WO1999020064A1

WO1999020064A1 - Cellular radio system with home area definition

Info

Publication number: WO1999020064A1
Application number: PCT/GB1998/003020
Authority: WO
Inventors: Alan James Clapton; David Gordon Smith
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 1997-10-15
Filing date: 1998-10-08
Publication date: 1999-04-22
Anticipated expiration: 2000-04-15
Also published as: AU9358998A

Abstract

A geographical zone specific to a given mobile telephone (10) is defined in a database (15) associated with the cellular telephone network, for example to allow differential tariffs in zones tailored to the individual users. On a registration signal being transmitted by the mobile telephone (10) the network identifies the currently serving cell (11) as a home cell for the mobile telephone, and stores the identity of the 'home cell' (11) as an attribute of the mobile telephone. The zone is then defined in relation to the home cell, for example as the 'neighbour list' of cells which are handover candidates from the home cell (11), or those cells within a predetermined distance of the home cell (11). As the network is modified by the addition of new cells, or the resiting of existing ones, the definition of the zone defined by each cell (11), as stored in the database (15), can be modified by the network planning function (14).

Description

CELLULAR RADIO SYSTEM WITH HOME AREA DEFINITION

This invention relates to cellular radio systems and in particular a system for defining a zone, specific to an individual user, for purposes of providing different types of service to the user according to whether he is within the zone so defined.

Cellular radio systems have now become well established in many parts of the world. A cellular radio system has a large number of "cells", each served by a radio base transceiver site. The radio base transceiver sites are each connected to a central switch (known as a mobile switching centre (MSC)) which routes calls to and from the individual base transceiver sites An individual user located within a cell can receive or originate telephone calls on a handset by means of a radio link with the radio base transceiver serving the cell in which he is currently located.

The essential feature of a cellular telephone system is that any telephone handset (known as a mobile station) can establish contact with whichever base transceiver site serves the cell in which it is currently located. For originating a call the mobile station establishes contact with whichever base transceiver site provides the best signal. On receiving an incoming call for a specified mobile station, the mobile switching centre determines which base transceiver site is currently within range of the mobile station, and set up a call by transmitting call set up protocols via the appropriate base transceiver site to the appropriate mobile station. Mobile stations may move from one cell to another, either between or during calls, and "handover" arrangements are provided to allow the mobile switching centre to monitor such a change of base transceiver site, and to maintain the telephone connection if a call is in progress when such a change happens.

In a typical cellular radio system, for example those following the "Global System for Mobile communications" (GSM) standard, each radio base station broadcasts a signal giving the control channel information for its own cell and those of the neighbouring cells. From time to time each mobile station scans the radio channels of the current serving cell and the neighbouring cells (defined by a "neighbour list" transmitted in the control information from the current cell), and carries out an assessment of the quality of the radio link on each. If the base station currently serving the mobile unit no longer provides the best signal quality of those scanned, a handover is initiated to another cell At this stage a new neighbour list is created, based on the new serving cell. The "neighbour list" (i.e. the identities of the cells whose control channels are to be indicated to the mobile station) is defined in the base site controller which controls the individual base transceiver site

From time to time the network is modified, for example by adding new base transceiver sites, or by rearranging the channel allocation in the base transceiver sites to cope with changes in demand, and the neighbour lists are modified by the network operator in consequence Some cellular radio systems offer different types of service depending on the current location of the mobile unit For example different tariffs may be available in different geographical areas Such facilities may be offered so that calls to fixed telephones within a predetermined area (defined by the area codes used in the fixed telephone network) are charged at a local rate if the mobile station is itself within the same geographical area, thereby reducing the price differential compared with calls from fixed telephones. Differential tariffs may also be used for users in predetermined zones, thus facilitating the planning of the provision of facilities (e.g new capacity) by encouraging users to operate their mobile telephones in predetermined (and therefore predictable) areas. In one particular application, a user may be given the facility to make calls at a tariff similar to the fixed-line rate when within a specified area. This allows the user to use his mobile handset as a replacement for a fixed-line telephone when within that specified area, allowing him, and the service provider, to avoid the expense of providing the fixed line Services may also be offered which only allow a limited geographical range, the telephone being inhibited from making and/or receiving calls (or certain classes of call, e g non-emergency calls) outside that geographical range. This would be useful if the telephone is to be loaned for use at a specific location (e.g. whilst the borrower is employed at a particular site), to reduce the temptation to retain it when he leaves.

By the nature of the cellular radio system, any such zones are most conveniently defined in terms of cells Thus a predetermined set of one or more cells will be determined as comprising a "zone" for the purposes described above. W097/1 3387 (TeliaAB) describes a method of a defining a geographical zone specific to a given mobile telephone, wherein the network identifies one or more cells as a home area for the mobile telephone, and stores the identity of these cell as an attribute of the mobile telephone defining its specified geographical "home zone" In general a single cell would be unattractive as a user-friendly zone; handover often occurs in moving from one side of a building to the other, as the building itself inhibits radio propagation. Therefore the cited reference allows several cells to be defined by the cellular radio system. The cells are defined by the mobile handset itself, which calls the network on a special number when the user wishes to identify a cell in which he is currently located as forming part of the 'home area' . This arrangement is inconvenient, as it requires the user to register separately in each cell forming part of the required 'home area'. This is time- consuming. It also requires knowledge of the cellular 'overlay' pattern in the area, which is not readily discernible on the ground, to ensure all the cells required have been covered There is also no control over how large an area is selected by the user.

A further problem is that as the cellular system is upgraded, the locations and extents of the individual cells (the 'overlay' pattern) will change. For zoning arrangements which are common to all users, or a known subset of users, such changes can be accommodated by adjusting, in the billing system or elsewhere, the identities of the cells to which the special tariff etc. applies. However this becomes increasingly difficult if the zones are defined differently for each user.

It would therefore be desirable to be able to define a zone specific to an individual user, which can nevertheless be kept updated as the cellular radio network evolves.

According to the invention there is provided a method of operating a cellular telephone network to define a geographical zone specific to a given mobile telephone, the cellular telephone network comprising means for storing attributes of associated mobile telephones, and a plurality of cellular radio base stations each defining a geographical cell; wherein the network identifies one cell as a home cell for the mobile telephone, and stores the identity of the home cell as an attribute of the mobile telephone defining its specified geographical zone, and the required geographical zone is defined as including the identified home cell and a predetermined group of other cells defined with reference to the home cell. As the cellular radio network evolves, these neighbouring cells may be redefined by the network, such that the geographical area defined by the cells remains substantially constant. This allows the use of a standard mobile station, as it does not require any information regarding the network configuration to be stored in the mobile station, and therefore the system can operate, regardless of any changes to the cellular reuse pattern, completely transparently to the mobile station.

Preferably, on setting up an outgoing call, the network identifies whether the mobile station is operating in a cell defined as forming part of the predetermined zone, and transmits a voice announcement or other indication at the beginning of the call that the mobile station is within, or is not within, the zone. This facility could be used, for example, to alert the user as to whether or not he is within a predetermined user-specific zone within which a special tariff applies.

A similar arrangement can be used for incoming calls, to allow either the calling party or the called party to benefit from a lower tariff. For example, in many call diversion arrangements, a user who has diverted calls to a mobile telephone from a fixed telephone is billed for any calls so diverted. The invention allows such calls to be charged at a special low tariff if the mobile telephone is within the predetermined zone The activation of the zone definition process may be carried out by the network operator, for example by selecting as home cell the cell covering a geographical location specified in any suitable manner ('ZIP' or postal code, latitude and longditude, etc) . Alternatively, the activation of the zone definition process may be carried out by the user, either on first switching on the mobile unit, or by dialling a special code. Preferably, means are provided to prevent a user repeating this process on subsequent occasions, to redefine his special zone according to his current whereabouts Such means may be overridden, under the control of the service provider, to allow for situations in which the mobile telephone is henceforth to be used generally at a different location: for example if the mobile unit changes owners, or if the existing owner changes his residence.

By concentrating all the main features of the invention in the network, any standard mobile telephone can be used with the invention. Also, when new cells are activated or cell planning changes (e.g. frequency reuse patterns) are made, the cells defining the zone can be redefined by the network to allow the geographical zone coverage to be maintained In a particular preferred arrangement, the predetermined group of other cells are the current neighbour list of the home cell, as defined in a conventional network for handover purposes.

An embodiment of the invention will now be described, with reference to the Figures, in which

Figures 1 and 2 are schematic diagrams of cellular radio networks, each illustrating a defined "home zone"

Figure 3 is a schematic illustrating the basic elements of the network taking part in the system according to the invention Figure 4 is a schematic illustrating the message flows which take place on setting up a home zone

Figure 5 is a schematic illustrating the elements of the network taking part in establishing an outgoing call

Figure 6 illustrates the message flows taking place when an outgoing call is made.

Figure 7 is a schematic illustrating the network elements taking part in an incoming call made to a mobile unit, and

Figure 8 illustrates the message flows taking place when an incoming call is made to the mobile unit. Figure 1 shows part of a cellular network Each cell A to X is served by a radio base station, typically at the centre of the cell. However, topographical, demographic and other reasons preclude a regular array of base stations, so cells are typically of irregular shapes and sizes, rather than as shown in Figure 1 . It should also be noted that coverage areas overlap in practice, although even at locations within such overlap areas one base station will give a better signal quality than another

The array may be varied from time to time as new base stations are brought into use, as illustrated by the modified network of Figure 2, which has two additional cells Y (within cell F) and Z (between cells A, B, C and D) . Figures 3, 5 and 7 show the basic architecture of the cellular radio network. The user's mobile telephone 10 is connected by a radio interface to a base station system 1 1 (Figure 3) or, at different times, 1 1 a (Figures 5 and 7).

The base station systems 1 1 , 1 1 a serve different cells, but are both connected either directly or indirectly to a switch 1 2, which controls the switching of telephone calls to and from any mobile stations currently connected to the base station systems 1 1 , 1 1 a.

The switch 1 2 has a number of associated functions, such as the "visitor location register" (VLR) which stores information relating to the last known location of each mobile station 1 0, identified as the base station system 1 1 , 1 1 a to which the mobile station is currently, or was last, working. The switch 1 2 can also connect various network functions such as an announcement machine 1 6 to mobile stations such as mobile station 1 0.

Also connected to the switch 1 2 is a service control point, (SCP) 1 3 which controls a number of services, including the home zone service. Registration calls sent to the switch 1 2 are routed to the service control point 1 3 in order to set up a home zone cell list for the respective mobile unit 10 in a data store 1 5. Subsequent calls from the same mobile station 1 0 are referred to the service control point 1 3 to identify whether the mobile station 10 is within a defined home zone, by retrieving data from the store 1 5.

As the network is upgraded and updated, cell planning data is provided from a planning input 14 to the individual base station sites 1 1 , 1 1 a, in order to update the neighbour list for each base station 1 1 . In one embodiment of the invention the same information is also supplied to the service control point 1 3 to identify, and from time to time to modify, the home zone cell list stored in the data store 1 5 relating to each individual mobile station 10. In an alternative embodiment of the invention, cell planning data is also used for this purpose, but the data used is not identical with the neighbour list.

As shown in Figures 5 and 7 the switch 1 2 is also connected to a billing centre 1 7 which generates bills for the users of the mobile telephones, according to the number and duration of calls, and the locations from which they are made.

A second user 1 8 is also shown on Figures 5 and 7. This is the user to whom the first user 1 0 is making a call in Figure 5, and from whom the first user 10 is receiving a call in Figure 7. Also in Figure 7 is shown the home location register 1 9 which has a permanent data store relating to a number of individual users including the user 10. The home location register records with which switch 1 2 (and therefore which visitor location register) the user is currently working, thereby allowing incoming calls to be routed to the user even if he is not currently connected to the same switch from which the call is received Also shown in Figure 8 is the gateway mobile switching centre 1 2b, through which incoming calls are received This is connected by way of the visited mobile switching centre ( 1 2)

The basic functioning of a cellular telephone network, as it relates to the present invention, and the establishment of a home zone, will now be described in more detail, with reference to Figure 3, which shows the relevant elements of a cellular network, and to Figure 4 which illustrates the process.

When a Mobile Station (MS) 1 0 is switched on, a base station 1 1 of the radio network (usually that with the strongest signal detected at the mobile unit) transmits a signal to inform the MS 1 0 of the list of cells and radio channels that can be used for service, based on the current serving cell identity. This list is stored in the MS, and is known as the "neighbour list" of the base station 1 1 . The MS periodically scans these cells and channels and carries out an assessment of the 'quality' of each radio link compared to the 'quality' of the serving channel. If the serving channel becomes degraded, for example because the mobile station has moved, handover to one of the other cells may be initiated. When the MS is handed over to another cell the neighbour list in the MS is replaced by that of the new serving cell

The list of cells and channels is determined by radio planning and is configured in the base station system (BSS) 1 1 by the network operator 14.

In order to define a user-specific "home zone" the user firstly decides on the geographical location by which his home zone is to be defined, takes his mobile telephone there, and switches it on (if not already switched on) . The base station 1 1 of the cell A within the mobile telephone 10 is located will then identify itself, and its neighbour list, to the mobile telephone 10 as usual.

To register the home zone, the user 1 0 dials a short code number (e.g. 4567) . This causes the network 1 1 , 1 2, 1 3 to invoke a process in which the SCP 1 3 is first informed of the current serving cell identity 1 1 . For example, in Figure 1 this may be the central cell A The SCP 1 3 next identifies the list of cells (for example cells A to G Figure 1 ) that are defined by the planning function 1 4 as forming a home zone defined with reference to the current serving cell A, by searching its copy of the radio planning database 14 using the current serving cell identity 1 1 as a key The SCP 1 3 then stores the list of cells in this user's personal data 1 5. The SCP 1 3 then instructs the switch 1 2 to connect the call to a confirmation voice announcement 1 6.

The function of establishing a home zone may be inhibited if the SCP 1 3 detects that a home zone is already defined for this user, e.g. by having an overwπte-protection facility in the data store 1 5 This prevents a user arranging for his home zone to follow him, thereby getting the benefits of the cheaper tariff wherever he happens to be The network operator may be given authority to delete a home zone record, to allow the user to define a new one, should a genuine need arise. The SCP 1 3 can now use the list of cells to determine whether the mobile unit 10 is located in the Home Zone during subsequent incoming or outgoing call set-ups. As shown in Figures 5 and 6, when the user 10 makes an outgoing call the SCP 1 3 is invoked by the switch 1 2. The current serving cell identity (e.g. E or

P) is passed to the SCP 1 3. The SCP retrieves the home zone cell list 1 5 stored during Registration and determines whether or not the user is located inside the home zone, by reference to the identity of the current serving cell 1 1 a. The SCP

1 3 instructs the switch 1 2 to inject a voice announcement or tone, generated by an announcement generator 1 6, at the start of the call, before ringing is heard, indicating whether or not this is a home zone tariff call. The SCP 1 3 also instructs the switch 1 2 to insert a home zone flag in the call record so that the appropriate tariff is applied by the billing system 1 7.

As shown in Figures 7 and 8, when an incoming call arrives at the mobile switching centre (MSC) 1 2 the SCP 1 3 is invoked. The SCP 1 3 retrieves the current serving cell identity for the called home zone user 1 0 from that part of the network which monitors the current location of each mobile unit in order to direct calls to them, known as the Home Location Register, (HLR) 1 9, and continues processing the call as follows:

• If the current serving cell identity (e.g. E) is in the list of home zone cells (A to G) stored by the SCP 1 3 during Registration, the called user 10 is considered to be located inside the home zone. The SCP 1 3 instructs the switch to configure the call record home zone flag to home zone = True, and to connect the call. The call record is output to the billing centre 1 7 in the normal way, but with the flag set. • If the current serving cell identity (e.g. P) is not in the list of home zone cells stored by the SCP during Registration, the called user 1 0 is considered to be located outside the home zone. The SCP 1 3 instructs the switch to configure the call record home zone flag to home zone = False, and connect the call. The call record is output to the billing centre

1 7 in the normal way.

It will be seen that the system can operate with standard mobile telephones. When new cells are activated or cell planning changes are made, the home zone cell list can be automatically updated by the SCP. For example, if a new base station Z is introduced (Figure 2), any home zone list based on the neighbour list of cell A would have cell Z added to its list, replacing cell C in the same way that it would be replaced in the neighbour list of cell A In the foregoing description the home zone based on a given cell has generally been described as being coterminous with the existing neighbour list based on that cell, as this allows the same planning database 1 4 to be used for both functions However, if it is desired to define the home zone differently from the neighbour zone, this can be achieved by generating separate data sets from the same source data.

For example, the neighbour list typically lists the six (or some other fixed number) base stations which give the best quality signals for mobile stations within a given cell, and hence those most likely to be handed over to. However, these cells will, collectively, cover a very much smaller area if the base stations are close together (e.g. in an urban environment, where base station siting is dictated by the amount of call traffic to be supported, and the need for small cells to provide coverage between tall buildings) than if the base stations are spaced a long way apart. It may therefore be preferable to define a home zone list by area: e.g. all cells wholly or partly within a predetermined radius 100 of the Home Cell (Figures 1 and 2) . Thus, in Figure 2, cell Z would replace cell C in both the home zone list, (as no part of cell C is now within the defined radius 100 of the centre of cell A), and the neighbour list (cell C now not being one of the nearest six cells, and therefore unlikely to be the best cell to which to be handed over from cell A). However, the low-power "hot spot" cell Y, introduced to cover a small region of high demand (or poor reception) within cell F would be added to the home zone list, as it lies within the defined radius 1 00, although its low power means that it is not part of the neighbour list for cell A.

Claims

1 . A method of operating a cellular telephone network to define a geographical zone specific to a given mobile telephone, the cellular telephone network comprising means for storing attributes of associated mobile telephones, and a plurality of cellular radio base stations each defining a geographical cell; wherein the network identifies one cell as a home cell for the mobile telephone, and stores the identity of the home cell as an attribute of the mobile telephone defining its specified geographical zone, and the required geographical zone is defined as including the identified home cell and a predetermined group of other cells defined with reference to the home cell.

2. A method according to claim 1 , wherein the predetermined group of other cells are the current neighbour list of the home cell, as defined in the network for handover purposes.

3. A method of operating a telephone network as claimed in claim 1 or 2 wherein the network identifies the home cell as being the cell currently serving the mobile telephone when it transmits a predetermined signal to the network, and the network only responds to the predetermined signal if no home cell is currently defined for the mobile telephone

4. A method of operating a mobile telephone network according to any preceding claim, wherein when a mobile telephone for which a home cell is defined sets up an outgoing call, the network identifies whether the mobile station is within one of the cells defined as forming part of the predetermined zone.

5 A method according to claim 4, wherein charges billed to the user are determined with reference to whether the user is within the defined zone.

6 A method according to claim 4 or 5, wherein on setting up a call, an indication is transmitted to the mobile telephone to alert the user to whether the telephone is within the defined zone.

7. A cellular telephone network, comprising means for storing attributes of associated mobile telephones, a plurality of cellular radio base stations each defining a geographical cell, wherein the network has means for defining one cell as a home cell for a mobile telephone, means for storing the identity of the home cell as an attribute of the mobile telephone and means for controlling the interaction between the network and the mobile telephone according to its location with respect to a geographical zone defined as including the identified home cell and a predetermined group of other cells defined with reference to the home cell.

8. A network according to claim 7, wherein the predetermined group of other cells are the current neighbour list of the home cell, as defined in the network for handover purposes

9. A network according to claim 7 or 8, having response means for responding to a predetermined signal transmitted from a mobile telephone such that the means for defining the home cell identifies the cell currently serving the mobile telephone has means for inhibiting the response means if a home cell is already defined for the mobile telephone

1 0. A network according to claim 7, 8 or 9, having means for identifying whether a mobile station is within one of the cells defined as forming part of the predetermined zone when a call is initiated involving the mobile station.

1 1 . A network according to claim 10, having means for determining charges billed to the user with reference to whether the user is within the defined zone.

1 2. A network according to claim 10 or 1 1 , having means for transmitting an indication to a mobile telephone to alert the user as to whether the telephone is within the zone defined for that telephone

1 3. A method of operating a cellular telephone network substantially as described with reference to the drawings.

1 4. A cellular telephone network substantially as described with reference to the drawings.