European GNSS (Galileo) open service (797926), страница 11
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The content of theSAR data is provided in paragraph 5.2.222212022Table 54. SAR Short RLM38© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 201411Parameters1Short RLM20SAR RLM dataStart bit = 01Short RLM1Part (4/4)SAR RLM dataStart bit = 0Beacon ID(1/3)20Short RLM1SAR RLM dataStart bit = 0Short RLM1FoStart bit = 1SAR RLM dataPart (3/4)MessagecodePart (2/4)Beacon ID(3/3)Part (1/4)Beacon ID(2/3)rP●● Short RLM41622●● Long RLM222222Part (5/8)Part (6/8)Part (7/8)Message codeParameters(1/5)141622Part (8/8)120Long RLM1SAR RLM dataltaParameters(4/5)su22DR2220Long RLM1Start bit = 01Parameters(3/5)Long RLM201SAR RLM dataAFCoTn1SAR RLM dataStart bit = 0Long RLM1Parameters(2/5)Start bit = 0SAR RLM dataLong RLM20tion1Start bit = 01SAR RLM dataStart bit = 020Long RLM1Beacon ID(2/3)1Part (4/8)SAR RLM dataStart bit = 020Long RLM1SAR RLM dataStart bit = 0Long RLM1Beacon ID(1/3)Start bit = 1SAR RLM dataPart (3/8)1122Parameters(5/5)Part (2/8)Beacon ID(3/3)Part (1/8)2022Table 55.
SAR Long RLMSpare SAR DataIn case no valid SAR data is to be transmitted, the satellite generates the spare SAR datafield according to Table 56.licSAR DataTotalSpare(bits)12122ubStart Bit = 1Table 56. Spare SAR DataForPA SAR receiver will use the sequence of start bits (and only these) to identify SAR dataparts belonging to SAR RLMs. If the start bit of the current data part is equal to zero, thenthe data part contains SAR relevant data.
If the start bit of the current data part is equal toone, the data part contains SAR relevant data only if the start bit of the next (immediatelysubsequent) data part is equal to zero.© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 2014395. Message Data ContentsThis section describes the data items above mentioned. Semantics, formats and othercharacteristics are provided for all items to be transmitted inside frames.tion5.1.
Navigation DataltaAFCoTnThe navigation data contain all the parameters required for the user to compute a completeposition, velocity and time (PVT) solution. They are stored on board each satellite with avalidity duration and broadcast world-wide by all the satellites of the Galileo constellation.The 4 types of data needed to perform positioning are:●● Ephemeris parameters, which are needed to indicate the position of the satellite to theuser receiver●● Time and clock correction parameters which are needed to compute pseudo-rangesu●● Service parameters which are needed to identify the set of navigation data, satellites,and indicators of the signal healthDR●● Almanac parameters, which are needed to indicate the position of all the satellites inthe constellation with a reduced accuracy5.1.1.
EphemerisThe ephemeris for each Galileo satellite is composed of 16 parameters, which are:●● 6 Keplerian parameterslic●● 6 harmonic coefficients●● 1 orbit inclination rate parameterub●● 1 RAAN rate parameter●● 1 mean motion correction parameter, andrP●● 1 reference time parameter t0e for the ephemeris data setThe ephemeris for each Galileo satellite is according to the characteristics stated in Table57.FoParameterBitsScalefactorUnitM0Mean anomaly at reference time32*2-31semi-circles**∆nMean motion difference from computed value16*2-43semi-circles/s**Eccentricity322-33N/AA1/2Square root of the semi-major axis322-19meter1/2Ω0Longitude of ascending node of orbital plane at 32*weekly epoch***2-31semi-circles**i0Inclination angle at reference time32*2-31semi-circles**ωArgument of perigee32*2-31semi-circles**e40Definition© European Union 2014Document subject to terms of use and disclaimers p.
i-iiOS SIS ICD, Issue 1.2, dd.mm 2014BitsScalefactorUnitRate of change of right ascension24*2-43semi-circles/s**Rate of change of inclination angle14*2-43semi-circles/s**CucAmplitude of the cosine harmonic correctionterm to the argument of latitude16*2-29radiansCusAmplitude of the sine harmonic correction term 16*to the argument of latitude2-29radiansCrcAmplitude of the cosine harmonic correctionterm to the orbit radius2-5metersCrsAmplitude of the sine harmonic correction term 16*to the orbit radiusCicAmplitude of the cosine harmonic correctionterm to the angle of inclination●Ω●t0e16*Amplitude of the sine harmonic correction term 16*to the angle of inclinationEphemeris reference timemeters2-29radians2-29radians1460seconds356suTotal Ephemeris Size2-5ltaCis16*AFCoTniDefinitiontionParameterTable 57.
Ephemeris ParametersDR*Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB.** Note that the ‘semi-circle’ is not a SI unit but can be converted as: 1 semi-circle = π rad.*** More precisely, Ω0 is the longitude of ascending node of orbital plane at the weekly epoch propagatedto the reference time t0e at the rate of change of right ascension.A single ephemeris is applicable to all signals of a specific satellite. The ephemeris iscomputed with respect to the apparent CoP common to every frequency.licThe user can compute the ECEF coordinates of the SV’s antenna phase centre position atGST time t utilizing the equations shown in Table 58.Descriptionπ = 3.1415926535898Ratio of a circle’s circumference to its diameterubConstantGeocentric gravitational constantωE = 7.2921151467 × 10-5 rad/sMean angular velocity of the Earthc = 299792458 m/sSpeed of lightComputationDescriptionA=(A1/2)2Semi-major axisForPμ = 3.986004418 × 1014 m3/s2n0 =μ√A3Computed mean motion (rad/s)tk = t-t0e*Time from ephemeris reference epochn = n0+ΔnCorrected mean motionM = M0+ntkMean anomalyM = E– e sin(E)Kepler’s Equation for Eccentric Anomaly E(may be solved by iteration)© European Union 2014Document subject to terms of use and disclaimers p.
i-iiOS SIS ICD, Issue 1.2, dd.mm 201441ComputationDescription sin ν cosν 1 − e 2 sin E (1 − e cos E ) = tan −1 (cos E − e ) (1 − e cos E ) ν = tan −1 True AnomalyArgument of Latitudeδu = Cussin2Φ + Cuccos2ΦArgument of Latitude Correctionδr = Crssin2Φ + Crccos2ΦRadius Correctionδi = Cissin2Φ + Ciccos2ΦInclination Correctionu = Φ + δuCorrected Argument of Latituder = A(1-e cos E) + δrCorrected Radius•= δii0 ++δi•i +i = i0i +tk i tkx' = r cos uy' = r sin• uΩ = Ω•0 + Ω - ωE tk - ωEt0eltaCorrected InclinationPosition in orbital planeΩ = Ω0 + Ω - ωE tk - ωEt0eCorrected longitude of ascending nodex = x'cos(Ω) - y'cos(i)sin(Ω)y = x'sin(Ω) + y'cos(i)cos(Ω)z = y'sin(i)GTRF coordinates of the SV antenna phase centerposition at time tsu*AFCoTn}tionΦ=v+ωTable 58. User Algorithm for Ephemeris Determinationt is Galileo System Time (see e.g.
paragraph 5.1.2). Furthermore, tk is the actual total time differencebetween the time t and the epoch time t0e (t0a for the almanacs) and it accounts for beginning or endDRof week crossovers.5.1.2. Galileo System Time (GST)The GST is given as 32-bit binary number composed of two parameters as follows:ublic●● The Week Number is an integer counter that gives the sequential week number fromthe GST start epoch. This parameter is represented with 12 bits, which covers 4096weeks (about 78 years). Then the counter is reset to zero to cover an additional periodmodulo 4096.rP●● 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 604799seconds and is reset to zero at the end of each week.The GST parameters are transmitted according to the characteristics stated in Table 59.DefinitionBitsScalefactorUnitWNWeek Number121weekTOWTime of Week201sFoParameterTotal Galileo System Time Size32Table 59.
GST ParametersThe GST start epoch is defined as 13 seconds before midnight between 21st August and22nd August 1999, i.e. GST was equal to 13 seconds at 22-08-1999 00:00:00 UTC.As GST is a continuous time scale, and UTC is corrected periodically with an integer numberof leap seconds, the Galileo navigation message contains all necessary parameters toconvert between GST and UTC.42© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 2014The epoch denoted in the navigation messages by TOW and WN will be measured relativeto the leading edge of the first chip of the first code sequence of the first page symbol. Thetransmission timing of the navigation message provided through the TOW is synchronisedto each satellite’s version of Galileo System Time (GST).5.1.3.
Clock Correction ParametersThe clock correction parameters are transmitted according to the values stated in Table60.Bitst0cClock correction data reference Time of Week14af0SV clock bias correction coefficient31*af1SV clock drift correction coefficient21*af2SV clock drift rate correction coefficient6*ScalefactorUnit60s2-34s2-46s/s2-59s/s2ltationDefinitionAFCoTnParameterTotal Clock Correction Size72Table 60. Galileo Clock Correction ParametersParameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB.su*Each Galileo satellite broadcasts its own clock correction data for all signals through therelevant signal, according to Table 61.Clock ModelX=(f1,f2)Satellite TimeCorrection ModelParametersServicesF/Nav(E1,E5a)af0 (E1,E5a)af1 (E1,E5a)af2 (E1,E5a)t0C (E1,E5a)Dual-Frequency (E1,E5a)Single-frequency E5aI/NAV(E1,E5b)af0 (E1,E5b)af1 (E1,E5b)af2 (E1,E5b)t0C (E1,E5b)Dual-Frequency (E1,E5b)Single-frequency E5bSingle-frequency E1ublicDRMessageTypeTable 61.
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