Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1996-09-30
2001-12-04
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S213000, C701S225000, C342S357490, C342S357490, C342S357490, C342S357490, C455S012100, C455S013200
Reexamination Certificate
active
06327534
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to commonly-owned applications, filed concurrently herewith, entitled “Position Determination Using One Low-Earth Orbit Satellite” having application number (to be assigned, Attorney Docket Number PA286), “Passive Position Determination Using Two Low-Earth Orbit Satellites” having application number (to be assigned, Attorney Docket Number PA287), “Time And Frequency Precorrection For Non-Geostationary Satellite Systems” having application number (to be assigned, Attorney Docket Number PA338), and “Determination Of Frequency Offsets In Communication Systems” having application number (to be assigned, Attorney Docket Number PA300), which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to object position determination using satellites. More specifically, the present invention relates to a method for determining the position of a user terminal in a satellite communications system using measurements performed at both ends of a communication link.
II. Related Art
A typical satellite-based communications system comprises at least one terrestrial base station (hereinafter referred to as a gateway), at least one user terminal (for example, a mobile telephone), and at least one satellite for relaying communications signals between the gateway and the user terminal. The gateway provides links from a user terminal to other user terminals or communications systems, such as a terrestrial telephone system.
A variety of multiple access communications systems have been developed for transferring information among a large number of system users. These techniques include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA) spread-spectrum techniques, the basics of which are well known in the art. The use of CDMA techniques in a multiple access communications system is disclosed in U.S. Pat. No. 4,901,307, which issued Feb. 13, 1990, entitled “Spread Spectrum Multiple Access Communication System Using Satellite Or Terrestrial Repeaters,” and U.S. patent application Ser. No. 08/368,570, filed Jan. 4, 1995, entitled “Method And Apparatus For Using Full Spectrum Transmitted Power In A Spread Spectrum Communication System, For Tracking Individual Recipient Phase Time And Energy,” U.S. Pat. No. 5,691,974, which are both assigned to the assignee of the present invention, and are incorporated herein by reference.
The above-mentioned patent documents disclose multiple access communications systems in which a large number of generally mobile or remote system users employ user terminals to communicate with other system users or users of other connected systems, such as a public telephone switching network. The user terminals communicate through gateways and satellites using CDMA spread-spectrum type communications signals.
Communications satellites form beams which illuminate a “spot” or area produced by projecting satellite communications signals onto the Earth's surface. A typical satellite beam pattern for a spot comprises a number of beams arranged in a predetermined coverage pattern. Typically, each beam comprises a number of so-called sub-beams (also referred to as CDMA channels) covering a common geographic area, each occupying a different frequency band.
In a typical spread-spectrum communications system, a set of preselected pseudorandom noise (PN) code sequences is used to modulate (i.e., “spread”) information signals over a predetermined spectral band prior to modulation onto a carrier signal for transmission as communications signals. PN spreading, a method of spread-spectrum transmission that is well known in the art, produces a signal for transmission that has a bandwidth much greater than that of the data signal. In a forward communications link (that is, in a communications link originating at a gateway and terminating at a user terminal), PN spreading codes or binary sequences are used to discriminate between signals transmitted by a gateway over different beams, and to discriminate between multipath signals. These PN codes are typically shared by all communications signals within a given sub-beam.
In a typical CDMA spread-spectrum system, channelizing codes are used to discriminate between signals intended for particular user terminals transmitted within a satellite beam on the forward link. That is, a unique orthogonal channel is provided for each user terminal on the forward link by using a unique “channelizing” orthogonal code. Walsh functions are generally used to implement the channelizing codes, with a typical length being on the order of 64 code chips for terrestrial systems and 128 code chips for satellite systems.
Typical CDMA spread-spectrum communications systems, such as disclosed in U.S. Pat. No. 4,901,307, contemplate the use of coherent modulation and demodulation for forward link user terminal communications. In communications systems using this approach, a “pilot” carrier signal (hereinafter referred to as a “pilot signal”) is used as a coherent phase reference for forward links. That is, a pilot signal, which typically contains no data modulation, is transmitted by a gateway throughout a region of coverage. A single pilot signal is typically transmitted by each gateway for each beam used for each frequency used. These pilot signals are shared by all user terminals receiving signals from the gateway.
Pilot signals are used by user terminals to obtain initial system synchronization and time, frequency, and phase tracking of other signals transmitted by the gateway. Phase information obtained from tracking a pilot signal carrier is used as a carrier phase reference for coherent demodulation of other system signals or traffic signals. This technique allows many traffic signals to share a common pilot signal as a phase reference, providing for a less costly and more efficient tracking mechanism.
When a user terminal is not involved in a communications session (that is, the user terminal is not receiving or transmitting traffic signals), the gateway can convey information to that particular user terminal using a signal known as a paging signal. For example, when a call has been placed to a particular mobile phone, the gateway alerts the mobile phone by means of a paging signal. Paging signals are also used to distribute traffic channel assignments, access channel assignments, and system overhead information.
A user terminal can respond to a paging signal by sending an access signal or access probe over the reverse link (that is, the communications link originating at the user terminal and terminating at the gateway). The access signal is also used when a user terminal originates a call.
When communications are required with a user terminal, the communications system may need to determine the position of the user terminal. The need for user terminal position information stems from several considerations. One consideration is that the system should select an appropriate gateway for providing the communications link. One aspect of this consideration is allocation of a communications link to the proper service provider (for example, a telephone company). A service provider is typically assigned a particular geographic territory, and handles all calls with users in that territory. When communications are required with a particular user terminal, the communications system can allocate the call to a service provider based on the territory within which the user terminal is located. In order to determine the appropriate territory, the communications system requires the position of the user terminal. A similar consideration arises when calls must be allocated to service providers based on political boundaries or contracted services.
A crucial requirement in position determination for a satellite-based communications system is speed. When communications are required with a particular user terminal, the gateway that will serve the user terminal should be selected ra
Levanon Nadav
Vembu Sridhar
Victor Edward B.
Louis-Jacques Jacques H.
Ogrod Gregory D.
Qualcomm Incorporated
Wadsworth Philip R.
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