IS-GPS-200H (797934), страница 17
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With the possible exception of "reserved forsystem use" pages and explicit repeats, each page contains different specific data in words threethrough ten. As shown in Figure 20-1, the pages of subframe 4 utilize seven different formats,while those of subframe 5 use two. The content of words three through ten of each page isdescribed below, followed by algorithms and material pertinent to the use of the data.20.3.3.5.1 Content of Subframes 4 and 5.Words three through ten of each page contain six parity bits as their LSBs; in addition, two noninformation bearing bits are provided as bits 23 and 24 of word ten in each page for paritycomputation purposes. The data contained in the remaining bits of words three through ten ofthe various pages 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:108IS-GPS-200H24 Sep 2013SubframePage(s)Data41, 6, 11, 16 and 21Reserved2, 3, 4, 5, 7, 8, 9 and 10almanac data for SV 25 through 32 respectively12, 19, 20, 22, 23 and 24Reserved13NMCT14 and 15Reserved for system use17Special messages18Ionospheric and UTC data25A-S flags/SV configurations for 32 SVs, plus SV health for SV 25through 3251 through 24almanac data for SV 1 through 2425SV health data for SV 1 through 24, the almanac reference time, thealmanac reference week number20.3.3.5.1.1 Data ID and SV ID.The two MSBs of word three in each page shall contain data ID.
Data ID number two (denotedby binary code 01) denotes the NAV data structure of D(t) which is described in this Appendix.Future data IDs will be defined as necessary.As shown in Table 20-V, the data ID is utilized to provide one of two indications: (a) for thosepages which are assigned to contain the almanac data of one specific SV, the data ID defines thedata structure utilized by that SV whose almanac data are contained in that page; and (b) for allother pages, the data ID denotes the data structure of the transmitting SV.The SV ID is given by bits three through eight of word three in each page as shown in Table 20V. Specific IDs are reserved for each page of subframes 4 and 5. The SV IDs are utilized in twodifferent ways: (a) for those pages which contain the almanac data of a given SV, the SV ID isthe same number that is assigned to the PRN code phase of that SV (reference Table 3-I), and (b)for all other pages the SV ID assigned in accordance with Table 20-V serves as the "page ID".IDs 1 through 32 are assigned to those pages which contain the almanac data of specific SVs(pages 1-24 of subframe 5 and pages 2-5 and 7-10 of subframe 4).
The "0" ID (binary all zeros)is assigned to indicate a dummy SV, while IDs 51 through 63 are utilized for pages containingother than almanac data of a specific SV. The remaining IDs (33 through 50) are unassigned.Pages which carry the same SV ID (e.g., in subframe 4, pages 1, 6, 11, 16 and 21 carry an ID of57, while pages 12 and 24 are designated by an ID of 62) may not be considered to containidentical data. The data in the pages with the same SV ID can be different.109IS-GPS-200H24 Sep 2013Table 20-V.
Data IDs and SV IDs in Subframes 4 and 5Subframe 4Subframe 5Page12345678910111213141516171819202122232425Data IDSV ID*Data IDSV ID*Note(2)Note(1)Note(1)Note(1)Note(1)Note(2)Note(1)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)57252627285729303132576252535457555658 Note(3)59 Note(3)5760 Note(3)61 Note(3)6263Note(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)12345678910111213141516171819202122232451* Use "0" to indicate "dummy" SV.
When using "0" to indicate dummy SV, use the data ID of the transmittingSV.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 SVs).20.3.3.5.1.2 Almanac Data.Pages 1 through 24 of subframe 5, as well as pages 2 through 5 and 7 through 10 of subframe 4contain the almanac data and a SV health word for up to 32 SVs (the health word is discussed inparagraph 20.3.3.5.1.3). The almanac data are a reduced-precision subset of the clock andephemeris parameters. The data occupy all bits of words three through ten of each page exceptthe eight MSBs of word three (data ID and SV ID), bits 17 through 24 of word five (SV health),and the 50 bits devoted to parity.
The number of bits, the scale factor (LSB), the range, and theunits of the almanac parameters are given in Table 20-VI. The algorithms and other materialrelated to the use of the almanac data are given in paragraph 20.3.3.5.2.110IS-GPS-200H24 Sep 2013The almanac message for any dummy SVs shall contain alternating ones and zeros with validparity.Users are cautioned against attempting to track a dummy SV since the results are unpredictable.The almanac parameters shall be updated by the CS at least once every 6 days while the CS isable to upload the SVs. If the CS is unable to upload the SVs, the accuracy of the almanacparameters transmitted by the SVs will degrade over time.For Block II and IIA SVs, three sets of almanac shall be used to span at least 60 days.
The firstand second sets will be transmitted for up to six days each; the third set is intended to betransmitted for the remainder of the 60 days minimum, but the actual duration of transmissionwill depend on the individual SV's capability to retain data in memory. All three sets are basedon six-day curve fits that correspond to the first six days of the transmission interval.For Block IIR/IIR-M, IIF, and GPS III SVs, five sets of almanac shall be used to span at least 60days. The first, second, and third sets will be transmitted for up to six days each; the fourth andfifth sets will be transmitted for up to 32 days; the fifth set is intended to be transmitted for theremainder of the 60 days minimum, but the actual duration of transmission will depend on theindividual SV's capability to retain data in memory.The first, second, and third sets are based on six day curve fits.
The fourth and fifth sets arebased on 32 day curve fits.111IS-GPS-200H24 Sep 2013Table 20-VI.Almanac ParametersParameterNo. ofBits**ScaleFactor(LSB)e162-21toa8212δi****16*2-19semi-circles16*2-38semi-circles/secA242-11Ω024*2-23semi-circlesω24*2-23semi-circlesM024*2-23semi-circlesaf011*2-20secondsaf111*2-38sec/sec•ΩEffectiveRange***Unitsdimensionless602,112secondsmeters* Parameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;** See Figure 20-1 for complete bit allocation in subframe;*** Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor;**** Relative to i0 = 0.30 semi-circles.20.3.3.5.1.3 SV Health.Subframes 4 and 5 contain two types of SV health data: (a) each of the 32 pages which containthe clock/ephemeris related almanac data provide an eight-bit SV health status word regardingthe SV whose almanac data they carry, and (b) the 25th page of subframe 4 and of subframe 5jointly contain six-bit health status data for up to 32 SVs.The three MSBs of the eight-bit health words indicate health of the NAV data in accordance withthe code given in Table 20-VII.
The six-bit words provide a one-bit summary of the NAV data'shealth status in the MSB position in accordance with paragraph 20.3.3.3.1.4. The five LSBs ofboth the eight-bit and the six-bit words provide the health status of the SV's signal components inaccordance with the code given in Table 20-VIII.
A special meaning is assigned, however, to the"6 ones" combination of the six-bit health words in the 25th page of subframes 4 and 5: it112IS-GPS-200H24 Sep 2013indicates that "the SV which has that ID is not available and there may be no data regarding thatSV in that page of subframes 4 and 5 that is assigned to normally contain the almanac data ofthat SV" (NOTE: this special meaning applies to the 25th page of subframes 4 and 5 only).
Thehealth indication shall be given relative to the "as designed" capabilities of each SV (asdesignated by the configuration code -- see paragraph 20.3.3.5.1.4). Accordingly, any SV whichdoes not have a certain capability will be indicated as "healthy" if the lack of this capability isinherent in its design or it has been configured into a mode which is normal from a userstandpoint and does not require that capability.Additional SV health data are given in subframe 1.
The data given in subframes 1, 4, and 5 ofthe other SVs may differ from that shown in subframes 4 and/or 5 since the latter may beupdated at a different time.The eight-bit health status words shall occupy bits 17 through 24 of word five in those 32 pageswhich contain almanac data for individual SVs. The six-bit health status words shall occupy the24 MSBs of words four through nine in page 25 of subframe 5 plus bits 19 through 24 of word 8,the 24 MSBs of word 9, and the 18 MSBs of word 10 in page 25 of subframe 4.The predicted health data will be updated at the time of upload when a new almanac has beenbuilt by the CS. The transmitted health data may not correspond to the actual health of thetransmitting SV or other SVs in the constellation.113IS-GPS-200H24 Sep 2013Table 20-VII.NAV Data Health IndicationsBit Position in PageIndication137138139000ALL DATA OK001PARITY FAILURE -- some or all parity bad010TLM/HOW FORMAT PROBLEM -- any departure from standard format (e.g.,preamble misplaced and/or incorrect, etc.), except for incorrect Z-count, asreported in HOW011Z-COUNT IN HOW BAD -- any problem with Z-count value not reflectingactual code phase100SUBFRAMES 1, 2, 3 -- one or more elements in words three through ten ofone or more subframes are bad101SUBFRAMES 4, 5 -- one or more elements in words three through ten of oneor more subframes are bad110ALL UPLOADED DATA BAD -- one or more elements in words threethrough ten of any one (or more) subframes are bad111ALL DATA BAD -- TLM word and/or HOW and one or more elements in anyone (or more) subframes are bad114IS-GPS-200H24 Sep 2013Table 20-VIII.MSBLSB0000000001000100001100100001010011000111010000100101010010110110001101011100111110000100011001010011101001010110110101111100011001110101101111100111011111011111*Codes for Health of SV Signal ComponentsDefinitionAll Signals OKAll Signals Weak*All Signals DeadAll Signals Have No Data ModulationL1 P Signal WeakL1 P Signal DeadL1 P Signal Has No Data ModulationL2 P Signal WeakL2 P Signal DeadL2 P Signal Has No Data ModulationL1 C Signal WeakL1 C Signal DeadL1 C Signal Has No Data ModulationL2 C Signal WeakL2 C Signal DeadL2 C Signal Has No Data ModulationL1 & L2 P Signal WeakL1 & L2 P Signal DeadL1 & L2 P Signal Has No Data ModulationL1 & L2 C Signal WeakL1 & L2 C Signal DeadL1 & L2 C Signal Has No Data ModulationL1 Signal Weak*L1 Signal DeadL1 Signal Has No Data ModulationL2 Signal Weak*L2 Signal DeadL2 Signal Has No Data ModulationSV Is Temporarily Out (Do not use this SV during current pass)**SV Will Be Temporarily Out (Use with caution)*****One Or More Signals Are Deformed, However The Relevant URA Parameters Are ValidMore Than One Combination Would Be Required To Describe Anomalies (Not including thosemarked with “**”)3 to 6 dB below specified power level due to reduced power output, excess phase noise, SV attitude, etc.** See definition above for Health Code 11111.*** Note: Deformed means one or more signals do not meet the requirements in Section 3.20.3.3.5.1.4 Anti-Spoof (A-S) Flags and SV Configurations.Page 25 of subframe 4 shall contain a four-bit-long term for each of up to 32 SVs to indicate theA-S status and the configuration code of each SV.
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