Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
1999-05-18
2001-09-04
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490, C342S357490, C701S215000
Reexamination Certificate
active
06285315
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to positioning systems using radio-frequency signal transmitting orbiting satellites.
BACKGROUND OF THE INVENTION
A receiver of a satellite based positioning system obtains measured data from a plurality of orbiting satellites by observing the transmission delay between the emission of the radio signals from the satellites and their reception at the mobile receiver or, more particularly, an antenna of the mobile receiver. The position of the device which is to be determined is commonly referred to as a ‘mark’. Each receiver is equipped to receive and process the radio frequency signals. For a receiver to be able to estimate the position of the mark, certain requirements need to be met. Although the particular requirements depend on the particular type of positioning system, both knowledge of the orbits of several satellites and radio frequency signals from the orbiting satellites is required for all types of positioning system. The other requirements which may need to be met depend on the type of positioning system.
Knowledge of the orbits of each of several satellites is necessary if the method used to estimate the location of the mark is based on triangulation using estimates of the distance from each satellite to the mark. Knowledge of the orbit of each satellite is required so that the position of each one can be determined at the time of transmission of each of the radio frequency signals used for distance measurement. This is normally provided in mathematical form, valid within certain accuracy limits for a specific period of time.
Dissemination of the orbital data is usually in the form of a model and by way of data transmission from the satellite itself. Other techniques are known such as the publication of precise orbit data some time later, or transmission over a terrestrial data link. In any case, a format for the data is usually sought which provides a balance between complexity, accuracy and the duration of the applicability or validity of the orbital model.
The parameters used in such models are ephemeral. For ideal satellite bodies in orbit above a single, perfectly spherical, uniform host (planet), the orbits described would be exactly elliptical. These orbits would, in principle, persist for long periods of time. In practice, however, the satellite is subject to influences other than the obvious gravitational and centripetal forces. These include but are not limited to: the effects of other (celestial) bodies, such as the Sun, the Moon and other planets; the solar wind, which is the result of a stream of particles continuously emitted from the Sun; gravitational anomalies caused by the non-uniformity of the Earth; and the effects of a non-spheroidal Earth-the Earth is approximately an oblate spheroid.
Consequently, it is practical to provide models, which are each valid for limited periods of time, covering the orbit of a satellite in a series of segments. Such time variable parameters for an orbit description have become known as ephemeris models. The balance of complexity for such models is carefully judged and depends on many application sensitive factors including the work load necessary for maintenance of the ephemeris models. These balances are frequently optimised for the most efficient data transmission from the satellites, but may not be optimised for other applications or data links.
The ephemeris data for a GPS satellite is contained in a data message of 1500 bits length, transmitted over a period of 30 seconds, of which approximately 900 are involved in the description of the ephemeris model. These 900 bits are referred as ephemeris data.
The ephemeris data is valid for typically one or two hours, depending on the factors influencing the orbit of the satellite.
It is proposed in U.S. Pat. No. 5365450 to include in a positioning system using radio-frequency signal transmitting, orbiting satellites, a terrestrial station which receives ephemeris data from all “in-view” satellites and transmits the ephemeris data to a mobile station on a cellular telephone channel. The data is transmitted over the cellular telephone channel much more quickly than it is transmitted by the satellites, allowing the mobile station to more rapidly determine its position than previously.
It is an object of the present invention to provide an improved satellite orbital model transmission format for elements of a positioning system in which the data link is a terrestrial data link.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a method of determining the position of a mobile station, comprising: receiving at a terrestrial station ephemeris data from each of a plurality of satellites, the ephemeris data being indicative of the orbit of the respective satellite; processing the ephemeris data to provide processed data which is indicative of the orbit of the respective satellite but is in such a form that less subsequent processing of the data is required to determine the information about the orbit of the satellite which is required to perform position determination; transmitting the processed data; receiving the processed data at the mobile station; and using the processed data at the mobile station in conjunction with signals received at said mobile station from the associated satellites to determine the position.
The processing of the ephemeris data may include a co-ordinate conversion process. In this case, the processed data preferably use a co-ordinate system to indicate the orbit of the satellite such that no co-ordinate conversion process is required when using the processed data at the mobile station to determine the position. The processed data may define the orbit of the respective satellite in Cartesian form.
The processed data preferably includes a time tag which is indicative of the time from which the processed data is valid or the time until which the processed data is valid.
According to second aspect of the present invention, there is provided a mobile receiver comprising: a first receiver channel for receiving positioning signals from a plurality of positioning satellites; a second receiver channel for receiving processed ephemeris data from a terrestrial station; and a processor connected to the first and second receivers and arranged to use the positioning signals in conjunction with the processed ephemeris data to compute an output representative of the position of the mobile receiver, wherein the second receiver channel and the processor are arranged respectively to receive and process the processed ephemeris data in a form in which the orbits of the satellites are so defined that the amount of processing required in the processor to generate the information about the satellite orbits which is needed to compute the output is less than that which would be required if the ephemeris data were received from the terrestrial station in the form transmitted by the satellites.
The processed ephemeris data is preferably in such a form that the processor does not need to perform a co-ordinate conversion process to compute the output. In this case, the processor is preferably arranged to process the processed data received from the terrestrial station with the satellite orbit defined in Cartesian form.
The processor may be arranged to detect a time tag in the processed ephemeris data and to determine the position of the mobile receiver only if the time tag indicates the data to be valid for the time at which the computations are made.
The second receiver channel may be a radio telephone receiver. In this case, the receiver preferably further comprises a transmitter for requesting processed ephemeris data prior to position determination being performed.
According to a third aspect of the present invention, there is provided, for use in a system for determining the position of a mobile receiver, a terrestrial station, comprising: a receiver for receiving ephemeris data from each of a plurality of positioning satellites, the ephemeris data being indicative of the orb
Kilpatrick & Stockton LLP
Mull Fred H
Symmetricom, Inc.
Tarcza Thomas H.
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