GB2492796A

GB2492796A - Communication apparatus allowing a secondary user the use of a communication capability until a primary user appearance is predicted

Info

Publication number: GB2492796A
Application number: GB201111938A
Authority: GB
Inventors: Christophe Rosik
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2011-07-12
Filing date: 2011-07-12
Publication date: 2013-01-16
Also published as: GB201111938D0

Abstract

A communication apparatus (3) can communicate with user apparatus (5) via a first communication capability, such as a first spectrum band, provided by a communication network and also as a secondary user (an opportunistic user) via a second communication capability allocated to a primary user (1). The communication apparatus (3) predicts the appearance of the primary user on the second communication capability and defines predictive eviction decisions for evicting user apparatus from the second communication capability using the prediction data to enable control of communication resources. The communication apparatus may be a base station (3) communicating with user equipment (5) in a cellular communication network.

Description

Communication System The present invention relates to communication apparatus and methods and to communication systems using such apparatus and methods.

Traditionally different communication systems are allocated, generally by licence, exclusive access to respective distinct spectrum bands (where a spectrum band is a range of frequencies) of the electromagnetic spectrum so as to avoid the danger of harmful interference between communication systems. This means that an allocated spectrum band is not used when and where the licensed communication system is not active ("present") in that spectrum band. As an example, spectrum bands allocated to a television broadcast communication system may be underused if the TV channels allocated to that spectrum band are not broadcasting 24 hours a day every day of the week.

In order to make use of such unused bandwidth (that is the parts of the spectrum where the licensees are not active for a given time), the idea of opportunistic access has been suggested.

This idea involves two different kinds of users: licensed users (or primary users) and secondary users (or opportunistic users). An example of such an opportunistic user system is cognitive radio in which either a network or a wireless nodes changes its transmission and reception parameters to take advantage of an unused spectrum band.

In opportunistic access, secondary users are allowed to use the licensed spectrum band in the absence of the primary user on the condition that they take protection measures to ensure that they do not harm the operations of the primary user.

A problem with this opportunistic access is to provide a way of enabling a secondary user to be evicted from the licensed spectrum band when the primary user appears, that is when the primary user starts using their licensed spectrum band, but which also enables the ongoing connections of the secondary user to be maintained with equivalent quality of service or with limited degradation of equivalent quality of service.

Embodiments of the present invention aim to provide a system that predicts appearances or apparitions of a primary user, that is which predicts usage of the licensed spectrum band by the primary user, and which enables a secondary user eviction procedure to be adapted to or based on the predicted appearances or apparitions of the primary user.

A communication apparatus is described for communicating with user apparatus via a first communication capability provided by a communication network, the communication apparatus also being capable of communicating with said user apparatus as an opportunistic, secondary user via the spectrum band provided by a second communication capability allocated to a primary user, the communication apparatus comprising: prediction means for predicting appearance of the primary user on the second communication capability and for providing prediction data; and resource control means for controlling available communication resources using the prediction data provided by the prediction means.

In an embodiment, a communication apparatus can communicate with user apparatus via a first spectrum band provided by a communication network and as a secondary user via a second spectrum band allocated to a primary user. The communication apparatus predicts the appearance of the primary user on the second spectrum band and controls available communication resources using the prediction data.

In an embodiment, a communication apparatus can communicate with user apparatus via a first spectrum band provided by a communication network and as a secondary user via a second spectrum band allocated to a primary user. The communication apparatus predicts the appearance of the primary user on the second spectrum band and defines predictive eviction decisions for evicting user apparatus from the second spectrum band using the prediction data.

Exemplary embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 comprises Figures la and lb which show diagrammatic representations of part of a cellular communication system, before and after a primary user appears; Figure 2 shows a block diagram illustrating components of a base station of a cellular communication network having opportunistic user capabilities; Figure 3 shows a block diagram illustrating components of a user equipment (UE) having opportunistic user capabilities; and Figure 4 shows a flow chart illustrating operations carried out by a base station having opportunistic user capabilities to predict appearances of a primary user and to determine a secondary user eviction procedure to be adapted to or based on the predicted appearances of the primary user.

Overview Figures la and lb show diagrammatic representations of part of a cellular communication network that has a number of base stations 3 associated with a plurality of user equipments (UE5) 5. Base stations, user equipments and other communication devices of a telecommunication network may also be referred to as nodes of the communication network.

This communication network or least one or more of its base stations 3 is shown in Figure la as occupying, as a secondary user, a spectrum band, BO, owned or licensed to a primary user, system or incumbent 1 (shown in Figure ib). In Figure la, the communication network is using the spectrum band BO to transmit and receive data because the owner of the band, the incumbent 1, was previously detected as absent from (that is not communicating in) the spectrum band BO whereas in Figurelb this is no longer possible because the incumbent 1 has appeared. As examples, a cellular network may operate as a secondary system (SS) or secondary user in an area such as a stadium, concert hall, conference centre, broadcast studio, etc. where a primary system (PS) frequently appears.

In the example shown in Figures la and ib, there are three base stations, eNB1, eNB2 and eNB3 variously associated with UEs. As shown in Figures la and ib, UE1 and UE2 are in the cell of base station eNB2 at the intersection of the cells of base stations eNB1 and eNB2, UE3 and UE4 are in the cell of base station eNB3 at the intersection at the intersection of the cells of base stations eNB1 and eNB3 and UE6 is about to enter the cell of eNB1. Thus, all of the UEs shown are just inside or just outside base station cells. It will be appreciated that this is just an example and that there may be an alternative or different arrangements of base stations and UEs.

The secondary user is allowed to occupy the primary user's spectrum band BO provided that it is able to stop using spectrum band BO immediately in the event the primary user decides to use the spectrum band BO. When the primary user "appears", that is is detected to be using its spectrum band, then the secondary or opportunistic system has to take protection measures to ensure it does not detrimentally affect the operations of the primary user and this may mean stopping using the spectrum band BO, unless the secondary or opportunistic system can guarantee that there will be no interference with the operation of the primary user.

In an attempt to ensure continuity of service when they have to stop using the spectrum band BO, secondary users can identify backup channels in the band used by the primary system so that they can transfer to the backup channel to ensure continuity of service when the spectrum band BO is no longer available. However, in the event a backup channel activation procedure fails or the available backup channel capacity is insufficient, then UEs located at the edge of a cell of a base station may have to be handed off to a neighbouring cell or cells so as, for example, to release radio resources in the cell to other UEs to limit QoS (Quality of Service) degradation, to reduce the load in the impacted cell so as to control the Connection Dropping Rate (CDR). This may also be necessary to facilitate service continuity if, for example, the cell coverage for the secondary opportunistic system band is reduced due to transmission power limitations or failure.

An eviction control mechanism is used by a base station 3 to decide upon the most appropriate solution to maintain, or at least not reduce severely, the QoS of ongoing connections already established using the opportunistic system, when the primary user appears or the opportunistic spectrum band is for some reason no longer available, for example due to transmission power limitations or failure. This mechanism uses admission control (AC) to try to avoid network congestion while also preserving the QoS of already accepted connections. This admission control may restrict the number of ongoing connections in the system or degrade some UEs QoS to satisfy a majority of ongoing UE's requirements. Admission control takes into account factors such as the Connection Dropping Rate and Connection Blocking Rates, both of which usually have a maximum defined in the network operators policy for network management.

An access control scheme, known as a guard band scheme, which holds some of the network resources available to a base station in reserve for in-bound handoff connections whilst retaining the rest of the resources is used to keep CDR and CBR below the network operators permitted maximum values, with the in-bound handoff reserve threshold or the ratio of resources reserved for in-bound handoff to the resources reserved for new calls being set dynamically as discussed below.

As will be described below, the present system provides a way of predicting the appearance(s) of a primary user and so of predicting the likely resulting increase in handover requests so that the size of the reserved radio resources pool of a base station can be adapted to this predicted increase in handover requests so as, if at all possible, to reduce the number of requests that cannot be served and to avoid increase in CDR. For example, in the case depicted by Figures la and ib, the present system would aim to predict resources that will be pre-empted by the primary user so that the eNBI can accept spectrum mobility handoff requests (that is handoff requests from another base station onto a different frequency channel) for UE1, UE2, UE3 and UE4 and can also support a physical mobility handover of UE6 to eNB1 as it enters the area covered by eNB1 to avoid a connection termination when UE6 goes outside the range of its current base station (not shown in Figures Ia and Ib).

In the example to be described below, a base station: 1-Predicts the primary user's appearance(s) in the spectrum band BO.

2-Determines the area of the cell where the primary user may appear and the UEs that may be impacted by its appearance.

3-Defines predicted eviction decisions taking into account the number of identified backup channel(s) in the area covered by the cell under consideration and the characteristics of the predicted primary user(s).

4-Determines the spectrum mobility handoff requests that would result from the eviction decisions.

5-Considers the expected additional handoff requests in the calculation of an admission control guard band in order to anticipate the impact on spectrum mobility upon the primary user's appearance in the spectrum band BO.

In this example, a base station thus makes predictive eviction decisions in order to estimate the impact of forced handoff in the event of the primary user's appearance in the spectrum band BO.

This estimate is then used to inform the in-bound handoff reserve threshold or ratio (guard band) of an adjacent base station.

In an example, the areas of a base station cell where a primary user may appear are predicted on the basis of historical data indicating when the primary user has appeared in the cell coverage area, including data such as the time of appearance, the pre-empted bandwidth, the geographical coverage. This historical data is then searched to check for patterns in the appearances of the primary user, for example to determine any periodicity in those appearances. The possible impact of these appearances for the base station cell and the UEs connected to the base station is then assessed and a decision made as to the eviction measures that should be taken to protect the primary user(s) while preserving the best optimized QoS for the connected UEs. Once the eviction measures have been determined, the handover rate to each adjacent cell is determined by considering the spectrum mobility requirements resulting from those eviction measures, and the guard band of the admission control for the appropriate adjacent base station(s) is(are) adjusted, if necessary or desirable, to minimize or at least reduce the CDR when the primary user appears in the spectrum band BO.

Example

Base Station Figure 2 shows a block diagram illustrating components of a base station 3 shown in Figure 1. As shown, the base station 3 includes transceiver circuitry 223 to transmit signals to and to receive signals via one or more antennas 225. A controller 227 is provided to control the operation of the base station in accordance with software stored in memory 237. The controller 227 is also able to communicate with other communication devices via a network interface 229. The software stored in memory 237 includes, among other things, an operating system 239, a communication module 241, a positioning module 242, a primary user status module 243, a secondary user control module 247, an impact determining module 249, a prediction module 251, a handover rate module 253 and an admission control module 255.

The operating system 239 is arranged to control operation of the base station 3. The communication module 241 provides the functionality to allow the base station to communicate with the UEs 5 via the transceiver circuitry 223 and the antenna 225 and to communicate with other network devices and nodes via the network interface 229 (which may be a copper or optical fibre interface or other suitable interface). The positioning module 242 allows the base station 3 to determine the location of the different UEs 5 -either from measurement data received from the UEs 5 or from signals transmitted to or received from the LiEs 5 by a plurality of network nodes (such as the base station 3). The primary user status module 243 operates to determine the status and characteristics of the primary user, that is its location and whether it is currently active in (that is appearing in) its spectrum band BO. The primary user may or may not have a fixed location. If the location of the primary user is fixed, then the location information may already be available to the primary user status module 243. The prediction module 251 operates to predict the future activity of the primary user in its spectrum band BO. The impact determining module 249 operates to determine the impact on the base station cell and the LiEs associated with the cell of the predicted future activity of the primary user in its spectrum band BO. The handover rate determining module 253 operates to determine a handover rate using the determined impact whilst the admission control module 255 operates to enable adjustment of the guard band of adjacent cells to which UEs may be handed off in the event of the predicted appearance of the primary user 1. The secondary user control module 247 operates to allocate subbands of the spectrum band BO to LiEs 5 and to inform the secondary users of these allocations.

UE

Figure 3 is a block diagram illustrating components of a UE 5, shown in Figure 1. As shown, the LiE includes transceiver circuitry 323 to transmit signals to and to receive signals from other nodes (e.g. a base station 3) of the communication system via one or more antennas 325. A controller 327 is provided to control operation of the UE in accordance with software stored in memory 337.

The UE 5 also includes a user interface 329 that is controlled by the controller 327 and which allows a user to interact with the UE 5. The software stored in memory 337 includes an operating system 339, a communication module 341, a positioning module 343, a sensor module 345, a reporting module 347, a transmission frequency control module 349 and a handover module 351.

The operating system 339 controls the operation of the UE 5. The communication module 341 controls communication between the UE 5 and external devices via the transceiver circuitry 323 and the antenna 325. The positioning module 343 operates to determine location information for the UE. It may be a GPS or similar satellite or terrestrial location determining module. The positioning module 343 sends regular position updates to the base station 3 either on demand or at predetermined time intervals. The sensor module 345 operates to sense for transmissions made by primary users. The sensor module will normally be able to sense for primary user transmissions within the entire licensed band BO (and perhaps in other frequency bands as well). However, the sensor module 345 may receive a sub-band assignment from the base station 3, which specifies a particular sub-band in which it is to sense for primary user transmissions. The results from the sensing module 345 are then transmitted back to the base station 3 by the reporting module 347.

The transmission frequency control module 349 operates to receive the information transmitted from the base station 3 identifying if there are any sub-bands within the licensed band SO in which the UE can transmit opportunistic signals without interfering with a primary user and to control the transmission frequency used by the transceiver circuitry 323 for such opportunistic transmissions accordingly. Although in this example the sensing is carried out by the UEs, sensing may additionally or alternatively be carried out by the base stations or other nodes of the communication network. The handover module 351 operates to receive and action handover instructions.

In the above description, the base station and UE have been described, for ease of understanding, as having a number of discrete modules. Whilst these modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the invention, in other applications, for example in systems designed with the inventive features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities. Also, even where discrete modules are ascertainable, functionality may be split differently than as shown so that, for example, a single module may carry out the operations carried out by one or more of the modules shown in Figure 2 or 3 or the operations carried out by a module shown in Figure 2 or 3 may be carried by two or more modules or the tasks may be differently distributed between modules.

Operation Figure 4 is flow chart illustrating the overall operation of a base station 3 in an embodiment. For ease of understanding, the flowchart is split into three tasks, tasks 1, 2 and 3. Task I concerns acquisition of data regarding activity of the primary user, task 2 concerns identification of patterns in recorded activity of the primary user to predict future activity and task 3 concerns determination of resultant action to optimise or at least improve resources in the event the predicted activity occurs. Task 1 would be undertaken by the primary user status module of Figure 2, task 2 by the prediction module of Figure 2 and task 3 by the impact determining module 249, the handover rate module 253 and the admission control module 255 of Figure 2. although there are other possibilities as discussed above. Handover rate and admission control are in this example carried out in parallel, in a periodic way, using latest available information.

Task I may be carried out at set times, possibly periodically, or the base station may be continuously sensing at SO for activity ("apparition") of the primary user in the spectrum band BO.

As mentioned above, this sensing may be direct sensing by the base station or may be as the result of reports forwarded to the base station from UEs. In task 1, the base station may also, at SOa, access an available common database or databases providing information relevant to the presence of the primary user. As an example, where the primary user is a TV broadcaster, then the base station may access a "regulatory" database with which the TV broadcaster is required to register in order to operate. As other examples, the common database may be a database shared by several communications operators or service providers that is used to share information about a detected incumbent, or available spectrum.

When activity ("apparition") of the primary user 1 is detected at Si, then at 52 the characteristics of the primary user are stored in a PS (Primary System) historic database DB. The characteristics stored will generally be the time at which activity is detected (the time at which activity ceases may also be recorded), the location within the cell of the primary user (if this is not fixed and so pre-stored in the database DB), its transmission power, its operating frequency and its bandwidth.

Generally, any set of characteristics that enables a determination to be made as to whether or not an opportunistic user would interfere with operation of the primary user when the primary user appears may be used. The location of the primary user may be determined from data received from sensor modules of UEs and/or from the base station and other base stations sensing for the primary user. The location may be approximate, namely the vicinity of a UE sensing a primary user, if only one UF that has detected the primary user, but a more accurate location will be possible, by triangulation or other known techniques, if several UEs detect the same primary user.

In this example, task 2 is carried out on a periodic basis as determined by a timer Ti. When the timer time has expired at S3a (that is time ttI), then at S3 the database DB is interrogated and at S4 the interrogated data is searched for patterns, in this example periodicity, by, for example, determining the time interval between apparitions, that is activity in the spectrum band BO. The time period t1 may be any appropriate time period, for example the database DB may be interrogated on an hourly basis. If at 85 a searched for pattern, for example a periodicity, is detected, the database is tagged at S6 with that periodicity, that is the times at which future occurrences of activity can be expected, so that the primary user that appears can easily be found.

If the primary user is not detected again within the determined periodicity, then the tag may be removed.

If the answer at 85 is no or the database has been tagged at 86, then the timer Ti is reset at 87 and task 2 restarts when ti has again expired at S3a. The database may be capable of storing one or more patterns so that different primary users that appear with different periodicities can be considered.

Task 3 is initialised upon initialisation of the overall operation and is executed each time a time period T2 expires. As shown in Figure 4, the database is checked on a periodic basis (when a timer T2 reaches a time t2) for an upcoming expected appearance of the primary user. The answer at 89 maybe yes when there is an appearance of the primary user in the spectrum band B expected within a few seconds. When the answer at 59 is yes, there is an upcoming appearance of the primary user in the spectrum band BO, then at SlO, the possible impact on the cell and UEs in the cell is determined. For example, the determination may be how many UEs in the cell are using the spectrum band BO of the primary user 1 and how many of those are on the edge of the cell and could conceivably be handed off to the base station of an adjacent cell. This information together with the radio resources available to the cell, the CDR and CBR set by the network operator and any channels reserved by any of the UEs currently operating in the spectrum band BO are used to determine how many of those UEs can be allocated resources available to the base station and how many of those on the edge of the cell may need to be handed off to an adjacent cell. In making this determination, account may also be taken of UEs such as UE6 in Figure 1 that may about to be handed over to the base station and may require radio resources. At 812, the information determined at 81 i is used to determine a handover rate for each adjacent cell and at 814 the guard band of the admission control for each adjacent cell is updated and passed to the base station of that cell. In the event a UE is under the coverage of more than one, say three, cells, the target cell for forced handover will be chosen based on the power levels of the candidate cells as measured by the UE so that the cell providing the highest power level will generally be chosen.

If the handover fails, the cell providing the second highest power level will generally be chosen.

The timer T2 is reset at Si 5 after step 514 or at 516 if the answer at S9 is no. Then when the timer T2 expires, that is reaches t2 again, at 517, the actual time is determined at 818 and task 3 starts again at SB. The actual time is used as reference when searching in the database for an upcoming appearance of a primary user (incumbent). Thus, as an example, if it is 8 o'clock, only a primary user that may appear in the current hour will be considered. Primary users that have or would have appeared at 7 o'clock are not considered.

Advantages The embodiments described above offer a number of advantages some of which are set out below.

Embodiments enable a secondary user eviction procedure to be adapted to or based on the predicted appearances or apparitions of the primary user. Predicting when a primary user may become active or appear should enable better dynamic admission control allowing a more accurate determination as to the radio resources required of adjacent base stations for handoff when the primary user appears. This in turn should avoid or reduce the possibility of connections commenced using resources pre-empted by the primary user being dropped.

Embodiments contribute to reducing the connection blocking rate. Thus, when the incumbent appears (so pre-empting the radio resources of a cell so that the cell has fewer resources to handle new connections), the possibility of performing handover of some connections to neighbouring cells or to the licensed band may offload the resources from the opportunistic band and so, will contribute to reducing the connection blocking rate.

Modifications and Alternatives Detailed embodiments have been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein. By way of illustration only a number of these alternatives and modifications will now be described.

In embodiments described above, a periodicity in the appearance of the primary user in the spectrum band BO is predicted. If the use of the spectrum band BO may be divided into sub-bands which may not interfere, so that, for example, the primary user could be operating on one subband or frequency and a secondary user still operating on another subband or frequency, then the prediction may be of the appearance of the primary user on the subband or frequency used by the second user or secondary users. Different periodicities may be searched for for different subbands or frequencies. Other patterns could be searched for, for example time intervals that are not periodic but have a recognisable pattern from which future activity can be predicted may be searched for. Also, changes in the pattern with time may be recorded, which may assist prediction if, for example, there is both a higher frequency and a lower frequency periodicity or pattern to the activity of the primary user in the spectrum band BO ora subband or frequency In embodiments, the licensed spectrum band BO may correspond to a TV channel but it also may correspond to any other channel that has another frequency bandwidth where opportunistic use of radio resources is accepted. In an example, the licensed spectrum band SO may correspond to a DVB-T channel of 6MHz or 8MHz bandwidth. As those skilled in the art will appreciate, there are other potential DVB-T configurations, and the standardization includes a 5MHz and 7MHz channel option. Also, there may be other options for primary users and the second user may be other than a cellular communication network.

The invention may be implemented by any cellular communication network. Where the invention is implemented in an LIE system, the base station will typically be formed by an LTE base station.

Multiple base stations are provided in an LIE system and they may each operate as masters controlling UEs within their cell(s). The base stations may operate autonomously in a de-centralised manner taking decisions about their respective localities without communicating with a higher network entity. The base stations may also co-operate with each other exchanging information over their "X2" interface and taking decisions based on information received from neighbouring base stations.

The UE5 described above may comprise any kind of communication node or device, including access points and user apparatus such as, for example, mobile (cellular) telephones, personal digital assistants, laptop computers, web browsers, etc. As described above, prediction of the appearance of the primary user is carried out by the base stations. Not all of the base stations within access range of the primary user need carry out the prediction. Rather, the prediction may be carried out by a base station or a number of base stations and the information made available to other base stations. In addition, it may be possible for the prediction to be carried out by another node within the network, for example one or more UEs. As another possibility, the prediction may be carried out by a master node in an ad hoc network applying a centralised resource control.

As described above, handover rate and admission control are carried out in parallel, in a periodic way. It may also be possible to carry out handover rate and admission control in sequence rather than in parallel and/or on demand or in accordance with a schedule that is not periodic.

Figures Ia and lb show opportunistic use for downlink or deployment communications. Uplink communications may alternatively or additionally make opportunistic use of the secondary communications capability.

In the above embodiments, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the cognitive node as a signal over a computer network, or on a recording medium. Further, the functionality performed by part or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the node in order to update its functionality. Similarly, although the above embodiments employed transceiver circuitry, at least some of the functionality of the transceiver circuitry can be performed by software.

Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

Claims

<claim-text>Claims 1. A communication apparatus for communicating with user apparatus via a first communication capability provided by a communication network, the communication apparatus also being capable of communicating with said user apparatus as a secondary user of a second communication capability allocated to a primary user, the communication apparatus comprising: prediction means for predicting appearance of the primary user on the second communication capability and for providing prediction data; and defining means for defining predictive eviction decisions for evicting user apparatus from the second communication capability using the prediction data to enable resource control means to control communication resources using the prediction data.</claim-text> <claim-text>2. A communication apparatus according to claim 1, further comprising: detection means for detecting appearance of the primary user on the second communication capability to provide detection data to enable the prediction means to provide the prediction data.</claim-text> <claim-text>3. A communication apparatus according to claim 2, wherein the detection means is arranged to detect a pattern in the appearance of the primary user on the second communication capability.</claim-text> <claim-text>4. A communication apparatus according to claim 2, wherein the detection means is arranged to detect a periodicity in the appearance of the primary user on the second communication capability.</claim-text> <claim-text>5. A communication apparatus according to any of claims, wherein the resource control means is configured to control communication resources available via the first communication capability for allowing transfer of a user apparatus that may be affected by an appearance of the primary user predicted by the prediction data to control by another communication apparatus of the communication network using the prediction data provided by the prediction means 6. A communication apparatus according to any of claims I to 4, wherein the resource control means is configured to control communication resources available via the first communication capability for allowing transfer of a user apparatus that may be affected by an appearance of the primary user predicted by the prediction data to another communication apparatus of the communication network using the prediction data provided by the prediction means and data indicating a number of back up communication channels available to the communication apparatus.7. A communication apparatus according to any of claims 1 to 4, wherein the communications network comprises a plurality of communication apparatus each having a communication range in which they have responsibility for communication with user apparatus within that communication range, wherein the communication apparatus comprises impact determining means for determining the user apparatus within its communications range that may be affected by an appearance of the primary user predicted by the prediction data.8. A communication apparatus according to claim 7, further comprising handover rate determining means for determining an additional number of handovers of user apparatus to another communications apparatus of the communication network that may be required using the impact determined by the impact determining means.9. A communication apparatus according to claim 8, further comprising admission control means for providing reserve data to control a number of communication channels said other communication apparatus reserves for transfer of user apparatus into its control using the determined additional number of handovers.10. A communication apparatus according to claim 9, wherein the admission control means is configured to communicate the reserve data to said other communication apparatus.11. A communication apparatus according to claim 9 or 10, wherein the reserve data determines the proportion of communication channels available to said other communication apparatus that said other communication apparatus reserves for transfer of user apparatus into its communication range rather than for new communications from other user apparatus.12. A communication apparatus according to any of claims 7 to 11, wherein the communications network comprises a cellular communications network and each said communication range represents a cell of the cellular communications network, wherein the impact determining means is arranged to determine the impact on any user apparatus at an edge of its cell.13. A communication apparatus according to claim 1, wherein the communications network comprises a cellular communications network having a plurality of communication apparatus each providing a cell of the communications network and further comprises: impact determining means for determining the user apparatus at an edge of its cell that may be impacted by the appearance of the primary user on the second communication capability; handoff request determining means for determining an expected number of additional handoff requests to a neighbouring cell that would result from the eviction decisions; and calculation means for calculating an adjustment to the proportion of communication channels the communications apparatus of a neighbouring cell reserves for transfer of user apparatus into its cell using the expected additional handoff requests.14. A communication apparatus according to any of claims 7 to 13, wherein the impact determining means is arranged to determine that a user apparatus is impacted if its use of the second communication capability would interfere with use by the primary user.15. A communication apparatus according to any preceding claim, wherein the first and second communication capability are spectrum bands.16. A communication apparatus according to any preceding claim, wherein the primary user is a television communication system.17. A system comprising a plurality of communication apparatus for communicating with user apparatus via the communication network, wherein at least one of the communication apparatus is according to any of claims ito 16.18. A system comprising a plurality of communication apparatus according to any of claims I to 16.19. A user apparatus for use in the system of claim 17 or 18, wherein the user apparatus is capable of communicating with a said communication apparatus as a secondary user of the second communication capability allocated to the primary user, the user apparatus comprising: sense means for sensing the appearance of the primary user on the second communication capability; report means for reporting sensing of the primary user to the communication apparatus; transmission control means for controlling whether transmission by the user apparatus is via the first communication or second capability; handover means for facilitating handover to another communication apparatus in response to a predicted appearance of the primary user on the second communication capability.20. A method performed by a communication apparatus for communicating with user apparatus via a first communication capability provided by a communication network and as a secondary user via a second communication capability allocated to a primary user, the method comprising: predicting appearance of the primary user on the second communication capability to provide prediction data; and defining predictive eviction decisions for evicting user apparatus from the second communication capability using the prediction data to enable control of communication resources using the prediction data.21. A communication apparatus configured to communicate with user apparatus via a first communication capability provided by a communication network and as a secondary user via a second communication capability allocated to a primary user, the communication apparatus comprising a processor configured by program instructions to: predict appearance of the primary user on the second communication capability and to provide prediction data; and define predictive eviction decisions for evicting user apparatus from the second communication capability using the prediction data to enable control of communication resources using the prediction data.22. A user apparatus for use in the system of claim 17 or 18, wherein the user apparatus is configured to communicate with a said communication apparatus via the communication network and as a secondary user via the second communication capability allocated to the primary user, the user apparatus comprising a processor configured by program instructions to: sense the appearance of the primary user on the second communication capability; report sensing of the primary user to the communication apparatus; control whether transmission by the user apparatus is via the first communication or second capability; facilitate handover to another communication apparatus in response to a predicted appearance of the primary user on the second communication capability.23. A computer program product comprising computer implementable instructions for causing a programmable communication node to become configured as the communication apparatus of any of claims 1 to 16 or 21 or the user apparatus of claim 19 or 22 or to carry out the method of claim 20.24. A tangible computer storage medium storing computer implementable instructions for causing a programmable communication node to become configured as the communication apparatus of any of claims 1 to 16 or 21 or the user apparatus of claim 19 or 22 or to carry out the method of claim 20.</claim-text>