WO2013075314A1

WO2013075314A1 - Methods and apparatus for component carrier selection

Info

Publication number: WO2013075314A1
Application number: PCT/CN2011/082860
Authority: WO
Inventors: Pengfei Sun; Na WEI; Wei Bai; Erlin Zeng; Haiming Wang; Wei Hong
Original assignee: Renesas Mobile Corporation
Priority date: 2011-11-24
Filing date: 2011-11-24
Publication date: 2013-05-30

Abstract

Systems and apparatus for physical uplink control channel (PUCCH) relocation. A base station provides information to one or more user devices to allow for the selection of a new component carrier for a PUCCH when a current PUCCH becomes unavailable. The information may comprise an explicit selection of a component carrier or a direction to use previously stored selection information. A user device may be informed of the unavailability of a component carrier through explicit signaling from a base station or from stored information, such as an on-off pattern of component carriers.

Description

METHODS AND APPARATUS FOR

COMPONENT CARRIER SELECTION

TECHNICAL FIELD:

[0001] The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs, and more specifically relate to mechanisms for managing the use of unlicensed frequency bands for wireless network communication.

BACKGROUND:

[0002] The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

DL downlink

eNodeB/eNB evolved Node B

HA Q hybrid automatic repeat request

LTE long term evolution

PDCCH physical downlink control channel

PDSCH physical downlink shared channel

PUCCH physical uplink control channel

PUSCH physical uplink shared channel

RPvC radio resource control

TVWS television white space

UE user equipment

UL uplink

[0001] Interest in wireless communication, particularly personal wireless communication, has increased more and more during the last few decades, and user demand for the ability to transmit and receive information wirelessly has proven insatiable. More and more users wish to spend more and more of their time communicating with one another, sharing data with others, and receiving data made available to the public at large or to large groups of users, so that serving the simultaneous activities of these users while providing an acceptable quality of service to each user has proven more and more challenging. Manufacturers and operators of wireless communication systems such as cellular networks have gone to great lengths to increase the data that can be carried in the portion of the radiofrequency spectrum allocated to them. Continued advances in the efficient use of the radiofrequency spectrum to carry data have led from the first wireless transmissions in the 1800's to the ubiquitous presence of wireless data communication in every aspect of everyday life.

SUMMARY:

[0003] The foregoing and other problems are overcome, and other advantages are realized, by the use of exemplary embodiments of this invention.

[0004] In one embodiment of the invention, an apparatus comprises at least one processor and at least one memory storing a program of instructions. The program of instructions is configured, with the at least one memory and the at least one processor to cause the apparatus to perform actions comprising at least delivering information to a device indicating a component carrier to be selected by the device for use as a physical uplink control channel when a component carrier being used by the device for a physical uplink control channel becomes unavailable.

[0005] In another embodiment of the invention, a method comprises wirelessly transmitting information to a device indicating a component carrier to be selected by the device for use as a physical uplink control channel when a component carrier being used by the device for a physical uplink control channel becomes unavailable. [0006] In another embodiment of the invention, a non-transitory computer readable storage medium stores a program of instructions, execution of which by a processor configures an apparatus to perform actions comprising at least delivering information to a device indicating a component carrier to be selected by the device for use as a physical uplink control channel when a component carrier being used by the device for a physical uplink control channel becomes unavailable.

[0007] These and other embodiments and aspects are detailed below with particularity.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0008] Figure 1 illustrates a cell of a wireless network in which embodiments of the present invention may be implemented;

[0009] Fig. 2 illustrates details of a base station according to an embodiment of the present invention;

[0010] Fig. 3 illustrates details of a user device according to an embodiment of the present invention;

[0011] Fig. 4 illustrates a sequence of operations according to an embodiment of the present invention; and

[0012] Fig. 5 illustrates a process according to an embodiment of the present invention.

DETAILED DESCRIPTION:

[0013] Systems and techniques according to various embodiments of the present invention recognize that the radiofrequency spectrum specifically allocated for use by cellular communication systems is limited, and that the need to operate within a limited spectrum imposes significant constraints on the communication capacity of any system. As the number of users increases, and as the demands of users increase, the load on a system increases, and the difficulty of accommodating simultaneous users concurrently increases. System capacity can be increased by the deployment of new communications infrastructure, but such deployment is costly and in addition can only meet communication needs up to a certain point. If the radiofrequency spectrum available to users of a network is being used at full capacity by users within a geographic area, the addition of new infrastructure such as new base stations will not increase the capacity of the network within that area because the limitation is imposed not by the available infrastructure, but by the capacity of the available radiofrequency spectrum to carry data. Operators of wireless networks and manufacturers of wireless devices and wireless network infrastructure are therefore seeking ways to increase the radiofrequency spectrum available for use by wireless networks. Various approaches to the problem of increasing the available spectrum introduce problems such as unreliability of various channels, so that mechanisms need to be found that allow these problems to be tolerated or overcome.

[0014] Various embodiments of the invention recognize the availability of significant frequency resources that may be used to carry control information. One significant resource is found in television white space (TVWS) bands. The use of TVWS bands carries numerous advantages. One of the advantages is a low cost. No license is required for the use of TVWS bands, and expanded frequency ranges gained through the use of these bands comes at a much lower cost than equivalent gains achieved through expansion of licensed bands such as LTE frequencies. Deployment can be flexible and new installations can be deployed as required, with less care being needed for integration of new installations with existing deployments than is necessary for equivalent installations using only LTE frequencies. TV band devices may therefore be used with applications for which constraints associated with costs or with difficulty of deployment might inhibit the use of conventional LTE devices. Use of TVWS frequencies in LTE networks provides the potential for significant increases in available bandwidth, but introduces problems associated with unreliability of carriers as those carriers become unavailable due to factors such as the needs of other users or regulatory changes.

[0002] The use of TVWS frequencies may be thought of as falling into two categories: standalone utilization, in which an entire cellular system, such as an LTE system, uses only TVWS frequencies, and hybrid utilization, in which both licensed and unlicensed bands are used for LTE communications, with a system using strategies that use appropriate bands as needed.

[0003] Embodiments of the invention recognize that the use of unlicensed bands presents a number of challenges that are not encountered in the use of only licensed LTE bands. Unlicensed bands are shared in an open access manner, so that it is not possible for any particular system to occupy an unlicensed band at all times. In addition, numerous sources of interference can be expected, as other systems begin and stop using various frequencies in the band. In addition, the availability of frequencies in unlicensed bands may change over time, as various countries introduce new regulations relating to shared band operation such as TVWS bands.

[0004] One important aspect of wireless communication is a physical uplink control channel, or PUCCH. PUCCH carries scheduling requests and HA Q feedback, as well as channel quality information. In LTE installations that use only LTE licensed bands, the PUCCH is associated with the uplink primary serving cell (PCell), which is configured by a higher layer. In systems using licensed LTE bands, PUCCH is highly reliable and can be expected to be available except under unusual circumstances. Such availability of the PUCCH is important for a number of aspects of operation, such as HA Q, which is time critical. In frequency division duplex (FDD) mode, for example, a user device or user equipment (UE) must send back acknowledgement bits to a base station, such as an eNodeB (eNB) 4 subframes after detection of a physical downlink shared channel (PDSCH).

[0005] When unlicensed bands are used in operation of an LTE system, such a

PUCCH design may be unworkable. For example, a primary component carrier (PCC) of an uplink Pcell may break down frequently or may be moved due to strong interference or to a regulatory change. UEs using such a disappearing channel may encounter periods in which they are unable to transmit control channel information. Such failures cause significant uplink performance limitations, particularly in the transmission of time critical acknowledgement bits. Therefore, PUCCH relocation must be accomplished quickly and reliably in response to a breakdown of an uplink Pcell, so that the uplink control procedure can be recovered.

[0006] If unlicensed bands are used for the PUCCH, the continued availability of the PUCCH cannot be assured. In operation, transmission in an unlicensed band can be expected to be turned on and off over time in unpredictable intervals as other systems share the frequencies. In addition, a frequency may be rendered wholly unavailable, or made newly available, due to interference or regulatory changes.

[0007] Embodiments of the invention also recognize that techniques that are sufficient for relocation of a PUCCH for a single UE, such as a handover procedure, are inadequate to meet the situation encountered when a Pcell breaks down. In such a case, large numbers of UEs are suddenly left without a PUCCH, and need a rapid relocation. Such a rapid relocation for large numbers of UEs cannot be achieved through handover, which was designed to deal with the needs of a transition between cells of a single UE.

[0008] Fig. 1 illustrates a cellular network 100 according to an embodiment of the present invention. The network 100 comprises a cell 102, served by a base station, with the base station implemented here as eNB 106. The network 100 serves a plurality of UEs 110A,. . .,110G, distributed through the cell 102. In one embodiment of the invention, the eNB 106 and the UEs 11 OA,. . .,110G may be configured to operate exclusively using unlicensed frequency bands, such as television white space bands. The eNB 106 may suitably be configured so as to be able to employ a plurality of component carriers available in the TVWS bands, with one component carrier being selected at any particular time for use as a PUCCH. Each of the UEs may also be configured to able to use the component carriers that can be used by the eNB 106, and to select as a PUCCH the same component carrier selected by the eNB. In order to provide uninterrupted service when a PUCCH becomes unavailable due to the unavailability of the component carrier being used, both the eNB 106 and the UEs 110A,. . .,110G use mechanisms according to embodiments of the present invention to quickly relocate the PUCCH from the unavailable component carrier to another component carrier. Depending on particular design choices, different UEs may use different component carriers, or groups of UEs or all UEs may use the same component carrier.

[0009] In one embodiment of the invention, each of the UEs within the cell

102, such as the UEs 110A,. . .,110G, is preconfigured with component carrier information, and a priority sequence to be followed to relocate the PUCCH if the PUCCH currently being used becomes unavailable. The priority sequence may suitably be established through signaling by the eNB 106. When relocation of the PUCCH to another component carrier is triggered for the UEs, such as through recognition that the PUCCH being used has been lost, the UEs for which relocation has been triggered follow their assign priority sequence to select a new component carrier to be used for the PUCCH. The priority sequence may be established for a single UE or for a group of UEs, and different priority sequences may be established for UEs using different PUCCHs. It will be recognized, however, that different UEs using the same PUCCH may use different priority sequences and may select different component carriers in response to loss of the PUCCH.

[0010] When relocation is triggered, a UE or group of UEs will find the next available component carrier listed in its assigned sequence, and select the component carrier as its PUCCH. The UE or group of UEs will then use the selected component carrier to transmit PUCCH information after a predefined duration.

[0011] Suitably, the priority sequence may be defined by a higher layer before delivery to the UEs, and may be periodically updated, such as after coordination between the eNB 106 and the UEs in the cell 102. Relocation may suitably be triggered implicitly, such as through recognition by a UE that its PUCCH is no longer available, or explicitly, for example, through an explicit layer 1 downlink signal.

[0012] In another embodiment of the invention, the eNB 106 explicitly triggers a UE or a group of UEs, such as one or more of the UEs 11 OA,. . .,110G, through explicit signaling. The eNB 106 directs the UEs to relocate their PUCCHs from the current component carrier to a specified target component carrier. Relocation may suitably be triggered using a fast layer one signal. The downlink layer 1 signal may suitably include an identification of the target component carrier, such as an index to the target component carrier. [0013] In additional embodiments of the invention, PUCCH resource reservation and selection occurs dynamically. In one embodiment, the PUCCH resources are explicitly assigned to each UE through radio resource control ( C) signaling. In another embodiment, resources for use as a PUCCH may be reserved across all component carriers that are configured for use as uplink component carriers, as opposed to dedicating a single component carrier for use as the PUCCH. In one alternative, a number N of resources are reserved in each component carrier, and in another alternative, a number N of resources are reserved across all component carriers. In each of these embodiments, PUCCH resource selection is defined using information contained in a downlink grant. A downlink grant transmitted by the eNB 106 to a UE suitably includes a resource indicator defining for the UE the resource to be used for the corresponding PUCCH. The indicator may suitably be chosen so that the maximum number of resources indicated is sufficient to accommodate a large number of UEs in a single component carrier while managing overhead.

[0014] In one or more embodiments of the invention, appropriate downlink control information (DCI) formats are used to deliver appropriate component carrier and triggering information. An indicator may include a bit sequence comprising sufficient bits to select an appropriate component carrier index when explicit targeting is used, or to indicate the use of a predefined priority sequence. For example, if a three-bit indicator is used, "000" may direct the use of a predefined priority sequence, while "001 "-"111" may each indicate a particular component carrier. One suitable mechanism for defining the indicator is to merge the indicator bits with the ARI bits in the downlink grant. [0015] Fig. 2 illustrates additional details of the eNB 106. The eNB 106 comprises a transmitter 202, receiver 204, and radiocontroller 206, as well as an antenna 208. The eNB 106 further comprises a processor 210, memory 212, and storage 214, communicating with one another and with the radiocontroller 206 over a bus 216. The eNB 106 employs data 218 and programs 220, suitably residing in storage 214. The data may suitably comprise priority sequence information 222, which may be delivered to UEs for use in selecting an appropriate component carrier. The data may further comprise a component carrier database 224, identifying and indexing available component carriers. The data 218 may additionally comprise an on-off pattern 226 and an availability change record 228. The on-off pattern 226 comprises information relating to predicted patterns of availability and unavailability of component carriers, and the availability change schedule 227 stores information relating to long term changes in the availability of component carriers, such as regulatory changes adding frequencies to or removing frequencies from available unlicensed bands.

[0016] The programs 220 may suitably comprise one or more mechanisms to be used for recognizing the failure of a PUCCH and directing appropriate relocation of the PUCCH. The programs 220 may, for example, comprise an interference monitor 228, a relocation trigger 230 module, and an on-off pattern scheduler 232. The interference monitor 228 directs the monitoring of interference in the environment and causes triggering of relocation of a PUCCH when the interference is such that the component carrier currently being used is effectively unavailable. The relocation trigger 230 may be invoked by the interference monitor 228, for example, or may be invoked when information relating to a change in availability of a component carrier is received from an external source, or at a designated time when a component carrier being used has been scheduled to become unavailable. Similarly, the on-off pattern scheduler 232 may invoke the relocation trigger 230 module in order to perform relocation according to an on-off pattern of the component carriers being used, causing switching between component carriers as one or another becomes unavailable. As an alternative or in addition, the on-off pattern scheduler 232 may create an on-off pattern and transmit this pattern to one or more UEs. UEs such as the UEs 11 OA,. . .,110G may store a pattern and perform automatic PUCCH relocation in the absence of a trigger, based on knowledge of availability and unavailability of component carriers provided by the pattern.

[0017] Suitably, the eNB 106 monitors the channel conditions and the

PUCCH continuously, so that relocation can be performed as soon as conditions change. Suitably, the eNB 106 may employ direct designation of a component carrier as a PUCCH, or may direct one or more UEs to perform relocation according to a predefined priority sequence, which has suitably been previously delivered by the eNB 106 according to the priority sequence information. Suitably, the eNB 106 may specifically designate component carriers for some UEs and may direct others to perform relocation according to a stored priority sequence. The eNB 106 may suitably designate component carriers or direct selection according to priority sequencing in order to insure that selection of component carriers will be managed in such a way that no PUCCH resource conflict occurs and PUCCH allocation is balanced among UEs.

[0018] For example, suppose that to the on-off pattern 226 indicates that an uplink component carrier is scheduled to turn off. The eNB 106 may examine the UEs in the cell 102 to determine whether each UE is aware of its relocation target, for example, through stored priority sequence information. For UEs which can find their relocation target, the eNB may simply direct them to relocate to their stored target. For example, the relocation trigger 230 may send to these UEs an indicator value directing relocation according to stored priority sequence information. For UEs which are unable to find their targets automatically, the eNB sends explicit relocation information, suitably by sending an indicator value designating a component carrier. A similar procedure may be used in cases in which an unscheduled change occurs, such as a change due to interference or a regulatory change that was not previously known. In cases in which sufficient time is not available for the eNB 106 to perform inquiries of UEs to determine if they are aware of their target component carrier, the eNB 106 may make a decision about whether to explicitly designate a carrier or direct use of stored information. For example, the eNB 106 may have previously obtained information as to whether the UEs are aware of their target carriers, and may be aware that this condition is not likely to have changed during the intervening time.

[0019] Fig. 3 illustrates additional details of the UE 11 OA, with the understanding that other UEs may be similarly configured. The UE 11 OA suitably comprises a transmitter 302, receiver 304, and radiocontroller 306, as well as an antenna 308. The UE 110A further comprises a processor 310, memory 312, and storage 314, communicating with one another and with the radiocontroller 306 over a bus 316. The UE 11 OA employs data 318 and programs 320, suitably residing in storage 314. The UE 110A is suitably configured to receive relocation signaling from the eNB 106 and select an appropriate PUCCH resource, such as an available component carrier, in response to the signaling from the UE 11 OA. Signaling may be detected through listening by the UE 11 OA in the common search space shared with other UEs, or in the search space dedicated to the UE or to a group of UEs to which the UE belongs. Relocation may suitably be performed under the control of a PUCCH relocation module 322, residing in storage 314 as part of the programs 320, and transferred to memory 312 as needed for execution by the processor 310.

[0020] When the UE 110A detects a relocation signal, the PUCCH relocation module 326 may select a different component carrier for the PUCCH according to information provided by the relocation signal. The component carrier selected as the PUCCH may be specified in the relocation signal, or may be a component carrier indicated by a priority sequence 324, suitably comprising part of the data 318 and delivered to the UE 110A by the eNB 106 based on the priority sequence information 222 stored by the eNB 106.

[0021] Alternatively or in addition, the UE 11 OA may automatically change from one PUCCH to another based on a stored on-off pattern 326, which may be a copy of the on-off pattern 226 maintained by the UE 106, or may be a portion of the on-off pattern 226, comprising on-off sequences only for component carriers used by the UE 11 OA. In this case, the PUCCH relocation module 322 may monitor the on-off pattern 326. When the on-off pattern 326 indicates that a component carrier being used will become unavailable, the PUCCH relocation module 322 selects a new component carrier, such as a component carrier indicated by the priority sequence 324.

[0022] Fig. 4 illustrates a diagram 400 showing sequencing of relocations according to one or more embodiments of the present invention. The relocations are performed based on information provided by the priority sequence 322 and the on-off pattern 226, and because this information is stored in the UE 11 OA, the relocations illustrated here can be performed without signaling from the eNB 106. [0023] The diagram 400 illustrates the use of component carriers 402, 404, and 406 according to a predefined sequence. The "on" state of each of the component carriers 402, 404, and 406 can be seen, with "on" states 408A and 408B being shown for component carrier 402, "on" state 410 being shown for component carrier 404, and "on" states 412A and 412B being shown for component carrier 406. Transmissions 414-424 are also shown. In the scenario illustrated by Fig. 4, with the transmissions 414, 418, and 422 being downlink grants and with the transmissions 416, 420, and 424 being uplink transmissions over a PUCCH. At the beginning of the scenario, the component carrier 402 is in use as the PUCCH. A transition to an "off state is scheduled, and once the component carrier 402 is no longer available, a relocation 426 is made to use the component carrier 404. The component carrier 404 is chosen because it is the next available component carrier shown in the priority sequence 322. After the component carrier 406 is chosen, transmissions 416 and 420 are conducted successfully. The component carrier 404 subsequently becomes unavailable, and a relocation needs to be made to a new component carrier. In this instance, both the component carrier 402 and the component carrier 406 are available, but a relocation 428 is made to use the component carrier 406 because the component carrier 406 has a higher priority in the priority sequence 322. A possible relocation 430 to the component carrier 402 is also shown here, but the relocation that is actually performed is the relocation 428.

[0024] Because of the need for fast relocation, embodiments of the invention discussed here may suitably use layer 1 signaling, which is not as reliable as higher layer signaling. Therefore, various embodiments of the invention provide mechanisms to compensate for failure of layer 1 signaling. For example, a UE may miss a downlink relocation signal. Techniques such as transmission diversity or repeating a signal over several subframes may reduce the probability of errors. However, if an error does occur, the UE will not send a signal over the PUCCH indicated by the relocation signal. The eNB 106 will recognize, upon failure to receive a signal on the expected component carrier, that relocation failed, and may therefore employ recovery techniques such as re-transmitting a downlink grant or a relocation signal.

[0025] Fig. 5 illustrates the steps of a process 500 according to an embodiment of the present invention. The process 500 may suitably be carried out using components such as the base station 106 and one or more UEs such as the UE 110A, illustrated in Figs. 1-3.

[0026] At step 502, a base station delivers information to one or more user devices allowing for automated recognition by the user devices of the unavailability of component carriers being used by one or more of the devices as a physical uplink control channel, and selection of a new component carrier to be used as a physical uplink control channel. The information may suitably comprise information such as an on-off pattern, a priority sequence, an unavailability schedule, and other information identifying when a component carrier may be expected to become unavailable and which component carrier should be selected to replace it.

[0027] At step 504, the base station monitors network conditions to detect unavailability of a component carrier being used by one or more UEs as a physical uplink control channel. At step 506, upon detection of network conditions indicating such unavailability, the base station signals one or more UEs to select new component carriers. Such signaling may specify component carriers to be selected, or may direct UEs to select component carriers based on predefined information. The base station may signal different UEs to select different component carriers, or may signal all UEs to select the same component carrier, or may signal some UEs to select specific component carriers and others to make their own selection based on predefined selection information, based on design choices. The base station need not signal all UEs to select new component carriers. At step 508, performed as an alternative or in addition to signaling by the base station, one or more UEs recognize the unavailability of a component carrier being used as a PUCCH, suitably based on locally stored information, and select a new component carrier based on predefined criteria.

[0028] While various exemplary embodiments have been described above it should be appreciated that the practice of the invention is not limited to the exemplary embodiments shown and discussed here. Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. In particular, it will be recognized that various specific embodiments discussed here are directed to relocations of a PUCCH by a UE operating in a system using TVWS bands for transmission of signals in a wireless cellular network. However, the invention is not limited to the use of TVWS bands, to relocations of a PUCCH, or even to wireless cellular networks. Instead, it can easily be seen that embodiments of the invention may be used for any scenario in which a change must be made from one wireless medium, such as a component carrier, to another.

[0029] Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. [0030] The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising:

at least one processor; and

at least one memory storing a program of instructions;

wherein the program of instructions is configured, with the at least one memory and the at least one processor to cause the apparatus to perform actions comprising at least:

delivering information to a device indicating a component carrier to be selected by the device for use as a physical uplink control channel when a component carrier being used by the device for a physical uplink control channel becomes unavailable.

2. The apparatus of claim 1, further comprising delivering information to the device indicating unavailability of a component carrier being used for a physical uplink control channel.

3. The apparatus of claim 1 or 2, wherein delivering information to the device indicating unavailability of a component carrier being used for a physical uplink control channel is based on information relating to a component carrier on an unlicensed frequency band, wherein the component carrier on the unlicensed frequency band is currently being used for the physical uplink control channel.

4. The apparatus of any preceding claim, wherein delivering information to the device indicating a component carrier to be selected comprises transmitting a priority sequence of available component carriers.

5. The apparatus of any preceding claim, wherein delivering information to the device indicating unavailability of a component carrier comprises delivering an on-off pattern to the device.

6. The apparatus of any preceding claim, wherein delivering information to the device indicating unavailability of a component carrier comprises explicitly signaling the device to trigger a selection of a new component carrier.

7. The apparatus of any preceding claim, wherein delivering information to the device indicating a component carrier to be selected comprises signaling the device to identify a component carrier to be selected.

8. The apparatus of any preceding claim, wherein delivering information to the device indicating a component carrier to be selected comprises signaling the device to select a carrier using predefined priority sequence information.

9. The apparatus of any preceding claim, further comprising monitoring interference affecting component carriers and identifying the presence of excessive interference preventing use of a component carrier.

10. An apparatus, comprising:

at least one processor; and

at least one memory storing a program of instructions;

wherein program of instructions is configured, with the at least one memory and the at least one processor to cause the apparatus to perform actions comprising at least:

recognizing unavailability of a component carrier currently being used for a physical uplink control channel based on information received from a base station indicating the unavailability of the component carrier; and

selecting a new component carrier for use as a physical uplink control channel based on information received from the base station indicating a new component carrier to be selected.

11. The apparatus of claim 10, wherein each of the component carrier currently being used and the new component carrier is a component carrier in an unlicensed frequency band.

12. The apparatus of claim 10 or 11, wherein recognizing unavailability of a component carrier comprises receiving a signal from the base station directing selection of a new component carrier.

13. The apparatus of any preceding claim, wherein selecting a new component carrier comprises selecting a new component carrier based on a predefined priority sequence received from the base station.

14. The apparatus of any preceding claim, wherein selecting a new component carrier comprises selecting a new component carrier explicitly identified by the base station.

15. The apparatus of any preceding claim, wherein recognizing unavailability of a component carrier comprises recognizing that the component carrier is scheduled to transition to an "off state.

16. The apparatus of claim 15, wherein recognizing that the component carrier is scheduled to transition to an off state is performed based on on-off pattern information received from the base station.

17. A method comprising:

wirelessly transmitting information to a device indicating a component carrier to be selected by the device for use as a physical uplink control channel when a component carrier being used by the device for a physical uplink control channel becomes unavailable.

18. The method of claim 17, further comprising transmitting information to the device indicating unavailability of a component carrier being used for a physical uplink control channel.

19. The method of claim 17 or 18, wherein transmitting information to the device indicating a component carrier to be selected comprises transmitting a priority sequence of available component carriers.

20. A non-transitory computer readable storage medium storing a program of instructions, execution of which by a processor configures an apparatus to perform actions comprising at least:

21. The computer readable storage medium of claim 20, further comprising delivering information to the device indicating unavailability of a component carrier being used for a physical uplink control channel.

22. The computer readable storage medium of claim 20 or 21, wherein delivering information to the device indicating a component carrier to be selected comprises transmitting a priority sequence of available component carriers.