On Generalized Signal Waveforms for Satellite Navigation (797942), страница 13
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The E6 (B&C) signal contains the value-added data and it is combined with OS signalsfor improved performance.2.4.2.4.3 Safety of Life (SoL)The mono-frequency SoL will be provided by each of the two signals: E1(B&C) and E5b.The dual-frequency SoL will be provided by the following dual-frequency signalcombination: E1(B&C) - E5b. It has to be noted that the Galileo Safety of Life frequencies arein Aeronautical Radio-Navigation Service (ARNS) bands allocated for GNSS.
The integritybroadcast and the protection provided in the ARNS bands are two important features of theGalileo SoL. A third important added value provided by Galileo to safety critical operations isthe frequency diversity offered by E1, E5a and E5b ARNS Galileo bands. Assumingcombined E1, E5a and E5b receivers and using a probabilistic theory related to involuntaryjamming of GNSS receivers, it has been shown that the probability of losing the dualfrequency navigation function has been assessed and computed to be approximately 15,000times lower in the case where a tri-frequency single system receiver is used instead of a dualfrequency single system receiver, making this event an improbable case.
This result isparticularly important for safety of life applications, such as civil aviation. Therefore,frequency diversity has an enormous potential as a simple interference mitigation means[J.-A. Avila-Rodriguez et al., 2007].28Global Navigation Satellite Systems2.4.2.4.4 Public Regulated Service (PRS)The PRS service will be provided by the E1-A and E6-A signals. These will use encryptedranging codes, navigation data and sub-carriers improving signal processing performances.2.4.2.4.5 Search And Rescue Service (SAR)The SAR distress messages will be detected by the Galileo satellites in the 406-406.1 MHzband and then broadcasted to the dedicated receiving ground stations in the 1544-1545 MHzband, called L6 (below the E2 navigation band and reserved for the emergency services). TheSAR data transmitted from SAR operators to distress emitting beacons will be used for alertacknowledgement of distress alerts and coordination of rescue teams.
The data will beembedded in the OS data of the signal transmitted in the E1 carrier frequency2.4.2.5Galileo C-bandThe Radio-Navigation Satellite Service (RNSS) portion of the RF spectrum is overcrowded.This is especially true on the E1/L1 band. Nevertheless even those bands that have not beenused yet will certainly be shared by many systems in the near future. Thus, the search of otherfree frequency resources is something that will occur with a high probability in the next years.During the World Radio Conference 2000 (WRC-2000), the Galileo program obtainedauthorization to use C-band frequencies between 5010 and 5030 MHz.
At the time, adedicated portion of the C-band was assigned for Radio-Navigation, but technicalcomplexities made it impossible for the first generation of Galileo.Indeed, phase noise problems, the higher free space attenuation (related to the use of omnidirectional antennae) and the strong signal attenuation due to rain made all the proposedsolutions not adequate for the first Galileo constellation.
However, in some decades thingscould have changed and C-band could be a real alternative. As suggested in[G.W. Hein et al., 2007b] and [G.W. Hein et al., 2007c], the C-band could be reserved formilitary/governmental applications leaving the L-band alone for civil users.
This would haveinteresting benefits to both types of user and consequences as depicted in that article.2.4.3 Galileo ModernizationGalileo is not yet in operation but already the so-called evolution program for the secondgeneration has started end of 2007. Galileo II could arrive somewhere around 2020 and isexpected to introduce new modernization elements analogous to the steps made by itscounterparts GPS and GLONASS.
Inter-Satellite Links (ISL) could be introduced at that timeand aeronautical certification could be of relevance. In fact, under current plans only the firstphase of Galileo – EGNOS – will be certified for aeronautical users.29Global Navigation Satellite Systems2.5GLONASS2.5.1GLONASS System OverviewThe GLObal NAvigation Satellite System (GLONASS – ГЛОНАСС: ГЛОбальнаяНАвигационная Спутниковая Система) is the Russian navigation satellite system and, likeGPS, it defines itself as a dual-use system.
It is operated for the Russian Federationgovernment by the Russian Space Forces. The system is governed by the CoordinationScientific Information Centre of the Ministry of Defense of the Russian Federation. Sincesome years the responsibility for GLONASS has been nominally delegated to Roscosmos,with funding coming from both Ministry of Defense and space agency budgets. WhenGLONASS was at peak efficiency it offered a standard – Coarse-Acquisition or “C/A” –positioning and timing service for civil users and a more accurate signal – Precision or“P Code” – available for Russian military use. The first three test satellites were placed inorbit in October 1982 with the first operational satellite entering service in December 1983.First plans aimed at making the system operational in 1991 but it was not until September24th, 1993 that the system was finally announced to enter operation.The GLONASS ground segment is entirely located within the former Soviet Union territory,thus regionally, unlike for GPS and Galileo where it is spread all over the world.
As aconsequence, GLONASS presents an inferior performance in the stability and predictabilityof the satellite orbits. The Ground Control Centre and Time Standards are located in Moscowand the telemetry and tracking stations are in Saint Petersburg, Ternopol, Eniseisk andKomsomolsk-na-Amure.The GLONASS nominal constellation is composed of 24 satellites in three orbital planes withascending nodes 120 degrees apart.
Of the 24 satellites, 21 are active while the other three,one in each plane, are spare satellites. In each plane, the eight satellites are equally spacedwith argument of latitude displacement of 45 degrees. Each of the satellites is identified by aslot number, which defines the corresponding orbital plane and the location within the plane:1-8 for the first plane, 9-16 for the second place and 17-24 for the third plane. The orbitalplanes have 15-degree argument of latitude displacement relative to each other.The satellites operate in circular orbits of 19,100 kilometres (25,440 km semi-major axis) atan inclination of 64.8 degrees, and each satellite completes the orbit in approximately 11hours 15 minutes.
The satellite orbit repeats thus after approximately 8 days and since eachplane contains 8 satellites there is a non-identical repeat after one sidereal day (not to confusewith the GPS sidereal day, which is different). The spacing of the satellites allows forcontinuous and global coverage of the terrestrial surface and the near-earth space, so that aminimum of 5 satellites are in view at any given time.30Global Navigation Satellite SystemsAs shown in Figure 2.17, the current GLONASS status is far away from its nominal numbersand as of May 9th, 2008, only 14 active GLONASS satellites are transmitting from space(these are green in the figure).
Two additional spacecraft are on orbit but have beentemporarily switched off and are currently in maintenance (in yellow in the figure). However,in September and November 2008, Russia plans to conduct triple launches of modernizedGLONASS satellites (GLONASS-M). If successful, that could ensure the envisagedcompletion of an 18-spacecraft constellation comprising all GLONASS-M satellites by theend of 2008.Figure 2.17.
Launch History of GLONASSThe initial GLONASS Program Budget of 2001 was arranged for reaching FOC in 2011.However the GLONASS program is speeding up on its course in accordance with apresidential directive issued January 18th, 2006. The new ambitious modernization plans ofGLONASS envisioned the achievement of minimal operational capability (18 satellites) againby end of 2007 and FOC by end of 2009. While this ambitious schedule has failed as of May2008, the program still pursues to reach the objectives by the end of 2008 with the extrabudget that has been set up for the years 2007 to 2011. See Figure 2.18 for more details.Besides reaching FOC, Russia also wants to achieve a comparable performance of GLONASSto that of GPS and Galileo until 2010 [G.W. Hein et al., 2007a].Figure 2.18.
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