IS-GPS-200H (797934), страница 27
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Each DC packet is made up of two different segments. The first segment contains34 bits for the CDC parameters and the second segment contains 92 bits of EDC parameterstotaling 126 bits. The CDC and EDC parameters form an indivisible pair and users must utilizeCDC and EDC as a pair. Users must utilize CDC and EDC data pair of same top-D and of sametOD.30.3.3.7.2.1 Differential Correction Data Predict Time of Week.The DC data predict time of week (top-D) provides the epoch time of week, in increments of 300seconds (i.e.
five minutes), at which the prediction for the associated DC data was performed.30.3.3.7.2.2 Time of Differential Correction Data.The time of DC data, tOD, specifies the reference time of week, in increments of 300 seconds(i.e., five minutes) relative to the GPS week, for the associated CDC and EDC data.30.3.3.7.2.3 SV PRN Identification.The PRN ID of both CDC and EDC of Figure 30-16 identifies the satellite to which the subject126-bit differential correction packet data applies (by PRN code assignment). A value of allones “11111111” in any PRN ID field shall indicate that no DC data is contained in theremainder of the data block.
In this event, the remainder of the data block shall be filler bits, i.e.,alternating ones and zeros beginning with one.182IS-GPS-200H24 Sep 2013CDC = Clock Differential CorrectionMSB19LSB223034PRN IDδaf0δaf1UDRA.8 BITS.13 BITS.8 BITS.5 BITSEDC = Ephemeris Differential CorrectionMSB1LSB23936PRN IDΔαΔβ.8 BITS.14 BITS.14 BITSLSBMSB523763ΔiΔγ.12 BITS.15 BITS.LSBMSB88766492ΔΩΔA•UDRA12 BITS12 BITS5 BITSFigure 30-16. Differential Correction Data Packet183IS-GPS-200H24 Sep 2013Table 30-X.ParameterPRN IDDifferential Correction ParametersNo. ofBits**ScaleFactor(LSB)8EffectiveRange***Unitssee textδaf0SV Clock Bias Correction13*2-35secondsδaf1SV Clock Drift Correction8*2-51seconds/secondUDRAUser Differential RangeAccuracy Index5*∆αAlpha Correction to EphemerisParameters14*2-34dimensionless∆βBeta Correction to EphemerisParameters14*2-34dimensionless∆γGamma Correction to EphemerisParameters15*2-32semi-circles∆iAngle of Inclination Correction12*2-32semi-circles∆ΩAngle of Right AscensionCorrection12*2-32semi-circles∆ASemi-Major Correction12*2-9metersChange Rate of User DifferentialRange Accuracy Index.5*•UDRAsee textsee text*Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;**See Figure 30-7 , 11 and 12 for complete bit allocation in Message types 34, 13 and 14;***Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor.30.3.3.7.3 Application of Clock-Related DC Data.The SV PRN code phase offset, uncorrected by clock correction coefficient updates, is given byequation 2 in paragraph 20.3.3.3.3.1 (see para.
30.3.3.2.3). If the matched pair of DC data for thesubject SV is available, the user may apply clock correction coefficient update values by;∆tsv = (af0 + δaf0) + (af1 + δaf1)(t − toc) + af2(t − toc )2 + ∆tr,where δaf0 and δaf1, (see Table 30-X), are given in message types 34 or 13, and all other termsare as stated in paragraph 20.3.3.3.3.1. Clock-related DC data shall not be applied to any SV184IS-GPS-200H24 Sep 2013transmitting clock correction parameters message(s) containing a top value greater than the top-Dvalue of messages types 34 or 13 containing the clock-related DC data.30.3.3.7.4 Application of Orbit-Related DC Data.The DC data packet includes corrections to parameters that correct the state estimates forephemeris parameters transmitted in the message types 10 and 11 (broadcast by the SV to whichthe DC data packet applies).
The user will update the ephemeris parameters utilizing a variationof the algorithm expressed in the following equations. The user will then incorporate theupdated quasi-Keplerian element set in all further calculations of SV position, as represented bythe equations in Table 30-II (see para. 30.3.3.1.3). Ephemeris-related DC data shall not beapplied to any SV transmitting message types 10 and 11 containing a top value greater than thetop-D value of message types 34 or 14 containing the ephemeris-related DC data.The user will construct a set of initial (uncorrected) elements by:Ai=A0ei=enii=i0-nΩi=Ω0-nαi=en cos(ωn)βi=en sin(ωn)γi=M0-n + ωnwhere A0, en, i0-n, Ω0-n, ωn and M0-n are obtained from the applicable SV’s message types 10 and11 data.
The terms αi, βi, and γi form a subset of stabilized ephemeris elements which aresubsequently corrected by ∆α, ∆β and ∆γthe values of which are supplied in the message types34 or 14 - as follows:αc=αi + ∆αβc=βi + ∆βγc=γi + ∆γ185IS-GPS-200H24 Sep 2013The quasi-Keplerian elements are then corrected byAc=Ai + ∆Aec=(αc2 + βc2)1/2ic=ii + ∆iΩc=Ωi + ∆Ωωc=tan-1 (βc/αc)M0-c=γc − ωc + ∆M0where ∆A, ∆i and ∆Ω are provided in the EDC data packet of the message type 34 or 14 and∆M0 is obtained from1− 3 µ 2 ∆A0∆M 0 =2 A0 3 A0[(t oe + WN oe * 604,800 ) − (t OD + WN * 604,800 )]where WNoe is the week number associated with the toe and WN is the current week number.The corrected quasi-Keplerian elements above are applied to the user algorithm fordetermination of antenna phase center position in Section 30.3.3.1.3, Table 30-II.30.3.3.7.5 SV Differential Range Accuracy Estimates.•The UDRAop-D and UDRA shall give the differential user range accuracy for the SV.
It must benoted that the two parameters provide estimated accuracy after both clock and ephemeris DC are•applied. The UDRAop-D and UDRA indices are signed, two’s complement integers in the rangeof +15 to -16 and has the following relationship:186IS-GPS-200H24 Sep 2013•Index Value1514131211109876543210-1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16UDRAop-D (meters)6144.003072.001536.00768.00384.00192.0096.0048.0024.0013.659.656.854.853.402.401.701.200.850.600.430.300.210.150.110.080.060.040.030.020.01<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<UDRA (10-6 m/sec)UDRAop-D6144.003072.00UDRAop-D ≤ 6144.001536.00UDRAop-D ≤ 3072.00768.00UDRAop-D ≤ 1536.00768.00384.00UDRAop-D ≤384.00192.00UDRAop-D ≤192.0096.00UDRAop-D ≤96.0048.00UDRAop-D ≤48.0024.00UDRAop-D ≤24.0013.65UDRAop-D ≤13.659.65UDRAop-D ≤9.656.85UDRAop-D ≤6.854.85UDRAop-D ≤4.853.40UDRAop-D ≤3.402.40UDRAop-D ≤2.401.70UDRAop-D ≤1.701.20UDRAop-D ≤1.200.85UDRAop-D ≤0.850.60UDRAop-D ≤0.600.43UDRAop-D ≤UDRAop-D ≤0.430.300.300.21UDRAop-D ≤0.210.15UDRAop-D ≤0.150.11UDRAop-D ≤0.110.08UDRAop-D ≤0.080.06UDRAop-D ≤0.060.04UDRAop-D ≤0.040.03UDRAop-D ≤0.030.02UDRAop-D ≤0.020.01UDRAop-D ≤0.010.005UDRAop-D ≤No accuracy prediction available—use at own riskFor any time, tk, other than top-D, UDRA is found by,•UDRA = UDRAop-D + UDRA (tk - top-D)30.3.3.8 Message Type 35 GPS/GNSS Time Offset.Message type 35, Figure 30-8, contains the GPS/Global Navigation Satellite System (GNSS)Time Offset (GGTO) parameters.
The contents of message type 35 are defined below. Thevalidity period of the GGTO shall be 1 day as a minimum.187IS-GPS-200H24 Sep 201330.3.3.8.1 GPS/GNSS Time Offset Parameter Content.Message Type 35 provides SV clock correction parameters (ref. Section 30.3.3.2) and also, shallcontain the parameters related to correlating GPS time with other GNSS time. Bits 157 through159 of message type 35 shall identify the other GPS like navigation system to which the offsetdata applies.
The three bits are defined as follows;000 = no data available,001 = Galileo,010 = GLONASS,011 through 111 = reserved for other systems.The number of bits, the scales factor (LSB), the range, and the units of the GGTO parameters aregiven in Table 30-XI. See Figure 30-8 for complete bit allocation in message type 35.30.3.3.8.2 GPS and GNSS Time.The GPS/GNSS-time relationship is given by,tGNSS = tE - (A0GGTO + A1GGTO (tE - tGGTO + 604800 (WN - WNGGTO)) + A2GGTO (tE - tGGTO +604800 (WN - WNGGTO))2)where tGNSS is in seconds, tE and WN are as defined in Section 20.3.3.5.2.4, and the remainingparameters are as defined in Table 30-XI.188IS-GPS-200H24 Sep 2013Table 30-XI.GPS/GNSS Time Offset ParametersNo. ofBits**ParameterScaleFactor(LSB)EffectiveUnitsRange***-35secondsA0GGTOBias coefficient of GPS time scalerelative to GNSS time scale16*2A1GGTODrift coefficient of GPS time scalerelative to GNSS time scale13*2-51sec/secA2GGTODrift rate correction coefficient ofGPS time scale relative to GNSStime scale7*2-68sec/sec2tGGTOTime data reference Time of Week1624WNGGTOTime data reference Week Number1320GNSS IDGNSS Type ID3604,784secondsweekssee text*Parameters so indicated shall be two's complement with the sign bit (+ or -) occupyingthe MSB;** See Figure 30-8 for complete bit allocation;*** Unless otherwise indicated in this column, effective range is the maximum rangeattainable with indicated bit allocation and scale factor.30.3.3.9 Message Types 36 and 15 Text Messages.Text messages are provided either in message type 36, Figure 30-9, or type 15, Figure 30-14.The specific contents of text message will be at the discretion of the Operating Command.Message type 36 can accommodate the transmission of 18 eight-bit ASCII characters.Message type 15 can accommodate the transmission of 29 eight-bit ASCII characters.The requisite bits shall occupy bits 39 through 274 of message type 15 and bits 128 through 275of message type 36.
The eight-bit ASCII characters shall be limited to the set described inparagraph 20.3.3.5.1.8.30.3.4 Timing Relationships.The following conventions shall apply.30.3.4.1 Paging and Cutovers.Broadcast system of messages is completely arbitrary, but sequenced to provide optimum userperformance. Message types 10 and 11 shall be broadcast at least once every 48 seconds. Allother messages shall be broadcast in-between, not exceeding the maximum broadcast interval in189IS-GPS-200H24 Sep 2013Table 30-XII. Message type 15 will be broadcast as needed, but will not reduce the maximumbroadcast interval of the other messages.
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