GB2429608A - Prioritising data flows requiring handover in a mobile communication system - Google Patents

Abstract

A method of handover in a mobile communication system comprises a first controller, e.g. a source base station subsystem (BSS) 3, setting a priority for each of two or more existing data flows from a mobile device 1 to a network 7. The multiple data flows may include both a circuit switched (CS) 5 data flow, such as a voice call, and a packet switched (PS) 6 data flow, such as a file download, which may occur in the dual transfer mode (DTM) of a GSM/EDGE radio access network (GERAN) 4. The first controller signals to a second controller the respective priorities for each data flow for which handover is requested. The first controller may indicate which of the existing data flows are critical so that, if the second controller can not allocate resources for all critical data flows, the handover is cancelled.

Description

A METHOD OF HANDOVER IN A MOBILE COMMUNICATION SYSTEM

This invention relates to a method of handover in a mobile communication system, in particular where there are both packet switched and circuit switched data flows.

When a mobile device moves out of a range of a base station, or there is congestion due to a large amount of traffic at the base station, then there needs to be a handover of the mobile device from the base station of one cell to another. There are particular problems in the situation where there are multiple connections in place, for example both a circuit switched (CS) connection or data flow, such as a voice call and a packet switched (PS) connection or data flow, such as a file download. There may even be multiple PS, or CS data flows, such as a video conference call, video and voice both being CS connections, although multiple CS data flows are less likely.

An example of a situation in which a PS and a CS call take place together is in the 3td generation partnership project (3GPP) global system for mobile communication (GSM)/enhanced data rates for GSM evolution (EDGE) radio access network (GERAN). In GERAN, dual transfer mode (DTM) is a mechanism that allows a mobile station to be engaged simultaneously in a CS call and in a PS session comprising one or more data flows. When operating in DTM it is necessary to get a handover for both CS and PS calls or data flows together, but there is no certainty about which type of data flow should take priority, nor whether a request for handover should fail, if not all of the data flows can be handed over.

As part of the proposed procedures for the handover of packet switched resources and for Release-7 enhancements to the DTM handover, a radio resource management entity, located in a base station controller (BSC) of a base station subsystem (BSS) fora new, or target', cell is requestedbythe BSC inthe BSS of the * * * * old, or source' cell to allocate PS resources, for PS handover, or both PS and CS * resources for DTM handover. The requested PS resources may comprise resources for multiple data flows.

: 30 These resources may be being used to support applications of different priorities, and, where the target BSC does not, or cannot allocate all requested :* :::: resources, it is preferable that those corresponding to high priority applications are allocated. However, no method exists to communicate from the source BSC to the target BSC the priorities of the requested resources for the CS and PS domains.

Furthermore, if not all resources are allocated by the target BSC, the source BSC may decide to abort the handover procedure. It may, for example, decide to attempt a handover to a different cell. Between allocating the resources and being informed that the handover has been cancelled, the target BSC cannot allocate the resources to any other mobiles.

This problem has not existed up to now as PS Handover and the enhancements to DTM Handover are new procedures which have not been completely defined.

Currently, the DTM Handover involves releasing all PS resources then carrying out a CS-only handover.

In accordance with a first aspect of the present invention, a method of handover in a mobile communication system comprises, in a first controller, setting a priority for each of two or more existing data flows from a mobile device to a network; and signalling from the first controller to a second controller, the respective priorities for each data flow for which a handover is requested In the present invention, a new information element is defined specifying the priority of each PS or CS connection. The prioritization of CS vs PS calls can be done without any response from the t-BSC Preferably, the first controller receives from the second controller, an indication of whether or not resources can be allocated for handover.[ Preferably, the indication from the second controller includes notification of which of the existing data flows can be allocated resources for handover.

In the case of multiple data flows, such as a CS and several PS calls, it is useful for the requesting party to know which of the calls will be handed over successfully before deciding on whether or not to proceed with the handover.

* ** Preferably, the first controller provides a further indication of which of the existing data flows are critical, such that if the second controller does not allocate resources for all critical data flows, the first controller will cancel the handover.

* s. Preferably, the second controller does not allocate resources for the data flows *S*s * : i** 30 unless resources for all critical data flows can be provided.

If a source controller requesting a handover gives an indication of whether or : not the call is critical, then the target is not left with allocated resources which are not S...

going to be used because the source then decides to cancel the handover.

There are different types of call or data flow to which the invention can be applied, but preferably, the data flows comprise one or more of a packet switched data flow, a circuit switched data flow, and a broadcast service.

Preferably, the priority of each data flow is determined in accordance with a schedule defined by a network operator. A user of the mobile device may be given the option to choose an appropriate schedule from a selection offered by the network operator.

Preferably, the schedule is specific to each mobile device, although a network operator could choose to apply a blanket policy for all devices.

Preferably, the second controller automatically allocates resources if it can handover all critical data flows; and signals a positive response to the first controller.

Preferably, the signalling from the first controller to the second controller is sent through a core network in a transparent container.

Preferably, the first controller comprises a source controller, or a network controller.

The invention can be applied to source controllers which are outside the core network, or those which are within the core network, according to the particular communication system concerned For a source controller, preferably, the first controller comprises a base station subsystem, a wireless access point; a gateway between an internet protocol network and a mobile communication system; or the mobile device.

There may be situations in which the mobile user decides on priority for handover, usually in advance of a particular situation occurring, but with direct interaction of the user via their mobile device.

An example of a method of handover in a mobile communication system will * ** now be described with reference to the accompanying drawing in which: Figure 1 is an example of a first system to which the method of the present invention can be applied; * * Figure 2 illustrates a conventional scheme for handover in dual transfer mode; S...

Figure 3 illustrates a scheme for handover in accordance with the method of the present invention; Figure 4 is an example of a second system to which the method of Fig. 3 can be **.* applied; and, Figure 5 is an example of a third system to which the method of Fig. 3 can be applied.

Fig.1 shows the main components of a GERAN or General Packet Radio Service (GPRS) system. A mobile device or mobile station (MS) 1 communicates 2 with a source base station controller (BSC) 3 within a base station subsystem (BSS) of GERAN 4. The source BSC 3 signals through either a circuit switched (CS) domain 5, or a packet switched (PS) domain 6, of a core network 7, dependent upon the type of data flow concerned. On each side for the PS domain, the signalling passes through a serving GPRS support node (SGSN) 8, 9 and on each side for the CS domain the signalling passes through a mobile switching centre (MSC) 10, Ii before reaching a target BSC 12 within a target BSS (not shown). Typically, the signalling from the source BSS to the target BSS is canied out using a transparent container which passes through the core network unchanged. In some situations, there is only one SGSN involved (if the s-BSS and t-BSS are connected to the same SGSN) and similarly, there may be only one MSC.

In Fig.2, a conventional method of operating the system of Fig. 1 is illustrated.

From the source BSS 13, a PS handover required message 15 is sent to the core network, PS part, 6 and the core network sends on PS handover request message 16 to the target BSS 14. Similarly, for the CS domain a handover required message 30 is sent to the core network, CS part, 5 and a handover request 31 is forwarded from the core network 5 to the target BSS 14. In response to these requests 16, 31 the target BSS 14 allocates resources, which cannot then be used by any other mobile station.

The target BSS then sends back a PS handover request acknowledge message 17 to the core network 6 and the core network in turn sends a PS handover command 18 to the source BSS 13. For the CS part, the target BSS 14 sends back a haiidover request * , ,* acknowledge message 32 to the core network, which in turn sends on a handover command 33 to the source BSS. If the resources allocated are not sufficient for all of *. the source BSS's requirements, then the source BSS 13 may decide to cancel the S..

* : ** * 30 handover and sends a PS handover cancel message 19 back to the core network and delete BSS packet flow context (PFC) procedure 20 is begun between the core network : .. 7 and the target BSS 14, resulting in the allocated resources being released. The PFC is *.*.

a PS data flow in the context of handover for GPRS. For the CS part a handover failure message 34 is sent to the core network 5 and a clear command 35 to the target BSS 14. Although a handover failure message already exists for use after the handover has been attempted and has failed; there is no existing mechanism to allow the source BSS to cancel a handover. Using this existing message in the present invention to allow the BSS to cancel the handover for the CS handover has not been suggested before.

This method does not take any account of priority of a data flow defined by the source BSS.

In the method of the present invention, as illustrated by Fig. 3, a new information element giving an indication of priority is provided to show which priority applies to a particular connection or data flow and thus which calls or data flows the source BSS considers to be most important for handover. The definition of priority must be in the source BSS or in another entity which has knowledge of all of the data flows involved in the handover. The source BSS, or other controlling entity also has control over whether or not to actually accept that handover based on the resources assigned by the target BSS, or target control entity.

For example, the indication can be broken down into low priority; high priority; and critical for the handover to be successful, or it may simply rank a series of priorities. For example, one instance of this information element is transmitted from the source BSS 13 to the target BSS 14 for each connection in the same messages as the request to allocate resources, as part of the handover procedure, for the corresponding connection. Alternatively, a single information element can include a list of all the data flows. Thus, a PS handover required message 21 and PS handover request message 22 include the information element indicating priority. . The information element defined allows the source BSS to communicate to the target BSS the priority for each connection for which resources are being requested to be allocated. This information can be used by the target BSS to allocate resources for connections which support high priority applications in preference to those used by lower priority applications. For the CS part a handover required message 36 is sent to the core * : * a 30 network 5 and a handover request 37 forwarded from the core network to the target BSS 14. 0*

: In a further modification, the source BSS can use the critical priority to indicate S. *.

which of the connections requested are critical. The critical priority level indicates that the source BSS will cancel the attempted handover if the corresponding resource is not allocated by the target BSS. If the target BSS cannot, or chooses not to, allocate resources for all of the connections which have critical' priority, it may cancel the handover immediately - not allocating any resources. An indication in the form of a iiew reason' code is defined to allow the target BSS 12 to indicate to the source BSS 1 3 through a PS handover reject message 23 and PS handover required reject message 24, that the handover cannot be completed as the target BSS cannot or chooses not to allocate resources for all the critical connections requested The equivalent message in the CS domain is a handover failure message 38 to the core network from the target BSS 14, indicating that critical resources have not been allocated and a handover required reject message 39 to the source BSS 13. If the handover is cancelled immediately, the target BSS uses the new reason code to indicate to the source BSS that one or more critical resources have not been allocated, and that it has therefore not reserved any resources.

Without this, the target BSS must follow the conventional procedure of allocating resources, signalling which resources have been allocated to the source BSS, then wait for the source to indicate to it that these resources are insufficient and that the handover is therefore cancel led.

Use of a unified prioritisation scheme applicable to both PS and CS resources allows an entity to rank the PS and CS resources relative to one another and so provide an improvement over existing systems.

The determination of relative priority for CS and PS calls may be controlled by the network operator setting these in advance and the source BSS simply applying a predefined schedule to give appropriate priorities to calls which the source BSS really wants to handover. However, this control is not limited to the source BSS and in certain circumstances, particularly with respect to the definition of critical and non- * critical connections, this could be done in the core network, or controlled by the mobile * device itself. For example, although for DTM, the source BSS is the only place where it is known that there are two call types, with handover of multiple PS calls or data : * 30 flows, the feature that only the source BSS has information about all of the calls does not apply, so the priority of the call could be defined within the core network. When : the decision on which calls are critical is taken in the BSS, then usually the mechanism :: :: is pre-programmed by a network operator, but it could be influenced.

If the target BSS is able to carry out the requested handover, then it sends a positive response to the source BSS 13 and will automatically carry out the resource allocation in the normal way. However, if not all of the resources can be allocated for those data flows deemed to be critical, no resources will be allocated.

Fig. 4 shows an alternative access arrangement with the same core network.

The mobile station 1 communicates via a generic IP-based access network 25 and generic access network (GAN) controller 26. This GAN controller and generic access network appear to operate like a GERAN BSS as far as the core network is concerned.

Generally, the access network 25 is a wireless network, at least with respect to communications with the mobile station, although it might have a non-wireless link to the BSC at the target end.

In functional terms, the applicability of the invention to systems other than GERAN can be illustrated by reference to Fig.5. A mobile device 31 connects to a transmitter or receiver 33 via a communication link 32, wired or wireless. The iS transmitter/receiver 33 communicates with a handover controller 35 and a network, or radio resource controller for a source cell. Via a core network 36, the network, or radio resource controller 37 for a target cell receives signalling messages and forwards these to a target transmitter/receiver 38. * Ia * . -., . *411 * I * S.. ** p * h

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Claims (13)

1. A method of handover in a mobile communication system, the method comprising, in a first controller, setting a priority for each ol two or more existing data flows from a mobile device to a network; and signalling from the first controller to a second controller, the respective priorities for each data flow for which a handover is requested.

2. A method according to claim 1, wherein the first controller receives from the second controller an indication of whether or not resources can be allocated for handover.

3. A method according to claim 2, wherein the indication from the second controller includes notification of which of the existing data flows can be allocated resources for handovcr.

4. A method according to claim 2 or claim 3, whereby the first controller provides a further indication of which of the existing data flows are critical, such that if the second controller does not allocate resources for all critical data flows, the first controller will cancel the handover.

5. A method according to claim 4, wherein the second controller does not allocate resources for the data flows unless resources for all critical data flows can be provided.

6. A method according to any preceding claim, wherein the data flows comprise one or more of a packet switched data flow, a circuit switched data flow, and a broadcast service.

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7. A method according to any preceding claim, wherein the priority of each data * 4.

* 30 flow is determined in accordance with a schedule defined by a network operator *

8. A method according to claim 7, wherein the schedule is specific to each mobile * SI * S device.

9. A method according to any preceding claim, wherein the second controller automatically allocates resources if it can handover all critical data flows; and signals a positive response to the first controller.

10. A method according to any preceding claim, wherein the signalling from the first controller to the second controller is sent through a core network in a transparent container.

Il. A method according to any preceding claim, wherein the first controller comprises a source controller, or a network controller.

12. A method according to any preceding claim, wherein the first controller comprises a base station subsystem, a wireless access point; a gateway between an internet protocol network and a mobile communication system; or the mobile device.

13. A method of handover in a mobile communication system, as hereinbefore described with reference to the accompanying drawings. * S. I * S

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