IS-GPS-200F (811524), страница 19
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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.114IS-GPS-200F21 Sep 2011Table 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 bad115IS-GPS-200F21 Sep 2011Table 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 3.116IS-GPS-200F21 Sep 201120.3.3.5.1.4 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 Configuration000Reserved001A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described in paragraph20.3.2 (e.g. Block II/Block IIA/IIR SV).010A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described in paragraph20.3.2, M-Code signal capability, L2C signal capability (e.g., Block IIR-M SV).011A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described in paragraph20.3.2, M-Code capability, L2C signal capability, L5 signal capability (e.g., Block IIF SV).100A-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described in paragraph20.3.2, M-Code capability, L1C signal capability, L2C signal capability, L5 signal capability, no SAcapability (e.g., GPS III SVs).Additional 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.117IS-GPS-200F21 Sep 201120.3.3.5.1.5 Almanac Reference Week.
Bits 17 through 24 of word three in page 25 of subframe 5 shall indicate thenumber of the week (WNa) to which the almanac reference time (toa) is referenced (see paragraphs 20.3.3.5.1.2 and20.3.3.5.2.2). The WNa term consists of eight bits which shall be a modulo 256 binary representation of the GPSweek number (see paragraph 6.2.4) to which the toa is referenced. Bits 9 through 16 of word three in page 25 ofsubframe 5 shall contain the value of toa which is referenced to this WNa.20.3.3.5.1.6 Coordinated Universal Time (UTC) Parameters. The 24 MSBs of words six through nine plus the eightMSBs of word ten in page 18 of subframe 4 shall contain the parameters related to correlating UTC time with GPStime.
The bit length, scale factors, ranges, and units of these parameters are given in Table 20-IX. The relatedalgorithms are described in paragraph 20.3.3.5.2.4.The UTC parameters shall be updated by the CS at least once every six days while the CS is able to upload the SVs.If the CS is unable to upload the SVs, the accuracy of the UTC parameters transmitted by the SVs will degrade overtime.20.3.3.5.1.7 Ionospheric Data. The ionospheric parameters which allow the "L1 only" or "L2 only" user to utilize theionospheric model (reference paragraph 20.3.3.5.2.5) for computation of the ionospheric delay are contained in page18 of subframe 4.
They occupy bits 9 through 24 of word three plus the 24 MSBs of words four and five. The bitlengths, scale factors, ranges, and units of these parameters are given in Table 20-X.The ionospheric data shall be updated by the CS at least once every six days while the CS is able to upload the SVs.If the CS is unable to upload the SVs, the ionospheric data transmitted by the SVs may not be accurate.118IS-GPS-200F21 Sep 2011ParameterNo. ofBits**Table 20-IX.UTC ParametersScaleFactor(LSB)EffectiveRange***UnitsA032*2-30secondsA124*2-50sec/sectLS8*1secondstot8212WNt81weeksWNLSF81weeksDN8****1tLSF8*1*7secondsdayssecondsParameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;*****602,112See 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;****Right justified.119IS-GPS-200F21 Sep 2011Table 20-X.Ionospheric ParametersParameterNo.
ofBits**ScaleFactor(LSB)α08*2-30secondsα18*2-27sec/semi-circleα28*2-24sec/(semi-circle)2α38*2-24sec/(semi-circle)3β08*211secondsβ18*214sec/semi-circleβ28*216sec/(semi-circle)2β38*216sec/(semi-circle)3*UnitsParameters so indicated shall be two's complement with the sign bit (+ or -) occupying the MSB;*****EffectiveRange***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.20.3.3.5.1.8 Special Messages. Page 17 of subframe 4 shall be reserved for special messages with the specificcontents at the discretion of the Operating Command.
It shall accommodate the transmission of 22 eight-bit ASCIIcharacters. The requisite 176 bits shall occupy bits 9 through 24 of word three, the 24 MSBs of words four throughnine, plus the 16 MSBs of word ten. The eight MSBs of word three shall contain the data ID and SV ID, while bits17 through 22 of word ten shall be reserved for system use.
The remaining 50 bits of words three through ten areused for parity (six bits/word) and parity computation (two bits in word ten). The eight-bit ASCII characters shallbe limited to the following set:120IS-GPS-200F21 Sep 2011Alphanumeric CharacterASCII CharacterCode (Octal)A-ZA-Z101 - 1320-90-9060 - 071++053--055. (Decimal point).056' (Minute mark)'047° (Degree sign)°370//057BlankSpace040::072" (Second mark)"04220.3.3.5.1.9 NMCT. Page 13 of subframe 4 shall contain the NMCT data appropriate to the transmitting SV. EachNMCT contains a two-bit availability indicator (AI) followed by 30 slots which may contain up to 30 valid six-bitERD values. The layout of these 31 data items is as shown in Figure 20-1.The two-bit AI in bits 9 and 10 of word three of page 13 of subframe 4 provide the user with the followinginformation.121IS-GPS-200F21 Sep 2011AINavigation Message Correction Table Availability00The correction table is unencrypted and is available to both precise positioning service users and standardpositioning service users.01The correction table is encrypted and is available only to authorized users (normal mode).10No correction table available for either precise positioning service users or standard positioning service users.11ReservedEach one of the 30 six-bit ERD slots in bits 11 through 24 of word three, bits 1 through 24 of words four throughnine, and bits 1 through 22 of word ten of page 13 of subframe 4 will correspond to an ERD value for a particularSV ID.
There are 31 possible SV IDs that these ERD slots may correspond to, ranging from SV ID 1 to SV ID 31.SV ID 32 is not a valid SV ID for any of the slots in an NMCT. The correspondence between the 30 ERD slots andthe 31 possible SV IDs depends on the SV ID of the particular transmitting SV in accordance with the following tworules: 1) the CS shall ensure via upload that no SV shall transmit an NMCT containing an ERD value which appliesto its own SV ID, and 2) the CS shall ensure via upload that all ERD values shall be transmitted in ascendingnumerical slot order of the corresponding SV ID. To illustrate: the SV operating as SV ID 1 will transmit (in order)ERD values which correspond to SV ID 2 through SV ID 31 in ERD slots 1 through 30 respectively, while the SVoperating as SV ID 31 will transmit ERD values which correspond to SV ID 1 through SV ID 30 in ERD slots 1through 30 respectively.Each ERD value contained in an NMCT ERD slot shall be represented as a six-bit two’s complement field with thesign bit occupying the MSB and an LSB of 0.3 meters for an effective range of ±9.3 m.
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