Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
1997-12-04
2002-07-02
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S457000, C342S465000
Reexamination Certificate
active
06414634
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of radio communications and, more particularly, to a method and apparatus for locating wireless terminals.
BACKGROUND OF THE INVENTION
There are a number of different types of communications systems that require information regarding the location of an object or element in order to operate efficiently.
For example, some wireless communications systems require information regarding the location of a receiving unit in order to efficiently route signals from a transmitting unit to the receiving unit, and vice versa.
In cellular communications systems, for example, the cellular network (i.e. the network of base stations) requires information regarding the identity of the cell in which a wireless terminal is located in order to efficiently route signals to and from the wireless terminal. Once the cell is identified, the cellular network can send a signal to the wireless terminal through a base station that provides coverage to the identified cell. This enables the cellular network to deliver the signal to the wireless terminal without having to transmit the signal through every base station. As a result, the cellular network is able to avoid consuming bandwidth in those cells in which the wireless terminal is not resident, and thus increase the overall efficiency of the cellular system.
Although present-day cellular networks identify the cell in which the wireless terminal is located, they do not identify the exact geolocation of the wireless terminal in that cell. The term geolocation as used herein refers to the point in two or three-dimensional space defined by a set of coordinates (e.g. longitude and latitude) and/or defined by a vector (i.e. distance and direction) from a known point in space. This lack of geolocation information greatly decreases the efficiency of the cellular system when the wireless terminal moves from cell to cell. In addition, the lack of geolocation information reduces the number of services that a given cellular system can provide (e.g. roadside assistance, fleet management, etc.).
To illustrate, cellular systems in North America presently use a so-called system-wide paging approach to identify the cell in which a wireless terminal is located. Pursuant to that approach, the wireless terminal periodically transmits identification information, referred to as registration, to the cellular network. Depending on the location of the wireless terminal, the registration signal can be received by any number of base stations, each base station covering a specific cell. The cellular network identifies the cell in which the wireless terminal is located by comparing the strength of the registration signal received at each base station. The base station that receives the strongest registration signal is identified as the cell in which the wireless terminal is presently located. Once the “present” cell is identified, the cellular system can then communicate with the wireless terminal through the base station that covers that cell.
If the wireless terminal moves out of the present cell, the cellular system must send a page to the wireless terminal through a plurality of cells and wait for the wireless terminal to send another registration. Once the new registration is received, the cellular system can then identify the new cell in which the wireless terminal is located by comparing the signal strengths, as described above. As a result, the cellular network must consume additional bandwidth to periodically identify the cell in which the wireless terminal is located.
In addition, if the user of the wireless terminal makes a call for help (e.g. because the user is in distress), the wireless network can not identify the geolocation from which the wireless user made the call. As a result, unless the user can accurately identify his or her location, the wireless network can provide only limited help in the dispatch of aid to the user. Thus, present-day cellular systems in North America, for example, are not very useful to other service providers, such as roadside assistance and medical emergency care.
One solution to this problem is to equip the wireless terminal with the ability to identify its own geolocation. For example, the wireless terminal can be equipped with a Global Positioning System (GPS) receiver that receives GPS signals and uses those signals to determine the geolocation of the wireless terminal. Once determined, the geolocation information can be periodically sent to the cellular network. This would enable the cellular network to periodically identify the geolocation of the wireless terminal without having to consume additional bandwidth sending pages. In addition, this solution would enable the cellular network to track the movement of the wireless terminal from cell to cell, and thus predict and/or anticipate the time to hand-off communications from one cell to the next. As a result, this solution would enable the cellular network to increase the overall efficiency of communications, and to provide additional information to service providers such as roadside assistance providers (e.g. to located a user in distress).
The just described solution, however, is disadvantageous because the additional hardware needed to equip the wireless terminal with the ability to identify its own geolocation would increase the price, size and weight of the wireless terminal to unappealing proportions. Indeed, there is an ongoing effort by those skilled in the art to reduce the price, size and weight of present-day wireless terminals (e.g. cell phones).
Techniques are known, outside the cellular communications arena, for identifying the geolocation of a transmitting unit. For example, in some satellite communications systems, the geolocation of a transmitting unit is identified by determining the times in which the line-of-sight components of a signal transmitted from the transmitting unit reached a respective receiver locations. The line-of-sight component of the so-called incoming signal at each receiver location is that component of the signal that propagated directly from the wireless terminal to the location at which the signal was received (i.e. the receiver location) without scattering or reflecting off structures in the environment. To determine the time-of-arrival of the line-of-sight component of the incoming signal, such satellite geolocation systems assume that the first-arriving component of the incoming signal is the line-of-sight component. Then, based on the time-of-arrival of the first-arriving component of the incoming signal at, for example, three receiver locations, the geolocation of the wireless terminal is calculated.
Such conventional geolocation systems, however, are hindered by their failure to consider the problems associated with scattering in the RF environment. Scattering refers to the phenomenon wherein signals traveling in an RF environment reflect off structures in the environment, and thus scatter in various different directions or paths in the RF environment. Specifically, scattering may cause a signal to travel more than one path between two points (e.g. a wireless terminal and a receiver location) in an RF environment. This so-called multipath phenomenon may cause an incoming signal at a receiver location to be composed of a plurality of so-called multipath components (i.e. repeated versions of the transmitted signal). Thus, depending on the propensity of the RF environment to scatter a signal, referred to herein as the scattering hostility, the incoming signal at the receiver location may be composed of a number of such multipath components.
Scattering and/or multipathing may cause the first-arriving component of the incoming signal to arrive at the receiver location very close in time to the time-of-arrival of the next-arriving multipath component of the incoming signal. A conventional geolocation system may not be able to distinguish between the two components, causing it to mistakenly determine that the time of arrival of the first-arriving component is at some intermedia
Harness & Dickey & Pierce P.L.C.
Issing Gregory C.
Lucent Technologies - Inc.
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