WO2011144589A1

WO2011144589A1 - Method for populating a neighbouring cell list, network element and communication system therefor

Info

Publication number: WO2011144589A1
Application number: PCT/EP2011/057920
Authority: WO
Inventors: Akhilesh Pokhariyal
Original assignee: Ip.Access Limited
Priority date: 2010-05-17
Filing date: 2011-05-17
Publication date: 2011-11-24
Also published as: GB2480432A; GB201008111D0

Abstract

A method for populating a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells is described. The method comprises, at a network element for supporting communication in at least one femto cell of a cellular communication network, maintaining a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on a handover success rate for neighbouring cells, and generating a neighbour cell list based at least partly on the record of preferred neighbouring cells.

Description

Title: METHOD FOR POPULATING A NEIGHBOURING CELL LIST, NETWORK ELEMENT AND COMMUNICATION SYSTEM THEREFOR

Description

Field of the invention

The field of this invention relates to a method for populating a neighbour cell list for use in relation to performing communication handovers between neighbouring cells. The invention is applicable to, but not limited to, a method for populating a neighbour cell list for use in relation to performing handovers of wireless communication unit communications between neighbouring cells at a network element operational in a communication system.

Background of the Invention

Wireless communication systems, such as the 3^rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS™), developed by the 3^rd Generation Partnership Project (3GPP™) (www.3qpp.org). The 3^rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs in 3GPP™ parlance) to communicate with wireless communication units within a relatively large geographical coverage area. Typically, mobile/portable wireless communication units, or User Equipment (UEs) as they are often referred to in 3G parlance, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network. Each macro-cellular RNS typically comprises a controller, in a form of a Radio Network Controller (RNC), operably coupled to the one or more NodeBs, via a so-called lub interface.

As a UE moves from a geographical coverage area of one communication cell to the geographical coverage area of an adjacent cell (termed a neighbouring cell in 3GPP parlance), in order for any active calls or data sessions to be maintained, a handover (also known as a handoff or handout) procedure is required to be performed. Here, each active call and/or data session is transferred from the source cell (i.e. the cell from which the UE is coming) to the target cell (i.e. the cell to which the UE is moving). For the practical realisation of performing handover procedures, each communication cell is assigned a list of potential target cells, typically referred to as a neighbour list, or neighbour cell list. UEs in a connected state (i.e. with one or more active calls or data sessions) are instructed by their current cell's NodeB to perform signal quality measurements for cells in the neighbour list for their current operating cell, and to report back to their current cell's NodeB when certain events corresponding to such measurements occur. The NodeB is then able to determine when a handover may be required for a UE connected thereto, and also to select a target cell with which the handover of the UE's communication is to be performed, based on the reporting of events by that UE.

In a traditional macro-cellular implementation, neighbour lists are typically generated from a complex analysis of network coverage maps that have been generated from drive tests and the like. The NodeBs supporting respective macro cells may then be manually configured with their individual neighbour lists. Such drive tests, and the subsequent analysis and manual configuration, are both time consuming and expensive. However, due to the generally static nature of macro cells, and the general longevity of their deployment, such drive tests and subsequent processing and manual configuration are typically not required to be performed too frequently, and are generally cost effective on such a large and slowly changing scale.

Lower power (and therefore smaller coverage area) femto cells (or pico-cells) are a recent development within the field of wireless cellular communication systems. Femto cells or pico-cells (with the term femto cells being used hereafter to encompass pico-cells or similar) are effectively communication coverage areas supported by low power base stations (otherwise referred to as Home NodeBs (HNBs)). These femto cells are intended to be able to be piggy-backed onto the more widely used macro-cellular network and support communications to UEs in a restricted, for example 'in-building', environment.

Typical applications for such femto HNBs include, by way of example, residential and commercial (e.g . office) locations, communication 'hotspots', etc., whereby an HNB can be connected to a core network of a communication system via, for example, the Internet using a broadband connection or the like. In this manner, femto cells can be provided in a simple, scalable deployment in specific in-building locations where, for example, network congestion at the macro- cell level may be problematic. Significantly, the majority of HNBs are likely to be owned and deployed by members of the public (as opposed to a Network Operator). As a result, a person deploying an HNB is unlikely to have the expertise or necessary data to be able to manually configure a neighbour list.

A known approach for generating a neighbour list within an HNB comprises providing the HNB with a NetWork Listen (NWL) receiver that detects neighbour cell transmissions, whereby the receiver and a processor perform physical layer measurements on the neighbouring cell transmissions in order to generate the neighbour list. However, NWL receiver performance is limited by factors such as measurement inaccuracies, limited sensitivity, indoor location, localized shadowing effects, etc. Accordingly, it may not be possible to guarantee that an HNB is always able to detect and populate its neighbour list(s) with all of the relevant information on macro neighbour cells based on its physical layer measurements alone.

Other ideas being proposed in this area are network assisted, and UE assisted neighbour list management. Network-assisted neighbour list management is intended to come into play when the HNB is unable to detect any neighbour cells. As such, the network-assisted approach is of limited benefit where the HNB has detected some neighbour cells, but not necessarily the most relevant neighbour cells. UE-assisted neighbour list management implies making use of UE measurements, such as measurements of detected neighbour cells, to augment neighbour list management. However, this increases the signalling overhead between the UE and the HNB. Such increased signalling overhead can cause an increase in interference to neighbouring cells, and also typically has a detrimental effect on the battery life of the UE. Accordingly, UE-assisted neighbour list management is not a desirable solution.

Field measurements from femto cell trials have shown that, typically, only one or two 3G/2G macro neig hbour cells provide optimal choices from a perspective of handover/cell reselection performance. One of the reasons is that the coverage area of a femto cell is a fraction of a size of the cell coverage area of a typical macro cell. Accordingly, there is a small likelihood of a femto cell deployment lying within overlapping coverage areas of more than one macro cell. Further, there is only a limited number of entry/exit routes (i.e. doors, garage, etc.) available in a typical residential/commercial premise, and the strongest macro cell signal along these entry/exit routes is the most desirable one in terms of handover performance. However, it is often the case that the H N B is not positioned near to such an entry/exit route, and as such it cannot be guaranteed that this target macro cell will always be present in the neighbour cell list if the population of the neighbour cell list is based solely on physical layer measurements made by the NWL receiver of the HNB.

Thus, a need exists for an improved method and technique for populating a neighbour cell list.

Summary of the invention Accordingly, the invention seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination. Aspects of the invention provide a method for populating a neighbour cell list, a network element and a communication system as described in the appended claims.

According to a first aspect of the invention, there is provided a method for populating a neighbour cell list for use in performing communication handovers of wireless communication units between neighbouring cells. The method comprises, at a network element for supporting communication in at least one femto cell of a cellu lar communication network, determining a communication handover success rate between a plurality of neighbouring cells, maintaining a record of preferred neighbouring cells, where the record of preferred neighbouring cells being populated is based at least partly on a communication handover success rate for neighbouring cells, and generating a neighbour cell list based at least partly on the record of preferred neighbouring cells.

In one example embodiment, a use of handover success rates for neighbouring cells when generating a neighbour cell list may enable the neighbour cell list to be more accurately tailored in order to suit the specific and individual environmental characteristics of a femto cell. In particular, the use of handover success rates for neighbouring cells in this manner may not be limited to what the network element is able to "see", i.e. to the physical layer measurements of neighbouring cells obtained through a NetWork Listen (NWL) cycle. Furthermore, the use of handover success rates to generate a neighbour cell list may be achieved without the need for assistance from a core network of the cellular communication network, or from wireless communication units within the femto cell.

According to an optional feature, the method may comprise maintaining a record of preferred neighbouring cells where the record may comprise information relating to at least a first neighbour cell. The record of preferred neighbouring cells may be populated based at least partly on a handover success rate for the at least first neighbouring cell. The method may further comprise generating a preliminary cell list based at least partly on physical layer measu rements for neighbouring cells, and if the at least first neighbouring cell within the record of preferred neighbouring cells is not present within the preliminary cell list, adding the at least first neighbouring cell to the preliminary cell list.

Thus, in one example embodiment, the use of communication handover success rates for neighbouring cells may be used to augment the use of network listen functionality when generating a neighbour cell list, thereby more accurately tailoring the neighbour cell list to suit the specific and individual environmental characteristics of a femto cell.

According to an optional feature, information relating to a neighbouring cell may be added to the record of preferred neighbouring cells when a number (X) of successful handovers to that neighbouring cell, for example as a percentage or ratio of a last Y handover attempts to that neighbouring cell, exceeds a threshold value.

According to an optional feature, information relating to a neighbouring cell may be removed from a record of preferred neighbouring cells when a number (X) of successful handovers to that neighbouring cell, for example as a percentage or ratio of a last Y handover attempts to that neighbouring cell, falls below a threshold value.

According to an optional feature, a communication handover success rate for a neighbouring cell may be determined based at least partly by way of monitoring signals from a core network of the cellular communication network. For example, a handover of a wireless communication unit to a neighbouring cell may be determined to have been successful upon receipt of a command to release assigned radio bearers from the core network within a defined period (T) from instructing the wireless communication unit to reconfigure at least one radio bearer.

According to an optional feature, a preliminary cell list may be generated based at least partly on physical layer measurements for neighbouring cells obtained through a NetWork Listen (NWL) cycle.

According to an optional feature, the method may comprise maintaining a record of preferred neighbouring cells. The record of preferred neighbouring cells may be populated based at least partly on a handover success rate for neighbouring cells. The method may further comprise performing a NetWork Listen (NWL) cycle to obtain physical layer measurements for neighbouring cells within the record of preferred neighbouring cells, and generating a neighbour cell list based at least partly on the obtained physical layer measurements for the preferred neighbouring cells.

Thus, in one example embodiment, an initial neighbour cell list may be generated based on the obtained physical layer measurements for the preferred neighbouring cells, enabling a communication cell to be operational more quickly since a full and time consuming comprehensive network listen cycle has not had to be performed in order to generate a valid neighbour cell list.

According to a second aspect, there is provided a network element for supporting communication in at least one femto cell of a cellular communication network. The network element comprises transceiver circuitry arranged to enable communication with at least one wireless communication unit located within the at least one femto cell. The network element further comprises a signal processing module arranged to determine a communication handover success rate between a plurality of neighbouring cells, maintain a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on a handover success rate for the neighbouring cell, and arranged to generate a neighbour cell list based at least partly on the record of preferred neighbouring cells.

According to a third aspect, there is provided a communication system comprising a network element for supporting communication in at least one femto cell of a cellular communication network. The network element comprises transceiver circuitry arranged to enable communication with at least one wireless communication unit located within the at least one femto cell. The network element further comprises a sig nal processing modu le arranged to determ ine a communication handover success rate between a plurality of neighbouring cells, maintain a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on the determined communication handover success rate for the neighbouring cell, and arranged to generate a neig hbour cell list based at least partly on the record of preferred neighbouring cells.

According to a fourth aspect of the invention, there is provided a tangible computer program product having executable program code stored therein for programming signal processing logic to perform a method for populating a neighbour cell list for use in performing communication handovers of wireless communication units between neighbouring cells. The code is operable for, at a network element for su pporting commu nication in at least one femto cell of a cellular communication network, determining a communication handover success rate between a plurality of neighbouring cells, maintaining a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on the determined commu nication handover success rate for neighbouring cells, and generating a neighbour cell list based at least partly on the record of preferred neighbouring cells.

According to a fifth aspect of the invention, there is provided an integrated circuit for a network element supporting communication in at least one femto cell of a cellular communication network. The network element comprising transceiver circuitry arranged to enable communication with at least one wireless communication unit located within the at least one femto cell. The integrated circuit comprises a signal processing module arranged to determine a communication handover success rate between a plurality of neighbouring cells; maintain a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on the determined communication handover success rate for neighbouring cells; and generate a neighbour cell list based at least partly on the record of preferred neighbouring cells.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter. Brief Description of the Drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

FIG. 1 illustrates an example of part of a cellular communication network.

FIG. 2 illustrates an example of a block diagram of a network element.

FIG's 3 and 4 illustrate simplified flowcharts of an example of a method for populating a neighbour cell list for use in performing communication handovers of wireless communication units between neighbouring cells.

FIG. 5 illustrates a simplified flowchart of an alternative example of a method for populating a neighbour cell list for use in performing communication handovers of wireless communication units between neighbouring cells according to some example embodiments of a further aspect of the present invention.

FIG. 6 illustrates a typical computing system that may be employed to implement signal processing functionality in example embodiments.

Detailed Description Examples of the invention will be described in terms of a third generation (3G) Home

NodeB (HNB) for supporting a femto cell within a Universal Mobile Telecommunications System (UMTS™) cellular communication network. However, it will be appreciated by a skilled artisan that the inventive concept herein described may be embodied in any type of network element for supporting a femto cell (or similar) within a cellular communication network.

In a number of applications, the adaptation of a network element in accordance with the examples of the invention effectively performs a method for populating a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells. For example, in a context of, say, a 3G UMTS™ wireless communication system, a network element such as a NodeB or Home NodeB may typically provide one or more neighbour cell lists to wireless communication units connected thereto. The wireless communication units may subsequently perform physical layer measurements for detected neighbour cells within the received neighbour cell lists, and upon certain events relating to such physical layer measurements occurring (for example as described in greater detail below), a wireless communication unit may report such an event back to the NodeB or Home NodeB. Based thereon, the NodeB or Home NodeB may initiate a handover procedure for that wireless communication unit.

The method comprises, at a network element for supporting communication in at least one femto cell of a cellular communication network, maintaining a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on a handover success rate for neighbouring cells. The method fu rther com prises generating a neighbour cell list based at least partly on the record of preferred neighbouring cells.

The use of handover success rates for neighbouring cells, when generating a neighbour cell list, enables the neighbour cell list to be more accurately tailored to suit the specific and individual environmental characteristics of a femto cell. In particular, the use of handover success rates for neighbouring cells in this manner is not limited to what the network element is able to "see", i.e. to the physical layer measurements of neighbouring cells obtained through a NetWork Listen (NWL) cycle. Furthermore, the use of handover success rates to generate a neighbour cell list may be achieved without the need for assistance from a core network of the cellular communication network, or purely and directly from wireless communication units within the femto cell.

Referring now to the drawings, and in particular FIG. 1 , an example of part of a cellular communication network, adapted in accordance with an example embodiment of the invention, is illustrated and indicated generally at 1 00. In FIG . 1 , there is illustrated an example of a communication system in a form of a third generation partnership project (3GPP™) UMTS™ network 100 that comprises a combination of a macro cell 185 and a plurality of 3G femto cells 150 in accordance with one embodiment of the invention. For the example embodiment illustrated in FIG. 1 , the radio network sub-system (RNS) comprises two distinct architectures to handle the respective macro cell and femto cell communications.

In the macro cell scenario, the RNS comprises a controller in the form of a Radio Network

Controller (RNC) 136 having, inter alia, signal processing logic 138. The RNC 136 is operably coupled to a macro NodeB 124 for supporting communications within the macro cell 185. The RNC 136 is further operably coupled to a core network element 142, such as a serving general packet radio system (GPRS) support node (SGSN)/mobile switching centre (MSC), as known.

I n a femto cell scenario, an RNS 1 1 0 com prises a network element, which for the illustrated example embodiment is in a form of a 3G Home NodeB (HNB) 130. The HNB 130 is arranged to perform a number of functions generally associated with a base station. The RNS 1 10 further comprises a controller in a form of a 3G Access controller (3G AC) 140. As will be appreciated by a skilled artisan, a Home HodeB (HNB), also referred to as a femto access point, is a communication element that supports communications within a communication cell, such as a 3G femto cell 150, and as such provides access to a cellular communication network via the 3G femto cell 150. One envisaged application is that an HNB 130 may be purchased by a member of the public and installed in their home. The HNB 130 may then be connected to a 3G AC 140 over the owner's broadband internet connection 160.

Thus, a 3G HNB 130 may be considered as encompassing a scalable, multi-channel, two- way communication device that may be provided within, say, residential and commercial (e.g . office) locations, 'hotspots' etc, to extend or improve upon network coverage within those locations. Although there are no standard, defined criteria for the functional components of a 3G HNB, an example of a typical HNB for use within a 3GPP system may comprise some traditional macro NodeB functionality and some aspects of the radio network controller (RNC) 136 functionality. For the illustrated embodiment, the HNB 130 comprises transceiver circuitry 155 arranged to enable communication with one or more wireless communication units located within the general vicinity of the communication cell 150, and in particular within the communication cell 150, such as User Equipment (UE) 1 14, via a wireless interface (Uu).

The 3G Access Controller 140 may be coupled to the core network (CN) 142 via an lu interface, as shown. In this manner, the HNB 130 is able to provide voice and data services to a cellular handset, such as UE 1 14, in a femto cell in contrast to the macro cell, in the same way as a conventional macro NodeB, but with the deployment simplicity of, for example, a Wireless Local Area Network (WLAN) access point.

In accordance with some example embodiments, the HNB 130 comprises a signal processing module 165 arranged to maintain a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on a handover success rate for neighbouring cell. The signal processing module is also arranged to generate a neighbour cell list based at least partly on the record of preferred neighbouring cells.

Referring now to FIG. 2, an example of a block diagram of the HNB 130 is shown. The example HNB 130 contains an antenna 202 coupled to the transceiver circuitry 155. More specifically for the illustrated example, the antenna 202 is preferably coupled to a duplex filter or antenna switch 204 that provides isolation between receive and transmit chains within the HNB 130.

The receiver chain, as known in the art, includes receiver front-end circuitry 206 (effectively providing reception, filtering and intermediate or base-band frequency conversion). The front-end circuitry 206 is serially coupled to the signal processing module 165. An output from the signal processing module 165 is provided to a transmit element of a network connection 210, for example operably coupling the signal processing module 165 to the access controller 140 of FIG. 1 via, say, a wireless or wired connection to the Internet 160. The controller 214 is also coupled to the receiver front-end circuitry 206 and the signal processing module 165 (generally realised by a digital signal processor (DSP)). The controller 214 and signal processing module 165 are also coupled to at least one memory device 216 that selectively stores operating regimes, such as decoding/encoding functions, synchronisation patterns, code sequences and the like.

As regards the transmit chain, this essentially includes a receiving element of a network connection 210, coupled in series through transmitter/modulation circuitry 222 and a power amplifier 224 to the antenna 202. The transmitter/modulation circuitry 222 and the power amplifier 224 are operationally responsive to the controller 214, and as such are used in transmitting data to a wireless communication unit, such as UE 1 18.

The signal processor module 165 in the transmit chain may be implemented as distinct from the processor in the receive chain . Alternatively, a single processor may be used to implement processing of both transmit and receive signals, as shown in FIG. 2. Clearly, the various components within the HNB 130 can be realised in discrete or integrated component form, with an ultimate structure therefore being merely an application-specific or design selection.

In accordance with some examples, the memory device 216 stores computer-readable program code thereon for programming the signal processing module 165 to perform a method for popu lati ng a neig h bou r cel l l ist for use in relation to performing handovers of wireless communication units between neighbouring cells. The program code is operable for, at a network element for supporting communication in at least one femto cell of a cellular communication network, maintaining a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on a handover success rate for neighbouring cells, and generating a neighbour cell list based at least partly on the record of preferred neighbouring cells.

In accordance with some example embodiments, the signal processing module 165 may be arranged to maintain a record of preferred neighbouring cells comprising information relating to one or more neighbour cells, the record of preferred neighbouring cells being populated based at least partly on a handover success rate for the one or more neighbouring cells.

For example, information relating to a neighbouring cell may be added to the record of preferred neighbouring cells when a number (X) of successful handovers to that neighbouring cell, for example as a percentage or ratio of a last Y handover attempts to that neighbouring cell, exceeds a threshold value. Similarly, information relating to a neighbouring cell may be removed from the record of preferred neighbouring cells when a number (X) of successful handovers to that neighbouring cell, for example as a percentage or ratio of a last Y handover attempts to that neighbouring cell, falls below a threshold value. This latter threshold value may be the same as the threshold value used for adding neighbouring cells to the record of preferred neighbouring cells. Alternatively, the threshold value used for removing neighbouring cells from the record of preferred neighbouring cells may be a lower value than the threshold value used for adding neighbouring cells to the record of preferred neighbouring cells in order to minimise the fluctuating addition and removal of neighbouring cells for which a handover success rate is in the region of the threshold values. Furthermore, this or these threshold values may be pre-defined, network programmable or user-definable. It is contemplated that the removal of information relating to a neighbouring cell, for which a number of successful handovers to that neighbouring cell falls below such a threshold value, may be prevented if that cell is the only cell for which the record comprises information.

Handover attem pts may be tracked by mon itori ng , for exam ple, physical layer measurement events reported by wireless communication units that are used to initiate handover procedures. For example, in a case of a 3G UMTS™ wireless communication system, intra- frequency handover attempts may be tracked by monitoring Event 1 c messages from wireless communication units indicating when a non-primary CPICH (Common Pilot Channel) provides a better quality of service than an active primary CPICH. Additionally/alternatively, inter-frequency handover attempts may be tracked by monitoring Event 2b messages from wireless communication units that indicate when an estimated quality of a currently used frequency is below a certain threshold and an estimated q uality of a non-used freq uency is above a certain threshold . Additionally/alternatively, inter-RAT handover attempts may be tracked by monitoring Event 3a messages from wireless communication units indicating when an estimated quality of the currently used UTRAN (UMTS™ Terrestrial Access Network) frequency is below a certain threshold and an estimated quality of another RAT system is above a certain threshold.

I n accordance with some example em bod iments, a handover su ccess rate for a neighbouring cell may be determined based at least partly by way of monitoring signals received from a core network of the cellular communication network. For example, a handover of a wireless communication unit to a neighbouring cell may be determined to have been successful upon receipt of a command to release assigned radio bearers from the core network within a defined period (T) from a defined point within the handover procedure, such as from a time and a point of instructing the wireless communication unit to reconfigure at least one radio bearer. In a case of a 3G UMTS™ network, such as the example illustrated in FIG. 1 , a handover may have been determined to have been successful upon receipt of an "lu Release" command from the core network, for example comprising a relevant cause value such as "successful relocation", within a defined period (T) after the network element (HNB 130 for the illustrated example) transmitted an "RB (Radio Bearer) Reconfiguration" message to the wireless communication unit.

In accordance with some example embodiments, the signal processing module 165 keeps track of the handover success rate for neighbouring cells to which handovers have been initiated. For example, the signal processing module 165 may be arranged to maintain a table of neighbour cell handover statistics within memory element 216. Such a table may comprise, for example, a list of neighbouring cells to which handovers have been initiated from the femto cell 150 supported by the HNB 130. Such a table may further comprise the results (e.g. success or failure) of the last Y handover procedures initiated for each of the neighbouring cells.

Thus, the signal processing module 165 may be arranged to maintain a record of preferred neighbouring cells comprising information relating to one or more neighbour cells based at least partly on the handover statistics within such a table. The neighbouring cells within the record of preferred neighbouring cells may further be rated based on, for example, their handover success rate, whereby those neighbouring cells that are identified as having a high handover success rate may be ranked higher than those with a lower handover success rate.

The signal processing module 165 may be further arranged to generate a preliminary cell list based at least partly on physical layer measurements for neighbouring cells, and if one or more neighbouring cell(s) within the record of preferred neighbouring cells is/are not present within the preliminary cell list, the signal processing module 165 may add one or more of the neighbouring cell(s) within the record of preferred neighbouring cells to the preliminary cell list. In this manner, a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells may be generated.

For example, referring back to FIG . 2 , the H NB 1 30 of the illustrated example may comprise a further receiver circuit 230, operably coupled to a further antenna 235, and arranged to enable the HNB 130 to perform NetWork Listen (NWL) operations. For example, the signal processing module 165 may be arranged to configure the receiver circuit 230 to cyclically 'listen' for radio frequency (RF) signals broadcast by neighbouring cells, and to perform physical layer measurements (e.g. signal quality measurements) for detected signals broadcast by neighbouring cells. In particular, the signal processing module 165 may configure the receiver circuit 230 to cyclically listen for RF signals broadcast by neighbouring cells over the same carrier frequency as that used by the HNB 130 (intra-frequency), over a different carrier frequency as that used by the HNB 130 (inter-frequency), and/or by way of a different radio access technology (RAT) as that used by the H NB 130 (inter-RAT). In this manner, the signal processing module 165 may generate the preliminary cell list based at least partly on physical layer measu rements for neighbouring cells obtained through a NetWork Listen (NWL) cycle.

Having generated a preliminary cell list, the signal processing module 165 may perform a comparison of preferred neighbouring cells (namely those included within the record of preferred neighbouring cells) with the preliminary cell list. If one or more preferred neighbouring cells is/are not included within the preliminary cell list (for example due to physical layer measurements made during the last NWL cycle being identified as too low), the signal processing module 165 may add the omitted preferred neighbouring cells to the preliminary cell list to thereby create a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells.

Upon determining that one or more preferred neighbouring cells have been omitted from a preliminary cell list, the signal processing module 165 may be arranged to only add the highest rated preferred neighbouring cell, or the N highest rated preferred neighbouring cells (where N may comprise a predefined and/or configurable integer value) to the preliminary cell list. In this manner, the increase in size of the preliminary cell list may be limited.

Upon determining that one or more preferred neighbouring cells have been omitted from the preliminary cell list, the signal processing module 165 may be arranged to add one or more of the omitted preferred neighbouring cells to the preliminary cell list, whilst removing one or more other neighbouring cells from the preliminary cell list. For example, the signal processing module 165 may remove a number of neighbouring cells from the preliminary cell list, where the number is substantially equal to the number of preferred neighbouring cells added to the preliminary cell list. Alternatively, the signal processing module 165 may remove one neighbouring cell from the preliminary cell list for the M^th and each subsequent preferred neighbouring cell added to the preliminary cell list (where M may comprise a predefined and/or configurable threshold value for an allowed number of preferred neighbouring cells to be added to the preliminary cell list without the need for cells to be removed therefrom).

The signal processing module 165 may be arranged to limit the number of neighbouring cells included within the preliminary cell list based at least partly on physical layer measurements therefor to a predefined and/or configurable maximum number of preliminary neighbour cells.

Having updated the preliminary cell list to comprise the one or more preferred neighbouring cell(s), the updated preliminary cell list may then be used as a basis for, say, a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells. It will be appreciated that, if no neighbouring cells within the record of preferred neighbouring cells have been omitted from the preliminary cell list, the unaltered preliminary cell list may be used as the basis for a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells.

As previously mentioned, in the context of, say, a 3G UMTS™ wireless communication system, a network element, such as a NodeB or Home NodeB, may typically provide one or more neig hbou r cell l ists to wi reless com m u nication u n its con nected thereto. The wireless communication units, when in a connected state, may subsequently perform physical layer measurements for detected neighbour cells within the received neighbour cell lists, and upon certain events relating to such physical layer measurements occurring, a wireless communication unit may report such an event back to the NodeB or Home NodeB, whereupon the NodeB or Home NodeB may initiate a handover procedure for that wireless communication unit. Accordingly, the record of preferred neighbouring cells may further comprise frequency and decoding information for the preferred neighbouring cells. This information may be provided to wireless communication units to enable the wireless communication units to synchronise with, and decode RF signals from, the neighbouring cells in order to facilitate the physical layer measurements thereof.

It is further contemplated that a wireless communication unit operating in an idle state may use such a neighbour cell list within cell selection and reselection procedures.

The generation of a neighbour list based on, for example, a NWL process can be time consuming due to the need to synchronise with and decode each detected signal. Accordingly, some example embodiments may comprise maintaining a record of preferred neighbouring cells, for example as described above, performing a NetWork Listen (NWL) cycle to obtain physical layer measurements for neighbouring cells within the record of preferred neighbouring cells, and generating a neighbour cell list based at least partly on the obtained physical layer measurements for the preferred neighbouring cells. In this manner, by prioritizing neighbouring cells within the record of preferred neighbouring cells, a selective NWL cycle may be performed in order to reduce the time taken to generate a neighbour cell list. For example, such a prioritized NWL cycle and subsequent neighbour list generation may be performed as part of a start-up routine for the HNB 130 in order to reduce the time taken for the HNB 130 to become operational. Having generated this initial neighbour cell list, the HNB 130 may subsequently perform more comprehensive NWL processes in order to generate a more comprehensive neighbour cell list. For example, having generated such an initial neig hbou r cell list, the H N B 1 30 may su bseq uently instigate a comprehensive NWL cycle in order to generate a preliminary cell list based on the physical layer measurements obtained during the NWL cycle, as described above. The HNB 130 may then perform a comparison of preferred neighbouring cells (namely those included within a record of preferred neighbouring cells) with the preliminary cell list. If one or more preferred neighbouring cells is/are not included within the preliminary cell list (for example d ue to physical layer measurements made during the last NWL cycle for such a cycle being too low), the HNB 130 may add the omitted preferred neighbouring cells to the preliminary cell list in order to create a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells.

Example embodiments have been described for populating a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells. In particular, examples of the proposed techniques comprise a network element, such as an HNB, making use of handover statistics to minimize the likelihood of the most important neighbour cell(s) not being present within the neighbour cell lists. Significantly, field measurements from femto cell trials have shown that typically only one or two 3G/2G macro neighbour cells provide optimal choices from a perspective of handover/cell reselection performance. One of the reasons for this is that the coverage area of a femto cell is a fraction of the size of the cell coverage area of a typical macro cell. Accordingly, the likelihood of a femto cell deployment lying within overlapping coverage areas of more than one macro cell is small. Further, there are only a limited number of entry/exit routes (i.e. doors, garage, etc.) available i n a typical residential/commercial premise, and the strongest macro cell signal along these entry/exit routes is likely to be the most desirable one in terms of handover performance. However, it is often the case that the HNB is not positioned near to such an entry/exit route, and as such it cannot be guaranteed that this target macro cell will always be present in the neighbour cell list if the population of the neighbour cell list is based solely on physical layer measurements made by the NWL receiver of the HNB. Accordingly, by minimizing the likelihood of such an optimal macro neighbour cell being omitted from the neighbour cell list for the femto cell, the proposed techniques enable handover success rates from the femto cell to be improved.

It is envisaged that use of the proposed techniques may be of particular benefit when an HNB is not able to detect a particular macro cell after the HNB has been moved to a new location within, say, a residential or commercial premise. Referring now to FIG's 3 and 4, there are illustrated simplified flowcharts 300, 400 of an example of a method for populating a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells. In summary, the method comprises, at a network element for su pporting commu nication in at least one femto cell of a cellu lar communication network, maintaining a record of preferred neighbouring cells. The record of preferred neighbouring cells is populated based at least partly on a handover success rate for neighbouring cells, and the method further comprises generating a neighbour cell list based at least partly on the record of preferred neighbouring cells.

In more detail, a part 300 of the example method illustrated in FIG. 3 starts at step 305 and moves on to step 310 with a detection of a handover attempt with a target neighbouring cell. For example, such a handover attempt may be detected by way of a physical layer measurement event reported by a wireless communication unit. Next, at step 315, it is determined whether or not the detected handover is successful. For example, in the case of a 3G UMTS™ network, such as the example illustrated in FIG. 1 , a handover may be determined to have been successful upon receipt of an "lu Release" command from the core network, for example comprising a relevant cause value such as "successful relocation", within a defined period (T) after the network element (e.g. HNB 130 for the illustrated example) transmit, say, an "RB Reconfiguration" message to the wireless communication unit. If it is determined that the detected handover is unsuccessful, the method moves on to step 320, where handover success results for the target neighbouring cell are updated with a 'failed handover attempt' indication. The method then ends at step 330. Conversely, if it is determined that the detected handover is successful, the method moves on to step 325, where handover success results for the target neighbouring cell are updated with a 'successful handover attempt' indication. The method then ends at step 330. Referring now to FIG. 4, a part 400 of an example method for generating a neighbour cell list is illustrated and starts at step 410. The method moves on to step 420, where a NetWork Listen (NWL) cycle is performed in order to obtain physical layer measurements for detected neighbouring cells. Next, at step 430, a preliminary list of neighbouring cells is generated based on the physical layer measurements obtained in the NWL cycle. One or more preferred neighbour cells is/are then identified, in step 440 , for example based on the handover success results maintained for neighbouring cells to which handovers has/have been attempted. It is then determined, in step 450, whether one or more preferred neighbour cells has/have been omitted from the preliminary cell list. If one or more preferred neighbour cells have been omitted from the preliminary cell list, the method moves on to step 460 where the omitted preferred neighbour cells are added to the preliminary list in order to generate a neig hbou r cell list for use in relation to performing communication handovers of wireless communication units between neighbouring cells. Th e method then ends at step 480. Referring back to step 450, if no preferred neighbour cells have been omitted from the preliminary cell list, the method moves on to step 470 where the preliminary list is used unaltered in order to generate a neighbour cell list for use in relation to performing communication handovers of wireless communication units between neighbouring cells. The method then ends at step 480.

Referring now to FIG. 5, there is illustrated an example of a flowchart 500 of a method for populating a neig hbou r cell list for use in performing communication handovers of wireless communication units between neighbouring cells according to some example embodiments of a further aspect of the present invention. The method starts at step 505, for example as part of a start-up routine for a network element, such as the HNB 130 illustrated in FIG. 1. The method then moves on to step 510 where preferred neighbouring cells are identified. Next, at step 515, physical layer measurements are obtained for the preferred neighbouring cells, for example by way of performing a selective NWL cycle. An initial neighbour cell list may then be generated, at step 520, based on the physical measurements obtained for the preferred neighbouring cells. In this manner, the generation of such an initial neighbour cell list enables a communication cell to be operational more quickly than currently possible, since a full and time consuming NWL cycle has not had to be performed in order to generate a valid neighbour cell list.

Having generated the initial neighbour cell list, a more comprehensive NWL cycle may subsequently be performed, as illustrated at step 525, in order to obtain a more comprehensive set of physical layer measurements for neighbouring cells. A more comprehensive neighbour cell list may then be generated based on the physical layer measurements obtained through the more comprehensive NWL cycle. In accordance with some example embodiments, and as illustrated in FIG. 5, having performed a more comprehensive NWL cycle in step 525, the method may comprise the subsequent step 530 of generating a preliminary list of neighbouring cells based on the results of the more comprehensive NWL cycle. Next, at step 535, the method may comprise determining whether or not one or more preferred neighbour cells has/have been omitted from the preliminary cell list. If one or more preferred neighbour cells has/have been omitted from the preliminary cell list, the method moves on to step 540 where the omitted preferred neighbour cells are added to the preliminary list to generate a neighbour cell list for use in performing communication handovers of wireless communication units between neighbouring cells. The method then ends at step 550. Referring back to step 535, if no preferred neighbour cells have been omitted from the preliminary cell list, the method moves on to step 545 where the preliminary list is used unaltered to generate a neighbour cell list for use in performing communication handovers of wireless communication units between neighbouring cells. The method then ends at step 550.

The present invention has been herein described with reference to a Home NodeB within a UMTS™ network. However, it is also envisaged that the inventive concept may be applied to any network element arranged to support communication within a communication cell of a network element, and arranged to populate a neighbour cell list for use in relation to performing communication handovers of wireless communication units between neighbouring cells. In particular, the inventive concept may be implemented within any such network element for which manual configuration and/or optimisation of neighbour cell lists is impractical and/or unfeasible.

In some examples, some or all of the steps illustrated in the flowcharts of FIG's 3, 4 and 5 may be implemented in hardware and/or some or all of the steps illustrated in the flowchart may be implemented in software.

Although some aspects of the invention have been described with reference to their applicability to a UMTS™ (Universal Mobile Telecommunication System) cellular communication system and in particular to a UMTS™ Terrestrial Rad io Access Network (UTRAN) of a 3^rd generation partnership project (3GPP™) system, it will be appreciated that the invention is not limited to this particular cellular communication system. It is envisaged that the concept described above may be applied to any other cellular communication system

Referring now to FIG. 6, there is illustrated a typical computing system 600 that may be em ployed to im plement sig nal processing fu nctionality in embod iments of the invention. Computing systems of this type may be used in access points and wireless communication units. Those skilled in the relevant art will also recognize how to implement the invention using other computer systems or architectures. Computing system 600 may represent, for exam ple, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment. Computing system 600 can include one or more processors, such as a processor 604. Processor 604 can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module. In this example, processor 604 is connected to a bus 602 or other communications medium.

Computing system 600 can also include a main memory 608, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by processor 604. Main memory 608 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 604. Computing system 600 may likewise include a read only memory (ROM) or other static storage device coupled to bus 602 for storing static information and instructions for processor 604.

The computing system 600 may also include information storage system 610, which may include, for example, a media drive 612 and a removable storage interface 620. The media drive 612 may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media 618 may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive 612. As these examples illustrate, the storage media 618 may include a computer-readable storage medium having particular computer software or data stored therein. ln alternative embodiments, information storage system 610 may include other similar components for allowing computer programs or other instructions or data to be loaded into computing system 600. Such components may include, for example, a removable storage unit 622 and an interface 620, such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units 622 and interfaces 620 that allow software and data to be transferred from the removable storage unit 618 to computing system 600.

Computing system 600 can also include a communications interface 624. Communications interface 624 can be used to allow software and data to be transferred between computing system 600 and external devices. Examples of communications interface 624 can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via communications interface 624 are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by communications interface 624. These signals are provided to communications interface 624 via a channel 628. This channel 628 may carry signals and may be implemented using a wireless medium, wire or cable, fiber optics, or other communications medium. Some examples of a communication channel include a phone line, a cellular phone link, an RF link, a network interface, a local or wide area network, and other communications channels.

In this document, the terms 'computer program product' 'computer-readable medium' and the like may be used generally to refer to media such as, for example, memory 608, storage device 618, or storage unit 622. These and other forms of computer-readable media may store one or more instructions for use by processor 604, to cause the processor to perform specified operations. Such instructions, generally referred to as 'computer program code' (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system 600 to perform functions of embodiments of the present invention. Note that the code may directly cause the processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system 600 using, for example, removable storage drive 622, drive 612 or communications interface 624. The control module (in this example, software instructions or computer program code), when executed by the processor 604, causes the processor 604 to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any signal processing circuit. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller, digital signal processor, or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units or processors, for example with respect to the beamforming module or beam scanning module, may be used without detracting from the invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controller. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as field programmable gate array (FPGA) devices. Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term 'comprising' does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to 'a', 'an', 'first', 'second', etc. do not preclude a plurality.

Thus, an improved method and apparatus for configuring handover parameters for populating a neig h bou r cell l ist for use i n relation to perform i ng handovers of wi reless communication units between neighbouring cells have been described, wherein the aforementioned disadvantages with prior art arrangements have been substantially alleviated.

Claims

Claims (GB)

1. A method for populating a neighbour cell list for use in performing communication handovers of wireless communication units between neighbouring cells, the method comprising, at a network element for supporting communication in at least one femto cell of a cellular communication network:

determining a communication handover success rate between a plurality of neighbouring cells;

maintaining a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on the determined communication handover success rate for neighbouring cells; and

generating a neighbour cell list based at least partly on the record of preferred neighbouring cells.

2. The method of Claim 1 wherein determining a communication handover success rate comprises performing a plurality of physical layer measurements for neighbouring cells, the method further comprising generating a preliminary cell list based at least partly on physical layer measurements for neighbouring cells.

3. The method of Claim 2 wherein the method further comprises:

performing a NetWork Listen (NWL) cycle to obtain physical layer measurements for neighbouring cells within the record of preferred neighbouring cells; and wherein generating a neighbour cell list is based at least partly on the obtained physical layer measurements for the preferred neighbouring cells.

4. The method of Claim 2 or Claim 3 wherein if at least a first neighbouring cell from the plurality of neighbouring cells within the record of preferred neighbouring cells is not present within the preliminary cell list, the method further comprises adding the first neighbouring cell to the preliminary cell list.

5. The method of Claim 4 wherein adding the first neighbouring cell to the preliminary cell list further comprises adding neighbouring cell information relating to the record of preferred neighbouring cells when a number (X) of successful handovers to that neighbouring cell as a ratio of a last Y handover attempts to that neighbouring cell exceeds a threshold value.

6. The method of Claim 4 or Claim 5 wherein the preliminary cell list is generated based at least partly on physical layer measurements for neighbouring cells obtained through a NetWork Listen (NWL) cycle.

7. The method of any of preceding Claims 1 to 3 wherein information relating to a neighbouring cell is removed from the record of preferred neighbouring cells when a number (X) of successful communication handovers to that neighbouring cell as a ratio of a last Y communication handover attempts to that neighbouring cell falls below a threshold value.

8. The method of any preceding Claim wherein a communication handover success rate for a neighbouring cell is determined based at least partly by way of monitoring at least one signal from a core network of the femto cell cellular communication network.

9. The method of Claim 8 wherein a communication handover of a wireless communication unit to a neighbouring cell is determined to have been successful upon receipt of a command to release at least one assigned radio bearer from the core network.

10. The method of Claim 9 wherein a communication handover of a wireless communication unit to a neighbouring cell is determined to have been successful upon receipt of the command to release at least one assigned radio bearer from the core network within a defined period (T) from instructing the wireless communication unit to reconfigure at least one radio bearer.

1 1. A network element for supporting communication in at least one femto cell of a cellular communication network, the network element comprising transceiver circuitry arranged to enable communication with at least one wireless communication unit located within the at least one femto cell, and a signal processing module arranged to:

determine a communication handover success rate between a plurality of neighbouring cells;

maintain a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on the determined communication handover success rate for neighbouring cells; and

generate a neighbour cell list based at least partly on the record of preferred neighbouring cells.

12. A communication system comprising a network element for supporting communication in at least one femto cell of a cellular communication network, the network element comprising transceiver circuitry arranged to enable communication with at least one wireless communication unit located within the at least one femto cell, and a signal processing module arranged to:

maintain a record of preferred neighbouring cells, the record of preferred neighbouring cells being populated based at least partly on the determined communication handover success rate for neighbouring cells; and generate a neighbour cell list based at least partly on the record of preferred neighbouring cells.

13. A tangible computer program product having executable program code stored therein for programming signal processing logic to perform a method for populating a neighbour cell list for use in relation to performing handovers of wireless communication units between neighbouring cells, the code operable for, at a network element for supporting communication in at least one femto cell of a cellular communication network:

14. The tangible computer program product of Claim 13 wherein the tangible computer program product comprises at least one of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory (ROM), a Programmable Read Only Memory (PROM), an Erasable Programmable Read Only Memory (EPROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), and a Flash memory.

15. An integrated circuit for a network element supporting communication in at least one femto cell of a cellular communication network, the network element comprising transceiver circuitry arranged to enable communication with at least one wireless communication unit located within the at least one femto cell, the integrated circuit comprising a signal processing module arranged to: determine a communication handover success rate between a plurality of neighbouring cells