WO2013045698A1

WO2013045698A1 - Localised cells

Info

Publication number: WO2013045698A1
Application number: PCT/EP2012/069350
Authority: WO
Inventors: Karol Drazynski; Troels Emil Kolding; Jeroen Wigard; Johanna Katariina Pekonen; Pawel Ochal; Jani Matti Johannes Moilanen; Klaus Ingemann Pedersen; Guillaume DECARREAU
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-09-30
Filing date: 2012-10-01
Publication date: 2013-04-04

Abstract

A technique comprising: receiving measurement information about measurements made at a plurality of first access cells of transmissions made by network transmitters; determining on the basis of said measurement information a set of said first access cells for association with a second access cell with which said set of first access cells at least partially overlap; updating neighbour cell information for said second access cell based at least partly on the result of said determining; and sending said updated neighbour cell information for said second access cell to one or more communication devices.

Description

DESCRIPTION

TITLE

LOCALISED CELLS

A mobile telecommunication network providing mobile telecommunication services to subscribers of the network can comprise an array of large area cells each dotted with smaller area localised cells.

Examples of mobile telecommunication services include communication of voice, electronic mail (email), text messages, data, multimedia etc..

A mobile telecommunication network typically operates in accordance with a wireless standard. Examples include GSM (Global System for Mobile) EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN), Universal Terrestrial Radio Access Networks (UTRAN), and evolved Universal Terrestrial Radio Access Networks (EUTRAN).

Localised cells are used in a mobile telecommunication network to supplement larger area cells. The localised cells are typically operated in a residential home or a small business, and can provide improvements in access to mobile telecommunication services via the mobile telecommunication network in the vicinity of the residential home or small business. Examples of locations where increased deployment of localised service areas are anticipated include populated urban areas such as large building complexes, and hot-spot public places such as exhibition centres, museums, railway stations or airports.

Some communication devices need to receive configuration information about a localised cell in order to detect and measure transmissions from that localised cell as a prel im inary step for possible reselection/handover to a local ised cell . This configuration information can be provided to communication devices in the form of a neighbouring cell list (NCL) via the cell with which it has an on-going connection or on wh ich it is cam ped in id le mode. However, the NCL space available for configuration information for localised cells can be limited.

There has been identified an increase in the deployment of localised cells as a future trend for mobile telecommunication networks. For networks involving large numbers of localised cells in a relatively dynamic network, the inventors have identified the challenge of efficiently providing a communication device with comprehensive configuration information about localised cells in the vicinity of the communication device.

It is an aim of the present invention to meet this challenge.

There is hereby provided a method, comprising: receiving measurement information about measurements made at a plurality of first access cells of transmissions made by network transmitters; determining on the basis of said measurement information a set of said first access cells for association with a second access cell with which said set of first access cells at least partially overlap; updating neighbour cell information for said second access cell based at least partly on the result of said determining; and sending said updated neighbour cell information for said second access cell to one or more communication devices.

In one embodiment, the network transmitters include transmitters of said plurality of first access cells and of said second access cell.

In one embodiment, the first access cells are femto cells and the second access cell is a macro cell; and the network transmitters include transmitters at said second access cell and one or more other macro access cells, and transmitters at said plurality of first access cells.

In one embodiment, the method further comprises: classifying said set of first access cells into a plurality of group representative access cells, and a plurality of group member cells each associated with one or more of the group representative access cells. In one embod iment, said classifying is performed accord ing to one or more indicators of how the first access cells of said set are related to each other in terms of overlapping coverage area.

In one embodiment, said indicators include indicators based on measurements made at a first access cell.

In one embod iment, the number of first access cells selected as group representative access cells is determined taking into account the amount of resources available for providing information about said first access cells in a neighbour cell list for signalling to one or more communication devices.

In one embodiment, the number of first access cells selected as group representative access cells is equal to the number of first access cells for which there are resources available in a neighbour cell list for signalling to one or more communication devices.

In one embodiment, the number of first access cells in said set of first access cells is greater than a number of first access cells for which there are resources in a neighbour cell list used for signalling neighbour cell information to said one or more communication devices, and wherein the method comprises communicating information about a first group of said set of first access cells in a first neighbour cell list, and sending information about one or more further groups of said set of first access cells in one or more respective further neighbour cell lists, if none of the first group or previous group of said first set of access cells are selected as a target handover cell for the communication device.

There is also provided a method comprising: sending to a communication device configuration information about the configuration of a first set of a plurality of first access cells associated with a second access cell with which said first set of first access cells at least partially overlap; receiving from said communication device measurement information about measurements made at the communication device of transmissions made by said first set of said first access cells; selecting on the basis of said measurement information a second set of first access cells from said plurality of first access cells; and sending to said communication device configuration information about the configuration of at least one or more of said second set of said plurality of first access cells, wherein said at least one or more of the second set of first access cells includes at least one first access cell not included in the first set of first access cells.

In one embodiment, the plurality of first access cells are classified into group representative cells and group member cells each associated with one or more of said group representative cells; wherein the first set of first access cells comprise said group representative access cells; and wherein said second set of first access cells includes a selected one or more of the group representative cells and one or more of the group member access cells associated with said selected one or more of the group representative cells.

In one embodiment, the method further comprises receiving information about the classification of said first access cells into said group representative cells and said member grou p access cells from a network node that collects measurement information about measurements made at said first access cells.

In one embodiment, the number of first access cells in said second set of first access cells is greater than a number of first access cells for which there are resources in a neighbour cell list used for signalling neighbour cell information to a communication device, and wherein the method comprises communicating information about a first group of said second set of first access cells in a first neighbour cell list, and sending information about a second group of said second set of first access cells in a second neighbour cell list if none of the first group of said second set of access cells are selected as a target handover cell for the communication device.

I n one embod iment, the method further comprises: communicating to said communication device information about one or more further respective groups of said second set of access cells in respective neighbour cell lists until one of said second set of access cel l s is sel ected as a ta rget ha ndover cel l for the communication device.

In one embodiment, the number of first access cells in said first set of first access cells is greater than a number of first access cells for which there are resources in a neighbour cell list used for signalling neighbour cell information to said one or more communication devices, and the method comprises communicating information about a first group of said first set of first access cells in a first neighbour cell list; and sending information about one or more further groups of said first set of first access cells in one or more respective further neighbour cell lists, if none of the first group or previous group of said first set of access cells are selected as a target handover cell for the communication device.

There is also provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive measurement information about measurements made at a plural ity of first access cells of transmissions made by network transmitters; and determine on the basis of said measurement information a set of said first access cells for association with a second access cell with which said set of first access cells at least partially overlap, which set of said first access cells is useful for updating neighbour cell information for said second access cell.

There is also provided an apparatus comprising: a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: send to a communication device configuration information about the configuration of a first set of a plurality of first access cells associated with a second access cell with which said first set of first access cells at least partially overlap; receive from said communication device measurement information about measurements made at the communication device of transmissions made by said first set of said first access cells; select on the basis of said measurement information a second set of first access cells from said plurality of fi rst access cel l s ; a nd send to said communication device configuration information about the configuration of at least one or more of said second set of said plurality of first access cells, wherein said at least one or more of the second set of first access cells includes at least one first access cell not included in the first set of first access cells.

There is also provided a computer program product comprising program code means which when loaded into a computer controls the computer to: receive measurement information about measurements made at a plural ity of first access cells of transmissions made by network transmitters; and determine on the basis of said measurement information a set of said first access cells for association with a second access cell with which said set of first access cells at least partially overlap, which set of said first access cells is useful for updating neighbour cell information for said second access cell.

There is also provided a computer program product comprising program code means wh ich when loaded into a com puter controls the computer to: send to a communication device configuration information about the configuration of a first set of a plurality of first access cells associated with a second access cell with which said first set of first access cells at least partially overlap; receive from said communication device measurement information about measurements made at the communication device of transmissions made by said first set of said first access cells; select on the basis of said measurement information a second set of first access cells from said plurality of first access cells; and send to said communication device configuration information about the configuration of at least one or more of said second set of said plurality of first access cells, wherein said at least one or more of the second set of first access cells includes at least one first access cell not included in the first set of first access cells.

In one embodiment, the first access cells are femto cells and the second access cell is a macro cell.

Embodiments of the invention are described in detail hereunder, with reference to the accompanying drawings, in which:- Figure 1 illustrates a mobile telecommunication network involving both macrocells and femtocells.

Figure 2 schematically illustrates an example of user equipment operable in the environment of Figure 1 ;

Figure 3 schematically illustrates an example of an apparatus suitable for use at the macro cell Node Bs (NBs) and femtocell Home NBs (HNBs) of Figure 1 ;

Figure 4 schematically illustrates an example of an apparatus suitable for use at the radio network controller (RNC) and HNB Gateway (HNB-GW) of Figure 1 ;

Figure 5 illustrates an example of the operation of the HNB-GW of Figure 1 in a first embodiment of the present invention;

Figure 6 illustrates an example of the operation of the RNC in said first embodiment of the present invention in the event of an on-going connection between a user equipment and the network;

Figure 7 illustrates an example of operations for the case of a user equipment in idle mode without an on-going connection with the network;

Figure 8 illustrates an example of an algorithm for the determination at step 504 of Figure 5;

Figure 9 illustrates an example of signalling between network elements for the first embodiment;

Figure 10 illustrates an example of the operation of the HNB-GW of Figure 1 in a second embodiment of the present invention; and

Figure 1 1 illustrates an example of the operation of the RNC of Figure 1 in the second embodiment of the present invention;

Embodiments of the invention are described below, by way of example only, in the context of mobile telecommunication networks operating in accordance with a 3GPP standard and providing 3G services via cellular base stations including macro NodeBs (NBs) and Home NodeBs (HNBs). However, the same kind of techniques are also of use in other kinds of mobile telecommunication networks comprising macro service areas dotted with localised service areas.

Figure 1 illustrates an example of a mobile telecommunication network (MTN) involving macro cells 4 served by macro NBs 2 and femto cells 7 served by HNBs 6. In Figure 1 , the triangular elements designate HNBs 6. For clarity purposes, only some femtocells 7 are illustrated by circles centred on the respective HNB 6, but each of the HNBs 6 serves a respective femtocell.

Only nine macrocells are shown in Figure 1 , but a mobile telecommunication network will typically comprise tens of thousands of macrocells. Only one of the macrocells is shown as being dotted with femto cells HNBs 6, but the other macrocells are also similarly dotted with femto cells HNBs 6.

Each macro NB 2 is connected to a radio network controller (RNC) 10 and to a core network (CN) 12.

These HNBs 6 provide femtocell access points within, for example, a residential home or small business location. The HNBs 6 are connected to a HNB gateway (HNB-GW) 14 of the CN 12 of the MTN using a broadband IP (Internet Protocol) backhaul via the internet 16.

The MTN supports idle-mode mobility between a HNB femto cell 7 and any macro NB cell 4 of the MTN, and also between HNB femto cells 7 of the MTN . The MTN also supports service continuity, including handover, between a HNB femto cell 7 and a macro NB cell 4 of same MTN, and also between HNB femtocells 7 of the MTN.

Subject to availabil ity of network resources, there is no d ifference in the user experience when using the services of a MTN via a HNB 6 of the MTN or via a macro NB 2 of the MTN.

Figure 2 shows a schematic partially sectioned view of an example of user equipment 8 that may be used for communicating with the macro NBs 2 and HNBs 6 of Figure 1 via a wireless interface. The user equipment (UE) 8 may be used for various tasks such as making and receiving phone calls, for receiving and sending data from and to a data network and for experiencing, for example, multimedia or other content. The UE 8 may be any device capable of at least sending or receiving radio signals to or from the macro NBs 2 and HNBs 6. Non-limiting examples include a mobile station (MS), a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. The UE 8 may communicate via an appropriate radio interface arrangement of the U E 8. The interface arrangement may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the UE 8.

The UE 8 may be provided with at least one data processing entity 203 and at least one memory or data storage entity 217 for use in tasks it is designed to perform. The data processor 21 3 and memory 21 7 may be provided on an appropriate circuit board 219 and/or in chipsets.

The user may control the operation of the UE 8 by means of a suitable user interface such as key pad 201 , voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 215, a speaker and a microphone may also be provided. Furthermore, th e U E 8 may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

Figure 3 shows an example of apparatus for use at the HNBs 6 and macro NBs 2. The apparatus comprises a radio frequency antenna 301 configured to receive and transmit radio frequency signals; radio frequency interface circuitry 303 configured to interface the radio frequency signals received and transmitted by the antenna 301 and the data processor 306. The radio frequency interface circuitry 303 may also be known as a transceiver. The apparatus also comprises an interface 309 via which it can send and receive information to and from one or more other network nodes eg., a control node or central entity like RNC, HN B-GW, HMS or O&M entity.. The information sent and received comprises RF measurement reports, configuration information of the cell or node or UE. The data processor 306 is configured to process signals from the radio frequency interface circuitry 303, control the radio frequency interface circuitry 303 to generate suitable RF signals to communicate information to the UE 6 via the wireless communications link, and also to exchange information with other network nodes via the interface 309. The memory 307 is used for storing data, parameters and instructions for use by the data processor 306.

Figure 4 shows an example of apparatus for use at the RNC 10 and the HNB-GW 14. The apparatus 400 includes a memory 402 for receiving and storing data of the kind mentioned below in the description of first and second embodiments, and a data processor 404 for processing data stored in memory 402 and making computations and determinations of the kind mentioned below in the description of first and second embodiments. The apparatus also comprises an interface 406 via which it can send and receive information to and from other network nodes such as a base station, NB or HNB. As described below, functions of the processor can include: selecting cells belonging to a group of cells, evaluating measurement reports or vicinity information, and selecting which cells are included into a NCL provided to a UE.

It would be appreciated that the apparatus shown in each of figures 2, 3 and 4 and described above may comprise further elements which are not directly involved with the embodiments of the invention described hereafter.

With reference to Figures 5 to 9 of the accompanying drawings, a technique according to a first embodiment of the present invention is described below for a UE 8 in an on-going connection with a macro NB 2, in which the serving macro NB 2 provides configuration information (such as a primary scrambling code in the case of a CDMA or WCDMA system) for neighbouring cells to the U E by means of a neighbour cell list (NCL). The NCL is compiled at a control node or central entity and provided by the control node or central entity towards the UE via a base station e.g. a base station of a macro cell or a femtocell.

Each deployed femtocell after booting makes measurements of transmissions it detects from macro cells and other femtocells during a network listening mode (NLM). The femtocells report these measurements to HNB-GW (or another central entity that collects information from femtocells such as an Operation and Maintenance (O&M ) entity or Hom e Nod e B M an agem ent Su bsystem ( H MS)) . Those measurements are received and kept by the HNB-GW (STEP 502 of Figure 5).

The HNB-GW next identifies clusters of femtocells within the sum of the femtocells it determines to be within the coverage area of the serving macro NB 2, and selects a respective representative cell for each cluster (STEP 504 of Figure 5).

According to one example, the number of clusters equals the number of femtocells for which there is room to provide configuration information in the NCL from the serving macro NB 2. Where priority is given to including configuration information for macrocells, the number of femtocells for which there is room to provide configuration information in the NCL will depend on the n umber of macro cel ls for wh ich configuration information is to be provided in the NCL.

One way for the HNB-GW to acquire information about how many femtocells can have their configuration information provided in the NCL of the serving macro NB 2 is to additionally report the macro NCL to the HNB-GW from the HNB together with the NLM measurements. The HNB-GW may determine how many entries in the NCL are already occupied, and knowing the maximum number of entries in the NCL the HNB- GW may determ i ne how many entries may be added with add itional cel l configuration information of e.g. femtocells. Configuration information of a cell comprises information required by a mobile station UE to detect, identify, distinguish, access, perform measurements of a cell, such as e.g., primary scrambling code, cell identifier, access group identifiers, access mode, access address.

Another way for the H N B-GW to know how many femtocells can have their configuration information (PSC) provided in the NCL of the serving macro NB 2 is to make an enquiry from the HNB-GW 14 to the RNC 10 controlling the serving macro NB 2. Another alternative is to configure the number manually at the HNB-GW by the Mobile Network Operator (MNO). Once the H N B-GW knows how many femtocells can have their configuration information (such as a primary scrambling code (PSC)) provided in the NCL of the serving macro NB 2, the HNB-GW 14 identifies a corresponding number of clusters of H N Bs 6 whose inter-relations meet predetermined criteria, and selects a representative HNB 6 for each cluster. The representative HNBs/femtocells are also referred to below and in the accompanying drawings as relay HNBs/cells and group representative access nodes/ access cells because of the way in which they can be used a s a n intermediate step to providing configuration information for all femtocells/HNBs in the vicinity of UE 8.

An example of an algorithm for identifying clusters of HNBs is illustrated in Figure 8. Each femtocell measures CPICH RSCP [W] for all other cells that it detects. This gives meas(i,x) where i is the ID of the measuring cell and x is a ID of a certain other cell. The sum (over all x) of meas(k,x)^*meas(l,x) gives a correlation between measurements of cell k and I. The meas(k,x) and meas(l,x) are normalized by CPICH RSCP[W] values seen at certain HNBs from the strongest neighboring cell, independently for k and I cell. RSCP is the Received Signal Code Power and CPICH is the Common Pilot Channel.

If the correlation between cells I and k is high, they are designated to be in the same cluster.

An alternative technique for identifying clusters is to use a mobile test station randomly moving around the coverage area of the macro NB, connecting itself to the strongest cells as it does so. At every handover/reselection, measurement reports from the mobile test station can be used to check which cells should belong to which one of an overlapping set of clusters.

A respective representative HNB/cell (or relay HNB/cell) is chosen for each cluster. The representative cell is chosen such that the distribution of other cells in the cluster in relation to the representative cell is as even as possible. In one example, the femtocell that is chosen for the representative cell is the one that has the most number of other cells in the cluster within its neighbour relation list and also detects transmissions from the serving macro HNB 2 with good signal strength.

According to one example, the representative cells have one or more of the following features: (i) the number of representative cells does not exceed the number of NCL entries available for femtocells; (ii) the representative cells have neighbouring cell relationships established; (iii) the representative cell of any cluster is the cell having the most neighbouring cells within that cluster; (iv) the total sum of cells included in the NCLs of the sum of the representative cells covers all the available femtocells in the macro cell; (v) the radio coverage of neighbouring femto cells within a cluster is ideally continuous; and (vi) the representative HNBs are distributed as proportionally as possible over the macro cell in terms of femto density per unit area.

The HNB-GW 14 next provides information about the clusters and their respective representative cells to the RNC controlling the serving macro NB 2 (STEP 506 of Figure 5).

For a UE 8 having an ongoing connection with macro NB 2, the RNC 10 may include details of the representative HNBs (including HNB 0 of Figure 9) in the connected (dedicated) mode NCL of the serving macro NB 2 (STEP 602 of Figure 6). The connected mode NCL of the serving macro NB 2 is transmitted from the serving macro N B 2 to U E 8. U E 8 u ses the configuration information (e.g. primary scrambling code) included in the NCL received from the serving macro NB 2 to measure transmissions from the HNBs included in the NCL (i.e. the representative HNBs), and reports the measurements to the RNC 10 via serving macro NB 2. The RNC 10 receives these measurements for the representative H NBs from UE 8 (STEP 604 of Figure 6). The RNC 10 identifies from these measurements a femtocl uster in the vicin ity of the U E 8 (in the example of Figure 9, the identified femtocluster is a cluster for which HNB 0 is the representative cell), and looks up which other HNBs belong to this femto-cluster (in the example of Figure 9, the femtocluster also includes HNB 1 , HNB 2 and HNB 3). The RNC formulates for a new Measurement Configuration message to U E 8 a dedicated NCL containing configuration information (e.g. primary scrambling code) for the femtocell belonging to the identified femto-cluster (STEP 606 of Figure 6). The new Measurement Configuration Message is sent from RNC 10 to UE 8 via serving macro NB 2, and UE is then able to detect and measure transmissions from the other femtocells in the cluster (i.e. HNB 1 , HNB 2 and HNB 3 in Figure 9), and report those measurements to RNC 1 0. Thus, if the measurements for any of these femtocells meet the predetermined criteria for a handover, i.e. if the radio conditions for any of these femtocells fulfil the required level, the UE 8 may be handed-over to such femtocell. Figure 9 illustrates the signalling for the plurality of network elements involved in this technique.

RNC 1 0 may also include details of the representative H N Bs in the NCL for reselection (in Idle Mode, CELL FACH, CELL_PCH, URA_PCH state) for macro NB 2 which is included in System Information Blocks 1 1/1 1 bis/12 (STEP 702 of Figure 7). A terminal operating in idle-mode (or CELL FACH, CELL_PCH, URA_PCH state), within the coverage area of macro NB 2 (i.e. camped on macro NB 2 but not having an on-going connection with macro NB 2) detects this NCL. The configuration information for the representative HNBs included in the NCL allows the terminal to detect and measure transmissions from any of the representative HNBs within detectable range, and choose to instead camp on one of those representative HNBs. Once camped on one of the representative HNBs, the terminal receives via system information broadcast from that representative HNB 6 another NCL including config u ration information for the H N Bs i n the same femtocl uster as that representative HNB, as well as surrounding macro cells or other representative HNBs (STEP 704 of Figure 7). The terminal can then choose to reselect to a HNB in this femtocluster as well as a macro cell or other representative HNB.

In a case where the measurements provided by the UE 8 indicate that two or more femtoclusters might contain the best femtocell for the UE 8, (e.g. due to overlapping cluster areas), the RNC 1 0 can provide in the U E-specific NCL of STEP 606 configuration information for the sum of the femtocells contained in each of those two or more clusters. The measurement reports returned by the UE 8 to RNC 10 for that combination of femtocells allows the RNC to make a determination as to which of those two or more clusters is best for UE 8. The above-described technique provides an automated way to dynamically find the best HNB for a communication device, even where the number of open access HNBs for a macro cell is m uch g reater than the n umber of H N Bs for wh ich configuration information can be provided in an NCL. The above-described technique is particularly useful for systems involving pre Release 8 AS (Access Stratum) terminals (legacy terminals) that are unable to detect a femto cell and reselect/handover to that cell without receiving configuration information for that femtocell from the network. Pre-Rel-8 Terninals are not capable of autonomously discover a Closed Subscriber Group (CSG) Cell (CSG is a Cell property).

Next, a technique according to a second embodiment of the invention is described with reference to Figures 10 and 1 1 of the accompanying drawings.

HNBs 6 report their Network Listening Mode (NLM) measurements to HNB-GW (or other central ized network element) (STEP 1 002 of Figure 1 0), and reports are delivered further to relevant (H)NBs.

A list of neighbor cell candidates are derived for macro NB 2 from these NLM measurements (STEP 1004 of Figure 10), and this list is forwarded to the RNC 10 controlling the macro NB 2.

RNC determines whether the number of femtocells included in the neighbor cell candidates l ist is more than the number of femtocells for wh ich configuration information (e.g . primary scrambling code in the case of a CDMA or WCDMA system) can be included in the Neighbour Cell List (NCL) for transmission by macro NB 2 (STEP 1 102 of Figure 1 1 ). If the result of this determination is negative, RNC 10 includes configuration information for all HNBs in the NCL for transmission by macro NB 2 (STEP 1 104 of Figure 1 1 ). If the result of the determination of STEP 1 102 is positive, RNC 10 updates the NCL for macro NB 2 with as many HNBs of the cand idate list as possible. T h e R N C selects HNBs with different NLM measurements so as to include in the NCL a set of HNBs that are well distributed over the coverage area of macro NB 2. The selection of HNBs for the NCL can be made also utilizing other information such as statistical information about how much each HNB is used (STEP 1 106 of Figure 1 1 ).

RNC receives back from UE 8 measurements made at UE 8 of transmissions made by the H N Bs incl uded in the NC L (STEP 1 108 of Figure 1 1 ). These UE measurements are correlated at RNC 10 with the above-mentioned NLM measurements made at the HNBs. A new set of HNBs is then selected from the list of neighbour cell candidates, based on how well the NLM measurements made at the HNBs correlate with the UE measurements (STEP 1 1 10 of Figure 1 1 ). Only H N Bs for which the degree of correlation exceeds a predetermined level are selected for this new set of HNBs.

RNC 10 then makes a determination as to whether the number of HNBs in the new subset of high correlation HNBs is more than the number of HNBs for which there is space to provide configuration information in the NCL from serving macro NB 2 (STEP 1 1 12 of Figure 1 1 ). If the result of this determination is negative, RNC 10 includes configuration information for all h igh correlation H N Bs in the NCL for transmission to UE 8 (STEP 1 1 14 of Figure 1 1 ). On the other hand, if the result of this determination is positive, RNC 10 updates the NCL for macro NB 2 with as many HNBs of the new sub-set of high correlation HNBs as possible. The RNC selects high correlation HNBs with different NLM measurements so as to include in the NCL a set of high correlation HNBs that are well distributed over the sum of the coverage areas of all the HNBs of the new sub-set of high correlation HNBs (STEP 1 1 16 of Figure 1 1 ). Again , as above, this selection can be made also util izing other information such as statistical information about how much each HNB is used.

Configuration information for the remainder of the high correlation HNBs not selected is included in one or more later U E-specific NCLs until UE 8 is handed over to another cell or configuration information for all of the new subset of high correlation HNBs 6 has been provided to UE 8 (STEPs 1 1 18 and 1 1 20 of Figure 1 1 ). This rotation of configuration information involves replacing the configuration information for one or more cells with configuration information for one or more other cells not included in a previous NCL. Rotation might be round robin or according to statistic evaluation eg., femtocells accessed by terminals more often than others or femtocells for which measurement reports are received more often, or measurement results show values higher than a pre-defined threshold.

In the event that UE 8 happens to report new UE measurements that defer significantly from earlier ones on which the new subset of high correlation HNBs was determined, the RNC repeats the correlation operation of STEP1 1 10 to determine a fresh subset of high correlation HNBs and repeats STEPS 1 1 12 to 1 120 for the fresh subset of high correlation HNBs.

A feature of the above-described technique is that a terminal (UE 8) will receive not only configuration information for macro cells, but also configuration information for all accessible HNBs in the vicinity of the terminal. The technique provides a way to efficiently and comprehensively provide HNB configuration information to terminals that require such information in order to detect and measure transmissions from a HNB as a preliminary step for reselection/handover to a HNB, despite the problem of limited NCL addressing space.

Techniques according to first and second embodiments of the present invention have been described for the example of providing configuration information about femtocells to a communication device having an ongoing connection with a macro cell or camped on a macro cell. However, the technique is equally applicable, for example to providing configuration information about any kind of neighbouring cell to a commun ication device having an ongoing connection with or camped on a femtocell or other kind of localised cell.

The above-described operations may require data processing in the various entities. The data processing may be provided by means of one or more data processors. Similarly various entities described in the above embodiments may be implemented within a single or a plurality of data processing entities and/or data processors. Appropriately adapted computer program code product may be used for implementing the embodiments, when loaded to a computer. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. A possibility is to download the program code product via a data network. Implementation may be provided with appropriate software in a server.

For example the embodiments of the invention may be implemented as a chipset, in other words a series of integrated circuits communicating among each other. The chipset may comprise microprocessors arranged to run code, application specific integrated circuits (ASICs), or programmable digital signal processors for performing the operations described above.

Embodiments of the invention may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

Programs, such as those provided by Synopsys, Inc. of Mountain View, California and Cadence Design, of San Jose, California automatically route conductors and locate components on a semiconductor chip using well established rules of design as wel l as l i braries of pre-stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e .g . , Opus, G DS I I , or the l i ke) may be transm itted to a semiconductor fabrication facility or "fab" for fabrication.

In addition to the modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described embodiment may be made within the scope of the invention.

Claims

1 . A method, comprising:

receiving measurement information about measurements made at a plurality of first access cells of transmissions made by network transmitters;

determining on the basis of said measurement information a set of said first access cells for association with a second access cell with which said set of first access cells at least partially overlap;

updating neighbour cell information for said second access cell based at least partly on the result of said determining; and

sending said updated neighbour cell information for said second access cell to one or more communication devices.

2. A method according to claim 1 , further comprising: classifying said set of first access cells into a plurality of group representative access cells, and a plurality of group member cells each associated with one or more of the group representative access cells.

3. A method accord ing to claim 2, wherein said classifying is performed according to one or more indicators of how the first access cells of said set are related to each other in terms of overlapping coverage area.

4. A method according to claim 3, wherein said indicators include indicators based on measurements made at a first access cell.

5. A method according to any of claims 2 to 4, wherein the number of first access cells selected as group representative access cells is determined taking into account the amount of resources available for providing information about said first access cells in a neighbour cell list for signalling to one or more communication devices.

6. A method according to claim 5, wherein the number of first access cells selected as group representative access cells is equal to the number of first access cells for which there are resources available in a neighbour cell list for signalling to one or more communication devices.

7. A method according to claim 1 , wherein the number of first access cells in said set of first access cells is greater than a number of first access cells for which there are resources in a neighbour cell list used for signalling neighbour cell information to said one or more communication devices, and wherein the method comprises communicating information about a first group of said set of first access cells in a first neighbour cell list, and sending information about one or more further groups of said set of first access cells in one or more respective further neighbour cell lists, if none of the first group or previous group of said first set of access cells are selected as a target handover cell for the communication device.

8. A method comprising:

sending to a communication device configuration information about the configuration of a first set of a plurality of first access cells associated with a second access cell with which said first set of first access cells at least partially overlap;

receiving from said commun ication device measurement information about measurements made at the communication device of transmissions made by said first set of said first access cells;

selecting on the basis of said measurement information a second set of first access cells from said plurality of first access cells; and

send ing to sa id commun ication device configuration information about the configuration of at least one or more of said second set of said plurality of first access cells, wherein said at least one or more of the second set of first access cells includes at least one first access cell not included in the first set of first access cells.

9. A method according to claim 8, wherein the plurality of first access cells are classified into group representative cells and group member cells each associated with one or more of said group representative cells; wherein the first set of first access cells comprise said group representative access cells; and wherein said second set of first access cells includes a selected one or more of the group representative cells and one or more of the group member access cells associated with said selected one or more of the group representative cells.

10. A method according to claim 8 or claim 9, comprising receiving information about the classification of said first access cells into said group representative cells and said member group access cells from a network node that collects measurement information about measurements made at said first access cells.

1 1 . A method according to claim 8, wherein the number of first access cells in said second set of first access cells is greater than a number of first access cells for which there are resources in a neighbour cell list used for signalling neighbour cell information to a commun ication device, and wherein the method comprises communicating information about a first group of said second set of first access cells in a first neighbour cell list, and sending information about a second group of said second set of first access cells in a second neighbour cell list if none of the first group of said second set of access cells are selected as a target handover cell for the communication device.

12. A method accord ing to claim 1 1 , comprising: communicating to said communication device information about one or more further respective groups of said second set of access cells in respective neighbour cell lists until one of said second set of access cells is selected as a target handover cell for the communication device.

13. A method according to claim 8, wherein the number of first access cells in said first set of first access cells is greater than a number of first access cells for which there are resources in a neighbour cell list used for signalling neighbour cell information to said one or more communication devices, and wherein the method comprises communicating information about a first group of said first set of first access cells in a first neighbour cell list; and sending information about one or more further groups of said first set of first access cells in one or more respective further neighbour cell lists, if none of the first group or previous group of said first set of access cells are selected as a target handover cell for the communication device.

14. An apparatus comprising : a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to: receive measurement information about measurements made at a plurality of first access cells of transmissions made by network transmitters; and determine on the basis of said measurement information a set of said first access cells for association with a second access cell with which said set of first access cells at least partially overlap, which set of said first access cells is useful for updating neighbour cell information for said second access cell.

15. An apparatus comprising : a processor and memory including computer program code, wherein the memory and computer program code are configured to, with the processor, cause the apparatus to:

send to a communication device configuration information about the configuration of a first set of a plurality of first access cells associated with a second access cell with which said first set of first access cells at least partially overlap;

receive from said com mu n ication device measu rement information about measurements made at the communication device of transmissions made by said first set of said first access cells;

select on the basis of said measurement information a second set of first access cells from said plurality of first access cells; and

send to said communication device configuration information about the configuration of at least one or more of said second set of said plurality of first access cells, wherein said at least one or more of the second set of first access cells includes at least one first access cell not included in the first set of first access cells.

16. A computer program product comprising program code means which when loaded into a computer controls the computer to: receive measurement information about measurements made at a plurality of first access cells of transmissions made by network transm itters; and determ ine on the basis of said measu rement information a set of said first access cells for association with a second access cell with which said set of first access cells at least partially overlap, which set of said first access cells is useful for updating neighbour cell information for said second access cell.

17. A computer program product comprising program code means which when loaded into a computer controls the computer to: send to a communication device configuration information about the configuration of a first set of a plurality of first access cells associated with a second access cell with which said first set of first access cells at least partially overlap; receive from said communication device measurement information about measurements made at the communication device of transmissions made by said first set of said first access cells; select on the basis of said measurement information a second set of first access cells from said plurality of first access cells; and send to sa id commun ication device configu ration information about the configuration of at least one or more of said second set of said plurality of first access cells, wherein said at least one or more of the second set of first access cells includes at least one first access cell not included in the first set of first access cells.