Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-11-16
2004-04-27
Tran, Sinh (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S456100, C455S041200, C455S457000, C342S457000, C342S357490
Reexamination Certificate
active
06728545
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system and method for computing the location of a mobile terminal in a wireless communications network, such as an ad-hoc wireless communications network. More particularly, the present invention relates to a system and method for computing the location of a mobile terminal in a wireless communications network, such as an ad-hoc terrestrial wireless communications network, based on estimated distances to a plurality of terrestrial reference terminals using error minimizing techniques, such as Gauss's postulate.
2. Description of the Related Art
Wireless communications networks, such as mobile wireless telephone networks, have become increasingly prevalent over the past decade. These wireless communications networks are commonly referred to as “cellular networks”, because the network infrastructure is arranged to divide the service area into a plurality of regions called “cells”.
Specifically, a terrestrial cellular network includes a plurality of interconnected base stations that are distributed geographically at designated locations throughout the service area. Each base station includes one or more transceivers that are capable of transmitting and receiving electromagnetic signals, such as radio frequency (RF) communications signals, to and from user terminals, such as wireless telephones, located in its coverage area. The communications signals include, for example, voice data that has been modulated according to a desired modulation technique and transmitted as data packets. As can be appreciated by one skilled in the art, the transceiver and user terminals transmit and receive the data packets in multiplexed format, such as time-division multiple access (TDMA) format, code-division multiple access (CDMA) format, or frequency-division multiple access (FDMA) format, which enables a single transceiver at the base station to communicate simultaneously with several user terminals in its coverage area.
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed for use by the military. In this type of network, each user terminal is capable of operating as a base station or router for the other user terminals, thus eliminating the need for a fixed infrastructure of base stations. Details of an ad-hoc network are set forth in U.S. Pat. No. 5,943,322 to Mayor, the entire content of which is incorporated herein by reference.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling user terminals to communicate with each other as in a conventional ad-hoc network, further enable the user terminals to access a fixed network and thus communicate with other user terminals, such as those on the public switched telephone network (PSTN), and on other networks such as the Internet. Details of these types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, and in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, the entire content of both of said patent applications being incorporated herein by reference.
In either conventional wireless communications networks, or in ad-hoc wireless communications networks, it may be necessary or desirable for a user terminal to be capable of knowing or determining its geographic location. Different types of location determining services and techniques for wireless communications networks are described in a publication by Nokia which can be found on the Nokia website at “www.nokia.com/press/background/pdf/mlbs.pdf”, the entire contents of which being incorporated herein by reference. In particular, the Nokia document states that location identification services are currently provided in wireless communications networks based on three major technologies. One of these technologies uses cell identification combined with Round Trip Time (RTT), Timing Advance (TA) and Measured Signal level (RX level), Time Difference of Arrival (TDOA) and Angle Of Arrival (AOA) techniques, the details of which can be appreciated by one skilled in the art. A second technology uses cellular signal timing based methods for code division multiple access (CDMA) and wideband code division multiple access (WCDMA). The third technology described in the Nokia document employs Global Positioning System (GPS) techniques.
Another list of methods and techniques currently used in the wireless communications industry for providing location services can be found at “www.911dispatch.com/911_file/location_tech.html”, the entire contents of which being incorporated herein by reference. Although the GPS technique is the last technique mentioned in this list, it generally is viewed as being more accurate than all of the other methods. Further details and descriptions of GPS based methods are set forth in a publication by J. J. Spilker Jr. entitled “Satellite Constellation and Geometric Dilution of Precision” in “GPS—Theory and Applications”, American Institute of Astronautics, Inc., 1996, in a publication by P. Axelrad et al. entitled “GPS Navigation Algorithms” in “GPS—Theory and Applications”, American Institute of Astronautics, Inc., 1996, in a publication by Bradford W. Parkinson entitled “GPS Error Analysis” in “GPS—Theory and Applications”, American Institute of Astronautics, 1996, and in a publication by N. Ashby et al. “Introduction to Relativistic Effects on the Global Positioning System” in “GPS—Theory and Applications”, American Institute of Astronautics, 1996, the entire contents of each of these publications being incorporated herein by reference.
Despite the fact that the GPS technique has been in use for a considerable duration of time and most of the world's navigation relies on this technique, the GPS technique is very susceptible to errors in measurement. Therefore, the GPS technique is capable of providing location determination results with very high accuracy only after performing a relative large number of measurements to remove such errors. A description of the shortcomings of GPS is set forth in a document by IMA entitled “
Mathematical Challenges in Global Positioning Systems
(GPS)” which can be found at “www.ima.umn.edu/gps”, the entire contents of this document being incorporated herein by reference. Certain other tests also demonstrate that the GPS technique is unsuitable for terrestrial-based networks.
In addition, other methods and techniques which do not use GPS satellites for determining mobile station locations in a wireless communications network typically require that the signal from the mobile station is received at at least two cell sites that can measure and process the delay between signals arrival, identify the direction of the signal based on “path signature” and determine the distance between mobile station and the cell towers. In all of these methods, the processing of the information is executed in a designated central processing unit (CPU) which is typically located at a cell tower next to the base station (BTS). Also, most of these methods were designed to comply with E911 requirements without requiring that excessive modifications be made to existing wireless communications systems. Examples of other location determining techniques are set forth in a document by CERN—European Organization for Nuclear Research, which can be found at “rkb.home.cern.ch/rkb/ANI16pp
ode98.html#SECTION00098000000000000000”, in a document by Wendy J Woodbury Straight entitled “Exploring a New Reference System”, which can be found at “menstorsoftwareince.com/profile
ewref.html”, and in a document entitled “An Introduction to SnapTrac Server-Aided GPS Technology”, which can be found at “www.snaptrack.com/pdf/ion.pdf”, the entire contents of each of the
Afshar Kamran
Buczynski Joseph J.
MeshNetworks, Inc.
Roylance Abrams Berdo & Goodman L.L.P.
Tran Sinh
LandOfFree
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