ICD Beidou (version 2.0) (797932), страница 8

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The effective range ofdτi is between 0 to 63.625 meters. IGP is not monitored when the dτi is111111110 (=63.750meters) and vertical ionosphere delay is not available when73BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Officethe dτi is 111111111 (=63.875meters).Making use of the ionospheric correction at grid points, the users computethe ionospheric correction for the intersection point of ionosphere and directionfrom user to observed satellite by interpolation and add it to the observedpseudo-range. The reference altitude of ionosphere is 375 km.5.3.3.8.2 Grid Ionospheric Vertical Error Index (GIVEI)The grid ionosphere vertical error (GIVE) describes the delay correctionaccuracy at ionosphere grid points and is indicated with GIVEI.

See Table 5-25for the relationship between GIVEI and GIVE.Table 5-25GIVEI definitionsGIVEIGIVE (meters, 99.9%)00.310.620.931.241.551.862.172.482.793.0103.6114.5126.0139.01415.01545.074BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office5.3.3.8.3 Suggestions on User Grid Ionospheric Correction AlgorithmThe user can select effective data of the grid points adjacent to or nearbythe observed intersection point with dτi and GIVEI to design the model andcompute the delay correction for ionospherc pierce point (IPP) by interpolation.The guiding fitting algorithm for user grid ionospheric correction is given asfollows:34IPP1Fig 5-192User IPP and Grid PointsFig 5-19 illustrates the user IPP and its surrounding grid points.

IPP,represented with geographic latitudes and longitudes as ( p ,  p ), is thegeographic location where the line-of-sight between the user and the satelliteintersects with the ionospheric layer. The positions of the four surrounding gridpoints are represented with (  i ,  i , i=1~4) and the vertical ionospheric delays onthe grid points are represented with VTECi(i=1~4) respectively. And ωi(i=1~4)shows the distance weight between IPP and the four grid points.As long as there are at least three grid points surrounding the user IPP areavailable and effective, the IPP ionospheric delay can be calculated from thevertical ionospheric delay of these effective grid points through the bilinearinterpolation algorithm.4Ionodelay p i 1i VTEC i4i 1Where x p  p  1 2  1i， yp  p  1 4  1，1  (1  x p )  (1  y p ) ， 2  x p  (1  y p ) ， 3  x p  y p ， 4  (1  x p )  y p75BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation OfficeIf any grid point of this observation epoch is marked as ineffective, itsweight is zero.For B2I, users need to multiply a factor k(f) to calculate the gridionospheric correction, and its value is as follows:f 2  1561.098 k(f)  12  f 2  1207.140 2Where, f1 refers to the nominal carrier frequency of B1I, f2 refers to thenominal carrier frequency of B2I, and the unit is MHz.76BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office6 AcronymsBDSBeiDou Navigation Satellite SystemBDTBeiDou Navigation Satellite System Timebpsbits per secondCDMACode Division Multiple AccessCGCS2000China Geodetic Coordinate System 2000dBWDecibel with respect to 1 wattGEOGeostationary Earth OrbitGIVEGrid point Ionospheric Vertical delay ErrorGIVEIGrid point Ionospheric Vertical delay Error IndexGLONASSGLObal Navigation Satellite SystemGPSGlobal Positioning SystemICDInterface Control DocumentIDIdentificationIERSInternational Earth Rotation and Reference Systems ServiceIGPIonospheric Grid PointIGSOInclined Geosynchronous Satellite OrbitAODCAge of Data, ClockAODEAge of Data, EphemerisIPPIonospheric Pierce PointIRMIERS Reference MeridianIRPIERS Reference PoleMcpsMega chips per secondMEOMedium Earth OrbitMHzMegahertzN/ANot ApplicableNAVNavigationMSBMost Significant BitNTSCNational Time Service CenterQPSKQuadrature Phase Shift Keying77BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation OfficeRHCPRight-Handed Circularly PolarizedRURARegional User Range AccuracyRURAIRegional User Range Accuracy IndexSOWSeconds of WeekSVSpace VehicleUDREUser Differential Range ErrorUDREIUser Differential Range Error IndexURAUser Range AccuracyUTCCoordinated Universal TimeWNWeek Number78BDS-SIS-ICD-2.02013-12.

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