WO2008073554A2

WO2008073554A2 - A radio access network and method of operation therefor

Info

Publication number: WO2008073554A2
Application number: PCT/US2007/079629
Authority: WO
Inventors: Gerard T. Foster
Original assignee: Motorola, Inc.
Priority date: 2006-12-12
Filing date: 2007-09-27
Publication date: 2008-06-19
Also published as: GB2444756B; WO2008073554A3; GB2444756A; GB0624756D0

Abstract

A radio access network comprises an access point (111) having an access point network address and supporting at least a first mobile node (117) over a radio air interface. An access proxy (115) for the access point (111) has an access proxy network address and a registration server (119) is coupled to the access proxy (115) and the access point (111) and registers the first mobile node (117) for the access point (111) in response to receiving a registration message for the first mobile node (117). The registration comprises an identification check of a subscription identity of the first mobile node (117). The access proxy (115) is arranged to generate a first address binding between the access point network address and the subscription identity and the access proxy network address in response to the registration of the first mobile node (117).

Description

A RADIO ACCESS NETWORK AND METHOD OF OPERATION THEREFOR

Field of the invention

The invention relates to a radio access network and method of operation therefor and in particular, but not exclusively, to an access proxy for a cellular communication system.

Background of the Invention

A method which has been used to increase the capacity of cellular communication systems is the concept of hierarchical cells wherein a macrocell layer is underlayed by a layer of typically smaller cells having coverage areas within the coverage area of the macrocell. In this way, smaller cells, known as microcells or picocells (or even femtocells) , are located within larger macrocells. The microcells and picocells have much smaller coverage thereby allowing a much closer reuse of resources. Frequently, the macrocells are used to provide coverage over a large area, and microcells and picocells are used to provide additional capacity in e.g. densely populated areas and hotspots. Furthermore, picocells can also be used to provide coverage in specific locations such as within a residential home or office.

In order to efficiently exploit the additional resource, it is important that handover performance between the macrocell layer and the underlying layer is optimised. The process of handover can be separated into three phases. Firstly, identifying that a handover might be required, secondly, identifying a suitable handover candidate and finally, switching the mobile user from one base station to another.

The current trend is towards introducing a large number of picocells to 3G systems. For example, it is envisaged that residential access points may be deployed having only a target coverage area of a single residential dwelling or house. A widespread introduction of such systems would result in a very large number of small underlay cells within a single macrocell.

However, underlaying a macrolayer of a 3G network with a picocell (or microcell) layer creates several issues. For example, the introduction of a large number of underlay cells creates a number of issues related to the identification of individual underlay cells when e.g. handing over to an underlay call. In particular, 3G communication systems are developed based on each cell having a relatively low number of neighbours and extending the current approach to scenarios wherein the mobile phone may need to consider large numbers of potential neighbour cells is not practical.

The introduction of a large number of access points/base stations supporting underlay cells also introduces a number of issues relating to the routing, addressing and implementation of the networks. In particular, the current hierarchical addressing used in cellular communication systems has a limited address space and does not allow an unlimited number of nodes to be introduced. In addition, it is important that routing and management operations retain a very high degree of security and mobile authentication which becomes increasingly difficult when needing to accommodate a large number of distributed nodes.

Specifically, in a current macro cell cellular system, the address system is defined with a balance between scope and speed of resolution for the expected architecture hierarchy. For example, in UMTS, 4096 RNC identities are available thereby limiting the total number of RNC addresses to 4096. Furthermore, a UMTS system typically has 4096 base station addresses available for each RNC but as the RNCs typically handle around 100 cells this tends to be sufficient.

The approach of managing the address resolution in a hierarchical fashion whereby a cell or mobile station is addressed by a set of fixed scope network address levels works well when the expected hierarchy relationships are met, e.g. around 100 Cells per RNC, and no more than a few thousand RNCs per operator.

However, the approach is unsuitable for systems where the number of nodes at a given level exceeds the address scope for that level. For example, the introduction of large numbers of base stations/access points supporting very small cells means that the number of cells may exceed the address scope, and it is accordingly not possible to resolve certain addresses within the defined scope.

Furthermore, in some cases it has been proposed that e.g. individual residential access points include at least some RNC functionality such that the individual residential access point is coupled to the network as an RNC entity with an individual RNC identity. However, as many tens of thousand residential access points may exist in a given network, this substantially exceeds the address scope for RNCs.

Also, underlaying a macrolayer of a 3G network with a picocell (or microcell) layer creates several issues for the management of handovers of mobile stations between the different layers. In particular, 3G communication systems are developed based on each cell having a relatively low number of neighbours and extending the current approach to scenarios wherein the mobile station may need to consider large numbers of potential neighbour cells is not practical.

One problem of extending current approaches to scenarios where there are many underlaying picocells is how to uniquely and efficiently identify a picocell (or microcell) . Specifically, it is not practically feasible to list every underlay cell as a potential neighbour of the macrocell as this would require very large neighbour lists. These large neighbour lists would e.g. result in the neighbour list exceeding the maximum allowable number of neighbours in the list, slow mobile station measurement performance as a large number of measurements would need to be made etc. It would furthermore require significant operations and management resource in order to configure each macrocell with a large number of neighbours. However, sharing identification codes (e.g. scrambling codes) for the pilot signals of the picocells results in a target ambiguity and prevents the mobile station in uniquely identifying a potential handover target .

Hence, an improved radio access network would be advantageous and in particular a network allowing increased flexibility, improved addressing, increased address scope, secure operation, improved handovers, improved support for large numbers of underlay cells, improved suitability for large numbers of potential handover target cells, improved suitability for underlay/overlay handovers, reduced neighbour lists, increased practicality, reduced measurement requirements and/or improved performance would be advantageous .

Summary of the Invention

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to a first aspect of the invention there is provided a radio access network comprising: an access point having an access point network address and being arranged to support at least a first mobile node over a radio air interface; access proxy means having an access proxy network address; registration means coupled to the access proxy means and the access point and being arranged to register the first mobile node for the access point in response to receiving a registration message for the first mobile node, the registration comprising an identification check of a subscription identity of the first mobile node; the access proxy comprising means for generating a first address binding between the access point network address and the subscription identity and the access proxy network address in response to the registration of the first mobile node.

The invention may allow improved operation in a radio access network. In particular, the invention may allow an increased addressing while ensuring secure operation. The invention may in some embodiments facilitate handover. The invention may in some embodiments facilitate or enable support of large numbers of underlay cells.

The invention may e.g. allow improved handover in a cellular communication system. In particular, the invention may facilitate or improve handovers in systems wherein a remote station may have a large number of potential handover targets. In particular, the invention may allow a reduced number of measurements being required by a remote station to determine a suitable handover target, may allow reduced neighbour lists and/or may reduce the required number of scrambling codes.

The invention may in particular e.g. allow efficient addressing of a number of access points exceeding an address scope of the network and/or efficient addressing of access points with shared pilot signal identities.

The access point may specifically be a base station or other equipment providing the air interface communication in underlay cells of a macrocell layer. The underlay cells may e.g. be micro-, pico- and/or femto-cells. The radio access network may be a Wireless Local Area Network or a cellular communication system such as the Global System for Mobile communication (GSM) or the Universal Mobile Telecommunication System (UMTS) . The mobile node may for example be a User Equipment or a mobile communication unit, e.g. of a 3rd generation cellular communication system such as UMTS.

The access proxy means may be part of a network controller such as a RNC or Base Station Controller (BSC) . The access proxy means may have an increased fan- out such that a single access proxy network address is translated into a plurality of access point addresses.

According to another aspect of the invention, there is provided a method of operation in radio access network including: an access point having an access point network address and being arranged to support at least a first mobile node over a radio air interface; access proxy means having an access proxy network address; the method comprising: registering the first mobile node for the access point, the registration comprising an identification check of a subscription identity of the first mobile node; and generating a first address binding between the access point network address and the subscription identity and the access proxy network address in response to the registration of the first mobile node.

These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment (s) described hereinafter.

Brief Description of the Drawings Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 illustrates an example of a cellular communication system in accordance with some embodiments of the invention;

FIG. 2 illustrates an example of an access proxy in accordance with some embodiments of the invention; and

FIG. 3 illustrates an example of method of operation in a radio access network in accordance with some embodiments of the invention.

Detailed Description of Some Embodiments of the Invention

The following description focuses on embodiments of the invention applicable to a CDMA cellular communication system and in particular to a 3^rd Generation Cellular communication system such as a UMTS System. However, it will be appreciated that the invention is not limited to this application but may be applied to many other networks including radio access functionality.

FIG. 1 illustrates an example of radio access network which in the specific example is a cellular communication system. In the system, a macro-layer is formed by macrocells supported by base stations. Furthermore, an underlay layer of picocells are supported by a large number of access points corresponding to picocell base stations. Specifically, each access point may have an intended coverage of a single house or dwelling, and for a typical macrocell coverage area of 10 to 30 km there may be hundreds or even thousands of picocells each supported by an individual access point.

In the system, the macro base stations each have a cell separation code in the form of a scrambling code that is unique within a given region which e.g. may be a reuse area for the cell scrambling codes. Specifically the macro base stations have an assigned scrambling code which is unique within the reuse area such that a set of defined neighbours for each cell always have unique cell scrambling codes. Furthermore, each macro-cell base station has a unique hierarchical network address given by a unique base station ID for a given serving RNC, which itself has a unique RNC ID for a given MSC. Furthermore, each MSC has a unique identity in the network .

Accordingly, the neighbour lists transmitted by the base stations comprise indications of macro-cells which all have different cell scrambling codes. Furthermore, for each macro neighbour cell, a unique network address of the base station supporting the macro cell can be determined from the detection of a specific neighbour cell pilot signal. Accordingly, a handover to a target macro cell may be initiated with an explicit and unique identification of the handover target base station.

In contrast, the access points (which in the specific example are base stations supporting picocells) use a scrambling code which is shared between a plurality of access points within the reuse area and specifically a given neighbour list may comprise indications of shared cell scrambling codes for a plurality of underlay cells that are all considered as neighbours/potential handover targets for the current cell. By sharing a scrambling code between a plurality of access points, a much reduced number of scrambling codes are required by the system. Furthermore, by keeping the number of scrambling codes low, the number of scrambling codes that must be evaluated by the remote station for handover determination can be reduced substantially thereby reducing the measurement time, power consumption and/or complexity of the remote station.

Also, for the access points there is no unique network address associated with each scrambling code. Rather, a mobile node detecting a scrambling code does not uniquely identify a given target access point for a handover but at best identifies only a network level address shared by a potentially large number of access points.

In some embodiments, all access points within a coverage area supported by a single RNC use the same scrambling code. However, it will be appreciated that in other embodiments, a plurality of shared scrambling codes may be available for the access points. Therefore, the access points may be divided into a number of groups with the access points of each group sharing a scrambling code but with different scrambling codes being used for different groups. In such embodiments, the scrambling codes may be allocated to the access points such that a reuse pattern is established with the interference between picocells having the same shared scrambling code being reduced or minimised. In the specific example of FIG. 1, one macro-base station 101 which supports a macrocell with a typical coverage area of 10-30 kilometres is illustrated. The macro base station 101 is coupled to a macro RNC 103 which is furthermore coupled to other macro base stations (not shown) . The macro RNC 103 is furthermore coupled to a core network 105 which interfaces to other radio access networks and RNCs. In the example, the macro RNC 103 is coupled to a first MSC 107 which is further coupled to a second MSC 109 serving a different set of RNCs than the first MSC 107.

The system furthermore comprises a large number of access points 111, 113 (for clarity only three access points are illustrated in FIG. 1). Each of the access points 109 supports a picocell having a coverage area of typically 10 to 50 meters. The access points 109 implement the required functionality of a UMTS base station in order to support UMTS communications within the picocell. However, in contrast to conventional UMTS base stations, the access points 109 use a common shared scrambling code.

Furthermore, in the example, each of the access points comprises RNC functionality such that the network interface to the access points 111, 113 is the same as to an RNC. In other words, each access point 111, 113 appears as an RNC to the network and each access point 111, 113 has an individual RNC identity (RNC ID) .

However, the address scope of hierarchical network addressing used in a cellular communication system such as UMTS is severely limited. In particular, the RNC address space is typically very limited (e.g. in UMTS only 4096 RNC IDs are available) , and therefore the required number of RNC addresses may significantly exceed the available number of unique RNC addresses when a large number of access points using RNC addressing are present.

In the system of FIG. 1, the network comprises an access proxy 115 coupled between the second MSC 109 and the access points 111, 113. The access proxy 115 provides address proxy functionality for the access points 111,

113 such that a lower number of RNC addresses may be used for addressing the access points 111, 113.

In the specific example, the access proxy 115 provides a single network address to the cellular network for all the access points 111, 113. Thus, a single RNC ID allocated to the access proxy 115 is shared by a large number of access points 111, 113. Thus, in the example, the access points 111, 113 are all proxied by the access proxy 107 such that the same RNC ID is shared on the northbound side of the access network (i.e. towards the core network 105 and specifically the second MSC 109) . The access proxy 115 provides a binding between the northbound side RNC ID which is shared by all access points 109 and a specific access point address on the southbound side of the access proxy 115 (i.e. towards the access points 109) .

Although an access proxy providing a limited number of (northbound side) addresses shared by a larger number of (southbound side) addresses provides an efficient and useful expansion of the available address space thereby allowing flexible and efficient architectures and systems with extremely large numbers of access points, a number of issues must be resolved.

A critical issue in a system such as that of FIG. 1 is how to establish an efficient and reliable proxy operation and in particular how to setup address bindings allowing data to be routed correctly through the access proxy 115.

Specifically, an efficient approach for enabling or facilitating handovers based on a non-unique target addressing must be established. In particular, it is important that a handover process can be executed efficiently and the correct bindings can be established despite a limited or non-unique target identification by the source network elements.

For example, in the system of FIG. 1, a mobile node 117 may initially be served by the macro base station 101. When monitoring the pilot signals (CPICHs) of the neighbour list, the mobile node 117 may detect the pilot signal of a first access point 111 of the access points 111, 113. The scrambling code may be decoded to provide identification data for the first access point 111. However, as the scrambling code is used by a large number of access points 111, 113, it is not possible for the source system to uniquely determine the identity of the first access point 111. Furthermore, as the access proxy 115 provides a single RNC ID shared by all the access points 111, 113, no unique 3GPP addressing of the first access point 111 is possible by the handover source system (i.e. by the mobile node 117, the macro base station 101 or the macro RNC 103 in the example) . In the specific example, the scrambling code may be uniquely associated with the RNC ID of the access proxy 115. In this case, the macro RNC 103 may determine the preference for a handover to the first access point 111 (based on the reported pilot signal measurements from the mobile node 117) and may accordingly transmit a handover request message addressed to the access proxy 115. However, when this handover request message is received at the access proxy 115, the access proxy 115 need to determine which access point 111, 113 the handover is intended for before the message can be forwarded to the correct access point 111, 113.

In the system of FIG. 1, the access proxy 115 is coupled to a registration server 119 which is further coupled to the access points 111, 113. It will be appreciated that although FIG. 1 illustrates direct connections between the registration server 119 and the address proxy 115 and access points 111, 113, the couplings may be via intermediate network nodes. For example, the registration server 119 may be coupled to the access points 111, 113 via the address proxy 115. An address binding is generated by the access proxy 115 in response to a secure registration of the mobile node 117 at the registration server .

Specifically, a secure registration process is initiated by the mobile node 117 accessing the first access point 111 before the mobile node 117 has been handed over to this. For example, the mobile node 117 may send a registration request message to the first access point 111 using a suitable uplink access channel when it detects the pilot signal from the first access point 111.

In response, the first access point 111 may send a registration request to the registration server 119. The registration may then proceed to perform a check of the subscription identity of the mobile node 111. For example, it may be verified that a subscription identity (e.g. an IMSI or a telephone number) is allowed to use the first access point 111 for communication. If the subscription check succeeds, the registration server 119 provides information to the access proxy 115 indicating that the subscription identity of the mobile node 117 has been registered for the first access point 111. The access point address (e.g. the RNC ID) of the first access point 111 is also provided to the address proxy 115.

In response, the access proxy 115 proceeds to create a binding of the northbound side shared address, the mobile node subscription identity and the first access point 111 address. Accordingly, if the access proxy 115 receives a handover request addressed to the access proxy 115 and including an indication of the subscription identity, the access proxy 115 forwards this handover request to the first access point 111. The handover procedure can then continue as a normal handover process between the source network elements (e.g. the macro RNC 103) and the first access point 111 with the access proxy 115 forwarding messages in accordance with the binding. As part of the handover process, the user data plane routing following the handover is established. However, as the unique identification of the handover target (i.e. the first access point 111) has been established at this point, a unique addressing can easily be established.

Thus, in the described approach the binding in the access proxy 115 is set up in advance of a network handover request being received by the access proxy 115. The binding is set up based on the active registration of the mobile node 117 from the access point side. Accordingly, when a handover request is received for the shared proxy address, the use of the information obtained by a registration from the mobile node 117 allows the ambiguity to be resolved so that the message can be forwarded to the uniquely identified access point.

Thus, in the system of FIG. 1, the access proxy 115 allows an extension of the address scope while providing a secure an efficient means of resolving ambiguities arising from sharing of addresses and/or pilot signal cell identifications. Thus, in particular, the system of FIG. 1 may provide a high degree of flexibility and may provide efficient performance, and in particular improved handover performance, for a system with a very large number of access points.

It will be appreciated that although the described examples focus on examples where each access point is associated with an RNC address, the described approach and principles also apply to other scenarios and in particular to access proxying at other levels of the addressing hierarchy.

In the previous example, a handover request message identifying the actual subscription identity of the mobile node 117 was generated by a network element serving the mobile node 117 prior to the handover. The subscription identity may be considered an identity which is statically associated with the subscription used by the mobile node 117. For example, the subscription identity may be a telephone number allocated to a given subscriber or may e.g. be an IMSI allocated to the subscription used by the mobile node 117. For example, the mobile node 117 may be a mobile phone comprising a Subscriber Identity Module (SIM) including the IMSI.

Thus, the subscription identity is directly associated with the static subscription and is not a temporary network address or an address reflecting a hierarchical topology of the network. The use of the actual subscription identity rather than a network address allows a reliable and secure identification and registration of the mobile node 117.

Although, the previous description was based on the handover request message including the actual subscription identity, it will be appreciated that in other embodiments more indirect indications of the subscription identity may be provided with the handover request.

For example, the handover request may be generated by the macro RNC 103 based on the measurement reports received from the mobile node 117. However, e.g. for legacy reasons, it may be impractical for the macro RNC 103 to include the actual subscription identity. For example, the IMSI or telephone number of the first access point 111 may not be readily available. The handover request message may comprise a subscription identity indication which enables or facilitates the appropriate binding being determined at the access proxy 5 115.

For example, the macro RNC 103 may generate a location indication for the mobile node 117 at the time of the handover request. Specifically, the macro RNC 103 may

10 include a specific location estimate for the mobile node 117 in the handover request message. When the handover request message is received at the access proxy 115, the location estimate may be compared with the location of access points for the bindings which are currently set

15 up, and the binding corresponding to the closest access point to the mobile node 117 may be used.

FIG. 2 illustrates an example of the access proxy 115 arranged to use indirect information to identify the 20 correct binding for an incoming handover request message.

The access proxy 115 comprises a registration interface 201 which interfaces the access proxy 115 to the registration server 119 and receives information of

25 mobile node registrations therefrom. In addition, when a registration of a mobile node has been successfully accomplished, the registration server 119 also transmits other data that may allow binding resolution for a received mobility message. For example, the access proxy

30 115 may receive location information for the access point as well as information provided by the mobile node 117 such as information of a previous serving cell etc. The registration interface 201 is coupled to a binding processor 203 which establishes the binding of the shared proxy network address and the subscription identity and the individual access point network address. The binding processor 203 further stores additional information for the binding, such as a location of the access point of the binding (e.g. the first access point 111 in the specific example) .

The access proxy 115 further comprises a core network interface 205 that interfaces to the second MSC 109 which receives the handover request message.

The core network interface 205 is coupled to an information extraction processor 207 which extracts the subscription identity indication from the received handover request message and feeds it to the binding processor 203.

The binding processor 203 compares the subscription identity indication to the stored additional information and identifies a suitable binding. For example, the binding processor 203 can compare a location estimate to the locations of the access points of the established bindings and select the binding with the closest access point .

The binding processor 203 and the information extraction processor 207 are coupled to an address translation processor 207 which receives the handover request message and the identified access point network address. The address translation processor 207 is coupled to an access point interface 211 through which the handover request message is forwarded to the identified access point.

The handover process then proceeds using the established binding between the shared proxy network address and the identified access point address.

In the previous examples, the subscription identity indication is included by the macro RNC 103 serving the mobile node 117 prior to the handover. However, it will be appreciated that information may be included elsewhere such as other network elements serving the mobile node 117 prior to the handover. For example, the macro base station 101 and/or the first MSC 107 may include suitable subscription identity indications.

It will be appreciated that any suitable subscription identity indication may be used without detracting from the invention. Examples of subscription identity indications that can be used in a 3GPP cellular communication system will be described in the following but it will be appreciated that many other types of information can alternatively or additionally be used and that a given embodiment may use more than one type of subscription identity indication data.

In some embodiments, the subscription identity indication may include a Common Pilot CHannel, CPICH, for a current serving cell for the first mobile node. The CPICH may comprise an identification of the serving cell and this identification may be used to identify the correct binding. For example, if the access proxy 115 serves access points for underlay cells in different macro cells, the CPICH of the serving cell can be used to identify or narrow the possible target access points.

In some embodiments, the subscription identity indication may include an identity of a macro-cell associated with the target access point. For example, it may be possible to determine the macro cell associated with the access point (e.g. all access points within a given macro cell may use the same CPICH and the identification of this can provide the originating RNC (e.g. the macro RNC 103) with information of the associated macro cell. Accordingly, if e.g. the access proxy 115 serves access points for underlay cells in different macro cells, the CPICH of the serving cell can be used to identify or narrow the possible target access points.

In some embodiments, the subscription identity indication may include a UMTS, Terrestrial Radio Access Network, Cell-ID, UTRAN Registration Area, URA, Location Area, LAC or Routing Area, RAC. For example, when this Mobility location of a mobile is provided from the Source network element where a mobile is currently camped, as part of a mobility procedure to move to coverage at the access point (Handover or Relocation) is in progress. Under these circumstances this supplied source information together with the IMSI of the mobile may be used to index at the address translation device a matching positional set of information that identifies a possible target Access Point that the mobile (known by IMSI) has previously registered at and the mobility procedure then progresses towards this Access Point. In some embodiments, the subscription identity indication may include a network controller address for a network controller currently serving the first mobile node. For example, the handover request message may include an indication of the ID of the macro base station 101 or macro RNC 103. E.g., if the access proxy 115 serves access points for underlay cells in different macro cells, the ID of the serving base station or RNC can be used to determine the identity of the current cell and thus to identify or narrow the possible target access points .

The previous examples have described the approach with reference to a handover request message. However, it will be appreciated that the principles apply to many different messages including other mobility messages such as those associated with Cell Updating, Handover, Relocation and shared Network Access and associated updates to the core network such as Location Area updates and Routing Area Updates.

In some embodiments, the network address of the access proxy 115 may not be uniquely identified by the pilot signal scrambling code transmitted by the access points. In such cases, the network elements currently serving the mobile node 117 may not be able to uniquely identify an address of the access proxy 115. For example, the same scrambling code may be associated with two or more access proxies. In such an embodiment, the core network may use further information to direct the handover request message towards the correct access proxy 115. For example, one or more network elements may use the subscription identity indication to direct the handover request message towards the correct access proxy.

As a specific example, the subscription identity indication may include a location estimate for the mobile node (e.g. merely an indication of the current serving cell) . If the detected scrambling code is associated with two access proxies, the location indication may be used to route the message to the proxy which serves access points closest to the current location estimate.

In some embodiments, the handover request message may be generated in response to a detection of a pilot signal which is not associated with a neighbour macro cell for the mobile node. For example, if a strong pilot signal is detected which cannot originate from a macro cell base station (known from the neighbour allocation and the frequency plan) , the serving RNC can generate a handover request message which includes additional information for the mobile, such as the current serving cell, a mobile node location etc. The message can be sent to the serving MSC which can use this information to direct the handover request message towards the appropriate access proxy. The access proxy can furthermore use the information to detect if a binding has been set op for a mobile node which has registered with associated information matching the information of the handover request message.

It will be appreciated that any suitable approach for registering a mobile node for an access point can be used. For example, the mobile node may send an attach request to the access point using a cellular access channel (e.g. it may send a RACH message) . In response, the access point may initiate a registration process for the mobile node.

As another example, the attach request may be transmitted using a different air interface than that used to communicate the user data with the mobile node. For example, the attach request may be transmitted using a Bluetooth™ or a Wireless Local Area Network (WLAN) air interface. In such examples, the access point may thus initiate the registration of the mobile node for cellular service via an access request communicated using a different air interface than the one that will be used for user plane traffic (i.e. the cellular air interface). Thus, both the access points and the mobile node may be multi-mode capable.

FIG. 3 illustrates an example of method of operation in a radio access network which includes an access point having an access point network address and being arranged to support at least a first mobile node over a radio air interface; and an access proxy having an access proxy network address.

The method starts in step 301 wherein the first mobile node is registered for the access point. The registration process comprises an identification check of a subscription identity of the first mobile node.

Step 301 is followed by step 303 wherein a first address binding is generated between the access point network address and the access proxy network address and the subscription identity in response to the registration of the first mobile node. It will be appreciated that the above description for clarity has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors .

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term comprising does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also the inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be worked and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order.

Claims

1. A radio access network comprising: an access point having an access point network address and being arranged to support at least a first mobile node over a radio air interface; access proxy means having an access proxy network address; registration means coupled to the access proxy means and the access point and being arranged to register the first mobile node for the access point in response to receiving a registration message for the first mobile node, the registration comprising an identification check of a subscription identity of the first mobile node; the access proxy comprising means for generating a first address binding between the access point network address and the subscription identity and the access proxy network address in response to the registration of the first mobile node.

2. The radio access network of claim 1 wherein the access proxy means further comprises: means for receiving a message for the first mobile node, the data packet comprising a subscription identity indication for the first mobile node; means for determining the access point network address in response to the first address binding and the subscription identity indication; and means for forwarding the message to the access point using the access point network address.

3. The radio access network of claim 2 wherein the radio access network furthermore comprises a network element serving the first mobile node prior to a handover to the access point, the network element being arranged to include the subscription identity indication in the message .

4. The radio access network of claim 2 wherein a network element serving the first mobile node prior to a handover to the access point is arranged to determine the access proxy network address in response to the subscription identity indication.

5. The radio access network of claim 2 wherein the message is a mobility message that is a handover message for a handover of the first mobile node from a macro cell to an underlay cell supported by the first access point.

6. The radio access network of claim 5 wherein a network element supporting the macro cell is arranged to generate the mobility message in response to receiving a detection indication from the first mobile node; the detection indication indicating a detection of a pilot signal not associated with a macro cell neighbour of the first macro cell.

7. The radio access network of claim 5 wherein the mobility message is a handover request message comprising a target handover address shared by a plurality of access points supported by the access proxy means.

8. The radio access network of claim 1 wherein the access point further comprises: means for receiving an attach request from the mobile node over a first air interface different than a second air interface used for user data communication from the mobile node; and means for initiating the registration in response to receiving the attach request.

9. The radio access network of claim 1 wherein the access proxy is arranged to bind the access proxy network address to a plurality of access point network addresses.

10. A method of operation in radio access network including : an access point having an access point network address and being arranged to support at least a first mobile node over a radio air interface; access proxy means having an access proxy network address; the method comprising registering the first mobile node for the access point, the registration comprising an identification check of a subscription identity of the first mobile node; and generating a first address binding between the access point network address and the subscription identity and the access proxy network address in response to the registration of the first mobile node.