GB2475906A

GB2475906A - A relay apparatus used in connection with the lte-a standard

Info

Publication number: GB2475906A
Application number: GB0921331A
Authority: GB
Inventors: Sivapathalingham Sivavakeesar; Sundarampillai Janaaththanan
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2009-12-04
Filing date: 2009-12-04
Publication date: 2011-06-08
Also published as: GB0921331D0; WO2011068242A1

Abstract

A telecommunication system comprising a control node and one or more relays, wherein at least one of said one of said relays is in a standby mode, and wherein each relay comprises a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node. The system further includes a plurality of user equipments, such that each user equipment and the first aspect of the one or more relays are assigned user equipment identifiers by the control node, and that said identifier is used by the control node to activate the first aspect of the relay in the standby mode.

Description

Relay Apparatus and Method

Technical Field

The present invention relates to a relay apparatus, a system in which said relay and others are operable to function and methods of use thereof. Further, the present invention is desirably used in connection with the Long Term Evolution Advanced (LTE-A) standard for mobile network technology.

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 This has been superseded by the LTE-A standard.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 from 2010 onwards as a natural evolution of GSM and UMTS.

Being defined as 3.9G (or 3G+) technology, LTE does not meet the requirements for 4G, also called IMT Advanced, as defined by the ITUI3GPP that has requirements such as peak data rates up to 1 Gbps.

In April 2008, 3GPP agreed to plans for future work on Long Term Evolution (LTE). A first set of 3GPP requirements on LTE Advanced was approved in June 2008. The standard calls 4 f for a peak data rate of 1 Gbps and also targets faster switching between power states and improved performance at the cell edge.

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 in the LTE and LTE-A standard is generally termed Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Certain types of E-UTRANs entities are termed eNode-Bs, and others termed relays.

The network uses a new Packet Core -the Evolved Packet Core (EPC) network architecture to support the E-UTRAN.

The pertinent functional elements are discussed below.

Evolved Universal Terrestrial Radio Access Network (E-UTRAN) The E-UTRAN for LTE consists of a single node, generally termed the eNodeB (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 evolved RAN performs many functions including radio resource management, admission control, scheduling, enforcement of 4 1 negotiated up-link Q0S, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of down-link/up-link user plane packet headers.

Serving Gateway (SGW) The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during interlay handovers. For idle mode UEs, the SGW terminates the downlink data path and triggers paging when downlink data arrives for the UE. It manages and stores UE contexts. The SGW also performs replication of the user traffic in case of lawful interception.

Mobility Management Entity (MME) The MME is the key control-node for the LTE access-network. It is responsible for idle mode UE tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation process and is also responsible for choosing the SGW for a liE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation. It is responsible for authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS) signalling terminates at the MME and it is also responsible for generation and allocation of temporary identities to IJEs. It checks the authorization of the UE to camp on the service provider's Public Land Mobile Network (PLMN) and enforces TIE roaming restrictions. The MME is the termination point in the network for ciphering/integrity protection for NAS signalling and handles the security key management. Lawful interception of signalling is also supported by the MME. The MME also provides the control plane function for mobility between LTE and 2G13G access networks with the S3 interface terminating at the MME from the SGSN (Serving GPRS Support Node). The MME also terminates the S6a interface towards the home HSS for roaming UEs.

Packet Data Network Gateway (PDN GW) 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.

Home Subscriber Server (HSS) The Home Subscriber Server (HSS) is a master user database that supports the IMS network entities that handle wireless communications sessions. It contains the subscription-related information, performs authentication and authorization of the user, and can provide information about the subscriber's location and IP information.

The table below describes the interfaces used between the primary functional elements.

LIE DESCRIPTION

REFERENCE

POINT ____________________________________________________

S1-MME Reference point for the control plane protocol between EUTRAN and MME. The protocol over this reference point is eRANAP and it uses Stream Control Transmission _____________ Protocol (SCTP) as the transport protocol Si-U Reference point between EUTRAN and SGW for the per-bearer user plane tunnelling and interlay path switching _____________ during handover. The transport protocol over this interface is (4 _____________ GPRS Tunnelling Protocol-User plane (GTP-U) S2a It provides the user plane with related control and mobility support between trusted non-3GPP [P access and the Gateway. S2a is based on Proxy Mobile IP. To enable access via trusted non-3GPP IP accesses that do not support PMIP, _____________ S2a also supports Client Mobile IPv4 FA mode S2b It provides the user plane with related control and mobility support between evolved Packet Data Gateway (ePDG) and _____________ the PDN GW. It is based on Proxy Mobile [P S2c It provides the user plane with related control and mobility support between UE and the PDN GW. This reference point is implemented over trusted andlor untrusted non-3GPP Access and/or 3GPP access. This protocol is based on Client _____________ Mobile [P co-located mode S3 It is the interface between SGSN and MME and it enables user and bearer information exchange for inter 3GPP access network mobility in idle and/or active mode. It is based on _____________ Gn reference point as defined between SGSNs S4 It provides the user plane with related control and mobility support between SGSN and the SGW and is based on Gn _____________ reference point as defined between SGSN and GGSN S5 It provides user plane tunnelling and tunnel management between SGW and PDN GW. it is used for SGW relocation due to UE mobility and if the SGW needs to connect to a non-collocated PDN GW for the required PDN connectivity.

Two variants of this interface are being standardized depending on the protocol used, namely, GTP and the IETF _____________ based Proxy Mobile [P solution [3] S6a It enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system ______________ (AAA interface) between MME and HSS S7 It provides transfer of (Q0S) policy and charging rules from Policy and Charging Rules Function (PCRF) to Policy and Charging Enforcement Function (PCEF) in the PDN GW.

______________ This interface is based on the Gx interface Sb Reference point between MMEs for MME relocation and _____________ MME to MME information transfer Si I Reference point between MME and SGW SG1 It is the reference point between the PDN GW and the packet data network. Packet data network may be an operator-external public or private packet data network or an intra-operator packet data network, e.g. for provision of IMS services. This reference point corresponds to Gi for 2GI3G ________________ accesses Rx+ The Rx reference point resides between the Application _____________ Function and the PCRF in the 3GPPTS 23.203 LTE-U This is the reference point between the user terminal and the __________________ eNB

S

Wn* This is the reference point between the Untrusted Non-3GPJ IP Access and the ePDG. Traffic on this interface for a TilE initiated tunnel has to be forced towards ePDG.

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 connected to multiple core networks. Thus, when a TilE 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 wireless device and the base station. The protocols of the non-access stratum (NAS) in the control plane terminate in the wireless device and in the mobility management entity (MME) of the core network.

LTE employs the shared-channel principle, which provides multiple users with dynamic access to the air interface.

Figure 2 shows the protocol layer architecture of a typical user terminal, eNodeB and mobility management entity. 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 UB, pages for the UEs over the air, broadcasts system information, controls UE measurement reporting such as the periodicity of Channel Quality Information (CQI) 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 IP 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.

Relaying has been identified as one of the key enabling teclmologies for LTE-A to improve the cell-edge performance. Given that numerous relays (relay nodes) need to be deployed, power consumption of each relay as well as cell sites is coming under intense scrutiny mainly

IL

because radio networks normally account for around 80% of the total electricity used by an operator.

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.

By contrast, type 2 relay nodes do not have a separate PCI, and are transparent to UEs.

Each relay in the network will have a link to a controlling eNB. This link is often termed the backhaul link. Each eNB will be linked to the core network, and this link is the eNB's backhaul link. The controlling eNB is sometimes referred to as a donor eNB, or D-eNB.

At present, the LTE Advanced system comprises two architectures. These are termed Architecture A and Architecture B. Architecture A comprises three variants, terms Alternative 1, Alternative 2 and Alternative 3.

Figure 3a shows a diagram of Alternative I and Alternative 3 in Architecture A. Figure 3b shows a diagram of Alternative 2. It will be noted that Alternative 2 is similar to Alti and Alt 3, but further includes a relay gateway.

In Alternatives 1, 2 and 3, the U-plane of the Si interface is terminated at the relay node. In the Alternative 1, the U-plane packets of a liE served by the relay node are delivered via a

L

Relay's P/S-GW. The UE's P/S-GW maps the incoming lP packets to the GTP tunnels corresponding to the EPS bearer of the UE and sends the tunnelled packets to the IP address of the relay node. The tunnelled packets are routed to the relay node via the Relay's P/S-GW, as if they were packets destined to the relay node as a UE.

Figure 4 shows a diagram of Architecture B. In Alterative 4, the U-plane of the Si interface is terminated at the D-eNB. The P/S-GW serving the 1fF maps the incoming IP packets to the GTP tunnels corresponding to the EPS bearer of the UE and sends the tunnelled packets to the IP address of the D-eNB. Upon the D-eNB receiving the tunnelled packets from the S-GW, the received packets are de-turmelled, and the inner user IF packets are mapped to Un radio bearers corresponding to the EPS bearer of the TIE.

Each EPS bearer of a UE connected to a relay node is mapped to separate radio bearers over the Un interface (one-to-one mapping). In order to identify individual UE bearers on the Un interface a TIE identifier needs to be added to one of the PDCP, RLC or MAC protocol layers.

Full details of these architectures can be found in document 3GPP TR 36.806, the contents of which are incorporated herein by reference.

The present invention seeks to enhance cell-edge performance, whilst conserving energy and avoiding resource wastage.

Disclosure of the Invention

According to a first aspect of the present invention there is provided a method of controlling a telecommunication system, said telecommunication system comprising: one or more user equipments; a relay comprising a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node; and a control node, wherein said method comprises the steps of: i) having said second aspect of said relay monitor communication sessions between said relay and said one or more users equipments, wherein, ii) if no communication session is detected within a predetermined period, said second aspect informs said first aspect and reverts to a standby mode; and iii) said first aspect informs said control node and reverts to a standby mode.

Preferably the second aspect takes periodic measurements at Li or L2 level to determine whether any communications sessions are currently supported.

It is preferred that the relay is a type 1 relay. Type I relays have been predominantly chosen within 3GPP as one of the candidate technologies to enhance the cell-edge performance.

Preferably the control node is either a D-eNB or a MME. It is preferred that the system will contain both entities. However, depending upon the architectures selected, the control node may be either a D-eNB or a MME.

It is preferred that the predetermined period is operable to be varied depending upon system conditions. Accordingly, the system can be adapted to conditions to at different times, or if particular events are occurring.

according to a second aspect of the present invention there is provided a telecommunication system comprising: i) a control node; and ii) a relay comprising a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node, wherein, said control node is operable to send a message to said first aspect of said relay to instruct said first aspect to revert to a standby mode.

It is particularly preferred that the first aspect instructs said second aspect to revert to a standby mode after receiving said message from the control node.

The system will typically further comprise: a plurality of user equipments, wherein, said control node preferably assigns identifiers to each UB and the first aspect of said relay, wherein the control node is operable to use said identifier of said first aspect to message the first aspect to revert to a standby mode. The D-eNB typically sets aside a plurality of E-UTRAN cell-level identifiers (e.g., C-RNTIs) for the purpose of semi-statically assigning them to the UE-parts (the first functional aspects) of the relays within its domain. These identifiers are the same as those used for liEs.

According to a third aspect of the present invention there is provided a telecommunication system comprising: i) a control node; ii) one or more relays, wherein at least one of said one of said relays is in a standby mode, and wherein each relay comprises a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node; iii) a plurality of user equipments, wherein, each user equipment and the first aspect of the one or more relays are assigned user equipment identifiers by the control node, and that said identifier is used by the control node 10* to activate the first aspect of the relay in the standby mode.

Preferably the first aspect activates the second aspect of the relay.

It is preferred that the control node maintains a record of whether the one or more relays in are an active mode or a standby mode.

Preferably the control node is a D-eNB or a MME. The nature of the control node will depend upon the architectures selected.

Preferably the identifiers are C-RNTIs.

In preferred embodiments, relays in the network will predominantly be type 1 relays. Type 1 Relays can have the functionalities of both an eNB and UE within it depending on how its functionalities are viewed. If it is the case, in the backhaul link it behaves like a I.JE whereas in the access link it behaves like an eNB. t

In the network a further relay may prompt the control node to activate the relay in standby mode.

Preferably the relay in standby mode periodically reverts to active mode without any message from a control node. In general, relays can be used within the centre of a domain to provide a higher quality of service in the domain by providing additional access points to the network.

However, relays may also be used at the cell edge to extend coverage. If relays are used to extend the coverage of a cell or domain, these relays cannot sleep continuously. This is because there is no other E-UTRAN entity to trace the presence of a TIE within the coverage area of the relay at the cell, and hence no local node to wake up the sleeping relay. However, such a relay can revert to a standby mode provided that it periodically reverts to an active mode in order to ascertain if any TIE within its coverage needs to be served Preferably the control node is an MME, and that the system further comprises a D-eNB, wherein, should the D-eNB wish to activate the relay in standby mode, it first indicates its intention to the MME. This arrangement is suitable for Architecture A, and particularly Alternative 1 and Alternative 3.

According to a fourth aspect of the present invention there is provided a relay operable to revert from a standby mode to an active mode after a first predetermined period, and revert back from said active mode to said standby mode after a second predetermined period.

Preferably the relay comprises a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node, such that only said second aspect periodically alternates between said standby and active modes.

It is preferred that one or both of the first and second predetermined period is calculated based on either the location of the relay or the time.

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

Figires used in the Background Section

Figure 1 shows an embodiment of LTE-A architecture.

Figure 2 shows the protocol layer architecture of a typical UE, eNB and MME.

Figure 3a shows a diagram of Alternative 1 and Alternative 3 in Architecture A. Figure 3b shows a diagram of Alternative 2 in Architecture A. Figure 4 shows a diagram of Architecture B. Figures used in the Specific Embodiments Figure 5 shows a representative domain of a D-eNB and three relay sub-cells.

Figure 6 shows an example of relay wake-up signalling from a control node.

Description of Preferred Embodiments

Relaying has been identified as one of the key enabling technologies for LTE-A to improve the cell-edge performance. To sufficiently achieve the desired goal, numerous relays need to be deployed. However, power consumption of each relay, as well as cell sites, is considerable, with radio networks normally accounting for around 80% of the total electricity used by an operator. As a result, there have been increased concern and statutory regulations being imposed on network operators to be energy-aware.

LTE-A networks need to support at least 1 Gbps in the downlink. One of the ways to meet this requirement in wireless communications is by locating the transmitter and receiver closer to one another, as stated in the Shannon channel capacity theorem: As long as the rate of communication is less than the channel capacity, the error rate may be made arbitrarily small (established from the Shannon-Hartley theorem). Accordingly when the wireless link bandwidth is not in abundance, the only way to increase the system capacity is by improving the link quality (i.e. the signal to noise ratio). For this, interference between relay and cell needs to be minimised, which results in small cell operation. In one extreme, high power consumption due to many small cells has significant environmental impact. In the other extreme, given the peak data rate requirement of LTE-A is extremely high, small relay size is one way to achieve very high mobile data throughput and capacity. One solution to meet these mutually conflicting requirements is through on-and-off relaying.

On demand relay operation is also desirable because relaying is not always beneficial, mainly because of the requirement of more radio resources to transmit data in different hops and the significant amount of interference caused due to a larger number of simultaneous transmissions.

A first aspect of the present arrangement may be considered to be how to revert a relay to a standby or sleep mode. A second aspect may be considered as to how to revert a sleeping relay back to an active mode.

Given that there exists various relay architectures, it is important to configure solutions that will best suit each of said architectures.

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

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

Energy saving and resource conservation is important for both aspects/parts of a relay.

The eNB-part (second aspect) of the relay may, if not controlled, unnecessarily broadcast SI (System Information) on BCH (Broadcast Channel) and D-SCH (Downlink Shared Channel), and/or transmit synchronisation channels and various kinds of RSs (reference signals), and keep the receiver circuitry ready for RACH (Random Access Channel) -thus causing unnecessary wastage of spectrum and energy resources. The present embodiment thus a provides for dynamically turning on and off various functionalities (including dynamically controlling the transmission of various channels namely BCH, D-SCH, different types of RSs and RACH) of the eNB-part of a relay depending on the traffic demand, current load, varying channel conditions and seasonal effect on the radio link. This may be because the network operator does not have enough radio and energy resources to continuously (and potentially unnecessarily) run a plurality of relays while experiencing severe relay induced interferences.

For example, for an economical solution, a significant number of relays may be required to support the data rates of 1 Gbps in LTE-A.

Thus, on seeing that there is no active sessions to support (i.e., all UEs within the relay coverage area are in their RRC IDLE mode), second aspect or the eNB-part of the relay can switch itself off after a predetermined time-out (TIDLE). This action is a signal for the first aspect of the relay, or the UE-part, to also switch off. In order to make this decision, the eNB-part of the relay can take periodic measurements taken at Li and/or L2 level to see whether the relay currently supports any active session.

In the present embodiment, it is preferred that a UE-part (first aspect) of a relay is permitted to revert to a standby/sleep mode, while making sure that either a D-eNB or an MME is able to re-activate the relay and subsequently communicate therewith whenever it is necessary.

Accordingly, as a relay is allowed to sleep, the present arrangement provides for a mechanism for the network (either E-UTRAN or MME depending on architectures) to retain the current status of each relay, and send a wake up call whenever it is necessary. For example, in a scenario where an UE -which is only in the coverage area of a relay in standby mode receives an incoming call/session, the network has to first wake up a relay before the network can send a paging to the UE. Therefore, the network needs to keep the current status of every relay.

Typically, every relay will send notification of its reverting to sleep to its D-eNB or relevant MME. On sending a message to revert to active mode, or to send the relay to sleep, the relevant D-eNB or MME will update its database on relay status.

Thus, whenever a UE-partlfirst aspect of a relay switches to standby mode, it has to notify the D-eNB/MME about its intention. Similarly whenever a D-eNB/MME dictates a relay to switch to the standby mode, the corresponding state (mode) of the relay will be maintained in the network.

In the case of Alternative 1 and Alternative 3 of relay Alternative A the Si interface terminates directly at relay nodes. Hence, under such circumstances in case an MME tries to contact any UE located within the coverage of a sleeping relay, the MME should first wake up the relay before starting any of its operations on any ordinary UE. For this purpose, the MME needs to be aware that the relay is sleeping.

In Alternative 2 and Architecture B, if an MME attempts to page a UE located within the coverage of a sleeping relay, and the D-eNB is aware of the attempt, the D-eNB can issue a wake-up message to the UIE-part of a sleeping relay.

Where a UE is within the coverage of both the D-eNB and a multitude of sleeping relays and D-eNB handles the initial call/session setup signalling as it will be described later, it is more appropriate for the D-eNB to wake up a relay (i.e., signalling the UB-part of a relay).

In case direct communication between a D-eNB and one of its relays is difficult, perhaps due to current network traffic or relay architecture used, then it is preferred that the D-eNB makes its intension know to the serving MvIE, such that the MME can subsequently trigger wake up calls directly. It should be noted that this arrangement is particularly suitable to Alternatives 1 and 3 in Architecture A using S1-AP.

To further understand the present invention, a discussion of the signalling requirements within the network will now be provided. Specifically, new Si, NAS, RRC or X2 signalling messages are introduced (depending upon the architectures used) that originate, respectively, from D-eNBsIMMEs and from the first aspectlUE-part of a relay.

For instance, two new Si, NAS, RRC or X2 signalling messages such as Wake Up and GoToSleep flow from the D-eNB/MME to a UE-part of a given relay, whereas RelayGoingToSleep originates from the TiE-part of a relay and is sent to the D-eNB/MME.

The purpose and a brief description of each of such messages is given below: i) Wake Up -issued by the D-eNB/MME for the purpose of waking up the UE-part of a relay that is in its power-saving IDLE mode. This signal is shown in Figure 6.

On receiving this signal from the D-eNB/MME, the UE-part of the relay will also wake up the eNB-part of the relay in question. This message contains the universal ID of the UE-part of the relay which is equivalent to IMSI (International Mobile Subscriber Identity) of a typical UE, or a semi-statically assigned C-RNTI. A.

ii) GoToSleep -this message is issued to an active UE-part of a relay by the D- eNB/MME at its discretion. For example, this may be for the purpose of inter-cell interference coordination (ICIC), or at the time of resource shortage. This message also contains the universal ID of the UE-part of the relay which is equivalent to IMSI of a typical UE.

iii) RelayGoingToSleep -issued by the UE-part of a relay to the D-eNB/MME on noting that the second aspectleNB-part of the relay is switched off after an inactive timeout (TIDLE).

The D-eNB/MME sets aside a subset of C-RNTIs from its available identifier pool for the purpose of assigning them to UE-parts of type 1 relays.

A database that contains the allocation of each of these identifies to UEs will have an additional flag to indicate whether such an identifier is assigned to a typical UE or to the UE-part of a relay. If assigned to a relay, the database may have an additional field to indicate if the relay being assigned is in its sleep or active mode. The database is operable to be reviewed by either or both of the D-eNB or an MME.

The D-eNB or an MME first reverts the status of a relay to an active mode before proceeding with any other operations.

The present arrangement provides a unitary solution applicable to all existing relay architectures, and is also suitable for any new relay architectures that does not solicit any change in the EPC.

In this case, the exchange of the new messages like Wake Up, GoToSleep, and RelayGoingToSleep should be between the serving MME and the UE-part of any relay.

Whenever a D-eNB or any active relay needs to wake up a neighbouring sleeping relay, they need to first indicate their intension to the serving MMIE first and which in turn will initiate special NAS signalling messages to the required sleeping relay subsequently.

The following provides a description of the network signalling in relation to the two architectures, including the three variants of Architecture A. Architecture A, Alternative 1 and Alternative 3 In this pair of architecture alternatives, a relay and its D-eNB do not maintain SI -AP or RRC signalling, and thus the exchange of the new messages Wake Up, GoToSleep, and RelayGoingToSleep are communicated via NAS or X2-AP, depending on whether the relay and D-eNBIMME maintains such interfaces.

Architecture A, Alternative 2 In this relay architecture alternative, a relay terminates the Si-AP and X2, while the D-eNB terminates Si-AP both towards a relay and the EPC. Hence, the exchange of the new messages WakeUp, GoToSleep, and RelayGoingToSleep are via SI-AP or X2-AP, depending on whether the relay and D-eNB maintains such interfaces. In this architecture, the exchange of the present signalling is between the relay in question and its D-eNB. The MME is not involved in the signal exchange.

Architecture B RRC signalling is used between any relay and a D-eNB. Hence, RRC signalling messages are used for the exchange of the new messages Wake Up, GoToSleep, and RelayGoingToSleep -specific details are provided in the section below. In this architecture, the exchange of signalling including relay status information is between the relay in question and its D-eNB with no MME involvement.

Under normal circumstances an eNB does not communicate directly with a UE which is in its RRC_IDLE mode. In order to enable a communication between a D-eNB and the first aspect/TIE-part of a relay, it is required to ensure that, from the RRC signalling perspectives of the D-eNB, the HE-part of the relay is always in its RRC-CONNECTED mode, although the UE-part can still be in its RRC IDLE mode.

In the present arrangement, the D-eNB sets aside a subset of E-UTRAN cell level identifiers, such as C-RNTI, to assign to the HE-part of every relay the D-eNB serves. This form of semi-static assignment is not problematic because the present relays will typically be stationary. Thus, unlike UEs, the UE-parts of relays will not move and change their D-4 L * eNB attachments. There is little difference between the information on TJE-part of the relay and UE kept by the MME and eNB. Accordingly a D-eNB is able to contact the UE-part of the relay as long as it knows its C-RNTI and still keeps RRC_Context pertaining to the UE-part of said relay provided that the relay is not broken.

A failback technique is provided to deal with the case that a relay is broken, whereby after several attempts of signalling messages originated from the D-eNB, if no corresponding response is received from a given relay, it will be declared broken and a corresponding state (mode) will be noted by the network.

In order to make it appear to the RRC signalling of the D-eNB that the UE-part of a relay is still in the RRC CONNECTED mode even when in fact the UE-part of the relay is in its IDLE mode, the D-eNB will not send a RRCConnectionRelease message to any relay it serves under any normal circumstance unless the relay in question is broken. The D-eNB should treat relay specific C-RNTIs in a different way. Accordingly, the RRC contexts pertaining to such identifiers that have been assigned to UE-parts of relays will still be kept in the D-eNB even when the UE-part of the relay is in the power saving IDLE mode.

More over, during the IDLE mode, the IJE-part of the relay ignores any paging from the D-eNB and hence this new RRC wake up message is proposed. The present arrangement makes this possible with the introduction of three new RRC signalling messages for activating and turning off relays. The D-eNB uses RRC signalling for this purpose.

I

Particularly, this way of RRC signalling has definite advantage over paging as the latter process is lengthy (PICH, PCH and the TilE access using RACH and so on) and time consuming. Tnstead, the RRC signalling messages can quickly wake up a sleeping relay and the UE-part of the relay can be brought to the required state (mode) quickly.

RRC Signalling Message definitions for relay Architecture B. RRC_RelayGoingToSleep The "RRC_RelayGoingToSleep" message is used by the UE-part of the relay to notify the D-eNB when it changes its state to sleeping mode.

Direction: RN-) D-eNB

Field Descriptions:

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

Cause This field indicates the reason as to why the relay has changed to _____________ sleeping mode.

State This indicates the present state (mode) of the TilE-part of the relay.

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) ________________________________ RRC_GoToSleep message The "RRC GoToSleep" message is used by the D-eNB to request the particular UE-part of the relay to sleep. It can be initiated at the time of resource shortage, for ICIC purposes or after a handover attempt wherein unsuccessful relay candidates will be asked to go to sleep, and the like.

Direction: D-eNB-) RN

Field Descriptions:

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

State This indicates the requested state (mode) change for the UE-p art of the _______________ relay.

Cause This filed will inform the reason as to why this TilE-part of the relay has to _______________ be turned off For example -"inactive" or "Interference".

I (IRID) RRC_ WakeUp message The "RR C_Wake Up" message is used by the D-eNB or an active RN in order to wake up the liE-part of the sleeping relay.

Direction: D-eNB /active RN -Sleeping RN

Field Descriptions:

Orig_sender This field indicates the identifier of the message initiator, if it is by an active _______________ relay.

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

State This indicates the requested state (mode) change of the UE-prt of the relay International This identifier is similar to IMSI and it is globally unique and permanent to Relay ID solely identify the IJE-part of a relay.

(IRID) _________________________________ In order that the present invention may be further understood, two examples, with reference to Figure 5 will now be described. These examples are generic to all Architectures, with the relevant network signalling provided that should be referenced with the description provided above.

In a first example, with reference to Figure 5, there is provided a UE 5 that is located within the domain of D-eNB 4. Relays 2, 3 are provided to extend the coverage of the D-eNB 4.

A further Relay 1 is provided within the domain of D-eNB 4. The D-eNB acts as a control node in its domain. The D-eNB controls communication sessions between user equipments (liEs) in the domain. As stated earlier, the Relays 1, 2, 3 are preferably Type 1 relays that comprise two aspects: the functionality of a user equipment and the functionality of a control node. The second aspect (the functionality of a control node) is operable to take periodic measurements at either Li or L2 level to determine whether any communication sessions with a LIE is supported.

L

In the present embodiment, Relay 1 is in a standby or sleep mode, whereas Relay 2 is in an active mode. It will be appreciated by those skilled in the art that Relay I would be the optimum access node for UE 5 to use.

In the present scenario, when a relay is in standby, and a UE is within the coverage of said sleeping relay, an active Relay 2 and the D-eNB 4, the UB 5 will use the D-eNB 4 or the active Relay 2 for camping on purposes. Once the D-eNB 4 or Relay 2 acquires the liE 5's traffic demand in terms of the required RBs, and noting that it cannot meet the QoS requirement of the UE's traffic, either the D-eNB 4 or Relay 2 can send a wake up call to the sleeping Relay 1. Given that the Relay 1 is located very close to UE 5, it would most likely be the optimum access node to handle the session. Thus, it is possible for the control node 4 -the D-eNB -to wake the sleeping Relay 1, or for a further relay, in this case active Relay 2, to wake said sleep Relay 1.

The wake up call may be triggered via the Serving MME if direct communication between a relay and its D-eNB is not possible. In case D-eNB triggers the wake-up call, it will be through the S1/X2/RRC signalling using the new WakeUP message described above. On the other hand, in case an active relay triggers such a wake up call, it can again use the same S1IX2 Signalling message and transmit same via the respective D-eNB 4. As the WakeUp message contains the IMSI-like ID of the relay (i.e., UE-part of the relay), it will be routed to the correct destination by the D-eNBs. 4 t_

It will be appreciated that the control node -which may be the MME or D-eNB, depending upon the Architecture Alternative used, will maintain a record of which mode each relay is currently in.

In the present embodiment, both Relays 1 and 2 belong to the same D-eNB 4, and hence the task is straightforward. If the Relays 1, 2 belong to different D-eNBs, the Wake Up message is routed via X2 interface between two D-eNBs. Once the relays which were initially in their STANDBY mode have been woken up, measurements in both the downlink and uplink will be taken to evaluate the most appropriate relays. Once the most appropriate relay or any other cell is identified, handover will take place in the conventional way.

Unselected relays that are not serving any active UE (i.e. no UEs in their RRC CONNECTED mode) will switch to STANDBY mode on receiving an "GoToSleep" message from their respective D-eNBs/MMEs or after non-activity timeout (TJDLE) -depending on whichever happens first.

On seeing an incoming call, the D-eNB 4 or an active relay can send the paging message originated from the MME to the UE 5 directly. If the traffic demand is too high for the camped on cell to support, it will wake up and choose the appropriate relay for a handover. 4 -.

The outgoing call can be handled in a similar way, whereby the initial control signalling takes place between the active Relay 2 or the D-eNB 4 and the UIE 5. On seeing that the traffic demand by the UE 5 cannot be met by the camped on cell, the traffic can be handed over to the most appropriate Relay 1. If the camped on cell is either a D-eNB 4 or another active Relay 2, they can either issue directly or get the serving MME to issue the wake up message to the most appropriate sleeping relays.

In a second example, also described with reference to Figure 5, there is provided a D-eNB controlling a domain, with a Relay 3 located at the domain edge to extend coverage. A UE 6 is located within the cell of Relay 3. It should be noted that the UE 6 is not within the coverage of any other access node.

If relays are used to extend the coverage, these relays cannot sleep continuously. This is because there is no other E-UTRAN entity to trace the presence of a UE 6 within the coverage area of the relay in question that is about to initiate an outgoing sessionlcall and to wake up a sleeping Relay 3. However, a Relay 3 can sleep provided that it wakes up periodically by itself in order to see whether there exists any LIE 6 within its coverage that needs to be served. The frequency of a wake-up cycle may depend on the traffic pattern of the cell. Cell planning is required (i.e., considering the worst-case peak traffic pattern in the relay region) before the frequency of this cycle pattern can be determined. For instance, the frequency of this cycle pattern in an urban area is higher than that of a rural area.

Sometimes the frequency of the sleep cycle can be zero meaning that the relay is ON all the time. According to this solution, a Relay 3 which is in standby mode periodically becomes J.__ alive and transmits BCH, D-SCH and RACH information. However, if there are no active UEs, the Relay 3 can switch to their power saving mode after a certain time out. In other words, they cannot sleep continuously. Instead each sleeping Relay 3 should come to life in an on-and-off manner by itself without being woken up by neighbouring active relays nor by a D-eNB 4. Thus a relay is operable in some scenarios to revert from a standby mode to an active mode after a further predetermined period, and revert back to a standby mode after a second predetermined period. Said first and second periods are determined as traffic patterns of the cell.

In an arrangement with a Relay 3 in standby mode and where an UE 6 in IDLE mode within its coverage is going to get an incoming sessionlcall, the MME or D-eNB 4 first needs to wake up the sleeping Relay 3 in order to facilitate the UE 6 to camp on the woken up relay.

On the other hand, in case of an outgoing call, the UE 6 needs to wait until the Relay 3 reverts to active status.

Industrial applicability

The present arrangement is particularly suitable for LTE-A telecommunication networks, however, it is also applicable for WiMAX (both IEEE 802.16e and IEEE 802.20) and Long range WiFi.

It should be noted that the above described embodiments are for reference and understanding only, and additional modification are included within the scope as defined by the claims.

Claims

Claims 1 A method of controlling a telecommunication system, said telecommunication system comprising: one or more user equipments; a relay comprising a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node; and a control node, wherein said method comprises the steps of: i) having said second aspect of said relay monitor communication sessions between said relay and said one or more users equipments, wherein, ii) if no communication session is detected within a predetermined period, said second aspect informs said first aspect and reverts to a standby mode; and iii) said first aspect informs said control node and reverts to a standby mode.
2. A method according to claim 1 wherein the second aspect takes periodic measurements at Li or L2 level to determine whether any communications sessions are currently supported.
3. A method according to either claim 1 or 2, wherein the relay is a type 1 relay.
4. A method according to any preceding claim wherein the control node is either a eNBoraMME.I
5. A method according to any preceding claim wherein the predetermined period is operable to be varied depending upon system conditions.
6. A telecommunication system comprising: i) a control node; and ii) a relay comprising a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node, wherein, said control node is operable to send a message to said first aspect of said relay to instruct said first aspect to revert to a standby mode.
7. A telecommunications system according to claim 6, wherein, said first aspect instructs said second aspect to revert to a standby mode after receiving said message from the control node.
8. A telecommunication system according to either claim 6 or 7, wherein said system further comprises: a plurality of user equipments, wherein, said control node assigns identifiers to each of the plurality of user equipments and the first aspect of said relay, wherein the control node is operable to use said identifier of said first aspect to message the first aspect to revert to a standby mode.
9. A telecommunication system comprising: i) a control node; ii) one or more relays, wherein at least one of said one of said relays is in a standby mode, and wherein each of said one or more relays comprises a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node; iii) a plurality of user equipments, wherein, each of the plurality of user equipments and the first aspect of the one or more relays are assigned user equipment identifiers by the control node, and that said identifier is used by the control node to activate the first aspect of the at least one relay in the standby mode.
10. A telecommunications system according to claim 9, wherein the first aspect activates the second aspect of the one or more relays.
11. A telecommunications system according to claim 9 or claim 10, wherein the control node maintains a record of whether the one or more relays in are an active mode or a standby mode.
12. A telecommunications system according to any of claims 9 to 11, wherein the control node is a D-eNB or a MME.
13. A telecommunications system according to any of claims 8 to 11, wherein the identifiers are C-RNTIs.
14. A telecommunications system according to any of claims 6 to 11, wherein the one or more relays are type I relays. * &
15. A telecommunications system according to any of claims 9 to 12, wherein a further relay may prompt the control node to activate the relay in standby mode.
16. A telecommunications system according to claim 15, wherein the relay in standby mode periodically reverts to active mode without any message from the control node.
17. A telecommunications system according to any of claims 9 to 11, wherein the control node is a MME, and that the system further comprises a D-eNB, wherein, should the D-eNB wish to activate the relay in standby mode, it first indicates its intention to the MME.
18. A relay operable to revert from a standby mode to an active mode after a first predetermined period, and revert back from said active mode to said standby mode after a second predetermined period.
19. A relay according to claim 18, further comprising a first aspect comprising the functionality of a user equipment and a second aspect comprising the functionality of a control node, such that only said second aspect periodically alternates between said standby and active modes.
20. A relay according to either claim 18 or claim 19, wherein one or both of the first and second predetermined period is calculated based on either the location of the relay or the time.