GB2452797A

GB2452797A - Handover in a mobile telecommunications network.

Info

Publication number: GB2452797A
Application number: GB0809290A
Authority: GB
Inventors: David Robert Lister; Neil Scully; Stefan Ulrich Thiel
Original assignee: Vodafone Group PLC
Current assignee: Vodafone Group PLC
Priority date: 2007-08-22
Filing date: 2008-05-22
Publication date: 2009-03-18
Also published as: GB0716316D0; GB0809290D0

Abstract

A system and method which allows mobile network users to be categorised according to their degree of mobility and provide them with a component of the network resources, which is dependent upon their mobility. For instance, a Low Mobility user can be allocated a Low Mobility portion of the Spectrum when interference from a High Mobility User is detected and/or a High Mobility User can be allocated a High Mobility portion of the spectrum when an adjacent micro base station is detected, particularly in the situation of the adjacent micro base station providing the High Mobility user with its best signal strength.

Description

HANDOVER IN A MOBILE TELECOMMUNICATIONS NETWORK

Field of the Invention

The present invention relates to a method and arrangement for controlling distribution of a network resource among network users in a telecommunications network including a mixture of micro and macro base stations. More particularly, the present invention relates to the handover between cells in a telecommunications network including a mixture of micro and macro base stations (BS).

Background

There have recently been proposals to allow access to the features and services provided by GSM and UMTS networks other than by accessing those networks in the conventional manner. In this regard, the conventional manner is by signalling between a mobile terminal and a conventional base station (macro base station) that has a dedicated connection to an MSC (Mobile Switching Centre), and which provides coverage in the cell occupied by the mobile terminal using cellular telecommunication (e.g. G SM or UMTS) communication transport protocols.

To increase network capacity, it has been proposed to provide additional special base stations (micro base stations), often referred to as femto cells, fernto base stations, pico cells, pico base stations or access points (APs). These micro base stations may be a dedicated network access point, or may be enhanced wireless internet hubs (i.e. providing wireless internet access, as well as wireless telecommunications network access). The range of micro base stations is significantly smaller than macro base stations, typically only providing coverage of the order of 20 to 30 metres, making them suitable for use, for example, at a subscriber's home or office.

I

It has also been proposed to use these APs in the Long Term Evolution (LTE) telecommunications network. LTE is potentially the next network implementation after the current 3G UMTS etc. An advantage of using an Access Point connected to the core network via an IP network is that existing broadband DSL connections can be used to link mobile terminals with the network core without using the capacity of the radio access network or transmission network of a mobile telecommunications network. In () this regard, these Access Points communicate with the core network via IP based communications, such as a (fixed) broadband IP network, and are typically routed via the Internet.

They are also able to provide mobile network access where there is no conventional radio access network coverage. For example, UMTS coverage could be provided by an access point where there is no conventional UMTS coverage (perhaps only GSM coverage).

The use of APs as an additional or alternative means for accessing the network therefore advantageously increases the network capacity.

Since these access points are not conventional macro base stations, however, additional challenges arise. For instance, in fttture networks, there is likely to be a heterogeneous mixture of micro base stations serving very small areas and macro base stations serving significantly larger areas. These micro base stations must coexist with the conventional macro base stations where the coverage area of one macro base station may potential overlap with tens or hundreds of micro base stations. From a mobility viewpoint, difficulties arise in seamlessly providing a mobile terminal (UE) a seamless connection when travelling across a region comprising both small and large cells (i.e. femto and macro cells).

For instance, with reference to Figure 1, consider UE I in a connected state, with macro base station 22 being its serving cell. If micro base stationlAP 20 is then found to provide UE 1 with the best signal strength, the UE's serving base station 22 will attempt to hand the UE I over to the AP 20. However, if the UE 1 is moving quite quickly, the handover procedure may not be completed in time, and the UE's network connection will be dropped. Even if the UE I is moving slowly, and the handover to AP 20 can be completed by the time the handover is effected, the UE may be moving beyond the range of the AP (since the range of an AP is typically only about 25 metres) and a further handover be required.

From these two examples, it can be seen that if the UE is moving, aiid particularly travelling quickly, the overhead in signalling associated with handover, especially to multiple small microcells, is large and would be detrimental to the system capacity. In addition, the call may simply fail to be handed over to the allocated resources within the appropriate connection time, which is particularly undesirable.

One possible solution to this would be to not necessarily connect the UE 1 to its "best cell". However, further problems arise if the UE is not handed over to the appropriate cell, in that high levels of uplink and downlink interference can arise due to the proximity of the UE I to the micro cell 20, as indicated in Figure 1.

This interference in turn impacts the performance of other users, such as UE 4, connected to the micro base station 20. There is therefore a requirement to support UE mobility, particularly highly mobile UEs, without adversely impacting the radio capacity of the system.

Existing solutions tend to rely on hierarchical cell layers (e.g. in GSM there is one layer for macro cells and another layer for micro cells) in which distinct frequency allocations are allocated to each layer. These solutions consume valuable spectrum resources, and reduce available capacity to either layer. Such solutions are inherently inefficient, as they are completely static and penalise all users on each layer regardless of their mobility.

Summary of the Invention

According to a first aspect of the present invention there is provided, in a telecommunications network including a radio access network comprising at least one macro base station and at least one micro base station, each for wirelessly communicating with mobile terminals over a network resource, a method of controlling distribution of the network resource, the method including: providing each mobile terminal with a mobility indication, being at least a first mobility indication or a second mobility indication; and upon determining a network parameter indicating the proximity of at least one mobile terminal with the first mobility indication to a micro base station, changing the distribution of' the network resource amongst mobile terminals in the vicinity of the micro base station.

This aspect of the invention allows network users to be categorised according to their degree of mobility and provide them with a component of the network resources, which is dependent upon their mobility. For instance, a Low Mobility user can be allocated a Low Mobility portion of the Spectrum when interference from a High Mobility User is detected andlor a High Mobility User can be allocated a High Mobility portion of the spectrum when an adjacent micro base station is detected, particularly in the situation of the adjacent micro base station providing the High Mobility user with its best signal strength.

According to a second aspect, the present invention provides, in a telecommunications iietwork including a radio access network comprising a plurality of base stations, each defining one or more cells, for wirelessly transmitting data that is receivable by one or more mobile terminals, wherein at least one of the base stations is an Access Point (AP), a method of controlling access to the plurality of base stations, the method including: providing each mobile terminal with a mobility indication, being at least a first mobility indication or a second mobility indication, and permitting mobile terminals with the first mobility indication to access macro base stations but not micro base stations.

A result of these aspects of the invention is that users identified as high mobility, say, will sacrifice their ability to handover to micro base stations and will not be allowed to use the full radio resource available to them when in the vicinity of one or more micro base stations. This sacrifice is advantageous, as it serves to minimise the level of interference that high mobility users would cause to users of micro base stations, whilst still enabling them to continue to communicate with a suitable, albeit non-optimum cell (on the basis of the instantaneous radio is conditions).

These aspects of the invention are based on the realisation that there is limited benefit from a UE being connected to the "best" cell offering the best radio conditions, when the UE is only likely to be connected to that "best" cell for a short period of time. There is a greater benefit in minirnising the signalling handover overhead and eliminating the actual delay that would normally occur while performing the handover.

Brief DescriDtion of the Drawings The present invention will now be described in relation to the Figures in which: Figure 1 illustrates an example of a moving mobile terminal creating signal interference in relation to a nearby Access Point; and Figure 2 illustrates an example mobile telecommunications network for receiving IP based communications from an access point in addition to communications from a conventional base station, in which the embodiments of the present invention may be implemented.

Detailed DescriDtion Key elements of a mobile telecommunications network, and its operation, will now briefly be described with reference to Figure 2.

Figure 2 shows elements for providing access to a GSM or UMTS network by both a conventional base station 3 and a micro or femto base station (AP 20).

The AP 20 provides a radio link 21 to mobile terminal I. Each base station (e.g. base station 3 and AP 20) corresponds to a respective cell of its cellular or mobile telecommunications network and receives calls from and transmits calls to a mobile terminal in that cell by wireless radio communication in one or both of the circuit switched or packet switched domains. Such a subscriber's mobile terminal (UE) is shown at I. The mobile terminal may be a handheld mobile telephone, a personal digital assistance (PDA) or a laptop computer equipped with a datacard.

In a GSM mobile telecommunications network, each base station 3 comprises a base transceiver station (BTS) 22 and a base station controller (BSC) 26. A BSC may control more than one BTS. The BTSs and BSCs comprise the radio access network.

In a UMTS mobile telecommunicatiois network, each base station 3 comprises a node B 22 and a radio network controller (RNC) 26. An RNC may control more than one node B. The node B's and RNC's comprise the radio access network.

In the proposed LTE mobile telecommunications network, each base station 3 comprises an eNode B, which effectively combines the functionality of the node B and the RNC of the UMTS network.

s Conventionally, in a GSM/UMTS network, the base stations are arranged in groups and each group of base stations is controlled by a mobile switching centre (MSC) 2 and an SGSN (Serving GPRS Support Node) 16. MSC 2 supports communications in the circuit switched domain -typically voice calls, and corresponding SGSN 16 supports communications in the packet switched domain -such as GPRS data transmissions. SGSN 16 functions in an analogous way to MSC 2. The base station 3 has a dedicated (not shared) connection to its MSC 2, typically a cable connection. This prevents transmission speeds being reduced due to congestion caused by other traffic.

In the LTE network, it is proposed that the base stations are arranged in groups and each group of base stations is controlled by a Mobility Management Entity (MME) and a User Plane Entity (UPE).

The radio link 2 1 from the AP 20 to the mobile terminal I uses the same cellular telecommunication transport protocols as the conventional base station 3 but with a smaller range -for example 25rn. The AP 20 appears to the mobile terminal I as a conventional base station, and no modification to the mobile terminal I is required to operate with the AP 20. The AP 20 performs a role corresponding to that of a GSM BTS 22 and BSC 26 andlor UMTS Node B and RNC andlor an LTE eNode B. Communications between the access point 20 and the core network 12 are IP based communications, and may be, for example, transmitted over a broadband IP network (and routed via the Internet). The communications are routed via MSC 32 or SGSN 34. The access point 20 converts the cellular telecommunications transport protocols used between the mobile terminal I and tile AP 20 to IP based signalling.

The connection 23 between the access point 20 and the core network 12 may use the PSTN telephone network. Typically a DSL cable connection connects the access point 20 to the PSTN network. The data is transmitted between the access point 20 and the core network 12 by IP transport/DSL transport (a backhaul connection). Tile bandwidth of the cable connection between tile access point and tile telephone exchange is shared with multiple other users (typically between 20 and 50 other users). This means that the speed of transmission of data between the access pomt 20 and tile telephone exchange varies significantly in dependence upon the activities of the other access point devices sharing tile Connection.

The access point 20 may be connected to the core network 12 by means other than a DSL cable and the PSTN network. For example, the access point 20 may be connected to tile core network 12 by a dedicated cable connection that is independent of the PSTN, or by a satellite connection between the access point and tile network core 12.

AP 20 would typically be configured to serve a Wireless Local Area Network (WLAN) located in a home or office, in addition to GSM/UMTS/LTE networks.

The WLAN could belong to the subscriber of the mobile terminal I, or be an independently operated WLAN. The owner of AP 20 can prescribe whether the AP is either open or closed, whereby an open AP is able to carry communications from any mobile device in the USM/UMTS/LTE network, and a closed AP is only able to carry communications from specific pre-designated mobile devices.

From tile description above, it will be understood that the coverage area of a mobile telecommunications network is divided into a plurality of cells, each of which is served by a respective base station. In order to allow a mobile terminal to maintain a call when the mobile terminal moves outside the coverage area of a cell, the call must be switched to an alternative cell automatically. Similarly, if the mobile terminal moves into a cell providing better coverage, the call will be automatically switched to the better coverage cell. The call must maintain the connection with the old cell, whilst handover is effected, until the new connection is known to have succeeded. Handover is a time critical process requiring action to be taken before the radio link with the original cell degrades to such an extent that the call is lost. Handover requires synchronisation of events between the mobile terminal and the network.

With this background in mind, an implementation of the first embodiment of the invention will now be described, which seeks to minimise interference in regard toAPs.

A first feature of this first embodiment of the invention is that each mobile user terminal (UE) that is able to access the system is labelled as either high or low mobility. This mobility indication may be based on the number of cell reselections and/or cell transit times applicable to a given mobile terminal over a certain period of time. Alternatively some other measure (e.g. doppler effect to measure terminal's speed or a location source in the terminal, such as GPS) may be used. Each user's mobility indication is preferably updated regularly. For instance, a UE may be labelled a High Mobility User (HMU) when its speed is higher than a predefined threshold. \Vhere its speed is at or below the threshold, it is labelled a Low Mobility User (LMU).

The mobility indication may be determined and designated by the terminal itself, or by a network component. Where the mobility indication is designated by the terminal itself, the designation is preferably communicated to the network.

The usefulness of the mobility indication in this embodiment of the invention is to provide a differentiatioii between UEs based upon their activity within the network. Designating a UE as a HMU, means that that UE is only able to connect to macro cells, but not micro cells, even if a micro cell provides that UE with the best radio conditions. This is recognition of the fact that that user is moving quite quickly about the network so the usefulness of APs to that user is lower relative to the disadvantage likely to be incurred through the increased use of signalling resources should that user be allowed to use APs.

Designating a UE as a LMU, on the other hand, merely differentiates that user from HMUs. LMUs are able to use macro cells and micro cells according to whichever cell provides the best radio conditions, as is the normal approach in current telecommunication networks.

A further feature of this embodiment of the invention is in relation to the use of the available comnlunicatjon channels. The present invention is particularly useful in networks utilising Orthogonal Frequency Division Multiple Access (OFDMA) to modulate signals on the uplink and/or downlinic communication channels.

OFDMA is a modulation scheme, in which a large frequency bandwidth can be considered to comprise of a number of multiple sub-carriers which cany the underlying information. In other words, OFDMA is multi-user version of OFDM that allows multiple accesses on the same channel. OFDM works by dividing a given spectrum block into a number of sub-channels, each of which is individually modulated and then transmitted orthogonally to minimize interference with one another. The demands of mobility and two-way communications led to the development of OFDMA, which can assign a subset of sub-carriers to individual users.

Next generation wireless communications standards incorporate Orthogonal Frequency Division Multiple Access (OFDMA). In particular, OFDMA is part of both the IEEE 802.16 Wireless Metropolitan Area Network (MAN) Air Interface standard (commonly referred to as WiMAX) and 3GPP LTE.

According to this embodiment of the invention, the channel spectrum available to UEs to communication on is divided into a high mobility spectrum component and a low mobility spectrum component. However, rather than implementing this division for all UE communications, the division is only implemented when certain potentially adverse network conditions are detected, such as: -an AP detecting an increase in noise from a UE with which it is not communicating; -a high mobility UE detecting its proximity to an AP, such as by detenniriing that a cell ID which provides it with a signal strength measurement belongs to an AP and/or -a macro cell determining the proximity of a high mobility UE, with which it is communicating, to an AP, such as via the receipt of a request to handover the UF to the AP.

Therefore, in this embodiment, where OFDMA is utilised, the OFDMA sub-carrier space is broken down into at least two segments, so that all sub-carriers in the first segment are designated as high mobility and all sub-carriers in the second segment are designated as low mobility. The spectrum split may be implemented in a similar manner to the Partial Usage of Sub Carriers (PUSC) as utilised in WiMAX. In WiMAX a PUSC mode may be utilised which partitions the set of sub carriers into sub channels and provides a pseudo-random distribution of sub carriers in the sub channels.

Preferably the total sub-carrier allocation is divided between both the small cell (femto cell) and the macro cell and the allocation does not overlap. The two segnients could be referred to as "high- mobility preferred", and "low mobility protected" respectively, when the division is put into effect.

The spectrum division may be implemented in any appropriate manner, and may be fixed or flexible. An example of a fixed approach would be to allocate half of the spectrum to high mobility users and the other half to low mobility users.

Where a flexible approach is chosen, it is preferably based upon load characteristics of the macro cell and micro cell concerned. Further, the split could be different for different macro cells.

A summary of the resource allocation and functionality of a low mobility user according to this embodiment of the invention is as follows: a. The user would be granted pennission to communicate on all sub- carriers including the low mobility protected sub-carriers and high-mobility preferred sub-carriers.

b. To maintain this resource allocation, this user would be required to handover to the micro base stations (ferntocells) when they become visible.

c. The low mobility user can access the full spectrum resource, including both the low-mobility and high-mobility options until an adverse network condition, caused by a proximate high mobility user, is detected. For instance, in the case of transient interference (e.g. a sudden increase in noise as measured at the micro base station) arising, the low-mobility user will be downgraded to a low-mobility protected spectnini allocation only.

d. On reduction of the transient (e.g. stabilisation of the rate of change of interference) the full allocation of spectrum shall be made available to the user once again.

In contrast, a high mobility user will have the following resource allocation and functionality in this embodiment of the invention: a. The high mobility user is initially granted the full spectrum allocation.

b. The high mobility user is only permitted to use macro base stations and is prohibited froin using micro base stations; c. Should the user experience a measurement from a micro cell (as signalled by the network, or by decoding a cell ID as a cell ID from a micro cell), then the measurement will be reported to the serving macro base station but no handover shall be performed d. When a measurement from a micro cell is determined, the user will be allocated spectrum in the high-mobility preferred band only.

e. Should the user's mobility reduce below a defined threshold, the full spectrum allocation will once again be assigned. Similarly, should the user handover to an alternative macro cell, the full spectrum allocation may once again be assigned.

This functionality will be described in greater detail in relation to the arrangement of Figure 1, where UF I is designated a high mobility user and UE 4 is a low mobility user.

UE 1 is active, and communicating with the network via macro cell 22, utilising the full spectrum range of the available communication channel(s). This will continue as long as UE I is a high mobility user, and not in a region covered by a micro cell.

When the High Mobility user, UE 1, does move into the vicinity of micro cell 20, it becomes necessary to switch UE 1 over from using the full spectrum range to communicate, to just the segment of spectrum allocated to high mobility users.

This trigger can be achieved in a number of different ways.

In a first approach, it is the UE's responsibility to determine when it is proximate micro cell 20 and to do this it utilises its neighbouring cell list (NCL).

When active, while the UE is communicating via its serving base station 22, it is also monitoring the signal strength of any neighbouring cells, in order to determine when it is receiving a stronger signal from a neighbouring cell, and should therefore handover to that neighbouring cell. The UE knows which cells to look out for, as it typically receives the NCL from the network listing cell IDs of adjacent and/or nearby cells.

In this first approach, the UE determines whether any micro cells are listed in the NCL, and if so, switches to communicating on only the high mobility spectrum in the uplink. The UE also preferably informs its serving base station 22, so that it also switches to communicating on only the high mobility spectrum in the downlink.

In order for the UE to be able to use the NCL to distinguish micro base stations from macro base stations, an additional indication is incorporated into the cell ID transmitted by all base stations.

In a second approach for triggering the spectrum allocation switch, the UE monitors all broadcasts received from neighbouring cells, and determines if any of these received broadcasts are from micro cells. Where a broadcast from a micro cell is received, then the liE will switch to the high mobility preferred band. This determination is again based upon the indication in the cell ID for micro base stations. In an alternative, rather than switching based upon any received broadcast from a micro cell, a threshold can be utilised, whereby the received broadcast signal needs to exceed a predetermined level before a switch is instigated.

In a third approach, the spectruni allocation switch will be triggered based upon the ability of the UE to handover to a micro cell. In this regard, based upon the UE's neighbouring cell signal strength measurements, if the UE is close enough to the micro cell 20, such that the micro cell provides the best network coverage for the UE, according to the system normal operation a handover request would be initiated in order to handover from macro cell 22 to the micro cell 20.

In this alternative approach, however, upon High Mobility UE 1 identifying its best cell 20 as a micro cell, since the UE is designated as a high mobility user, instead initiating handover to the micro cell 20, the UE I will notify the macro cell and switch over to using only the High Mobility Spectrum, rather than the Full Spectrum, in order to limit any interference that the micro cell 20 may experience from the UE's communications to and from the macro cell 22.

In a fourth approach, it is the serving base stationlcore network that triggers the high mobility UE to switch its spectrum allocation. In this approach, the UE sends its signal strength (or other suitable parameter) measurement reports to the serving base station, which analyses the measurements. As per the above approaches, the serving base station will trigger the spectrum switch when it either: determines a broadcast from one or more micro cells to be included in the signal strength measurements; determines a broadcast from one or more micro cells to be included in the signal strength measurements and which exceeds a signal level threshold; or determines a broadcast from a micro cell to provide the best signal strength measurement.

The micro cell may be again distinguished from macro cells via an identifier, such as a check bit, in its cell ID. Alternatively, the serving base station may have access to a list of cell IDs that correspond to micro base stations, which may be determined by signalling the network. According to a still further alternative, micro cells may be distinguished by using Cell IDs appropriate to a particular layer of cells that have a similar property (e.g. Power rating, Coverage area, etc).

From the micro cell's viewpoint, when UE 1 moves into the vicinity of micro cell 20, the micro cell will start detecting interference from the UE, caused by the UE's comnutnjcatjons with the macro cell 22. That is, signalling on the control channels between UE I and macro cell 22 will be picked up by the micro cell as a high rate of change (increase) of the noise level. This is because, when the micro cell is utilising the full frequency spectrum to communicate with UE 4, it may be using the same sub-carriers for sending and receiving communications as UE 1. The micro cell 20 will start to "see" communi cations on the sub-carriers that it cannot decode, due to those communications not being intended for it. This undecodable signal activity will therefore appear as noise.

Upon the micro cell 20 rccognising the increased noise, the micro cell switches over to utilising the component of the spectrum set aside for low mobility users.

It preferably also notifies its active low mobility users of this spectrum restriction, so that they can also send their uplink communications on the appropriate spectrum.

In this embodiment, the micro cell 20 utilises a learning behaviour in determining when to trigger the spectrum switch. That is, the micro cell is configured to learn from the interference pattern that it experiences, such that it is better able to recognise the type of interference that occurs when several high mobility users are nearby and traversing its coverage area, as distinct from other types of interference that it may experience.

Occurrence of particular patterns in the noise variations will be correlated with the arrival of high mobility users. One possible pattern is a strong and fast increase in the noise rise. Patterns that always occur when high mobility users are nearby or within the coverage area, and that do not occur when there are no high mobility users, will be identified. By utilising this learning behaviour, it is possible to predict when high mobility users are arriving.

It is to be appreciated that there is likely to be a learning curve for the micro cell in recognising the frequency of the change in noise rise as an indication of nearby high mobility users, and using this change as a trigger for switching between full spectrum usage and low mobility spectrum usage. That is, the micro cell 20 preferably monitors the rate of change of interference, and this can vary considerably depending upon the number of high mobility UEs which are in its vicinity, as well as the speed of each of those UEs. Therefore, although an interference rate threshold may be used to initiate the switch over, it is more preferable to utilise a learning behaviour of the micro cell. With this approach, although a switchover may not happen immediately and benefit the first high mobility UEs, the femto cell's effectiveness will improve.

Therefore, from this description, it is apparent that in the embodiments of the invention just described, sub-carrier resource allocation occurs at both the serving macro cell (supporting the high mobility user) and the femtocells (supporting primarily the low mobility users).

Once the spectrum split has occurred, the high mobility user 1 and the micro cell 20 will revert to using the full spectrum again, ideally once the high mobility user I is no longer in conflict with the micro cell 20.

From the micro cell's perspective, this may occur when it no longer detects noise rise changes in the signalling channel. Alternatively, a simple time base delay may be implemented.

From the high mobility user's point of view, this may occur when the UE 1 leaves the area of the micro cell 20. This may be determined by: the micro cell no longer providing the UE with the strongest signal strength; the UE no longer receiving broadcasts from the micro cell; the broadcast received from the micro cell being below a given threshold; the micro cell no longer being included in the UE's Neighbouring Cell List; the cell now providing the UE with its strongest signal strength is a macro cell; or the UE I is handed over to a different macro cell.

According to a still further alternative, whilst utilising the High Mobility spectrum, the user may be changed from a High Mobility user to a Low Mobility user. In this situation, if a micro cell provides the UE with the best signal coverage (which is almost certainly the case), then the UE will handover to the micro cell and revert to using the full spectrum for signalling. Alternatively, the UE may have recently just moved outside the range of the micro cell 20, before changing to a low mobility user, such that macro cell 22 is providing it with its best signal strength. In this case, the UE will also revert to using the full spectrum for signalling, and remain in the macro cell.

A time base delay may also be used, either separately, or in conjunction with any of the above techniques (e.g. UE 1 reverts to full spectrum signalling a predetermined period of time after it is handed over to a different macro cell).

These embodiments of the invention have the advantage of reducing the amount of signalling that would normally be required. Further, there is better throughput for both high mobility users on macro cells and low mobility users on micro cells when the spectrum is split, as they can use better Mobile Coding Schemes (MCS) due to there being less interference, even though less spectrum is available to each group of users. It is also considered that a more stable system is likely to result from utilising these embodiments of the invention, as there are fewer handover problems and less noise.

The embodiments of the invention have been described with particular reference to OFDMA, however, they may equally be applied to other frequency modulation schemes which allow multiple users to utilise the same frequency carrier.

Further, the embodiments of the invention have been described in relation to designating two different types of users, namely high mobility and low mobility users, but additional designations may also be utilised. For instance, a medium mobility user type may be incorporated, adding an extra degree of flexibility.

Additionally, whilst it is preferable that users be able to change from high mobility users, to low mobility users, dependent upon their degree of movement, it is also possible for certain users to be statically designated high mobility or low mobility. For instance, a user may be statically designated as a high mobility user if their network contract excludes the use of micro cells as a means to access the network. This static designation may be permanent or temporary. For instance, a temporary static designation may be applied on a regional basis, such as if the UE is roaming and moved outside their home country.

The embodiments have also been described in relation to the macro base stations and micro base stations being responsible for determining when the spectrum division should be implemented. Alternatively, however, the division could be coordinated by the core network. For instance, if a macro cell receives a handover request for a HMU to a micro cell, it could inform the core network of such a request. The core network could then access a list of micro cells in the vicinity of that macro cell, and instruct those micro cells to effect the spectrum division for all of their users. The core network could then monitor the network to determine when to remove the network division, such as upon being informed that the HMU necessitating the network division has moved on to another macro cell.

Claims

CLAIMS: 1. In a telecommunications network including a radio access network comprising at least one macro base station and at least one micro base station, each for wirelessly communicating with mobile terminals over a network resource, a method of controlling distribution of the network resource, the method including: providing each mobile terminal with a mobility indication, being at least a first mobility indication or a second mobility indication; and upon determining a network parameter indicating the proximity of at least one mobile terminal with the first mobility indication to a micro base station, changing the distribution of the network resource amongst mobile terminals in the vicinity of the micro base station.
2. The method of claim I wherein the network resource is a frequency spectrum and step of changing the network resource distribution includes at least one of: for the at least one mobile terminal with the first mobility indication, changing from access to the full spectrum to access to a first spectrum component; and for any mobile terminals with the second mobility indication which are communicating with the micro base station, changing from full spectrum access to access to a second spectrum component, which does not overlap with the first spectrum component.
3. The method of claim I or 2 wherein the step of determining a network parameter indicating the proximity of at least one mobile terminal to the micro base station comprises at least one of: the micro base station detecting interference on the network resource due to the at least proximate mobile terminal with the first mobile indicator; a mobile terminal with the first mobility indicator identifying an indicator of the micro base station on a Neighbouring Cell List; a mobile terminal with the first mobility indicator determining a signal strength measurement, and identifying the measurement as relating to the micro base station; a macro base station serving a mobile terminal having a first mobility indicator receiving a signal strength measurement relating to the micro base station; and a macro base station serving a mobile terminal having a first mobility indicator receiving a handover request to the micro base station.
4. The method of any one preceding claim further including restoring the distribution of the network resource: after a predetermined time period; andlor once the at least one mobile terminal is determined as no longer being proximate to the micro base station.
5. The method of claim 4 wherein the step of restoring the network resource distribution includes at least one of: for the at least one mobile terminal with the first mobility indication, changing from a first spectrum component to full spectrum access; and for any mobile terminals with the second mobility indication which are communicating with the micro base station, changing from a second spectrum component to full spectrum access.
6. The method of claim 4 or 5 wherein the step of determining that the at least one mobile terminal is no longer proximate to the micro base station includes at least one of: the micro base station no longer detecting interference from the at least one mobile terminal with a first mobility indicator; an active terminal having a first mobility indicator handing over from its serving macro-base station to a second macro base station; a mobile terminal with the first mobility indicator no longer identifying an indicator of the micro base station on a Neighbouring Cell List; a mobile terminal with the first mobility indicator no longer measuring, or at least no longer measuring a signal of appropriate strength, from the micro base station; and a macro base station serving a mobile terminal having a first mobility indicator no longer receiving a signal strength measurement, or at least no longer receiving a measurement of an appropriate strength, from the micro base station.
7. The method of any one preceding claim wherein the mobility indication is provided to each mobile terminal based upon a measurement relating to its speed such that the first mobility indication is a high mobility indication and the second mobility indication is a low mobility indication.
8. The method of claim 7 wherein the measurement relating to speed is determined using at least one of: a measure of the number of cell reselections performed by the mobile terminal; a measure relating to the mobile terminal's transit time between cells; a measure of a Doppler frequency relating to the mobile terminal; and a measure relating to the location of the mobile terminal.
9. The method of any one preceding claim wherein the mobility indication for each mobile terminal is updated after a predetermined interval.
10. The method of any one preceding claim wherein the network resource is at least one frequency channel divided into sub-carriers using Orthogonal Frequency Division Multiple Access (OFDMA).
11. In a telecommunications network including a radio access network comprising at least one macro base station and at least one micro base station, each for wirelessly communicating with one or more mobile terminals over a network resource, a method of controlling distribution of the network resource, the method including: providing each mobile terminal with a mobility indication, being at least a first mobility indication or a second mobility indication; and permitting mobile terminals with the first mobility indication to access macro base statiomis but not micro base stations.
12. The method of claim 11 further including upon determining a network parameter indicating the proximity of at least one active mobile terminal with the first mobility indication to a micro base station, changing the distribution of the network resource amongst mobile terminals in the vicinity of the micro base station.
13. A mobile terminal configured for use in a telecommunications network, including a radio access network comprising at least one macro base station and at least one micro base station, each defining a cell and each being configured to wirelessly communicate with the mobile terminal, wherein the mobile terminal includes: a memory means adapted to store a mobility indication; and a cell reselection means configured to utilise the mobility indication in deciding whether to transfer between cells.
14. The mobile terminal of claim 13 wherein the mobility indication is either a high mobility indication or a low mobility indication and the cell reselection means is further configured to only transfer to a macro base station when the mobility indicator is a high mobility indicator.
15. The mobile terminal of claim 13 or 14 further including a mobility indication determination means configured to determine the mobility indication using information relating to the speed of the terminal.
16. A micro base station configured for use in a telecommunications network, including a radio access network comprising at least one macro base station, the micro base station being configured to serve one or more mobile terminals, such that the one or more mobile terminals wirelessly communicate with the network via the micro base station, and the micro base station further includes: monitoring means configured to monitor at least one network condition and switching means which, upon detenmning that a monitored condition is met, is configured to switch from communicating with the one or more mobile terminals for which it is a serving base station from a given frequency spectrum to a component of the frequency spectrum.
17. The micro base station of claim 16 wherein the component of the frequency spectrum is a component reserved for mobile terminals having a low mobility.
18. The micro base station of claim 16 or 17 wherein the monitoring means is configured to monitor a rate of change of noise in the given frequency spectrum.
19. A macro base station configured for use in a telecommunications network, including a radio access network comprising at least one micro base station, the macro base station being configured to serve one or more mobile terminals with a first mobility indication, such that the one or more mobile terminals wirelessly communicate with the network via the macro base station, and the macro base station further includes: monitoring means configured to monitor at least one network condition; and switching means which, upon determining that a monitored condition is met, is configured to switch from communicating with the one or more mobile terminals for which it is a serving base station from a given frequency spectrum to a component of the frequency spectrum.
20. The macro base station of claim 19 wherein the monitored condition is the proximity of a mobile terminal for which it is a serving base station to a neighbouring micro base station.
2 1. The macro base station of claim 19 or 20 wherein the monitoring means is configured to determine that the mobile terminal is proximate a micro base station by at least one of the following: receiving a signal strength measurement from the mobile terminal which relates to the micro base station; and receiving a handover request from the mobile terminal having a high mobility indication to a micro base station.
22. A method substantially as herein described with reference to the accompanying drawings.
23. A telecommunication system substantially as herein described with reference to the accompanying drawings.
24. A micro base station substantially as herein described with reference to the accompanying drawings.
25. A macro base station substantially as herein described with reference to s the accompanying drawings.