IS-GPS-200F (811524), страница 32
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The MSB of each four-bit term shall be the A-S flag with a "1"indicating that A-S is ON. The three LSBs shall indicate the configuration of each SV using the following code:Code000001SV ConfigurationReservedA-S capability, plus flags for A-S and "alert" in HOW; memory capacity as described in paragraph20.3.2 (e.g. Block II/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 SV).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 12 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.208IS-GPS-200F21 Sep 201140.3.3.5.1.5 Almanac Reference Week.
The almanac reference week shall be as specified in Appendix II, paragraph20.3.3.5.1.5.40.3.3.5.1.6 Coordinated Universal Time (UTC) Parameters. The UTC parameters shall be as specified in AppendixII, paragraph 20.3.3.5.1.6.40.3.3.5.1.7 Ionospheric Data. The ionospheric data shall be as specified in Appendix II, paragraph 20.3.3.5.1.7.40.3.3.5.1.8 Special Messages. The special messages shall be as specified in Appendix II, paragraph 20.3.3.5.1.8.40.3.3.5.1.9 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 40-1.The two-bit AI in bits 9 and 10 of word three of page 13 of subframe 4 provide the user with the followinginformation.AINavigation Message Correction Table Availability00The correction table is unencrypted and is available to both precise positioning service users andstandard positioning service users.01The correction table is encrypted and is available only to precise positioning service users (normalmode).10No correction table available for either precise positioning service users or standard positioningservice users.11Reserved.Each 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 65 to SV ID 95.The correspondence between the 30 ERD slots and the 31 possible SV IDs depends on the SV ID of the particulartransmitting SV in accordance with the following two rules: 1) the CS shall ensure via upload that no SV shalltransmit an NMCT containing an ERD value which applies to its own SV ID, and 2) the CS shall ensure via uploadthat all ERD values shall be transmitted in ascending numerical slot order of the corresponding SV ID. To illustrate:the SV operating as SV ID 65 will transmit (in order) ERD values which correspond to SV ID 66 through SV ID 95in ERD slots 1 through 30 respectively, while the SV operating as SV ID 95 will transmit ERD values whichcorrespond to SV ID 65 through SV ID 94 in ERD slots 1 through 30 respectively.209IS-GPS-200F21 Sep 2011Each 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.
A binary value of “100000”shall indicate that no valid ERD for the corresponding SV ID is present in that slot.40.3.3.5.2 Algorithms Related to Subframe 4 and 5 Data. The algorithms related to subframe 4 and 5 data shall beas specified in Appendix II, Section 20.3.3.5.2.40.3.4 Timing Relationships. The timing relationships shall be as specified in Appendix II, Section 20.3.4.40.3.5 Data Frame Parity.
The data frame parity shall be as specified in Appendix II, Section 20.3.5.210IS-GPS-200F21 Sep 2011.
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