Signal structure and processing technique for providing...

Details Signal structure and processing technique for providing... Signal structure and processing technique for providing...

2001-01-08

2002-08-27

Phan, Dao (Department: 3662)

Communications: directive radio wave systems and devices (e.g.,

Directive

Including a satellite

C342S357490, C342S461000

Reexamination Certificate

active

06441777

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to obtaining highly precise position, velocity, time and attitude measurements and their time derivatives by the use and processing of multiple signals separated in frequency and by the use of these signals and their sum and difference components. One application of this multiple signal measurements technique is in the resolution of the integer cycle ambiguities associated with precise carrier phase measurements of the signals used in satellite navigation systems such s the U.S. Global Positioning System (GPS), or the Russian Global Orbiting Navigation Satellite System (GLONASS), or other systems. One implementation of this multiple signal technique is to use dual or “split spectrum” signals that involves a moderate frequency separation of the signals (or signal energy), and employs an additional signal or signals separated by a greater amount(s) to provide for the progressive resolution of the integer cycle wavelength ambiguities associated with progressively more narrow lane widths (or difference frequency wavelengths). This process continues until the relative phase of the carrier itself is measured and the integer cycle wavelength ambiguities of the carrier signals are also resolved. The technique of the invention involves a signal structure with three or more signal components normally operating in one or more of the bands assigned to GPS, GLONASS or other systems. These signals are used in combination with one or more additional signal(s) at frequencies substantially separated from the dual, or split spectrum, signals. This approach provides significant performance improvements over conventional implementations and can be configured in various ways. The system performance improvements compared to currently available systems include improved accuracy, integrity, availability, continuity, and reductions in the time intervals required to obtain a navigation (or related) determination and in the capabilities of the user equipment to operate dynamically, and/or in a signal interference environment.
BACKGROUND OF THE INVENTION
The United States, the Russian Federation and others (including the Europeans) have established, or plan to establish, orbiting satellite navigation systems. The GPS system, the GLONASS system and other systems, employ constellations of orbiting satellites which transmit signals to receivers on the earth (ground, airborne, marine) and in space which are used to determine precise three-dimensional position, velocity and time (e.g., latitude, longitude, altitude, 3D velocity and time) and in some cases angle (e.g., vehicle attitude) as well as differences and time derivatives of these parameters. Such signals can be used, for example, for navigation, surveying, timing, positioning and for measuring dimensional and other changes over time. Both the GPS and GLONASS systems use two separated bands of frequencies in the L-band portion (~1-2 GHz) portion of the electromagnetic spectrum. These bands have been allocated for radionavigation satellite services by the International Telecommunications Union (ITU).
In the case of both the GPS system and the GLONASS system, the frequency bands are designated L
1
for the higher frequency band and L
2
for the lower frequency band. A detailed description of the signal structure used for the GPS system is provided in Kayton, M. and W. R. Fried, Avionics Navigation Systems, 2d Ed., Chapter V, Satellite Radionavigation by A. J. Van Dierendonck, Section 5.5.5 GPS Signal Structure, pp. 213-282, John Wiley and Sons, Inc., New York, N.Y., 1997, which description is hereby incorporated by reference herein.
Referring to the drawings,
FIG. 1
shows the existing GPS signal structure, generally designated by reference numeral
10
. In
FIG. 1
, C/A designates the existing GPS coarse/acquisition code modulation on the L
1
carrier, while P/Y indicates the GPS precise/encrypted code modulation of the L
1
and L
2
carriers, and L
2
&phgr; indicates the “carrier phase” part of the P/Y-code signal at L
2
that is authorized for civil use (for ionospheric correction).
For the L
1
band, the signal energy of the C/A-code is concentrated at the center of the bands
12
, with very little C/A-code energy at or near the P/Y-code nulls
14
,
16
. For the L
2
band, there is no C/A-code signal centered in the band
18
and no C/A-coded signal at or near the P/Y-code nulls
20
,
22
.
Throughout the drawings, the frequency occupancies of the bands (to their first spectral nulls) are shown, not the shape of the waveform, or signal power distribution, of each band. Those skilled in the art who have reviewed the present disclosure will readily appreciate the waveform shape in each situation.
Known systems have a number of drawbacks including the following: First, civil (Standard Positioning Service, or SPS) accuracy for differential systems using C/A-code corrections is normally to within several meters. To obtain accuracy within centimeters or decimeters adds considerable cost and complexity to the user equipment and is reliably achieved only by the use of techniques involving differential measurements of the carrier phases of the received signals. One problem in achieving high accuracy is the need to resolve the integer cycle wavelength ambiguity associated with the carrier phase measurements. To accomplish this with the current signal structure now requires the use of sophisticated and expensive software processing, moderate to long observation periods for high accuracy, statistical estimates of the probabilities associated with the observations and careful measurements of the effects of the troposphere, the ionosphere and other error contributors on the signals, especially at large differential system (reference to rover) separation distances. Second, the signal modulations currently provided for civil and military uses (e.g., C/A-codes and P/Y-codes) have maxima near one another or are collocated in frequency (e.g., , both the C/A-codes and the L
1
P/Y-codes for GPS are centered at the GPS L
1
center frequency). This arrangement is undesirable for some military purposes as well as for some civil applications.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to improve accuracy and other performance characteristics at a moderate cost.
It is a further object of the invention to separate the signals available for civil use from the maxima of the signals for military use. This can be accomplished by (a) moving the civil signals away from the center of the band if the planned military signals (Lm) are to occupy the center of the band, or (b) moving the planned military signals away from the center of the band if the existing and planned civil signals are to be in the center of the band. While the first option (a) will be disclosed in detail, either can be used.
To achieve the above and other objectives, the present invention improves position, velocity, time and angle (attitude) determinations obtained by user equipment receiving radionavigation satellite (or other) signals by establishing and exploiting a new signal structure. This signal structure provides a number of features including means for rapidly and accurately resolving the carrier cycle integer ambiguities in the use of the signals for carrier phase measurement applications. This is accomplished by user systems using three (3) or more signals obtained from four (4) or more satellite (or other) signal transmitters. Specifically, addressing the use of the designated signal structure with GPS signals (and applicable to GLONASS and other signals), the existing signal structure for the GPS L
1
band or the L
2
band, or both, is modified to use dual (or split spectrum) signals. One representative implementation of the technique would be to use a pair of GPS coded signals (such as coarse acquisition, or C/A-code, signals, or other coded signals) at, or near (within several MHz, e.g., 2 to 6 MHz) of the P/Y-code nulls. The P/Y-code nulls refer to the GPS precision coded (PPS or P-coded) signals, with bi-phase modu

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