Galileo OS SIS ICD (797928), страница 12
Текст из файла (страница 12)
This offset is induced by satelliteclock noise or satellite inter-frequency group delay variations over the prediction timeinterval.Any dual-frequency user receiver can synchronise the received time signals to GST.For single frequency user receivers the Broadcast Group Delay and the ionospheric correctionare additionally required, considering the following guidelines:BBBBBBBB©, 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.0Draft023/05/2006Page68The coefficients of the model do not include correction for relativistic effects.Therefore the user receiver applies the correction of relativistic effects separately.A user receiver performing pseudorange measurement with signal X does not need toapply inter-frequency bias correction.A user receiver performing pseudorange measurement with any signal different fromX and using the satellite time model for signal X needs to apply an appropriate interfrequency bias correction to retrieve the satellite TOT.
The inter-frequency biascorrection term is determined using the BGD values.10.1.2.2 Galileo System Time (GST)The GST is given as 32-bit binary number composed of two parts as follows: The Week Number is an integer counter that gives the sequential week number fromthe origin of the Galileo time. This parameter is coded on 12 bits, which covers 4096weeks (about 78 years). Then the counter is reset to zero to cover additional periodmodulo 4096. The Time of Week is defined as the number of seconds that have occurred since thetransition from the previous week. The TOW covers an entire week from 0 to 604800seconds and is reset to zero at the end of each week.
This leads to code this parameteron 20 bits. Note that this TOW is generated by the satellite as it gives the epoch whenthe navigation data is down-linked from the satellite.The GST parameters are transmitted according to the characteristics stated in Table 53.468HScalefactorParameterDefinitionWNWeek Number121weekTOWTime of Week20321secondGalileo System Time - TotalBitsUnitTable 54: GST parametersThe start time for the Galileo System Time is [TBD].10.1.2.3 Clock CorrectionThe clock correction parameters are transmitted according to the values stated in Table 54.469HParameterDefinitiont0cClock Reference timeBBaf0BBaf1BBaf2BBBitsConstant Parameterst1 order parameterPPnd2 order parameterPPClock Correction Parameters - TotalScalefactor146028-33181272PP-452PP-65PTable 55: Galileo clock correction parameters©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p.
2-4.Seconds22UnitPSecondss/ss/s2PPReference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page69Each Galileo satellite broadcasts its own clock correction data for all signals through therelevant signal, according to Table 55.470HMessageF/Nav(E5a)I/NAV(E5b, E1)Type ofSatelliteClocksSatellite time correctionmodel parametersServices(E5a, E1)aBf0B (E5a, E1)afB 1B (E5a_E1)afB 2B (E5a,E1)t0B CB (E5a_E1)Dual-Frequency (E5a, E1) OSSingle-frequency E5a OS(E5b, E1)aBf0B (E5b, E1)afB 1B (E5b_E1)afB 2B (E5b,E1)t0B CB (E5b_E1)Dual-Frequency (E5b, E1) OSSingle-frequency E5b OSSingle-frequency E1 OSTable 56: Galileo clock correction data within F-NAV navigation message10.1.2.4 Broadcast Group DelayThe Broadcast Satellite Group Delay (BGD(Ey, Ex)) data relative to Galileo frequencies Exand Ey, which is broadcast through the navigation data message, is defined in Eq.
14:471HBGD(Ey,Ex ) =Tx − Ty2⎛ Ey ⎞⎜ ⎟ −1⎝ Ex ⎠Eq. 14where:Ex and Ey denote two Galileo single frequency signals Ty (Tx) is the group delay of the satellite transmitting chain on Ey (Ex) Galileo singlefrequency signal, from baseband modulator output up to the antenna phase centre.The Broadcast Group Delay (BGD) is coded according to the values stated in Table 56.472HParameterDefinitionBitsBGDE5a/E1 BGD for single Frequency E5a Open ServiceBGDE5b/E1 BGD for single Frequency E5b Open ServiceTotal Group Delay parameters10*10*20Scale factor-3222-32PPPPUnitsecondsseconds*: Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSBTable 57: BGD parametersEach Galileo satellite broadcasts its own BGD data for all signals, through the relevant signalaccording to Table 57.473H©, 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.0Draft023/05/2006Page70MessageType of Satellite ClocksBGD(X)ServicesF/Nav (E5a)(E5a, E1)BGD(E5a, E1)Single-frequency E5a OSI/Nav (E5b, E1)(E5b, E1)BGD(E5b, E1)Single-frequency E5b OSSingle-frequency E1 OSTable 58: BGD values mapping on messages and services©, 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.0Draft023/05/2006Page7110.1.2.5 Ionospheric correctionA global model is used to apply the ionospheric corrections for all services, including thefollowing parameters: 3 global Effective Ionisation Level Az parameters computed using the 3 broadcastcoefficients a0, a1 and a2. 5 “Ionospheric Disturbance Flag” (also referred to as “model storm flag” or “stormflag”), provided separately for five different regions as stated in Table 58:47HDefinitionai0Effective Ionisation Level 1rst order parameter12N/Adimensionlessai1Effective Ionisation Level 2nd order parameter12N/Adimensionlessai2Effective Ionisation Level 3rd order parameter12N/AdimensionlessSF1Ionospheric Disturbance Flag (or storm flag) for region 11N/AdimensionlessSF2Ionospheric Disturbance Flag (or storm flag) for region 21N/AdimensionlessSF3Ionospheric Disturbance Flag (or storm flag) for region 31N/AdimensionlessSF4Ionospheric Disturbance Flag (or storm flag) for region 41N/AdimensionlessSF5Ionospheric Disturbance Flag (or storm flag) for region 5141N/AdimensionlessBBBBBBBBBBBBBBBBBitsScalefactorParameterTotal ionosphere parametersUnitTable 59: Ionospheric correction parametersIt is assumed that the ionospheric model corrects 70% of the ionosphere when operating onE5a, E5b, E6 and L1 frequencies.
Furthermore, it is assumed that the ionospheric stormycondition is transmitted to the user receiver.The effective ionisation level is computed according to Eq. 15:475HAz = ai 0 + ai1 ⋅ μ + ai 2 ⋅ μ 2Eq. 15where μ is the modified dip latitude MODIP.The “Ionospheric Disturbance Flag” (also referred to as “model storm flag” or “storm flag”)has the following values: [0…No disturbance / 1…Disturbance] in the region, where theregions are defined as: region 1: for the northern region ( 60° < MODIP < 90°) region 2: for the northern middle region (30° < MODIP < 60°) region 3: for the equatorial region (-30° < MODIP < 30°) region 4: for the southern middle region (-60° < MODIP < -30°) region 5: for the southern region ( -90° < MODIP < -60°)©, 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.0Draft023/05/2006Page7210.1.2.6 UTC ConversionThese data include the parameters for the conversion of GST to UTC.The UTC time tUTC is computed through 3 different cases as follows.BBCase a:Whenever the effective time indicated by the WNLSF and the DN values are not in the past(relative to the user's present time), and the user's present time does not fall in the time spanwhich starts at DN+3/4 and ends at DN+5/4, tUTC is computed according to Eq. 16:BBBB476Ht UTC = (tE - ΔtUTC) [modulo 86400] secondsBBBBBEq. 16Bwhere:tE is the GST relative to the start of the week, as estimated by the receiver throughGST determination algorithmΔtUTC is computed as: ΔtUTC = ΔtLS + A0 + A1 * [tE - t0t + 604800*(WN - WNt)]BBBBBBBBBBBBBBBBBBCase b:Whenever the user's current time falls within the time span of DN + 3/4 to DN + 5/4, tUTC iscomputed according to Eq.
17:BB47HtUTC = W [modulo (86400 + ΔtLSF - ΔtLS)] secondsBBBBBEq. 17Bwhere:W = (tE - ΔtUTC - 43200) [Modulo 86400] + 43200 seconds andthe definition of tE and ΔtUTC are the same as specified in case aBBBBBBBBCase c:Whenever the effective time of the leap second event, as indicated by the WNLSF and DNvalues, is in the "past" (relative to the user's current time), tUTC is computed according to Eq.18:BBB478HtUTC = (tE - ΔtUTC) [modulo 86400] secondsBBBBBBEq.
18BwheretE has the same definition as in case a and bΔtUTC is computed according to Eq. 19:BBBB479HΔtUTC = ΔtLSF + A0 + A1 * (tE - t0t + 604800*(WN - WNt))BBBBBBBBBBBBBBEq. 19withA0: constant term (in seconds) of polynomial describing the offset between Galileo andTAI time scales at the time tEA1: rate of change (in seconds per second) of the offset between GST and TAI timescalesBBBBBB©, 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.0Draft023/05/2006Page73ΔtLS: offset due to the integer number of leap seconds between TAI and UTCt0t: time of validity of the UTC offset parametersWNt: UTC reference week numberWNLSF: week number for the leap second adjustment, namely Galileo week numbermodulo 256 to which the DN is referencedDN: day number for the leap second adjustment; “Day one” is the first day relative tothe end/start of week.
The range of the DN is one week and the accuracy is 1 day.Then it is coded on 3 bits.ΔtLSF: offset due to the introduction of a leap second at WNLSF and DNBBBBBBBBBBBBThe parameters for UTC conversion are defined according to the values stated in Table 59.480HParameterA0A1ΔtLSt0tWNtWNLSFDNΔtLSFBBBBBBBBBBBBBBDefinitionConstant term of polynomial1st order term of polynomialDelta time due to leap secondsReference time for UTC dataUTC reference Week NumberWeek Number of the Leap SecondDay Number of the Leap SecondDelta time due to leap secondPPGST-UTC Conversion Parameters - TotalBits3224888838Scalefactor2-302-5013600111 …71PPPP99Table 60: Parameters for the GST - UTC conversion©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p. 2-4.UnitsecondsSeconds/secSecondsSecondsWeeksWeeksDaysSecondsReference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page7410.1.2.7 GPS to Galileo System TimeThe difference between the Galileo and the GPS time scale is given by Eq.
20:481HΔtSystems = tGalileo - tGPS = A0G + A1G * [tGalileo - t0G + 604800*(WN - WNOG)] secondsBBBBBBBBBBBBBBBBEq. 20with:A0G: constant term of the offset Δtsystems [seconds]A1G: rate of change of the offset Δtsystems [seconds/second]t0G: reference time for GGTO data [seconds]tGalileo: GST time [seconds]tGPS: GPS time [seconds]WN: GST Week NumberWN0G: Week Number of GGTO referenceBBBBBBBBBBBBBBBBThe GPS/Galileo Time Offset Parameters is formatted according to the values stated in Table60.482HParameterA0GBBBitsBt0GBB162WN0GBBSecondsRate of change of the offset Δtsystems122-51Sec/secReference time for GGTO data83600SecondsWeek Number of GGTO reference61WeekPPBBBUnits-35Constant term of the polynomial describing the offsetΔtsystemsBA1GScale factorBTotal GST - GPS conversion parametersPP36Table 61: Parameters for the GPS time conversion10.1.3 Service parameters10.1.3.1 Satellite IDThe satellite Identification is coded with 6 bits and has the characteristics given in Table 61.483HParameterSVIDBBDefinitionSatellite IdentificationBits6Scale FactorN/AUnitDimensionlessValues1 … 64Table 62: Satellite ID10.1.3.2 Issue Of Data and Reference TimeThe Issue of Data (IOD) indicates the set (applicable issue) of data broadcasted by the satelliteto the user.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
