SSTL has been involved in 26 satellite missions andbecome a world-leader in supplying small satellites platforms. SSTL manufactures itsown range of GNSS receivers, which are operated on-board its own satellites andsupplied externally as sub-systems.
The academic partner was Surrey Space Centre(SSC), who specialise in all areas of space research including GNSS at the Universityof Surrey. Common office locations and the close working relationship betweenSSTL and SSC provide the ideal environment for the CASE student.16Introduction1.2 The future of GNSSThe generic term GNSS is currently used to encompass two operational systems : theUS Global Positioning System (GPS) and the Russian (GLONASS). Althoughoriginally conceived for military use, in recent years civilian use of GNSS hasincreased rapidly. Recent market research [Research and Markets 2006] has projectedthe worldwide market value of GPS as reaching $22 billion by 2008.
A huge everexpanding range of applications for GNSS receivers has resulted in their adoption intomany aspects of daily modern life. In turn, the number of GNSS applications forspace-borne users has also increased. GPS is predominantly used for mostapplications mainly due to smaller numbers of operational GLONASS satellites. TheUS has already started its campaign of GPS modernisation, with two block IIR-Msatellites currently operational and potentially five more to be launched in 2007.GPS modernisation aims to improve upon the existing system by broadcastingadditional military and civil signals. This is intended to satisfy the increasing civildemand for high-precision dual frequency systems. However, competition for thealready large GNSS market is set to increase with the introduction of the EuropeanGNSS, Galileo.This new generation of GNSS will provide more satellites transmitting a range ofhigh-bandwidth, high precision signals with precise ephemeris and integritymonitoring.
The new signals can potentially provide a number of performanceadvantages over the existing systems. However, the new complex signalspecifications require new receiver architectures and new techniques to achieve signalacquisition and tracking.This research project was formed to study the impact and implications of newgeneration GNSS on receiver design with emphasis on space applications. Theexpected outcomes of this project were as follows.17Introduction To further develop SSTL’s space GNSS receiver designs – Providing aplatform capable of receiving the new generation of GNSS signals in order toderive benefit for space applications. To analyse the impact of the new GNSS on receiver design – Providing acomprehensive comparative study of the receiver techniques required forreceiving future GNSS signals, while developing novel, beneficial approacheswhere possible.This thesis describes the work carried out to achieve these goals, with particularemphasis given to a novel technique for tracking Binary Offset Carrier (BOC)modulated signals.The work described in this thesis was carried out at a very timely moment in thedevelopment of global navigation satellite systems.
The world as a whole, with itsbillions of potential customers, is now perceived as a customer of such systems, notjust the military and specialist users. During the period of my work (starting fromSeptember 2003) there have been important international agreements anddevelopments, which have confirmed or at least recommended the structure ofentirely new signals. A new range of different coding and modulation schemes hasbeen conceived to serve an expanding multi-faceted market. The Americans areimplementing significant changes and hopefully improvement in the development ofthe next generation of GPS. There may well be implemented soon the independentEuropean Galileo system, which will also adopt new codes and modulations, as wellas the latest technology in atomic clocks. As a student of Surrey University I waswell placed to make a contribution to these challenging developments at boththeoretical and practical level under the joint auspices of Surrey Space Centre andSurrey Satellite Technology Ltd.
Shortly before this research began SSTL achieved acontract to design and build the first ever test satellite Giove-A of the Galileo signalsand technology. The satellite was launched on the 28th of December 2005. Theopportunity existed then to design and build a test transmitter (see [Blunt 2005]) forinstallation on the satellite before launch; and also to design and build appropriatereceivers to monitor the transmissions both in ground based simulations or emulationsand real live tests after launch.
I am grateful to the technical and financial support18Introductionfrom the GNSS team of the company headed by one of my supervisors Dr MartinUnwin, which made this possible.Before describing in detail the point, purpose and potential novelty of these practicaldevelopments, the beginning chapters of this thesis lead up to a description of atheoretical novelty, initiated jointly by myself and my other supervisor Dr StephenHodgart of Surrey Space Centre. An important feature of the new signals for bothGPS modernisation and Galileo is an entirely new kind of modulation called BOC(Binary Offset Carrier).
A family of modulations based on BOC are characterised bya sub-carrier modulation imposed on the code-modulation. The effect is well knownto create a split spectrum (see Figure 3-9). It is perhaps surprising that a family ofsignals using this modulation and their precise specification was agreedinternationally (see Table 3-2 and Table 3-3) for both new GPS and Galileo, despitethe reservations published in many papers on the practical difficulties in realising agood working BOC receiver. The notorious perceived difficulty is due to thecharacteristic multi-peaked correlation function. In our view all known receivers, orreceiver principles, have problems with this: either because the receiver is not fail safeand is potentially unreliable (the so-called bump-jumping receiver [Fine and Wilson1999]); or the multi-peaks are eliminated at the very substantial cost in muchdegraded accuracy [Bello and Fante 2005].With my work under Dr Hodgart what seems to be an entirely new and originalmethod has been developed which entirely solves the problem of tracking BOC.
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