WO2005027556A1

WO2005027556A1 - Selection of a target network for a seamless handover from a plurality of wireless networks

Info

Publication number: WO2005027556A1
Application number: PCT/EP2003/010183
Authority: WO
Inventors: Anand R. Prasad; Hu Wang
Original assignee: Ntt Docomo, Inc.
Priority date: 2003-09-12
Filing date: 2003-09-12
Publication date: 2005-03-24
Also published as: EP1665853A1; CN100512538C; JP2007515826A; JP4585969B2; CN1849840A; AU2003271605A1

Abstract

Method and device for deciding a handover of a communication link between a mobile device and a current network to one of a number of available networks, including determining network parameters for each if the available networks and determining a set of candidate networks basically suitable for handling the communication with the mobile device. From the set of candidate networks a target network is selected, based on a comparison of link parameters describing a communication link between the mobile device and each candidate network. A handover is then performed to the selected target network. The invention enables a seamless inter-network handover and avoids significant degradation of service or service termination.

Description

SELECTION OF A TARGET NETWORK FOR A SEAMLESS HANDOVER FROM A PLURALITY OF WIRELESS NETWORKS

Field of the Invention

The invention relates to a method and device for deciding a handover of a communication link between a mobile device and a current network to one of a plurality of available networks .

Technological Background

Wireless communication networks are becoming increasingly popular and co-exist with or even replace traditional fixed wireline communication networks. Wireless communication networks enable users to wirelessly transmit information to another user or device, such as during a telephone conversation between telephone terminals or a data communication between computing devices. A mobile telephone is one type of wireless communication device, widely used in voice and/or data communications. Similarly, a mobile computer is a type of wireless communication device, able to connect to wireless communication networks for data transmission and/or for assisting in voice communications with other communication or computing devices.

A number of different communication standards and technologies for wireless communication networks exist, offering different types of services, and networks operating according to the same or different standards may be co- located in the same geographical area or may partially overlap one another. Individual networks may also operate according to different communication standards, depending on an access technology desired by the mobile device. Likewise, mobile devices may have the capability to operate according to different standards, depending on the access technology offered by a wireless network. A wireless communication network may have a cellular network structure, examples being mobile communication networks such as GSM (Global System for Mobile Communications) , UMTS (Universal Mobile Telecommunications System) , 3G (Third Generation) or beyond 3G network, etc. A cellular network is generally sub-divided into individual cells in order to more efficiently use the available frequency spectrum for wireless transmissions between mobile devices. Two cells of the network cover given geographical areas, which may be adjacent to one another or at least partially, overlap one another.

When a mobile device engaged in a voice or data communication moves from one cell of the communication network to another cell of the communication network, a handover between these cells is performed, to hand over an ongoing communication from one cell to the other. As the individual cells of the communication network cover a larger geographical region, the mobile device can freely move within the coverage area of the network, without experiencing an interruption of an ongoing voice or data communication.

For example, if a user of a mobile device is engaged in a voice or data communication with another party, his mobile device may be connected through a first one of the cells of a serving communication network, so that communications are handled by this first cell. The other party involved in the communication may be directly connected to the network, or may be a subscriber of another network, e.g., another mobile communications network or a traditional fixed wireline communication network. When the mobile device subsequently moves into the coverage area of a second cell of the serving network, communications are handed over to the second cell of the network. After the handover, communications between the mobile device and the other party will be routed through the second cell of the network.

According to another example, the mobile device may use a service provided by a service provider, such as an email service provided by an email service provider. Again, similar to the previous example, any communication data exchanged between the service provider and the mobile device are routed from the mobile device to a cell of the serving network and then to the service provider or vice versa. Further, if the mobile device now moves into the coverage area of another cell of the serving mobile communication network, all communications pertaining to the service from the service provider are handed over to the other cell .

Usually, in neither case the user of the mobile device will notice the handover, i.e., voice communications will be maintained uninterrupted and the used email service will be continued without interruption.

If, however, the mobile device moves beyond a coverage area of the serving network or current network, communications can no longer be handled in this network, and a handover to a second network or new network becomes necessary. For example, in order to move communications from a current network to a new network, a mobile device could terminate a communication path between the mobile device and the current network, and thereafter connect to the new network, in order to reestablish the communication path through the new network.

However, as noted above, there may be a number of different wireless communication networks available for the handover. For example, in the same geographical area there may be networks of different operators, networks in accordance with different communication standards and providing for different access technologies. Therefore, before the handover to the new network can take place, an appropriate one of the networks must be selected.

While it is conceivable to for example base a handover decision on a comparison of a signal strength of signals from the individual networks, this may not lead to appropriate results for different networks operating in accordance with different network and access technologies and may even cause a termination of services.

Summary of the Invention

It is therefore desirable to provide for an improved handover decision for selecting a network for a handover of a communication link between a mobile device and a current network.

This object of the invention is solved by a method for deciding a handover of a communication link between a mobile device and a current network to an available network, the communication link providing a communication service to the mobile device, including obtaining network parameters describing at least one available network, selecting candidate networks illegible for a handover from the available networks ^'based on the network parameters, obtaining link parameters for each candidate network, the link parameters describing a communication link between the mobile device and each candidate network after the handover, selecting a target network from the candidate networks based on a comparison of the link parameters of each candidate network, and performing a handover of the communication link from the current network to the target network. Accordingly, the invention allows for selecting an appropriate one of available networks for a handover, by considering parameters describing the available networks, and link parameters describing the communication link between the mobile device and the available networks after the handover. By selecting networks illegible for a handover, e.g. with the required capabilities to handle the handover and the communication service after the handover, a termination of services, e.g. due to incompatibilities of the network and the mobile device, can be avoided. Moreover, by selecting a target network from the candidates based on link parameters, a most appropriate one of the candidates can be selected for the handover . A link parameter for a signal quality may be measured for each candidate network, based on at least one of a signal strength, packet arrow rate and bit arrow rate . Accordingly, the selection of a target network can consider the signal quality expected after the handover .

Further, a link parameter for a service quality may be estimated for each candidate network based on the signal quality . As a service quality directly describes the characteristics of a service , as perceived by a user, the selection can be further improved .

Moreover, a link parameter specifying an available time until the handover can be determined and the selection of candidate networks and the target network can be based on the available time .

Also, a link parameter may be determined describing the network latency, corresponding to an amount of context information transferable before the handover . Accordingly, the selection passes may also consider a preparatory phase before the handover, for transferring context parameters and similar .

Still further, for each candidate network a link parameter may be determined, based on a duration of service provision by the candidate networks, depending on a device location, the device speed and the device direction of motion, and a coverage area of the candidate network. This may make it advisable to refrain from a handover to a network, if the duration of service is for example below a certain threshold.

The selection operation may be based on device travel path information . This may include obtaining information on a path of travel of the mobile device , selecting candidate networks along the path of travel , and selecting a sequence of target networks for a sequence of handovers based on the path of travel . Accordingly, networks for handovers may be scheduled beforehand, allowing to increase for example the time for preparatory phases of the handovers .

The network parameters of a network may include at least one of a coverage area, network resources, a network deployment, and a stakeholder.

Further, service parameters describing the communication service may be obtained, and the selection step for selecting candidate networks may be further based on the service parameters. The service parameters may include at least one of a service type, a minimum data rate, a cost of service, a service level agreement, subscription information and quality of service parameters.

Still further, device parameters describing the mobile device may be obtained, and the selection step for selecting candidate networks may be further based on the device parameters. The device parameters may include at least one of access technology capabilities, display characteristics and processing capabilities.

According to a further embodiment, the link parameters of the target network may be compared with the link parameters of the current network, and the handover of the communication link from the current network to the target network may be performed only if the comparison indicates an improvement of at least one of the communication link and the communication service. Accordingly, if the determination reveals that the service provision provided by the current network is superior to the service provision after the handover to the target network, a handover may be cancelled. These operations may be particularly applicable in cases of co-located networks, i.e., if the current network and the target network are co- located in the same geographical area. The necessity to decide a handover may be triggered based on at least one of a signal quality, a service quality, a path of travel of the mobile device and a lapse of a predetermined time interval. Still further, a signal quality of the communication link between the mobile device and the current network may be determined, and the handover to the target network may be performed at an earlier point in time, if the signal quality is low.

According to another embodiment, a program may embody instructions adapted to carry out any of the above operations. Moreover, a computer-readable medium may be provided, in which a program is embodied, where the program is to make a data processing device or group of data processing devices execute any of the above operations. A computer program product may comprise the computer-readable medium.

The object of the invention is further solved by control means for deciding a handover of a communication link between a mobile device and a current network to an available network, the communication link providing a communication services to the mobile device, including a network parameter handler for obtaining network parameters describing at least available network, a network selector for selecting candidate networks illegible for a handover from the available networks based on the network parameters, a link parameter handler for obtaining link parameters for each candidate network, the link parameter describing the communication link between the mobile device and each candidate network after the handover, wherein the network selector is adapted to select a target network from the candidate networks based on a comparison of the link parameters of each candidate network, and a handover handler for performing a handover of the communication link from the current network to the target network.

Further advantageous embodiments of the invention are disclosed in further dependent claims. Brief Description of the Drawings

Fig . 1 illustrates elements of a communication environment for a handover decision of a communication link between a mobile device and a current network to another network according to a first embodiment of the invention;

Fig . 2 illustrates operations of a method for deciding a handover of a communication link to another network according to an embodiment of the invention;

Fig . 3 illustrates operations of a method for deciding a handover of a communication link from a current network to another network according to an embodiment of the invention, particularly illustrating operations to select a target network;

Fig . 4 illustrates a communication environment for deciding a handover of a communication link from a current network to another network according to an embodiment of the invention, particularly illustrating consideration of an estimated duration of services ;

Fig . 5 illustrates operations for deciding a handover of a communication link from a current network to another network according to an embodiment of the invention, particularly illustrating consideration of a path of travel of a mobile device ;

Fig . 6 illustrates elements of a communication environment for deciding a sequence of handovers of a communication link between networks according to another embodiment of the invention; Fig. 7 illustrates operations of a method for deciding a handover of a communication link from a current network to another network according to an embodiment of the invention, particularly illustrating operations to select candidate networks;

Fig. 8 illustrates operations of a method for deciding a handover of a communication link from a current network to another network according to an embodiment of the invention, particularly illustrating operations for deciding the necessity of performing a handover; and

Fig. 9 illustrates elements of a communication environment for a handover decision of a communication link between a mobile device and a current network to another network according to an embodiment of the invention, particularly illustrating a service provider and a preparatory phase of the handover.

Detailed Description of the Preferred Embodiments

In the following a first embodiment of the invention will be described with regard to Fig. 1.

Fig. 1 illustrates elements of a communication environment for deciding a handover of a communication link between a mobile device and a current network to a target network.

Generally, a user of a mobile device may be engaged in a voice or data communication with another party, while his mobile device is connected through a serving communication network, i.e., a current network. Similarly, a user of the mobile device may use a service provided by a service provider, such as an email service provided by an email service provider, or similar, and any communication exchanged between the service provider and the mobile device are routed through the current network.

When the mobile device moves within the coverage area of the current network, communications can generally be maintained through the current network, e.g., by handing over the communications between different coverage sub-areas or cells of the current network. If, however, the mobile device moves beyond a coverage area of the current network, communications can no longer be handled in the current network, and a handover of communications to a target network becomes necessary.

There may be a number of different wireless communication networks available for the handover. For example, in the same geographical area there may be a number of other networks, networks of different operators, networks in accordance with different communication standards and providing for different access technologies.

Therefore, before the handover to the new network can take place, an appropriate one of the networks from amongst the number of available networks must be selected.

The current network and a selected target network may be managed by different operators or stakeholders and may use the same or different access technologies. Therefore, as noted above, a handover of communications between different types of networks using different communication standards and operated by different stakeholders may be desired or required. Such inter-network handovers may require a substantial amount of time for performing the necessary negotiations between the different networks, e.g. including agreeing on characteristics of the communication link, the service to be handed over and similar. Moreover, an internetwork handover may be computationally complex and may require the exchange of larger amounts of data between a network currently handling communications and a new network. For example, the new network selected for taking over communications from the current network may be required to negotiate with the current network characteristics of the ongoing communications, such as of a voice communication or service provision, and the networks may have to exchange subscriber and authorization information, and the new network may have to reserve appropriate resources for handling the communications .

Accordingly, a network for taking over communications from the current network must be carefully but quickly selected, in order to avoid incompatibilities and problems during the handover, including a termination of service during the handover, due to unrecoverable problems occurring during the handover, and to allow enough time to prepare the handover. Moreover, the complexity of inter-network handovers and associated occupation of network processing and transmission capacities makes it desirable to reduce a number of handovers to be performed.

The communication environment of the embodiment of the invention shown in Fig. 1 enables an appropriate selection of a target network from amongst a number of available networks, for enabling the above described handover between two networks. More precisely, the communication environment shown in Fig. 1 enables an appropriate selection of a target network from a number of available networks. In a first step a number of candidate networks is selected from the available networks based on network parameters describing the available networks. In a second selection step a target network is then selected from the candidate networks based on link parameters describing a communication link between the mobile device and the candidate networks .

A most appropriate one of the available networks can thus be quickly selected with a reduced number of operations and communication overload, and a seamless handover of a communication service from the current network to the new network can be carried out . Seamless handover stands for a handover, which does not involve a significant degradation of the communication link and communication service provided. Ideally, the user of the mobile device will not even notice the seamless handover.

A preparatory phase of the handover, performed after selecting the target network and the actual handover, enables the target network to prepare and swiftly take over communications during the actual handover, and thus enables the target network to readily continue the ongoing communications, e.g. a communication with another mobile device or a service provided by a service provider.

By considering the network parameters, a general selection of candidate networks from amongst the available networks can be conducted, selecting only those ones of the available networks, which fulfil certain basic requirements, i.e., are compatible with the mobile device and/or the communication service and are generally available for a handover. Any network which is for example incompatible with the mobile device and its communication link to the current network and/or the provided service, or is not available for other reasons, e.g. lacking communication resources or forbidding a handover, will be cancelled from the set of networks considered for the handover.

By considering only networks with sufficient resources as candidate networks, a load balancing between networks becomes possible.

Moreover, the selection process involves selecting a target network from the compatible networks, i.e., from the network candidates based on the link parameters describing the potential future communication link between the mobile device and each one of the candidate networks. The link parameters are compared and the network with the best set of link parameters is selected as target network. Referring now in detail to Fig. 1, the communication environment includes a current network 110, a mobile device 120, and a target network 130. The current network 110 includes control means 100, for handling the selection process and the handover of communications to the target network. Further, Fig. 1 illustrates two exemplary further networks 131 and 132. In the selection process illustrated in Fig. 1, it is, however, assumed that the network 130 is selected as target network.

The control means 100 preferably comprise a network parameter handler for obtaining network parameters describing the plurality of available networks, and a link parameter handler 102 for obtaining link parameters for each of a plurality of candidate networks, the link parameters describing a communication link between the mobile device and each of the candidate networks after the handover. Further, the control means 100 preferably comprise a network selector 103 for performing the selection operations of candidate networks and a target network. More precisely, the network selector 103 is provided for selecting candidate networks eligible for a handover from the plurality of available networks, in the present case the target network 130 and exemplary further networks 131 and 132. Further, the network selector 103 is provided for selecting, from the candidate networks, a target network based on a comparison of the link parameters of each candidate network with one another.

Still further, the control means 100 preferably comprise a handover handler 104 for performing the handover of the communication link to the target network 130. The handover handler thus will be responsible for switching over the communication link 160, illustrated between the mobile device 120 and the current network 110 to the communication link 161 between the mobile device and the target network 130, e.g. as known in the art. The handover is generally indicated at 151. It is noted that the control means 100, while in Fig. 1 generally indicated as comprised by the current network 100, may in alternate embodiments at least partially be located at other locations, such as at the mobile device 120, illustrated by the dotted box 100. Further, the control means 100 may be at least partially located at another network.

In the following an exemplary operation of the communication environment in Fig. 1 will be outlined, for handing over a communication link between the mobile device and the current network to the target network.

As an initial situation it is assumed that the mobile device has an active communication link 160 to the current network 110. The communication link 160 may be used to provide a communication service from another party, e.g. another mobile device or a service provider, to the mobile device 120. For example, the service could be a voice service, any kind of data service, such as an email service, and similar.

Further, it is assumed in the initial situation that the communication link 160 between the mobile device and the current network 110 is to be handed over to a new network, e.g. due to a movement of the mobile device out of the coverage area of the current network, due to. overload conditions experienced in the current network or similar. Further, the necessity or desire to perform a handover of communications from the current network to a new network may be reached based on other considerations, such as costs, network bandwidth, service characteristics and similar.

Based on this initial situation the control means 100 will proceed to determine all networks in the vicinity of the current network 110 which are generally available for handling wireless communication operations. Information on adjacent, overlapping or co-located wireless communication networks may be stored at the current network based on network deployment data received from other network operators. This information may be permanently stored at the current network. Further, e.g., if wireless communication networks of dynamically changing size are in the vicinity of the current network, the detection of available networks may also include a step of scanning a communication environment, e.g. by detecting and analysing beacon signals from wireless communication networks, in order to determine presence and/or other information regarding wireless communication networks with dynamically changing size and/or behaviour.

In the present case it is assumed that three networks are detected as available networks in the vicinity of the current network 110. These three networks, the network 130, the network 131 and the network 132 are illustrated as examples only, it is noted that a larger number of available networks may be detected, or a smaller number of available networks, including a single available network.

After the determination of the available networks, the network parameter handler 101 obtains network parameters from each one of the available networks, i.e., from the networks 130, 131 and 132. While the network parameter handler 131 may obtain the network parameters based on an interrogation of the networks 130-132, the network parameters may at least partially be stored beforehand at the current network, e.g. based on information obtained from other network operators upon network deployment. This information could be updated from time to time based on notifications from network operators operating the networks 130-132. However, if one of the networks 130-132 is a network with dynamically variable characteristics, such as shape, the network parameter handler 101 may, upon detecting the necessity or desire to perform a handover, interrogate this network using a network parameter request message. The network parameter request message may include a specification of the nature of the network parameters desired, or may generally indicate the desire to obtain network parameters . The network parameters collected by the network parameter handler 101 generally include any information describing the available networks, such as a type of network, a communication standard used, characteristics of the network, a network operator or stakeholder, the availability of communication resources, the type of available communication resources, access technologies supported, a coverage area of the networks, characteristics of the network deployment and similar. The network parameters may be stored in a storage unit at the current network 110, or at any other location in the communication environment. After collecting the network parameters, the network selector 103 performs a selection operation 154 to select candidate networks from the available networks, i.e., all networks that are generally compatible and able to take over the communications with the mobile device 120 during the handover.

In the present example it is assumed that the networks 130 and 131 are selected as candidate networks in operation 154, as indicated by reference numeral 170.

The network parameters generally describe all information required for determining whether an available network is sufficiently compatible with the mobile device and/or the current network and in the position to take over communications or a communication link between the mobile device 120 and the current network 110. Accordingly, the selection operation performed by the network selector 103 in operation 154 will identify all networks which are generally suitable and available for taking over communications, the selection operations including for example the comparison of the requirements of the communication link 160 and/or the communication service provided, characteristics of the mobile device and similar.

The selection operation may involve a comparison of basic requirements for a handover of the communications between the current network and the mobile device with the corresponding network parameters of the available networks . Any network failing to fulfil at least one of the basic requirements will be excluded from the list of candidate networks, as attempting a handover to these networks would result in a termination of services.

After selecting candidate networks, the link parameter handler 102 becomes active to obtain link parameters for each of the candidate networks, wherein the link parameters describe a potential new communication link between the mobile device and each of the candidate networks after the handover. The link parameters generally describe the characteristics of the future communication link after a handover, and thus can be used to select, from the number of candidate networks, a target network for the handover, in the present case the target network 130. It is noted that this future communication link will generally not yet be physically established.

The link parameters may depend on factors such as the location of the mobile device, a velocity of the mobile device, a moving direction of the mobile device, and further positioning or path of travel information pertaining to the mobile device. Further, the link parameters may reflect a signal strength of signals received from each one of the candidate networks, a packet error rate, a bit error rate, a network latency, as it will be outlined further below.

After the link parameter handler has collected all link parameters for each of the candidate networks, the network selector 103 performs a second selection operation 155 for selecting a target network from the candidate networks. The selection will preferably identify that one of the candidate networks, which will be in the position to provide for the best communications during and/or after the handover, i.e., which is able to perform the best seamless handover of the communications . In the present example it is assumed that the second selection step 155 identifies the network 130 as target network, as illustrated at 171.

After selecting the target network 130, the handover handler 104 performs the actual handover, by switching the communications from the communication link 160 to the communication link 161. It is noted, that the actual handover can be triggered also by the mobile device 120, in which case the mobile device 120 will issue a handover command to the handover handler and proceed to establish the communication link 161 to the target network 130.

The invention enables a superior selection of a target network for handing over communications between the mobile device and the current network. A reduction of communication and processing operations for selecting a target network can be significantly reduced, as in a first operation a number of candidate networks are selected, being compatible for a handover, and by only then performing the more complex measurements in association with obtaining the link parameters on the number of identified candidate networks. Accordingly, link parameters need only be obtained for the smaller number of candidate networks, leading to a reduced overhead for selecting the target network. Further, as the selection considers the characteristics of the networks, a fundamental problem during the handover can be avoided, and a seamless handover without significant service degradation or termination can be provided.

In the following the communication environment shown in Fig. 1 will be outlined in further detail. It is noted that the following constitutes examples only and should not be construed as limiting the invention.

The mobile device 120 shown in Fig. 1 is shown as a mobile telephone, but may instead also be any other kind of mobile communication device. For example, the mobile device may be a mobile computing device and similar, including laptop computers, PDAs (Personal Digital Assistance), etc. The mobile device 100 is involved in a one- or bi-directional communication with the service provider 140 or any other element of a communication system, including another mobile or fixed wireline communication device.

The mobile device may operate in accordance with any standard, such as GSM, UMTS, D-AMPS and, may operate according to a wireless LAN standard or standard for wireless communication networks with distributed medium access control, including IEEE 802.11, "Wireless LAN and medium access control (MAC) and physical layer PHY) specification", 1999, 3G (Third Generation) or beyond 3G networks, etc. A heterogeneous or ad-hoc network is a wireless network formed without a central administration or without a centralized management of communication resources, such as assignment of communication channels to communicating parties, etc.

The mobile device may be capable of implementing a plurality of standards or access technologies and thus be able to connect to wireless communication networks operating in accordance with different standards.

The mobile device may further be able to operate more than one RF connection to support the different standards. Further, this enables the mobile to maintain an active communication with the current network, while at the same time monitoring signals from other communication networks. Here, RF connection stands for the capability of the mobile device to receive and analyze information transmitted on a particular frequency, time slot, with a particular code, and similar, depending on the access technology used by a network. For example, the mobile device may also be able to maintain at least one RF connection according to each access technology the mobile device supports, such as GSM, UMTS, D- AMPS, wireless LAN standards, 3G (Third Generation) or beyond 3G networks, and similar. Communications carried out by or using the mobile device 100 may involve voice communications and/or data communications, e.g., in a regular telephone call or in a data communication between the service provider and the mobile device. Combined approaches are also conceivable.

The mobile device may obtain any kind of communication service from the service provider 140, such as a data service pertaining to news provision, email services, local event information, traffic information, booking services, banking transaction services, and similar. Also, the communication service may include access to a communication network of a company, including company-wide communication networks provided with a firewall for restricting access from the outside .

The mobile device 120 preferably includes a processor and a memory for storing coded instructions for implementing the communications functionalities of the mobile device, possibly including functionality of the control means 100 for selecting the target network 130, instructing the current network to perform a handover, to provide information on the target network to the mobile device, and similar.

The mobile device may also include means to determine the necessity of an inter-network handover from the current network to a new network and may base the handover decision on information received from the current network and/or the target network. For example, the current network may suggest a handover, if a communication load at the current network is excessive, or if resource requirements for the communication service have changed and cannot any longer be satisfied by the current network. Moreover, it is conceivable that the mobile device decides to perform the inter-network handover if communication requirements change and/or if the current network is unable to allocate sufficient or appropriate resources for the communication. For example, a transmission bandwidth requirement during a communication may change, if larger amounts of data need to be transmitted in the service application, or if communication requirements need to fulfill certain standards, such as a real-time requirement.

The current network 110 may constitute any kind of wireless communication network operating to any communication standard or combinations thereof, such as GSM, UMTS, D-AMPS, wireless LAN standards, 3G (Third Generation) or beyond 3G networks, etc. Still further, the current network may form at least part of a heterogeneous communication network, such as an ad- hoc communication network. It is possible that the current network integrates at least parts of the control means 100, and may include at least one processing unit and at least one memory for storing coded instructions making the processor, when loaded, to execute the above-outlined functionality of the control means and/or other functionality of the current network.

Any kind of wireless communication network may constitute the target network 130, similar to the current network. The current network and the target network may be operated by different stakeholders, i.e., different operating entities, however, it is also possible that the current network and the target network constitute different networks operated by the same stakeholder, or may even constitute different separate portions of a single communication network.

While it is possible that the current network and the target network operate according to the same communication standard, it is well possible that the current network and the target network operate according to different communication schemes. For example, the current network may operate according to the GSM standard, while the target network constitutes a heterogeneous communication network operating according to the IEEE 802.11 standard. Along the same line, the further networks 131 and 132 shown in Fig. 1 may constitute any kind of communication network operating according to any communication standard, being the same or different from the current network and/or target network. While in the present case it is assumed that the target network 130 is selected for the handover, in other examples it may well be possible that another of the communication networks, i.e., network 131 or network 132, is selected for a handover.

The embodiment of Fig. 1 illustrates operations to suitably select an appropriate new network as target network for handing over communications, allowing to seamlessly transfer communication services without degradation or termination of a communication service obtained by the mobile device 120.

In the following a further embodiment of the invention will be described with regard to Fig. 2.

Fig. 2 illustrates operations of a method for deciding a handover of a communication link between a mobile device and a current network to a target network, the communication link for example carrying a communication service from a service provider. The operations of Fig. 2 may be carried out using the communication environment as shown in Fig. 1, however, Fig. 2 is not limited thereto.

In Fig. 2 it is assumed that a decision to perform a handover of communications was reached, e.g. due to detection of a reduced signal and/or service quality of communications between the mobile device and the current network, as noted above. However, it is also conceivable to perform the operations of Fig. 2 in intervals, e.g. after lapse of a certain time limit, in order to identify another network, which would be better suited for handling the communications with the mobile device 120 as compared to the current network. This may include improved service characteristics, such as increased bandwidth, reduced time delays, reduced costs and similar.

Consequently, in a first operation 201, network parameters are obtained for a plurality of available networks. The available networks, as outlined before, may for example be detected by scanning beacon signals from networks in the vicinity of the current network, or may be obtained from network registries, indicating network identities, coverage areas and similar. The step of obtaining network parameters may be based on interrogating the available networks, and/or by reviewing network registries indicating network capabilities, such as supported access technologies, communication standards, the identity of a stakeholder or operator of the network and similar.

Further, the network parameters may indicate a network deployment characteristic, e.g. indicating an arrangement of cells of the network, a capacity of the cells, supported communication bandwidth, supported data types for communication services, and similar. Still further, the network parameters may indicate available network resources of each of the available networks, such as resources available for supporting voice services, data services, and similar.

Also, the network parameters may specify a coverage area of the network, and resources available in certain regions of the coverage area, e.g. individual cells of the network.

After obtaining network parameters for the available networks, in an operation 202, candidate networks are selected based on the network parameters. The selection operation preferably rules out any networks which are not or not sufficiently compatible or able to take over communications between the mobile device and the current network during and/or after the handover. For example, only networks will be selected as candidate networks which provide for required access technologies, support the required handover mechanisms for taking over communications with the mobile device, are operated by a steak holder generally accepting or allowing handovers from the current network, provide required resources for performing the handover and for carrying on the communications after the handover and which support the communication service. Further, only those networks will be selected as candidate networks, which are appropriately located, i.e., provide for a suitable coverage area.

Operation 202 thus leads to a set of candidate networks, which are generally suitable and/or available for handling the communications with the mobile device 120.

In the following, in an operation 203, link parameters are obtained for the set of candidate networks selected in operation 202. As the link parameters are only obtained for the candidate networks, as opposed to the entire set of available networks, a required communication and processing overhead for selecting a target network can be reduced.

The link parameters are obtained for each individual candidate network and describe a communication link between the mobile device and the candidate network after the handover. The link parameters thus indicate the characteristics and/or performance of the communication links between the mobile device and the candidate networks during and/or after the handover. The link parameters may describe features of the mobile device, such as location, speed and direction of movement, and describe a signal quality and/or service quality of the communication links, travel path information of the mobile device, including for example GPS location information and similar.

Operation 203 may include obtaining a link parameter describing a signal quality for each candidate network, e.g. based on at least one of a signal strength of signals exchanged with the respective candidate network, a packet error rate and a bit error rate .

Further, operation 203 may include obtaining a link parameter describing a service quality for each candidate network, e.g. based on the determined signal quality. This operation may be based on an estimation of the service quality by assuming a certain service quality based on an available signal quality. The service quality for each candidate network may depend on a communication service provider. For example, a voice service may be relatively insensitive to transmission errors, while a data service may have a low error tolerance, and may require a low bit or packet error rate .

Further, operation 203 may include determining a link parameter specifying an available time until the handover, and the selection operation 204 may be based on the available time before the handover. For example, candidate networks could be favoured which allow a larger time before the handover has to take place, and thus allow a better preparation of the handover. The amount of time available between the handover decision and the actual handover may depend on a coverage area of the candidate networks, a device location, device speed and direction of movement of the mobile device.

Further, operation 203 may include detecting a link parameter representing a network latency of each of the candidate networks, the network latency corresponding to an amount of context information transferable before the handover takes place. Usually, in the preparatory phase of a handover context information describing the communication link, the communication service and further features in association with the handover, including security and authorization information, will be exchanged between the current network and the target network before the handover. The network latency, describing the delay that will occur in transferring the context parameters from the current network to the target network, is therefore an important factor. The network latency can be reduced, if extensive operations need to be performed before the context parameters can be transferred to the target network, for example, if the current network and the target network are operated by different steak holders, prior to the handover a trust relationship may have to be established prior to the context parameter transfer. Therefore, networks that already have a trust relationship with the current network will involve lower network latency, and allow a larger amount of context parameters to be transferred to the target network. Accordingly, networks with low network latency will be preferred as target network.

Further, operation 203 may include determining a link parameter for a duration of service provision by each of the candidate networks based on the device location, the device speed and the device direction of motion, and a coverage area of the candidate network. If a constant movement of the mobile device is assumed, a duration of service can be calculated for each of the candidate networks, reflecting the time difference between entering the candidate network, i.e. the handover, and the point in time of leaving the candidate network, i.e. the point in time where the handover to another network will have to take place. As inter-network handovers are complex and require substantial computations and data exchange, candidate networks providing a long duration of service will be preferred.

Still further, the selection operation of a target network may be based on device travel path information. For example, if a mobile device is identified as travelling in a train, scheduled path information of the train can be used to determine candidate networks and/or a target network. According to another example, travel path information could be obtained from travel path information from a navigation system, e.g. of a vehicle accommodating the mobile device. A scheduled path of the mobile device could then be detected based on destination information entered into the navigation equipment. The travel path information can then be used to select a candidate network and/or a target network. Further, the travel path information could be updated each time the destination information is changed, or if the vehicle deviates from the scheduled travel path based on the destination information, in which case alternate travel path information could be calculated from the deviation on.

According to another example, the information on the path of travel of the mobile device can be used to select a set of candidate networks along each portion of the path of travel. Further, based on the path of travel of the mobile device, a target network could be selected for each portion of the path of travel, and a sequence of target networks can be selected for a sequence of subsequent handovers along the path of travel .

The link parameters collected for each candidate network are then reviewed for each of the candidate networks, e.g. in a link parameter table, and a target network from the candidate networks is selected based on a comparison of the link parameters of the individual networks in an operation 204.

According to an example, the selection operation may involve selecting a "winning network" for each of a plurality of link parameters. The "winning network" determinations could then be added for each of the candidate networks, and the candidate network with the highest score could be selected as target network.

If a plurality of candidate networks reach the same score, a sub-selection operation on the sub-selection set of candidate networks with the same score can be performed. In this step, for each link parameter, the "winning network" can again be determined for each of the candidate networks having reached the same score. Then, again, the candidate network with the highest score in the sub-selection set can be selected as target network. If in the sub selection operation again a plurality of networks reaches the same score, the above sub- selection operation could be repeated by again selecting the winning network from this set of networks.

According to another example, it is also conceivable to associate each link parameter for each of the candidate networks with a certain value between two limits, e.g. between 0 and 100, the value reflecting a level of agreement between the link parameter and a requirement for the handover. For example, high signal strength could be associated with a high number, and low signal strength could be associated with a low number. Similarly a high available bandwidth for a communication link may be associated with a high number, and a low bandwidth for the communication link may be associated with a low number.

Again, the values for the individual link parameters for each of the candidate networks could be entered into a table, and then the entries for each candidate network can be summed up . The candidate network with the highest score is then selected as target network.

It is noted that the above strategies for a selection operation of a target network constitute examples only and should not be construed as limiting the invention. Any other selection technique for determining a target network based on a comparison of the link parameters may be applied in the selection operation 204.

Thereafter, in an operation 205 the handover is performed to the target network.

It is noted that the operations of Fig. 2 may be carried out using the control means 100 shown in Fig. 1.

In the following a further embodiment of the invention will be regarded with regard to Fig. 3. Fig. 3 illustrates operations or deciding a handover of a communication link between a mobile device and a current network to a target network, further illustrating operations prior to the actual handover.

The operations shown in Fig. 3 may be carried out using the communication environment shown in Fig. 1, however, Fig. 3 is not limited thereto.

In a first operation 301 available networks are determined, e.g. as outlined with regard to previous embodiments. The available networks prefer the include all networks available in the vicinity of the current network, such as neighbouring networks, overlapping networks or co-located networks.

Thereafter, in an operation 302 network parameters are obtained for each one of the available networks, as noted before. In an operation 303 candidate networks are selected based on a comparison of the network parameters, in order to exclude any networks which are generally incapable of taking over communications, also as noted before. In an operation 304 link parameters are obtained for each one of the candidate networks, and in an operation 305 a target network is selected from the candidate networks based on a comparison of the link parameters, as determined with regard to previous embodiments .

Thereafter, in an operation 306 it is determined whether a trust relationship exists between the current network and the target network. This operation may also include determining a trust relationship between the target network and a service provider, the service provider providing a communication service for the mobile device as noted above.

If mutual trust relationships between the current network, the target network and/or the service provider are not already available, they may be generated on the fly, in the preparatory phase of the handover. Accordingly, the preparatory phase of the handover may include operating trust relationships between the current network, the target network and the service provider, avoiding time consuming trust negotiations during the actual handover. A trust relationship between two entities such as the current network, the target network and the service provider may include mutually verifying the identities for authentication purposes, exchanging security parameters for secure data transfer, and determining the authorization of each entity to access the respective other entity.

Further preparing the actual handover, trust relationships may be established between the current network, the target network and the service provider. A trust relationship between two entities may include mutually verifying the identities for authentication purposes, exchanging security parameters for security data transfer, and determining the authorization of each entity to access the respective other entity.

According to an example, the point-to-point (PTP) extensible authentication protocol (EAP) may be used to authenticate two entities for creation of trust. EAP defines an authentication protocol for communication between peers over point-to-point links. Basically, one of the entities requests a proof of identity from the other entity, which proof may be, for instance, a simply one-time-password or some challenge- response type authentication, or a complex protocol like EAP TLS (Transport Layer Security) protocol, which performs negotiation as well as distribution of session keys. A request for authentication is sent from one of the two entities to the other and receives in return a response, which is validated by an authenticator . Still further, other authentication schemes for creating trust between two entities can be used, such as the RADIUS protocol, constituting an indirect authentication scheme, where authentication is run against a central server storing respective identity data for every known communicating entity. Still further, public/key cryptography can be used to build systems with mutual trust, such as the RSA algorithm, which can be used for encryption and. decryption. Public/key cryptography uses a pair of keys, the public and private key. Either key can be used for encryption and respective decryption. Initially, key pairs are generated, the private key is stored with the respective entity, and the public key is made known to third parties, including the respective other entity. Using the private and public keys, a secure communication between the two entities becomes possible.

The trust relationships between the current network, the target network and the service provider may be created on- the-fly, i.e., during the preparatory phase of a handover, or may be created beforehand, e.g., upon network deployment, after reaching frame agreements between stakeholders of the current network, the target network and/or the service provider, or at any other point in time.

In an operation 307 context parameters are then transferred from the current network to the target network, as a second portion of the preparatory phase of the handover. The context parameters describe any aspects of the communication environment and are deuced by the target network to prepare the set up of the communication link and/or communication service between the target network and the communication device, in order to more quickly switch over the communication link between the mobile device and the current network to the target network during the handover, and in order to facilitate the communication service.

In operation 307, ^'the context information may include anything that can be observed with computers in connection with the communication link to be handed over to the target network. The context information supports the target network in the task of establishing the communication link to the mobile device, and may further support the target network in maintaining a service provided by the service provider to a user of the mobile device. Examples of the context information include user-related information such as user profiles, e.g., including a user ID, user authorizations, user preference, user behavior, etc. Further, examples include information pertaining to the communication link to be established between the target network and the mobile device, and include an access technology required for the mobile device, capabilities of the mobile device, and similar. Still further, examples include information pertaining to the service provided by the service provider, and include a service type, a service level agreement, service characteristics such as user settings and preferences for obtaining the service, user subscription information, and similar.

The context parameters can be collected at the current network and then transmitted to the target network. Alternatively, or in addition thereto, the mobile device may collect at least some context parameters and may instruct the current network to transfer the context parameters to the target network.

The transfer of the context from the current network to the target network may be performed directly, e . g . , via a communication link established between the current network and the target network, or may be transmitted over the service provider to the target network, e . g . , via communication links between the current network and the service provider, and between the service provider and the target network. It is furthermore possible that a portion of the context parameters is transmitted directly from the current network to the target network, e . g . , context parameters pertaining to the communication link to be established between the target network and the mobile device , and another portion of the context parameters can be transmitted from the current network to the target network via the service provider, e . g . , context parameters pertaining to the service provided . Based on the context parameters the target network can determine and allocate the required resources, contact the service provider to prepare the set-up of the communication service, prepare the establishing of a communication link to the mobile device based on a specified access technology and/or access characteristics, and similar.

The context parameters thus enable the target network to take all preparatory steps before the handover, so that the actual handover can be carried out in a short amount of time and without an interruption of the service provided to the user of the mobile device .

After the creation of trust and the context transfer, the actual handover is performed in an operation 306. The current network and/or the mobile device may initiate the handover. For example, it is possible that the current network instructs the mobile device to perform the handover and transmits relevant data to the mobile device or, vice versa, it is possible that the mobile device instructs the current network to perform the handover.

The handover may include creating of security parameters at the target network and exchanging of the security parameters with the mobile device. In an example, the security parameters are exchanged between the target network and the mobile device prior to the handover through the current network with an exchange of security parameters before the actual handover, authentication operations after the handover can be of reduced complexity, and further accelerate the handover procedure .

It is also possible that the current network generates security parameters for transmission to the target network and the mobile device, e.g., on the basis of authentication and authorization data generated and stored in association with the communication link between the current network and the mobile device prior to the handover.

The embodiment enables a fast handover of communications from the current network to the target network without experiencing a significant degradation of services during the handover. Further, the handover becomes possible between different networks, e.g., operated by different stakeholders, allowing to re-use existing networks and exchanging communication traffic between different networks. Further, by providing a standardized solution for performing the handover, existing communication protocol can be used to exchange the required messages between the current network, the mobile device, the service provider and the target network. Still further, as to the handover a mutual trust relationship is established, security levels can be maintained, i.e., communications will not be handed over into an untrusted environment. For example, messages required for determining and/or creating mutual trust relationships and messages required for transferring context information to the target network can be added on existing messages and/or data messages, thus requiring only minimal adaptations to wireless systems operating under communication standards, such as GSM, UMTS, D-AMPS, the IEEE 802.11 standard, and others.

Fig. 3 illustrates operations of an inter network handover, including selecting an appropriate target network for the handover, performing a preparatory phase of the handover, and finally switching over the communication link. The embodiment shown in Fig. 3 enables a seamless handover of communications from the current network to the target network, minimizing a degradation of services during and after the handover, and avoiding determining of services during the handover. It is noted that the operations of Fig. 3 may be carried out using the control means 100 shown in Fig. 1.

In the following a further embodiment of the invention will be described with regard to Fig. 4. Fig. 4 illustrates elements of a communication environment for deciding a handover between a mobile device and a current network to a target network, particularly illustrating consideration of a duration of service.

As noted above, the network handovers are complex and may thus require a substantial amount of time, communication resources and processing resources. Accordingly, it is desirable to only perform the smallest number of necessary handovers, in order to improve uninterrupted service provision.

Fig. 4 illustrates a current network 110 in a communication link to a mobile device 120. Further, Fig. 4 illustrates a first candidate network 401 for taking over communications with the mobile device and illustrates a second candidate network 402 also suitable for taking over communications with the mobile device 120. The network 110 is shown partially overlapping with the first candidate network 401 and further partially overlapping with the second candidate network 402.

Moreover, Fig. 4 illustrates an estimated path or trajectory 410 of the mobile device 120, i.e. a travel path estimated for the mobile device. The travel path may be estimated based on a location measurement of the mobile device, e.g. using a triangulation as known in the art and may further be based on a calculation of a direction of movement and a velocity. A direction of movement and a velocity can be computed from the sequence of triangulation measurement regarding the mobile device, also as known in the art. Assuming constant behaviour of the mobile device, e.g. within a certain time period, the trajectory 410 of the mobile device as shown in Fig. 4 is determined. The trajectory 410, as illustrated in Fig. 4, first runs through the coverage area of the current network

110 then through the coverage area of the first candidate 401 and then the second candidate network 402. More precisely, the estimated movement of the mobile device will first reach a mutual coverage area of the current network 110 and the first candidate network 401, will then reach a mutual coverage area of all three networks, i.e. of the current network, the first and second candidate networks and will then, in this sequence, leave the coverage area of the current network 110, the coverage area of the first candidate network and then the coverage area of the second candidate network.

With the estimated movement over time of the mobile device 120, and knowing the coverage area of the first candidate network 401 and the second candidate network 402, a calculation operation is performed to determine a first potential duration of service T2 by the first candidate network 401 and a second duration of service T2 by the second candidate network 402. It is noted that Fig. 4 only shows an example, and a larger number of candidate networks and different sizes, location and similar may be present.

In the example of Fig. 4, the first duration of service Tl and the second duration of service T2 reveal that the mobile device will only be served by a short amount of time by the first candidate network 401, but will be served by the second candidate network 402 for a much longer period of time.

Thus, even though the mobile device first enters the coverage area of the first candidate network 401, and then enters the coverage area of the second candidate network 402, it will be preferable to maintain communications between the current network and the mobile device, until the mobile device enters the second candidate network 402, as this handover will lead to a longer duration of service in the following network.

According to another example, a handover to another network may only be considered in case the projected duration of service is above a minimum duration of service threshold. It is noted that the operations of Fig. 4 may be carried out using the control means 100 shown in Fig. 1.

Further, it is noted that many alterations and variations of this basic principle are possible, including a more accurate determination of the location of the mobile device over time, considering further parameters such as apology of the networks, and similar.

In the following a further embodiment of the invention will be described with regard to Fig. 5.

Fig. 5 illustrates operations for deciding the handover of a communications from a current network to a target network, particularly illustrating a time-sequence of such handovers between a sequence of target networks. The operations shown in Fig. 5 may be carried out using the communication environment shown in Fig. 1, however Fig. 5 is not limited thereto.

As briefly noted before, a path of travel information of the mobile device can be used to facilitate the selection operations of candidate networks and/or a target network. More precisely, if information on a path of travel of the mobile device is known, handovers between networks in different geographical areas along the path of travel of the mobile device can be considered beforehand, allowing a better preparation of the individual handovers, including trust, transfer of context parameters and similar as noted to previous embodiments.

In a first operation 501, information on a path of travel of the mobile device is obtained. For example, this information may be made available by estimating a path of travel based on location, speed and direction of movement of the mobile device. Further, a path of travel information of the mobile device may be obtained from a user specifying the travel plan, e.g. when travelling by car or train, airplane or any other means. Prior to departure, a user could be prompted by his mobile device to specify and available travel path information, such as used means for travelling, e.g. car, train, plane, major locations along the path, such as cities, highways, roads, train connections and similar, as well as estimated times for reaching these locations if available.

Alternatively, operation 501 could include an automatic determination of a path of travel of the mobile device, e.g. based on a vehicle navigation system planning a path of travel of a vehicle accommodating the mobile device based on destination information and the destination information may be entered by a user travel path information and could then be obtained from the navigation system, calculating a past path for a vehicle. In addition thereto, if the driver of the vehicle, e.g. due to a traffic situation, decides to deviate from the proposed travel path of the vehicle and thus by the mobile device, a travel path of the vehicle will be recalculated by the navigation system, and, this information can be made available for recalculating a path of travel of the mobile device.

Further, a past movement of the mobile device, e.g. available from information collected by the current network, may be used to determine a future path of travel of the mobile device. For example, if a mobile device moves along a highway or other road, knowledge about a past movement of the mobile device will allow a determination that the mobile device will continue travelling along the highway road for the near future. Likewise, a past movement of the mobile device could be used to determine a train boarded by a user of the mobile device, and, using train schedule and track information, a future path of travel of the mobile device can be determined.

The operation 501 will preferably be carried out by the operation 100 shown in Fig. 1 for any other element of the network or other entity of the communication environment. Having acquired travel path information of the mobile device in accordance with operation 501, in an operation 502 candidate networks are selected along the path of travel . The selection operation may include selecting of candidate networks, e.g. as outlined with regard to previous embodiments, for each location along the path of travel.

Knowing the path of travel and thus the networks along the path, it is also possible to beforehand determine link parameters, such as a duration of service, a estimated Signal and/or service quality, as outlined above.

Thereafter, an operation 503, a sequence of target networks for a sequence of handovers based on these parts of travel can be selected. This selection operation preferably includes selecting a target network for each position of the mobile device along the path of travel . The selection of each individual network may be carried out as outlined with regard to previous embodiments, while in each step in the sequence substituting the respective target network as current networks, in order to determine a further target network for a handover.

The operation shown in Fig. 5 allow to further improve the handover decision, while making use of a path of travel information, and allows to provide for a prolonged preparation phase for the actual handovers as future handovers can be determined in advance .

It is noted that the operations of Fig. 5 may be carried out using the control means 100 shown in Fig. 1.

In the following the embodiment of the invention will be described with regard to Fig. 6.

Fig. 6 illustrates elements of a communication environment for deciding a sequence of handovers along a path of travel of a mobile device. Fig. 6 particularly illustrates a current network 110 for currently handling communications with a mobile device 120, e.g., as outlined with regard to previous embodiments .

Further, Fig. 6 illustrates a path of travel 610 of the mobile device, leading through a plurality of networks 601, 602 and 603 along the path of travel. More precisely, the mobile device first travels from the current method 110 into the coverage area of the subsequent network 601. Then the mobile device enters a geographical area and is mutually covered by the network 601 and the network 602, and then enters a geographical area covered by the network 601, 602 and 603. Thereafter, the mobile device enters a geographical area only covered by the network 602 and 603 and then travels through a geographical region only covered by the network 603.

In the above scenario, with the travel path and the networks along the travel path known, based on the network parameters and the link parameters appropriate candidate networks along the path of the travel 610 can be selected, as outlined with regard to previous embodiments.

In Fig. 6 it is presumed that the networks 601, 602 and 603 already constitute a selection of candidate networks along the path of travel. Thus, with the network 601, 602 and 603 given as candidate networks, a target network can now be selected for each location along the path of travel of the mobile device. The selection of the respective target network may be as outlined with regard to previous embodiments.

In the example, as the mobile device first moves into the coverage area of the network 601, the network 601 will be selected as a first target network. However, then, even though the mobile device then enters the coverage area of the network 602 before entering the coverage area of the network 603, the network 602 may not be selected at a target network. Instead, the network 603 may be selected as subsequent target network, due to considering a duration of service, for example as outlined with regard to Fig. 4.

It is noted that the example of Fig. 6 only shows one possible scenario and that many variations of the principles described in Fig. 5 and Fig. 6 are possible. Most importantly, a far larger number of networks may be available along the path of travel of the mobile device, i.e. a larger number of candidate networks will be available.

Based on the selection of the target network 601 and 063 along the path of travel 610 of the mobile device, the individual handovers of the current network to the network 601, and from the network 601 to the network 603 can be suitably be prepared, e.g. by checking and/or creating trust relationships between the current network and the network 601, and between the network 601 and the network 603. Further, the individual handovers can be prepared by suitably transferring context information from the current network to the network 601, facilitating the handover to the network 601, and, context parameters can be transferred from the network 601 to the network 603 to suitably prepare the handover from the network 601 to the network 603.

According to another example, knowing a destination of the mobile device, e.g. in a vehicle equipped with a navigation system, information on coverage areas of networks between the point of departure and the destination can be obtained, e.g. from network deployment registries, and a route for travel could be determined based thereon. For example, a route for travel could be determined for maintaining full coverage during the travel. Further, a route of travel could be determined based on a cost of service during the travel . Still further, a route of travel could be determined based on multiple factors, or any link parameter (s) , e.g. as selected by a user. Further, an expected speed of the mobile device, e.g. on a highway or in an urban area could be used to select appropriate networks along a route of travel. For example, in a city or in a traffic jam a wireless LAN network may be suitable for providing service, while during fast travel another network type such as a 3G (Third Generation) or beyond 3G network may be suitable.

In the following, a further embodiment of the invention will be described with regard to Fig. 7.

Fig. 7 illustrates operations for deciding a handover of a communication link between a mobile device and a current network to a new network, particularly illustrating further operations for selecting a set of candidate networks.

In a first operation 701 network parameters for each one of a plurality of available networks are obtained, e.g. as outlined with regard to previous embodiments. Thereafter, in an operation 702 device parameters are obtained, the device parameters describing the mobile device. For example, the device parameters may include at least one of a description of technology capabilities of a mobile device, display characteristics of the mobile device and processing capabilities of the mobile device. For example, a small display may not give any benefit when moving to a network with higher bandwidth.

Further, for example a mobile device may be capable of establishing communication link according to one access technology or a plurality of different access technologies . For example, a mobile device may be capable of establishing only one connection or may be able to establish a plurality of simultaneous connections, e.g. according to different access technologies. The access technology capabilities of the mobile device may be used in a subsequent selection operation of candidate networks, in order to determine whether an available network is suitable and capable for taking over communications with the mobile device.

Similarly, display characteristics may be determined, e.g. specifying display characteristics of the mobile device and entering the provision of data in certain formats, with certain settings and similar. Still further, the device parameters may specify processing capabilities of the mobile device, specifying the ability to handle a certain amount of data provided by a network.

The above device parameters can further facilitate the selection of the candidate networks, as any networks not able to heat the squired access technology capabilities, display characteristics and processing capabilities can be ruled out from the set of candidate networks. It is noted that the above constitutes examples only, and that further device parameters are conceivable .

In an operation 703 service parameters describing the communication service are obtained. The service parameters may for example specify a service type of the communication service provided to the mobile device, e.g. a voice service, a data service, a real time service and similar characteristics. Further, the service parameters may include determination of a minimum data rate required for providing the service, e.g. in a voice or video application. Further, the service parameters may indicate a cost of service of provision of the service, e.g. for the mobile device, and through each of the available networks. Still further, the service parameters may include a service level agreement, indicating a level of service compatibility between an available network and the provided communication service. Ideally, an available network is able to meet entire set of service requirements, and thus has a full service level agreement. In a less then ideal case, an available network able to meet some service level requirements, e.g. data rate, may not able to meet other service level requirements, such as a maximum delay requirement .

Further, the service parameters may include a service level agreement or subscription information, indicating a subscription of the communication service where features thereof by a user of the mobile device.

Finally, the service parameters may include also quality of service, QoS, parameters.

The operations for obtaining network parameters, device parameters and service parameters are followed by operation 704, for selecting candidate network from the available networks . The device parameters and the service parameters allow a better decision of a basic compatibility of an available network and thus specification of an available network as candidate network.

Thereafter, in an operation 705 link information for each of the selected candidate networks is obtained, as outlined with regard to previous embodiments

Further, an operation 706 a target network is selected from the candidate networks also as outlined with regard to previous embodiments, and, in an operation 707 the handover is performed, as noted before.

The operations of Fig. 7 show an improved selection of candidate networks from a number of available networks, by considering device parameters and service parameters in addition to network parameters.

The device parameters may be obtained by interrogating the mobile device, e.g. based on a request message of the current network, or may be obtained by a look-up operation in the registry indicating the capabilities and device parameters of a mobile device communicating with the current network. Still further, the service parameters may be determined by inquiring a service provider and/or the mobile device, or may be obtained by performing a look-up operation in a service registry, e.g. available at the current network.

It is noted that the operations of Fig. 7 may be carried out using the control means 100 shown in Fig. 1.

In the following a further embodiment of the invention will be described with regard to Fig. 8.

Fig. 8 illustrates operations of a method for deciding a handover of a communication link between a mobile device and a current network to a target network, particularly outlining further operations for selecting candidate networks and for reaching a decision whether to perform the handover or to maintain the present communication link.

In a first operation 801 it is determined whether a handover is required. As noted above, when a mobile device travels within the coverage area of a wireless network, communications can usually be handled within the wireless communication network, e.g. by handing over the communications with the mobile device from one cell of the wireless network to another cell of the wireless network. However, if the mobile device reaches a boundary of a coverage area of the wireless network, in the present case the current network, or reaches a region within the coverage area with heavy shielding, e.g. by mountains or buildings, communications can no longer be handled within the current network and need to be handed over to another wireless communication network.

This so-called inter-network handover of a mobile device engaged in a communication with another party, such as another mobile device or a service provider, may take place between networks with adjacent geographical coverage areas. In this case communications between the mobile device and the current network are handed over to the new network, if the mobile device approaches the boundary of the coverage area of the current network. Moreover, an inter-network handover may also take place between networks covering overlapping or even the same geographical regions, e.g., if a first network experiences an overload condition, or if a communication connection with the current network is bad or interrupted, if a service requirement cannot be met, etc. Also, a handover of communications may be required in cases where a mobile user obtains services from a service provider and when the current network handling the communication is not or not any longer able to provide the requested service characteristics, such as bandwidth, service features and similar.

The decision to perform a handover in this case can e.g. be reached based on a measurement of a signal strength of communication signals received at the mobile device from the current network, or of signals from the mobile device received at the current network, by comparing the signal strength with e.g. a minimum threshold required for maintaining the communication.

In addition to simply measuring a signal strength, the basic decision to perform a handover may also be based on a bit error rate and/or packet error rate of communication signals received at the mobile device or the current network. As in the case of the signal strength a decision to perform a handover could be reached based on a comparison of the bit error rate and/or packet error rate with corresponding thresholds. Combined approaches based on the signal quality, the packet error rate and bit error rate may be realized.

Alternatively, or in addition thereto, a basic decision to perform a handover may also be reached based on a measured or estimated service quality of a communication service provided to the mobile device, such as the mobile device 120 of Fig. 1. The service quality can be considered optimum criteria for deciding the necessity to perform a handover, as the service quality is what matters to a user of the mobile device. The service quality may be e.g. estimated based on a signal quality, bit error rate or packet error rate. For example, a service quality of a particular communication service, e.g. as perceived by user or test operator, could be heuristically determined by simulating various conditions in connection with signal quality, packet error rate and/or bit error rate. Based on the simulation, minimum threshold for signal strength, packet error rate or bit error rate in view of the communication service may be determined and e.g. entered into a look-up table. This process could be repeated for all types of communication services, arriving at a look-up table with threshold values for signal strength, packet error rate and/or bit error rate in view of each particular service.

During operation, a handover decision could then be reached by interrogating the look-up table based on measured parameters signal strength, packet error rate and/or bit error rate .

Still further, a service quality could be determined by a user operating the mobile device, and a user, when perceiving the service quality as too low, could trigger the handover decision, e.g. by pressing a predefined key or sequences of keys, to trigger the handover decision.

Still further, the basic handover decision may be reached by reviewing travel path information, e.g. as it was outlined with regard to Figs. 4 - 6. Knowing the position of the mobile device and/or its future movement, and knowing the coverage areas of networks along the path of travel of the mobile device, the basic handover decision can be triggered.

Still further the basic handover decision could be triggered in certain intervals, e.g. by a timer, e.g. every minute or after lapse of any other time limit. Such a triggering of the basic handover decision enables a mobile device to always use the most appropriate wireless communication network. For example, in the case of multiple overlapping or co-located wireless networks, suitable for providing a communication service to a mobile device, the mobile device would be able to always use the network providing the communication at the lowest cost, at the highest data rate, with desired quality of service requirements, and similar.

If in operation 801 the decision is "Yes", indicating that the basic decision to perform a handover was reached, in an operation 802 available communication networks are detected and network parameters of these networks are obtained, as outlined with regard to previous embodiments.

If in operation 801 the decision is "No", indicating that a handover at the present point in time is not desired, the flow of operations is halted, until the handover decision is reached.

Operation 802 may further include obtaining device parameters and/or service parameters, as detailed with regard to previous embodiments.

In an operation 803 a selection of candidate networks from the set of available networks is then performed, by determining networks which are generally in the position or compatible to take-over the communication link from the mobile device, based on a comparison of the network parameters, the device parameters and/or service parameters, as detailed with regard to previous embodiments.

In an operation 804 it is then determined whether any candidate networks could be identified. If in operation 804 the decision is "No", indicating that candidate network could not be determined at the present point in time, the flow of operation is halted in an operation 805, e.g. for a certain amount of time, and then the flow precedes to operation 801. If in operation 804 the decision is "Yes", indicating that at least one candidate network could be identified, in an operation 806 link parameters for the candidate network or candidate networks are obtained, as detailed with regard to previous embodiments. Then, in an operation 807 a target network is selected based on the obtained link parameters, as detailed with regard to previous embodiments. If only one candidate network was identified, the selection operation 807 for determining a target network simply involves designating the single candidate network as target network.

Thereafter, in an operation 808 link parameters of the current network are obtained. Preferably, the link parameters obtained for the current network correspond to those obtained for the candidate network or candidate networks. For example, the link parameters of the current network can be determined by performed corresponding look-up operations of registries, to determine a signal quality, a service quality, in available time until the handover, an estimated duration of service provision and similar, as detailed with regard to previous embodiments.

Thereafter, in an operation 809 the link parameters of the current network and the target networks are compared, similar to the operations for selecting a target network in operation 807.

Thereafter, in an operation 810 it is determined whether the handover will lead to an improvement of link and/or service quality. This decision, similar to the selection of the target network, will indicate, whether the current network or the target network are most appropriate for handling the communication service. If in operation 810 the decision is "Yes", indicating that the target network will be more appropriate for handling the communications with the mobile device, the handover is performed in an operation 811. Preferably, before actually performing the handover in operation 811, a preparatory phase of the handover is performed, including creating crust relationships between the current network, the target network and a service provider or other mobile device in communication with the mobile device 120.

If in operation 810 the decision is "No", indicating that the current network is more suitable for handling the communications with the mobile device, in an operation 812 the communication link and service is maintained with the current network. Thereafter, the flow proceeds to operation 801, again waiting for a basic handover decision.

According to another embodiment, after reaching the basic decision to perform a handover, e.g., as outlined in operation 801, the actual handover may have to be performed very soon, e.g. if the mobile device travels at a high velocity towards the boundary of the coverage area of the current network, to avoid a termination of the communication service. However, if the actual handover is not determined by a hard requirement, an optimum point in time for the handover can be chosen. For example, after determining a target network for handover, a signal quality of the communication link between the mobile device and the current network may be determined and monitored, and the handover to the target network may be performed at an earlier point in time or immediately, if the signal quality, service quality or any other link parameter is low or falls below a threshold. Likewise, if the signal quality, service quality or any other link parameter is high or remains above the threshold, the execution of the actual handover could be put on hold.

According to another example, in a network overlay situation, an upward vertical handover VHO, e.g. to a foreign network, should be delayed as long as possible, due to service quality considerations, while a downward VHO, e.g. to an own network, should be performed as soon as possible, for the same reasons . It is noted that the operations of Fig. 9 may be carried out using the control means 100 shown in Fig. 1.

In the following a further embodiment of the invention will be described with regard to Fig. 9.

Fig. 9 illustrates elements of a communication environment similar to the one shown in Fig. 1, additionally showing a service provider 140, providing a communication service to the mobile device 120. The remaining elements of Fig. 9 are substantially as shown in Fig. 1, and therefore a further detailed description thereof is omitted at this point. The control means is generally illustrated at 100, while the illustrations of the network parameter handler, the link parameter, the network selector and of the handover handler are omitted for simplicity reasons. Further, the illustrations for collecting network parameters and link parameters and for selecting the candidate networks and the target network are omitted for simplicity reasons.

In Fig. 9 it is presumed that the service provider 140 provides a communication to the mobile device 120. The communication service, as noted before, may include any kind of voice and/or data service. Before the handover, the communication service is considered to be provided via the current network 110 via a communication link 901 between the service provider and the current network and a communication link 160 between the current network and the mobile device. The communication 901 may be a wireless link, as illustrated in Fig. 9. However, may also be at least partially a wire line connection.

After the handover, the communication service will be provided to the mobile device via the target network 130, through a communication link 902 between the service provider and the target network and a communication link 161 between the target network and the mobile device. The selection operations for determining the target network from the networks 130 - 132 preferably are as outlined with regard to previous embodiments.

Thereafter the handover of communications is performed, as illustrated at 151. The handover of the communications with the mobile device from the current network and the target network include two phases, a preparatory phase of the handover and the actual handover itself, for improving provision of a seamless handover. The communication environment of the embodiment of the invention shown in Fig. 9 enables a seamless handover of a communication service from a current network to a target network by performing the preparatory phase of the handover. Seamless handover stands for a handover that does not involve a significant degradation of the communication link and communication service provided. Ideally, the user of the mobile device will not even notice the seamless handover. The preparatory phase of the handover allows the target network to more quickly take over communications during the actual handover and further enables the target network to readily continue the ongoing communications, e.g. a communication with another mobile device or a service provided by a service provider.

The preparatory phase of the handover of the present embodiment includes creating trust relationships between the current network, the target network and the service provider, and by transferring context information from the current network to the target network prior to performing the actual handover. Thus, as a trusted environment between the current network and the target network and the service provider is established in preparation of the handover, time consuming trust negotiations during the handover can be avoided. Moreover, as the target network already holds information characterizing e.g. the communication link to the mobile device to be handed over from the current network, the set-up of the communication link can be prepared the actual handover can be performed at a reduced time delay. The communication link is a connection between the mobile device and a network for exchanging information, such as data or voice. Moreover, as the target network may obtain context information on the communication service to be handed over, the set-up of the communication service can be prepared and an interruption of services can be avoided.

First, the creation of mutual trust relationships will be described.

A trust relationship between two entities may include mutually verifying the identities for authentication purposes, exchanging security parameters for security data transfer, and determining the authorization of each entity to access the respective other entity.

According to an alternative, in the preparatory phase of the handover, the existence of a trust relationship between the current network 110 and the target network 130 may be determined, as indicated at 904 in Fig. 9. This determination operation may be performed by the current network, reviewing, e.g., registration information, in order to determine whether at a previous point in time a trust relationship has been established between the current network and the target network. For example, the trust relationship could have been established at an earlier point in time, e.g., during a previous handover procedure, or on network deployment.

The determination operation may include the exchange of messages between the current network and the target network in order to determine an existing trust relationship, and/or to verify an existing trust relationship. This may involve the exchange of security parameters for verification purposes .

Similarly, in another operation it may be determined whether a trust relationship exists between the current network 110 and the service provider 140. In this case, the current network and/or the service provider may determine the existence and/or verify a mutual trust relationship.

Still further, similar operations may be performed to determine the existence and/or to verify a trust relationship between the service provider 140 and the target network 130.

The above operations for determining the existence of mutual trust relationships between the current network, the service provider and the target network, and the verification of the mutual trust relationships may be handled by the control means 100, which, as noted in connection with Fig. 1, may form a separate entity and/or which may be at least partially realized as an integral part of the current network and/or the mobile device, the target network and/or the service provider .

If the determination operation reveals that only some of the mutual trust relationships exist, the missing trust relationships can be created.

In a first example, a mutual trust relationship exists between the current network 110 and the service provider 140, and a mutual trust relationship exists between the current network 110 and the target network 130. However, between the service provider 140 and the target network 130, a mutual trust relationship could not be detected. In this case, the current network 110, having mutual trust relationships with the service provider and the target network, will mediate between the service provider and the target network, in order to also create a trust relationship between the service provider and the target network. The mediation may include an exchange of trust-related information and parameters with the service provider and the target network, including security parameters. The creation of the trust relationship between the service provider and the target network may involve a direct transmission of information between the service provider and the target network, however, in an alternative it is also possible that the trust relationship between the service provider and the target network is generated solely based on an exchange of trust-related information between the current network and the service provider on the one hand and on the other hand between the current network and the target network.

In another example, mutual trust relationships exist between the current network 110 and the service provider 140, and between the service provider 140 and the target network 130. However, a mutual trust relationship between the current network and the target network does not yet exist. In this scenario, similar to the above example, the service provider mediates for generating a trust relationship between the current network and the target network.

If more than one mutual trust relationship between the current network, the target network and the service provider is missing, a determination operation can be performed, in order to determine another entity of the network environment having mutual trust relationships for mediating in the creation of the missing trust relationships. This further entity could, e.g., be another network or another service provider .

According to another example, the target network contacts the service provider about trust relation information in order to further facilitate the creation of trust. For example, the target network may contact the service provider regarding trust information of a trust relationship between the service provider and the current network.

After the above-outlined determination operations for determining and/or creating mutual trust relationships between the current network, the target network and the service provider, the context transfer takes place between the current network and the target network, e.g., as outlined above . Secondly, the transfer of context parameters will be described.

In the preparatory phase of the handover, further to creating trust relations between the current network, the target network and the service provider, context parameters will be transferred from the current network to the target network, as indicated at 905. Using the context parameters, the target network will perform a preset-up of the communication links 902 and 161. For example, the communication 902 between the service provider and the target network may be made fully operable in the preparatory phase, if the service provider is able to establish more than one communication link at the same time. In this case communications will still be handled via the communication link 901, however, the communication link 902 will also be operable.

A context parameter preferably characterizes the communication link and the communication service. For example, a context parameter may describe the technical characteristics or requirements to establish and/or maintain the communication link 160 between the mobile device 120 and the current network 110. Further, a context parameter may describe the technical characteristics or requirements to establish and/or maintain the communication service for the mobile device or a user of the mobile device. o

The characteristics of the communication link between the mobile device and the current network may include information on an access technology to be used for the communication link, a data rate for transmission, information regarding error coding or error protection, and similar. Further, the characteristics of the communication link may include information on a communication channel which is to be used, a time slot, a frequency, an access code, and similar. The context parameters may pertain to any characteristic of the communication service provided to the mobile device . As noted above , the communication service may include any type of data or voice service for the mobile device , provided, e . g . , by a service provider or another mobile device . Consequently, the context parameters may describe the service type , application settings of a service application, user preferences , subscription information, authorizations for use of service features , user settings , and similar .

This may also include context parameters defining a characteristic of the mobile device , such as an identity of the mobile device , a device type , and similar . Further, context parameters may specify capabilities of the mobile device , e . g . , processing capabilities , display capabilities such as a size of a display of the mobile device , display type , and similar . Further, the context parameters may specify authorization information, security information, and similar . Still further, the context parameters may specify service subscriptions of a user of the mobile device and any other information relevant with regard to the mobile device .

Context parameters may also include positional information of a mobile device , such as a location of the mobile device , a velocity of the mobile device , a moving direction of the mobile device , and similar . This information may enable a prediction of a location of the mobile device during the handover, signal strength to be used when establishing the communication link 161 after the handover, etc .

Also , the context parameters may include characteristics of the current network and/or target network . This may include information on a trust relationship between the current network and a service provider, characteristics of the current network such as access technology used for the communication link, a type of network, and similar . According to an alternative, the method may include an operation to decide whether a context parameter is an independent context parameter, an independent context parameter being a context parameter applicable to at least one of the communication link and the communication service after the handover. Still further, the method may include an operation for deciding whether a context parameter is a dependent context parameter, a dependent context parameter being a context parameter that is not applicable to the communication link and communication service after the handover. Only the independent context parameters may be transmitted to the target network. Accordingly, only context parameters applicable to the communication link and/or service will be transferred, and a communication requirement and a time required for transferring the context parameters can be reduced.

The decision process for deciding independent and dependent context parameters may be based on at least one of an access technology at the current network and the target network, a stakeholder of the current network, a stakeholder of the target network, and a trust relationship between the current network and the target network.

According to another embodiment, priorities may be assigned to the context parameters or to sets of the context parameters, and the context parameters or sets of context parameters may be transmitted to the target network based on the priority. Accordingly, more important context parameters can be transmitted at an earlier point in time.

For example, the context parameters required for establishing the communication link between the mobile device and the target network are given a highest priority, and context parameters required for maintaining the communication service after the handover may be given a second highest priority. The priorities may be assigned based on a policy, and the priority may depend on at least one of a service type, a service level agreement, the target network, an access technology used, and a stakeholder of the target network.

Moreover, a context parameter can be constituted by at least one of the group consisting of a characteristic of the mobile device, a characteristic of the communication link, a characteristic of the communication service, and a characteristic of the current network and/or target network.

In order to appropriately schedule the context transfer, an available time before the handover takes place can be determined. Moreover, the portion of the context parameters to be transferred can be determined based on the available time and/or may be based on the priority given to the context parameters .

Then, during the actual handover, only the communication link 160 is switched over to the communication link 161, and a seamless transfer of the communication service can be obtained.

If the mobile device is capable of establishing more than one RF connection, it is also possible that the communication link 161 is also made operable in the preparatory phase of the handover, in which case the mobile device maintains the communication service via the communication link 160, and already holds the communication 161 in an operable state. Then, during the handover, the communications could simply be switched over to the target network. It is also possible, that for a brief amount of time data pertaining to the communication service are transmitted via both, the current network and the target network, and that for completing handover the communication links 601 and 160 are simply switched off. In this case a fully seamless handover becomes possible . The service provider 140 may be constituted by any kind of entity providing any kind of communication service to subscribers, e.g., to a mobile device, through a wireless network such as the current network 110 and the target network 130. As noted above, the communication service may pertain to any kind of data or voice service, e.g., a service to which the user of the mobile device 120 has subscribed. The service provider may form part of one of the networks , e.g. , the current network or the target network, or may form a separate entity, communicating with the current network and the target network to wireline or wireless communication links . While the service provider may be a larger organization serving a large number of service subscribers, it is also possible that a communication device constitutes the service provider, providing a service to the mobile device 120. For example, the service provider could be a home computer, a PDA, a laptop computer, or any other mobile device exchanging data with the mobile device 120.

The operations described above in Fig. 9 may be performed by the control means 100, which may be at least partially integrated into the current network 110, the mobile device 120, the target network 130, and the service provider 140, or may form a separate entity.

It is noted that a program or programs may be provided having instructions adapted to cause a data processing device or a network of data processing devices to realize elements of the above embodiments and to carry out the operations of at least one of the above embodiments.

Also, a computer-readable medium may be provided having a program embodied thereon, where the program is to make a computer or a system of data processing devices to execute functions or operations of the features and elements of the above-described examples. A computer-readable medium can be a magnetic or optical or other tangible medium on which a program is recorded, but can also be a signal, e.g. analog or digital, electronic, magnetic or optical, in which the program is embodied for transmission. Further, a data structure or a data stream may be provided including instructions to cause data processing means to carry out the above operations. The data stream or the data structure may constitute the computer-readable medium. Still further, a computer program product may be provided comprising the computer-readable medium.

Claims

1. Method for deciding a handover of a communication link between a mobile device and a current network to an available network, the communication link providing a communication service to the mobile device, including: obtaining network parameters describing at least one available network; selecting at least one candidate network eligible for a handover from the available networks based on the network parameters; obtaining link parameters for each candidate network, the link parameters describing a communication link between the mobile device and each candidate network after the handover; selecting a target network from the candidate networks based on a comparison of the link parameters of each candidate network; and performing a handover of the communication link from the current network to the target network.

2. Method of claim 1, including measuring a link parameter for signal quality, for each candidate network, based on at least one of a signal strength, packet error rate and bit error rate.

3. Method of at least one of the preceding claims, including estimating a link parameter for service quality, for each candidate network, based on the signal quality.

4. Method of at least one of the preceding claims, including determining a link parameter specifying an available time until the handover and performing the selection of candidate networks and the target network based on the available time.

Method of at least one of the preceding claims, including determining, for each candidate network, link parameter for network latency, the network latency corresponding to an amount of context information transferable before the handover takes place.

6. Method of at least one of the preceding claims, including estimating, for each candidate network, a link parameter for duration of service provision by each candidate network based on the device location, the device speed and the device direction of motion and a coverage area of the candidate network.

7. Method of at least one of the preceding claims, including performing the selection operation based on device travel path information.

8. Method of at least one of the preceding claims, including obtaining information on a path of travel of the mobile device; selecting candidate networks along the path of travel; and selecting a sequence of target networks for a sequence of handovers based on the path of travel .

9. Method of at least one of the preceding claims, wherein the network parameters include at least one of a: - coverage area; - network resources; - network deployment; and - stakeholder.

10. Method of at least one of the preceding claims, including obtaining service parameters describing the communication service and wherein the selection step for selecting candidate networks is further based on the service parameters .

11. Method of claim 10, wherein the service parameters include at least one of a: - service type; - minimum data rate; - cost of service; - service level agreement; - subscription information; and - QoS parameters .

12. Method of at least one of the preceding claims, including obtaining device parameters describing the mobile device, and wherein the selection step for selecting candidate networks is further based on the device parameters .

13. Method of claim 12 , the device parameters including at least one of: - access technology capabilities; - display characteristics; and - processing capabilities.

14. Method of at least one of the preceding claims, including comparing the link parameters of the target network with link parameters of the current network and performing the handover of the communication link from the current network to the target network only if the comparison indicates an improvement of at least one of the communication link and the communication service.

15. Method of at least one of the preceding claims, including deciding a handover based on at least one of a: - signal quality,- - service quality; - path of travel of the mobile device; and - lapse of a predetermined time interval.

16. Method of at least one of the preceding claims, including determining a signal quality of the communication link between the mobile device and the current network and performing the handover to the target network immediately, if the signal quality falls below a threshold.

17. A program having instructions adapted to carry out the method of any one of claims 1 to 16.

18. A computer readable medium, in which a program is embodied, wherein the program is to make data processing means execute the method of any one of claims 1 to 16.

19. A computer program product comprising the computer readable medium of claim 18.

20. Control means for deciding a handover of a communication link between a mobile device and a current network to an available network, the communication link providing a communication service to the mobile device, including: a network parameter handler for obtaining network parameters describing at least one available network; a network selector for selecting candidate networks eligible for a handover from the available networks based on the network parameters ; a link parameter handler for obtaining link parameters for each candidate network, the link parameters describing a communication link between the mobile device and each candidate network after the handover; wherein the network selector is adapted to select a target network from the candidate networks based on a comparison of the link parameters of each candidate network; and a handover handler for performing a handover of the communication link from the current network to the target network.

21. Control means of claim 20, wherein the link parameter handler is adapted to measure a link parameter for signal quality, for each candidate network, based on at least one of a signal strength, packet error rate and bit error rate .

22. Control means of at least one of the claims 20 - 21, wherein the link parameter handler is adapted to estimate a link parameter for service quality, for each candidate network, based on the signal quality.

23. Control means of at least one of the claims 20 - 22, wherein the link parameter handler is adapted to determine a link parameter for an available time until the handover and performing the selection of candidate networks and the target network based on the available time.

24. Control means of at least one of the claims 20 - 23, wherein the link parameter handler is adapted to determine, for each candidate network, a link parameter for network latency, the network latency corresponding to an amount of context information transferable before the handover takes place .

25. Control means of at least one of the claims 20 - 24, wherein the link parameter handler is adapted to estimate, for each candidate network, a link parameter for duration of service provision by each candidate network based on the device location, the device speed and the device direction of motion and a coverage area of the candidate network.

26. Control means of at least one of the claims 20 - 25, wherein the link network selector is adapted to perform the selection operation based on device travel path information.

27. Control means of at least one of the claims 20 - 26, wherein the link parameter handler is adapted to obtain information on a path of travel of the mobile device; and wherein the network selector is adapted to select candidate networks along the path of travel and to select a sequence of target networks for a sequence of handovers based on the path of travel .

28. Control means of at least one of the claims 20 - 27, wherein the network parameters include at least one of a: - coverage area; - network resources; - network deployment ; and - stakeholder .

29. Control means of at least one of the claims 20 - 28, wherein the link parameter handler is adapted to obtain service parameters describing the communication service and wherein the selection step for selecting candidate networks is further based on the service parameters.

30. Control means of claim 29, wherein the service parameters include at least one of a: - service type; - minimum data rate; - cost of service; - service level agreement; - subscription information; and - QoS parameters .

31. Control means of at least one of the claims 20 - 30, wherein the link parameter handler is adapted to obtain device parameters describing the mobile device, and wherein the selection step for selecting candidate networks is further based on the device parameters .

32. Control means of claim 30, the device parameters including at least one of : - access technology capabilities; - display characteristics; and - processing capabilities.

33. Control means of at least one of the claims 20 - 32, wherein the handover handler is adapted to compare the link parameters of the target network with link parameters of the current network and to perform the handover of the communication link from the current network to the target network only if the comparison indicates an improvement of at least one of the communication link and the communication service.

34. Control means of at least one of the claims 20 - 33, wherein the handover handler is adapted to decide a handover based on at least one of a : - signal quality; - service quality; - path of travel of the mobile device; and - lapse of a predetermined time interval .

5. Control means of at least one of the claims 20 - 34, wherein the handover handler is adapted to determine a signal quality of the communication link between the mobile device and the current network and to perform the handover to the target network immediately, if the signal quality falls below a threshold.