WO2008066434A1

WO2008066434A1 - Handover procedure based on cell capabilities

Info

Publication number: WO2008066434A1
Application number: PCT/SE2006/050529
Authority: WO
Inventors: Andreas Olsson
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 telecommunication where many overlapping radio systems are present in the same area, the system is adapted to request information relating to wireless capabilities about a second, non-serving, cell and to make the handover decisions based upon information received in response to the request for information relating to the wireless capabilities about the second, non-serving, cell.

Description

Handover procedure based on cell capabilities

TECHNICAL FIELD

The present invention relates to a method and a system for exchanging information within a cellular telecommunication system. In particular the present invention relates a method and system for exchanging infoπnation 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) have been introduced. GPRS is a digital mobile technology where data can be sent in packet switched mode over the GSM air interface 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.

Today the general type of a neighboring cell belonging to another radio technology is known to the radio network. Thus, the Base Station System (BSS) has information about whether or not a neighboring cell is capable of WCDMA. Similarly the Radio Network Controller (RNC) knows if a cell is GSM capable or not. This is the one piece of system information that the radio network relies upon in a hand-over situation.

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 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 belong to different radio technologies.

In accordance with one aspect of the present invention a request is transmitted requesting detailed wireless capabilities for a wireless neighboring cell that are 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.

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 wireless neighboring cell that belongs to another node once such information has been given to the node.

Advantageously such a method and system is combined with a method and a system where desired detailed information about the capabilities of a mobile station is also communicated to the serving radio access node(s). For example a mobile station may 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. Also a node of a cellular telecommunication system can be enabled to request detailed information relating to wireless capabilities for a particular mobile station from another node in a combined system.

Using such a system operation in this manner will result in a radio system network where all nodes in a combined radio network has knowledge of the full set of wireless capabilities of all neighboring cells, regardless of what telecommunication standard is employed by a particular cell at any time. 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 with co-existing radio technologies deployed in an overlapping structure.. 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 with in a cellular telecommunication system,

- Fig. 3 is a view of a an exchange protocol for exchanging information with in a cellular telecommunication system, and - Fig. 4 is a flow chart illustrating different steps performed when requesting and updating information regarding capabilities of neighboring nodes in a cellular telecommunication system.

DETAILED DESCRIPTION In Fig.l , 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. 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 the 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, transporting packet switched data, 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.

Furthermore, each BSS is associated with a Radio Resource Management (RRM) 109. The RRM 109 can typically be integrated in the BSC 105, but can be located at other locations. Radio resource management (RRM) is the system level control of radio transmission characteristics in wireless communication systems, for example cellular networks, wireless networks and broadcasting systems. RRM involves strategies and algorithms for controlling parameters such as transmit power, channel allocation, handover criteria, modulation scheme, error coding scheme, etc. The objective is to utilize the limited radio spectrum resources and radio network infrastructure as efficiently as possible.

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. 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 WCDMA cell where the MS is located isn't capable of HSDPA the performance boost after the handover 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 GSM to WCDMA.

However, due to the lack of information exchange in existing combined radio networks, the BSS cannot make the decision above based on whether the neighbor cell is capable of

HSDPA or not. 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 with each other.

In Fig. 2, an overview of information exchanged between two arbitrary RRMs associated with different radio systems is depicted. Thus, a first RRM 201 associated with the BSS currently in control of a connection to a particular Mobile Station first transmits a request 205 to a second RRM 203 associated with a non-serving cell of a second overlapping radio network. The request 205 is a request for information relating to the capabilities of the non- serving cell such as for example HSPA (High Speed Packet Access) support, Enhanced HSPA Support or Modulation support (e.g. QPSK or QPSK/16QAM). If on the other hand a RNC of a WCDMA system were to request information from a BSC of a GSM system such requested information could include; the DTM support, EGPRS support, Uplink TBF mode support, Multiple TBF support, GERAN Evolution support, etc. The non-serving RRM 203 responds by sending an answer to the request 205 in a message 207.

Using the information received in message 207 the RRM 201 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 associated with the RRM 203 given a particular set of input parameters.

In Fig. 3, the information exchange protocol between two 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 addressed to a non-serving cell of an overlapping radio system network asking for information relating to the capabilities of the non-serving cell. The request 31 1 may be transmitted in a format conformant with the RIM Single Report procedure as defined in the standard 3GPP 44.018 (RIM=RAN Information Management, RAN=Radio Access Network).

In order to utilize existing RIM procedures defined in the standard 3GPP 44.018, a new RIM Application Identity is created for this purpose. The new added RlM Application Procedure can for example be termed "Inter Radio Access Technology (IRAT) neighboring cell radio technology capability".

The request 31 1 is preferably routed through a number of Serving GPRS Support Nodes

(SGSN) 303 and 305. 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 Hill set of intervvorking with the connected radio network. Through the SGSNs the request 31 1 arrives at an RNC 307 of an overlapping cell of a WCDMA radio network. The node corresponding to SGSN is called GW in the LTE system.

In response to the request for radio network capabilities, the RNC 307 of the overlapping cell of the WCDMA radio network returns a response message 313 back to the BSC 301 Using the information received in the message 313, the BSC can then make a better decision in situations relating to handover from the GSM network to the WCDMA network.

In Fig 4, 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 401 , a node of a first radio network that is to make a handover decision checks if it has information about the non-serving cell that it may want to handover to. If the node already has that information at hand the procedure proceeds directly to a step 409 else the procedure proceeds to a step 403. In step 403 the node transmits a request for information about the capabilities of the non-serving cell belonging to another radio system network. Next, in a step 405, the node of said first radio networks receives an answer to the request.

Thereupon, in a step 407. the node adds the information received in step 405 to a memory for storage for future needs. Hence, the next time the node is needs to have information about capabilities of the same cell there is no need to send out a request, instead the node can check the memory for that information. Further, in a preferred embodiment, the request in step 403 also contains a request to update the node requesting the information should there be a change in capabilities in the non-serving cell in the future so that the information stored by a node always is up to date. Finally, in a step 409, the node makes a handover decision using the information about the non-serving cell. 50529

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 of all neighboring cells, regardless of what telecommunication standard is employed by a particular cell at any time. The access and use of such information in a handover situation will significantly improve the likelihood of making an optimized handover decision in a given node of the combined cellular radio network.

Claims

1. A method of making a handover decision for a wireless telecommunication connection in a radio system (100) set up via a first controlling node (105) associated with a first cell, the method characterized by the steps of:

- requesting (403) information relating to wireless capabilities about a second, non-serving, cell, and

- making the handover decision (409) based upon information received in response to the request for information relating to the wireless capabilities about the second, non-serving, cell.

2. The method according to claim 1 , characterized in that the first and second cell are operated using different radio technologies.

3. The method according to claim 1 or 2, characterized in that the request is sent to the second non-serving cell 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 all neighboring cells of the controlling node.

6. The method according to any of claims 1 - 5, characterized in that the request is routed through one or many Serving GPRS Support Nodes (SGSN) (303; 305).

7. The method according to any of claims 1 - 6, characterized in that the controlling node belongs to a Global System for Mobile Communication (GSM), GSM network and the non- serving cell belongs to a Wideband Code Division Multiple Access (WCDMA) network, or vice versa.

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

9. A cellular telecommunication system comprising a number of overlapping radio access networks, each radio access network comprising a number of cells and where cells belonging to different radio access networks at least partly overlap, characterized by: - means in a controlling node of at least one, first, of the radio access networks for requesting (403) information relating to wireless capabilities about a non-serving cell belonging to another, second, radio access network, and - means for making a handover decision (409) based upon information received in response to the request for information relating to the wireless capabilities about the non-serving cell.

10. The system according to claim 9, characterized in that the first and second radio access networks are operated using different radio technologies.

1 1. The system according to claim 9 or 10, characterized by means for requesting information relating to the non-serving cell using a predefined protocol.

12. The system according to any of claims 9 - 1 1 , characterized by means for only sending the request if the controlling node is unable to retrieve the requested information locally.

13. The system according to any of claims 9 - 12, characterized by mean for sending the request to all neighboring cells of the controlling node.

14. The system according to any of claims 9 - 13. characterized by means for routing the request through one or many Serving GPRS Support Nodes (SGSN) (303; 305).

15. The system according to any of claims 9 - 14, characterized in that the controlling node belongs to a Global System for Mobile Communication (GSM), GSM network and the non-serving cell belongs to a Wideband Code Division Multiple Access (WCDMA) network, or vice versa.

16. The system according to any of claims 9 - 15, characterized by means for storing the received information locally.