WO2012148009A1

WO2012148009A1 - A wireless telecommunications system

Info

Publication number: WO2012148009A1
Application number: PCT/JP2012/061932
Authority: WO
Inventors: Sivapathalingham Sivavakeesar
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2011-04-28
Filing date: 2012-05-01
Publication date: 2012-11-01
Also published as: GB201107282D0; GB2490366A

Abstract

A wireless telecommunications system comprises (a) a base station, (b) a first relay node with a backhaul link to the base station, and an access link to one or more user equipments, (c) one or more further nodes. The system is operable to determine the bottleneck of the overall link consisting of the access link and backhaul link of the relay node in terms of physical resource blocks (PRB) usage being measured separately on access link and backhaul link. Further, the said overall link is considered from the perspective of a said user equipment and transmit the determined bottleneck information to each of the one or more further nodes.

Description

DESCRIPTION

TITLE OF INVENTION:

A WIRELESS TELECOMMUNICATIONS SYSTEM

TECHNICAL FIELD

The present invention relates to L2 measurements taken on the relay backhaul of a relay node (especially a Type- 1 in- band relay) as applicable in the context of 3GPP Long Term Evolution (LTE) -Advanced. The arrangement is particularly useful in relation to cell load-balancing.

BACKGROUND ART

The first release of the LTE was referred to as release-8 , and provided a peak rate of 300 Mbps , a radio network delay of less than 5ms, an increase in spectrum efficiency and new architecture to reduce cost and simplify operation .

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

20 10 onwards as a natural evolution of GSM and UMTS .

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

In April 2008 , 3GPP agreed to the 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 for a peak data rate of 1 Gbps and also targets faster switching between power states and improved performance at the cell edge.

The section below briefly discusses the network architecture of an LTE wireless communications network. Further details may be found at www.3gpp. org.

The base station - or 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 negotiated up-link 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 physical layer is often termed Layer 1 . The Medium Access Control layer (MAC) , Radio Link Control (RLC) layer, and Packet Data Control Protocol (PDCP) layer are collectively know as Layer 2. The Radio Resource Control is usually termed Later 3.

An LTE network provides two interfaces: S I interface to connect the eNodeBs to the core network gateway, and an X2 interface to perform inter-base station connections .

Relaying is considered as an economical way of extending the coverage of a wireless communication system by improving the cell-edge throughput and system capacity. 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, and is achieved by the Un interface. 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 . A D-eNB controls network traffic within a domain . Said domain may include a plurality of further nodes. Domains located geographically next to one another may be termed neighbouring domains.

A UE connected directly to a D-eNB is considered to be directly linked, or to comprise a direct link. Such a UE may be termed a Macro UE, or a M-UE.

A UE's connection to a relay node is termed an access link. This is achieved by the Uu interface . A UE connected to a relay node is often termed R-UE.

In order to support network radio link operations, radio resource management (RRM) , network operations and maintenance (OAM) , and self-organising networks (SON) , generally measurements are taken by an eNB and are transferred over standardised interfaces. In this connection, a number of layer 2 (L2) measurement parameters are defined in TS 36.3 14. A copy of this documents is available at www.3gpp.org. The contents thereof are hereby incorporated by reference .

For a D-eNB , the L2 measurements have specific significance in the following areas:

i) Cell load-balancing;

ii) OAM performance monitoring; and

iii) Configuration optimization

In current network architectures, some of these L2 measurements are taken by an eNB per quality of service class identifier (QCI) and/ or UE . Six different types of measurement parameters have been defined, as specified in TS 36.3 14 - they consist of:

1 . PRB usage : this is to measure the usage of time and frequency resources . This is measured to perform cell load balancing, where PRB usage is used for information signalled across the X2 interface, and OAM performance monitoring.

2 . Received Random Access Preambles: the measured quantity in this case is the number of received Random Access preambles during a time period over all PRACHs configured in a cell. This is used for configuration optimization

3. Number of active UEs: this measures the number of active UEs per QCI for OAM performance monitoring.

4. Packet Delay: this is to measure L2 Packet Delay for OAM performance monitoring.

5. Data Loss : this is to measure packets that are dropped due to congestion, traffic management etc for OAM performance monitoring.

6. Scheduled IP Throughput: this is to measure over Uu the IP throughput independent of traffic patterns and packet size . This measurement is performed per QCI per UE.

These measurements are executed by the L2 sub-layers, i. e . PDCP, RLC and MAC .

Load balancing is one aspect of SON being built into the design of LTE. The obj ective of load balancing is to counteract local traffic load imbalance between neighbouring cells with the aim of improving the overall system capacity. In order to detect an imbalance , comparing with neighbouring cell loads is desirable . This is method is typically achieved with the exchange of cell load information via the X2 interface . One way to convey the load is through the periodic measurement of PRB usage . The present invention seeks advantages in how load balancing within the network is performed.

EP 2,207,277, US 2008/080436, WO 2010/121661, WO 2009/131898 and GB 2,475,851 relate to documents in related technical fields.

SUMMARY OF INVENTION

According to a first aspect of the present invention there is provided a wireless telecommunications system comprising: a base station; a first relay node with a backhaul link to the base station, and an access link to one or more user equipments; and one or more further nodes, wherein, the system is operable to determine the bottleneck of the overall link consisting of the access link and backhaul link of the relay node in terms of physical resource blocks (PRB) usage being measured separately on access link and backhaul link, wherein the said overall link is considered from the perspective of a said user equipment and transmit the determined bottleneck information to each of the one or more further nodes.

Preferably the base station is a D-eNB. The above arrangement allows for meaningful load- balancing operations to be performed in the system. For example , if the relay node has capacity on its access link, but the backhaul link is exhausted (for example due to encapsulation overhead, increased backhaul signalling, and channel impairments) , the present arrangement allows for neighbouring nodes to ascertain that the relay node is not a candidate to receive further wireless communication traffic . PRB usage in the present arrangement is individually and separately measured on the Uu interface and the Un interface by different entities - i. e . , on the access link relevant measurements are taken by a relay whereas on the backhaul link the D-eNB is responsible for such measurements . The bottleneck of the overall link (both the Uu and Un interfaces) is determined in terms of PRB usage for the purpose of cell load-balancing and OAM performance monitoring.

Thus, it will be apparent that the present arrangement makes use of two separate measurements to determine the overall load on a given relay node, and thus determine the bottleneck in the overall link consisting of the access link and backhaul link of a given relay node .

It is preferable that the base station is configured to take backhaul link specific PRB usage and disseminate it to one or many relay nodes being served by itself and other further nodes (neighbouring nodes) , while each relay node is configured to take access link specific PRB usage and each relay node determines its resource bottleneck based on the backhaul link specific PRB usage obtained from its base station and the access link specific PRB usage it measured .

Preferably, the backhaul link specific PRB usage measured by a base station can be further measured per each relay being served by it

It is preferable that the relay node is configured to acquire details of it's backhaul link from the base station on demand, if required, and that the relay node use such details to calculate its combined load condition

Preferably, the relay node is operable to transmit the determined bottleneck information to the one or more further nodes using the X2 interface . If the relay node does not maintain an X2 interface with each of the one or more further nodes, it is preferred that the relay node uses the base station's proxy functionality to transmit the determined bottleneck information to the one or more further nodes. It is preferable that the one or more further nodes is/ are of Rel-8 / 9 eNB type.

In wireless communication systems, the total number of available subcarriers depends on the overall transmission bandwidth of the system. LTE systems define bandwidths from 1 .25 MHz to 20 MHz. A PRB is defined as consisting of 12 consecutive subcarriers for one slot (0.5 msec) in duration. A PRB is the smallest element of resource allocation assigned by a base station. It is preferred that the bottleneck information is determined by the following operation:

PRB usage to be disseminated to the one or more further nodes

= max{ PRB usage on access link,

PRB usage on backhaul}.

The arrangement looks to find the highest PRB usage on either the backhaul link and the access link, and use this value as a load condition of a relay node . If one of the two links is at or close to capacity, it does not matter if the other link has capacity; the relay will be at or close to capacity. The bottleneck information is based on the load condition .

It is preferred that the PRB usage may be calculated as a percentage of total available resource (ie if the usage on the backhaul link is l Omb, and the total bandwidth of the link is 50mb, then the link is at 20% capacity) .

Preferably the system further comprises one or more user equipments directly linked to the base station. It is preferred that if the relay node shares radio resources with said one or more directly linked user equipments, the relay node is operable to directly obtain details of its backhaul link from the base station .

It is preferred that if the relay node does not share radio resource with said one or more directly linked user equipments, the relay node is operable to demand information regarding its backhaul link from the base station.

In a second aspect of the present invention there is provided a wireless telecommunications system comprising: a base station; and a relay node and a further node, said relay node comprising a backhaul link to the base station, and respective access link to one or more user equipments, wherein, the relay node is operable to make a measurement of its PRB usage on the access link and transmit measured PRB usage to the further node, the further node is operable to identify the relay node 's base station, obtain information regarding the backhaul link specific PRB usage and collate a load condition for the relay node based on the obtained information in order to determine the bottleneck of the overall link consisting of the access link and the backhaul link from the perspective of a said user equipment.

It is preferable that in case a further node receives backhaul specific PRB usage of a relay from a base station, it will identify the relay and request the access link specific PRB usage on demand in order to determine the bottleneck of the overall link.

For any node (can be a base station, a relay, or a further node) to determine the overall bottleneck of a relay node, two pieces of relay-specific information (i. e . , PRB usage of both access link and backhaul link) needs to be available . No matter in what sequence they are received, if only one piece of information is available, the node can obtain the other piece from the respective relay or the D-eNB on demand. Preferably the obtained backhaul link specific PRB usage being measured by a base station can be further measured per each relay being served by it.

It is preferable that the further node is a base station that has capabilities as stipulated by Rel- 10. In another preferred arrangement the further node is a relay node .

In this arrangement neighbouring nodes are operable to determine the load condition for relay nodes. It will be appreciated that in arrangements with multiple relay nodes associated with a D-eNB , a relay node will disseminate its access link load information to each of the relay nodes .

Preferably the bottleneck on the overall link is determined by the following protocol:

PRB usage to be disseminated to the one or more further nodes

= max{ PRB usage on access link,

PRB usage on backhaul}.

According to a third aspect of the present invention there is provided a wireless telecommunications system comprising: a base station; a first relay node with a backhaul link to the base station, and an access link to one or more user equipments; and one or more further nodes, wherein, the system is operable to determine the bottleneck of the overall link consisting of the access link and backhaul link of the relay node in terms of load being measured separately on access link and backhaul link using the following protocol: PRB usage to be disseminated to the one or more further nodes = max{ PRB usage on access link, PRB usage on backhaul}, wherein the said overall link is considered from the perspective of a said user equipment.

According to the present invention there is provided a wireless telecommunications system that is operable to selectively implement the first aspect of the present invention and the second aspect of the present invention.

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

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows an example of part of a network architecture .

Figure 2 shows a sequence involved in disseminating a relay node's load to neighbouring nodes in accordance with a first embodiment.

Figure 3 illustrates how PRB usage measurements from a relay node are interpreted by a neighbour node in accordance with a second embodiment.

DESCRIPTION OF EMBODIMENTS

The present arrangement relates to a wireless telecommunications system. Such systems generally comprise one or more base stations. In long term evolution systems these are termed eNBs. Each eNB will be linked to the core network. The controlling eNB is generally referred to as a D-eNB . A D-eNB controls network traffic originating from or destined to one or more relays within a domain. Said domain may include a plurality of further nodes . Domains located geographically next to one another may be termed neighbouring domains.

In LTE Rel- 10 and further future releases D-eNBs will have capabilities to serve both UEs and relay nodes . Under such circumstances, a D-eNB will maintain a direct link with a M-UE, which it serves via the Uu interface and a backhaul link to serve a relay node via the Un interface . A relay node will maintain an access link to

a UE (termed R-UE) that is connected via the Uu interface .

Figure 1 shows an example of part of an LTE network architecture . Here, D-eNB 10 maintains a direct link with macro UE (M-UE) 12. This link is supported by the Uu interface . D-eNB 10 is also connected to a relay node 14. This connection is supported by the Un interface, and is termed the relay node 's backhaul link.

Type 1 Relay nodes are operable to support a communication link to a UE 16 in the same manner as a D- eNB . The link between a relay node 14 and a UE is via the Uu interface. UEs connected to a relay node are termed relay-UEs, or R-UEs .

The 3GPP agreed that relay nodes should perform the L2 measurements on the Uu in the same way as an eNB does without any consideration of the Un. Thus, a relay node is required to take L2 measurements on its access link and report to its OAM , whereas the D-eNB 10 has to take measurements on the relay node 's backhaul and report to its respective OAM . This type of independent operation will not cause undesirable effect in terms of the way they are interpreted by different entities/ nodes in the network in the case of many of the L2 measurement metrics/ parameters as listed above . However, the measurement of PRB usage, if taken and treated independently, will create a wrong picture, especially to the neighbour nodes of a relay node, and thereby will lead to undesirable effects . This is because when considering load balancing, the resource status of the relay node's backhaul is an important input to the calculation of the total relay node resource status . Thus, if either a relay node's 14 access link or backhaul link resources are exhausted, that relay node 14 will not be in a position to serve further R-UEs.

A relay differs from other E-UTRAN nodes in that it needs to maintain two independent wireless links simultaneously. Either or both of these links may be in-band. The backhaul link is as important as the access link in the operation of a relay node . Applying a strict modular principle, and thereby treating these links independently for L2 measurement purposes may give a false result. Applying optimisations independently on each link will not bear what L2 measurements are trying to achieve : if there is capacity on the access, but the backhaul link is exhausted namely due to increased backhaul signalling, encapsulation overhead and channel impairments the relay is effectively at its full operating capacity. Thus the result regarding the indication that the access link is able to support further wireless communication sessions is potentially misleading.

Optimisation operations have to be coordinated together on the access and backhaul links for an effective relay load- balancing operation. Although it is important that a relay node is treated differently to a D-eNB, if measurements are taken on the Uu interface and the Un interface independently, conveying the appropriate information of a relay node to neighbouring nodes for them to use these measurements in their load-balancing and handover decisions is important. Further constrains are that OAMs of a relay node and its D- eNB can have limited interactions - whether or not this limited number of interactions is enough to achieve the necessary OAM / SON and other optimisations and load- balancing is questionable, because constant interactions are preferred.

The PRB usage of an access link cannot serve its purpose unless combined with the associated measurement of backhaul link. The L2 measurement on the Uu interface is not sufficient to perform meaningful relay node load- balancing. Relying on the Uu interface measurements that are not representative of a specific relay node 14 will compromise the usefulness/ accuracies of the measurements.

According to a first embodiment there is provided a wireless telecommunications system comprising a base station - which is preferably a D-eNB - , a first relay node with a backhaul link to the base station, and an access link to one or more user equipments . Also provided is one or more further nodes. The system is operable to assess a combined load condition for the access link and backhaul link of the relay node and transmit same to each of the one or more further nodes. Thus, the system is operable to determine the bottleneck of the of the overall link consisting of the access link and backhaul link of the relay node in terms of the load, wherein the said overall link is considered from the perspective of a said user equipment and transmit the determined bottleneck information to each of the one or more further nodes.

According to this embodiment, it is disclosed that before disseminating the PRB usage measurement to neighbouring nodes, a relay node has to consider the combined PRB usage of both the access and backhaul links . This can be performed by the following operation:

The PRB usage to be disseminated to neighbouring nodes by a relay node

= max{ PRB usage on Uu, PRB usage on backhaul} ( 1 )

The above operation is governed by a maximization protocol.

The PRB usage may be calculated as a percentage of the total available resource.

The present arrangement addresses problems associated with load-balancing and handovers involving one or more relays. It particularly differs from the prior art referred to in the opening section of this document in what parameter is used (PRB usage) , how the parameter is acquired and implemented , and the timings of when the parameter is acquired.

It will be appreciated that the maximisation protocol needs to be performed irrespective of whether or not a relay node 14 is treated differently from M-UEs 12 by the D-eNB 10 for L2 measurements . This is also true no matter whether or not a relay node uses a specific set of radio resources that is different from that being used by a M-UE .

Relay nodes differ from other E-UTRAN nodes in that they have a wireless backhaul. By contrast an eNB typically maintains a wired backhaul. This link would typically comprise one or more optical fibres. In certain scenarios, an eNB backhaul can be a point-to-point out-of-band microwave link. Therefore, bandwidth is generally freely available on an eNB 's backhaul due to the massive amount of data that can be transmitted through an optical fibre .

By contrast, bandwidth can be very limited in a wireless relay node backhaul. In the case of an in-band relay node, the capacity and quality of the backhaul link is not better than those of the access link. Consider a scenario: a relay node disseminates its PRB usage to its neighbours, and suppose the load on access link is low, whereas the load on the backhaul is at capacity. Such dissemination may invite neighbouring nodes with a load-imbalance, or high capacity access links to consider handing over some of the cell edge traffic to the relay node as a way to redress the load imbalance problem. Given the exhausted backhaul link, the relay node will not be able to accept such handovers, and such an attempt will likely lead to a failed handover or unnecessary wasteful load balancing operations. The likelihood for this to happen in the case of an eNB is very minimal, as its backhaul capacity is much higher than that of a relay backhaul (due to the presence of a wired backhaul) . Load balancing through handover rejection may work in the case of eNB , but not with a relay node without wasting resources and incurring latency. Hence, if the load balancing is left to be effected through handover rejection, the cost and adverse effect would be high.

The problem gets aggravated when one of the neighbouring nodes is a legacy node, such as a Rel-8 / 9 eNB . This is because such an eNB does not perceive a relay node as a relay node, but as an eNB . In other words, it cannot determine whether the relay node comprises a wired or wireless backhaul link.

Any relay node, or its respective D-eNB , can perform the maximum-operation as set out in equation ( 1 ) . However, it is preferred that the relay node performs the operation . It is particularly preferred that the base station is configured to transmit details of the relay node 's backhaul link to the relay node, and that the relay node determines the bottleneck information.

If a relay node and M-UE share the same radio resources, the load information of D-eNB is readily available to the relay node - hence it is straightforward for the relay node to obtain the information. This is because a relay node can get the load information of the D-eNB in its capacity as a neighbour of the D-eNB . Thus, it is preferred that the system further comprises one or more user equipments directly linked to the base station, and further wherein if the relay node shares radio resources with said one or more directly linked user equipments, the relay node is operable to directly obtain details of its backhaul link from the base station.

If the relay node uses a different set of radio resources than that being used by any active M-UEs, the D-eNBs are required to measure this separately and distribute the information to each associated relay node to allow for each of them to do the maximum-operation (equation 1 above) . This is also true irrespective of whether each RN uses a specific set of resources or shares resources with other relays served by the same D-eNB .

The relay node is configured to acquire details of its backhaul link from the base station on demand . Thus, if the relay node does not share radio resource with said one or more directly linked user equipments, the relay node is operable to request information regarding its backhaul link from the base station on demand.

A relay node does not necessarily maintain the X2 interface with every neighbouring node . However, as it uses the D-eNB 's proxy functionality, the D-eNB can also perform the above maximum operation after having performed the Deep Packet Inspection (DPI) operation when a load information packet of a relay node traverses via the D-eNB .

The D-eNB can take a common Un PRB usage measurement for all of the relay nodes that it serves, or make a specific Un PRB measurement and transmit it to the relevant relay node . In either case, it is preferred that corrective measures are taken for a relay node to disseminate the combined PRB usage (load information) after performing the above-mentioned maximum-operation.

Figure 1 illustrates a process of disseminating the load information of a relay node to its neighbours. Initially the D- eNB 10 indicates its load information via the X2 interface to each of its neighbours . If the load indication message is specific to relays, the D-eNB 1 0 has to additionally pass that load indication information to each of the relay nodes under its control. In case the relay nodes and M-UEs use the same set of radio resources , the current load indication mechanism is sufficient.

Once a relay node acquires its backhaul-specific load, it is in a position to perform the maximum operation (as formulated by equation ( 1 )) . Once this is performed, the given relay node can disseminate the combined load to its neighbouring nodes. If the relay node does not maintain an X2 interface with each neighbouring node , it can use the D- eNB's proxy functionality for such load indication dissemination .

In a second embodiment, a neighbouring node performs the maximum operation (as formulated by equation ( 1 )) for a given relay node . This method is facilitated when all neighbouring nodes are operable to interpret a relay node as a relay node (as opposed to an eNB) . Accordingly, a relay node takes the PRB usage measurement (or load information) on the access link and disseminates the data to its neighbours. When a neighbour node receives the PRB usage measurement from one of its neighbouring relay nodes, it will await a PRB measurement pertaining to the backhaul from the respective D-eNB , if it has not already received it. If required, the neighbour node can obtain such a measurement from the D- eNB on-demand .

In this embodiment there is thus provided a wireless telecommunications system comprising a base station (typically a D-eNB) , a relay node and a further node . The further node is preferably a base station that has capabilities as stipulated by Rel- 10 (and ideally configured to support future releases) . Alternatively, the further node may be a relay node. The relay node comprising a backhaul link to the base station, and respective access link to one or more user equipments . The relay node is operable to make a measurement of its PRB usage on the access link and transmit same to the further node, and the further node is operable to identify the relay node's base station, obtain information regarding the backhaul link specific PRB usage and collate a load condition for the relay node based on the obtained information . The present system thus permits the determination of a bottleneck of the overall link consisting of the access link and the backhaul link from the perspective of a said user equipment.

According to the second embodiment, it is also possible that in case a further node receives backhaul specific PRB usage of a relay from a base station, it will identify the relay and request the access link specific PRB usage on demand in order to determine the bottleneck of the overall link.

It can be now understood that according to the previous embodiments, for any node (can be a base station, a relay, or a further node) to determine the overall bottleneck of a relay node, two pieces of relay-specific information (i . e . , PRB usage of both access link and backhaul link) needs to be available. No matter in what sequence they are received, if only one piece of information is available, the node can obtain the other piece from the respective relay or the D-eNB on demand .

The obtained backhaul link specific PRB usage measured by the base station can be further measured by each relay being served by the base station.

If the D-eNB 10 treats the relay node 14 as an M-UE 12 from the perspectives of L2 measurements, the D-eNB takes the combined PRB usage measurement (considering relay node and M-UE) and disseminates it as required by the legacy Rel-8 / 9 L2 measurement mechanism. This is applicable when rela nodes and M-UEs share the same set of radio resources.

Situations where relay nodes uses a specific set of radio resources that differs from those being used by M-UEs , it is preferable for the D-eNB to take separate PRB usage measurements different from that of the M-UEs . In one embodiment, the D-eNB can treat each relay node it controls differently, and take relay node specific PRB usage measurement pertaining to the respective backhaul links.

Irrespective of how the D-eNB obtains PRB usage measurements, neighbouring nodes have to wait for such a measurement and combine the data with that received from a given relay node . Once a neighbour node has received the PRB usage measurement pertaining to an access link and the backhaul link of a relay node from a given relay node and the D-eNB respectively, the neighbour node has to perform the maximum operation . The neighbour node is required to take the PRB usage measurement resulting from the maximum operation into consideration for any of its load balancing or handover related operations involving a respective relay node .

The PRB usage in the above context means the downlink PRB usage for traffic, uplink PRB usage for traffic, downlink Total PRB usage, and uplink Total PRB usage .

The overall idea is to determine the bottleneck of the overall link consisting of the access link and backhaul link of the relay node in terms of the load . The overall link is considered from the perspective of an R-UE. The load condition on either the access link or the backhaul link is measured in terms of the PRB usage . This PRB usage, of either the access link or the backhaul link can preferably be a relative measure in that it is the ratio or percentage of used PRB to the overall capacity.

The total PRB usage may be calculated based on the following equations: total PRB usage = (RN PRBs + UE PRBs)

/ total PRBs

where, RN PRBs indicate the PRB used for info to/ from a relay node connected to the D-eNB ; UE PRBs indicate the PRB used for info to / from a UE connected to the

D-eNB ; and total PRBs indicate the total PRB capacity (used and unused PRBs) . Also:

Total PRB usage per RN = RN PRBs / total PRBs .

Further, if needed, the PRB usage can be measured seperately per different QCIs . In this connection the following two statements apply:

i) RN PRBs for a certain QCI

/ total PRBs;

ii) (RN PRB + UE PRB s) for a certain

QCI / total PRBs . In the case of Received Random Acces s Preambles, given that a Rel- 10 relay node can access the network in the capacity of a UE, a single measurement is sufficient by treating a relay node as a M-UE . If a relay node uses a different sets of preambles (either on the same PRACH being used by M-UEs or on a different relay specific R-PRACH) from those used by M-UEs, a separate L2 measurement for Received Random Access Preambles has to be taken by the D- eNB . Figure 2 illustrates the sequence involved in disseminating the load of an RN 14 to one or more further nodes (i. e . , any of its neighbours) as per the first embodiment. Initially the D-eNB 10 is supposed to indicate its load via the X2 interface to its neighbours . If the load indication message is specific to relays 14 , the D-eNB 10 has to additionally pass the details of the backhaul link of an RN 14 in question , especially the load indication information, on to every RN 14 it serves . On the other hand, in case relays 14 and M-UEs 12 use the same set of radio resources, the current load indication mechanism is suffice - hence, in this case the D- eNB 10 does not need to pass the backhaul-specific details of an RN 14 in question to that particular RN 14. In other words, such information is directly and automatically available from the D-eNB 10. M-UEs 1 2 are one or more user equipments directly linked to the base station D-eNB 10.

In case an RN 14 has not received the details of the backhaul link from the D-eNB 10 or if an RN 14 does not share radio resource with one or more directly linked user equipments (i. e . , M-UEs 12) , the RN 14 in question can request information regarding its backhaul link from the base station, D-eNB 1 0 , on demand.

Once an RN 14 has got to know its backhaul specific load, it has to perform the maximum operation as formulated by equation ( 1 ) in order to assess a combined load condition considering the access link and the backhaul link. Once this is performed, the given RN 14 can disseminate the details of its load condition (i.e . , combined load considering both the access link and the backhaul link) to one or more further nodes (i. e . , any of its neighbours) . In case it does not maintain the X2 interface with every neighbour, it can use the D-eNB 's 10 proxy functionality for such load indication dissemination .

Figure 3 illustrates how PRB usage measurements from a relay node 14 are interpreted by a further node (i. e . , a neighbour node of an RN 14 in question) in accordance with a second embodiment. In operation ( 1 ) , an RN 14 disseminates the RN-specific load information to its neighbours via X2 interface. For this purpose, an RN 14 in question makes a measurement of its PRB usage on the access link and transmit measured PRB usage to the further node (i.e . , a neighbour node of an RN 14 in question) . A D-eNB 10 will receive such information because of its capacity as a neighbour node . If an RN 14 does not maintain an X2 interface with all of its neighbours, it can use the proxy functionality of the D-eNB 10 to disseminate the load information as indicated by operation (2) . With the operation (3) , a further node (i. e . , a neighbour node of an RN 14 in question) requests to obtain information regarding the relay node's PRB usage on the backhaul link (especially the load information) from the D-eNB 10 of an RN 14 in question on demand (i. e . , pull approach from the perspective of a neighbour node) in response to operation (2) and the D-eNB will supply such information as indicated by operation (4) . In case the RN 14 in question and all M-UEs 12 share the same physical radio resources, the D-eNB 's load information (i. e . , total PRB usage) is enough without having to consider relay- specific PRB usage on the backhaul.

The operation of (3) to send the RESOURCE STATUS REQUEST message by a neighbour node for the purpose of requesting the corresponding PRB usage measurement from the respective D-eNB of the RN in question on demand as indicated in Figure 3 may not be needed in case D-eNB periodically sends (e . g. , push approach from the perspective of the D-eNB) the PRB usage measurement to its neighbour node . Based on the obtained information, a neighbour node will determine the bottleneck of a relay node by considering the loads of both the access link and the backhaul link as indicated by operation (5) .

As will be understood, a wireless telecommunications system can selectively implement the solutions as proposed by first embodiment or the solutions as proposed by second embodiment depending on the capabilities of one or more further nodes (i.e . , a neighbour node of an RN 14 in question) . In case a further node is a legacy node whose operations are governed as stipulated by Rel-8 / 9 , the solutions as proposed by first embodiment need to be implemented - in this case the solutions of the second embodiment cannot work at all. On the other hand, a further node is built in accordance with Rel- 10 or future releases , the solutions as proposed by second embodiment can preferably implemented although the solutions of the first embodiment can still work.

It is noted that the present invention may be expressed as below.

A first wireless telecommunications system comprises a base station;

a first relay node with a backhaul link to the base station, and an access link to one or more user equipments; and

one or more further nodes,

wherein, the system is operable to determine the bottleneck of the overall link consisting of the access link and backhaul link of the relay node in terms of the load, wherein the said overall link is considered from the perspective of a said user equipment and transmit the determined bottleneck information to each of the one or more further nodes. In the first wireless communications system, the base station may be a D-eNB .

In the first wireless communications system, the base station may be configured to transmit details of the relay node 's backhaul link to the relay node, and that the relay node determines the bottleneck information.

In the first wireless communications system, the relay node may be configured to acquire details of it's backhaul link from the base station on demand.

In the first wireless communications system, the relay node may be operable to transmit the determined bottleneck information to the one or more further nodes using the X2 interface . In the first wireless communications system, the base station may comprise proxy functionality, and the relay node uses the base station's proxy functionality to transmit the determined bottleneck information to the one or more further nodes.

In the first wireless communications system, the one or more further nodes may be of Rel-8 / 9 eNB type .

In the first wireless communications system, the determined bottleneck information of the relay node may be calculated using its usage of physical resource blocks (PRB) .

In the first wireless communications system, the load condition may be determined by the following maximization operation :

PRB usage to be disseminated to the one or more further nodes

= max{ PRB usage on access link,

PRB usage on backhaul}.

In the first wireless communications system, the PRB usage may be calculated as a percentage of total available resource . In the first wireless communications system, the system further may comprise one or more user equipments directly linked to the base station, and further if the relay node shares radio resources with said one or more directly linked user equipments, the relay node may be operable to directly obtain details of its backhaul link from the base station.

In the first wireless communications system, if the relay node does not share radio resource with said one or more directly linked user equipments, the relay node may be operable to request information regarding its backhaul link from the base station on demand .

A second wireless telecommunications system comprises a base station ; and

a relay node and a further node , said relay node comprising a backhaul link to the base station, and respective access link to one or more user equipments, wherein,

the relay node is operable to make a measurement of its PRB usage on the access link and transmit measured PRB usage to the further node,

the further node is operable to obtain information regarding the relay node's PRB usage on the backhaul link and collate a load condition for the relay node in order to determine the bottleneck of the overall link consisting of the access link and the backhaul link from the perspective of a said user equipment.

In the second wireless communications system, the further node may be a base station that has capabilities as stipulated by Rel- 10.

In the second wireless communications system, the further node may be a relay node .

In the second wireless communications system, the load condition may be determined by the following protocol:

PRB usage to be disseminated to the one or more further nodes

= max{ PRB usage on access link,

PRB usage on backhaul}.

A wireless telecommunications system may be operable to selectively implement the first wireless telecommunications system and the second wireless telecommunications system .

The above described specific embodiments are described by way of example only, and many variations and modifications are available within the scope of the present invention.

Claims

1 . A wireless telecommunications system comprising: a base station;

one or more further nodes,

wherein, the system is operable to determine the bottleneck of the overall link consisting of the access link and backhaul link of the relay node in terms of physical resource blocks (PRB) usage being measured separately on access link and backhaul link,

wherein the said overall link is considered from the perspective of a said user equipment and transmit the determined bottleneck information to each of the one or more further nodes .

2. A wireless communications system according to claim 1 , wherein the base station is a D-eNB .

3. A wireless communications system according to claim 1 or 2 , wherein the base station is configured to take backhaul link specific physical resource blocks (PRB) usage and disseminate it to one or many relay nodes being served by itself and other further nodes, while each relay node is configured to take access link specific physical resource blocks (PRB) usage and each relay node determines its resource bottleneck based on the backhaul link specific physical resource blocks (PRB) usage obtained from its base station and the access link specific physical resource blocks (PRB) usage it measured.

4. A wireless communications system according to any of claim 1 to 3 , wherein the backhaul link specific physical resource blocks (PRB) usage measured by a base station can be further measured per each relay being served by it

5. A wireless communications system according to claim 3 or 4 , wherein the relay node is configured to acquire backhaul link specific physical resource blocks (PRB) usage from the base station on demand rather than requiring a base station to disseminate it. 6. A wireless communications system according to any of claims 3 to 5 , wherein the relay node is operable to disseminate the determined bottleneck information to the one or more further nodes wireless communications system according claim 6, wherein the relay node is operable to disseminate the determined bottleneck information to the one or more further nodes using the X2 interface.

8. A wireless communications system according to any of claims 3 to 7 , wherein the base station comprises proxy functionality, and the relay node uses the base station's proxy functionality to transmit the determined bottleneck information to the one or more further nodes .

9. A wireless communications system according to any preceding claim, wherein the one or more further nodes is / are of Rel-8 / 9 eNB type.

10. A wireless communications system according to any preceding claim, wherein the bottleneck on the overall link is determined by the following maximization operation:

PRB usage to be disseminated to the one or more further nodes

= max{ PRB usage on access link,

PRB usage on backhaul}.

1 1 . A wireless communications system according to claim 10, wherein the PRB usage is calculated as a percentage of total available resource on either link.

12. A wireless communications system according to any preceding claim, wherein the system further comprises one or more user equipments directly linked to the base station, and further wherein if the relay node shares radio resources with said one or more directly linked user equipments, the relay node is operable to directly obtain details of its backhaul link from the base station.

13. A wireless communications system according to claim 12 , wherein if the relay node does not share radio resource with said one or more directly linked user equipments, the relay node is operable to request information regarding its backhaul link from the base station on demand.

14. A wireless telecommunications system comprising: a base station; and

a relay node and a further node, said relay node comprising a backhaul link to the base station, and respective access link to one or more user equipments, wherein,

the further node is operable to identify the relay node's base station, obtain information regarding the backhaul link specific PRB usage and collate a load condition for the relay node based on the obtained information in order to determine the bottleneck of the overall link consisting of the access link and the backhaul link from the perspective of a said user equipment.

15. A wireless communications system according to claim 14 , wherein the obtained backhaul link specific physical resource blocks (PRB) usage being measured by a base station can be further measured per each relay being served by it

16. A wireless communications system according to claim 14 , wherein the further node is a base station that has capabilities as stipulated by Rel- 10.

17. A wireless communications system according to claim 14 , wherein in case a further node receives backhaul specific PRB usage of a relay from a base station, it will identify the relay and request the access link specific PRB usage on demand in order to determine the bottleneck of the overall link.

18. A wireless communications system according to any of claims 14 to 17, wherein bottleneck on the overall link is determined by the following protocol:

PRB usage to be disseminated to the one or more further nodes

= max{ PRB usage on access link,

PRB usage on backhaul}.

19. A wireless telecommunications system that is operable to selectively implement the system of claim 1 and the system of claim 14.

20. A wireless telecommunications system comprising: a base station;

one or more further nodes,

wherein, the system is operable to determine the bottleneck of the overall link consisting of the access link and backhaul link of the relay node in terms of load being measured separately on access link and backhaul link using the following protocol:

PRB usage to be disseminated to the one or more further nodes

= max{ PRB usage on access link,

PRB usage on backhaul}, wherein the said overall link is considered from the perspective of a said user equipment.