European GNSS (Galileo) open service (797926), страница 8
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Secondary Code Sequences (Part 2)rP3.5.2. Secondary Codes AssignmentFoThe assignment of the secondary codes of paragraph 3.5.1 to the signal components isaccording to Table 21. For the 4, 20 and 25 bit secondary codes the same code is usedfor all associated primary codes. For the 100 bit codes, an independent secondary code isassigned for each primary code.ComponentSecondary Code AssignmentE5a-ICS201E5a-QCS1001-50E5b-ICS41E5b-QCS10051-100E6-BN/A© European Union 2014Document subject to terms of use and disclaimers p.
i-iiOS SIS ICD, Issue 1.2, dd.mm 201421ComponentSecondary Code AssignmentE6-CCS1001-50E1-BN/AE1-CCS251Table 21. Secondary Code Assignment3.6.1. Primary code assignment to satellitestion3.6. Code Assignments to SatellitesThe E5a-I, E5a-Q, E5b-I, E5b-Q, primary codes (defined in Section 3.4.1) and E1-B, E1-Cprimary codes (defined in Annex C of the electronic version of this ICD) will be allocated tothe space vehicle IDs (SVID) as follows:●●3.6.2. Secondary code assignment to satellitesltaAFCoTnTo SVID n (with n = 1 to 36) are assigned the corresponding E5a-I, E5a-Q, E5b-I,E5b-Q, E1-B and E1-C primary code number n.●●suThe E5a-I, E5a-Q, E5b-I, E5b-Q, and E1-C secondary codes (defined in Section 3.5.1) areallocated to the space vehicle IDs (SVID) as follows:The following secondary codes are assigned according to SVID n (with n = 1 to 36):○○DRsecondary code CS100n for the signal component E5a-Q (i.e.
CS1001 to SVID 1)○○●●secondary code CS100(n+50) for the signal component E5b-Q (i.e. CS10051 toSVID 1)The following secondary codes are assigned to all SVIDs (1 to 36):secondary code CS201 for the signal component E5a-I (same for all SVIDs)○○secondary code CS41 for the signal component E5b-I (same for all SVIDs)○○secondary code CS251 for the signal component E1-C (same for all SVIDs)ForPublic○○22© European Union 2014Document subject to terms of use and disclaimers p.
i-iiOS SIS ICD, Issue 1.2, dd.mm 20144. Galileo Message Structure4.1. General Message Format Specification4.1.1. General Navigation Message ContenttionThe Galileo signal-in-space data channels transmit different message types according tothe general contents identified in Table 22 below. The F/NAV types of message correspondto the OS and the I/NAV types of message correspond to both OS and CS.ServicesComponentF/NAVOSE5a-II/NAVOS/CSC/NAVCSltaAFCoTnMessage TypeE5b-I and E1-BE6-BTable 22. Message Allocation and General Data Content4.1.2. General Navigation Message StructuresuNote: The C/NAV message format is not the subject of this SIS ICD.DRThe complete navigation message data are transmitted on each data component as asequence of frames.
A frame is composed of several sub-frames, and a sub-frame in turnis composed of several pages. The page is the basic structure for building the navigationmessage.rPublicFor all message types, only the message pages include a ‘type’ marker to identify thecontent of each page received by the user. There is no management data transmittedwithin the navigation message to indicate subframe and frame structures, and indeedthese higher level structures should be considered as the typical flow of pages reflectingthe current Galileo navigation message design, which may evolve together with futureevolutions of Galileo. This evolution may also involve the inclusion of additional new pagetypes beyond the types defined in this version of the Galileo OS SIS ICD.
A user receiver isexpected to be able to recognize page types and to react properly and in a well controlledmanner to page types unknown to its software as well as to variations in the order ofreceived pages.4.1.3. Bit and Byte Ordering CriteriaFoAll data values are encoded using the following bit and byte ordering criteria:●● For numbering, the most significant bit/byte is numbered as bit/byte 0●● For bit/byte ordering, the most significant bit/byte is transmitted first4.1.4.
FEC Coding and Interleaving Parameters4.1.4.1. FEC EncodingThe convolutional encoding for all data pages on all signal components is performedaccording to the parameters given in Table 23.© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 201423ValueCoding Rate½Coding SchemeConvolutionalConstraint Length7Generator PolynomialsG1=171oG2=133oEncoding SequenceG1 then G2Table 23. Data Coding ParameterstionCode ParameterltaAFCoTnFigure 13 depicts this convolutional coding scheme.
Decoding can be implemented usinga standard Viterbi decoder.suFigure 13. Convolutional Coding SchemeNote: Figure 13 describes an encoder where the second branch is inverted at the end.4.1.4.2. InterleavingDRFor each message type, the FEC encoded page is interleaved using a block interleaver withn columns (where data is written) and k rows (where data is read), as shown in Table 24.ParametersMessage TypeI/NAVBlock interleaver size (Symbols)488240Block interleaver dimensions (n columns x k rows)61 x 830 x 8licF/NAVubTable 24. Interleaving Parameters4.1.5.
Frame and Page TimingForPTime stamps are inserted in the navigation message at regular intervals by the broadcastingsatellite to identify absolute Galileo System Time (GST). The exact timing of the pageframe boundaries is used to identify fractional GST timing (less than one frame period).This is measured relative to the leading edge of the first chip of the first code sequenceof the first page symbol of the page containing the TOW.
The transmission timing of thenavigation message provided through the TOW is synchronised to each satellite’s versionof GST.4.2. F/NAV Message Description4.2.1. General Description of the F/NAV MessageThe F/NAV message structure is presented in Figure 14, where the duration of each entityis indicated.24© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 20144.2.2. F/NAV Page LayouttionFigure 14. F/NAV Message Structure488F/NAV WordDRPage type6lta12F/NAV SymbolsTotal (symb)suSync.AFCoTnThe page layout for the F/NAV message type is according to Table 25 where the symbolsallocation and bits allocation are shown separately. The different fields composing thislayout are defined in the sections below.Navigation DataCRC20824500TailTotal (bits)6244Table 25. F/NAV Page Layout4.2.2.1.
Synchronisation PatternlicThe synchronization pattern allows the receiver to achieve synchronisation to the pageboundary.4.2.2.2. Tail BitsubNote: The synchronisation pattern is not encoded. The F/NAV synchronisation pattern is101101110000rPThe tail bits field consists of 6 zero-value bits enabling completion of the FEC decoding ofeach page’s information content in the user receiver.4.2.2.3.
F/NAV WordThe useful data are contained in the F/NAV word composed ofFo●● A page type field (6 bits) enabling to identify the page content as defined in paragraph4.2.4●● A navigation data field (208 bits) whose structure is presented in paragraph 4.2.4●● A CRC (24 bits) to detect potential bit errors, according to paragraph 5.1.9.4.
The CRCis computed on the Page Type and Navigation Data fields.4.2.3. F/NAV Frame LayoutThe F/NAV E5a-I message data packet transmission sequence is according to Table 26where a whole frame is shown. Note that the odd numbered sub-frames contain the© European Union 2014Document subject to terms of use and disclaimers p. i-iiOS SIS ICD, Issue 1.2, ?????????? 201425page type 5 and the even numbered sub-frames contain the page type 6.
This allowsthe transmission of the almanacs for three satellites within two successive sub-frames(100 seconds). The parameter k is transparent for the user. It is set by the Galileo systemfor each of the active satellites, such as to improve almanac transport time by exploitingsource diversity.Page Content2Ephemeris (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 1ltationSVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GSTand Data validity statusAFCoTn1SVID, clock correction, SISA, Ionospheric correction, BGD, Signal health status, GSTand 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, GSTand Data validity statussu1Ephemeris (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, GSTand 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, GSTand Data validity status2Ephemeris (1/3) and GSTublic2Subframe 6FoSubframe 5rPSubframe 4Subframe 3DRSubframe 2Subframe 1PageType263Ephemeris (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, GSTand 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)© European Union 2014Document subject to terms of use and disclaimers p.
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