GB2481252A

GB2481252A - Use of virtual MAC entities in relays in a telecommunications system

Info

Publication number: GB2481252A
Application number: GB1010301.8A
Authority: GB
Inventors: Sivapathalingham Sivavakeesar; Sundarampillai Janaaththanan
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2010-06-18
Filing date: 2010-06-18
Publication date: 2011-12-21
Also published as: WO2011158966A1; GB201010301D0

Abstract

In a relay node 24 of a telecommunications network, one or more virtual MAC entities for transmission on the backhaul link to a donor eNodeB are created or deactivated to enhance MAC layer functionality in response to a plurality of user equipment UE1-UEn dynamically connecting and disconnecting to the relay node. The number of virtual MAC entities created may correspond to the number of UEs served directly by the relay node, the different types of quality class indicator (QCI) supported by the relay node or the amount of overall traffic handled by the relay node. This allows more than one HARQ process corresponding to the relay node being scheduled simultaneously during a downlink backhaul sub-frame enabling more data to be pushed on the backhaul link.

Description

Telecommunications System

Technical Field

The present invention relates to a telecommunications method and system. The present invention is desirably used in connection with the Long Term Evolution Advanced (LTE-A) standard for mobile network technology. The present invention is particularly adapted to use with relays in said system, and generally to relay HARQ.

Background

The increase of mobile data, together with an increase of mobile applications (such as streaming content, online gaming and television and internet browsers) has prompted work on the LTE standard. This has been superseded by the LTE-A standard.

LTE-A or LTE Advanced is currently being standardized by the 3GPP as an enhancement of LTE. LTE mobile communication systems are expected to be deployed as a natural evolution of GSM and UMTS.

To aid further understanding of the present invention, a brief disclosure of LTE and LTE-A architecture will now be provided in conjunction with Figure 1. The radio access network in the LTE and LTE-A standard is generally termed Evolved Universal Terrestrial Radio Access Network (E-UTRAN). In E-UTRAN, a base station is typically termed an eNode-B (often abbreviated to eNB). Another type of E-UTRAN are termed relay nodes, or sometimes just relays. Typically, one or more relays will be controlled by an eNB. This controlling eNB is usually termed a donor eNB or D-eNB.

The network uses a new Packet Core -the Evolved Packet Core (EPC) network architecture to support the E-UTRAN. The E-UTRAN for LTE consists of a single node, generally termed the eNB that interfaces with a given mobile phone (typically termed user equipment, or user terminal). For convenience, the term UE -user equipment -will be used hereafter.

The eNB hosts the physical layer (PHY), Medium Access Control layer (MAC), Radio Link Control (RLC) layer, and Packet Data Control Protocol (PDCP) layer that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. The eNB performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated up-link quality of service (QoS), cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of down-link/up-link user plane packet headers.

The mobile system will also typically include a packet data network gateway. The packet data network gateway provides connectivity to the UE to external packet data networks by being the point of exit and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one PDN GW for accessing multiple PDNs. The PDN GW performs policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening.

The purpose of the LTE-A standard system is to allow for service providers to reduce the cost of providing a network by sharing E-UTRANs but each having separate core networks. This is enabled by allowing each E-UTRANs -such as an eNB -to be cormected to multiple core networks. Thus, when a UE requests to be attached to a network, it does so by sending an identity of the appropriate service provider to the E-UTRAN.

LTE and LTE-A uses multiple access schemes on the air interface: Orthogonal Frequency Division Multiple Access (OFDMA) in downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) in uplink. Furthermore, MIMO antenna schemes form an essential part of LTE. E-UTRA employs two synchronisation channels -primary and secondary -for the UE air interface synchronisation.

* The layer-i (Li) and layer-2 (L2) protocols of the air interface terminate in the wireless device and in the eNB. The layer-2 protocols include the medium access control (MAC) protocol, the radio link control (RLC) protocol, and the packet data convergence protocol (PDCP). The layer-3 (L3) radio resource control (RRC) protocol also terminates in both the UE and the eNB. The protocols of the non-access stratum (NAS) in the control plane terminate in the UE and in the mobility management entity (MME) of the core network.

The MAC data communiction protocal sub-layer, also known as the Medium Access Control, is a sublayer of the data link layer specified in the seven-layer OSI model (layer 2). It provides addressing and channel access control mechanisms that make it possible for several UEs or network nodes to communicate within a multi-point network LTE employs the shared-channel principle, which provides multiple users with dynamic access to the air interface. * 4

Figure 2 shows the protocol layer architecture of a typical UE and eNB. In the control-plane, the non-access stratum protocol, which runs between the MME and the UE, is used for control-purposes such as network attach, authentication, setting up of bearers, and mobility management. All NAS messages are ciphered and integrity protected by the MME and UE.

The RRC layer in the eNB makes handover decisions based on serving cell and neighbouring cell measurements sent by the UE, pages for the UEs over the air, broadcasts system information, controls UE measurement reporting such as the periodicity of Channel Quality Information reports and allocates cell-level temporary identifiers to active UEs. It also executes transfer of UE context from the source eNB to the target eNB during handover, and does integrity protection of RRC messages. The RRC layer is responsible for the setting up and maintenance of radio bearers.

The PDCP layer is responsible for compressing/decompressing the headers of user plane lIP packets.

The RLC layer is used to format and transport traffic between the UE and the eNB. The RLC layer also provides in-sequence delivery of Service Data Units (SDUs) to the upper layers and eliminates duplicate SDUs from being delivered to the upper layers. It may also segment the SDUs depending on the radio conditions.

In LTE-A, relays are generally defined in two categories: type 1 and type 2. Type 1 relay nodes have their own PCI (Physical Cell ID) and are operable to transmit its common channel/signals. UEs receive scheduling information and HARQ feedback directly from the relay node. It is also possible for type 1 relay nodes to appear differently to eNBs to allow for further performance enhancement.

The primary proposal is to predominantly use Type 1 relays in next generation networks.

Type 1 relays may be considered as containing the functionalities of both an eNB (control node) and UE (user equipment), depending on how its functionalities are viewed. Thus, in the backhaul link the relay behaves like a UE (which is operated by the functionality of a UE), whereas in the access link it behaves like an eND (which is operated by the functionality of an eNB). Or, put another way, the D-eNB sees the relay as a UE, whereas the UE sees the relay as an ordinary eND.

Disclosure of the invention

According to the present invention there is provided a telecommunications system including a MAC layer, the system comprising: a D-eNB; a relay node; a plurality of UE operable to wirelessly connect to the relay node, wherein the system is operable to create or delete one or more virtual MAC entities to enhance the system's MAC layer functionality.

The MAC layer's functionality includes providing addressing and channel access control mechanisms that allow multiple UEs or network terminals to communicate within a multi-point network.

It is preferred that the system is operable to dynamically vary the number of virtual MAC entities in the system based on predetermined criteria.

The present mechanism assumes, in a preferred arrangement that the D-eNB can differentiate the relays from the ordinary user terminals, at least from the perspectives of MAC-sub-layer functionalities.

Depending on the different types of traffic being served by the relay, additional virtual MAC (V-MAC) entities may be created for transmission on the backhaul link between the relay node and the eNB.

It is particularly preferred that the plurality of UE may comprise different QoS class identifiers. In LTE-A, the QoS class identifier, or QCI, is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment which have been pre-configured by the network operator. In accordance with a first predetermined criteria, it is particularly preferred that the number of V-MAC entities supported by the system corresponds to the number of different QCIs. Additionally, it is also preferred that additional V-MAC entities are created to I) handle OAM (operation and management) signalling, 2) handle Si /X2 signalling, and 3) to handle TilE attachment on the backhaul link.

For example, assume that a given relay node needs to support three types of QCI traffic being generated by one or more UEs being served by the relay, three different V-MAC entities will be created/managed on the D-eNB side in order to control traffic of each QCI type. It is particularly preferred that each of these individual MAC entities in turn will have eight parallel HARQ processes as specified in the LTE Rel-8 HARQ procedure. Thus, it is preferred that the number of V-MAC entities that need to be created and managed by the system in order to handle a given relay depends on different QCIs that need to be supported by the given relay on its access link.

In an alternatively arrangement, and in accordance with an alternative predetermined criteria, the number of virtual MAC entities created by the system corresponds to the number of UE connected to the relay. In this arrangement, it is preferred that each UE that attaches to the relay node is assigned a V-MAC. Therefore, it is preferred that a V-MAC is dynamically created by the system on connection of the liE, and is removed or deleted when the liE disconnects from the network.

In another particularly preferred embodiment the predetermined criteria specifying the number of virtual MAC entities created corresponds to the amount of overall traffic handled by the relay node.

Preferably, each of the V-MAC entities are independently treated in much the same way as the MAC entities corresponding to different user terminals being handled within the MAC sub-layer of D-eNB directly, at least for the purpose of scheduling.

However, priority handling of different V-MAC entities may be achievable based on the QCI.

It is preferred that, while handling priority, starvation of low QCI traffic by high QCI traffic is minimised by employing Prioritised Bit Rate (PBR), whereby a PBR is configured for each

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V-MAC entity by the D-eNB. Each PBR governs the data rate that can be provided to one V-MAC entity before allocating any resource to a lower-priority V-MAC entity.

Accordingly, with this arrangement it can be expected that more than one HARQ processes corresponding to a relay node will be scheduled simultaneously during a backhaul sub-frame and thereby, enabling more data to be pushed on the backhaul link than the amount of data that would otherwise be pushed according to the conventional MAC scheduling approach.

In a preferred embodiment, the relay node comprises control means operable to control grouping of the virtual MAC entities corresponding to the different QCI UE groups connected in the access link.

In a preferred embodiment, the relay node maintains two separate MAC sub-layers.

According to a second aspect of the present invention, there is provided a method in a telecommunications network, wherein one or more virtual MAC entities are created or deactivated to enhance MAC layer functionality in response to a plurality of LIE dynamically connecting and disconnecting to a relay node.

Preferably the relay node comprises a backhaul link to a D-eNB, and the virtual MAC improve data transmission on said backhaul link.

It is preferred that the number of virtual MAC entities is varied to correspond to the number of UE connected to the relay node.

Preferably the number of virtual MAC entities is varied based on the number of differing QCT in the UE connected to the relay node.

Additionally the number of virtual MAC entities may be varied based on the total traffic load on the relay node.

In order that the present invention be more readily understood, specific embodiments thereof will now be described with reference to the accompanying drawings.

Description of the drawings

Figure 1 shows an overview of LTE-A network architecture.

Figure 2 shows a protocol layer architecture of a conventional UB and eNB.

Figure 3 shows an example of an eNB, relay and UIE in the present arrangement.

Figure 4 shows the control/user-plane protocol stack in the present arrangement.

Figure 5 illustrates as to how V-MAC entities will be created according to a first embodiment.

Figure 6 illustrates a mechanism for simultaneously scheduling multiple HARQ processes corresponding to a relay node according to a second embodiment.

Figure 7 shows an example of multiple MAC entities according to the third embodiment.

Description of preferred embodiments

Relaying has been considered for LTE-Advanced as an economical mechanism to support group mobility, temporary network deployment, and improved cell-edge throughput and/or to extend the coverage to new areas. The introduction of relay nodes in such type of systems d translates a single communication link -i.e. from eNB to UE -into two independent links, namely an access link between the UE and the relay and a backhaul link between the relay and the eNB. Figure 3 shows an example of this arrangement. In this arrangement, a D-eNB is provided. A relay node 12 is operable to communicate with the D-eNB on its backhaul link 16. A UE 14 is provided that wirelessly communicates with the relay node on its access link 18.

The frequency spectrum used in telecommunications networks is limited, and hence it is expected that the first generation of LIE-Advanced relays are going to be of predominantly in-band type, which use the same frequency band in both of the access and backhaul links 16, 18. The introduction of in-band relays has resulted a number of technical challenges that must be overcome in order to maximize relaying efficiency. For instance, simultaneous transmission and reception by an in-band relay should be avoided so as to prevent the relay node 12 from self-interference. In other words, the relay node 12 should not transmit when it is supposed to receive data, and vice versa. It is thus a requirement to create "Transmission Gaps" in the access link. These gaps can be created by configuring the MBSFN sub-frames on the access link, as already agreed within the 3GPP. However, MBSFN sub-frames cannot be configured in sub-frame numbers 0, 4, 5, and 9 of the radio frame (as these sub-frames are used for network control signals), thereby imposing stringent constraints in terms of the availability of backhaul link transmission opportunity, i.e. relay cannot receive anything on the backhaul link during these sub-frames in a radio frame; instead it has to perform the access link 18 transmission during these sub-frames.

It is expected that the D-eNB 10 will have fewer transmission opportunities in a radio frame on the backhaul link to communicate with any relay node. Further difficulties may arise if a

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relay node is loaded to its maximum level, meaning that it is simultaneously serving a large number of users or simultaneously handling a large number of bandwidth consuming applications, or the mixture of both. Consequently, a significant number of data blocks have to be transmitted to the respective relay node via the relay's backhaul link to the eNB, even though the backhaul link transmission opportunities may be below the required level.

Moreover, according to the legacy LTE standards, the D-eNB 10 schedules only one HARQ process associated with a MAC entity in a sub-frame of the radio frame. Transmission of these transport blocks belonging to aggregated traffic of one or more UEs on the backhaul requires significant radio frames, and thereby reduces the throughput of the overall system.

As a result, a relay node 12 may find it difficult to cope up with the access link demand in terms of supporting the required quality of service (QoS) and data rate, because the data transmission rate in the backhaul link 16 is significantly lower. This is not a severe bottleneck in LTE,. because the eNB can transmit to the same IJE 14 potentially in every sub-frame (possibly by employing different HARQ processes) of a radio frame. However, in the case of LTE-A relays there is a severe constraint being imposed in terms of the number of sub-frames being available for backhaul transmission. In order to rectify the above problem, it is important to minimise the number of transmission time intervals (TTIs) required on the backhaul link; i.e. it is required to maximise the amount of data being transmitted per TTI on the backhaul link 16. This is possible by increasing the number of MAC PDUs that can be transmitted on the backhaul per TTI.

The present arrangement provides for a mechanism that allows scheduling of multiple HARQ processes in a single sub-frame, at least for those relay nodes which demand a significant amount of backhaul data for serving the user terminals within their coverage. The proposed mechanism introduces minor modification on the backhaul link in connection with the D-eNB's MAC layer, while no changes are required on the access link 18 of the relay node 12, or on the direct link (i.e., D-eNB-to-UE links).

In order to increase the data pumping rate at the MAC sub-layer on the backhaul link 16, the present arrangement comprises three mechanisms to create and maintain multiple virtual MAC entities 20 (termed V-MAC entities or V-MACs) at either ends of the backhaul. In other words, the main objective of the different embodiments is to allow more than one HARQ processes corresponding to a relay node being scheduled simultaneously during a DL backhaul sub-frame and thereby, enabling more data to be pushed on the DL backhaul link than the amount of data that would otherwise be pushed according to the conventional MAC scheduling approach. Although the main principle behind these three mechanisms are the.

same, they vary in terms of the criteria being used to determine the number of Virtual MAC.

(V-MAC) entities 20 that need to be maintained and the rules governing exactly when they need to be instantiated and deleted. Accordingly, the main three criteria are; i) Embodiment 1: number of UEs (denoted R-UEs from now on wards) served directly by a relay node 12 ii) Embodiment 2: different types of QCIs supported by a relay node 12 iii) Embodiment 3: amount of overall traffic handled by a relay node 12 Fig. 4 shows the control/user-plane protocol stack in the present arrangement.

Representations are given for a UE 14, the relay node 12, the D-eNB 10 and the MME 22.

From the layer 2 perspective, a relay node 12 simultaneously maintains two separate MAC sub-layers 24, 26 -one for the backhaul link 16 and the other for the access link 18. This is because, as agreed within the 3GPP, any type-I relay node has to face two different interfaces

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on the access and backhaul links. On the access link a relay may function as an eNB whereas on the backhaul the same relay may function as a UE. Hence, the MAC entities being maintained by a relay on the access and the backhaul links are different. Although the way MAC entities are maintained on the access link by the relay is kept in tact the present arrangement considers how and when V-MAC entities 20 need to be instantiatedldeleted on the backhaul side of any relay. This is to ensure backward compatibility so that this scheme should equally work with legacy UEs.

Embodiment 1 * The exact number of V-MAC entities 20 that need to be maintained by any relay node 12 and the respective D-eNB 10 to handle the traffic on the backhaul depends on the exact number of R-UEs being served by the same relay on the access link. Hence, when a new MAC entity is created by the relay to handle a UE 14 on the access link, a corresponding V-MAC entity will be created on the backhaul link 16 by a relay node 12 and subsequently the relay node 12 will notify the respective D-eNB 10 to create a corresponding V-MAC entity on its side. There is a one-to-one correspondence between the number of V-MAC entities 20 created on the access side of a relay and the V-MAC entities 20 created on the backhaul side of the same relay node 12. Accordingly whenever the created MAC entity on the access link is deleted/removed/deactivated, the same will happen on the backhaul at either ends. By employing new RRC signalling messages or through MAC control elements, a relay node 12 and the respective D-eNB 10 can coordinate the creation/removal/deactivation of V-MAC entities 20 on either end of the backhaul link 16. Although conventionally a MAC controller handles operations, namely discontinuous reception (DRX), scheduling, Random Access Channel (RACH) and timing advance, its functionalities can be augmented to support the management of V-MAC entities 20 on the backhaul and to maintain the necessary mapping between one or more real MAC entities of the relay being maintained on the access link and a V-MAC entity 20 being maintained by the relay node 12 on the backhaul link 16.

Fig. 5 illustrates as to how V-MAC entities 20 will be created according to a first embodiment. The actual number of V-MAC entities depends on the actual number of R-UEs being served by a given relay. In this case the respective MAC sub-layers of both the relay in question and the D-eNB 10 will exchange the required signalling message in order to create/remove a V-MAC entity whenever a new R-UIE attaches/detaches the relay in question respectively. A set of exemplary RRC signalling messages being used for this purpose is set out below.

1. RR C_A ddNewMA C Entity The "RRC_ AddNewMA C_Entity" message is used by the EMC to signal the creation of new V-MAC entity whenever a relay node is going to serve a new UE. This V-MAC is going to be treated by the D-eNB in the same way it does the MAC entity associated with the UE it directly serves.

Direction: RN-) D-eNB (however, this signal can flow from either end)

Field Descriptions:

C-RNTI The cell level identifier for the TilE-part of the relay, assigned by the _________ D-eNB.

]IMSI This field indicates the unique identifier of the UE for which this V-MAC ______________ entity needs to be created on the backhaul.

International This identifier is similar to IMSI and it is globally unique and permanent to Relay ID solely identify the TiE-part of a relay.

(IRID) ________________________________ 2. RRC_RemoveNewMA C_Entity 4.

The "RRC_ Re,noveNewMA C_Entity" message is used by the EMC belonging to the MAC sub-layer of an RN question to request the deletion of an existing V-MAC entity whenever that RN stops supporting a given QCI traffic type.

Direction: RN-* D-eNB (however, this signal can flow from either end)

Field Descriptions:

C-RNTI The cell level identifier for the UE part of the relay, assigned by the _________ D-eNB.

IMSI This field indicates the unique identifier of the UE for which this V-MAC _______________ entity needs to be created on the backhaul.

International This identifier is similar to IMSI and it is globally unique and permanent to Relay ID solely identify the UE-part of a relay.

(IRID) ________________________________ In the present embodiment a relay is treated at the MAC-level as being consisting of multiple UEs on the backhaui by the respective D-eNB depending on the number of R-IJEs being served on the access link by the relay. As soon as an UL grant is issued by a relay to an R-UE in question after the RACH procedure, a new conventional MAC entity corresponding to the R-UE in question will be created at the relay on the access link. The relay will then create a corresponding V-MAC entity at the backhaul and inform the D-eNB for the creation of a corresponding V-MAC entity on the other end of the backhaul -accordingly both V-MAC entities created at either ends of the backhaul correspond to the R-UE that received a UL grant on the access link. This occurs when the R-UE initiates either a Service Request, performs an initial network access or when an R-UE is handed to a relay. If a R-UE switches to RIRC_IDLE mode after having initiated the initial access on the access link, the V-MAC entities will be kept active as long as the corresponding MAC entities on the access link are active. In other words, when the MAC entity at the relay end of the access link ceases to exist or is deactivated on being informed that the R-UE in question is idling on the access link, the corresponding V-MAC entities of the backhaul link will be removed or deactivated depending on how the MAC-entity of the relay end of the access link is handled.

Embodiment 2 The second embodiment provides a mechanism whereby the actual number of Virtual MAC (V-MAC) entities 20 being maintained by a relay node 12 and respective D-eNB 10 on the backhaul link 16 depends on the variety of traffic types (i.e., QCIs) that need to be handled by the relay.

Suppose a given relay node 12 needs to support 3 types of QCI traffic being generated by one or more R-UEs being served by the relay, 3 different V-MAC entities will be created/managed on the D-eNB side in order to take care of each QCI. Nine QCIs have been defined in the LTE-A specification, and hence a maximum of 9 V-MAC entities may be needed to handle user plane traffic. In addition, in order to handle S1/X2 control plane and OAM data, additional V-MAC entities may need to be created on either side of the backhaul link. Each of these V-MAC entities (at least for the purpose of scheduling) are independently treated in the same way as the MAC entities corresponding to different user terminals being handled directly within the MAC sub-layer of D-eNB, or by a relay on the access link, (at least for the purpose of scheduling). However, priority handling of different V-MAC entities will be possible based on the QCI. In order to ensure that high-priority traffic belonging to higher QCI V-MAC entities does not starve lower priority traffic belonging to lower QCI V-MAC entities, Priontised Bit Rate (PBR) can be employed. According to this embodiment, a PBR is configured for each V-MAC entity by the D-eNB 10. Each PBR governs the data rate that can be provided to one V-MAC entity before allocating any resource to a lower-priority V-MAC entity.

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A new V-MAC entity will be created corresponding to a new QCI type on either side of the backhaul (provided that it does not exist already) only when the relay/D-eNB ascertains the actual QCI type of the traffic to be generated by any new R-UE. Under normal circumstances this occurs when the relay receives an initial context setup request from its serving MME 22 after the R-UE has initiated the RRC ConnectionlService Request. The relay will create the new V-MAC entity if does not exist, or if already present let the request be handled by the appropriate V-MAC entity 20. The respective D-eNB 10 is notified. The MAC sub-layer of the D-eNB will then routes the traffic to the appropriate V-MAC entity if it already exists, or creates a new V-MAC entity if needed.

Similarly, a QCI-based V-MAC entity will be removed from either end of the backhaul link 16 when all R-UEs being currently served by a given relay cease to generate a given QCI type traffic. This situation is again first learnt by the relay and after removing the unnecessary QCI-based V-MAC entities on its side, it will send appropriate notification to the respective D-eNB for it to remove or deactivate unnecessary V-MAC entities.

New RRC signalling messages or MAC control elements can be used between a relay and the respective D-eNB in order to coordinate the maintenance of V-MAC entities on the backhaul link. Given that the type of the traffic that is going to be generated by any R-UIE is known only after the R-LTE has made the initial access, a separate V-MAC entity may exist permanently on either side of a backhaul link in order to handle such initial access by each R-UE. Also, two more permanent MAC entities are needed to handle S1IX2 control plane and OAM data.

Fig. 6 shows an exemplary diagram illustrating the proposed mechanism for simultaneously scheduling multiple HARQ processes corresponding to a relay node according to embodiment 2. Each UE has only one individual MAC entity both on the relay's access link and on the direct link (i.e. D-eNB-to-UE link). However, it is not the case with a relay backhaul as it has multiple Virtual MAC (V-MAC) entities in the MAC sub-layer of both the relay node 12 the D-eNB 10. The exact number of V-MAC entities 20 depends on the varieties of traffic type each R-UE being served by an relay in question generates in terms of the QCI that each of UE traffic belongs to. In other words, there is a V-MAC entity corresponding to each QCI.

Different varieties of R-UE traffic are multiplexed based on QCI and subsequently each of the combined traffic will be handled by each V-MAC entity. An Extended MAC Controller (EMC) 30 is provided which is responsible for maintaining the required mapping between respective MAC entities of a relay node 12 and those of the D-eNB 10.

When a UE 14 falls within the coverage of a relay node 12, it will connect using a conventional UE attachment procedure. Once the UE 14 is attached, the (EMC) block within the respective relay node, which handles the virtual grouping of the MAC entities corresponding to the different user terminals being connected in the access link 18, will assign the newly attached UE to one of the already existing virtual groups depending on the traffic QCI. If a V-MAC entity 20 corresponding to a particular QCI does not exist already, it will be created on demand. Note that this EMC can be implemented by simply adding the necessary features to the conventional MAC controller block.

Apart from the virtual grouping task, the EMC 30 also handles signalling messages between the respective MAC sub-layers of relay node and the respective D-eNB 10 on the backhaul link. Whenever a new V-MAC entity 20 needs to be created/removed, it will be signalled a accordingly using new AS signalling. Each signalling message includes both a unique identifier of the relay node and the QCI related to the given V-MAC entity. Although RRC signalling is preferred for convenience, any other type of signalling that suits the relay architecture type can be used. A set of exemplary RRC signalling messages being used for this purpose is set out below.

3. RR C AddNewMA CEntitv The "RRC_ AddNewMA C_Entity" message is used by the EMC to signal the creation of new V-MAC entity whenever a relay node is going to support a new QCI traffic type.

Direction: RN-* D-eNB (however, this signal can flow from either end)

Field Descriptions:

C-RNTI The cell level identifier for the UE-part of the relay, assigned by the _______ D-eNB.

QCI This field indicates the QCI type that is associated with the creation of new _____________ VMAC entity.

(IRID) ________________________________ 4. RRCRemoveNewMAC_Entity The "RRC_ RernoveNewMA C_Entity" message is used by the EMC belonging to the MAC sub-layer of an RN question to request the deletion of an existing V-MAC entity whenever that RN stops supporting a given QCI traffic type.

Direction: RN-D-eNB (however, this signal can flow from either end)

Field Descriptions:

C-RNTI The cell level identifier for the IJIE part of the relay, assigned by the _________ D-eNB.

QCI This field indicates the QCI type that is associated with the removal of ______________ existing V_MAC entity.

(IRID) _____________________________________________ 4' In the present embodiment it is not necessarily expected that a D-eNB 10 will be able to differentiate a relay from other macro-UEs being served directly by the D-eNB 10. As soon as an UL grant is issued by a relay to an R-UE in question after the RACH procedure, a new conventional MAC entity corresponding to the R-UE in question will be created at the relay on the access link. The relay will then create a corresponding V-MAC entity 20 at the backhaul and inform the D-eNB for the creation of a corresponding V-MAC entity 20 on the other end of the backhaul -accordingly both V-MAC entities created at either ends of the backhaul correspond to the R-UE that received a UL grant on the access link. This occurs when the R-UE initiates either a Service Request, performs an initial network access or when an R-UE is handed to a relay. If a R-UE switches to RRC JIDLE mode after having initiated the initial access on the access link, the V-MAC entities will be kept active as long as the corresponding MAC entities on the access link are active. In other words, when the MAC entity at the relay end of the access link ceases to exist or is deactivated on being informed that the R-UE in question is idling on the access link, the corresponding V-MAC entities of the backhaul link will be removed or deactivated depending on how the MAC-entity of the relay end of the access link is handled.

Embodiment 3 According to the third embodiment, the main deciding factor governing the number of V-MAC entities 20 that are to be maintained at either ends of the backhaul is the total amount of traffic to be handled by the relay in question. There is not always necessarily a 1-to-i correspondence between the MAC entities of the access link 18 and the V-MAC entities of 4,-.

the bacldiaul link 16. Instead, one or group of MAC entities being maintained on the access side of a relay will be mapped on to a single V-MAC entity of the backhaul depending on the load demanded by a given R-UE traffic. This is because each V-MAC on the backhaul side of a relay can support only given amount of traffic per TTI.

Each of these individual V-MAC entities in turn will have eight parallel HARQ processes as specified in the LTE Rel-8 HARQ procedure. Accordingly, the present embodiment allows that than one HARQ processes corresponding to a relay node will be scheduled simultaneously during a DL backhaul sub-frame and thereby, enabling more data to be pushed on the DL backhaul link than the amount of data that would otherwise be pushed according to the conventional MAC scheduling approach.

As mentioned before, there in n-to-i (where n > I) relationship between the actual MAC entities created on the access side of a relay node and the V-MAC entity that is created on-demand on the backhaul side of a relay and the respective D-eNB 10. In this embodiment, each V-MAC entity is configured to handle only a limited amount of traffic and, depending on the total amount of traffic generated on the access side, an appropriate number of V-MAC entities will be created on the backhaul side of a relay and the respective D-eNB 10 on demand by the Extended MAC Controller (EMC) 30. The EMC also performs grouping of different MAC entities on the access link and maps them to a V-MAC entity on the backhaul link 16 to the D-eNIB 10.

Whenever a TilE 14 falling within the coverage of a relay node is connected using the conventional UE attachment procedure, the EMC block within the respective relay node 12 will handle as to what V-MAC entity the newly created MAC entity pertaining to the newly attached R-UE has to be mapped to depending on the current load of each existing V-MAC entities and the demand of the new MAC entity. If all of the existing V-MAC entities have reached their capacity, a new V-MAC entity will be instantiated and the new MAC entity will be mapped on to the new virtual entity. On the other hand, if any of the existing V-MAC entities is under-loaded on the backhaul, the new UE traffic and hence the associated MAC entity being created on the access link by the relay will be mapped on to and subsequently handled by the most under-loaded V-MAC entity of the backhaul.

Fig. 7 shows an example of multiple MAC entities according to the third embodiment.

In all embodiments, the EMC can be implemented by simply adding the necessary features to the conventional MAC controller block. Apart from the virtual grouping task performed by the EMC, it also handles the signalling messages between the relay node and the respective D-eNB on the backhaul link using new AS (e.g. RRC) signalling messages or MAC Control elements. Using this signalling, the respective MAC sub-layers of either end of the backhaul can communicate in priory for the management of V-MAC creationldeletion process.

It is to be understood that the above described specific embodiments are for illustrative purposes only, and should not be used to unduly limit the claims.

Claims

Claims 1. A telecommunications system including a medium access control (MAC) layer, the system comprising: a donor eNode-B (D-eNB); a relay node; a plurality of user equipment (UE) operable to wirelessly connect to the relay node, wherein the system is operable to create or delete one or more virtual MAC entities to enhance the system's MAC layer functionalities.
2. A telecommunications system according to claim 1, wherein the system is operable to dynamically vary the number of virtual MAC entities in the system based on predetermined criteria.
3. A telecommunications system according to claim 2, wherein the number of virtual MAC entities created corresponds to a number of the plurality of UE wirelessly connected to the relay node.
4. A telecommunications system according to claim 2, wherein the number of virtual MAC entities is calculated based on the traffic load on the relay node.
5. A telecommunications system according to claim 2, wherein the plurality of UE connect to the relay node are categorised based on their quality of service class identifiers (QCI), and wherein the number of virtual MAC entities created corresponds to the number of different QCI.
6. A telecommunications system according to claim 5, wherein an additional virtual MAC entity is created to handle OAM signalling.
7. A telecommunications system according to claim 5, wherein an additional virtual MAC entity is created to handle S 1/X2 signalling.
8. A telecommunications system according to claim 5, wherein an additional virtual MAC entity is created to handle UE attachment on the backhaul link.
9. A telecommunications system according to any of claims 3 to 8, wherein the relay node is operable to dynamically create virtual MAC entities following connection to the network by a UE.
10. A telecommunications system according to claim 3, wherein on creation of an actual MAC entity on an access link by the relay node on successful network access by a UE, the relay is operable to create a corresponding virtual MAC entity on a backhaul link between the relay node and the D-eNB.
II. A telecommunications system according to any preceding claim, wherein each virtual MAC entity comprise eight parallel HARQ processes.
12. A telecommunications system according to any preceding claim, wherein said relay node comprises a MAC layer, said MAC layer comprises controlling means operable to maintain mapping between respective virtual MAC entities of the relay node and the D-eNB.
13. A telecommunications system according to any preceding claim, wherein said relay node comprises a MAC layer, said MAC layer comprises controlling means operable to maintain mapping between one or more real MAC entities of an access link and respective Virtual-MAC entities of a backhaul link.
14. A telecommunications system according to claim 12, wherein the controlling means is further operable to control signalling messages between the respective MAC layers of the relay node and the D-eNB.
15. A telecommunications system according to any preceding claim, wherein the relay node maintains two separate MAC sub-layers.
16. A method in a telecommunications network, wherein one or more virtual medium access control (MAC) entities are created or deactivated to enhance MAC layer functionality in response to a plurality of user equipment (UE) dynamically connecting and disconnecting to a relay node.
17. A method according to claim 16, wherein the relay node comprises a backhaul link to a D-eNB, and the virtual MAC entities improve data transmission on said backhaul link.
18. A method according to claim 16 or claim 17, wherein the number of virtual MAC entities is varied to correspond to the number of UE connected to the relay node.
19. A method according to claim 16 or claim 17, wherein the number of virtual MAC entities is varied based on the number of differing quality of service class identifiers (QCI) in the IJE connected to the relay node.

20 A method according to claim 16 or claim 17, wherein the number of virtual MAC entities is varied based on the total traffic load on the relay node.