"2020最新GPS IS-800G文档授权说明"

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IS-GPS-800G

14 May 2020

The clock rates are offset by f/f = -4.4647E-10, which is equivalent to a change in the L1C-code

chipping rate of 1.023 MHz by a f = -4.5674E-4 Hz. This results in an offset L1C-code chipping

rate of 1.02299999954326 MHz. The nominal carrier frequency (f

) - as it appears to an observer

on the ground - shall be 1575.42 MHz.

The requirements specified in this IS shall pertain to the signal contained within a 30.69 MHz

bandwidth centered about the L1 nominal frequency.

The L1C signal shall utilize a modulation technique of BOC (f

, 1) which specifies a subcarrier

frequency of f

× 1.023 MHz and a spreading code chipping rate of 1 × 1.023 MHz = 1.023 MHz.

3.2.1.2 Signal Polarization

The transmitted signal shall be Right-Hand Circularly Polarized (RHCP).

For an angular range of 13.8 degrees from nadir, the L1 ellipticity shall be no worse than 1.8 dB.

3.2.1.3 Carrier Phase Noise

The phase noise spectral density of the unmodulated carrier shall be such that an approximation to

the third order Jaffe-Rechtin phase lock loop, closed-loop transfer function H(f) such that |1 - H(f)|

= f

/(f

+ f

) where f

= 3B

/(5), which has a 10 Hz one-sided loop noise bandwidth, shall be able

to track the carrier to an accuracy of 0.035 radians rms.

3.2.1.4 Spurious Transmissions

In-band spurious transmissions, from the SV, shall be at or below -40 dBc over the band specified

in 3.2.1.1. In-band spurious transmissions are defined as transmissions within the band specified

in 3.2.1.1 which are not expressly components of the L1 signal.

3.2.1.5 Correlation Loss

Correlation loss is defined as the difference between the SV power received in the bandwidth

defined in 3.2.1.1 and the signal power recovered in an ideal correlation receiver of the same

bandwidth using an exact replica of the waveform within an ideal sharp-cutoff filter bandwidth

centered at L1, whose bandwidth corresponds to that specified in 3.2.1.1 and whose phase is

linear over that bandwidth. The correlation loss apportionment due to SV modulation and filtering

imperfections shall be 0.2 dB maximum.



IS-GPS-800G

14 May 2020

3.2.1.6 Signal Component Phasing

3.2.1.6.1 Phase Relationship

Carriers of the two L1C components defined in Section 3.1 shall be in the same phase within ±100

milliradians. Carriers of the two L1C components shall be in the same phase (within ±100

milliradians) as the P(Y)-code carrier. See IS-GPS-200 for phase relationships to other L1 signals.

3.2.1.6.2 Phase Continuity

While a satellite is broadcasting standard L1C

code and standard L1C

code signals with data

which indicates L1C signal health is OK, there will not be any commanded operation causing an

intentional phase discontinuity. This does not apply to phase discontinuities caused by signal

modulation. Phase discontinuities are subject to the requirements of 3.2.1.6.1.

3.2.1.7 Signal Characteristics

3.2.1.7.1 Signal Coherence

All transmitted signals for a particular SV shall be coherently derived from the same on-board

frequency standard. On the L1 carrier, the chip transitions of the two modulating signals, L1C

and L1C

, shall be such that the average time difference between them (i.e. L1C

/L1C

), and

between each and the transitions of L1P(Y) (i.e. L1C

/L1P(Y), L1C

/L1P(Y)), do not exceed 10

nanoseconds.

The variable time difference shall not exceed 1 nanosecond (95% probability), when including

consideration of the temperature and antenna effect changes during a vehicle orbital revolution.

Corrections for the bias components of the time difference are provided to the US in the CNAV-2

message using parameters designated as ISCs (reference paragraph 3.5.3.9.1).

3.2.1.7.2 Signal Distortion

The duration of the “+1 polarity” portions of the BOC (1, 1) code shall equal the duration of the “-1

polarity” portions of the BOC (1, 1) code within 5 nanoseconds as measured at the zero crossing

point.

The duration of the “+1 polarity” portions of the BOC (6, 1) code shall equal the duration of the “-1

polarity” portions of the BOC (6, 1) code within 5 nanoseconds as measured at the zero crossing

point.

3.2.1.8 Equipment Group Delay

Equipment group delay is defined as the delay between the signal radiated output of a specific SV

(measured at the antenna phase center as observed from the signal’s zero crossings) and the

output of that SV's on-board frequency source; the delay consists of a bias term and an

uncertainty. The bias term is of no concern to the US since it is included in the clock correction

parameters relayed in the navigation data, and is therefore accounted for by the user computations

IS-GPS-800G

14 May 2020

of system time. The uncertainty (variation) of this delay, as well as the group delay differential,

between the reference signal and the signals of L1C, are defined in the following subsections.

3.2.1.8.1 Group Delay Uncertainty

The effective uncertainty of the group delay shall not exceed 1.5 nanoseconds (95% probability).

3.2.1.8.2 Group Delay Differential

Not applicable. See Sections 3.2.1.7.1 (Signal Coherence) and 3.5.3.9.1 (Inter-Signal Group Delay

Differential Correction).

3.2.1.8.3 Space Service Volume (SSV) Group Delay Differential

The group delay differential for the radiated L1 signal with respect to the Earth Coverage signal for

users of the Space Service Volume are provided in http://www.igs.org/products/ssv

3.2.1.9 Signal Power Levels

The SV shall provide an L1C signal strength at End-of-Life (EOL), worst-case, in order to meet the

minimum effective received signal levels specified in Table 3.2-1. Any combining operation done

by the SV and associated loss is compensated by an increase in SV transmitted power and thus

transparent to the user segment. For terrestrial users, the minimum effective received signal power

is measured at the output of a 3 dBi linearly polarized user receiving antenna (located near

ground) at worst normal orientation, when the SV elevation angle is higher than 5 degrees and

assuming 0.5 dB atmospheric loss. For orbital users, the minimum effective received signal power

is measured at the output of a 0 dBi ideal right-hand circularly polarized (i.e. 0 dB axial ratio) user

receiving antenna (in geosynchronous orbit) at 23.5 degrees off nadir and using 0 dB atmospheric

loss. The received signal levels are observed within the in-band allocation defined in Para. 3.2.1.1

The SV shall provide signals with the following characteristic:

the off-axis relative power (referenced to peak transmitted power) shall not decrease by more than

2 dB from the Edge-of-Earth (EOE) to nadir,

nor more than 10 dB from EOE to 20 degrees off nadir,

and no more than 19.5 dB from EOE to 23.5 degrees off nadir; the power drop off between EOE

and 23.5 degrees off nadir shall be in a monotonically decreasing fashion.

Higher received signal levels than those shown in Table 3.2-1 can be caused by such factors as

SV temperature-induced transmitter power variations, voltage variations and power amplifier

variations, and due to variability in link atmospheric path loss. The terrestrial user’s maximum

received signal power level resulting from these factors is not expected to exceed -154 dBW total

for the composite L1C signal. For purposes of establishing user receiver dynamic range for

IS-GPS-800G

14 May 2020

3.2.2.1.1 Ranging Code Structure

Both L1C

(t) and L1C

(t) are constructed using the same method. Each ranging code is derived

from a unique length-10223 sequence with a common 7-bit expansion sequence inserted at a PRN

signal number-dependent point.

The unique length-10223 sequence for each ranging code is derived from a single fixed length-

10223 sequence called a Legendre sequence L(t), for t = 0, …, 10222. L(t) is defined as,

L(0) = 0 ;

L(t) = 1, if there exists an integer x such that t is congruent to x

modulo 10223;

L(t) = 0, if there exists no integer x such that t is congruent to x

modulo 10223.

Table 6.2-1 in Section 6.2.3 provides the generated sequence of the above defined L(t).

The above Legendre sequence is used to construct the unique length-10223 sequence used for

each ranging code. This sequence, called a Weil-code, is the exclusive-or of L(t) and a shift of

L(t). A Weil-code W

(t ; w) is specified by Weil Index w, ranging from 1 to 5111, which represents

the shift of L(t) and is defined as,

(t ; w) = L(t)  L( (t + w) modulo 10223 ) for t = 0 to 10222.

Assignment of Weil Index, w, by PRN signal number, i, is given in Table 3.2-2.

Finally, the ranging code is constructed by inserting a fixed expansion sequence into the Weil-

code. The expansion sequence is composed of seven bit values 0 1 1 0 1 0 0. The insert point is

specified by Insertion Index p, where p = 1 to 10223. The expansion sequence is inserted before

the p

value of the Weil-code.

Thus the ranging code L1C

(t)/L1C

(t) is defined as,

L1C

(t)/L1C

(t) = W

(t ; w), for t = 0, 1, . . . , p - 2;

L1C

(t)/L1C

(t) = 0, for t = p - 1;

L1C

(t)/L1C

(t) = 1, for t = p;

L1C

(t)/L1C

(t) = 1, for t = p + 1;

L1C

(t)/L1C

(t) = 0, for t = p + 2;

L1C

(t)/L1C

(t) = 1, for t = p + 3;

L1C

(t)/L1C

(t) = 0, for t = p + 4;

L1C

(t)/L1C

(t) = 0, for t = p + 5;

L1C

(t)/L1C

(t) = W

(t - 7 ; w), for t = p + 6, p + 7, . . ., 10229.

Assignment of Insertion Index, p, by PRN signal number, i, is given in Table 3.2-2. The generation

of L1C

-code and L1C

-code is conceptually described in Figure 3.2-1.

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