Интерфейсный документ GPS (1015430), страница 15
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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.IS-GPS-200D7 Dec 2004102A 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, 9 and 10:almanac data for SV 25 through 32 respectively;•Pages 12, 19, 20, 22, 23 and 24:(reserved);•Page 13:•Pages 14 and 15:•Page 17:special messages;•Page 18:ionospheric and UTC data;•Page 25:A-S flags/SV configurations for 32 SVs, plus SV health for SV 25NMCT;reserved for system use;through 32.b.Subframe 5:•Pages 1 through 24:•Page 25:almanac data for SV 1 through 24;SV health data for SV 1 through 24, the almanac reference time, thealmanac reference week number.IS-GPS-200D7 Dec 200410320.3.3.5.1.1 Data ID and SV ID.
The two MSBs of word three in each page shall contain data ID. Data ID numbertwo (denoted by 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 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 SV ID is given by bits three through eight of word three in each page as shown in Table 20-V. Specific IDsare reserved for each page of subframes 4 and 5.
The SV IDs are utilized in two different ways: (a) for thosepages which contain the almanac data of a given SV, the SV ID is the same number that is assigned to the PRN codephase of that SV (reference Table 3-I), and (b) for all other pages the SV ID assigned in accordance with Table 20-Vserves as the "page ID". IDs 1 through 32 are assigned to those pages which contain the almanac data of specificSVs (pages 1-24 of subframe 5 and pages 2-5 and 7-10 of subframe 4).
The "0" ID (binary all zeros) is assigned toindicate a dummy SV, while IDs 51 through 63 are utilized for pages containing other than almanac data of aspecific 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 of 57, while pages 12and 24 are designated by an ID of 62) may not be considered to contain identical data. The data in the pages withthe same SV ID can be different.IS-GPS-200D7 Dec 2004104Table 20-V.Data IDs and SV IDs in Subframes 4 and 5Subframe 4Page12345678910111213141516171819202122232425Subframe 5Data 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:Note 2:Note 3:Data ID of that SV whose SV ID appears in that page.Data ID of transmitting SV.SV ID may vary (except for IIR/IIR-M/IIF SVs).IS-GPS-200D7 Dec 200410520.3.3.5.1.2 Almanac Data. Pages 1 through 24 of subframe 5, as well as pages 2 through 5 and 7 through 10 ofsubframe 4 contain 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 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, thescale factor (LSB), the range, and the units of the almanac parameters are given in Table 20-VI.
The algorithmsand other material related to the use of the almanac data are given in paragraph 20.3.3.5.2.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 II and IIA SVs, three sets of almanac shall be used to span at least 60 days.
The first and second sets willbe transmitted 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 and IIF SVs, multiple sets of almanac parameters shall be uploaded to span at least60 days.IS-GPS-200D7 Dec 2004106ParameterTable 20-VI.Almanac ParametersScaleFactor(LSB)EffectiveRange***No.
ofBits**-21Unitse162toa8212δi****16*2-19semi-circles16*2-38semi-circles/secA242-11Ω024*2-23semi-circlesω24*2-23semi-circlesM024*2-23semi-circlesaf011*2-20secondsaf111*2-38sec/sec•Ωdimensionless602,112secondsmeters* 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.IS-GPS-200D7 Dec 200410720.3.3.5.1.3 SV Health. Subframes 4 and 5 contain two types of SV health data: (a) each of the 32 pages whichcontain the clock/ephemeris related almanac data provide an eight-bit SV health status word regarding the SVwhose almanac data they carry, and (b) the 25th page of subframe 4 and of subframe 5 jointly contain six-bit healthstatus data for up to 32 SVs.The three MSBs of the eight-bit health words indicate health of the NAV data in accordance with the code given inTable 20-VII.
The six-bit words provide a one-bit summary of the NAV data's health status in the MSB position inaccordance with paragraph 20.3.3.3.1.4. The five LSBs of both the eight-bit and the six-bit words provide thehealth status of the SV's signal components in accordance with the code given in Table 20-VIII. A specialmeaning is assigned, however, to the "6 ones" combination of the six-bit health words in the 25th page ofsubframes 4 and 5: it indicates that "the SV which has that ID is not available and there may be no data regardingthat SV in that page of subframes 4 and 5 that is assigned to normally contain the almanac data of that SV"(NOTE: this special meaning applies to the 25th page of subframes 4 and 5 only).
The health indication shall begiven relative to the "as designed" capabilities of each SV (as designated by the configuration code -- see paragraph20.3.3.5.1.4). Accordingly, any SV which does not have a certain capability will be indicated as "healthy" if thelack of this capability is inherent 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 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 32 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 18 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.IS-GPS-200D7 Dec 2004108Table 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 badIS-GPS-200D7 Dec 2004109Table 20-VIII.
Codes for Health of SV Signal ComponentsMSBLSB0000000001000100001100100001010011000111010000100101010010110110001101011100111110000100011001010011101001010110110101111100011001110101101111100111011111011111***DefinitionAll 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)**SpareMore 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.IS-GPS-200D7 Dec 200411020.3.3.5.1.4 Anti-Spoof (A-S) Flags and SV Configurations.
Page 25 of subframe 4 shall contain a four-bit-longterm for each of up to 32 SVs to indicate the A-S status and the configuration code of each SV. The MSB of eachfour-bit term shall be the A-S flag with a "1" indicating that A-S is ON. The three LSBs shall indicate theconfiguration of each SV using the following code:CodeSV Configuration001“Block II/IIA/IIR” SV (A-S capability, plus flags for A-S and "alert" in HOW; memorycapacity as described in paragraph 20.3.2).010“Block IIR-M” SV011“Block IIF” SVAdditional codes will be assigned in the future, should the need arise.These four-bit terms shall occupy bits 9 through 24 of word three, the 24 MSBs of words four through seven, andthe 16 MSBs of word eight, all in page 25 of subframe 4.Since the anti-spoof information is updated by the CS at the time of upload, the anti-spoof data may not correspondto the actual anti-spoof status of the transmitting SV or other SVs in the constellation.IS-GPS-200D7 Dec 200411120.3.3.5.1.5 Almanac Reference Week.
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