IS-GPS-705D (797936), страница 4
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The clock rates are offset by Δf/f = 4.4647E-10, equivalent to a change in the I5 and Q5-code chipping rate of 10.23 MHz offset by aΔf = -4.5674E-3 Hz. This is equal to 10.2299999954326 MHz. The nominal carrier frequency(f0) -- as it appears to an observer on the ground - shall be 1176.45 MHz, or 115 times 10.23MHz.3.3.1.2 Correlation Loss.Correlation loss is defined as the difference between the SV power received in the bandwidthdefined in 3.3.1.1 (excluding signal combining loss) and the signal power recovered in an idealcorrelation receiver of the same bandwidth using an exact replica of the waveform within anideal sharp-cutoff filter bandwidth centered at L5, whose bandwidth corresponds to that specifiedin 3.3.1.1 and whose phase is linear over that bandwidth.
The correlation loss apportionment dueto SV modulation and filtering imperfections shall be 0.6 dB maximum.3.3.1.3 Carrier Phase Noise.The phase noise spectral density of the un-modulated carrier shall be such that a phase lockedloop of 10 Hz one-sided noise bandwidth shall be able to track the carrier to an accuracy of 0.1radians root mean square (RMS). See additional supporting material for phase noisecharacteristics in section 6.3.2.3.3.1.4 Spurious Transmissions.In-band spurious transmissions, from the SV, shall be at or below -40 dBc over the bandspecified in 3.3.1.1. In-band spurious transmissions are defined as transmissions within the bandspecified in 3.3.1.1 which are not expressly components of the L5 signal.8IS-GPS-705D24 Sep 20133.3.1.5 Phase Quadrature.The two L5 carrier components modulated by the two separate bit trains (I5-code plus data andQ5-code with no data) shall be in phase quadrature (within ±100 milliradians) with the Q5 signalcarrier lagging the I5 signal by 90 degrees.
Referring to the phase of the I5 carrier when I5i(t)equals zero as the "zero phase angle," the I5 and Q5-code generator output shall control therespective signal phases in the following manner: when I5i(t) equals one, a 180-degree phasereversal of the I5-carrier occurs; when Q5i(t) equals one, the Q5 carrier advances 90 degrees;when the Q5i(t) equals zero, the Q5 carrier shall be retarded 90 degrees (such that when Q5i(t)changes state, a 180-degree phase reversal of the Q5 carrier occurs). The resultant nominalcomposite transmitted signal phases as a function of the binary state of the modulating signalsare as shown in Table 3-II.3.3.1.6 Signal Power Levels.The SV shall provide, at a minimum, worst-case I5 and Q5 navigation signal strength at end-oflife (EOL), in order to meet the levels specified in Table 3-III. The minimum received power ismeasured at the output of a 3 dBi linearly polarized user receiving antenna (located near ground)at worst normal orientation, when the SV is above a 5-degree elevation angle.
The receivedsignal levels are observed within the in-band allocation defined in paragraph 3.3.1.1. Additionalrelated data is provided as supporting material in paragraph 6.3.1.The GPS III SV shall provide L5 signals with the following characteristic: the L5 off-axisrelative power (referenced to peak transmitted power) shall not decrease by more than 2 dB fromthe Edge-of-Earth (EOE) to nadir, and no more than 18 dB from EOE to 26 degrees off nadir; thepower drop off between EOE and ±26 degrees shall be in a monotonically decreasing fashion.Table 3-II. Composite L5 Transmitted Signal Phase**Code StateNominal Composite L5Signal Phase*0°-90°+90°180°***I5Q501010011Relative to 0, 0 code state with positive angles leading and negative angles lagging.Based on the composite of two L5 carrier components at the same power.9IS-GPS-705D24 Sep 2013Table 3-III.
Received Minimum RF Signal StrengthSignalSVI5Q5Block IIF-157.9 dBW-157.9 dBWGPS III-157.0 dBW-157.0 dBW3.3.1.6.1 Space Service Volume (SSV) Received Signal Power Levels.The SV shall provide, at a minimum, worst-case I5 and Q5 navigation signal strength at end-oflife (EOL), in order to meet the SSV levels specified in Table 3-IV. The minimum receivedpower is measured at the output of a 0 dBi right-hand circularly polarized (i.e. 0 dB axial ratio)user receiving antenna at normal orientation at the off-nadir angle of 26.0 degrees. The receivedsignal levels are observed within the in-band allocation defined in paragraph 3.3.1.1.Table 3-IV.
Space Service Volume (SSV) Received Minimum RF Signal Strength forGPS III and Subsequent Satellites over the Bandwidth Specified in 3.3.1.1 – GEO BasedAntennasSignalSVGPS III andI5Q5-182.0 dBW-182.0 dBWSubsequent Blocks3.3.1.7 Equipment Group Delay.Equipment group delay is defined as the delay between the signal radiated output of a specificSV (measured at the antenna phase center) and the output of that SV's on-board frequencysource; the delay consists of a bias term and an uncertainty. The bias term on L1/L2 P(Y) is of noconcern to users since it is included in the clock correction parameters relayed in the NAV data,and is therefore accounted for by user computations of system time (reference paragraphs20.3.3.2.3, 20.3.3.3.2.3 and 20.3.3.3.2.4).
The uncertainty (variation) of these delays as well asthe group delay differential between the signals of L1, L2, and L5 are defined in the following.3.3.1.7.1 Group Delay Uncertainty.The effective uncertainty of the group delays shall not exceed 3.0 nanoseconds (95%probability).10IS-GPS-705D24 Sep 20133.3.1.7.2 Group Delay Differential.The group delay differential between the radiated L1 and L5 signals (i.e. L1 P(Y) and L5 I5; andL1 P(Y) and L5 Q5) is specified as consisting of random plus bias components.
The meandifferential is defined as the bias component and will be either positive or negative. For a givennavigation payload redundancy configuration, the absolute value of the mean differential delayshall not exceed 30.0 nanoseconds. The random plus non-random variations about the mean shallnot exceed 3.0 nanoseconds (95% probability), when including consideration of the temperatureand antenna effects during a vehicle orbital revolution. L1 and L2 group delay differential isdescribed in 3.3.1.7.2 of IS-GPS-200.
Corrections for the bias components of the group delaydifferential are provided to the users in the NAV message using parameters designated as TGD(reference paragraph 20.3.3.3.3.2 of IS-GPS-200) and Inter-Signal Correction (ISC) (referenceparagraph 20.3.3.3.1.2).3.3.1.7.3 Space Service Volume Group Delay Differential.The group delay differential between the radiated L5 signal, with respect to the Earth Coveragesignal, for users of the Space Service Volume are provided in http://www.igs.org/products/ssv3.3.1.8 Signal Coherence.All transmitted signals on the same carrier for a particular SV shall be coherently derived fromthe same on-board frequency standard.
On the L5 channel, the chip transitions of the twomodulating signals, L5I and L5Q, shall be such that the average time difference between them,and between each and the transitions of L1 P(Y), do not exceed 10 nanoseconds. The variabletime difference shall not exceed 1 nanosecond (95% probability), when including considerationof the temperature and antenna effect changes during a vehicle orbital revolution. Corrections forthe bias components of the group delay differential are provided to the users using parametersdesignated as ISCs (reference paragraph 20.3.3.3.1.2).3.3.1.9 Signal Polarization.The transmitted signal shall be right-hand circularly polarized (RHCP). For the angular range of±13.8 degrees from nadir, L5 ellipticity shall be no worse than 2.4 dB.
Nominal values are listedin section 6.3.3.3.3.2 PRN Code Characteristics.The characteristics of the I5-codes and the Q5-codes are defined below in terms of their structureand the basic method used for generating them. Figures 3-2 and 3-3 depict simplified blockdiagrams of the scheme for generating the 10.23 Mbps I5i(t) and Q5i(t) patterns, and for modulo2 summing the I5 patterns with the NAV bit train, D5(t), which is rate 1/2 encoded and clocked at100 sps. In addition, the 100 sps are modulated with a 10-bit Neuman-Hofman code that isclocked at 1 kHz. The resultant composite bit trains are then used to modulate the L5 in-phasecarrier.
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