IS-GPS-200F (811524), страница 18
Текст из файла (страница 18)
Asshown 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 is described below, followed by algorithms and materialpertinent to the use of the data.20.3.3.5.1 Contents of Subframes 4 and 5. 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:Subframe4Page(s)Data1, 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 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 SV109IS-GPS-200F21 Sep 2011whose 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 IDs arereserved for each page of subframes 4 and 5. The SV IDs are utilized in two different ways: (a) for those pageswhich contain the almanac data of a given SV, the SV ID is the same number that is assigned to the PRN code phaseof 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.110IS-GPS-200F21 Sep 2011Table 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: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).111IS-GPS-200F21 Sep 201120.3.3.5.1.2 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, 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 20.3.3.5.2.The almanac message for any dummy SVs shall contain alternating ones and zeros with valid parity.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 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, IIF, and GPS III SVs, five sets of almanac shall be used to span at least 60 days. The first,second, and third sets will be transmitted for up to six days each; the fourth and fifth sets will be transmitted for upto 32 days; the fifth set is intended to be transmitted for the remainder of the 60 days minimum, but the actualduration of transmission will depend on the individual 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 are based on 32 day curvefits.112IS-GPS-200F21 Sep 2011Table 20-VI.Almanac ParametersParameterNo. ofBits**ScaleFactor(LSB)e162-21toa8212δi****16*2-19semi-circles16*2-38semi-circles/secA242-11metersΩ024*2-23semi-circlesω24*2-23semi-circlesM024*2-23semi-circlesaf011*2-20secondsaf111*2-38sec/sec•ΩEffectiveRange***Unitsdimensionless602,112seconds* 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 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 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 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: it113IS-GPS-200F21 Sep 2011indicates 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 20.3.3.5.1.4).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.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.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
