Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
1999-04-30
2001-01-09
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C342S461000
Reexamination Certificate
active
06172639
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to obtaining highly precise position, velocity, time and attitude measurements by the use and processing of multiple signals separated in frequency and their sum and difference measurements. One application is in the resolution of the integer cycle ambiguities associated with precise carrier phase measurements of the signals used in satellite navigation systems such as the U.S. Global Positioning Satellite (GPS) System or the Russian Global Orbiting Navigation Satellite System (GLONASS), or other systems. The use of dual or “split spectrum” signals in one or more bands assigned to GPS, GLONASS or other systems provides substantial performance improvements over current implementations. This approach, which can be implemented in various configurations, provides significant system performance improvements including improvements in accuracy, integrity, availability and continuity.
BACKGROUND OF THE INVENTION
Both the United States and the Russian Federation have established orbiting satellite navigation systems, and the Europeans are planning a system. The GPS system and the GLONASS system each employ a constellation of orbiting satellites which provide signals to receivers on the earth (ground, airborne, marine) and in space which are used to determine precise three-dimensional positions and time (e.g., latitude, longitude, altitude, time). Such signals can be used, for example, for navigation, surveying, timing, positioning and for measuring dimensional and time changes. Both the GPS and GLONASS systems each use two separated bands of frequencies in the L-band portion of the electromagnetic spectrum which have been allocated for radionavigation satellite services by the International Telecommunication Union (ITU).
In the case of both the GPS system and the GLONASS system, the frequency bands are designated L1 for the higher frequency band and L2 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,
2
d 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 L1 carrier, while P/Y indicates the GPS precise/encrypted code modulation of the L1 and L2 carriers, and L2&phgr; indicates the “carrier phase” part of the P/Y-code signal at L2 that is authorized for civil use (for ionospheric correction).
For the L1 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 L2 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 the following drawbacks. First, accuracy is normally to within several meters; accuracy to within centimeters or decimeters adds considerable cost and complexity and is reliably achieved only by the use of differential measurements of the carrier phases of the received signals. One problem in achieving high accuracy is the problem of resolving the integer wavelength ambiguity associated with the carrier phase measurements. Second, modulations provided for civilian and military uses have maxima near one another (or collocated in frequency), which is undesirable for some military purposes.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to improve accuracy at a moderate cost.
It is a further object of the invention to separate the signals available for civilian 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 bands. While the first option will be disclosed in detail, either can be used.
To achieve the above and other objects, the present invention improves position, velocity, time and attitude determinations using radionavigation satellite signals by the use of a new signal structure which 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. Specifically, for the use with GPS signals (and applicable to GLONASS and other signals), the existing signal structure for either the L1 band or the L2 band, or both, is modified to use dual signals by locating a pair of GPS coded signals (such as coarse/acquisition, or C/A, signals, or other coded signals) at, or near - (within several MHz of), the P/Y-code nulls. The P/Y-code nulls refer to the GPS (or GLONASS) precision coded (P-code) signals, with bit rates of 10.23 Mbps for GPS and 5.11 Mbps for GLONASS. The Y-code is the encrypted GPS P-code, at the P-code bit rate. The first nulls of these codes occur at a frequency offset above and below their carrier center frequencies by the code bit (or “chipping”) rate and thereby constitute a first lower null and a first upper null. In the case of the L2 band, a first coded signal could be located near (or at) the frequency corresponding to the lower P/Y-code null and a second coded signal could be located near (or at) the frequency corresponding to the upper P/Y-code null. In the case of the L1 band, a third coded signal could be located near (or at) the frequency corresponding to the lower P/Y-code null and a fourth coded signal could be located near (or at) the frequency corresponding to the upper P/Y-code null. Permanently, or for a transitional period in this exemplary configuration, a coded signal could also be located (or retained) at the carrier frequency corresponding to the current C/A code of the GPS signal in the L1 band, for backward compatibility purposes.
The present invention offers the advantage of permitting GPS and other users to obtain accurate position, velocity, time, attitude and other information, from measurements obtained between a user and a set of spacecraft emitters (such as GPS satellites), or other emitters, including ground-based emitters. These measurements are of range, range difference, range rate (singly or in combination), differential carrier phase and phase differences, using three or more separate signals operating at differing frequencies such that the signals, their sum and difference signal frequencies, their differential carrier phases and their phase differences provide ranging and other information which provides a means for resolving the range, range difference, carrier phase and phase difference ambiguities as well as the integer cycle ambiguities associated with measurements of the relative carrier phase of the signals. The multiple frequency step-wise resolution of the differential carrier phase integer cycle ambiguities is a significant aspect of the present invention.
REFERENCES:
Keith McDonald, “GPS Civil Modernization Activity”, ION Newsletter, Mar. 6, 1998.
Keith McDonald, “Technology, Implementation and Policy Concerns for a Future GNSS,” Geomatics Info Magazine, Feb., 1998, pp. 30-33.
McDonald, Keith D., “GPS Civil Modernization Activity,” ION Newsletter, Mar. 6, 1998.
McDonald, Keith D., “Technology, Implementation and Policy Concerns for a Future GNSS,” Geomatics Info Magazine, Feb. 1988, pp. 30-33.
McD
Blank Rome Comisky & McCauley LLP
Phan Dao L.
Tarcza Thomas H.
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