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A Search for Spectrum: Gnss Signals in S-Bandpart 1

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A Search for Spectrum: Gnss Signals in S-Bandpart 1 WORKING PAPERS A Search for Spectrum: GNSS Signals in S-Band Part 1 Your GNSS S-band spectrum here? Frequency allocations suitable for GNSS services are getting crowded. System providers face an ever tougher job as they try to bring on new signals and services while maintaining RF compatibility and, in some cases, spectral separation. This two-part column explores the possibility, advantages, and disadvantages of using allocations in a portion of the S-band spectrum. ISIDRE MATEU n recent years, researchers have compatibility with the adjacent radio CNES (FRENCH SPACE AGENCY) explored possible new allocations astronomy band and GLONASS could MATTEO PaONNI for Radio Determination Satellite be achieved. INSTITUTE OF GEODESY AND NAVIGATION, IService (RDSS) and Radio Naviga- In any case, any signal occupying UNIVERSITY FAF MUNICH tion Satellite Service (RNSS) spectrum the whole E1/G1 band would have to be JEAN-LUC ISSLER from a regulatory point of view. These backward-compatible and symmetrical CNES studies have mainly discussed S-band in spectrum and correlation character- BERND EISSFELLER and C-band in addition to L-band. istics to avoid creating pseudoranging INSTITUTE OF GEODESY AND NAVIGATION, The International Telecommuni- bias. Furthermore, having a very wide UNIVERSITY FAF MUNICH cations Union (ITU) Radio Regula- band signal in the lower and upper L- tions define RNSS as a subset of RDSS. bands would potentially allow significant LIONEL RIES, CYRILLE BOULANGER Although the allocations are differenti- improvement in terms of pseudoranging CNES (FRENCH SPACE AGENCY) ated — RDSS usually has a paired uplink performance thanks to the very accurate PaOLO MULASSANO — both can actually be used for satellite dual-frequency, wideband ionospheric ISTITUTO SUPERIORE MARIO BOELLA, TORinO, ITALY navigation. correction and raw pseudoranges that MARIO CAPORALE The eventual need of GNSS systems would be available. In fact, this is the ASI (ITALIAN SPACE AGENCY) for additional frequency resources or only way for any new signal to signifi- SYLVAIN GERMAINE, JEAN-YVES GUYOMARD signals in S-band and/or C-band is not cantly improve the pseudoranging per- ANFR (FRENCH NATIONAL AGENCY OF driven by the desire to improve the pseu- formance, because C-band today is only FREQUENCIES) doranging or timing performance, but 20 MHz wide (5010–5030 MHz) and S- FREDERIC BaSTIDE, JEREMIE GODET, DOMiniC HAYES primarily to introduce alternative and band is restricted to 16.5 MHz (2491.75 EUROPEAN COMMISSION complementary capabilities to those MHz ±8.25 MHz. DaMIEN SERanT, PaUL ThEVENON, OliVIER JUliEN services already offered by systems now “Note that an alternate binary offset ENAC (FRENCH CIVIL AVIATION UNIVERSITY) in operation or under development. carrier with CBOC on each side — that In fact, GNSS pseudoranging or tim- we could define as AltBOC(15, CBOC), ANTHONY R. PRATT ing performance could be improved with for example — or an equivalent signal ORBSTAR LTD. U.K. availability of new code division multi- filtered in the E1/G1 band could by itself JOSE-ANGEL AVILA-RODRIGUEZ, STEfan ple access (CDMA) signals in the upper prove superior in terms of accuracy WALLNER, GUENTER W. HEIN L-band alone. These could be defined in compared to the current multiplexed EUROPEAN SPACE AGENCY/ESTEC, NOORDWIJK, the so-called E1+G1 band, for example, BOC (MBOC) planned for Galileo E1 THE NETHERLANDS where some room is still available if and GPS L1, while still preserving the www.insidegnss.com SEPTEMBER 2010 InsideGNSS 65 WORKING PAPERS Horizontal trajectories 0.8 technically feasible, tighter hybridizations between mobile 0.7 0.6 from the perspec- communication services and naviga- 0.5 tives of link budget tion services. 0.4 and radio frequency The list of imaginable applications North 0.3 compatibility. We based on the combined use of S- and L- 0.2 must also under- band or S-band alone is a lengthy one, 0.1 0.0 line the fact that the including the following: -0.1 results presented in • An accurate self-positioning of 0.0 0.5 this column neither future Globalstar mobile phones East pretend to cover using Galileo, without the need to all solutions agree to 1cm RMS the whole palette of add any L-band hardware in the Glo- GNSS signals and balstar (or other mobile com) termi- FIGURE 1 Example of accuracy close to one centimeter provided by the in- teger ambiguity resolution on undifferenced phase (IARUP) technique frequency resources nal to save costs in this equipment. using GPS L1 and L2 signals that could be dis- Single-frequency S-band ionospheric cussed, nor pretend correction could be provided using necessary backward compatibility with to be an official baseline for an evolved techniques such as those described a composite BOC (CBOC) in E1. Galileo system. in other research on this topic listed In principle, another very important Future developments could be in dif- in the Additional References. field for improving accuracy worldwide ferent or complementary directions to • Assistance of GNSS acquisition without the need of extra frequency those that we will discuss here. Having indoor using Globalstar signals, or bands (that is, in addition to L-band) is a said this, we recall that the main objec- using other mobile communication technique called integer ambiguity reso- tive of the authors is to open a construc- signals also transmitted in S-band lution on undifferenced phase (IARUP) tive discussion on where GNSS could • To perform the orbit and time deter- or possible equivalent techniques, which evolve to. The first part of this column mination of both Galileo (or another will allow very precise positioning accu- will take up the issues of S-band’s poten- GNSS system) and Globalstar sat- racies close to a few centimeters in real tial for GNSS operations, presenting ellites, thanks to a single ground time (See Figure 1). IARUP is described results of several comparative technical network of updated Galileo Sensor further in the paper by D. Laurichesse analyses. Station (receivers), using double dif- and F. Mercier listed in the Additional Part 2, which will follow in the Octo- ference measurements in S-band, Resources section at the end of this ber issue of Inside GNSS, will focus on single frequency ionospheric deter- article. (We should point out that such the subject of compatibility and interop- mination in S-band, and intersystem techniques are also known by the acro- erability with other systems operating assistance/cross-validations thanks nym PPP-Wizard, standing for “Precise at S-band as well as signal modulations to L-band measurements. A GNSS Point Positioning With Integer Zero-dif- that might work well for GNSS services system could then offer the time and ference Ambiguity Resolution Demon- there. orbit determination of Globalstar stration.”) and/or other mobile satellite service Having this in mind and recalling Potential Benefits of S-band (MSS) systems, if the necessary relat- that our objective is to focus on S-band, for Navigation ed security measures were taken. alternative solutions that employ C-band New functions and services that could • To assist the acquisition of MSS sig- and/or G1/G2. L-band will not be dis- be imagined for potential S-band signals nals like the Globalstar ones, provid- cussed further in this article, except for do not necessarily include the improve- ing an accurate time, without requir- the relevant L/S-band link budget com- ment of the ionospheric correction. ing any L-band–specific hardware in parisons. Regarding C-band, several In fact, a new signal in the G1 L-band the mobile com terminal. studies have been undertaken in recent would also significantly improve the • To use the communication channel years to investigate the suitability of this ionospheric correction efficiency as dis- to provide assisted-GNSS to a GNSS- frequency band for GNSS purposes and cussed above. embedded receiver. This would allow possible alternatives for a signal baseline, Moreover, Globalstar, a low Earth communication to support GNSS. mainly in the framework of the Europe- orbit (LEO) mobile telecommunication A possible approach could be, for an Space Agency’s GNSS Evolution Pro- constellation, also applies S-band Dop- instance, to use the Open Mobile gram. (The interested reader can refer to pler compensation based on radio links Alliance–Secure User Plane Loca- the papers by J. A. Avila-Rodriguez et between the ground and the LEO satel- tion (OMA-SUPL) approach. alia (2008b) and A. Schmitz-Peiffer et lites in addition to its GPS on-board real- • To allow RDSS multi-constellation alia listed in Additional Resources.) time orbit determination and synchro- positioning in S-band by means This two-part column will show that nization. Further, the new functions and of Beidou/Compass future S-band potential new services in S-band are services provided by S-band are rather signals or from the Indian IRNSS/ 66 InsideGNSS SEPTEMBER 2010 www.insidegnss.com WORKING PAPERS PMDr: Leeheim Vorgang: B2 001/00374/09 BEIDOU-1B GINS, which is also planned to tance in S- and Empfangsantenne: MBA Polarisation: Zirkular transmit at 2491 MHz. An example L-band, thanks Richtung: 102.8° Elevation: 04.2° -63 of the signal that could be employed to the previous- ] bm -66 Figure 2 [d is shown in , which depicts ly mentioned the Chinese geostationary orbit Asian, U.S., and ator -69 satellite (GSO) RDSS signal at 2491 European sys- ys al -72 MHz. The paper by T. Grelier et alia tems. An (2006) cited in Additional Resourc- All these appli- -75 sung es has measured and analyzed cations might be le -78 the Beidou GNSS S-band pseudo- satisfied by a single Ab 75 75 75 75 75 75 75 75 75 75 noise (PN) code spectrum lines.
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