GB2475834A

GB2475834A - Handover method in media independent handover based on geographical location

Info

Publication number: GB2475834A
Application number: GB0920771A
Authority: GB
Inventors: Ankur Khandelia
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2009-11-26
Filing date: 2009-11-26
Publication date: 2011-06-08
Anticipated expiration: 2029-11-26
Also published as: GB201201520D0; GB2475834B; GB0920771D0; GB2488202B; GB2488202A

Abstract

There is discussed a mobile communication device having means for monitoring its geographical position and a database storing data associating a plurality of geographical locations with respective wireless communication networks. During a handover operation, the mobile communication device calculates if the current geographical position satisfies a proximity criterion to one of the plurality of geographical locations, and if it does initiates handover of a communication link to an access point to the wireless communication network associated with that geographical location. By storing data associating such geographical locations with respective wireless communication networks, it is not necessary to query for available networks and therefore the handover operation is facilitated and the amount of network signalling is reduced. The database also stores one or more time durations associated with previous handover operations. The mobile communication device calculates a time interval associated with a handover operation using said stored time durations, estimates a geographical position where the mobile communication device will be after said calculated time interval has passed using the geographical position of the mobile communication device as determined at two or more different timings and sends to a remote network device a message specifying the estimated geographical position and requesting information on access points associated with the estimated geographical position. By using such an estimated geographical position, it is more likely that the list of networks provided by the network will be relevant when handover actually takes place. The application lies in media independent handover (MIH) of the IEEE 802.21 specification.

Description

MOBILE COMMUNICATION DEVICE AND METHOD OF OPERATION THEREOF

The present invention is concerned with handover operations performed when a mobile communication device switches access points to a wireless communication network.

The present invention has particular, but not exclusive, relevance to handover operations between two access points in a heterogeneous wireless communication network.

The background to the invention will be described in the context of Media Independent Handover, as described in IEEE Specification 802.21, although the invention also has applicability outside this Specification. IEEE Specification 802.21 has been developed to standardise aspects of the handover between networks of the same type as well as handover between different network technologies. Such Media Independent Handover allows, for example, a user of a cellular phone to handover from an access point to a Public Land Mobile Network (PLMN) to an access point of a Wireless Local Area Network (WLAN) when the user enters either their home or office in accordance with configured network preferences.

Media Independent Handover (MIH) separates handover into two main parts: Handover Initiation and Handover Preparation. The Handover Initiation part involves Network Discovery, Network Selection and Network Negotiation components. As defined in IEEE Specification 802.21 (whose contents are incorporated herein by reference): A) the M[H process starts with the a MIII agent in the mobile communication device receiving an indication that a link is going down; B) the MIII agent in the mobile communication device checks its policy configuration parameters to determine if link has gone below a threshold value for a specified period of time; C) if MIH agent in the mobile communication device determines link has gone below the threshold value for the specified period of time, the MIH agent sends a Get_Information request to the MIH Information Server (IS) specifying either the current Cefl ID or the current GPS co-ordinate; D) the Mifi IS identifies networks in the proximity of the specified current Cell_ID or GPS co-ordinate, and sends a Get_Information response listing the identified networks and giving details of their cost of connection, security parameters, quality of service, operator ID etc. E) the MIH agent in the mobile communication device evaluates the list of networks based on its policy configuration parameters and identifies candidate networks for connection; F) the MIlE agent in the mobile communication device sends a Candidate_Query request specifying the candidate networks to the MIII mobility management server in the network; G) the MIlE mobility management server resource queries to the candidate networks, and then sends a Candidate_Query response to the MI1H agent in the mobile communication device detailing the responses to those resource queries; H) the MIII agent in the mobile communication device analyses the resources of the candidate networks, and selects a network for connection; I) the MIII agent in the mobile communication device sends a Commit request specifying the selected network to the MIH server in the network; F) the MIII server forward the commit request to the selected network, receives reply and sends Commit response to MIH agent in the mobile communication device; and G) the MIII agent in the mobile communication device commences setting up a communication link with the selected network.

An object of the present invention is to provide a more efficient way of performing a handover operation.

As set out above, the handover initiation procedure set out above involves the MIII agent in the mobile communication device sending various requests to the network and then awaiting the responses to those requests. This involves both a delay in the handover operation and also a significant amount of signalling on the network.

Another problem with the handover procedure set out above is that during the time required to send the various requests and receive the corresponding response, the position of the mobile communication device may have changed to such an extent that the list of networks provided by the MIlE information server is no longer valid.

Aspects of the invention are set out in the accompanying claims.

In one embodiment of the invention, a mobile communication device has means for monitoring its geographical position and a database configured to store data associating a plurality of geographical locations with respective wireless communication networks. During a handover operation, the mobile communication device calculates if the current geographical position satisfies a proximity criterion to one of the plurality of geographical locations, and if it does initiates handover of a communication link to an access point to the wireless communication network associated with that geographical location. The stored geographical locations may correspond to places where the user of the mobile communication device frequently visits, for example their home or workplace. By storing data associating such geographical locations with respective wireless communication networks, it is not necessary to query the network for available networks and therefore the handover operation is facilitated and the amount of network signalling is reduced.

In another embodiment of the invention, a mobile communication device has a database storing one or more time durations associated with previous handover operations.

The mobile communication device calculates a time interval associated with a handover operation using said stored time durations, determines the geographical position of the mobile communication device, estimates a geographical position where the mobile communication device will be after said calculated time interval has passed using the geographical position of the mobile communication device as determined two or more different timings, and sends to a remote network device a message specifying the estimated geographical position and requesting infonnation on access points associated with the estimated geographical position.

By using such an estimated geographical position, it is more likely that the list of networks provided by the network will be relevant when handover actually takes place.

In a further embodiment, a mobile communication device has means for monitoring its geographical position using one or more received position signals. The mobile communication device initiates handover of a communication link in response to the behaviour of said one or more received position signals. In this way, for example, when the strength of the received position signals drops on entering a building, the mobile communication device can automatically look for a new network. This is advantageous as there may be a local network in a building which provides a better quality of service or a reduced cost in comparison with available networks outside of the building.

Various exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 schematically shows a communication system according to a first embodiment of the present invention; Figure 2 schematically shows the main components of a cellular phone forming part of the communication system illustrated in Figure 1; Figure 3 is a flow chart showing operations performed in the cellular phone illustrated in Figure 2 in response to an indication of a link going down; Figure 4 is a diagram illustrating the calculation of direction and speed of travel from two location co-ordinates; Figure 5 is a diagram illustrating the availability of access points along the direction of movement of the cellular phone; and Figure 6 schematically shows the main components of an alternative cellular phone to the cellular phone illustrated in Figure 2.

A first embodiment of the invention will now be described with reference to Figures 1 to 5. As shown in Figure 1, a cellular phone 1 in accordance with the present invention can communicate, via various access networks 3a-3c, with an operator network 5. In the exemplary arrangement of Figure 1, the cellular phone I can communicate with a wireless LAN 3a, a public land mobile network (PLMN) 3b and a WiMAX network 3c. The available access networks will depend upon the position of the cellular phone 1. For example, in some locations only a PLMN may be available, while in some other locations only a Wireless LAN may be available. But recently there have been more and more locations in which a choice of access technologies is available.

The operator network 5 is attached to a Media Independent Handover Server 7. The operator network 5 also provides a gateway (not shown) to the Internet 9 allowing downloading of information from the World Wide Web to the cellular phone 1.

In this embodiment, the access teclmologies 3, the operator network 5, the M server 7 and the Internet 9 are conventional and will not therefore be described in detail. The cellular phone 1, however, includes novel functionalities which enable more efficient handover operations.

As shown in Figure 2, the cellular phone I has: -an aerial 21a which is connected to a 2G13G transceiver 23a for receiving radio signals from a PLMN; -an aerial 21b which is connected to an IEEE 802 transceiver 23b for receiving radio signals from an IEEE 802 network such as a wireless LAN or a WiMAX network; and -a GPS aerial 21c which is connected to a GPS receiver for receiving signals from satellites of the Global Positioning System.

The transceiver 23a recovers message data from the signals detected by the aerial 21a, and forwards the message data to a processor 25. The transceiver 23a also receives signals from the processor 25, and converts them into radio signals for transmission by the aerial 21 a.

Similarly, the transceiver 23b recovers message data from the signals detected by the aerial 21b, and forwards the message data to the processor 25. The transceiver 23b also receives signals from the processor 25, and converts them into radio signals for transmission by the aerial 21b.

The GPS receiver 23c processes the signals received by the GPS aerial 21c to calculate geographical location co-ordinates for the cellular phone 1, hereafter called GPS co-ordinates, and forward the GPS co-ordinates to the processor 25.

The cellular phone I also includes a microphone 27 and a loudspeaker 29 which are both connected to the processor 25 via a speech coder/decoder 31 In particular, acoustic signals detected by the microphone 31 are converted into digital data by an analog-to-digital converter (ADC) 33, the digital data is encoded by the speech coder/decoder 31 and the encoded data are output for processing by the processor 25. Encoded data output by the processor 25 is decoded by the speech coder/decoder 31, and the resultant decoded data is input to drive circuitry 35 for the loudspeaker 29.

The cellular phone 1 also has a keyboard 37 and a display 39 which are connected to the processor 25. The keyboard 37 receives user input, and the display 39 displays information to the user. The cellular phone 1 also has memory 41, which in practice may consist of two or more memory devices having different properties. The memory 41 includes a first memory region 43 storing applications which are executed by the cellular phone, a second memory region 45 storing data, and a third memory region 47 providing working memory. It will be appreciated that this is a schematic representation and the memory regions need not consist of contiguous memory addresses The cellular phone 1 discussed so far with relation to Figure 2 are schematically representative of conventional features of a cellular phone 1. According to the present invention, the cellular phone 1 includes a novel MIH client 49 which is able to execute: -an Update_Database sub-routine 51; -a Location Analysis sub-routine 53; and -a Proximity_Checking sub-routine 55.

The MIH client 49 and associated sub-routines make use of a novel database 57, hereafter referred to as the MN database 57, stored in the second memory region 45 of the cellular phone 1.

Figure 3 show the operations performed by the cellular phone 1 following receipt of a "link going down indication" at Si. First, the MIH client 49 initiates the Location_Analysis sub-routine 53, which determines the current GPS co-ordinates P1(Xi,Y1,Z1,T1) and then in a split of time afterwards (in this embodiment in the region of 10-2Oms) determines a revised GPS co-ordinate P2(X2,Y2,Z2,T2). From the position co-ordinates P1 and P2, the Location_Analysis sub-routine 53 determines the direction 0 of movement and the speed V of the cellular phone 1. In particular, as shown in Figure 4, the direction 0 of movement is determined by the angle between the positions P1 and P2, while the speed V is determined from the distance a between the positions P1 and P2.

As data relating to a handover operation is determined, it is stored in the Mill-I database 57. Table 1 shows exemplary entries in the MN database 57. As shown, each entry has the corresponding positions P1 and P2, and the original network (network A) from which the handover is to be made. Each entry also includes three time values: Tis, Tcq and Tcr. Tis is the time interval between the sending of a Get-Information request and receiving the Get_Information response; Tcq is the time interval between sending the Candidate Query request and receiving the Candidate_Query response; and Tcr is the time interval between sending the Commit request and the Commit response.

The MN database 57 also stores data indicating the destination network for the handover operation (network B), the criteria which were used to select the destination network, the JP address (if applicable) and the network type. Each entry may also store a position P3 representative of where the handover operation actually took place.

Returning to Figure 3, following execution of the Location_Analysis sub-routine 53, the Miff client 49 initiates, at S5, the Proximity_Checking sub-routine 55 which determines if any of the co-ordinates in the MIlE! database 57 relating to previous handovers is within a predefined distance, in this embodiment ten metres, from the position P2. The MIR client 49 checks, at S7, the output of the Proximity_Checking sub-routine 55.

If a co-ordinate in the MN database 57 for a previous handover is within the predefined distance of the position P2, then in this embodiment the MN client 49 does not send a Get_Information request or a Candidate_Query request, but rather retrieves, at S9, the destination network corresponding to that previous handover and directly sends, at S23, a

S

Commit request identifying this destination network. This is based on the assumption that if it had previously been determined that the destination network was the best network to handover to for a nearby location, then it is likely that the same network would be the best network to handover to for the present instance.

GPS Position P1 GPS Position P2 Network A Tis Tcq Tcr Network B Switching IP address Network GPS Position P3 Criteria (if Type applicable) X11,Y11,Z11,T11 X21,Y21,Z21,T21 Orange 10 20 25 BT BT Open Wireless X3j,Y31,Z31,T31 zone LAN X12,Y12,Z12,T12 X22,Y22,Z22,T22 BT 20 25 30 T-Mobile Q0S better Cellular X13,Y13,Z3,T13 X23,Y23,Z23,T23 T-Mobile 20 15 35 Non-POA Security Wireless Co

LAN

Table 1: Contents of the MIH Database If the position P2 is not within a predefined distance of a co-ordinate recorded in the MIH database 57 for a previous handover, then the MN client 49 evaluates, at SI I, the response time data stored in the MIH database 57 and calculates a mean average weighted time Twa using the formula: Tis Tcq Tcr Twa= + + Wi W2 W3 where Wi is the number of times Tis appears in the database, W2 is the number of times Tcq appears in the database and W3 is the number of times Tcr appears in the database.

In other words, Twa corresponds to the summation of the average time for Tis, the average time for Tcq and the average time for Tcr.

The MIH client 49 then predicts, at S13, the location co-ordinates where the user will be after the time Twa using the previously determined direction 0 and speed V of movement.

The MI1H client 49 then sends, at S15, a Get Information request to the MIH Information Server specifying the predicted location co-ordinates, not the current location co-ordinates.

Following receipt, at S17, of the Get_Information response providing details of neighbouring networks associated with the predicted location co-ordinates, the MIlE-i client 49 selects candidate networks in a conventional manner and sends, at S19, a Candidate_Query request to the MN mobility management server. In this embodiment, the MN client 49 is able to modify the policy set logic which is used to select candidate networks to take account of the direction 0 and speed V information for the cellular phone 1. For example, consider the scenario illustrated in Figure 5. The Get_Information response may specify access points A, B, C, D and E as shown in Figure 5. But as the MIH client 49 knows the direction and speed of movement of the user, the MIH client 49 can select only those access points which fall in the direction of user movement (access points A and B in Figure 5). If insufficient access points are in the direction of user movement, then it can look up to 45° from the direction of user movement (to include access point C in Figure 5). If insufficient suitable access points are available, the search can again be widened, for example to look up to 60° from the direction of movement. After a few access points have been identified, other conventional policy parameters such as cost of network, quality of service etc. can be used to identify candidate networks.

Following receipt, at S2 1, of the Candidate_Query response, the MN client selects one of the candidate networks in a conventional manner and sends, at S23 a Commit request identifying the selected network. Following receipt, at S25, of the Commit response, the MIII client opens up the link adaptor for handover and sends, at S27, a Complete request to the new network. The handover operation then completes in a conventional manner.

When the handover operation is completed, the Update_Database sub-routine 51 updates the MIH database 57 with information relating to the handover operation.

In the first embodiment, as described above, two main procedures are provided for achieving a more efficient handover operation.

The first procedure involves checking if a previous handover operation had been performed in a nearby location, and if so sending a Commit request identifying the destination network for that previous handover operation. In this way, both the time taken for the handover operation and network signalling may be reduced.

The second procedure involves predicting the location at which a handover operation will take place, and specifying the predicted location in the Get_Information request. This results in the networks identified in the Get_Information response being more likely to be relevant.

As users regularly revisit the same places (home, work, shopping complex etc.), the MIII database 57 will quickly be populated with the locations of those places. This means that the first procedure should result in a significant reduction in handover messaging, which is desirable in order both to conserve battery life of the cellular phone 1 and to free up network bandwidth.

The second procedure is particularly advantageous when the cellular phone is moving at a fast speed, for example in a car. By predicting the position of the cellular phone when the handover takes place, less abortive handover operations will occur and the total number of handover operations will also be reduced.

Both the first and second procedures can result in a quicker handover operation. It is expected that the average handover time will reduce by as much as 40-50% by reducing the number of handover operations and the number of steps performed in many of the handover operations.

In the first embodiment, all the handover operations were triggered when link adapters (WiFi, WiMAX, etc. layers) were going down. A second embodiment will now be described with reference to Figure 6 in which a handover criterion is determined as a function of the GPS signal. In Figure 6, components which are the same as corresponding components of the first embodiment have been referenced by the same numerals and will not be described in detail again.

In this embodiment, when the GPS receiver 23c' is unable to calculate the GPS co-ordinates due to a loss of detection of the one or more position signals, the GPS receiver 23' sends a "loss of GPS signal" indication to the processor 25. The GPS_Handover sub-routine 61 monitors the signals from the GPS receiver 23c', and keeps a record of the most recently received GPS position co-ordinates. In response to detection of the "loss of signal" indication from the GPS receiver 23', the GPS_Handover sub-routine 61 initiates a handover operation by sending a signal to the MIH Client 49'.

Following receipt of a signal from the GPS Handover sub-routine 61 specifying that the GPS signal has been lost and giving the last known GPS position co-ordinates, the MIH Client 49' checks if the last known GPS position co-ordinates are nearby any of the position co-ordinates specified in the MIH database 57 for previous handover operations. If the last known GPS position co-ordinates are nearby the co-ordinates for a previous handover operation, then the MIH Client 49' sends a Commit request to the destination network for that previous handover operation. Otherwise, the Mill-I Client 49' proceeds by sending a Get Information request to the MIH Information Server specifying the last known GPS position co-ordinates and the handover procedure then continues in a conventional manner.

The optimal network inside a building is often different from the optimal network outside of a building. For example, a wireless LAN may be available inside the building which is not available outside of the building. The procedure of the second embodiment takes advantage of the fact that often GPS position signals are lost when a cellular phone I moves indoors in order to expedite handover.

MODIFICATIONS AND FURTHER EMBODIMENTS

In the second embodiment, a handover operation is initiated in response to a "loss of GPS signal" indication. In alternative embodiments, it is not necessary for there to be a complete loss of GPS signal, but rather only a drop in the signal strength of the received position signals from the GPS satellites which is indicative of the cellular phone moving into a building.

It will be appreciated that the triggering of a handover operation in dependence on a property of received position signals is independently inventive from the modifications to the handover initiation procedure described in the first embodiment. There is no necessity for the MIFf client to check if the last known GPS co-ordinates are nearby any co-ordinates stored in the MU-I database.

In the first embodiment, if the current GPS position co-ordinates satisfy a proximity condition with a co-ordinate stored in the MIT-I database, then the MIH client directly sends a Commit request without sending a Get Information request. In an alternative embodiment, the MIH client sends a Get_Information request specifying current or predicted GPS position co-ordinates in addition to the Commit request. This has the advantage of allowing verification that the last selected destination network is still available. If it is not, then the handover initiation operation can proceed in the normal way by sending the Candidate Query request.

In the first embodiment, it is checked whether the current GPS position co-ordinates are within ten metres of position co-ordinates stored in the. MIH database. It will be appreciated that a different proximity condition could be used. For example, the proximity condition could be with twenty metres. Alternatively, there may be a more complicated proximity condition in which the proximity in one direction may be more important than in another direction, which may be relevant for example in a multi-story building in which J 5 different wireless LANS are provided on different floors.

Although both the sending of a Gel_Information request with a predicted GPS position co-ordinate and the direct sending of a Commit request if the current GPS position co-ordinate matches a stored co-ordinate utilise the MIH database, it will be appreciated that these two procedures are separable and need not be present in the same embodiment of the invention.

In the first embodiment, the Global Positioning System is used to determine the geographical position of the cellular phone. It will be appreciated that the geographical position could alternatively be determined utilising position signals provided by other global navigation satellite systems such as GLONASS and GALILEO. Further, the geographical position could alternatively be determined using position signals provided by a terrestrial navigation system such as LORAN or E-LORAN or E-LORAN or a system using pseudolites or pseudo-satellites. In addition, techniques such as assisted GPS can be used to quickly get a GPS co-ordinate fix. Further, techniques such as Angle-Of-Arrival (AOA) and Uplink-Time-Difference-On Arrival (U-TDOA) could be used in which the radio signals from the cellular phone detected by multiple base stations of an access network are processed to determine location co-ordinates for the cellular phone, and these location co-ordinates are then sent back to the cellular phone. All that is required is a technique to determine the geographical position of the cellular phone.

While the embodiments of the invention discussed above conform with the Media Independent Handover procedure defined in the IEEE 802.21 Specification, it will be appreciated that this is not essential. The invention may be implemented in any system which incorporates multiple access networks, both presently existing and to be defined in the future.

For example, the invention could be applied in conjunction with the Access Network Discovery and Selection Function (ANDSF) proposed by the Third Generation Partnership Project (3GPPTM), see for example 3GPP TS 23.402. The invention could also be applied in the context of Unlicensed Mobile Access (UMA), also called Generic Access Network (GAN), Single Radio Voice Call Continuity (SRVCC), Mobile IP (e.g. Proxy Mobile IP v6) and. any other intra-mobility/inter-mobility technologies which may form part of the next generation technologies such as LTE and WiMAX.

Although the embodiments discussed above involve a cellular phone, it will be appreciated that the invention may be applied in any mobile communication device. For example, the invention could also be applied in a personal digital assistant, a portable computer or a satellite telephone. Further, the mobile device need not be able to communicate with a wireless communication network, but need only be able to monitor messages sent by the wireless communication network to extract network address parameters identifying network areas. Data stored by the mobile device can subsequently be downloaded via a connect to a computer, for example, the connection being wired or wireless.

The embodiments described with reference to the drawings comprises a processing apparatus and involve processes performed in the processing apparatus. The invention also extends to computer programs, particularly computer 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 to source code and object code such as in partially compiled form, or in any other form suitable for using in the implementation of the processes 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 a hard disc, or an optical recording medium. Further, the carrier may be a transmissible carrier such as an electronic or optical signal which may be conveyed via electrical or optical cable or by radio or other means.

The carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

Although the invention may be implemented by software, it will be appreciated that alternatively the invention could be implemented by hardware devices or a combination of hardware devices and software.

Claims

CLAIMS1. A mobile communication device operable to communicate with a plurality of wireless communication networks, the mobile communication device comprising: means for monitoring the geographical position of the mobile communication device; database means arranged to store data associating a plurality of geographical locations with respective wireless communication networks; means for determining whether a handover criterion has been satisfied; means for calculating, in response to the determining means determining that a handover criterion has been satisfied, if the geographical position determined by said monitoring means satisfies a proximity criterion to one of the plurality of geographical locations; and means operable, in response to the calculating means calculating that the geographical position satisfies a proximity criterion to one of said plurality of geographical locations, to initiate handover of a communication link to an access point to the wireless communication network associated with that geographical location.
2. A mobile communication device according to claim 1, wherein the monitoring means is operable to utilise a global navigation satellite system.
3. A mobile communication device according to claim I or 2, wherein said monitoring means is operable to monitor the geographical position of the mobile communication device using one or more received position signals, and wherein said handover criterion is dependent on the quality of said one or more received position signals.
4. A mobile communication device according to claim 3, wherein said handover criterion relates to the quality of said one or more received position signals being insufficient to determine the geographical position of the mobile communication device.
5. A mobile communication device operable to communicate with a plurality of wireless communication networks, the mobile communication device comprising: means for storing one or more time durations associated with previous handover operations; nieans for calculating a time interval associated with a handover operation using said stored time durations; means for determining the geographical position of the mobile communication device; means for estimating a geographical position where the mobile communication device will be after said calculated time interval has passed using the geographical position of the mobile communication device as determined by said determining means at two or more different timings; and means for sending to a remote network device, via an access point to a first wireless communication network, a message specifying the estimated geographical position and requesting information on access points associated with the estimated geographical position.
6. A mobile communication device according to claim 5, wherein said determining means is operable to utilise a global navigation satellite system.
7. A mobile communication device according to claim 5 or 6, wherein the sending means is arranged to send said message in response to a handover condition for handing over a communication link with the first wireless communication network being satisfied.
8. A mobile communication device according to any of claims 5 to 7, wherein for each of said previous handover operations, said storing means is operable to store one or more time durations, each time duration corresponding to the time taken to respond to a corresponding message during a handover initiation procedure.
9. A mobile communication device according to claim 8, wherein the estimating means is operable to determine a direction of movement and a speed of movement from two determined geographical positions at different timings, and to estimate the geographical position of the mobile communication device after said estimated time interval using a projection based on said direction of movement and speed of movement.
10. A mobile communication device comprising: means for monitoring the geographical position of the mobile communication device using one or more received position signals; and means for initiating handover of a communication link in response to a handover criterion being satisfied, wherein said handover criterion is dependent on said one or more received position signals.
11. A mobile communication device according to claim 10, wherein said handover condition is dependent on the quality of said one or more received position signals.
12. A mobile communication device according to claim 11, wherein said handover condition relates to the quality of said one or more received position signals being insufficient to determine the geographical position of the mobile communication device.
13. A method of operation of a mobile communication device which is operable to communicate with a plurality of wireless communication networks, the method comprising: monitoring the geographical position of the mobile communication device; storing data associating a plurality of geographical locations with respective wireless communication networks; determining whether a handover criterion has been satisfied; calculating, in response to a determination that a handover criterion has been satisfied, if the geographical position of the mobile communication device satisfies a proximity criterion to one of the plurality of geographical locations, and if so calculating initiating handover of a communication link to an access point to the wireless communication network associated with that geographical location.
14. A method according to claim 13, wherein the monitoring step comprises processing position signals from a global navigation satellite system.
15. A method according to claim 13 or 14, wherein the handover criterion is dependent on the quality of said one or more received position signals.
16. A method according to claim 15, wherein said handover criterion relates to the quality of said one or more received position signals being insufficient to determine the geographical position of the mobile communication device.
17. A method of operation of a mobile communication device operable to communicate with a plurality of wireless communication networks, the method comprising: storing one or more time durations associated with previous handover operations; calculating a time interval associated with a handover operation using said stored time durations; determining the geographical position of the mobile communication device; estimating a geographical position where the mobile communication device will be after said calculated time interval has passed using the geographical position of the mobile communication device determined at two or more different timings; and sending to a remote network device, via.an access point to a first wireless * iS communication network, a message specifying the estimated geographical position and requesting information on access points associated with the estimated geographical position.
18. A method according to claim 17, wherein said determining comprises processing position signals from a global navigation satellite system.
19. A method according to claim 17 or 18, wherein said sending of said message is in response to a handover condition for handing over a conmiunication link with the first wireless communication network being satisfied.
20. A method according to any of claims 17 to 19, wherein for each of said previous handover operations, one or more time durations is stored, each time duration corresponding to the time taken to respond to a corresponding message during a handover initiation procedure.
21. A method according to claim 20, wherein the estimating step comprises determining a direction of movement and a speed of movement from two determined geographical positions at different timings, and estimating the geographical position of the mobile communication device after said estimated time interval using a projection based on said direction of movement and speed of movement.
22. A method of operation of a mobile communication device, the method comprising: monitoring the geographical position of the mobile communication device using one or more received position signals; and initiating handover of a communication link in response to a handover criterion being satisfied, wherein said handover criterion is dependent on said one or more received position signals.
23. A method according to claim 22, wherein said handover condition is dependent on the quality of said one or more received position signals.
24. A method according to claim 23, wherein said handover condition relates to the 1 5 quality of said one or more received position signals being insufficient to determine the geographical position of the mobile communication device.
25. A computer program comprising instructions for programming a mobile communication device to implement a method as claimed in any of claims 13 to 24.
26. A storage medium storing a computer program as claimed in claim 25.
27. A signal conveying a computer program as claimed in claim 25.