IS-GPS-200H (797934), страница 23
Текст из файла (страница 23)
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 messages types 12, 31, and 37. The datagiven in message type 10 may differ from that shown in other messages of the transmitting SVand/or other SVs since the latter may be updated at a different time.156IS-GPS-200H24 Sep 201330.3.3.1.1.3 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.30.3.3.1.1.4 Elevation-Dependent (ED) Accuracy.Bits 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 or the current ephemeris curve fit interval. Whilethe 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< URAED143072.00< 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≤9.6534.85< URAED≤6.85157(or no accuracy prediction is available)IS-GPS-200H24 Sep 201323.40< 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≤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≤0.01-15-16< URAEDNo accuracy prediction available-use at own riskFor each URAED index (N), users may compute a nominal URAED value (X) as given by:• If the value of N is 6 or less, but more than -16, X = 2(1 + N/2),• If the value of N is 6 or more, but less than 15, X = 2(N - 2),158IS-GPS-200H24 Sep 2013• N = -16 or N = 15 shall indicate the absence of an accuracy prediction and shall advise thestandard positioning 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., measurementdeweighting, RAIM, FOM computations).
Integrity properties of the IAURAED are specifiedwith respect to the scaled (multiplied by either 4.42 or 5.73 as appropriate) upper bound valuesof the broadcast URAED index (see 30.3.3.1.1).For the nominal URAED value and the IAURAED value, users may compute an adjusted URAEDvalue as a function of SV elevation angle (E), for E ≥ 0, as follows:= Nominal URAED (sin(E+90 degrees))Adjusted Nominal URAEDAdjusted IAURAED= IAURAED (sin(E+90 degrees))URAED and IAURAED account for SIS contributions to user range error which include, but arenot limited to, the following: LSB representation/truncation error, alongtrack ephemeris errors,and crosstrack ephemeris errors. URAED and IAURAED do not account for user range errorcontributions due to the inaccuracy of the broadcast ionospheric data parameters used in thesingle-frequency ionospheric model or for other atmospheric effects.30.3.3.1.2 Message Type 10 and 11 Ephemeris Parameter Characteristics.For each ephemeris parameter contained in message types 10 and 11, the number of bits, thescale factor of the least significant bit (LSB) (which is the last bit received), the range, and theunits are as specified in Table 30-I.
See Figures 30-1 and 30-2 for complete bit allocation inmessage types 10 and 11.30.3.3.1.3 User Algorithm for Determination of SV Position.The user shall compute the ECEF coordinates of position for the SV’s antenna phase center(APC) utilizing a variation of the equations shown in Table 30-II. The ephemeris parameters areKeplerian in appearance; however, the values of these parameters are produced by the CS (BlockIIR-M/IIF) and SS (GPS III) via a least squares curve fit of the predicted ephemeris of the SVAPC (time-position quadruples: t, x, y, z expressed in ECEF coordinates). Particularsconcerning the applicable coordinate system are given in Sections 20.3.3.4.3.3 and 20.3.3.4.3.4.159IS-GPS-200H24 Sep 2013The sensitivity of the SV’s position to small perturbations in most ephemeris parameters isextreme.
The sensitivity of position to the parameters A, Crc-n, and Crs-n is about onemeter/meter. The sensitivity of position to the angular parameters is on the order of 108meters/semi-circle, and to the angular rate parameters is on the order of 1012 meters/semicircle/second. Because of this extreme sensitivity to angular perturbations, the value of π used inthe curve fit is given here.
π is a mathematical constant, the ratio of a circle’s circumference toits diameter. Here π is taken as 3.1415926535898.160IS-GPS-200H24 Sep 2013Table 30-I. Message Types 10 and 11 Parameters (1 of 2)ParameterNo. ofBits**ScaleFactor(LSB)1WNWeek No.13URAED IndexED Accuracy Index5*Signal health(L1/L2/L5)EffectiveRange***Unitsweeks(see text)31(see text)topData predict time of week11300∆A ****Semi-major axis difference atreference time26*2-9metersAChange rate in semi-majoraxis25*2-21meters/sec∆n0Mean Motion difference fromcomputed value at referencetime17*2-44semi-circles/sec∆n0Rate of mean motiondifference from computedvalue23*2-57semi-circles/sec2M0-nMean anomaly at referencetime33*2-32semi-circlesenEccentricity332-34ωnArgument of perigee33*2-32••****604,5000.03secondsdimensionlesssemi-circlesParameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;**See Figure 30-1 for complete bit allocation in Message Type 10;Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor.****Relative to AREF = 26,559,710 meters.161IS-GPS-200H24 Sep 2013Table 30-I.
Message Types 10 and 11 Parameters (2 of 2)ParameterNo. ofBits**ScaleFactor(LSB)EffectiveRange***Units604,500secondstoeEphemeris data reference time of week11300Ω0-nLongitude of Ascending Node of OrbitPlane at Weekly Epoch33*2-32semi-circles17*2-44semi-circles/sec•ΔΩ****Rate of right ascension differencei0-nInclination angle at reference time33*2-32semi-circlesi0-n –DOTRate of inclination angle15*2-44semi-circles/secCis-nAmplitude of the sine harmonic correctionterm to the angle of inclination16*2-30radiansCic-nAmplitude of the cosine harmoniccorrection term to the angle of inclination16*2-30radiansCrs-nAmplitude of the sine correction term tothe orbit radius24*2-8metersCrc-nAmplitude of the cosine correction term tothe orbit radius24*2-8metersCus-nAmplitude of the sine harmonic correctionterm to the argument of latitude21*2-30radiansCuc-nAmplitude of the cosine harmoniccorrection term to the argument of latitude21*2-30radians*Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;**See Figure 30-1 and Figure 30-2 for complete bit allocation in Message Types 10 and 11;***Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor.****•Relative to ΩREF = -2.6 x 10-9 semi-circles/second.162IS-GPS-200H24 Sep 2013Table 30-II.
Elements of Coordinate System (part 1 of 2)Element/Equationµ = 3.986005 x 1014 meters3/sec2•DescriptionWGS 84 value of the earth’s gravitational constant for GPS userΩe = 7.2921151467 x 10-5 rad/secWGS 84 value of the earth’s rotation rateA0 = AREF + ∆A *Semi-Major Axis at reference time•Semi-Major AxisAk = A0 + (A) tkn0 =µComputed Mean Motion (rad/sec)A03tk = t – toe **Time from ephemeris reference time•∆nA = ∆n0 +½ ∆n0 tkMean motion difference from computed valuenA = n0 + ∆nACorrected Mean MotionMk = M0 + nA tkMean AnomalyMk = Ek – en sin EkKepler’s equation for Eccentric Anomaly (radians)(may be solved by iteration) sin ν k νk = tan-1 cos ν k True Anomaly 1 − e 2 sin E / (1 − e cos E ) nknk = tan-1 ()(−−cosEe/1ecosEknnk) e + cos ν k Ek = cos-1 n1 + e n cos ν k *Eccentric AnomalyAREF = 26,559,710 meters** t is GPS system time at time of transmission, i.e., GPS time corrected for transit time (range/speed of light).Furthermore, tk shall be the actual total difference between the time t and the epoch time toe, and must accountfor beginning or end of week crossovers.
That is if tk is greater than 302,400 seconds, subtract 604,800seconds from tk. If tk is less than -302,400 seconds, add 604,800 seconds to tk.163IS-GPS-200H24 Sep 2013Table 30-II.Elements of Coordinate System (part 2 of 2)Element/Equation *Φk = νk + ωnDescriptionArgument of Latitudeδuk = Cus-nsin2Φk + Cuc-ncos2ΦkArgument of Latitude Correctionδrk = Crs-nsin2Φk + Crc-ncos2ΦkRadial Correctionδik = Cis-nsin2Φk + Cic-ncos2ΦkInclination Correctionuk = Φk + δukSecond HarmonicPerturbationsCorrected Argument of Latituderk= Ak(1 – en cos Ek) + δrkCorrected Radiusik= io-n + (io-n-DOT)tk + δikCorrected Inclinationxk' = rk cos ukPositions in orbital planeyk' = rk sin uk•••Ω = ΩREF + ∆Ω ***••Rate of Right Ascension•Ωk = Ω0-n + ( Ω − Ωe ) tk – Ωe toeCorrected Longitude of Ascending Nodexk = xk' cos Ωk − yk' cos ik sin Ωkyk = xk' sin Ωk + yk' cos ik cos ΩkEarth-fixed coordinates of SV antenna phase centerzk = yk' sin ik•*** ΩREF = −2.6 x 10-9 semi-circles/second.30.3.3.2 Message Types 30 Through 37 SV Clock Correction Parameters.30.3.3.2.1 Message Type 30 Through 37 SV Clock Correction Parameter Content.The clock parameters in any one of message types 30 through 37 describe the SV time scaleduring the period of validity.
The parameters are applicable during the time in which they aretransmitted. Beyond that time, they are still applicable, however, the most recent data set shouldbe used since the accuracy degrades over time.The general format of message types 30 through 37 includes data fields for SV clock correctioncoefficients. Any one of message types 30 through 37 in conjunction with message types 10 and11 provides users with the requisite data to correct SV time and to calculate SV positionprecisely.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
