WO2013050083A1

WO2013050083A1 - Determination of transmission timing information after activation of a cell

Info

Publication number: WO2013050083A1
Application number: PCT/EP2011/067587
Authority: WO
Inventors: Chunli Wu; Benoist Pierre Sebire; Claudio Rosa
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-10-07
Filing date: 2011-10-07
Publication date: 2013-04-11

Abstract

A method comprises, determining if transmission timing information is to be determined for an activated cell and if said timing advance information is to be updated, causing a process to be performed to determine timing advance information.

Description

DETERMINATION OF TRANSMISSION TIMING INFORMATION AFTER

ACTIVATION OF A CELL

The present invention relates to a method and apparatus and in particular but not exclusively to a method and apparatus for use in an aggregated carrier environment.

A communication device can be understood as a device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit communication via a communication system and can thus be used for accessing various service applications.

A communication system is a facility which facilitates the communication between two or more entities such as the communication devices, network entities and other nodes. A communication system may be provided by one or more interconnect networks. One or more gateway nodes may be provided for interconnecting various networks of the system. For example, a gateway node is typically provided between an access network and other communication networks, for example a core network and/or a data network.

An appropriate access system allows the communication device to access to the wider communication system. An access to the wider communications system may be provided by means of a fixed line or wireless communication interface, or a combination of these. Communication systems providing wireless access typically enable at least some mobility for the users thereof. Examples of these include wireless communications systems where the access is provided by means of an arrangement of cellular access networks. Other examples of wireless access technologies include different wireless local area networks (WLANs) and satellite based communication systems .

A wireless access system typically operates in accordance with a wireless standard and/or with a set of specifications which set out what the various elements of the system are permitted to do and how that should be achieved.

Examples of radio access networks include, GSM (Global System for Mobile) , EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN) , Universal Terrestrial Radio Access Networks (UTRAN) and evolved UTRAN (E-UTRAN) .

In the Long Term Evolution (LTE) System, downlink transmissions are made according to an orthogonal frequency division multiple access (OFDMA) technique, and uplink transmissions are made according to a single carrier frequency division multiple access (SCFDMA) technique. Each transmission is made using a group of orthogonal sub- carriers. Sub-carriers are grouped into units called resource blocks, and a communication device can make or receive transmissions using groups of resource blocks ranging up to a predetermined maximum number of resource blocks within a predetermined frequency block called a component carrier. A further LTE development provides for carrier aggregation, where two or more component carriers are aggregated in order to support transmission bandwidths wider than that defined by a single component carrier. Capable communication devices can receive or transmit simultaneously on a plurality of component carriers.

There is also proposed the possibility to deactivate one or more SCells for uplink transmissions from a communication device until those one of more SCells are required. Deactivation of SCell(s) reduces power consumption at the communication device for the period that the SCell(s) are deactivated. The monitoring activity of the communication device is reduced; the communication device does not perform PDCCH monitoring or make channel quality information (CQI) measurements for deactivated SCell(s) . The uplink activity in a deactivated SCell is also stopped; the communication device does not transmit any sounding reference signals (SRS) for deactivated SCell (s) .

Timing advance (TA) values/commands are used to control the timing of uplink transmissions within a timeslot with the aim of compensating for propagation delays.

In one embodiment, the uplink transmission timing information is timing advance information.

STATEMENT OF INVENTION According to a first aspect, there is provided a method comprising responsive to activation of a cell determining if transmission timing information is to be determined; and if said transmission timing information is to be updated, causing a process to be performed to determine transmission timing information.

According to another aspect, there is provided a method comprising responsive to activation of a secondary cell determining if timing advance information is to be updated for that secondary cell based on a parameter associated with said secondary cell; and if said timing advance information is to be updated, causing a random access procedure to be performed to determine updated timing advance information.

According to a further aspect, there is provided a method comprising determining after activation of a secondary cell that timing advance information is to be updated for that secondary cell if current timing advance information is deficient; and causing a random access procedure to be performed to determine updated timing advance information

According to another aspect, there is provided an apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to: responsive to activation of a cell determine if transmission timing information is to be determined; and if said transmission timing information is to be updated, cause a process to be performed to determine transmission timing information .

According to another aspect, there is provided an apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to responsive to activation of a secondary cell determine if timing advance information is to be updated for that secondary cell based on a parameter associated with said secondary cell; and if said timing advance information is to be updated, cause a random access procedure to be performed to determine updated timing advance information.

According to a further aspect, there is provided an apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to: determine after activation of a secondary cell that timing advance information is to be updated for that secondary cell if current timing advance information is deficient; and cause a random access procedure to be performed to determine updated timing advance information

Some embodiments will now be described by way of example only with reference to the accompany drawings, in which: Figure 1 shows an example of a system where some embodiments may be implemented;

Figure 2 shows an example of a communication device

Figure 3 shows an example of a control apparatus; Figure 4 schematically shows an aggregated carrier;

Figure 5 shows a first scenario where embodiments may be applied;

Figure 6 shows a second scenario where embodiments may be applied; Figure 7 shows a first method; and Figure 8 shows a second method.

In the following certain exemplifying embodiments are explained with reference to a wireless communication system serving devices adapted for wireless communication. Therefore, before explaining in detail the exemplifying embodiments, certain general principles of a wireless system, components thereof, and devices for wireless communication are briefly explained with reference to system 10 of Figure 1, device 20 of Figure 2 and control apparatus 30 of Figure 3 to assist in understanding the technology underlying the described examples.

A communication device can be used for accessing various services and/or applications provided via a communication system. In wireless or mobile communication systems the access is provided via a wireless access interface between mobile communication devices and an appropriate access system. A communication device may access wirelessly a communication system via a base station. A base station site can provide one or more cells of a cellular system. A base station can provide, for example, three carriers, each carrier providing a cell. In figure 1, for example, a base station 12 is shown to provide three cells 1, 2 and 3. Each cell provides a carrier Fl, F2 and F3, respectively. Each communication device 20 and base station may have one or more radio channels open at the same time and may receive signals from more than one source.

It should be appreciated that the number of carriers provided by each base station may be more or less than three and/or may vary over time.

It is noted that at least one of the cells 1 to 3 can be provided by means of remote radio heads of base station 12. In some embodiments at least one of the carriers may be provided by a station that is not co-located at base station 12 but could only be controlled by the same control apparatus as the other cells. This possibility is denoted by station 11 in Figure 1. For example, block 13 could be used to control at least one further station, for example an intra-eNB. Interaction between the different stations and/or controllers thereof may also be arranged otherwise, for example if a station is provided as an inter-site eNB . The controller of a cell has enough information for all of the aggregated carriers (cells) . A base station is typically controlled by at least one appropriate controller so as to enable operation thereof and management of mobile communication devices in communication with the base station. The control entity can be interconnected with other control entities. The control entity may be part of the base station. In Figure 1 the controller is shown to be provided by block 13. The controller apparatus may comprise at least one memory, at least one data processing unit and an input/output interface. It shall be understood that the control functions may be distributed between a plurality of control units. The controller apparatus for a base station may be configured to execute an appropriate software code to provide the control functions as explained below in more detail.

In Figure 1 the base station 12 is connected to a data network 18 via an appropriate gateway 15. A gateway function between the access system and another network such as a packet data network may be provided by means of any appropriate gateway node, for example a packet data gateway and/or an access gateway. A communication system may thus be provided by one or more interconnect networks and the elements thereof, and one or more gateway nodes may be provided for interconnecting various networks.

An example of a standardized architecture is known as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE is being standardized by the 3rd Generation Partnership Project (3GPP) . The various development stages of the 3GPP LTE specifications are referred to as releases. A development of the LTE is often referred to as LTE-Advanced (LTE-A) .

A communication device can access a communication system based on various access techniques, such as code division multiple access (CDMA) , or wideband CDMA (WCDMA) . The latter technique is used by communication systems based on the third Generation Partnership Project (3GPP) specifications. Other examples include time division multiple access (TDMA) , frequency division multiple access (FDMA), space division multiple access (SDMA) and so on. A non-limiting example of mobile architectures where the herein described principles may be applied is known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) . In LTE, an orthogonal frequency division multiple (OFDMA) access technique is used.

A non-limiting example of a base station of a cellular system is what is termed as a NodeB or evolved NodeB (eNB) in the vocabulary of the 3GPP specifications.

Figure 2 shows a schematic, partially sectioned view of a communication device 20 that a user can use for communications. Such a communication device is often referred to as user equipment (UE) or terminal. The device may be mobile or have a generally fixed location. An appropriate communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS) such as a mobile phone or what is known as a 'smart phone', a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. A communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia, positioning data, other data, and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet.

A communication device is typically provided with at least one data processing entity 23, at least one memory 24 and other possible components 29 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with base stations and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 26.

The user may control the operation of the communication device by means of a suitable user interface such as key pad 22, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 25, a speaker and a microphone are also typically provided. Furthermore, a communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto. The device 20 may receive and transmit signals 28 via appropriate apparatus for receiving and transmitting signals. In Figure 2 transceiver apparatus is designated schematically by block 27. The transceiver apparatus is provided with radio capability. The transceiver may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

Figure 3 shows an example of a control apparatus 30 for an access node, for example to be coupled to and/or for controlling a station of a radio service area, for example one of the nodes 11 or 12 of Figure 1. The control apparatus may in some embodiments be part of the base station itself. The control apparatus 30 can be arranged to provide control on configurations, measurements, information processing and/or communication operations of an access node. A control apparatus in accordance with Figure 3 can be configured to provide control functions in association with generation, communication and interpretation of information regarding carrier aggregation and/or other operations. For providing the desired operation, the control apparatus 30 comprises at least one memory 31, at least one data processing unit 32, 33 and an input/output interface 34. Via the interface the control apparatus can be coupled to the relevant node. The control apparatus 30 can be configured to execute an appropriate software code to provide the control functions.

It should be appreciated that Figure 1 shows only one scenario where embodiments may be used. Carrier aggregation (CA) can be used to increase performance. In carrier aggregation a plurality of carriers are aggregated to increase bandwidth. Carrier aggregation comprises aggregating a plurality of component carriers into a carrier that is referred to in this specification as an aggregated carrier. For example, Release 10 (Rel-10) of the E-UTRA specifications introduces carrier aggregation (CA) , where two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths . In CA it is possible to configure a communication device to aggregate a different number of CCs originating from the same eNodeB (eNB) and of possibly different bandwidths in the uplink (UL) and/or downlink (DL) . In this regard a reference is made to Figure 4 which shows five component carriers which have been aggregated. Each component carrier is 20MHz in this example, giving an aggregated bandwidth of lOOMHz.

When CA is configured, the communication device, for example a user equipment (UE) only has one radio resource control (RRC) connection with the network. At radio resource control (RRC) connection establishment / re-establishment / handover, one serving cell provides the non access stratum (NAS) protocol mobility information (e.g. TAI ; tracking area identity) and at RRC connection re-establishment/handover, one serving cell provides the security input. The security input may be one ECGI (E-UTRAN cell global identifier) , one PCI (physical cell identifier and one ARFCN (absolute radio frequency channel number) . This serving cell is referred to as the Primary Cell (PCell) . In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC) . Depending on UE capabilities, Secondary Cells (SCells) can be configured to form together with the PCell a set of serving cells. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC) .

The configured set of serving cells for a UE therefore can consist of one PCell and one or more SCells. In is noted that 3GPP Release 8 terminals / user equipments are assumed to be served by one serving cell, while LTE-Advanced capable terminals / user equipments can receive or transmit simultaneously on multiple serving cells.

In order to compensate for propagation delays in LTE, timing advance (TA) information is signalled by the eNB to the UE . When receiving a timing advance command (TAC) , the UE adjusts its uplink transmission timing. A timing advance command may be received in a random access response or in a MAC (medium access control) control element. The validity of a timing advance command is controlled by a TA timer. As long as the TA timer is running, the timing advance remains valid and uplink transmissions can take place on the shared channel. Every time a timing advance command is received, the TA timer is restarted. When the TA timer expires, uplink synchronisation is required and no uplink transmission can take place on a shared channel. In order for the eNB to assess the timing adjustment needed at the UE, a random access procedure is usually started. It has been suggested that the support of the use of multiple timing advances in case of LTE uplink carrier aggregation be specified. Multiple TA may be needed to cope with non- collocated receivers on the network side i.e. for the RRH (remote radio heads) and frequency selective repeaters scenarios .

Some embodiments may be used where eNBs and UEs are deploying carrier aggregation and where in one of the carriers remote radio equipment is used to provide either hotspot coverage or coverage extensions.

Reference is made to Figure 5 where a first frequency fl provides macro coverage in cells and a second frequency f2 is used by Remote Radio Heads (RRHs) to improve throughput at hot spots. As can be seen the areas covered by f2 RRHs is much smaller and overlies the coverage area provided by the macro cells. Mobility is performed based on fl coverage, fl and f2 may be of different bands, e.g., fl = {800 MHz, 2 GHz} and f2 = {3.5 GHz}, etc. f2 RRHs cells may be aggregated with the underlying fl macro cells.

Reference is made to Figure 6 where frequency selective repeaters are deployed so that coverage is extended for one of the carrier frequencies, fl and f2 cells of the same eNB can be aggregated where coverage overlaps. Some cells have a macro cell coverage at frequency f1. Overlying the macro cell may be a second cell having a frequency of f2 which may substantially overlap the macro cells. Repeaters may extend the coverage at the second frequency f2 in some cells. A TA group concept was introduced for such scenarios with which a set of serving cells have uplink resource sharing the same TA value. In the scenario of Figure 6 with frequency selective repeaters, multiple TAs may only be required when the UE is under the coverage of the repeaters.

The TA value and TA group could change if the UE moves in- between the repeater's coverage. It may happen that the TA group changes when the SCell is deactivated. The eNB may not be aware of that change when the eNB activates the SCell. The eNB would assume the same TA group and TA value for the UL transmissions of the SCell, as prior to deactivation. The wrong UL timing may cause interference for UL reception at the eNB.

It has been proposed to always initiate a RACH (Random access channel) upon activation. This may be inefficient as for most of the cases the SCell will remain in the same group and there is still a valid TA value for the group. Further contention based RACH initiated from the UE side on SCell would need to be supported.

It has been suggested that the UE should report the DL timing difference and based on the information eNB could reconfigure the group as needed. However, there is no accurate requirement defined for DL timing difference evaluation. Reference will now be made to Figure 7 which shows a first method .

In step SI, the UE detects a problem for the UL of an SCell. For example it could be determined that the timing advance information is deficient. This may be directly or indirectly determined. The problem may be determined directly from the UL of the SCell or may be determined indirectly from the DL of the cell. Alternatively, the problem may be determined from another parameter. That parameter may be associated with the SCell itself.

By way of example only, a detection of UL problem on a SCell may be in response to the occurrence of for example the required TA value exceeding the maximum allowed amount of the magnitude of the timing change while still keeping the SCell in the current TA group. Alternatively or additionally a problem may be determined if the DL receiving timing of a SCell has changed by more than X s during the last Y subframes.

In step S2, the UE will send an UL problem indication to the eNB . This is sent via the PCell or potentially another SCell.

In step S3, the eNB would then order the UE to initiate RACH. By way of example only, the eNB may send a physical data control channel PDCCH order to initiate (non-contention based) RACH for the corresponding SCell. In step S4, random access is performed. Where a random access is performed, in some embodiments, this may be non contention based random access. In non contention based random access, the preamble is pre-assigned by the eNB and provided by the eNB to the UE . The UE transmits the assigned preamble on the SCell. The eNB responds with a random access response on the PDCCH which includes the timing alignment information.

In step S5, the UE can use the new TA information in the UL communications with the eNB for the SCell.

Alternatively, in some embodiments, when the UE detects any problem for the UL of an SCell, the UE will trigger RACH on the SCell. This may be used where contention based RACH is available on the UE's SCell.

One or more MAC CEs may be defined for the UL problem indication. This may be regarded as a RACH request. This may comprise the index of the problematic SCell.

It should be appreciated that this is only one way in which information may be passed between the UE and eNB.

In some embodiments, for the period between the UE detecting the problem and receiving new TA value, the UE may not send UL transmissions on the concerned SCell. The UE may communicate with the eNB on the serving cell which is still working (e.g. PCell) . With the report from the UE, the situation of the last unknown/undetectable UL problem (from eNB side) may be avoided. Having the possibility of having non-contention based RACH may simplify the system design. The RACH may only be initiated when needed.

Reference is made to Figure 8 which shows another embodiment. Instead of the UE reporting the problem or initiating RACH, it is configurable per SCell whether or not upon SCell activation the UE should wait until it gets a valid TA before any UL transmission can take place. For potentially problematic cells (covered by repeaters for example) , the SCell may be configured to have no UL transmission until a valid TA is received by the UE . In step Tl, a determination is made as to whether the SCell is one for which a valid TA must be obtained before activation. This information may be obtained by means of for example a broadcast message or information from the eNB. This configuration of whether a SCell always requires a RACH process may be performed by a eNB and/or a control node.

For such a SCell, the eNB may always initiate Random Access procedure after activation of the problematic SCell so there is no concern that the UE will send something on the on the UL with wrong timing. The random access procedure is thus performed in step T2. This may be as previously discussed.

In step T3, the new TA may be used by the UE . For the cells without a problem, these cells would be configured so that there would be no need to wait for a new TA. Thus UL transmission can be performed, without delay, upon activation if the SCell is in a group that already has valid TA. This is assuming that the TA is valid and for example the TA timer has not expired.

The initiating RACH command may be the same as the normal PDCCH order following the activation command. Alternatively the command may be an extended activation command that has a dedicated preamble index and PRACH (physical random access channel) index, as well as the cell index of the cell for which the random access is to be performed. A new trigger for random access may be defined.

This embodiment of making the need to performing RACH configurable per SCell, may be more efficient than applying RACH to all the cells.

In some embodiment, responsive to activation of a cell, a determination is made as to if timing advance information is to be determined. This may be before the cell is activated, as the cell is activated or after the cell is being activated .

In the described embodiments, timing advance information is used. It should be appreciated that in other embodiments alternative transmission timing information may be used. Embodiments may be used in networks where two or more point carrier aggregation and two or more timing advance in UL is enabled. This may be in the context of an LTE network or any other suitable network. Some embodiments may be used where one or more of the carriers remote radio equipment is used to provide for example hot spot coverage or coverage extension.

The above-described operations may require data processing in the various entities. The data processing may be provided by means of one or more data processors. These data processors may operate in conjunction with one or more memories.

Appropriately adapted computer program code product or computer program code may be used for implementing the embodiments, when loaded to a computer or one or more processors. The program code for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. Alternatively or additionally the computer program code may be stored in one or more memories. A possibility is to download the program code product via a data network. Implementation may be provided with appropriate software in a server.

The computer program code may comprise one or more computer executable instructions which when run on one or more processors cause one or more of the method steps to be performed . For example the embodiments may be implemented by a single chip or as a chipset. A chipset is a series of integrated circuits communicating among each other. The chipset may comprise microprocessors arranged to run code, application specific integrated circuits (ASICs), or programmable digital signal processors for performing the operations described above .

Embodiments may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate. Programs, such as those provided by Synopsys, Inc. of Mountain View, California and Cadence Design, of San Jose, California automatically route conductors and locate components on a semiconductor chip using well established rules of design as well as libraries of pre-stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for fabrication .

In addition to the modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described techniques may be made, and that the described techniques have application in other communication systems and/or different communication standards .

Claims

CLAIMS :

1. A method comprising: responsive to activation of a cell determining if transmission timing information is to be determined; and if said transmission timing information is to be updated, causing a process to be performed to determine transmission timing information.

2. A method as claimed in claim 1, wherein said determining if transmission timing information is to be updated is responsive to a determination of an uplink timing problem for said cell.

3. A method as claimed in claim 1, wherein said determining if transmission timing information is to be updated is responsive to a determination that current transmission timing information exceeds a maximum amount of permitted timing change.

4. A method as claimed in claim 1, wherein said determining if transmission timing information is to be updated is responsive to a determination of downlink timing differences.

5. A method as claimed in any preceding claim, wherein said determining is performed by a user equipment.

6. A method as claimed in any preceding claim, wherein said causing comprises triggering a random access procedure for said cell.

7. A method as claimed in any preceding claim, wherein said causing comprises sending a message to a base station.

8. A method as claimed in claim 7, wherein responsive to said message said base station triggers a random access procedure.

9. A method as claimed in claim 1, comprising determining if transmission timing information is to be updated based on information associated with said cell.

10. A method as claimed in claim 9, wherein said information associated with said cell comprises a parameter indicating if said transmission timing information is to be updated.

10. A method as claimed in claim 9 or 10, comprising receiving said information associated with said cell from a base station associated with said cell.

11. A method as claimed in any preceding claim, wherein said process to determine transmission timing information comprises a random access procedure.

12. A method as claimed in claim 11, wherein said random access procedure comprises a non contentious random access procedure .

13. A method as claimed in any preceding claim, wherein said cell comprises a secondary cell.

14. A method as claimed in any preceding claim, comprising preventing at least some uplink transmissions to said cell while said transmission timing information is being updated.

15. A method comprising: responsive to activation of a secondary cell determining if timing advance information is to be updated for that secondary cell based on a parameter associated with said secondary cell; and if said timing advance information is to be updated, causing a random access procedure to be performed to determine updated timing advance information.

16. A method comprising: determining after activation of a secondary cell that timing advance information is to be updated for that secondary cell if current timing advance information is deficient; and causing a random access procedure to be performed to determine updated timing advance information.

17. A computer program comprising computer executable instructions which when run are configured to perform the method of any preceding claim.

18. An apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to: responsive to activation of a cell determine if transmission timing information is to be determined; and if said transmission timing information is to be updated, cause a process to be performed to determine transmission timing information.

19. An apparatus as claimed in claim 18, wherein the at least one memory and computer program code are configured to with the at least one processor determine an uplink timing problem for said cell to determine that transmission timing information is to be updated.

20. An apparatus as claimed in claim 18, wherein the at least one memory and computer program code are configured to with the at least one processor to determine that current transmission timing information exceeds a maximum amount of permitted timing change to determine that transmission timing information is to be updated.

21. An apparatus as claimed in claim 18, wherein the at least one memory and computer program code are configured to with the at least one processor to determine downlink timing differences to determine that transmission timing information is to be updated.

22. An apparatus as claimed in any of claims 18 to 21, wherein the at least one memory and computer program code are configured to with the at least one processor to trigger a random access procedure for said cell.

23. An apparatus as claimed in any of claims 18 to 22, wherein the at least one memory and computer program code are configured to with the at least one processor to send a message to a base station.

24. An apparatus as claimed in claim 18, wherein the at least one memory and computer program code are configured to with the at least one processor to determine if transmission timing information is to be updated based on information associated with said cell.

25. An apparatus as claimed in claim 24, wherein said information associated with said cell comprises a parameter indicating if said transmission timing information is to be updated .

26. An apparatus as claimed in claim 24 or 25, wherein the at least one memory and computer program code are configured to with the at least one processor to receive said information associated with said cell from a base station associated with said cell.

27. An apparatus as claimed in any of claims 18 to 26, wherein the at least one memory and computer program code are configured to with the at least one processor to determine transmission timing information from a random access procedure .

28. An apparatus as claimed in claim 27, wherein said random access procedure comprises a non contentious random access procedure .

29. An apparatus as claimed in any of claim 18 to 28, wherein said cell comprises a secondary cell.

30. An apparatus as claimed in any of claims 18 to 29, wherein the at least one memory and computer program code are configured to with the at least one processor to prevent at least some uplink transmissions to said cell while said transmission timing information is being updated.

31. An apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to: responsive to activation of a secondary cell determine if timing advance information is to be updated for that secondary cell based on a parameter associated with said secondary cell; and if said timing advance information is to be updated, cause a random access procedure to be performed to determine updated timing advance information.

32. An apparatus, said apparatus comprising at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to with the at least one processor cause the apparatus at least to: determine after activation of a secondary cell that timing advance information is to be updated for that secondary cell if current timing advance information is deficient; and cause a random access procedure to be performed to determine updated timing advance information.

33. A user equipment comprising apparatus as claimed in any of claims 18 to 32.