Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-08-27
2002-02-12
Maung, Nay (Department: 2661)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S432300, C455S433000
Reexamination Certificate
active
06347227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the problem of positioning of a mobile station (“MS”) in a Public Land Mobile Network (“PLMN”), and more particularly to the problem of establishing the most accurate estimate of the last known position of the mobile station when the mobile station has switched off or has left the coverage area of the network.
RELATED ART
There are currently developing various commercial and regulatory needs to be able to use the Public Land Mobile Network (“PLMN”) to geographically locate Mobile Stations (“MS”). An example of a PLMN is the GSM (“Global System for Mobile communications”) system. A simplified schematic of a GSM system is shown in
FIG. 1
a
. There is first a mobile station
110
which is usually the only equipment the subscriber sees from the whole system. The subscribers telephone, or terminal, connects over a radio interface to Base Station Sub-System (“BSS”)
120
. Roughly speaking, the Base Station Sub-System
120
groups together the infrastructure machines which are specific to the radio cellular aspects of GSM.
The BSS
120
is in direct contact with mobile stations through the radio interface. On the other side, the BSS
120
is in contact with the switches of the Switching System (“SS”)
130
. The role of the BSS
120
can be summarised as to connect the mobile station
110
and the Switching System
130
, and hence the mobile station's user with other telecommunications users. The BSS
120
has to be controlled and is thus also in contact with the Operation Sub-System (“OSS”)
140
.
The Switching Sub-system
130
includes the main switching functions of GSM, as well as the databases need for subscriber data and mobility management. The main role of the Switching Sub-system is to manage the communications between the GSM users and other telecommunications network users. These other networks can include other PLMNs
151
, the PSTN (“Public Switched Telephone Network”)
152
, CSPDN (“Circuit Switched Public Data Network”)
153
, PSPDN (“Packet Switched Public Data Network”)
154
, and ISDN (“Integrated Services Digital Network”)
155
.
Within the SS, the basic switching function is performed by the Mobile Services Switching Centre (“MSC”)
131
, whose main function is to co-ordinate the setting-up of calls to and from GSM users. The MSC
131
has interfaces with the BSS
120
on one side and with the external networks
150
on the other side. However, the direct connections between the external networks
150
and a GSM system are routed through a Gateway-MSC (“GMSC”), not shown here. All incoming calls for a GSM/PLMN network will be routed to one or more GMSCs which work as an incoming transit exchange for the GSM/PLMN. Besides MSCs
131
, the Switching Sub-system
130
includes databases. Subscriber information relevant to the provision of telecommunications services is held on the infrastructure side in the Home Location Register (“HLR”)
132
, independently of the actual location of the subscriber. The HLR
132
also includes some information related to the current location of the subscriber. Every telecommunications system includes a database containing a variety of information concerning each subscriber, such as the subscription limitations, the services subscribed to, charging information, etc. In a fixed network, each subscriber is connected to one local switch, for a long time. Every call involving this subscriber goes through this switch. This is then the natural place to store the subscriber related information. In a system dealing with moving subscribers, there is no such natural place for storage. However, two kinds of data to be stored (location information and subscriber data) call for a common storage solution. This is the choice made in GSM, and the HLR
132
is the database for both sets of information.
If location information is needed only for the establishment of mobile terminating calls, the rest of the information is needed at various moments during any call. Basically, it is the visited Mobile Switching Centre
131
, the one in charge of a mobile subscriber engaged in a call, which needs these pieces of information. This would result in a substantial signalling load if the MSC
131
had to interrogate the HLR each time it needs some piece of information.
To avoid this signalling load, the data record of a subscriber is copied into a database close to the MSC
131
while this subscriber is registered in a location area (“LA”) controlled by the MSC
131
. This database is the Visitor Location Register (“VLR”)
133
. The information regarding those subscribers which are registered under an MSC
131
connected to the VLR
133
is stored in the VLR
133
, but only temporarily.
This introduces new functions. The subscriber information has to be copied when the subscriber enters a new MSC/VLR area. Conversely, the corresponding record has to be erased in the previous MSC/VLR area in which the subscriber was registered. This updating of the databases is done when certain events occur. These events include call set-up, handovers, call complete, IMSI (International Mobile Subscriber Identity) attach (i.e. when the mobile station switches on), IMSI detach (i.e. when the mobile station switches off) and location updates.
As mentioned above, there is increasing demand for the development of PLMN-based positioning. PLMN-based positioning can be considered to consist of four parts: a Positioning Procedure, a positioning gateway, applications, and signalling mechanisms.
The first of these four parts is a Positioning Procedure. This is a mechanism which is used by the network, e.g. GSM, to find out and report relative, or in some cases absolute, data about the location of the Mobile Station. Different Positioning Procedures can exist in the network simultaneously. These different Positioning Procedures can each have their own technical solutions and degrees of accuracy. The degrees of accuracy can range from the whole Service Area of the PLMN down to below 100 meters. However, in general, the higher the degree of accuracy, the higher the cost to the network in terms of signalling capacity and load.
One example of such a Positioning Procedure is GPS, Global Positioning System. GPS is satellite based system wherein a mobile station must be equipped with a GPS terminal. The GPS terminal can determine its position through reception of signals from at least three satellites. The position of the mobile station can then be acquired by the application, for example, polling the GPS terminal, after which the position information is sent over the network to the application.
Another possible Positioning Procedure is for the PLMN to measure the wave propagation time for the signal from the mobile station to a base station. The propagation time then corresponds to the position of the mobile station. The position of the MS can then be determined with certainty by repeating these measurements from two more base stations. It is also known to determine the mobile stations position by having the mobile station perform measurements on the signals from three base stations instead.
The second part of PLMN-based positioning is a positioning gateway. In the present patent application this will be referred to as a Mobile Positioning Centre (“MPC”)
170
. The Mobile Positioning Centre uses the data from the Positioning Procedure, e.g. GPS, to calculate the absolute position of the Mobile Station and distribute the position information to the applications, discussed below. The MPC
170
is connected to the PLMN via the Gateway Mobile services Switching Centre (“GMSC”). An example of a possible system using a Mobile Positioning Centre
170
is shown in
FIG. 1
b.
The third part of PLMN-based positioning consists of the applications that are the users of the positioning information retrieved from the network. The applications send the request for positioning information to the Mobile Positioning Centre
170
, which retrieves the information from the network in a method according to the present invention and then forwards
Burns Doane Swecker & Mathis L.L.P.
Davis Temica M.
Maung Nay
Telefonaktiebolaget LM Ericsson
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