Интерфейсный документ GPS, страница 20

The CS will assure that the toe value, for at least the first data set transmitted by an SV after an upload, isdifferent from that transmitted prior to the cutover. See Section 20.3.4.5 for additional information regarding toe.30.3.3.1.1.1 Transmission Week Number. Bits 39 through 51 of message type 10 shall contain 13 bits which are amodulo-8192 binary representation of the current GPS week number at the start of the data set transmission interval(see paragraph 6.2.4).

These 13 bits are comprised of 10 LSBs that represent the ten MSBs of the 29-bit Z-count asqualified in paragraph 20.3.3.3.1.1, and 3 MSBs which are extra bits that extend the range of transmission weeknumber from 10 to 13 bits.IS-GPS-200D7 Dec 200415530.3.3.1.1.2 Signal Health (L1/L2/L5). The three, one-bit, health indication in bits 52 through 54 of message type10 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 been built by the CS.

Thetransmitted health data may not correspond to the actual health of the transmitting SV.Additional SV health data are given in the almanac in messages types 12, 31, and 37. The data given in messagetype 10 may differ from that shown in other messages of the transmitting SV and/or other SVs since the latter maybe updated at a different time.30.3.3.1.1.3 Data Predict Time of Week.

Bits 55 through 65 of message type 10 shall contain the data predict timeof week (top). The top term provides the epoch time of week of the state estimate utilized for the prediction ofsatellite quasi-Keplerian ephemeris parameters.IS-GPS-200D7 Dec 200415630.3.3.1.1.4 SV Accuracy. Bits 66 through 70 of message type 10 shall contain the ephemeris User RangeAccuracy (URAoe) index of the SV for the unauthorized (non-Precise Positioning Service) user. URAoe index shallprovide the ephemeris-related user range accuracy index of the SV as a function of the current ephemeris messagecurve fit interval.

While the ephemeris-related URA may vary over the ephemeris message curve fit interval, theURAoe index (N) in message type 10 shall correspond to the maximum URAoe expected over the entire curve fitinterval.The URAoe index is a signed, two’s complement integer in the range of +15 to –16 and has the followingrelationship to the ephemeris URA:URAoe Index1514131211109876543210-1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16URAoe (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<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<URAoeURAoe ≤6144.00URAoe ≤3072.00URAoe ≤1536.00URAoe ≤768.00URAoe ≤384.00URAoe ≤192.00URAoe ≤96.00URAoe ≤48.00URAoe ≤24.00URAoe ≤13.65URAoe ≤9.65URAoe ≤6.85URAoe ≤4.85URAoe ≤3.40URAoe ≤2.40URAoe ≤1.701.20URAoe ≤URAoe ≤0.85URAoe ≤0.60URAoe ≤0.43URAoe ≤0.30URAoe ≤0.21URAoe ≤0.15URAoe ≤0.11URAoe ≤0.08URAoe ≤0.06URAoe ≤0.04URAoe ≤0.03URAoe ≤0.02URAoe ≤0.01No accuracy prediction available—use at own riskIS-GPS-200D7 Dec 200415730.3.3.1.2 Message Type 10 and 11 Ephemeris Parameter Characteristics.

For each ephemeris parameter containedin message types 10 and 11, the number of bits, the scale factor of the least significant bit (LSB) (which is the lastbit received), the range, and the units are as specified in Table 30-I. See Figures 30-1 and 30-2 for complete bitallocation in message types 10 and 11.30.3.3.1.3 User Algorithm for Determination of SV Position.

The user shall compute the ECEF coordinates ofposition for the SV’s antenna phase center (APC) utilizing a variation of the equations shown in Table 30-II. Theephemeris parameters are Keplerian in appearance; however, the values of these parameters are produced by the CSvia a least squares curve fit of the predicted ephemeris of the SV APC (time-position quadruples: t, x, y, z expressedin ECEF coordinates). Particulars concerning the applicable coordinate system are given in Sections 20.3.3.4.3.3and 20.3.3.4.3.4.The sensitivity of the SV’s position to small perturbations in most ephemeris parameters is extreme.

The sensitivity ofposition to the parameters A, Crc-n, and Crs-n is about one meter/meter. The sensitivity of position to the angularparameters is on the order of 108 meters/semi-circle, and to the angular rate parameters is on the order of 1012meters/semi-circle/second. Because of this extreme sensitivity to angular perturbations, the value of π used in the curvefit is given here. π is a mathematical constant, the ratio of a circle’s circumference to its diameter. Here π is taken as3.1415926535898.IS-GPS-200D7 Dec 2004158Table 30-I.Message Types 10 and 11 Parameters (1 of 2)No.

ofBits**ScaleFactor(LSB)Week No.131SV accuracy5*Signal health(L1/L2/L5)31ParameterEffectiveRange***Unitsweeks(see text)(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•604,500seconds∆n0•Rate of mean motiondifference from computedvalue23*2-57semi-circles/sec2M0-nMean anomaly at referencetime33*2-32semi-circlesenEccentricity332-34ωnArgument of perigee33*2-32**********0.03dimensionlesssemi-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.IS-GPS-200D7 Dec 2004159Table 30-I.Message Types 10 and 11 Parameters (2 of 2)ParameterNo.

ofBits**ScaleFactor(LSB)EffectiveRange***604,500UnitstoeEphemeris data reference time of week11300Ω0-n****Reference right ascension angle33*2-32semi-circles•∆ΩRate of right ascension difference17*2-44semi-circles/seci0-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 sine harmonic correctionterm to the argument of latitude21*2-30radians*****seconds******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.****Ω0-n is the right ascension angle at the weekly epoch (Ω0-w) propagated to the reference time at the rate•of right ascension {ΩREF Table 30-II }.*****Relative to ΩREF = -2.6 x 10-9 semi-circles/second.•IS-GPS-200D7 Dec 2004160Table 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) tkµn0 =Computed Mean Motion (rad/sec)A 03tk = 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  (cos E k − e n ) / (1 − e n cos E k ) -1 e + cos ν k Ek = cos-1  n1 + 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.IS-GPS-200D7 Dec 2004161Table 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 + δuk= Ak(1 – en cos Ek) + δrkCorrected Radiusik= io-n + (io-n-DOT)tk + δikCorrected Inclinationxk' = rk cos ukPositions in orbital planeyk' = rk sin uk••Rate of Right AscensionΩ = ΩREF + ∆Ω ***•PerturbationsCorrected Argument of Latituderk•Second Harmonic••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• = −2.6 x 10-9 semi-circles/second.*** ΩREFIS-GPS-200D7 Dec 200416230.3.3.2 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 oneof message types 30 through 37 describe the SV time scale during the period of validity. The clock parameters in adata set shall be valid during the interval of time in which they are transmitted and shall remain valid for anadditional period of time after transmission of the next data set has started.The general format of message types 30 through 37 includes data fields for SV clock correction coefficients. Anyone of message types 30 through 37 in conjunction with message types 10 and 11 provide users with the requisitedata to correct SV time and to calculate SV position precisely.