WO2009022950A1

WO2009022950A1 - Improved communication between base station in a cellular network

Info

Publication number: WO2009022950A1
Application number: PCT/SE2007/050545
Authority: WO
Inventors: Magnus Johansson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2007-08-13
Filing date: 2007-08-13
Publication date: 2009-02-19

Abstract

A method for use in a cellular system (100) in which there can be a plurality of base stations (113, 123), each of which services at least one cell (111, 121) in the system by routing all traffic to and from users (112, 122) in the cell. The system additionally comprises at least one ASN-GW (130), an Access Service Network Gateway, which serves to connect at least a first number of said base stations to a Connectivity Service Network. The method comprises assigning to each of said base stations (113, 123) which are connected to said ASN-GW (130) an identity (BSID) which is unique at least among said number of base stations (111, 121), and the method additionally comprises assigning to each base station the ASN-ID, in other words the identity of the ASN-GW, to which the base station is connected.

Description

TITLE

Improved communication between base stations in a cellular network.

TECHNICAL FIELD The present invention discloses a method and a device for improved communication between base stations in a cellular network.

BACKGROUND

Cellular wireless access networks such as, for example, GSM, WCDMA and Mobile WiMAX, comprise a number of so called Base Stations, each of which services a geographical area, a so called cell, within the network. One of the roles of a base station with respect to users in the cell which the base station services is to route all traffic to and from those users. The equipment by means of which a user communicates with the system is sometimes referred to as a mobile terminal or a mobile station, MS.

The MSs can move between the cells, and the access network performs handover of the MS between the base stations of the cells, which in different systems is done with varying degrees of interaction with the MSs.

In order to facilitate handover between different base stations, a base station may broadcast information about its neighbouring base stations to the MSs in its cell, so that the MSs may quickly synchronize to new base stations, and have access to information about a new base station even before the handover is actually carried out, which will reduce the handover interruption time. This is a mechanism which is applied in, for example, Mobile WiMAX.

The information about neighbouring base stations may change dynamically, which means that there is a need for communication between base stations in order for base stations to be able to keep their neighbour information up to date. Base stations may communicate directly with each other, or the signalling between them can be done via another node in the network, usually a node which is "higher up" in the hierarchy of the network. In Mobile WiMAX, signalling between base stations is at present carried out via a so called Access Service Network Gateway, an ASN-GW.

An ASN, access service network, will here be defined as comprising one ASN-GW and the base stations which are connected to that ASN-GW.

Each base station in the network has a so called BSID, a base station ID, in other words a specific identity for that base station in the network. An ASN- GW is configured with the BSID of the base stations connected to it, which makes communication between base stations which are connected to one and the same ASN simple, since the ASN-GW can route messages to the correct BS based on the BSID, which is included in the message.

However, a problem arises when neighbouring base stations are connected to different ASN-GWs, since an ASN-GW which receives a message destined for a base station which is connected to another ASN-GW will not necessarily have any knowledge of the base station for which the message is intended.

SUMMARY

Thus, as has been explained above, there is a need for a solution to the problem of exchanging messages between neighbouring base stations which are connected to different ASN-GWs.

This need is addressed by the present invention in that it discloses a method for use in a cellular wireless access system in which there can be a plurality of base stations, each of which services at least one cell in the system by routing all traffic to and from users in the cell. The system in which the invention may be applied additionally comprises at least one ASN-GW, an Access Service Network Gateway, which serves to connect at least a first number of said base stations to a core network such as, in the WiMAX case, a Connectivity Service Network , and the method of the invention comprises (assigning to each of the base stations which are connected to said ASN-GW an identity which is unique at least among said number of base stations. According to the method of the invention, each base station is also assigned the identity of the ASN-GW to which the base station is connected.

Suitably but not necessarily, the ASN-GW identity which is assigned to a base station is comprised in the identity of the base station.

The invention also discloses a base station and an ASN-GW with novel functions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, with reference to the appended drawings, in which

Fig 1 shows an overview of a system in which the invention may be applied, and

Fig 2 shows another view of a system in which the invention may be applied, and Fig 3 shows two ASN-GWs with Base Stations, and

Fig 4 shows a method according to the invention, and

Fig 5 shows a block diagram of a base station of the invention, and

Fig 6 shows a block diagram of an ASN Gateway of the invention.

DETAILED DESCRIPTION

Fig 1 shows a schematic overview of a system 100 in which the invention may be applied. As shown, the system comprises a number of cells, two of which, 121 , 11 1 , are shown, but it should be realized and pointed out that the number of cells may be varied more or less freely in the system 100.

In each cell of the system 100 there may be a number of users with so called Mobile Stations, MSs, one of which is shown in each of the cells 111 ,121 , the users being referenced as 112 and 122 respectively. The system 100 comprises a number of base stations, BSs, with each cell of the system being serviced by one base station in the sense that all traffic to and from MSs in the cell is routed via the base station which services that cell.

As explained previously in this text, the MSs of the system may move between the cell, and as the MSs move, they are handed over from one cell to another, in the sense that traffic to and from the MS is routed via the Base Station of the new cell in which the MS is located.

In order to facilitate hand over, a BS will broadcast information about its neighbouring base stations to "its" MSs. As a consequence of this, there will arise a need for neighbouring BSs to communicate with each other, so that information may be exchanged.

As shown in fig 1 , the system 100 comprises at least one so called ASN-GW, Access Service Network Gateway, 130, which serves to connect, in this example, the base stations 113, 123 to a core network such as, in the WiMAX case, a Connectivity Service Network, CSN.

The ASN-GW 130 also serves as a "relay station" for signaling between the base stations 113, 123, which are connected to the ASN-GW 130, for example for relaying such messages as those described above. In order to be able to carry out the "relay functionality", the ASN-GW is configured with all of the Base Station IDs, BSID, of the base stations which are connected to it, so that the ASN-GW 130 can route messages to the correct BS based on the BSID of the "addressee" BS, which is included in the message from the sending BS.

However, consider instead a system in which neighbouring BSs are connected to different ASN-GWs. Such a system is schematically shown in fig 2.

As shown in fig 2, the system comprises a number of cells A-K, each of which is serviced by a Base Station with the corresponding reference letter, i.e. A-K. Base Stations A, B, C, D, E and F "belong" to a first gateway ASN- GW 1 , while BSs G, H, I, J, K and L "belong" to a second gateway ASN-GW 2.

As will be realized, a message from, for example, BS A to its neighbor BS H will be difficult to forward for the ASN-GW of BS A, ASN-GW 1 , since ASN- GW 1 is only configured with the BSIDs of the BS which are connected to that ASN-GW, and BS L belongs to ASN-GW 2.

Fig 3 shows the signaling paths for the system of fig 2. As shown, communication between BS A and BS B goes via reference point R6, which is the interface between a BS and its ASN-GW in WiMAX, only, i.e. ASN-GW 1. However, communication between BS A and BS L needs to go via reference point R4 as well, i.e. to pass from ASN-GW1 to ASN-GW 2, since BS L "belongs" to ASN-GW 2. R4 is the WiMAX name for the interface between ASN-GWs.

In order for ASN-GW 1 to be able to route messages to BS L, it would need to be configured with the BSID of BS L, as well as being configured with the information that BS L can be reached through ASN-GW 2.

The present invention proposes to address situations such as the one depicted above, i.e. how to pass messages between BSs which are connected to different ASN-GWs. The solution which is proposed by the invention is to assigning to each of the base station involved the identity of the ASN-GW, the ASN-ID, to which the base station is connected. The expression "to assign" is here used in the sense that the ASN-ID of the ASN- GW of the base station is included in, inter alia, some of the messages sent from the base station. Suitably, this is done by incorporating the ASN-ID in the identity of the base station, in other words in the BSID, although it could also be possible to include the ASN-ID separately.

Fig 4 shows one possible way of incorporating the ASN-ID of a base station in the base station's BSID: fig 4 shows a BSID as used in the Mobile WiMAX system, in which the invention may be particularly advantageously employed.

The BSID in Mobile WiMAX consists of 48 bits, as defined in IEEE 802.16-

2004, section 6.3.2.3.2.

The 24 most significant bits, MSBs, are used to define the operator ID₁ while the 24 least significant bits, LSBs, may be used arbitrarily by the operator.

Thus, the present invention proposes to use at least some of the 24 LSBs of the BSID to indicate the ASN-ID, as is also shown in fig 4. Naturally, the number of bits shown in fig 4 as used in the BSID to signify the ASN-ID is only an example, as is the placement of the ASN-ID within the BSID.

Thus, the number of bits of the BSID used to signify the ASN-ID can be varied, as can the placement of those bits within the BSID. However, the number of bits used for this purpose, as well as their placement within the BSID, should preferably be standardized within the system, in this example the WiMAX system.

Thus, by means of the solution proposed by the invention, the objective of facilitating communication between base stations which belong to different ASN-GWs is reached with a small processing load in the ASN-GWs of the system. The invention also discloses a base station for use in a cellular wireless access system in which there can be a plurality of base stations.

A rough block diagram of such a base station 500 is shown in fig δ.The base station 500 of the invention is equipped with means such as a receive part Rx 540 and a Transmit part Tx 550 as well as an antenna 560 for servicing at least one cell in the system by routing all traffic to and from users in the cell, and the base station comprises means such as an R6 interface for connection to an ASN-GW, an Access Service Network Gateway, by means of which the base station can be connected to a Connectivity Service Network.

The base station 500 is also equipped with means such as a computer 520 and a memory 530 for incorporating a specific identity, a BSID, Base Station Identity, in messages which it transmits, and the base station 500 additionally comprises means such as the computer 520 and the memory 530 for incorporating a specific identity, an ASN-ID, of the ASN-GW to which the base station is connected in at least some of said messages.

Suitably but not necessarily, the base station 500 incorporates its ASN-ID as part of its BSID, preferably among the 24 LSBs of its BSID.

The invention also discloses a node for use as an ASN-GW with the functions described above. In other words, the ASN-GW of the invention is an Access Service Network Gateway for use in a cellular wireless access system in which there can be a plurality of base stations.

An ASN-GW 600 of the invention is shown in a rough block diagram in fig 6, and is equipped with means such as an R6 interface 610 for letting a number of base stations in the system be connected to it, and is also equipped with means such as an R4 interface for connecting those base stations to a Connectivity Service Network. The R4 and R6 interfaces are shown in a common block 610 in fig 6, in order to indicate that those functions may be handled by one and the same component in the ASN-GW 600, although this is of course not a necessity.

The ASN-GW 600 of the invention also comprises means such as a computer 620 for transmitting a message from a first base station which is connected to the ASN-GW 600 to a second base station which is connected to a second ASN-GW in the system, and the ASN-GW 600 also comprises means for detecting the ASN-ID of the second ASN-GW, said ASN-ID being comprised in a message from the first base station. The detecting means are suitably the computer 620 assisted by a memory 630.

In a preferred embodiment, the detecting means 620, 630 of the ASN-GW can detect the ASN-ID of the other ASN-GW in the BSID of the first base station, and possibly the detecting means 620, 630, can also detect the ASN- ID of the other ASN-GW among the 24 LSBs of the BSID of the first base station.

The invention is not limited to the examples of embodiments described above and shown in the drawings, but may be freely varied within the scope of the appended claims.

Claims

1. A method for use in a cellular wireless access system (100) in which there can be a plurality of base stations (113, 123), each of which services at least one cell (1 11 , 121) in the system by routing all traffic to and from users (112, 122) in the cell, the system additionally comprising at least one ASN-GW (130), an Access Service Network Gateway, which serves to connect at least a first number of said base stations to a Connectivity Service Network, the method comprising assigning to each of said base stations (113, 123) which are connected to said ASN-GW (130) an identity (BSID) which is unique at least among said number of base stations (111 ,121), the method being characterized in that it additionally comprises assigning to each base station the ASN-ID, in other words the identity of the ASN-GW, to which the base station is connected.

2. The method of claim 1 , according to which the ASN-ID which is assigned to a base station (111 , 121) is comprised in the identity of the base station (113, 123), the BSID of the base station

3. The method of claim 1 or 2, according to which the ASN-ID is comprised among the 24 LSBs of the BSID of the base station.

4. A base station (500) for use in a cellular wireless access system (100) in which there can be a plurality of base stations (113,123), said base station being equipped with means (520, 530, 540, 550, 560) for servicing at least one cell in the system by routing all traffic to and from users in the cell, the base station comprising means (510) for connection to an ASN-GW, an Access Service Network Gateway, by means of which the base station can be connected to a Connectivity Service Network, the base station being equipped with means (520, 530) for incorporating a specific identity, a BSID, Base Station Identity, in messages which it transmits, the base station being characterized in that it additionally comprises means (520, 530) for incorporating a specific identity, an ASN-ID, of the ASN-GW to which the base station is connected in at least some of said messages.

5. The base station (500) of claim 4, which incorporates the ASN-ID as part of its BSID.

6. The base station (500) of claim 5, which incorporates the ASN-ID among the 24 LSBs of its BSID.

7. A node (600) for use as an ASN-GW, an Access Service Network Gateway, in a cellular wireless access system (100) in which there can be a plurality of base stations (113, 123), said ASN-GW (600) being equipped with means (610) for letting a number of said base stations be connected to it and for connecting those base stations to a Connectivity Service Network , the ASN-GW also comprising means (620) for transmitting a message from a first base station which is connected to it to a second base station which is connected to a second ASN-GW in the system, the ASN-GW also being characterized in that it comprises means (620, 630) for detecting the identity, the ASN-ID, of the second ASN-GW, said ASN-ID being comprised in a message from the first base station.

8. The ASN-GW (600) of claim 7, in which the detecting means (620, 630) can detect the ASN-ID of the other ASN-GW in the BSID of the first base station.

9. The ASN-GW (600) of claim 8, in which the detecting means (620, 630) can detect the ASN-ID of the other ASN-GW among the 24 LSBs of the BSID of the first base station.