IS-GPS-200F (811524), страница 31
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Words three through ten of each page contain six parity bits as theirLSBs; in addition, two non-information bearing bits are provided as bits 23 and 24 of word ten in each page forparity computation purposes. The data contained in the remaining bits of words three through ten of the variouspages in subframes 4 and 5 are described in the following subparagraphs.A brief summary of the various data contained in each page of subframes 4 and 5 is as follows:a. Subframe 4:· Pages 1, 6, 11, 16 and 21:(reserved);· Pages 2, 3, 4, 5, 7, 8, and 9:· Page 10:almanac data for SV ID 89 through 95 (PRN 57 through 63) respectively;(reserved);· Pages 12, 19, 20, 22, 23 and 24:· Page 13:(reserved);NMCT;· Pages 14 and 15:reserved for system use;· Page 17:special messages;· Page 18:ionospheric and UTC data;204IS-GPS-200F21 Sep 2011· Page 25:A-S flags/SV configurations for 31 SVs, plus SV health for SV ID 89 through 95 (PRN 57through 63).b.
Subframe 5:· Pages 1 through 24:· Page 25:almanac data for SV ID 65 through 88 (PRN 33 through 56);SV health data for SV ID 65 through 88 (PRN 33 through 56), the almanac reference time, thealmanac reference week number.40.3.3.5.1.1 Data ID and SV ID. The two MSBs of word three in each page shall contain the data ID. Data IDnumber two (denoted by binary code 01) denotes the LNAV data structure of D(t) which is described in thisAppendix.
Future data IDs will be defined as necessary.As shown in Table 40-V, the data ID is utilized to provide one of two indications: (a) for those pages which areassigned to contain the almanac data of one specific SV, the data ID defines the data structure utilized by that SVwhose almanac data are contained in that page; and (b) for all other pages, the data ID denotes the data structure ofthe transmitting SV.The six LSBs of the SV ID are given by bits three through eight of word three in each page as shown in Table 40-V.Specific IDs are reserved for each page of subframes 4 and 5. The SV IDs are utilized in two different ways: (a) forthose pages which contain the almanac data of a given SV, the SV ID is equal to 32 plus the number that is assignedto the PRN code phase of that SV (reference Tables 3-Ia and 3-Ib), and (b) for all other pages the SV ID assigned inaccordance with Table 40-V serves as the "page ID".
IDs 65 through 95 are assigned to those pages which containthe almanac data of specific SVs (pages 1-24 of subframe 5 and pages 2-5 and 7-9 of subframe 4). The "0" ID(binary all zeros) is assigned to indicate a dummy SV, while IDs 115 through 127 are utilized for pages containingother than almanac data of a specific SV. IDs 116 through 126 have the same data as LNAV-L IDs 52 through 62.ID 115 is the LNAV-U analog of ID 51 in LNAV-L, while ID 127 is the LNAV-U analog of ID 63 in LNAV-L.Pages which carry the same SV ID (e.g., in subframe 4, pages 1, 6, 11, 16 and 21 carry an ID of 121, while pages 12and 24 are designated by an ID of 126) may not be considered to contain identical data.
The data in the pages withthe same SV ID can be different. Pages 1, 6, 11, 16 and 21 reference Appendix II. Pages 12, 19, 20, 22, 23 and 24reference Appendix II. Pages 14 and 15: (Reference Appendix II)205IS-GPS-200F21 Sep 2011Table 40-V.Data IDs and SV IDs in Subframes 4 and 5Subframe 4PageData IDSubframe 5SV ID*Data ID(Note 4)12345678910111213141516171819202122232425Note(2)Note(1)Note(1)Note(1)Note(1)Note(2)Note(1)Note(1)Note(1)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)Note(2)121899091921219394950121126116117118121119120122 Note(3)123 Note(3)121124 Note(3)125 Note(3)126127SV ID*(Note 4)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(1)Note(2)656667686970717273747576777879808182838485868788115* Use "0" to indicate "dummy" SV.
When using "0" to indicate dummy SV, use the dataID of the transmitting SV.Note 1:Data ID of that SV whose SV ID appears in that page.Note 2:Data ID of transmitting SV.Note 3:SV ID may vary (except for IIR/IIR-M/IIF / and GPS III SVs).Note 4:For almanac data pages, the SV ID relationship to PRN ID is defined inTable 3-Ia and Table 3-Ib206IS-GPS-200F21 Sep 201140.3.3.5.1.2 Almanac Data. Pages 1 through 24 of subframe 5, as well as pages 2 through 5 and 7 through 9 ofsubframe 4 contain the almanac data and a SV health word for up to 31 SVs (the health word is discussed inparagraph 40.3.3.5.1.3). The almanac data are a reduced-precision subset of the clock and ephemeris parameters.The data occupy all bits of words three through ten of each page except the eight MSBs of word three (data ID andSV ID), bits 17 through 24 of word five (SV health), and the 50 bits devoted to parity.
The number of bits, the scalefactor (LSB), the range, and the units of the almanac parameters are given in Table 20-VI. The algorithms and othermaterial related to the use of the almanac data are given in paragraph 40.3.3.5.2.The almanac message for any dummy SVs shall contain alternating ones and zeros with valid parity.The almanac parameters shall be updated by the CS at least once every 6 days while the CS is able to upload theSVs. If the CS is unable to upload the SVs, the accuracy of the almanac parameters transmitted by the SVs willdegrade over time.For Block IIA SVs, three sets of almanac shall be used to span at least 60 days.
The first and second sets will betransmitted for up to six days each; the third set is intended to be transmitted for the remainder of the 60 daysminimum, but the actual duration of transmission will depend on the individual SV's capability to retain data inmemory. All three sets are based on six-day curve fits that correspond to the first six days of the transmissioninterval. For Block IIR/IIR-M, IIF and GPS III SVs, multiple sets of almanac parameters shall be uploaded to spanat least 60 days.40.3.3.5.1.3 SV Health. Subframes 4 and 5 contain two types of SV health data: (a) each of the 31 pages whichcontain the clock/ephemeris related almanac data provide an eight-bit SV health status word regarding the SV whosealmanac data they carry, and (b) the 25th page of subframe 4 and of subframe 5 jointly contain six-bit health statusdata for up to 31 SVs.The three MSBs of the eight-bit health words indicate health of the LNAV data in accordance with the code given inTable 20-VII.
The six-bit words provide a one-bit summary of the LNAV data's health status in the MSB position inaccordance with paragraph 40.3.3.3.1.4. The five LSBs of both the eight-bit and the six-bit words provide the healthstatus of the SV's signal components in accordance with the code given in Table 20-VIII. A special meaning isassigned, however, to the "6 ones" combination of the six-bit health words in the 25th page of subframes 4 and 5: itindicates that "the SV which has that ID is not available and there may be no data regarding that SV in that page ofsubframes 4 and 5 that is assigned to normally contain the almanac data of that SV" (NOTE: this special meaningapplies to the 25th page of subframes 4 and 5 only). The health indication shall be given relative to the "asdesigned" capabilities of each SV (as designated by the configuration code -- see paragraph 40.3.3.5.1.4).Accordingly, any SV which does not have a certain capability will be indicated as "healthy" if the lack of thiscapability is inherent in its design or it has been configured into a mode which is normal from a user standpoint anddoes not require that capability.207IS-GPS-200F21 Sep 2011Additional SV health data are given in subframe 1.
The data given in subframes 1, 4, and 5 of the other SVs maydiffer from that shown in subframes 4 and/or 5 since the latter may be updated at a different time.The eight-bit health status words shall occupy bits 17 through 24 of word five in those 31 pages which containalmanac data for individual SVs. The six-bit health status words shall occupy the 24 MSBs of words four throughnine in page 25 of subframe 5 plus bits 19 through 24 of word 8, the 24 MSBs of word 9, and the 12 MSBs of word10 in page 25 of subframe 4.The predicted health data will be updated at the time of upload when a new almanac has been built by the CS.
Thetransmitted health data may not correspond to the actual health of the transmitting SV or other SVs in theconstellation.40.3.3.5.1.4 Anti-Spoof (A-S) Flags and SV Configurations. Page 25 of subframe 4 shall contain a four-bit-longterm for each of up to 31 SVs to indicate the A-S status and the configuration code of each SV transmitting with aPRN number in the range of 33 through 63.
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