WO2014079486A1

WO2014079486A1 - Supporting moving relay nodes

Info

Publication number: WO2014079486A1
Application number: PCT/EP2012/073206
Authority: WO
Inventors: Vinh Van Phan; Ling Yu; Kari Veikko Horneman
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2012-11-21
Filing date: 2012-11-21
Publication date: 2014-05-30

Abstract

There is provided support for moving relay nodes in a communications net- work. A node of a backhaul network terminating a connection of user equipment connected to the backhaul network via a relay node is determined at a node terminating a control and management connection of the relay node in the backhaul network. Information identifying the node terminating the control and management connection of the relay node is sent to the node terminating the connection of the user equipment. Switching of a wireless link of the relay node to the backhaul network is performed without connections associated with the user equipment connected by the relay node. After completion of the switching, information defining the connection of the user equipment on the wireless link is transmitted to the new node providing the wireless link to the relay node.

Description

DESCRIPTION

TITLE SUPPORTING MOVING RELAY NODES FIELD

The present invention relates to wireless communications networks and particularly to wireless communications networks including relay nodes connected to a backhaul network over a wireless link.

BACKGROUND

In radio communication networks, such as mobile communications network complying to the Long Term Evolution (LTE) or the LTE-Advanced (LTE-A) of the 3^rd Generation Partnership Project (3GPP), radio coverage is provided by evolved NodeBs (eNBs). However, it may be that the coverage areas of the eNBs are insufficient to enable certain user equipment (UE) to communicate properly with any eNB. In order to enable the UE to communicate, the network deployment may be extended by so called Relay Nodes (RN).

The Relay Nodes are low power base stations that will provide enhanced cov- erage and capacity at cell edges and it can also be used to connect to remote areas without fiber connection.

The Relay Node is connected to the Donor eNB (DeNB) via a radio interface, Un, which is a modification of the E-UTRAN air interface Uu. Hence in the Donor cell the radio resources are shared between UE served directly by the DeNB and the Relay Nodes.

Mobility of the UE causes timely variance in capacity requirement in the deployed networks. The need for high capacity in a specific area and the mobility of the users is combined in populated public transportation for example passenger trains, ferries or cruise ships.

However, the current 3GPP Release 10 specifications specify a fixed relay architecture, which provides deployment of RNs in fixed locations. Due to the fixed nature of the architecture, it is not suitable for extension of network capacity in scenarios such as the populated public transportation, where increased capacity is required from the overlaying network onboard a moving vehicle. BRIEF DESCRIPTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to a more detailed description that is presented later.

Various embodiments comprise method(s), apparatus(es), a computer program product and a system as defined in the independent claims. Further embodiments are disclosed in the dependent claims.

According to an aspect of the invention there is provided a method comprising, determining a node terminating a control and management connection of a relay node in a backhaul network, said connection comprising a wireless link, identifying, at the node terminating the control and management connection of the relay node, user equipment con- nected to the backhaul network via the relay node, determining, at the node terminating the control and management connection of the relay node in the backhaul network, a node of the backhaul network terminating a connection of the user equipment.

According to an aspect of the invention there is provided a method comprising, connecting a relay node to a backhaul network by a wireless link, determining a node ter- minating a control and management connection of the relay node in the backhaul network, connecting user equipment to the backhaul network via the relay node, determining a node of the backhaul network terminating a control and management connection of the user equipment attached to the backhaul network via the wireless link, and transmitting information identifying the node terminating the control and management connection of the relay node to the node terminating the connection of the user equipment.

According to an aspect of the invention there is provided a method comprising, providing user equipment a connection on a first wireless link to a source node towards a backhaul network, switching the first wireless link to a second wireless link to a target node, without connections associated with the user equipment, transmitting, to the target node, after completion of the switching, information defining the connection of the user equipment on the wireless link.

According to another aspect of the invention there is provided an apparatus comprising at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform a method according to an aspect.

According to another aspect of the invention there is provided an apparatus comprising means configured to perform a method according to an aspect.

According to another aspect of the invention there is provided a computer program product comprising executable code that when executed, cause execution of functions of a method according to an aspect.

According to another aspect of the invention there is provided a system comprising one or more apparatuses according to an aspect.

Although the various aspects, embodiments and features of the invention are recited independently, it should be appreciated that all combinations of the various aspects, embodiments and features of the invention are possible and within the scope of the present invention as claimed.

Some embodiments may provide mobility to moving relay nodes. In this way connections of the relay nodes to a core network and UE connected to the core network via the relay nodes may be provided, when the relay node moves from a coverage area of one base station to a coverage area of another base station.

Further advantages will become apparent from the accompanying description.

BRIEF DESCRI PTION OF THE DRAWI NGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which

Figure 1 illustrates a communications network supporting mobility of relay nodes according to an embodiment;

Figure 2 illustrates an apparatus suitable to implement any of the described embodiments;

Figure 3a illustrates information flow between nodes of a communications network supporting mobility of relay nodes upon attachment of a relay node according to an embodiment; and

Figure 3b illustrates information flow between nodes of a communications network supporting mobility of relay nodes upon handover of a relay node according to an embodiment.

DETAILED DESCRIPTION

Example embodiments of the present invention will now be de-scribed more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Although the specification may refer to "an", "one", or "some" em- bodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Like reference numerals refer to like elements throughout.

Some embodiments provide support for mobility of relay nodes and User

Equipment, UE, deployed aboard moving vehicles, when the UE is served by or camping in the moving RN or cell thereof. As the RN is moved, its wireless link towards a backhaul network changes and also a node terminating connections of the RN in the backhaul network may change. With the changing connectivity of the RN, also backhaul connections of the UE connected to the RN are changed. For UE served by the RN this means that a path switch is executed to maintain attachment of the UE to the backhaul network, i.e. to a node terminating a connection of the UE, after handover of the RN. For UE camping in idle mode under the RN, this means performing a location update of the UE after handover of the RN to keep the UE reachable by the backhaul network.

Embodiments are applicable to any base station, relay node, user equipment

(UE), server, corresponding component, and/or to any communication system or any combination of different communication systems that support required functionalities.

Embodiments of the present invention may be implemented in various devices and systems, where radio signals may be used to carry data between devices such as handheld and infrastructure communications devices. Examples of the devices comprise user equipment (UE), a relay node (RN), a mobile phone, a base station (BS), a Node-B (NB), an evolved NB (eNB), a Donor eNB (DeNB), a Relay Node (RN) and a server, for example. In some embodiments UE may operate as a RN for other UE.

The protocols used, the specifications of communication systems, servers and user terminals, especially in wireless communication, develop rapidly. Such development may require extra changes to an embodiment. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, embodiments.

User equipment (UE) may refer to any user communication device. A term "user equipment" as used herein may refer to any device having a communication capability, such as a wireless mobile terminal, a Personal Data Assistant (PDA), a smart phone, a personal computer (PC), a laptop computer, a desktop computer, etc. For example, the wireless communication terminal may be a TErrestrial Trunked RAdio (TETRA), an Universal Mobile Telecommunications System (UMTS), an LTE, LTE-A or Global System for Mobile Communications / Enhanced Data Rates for GSM Evolution (GSM/EDGE) smart mobile terminal. Many different radio protocols to be used in communications systems exist. Some examples of different communication systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E-UTRAN), long term evolution (LTE®, known also as E-UTRA), long term evolution advanced (LTE-A®), Wireless Local Area Network (WLAN) based on IEEE 802.11 stardard, worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS) and systems using ultra-wideband (UWB) technology. IEEE refers to the Institute of Electrical and Electronics Engineers. LTE and LTE-A are developed by the Third Generation Partnership Project 3GPP.

In the following, different exemplifying embodiments will be described using, as an example of an access architecture to which the embodiments may be applied, a radio access architecture based on long term evolution advanced (LTE Advanced, LTE-A), that is based on orthogonal frequency multiplexed access (OFDMA) in a downlink and a single-carrier frequency-division multiple access (SC-FDMA) in an uplink, without restrict- ing the embodiments to such an architecture, however. It is obvious for a person skilled in the art that the embodiments may also be applied to other kinds of communications networks having suitable means by adjusting parameters and procedures appropriately.

In the context of LTE-A a base station controlling communications within its coverage area (including relayed connections) is called eNB (also known as donor eNB in the art), while a node relaying connections to/from the eNB under the control of the eNB is called a Relay Node, RN.

The current LTE-A Release 10 specifications do not consider mobility of RNs. In the following embodiments, when a RN moves, its wireless connection towards a backhaul network is switched from one DeNB to another as the RN moves between their cov- erage areas. In this way the RN may be connected to the DeNB under which coverage area it is located. Accordingly, in the switching a handover of the RN from a source DeNB to a target DeNB is performed.

It should be appreciated that embodiments described herein may be applied to not only access networks including DeNBs connected to RNs on wireless links but to ac- cess networks in general that include nodes providing wireless access to UE, wherein the nodes are connected by wireless connections to a backhaul network, e.g. towards a core network.

Figure 1 illustrates a simplified view of a communication environment only showing some elements and functional entities, all being logical units whose implementa- tion may differ from what is shown. The connections shown in Figure 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the systems also comprise other functions and structures. It should be appre- ciated that the functions, structures, elements and the protocols used in or for communication are irrelevant to the actual invention. Therefore, they need not to be discussed in more detail here.

In the example of Figure 1 , a radio system based on long term evolution ad- vanced (LTE Advanced, LTE-A) network elements is shown. However, the embodiments described in these examples are not limited to the LTE-A radio systems but can also be implemented in other radio systems.

Figure 1 shows DeNBs 102 and 104 connected to a Core Network, CN, 110 of a communication system. The DeNBs are connected to each other over an X2 interface and to the CN over an S1 interface. The DeNBs provide radio access to the RN 106, when the RN is located within their respective coverage areas. The RN connects to the DeNB that provides access to the RN, over a wireless radio link. The RN connects to the CN on a control and management connection, for example a control plane connection, via the wireless link. The control and management connection may be established upon RN acti- vation, where the RN becomes an active serving node in a radio access network of the communications system. The control and management connection is terminated at the CN in MME_RN 110 serving the RN. The MME_RN may be preselected and pre-configured by the communications system so that upon establishment of a radio access connection for the RN, the RN is directed or re-directed to the selected MME_RN.

The RN provides radio access to UE 108 under the control of the DeNB. The

RN may be moving from a coverage area of one DeNB to a coverage area of another DeNB, for example from DeNB 102 to DeNB 104. The RN may be located for example in a moving vehicle, including but not limited to a train, a bus, a ship, or an aircraft. The UE on board the vehicle with the RN may connect to the RN on a wireless connection, for example on a radio bearer.

The DeNB may allocate resources to the RN. The resources may comprise for example one or more time slots and/or frequencies, that the RN uses for relaying between the UE and the wireless link to the DeNB. The wireless link between the RN and the DeNB connects the UE under the RN towards the CN. The UE connects to the CN via the RN and DeNB on a control and management connection that is terminated in the CN at a

Mobility Management Entity 114 serving the UE, MME_UE. The UE may also connect to the CN via the RN and the DeNB on a user plane connection that is terminated in a Serving- Gateway 112 serving the UE, S-GW_UE. The S-GW_UE and the MME_UE are connected over an interface S11.

In an embodiment a Mobility Management Entity serving the RN, MME_RN connects to one or more nodes of the CN terminating the connections of the UE connected to the CN via the RN. User plane connections of the UE are terminated by a S-GW_UE and control plane connections of the UE are terminated by a MME_UE. Accordingly, depending on the established connections of the UE, the terminating nodes include a MME_UE or both a MMEUE and a S-GW_UE. The interface between the terminating nodes of the RN and the UE is illustrated by item 116. The interface between the terminating nodes provides the MME_RN to inform the connected nodes about a mobility attachment of the moving RN, e.g. informing an attached/connected DeNB. Also the MME_UE may inform the MME_RN about an attachment of UE provided that information about the serving MME_RN is informed to the MMEUE during UE attachment.

In some embodiments, a donor system or a Donor eNB may refer to a system whose resources are allocated to a RN. The donor system may be a network of an operator, for example. The RN may be for example a RN in a group of interconnected RNs. The RN may connect wirelessly to the donor system on a relay link or a wireless-backhaul connection provided by the donor system.

It should be appreciated that in different embodiments a core network may comprise a backhaul network encompassing a transport network between cell sites and associated controller, gateway sites or base stations. The backhaul network facilitates connection management and mobility management of the UE accessing the backhaul via the base stations.

Figure 2 is a block diagram of an apparatus 200 according to an embodiment of the invention. The apparatus may comprise a DeNB, a RN, MME, S-GW described in the embodiments. Although the apparatus has been depicted as one entity, different modules and memory may be implemented in one or more physical or logical entities. The apparatus may be a terminal suitable for operating as a termination point for telecommunication sessions. Examples of the apparatus include but are not limited to UE, a mobile phone, communicator, PDA, application server, a computer or a gateway.

The apparatus 200 comprises an interfacing unit 202, a central processing unit (CPU) 208, and a memory 210, that are all being electrically interconnected. The interfacing unit comprises an input 204 and an output unit 206 that provide, respectively, the input and output interfaces to the apparatus. The input and output units may be configured or arranged to send and receive data and/or messages according to one or more protocols used in the above-mentioned communication standards. The memory may comprise one or more applications that are executable by the CPU.

The CPU may comprise a set of registers, an arithmetic logic unit, and a control unit. The control unit is controlled by a sequence of program instructions transferred to the CPU from the memory. The control unit may contain a number of microinstructions for basic operations. The implementation of micro-instructions may vary, depending on the CPU design. The program instructions may be coded by a programming language, which may be a high-level programming language, such as C, Java, etc., or a low-level programming language, such as a machine language, or an assembler. The electronic digital computer may also have an operating system, which may provide system services to a computer program written with the program instructions. The memory may be a volatile or a non-volatile memory, for example EEPROM, ROM, PROM, RAM, DRAM, SRAM, firmware, programmable logic, etc.

An embodiment provides a computer program embodied on a distribution medium, comprising program instructions which, when loaded into an electronic apparatus, cause the CPU to perform according to an embodiment of the present invention.

The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

The apparatus 200 may also be implemented as one or more integrated circuits, such as application-specific integrated circuits ASIC. Other hardware embodiments are also feasible, such as a circuit built of separate logic components. A hybrid of these different implementations is also feasible. When selecting the method of implementation, a person skilled in the art will consider the requirements set for the size and power consumption of the apparatus 200, necessary processing capacity, production costs, and production volumes, for example.

In an embodiment the input unit may provide circuitry for obtaining data, sig- nailing, signalling messages and/or transmissions to the apparatus. The obtaining may comprise receiving radio frequency signals from an antenna, for example. In another example the obtaining may comprise receiving baseband signals from an RF unit or a wired communications interface, e.g. an Ethernet interface. Accordingly, data, signalling, signalling messages and transmissions in embodiments of the present disclosure may be pro- vided as RF signals or baseband signals.

In an embodiment the output unit may provide circuitry for transmitting data, signalling, signalling messages and/or transmissions from the apparatus. The transmitting may comprise transmitting radio frequency signals from an antenna, for example. In another example the transmitting may comprise transmitting baseband signals to an RF unit or a wired communications interface, e.g. an Ethernet interface. Accordingly, data, signalling, signalling messages and transmissions in embodiments of the present disclosure may be provided as RF signals or baseband signals. Figure 3a illustrates information flow between nodes of a communications network supporting mobility of relay nodes upon attachment of a relay node according to an embodiment. The illustration of Figure 3a uses the architecture and nodes illustrated in Figure 1. The CN nodes terminating connections of the UE are illustrated by a network node MME_UE/S-GW_UE 316 combining the functionalities of the MME_UE and S-GW_UE, although the nodes may be implemented also separately as illustrated in Figure 1 . In the following the information flow and tasks executed by the nodes involved in the information flow is explained. In the illustrated information flow the RN 106 resides within the coverage area of the DeNB 102 and has established a wireless link to the DeNB. The wireless link may be established using procedures of a Radio Resource Control, RRC, protocol. Accordingly, the RN is identified on the wireless link by an identifier, a Radio Network Temporary Identifier, RNTI, assigned during the establishment of the wireless link. In the context of the LTE-A the wireless link may be referred to as a Radio Bearer, RB.

In 322, the DeNB serving the RN is provided information of a node terminating a control and management connection of the RN in the backhaul network. This may be performed by an attachment procedure of the RN to the CN, for example.

A typical attachment procedure comprises a RN requesting the attachment to a CN on the RRC connection to a DeNB. Then, the DeNB may request attachment of the RN over an S1 interface to a MME_RN, according to a procedure over the S1 interface em- ploying S1 Application Protocol, S1AP. Following the request, the MME_RN establishes a control plane connection and zero or more user plane connections for the RN. The connections may be identified by information identifying one or more nodes, e.g. MME_RN or S- GW_RN, terminating connections of the RN in the CN. This information may comprise an address, for example an Internet Protocol, IP, address. This information is transmitted by the MME_RN to the DeNB. The user plane connections are carried in tunnels between the

S-GW_RN and the DeNB, for example according to a GPRS Tunnelling Protocol, GTP. The tunnels may be identified by Tunnel Endpoint Identifiers, TEIDs, which may be transmitted to the DeNB together with the address of SG_W_RN. The information received at the DeNB may be included in a context of the RN at the DeNB.

In different embodiments a control plane connection between a MME and a

DeNB for the RN may be identified by an identifier associated with the control plane connection over an interface. One example of such an identifier comprises an S1 Application Protocol identifier, S1AP ID, identifying the control plane connection for the RN over the S1 interface between DeNB and MME_RN. A user plane connection between an S-GW_RN and DeNB for RN may be identified by TEIDs.

The DeNB serving the RN may provide 328a information of MME_RN to all connected MME/S-GW (which have the potential to be selected to serve UE connecting to the CN via RN). This may be performed during or after an attachment procedure of the RN to the CN, for example the attachment described in step 322 in Figure 3a.

It should be appreciated that the MME_RN serving the RN may be static or it may change as the RN moves from a service area of one MME_RN to another. In the static case the MME_RN is statically configured and unchanged, regardless of the mobility of the RN between DeNBs. In this case, the DeNB connected to the RN may not have a direct S1 connection to the MME_RN. However, the DeNB may be kept updated of the MME_RN information such as an Internet Protocol, IP, address of the MME_RN so that the DeNB can inform MME_UE of the MME_RN. In the case of the changing MME_RN, a source MME_RN trans- fers the context of the RN including that of UE served by the RN to a target MME_RN.

In 324, UE attaches to the CN via the RN. The attachment procedure of the UE may be preceded by the UE establishing a wireless connection to the RN, for example using procedures of a Radio Resource Control, RRC, protocol. Accordingly, the UE is identified on the wireless connection to the RN by an identifier, a Radio Network Tempo- rary Identifier, RNTI. In the context of the LTE-A the wireless link may be referred to as a Radio Bearer, RB. The RNTI of the UE may be used to identify a connection of the UE also on the wireless link between the RN and the DeNB.

In an embodiment, the RN assigns the UE a local RNTI that identifies the UE on the wireless link between the RN and the DeNB. The local RNTI may be for example the same as the RNTI of the UE used for communication between the UE and the RN or different. However, the UE does not need to know how the connection of the UE is addressed between the RN and the DeNB.

The attachment of the UE may follow the procedure explained above for the RN with the difference that the DeNB is involved in the procedure by relaying S1 interface signalling messages between the RN and the MME_UE. The information received from the

MMEUE including information, e.g. identifiers or IP addresses identifying one or more nodes terminating connections of the UE in the CN and possible TEID information may be used to establish a context of the UE at the RN.

The DeNB may derive information identifying the UE and information identify- ing one or more nodes, e.g. MME_UE and/or S-GW_UE, terminating connections of the UE in the CN, from signalling messages over the S1 interface between the UE and the MME_UE. In this way the DeNB may determine 326 that UE is connected to the CN via the RN. It should be appreciated that, the determining 326 of the UE may be made embedded in the attachment procedure, i.e. during the attachment procedure before its completion, or it may be performed as a separate step as illustrated in step 326.

After determining 326 the UE connecting via the RN, the DeNB may transmit 328b the MME_UE/S-GW_UE an address of the MME_RN. In this way when UE attaches to the network via RN with either Initial Attach or Tracking Area Update or Handover procedure, MMEUE may contact MME_RN to update 330 the context of the UE to MME_RN, for example to update information identifying the terminating nodes and TEID information. In case, the address of the MME_RN has been informed already with the attachment of the RN in 328a, the transmission of the address associated with the UE attachment may be omitted to avoid generating too much traffic.

In an embodiment, the DeNB serving the RN is provided information of a node terminating a control and management connection of the RN in the backhaul network by a Handover procedure or a Tracking Area Update. During or following these procedures the DeNB receives information identifying the UE and CN nodes terminating connections of the UE. This information is available to the DeNB serving the RN from signalling messages related to those procedures.

An embodiment concerns defining a set of nodes of a backhaul network, for example the CN for a relay node that is moving in geographical operating area. The nodes comprise more than one, for example two, three, four or more, nodes that terminate a connection of UE in the backhaul network. These nodes may comprise MME_UE for control plane connections and S-GW_UE for user plane connections. A DeNB connecting the RN to the CN may determine UE connected to the CN over the moving RN as described with steps 324 and 326 above. Then the DeNB may communicate 328a, 328b, with the defined set of MMEUE to update information identifying the MME_RN to the MME_UE and/or S-GW_UE and to receive updates from the MME_UE and S-GW_UE regarding the MME_UE terminating the connection of the UE. In this way updates of the MME_RN address may be sent to all MME_UE that may be used to serve UE in the geographical region of movement of the RN. This is especially advantageous in usage scenarios of moving RNs, where RNs move in substantially limited geographical regions for exams in trains operating a specific route, for example in a country, a part of a country or between two cities.

It should be appreciated that although in Figure 3a, the deNB transmits in step 328a the address of the MME_RN to MME_UE after an attachment of the RN in 322 and in step 328b after an attachment of the UE in 324, the address of the MME_RN may be trans- mitted during the attachment of the RN in 322 or after the attachment of the RN, before the attachment of the UE in 324. Accordingly, the transmission of the address of the MME_RN may be triggered by attachment of the RN. In this way the transmission is specific to the attachment of the RN and the address is communicated to all MMEs/S-GWs connected to the deNB, so that a UE context update may be received from the MMEs/S-GWs, after or during UE attaches to the network and is served by MME/S-GW selected from the MMEs/S-GWs informed by the DeNB.

It should be further appreciated that although the step of transmitting 328b the address of the MME_RN to MME_UE is described as a separate step following the UE attachment 324, the address may be transmitted also during the attachment of the UE in 324. In this way, an attachment of the UE to the CN may trigger the transmission, to facilitate receiving UE context updates from the MMEs/S-GWs.

Figure 3b illustrates information flow between nodes of a communications network supporting mobility of relay nodes upon handover of a relay node according to an embodiment. The illustration of Figure 3b uses the architecture and nodes illustrated in Figure 1. The nodes terminating the connections of the UE are illustrated by a single node 316 similar to Figure 3a. In the following the information flow and tasks executed by the communicating entities involved in the information flow is explained. The handover of the RN is performed between a source DeNB 102 and a target DeNB 104. In the illustrated scenario, the RN 106 has established a wireless link to the source DeNB 102.

In 342 a signalling connection of the RN may be established between the source DeNB and the MME_RN. The signalling connection may comprise a control plane connection, for example an S1 Application Protocol connection that carries NAS signalling between the RN and the MME_RN. The signalling connection may be established by an attachment procedure of the RN described in step 322.

In 344 a measurement report is sent by the RN. The transmitting of measurement reports may be controlled by the DeNB, as conventional.

In steps 346 to 356 the first wireless link is switched to a second wireless link to a target node, without connections associated with UE connected to the RN. The RN may be serving zero or more UE. When UE are connected to the RN, a switch of the wireless link of the RN towards the DeNB causes also connections of the UE via the RN towards the DeNB to be switched. These connections include connections, for example a control plane and zero or more user plane connections relayed over the wireless link between the UE and the DeNB. The connections of the UE may be defined identifiers of the nodes in the CN that terminate the connections. For user plane connections TEID information is used to identify a tunnel endpoint, e.g. an endpoint at S-GW_UE. In this way, TEID identifies a connection of UE in the interface between eNB and S-GW. The information identifying the connection may be provided in a context of the UE stored in the RN.

In the following an example is described of implementing a switch of the wireless link between the source and the target DeNBs.

In 346 the DeNB determines that a handover of the RN should be performed. The source DeNB determines a target DeNB for the RN. In this example the target DeNB is the DeNB 104.

In 348, the source DeNB send a handover request to the target DeNB including information indicating handover of the RN to the target DeNB. In an embodiment the handover request includes information defining one or more connections of the RN to the CN without information of an associated UE served by the RN. The connections may include a control and management connection of the RN to the CN, for example a control plane connection, aggregated mobile backhaul connections, bearer services of a relay node and/or an Operation, Administration and Maintenance, OAM, connection of the RN, without a specific associated user equipment. The information defining a connection may include an identifier of the connection, for example an identifier/address of the MMRRM, S-GW_rn and/or S1APID/TEID information.

It should be appreciated that the RN may have further connections towards the CN, for example connections associated to UE connected to the RN and over the wireless link to the CN. However, information regarding these connections is pruned and the handover request is sent without information identifying the connections associated to UE connected to the RN. In this way no UE bearer contexts are needed to be transferred from the source DeNB to the target DeNB over X2. But U-plane data forwarding from the source DeNB to the target DeNB over X2 may follow, as conventional with handovers.

In an embodiment, the UE connected to the RN over a wireless connection is identified on the wireless link between the RN and the DeNB by a local RNTI. The local RNTI may comprise for example the same as the RNTI of the UE used for communication between the UE and the RN or different. However, the UE does not need to know how the connection of the UE is addressed between the RN and the DeNB. The local RNTI may be communicated to the target DeNB in the handover request. When a local RNTI is used on the wireless link between the RN and the DeNB, radio connections of the UEs served by RN may not be changed by a switch of the wireless link from one DeNB to another even if the DeNB providing the S1 interface changes. This facilitates UE context mapping in the DeNB.

In 350 the target DeNB determines to execute the switch of the RN without connections associated with the UE connected to the RN. The execution may comprise reserving resources for serving the RN on the basis of the information received in the handover request.

In 352 a handover response is sent to the source DeNB to indicate that the target DeNB is ready to receive the incoming handover.

In 354 a handover command is sent to the RN including information to access the target DeNB. The source DeNB forwards 355 data destined to the RN and/or UE to the target DeNB. The forwarded data may include data of the connections over the wire- less link including the connections associated with the UE connected to the RN. In this way data loss due to the switch of the wireless link may be reduced.

In 356 the RN transmits a handover complete message to the target DeNB to indicate that the handover procedure is complete. The target DeNB can now provide the connections switched in steps 348 and 350, including for example a control and management connection 358 of the RN to the MME_RN in a conventional manner similar to a handover of UE between eNBs described in 3GPP TS 36.300 V10.8.0 (2012-06); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA)

and Evolved Universal Terrestrial Radio Access Network

(E-UTRAN); Overall description; Stage 2; (Release 10), Section 10.2.2.

In steps 359, 360 and 364 the MME_RN triggers a path switch for UE connected to the CN via the RN. In 360 the MME_RN notifies the MME_UE and SGW_UE of the DeNB change and therefore MME_UE and SGW_UE can switch downlink data path to the target DeNB.

In 359 the MME_RN determines the MME_UE to be notified. This may be performed on the basis of stored UE contexts received for example in step 330 as described in Figure 3a. The MME_UEs to be notified may be determined on the basis of MME_UE addresses stored in the UE contexts.

In 360 the MME_RN informs the MME_UE about the handover of the RN for example by a message comprising information indicating a switch of the DeNB of the RN.

In 364 the path switch of the UE connected to the RN is executed for UE served by the RN. In the path switch the connections of the UE are switched from the source DeNB to the target DeNB. Accordingly, in the path switch the attachment of the UE to the CN is changed, whereby the context of the UE may be updated to reflect the change. The UE context may be updated to the MME_RN by MMEJJE as in Step 330 of Figure 3a.

In 362 the RN transmits to the target DeNB information defining connections of the user equipment connected to the RN on the wireless link towards the CN. In this way the target DeNB may be provided information of the connections of the UEs connected to the RN, although the definitions of the connections were not transferred to the target DeNB by the source DeNB in the handover in steps 346 to 356. Accordingly, in 362 the RN may provide the radio-bearer contexts of individual UEs including TEIDs and

MME_UE/S-GW_UE information to the target DeNB for possible bearer mapping, QoS mapping and packet scheduling on appropriate aggregated RN bearers.

In 366, the DeNB establishes a mapping of the connections between the MME_UE and/or S-GW_UE and the target DeNB and the wireless link towards the RN using the information received in 362.

It should be appreciated that the connections of the UE may comprise one or more uplink connections and/or one or more downlink connections. The uplink and down- link connections may be switched 364 separately in the network nodes that provide the connections, e.g. MME_UE/S-GW_UE and DeNB. Accordingly, the path switch of the uplink connections may be performed by the DeNB, in this example the target DeNB, when UE context transfer 362 is received comprising uplink context information. The target DeNB can establish a mapping 366 on the basis of the uplink context information to map the uplink connections of the UE to the right GTP tunnels towards the right S-GW_UE. The path switch of the downlink connections may be performed by the MME_UE/S-GW_UE, when information of the handover of the RN is received 360 from MME_RN.

In 368, the connections of the UE preceding the switch of the RN from the souce DeNB to the target DeNB have been re-established and the UE can communicate towards the CN nodes terminating its connections.

An embodiment comprises defining a set of nodes of a backhaul network, for example the CN, for a relay node that is moving in geographical operating area. The set of nodes may comprise more than one, for example two, three, four or more, nodes that can terminate a connection of UE in the backhaul network. These nodes may comprise MME_UE for control plane connections and S-GW_UE for user plane connections, for example. The RN may move within the geographical area from one DeNB to another, where a wireless link connecting the RN to a source DeNB is switched to the target DeNB, as the RN moves from a coverage area of one DeNB to a coverage area of another. After switch- ing of the wireless link, the target DeNB may inform the set of backhaul network nodes about the switch of the DeNB as illustrated in step 360. In this way the MME_RN serving the RN is known to the set of backhaul network nodes. This provides the set of backhaul network nodes to contact MME_RN to inform an attachment of UE. Accordingly, the MME_UE serving the attached UE may contact the MME_RN to update the necessary contexts of the attached UE. Accordingly, the MME_RN may receive from MME_UE information when the UE attaches to the network with either Initial Attach or Tracking Area Update or Handover procedure.

An embodiment comprises assigning an exclusive set of tunnel endpoint identifiers, TEIDs, to UE attached to the CN over a wireless link via a RN so that TEIDs of those active UEs served by RN may be kept unchanged regardless of the RN mobility.

The attachment may be performed as described in 324. The set of TEIDs may be reserved for moving RNs, where the wireless link is switched from a source DeNB to a target DeNB. A tunnel may be implemented using GTP, where a TEID field has a length of 32 bits, whereby the field may have over 4 billion possible values. A part of these values may be reserved for the moving RNs. In one example 1000 sets of TEIDS are formed from 32 bit TEID values, where each set comprises 10000 different TEID values. One such set may be assigned to the RN when the RN is attached and one or more tunnels are estab- lished between the DeNB serving the RN and S-GW_RN. In one example the MME_RN assigns a set and informs the assigned set to the S-GW_RN, for example when instructing the S- GW_RN to establish bearers for the RN as a part of a conventional bearer setup procedure. The MME_RN may also inform the MME_UE as a part of informing the attachment of the RN for example in step 328a illustrated in Figure 3a. By assigning the RN TEIDs from a set reserved to moving RNs, the TEIDs may be kept the same even if the wireless link of the RN to the DeNB is switched between DeNBs. Accordingly, since the RN uses reserved/assigned TEID sets to establish tunnels for the UE served by the RN, switching the RN from one DeNB to another does not require switching the TEIDs of the UE tunnel to- wards S-GW_UE.

It should be appreciated that it is not necessary to have any UE connected to the moving RN that is switched between DeNBs, but the handover may be performed without any UE connected to the CN via the RN. The MME_RN and the DeNB serving the RN may still communicate with MME_UE and S-GW_UE as described with Figures 3a and 3b to keep them updated about the current MME_RN. In this way the MME_RN is known to the UE when they attach to the CN.

The steps/points and related functions described above in Figures 3a and 3b are in no absolute chronological order, and some of the steps/points may be performed simultaneously or in an order differing from the given one. Other functions can also be executed between the steps/points or within the steps/points, and other signalling messages may be sent between the illustrated messages, and other transmissions of data may be sent between the illustrated transmissions. Some of the steps/points or part of the steps/points can also be left out or replaced by a corresponding step/point or part of the step/point.

The techniques described herein may be implemented by various means so that an apparatus implementing one or more functions described with an embodiment comprises not only prior art means, but also means for determining a node terminating a control and management connection of a relay node in a backhaul network, said connection comprising a wireless link, identifying, at the node terminating the control and man- agement connection of the relay node, user equipment connected to the backhaul network via the relay node, determining, at the node terminating the control and management connection of the relay node in the backhaul network, a node of the backhaul network terminating a connection of the user equipment.

According to another aspect the techniques described herein may be imple- mented by various means so that an apparatus implementing one or more functions described with an embodiment comprises not only prior art means, but also means for connecting a relay node to a backhaul network by a wireless link, determining a node termi- nating a control and management connection of the relay node in the backhaul network, connecting user equipment to the backhaul network via the relay node, determining a node of the backhaul network terminating a control and management connection of the user equipment attached to the backhaul network via the wireless link, and transmitting information identifying the node terminating the control and management connection of the relay node to the node terminating the connection of the user equipment.

According to another aspect the techniques described herein may be implemented by various means so that an apparatus implementing one or more functions described with an embodiment comprises not only prior art means, but also means for providing user equipment a connection on a first wireless link to a source node towards a backhaul network, switching the first wireless link to a second wireless link to a target node, without connections associated with the user equipment, transmitting, to the target node, after completion of the switching, information defining the connection of the user equipment on the wireless link.

More precisely, the various means comprise means for implementing functionality of a corresponding apparatus described with an embodiment and it may comprise separate means for each separate function, or means may be configured to perform two or more functions. For example, these techniques may be implemented in hardware (one or more apparatuses), firmware (one or more apparatuses), software (one or more mod- ules), or combinations thereof. For a firmware or software, implementation can be through modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in any suitable, processor/computer-readable data storage medium(s) or memory unit(s) or article(s) of manufacture and executed by one or more processors/computers. The data storage medium or the memory unit may be implemented within the processor/computer or external to the processor/computer, in which case it can be communicatively coupled to the processor/computer via various means as is known in the art.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1 . A method comprising:

determining a node terminating a control and management connection of a relay node in a backhaul network, said connection comprising a wireless link;

identifying, at the node terminating the control and management connection of the relay node, user equipment connected to the backhaul network via the relay node;

determining, at the node terminating the control and management connection of the relay node in the backhaul network, a node of the backhaul network terminating a connection of the user equipment.

2. A method according to claim 1 , comprising:

determining a switch of a node terminating the wireless link towards the backhaul network; and

transmitting an identifier of a new node terminating the wireless link towards the backhaul network, to the nodes terminating the connection of the user equipment.

3. A method according to claim 1 or 2, comprising:

receiving, at the node terminating the control and management connection of the relay node, information identifying the user equipment, when the user equipment at- taches to the backhaul network, said user equipment attached to the backhaul network preferably by an Initial Attach, Tracking Area Update or a Handover Procedure.

4. A method according to any one of the preceding claims,

defining a connection of the user equipment using tunnel end point identifiers, TEI DS;

assigning a set of tunnel endpoint identifiers to a relay node upon an attachment of the relay node to the communications network, and

informing the assigned set of tunnel end point identifiers to the node terminating connections of the user equipment.

5. A method comprising:

connecting a relay node to a backhaul network by a wireless link; determining a node terminating a control and management connection of the relay node in the backhaul network;

connecting user equipment to the backhaul network via the relay node;

determining a node of the backhaul network terminating a control and management connection of the user equipment attached to the backhaul network via the wire- less link; and

transmitting information identifying the node terminating the control and management connection of the relay node to the node terminating the connection of the user equipment.

6. A method according to claim 5, wherein a switch of a node terminating the wireless link in the backhaul network is executed without connections associated with the user equipment, comprising:

receiving information defining the connection of the user equipment on the wireless link before the switch, in response to the completion of the switch; and

connecting the user equipment to a node in the backhaul network over the switched wireless link on the basis of the received information.

7. A method comprising:

providing user equipment a connection on a first wireless link to a source node towards a backhaul network;

switching the first wireless link to a second wireless link to a target node, without connections associated with the user equipment;

transmitting, to the target node, after completion of the switching, information defining the connection of the user equipment on the wireless link.

8. A method according to any one of the preceding claims, wherein a connection of the user equipment on the wireless link is defined by information comprising radio bearer context of the user equipment, said information preferably comprising a Radio Network Temporary Identifier, RNTI.

9. A method according to any one of the preceding claims, wherein a switch of the wireless link between a source node and a target node, comprises a handover of one or more or a combination of a control plane connection, aggregated mobile backhaul con- nections, bearer services of a relay node or an Operation, Administration and Maintenance, OAM, connection of the relay node, without a specific associated user equipment context.

10. A method according to any one of the preceding claims, comprising:

connecting the user equipment to the relay node on a wireless link; identifying the user equipment on the wireless link between the relay node and the user equipment; identifying the connection of the user equipment on the wireless link towards the backhaul network;

mapping the wireless link between the relay node and the user equipment to the connection on the wireless link towards the backhaul network.

11 . A method according to any one of the preceding claims, wherein the wireless link is switched from a source access node of an access network to a target access node of the access network, said access nodes terminating the wireless link form the relay node towards the backhaul network.

12. A method according to any one of the preceding claims, wherein the relay node is moved within a geographical operating area comprising at least a part of service areas of a plurality of nodes terminating connections of the user equipment in the backhaul network, and the node terminating the control and management connection of the relay node communicates with the nodes terminating connections of the user equipment for informing an attachment of the relay node and receiving information of attachment of user equipment via the relay node.

13. A method according to any one of the preceding claims, wherein a node terminating a connection in the backhaul network comprises a node terminating a control plane connection, for example one of a mobility management entity and a donor evolved Node B, or a network node terminating a user plane connection, for one example a system gateway, S-GW, and for another example donor evolved Node B, or a network node terminating both the control plane connection and the user plane connection, for example a combined mobility management entity and serving gateway, MME/S-GW.

14. An apparatus comprising means configured to perform a method according to any one of claims 1 -13.

15. An apparatus according to claim 14, comprising at least one from a group of a mobility management entity, a relay node and a donor evolved Node B.

16. A communications system comprising at least two apparatuses according to any one of claims 14 and 15.