Galileo OS SIS ICD (797928), страница 9
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2-4.Reference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page48G1InputDDDDDDG2Figure 14: Convolutional coding schemeDecoding can be easily implemented using a standard Viterbi decoder.9.1.4.2 InterleavingFor each message type, the FEC encoded page is interleaved in block interleaver with ncolumns (where data is written) and k rows (where data is read), as shown in Table 26. Theinterleaving parameters (n and k) are specific to each type of message.438HMessage TypeParameterBlock interleaver size (Symbols)Block interleaver dimensions (n columns x k rows)F/NAV48861 x 8I/NAV24030 x 8Table 27: Interleaving parameters9.1.5 Page processing sequence at receptionIn order to retrieve the useful data from each page of message, the user receiver performs thefollowing tasks:a) Detects or confirms synchronisation patternb) De-interleaves page symbols (as presented in Table 28)439Hc) Decodes page symbols into data bits thanks to the Viterbi decoding algorithm (aspresented in Par.
9.1.4.1)40Hd) Decrypts data where applicablee) Calculates and compares received checksumf) Extracts information from page 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.0Draft023/05/2006Page499.1.6 Frame TimingTime stamps are inserted in the navigation message at regular intervals, by the broadcastingsatellite, to identify absolute GST in multiples of the shortest page period of 1 second.
Theexact timing of the message frame boundaries is used to identify fractional GST timing (lessthan one frame period). This is measured relative to the leading edge of the first chip of thefirst code sequence of the first frame symbol.The transmission timing of the navigation message provided through the TOW issynchronised to each satellite's version of Galileo System Time (GST).The epoch denoted by each TOW refers to the preceding frame boundary.9.2F/NAV MESSAGE DESCRIPTION9.2.1 General description of the F/NAV messageThe F/NAV message structure is presented in Figure 15, where the duration of each entity isindicated:41HMessageFrame600 seconds1 Frame = 12 Sub-FramesSub-Frame50 seconds1 Sub Frame = 5 PagesPage10 secondsFigure 15: F/NAV Message Structure9.2.2 F/NAV Page LayoutThe page layout for the F/NAV E5a-I Channel is according to Table 27, where the symbolsallocation and bits allocation are shown separately.42H©, 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.0Draft023/05/2006Page50SyncSymbolsTotal[symbols]12488500WordPage typeNavigation DataCRC620824TailTotal [bits]6244Table 28: F/NAV E5a-I page layout9.2.2.1 Tail bitsThe tail bits field consists of 6 zero-value bits enabling completion of the FEC decoding ofeach page’s information content in the user receiver.9.2.2.2 F/NAV WordThe useful data are contained in the F/NAV word composed of:- A type field (6 bits) enabling to identify the word content, as defined in Par. 9.2.4- A navigation data field (208 bits), whose structure is presented in Par. 9.2.4)- A CRC (24 bits) to detect potential bit errors, according to Par. 10.1.3.4.43H4H45H9.2.3 F/NAV Frame LayoutThe F/NAV E5a-I message data packet transmission sequence is according to Table 28, wherea whole frame is shown.
Note that the parameter k is defined in Table 29.A frame is composed of 12 sub-frames and lasts 600 seconds; each sub-frame is composed of5 pages and lasts 50 seconds; each page lasts 10 seconds (see Figure 15).46H47H©, 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.0Draft023/05/2006Page51raSubframe 8Subframe 7Subframe 6Subframe 5Subframe 4Subframe 3Subframe 2Subframe 1Page Page contenttype1SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW5Almanac for satellite k and almanac for satellite (k+1) part 11SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW6Almanac for satellite (k+1) part 2 and almanac for satellite (k+2)1SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW5Almanac for satellite (k+3) and almanac for satellite (k+4) part 11SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW6Almanac for satellite (k+4) part 2 and almanac for satellite (k+5)1SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW5Almanac for satellite (k+6) and almanac for satellite (k+7) part 11SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW6Almanac for satellite (k+7) part 2 and almanac for satellite (k+8)1SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW5Almanac for satellite (k+9) and almanac for satellite (k+10) part 11SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW6Almanac for satellite (k+10) part 2 and almanac for satellite (k+11)1SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p.
2-4.Subframe 10Subframe 11Subframe 12Reference:Issue:Revision:Date:GAL OS SIS ICD/D.0Draft023/05/2006Page522Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW5Almanac for satellite (k+12) and almanac for satellite (k+13) part 11SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW6Almanac for satellite (k+13) part 2 and almanac for satellite (k+14)1SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW5Almanac for satellite (k+15) and almanac for satellite (k+16) part 11SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GST and Data validity status2Ephemeris (1/3) and GST3Ephemeris (2/3) and GST4Ephemeris (3/3), GST-UTC conversion, GST-GPS Conversion and TOW6Almanac for satellite (k+16) part 2 and almanac for satellite (k+17)Table 29: F/NAV E5a-I message data packet transmission sequenceNote that the odd numbered sub-frames contain the page type 5 and the even numbered subframes contain the page type 6.
This allows the transmission of the almanacs for threesatellites within two successive sub-frames (100 seconds), thus the almanacs of the entireGalileo constellation (nominal 30 satellites, almanac capacity of 36 satellites) within 20minutes.©, 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.0Draft023/05/2006Page53The start of transmission of pages at each satellite is synchronized with the GST in such away that the sub-frame ID is equal to (SVID +Δt/50) modulo 12, according to Table 29.48HSVt0BBt0+50BBt0+100BBt0+150BBt0+200BBt0+250BBt0+300BBt0+350BBt0+400BBt0+450BBt0+500BBt0+550BBt0+600BBt0+650BBt0+700BBt0+750BBt0+800BBt0+850BBt0+900BBt0+950BBT0+1000BBSVSVSVSVSVSVSVSVSVSVSV1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18-19-20-21-22-23-24-252627282930313233343536123456789101112k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19234567891011121k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19345678910111212k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19456789101112123k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19567891011121234k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19678910111212345k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19789101112123456k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19891011121234567k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19910111212345678k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19101112123456789k=1k=1k=1k=1k=1k=1k=19k=19k=19k=1k=19k=19111212345678910k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19121234567891011k=1k=1k=1k=1k=1k=1k=19k=19k=19k=19k=19k=19123456789101112k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1234567891011121k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1345678910111212k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1456789101112123k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1567891011121234k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1678910111212345k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1789101112123456k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1891011121234567k=19k=19k=19k=19k=19k=19k=1k=1k=1k=1k=1k=1910111212345678©, 2006, European Space Agency / Galileo Joint UndertakingDocument subject to terms of use and disclaimers p.
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