GB2418568A - A method of estimating the cell location of a mobile terminal in a heterogeneous network environment - Google Patents

Abstract

In a heterogeneous network environment comprising a first cellular network (12) and a second cellular network (11), a method of estimating the cell location of a mobile terminal (27) in said first cellular network (12), which method comprises the step of using said second cellular network (11) to provide said first cellular network (12) with cell location data representing an estimated location of said mobile terminal (27) in a cell or cells of said first cellular network (12) or said second cellular network (11).

Description

24 1 8568 - 1 -

A METHOD OF ESTIMATING THE CELL LOCATION OF A MOBILE

TERMINAL IN A HETEROGENEOUS NETWORK ENVIRONMENT

FIELD OF THE INVENTION s

The present invention relates to a method of estimating the cell location of a mobile terminal in a heterogeneous network environment, a computer program, a computer program product, a substantially unidirectional data transmission network, a bi-directional data communication network, a network node for use therein, and to a 0 multi-mode mobile terminal.

BACKGROUND TO THE INVENTION

Methods and networks for transmitting electronic data (such as digital audio, is video and computer data) are becoming ever more numerous and widespread. The different types of transmission method and the operators of the networks are also becoming more numerous. Users now have access to a wide range of mobile devices (such as mobile telephones, personal digital assistants (PDA) and notebook computers - hereinafter "mobile terminals") providing access to such networks for the transmission and reception of such data locally, nationally and around the world.

Mobile terminals are now being manufactured that comprise plurality of interfaces for accommodating the different network types and standards. For example a PDA may have a GSM interface for making/receiving telephone calls and transmitting/receiving SMS text messages, and a wireless LAN (WLAN) interface 2s for accessing the Internet or other computer network. It is expected that these and future "multi-mode" mobile terminals will become even more popular with users and manufacturers.

Digital broadcast networks (such as American Television Standards Committee (ATSC), European Telecommunications Standards Institute Digital Video Broadcasting (DVB) and Japanese Integrated Service Digital Broadcasting (ISDB)) are generally intended to offer point-to-multipoint unidirectional data transfer, although some schemes have been proposed for limited capacity data transfer from mobile terminals back to the broadcast network (for example DVB-Return Channel as Terrestrial). Currently data is transmitted from a number of transmitters to provide - 2 - coverage for a certain large geographical area (80km radius). Digital broadcast networks are characterized by high data transfer rates on the downlink. For example a DVB network may broadcast multiplexed data transmission streams at a rate of the order of tens of Mbps. In contrast, mobile cellular networks offer a point-to-point bi directional voice and limited data service between terminals (either mobile of fixed).

Data transfer rates in mobile cellular networks are generally lower than digital broadcast networks. For example IMT-2000 (e.g. UMTS) networks will offer a bandwidth of approximately 2Mbps.

0 Attention has recently been turned to use of digital audio and video broadcast networks for transmission of datagrams. For example the DVBHandheld (DVB-H) standard has been proposed to permit mobile terminals to receive data (e.g. Web pages and e-mails) from broadcast networks. The present DVB-H draft (document A081) is available at wvw.dvb.org. In the future it is expected that the number of broadcast transmitters will increase, with each having a smaller area of coverage.

Thus the digital broadcast network is and will be "cellular" insofar as the total geographical area covered by the network is divided into a number of"cells", each delimited by the area of coverage of one (or a few) transmitter(s).

With increasing popularity of multi-mode mobile terminals, it will be important that the different network providers co-operate to provide a seamless service from the perspective of the user. Accordingly it is envisaged that heterogeneous networks (i.e. networks using mutually incompatible access technologies and/or under different administrative domains) should inter-work to this 2s end, and this is subject of on-going research and development.

One aim of the inter-working of the networks is to offer "seamless roaming" to users. This can be defined as the ability to reduce the effect that changes at the network level have on the end-user's perception of a service. Ideally, the end-user would not notice, and would not need to be informed, when service is handed over vertically (i. e. from one service provider to another) or horizontally (i.e. from one network cell to another). Heterogeneous Roaming Agreements (HRAs) between service providers and network operators will offer the user the ability roam over different network types and technologies (e.g. GPRS, UMTS, WEAN, DVB) under as different administrative domains whilst paying only a single invoice, undergoing one - 3 - authentication process, etc. It is envisaged that in an inter-working environment different networks will be able to co-operate to provide improved services to the user since their areas of coverage will overlap. "Load-balancing" between networks may be administered, such that e-mails may be delivered to a user through a UMTS network, whilst an attachment to the e-mail is delivered over a DVB network for example. In this scenario it is important for the DVB network to know in which DVB cell the mobile terminal resides so that datagrams can be encapsulated and multiplexed into the lo MPEG transmission stream by a DVB Gateway at the correct multiplexer and then transmitted from the correct DVB transmitter.

Therefore one particular problem in this inter-working of networks environment is mobile terminal location discovery and tracking in cellular coverage networks where there is no uplink (or only a very limited bandwidth uplink) available. Whilst a similar problem has many solutions in the field of mobile cellular networks (where communication is bi-directional), to the best of the applicant's knowledge it has not been addressed for broadcast type cellular coverage networks (where communication is substantially uni-directional) in a heterogeneous inter networking environment. A solution to this problem is important for the aforementioned reasons and also to facilitate horizontal handover between transmitters in the broadcast network, vertical handover between the mobile and broadcast networks and in the provision of location-based broadcast services, for

example.

WO 2004/004397 discloses a method for approximating cell geometry in a DVB-T transmission system. Part of the method relies on determining the DVB cell location of a mobile terminal in the system. It is assumed that each mobile terminal is equipped with a satellite global positioning (GPS) receiver. In use, the GPS co ordinates are obtained and used to determine in which cell of the DVB network the mobile terminal resides. This is done by comparing the GPS co-ordinates with the longitude and latitude data transmitted by the DVB network in the Network Information Table (NIT). Reliance on GPS is not practical as not all mobile terminals are equipped with a GPS or similar system. Furthermore, GPS signals are transmitted from satellites at relatively low power levels and the signal strength at the mobile - 4 - terminal is unlikely to be useable inside buildings or in cities where many obstructions exist, for example.

Thus it is apparent that there is a need for an improved method of estimating the cell location of a mobile terminal in a heterogeneous network environment, and in particular the cell location of a mobile terminal in a substantially unidirectional cellular network.

SUMMARY OF THE PRESENT INVENTION

According to the present invention there is provided in a heterogeneous network environment comprising a first cellular (or cell coverage type) network and a second cellular (or cell coverage type) network, a method of estimating the cell location of a mobile terminal in said first cellular network, which method comprises the step of using said second cellular network to provide said first cellular network with cell location data representing an estimated location of said mobile terminal in a cell or cells of said first cellular network or said second cellular network. A heterogeneous network environment may mean an environment in which there are two or more electronic data networks that utilise incompatible access technologies (e.g. GPRS/UMTS/DVB/WLAN). In the context of the present invention the environment will be that where mobile terminals receive and/or transmit data over an air or wireless interface. As used throughout this document "cellular" network may mean any network in which the total area of coverage is divided into a plurality of cells for transmission to and/or reception of data from mobile terminals roaming in the network, and "cellular" in the context of a unidirectional or asymmetric communication network is intended to mean nothing more than coverage is provided by such a cellular structure. In this connection it is to be noted that, to the best of the applicant's knowledge, the term "cellular" has not been applied to broadcast networks in the art. Cell location data may mean any electronic data representing the identity of a cell or cells in which it is estimated that the mobile terminal resides. The cell location data may represent a location area in the first or second cellular network for example. Furthermore the estimated cell or cells may be either in the first or second network. The second cellular network may look up cell location data stored in computer memory on a network node therein, and transmit the result toward the first cellular network. A cell may be defined as the geographic area encompassing the - 5 - signal range from one transmitter. For broadcast cellular networks that are unidirectional the cell size is not dependent on the transmission power of mobile terminals using the network.

sPreferred steps in the method are set out in claims 2 to 23 of the appended claims to which attention is hereby directed.

According to another aspect of the present invention there is provided a computer program comprising computer executable instructions for causing a first locellular network and a second cellular network to perform the method steps as set out above and in the appended claims.

According to another aspect of the present invention there is provided a computer program product storing computer executable instructions as set out above.

Advantageously, the computer program product is embodied on a record medium, in a computer memory, in a read-only memory or on an electrical carrier signal.

20According to another aspect of the present invention there is provided in a heterogeneous network environment comprising a first cellular network and a second cellular network, a method of estimating the cell location of a mobile terminal in said first cellular network, which method comprises the steps of: (a) performing the method steps of any of claims 2 to 7 to which 25reference is made; (b) determining whether or not said estimated location is accurate, and if not, performing the method steps of any of claims 8 to 14 to which reference is made.

Preferably, the method further comprises the steps of determining whether or 30not said estimated location after step (b) is accurate, and if not, performing the method steps of claim 15 to which reference is made.

According to another aspect of the present invention there is provided a substantially unidirectional data transmission network comprising a plurality of 35transmitters dividing a physical area into a plurality of cells, which network - 6 - comprises a network node having memory storing computer executable instructions for performing the first cellular network method steps as set out above.

There is also provided for use in the substantially unidirectional data s transmission network above, a first network node having memory storing computer executable instructions for performing the first cellular network method steps set out above. The first network node may be a DVB Gateway for example.

According to another aspect of the present invention there is provided a bi o directional data communication network comprising a plurality of transmitters dividing a physical area into a plurality of cells, which network comprises a network node having memory storing computer executable instructions for performing the second cellular network method steps as set out above.

There is also provided for use in the bi-directional data communication network above, a second network node comprising memory storing computer executable instructions for performing the second cellular network method steps set out above. The second network node may be a gateway GPRS support node (GGSN)

for example.

According to another aspect of the present invention there is provided a multi mode mobile terminal comprising a memory storing computer executable instructions that when executed cause the mobile terminal to listen on a first interface for an identifier of a cell in a first cellular network in which the mobile terminal resides, and 2s upon receipt thereof, transmit said identifier from a second interface to a second cellular network in which the mobile terminal resides. The first cellular network may be a cellular broadcast network and the second cellular network may be a third or fourth generation mobile network for example. The first and second interfaces on that multi-mode mobile terminal may be physically different interfaces or a single reconfigurable interface for example.

According to another aspect of the present invention there is provided a method of estimating the cell location of a mobile terminal in a cellular or "multi coverage area" broadcast network, which method comprises the step of transmitting to said cellular broadcast network cell location data representing an estimated - 7 - location of said mobile terminal in (a) a cell or cells of said cellular broadcast network, or (b) another cellular network having a cell that overlays a cell in said cellular broadcast network. The cellular broadcast network may be any asymmetric data transfer network such as a digital audio and/or video broadcast network, for s example using DVB, ATSC or ISDB. The step of transmitting may be performed over the cellular broadcast network if there is an uplink (e.g. DVB-RCT), or may be performed via another network (e.g. obtaining location data therefrom or using the other network as an uplink for the broadcast network).

lo BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the how the invention may be put into practice, a preferred embodiment of the invention applied in a heterogeneous network environment comprising a UMTS and a DVB network will be described, by way of example only, to the accompanying drawings, in which: Fig. I is a block diagram of a heterogeneous network environment comprising a mobile network and a broadcast network having a dedicated logical interface therebetween; Fig. 2 is a block diagram of part of an IMT-2000 UMTS network and its connection to external packet data networks (PDNs); Fig. 3 is a block diagram of a gateway GPRS support node (GGSN) or serving GPRS support node (SGSN) of the UMTS network of Fig. 2; Fig. 4 is a block diagram of part of a DVB network; 2s Fig. 5 is a block diagram of a DVB Gateway of the DVB network of Fig. 4; Fig. 6 is a map of the United Kingdom showing how it may be served by DVB-T transmitters of the DVB network shown in Fig. 4; Fig. 7a is a high- level block diagram of the DVB network of Fig. 4; Fig. 7b is a high-level block diagram of a heterogeneous network environment comprising the UMTS network of Fig. 2 and the DVB network of Fig. 4, with a link therebetween; Fig. 8 is a schematic representation of the signalling procedure for a registration procedure of a Mobile Terminal at a DVB network, and three cell location methods according to the present invention for locating the mobile terminal within a cell of the DVB network; - 8 - Fig. 9 is a flowchart of the steps of a set of computer executable instructions of a first location method in accordance with the present invention; Fig. 10 is a schematic representation of the overlap between DVB cells and UMTS cells in a heterogeneous network environment; Fig. 11 is a schematic representation of the overlap of Fig. 10 useful in determining a successful mapping between cells of the UMTS network and cells of the DVB network; Fig. 12 is a flowchart of the steps of a set of computer executable instructions of a second location method in accordance with the present invention; 0 Fig. 13 is a flowchart of the steps of a set of computer executable instructions of a third location method in accordance with the present invention; Fig. 14 is a flowchart of the steps of a set of computer executable instructions of a fourth location method in accordance with the present invention; and Fig. 15 is a block diagram of a multi-mode mobile terminal in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Fig. 1 a heterogeneous network generally identified by reference numeral 1 0 comprises a mobile network 11 and a broadcast network 1 2. The broadcast network 12 may be considered as a first cellular network and the mobile network 11 may be considered as a second cellular network in the heterogeneous network environment. Each of the two networks 11, 12 is under a different administrative domain and they are heterogeneous i.e. the protocols for access, transmission and handling of data are different between the networks. A multi-mode Mobile Terminal (MT) has interfaces (or a single re-configurable interface) for accessing both of the networks 11, 12. The mobile network 11 may provide access for a MT over a wireless link via a wireless local area network 13 (WLAN) interface or via a UMTS radio access network (RAN) 14 interface for example. Depending on the service used by the user, data may be routed from the mobile network 11 to the Internet 15 or to another network such as a public land mobile network (PLMN), not shown. The broadcast network 12 is asymmetric in data transfer, and offers a much greater bandwidth on the downlink than on the uplink from the MT. The same data is broadcast from a transmitter 16 for reception by a large number of MTs in range of the transmitter 16. - 9 -

Referring to Fig. 2 the mobile network 11 is shown in greater detail. In particular it comprises a UMTS network 11 that is divided into (a) the Core Network (CN) 17 consisting of the gateway GPRS support node (GGSN) 18 and the serving GPRS support node (SGSN) 19, and (b) the UMTS Terrestrial Radio Access Network (UTRAN) 20 consisting of the radio network controller (RNC) 21 and Node B 22. The GSNs (i.e. the GGSN and SGSN) constitute the backbone of the UMTS network 11. A brief description of the functionality of the network nodes shown in Fig. I relevant to the invention is given as follows: 0 (1) Gateway GPRS Support Node (GGSN) 18: the GGSN 18 is used as an interface from a cellular network to external Packet Data Networks (PDNs) 23. The PDN 23 may be the Internet 15 or a wide area network (WAN) for example, although in this particular case one of the PDNs is the broadcast network 12. The GGSN 18 maintains routing information required to tunnel user data packets to the SGSN 19 serving a particular subscriber. Other functions include network and subscriber screening and address mapping.

(2) Serving GPRS Support Node (SGSN) 19: the SGSN 19 delivers packets to subscribers within its service area. The SGSN 19 detects new MTs within a given service area, processes registrations of new mobile subscribers and keeps record of their location inside a given service area.

(3) Radio Network Controller (RNC) 21: the RNC 21 is the network element responsible for the control of the radio resources within the UMTS Terrestrial Radio Access Network (UTRAN) 20. The RNC 21 is responsible for load and congestion control of its own cells.

(4) Node B 22: the main function of the Node B 22 is to perform the air interface processing (channel coding and interleaving, rate adaptation, spreading, etc.). It also performs some Radio Resource Management. It logically corresponds to the GSM Base Station.

MTs 27 combined with the User Subscriber Identity Module (USIM) are referred to by the term "User Equipment" in UMTS terminology. However, throughout the present document the term "Mobile Terminal (MT)" is used generically to indicate such devices and any other wireless network access device.

"Mobile Station (MS)", a term used in the context of GSM and GPRS networks, is equivalent to the User Equipment.

Packet Data Protocol (PDP) is the generic name for packet data transfer during an active session (see H. Kaaranen et al. "UMTS Networks" John Wiley and Sons, 2001). Before the MT 27 can exchange data with a host on the external PDN s 23, the MT 27 must first establish a virtual connection with the mobile network 11.

This is similar to a dial-up connection established through the Public Switched Telephone Network (PSTN) in order to access a particular Internet Service Provider (ISP). In UMTS, virtual connections created and maintained within the network are referred to as "PDP contexts". The PDP context provides information to support lo packet delivery between the MT 27 and the mobile network 12 and contains all parameters describing the packet data connection by means of end-point addresses and QoS. The PDP contexts are maintained and stored in the MT 27, SGSN 19 and GGSN 18. A single MT may have several PDP contexts associated with it. The information contained within the PDP contexts is dynamic and changes as a result of user mobility.

The GGSN 18, SGSN 19 and the MT 27 maintain PDP contexts that list different items of information relevant to routing user data packets through the UMTS network 12. The GGSN 18 maintains activated PDP contexts consisting of routing information that allows the GGSN 18 to forward downlink user data packets to the serving SGSN 19. The SGSN 19 maintains activated PDP contexts consisting of routing information that enables the SGSN 19 to forward user data packets either to the GGSN 18 in the uplink direction or to the serving RNC 21 in the downlink direction. 2s

The MT 27 activates a PDP context by sending an Activate PDP Context Request message to the SGSN 19. The SGSN 19 validates the Activate PDP Context Request using the information provided by the MT and the PDP context subscription records. The SGSN 19 then sends a Create PDP Context Request message to the serving affected GGSN 18. The GGSN 18 creates a new entry in its PDP context table. The new entry allows the GGSN 18 to route PDP Packet Data Units (PDUs) between the SGSN 4 and the packet data network. The GGSN 18 then returns a Create PDP Context Response message to the SGSN 19.

3s A PDP context establishes a mapping between a single subscriber and a 11 generic PDP address (e.g. an IF address). A PDP context does not contain any references to external networks (e.g. addresses of web or email servers located outside of the UMTS network) or address identifiers for specific services that may be accessed by the subscriber while using a given PDP address.

Fig. 3 shows the GGSN 18 in more detail that comprises a case 31 having network interface ports 35 and 36 to which respective cables 37 and 38 provide a physical link to an external network (e.g. PDN) and the UMTS network 11. Two network interface cards 39 and 40 are connected to their respective network interface lo ports 35 and 36. A hardware packet switch 41 connects the network interface cards 39, 40 and a central processing unit (CPU) 42 can communicate with a routing table 43 and router management tables 44. Each network interface card 39, 40 comprises a link layer protocol controller 45 that has access to an interface management table 46 and a hardware address table 47 (e.g. Address Resolution Protocol cache). In is communication with the link protocol controller 45 is a network protocol-forwarding engine 48 having access to a forwarding table 49 (route cache),-and an interface queue manager 50. Both the network protocol forwarding engine 48 and interface queue manager 50 have an interface to and from the packet switch 41 respectively.

In use, the GGSN 18 sends packets to and receives packets from various SGSNs (e.g. SGSN 19) and the various external PDNs as described above. An electronic memory 51 (e.g. RAM) stores computer executable instructions for performing the various GGSN method steps and storing the various databases described below. Various types of GPRS support node are available and the present 2s invention is not limited to that described above. Further examples are available from Cisco Systems, Inc. (www.cisco.com), Siemens AG (www. siemens.com) and Alcatel (www.alcatel.com! for example.

The SGSN 19 is similar in construction and operation to the GGSN 18.

However, in addition to the PDP contexts, the memory in the SGSN 19 stores a context database that contains all mobility management (MM) contexts for the subscribers within its service area. Further details of UMTS networks can be found in Third Generation Partnership Project, Technical Specification 23.060 v5.2.0, General Packet Radio Service (GPRS) ; Service Description; Stage 2, Release 5, June 2002. 3s

In use, each Node B 22 sends data to and receives data from MTs 27 within a UMTS cell over a wireless link. Network operators generally model UMTS cells as hexagonal, although in principle any shape can be used. This permits the mobile network operator to plan network coverage over a geographical area by tessellating a plurality of UMTS cells. MTs roaming within an area covered by a UMTS network can receive substantially seamless service through handoff between the UMTS cells.

UMTS cells are typically of between approximately less than Ikm in radius and up to approximately lOkm in radius. Size is usually limited by the transmission power of the MT 27.

The UMTS network 11 keeps track of the location of each MT 27 by dividing the network into a number of "location areas" (LAs), each of which comprises one or more UMTS cell and that is identified by a location area identifier (LAI). Each Node B in a particular LA broadcasts the LAI associated with that LA. When the MT 27 detects a new LAI, a registration update procedure is triggered to inform the network of the approximate location of the MT 27. The current LA of each MT 27 is stored in a Visitor Location Register (VLR) (see Fig. 2) in the Core Network 17. When data is to be sent from the mobile network 11 to the MT 27, the VLR is interrogated to obtain the last LA from which the MT 27 sent an update. The GGSN instructs the UMTS cells in that LA to page the MT 27. The MT responds, allowing the network to identify the Node B 22 and thereby the cell in which the MT 27 resides. The data is then routed to that Node B and on to the MT 27.

Referring to Fig. 4 the broadcast network 12 is shown in greater detail. In particular, it comprises a DVB network having a central multiplexer 60 that receives a number of separate inputs (for example audio, video, etc.) that are each encoded into a respective MPEG transport stream (MPEG-TS) with an MPEG-2 encoder 61.

Data from an external PDN (e.g. Internet) may be multiplexed into the MPEG-TS by a DVB Gateway 62, either as a separate channel or by exchanging stuffing packets in the MPEG-TS for packets containing data, e. g. IP packets. In particular the DVB gateway 62 operates by taking IP datagrams received from the external PDN and inserts them into DVB-TS packets according to the Multi Protocol Encapsulation (MPE) for example (see EN 301 210 at www.etsi.org). The multiplexed streams are transmitted over and ATM (Asynchronous Transfer Mode) or SDH (Synchronous Digital Hierarchy) network 63 to a number of regional multiplexers 64. The regional - 13 multiplexers 64 may multiplex further streams into that received from the central multiplexer 60. For example local news and weather content 65 may be multiplexed into main MPEG-TS from the central multiplexer 60.

The regional multiplexers 64 forward the MPEG-TS to a DVB transmitter 66.

DVB may be broadcast via a number of standards: DVB-S (satellite), DVB-T (terrestrial) and DVB-C (cable). The present invention is primarilyconcerned with distribution under the DVB-T standard i.e. from a number of fixed transmitters mounted some distance above the ground, although it is also applicable to any 0 cellular broadcast standard such as DVB-S in which one or more satellite is used to transmit data to a specific area or a number of sectors on the earth's surface. Each transmitter 66 broadcasts data to a DVB cell i.e. a limited geographical area of coverage. Thus the DVB network can be considered "cellular".

Referring to Fig. 5 the DVB gateway 62 comprises a case 70 housing an electronic memory 71 (e.g. RAM), one or more CPU 72, one or more switch 73, and one or more physical interface 74. All of these components are in electronic communication with one another. Each physical interface 74 is connected to a network such as an external PDN (e.g. the Internet), a WAN or LAN. One of the physical interfaces provides a connection for transfer of data to an interface on the central multiplexer 60 in the UMTS network 11 described above.

In use, frames are received from the external PDN by a link layer protocol controller (not shown) that handles the link layer protocol (e.g. HDLC, Ethernet) used over the physical link. Frame integrity is checked and valid frames are converted into packets (e.g. IP packets) by removing the link layer header and, if necessary, the packets are queued in a queue stored in the memory 71. One packet at a time is removed from the queue by a network protocol-forwarding engine and is encapsulated in sub- network data unit and placed in the payload of a transport stream (TS) packet at the MPEG-2 level with an encapsulator (not shown). The TS packet is passed through the switch 73 to the appropriate physical interface 74 on the DVB network 11 and is transmitted as an MPEG-2 TS to the central multiplexer 60. In this way PDUs from external PDNs can be multiplexed into the main TS by the broadcast operator.

Referring to Fig. 6 a map 80 of the United Kingdom illustrates how the population may be served by a number of DVB cells 81. Although each DVB cell 81 is idealised as providing coverage to a circular area, the actual coverage will be dependent on a large number of factors including geography, weather, etc. The range of DVB cell radii may be from hundreds of metros up to tens of kilometres. For example a large DVB cell may have a radius of about 80km and a small DVB cell may have a radius of about loam. Smaller DVB cells may be provided within larger DVB cells where signal strength from the main transmitter is poor for example. Thus a broadcast operator may selectively broadcast content and/or data to a number of lo transmission regions or to individual cells. It is envisaged in future that a larger number of (smaller size) DVB cells will be provided to enable datagram delivery to mobile terminals using DVB-H for example.

To the best of the applicant's knowledge and belief there are no location discovery and tracking methods for MTs having an interface that can access broadcast networks, for example digital audio/video broadcast networks.

There is standardization in broadcast distribution networks only at the physical and MAC (Media Access Control) layers, and to some extent in settop box (STB) design and functionality. Therefore to enable inter-working between the mobile network 11 and the broadcast network 12, it is helpful to provide a generic model for a broadcast network. Referring to Fig. 6a, the broadcast network 12 can be considered to comprise a national multiplex 90 (i.e. content aggregation and multiplexing, management systems and head-end), a distribution network 91 (e.g. an ATM network) and regional multiplexes 92 (comprising local content addition and remultiplexing, and transmission infrastructure).

Referring now to Fig. 6b, a model for inter-working of broadcast and mobile networks generally identified by reference numeral 95 comprises a UMTS network 96 and a DVB network 97. The UMTS network has a UMTS core 98 (i.e. Core Network) and a UMTS access 99 (i.e. UTRAN and Node B). The DVB network comprises a DVB core 100 (i.e. the national multiplex 60 mentioned above) and a DVB access network 101 (i.e. the regional multiplexes 64 mentioned above). The distribution network 63 between the DVB core 95 and the DVB access 101 is modelled as a logical link 102, as the exact nature of the link will be different in each - 15 particular DVB network and therefore only plays a transport role in the context of the present invention.

An "Inter-networking Of Networks" (IoN) link 103 is provided between the UMTS core 98 and DVB core 100. The ToN link 103 is a logical connection between a network node (e.g. GGSN 18) in the UMTS core 98 and a network node (e.g. DVB Gateway 62) in the DVB core 100. The connection may be a dedicated wired connection between respective interfaces on these network nodes or may be established via a Virtual Private Network (VPN) over an external PDN (e.g. Internet)

lo for example.

As explained above, each Public Land Mobile Network (PLMN) of a network operator presently combines LA tracking with paging, whereby a MT's current UMTS cell may be identified. Current broadcast networks do not incorporate any tracking or discovery methods for devices having interfaces that can receive data from the broadcast network. This is because most devices (e.g. set-top boxes and televisions with digital tuners) originally designed for use with broadcast networks are fixed in a physical location, at least while in use. In the future it is expected that MTs will be multi-modal i.e. have one or more interface that can receive data from one or more network including a broadcast network. In view of the fact that broadcast operators can now multiplex datagrams (for example from external PDNs such as the Internet) into the MPEG-TS (as described above), it is important for the broadcast operators to know the location of MTs so that the data can be multiplexed at the correct location. Thus it is important for broadcast networks to incorporate some form of MT location and tracking functionality so that inter alla the DVB cell location can be discovered and data multiplexed into the MPEG-TS at the correct point in the network.

The applicant has devised four methods to provide location and tracking functionality in broadcast networks: (A) DVB based location tracking with UMTS uplink; (B) Location Discovery using UMTS network; (C) Location Area update in UMTS with DVB paging; (D) Combination method - 16 - Referring to Fig. 8 the signalling procedure for each method is given together with the necessary registration procedure. Each MT 27 must register with both the mobile network 11 and DVB network 12 before each method is operable. At step Sl the MT 27 registers with the GGSN 18. At step S2 the GGSN 18 contacts the HER to activate the location monitoring and paging function required to keep track of the MT 27 in the UMTS network 11. At step S3 the MT 27 activates a PDP context at the GGSN 18 by sending an Activate PDP Context message to the SGSN 19 as described above. At step S4 the GGSN 18 transmits via the IoN link 103 a message to the DVB lo Gateway 62 to advise that a MT with IMSI xxxxxx has registered in the UMTS network 11. The DVB Gateway 62 stores the IMSI in a DVB database in memory at step S5 (together with a mapping to any MT identifier the DVB network might use).

Effectively the DVB network 12 'trusts' that the UMTS network 11 has authenticated and authorised the user of MT 27. This is advantageous as it mitigates the need for Is any AAA (Authentication, Authorisation and Accounting) procedures over the DVB network. This procedure is analogous to the subscriber management procedures described in ETSI TR 101 957 (7.2. 4.2 IMSI as the user authentication identifier) that describes interworking between HIPERLAN/2 3G networks and to which reference is specifically made in this respect.

Alternatively, the DVB network 12 may not 'trust' the AAA of the UMTS network 11 and may perform its own AAA. In this scenario, the DVB network 12 may use its own Network Access Identifier (NAI) and the procedure may be analogous to the subscriber management procedures described in ETSI TR 101 957 2s (7.2.4.1 NAI as the user authentication identifier). A third party uplink is required to convey messages from the MT 27 to the DVB network 12 which might be provided by the UMTS network 11 and the loN link 103 for example. If the DVB network 12 does use its own NAI, it is important that the UMTS network 11 informs the DVB network of the IMSI when forwarding the response from the MT 27 over the loN link 103. Upon receipt the DVB network 12 should map the IMSI to the NAI and store the mapping in the DVB database.

In summary, it is important that during registration the two networks make use of some common identifier, which is then stored in memory on each network, 3s whereby each network may subsequently identify the MT 27.

- 17 - (A) DVB based location tracking with UNITS unlink It is possible to design location and paging software that could be stored and executed at the DVB Gateway 62. The software would be analogous to location and paging software for cellular mobile networks. The only requirement would be a return path to provide a communication channel from mobile devices back to the DVB network. This could be provided under DVB-RCT (Return Channel Terrestrial)

for example.

Many publications have proposed methods for paging cells in cellular mobile networks, e.g. M. Verkama and C. Rose, Paging Strategies for Highly Mobile Users, Proc. ICUPC 96, Nov 1996, and D. O. Awduche, A. Ganz and A. Gaylord, An Optimal Search Strategy for Mobile Stations in Wireless Networks, Proc. ICUPC 96, is Nov. 1996, to which reference is specifically made in this respect. Any such scheme could be adapted from cellular mobile networks for use in cellular broadcast networks, taking into account the parameters of DVB-T cell size and MT mobility, to define suitable Location Areas (should they be required) and a paging strategy.

Future versions of DVB (e.g. DVB-Handheld) will provide for broadcast of a unique broadcast cell identifier from each transmitter. In this way each MT will be able to extract and store in memory the cell identifier representing the transmitter from which it has received data. Assuming the existence of a suitable communication channel back to the broadcast network, the broadcast network might operate in an analogous way to present location and paging strategies in cellular mobile networks. 2s

Referring to Fig. 9 a method in accordance with paging scheme (A) is generally identified by reference numeral 110. At step Sl, the DVB Gateway 62 queries a DVB database I 10 for details of the current Location Area of the MT that is to be located in the DVB network. The DVB database 110 searches for a record of the MT (by IMSI or NAI) and outputs the identity of the Location Area associated therewith. At step S2 the DVB Gateway 62 instructs paging in the DVB cell or cells of that Location Area. At step S3 the DVB Gateway 62 awaits a response from the UMTS network 11. If the MT is within the LA, the MT will receive one ofthe pages from a DVB transmitter at step S4. At step S5 the MT extracts and stores the DVB as cell identifier ofthe DVB transmitter in memory. Reception of the page triggers the - 18 - MT to activate a PDP context with the GGSN at step S6 as described above. Once the PDP context has been established, the MT transmits the DVB cell identifier to the GGSN 18 via the Node B 22 and SGSN 19 at step S7. At step S8 the GGSN 18 sends the IMSI of the MT 27 and the DVB cell identifier to the DVB Gateway 62 over the s loN link 103. The DVB Gateway 62 receives the data and then maps the received DVB cell identifier to the IMSI stored in the DVB Database 110. In this way a cellular broadcast network (e.g. the DVB network) can obtain a broadcast cell identity in which the MT resides, by paging one or more broadcast cell on a downlink, and receiving the broadcast cell identity via a mobile network (e.g. UMTS 0 network) uplink. One advantage of this is that the broadcast network does not have to be bi-directional. Furthermore, there will be a high probability of successfully finding a MT. However, there will be a relatively high signalling and database management cost as a result. In view of the scarce radio resource the applicant has devised further solutions taking this into account.

(B) Location Discoverv using UMTS network As mentioned above, the UMTS network 11 already maintains a record of the current LA of each MT so that only a small number of cells need to be paged to discover the UMTS cell in which the MT resides. As also mentioned, location and paging strategies are well developed in cellular mobile networks, and it is logical to take advantage of technology available in that area. The insight by the applicant is that since future MTs will almost certainly be multi-mode i.e. each comprises one or more interface for connecting to number heterogeneous networks, the various 2s interfaces on the MT will be in one physical location. Thus provided that the overlap between the broadcast cells and mobile cells is known, the LA data gathered and kept up to date in the mobile network can be used to approximately map the MT's position Referring to Fig. 10 a DVB cell map overlaid with a UMTS cell map generally identified by reference numeral 120 comprises a plurality of UMTS cells 121 and two DVB cells 122. The UMTS cell map further shows three LAs 123, 124, 125, each of which comprises a plurality of the UMTS cells 121. Each DVB cell 122 is larger in terms of geographical coverage area that each UMTS cell 121. Thus the 3s UMTS network operator and the DVB network operator may collaborate to compile - 19 - an electronic mapping database comprising a mapping between each DVB cell 122 and the or each UMTS cell 121 covered thereby. For example, for the map shown in Fig. 9, the database may contain entries as follows: UMTS LA DVB Cell ID LA#1,LA#2 Cell#1 LA #3, LA #2 Cell #2 s This mapping database may be stored on a network node either on the UMTS network (e.g. on the GGSN), on the DVB network (e.g. on the DVB Gateway), or may be stored, operated and updated by a third party.

lo However, it is apparent from Fig. 10 and from the table above that there might be a drawback to this method. In particular, UMTS LAs 123, 124, 125 may map badly to DVB cells 122. For example, a MT located in LA 124 might be served by either of the DVB cells 122. In order to estimate the accuracy of the proposed mapping method, the impact of the relative size of the DVB cells and UMTS LAs is was investigated. Referring to Fig. 11, various relative sizes generally identified by reference numeral 130 comprises a first relative size 131 where the DVB cell size is the same as the UMTS LA; a second relative size 132 where the DVB cell size is twice the UMTS LA; and a third relative size 133 where the DVB cell size is four times the UMTS LA. In each case the worst alignment scenario has been assumed i.e. the edge of each DVB cell lies in the middle of a UMTS LA, and that both DVB cells and UMTS LAs are square.

In the worst case scenario, UMTS LAs can be categorized as "corner" 134, "edge" 135 or "middle" 136. The probability of successfully mapping a UMTS LA to 2s the correct DVB cell from each category of LA can be defined as Pc, Pe and Pm.

Furthermore the ratio of DVB cell length to UMTS LA side length can be defined as: DVBSideLength or UMTSSideLength,B From Fig. 11 it is apparent that the probability, Ps, of successfully mapping a - 20 - MT to a DVB cell can be expressed as: 4P. + 4(p-1)Pe + (' 1) Pm s - (a + 1)2 and that the probability for a correct mapping for each of the categories of LA is Pc = 0.25, Pe = 0 5 and Pm = 1. Therefore, substituting and simplifying: is=+ Solving this equation for Ps = 0.95 i.e. a 95% probability that there will be a lo successful mapping, r = = 40. In other words given a large DVB-T cell size of 80km (i.e. 640km2), the maximum UMTS LA area to achieve this success rate is 2km (i.e. 4km2). Even with UMTS pico-cell configurations, this criterion is unlikely to be met as UMTS cells are usually of this in order in size, let alone the location areas. To improve the accuracy of the method it would be possible to require the UMTS network to page UMTS cells instead of UMTS LAs, with the mapping database described above mapping UMTS cells to DVB cells instead. Unfortunately this would almost certainly place too much signalling load on the UMTS network.

Referring to Fig. 12 a method in accordance with paging scheme (B) is generally identified by reference numeral 140, showing both versions: the extra steps required to page individual cells are shown in dashed outline. At step Sl the DVB Gateway 62 uses the IoN link 103 to request the GGSN to advise the current LA or UMTS cell ID of the MT. The DVB Gateway 62 will use an identifier such as the IMSI number so that the GGSN may lookup the correct PDP context. At step S2 the GGSN 18 accesses the HER to lookup the current LA. If the DVB Gateway 62 has requested the UMTS cell ID from the GGSN, the GGSN then instructs paging of the MT's present LA at step S3 and awaits a response from the MT at step S4. At step S5 the GGSN 18 responds to the DVB Gateway 62 over the loN link 103 either with the MT's current LA or UMTS cell ID. At step S6, the DVB Gateway 62 accesses the aforementioned mapping database using the current LA or UMTS cell ID to lookup the DVB cell ID.

- 21 - In this way a broadcast cell ID in which a MT is resident can be discovered utilising a mobile network to provide a current mobile cell or location area, and by referencing an electronic database comprising a mapping between mobile cells/location areas and broadcast cells.

It is possible that the mapping database might be stored at different locations on different networks. For example if the mapping database is stored on the UMTS network 11, then the DVB Gateway 62 may interrogate the UMTS network for a DVB cell identifier for a particular MT using the IMSI number for example. The UMTS network will respond with the DVB cell ID having carried out the lookup procedures described above. If the mapping database is stored on the DVB network, the DVB Gateway 62 may simply request the present LA or UMTS cell ID for a particular MT. Once that data is received the mapping database may be used as described above to estimate the current DVB cell of the MT. The mapping database may be stored and maintained by a third party who provides remote access to the database for receiving and responding to queries from either the UMTS network 11 or the DVB network 12. It is preferred that the mapping database is stored in the DVB network 12 however, since signalling is minimised.

(C) Location Area update in UMTS with DVB paging It appears that a pure DVB-T based or a UMTS LA or cell based method of location and tracking does not provide reliable location and tracking of MTs in the DVB-T network at a reasonable cost in terms of signalling and database management. Paging scheme (C) devised by the applicant provides a hybrid method that improves the network cost of locating and tracking MTs in the DVB network. In particular, the hybrid solution utilises existing UMTS LA data to estimate the physical position of a MT within 2 or 3 DVB cells, and then pages these DVB cells to accurately determine the DVB cell in which the MT resides.

Thus the network operators amend the aforementioned mapping database so that when queried with a UMTS LA, the database returns all possible DVB cell IDs that may serve that location area.

- 22 - Referring to Fig. 13 steps in the method of paging scheme (C) are generally identified by reference numeral 150. At step S1 the DVB Gateway 62 uses the IoN link 103 to request the data representing the current UMTS LA from the GGSN 18.

At step S2 the GGSN 18 references the HER to obtain the current LA, and replies to the DVB Gateway 62 with this data. At step S3 the DVB Gateway 62 queries the DVB Database (containing the mapping database) to obtain a mapping between the UMTS LA and a plurality of DVB cell IDs. At step S4 the DVB Gateway 62 instructs paging for the MT in all of those DVB cells identified by the mapping database. At step S5 the DVB Gateway awaits a response from the UMTS network.

When the MT receives a page from one of the DVB transmitters at step S6, it extracts at step S7 the DVB cell identifier that is broadcast by the DVB transmitter and stores it in an electronic memory (e.g. RAM) on the MT. At step S8, the MT activates a POP context in the UMTS network 11 as described above. At step S9, t5 once the PDP context has been activated, the MT transmits the DVB cell identifier over the UMTS network to the GGSN 18. The GGSN 18 then informs the DVB Gateway 62 of the DVB cell identifier it has received together with the IMSI of the MT at step S 10. In this way the DVB Gateway 62 may obtain the DVB cell identifier for each MT in the DVB network 12. In this way the maximum available data from the UMTS network is utilised without increasing the signalling load in the UMTS network unduly. Furthermore the method provides accuracy of locating each MT in the DVB network 12 since the MT is forced to respond to a page from its serving DVB transmitter.

2s (D) Combination Method Referring to Fig. 14 steps in a fourth method according to paging scheme (D) generally identified by reference numeral 160 comprises elements of the three paging schemes (A), (B) and (C) described above. The aim of this fourth method is to reduce signalling cost whilst providing greater levels of accuracy in the event of an unsuccessful mapping. The mapping database is adjusted to comprise mappings between (1) the UMTS LAs and one or more DVB cell ID, and (2) the UMTS cell ID and one or more DVB cell ID.

At step Sl the DVB Gateway 62 obtains the MT's current UMTS LA as - 23 described above and maps it to a DVB cell. At step S2, the DVB Gateway 62 checks the accuracy of the mapping. Inaccuracy may be immediately apparent if the mapping database maps a UMTS LA to more than one DVB cell. If this does not happen, the DVB network 12 may commence transmission of data to the MT using s the DVB transmitter identified as mapping to the UMTS LA. However if the mapping was unsuccessful, the DVB Gateway 62 may not receive an acknowledgement from the MT (see below). If the mapping check is unsuccessful, the method proceeds to step S3 where the DVB gateway 62 requests UMTS cell data from the UMTS network 11 as described above. Thus the UMTS network 11 may 0 have to page the current LA of the MT to obtain this data and respond. The UMTS cell ID is used by the DVB network 12 to attempt the mapping to a DVB cell again.

At step S4 the same mapping check is performed as at step S2. If the mapping is still unsuccessful, the DVB gateway 62 may instruct paging of the DVB cells that map to the UMTS LA and/or the UMTS cell ID at step S5. In this way the signalling load and accuracy ofthe method are gradually increased until the MT is located.

It will be appreciated that the invention is applicable to any cellular coverage or multi coverage area network in a heterogeneous network environment, although the invention is of particular benefit for estimating cell location in broadcast cellular networks that do not have an uplink from the MTs or in cellular networks where there is no provision for location discovery and update.

One particular advantage of the paging schemes (B) and (C) of the invention is that the cellular broadcast network does not have to assign resources for tracking MTs. Since the mobile cell location data is available from and kept up to date in the cellular mobile network, the broadcast network may map this data to broadcast cells when a MT needs to be located in the broadcast cells.

Referring to Fig. 15 part of the MT 27 is shown in greater detail. It comprises a memory 170, a CPU 171, amplifiers 172, a display 173 (and an input means not shown e.g. keyboard, touch-sensitive screen), digitalsignal processing (DSP) 174, radio control 175 and an antenna 176. The aforementioned parts are in electronic communication with one another. In use, data may be sent to and received from the both the UMTS network 11 and DVB network 12 by means of one or more interface 3s (not shown) and the antenna 176 over a wireless link. The MT 27 may have multiple - 24 physical antennae to cope with different radio signals, wavelengths, etc. from the various networks to which it has access.

The memory 170 of the MT 27 stores computer executable instructions that s when executed perform the MT method steps mentioned in either paging scheme (A), (C) or (D) above. In particular, when the MT receives a paging signal from a DVB transmitter that contains a DVB cell ID, the MT method steps are executed: the MT activates or utilises a UMTS interface to forward that DVB cell ID to the UMTS network 11 for example. Such computer executable instructions may be uploaded 0 onto firmware at point of manufacture of the MT or the memory therefor, or downloaded over one of the networks to which the M 27 has access for example.

The computer executable instructions may also cause the MT 27 to activate another interface ready to receive data. For example, the DVB Gateway 62 may signal the GGSN 18 via the loN link 103 to send data (via PDP context) to the MT 27. The data contains an instruction to the MT 27 to activate the DVB interface (if not already activated) and listen to some particular channel. On receipt of the data from the UMTS network 11, the MT 27 activates its DVB interface and listens to the appropriate channel. The MT 27 may also send some form of acknowledgement to the DVB Gateway 62 via the UMTS network 11. Upon receipt of the acknowledgement or after expiration of a short timer, the DVB Gateway 62 instructs transmission of data to the MT 27. This provides power saving functionality for the MT 27 and is useful as the DVB network is not provided with a paging channel.

As used herein the term "multi-mode" with reference to a MT is intended to mean that the MT can access more than one network. This functionality may be provided with a number of different physical interfaces in the MT. However, it is expected that future MTs will have one reconfigurable interface that can be re configured to connect to more than one network by means of software download from one of the networks it already accesses for example. Such single interface MTs are also included by this term.

Although the embodiment of the invention described with reference to the drawings comprises computer apparatus and methods performed in computer apparatus, the invention also extends to computer programs, particularly computer - 25 programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the methods according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a ROM, for example a CD ROM or a semiconductor ROM, or a magnetic recording medium, for example a floppy disc or hard disk. Further, the carrier may be a transmissible carrier such as an electrical or optical signal that may be conveyed via electrical or optical cable or by radio or other means.

When the program is embodied in a signal that may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or other device or means. Alternatively, the carrier may be an integrated circuit in which the program IS is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant methods.

Claims (35)

- 26 - CLAIMS

1. In a heterogeneous network environment comprising a first cellular network and a second cellular network, a method of estimating the cell location of a mobile terminal in said first cellular network, which method comprises the step of using said second cellular network to provide said first cellular network with cell location data representing an estimated location of said mobile terminal in a cell or cells of said first cellular network or said second cellular network.

lo

2. A method according to claim 1, further comprising the step of using said second cellular network as an uplink for said first cellular network, whereby said mobile terminal may transmit said cell location data toward said first cellular network.

3. A method according to claim 1 or 2, further comprising the steps of said first cellular network instructing paging for said mobile terminal in one or more first network cells, and a first network transmitter in the or each first network cell transmitting a respective first network cell identifier during said paging that uniquely identifies that first network cell in said first cellular network.

4. A method according to claim 3, wherein said one or more first network cells comprises a location area of said mobile terminal in said first cellular network, the method further comprising the step of storing location area data representing said location area in an electronic database accessible by said first cellular network.

5. A method according to claim 3 or 4, wherein upon receipt of a paging message the method further comprises the steps of said mobile terminal extracting said first network cell identifier and transmitting said first network cell identifier to said second cellular network for onward transmission toward said first cellular network.

6. A method according to claim 5, further comprising the steps of receiving said first network cell identifier on said second cellular network and transmitting said first network cell identifier to said first cellular network.

- 27 -

7. A method according to claim 6, wherein said transmission step comprises the step of transmitting said first network cell identifier over a logical link between a respective network node on said first and second cellular networks.

s

8. A method according to any preceding claim, further comprising the step of said first cellular network transmitting a request to said second cellular network for said cell location data.

9. A method according to any preceding claim, further comprising the steps of 0 said second cellular network instructing paging for said mobile terminal in one or more second network cells, and a second network transmitter in the or each second network cell transmitting a respective second network cell identifier during said paging that uniquely identifies that second network cell in said second cellular network.

10. A method according to claim 9, wherein said one or more second network cells comprises a location area of said mobile terminal in said second cellular network, the method further comprising the step of storing location area data representing said location area in an electronic database accessible by said second cellular network.

11. A method according to claim 9 or 10, wherein upon receipt of a paging message the method further comprises the steps of said mobile terminal extracting said second network cell identifier and transmitting said second network cell identifier to said second cellular network for onward transmission toward said first cellular network.

12. A method according to claim 11, further comprising the steps of receiving said second network cell identifier on said second cellular network and transmitting said second network cell identifier to said first cellular network.

13. A method according to claim 12, wherein said transmission step comprises the step oftransmitting said second network cell identifier over a logical link between a respective network node on said first and second cellular networks. - 28

14. A method according to any preceding claim, wherein there is provided an electronic database accessible by said first and/or second cellular network, which database comprises a mapping between a first network cell and a second network cell corresponding to a physical overlap between those cells, the method further comprising the step of querying said electronic database to lookup a first network cell corresponding to a second network cell.

15. A method according to claim 14, wherein said electronic database comprises a mapping between one or more second network cell and a plurality of first network lo cells, the method further comprising the steps of receiving data representing said plurality of first network cells and instructing paging of those first network cells for said mobile terminal.

16. A method according to claim 15, wherein said electronic database comprises a mapping between a location area in said second cellular network and one or more second network cell corresponding thereto.

17. A method according to any preceding claim, wherein said cell location data comprises a first network cell identifier, a second network cell identifier or a second network location area identifier.

18. A method according to any preceding claim, wherein said first cellular network is substantially unidirectional in transmission of data, and said second cellular network is bi-directional.

19. A method according to any preceding claim, wherein said first cellular network comprises a broadcast network.

20. A method according to claim 19, wherein said broadcast network comprises a digital video, audio and/or data transmission network.

21. A method according to any preceding claim, wherein said second cellular network comprises a mobile cellular network.

22. A method according to claim 21, wherein said mobile cellular network - 29 comprises a third or fourth generation mobile cellular network.

23. A method according to any preceding claim, wherein said mobile terminal is a multi-mode mobile terminal. s

24. A computer program comprising computer executable instructions for causing a first cellular network and a second cellular network to perform the method steps of any of claims 1 to 23.

lo

25. A computer program product storing computer executable instructions in accordance with claim 23.

26. A computer program product as claimed in claim 24, embodied on a record medium, in a computer memory, in a read-only memory or on an electrical carrier signal.

27. In a heterogeneous network environment comprising a first cellular network and a second cellular network, a method of estimating the cell location of a mobile terminal in said first cellular network, which method comprises the steps of: (a) performing the method steps of any of claims 2 to 7; (b) determining whether or not said estimated location is accurate, and if not, performing the method steps of any of claims 8 to 14.

28. A method according to claim 27, further comprising the steps of determining 2s whether or not said estimated location after step (b) is accurate, and if not, performing the method steps of claim 15.

29. A substantially unidirectional data transmission network comprising a plurality of transmitters dividing a physical area into a plurality of cells, which network comprises a network node having memory storing computer executable instructions for performing the first cellular network method steps of any of claims I to23.

30. For use in the substantially unidirectional data transmission network of claim 29, a network node having memory storing computer executable instructions for - 30 performing the first cellular network method steps of any of claims I to 23

31. A bi-directional data communication network comprising a plurality of transmitters dividing a physical area into a plurality of cells, which network comprises a network node having memory for storing computer executable instructions for performing the second cellular network method steps of any of claims 1 to23.

32. For use in the bi-directional data communication network of claim 31, a l o network node comprising memory storing computer executable instructions for performing the second cellular network method steps of any of claims I to 23.

33. A multi-mode mobile terminal comprising a memory storing computer executable instructions that when executed cause the mobile terminal to listen on a IS first interface for an identifier of a cell in a first cellular network in which the mobile terminal resides, and upon receipt thereof, transmit said identifier from a second interface to a second cellular network in which the mobile terminal resides.

34. A multi-mode mobile terminal as claimed in claim 33, wherein said computer executable instructions further comprise instructions for causing said mobile terminal to listen on said second interface to said second cellular network for start data, and upon receipt thereof, listen on said first interface for commencement of data transmission from said first cellular network.

35. A multi-mode mobile terminal as claimed in claim 33 or 34, wherein said first and second interfaces are provided by a single reconfigurable interface.