Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-06-22
2003-10-21
Vuong, Quochien (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S433000
Reexamination Certificate
active
06636742
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a method for determination of the location of terminal equipment in a cellular mobile communications system including several base transceiver stations and wherein the terminal equipment may move from one cell to another and from one traffic area to another during the traffic connection.
TECHNICAL BACKGROUND
When a terminal in a mobile telephone network is in a traffic or signalling connection with the network, information about the location and movement of the terminal equipment in the network has not been of primary importance in most cases. However, in some cases information about the location and movement of the terminal equipment is a desirable network operator service. One such case is e.g. when the authorities for some reason wish to trace the movement of a certain terminal in the network.
The following is a description of the structure and operation of a mobile telephone network using as an example the GSM mobile telephone network shown in FIG.
1
. Other digital mobile telephone networks include the same network elements as those in the GSM network. Communication between the network and mobile station MS in the cell takes place via the radio path by way of base transceiver station BTS. Base transceiver stations BTS are connected to base station controller BSC. Several base transceiver stations BTS are usually under the control of one base station controller BSC and they can be chained to one another or cabled directly to the base station controller, as is illustrated in the figure. The geographical area covered by these base transceiver stations is called location area LA and the calls intended for the mobile stations in this area are sent through these base transceiver stations.
FIG. 1
shows six location areas. The mobile station may move within the location area without any need to update the location data concerning the mobile station.
Several base station controllers are connected to one mobile switching centre MSC, which carries out the main switching functions of the mobile telephone network. In addition, it connects the mobile telephone network with external networks. The entity of location areas under the management of the mobile switching centre is called the switching centre area. In the figure, the switching centre area of the MSC
1
switching centre includes location areas a, b and c, while the switching centre area of the MSC
2
switching centre includes location areas d, e and f. All calls beginning from and ending in the switching centre area are relayed by way of the same mobile switching centre. If a mobile station network includes several mobile switching centres like switching centres MSC
1
and MSC
2
in the figure, their switching centre areas together form the system area of the mobile communications network, which means the geographical area covered by one network. The network is almost always run by one operator.
The mobile telephone network also includes various databases. Subscriber data is stored permanently in home location register HLR, irrespective of the current location of the subscriber. If the network is large and there are many subscribers, then several home location registers are used, in the figure these are HLR a, HLR b and HLR c respectively. The number space is divided to these registers, whereby the search for subscriber data is quicker. Visitor location register VLR is nowadays integrated with each mobile switching centre and the subscriber data fetched from the home location register is stored therein while the subscriber visits the area of the VLR, that is, the switching centre area. For example, in
FIG. 1
subscriber data of a mobile station located in cell
1
is stored in home location register
5
connected to mobile switching centre MSC
1
. Mobile station MS may move freely within the location area a without any need to update this data.
Location update is done every time when the subscriber connects to the network. When a subscriber e.g. in cell
1
,
FIG. 1
, turns on his mobile station MS, it signals a location update request to base transceiver station
2
, and the request is directed by way of base station controller
3
to mobile switching centre MSC
1
and further to visitor location register VLR indicated by reference number
5
. The register asks the subscriber to send his subscriber code, from which the VLR learns the subscriber's home location register, which in this case is HLR a. Visitor location register VLR asks home location register HLR a to send the authentication parameters needed for the identification of the subscriber and for encrypting the connection. After a successful authentication of the subscriber, home location register HLR a knows that area of the visitor location register, that is, the mobile switching centre, in which the subscriber is located and it sends subscriber data to visitor location register
5
in question. The subscriber's location is now updated, that is, HLR knows the address of VLR
5
, and VLR
5
knows the location area a, wherein the mobile station is located.
Location update is also done every time when a subscriber moves from one location area to another, e.g. when in
FIG. 1
mobile station MS moves from location area
11
to location area
12
. This update is done on the mobile station's initiative, which informs the visitor location register about the changed location area. If the location area belongs to the same switching centre area, that is, to the control of same visitor location register VLR, as in our example, then there is no need to change the address of visitor location register
5
which is stored in home location register HLR a. The address is changed only if the subscriber moves to another switching centre area, e.g. from location area c to location area d, whereby visitor location register
7
tells its address to home location register HLR a, and the home location register sends the subscriber data to visitor location register
7
.
Location update can also be made periodically at certain intervals (Periodic Location Update). Hereby the location update is triggered off when the time counter in the mobile station is full.
Based on the above it is known that the home location register always knows the visitor location register connected to the mobile switching centre in whose mobile services switching centre area the subscriber is located, and the visitor location register knows in which location area the subscriber is located. The code of the location area is unambiguous. When the subscriber is moving in any network, this data is updated. This is also true in part, if the subscriber is moving in the network of such another operator, with whom the own operator has a roaming contract. In this case the only thing which the home location register knows about the subscriber is whose network the subscriber is registered with. In case of a foreign country, what is known is in which country and in which operator's network the subscriber is located.
System management is an important part of the mobile telephone system. In most cases the management function is centralised in an Operation & Maintenance Centre OMC, from which the configuration, management and testing of network elements and downloading of software etc. are performed by remote control and in a centralised manner. In the figure, the dashed lines beginning from operation and maintenance centre
8
and ending in network elements illustrate management connections. Another important mobile telephone system is the network planning system, which is used for computing the network topology when new cells are added, old ones are removed and cell sizes are changed. This network planning system knows the co-ordinates of base transceiver stations and the coverage areas of cells. Network planning can also be included in the system management.
Reference is now made to FIG.
2
and to
FIGS. 3A-3B
.
FIG. 2
shows in a condensed manner that information essential for the invention which the different network elements have about the subscribe
Gröhn Tuomo
Torkki Markus
Cohen & Pontani, Lieberman & Pavane
Sonera Oyj
Vuong Quochien
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