Method of operating a dual mode mobile telephone

METHOD OF OPERATING A DUAL MODE MOBILE TELEPHONE

0002The present invention relates to mobile communication systems and more particularly to a method of operating a mobile communication device within a geographical area having overlapping coverage from first and second mobile telephone networks, where said first network is the home network of the mobile communication device and said first and second networks provide respective first and second sets of services. The present invention also relates to a system for performing this method of operation.

0003A number of digital mobile telephone standards are in use throughout the world. These include the European GSM standard and the US TDMA standard. However, due to the ever increasing demand for mobile telephone services many, if not all of these standards are likely to be superseded by new standards offering increased network capacity and/or increased data transmission rates. In particular, the European Telecommunications Standards Institute (ETSI) is currently developing a so called third generation mobile environment known as the Universal Mobile Telecommunication System (UMTS) which it is expected will be operational by 2002. UMTS will operate in the 2GHz frequency band and will offer data transmission rates of up to 2Mbits/sec, compared to a rate of only 9.6Kbits/sec offered by the existing GSM standard.

0004In the transition from second generation standards to third generation standards, there is likely to be a period when both second and third generation standards will have to coexist. It is also possible that such coexisting networks will be operated by different operators. As with all previous standards, networks implementing the new standards are likely to be introduced piece-meal, extending their geographical coverage over time. It may also be the case that the geographical coverage offered by third generation networks will always be less than that offered by second generation networks due to the need to sustain high bit rate transmissions with the former.

0005It is proposed (in Europe at least) to enable mobile stations registered with a third generation network as the "home" network (i.e. the network to which the mobile stations subscribe) to transfer to a second generation network when the stations are outside the coverage area of the home network, with appropriate cross-billing agreements between the network operators, to alleviate the possible geographical limitations. This transfer will operate in substantially the same way as the "roaming" function of conventional GSM networks (GSM 03.22) where a station can register with an alternative network when the RF connection between the mobile station and the home network is too weak to support a traffic channel. Of course third generation terminals will have to be dual mode, e.g. UMTS/GSM, in order to take advantage of this facility.

0006The inventors of the present invention have addressed the problem of how mobile stations registered with earlier generation networks, e.g. second generation networks, as their home network may gain access to new services only available through new generation networks, e.g. third generation networks. This may be a requirement of reciprocal arrangements between second and third generation network operators. As far as the inventors are aware this problem has not been previously addressed.

0007According to the present invention there is provided a method of operating a mobile communication device within a geographical area having overlapping coverage from first and second mobile telephone networks, where said first network is the home network of the mobile communication device and said first and second networks provide respective first and second sets of services in said geographical area, the method comprising registering the device with said first network when a service of said first set is requested and registering the device with said second network when a service of said second set, but not of said first set, is requested.

0008Typically, although not essentially, the overall geographical coverage of said second network is less than that of said first network, as is likely to be the case in the period following the introduction of a new mobile telephone standard which is implemented by said second network.

0009Preferably, a service provided by said second network, but not by said first network, is a high transmission rate service, that is at a higher transmission rate than is possible with services provided by said first network. Examples of high bit rate services are internet browsing, videophone, and data downloading.

0010The request for a service may be made by the mobile communication device, e.g. in response to a user input, or by the first network, e.g. in response to an incoming call made to the mobile communication device. In either case, in the event that a service of said second set, but not of said first set, is requested, registration with said second network may be carried out automatically under the control of said first network. In this event, there is no need for the user of the mobile communication device to be aware of the change of registration. Alternatively, a decision on a change of registration may be made by a user via a user interface of the mobile communication device.

0011In one embodiment of the present invention, said first network is a GSM network and said second network is a UMTS network and said mobile communication device is a dual mode UMTS/GSM device.

0012According to a second aspect of the present invention there is provided a mobile telecommunication system comprising at least first and second mobile telephone networks having an overlapping geographical area of coverage and a multiplicity of mobile communication devices, wherein said first network is the home network of the mobile communication devices and said first and second networks are arranged to provide respective first and second sets of telephonic services in said geographical area, the system comprising control means for registering a communication device with said first network when a service of said first set is requested and for registering the device with said second network when a service of said second set, but not of said first set, is requested.

0013The control means may comprise means associated with each of the mobile communication devices for transmitting a deregistration request to the first network and for transmitting a registration request to the second network when a service of said second set, but not of said first set, is requested. Alternatively, the control means may comprise means associated with the first network for responding to a request from a communication device for a service of said second set, but not of said first set, by re-registering the communication device with the second network.

0014The mobile communication devices may be, for example, mobile telephones, combined mobile telephone/personal digital assistant devices, or other devices which use wireless telephonic communication.

0015For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which:

0016Figure 1 shows schematically the geographical coverage area of example second and third generation mobile telephone networks; Figure 2 shows in block diagram form the architectures of the second and third generation networks of Figure 1 ;

0017Figure 3 shows a flow diagram of the operation of a mobile station in the coverage area of the networks of Figure 1 ; Figure 4 shows at the signaling level an implementation of the method of Figure 3 for circuit switched transmission; and

0018Figure 5 shows at the signaling level an implementation of the method of Figure 3 for packet switched transmission.

0019As already noted above, in Europe, UMTS networks are likely to be introduced with only limited geographical coverage. This situation is illustrated in Figure 1 where the coverage 1 provided by the UMTS network falls within the coverage area 2 of a pre-existing GSM network. When a UMTS compatible mobile station (MS) 3, which has the UMTS network as its home network (or home public land mobile network HPLMN), is located within the UMTS network coverage area 1 , the MS 3 is registered with the UMTS network and is able to make use of all the services provided by that network (or at least those services to which the MS user has subscribed). Providing that the MS is also GSM compatible, and that an appropriate agreement exists between the operators of the UMTS and GSM networks, when the MS detects that it has moved outside of the UMTS network coverage area 1 it is able to register with the GSM network (as a visiting public land mobile network VPLMN) and to make use of the services provided by the GSM network. The services provided by the GSM network are likely to be more limited than those provided by the UMTS network but this disadvantage is more than offset by the increased coverage area available to the UMTS network subscriber. This arrangement is similar in principle to the 'roaming for coverage' function available with current GSM MSs, e.g. which operates when a MS moves from one country to another, as defined in GSM specification 03.22.

0020The architectures of the GSM and UMTS networks are shown schematically in Figure 2 where the dual-mode GSM/UMTS MS 3 communicates with either the UMTS BSS (base station subsystem) 4 and the GSM/GPRS (global packet radio service) core network 5 or with the GSM/DCS BSS 6 and the GSM/GPRS core network 7. The two core networks 5,7 cooperate according to a roaming agreement between the two network operators.

0021Consider now the case where the MS 3 is registered with the GSM network as its HPLMN. The MS 3 may make use of the GSM services throughout the GSM coverage area 2, including the UMTS coverage area 1 because of the overlapping coverage which exists there. However, if the MS 3 requires to make use of a service provided by a UMTS network (i.e. as a VPLMN) but not by the GSM network, the MS 3 must 'roam' for that service. This is different from the conventional 'roaming for coverage' offered by GSM and is not defined in GSM specification 03.22. Figure 3 is a flow diagram of the roaming for service operation illustrating that the HPLMN will be selected by the MS 3 so long as that network is available and the selected service is provided by the HPLMN.

0022Roaming for service differs from traditional roaming for coverage in that, with the former, location updates and thus location registration are not necessarily required because the MS 3 can remain registered with the home GSM network which knows the location of the MS 3.

0023Figure 4 illustrates a possible implementation scenario for the roaming for service function where data transmission between the MS 3 and the networks is by circuit switched transmission (i.e. where one or more traffic channels are reserved for the duration of the transmission). The following legends are used in Figure 4:

0024MS Mobile Station

0025RAN Radio Access Network

0026CN Core Network

0027GSM-op GSM operator, owner of the first network UMTS-op UMTS operator, owner of the second network

0028The following table contains a description of the messages of Figure 4:

0029A-HORequired indication from the radio access network that handover is needed

0030MAP-prepare-HO handover request between networks

0031A-HORequest handover request to the radio access network

0032A-HOAck acceptance of handover request from the radio access network

0033MAP-prepare-HO-resp response to handover request between networks A-HOCommand handover command to the radio access network HOCommand handover command to the MS HOAccess MS sends access attempt to the radio access network

0034A-HOdetect the radio access network informs network that the MS's access attempt has been detected

0035MAP-process-access- indication that handover process is ongoing sig

0036HOComplete the radio access network informs the MS that handover process has been completed

0037A-HOComplete the radio access network informs network that handover process has been completed MAP-send-end-sig the second network informs the first network that handover process has been completed

0038A-clr-command the first network commands the radio access network to release reserved radio resources

0039Signaling can be divided into eight main steps as follows:

00401. The MS sends a service request with quality of service (QoS) parameters to the GSM network. These QoS parameters may include bit transmission rate, bit error rate, and transmission delay.

00412. The GSM network analyses the available resources for the service. The GSM network detects that it cannot provide the requested quality of service thus it sends a handover request to the UMTS network.

00423. The UMTS network accepts the handover request. The MS is commanded to the UMTS network with handover command and the MS makes an access attempt after the

0043MS has changed to the UMTS network's cell.

00444. Handover access has been detected by the UMTS network and the resources of the GSM network are released.

00455. The MS continues the service request signaling with the UMTS network. 6. The UMTS network starts billing procedure in order to bill the GSM network for the service.

00467. When the service is released the billing procedure is stopped.

00478. The MS selects the GSM network if it is available.

0048Figure 5 illustrates a possible implementation scenario for the roaming for service function where data transmission between the MS 3 and the networks is by packet switched transmission (i.e. where transmission time slots are dynamically allocated for transmission according to demand and priority). The following legends are used in Figure 5:

0049MS Mobile Station BSS Base Station Subsystem

0050SGSN Service GPRS Support Node

0051GPRS General Packet Radio Service

0052GGSN Gateway GPRS Support Node

0053RAN Radio Access Network IP Destination Internet Protocol Node

0054The following table contains a description of the messages of Figure 5: SENDER(session, application session in the MS requests quality of sender_Tspec)r service described in sender_Tspec

0055UPCALL(session, error message with code "quality of service resv_error) cannot be provided"

0056MM-RA-update routing area update message

0057SGSN context request context for the MS is requested

0058GTP-SGSN context context request between two GGSNs request

0059GTP-SGSN context context request confirmation response

0060Cancel location location canceled from the previous SGSN

0061Cancel location ack location cancellation acknowledgment

0062SGSN context the MS context activation accepted by GGSN response

0063MM-RA- routing area updating confirmation updateAccepted path(sender, quality of service request to the destination IP sender_Tspec) node rsvp(Tspec) merged quality of service request to the previous

0064IP node

0065UPCALL(session, connection and quality of service confirmation resv_confirm) RELEASE(session) session release resvTear(session) resource release between IP nodes

0066Again, signaling can be divided into eight main steps as follows:

00671. Application in the MS sends a service request with quality of service parameter to the GSM network.

00682. Available radio resources are analysed and a service request is rejected due to the lack of resources. The MS selects the UMTS network.

00693. The GSM and the UMTS network exchange information about the MS and finally the UMTS network accepts the MS to access the network. 4. Application in the MS sends a service request with quality of service parameter to the

0070UMTS network.

00715. The UMTS network has radio resources available and it sends path-message to the destination IP node. Resources for the session are found and the MS is confirmed about the resource reservations. 6. Data transfer between application starts. Billing and roaming starts.

00727. Application is closed or timer expires. The session is closed and resource reservations are released. 8. The MS selects the GSM network. The UMTS network bills the GSM network for the service.

0073In the implementations of Figures 4 and 5, it is the GSM network which determines, from the request made by the MS, whether or not it can provide the requested service and therefore whether or not the MS must be handed over to the UMTS network. In this way, the operation can be transparent to the user who is unaware that a handover has occurred. In an alternative approach however, the MS may be configured such that it is able to determine when a requested service is not provided by the GSM network. The MS may then automatically, or following a prompt from the user, de-register with the GSM network and subsequently register with the UMTS network.

0074It will be appreciated by those of skill in the art that further modifications may be made to the above described embodiments without departing from the scope of the present invention. For example, the invention may be used to provide service roaming between any two or more networks which provide different numbers or levels of service, e.g. two GSM or two UMTS networks.

0075Glossary

0076BSS Base Station Subsystem

0077DCS Digital Cellular System (at 1800 MHz)

0078DECT Digital European Cordless Telecommunications

0079HLR Home Location Register

0080HPLMN Home Public Land Mobile Network

0081IETF Internet Engineering Task Force

0082IMSI International Mobile Subscriber Identity

0083IP Internet Protocol

0084GPRS General Packet Radio Service

0085GSM Global System for Mobile Communications

0086MS Mobile Station

0087RSVP Reservation Set-up Protocol

0088UMTS Universal Mobile Telecommunications System