IS-GPS-705D (797936), страница 9
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Message type 13 - Clock Differential Correction53IS-GPS-705D24 Sep 20131159PRN8 BITS6BITS6BITSDIRECTION OF DATA FLOW FROM SV100 BITS2 SECONDS386150396221MESSAGETOW COUNT*17 BITStop-D11 BITSMESSAGE TYPE IDPREAMBLEEDCtOD11 BITSMSB FIRST39 MSBsDC DATA TYPE – 1 BIT"ALERT" FLAG - 1 BITDIRECTION OF DATA FLOW FROM SV100 BITS2 SECONDSMSB FIRST154155101EDCEDC53 LSBs46 MSBsDC DATA TYPE – 1 BITDIRECTION OF DATA FLOW FROM SV100 BITS2 SECONDS247201MSB FIRST277EDCRESERVEDCRC46 LSBs30 BITS24 BITS* MESSAGE TOW COUNT = 17 MSBs OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGEEDC = Ephemeris Differential CorrectionFigure 20-13. Message type 14 - Ephemeris Differential Correction54IS-GPS-705D24 Sep 20131159PRN8 BITS6BITS6BITSMSB FIRSTDIRECTION OF DATA FLOW FROM SV100 BITS2 SECONDS383921MESSAGETOW COUNT*TEXT MESSAGE (29 8-BIT CHAR)62 MSBs17 BITSMESSAGE TYPE IDPREAMBLE"ALERT" FLAG - 1 BITMSB FIRSTDIRECTION OF DATA FLOW FROM SV100 BITS2 SECONDS101TEXT MESSAGE (29 8-BIT CHAR)BITS 63-162MSB FIRSTDIRECTION OF DATA FLOW FROM SV100 BITS2 SECONDS271201275277TEXT MESSAGE (29 8-BIT CHAR)CRC4BITS70 LSBsTEXT PAGE24 BITSRESERVED – 2 BITS* MESSAGE TOW COUNT = 17 MSB OF ACTUAL TOW COUNT AT START OF NEXT 6-SECOND MESSAGEFigure 20-14.
Message type 15 – Text55IS-GPS-705D24 Sep 201320.3.3.1 Message Types 10 and 11 Ephemeris and Health Parameters.20.3.3.1.1 Message Types 10 and 11 Ephemeris and Health Parameter Content.The contents of the SV health, ephemeris representation and accuracy parameters in messagetypes 10 and 11 are defined below, followed by material pertinent to the use of the data.Message type 10, in conjunction with message type 11, provides users with the requisite data tocalculate SV position. The general format of message types 10 and 11 consists of data fields forreference time tags, a set of gravitational harmonic correction terms, rates and rate corrections toquasi-Keplerian elements, and an accuracy indicator for ephemeris-related data.The broadcast group delay differential correction terms apply to the pseudorange measurementsproduced by an ideal correlation receiver with a bandwidth of 20.46 MHz centered at thereference waveform nominal frequency whose phase is linear over that bandwidth using an exactreplica of the reference waveform in an early-late discriminator having a correlator spacing of97.75 nanoseconds.
The group delay differential correction terms may not apply to pseudorangemeasurements produced by different methods due to potential distortion of the transmittedwaveform. Users employing pseudorange measurement methods different from the definedmethod must account for the potential inapplicability of the group delay differential correctionterms.The toe term shall provide the user with a convenient means for detecting any change in theephemeris representation parameters. The toe is provided in both message type 10 and 11 for thepurpose of comparison with the toc term in message type 30 - 37.
Whenever these three terms donot match, a data set cutover has occurred and new data must be collected. The timing of the toeand constraints on the toc and toe are defined in paragraph 20.3.4.4.Any change in the message type 10 and 11 ephemeris data will be accomplished with asimultaneous change in the toe value. The CS will assure the toe value for Block IIR-M/IIF andSS will assure the toe value for GPS III, for at least the first data set transmitted by an SV after anupload, is different from that transmitted prior to the cutover. See Section 20.3.4.5 for additionalinformation regarding toe.The CNAV messages contain information that allows users to take advantage of situations whenintegrity is assured to the enhanced level.
This is accomplished using a composite integrityassured URA value in conjunction with an integrity status flag. The composite integrity assuredURA (IAURA) value is the RSS of an elevation-dependent function of the upper bound value ofthe URAED component and the upper bound value of the URANED component.
The compositeIAURA value is assured to the enhanced level only when the integrity status flag is “1”;otherwise the IAURA value is assured to the legacy level.56IS-GPS-705D24 Sep 2013Bit 272 of Message Type 10 is the Integrity Status Flag (ISF). A "0" in bit position 272 indicatesthat the conveying signal is provided with the legacy level of integrity assurance. That is, theprobability that the instantaneous URE of the conveying signal exceeds 4.42 times the currentbroadcast IAURA value, for more than 5.2 seconds, without an accompanying alert, is less than1E-5 per hour.A "1" in bit-position 272 indicates that the conveying signal is provided with an enhanced levelof integrity assurance.
That is, the probability that the instantaneous URE of the conveyingsignal exceeds 5.73 times the current broadcast IAURA value, for more than 5.2 seconds,without an accompanying alert, is less than 1E-8 per hour. The probabilities associated with thenominal and lower bound values of the current broadcast URAED index, URANED indexes, andrelated URA values are not defined.In this context, an "alert" is defined as any indication or characteristic of the conveying signal, asspecified elsewhere in this document, which signifies to users that the conveying signal may beinvalid or should not be used, such as the health bits not indicating operational-healthy,broadcasting non-standard code parity error, etc.Bit 273 of Message Type 10 indicates the phase relationship between L2C and P(Y) as specifiedin section 3.3.1.5.1 of IS-GPS-200.20.3.3.1.1.1 Transmission Week Number.Bits 39 through 51 of message type 10 shall contain 13 bits which are a modulo-8192 binaryrepresentation of the current GPS week number at the start of the data set transmission interval(see paragraph 6.2.4 of IS-GPS-200).20.3.3.1.1.2 Signal Health (L1/L2/L5).The three, one-bit, health indication in bits 52 through 54 of message type 10 refers to the L1,L2, and L5 signals of the transmitting SV.
The health of each signal is indicated by,0 = Signal OK,1 = Signal bad or unavailable.The predicted health data will be updated at the time of upload when a new data set has beenbuilt by the CS. The transmitted health data may not correspond to the actual health of thetransmitting SV.Additional SV health data are given in the almanac in message types 12, 31, and 37. The datagiven in message type 10 may differ from that shown in the other messages of the transmittingSV and/or other SVs since the latter may be updated at a different time.57IS-GPS-705D24 Sep 201320.3.3.1.1.3 Data Predict Time of Week.Bits 55 through 65 of message type 10 shall contain the data predict time of week (top).
The topterm provides the epoch time of week of the state estimate utilized for the prediction of satellitequasi-Keplerian ephemeris parameters.20.3.3.1.1.4 Elevation-Dependent (ED) AccuracyBits 66 through 70 of message type 10 shall contain the elevation-dependent (ED) componentUser Range Accuracy (URAED) index for the standard positioning service user. The URAEDindex shall provide the ED-related URA index for the current ephemeris curve fit interval.While the ED-related URA may vary over the ephemeris curve fit interval and over the satellitefootprint, the URAED index (N) in message type 10 shall correspond to the maximum URAEDexpected over the entire ephemeris curve fit interval for the worst-case location within the SVfootprint (i.e., nominally two points at the edge of the SV footprint).
At the best-case locationwithin the SV footprint (i.e., nominally directly below the SV along the SV nadir vector), thecorresponding URAED. is zero.The URAED index is a signed, two’s complement integer in the range of +15 to -16 and has thefollowing relationship to the ED URA:URAED IndexURAED (meters)156144.00< URAED (or no accuracy prediction is available)143072.00< URAED ≤6144.00131536.00< URAED ≤3072.0012768.00< URAED ≤1536.0011384.00< URAED ≤768.0010192.00< URAED ≤384.00996.00< URAED ≤192.00848.00< URAED ≤96.00724.00< URAED ≤48.00613.65< URAED ≤24.0059.65< URAED ≤13.6546.85< URAED ≤589.65IS-GPS-705D24 Sep 201334.85< URAED ≤6.8523.40< URAED ≤4.8512.40< URAED ≤3.4001.70< URAED ≤2.40-11.20< URAED ≤1.70-20.85< URAED ≤1.20-30.60< URAED ≤0.85-40.43< URAED ≤0.60-50.30< URAED ≤0.43-60.21< URAED ≤0.30-70.15< URAED ≤0.21-80.11< URAED ≤0.15-90.08< URAED ≤0.11-100.06< URAED ≤0.08-110.04< URAED ≤0.06-120.03< URAED ≤0.04-130.02< URAED ≤0.03-140.01< URAED ≤0.02URAED ≤0.01-15-16No accuracy prediction available-use at own riskFor each URA index (N), users may compute a nominal URA value (X) as given by:• If the value of N is 6 or less, X = 2(1 + N/2),• If the value of N is 6 or more, but less than 15, X = 2(N - 2),59IS-GPS-705D24 Sep 2013• N = 15 shall indicate the absence of an accuracy prediction and shall advise the standardpositioning service user to use that SV at his own risk.For N = 1, 3, and 5, X should be rounded to 2.8, 5.7, and 11.3 meters, respectively.The nominal URAED value (X) is suitable for use as a conservative prediction of the RMS EDrange errors for accuracy-related purposes in the pseudorange domain (e.g., measurement deweighting, RAIM, FOM computations).
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