Galileo OS SIS ICD (797928), страница 11
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2-4.ReservedDnype4IOWord Type 4: Ephemeris (4/4), and clock correction parametersTotalaf1af216161428181210BBBBBBBBB6BBBaf061t0CPageCISGAL OS SIS ICD/D.0Draft023/05/2006CICReference:Issue:Revision:Date:8128Table 44: Bits allocation for word type 4Word Type 5: BGD, signal health and data validity status, Ionospheric correction and GSTReservedTOWBWNRegion 11Region 2Region 3Region 4Region 5ai312Bai212BBBBBai1BE5bDVS1 12B2BE5bHS10BBGDE5a/E16GSTIonosphericdisturbance flagAzBType=5Ionospheric correction1 1 1 1 1220Total36128Table 45: Bits allocation for word type 5GST-UTC conversion, signal health and data validity status page is formatted according to thevalues stated in Table 45.461HWord Type 6: GST-UTC conversion parameters, signal health and data validity statusE1BHSE1BDVSTotal8 8 3 8 1021128BBBBBBBBBBBBB8 8BBB24BA132BA010BReserved6∆tLSt0tWNtWNLSFDN∆tLSFType=6BBGDE5b/E1GST-UTC conversion parametersTable 46: Bits allocation for word type 6The almanac for 3 satellites is transmitted on 4 pages formatted according to the values statedin Table 46 to Table 49.462H463HSVSVID1 (1/2)BB©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p.
2-4.er0WpeIWord Type 7: Almanac for SVID1 (1/2), almanac reference time and almanac reference weeknumberTotalωδi6171116118GAL OS SIS ICD/D.0Draft023/05/2006Page62Pe8(∆a)1/22SVID16Reference:Issue:Revision:Date:Ω ΩBBaf0BBP•01611142128Table 47: Bits allocation for word type 7Word Type 8: Almanac for SVID1 (2/2) and SVID2 (1/2))SVSVID1 (2/2)(∆a)1/2eω617111616M0ReservedBB161BPBTotalBBPBBB0BBBSVStatus(E5bHS)SVID2B11 2 2af1B6 16BΩBM0IODa2SVID1Type=86SVSVID2(1/2)BSVStatus(E1BHS)B128Table 48: Bits allocation for word type 8Word Type 9: Almanac for SVID2 (2/2) and SVID3 (1/2))SVSVID2(2/2)SVSVID3(1/2)11 2 2 61711BPPBBδiωBBΩ0Total1/2BBBBaf1BBaf0BBBBB•ΩδiIODaSVID2Type=9BBeB(∆a)1/2BSVStatus(E5bHS)SVStatus(E1BHS)SVID3B62 6 11111416 112128Table 49: Bits allocation for word type 9Word type 10: Almanac for SVID3 (2/2) and GST-GPS conversion parametersBBBt0GBWN0GBB©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p.
2-4.BBBA1GBBBBA0GBBBB•ΩB0BΩ2/2BBBBBM0af0af1SVStatus(E5bHS)SVStatus(E1BHS)SVID3IODaType=10BReservedGST-GPS conversionparametersSVSVID3(2/2)Total626141116 14 11 2 2Reference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page63161286 2128Table 50: Bits allocation for word type 10During the initialisation phase when no data is up-linked via the C-band to the satellite, thesatellite generates and downlinks the dummy message on E5b/E1 replacing the pages in thenominal sequencing, according to Table 50.46H113BBTotal16 120Total18TailDummy data (1/2)24Tail80Reserved1CRCE1BType=0Total [bits]Tail6 1201Type=08Even/Odd=124Dummydata(2/2)Even/Odd=080120Total [bits]1B1BDummydata(2/2)6Tail112Reserved1CRCE5b1Type=0Dummy data (1/2)Even/Odd=1Type=0E1BEven/Odd=0E5b-I6 120Table 51: I/NAV dummy message with bits allocationwithEven/Odd (1 bit): to indicate the part of the page (0=even/1=odd) that is broadcastDummy Data (194 bits = 81 bits +113 bits): composed of dummy dataCRC (24 bits): computed on the Page Type and Data fields for the Even/Odd page ofthe same frequency (“vertical CRC”), and the CRC is always broadcast on the secondpart of the vertical pageReserved (8 bits)The dummy data word (192 bits) is formatted according to Table 51.465H©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p.
2-4.GAL OS SIS ICD/D.0Draft023/05/2006Page64Type = 63Reference:Issue:Revision:Date:TOWWNDummy sequenceData62012156192Dummy Data (1/2)(112 bits)Dummy Data (2/2) (80bits)Table 52: Dummy word with bits allocationwithWord Type (6 bits): to indicate the word type dummy message, which is defined astype 63 (Type=111111) TOW (20 bits): to broadcast the on-board Time of Week (time with 1second accuracy) WN (12 bits): to broadcast the on-board Week Number Dummy sequence (154 bits): this is an arbitrary.The dummy sequence is1372EC4D3B4F84DCBB134ED3E1372EC4D3B4F8coded in hexadecimal plus two bits at the end which are “00”.©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p. 2-4.Reference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page6510.
MESSAGE DATA CONTENTSThis section describes the data items above mentioned. Semantics, formats and otherrequirements are provided for all items to be transmitted inside frames.10.1 NAVIGATION DATAThe navigation data contain all the parameters that enable the user to perform positioningservice. They are stored on board each satellite with a validity duration and broadcast worldwide by all the satellites of the Galileo constellation.The 4 types of data needed to perform positioning are specified in the following section: Ephemeris: needed to indicate the position of the satellite to the user receiver Time and clock correction parameters: needed to compute pseudo-range Service parameters: needed to identify the set of navigation data, satellites, andindicators of the signal health. Almanac: to indicate the position of all the satellites in the constellation with areduced accuracy.10.1.1 EphemerisThe ephemeris for each Galileo satellite is composed of 16 parameters, which are: 6 keplerian parameters, 6 harmonic coefficients, 1 orbit inclination parameter, 1 LAN rate correction parameter, 1 mean motion correction parameter and 1 reference time parameter t0e for the ephemeris data setThe total data size of these 16 parameters is 356 bits.©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p.
2-4.Reference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page66The ephemeris for each Galileo satellite is according to the characteristics stated in Table 52.46HDefinitionBitsScalefactorM0Mean anomaly at reference time32 *2-31∆nMean motion difference from computed value16 *-43ParameterBBPP2PPUnitSemi-circlesSemi-circles/sEccentricity322-33N/ASquare root of the semi-major axis322-19meters1/2Longitude of ascending node of orbital plane atweekly epoch32 *2-31Semi-circlesInclination angle at reference time32 *2-31Semi-circlesArgument of perigee32 *2-31Semi-circlesRate of right ascension24 *2-43Semi-circles/sRate of inclination angle14 *2-43Semi-circles/sAmplitude of the cosine harmonic correction term tothe argument of latitude16 *2-29RadiansCusAmplitude of the sine harmonic correction term to theargument of latitude16 *2-29RadiansCrcAmplitude of the cosine harmonic correction term tothe orbit radius16 *2-5MetersCrsAmplitude of the sine harmonic correction term to theorbit radius16 *2-5CicAmplitude of the cosine harmonic correction term tothe angle of inclination16 *2-29RadiansCisAmplitude of the sine harmonic correction term to theangle of inclination16 *2-29Radianst0eEphemeris reference time1435660Secondsea1/2PPΩi0BB0BωPPPPPPPPPPPP•ΩPP•iCucBBBBBBBBBBBBBBTotal ephemeris sizePPPPPPPPPMetersPPPPP*: Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB.Table 53: Ephemeris parametersA single ephemeris is applicable to all signals of a specific satellite.The ephemeris is computed with respect to the apparent CoP common to every frequency.The validity interval (fit interval) for the Galileo ephemeris message is 4 hours.Four messages cover the 12 hours orbit predictions generated by the orbit determinationprocess.
All messages can be computed and uploaded to the satellite in a single step.The nominal period of update is 3 hours.©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p. 2-4.Reference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page67The 1-hour overlap interval is helpful against short outages or delays.10.1.2 Time Correction and Clock Correction Parameters10.1.2.1 Satellite time correction dataIn order to perform pseudo-range measurements, the user receiver needs to have an accurateknowledge of GST and of the satellite signal time of transmission (TOT) in GST.Due to the complexity to directly steer the physical satellite clocks to the system time, eachsatellite transmits time correction data. The predicted offset of the physical satellite signalTOT relative to the satellite signal X in GST can be computed for each signal using these timecorrection data, according to the following Eq.
12:467HTOTC (X) = TOT m(X) – ΔtSV(X)BBBBEq. 12Bwhere:TOTC(X) is the corrected satellite TOT for the signal X in GST time TOTm(X) is the physical satellite TOT for the signal X retrieved through pseudorangemeasurements. ΔtSV(X) is the satellite time correction for the signal X computed by means of the timecorrection data retrieved from the navigation message.This satellite time correction is modelled through the following second order polynomial:BBBBBBΔtSV(X) = af0(X) + af1(X)*(t - t0C(X)) + af2(X)*(t - t0C(X))2 [seconds]BBBBBBBBBBBBPPEq. 13where:af0(X), af1(X), and af2(X) are respectively the polynomial coefficients corresponding tophase error, frequency error and rate of change of frequency error for satellite clock ondual frequency signal X. toc is the reference time for the clock correction [seconds] t is the GST [seconds]Note that the satellite time correction model only describes the evolution of the offset of thephysical satellite signal TOT relative to the satellite signal TOT in GST over a valid timeinterval and referenced to the satellite antenna phase centre.
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