European GNSS (Galileo) open service (797926), страница 13
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IOD Values Mapping on Data TypeEach IOD has an associated reference time parameter disseminated within the batch.licNote: the broadcast group delay, ionospheric corrections, GST-UTC and GST-GPSconversion parameters, navigation data validity status and signal health statusare not identified by any issue of data value.5.1.9.3. Navigation Data Validity and Signal Health StatusrPubThe signal health status and data validity status refer to the transmitting satellite. Thesestatus flags are used as service performance level notification (e.g. notification of satellitenon availability).
The navigation data validity status transmitted on E5a, E5b and E1, iscoded on 1 bit, according to Table 69 and Table 70.DefinitionBitsScalefactorUnitE5aDVSE5a Data Validity Status1N/AdimensionlessFoParameterTable 69. Data Validity Satellite Status (transmitted on E5a)ParameterDefinitionBitsScalefactorUnitE5bDVSE5b Data Validity Status1N/AdimensionlessE1-BDVSE1-B Data Validity Status1N/AdimensionlessTable 70. Data Validity Satellite Status (transmitted on E5b and E1-B)The data validity status bit has the values shown in Table 71:48© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 2014Data Validity StatusDefinition0Navigation data valid1Working without guaranteeTable 71.
Data validity Status Bit ValuesThe E5a signal health status transmitted on E5a-I is coded on 2 bits according to Table 72DefinitionBitsScalefactorUnitE5aHSE5a Signal Health Status2N/AdimensionlesstionParameterTable 72. Signal Health Status for E5a (transmitted on E5a)The E5b and E1-B signal health status transmitted on E5b and E1-B are coded on 2 bitsaccording to Table 73.DefinitionE5bHSE5b Signal Health StatusE1-BHSE1-B Signal Health StatusScalefactorUnit2N/Adimensionless2N/AdimensionlessBitsltaAFCoTnParametersuTable 73.
Signal Health Status for E5b and E1 (transmitted on E5b and E1-B)The signal status bits have the values shown in Table 74.Signal Health StatusDefinitionSignal OK1Signal out of service2Signal will be out of service3Signal Component currently in TestDR05.1.9.4. ChecksumlicTable 74. Signal Health Status Bit ValuesrPubThe checksum, which employs a CRC technique, is used to detect the reception of corrupteddata. The checksum does not include the frame synchronisation pattern or the tail bit fieldssince these do not form part of the required message information. For the F/NAV and I/NAVdata, a CRC of 24 bits is generated from the generator polynomial G(X) described below.G(X) = (1 + X) P(X)Eq. 22P(X) is a primitive and irreducible polynomial given by the following equation.Eq.
23FoP(X) = X23 + X17 + X13 + X12 + X11 + X9 + X8 + X7 + X5 + X3 + 1The CRC is composed of a sequence of 24 parity bits pi; for any i from 1 to 24, pi is thecoefficient of X24-i in R(X) where:●● R(X) is the remainder of the binary polynomial algebra division of the polynomialm(X) X24 by G(X) and●● m(X)=m1Xk-1 +…+ mk-2X2 + mk-1X + mk with m1, m2,..., mk the sequence of k-bits informationto be protected by the CRC, and m1 as the MSB.© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 2014495.1.10.AlmanacThe almanac data is a reduced-precision subset of the clock and ephemeris parameters ofthe active satellites in orbit. The user receiver utilises the algorithm described in paragraph5.1.1 to compute the positions of the Galileo satellites.
All other parameters appearing inthe equations of Table 58, but not included in the content of the almanac, are set to zerofor satellite position determination.The Galileo almanac orbital parameters consist oftion●● Semi-major axis●● Eccentricity●● Inclination●● Longitude of the ascending node●● Argument of perigeeltaAFCoTn●● Mean anomalysuA reduced set of clock correction parameters is provided as well in the almanac for eachsatellite including the time of applicability toa of the almanac data. This almanac referencetime t0a is referenced to the almanac reference week (WNa). The WNa term consists of twobits which is a Modulo 4 binary representation of the GST week number.DRAdditionally, a predicted satellite health status is provided for each of these satellites,giving indications on the satellite’s signal components health and navigation data health.Finally, the IODa allows identifying without ambiguity an almanac batch.
The almanacparameters are transmitted according to the characteristics stated in Table 75.DefinitionBitsScalefactorUnitSVIDSatellite ID (1 constellation of 36 satellites)61dimensionlessΔ(A1/2)Difference with respect to the square root ofthe nominal semi-major axis (29 600 km)13*2-9meters1/2Eccentricity112-16dimensionlessInclination at reference time relative toi0 = 56°11*2-14semi-circles***Ω0Longitude of ascending node of orbital planeat weekly epoch****16*2-15semi-circles***●ΩRate of change of right ascension11*2-33semi-circles/s***ωArgument of perigee16*2-15semi-circles***M0Satellite mean anomaly at reference time16*2-15semi-circles***af0Satellite clock correction bias “truncated”16*2-19saf1Satellite clock correction linear “truncated”13*2-38s/sE5aHS**Satellite E5a signal health status2N/AdimensionlessE5bHS**Satellite E5b signal health status2N/AdimensionlessE1-BHS**Satellite E1-B signal health status2N/AdimensionlesslicParametereForPubδiTotal Satellite Almanac Size50131(F/NAV)133(I/NAV)© European Union 2014Document subject to terms of use and disclaimers p.
i-iiOS SIS ICD, Issue 1.2, dd.mm 2014ParameterDefinitionBitsScalefactorUnitIODaAlmanac Issue Of Data4N/Adimensionlesst0aAlmanac reference time10600sWNaAlmanac reference Week Number21weekTotal Almanac References Size16Table 75. Almanac ParametersParameters so indicated are two’s complement, with the sign bit (+or-) occupying the MSB.The F/NAV almanac transmitted on the E5a-I component contains the signal health status E5aHS.
TheI/NAV almanac transmitted on the E5b-I and E1-B components contains both signal health status E5bHSand E1-BHS.The two-bit health status is encoded as per Table 78.*** Note that the ‘semi-circle’ is not a SI unit but can be converted as: 1 semi-circle = π radian.**** More precisely, Ω0 is the longitude of ascending node of orbital plane at the weekly epoch propagatedto the reference time t0a at the rate of change of right ascension.ltaAFCoTn5.1.11.Signal – In – Space Accuracy (SISA)tion***suSignal – In – Space Accuracy (SISA) is a prediction of the minimum standard deviation(1-sigma) of the unbiased Gaussian distribution which overbounds the Signal – In – SpaceError (SISE) predictable distribution for all possible user locations within the satellitecoverage area.
When no accurate prediction is available (SISA = NAPA), this is an indicatorof a potential anomalous SIS.The SISA Index shall be encoded according to the values stated in the following table.SISA ValueDRSISA Index0.........490 cm to 49 cm with 1 cm resolution50.........7450 cm to 0.98 m with 2 cm resolution75.........991 m to 2 m with 4 cm resolution100....... 1252 m to 6 m with 16 cm resolutionlic126....... 254ub255SpareNo Accuracy Prediction Available (NAPA)Table 76. SISA Index ValuesrPThe Signal – In – Space Accuracy (SISA) shall be coded according to the values stated in thefollowing table.DefinitionBitsScale factorUnitsSISA(E1,E5a)SISA index for dual frequency E1-E5a8N/AdimensionlessSISA(E1,E5b)SISA index for dual frequency E1-E5b8N/AdimensionlessFoParameterTable 77.
SISA Parameters5.2. SAR RLM DataEach Return Link Message encapsulated in a SAR data page contains the following data:●● Beacon ID (60 bits):The Beacon ID is identical to the 60 bits (15 Hexadecimal characters) of the standardbeacon identification defined in the COSPAS – SARSAT T.001 document (Specificationfor Cospas – Sarsat 406MHz Distress Beacons). It uniquely identifies the beacon towhich the RLM is addressed.© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 201451●● Message code (4 bits):The Message Code defines the Return Link Service according to Table 78.RLMShort-RLMShort-RLMShort-RLMLong-RLMMessage Code (4 bits)Return Link Service0001Acknowledgement Service1111Test ServiceOther codesSpareAll codes to be definedSpareTable 78. SAR RLM Message Code ValuesMessageCode4tionReservedBit 79Bit 78Bit 77Bit 76Bit 75Bit 80Parity ParitySpareTable 79. SAR Short-RLM Data ValuesCombinations of Message Code [0001] (Acknowledgement Service) with other values of bits 65 – 66 arespare.
Refer to COSPAS – SARSAT T.001 document for the service description of the acknowledgementType 1.Bit numbers are counted after concatenating the four parts of Short-RLM data described in section4.3.7 “SAR Field Structure”. Bit 1 is received first, Bit 80 is received last.ForPThe Parameters field values for Long-RLM are currently not defined.52Bit 74Bit 731Bit 721Bit 711Bit 700Bit 691Bit 68su1Bit 67Bit 660ub**016lic*15 Hex Id 1Bit 65Test ServiceBit 64DRAcknowledgement15 Hex Id 0Service - Type 1*Bit 63Bit 61Bit 60toBit 1**60Short-RLM Parameters FieldBit 62Beacon IdReturn LinkServiceltaAFCoTn●● Parameters field (16 bits for the short RLM, 96 bits for the long RLM):The Parameters field provides the information related to the specific Return LinkService identified by the “Message Code”.The last bit of the Parameters field, i.e.
bit 16 of the Short-RLM Parameters field andbit 96 of the Long-RLM Parameters field, is a SAR RLM data parity bit. This parity bitshall ensure that the total number of ones (1) in the fields “Beacon ID”, “MessageCode” and “Parameters”, (including spare bits), is even.The Parameters field values for Return Link Services based on Short-RLM are definedin Table 79:© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 20146.
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