IS-GPS-200F (811524), страница 29
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The UDRAop-D and UDRA shall give the differential userrange accuracy for the SV. It must be noted that the two parameters provide estimated accuracy after both clock andephemeris DC are applied. The UDRAop-D and UDRA indices are signed, two’s complement integers in the range of+15 to -16 and has the following relationship:Index Value1514131211109876543210-1UDRAop-D (meters)6144.003072.001536.00768.00384.00192.0096.0048.0024.0013.659.656.854.853.402.401.701.20<<<<<<<<<<<<<<<<<UDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-DUDRAop-D6144.00≤ 6144.00≤ 3072.00≤ 1536.00≤768.00≤384.00≤192.00≤96.00≤48.00≤24.00≤13.65≤9.65≤6.85≤4.85≤3.40≤2.40≤1.70185UDRA (10-6 m/sec)3072.001536.00768.00384.00192.0096.0048.0024.0013.659.656.854.853.402.401.701.20IS-GPS-200F21 Sep 2011-2-3-4-5-6-7-8-9-10-11-12-13-14-15-160.850.600.430.300.210.150.110.080.060.040.030.020.01<<<<<<<<<<<<<UDRAop-D ≤1.200.85UDRAop-D ≤0.850.600.600.43UDRAop-D ≤UDRAop-D ≤0.430.300.300.21UDRAop-D ≤UDRAop-D ≤0.210.150.150.11UDRAop-D ≤UDRAop-D ≤0.110.080.080.06UDRAop-D ≤UDRAop-D ≤0.060.04UDRAop-D ≤0.040.03UDRAop-D ≤0.030.02UDRAop-D ≤0.020.01UDRAop-D ≤0.010.005No 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/GlobalNavigation Satellite System (GNSS) Time Offset (GGTO) parameters. The contents of message type 35 are definedbelow. The validity period of the GGTO shall be 1 day as a minimum.30.3.3.8.1 GPS/GNSS Tiem Offset Parameter Content. Message Type 35 provides SV clock correction parameters(ref. Section 30.3.3.2) and also, shall contain the parameters related to correlating GPS time with other GNSS time.Bits 155 through 157 of message type 35 shall identify the other GPS like navigation system to which the offset dataapplies. 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 are given in Table 30XI.
See Figure 30-8 for complete bit allocation in message type 35.186IS-GPS-200F21 Sep 201130.3.3.8.2 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 remaining parameters are asdefined in Table 30-XI.Table 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, Figure30-9, or type 15, Figure 30-14. The specific contents of text message will be at the discretion of the OperatingCommand.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.187IS-GPS-200F21 Sep 2011The requisite bits shall occupy bits 39 through 274 of message type 15 and bits 128 through 275 of message type 36.The eight-bit ASCII characters shall be limited to the set described in paragraph 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 provideoptimum user performance. Message types 10 and 11 shall be broadcast at least once every 48 seconds. All othermessages shall be broadcast in-between, not exceeding the maximum broadcast interval in Table 30-XII. Messagetype 15 will be broadcast as needed, but will not reduce the maximum broadcast interval of the other messages.Type 15 messages that are longer than one page will not necessarily be broadcast consecutively.Table 30-XII.Message Broadcast IntervalsMessage DataMessage Type NumberMaximum Broadcast Intervals †Ephemeris10 & 1148 secClockType 30’s48 secISC, IONO30 *288 secReduced Almanac31* or 1220 min**Midi Almanac37120 min**EOP32*30 minUTC33*288 secDiff Correction34* or 13 & 1430 min***GGTO35*288 secText36* or 15As needed*Also contains SV clock correction parameters.** Complete set of SVs in the constellation.*** When Differential Corrections are available.†The intervals specified are maximum.
As such, the broadcast intervals may be shorter than thespecified value.188IS-GPS-200F21 Sep 201130.3.4.2 SV Time vs. GPS Time. In controlling the SVs and uploading of data, the CS shall allow for the followingtiming relationships:a.Each SV operates on its own SV time;b.All time-related data (TOW) in the messages shall be in SV-time;c.All other data in the Nav message shall be relative to GPS time;d.The acts of transmitting the Nav messages shall be executed by the SV on SV time.30.3.4.3 Speed of Light.
The speed of light used by the CS for generating the data described in the aboveparagraphs isc = 2.99792458 x 108meters per secondwhich is the official WGS 84 speed of light. The user shall use the same value for the speed of light in allcomputations.30.3.4.4 Data Sets. The toe shall be equal to the toc of the same CNAV data set.
The following rules govern thetransmission of toe and toc values in different data sets: (1) The transmitted toc will be different from any valuetransmitted by the SV during the preceding seven days; (2) The transmitted toe will be different from any valuetransmitted by the SV during the preceding six hours.Cutovers to new data sets will occur only on hour boundaries except for the first data set of a new upload. The firstdata set may be cut-in (reference paragraph 30.3.4.1) at any time during the hour and therefore may be transmittedby the SV for less than one hour.The start of the transmission interval for each data set corresponds to the beginning of the curve fit interval for thedata set. Each data set remains valid for the duration of its transmission interval, and nominally also remains validfor the duration of its curve fit interval.
A data set is rendered invalid before the end of its curve fit interval when itis superseded by the SV cutting over to the first data set of a new upload.Normal Operations. The message type 10, 11, and 30-37 data sets are transmitted by the SV for periods of twohours. The corresponding curve fit interval is three hours.189IS-GPS-200F21 Sep 201130.3.4.5 Reference Times. The LNAV reference time information in paragraph 20.3.4.5 also applies to the CNAVreference times.30.3.5 Data Frame Parity. The data signal contains parity coding according to the following conventions.30.3.5.1 Parity Algorithm.
Twenty-four bits of CRC parity will provide protection against burst as well as randomerrors with a probability of undetected error ≤ 2-24 = 5.96×10-8 for all channel bit error probabilities ≤ 0.5. The CRCword is calculated in the forward direction on a given message using a seed of 0. The sequence of 24 bits(p1,p2,...,p24) is generated from the sequence of information bits (m1,m2,...,m276) in a given message. This is done bymeans of a code that is generated by the polynomial24g (X ) = ∑ g i X ii=0wheregi = 1for i = 0,1,3, 4,5, 6,7,10,11,14,17 ,18, 23, 24= 0 otherwiseThis code is called CRC-24Q. The generator polynomial of this code is in the following form (using binarypolynomial algebra):g (X ) = (1 + X )p (X )where p(X) is the primitive and irreducible polynomialp(X) = X23 + X17 + X13 + X12 + X11 + X9 + X8 + X7 + X5 + X3 + 1When, by the application of binary polynomial algebra, the above g(x) is divided into m(x)x24, where theinformation sequence m(x) is expressed asm(X) = mk + mk −1X + mk − 2X2 + ⋅ ⋅ ⋅ + m1Xk −1190IS-GPS-200F21 Sep 2011The result is a quotient and a remainder R(x) of degree < 24.
The bit sequence formed by this remainder representsthe parity check sequence. Parity bit pi, for any i from 1 to 24, is the coefficient of x24-i in R(x).This code has the following characteristics:1) It detects all single bit errors per code word.2) It detects all double bit error combinations in a codeword because the generator polynomial g(X) has a factor of atleast three terms.3) It detects any odd number of errors because g(X) contains a factor 1+X.4) It detects any burst error for which the length of the burst is ≤ 24 bits.5) It detects most large error bursts with length greater than the parity length r = 24 bits.
The fraction of error burstsof length b > 24 that are undetected is:a) 2-24 = 5.96 × 10-8, if b > 25 bits.b) 2-23 = 1.19 × 10-7, if b = 25 bits.191IS-GPS-200F21 Sep 201140. APPENDIX IV GPS NAVIGATION DATA STRUCTURE FOR LNAV DATA, D(t), FOR PRN 33-6340.1 Scope. This appendix describes the specific legacy navigation (LNAV) data structure denoted by data IDnumber 2 for the upper set of PRN numbers (PRN 33-63). This data ID number, when transmitted as part of theLNAV data, shall be represented by the two-bit binary notation as 01. Data ID number 1 is no longer in use.
TheLNAV data structure for the upper set of PRN numbers is denoted as LNAV-U. The LNAV data structure for thelower set of PRN numbers (LNAV-L) is described in Appendix II.40.2 Applicable Documents. Applicable documents shall be as specified in Appendix II, Section 20.2.40.3 Requirements40.3.1 Data Characteristics. The data characteristics shall be as specified in Appendix II, Section 20.3.1.40.3.2 Message Structure. The message structure shall be as specified in Appendix II, Section 20.3.2 except asindicated by Figure 40-1.192IS-GPS-200F21 Sep 2011DIRECTION OF DATA FLOW FROM SV150 BITSWORD 1MSB FIRST3 SECONDSWORD 2WORD 3WORD 4WORD 571SUBFRAMENO.PAGENO.131TLM1N/A22 BITS61HOWC P73 77 8391121WNt P22 BITSP10BITS23 BITS***C/A OR P ON L2 - 2 BITSURA INDEX - 4 BITSSV HEALTH - 6 BITSP2 MSBs150 BITSIODC - 10 BITS TOTAL1N/A18124 BITS***P16BITS***WORD 8197TGDMSB FIRST3 SECONDSWORD 7151PL2 P DATA FLAG - 1 BITDIRECTION OF DATA FLOW FROM SVWORD 624 BITS***WORD 9211 219P8 BITSWORD 10241toc16 BITSPa f28BITS8 LSBs271af116 BITSa f0Pt P22 BITSIODC - 10 BITS TOTAL*** RESERVEDP = 6 PARITY BITSt = 2 NONINFORMATION BEARING BITS USED FOR PARITY COMPUTATION (SEE PARAGRAPH 20.3.5)C = TLM BITS 23 AND 24.
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