GB2455706A

GB2455706A - Inter-RAT handover signalling and related mobile radio communications device

Info

Publication number: GB2455706A
Application number: GB0724229A
Authority: GB
Inventors: Caroline Jactat; David Lecompte
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2007-12-12
Filing date: 2007-12-12
Publication date: 2009-06-24
Also published as: WO2009075378A1; GB0724229D0

Abstract

The present invention provides for a method of delivering inter-RAT handover signalling from a mobile radio communications device operating within a mobile radio communications network, and including the step of sending a tracking area update signal piggybacked with a handover complete signal for enabling mobile terminated service reception and to a mobile radio communications device arranged for such handover.

Description

INTER-RAT HANDOVER SIGNALLING AND RELATED

MOBILE RADIO COMMUNICATIONS DEVICE

The present invention relates to a method of delivering inter-RAT handover signalling from a mobile radio communications device operating within a mobile radio communications network, and to such a mobile radio communications device.

For mobile radio communications device User Equipment (UE) such as cell phone handsets, it is an increasing common characteristic that such devices have the potential to operate in accordance with a variety of Radio Access Technologies (RATs).

Various scenarios arise in which it is required that the UE toperform a handover from one RAT to another RAT and such handover procedures are known to restrict the functionality of the handset during handover.

For example, during a handover procedure to a RAT such as E-UTRAN, a Network Access Server (NAS) Tracking Area Update Request message is sent subsequent to handover completion on the Radio Resource Control (RRC) side of the connection in order to update the data relating to the location of the UE for the Home Subscriber Server (LISS).

However, from a time that the UE receives the message from the source access system requesting handover to E-TRAN, to the HSS update concerning the new mobile radio communications device location, the device is not able to receive calls. That is, Mobile Terminated (MT) server reception is not allowed prior to the HSS being updated subsequent to the Tracking Area Update.

The requirement for such handovers, and related service shortfalls, arise in particular when the mobile radio communications device is found to be fast moving, such as when used aboard a fast moving train for example and when changes between different RATs within a Public Land Mobile Network (PLMN) are required.

The present invention seeks to provide for a method of delivering inter-RAT handover signalling, and to a related mobile radio communications device arranged for providing such signalling, and having advantages over known such methods and devices.

According to a first aspect of the present invention there is provided a method of delivering inter-RAT handover signalling from a mobile radio communications device operating within a mobile radio communications network, and including the step of sending a tracking area update signal combined with a handover complete signal for enabling mobile terminated service reception.

The method is advantageous insofar as it can allow MT service reception as soon as the handover has been completed. Further, the adoption mentioned can advantageously lead to a reduction in the signallingload in the Evolved Packet Service (EPS) system and particularly at the E-TRAN and S 1 interfaces.

In addition to the potential advantages of signalling load reduction, further advantages arise in particular in view of the relatively early Tracking Area Update request signalling can be achieved by way of the present invention.

For example, improved user-experience can be achieved through a provision of greater service continuity since the window within which the mobile radio communications device cannot receive calls is reduced.

As noted above, MT service reception can be achieved as soon as handover completion has occurred and this compares particularly favourably with the current state of the art which does not allow MT service reception before the HSS has been updated further to the Tracking Area Update.

As a further advantage, early authentication of the mobile radio communications device by target EPS Core Network can be achieved and further, the early release of bearer resources in the source system can be achieved and which, as a further advantage, can be assigned to another mobile radio communications device as required.

Preferably, the Timing Advance Update signal comprises a NAS Timing Advance Update signal and, further, the handover complete signal comprises a RRC Handover signal.

As will be appreciated from the following description, the method can prove particularly advantageous insofar as the Tracking Area Update request message is piggybacked with the handover complete message.

Of course, it will he appreciated that in one example, the inter-RAT handover signalling relates to a handover to E-TRAN.

According to another aspect of the present invention there is provided a mobile radio communications device for operation within a mobile radio communications network and arranged to produce inter-RAT handover signalling, the said device further including means for sending a Tracking Area Update signal combined with a handover complete signal and for enabling mobile terminated service reception.

Such a device can therefore exhibit the advantages of the method outlined above.

Thus, the Tracking Area Update signal can comprise a NAS tracking area update signal, and the handover complete signal can comprise a RRC handover complete signal.

As with the method noted above, the device of the present invention can be arranged such that the tracking area update signal is piggybacked with the handover complete signal.

Yet further, the device can be arranged for handover to a E-UTRAN.

The present invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a signalling diagram illustrating an inter-RAT handover procedure according to the current art; and Fig. 2 is a signalling diagram in similar form but arising in accordance with the method and device of the embodiment of the present invention.

Figs. I and 2 serve to illustrate the present invention in relation to an inter-RAT handover to E-UTI N and based on handover sequences from UTRAN to E-UTRAN, and from GERAN to E-UTRAN.

Turning first to Fig. I there is illustrated known handover signalling arising in relation to a mobile radio communications device 10 and an associated source access system 12, target eNodeB 14, source core network 16. target Evolved Packed Call (EPC) 18 and}{SS 20.

In Fig. I, there is illustrated a handover request signal 22 delivered from the source core 16 to the source access system 12 although it should be appreciated that during the preparation of phase of' the handover, the target EPC 18 has previously forwarded to the Source core network 16 "a call network transparent container" containing target call network information such as, for example, Timing Advance Index information within a Forward Communication Response message.

Subsequent to receipt of the signal 22. the source access system 12 issues a handover command signal 24 to the mobile radio communications device 10.

In accordance with the current art, a handover complete signal 26 is then sent from a mobile radio communications device 10 to the target eNodeB 14 which, in turn, issues a relocation complete signal 28 to the target EPC 18.

A forward relocation complete signal 30 is then returned from the target EPC 18 to the source core network 16 which replies with a forward communjcatjoi complete acknowledge signal 32 which then precedes the Bearer Update as indicated.

A separate update transfer signal 34 is then issued from the mobile radio communications device 10 to the target e-NodeB 14 and which comprises a NAS Tracking Area Update request.

It should be appreciated that the mobile radio communications device 10 can readily determine that it is located within a new Tracking Area in view of' the call network information contained within the handover command.

Optional security functions 36, will be introduced in between the signalling illustrated and prior to an update location signal 38 which, in this instance, is performed as part of the Tracking Area Update procedure.

Subsequent to the receipt of this signal 38, the 1-ISS 20 is arranged to produce a cancel location signal 40 and directed to the source call network 16 a system can be arranged such as illustrated at 42 so as to allow for the release of the lu resource if the source RAT is recognised as UTRAN.

A cancel location acknowledge signal 44 is returned from the source core network 16 to the IISS 20 and which can be followed by the provision of a bearer delete scenario 46 and a subsequent insert subscriber data scenario 48 prior to update location acknowledge signal 50 being returned from the HSS 20 to the target EPC 18.

Finally, the downlink direct transfer signal 52 is delivered from the target EPC 18 onwards to the mobile radio communications device 10 and which confirms that the NAS Tracking Area Update has been accepted.

By way of comparison, the signalling arising in relation to an embodiment of the present invention is now described in relation to Fig. 2.

As will he appreciated, the same elements comprising user equipment 10, the source access system 12, the target eNodeB 14, the source core network 16, the target EPC 18 and the HSS 20 are as illustrated as before, as is the initial handover required signalling 22 and the handover command 24.

However, and importantly in relation to the concept of the present invention, when the handover complete signal 54 is transmitted from the mobile radio communications device 10 to the target eNodeB 14 piggybacked therewith is the NAS Tracking Area Update request message.

As above, on the basis of the call network information found within the handover command, the mobile radio communications device can determine that it is now located within a new tracking area.

Relocation complete signalling 56, forward relocation complete signalling 58 and forward relocation complete acknowledgement 60 signals are sent in the same manner as signals 28, 30 and 32 illustrated above in relation to the current art and prior to a bearer update as shown.

A level of security functionality 62 is again provided prior to an update location signal 64 being delivered from the target EPC 18 to the HSS 20 and, a cancel location signal 66 returned from the FISS 20 to the source core network 16.

Functionality relating to the release lu resource 68 is again provided and subsequent to a cancel location acknowledgement signal 70 which itself is then followed by the bearer delete option 72 and insert subscriber data option 74 established prior to the update location acknowledgement signal 76 returned from the HSS 20 to the target EPC 18. and the subsequent downlink direct transfer 78 comprising confirmation that the NAS tracking area update has been accepted.

This latter part of the signalling diagram Fig. 2 is of course identical to that illustrated in relation to Fig. I although it will be appreciated that the timing of which such signalling can be provided is advantageously brought forward in accordance with the present invention and in view of the employment of the piggybacked handover complete/Tracking Area Update request signal 54 delivered from the mobile radio communications device 10 to the target eNodeB 14.

Such advantageous early despatch of the Tracking Area Update request as illustrated in accordance with the piggybacked signalling 54 of the illustrated embodiment of the present invention, it proves readily possible to allow MT service reception as soon as handover completion has occurred and which leads to associated advantages such as a reduction in signalling load in the EPS system and an approved more reliable user-experience.

Early authentication of the mobile radio communications device by the target EPS core network can be achieved as can however additionally early release of bearer resources which can then be assigned to another mobile radio communications device as required.

It should be appreciated that the Tracking Area Update request message piggybacked with the handover complete signalling can comprise an NAS Information Element (lE) and NAS Data Unit (DLJ) conveyed in the S Fig. 1 handover notify signalling from the eNodeB to the Mobile Management Entity (MME).

Claims

I. A method of delivering inter-RAT handover signalling from a mobile radio communications device operating within a mobile radio communications network, and including the step of sending a tracking area update signal combined with a handover complete signal for enabling mobile terminated service reception.
2. A method as claimed in Claim 1, wherein the tracking area update signal comprises a NAS Tracking area update.
3. A method as claimed in Claim I or 2 wherein the handover complete signal comprises a RRC Handover signal..
4. A method as claimed in Claim 1, 2 or 3,wherejn the tracking area update request message is piggybacked with the handover complete message.
5. A method as claimed in Claim 1, 2, 3 or 4 the inter-RAT handover signalling relates to a handover to E-TRAN.
6. A mobile radio communications device for operation within a mobile radio communications network and arranged to produce inter-RAT handover signalling, the said device further including means for sending a tracking area update signal combined with a handover complete signal and for enabling mobile terminated service reception.
7. A device as claimed in Claim 6, wherein the tracking area update signal comprises a NAS tracking area update signal.
8. A device as claimed in Claim 6 or 7, wherein the handover complete signal comprises a RRC handover complete signal.
9. A device as claimed in Claim 6. 7 or 8, and arranged such that the tracking area update signal is piggybacked with the handover complete signal.
10. A method of delivering inter-RAT handover signalling substantially as hereinbefore described, with reference to, and as illustrated in, Fig. 2 of the accompanying drawings.
11. A mobile radio communications device operation with a mobile radio communications network and derived for inter-RAT handover signalling and substantially as hereinbefore described with reference to the accompanying drawings.