WO2008066435A1

WO2008066435A1 - A method of managing a handover procedure in a cellular telecommunication network

Info

Publication number: WO2008066435A1
Application number: PCT/SE2006/050530
Authority: WO
Inventors: Andreas Olsson; Erik Westerberg
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2006-11-30
Filing date: 2006-11-30
Publication date: 2008-06-05

Abstract

In a method and a system for making a handover decision for a wireless telecommunicatio connection in a radio system, the system is adapted to request information relating to wireless capabilities about a mobile station for which is to make a handover decision, and make the handover decision based upon information received in response to the request for information relating to the wireless capabilities about the mobile station.

Description

A METHOD OF MANAGING A HANDOVER PROCEDURE IN A CELLULAR TELECOMMUNICATION NETWORK

TECHNICAL FIELD

The present invention relates to a method and a system for exchanging information within a cellular telecommunication system, hi particular the present invention relates a method and system for exchanging information within a system being combined of many different mobile telecommunication standards.

BACKGROUND Today a number of different standards for cellular telecommunication exist. Examples of such standards include: Global System for Mobile Communication (GSM), Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA) among others.

Furthermore, within a number of the existing standards different sub-standards have been developed. For example, within GSM the General Packet Radio Services (GPRS) and the Enhanced Data rates for GSM Evolution (EDGE) or Enhanced GPRS (EGPRS) have been introduced. GPRS is a mobile data service a\ailable to users of GSM mobile phones, and EDGE is a digital mobile phone technology that allows for increased data transmission rate and improved data transmission reliability. Similarly within WCDMA, the High-Speed Downlink Packet Access (HSDPA) has been introduced. HSDPA is an evolution of the WCDMA standard. HSDPA achieves the increase in the data transfer speeds by defining a new transport channel: a high-speed downlink shared channel (HS-DSCH) that operates in a different way from existing WCDMA channels and is used for downlink communications to the mobile. Other standards such as CDMA and Long Term Evolution (LTE) have or will potentially have other sub-standards. All these standards may exist side by side or even overlapping within an area served by an operator and the operator of such a combined network of different standards is faced with the problem of having to manage the resources within the combined network in a way that both maximizes the use of the combined resources and maximizes the service provided to each mobile user within the combined network.

Furthermore, in such a complex environment where a number of different cellular telecommunication system exist side by side with wholly or partly overlapping coverage for a particular area, the mobile stations also have different requirements and support different standards. Today the general type of a mobile station is known to the radio network. Thus, the Base Station System (BSS) may have information about whether or not a mobile station is capable of WCDMA.

However, the existing protocols for performing hand-over between different radio systems having different capabilities have proven to be inefficient and far from optimized in terms of radio system usage and in terms of service level for the end-user.

Thus, in order to improve performance in situations where a multitude of standards co-exist within the same area of the network, an improved method of hand-over between cells having different capabilities is desired.

SUMMARY

It is an object of the present invention to overcome or at least reduce some of the problems associated with existing methods for hand-over between cells having different capabilities.

It is another object of the present invention to provide a method and a system that is capable of taking advantage of all capabilities with in a radio network comprising a multitude of coexisting radio standards and to maximize the combined use of all resources within the combined network.

These object and others are obtained by providing a method and a system as set out in the appended claims. Hence, a method and a system are provided where desired detailed information about the capabilities of a mobile station is communicated to the serving radio access node(s).

In accordance with one aspect of the present invention a mobile station transmits a message indicating its full capabilities to the Base Station Subsystem (BSS), for example as a response to a request from the BSS, so that an informed decision can be made by the serving radio system node when and if hand-over should be made to another cell and potentially to another radio system node.

In accordance with a second aspect of the present invention a node of a cellular telecommunication system is enabled to request detailed information relating to wireless capabilities for a particular mobile station from another node in a combined system.

In accordance with a second aspect of the present invention a node of radio system is provided with a facility to maintain the wireless capabilities for a mobile station having a radio technology different from the node once such information has been given to the node.

Such a method and system will result in a radio system network where all nodes in a combined radio network has knowledge of the full set of wireless capabilities the mobile station for which it responsible to handle handovers. The access and use of such information in a handover situation will significantly improve the likelihood of making an optimized hand-over decision in a given node of the combined cellular radio network. As a result the user of the mobile equipment will experience better performance.

Advantageously such a method and system is combined with a method and a system where desired detailed information about the capabilities of neighboring cell belonging to a different radio access network is communicated to the serving radio access node(s) in particular if the serving access node and the non-serving cell belongs to different radio technologies, for example a request can be transmitted requesting the wireless capabilities for a wireless neighboring cell that is currently unknown to the serving node(s) so that an informed decision can be made by the serving radio system node when and if hand-over should be made to another cell and potentially to another radio system node. Such a radio system can also be provided with a facility to maintain the wireless capabilities for a wireless neighboring cell that belongs to another node once such information has been given to the node.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawings, in which:

- Fig. 1 is a general overview of a cellular telecommunication system - Fig. 2 is a basic view of an exchange protocol for exchanging information within a cellular telecommunication system,

- Fig. 3 is a view of a an exchange protocol for exchanging information within a cellular telecommunication system,

- Figs. 4a - 4c are views of different protocols for retrieving wireless capabilities relating to a mobile station, and

- Fig. 5 is a flow chart illustrating different steps performed when requesting and updating information regarding capabilities of a mobile station in a cellular telecommunication system.

DETAILED DESCRIPTION

In Fig. 1 , a general view of a radio network system 100 covering an area is depicted. In the exemplary embodiment depicted in Fig. 1, the radio network system is a GSM system. The GSM system 100 comprises a base station (BS) 101, which can also be termed Base Transceiver Station (BTS). The base station 101 serves a number of mobile terminals; usually termed Mobile stations (MS) 103, located within the area covered by the base station 101. The base station 101 is also connected to a Base Station Controller (BSC) 105. The base station 101 and BSC 105 are both part of a Base Station Subsystem (BSS) The Base Station Subsystem (BSS) is the section of a GSM network which is responsible for handling traffic and signaling between a mobile phone and the Network Switching Subsystem. The BSS carries out transcoding of speech channels, allocation of radio channels to mobile phones, paging, quality management of transmission and reception over the Air interface and many other tasks related to the radio network. The BSS also comprises an additional unit termed Mobile Content Management Unit (MCMU) 109. The MCMU is most often not a separate unit but rather a logical functionality. The task for the MCMU will be described in more detail below.

The same area covered by the GSM system 100 may also be covered by another radio network system, for example a WCDMA system. By way of example the data service in such a combined GSM/WCDMA radio network will now be described. It should be noted that other combinations of different radio networks also are feasible.

Assume that the end-user, in this case the mobile station (MS), is connected to the GSM system. Assume further that the GSM system is enabled to operate using EDGE and that the MS also supports EDGE. If in this scenario the MS is capable of HSDPA it is in many cases beneficial to the end-user to handoff from the GSM/EDGE network to the WCDMA/HSDPA network. However, if the MS supports WCDMA but is not capable of HSDPA, the performance boost after the handoff is for most scenarios not sufficient to compensate for the radio outage required to perform the handover. Thus, in almost all these cases it will not be advantageous to initiate a handover from the GSM/EDGE system to the WCDMA/HSPDA system for this particular mobile station.

However, due to the lack of information exchange in existing combined radio networks regarding the wireless capabilities of individual mobile stations, the BSS cannot make the best decision in the scenario outlined above. The same problem can be expected in other Inter Radio Access Technology (IRAT) scenarios such as GSM/LTE, WCDMA/LTE and CDMA/LTE systems and other. The system as described herein is therefore provided with an information exchange protocol enabling different radio networks covering the same area to exchange information related to radio capabilities of individual mobile stations with each other and also to request such information directly from the individual mobile stations. The information relating to each individual mobile station is managed and stored by the Mobile Content Management Unit (MCMU) 109 depicted in Fig.1.

In Fig. 2, an overview of information exchanged between two arbitrary MCMUs associated with different radio systems is depicted. Thus, a first MCMU 201 associated with the BSS currently in control of a connection to a particular Mobile Station first transmits a request 205 to a second MCMU 203 associated with a non-serving cell of a second overlapping radio network. The request 205 is a request for information relating to the wireless capabilities of the mobile station in the overlapping radio network. The MCMU 203 of the non-serving cell non-serving 203 responds by sending an answer to the request 205 in a message 207 containing the requested information.

Using the information received in message 207 the BSS can make an informed decision whether or not it is in the interest of the combined overall system to make a handover to the non-serving cell given the complete information about the wireless capabilities of the mobile station.

In Fig. 3, the information exchange protocol between to Base Station Subsystems or the like is shown in more detail. In order to provide better understanding the exchange protocol will now be exemplified with a protocol between a GSM network and a WCDMA network. However, the same or similar protocol can be utilized between any two or more radio network systems.

First the controlling BSC 301 of a GSM network currently in control of a connection to a particular Mobile Station transmits a request 31 1 asking the core network (CN) for information relating to the wireless capabilities of a particular mobile station.

The request 311 is preferably routed to the serving GPRS Support Nodes (SGSN) 303. An SGSN is a node which in some sense carries out the same function as the Foreign Agent in Mobile IP. However, an SGSN is actually considerably more complex since it also does the full set of interworking with the connected radio network. If the SGSN 303 does not hold the relevant information regarding the mobile station that the request is concerned with, the request is routed onwards to an SGSN that hold such information. This can for example be executed by forwarding a message to the Home Location Register (HLR) 305, which in turn directs the request to an SGSN holding the relevant information. For LTE the SGSN node is termed GW. Finally, the SGSN that hold the requested information returns the information about the wireless capabilities of the mobile station to the BSC 301 in a reply 313. The BSC can then make a better decision in situations relating to handover from the GSM network to the WCDMA network.

In Fig. 4a, another procedure for obtaining information relating to the wireless capabilities of a mobile station is illustrated. In accordance with the procedure described in conjunction with Fig. 4, an MCMU 401 transmits a request to a Mobil Station MS 403 and requests the wireless Capabilities of the MS 403 in a request 405. The MS 403 replies with a message containing the requested information in a message 407.

The protocol used for obtaining information from a mobile station may differ in different cellular telecommunication standards. In Fig 4b an exemplary message structure as it may be implemented in 3GPP 44.060 is illustrated. Hence, the BSC 41 1 of a GSM system issues a request 415 as a RLC control signal message and the mobile station MS 403 replies to that message in a reply message 417. The RLC Control signaling messages will have to be standardized in 3GPP 44.060. In Fig 4c yet another exemplary message structure is illustrated. Hence, the RNC 421 of a WCDMA system issues a request as an RRC control signal message 425 and the mobile station MS 403 replies to that message with a reply message 427. The RRC Control signaling messages will have to be standardized.

The information requested about the wireless capabilities will of course differ depending on the radio technology of the system asking for the information and other circumstances. For example BSC of a GSM system could request WCDMA capability relating to a mobile station and request information like:- HSPA (High Speed Packet Access) support; Enhanced HSPA Support; Modulation support (QPSK or QPSK/16QAM); UE category (i.e. the maximum bandwidth). Similarly, a RNC of a WCDMA system could request GSM capability relating to a mobile station and request information like ;DTM support; EGPRS support; GMSK or GMSK and 8-PSK; Multislot Class (i.e. the maximum bandwidth); GERAN Evolution support. - S -

In Fig 5, a flowchart illustrating some of the basic steps performed within a Base Station Subsystem or the like when making decisions relating to handover from one radio network system to another radio network system.

First, in a step 501, a node of a first radio network that is to make a handover decision checks if it has information about the full wireless capabilities of the mobile station that it may want to handover control of. If the node already has that information at hand the procedure proceeds directly to a step 509 else the procedure proceeds to a step 503. In step 503 the node transmits a request for information about the capabilities of the mobile station. The request transmitted in step 503 may be sent either through the core network (CN) as illustrated in conjunction with Figs. 2 and 3 or it may be transmitted to the mobile station itself as illustrated in conjunction with Fig. 4 a - c or both.

Next, in a step 505, the node of said first radio networks receives an answer to the request. Thereupon, in a step 507, the node adds the information received in step 505 to a memory for storage for future needs. Hence, the next time the node is needs to have information about capabilities of the same mobile station there is no need to send out a request, instead the node can check the memory for that information. Finally, in a step 509, the node makes a handover decision using the information about the non-serving cell.

Using the method and system as described herein will result in a radio system network where all nodes in a combined radio network has knowledge of the full set of wireless capabilities the mobile station for which it responsible to handle handovers. The access and use of such information in a handover situation will significantly improve the likelihood of making an optimized hand-over decision in a given node of the combined cellular radio network. As a result the user of the mobile equipment will experience better performance.

Claims

1. A method of making a handover decision for a wireless telecommunication connection in a radio system (100) set up via a controlling node (105) controlling a connection to a mobile station (103), characterized by the steps of:

- requesting (503) information relating to wireless capabilities about the mobile station, and

- making the handover decision (509) based upon information received in response to the request for information relating to the wireless capabilities about the mobile station.

2. The method according to claim 1 , characterized in that the request relates to information regarding wireless capabilities of a radio technology different than the radio technology supported by the controlling node.

3. The method according to claim 1 or 2, characterized in that the request is sent using a predefined protocol .

4. The method according to any of claims 1 - 3, characterized in that the request only is sent if the controlling node is unable to retrieve the requested information locally.

5. The method according to any of claims 1 - 4, characterized in that the request is sent to the mobile station (103).

6. The method according to any of claims 1 - 5, characterized in that the request is sent to one or many Serving GPRS Support Nodes (SGSN) (303).

7. The method according to any of claims 1 - 6, characterized by the additional step of storing the received information locally.

8. A radio system (100) comprising a number of different radio access networks, where the different radio access networks, at least partly, overlap, each radio access network having a number of controlling nodes (105) for controlling connections to mobile stations (103) within reach of the respective controlling nodes, characterized by - means in one controlling node (105) for requesting information relating to wireless capabilities about a particular mobile station, and

- means in said one controlling node (105) for making the handover decision based upon information received in response to the request for information relating to the wireless capabilities about the mobile station.

9. The system according to claim 8, characterized by means for requesting information regarding wireless capabilities of a radio technology different than the radio technology supported by the controlling node.

10. The system according to claim 8 or 9, characterized by means for sending the request using a predefined protocol.

1 1. The system according to any of claims 8 - 10, characterized by means for only sending the request if the one controlling node is unable to retrieve the requested information locally.

12. The system according to any of claims 8 - 1 1 , characterized by means for sending the request to the mobile station (103).

13. The system according to any of claims 8 - 12, characterized by means for sending the request to one or many Serving GPRS Support Nodes (SGSN) (303).

14. The system according to any of claims 8 - 13, characterized by means for storing the received information locally.