WO2015174905A1

WO2015174905A1 - Handling of uplink transmission-timing differences

Info

Publication number: WO2015174905A1
Application number: PCT/SE2015/050459
Authority: WO
Inventors: Mattias TAN BERGSTRÖM; Magnus Larsson; Muhammad Kazmi
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-05-12
Filing date: 2015-04-23
Publication date: 2015-11-19
Also published as: AR100416A1

Abstract

Techniques for managing differences in uplink transmit timing among aggregated carriers or groups of carriers. In one group of embodiments of these techniques, a mobile terminal- based mechanism is provided. In an example method according to these embodiments, a mobile terminal determines (830) that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold and, in response to said determining, takes (840) an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

Description

HANDLING OF UPLINK TRANSMISSION-TIMING DIFFERENCES

TECHNICAL FIELD

The presently disclosed techniques relate to handling timing differences in Timing Advance Groups in a communication device capable of Carrier Aggregation, such a mobile terminal device.

BACKGROUND

With ever-increasing demands on increased capacity and service in wireless

telecommunication networks, solutions continue to be provided to meet that demand. An example is the 4^th-generation wireless communication network commonly referred to as Long-Term Evolution (LTE) and more formally known as the Evolved Universal Terrestrial Access Network (E-UTRAN), specified by the 3^rd Generation Partnership Project, 3GPP. LTE is a standard for wireless data communications technology and an evolution of the GSM/UMTS standards. The goal of LTE was to increase the capacity and speed of wireless data networks. As a further development, 3GPP has developed specifications for even more features, often referred to under the umbrella term "LTE Advanced." These features include the further introduction of multicarrier techniques, which facilitate use of ultra wide bandwidth, up to 100 MHz of spectrum, to support very high data rates.

Release 10 of 3GPP's specifications for LTE (referred to hereinafter as "LTE Rel-10") have been standardized, providing support for Component Carrier (CC) bandwidths up to 20 MHz, which is the maximal LTE Release 8 (Rel-8) carrier bandwidth. LTE Rel-10 operation with a total bandwidth wider than 20 MHz is possible, when two or more LTE CCs are used by an LTE Rel-10 terminal. A straightforward way to obtain bandwidths wider than 20 MHz is by means of Carrier Aggregation (CA). CA implies that an LTE Rel-10 terminal can receive (and transmit, in some cases) multiple CCs, where the CCs each have, or at least the possibility to have, the same structure as a Rel-8 carrier. The basic concept behind CA is illustrated in Figure 1 . It should be noted, however, that aggregated carriers need not be adjacent to one another.

Release 10 of the LTE standards provides support for up to five aggregated CCs, where each CC is limited in the radio-frequency (RF) specifications to have one of six bandwidths, namely bandwidths of 6, 15, 25, 50, 75, or 100 resource blocks (RBs), corresponding to 1 .4, 3, 5, 10, 15, and 20 MHz, respectively.

The number of aggregated CCs as well as the bandwidth of the individual CCs may be different for uplink and downlink. A symmetric configuration refers to the case where the number of CCs in downlink (DL) and uplink (UL) is the same, whereas an asymmetric configuration refers to the case that the number of CCs is different in DL and UL. It is important to note that the number of CCs configured in the network may be different from the number of CCs seen by a terminal: A terminal may support more downlink CCs than uplink CCs, for example, even though the network offers the same number of uplink and downlink CCs.

CCs are also referred to as cells or serving cells. More specifically, in an LTE network the cells aggregated by a terminal include one carrier denoted the primary component carrier or primary Serving Cell (PCell), and one or more others referred to as secondary component carriers or secondary Serving Cells (SCells). The term "serving cell" comprises both PCell and SCells. All UEs have one PCell; exactly which cell is a PCell is terminal-specific. The PCell for a given UE is considered "more important" to the UE than its SCells, since vital control signaling and other important signaling are typically handled via the PCell. Uplink control signaling is always sent on a UE's PCell. The component carrier configured as the PCell is the primary CC, whereas all other component carriers are secondary serving cells.

During initial access, a LTE Rel-10 terminal behaves similarly to a LTE Rel-8 terminal, i.e., to a terminal that does not support aggregation of carriers. However, upon successful connection to the network a Rel-10 terminal may - depending on its own capabilities and the network - be configured with additional serving cells in the uplink and downlink.

Configuration is done using Radio Resource Control (RRC) signaling. Because of the heavy signaling and rather slow speed of RRC signaling, it may typically be the case that a terminal is configured with multiple serving cells, even if not all of them are currently used.

With the concept of SCells, additional bandwidth resources can be configured and de- configured dynamically, in response to the UE's needs. The configuration and de- configuration of cells is signaled by the eNB and performed with RRC signaling, which is slow. Since RRC signaling is heavy and slow, the concepts of activation and deactivation, as distinct from configuration and de-configuration, have been introduced for SCells. For a given UE, the eNB can deactivate any configured serving cells that the eNB decides the UE should not use or does not need for the moment. Activation and deactivation of SCells are performed with Medium Access Control (MAC) signaling, which is faster than RRC signaling. The activation/deactivation procedure is described in detail in section 5.13 of 3GPP TS 36.321 , v. 1 1 .3.0, available at www.3gpp.org. Each SCell is configured with a SCelllndex, which is an identifier or so called Cell Index which is unique among all serving cells configured for this UE. The PCell always has Cell Index 0, while an SCell can have an integer cell index of 1 to 7. The Rel-10 Activation/Deactivation MAC control element (CE) is defined in section 6.1 .3.8 of 3GPP TS 36.321 , and consists of a single octet containing seven C-fields and one R-field. Each C-field corresponds to a specific SCelllndex and indicates whether the specific SCell is activated or deactivated. The UE will ignore all C-fields associated with Cell Indices not being configured. The Activation/Deactivation MAC CE always indicates the activation status of all configured SCells, meaning that if the eNB wants to activate one SCell it has to include all configured SCells, setting the bit corresponding to each one to indicate activated or deactivated, even if the status for the corresponding SCell has not changed.

If a UE's secondary serving cell is activated, the UE has to monitor the Physical Downlink Control Channel (PDCCH) and Physical Downlink Shared Channel (PDSCH) for that serving cell. This implies a wider receiver bandwidth, higher sampling rates, etc., at the UE, resulting in higher power consumption than if that serving cell were deactivated.

To preserve orthogonality among the uplink signals received at the LTE base station (known as an "eNodeB" or "eNB"), the uplink transmissions from multiple UEs need to be received at the eNodeB in a time aligned fashion. This means that the transmit timing of those UEs that are under the control of the same eNB should be adjusted to ensure that their received signals arrived at the eNB receiver at approximately the same time - more specifically, time aligned so that any difference in timing is well within the during of the cyclic prefix (CP) that appears at the beginning of each LTE subframe. This ensures that the eNodeB receiver is able to use the same resources (i.e., the same discrete Fourier Transform (DFT) or Fast Fourier Transform (FFT) resources) to receive and process the signals from multiple UEs.

Since UEs may be located at different distances from the eNodeB, as seen in Figure 2, the UEs will need to initiate their uplink transmissions at different times. A UE far from the eNodeB needs to start transmission earlier than a UE that is close to the eNodeB. This can be handled by time advance (TA) of the uplink transmissions, for example, whereby a UE starts its uplink transmission before a nominal time given by a timing reference. This concept is illustrated in Figure 3.

The uplink timing advance is maintained by the eNodeB through timing advance commands transmitted to a UE, based on measurements of uplink transmissions from that UE. Through timing advance commands, the UE is ordered to start its uplink transmissions earlier or later than a current uplink transmission timing.

There are strict relationships between downlink transmissions and the corresponding uplink transmission. Examples of these are: the timing between a Downlink Shared Channel (DL-SCH) transmission on PDSCH to the corresponding hybrid automatic-repeat request (HARQ) ACK/NACK feedback transmitted on the uplink, either on the Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH);

the timing between an uplink grant transmission on PDCCH to the corresponding uplink shared channel (UL-SCH) transmission by the UE on PUSCH.

By increasing the timing advance value for a UE, the UE processing time between the downlink transmission and the corresponding uplink transmission decreases. For this reason, an upper limit on the maximum timing advance has been defined by 3GPP, to provide a lower limit on the processing time available for a UE. For LTE, the maximum timing advance value has been set to roughly 667 microseconds, which corresponds to a cell range of roughly 100 kilometers. (Note that the timing advance value compensates for the round- trip delay.)

In LTE Release 10 there is only a single timing advance (TA) value per UE, and all uplink cells are assumed to have the same transmission timing. The timing reference point for the TA is the receive timing of the primary DL cell. In LTE Release 1 1 , however, support for multiple TA values was introduced, whereby one UE may have different TA values for different cells. One reason for the introduction of multiple TA values is to allow a UE to support UL transmission to multiple UL reception points. Since a UE will generally have different round trip delays to different physical nodes, the UE will generally need different TA values to these different physical nodes. A UE might also need different TA values for uplink transmissions to cells in different bands. According to current assumptions in 3GPP, the eNB may group together those serving cells of a UE for which the same TA value may be used, in a so-called timing advance group (TAG). A timing advance group (TAG) might also be referred to as a "time advance group" or "timing alignment group"; these terms refer to exactly the same thing, and are used interchangeably herein. TA grouping is signaled by the network using RRC signaling. TA grouping can be done depending on deployment, for example, where uplink serving cells terminated at the same physical node are grouped in to the same TA group.

Serving cells in the same TA group share a TA value and the downlink of one serving cell in the TA group is used as timing reference. For each TA value there is an associated timer called TA timer. The UE considers the serving cell in a TA group in-synch, i.e,. time aligned, while the TA timer associated with that TA groups TA value is running. If a serving cell is considered time aligned by the UE, then the UE is allowed to perform PUCCH, PUSCH and sounding reference signal (SRS) transmissions on that serving cell. A TA timer is started or restarted upon each reception of a TA command addressed to the associated TA group. TA commands are discussed further, below.

In LTE, as in any communication system, a mobile terminal may need to contact the network (via the eNodeB) without yet having a dedicated resource in the uplink (from UE to base station). To handle this, a random access procedure is available, whereby a UE that does not have a dedicated uplink resource may transmit a signal to the base station. The first message (MSG1 or preamble) of this procedure is typically transmitted on a special resource reserved for random access, a physical random access channel (PRACH). This channel can, for instance, be limited in time and/or frequency (as in LTE). Figure 4 illustrates an example of how uplink resources may be reserved for random-access-preamble

transmission. The resources available for PRACH transmission are identified to mobile terminals as part of the broadcasted system information (or as part of dedicated RRC signaling in some cases, such as in the case of a handover).

In LTE, the random access procedure can be used for a number of different reasons. Among these reasons are:

initial access, for UEs in the LTEJDLE or LTE DETACHED states;

an incoming handover;

resynchronization of the uplink;

a scheduling request, for a UE that is not allocated any other resource for contacting the base station; and

positioning.

The contention-based random access procedure used in LTE is illustrated in Figure 5. The UE starts the random access procedure by randomly selecting one of the preambles available for contention-based random access. The UE then transmits the selected random access preamble on the physical random access channel (PRACH) to the eNodeB in the Radio Access Network (RAN).

The RAN acknowledges any preamble it detects by transmitting a random access response (MSG2), which includes an initial grant to be used on the uplink shared channel, a temporary Cell Radio Network Temporary Identification (C-RNTI) for the UE, and a time advance (TA) update. The TA update is based on the timing offset of the preamble measured by the eNodeB on the PRACH. The MSG2 is transmitted in the downlink to the UE and its corresponding PDCCH message cyclic redundancy check (CRC) is scrambled with a Random Access Radio Network Temporary Identifier (RA-RNTI). After receiving the random access response (MSG2), the UE uses the grant to transmit a message (MSG3) back to the RAN. The MSG3 is used, in part, to trigger the establishment of radio resource control (RRC) and in part to uniquely identify the UE on the common channels of the cell. The timing advance command that was provided to the UE in the random access response is applied in the UL transmission in MSG3. The eNB can change the resources blocks that are assigned for a MSG3 transmission by sending a UL grant having its CRC scrambled with a Temporary Cell Radio Network Temporary Identifier (TC- RNTI).

The procedure ends with the RAN solving any preamble contention that may have occurred for the case that multiple UEs transmitted the same preamble at the same time. This can occur, since each UE randomly selects when to transmit and which preamble to use. If multiple UEs select the same preamble for the transmission at the same time on the

Random Access Channel (RACH), there will be contention between these UEs. The RAN resolves this contention using the contention resolution message (MSG4). MSG4, which is sent by the eNodeB for contention resolution, has its PDCCH Cyclic Redundancy Check (CRC) scrambled with the C-RNTI if the UE previously has a C-RNTI assigned. If the UE does not have a C-RNTI previously assigned has its PDCCH CRC is scrambled with the TC- RNTI.

A case when contention occurs is illustrated in Figure 6, where two UEs transmit the same preamble, p₅, at the same time. A third UE also transmits at the same RACH, but since it transmits with a different preamble, p there is no contention between this UE and the other two UEs.

The UE can also perform non-contention-based random access. A non-contention-based random access or contention-free random access can be initiated by the eNB, for example, to get the UE to achieve synchronization in the uplink. The eNB initiates a non-contention- based random access either by sending a PDCCH order or indicating it in an RRC message. The latter of these two approaches is used in the case of a handover.

In LTE in Rel-10, the random access procedure is limited to the primary cell only. This means that the UE can only send a preamble on the primary cell. Furthermore, MSG2 and MSG3 are received and transmitted only on the primary cell. However, MSG4 can be transmitted on any downlink cell, in Rel-10.

In LTE Rel-1 1 , the current assumption is that the random access procedure will be supported also on secondary cells, at least for the UEs supporting Rel-1 1 carrier aggregation. So far, it is assumed that only network-initiated random access will be performed on SCells.

TA values are used by the UE to offset the UL transmission timing relative to a reference. The current assumption in 3GPP is that the downlink reception timing of a serving cell is used by the UE as the timing reference, and the uplink transmission timing will be offset relative to the downlink reception timing of that serving cell, which is referred to as the timing reference cell. At preamble transmission, the UE uses a TA value of zero, and the preamble will therefore be transmitted at the time of downlink reception of the timing reference cell. When the eNB receives the preamble, it measures the time misalignment of the received preamble, relative to a desired uplink reception timing on the cell on which the preamble was transmitted. Based on this measured misalignment, the eNB creates an initial TA command, which is sent to the UE in the random access response message (MSG2). When the UE receives this TA command, it will apply the indicated TA value to the TA group that includes the cell on which the preamble transmission was performed. The TA value tells the UE how much to advance the uplink transmission in subsequent uplink transmissions on the cells belonging to that TA group.

Because a UE can move, the round trip time to the uplink reception points can change and the TA values might then become inaccurate. Therefore, when receiving uplink

transmissions from a UE on a cell, the eNB measures the time misalignment of the uplink signals from that UE on that cell. If measured time misalignment of the uplink signals from that UE on a cell is judged by the eNB to be too large, the eNB can create a TA command message containing a delta update to the TA value used by that UE. The UE will, when receiving such a TA command, increase or decrease the TA value according to the delta update. The initial TA command is an 1 1 -bit value, and is sent in the random access response message. An initial TA command tells the UE how much the addressed TA value should be advanced. The addressed TA value is the TA value that is associated with the TA group to which the cell where the preamble was sent belongs. In other words, if a UE performs random access on a cell belonging to TA group x, then the TA value associated with TA group x is the TA value addressed by the initial TA command.

Subsequent TA commands are 6-bit values and are sent in TA command MAC Control Elements (CEs). These TA command MAC CEs also contain, aside from the TA command itself, a TA group identity. The TA value associated with the identified TA group is the TA value by the TA command MAC CE. A TA command tells the UE how much the TA value should be advanced.

It has been agreed in 3GPP that, for the serving cells in the same TA group as the PCell, the downlink reception timing of the PCell should be the timing reference. For serving cells in a TA group not containing the PCell, the downlink reception timing of a serving cell selected by the UE should be used as timing reference.

When receiving a TA command, whether it is an initial or subsequent TA command, the UE will apply the TA command and start an associated TA timer. The UE will consider the serving cells belonging to a TA group as uplink (UL) in-synch, i.e., UL time-aligned, as long as the associated TA timer is running. While the UE considering a cell to be UL time-aligned, normal UL transmissions are allowed. When a cell is not considered to be UL time-aligned, only Physical Random Access Channel (PRACH) transmissions are allowed.

In addition to the TA-based adjustment of the uplink transmit timing, there is also a predefined requirement on the UE to autonomously adjust its uplink timing in response to drifts in the eNodeB transmit timing. More specifically, the UE is required to follow changes in the frame transmit timing of the serving cell and to correspondingly adjust its transmit timing for each transmission. The UE typically uses one or more reference signals to track the downlink timing of the serving cell, e.g., a common reference signal, synchronization signals, etc. The serving cell timing may change due to any of several different reasons, such as variations in radio conditions, imperfection in clocks, maintenance activities in the network, deliberate attempts by the network to change timing, etc. In addition to tracking these changes in eNB timing, it is also required that the UE change its timing (increase or decrease) at no more than a certain rate. This is to make sure that the UE does not change the timing too fast. This requirement stems from the fact that if the UE changes its timing in the order of several microseconds from one subframe to another, the base station receiver may not be able to cope with the received signals. This would result in degraded

demodulation of the signals transmitted by the UE.

The current specification, 3GPP TS 36.300 Annex J, v. 12.1 .0 (March 2014), states that a UE should cope with a relative propagation delay difference of up to 30 microseconds among the component carriers to be aggregated in inter-band non-contiguous CA. This requirement pertains to the downlink. The UE is also required to support a certain maximum uplink transmission time difference between signals transmitted on its uplink PCell and uplink SCell; this is approximately 32.5 microseconds. This is also the maximum transmission timing difference between TAGs, e.g., between a primary TAG (pTAG) and a secondary TAG (sTAG) or between any two sTAGs.

Radio link failure is a procedure defined in LTE whereby the UE determines that the current radio link is no longer usable and therefore tries to reestablish a connection to the network.

Radio Link Failure (RLF) is triggered by any of the following events:

Poor radio quality: The UE will monitor the radio quality of the link and if the quality falls below a threshold for a certain time then the terminal will trigger RLF.

Random Access Failure: The terminal will trigger RLF if too many unsuccessful random access procedure attempts have been done.

RLF retransmissions: In the Radio Link Control (RLC) layer the terminal will count the number of retransmissions; if this exceeds a certain threshold then the terminal will trigger RLF.

When RLF is triggered the terminal will, among other things, try to reestablish its connection to the network by sending an RRC Connection Re-Establishment.

The rapid development of new features, like those discussed above, means that a diversity of UEs, with varying capabilities and support for particular features, are likely to be simultaneously present in an advanced network. Techniques to address this diversity of capabilities are needed.

SUMMARY

A mobile terminal may be limited with respect to how much of an uplink (UL) transmission timing difference between two or more aggregated carriers or groups of aggregated carriers it can support. However, there is no mechanism in the LTE specifications to prevent this limitation from being exceeded.

The techniques disclosed herein include methods for avoiding the situation in which a mobile terminal's capability for uplink (UL) transmission timing difference (T diff) between uplink serving cells is exceeded.

In one group of embodiments of these techniques, a mobile terminal-based mechanism is provided. In this case the terminal:

determines whether the UL transmission timing difference (T diff) between uplink serving cells exceeds a predetermined threshold (e.g., 32.5 με); when T diff exceeds the threshold, the terminal takes one or more actions to solve the problem, e.g., deactivating or deconfiguring one or more serving cells, triggering RLF, stopping a TA timer associated with a serving cell, inhibiting uplink transmission for that serving cell, etc.

In another group of embodiments, the same actions are taken by a network node, such as a base station, for a given UE.

According to a first aspect of the inventive techniques and apparatus disclosed herein, a method in a mobile terminal adapted for aggregating carriers in a wireless communication network comprises determining that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold and, in response to said determining, taking an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions. According to another aspect, a mobile apparatus adapted to aggregate carriers in a wireless network is further adapted to carry out the method of the first aspect above, i.e., to determine that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold, and to take an action with respect to at least one uplink carrier, in response to said determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

According to another aspect, a method in a network node of handling a mobile terminal adapted to aggregate carriers in a wireless communications network comprises determining that a difference in uplink transmit timing for the mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold and, in response to said determining, taking an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

According to still another aspect, a network node for use in a wireless communications network supporting aggregation of carriers is further adapted to carry out the method summarized immediately above, i.e., to determine that a difference in uplink transmit timing for a mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold, and to take an action with respect to at least one uplink carrier, in response to said determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

According to yet another aspect, a mobile terminal apparatus adapted to aggregate carriers in a wireless communication network. The mobile terminal apparatus comprising a radio transceiver circuit configured to communicate with one or more base stations and a processing circuit configured to process the signals transmitted and received by the radio transceiver circuit. The processing circuit is further configured to determine that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold and take an action with respect to at least one uplink carrier, in response to said determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

According to a further aspect, a network node apparatus adapted for use in a wireless communication network supporting aggregation of carriers. The network node apparatus comprising a processing circuit configured to determine that a difference in uplink transmit timing for a mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold and in response to said determining, take an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

Variants of the embodiments summarized above are described in detail below, as are various apparatuses configured to carry out one or more of the methods described herein.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 illustrates the general concept of carrier aggregation. Figure 2 illustrates a cell serving two UEs, at different distances from the serving eNodeB.

Figure 3 illustrates how timing advance of UL transmissions depends on distance to the eNodeB.

Figure 4 illustrates the allocation of specific time-frequency resources to transmissions of random-access preambles. Figure 5 is a signal flow diagram illustrating signaling for a contention-based random access procedure in LTE. Figure 6 illustrates a scenario involving contention-based access between UEs.

Figure 7 is a process flow diagram illustrating an example method according to the presently disclosed techniques.

Figure 8 is another process flow diagram, illustrating an example method as carried out by a mobile terminal.

Figure 9 is a process flow diagram illustrating an example method as carried out by a base station or other network node.

Figure 10 is a block diagram illustrating components of an example mobile terminal. Figure 1 1 is a block diagram illustrating components of an example network node. Figure 12 is another block diagram, illustrating components of an example base station. Figure 13 illustrates another view of an example mobile terminal. Figure 14 provides another view of an example base station.

DETAILED DESCRIPTION

The 3GPP specification 3GPP TS 36.300 Annex J, v. 12.1 .0 (March 2014), specifies how much propagation delay difference between aggregated cells a UE should support. Although a UE is permitted to support a larger propagation delay difference, this value provides the UE industry with an upper bound, which can be used to determine the amount of buffer memory that is required. This is an important characteristic, in order to keep down the complexity and cost of consumer-oriented UEs. However, the 3GPP standards do not specify the UE actions that should be taken in the event this maximum propagation delay difference is exceeded. This may result in error situations with, for example, erroneous uplink transmission timings as a result, which will lead to interference in the system.

For the sake of readability and clarity, some terms that will be used throughout this document are defined below: T diff - This value represents an uplink transmission timing difference between uplink transmissions of signals in the uplink cells for a terminal. If the terminal is configured with two uplink serving cells, e.g., a PCell and an SCell, then the uplink transmission timing difference T diff is between the timings of the uplink signals in these two serving cells. In the case of more than two uplink serving cells, the uplink transmission timing difference T diff is derived based on a rule or a function, e.g., a maximum of all differences, a mean of all differences, etc. For example, if the terminal is configured with three serving cells (or groups of cells, e.g., TAGs) to which the terminal sends uplink transmissions, the terminal would send uplink

transmissions to Cell A at time T_A, to Cell B at time T_B and to Cell C at time T_c. T diff may then be computed as the largest distance in time between these UL

transmission times, i.e., max(T_A, T_B, T_c) - min(T_A, T_B, T_c).

T_diff_max - This value is the maximum T diff supported by the terminal. As explained earlier, this value is in LTE must be at least roughly 30.25 microseconds. In other words, a UE shall be able to transmit uplink transmissions that are separated in time by up to 30.25 microseconds. However, a terminal may support larger time differences.

Terminal: In the present document, the terms "terminal," "mobile," "mobile terminal," "wireless terminal," and the like are used. These terms refer to any type of wireless device capable of communicating with a wireless network node and/or with another terminal over radio signals. A terminal may also be referred to here and in other contexts as user equipment (UE), a wireless device, a radio communication device, and/or a target device, and may refer to a device-to-device (D2D) UE, a machine- type UE or UE capable of machine-to-machine communication (M2M), a sensor equipped with UE, a wireless-equipped iPAD or tablet, a smart phone, a laptop embedded equipped (LEE), laptop mounted equipment (LME), a wireless USB dongle,a Customer Premises Equipment (CPE), etc.

Network node: The generic terminology "radio network node" or simply "network node (NW node)" may be used to describe some of the embodiments detailed herein. A network node may typically be a node serving and/or configuring a wireless terminal with one or more parameters and/or procedures. It can be any kind of network node, including a base station, radio base station, base transceiver station, base station controller, network controller, evolved Node B (eNB), Node B, relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH), or even core network node, etc. The network node described herein may in some cases comprise two (or even more) physical nodes acting in concert. The mechanisms described herein can be used to avoid that a terminal's maximum supported uplink transmission difference between cells is exceeded, i.e., to avoid that T diff exceeds T_diff_max. In some of the disclosed embodiments, this is achieved by the terminal detecting that applying an adjustment in uplink transmission timing for one or more cells would result in that T_diff_max is exceeded (or T diff is close to T_diff_max by a threshold), and then taking one or more actions to avoid such that T_diff_max is not exceeded.

Alternatively the terminal will, after an adjustment in uplink transmission timing has been performed, determine whether T diff exceeds T_diff_max (or T diff is close to T_diff_max by a threshold) and then take the one or more actions as described herein. The value of T_diff_max supported by a particular UE may be a pre-defined value, e.g., as specified in a standard, or as indicated by the UE to a network node as part of a UE capability message. The T diff at the UE may exceed a threshold (T_diff_max) due to one or several reasons, e.g., due to applying different values of TA values on different serving cells, autonomous adjustment of UL transmit timing, internal drift in the UE transmit timing due to imperfections in the clocks etc.

In some embodiments, the terminal will deactivate or deconfigure one or more serving cells such that UL transmissions are not sent too far apart in time. The serving cell can be a PCell or SCell and it may belong to a pTAG or sTAG. The PCell and SCell(s) may be served or managed by the same or different network nodes, as follows:

in one example, the PCell and SCell may be served by the same eNodeB;

in another example, the PCell and SCell may be served by different eNodeBs:

in yet another example, the PCell and SCell may be served by an eNodeB and a remote radio head (RRH) respectively;

in yet another example, the PCell and one SCell may be served by an eNodeB while one or more remaining SCells may be served by a RRH or another eNodeB.

In some embodiments the terminal will stop one or more time alignment timers, which will have the result that the terminal will not perform UL transmissions to the cells associated with the stopped timers.

In some embodiments a network node may determine the uplink transmission timing difference and if it exceeds a threshold then it takes an action, e.g., deactivating or de- configuring one or more serving cells.

The terminal may also consider the experienced quality for serving cells when deciding whether to deactivate cells or stop TA timers. For example, if the terminal has identified that T diff exceeds T_diff_max, or that that T diff is close to T_diff_max by a threshold and it therefore plans to deactivate a cell, the terminal, in some embodiments then considers whether the experienced quality is good or bad (e.g., by comparing a quality metric such as CQI to a threshold). If the quality becomes or already is bad, then the terminal deactivates the cell, otherwise the terminal refrains from deactivating the cell.

One example implementation of these techniques is that a UE configured with pTAG and sTAG shall stop transmitting on the SCell if the uplink transmission timing difference between PCell and SCell exceeds the maximum value the UE can handle. This approach can be specified in the 3GPP specifications for LTE, for example, in 3GPP TS 36.133. It is possible, of course, that a terminal takes more than one action. Thus, for example, the terminal may both deactivate a serving cell and stop timers.

In some embodiments, the terminal deactivates and/or deconfigures one or more cells to avoid that UL transmissions are sent with a T diff larger than T_diff_max.

To avoid a situation where UL transmissions are transmitted with a larger time difference than T_diff_max, it is not necessary to deactivate and/or deconfigure serving cells that do not have any configured uplink. Hence, the terminal may only perform deactivation and/or deconfiguration of the serving cells with a configured uplink, in some embodiments. Even though not supported by current LTE specification, if deactivation is possible for only the uplink part of a serving cell, then the terminal may deactivate the uplink part while leaving the activation status of the downlink part of a serving cell unchanged.

Since the cells in LTE are grouped together in TA groups, where all cells in a TA group share the UL transmission timing, the terminal needs to deactivate and/or deconfigure all cells in a TA group to reduce T diff. If the terminal has detected that the UL transmissions in a TA group A and TA group B are too far apart in time (i.e., exceeding T_diff_max) then the terminal would either deactivate and/or deconfigure all serving cells in TA group A or all cells in TA group B, or both. How the selection of TA group(s) is done is explained below.

Whether reporting of autonomous deactivation should be done or not could also be determined based on a predefined rule, such as a rule in a specification.

When the terminal deactivates a serving cell it may be modelled in the terminal as stopping a deactivation timer, or expiring the deactivation timer. For example, in LTE the terminal maintains an sCellDeactivationTimer, which can be used for this purpose. Upon expiry of this timer, the terminal will deactivate the associated the serving cell and perform certain actions.

In the event that a UE is adapted and/or configured by the network to report or indicate that the UE has deactivated or deconfigured the UL SCell due to transmit time difference between TAGs exceed the threshold, the UE sends this information (explicit message or indication) to the network node via lower layer or higher layer signaling message on a suitable channel. Examples of lower and higher layer signaling messages are MAC commands and RRC messages, respectively. These are examples of an explicit indication, which may also include an identity of the uplink SCell or sTAG that the UE has deactivated and/or de-configured.

The network node uses this received message (i.e., an explicit indication of deactivation or deconfiguration) to determine that the UE has stopped transmission on certain UL SCell. The network node may, in response, take a particular action. Examples of actions are: stop scheduling the UE (uplink scheduling) on that uplink SCell, configure the UE with another uplink SCell that can ensure that the transmit time difference between TAGs remains below the threshold, etc. The UE may also indicate to the network node that it has reactivated or reconfigured autonomously the previously deactivated and/or deconfigured UL SCell (see discussion of reactivation and reconfiguration, below).

As an example, the UE may send one bit of information via a MAC command. An example of such a command might take on values ofO or 1 , meaning that the UE has deactivated an uplink SCell or activated an uplink SCell, respectively. The information may also include additional information such as an identifier of the uplink SCell, e.g., a cell ID, a temporarily assigned ID (e.g., ID = 0 for first uplink SCell and ID= 1 for second uplink SCell if UE is configured with two uplink SCells). In some embodiments, a bitmap is sent, where each bit in the bitmap corresponds to a serving cell and the terminal sets the bit corresponding to a cell to 1 (or 0) if the cell has been deactivated and/or deconfigured and to 0 (or 1 ) if the cell has not been deactivated and/or deconfigured.

According to some embodiments, a terminal may autonomously reactivate a cell which it has earlier deactivated. The same mechanisms can also be applied to reconfigure a cell which the terminal has autonomously deconfigured. In the examples described below, however, it will be used as an example that the UE reactivates a cell. If the terminal has autonomously deactivated a serving cell, the terminal may be configured to re-activate the serving cell given fulfillment of one or more conditions. Example conditions include:

T diff no longer exceeds T_diff_max.

the time since the deactivation does not exceed a time T.

an uplink signal quality of uplink signal transmitted by the UE is above a threshold, e.g., as indicated by HARQ feedback received in the downlink.

an explicit indication to reactivate one or more serving cells previously deactivated by the UE is received from the network.

Upon reactivation of cells, the terminal may activate only those serving cells in the TA group that were autonomously deactivated by the terminal, in some embodiments. This would ensure that the terminal would only reactivate serving cells that the network has intended to be activated. For example, assume that in a TA group there are two serving cells, Cell A and Cell B, where initially Cell A was activated and Cell B was deactivated. If the terminal deactivated Cell A according to the techniques described above, then the terminal may, upon reactivation, only reactivate Cell A, but not Cell B, since the latter was not activated initially. This will ensure that the terminal is not autonomously activating cells which the network did not intend to be activated. On the other hand, the terminal may be allowed to, based on some criteria, to also reactivate other cells in the TA group. For instance, in the example explained above, the terminal may be allowed to activate Cell B upon reactivation of Cell A. This would allow for faster activation of serving cells and hence improved user experience (e.g., a higher user bit rate) and system performance (e.g., higher uplink throughput, lower UL interference, etc.).

Another possibility to avoid that UL transmissions with a timing difference exceeding T_diff_max is that the terminal stops (or, equivalent^, expires/considers expired) time alignment (TA) timers. If the time alignment timer is not running, the terminal is not allowed to transmit uplink signals (except in some cases a Random Access preamble) in the associated serving cells.

Whether the terminal should stop the TA timer upon detection of T diff exceeding of T_diff_max may be configured by the network, in some embodiments, or it may be a pre- defined behavior. In some parts of the current LTE specifications, stopping a timer and expiring a timer trigger different actions. It should be noted that stopping of timers is only used as an example and the methods herein can also be applied to expire TA timers.

One benefit of stopping the TA timer to avoid uplink transmissions with a too large transmission timing difference, is that stopping TA timers only affects the uplink

transmissions, i.e., downlink reception is still possible. This means that, if not made impossible due to other reasons, the terminal could continue reception in downlink and hence the downlink performance could potentially be maintained, even though the uplink transmissions will be halted in the serving cells for which a TA timer has been stopped. The UE may also resume the TA timer if it is expected or estimated by the UE that the uplink timing difference between uplink transmissions to the serving cells falls below or becomes equal to T diff _max. When the TA timer starts running again, the terminal is allowed to transmit uplink signals in the associated serving cells. When resuming the TA timer, it may be started from the timer value which it had when it was stopped. Alternatively the timer could be resumed and started from a preconfigured value, such as the TA timer value configured by the network.

If the terminal should stop a TA timer and/or deactivate and/or deconfigure cells in a TA group, it may be the case that there are multiple TA groups to select from. Below are provided some examples for how this selection can be done. It should be noted that it would be possible to select more than one TA group. For example, if the UL transmission timings in two TA groups are too far apart, the terminal may deactivate and/or deconfigure and/or stop the associated TA timers of both TA groups.

In some embodiments, a network node (e.g., a serving network node) may provide information to the terminal for use in selecting which TA group's TA timer to stop in the event that a TA timer needs to be stopped, or which TA group's serving cells to deactivate in the event that serving cell deactivation should be done by the terminal.

In some embodiments, the network node provides indicators for each of one or more TA groups, which indicate whether or not their TA timers can be stopped according to the techniques described herein, and indicators (which may be the same indicators or a different indicators) that indicate whether or not the cells in that TA group can be deactivated as described herein. In other embodiments, the network node (e.g., a serving network node) provides priorities associated with the TA groups, where this priority dictates in which order the terminal should select TA groups. For instance, in some embodiments, the TA group with the highest indicated priority value should be selected. The UE then selects the TA group according to their associated priorities indicated by the network node and takes an action for the selected TA group, e.g., deactivating and/or deconfiguring serving cell(s) in that TA group. For example, the network node may indicate priority 1 for TA group A, and priority 7 to a TA group B and priority 3 to a TA group C. The terminal would then, in case TA group B or TA group C should be selected, select TA group B. In some embodiments, the network may indicate that a terminal should select a TA group based on performance metrics associated with the cells in that TA group. For example, the network may direct the terminal to select the TA group in which cells of poor signal quality and/or signal strength are present. Such cells would in general not provide good

performance compared to cells with good signal quality and or strength. The terminal may select a TA group based on pre-defined rules. Some TA groups may be considered more important than others and therefore these TA groups may not be selected for TA timer stopping or cell deactivation. For example, the TA group containing the PCell is usually considered more important than other TA groups since important control signaling is carried over the PCell and hence this TA group may never be selected over another TA group, in some embodiments.

According to another rule, a terminal selects the TA groups based on the TA groups' indices and may, for example, select the TA group with the highest, or lowest, index, or the TA group with the lowest index aside from the TA group containing the PCell.

It is also possible that the terminal selects a TA group based on performance metrics associated with the serving cells in that TA group. For example, the terminal may select the TA group in which serving cells of poor signal quality and/or signal strength are present. Such serving cells would in general not provide good performance compared to serving cells with good signal quality and or strength. One example metric which could be used for this is CQI, which is used to determine the radio conditions in a serving cell. In some embodiments, the terminal randomly selects a TA group to stop.

It may be important for the network node to know the activation/configuration status of a terminal's serving cells and the status of the UE's TA timers. Some of the techniques described above allow the terminal to autonomously deactivate and/or deconfigure cells and/or to stop TA timers before their usual expiration time, i.e., before the network node would expect such timers to stop or expire. Any of several mechanisms can be used, in some embodiments, to allow the network node to be aware of the activation/configuration status of serving cells as well as the status of the UE's TA timers. One possibility is that the terminal reports to the network node in the event that it has deactivated or de-configured serving cell(s), or stopped a TA timer. The indication could be separate for each of these actions, which would be beneficial if the terminal supports more than one of these actions. The network may need to perform different tasks in response to these different actions. The indication can be a pre-defined signal such as a pre-defined CSI value for the deactivated SCell (e.g., CQI index = 0). The indication can also be a predefined pattern such as pre-defined CSI values for the deactivated SCell (e.g., CQI index = 0, 1 , 0,1 ).

Whether or not the terminal should report to the network node in the event that it has autonomously deactivated a serving cell and/or report to the network node in the event that it has stopped a TA timer as described herein could be configured by the network node. The network node may use an RRC message to indicate whether this should be done, for example, such as the RRC message used for configuring of the cell, or an RRC message used for configuring TA groups.

In some embodiments, the network uses a MAC message to indicate whether the terminal should report to the network node in the event that it deactivates a serving cell and/or whether the terminal should report to the network node in the event that it has stopped a TA timer. On possible MAC message to use for this is the activation/deactivation MAC control element, or it may be a new MAC message.

In some embodiments of the presently disclosed techniques, the terminal triggers Radio Link Failure (which sometimes is referred to as declaring RLF) to avoid that UL transmissions are sent with a T diff larger than T_diff_max. This could be implemented by adding a new trigger for RLF.

Upon reestablishment to the network after RLF, the terminal may indicate to the network that RLF was triggered due to T diff exceeding T_diff_max. This information could be valuable for the operator, such that the operator could reconfigure its network to avoid that T diff would exceed T diff max. Whether the terminal should trigger/declare RLF to avoid that UL transmissions are sent with a T diff larger than T_diff_max may be configured by the network, or it may be a pre-defined behavior for the terminal.

In some embodiments, the terminal indicates to the network that a handover should be done to avoid that UL transmissions are sent with a T diff larger than T_diff_max. Whether the terminal should indicate to the network that a handover should be done may be configured by the network or it may be a pre-defined.

It has so far been assumed that T_diff_max is a static or pre-defined value specified in a specification, e.g., in LTE it is specified to be roughly 30.25 microseconds. However, in some embodiments, T_diff_max for a UE may be configured by the network node. A larger value of T_diff_max may cause degradation in the uplink reception quality of the uplink signals received from the UE. Therefore, in some embodiments the network node (e.g., a serving eNodeB, RRH, etc.) may select or determine a value of the T_diff_max based on one or more of the following criteria:

1 . an amount of degradation in the UL signal quality that the network node can tolerate.

2. a type of uplink receiver type, e.g., whether or not the receiver in a serving cell is capable of mitigating interference caused by other UEs in neighbor cells.

3. a robustness level of the uplink receiver, e.g., to what extent the receiver can receive and resolve multi-path.

4. the radio environment, e.g., whether the radio environment is dispersive or not and level of dispersion or multipath delays, etc.

5. an amount and/or frequency of the drift in downlink transmission timing of downlink signals that are received or which are expected to be received by the UE.

6. UE capability in terms of maximum supported T_diff_max_.(described

below).

7. UE-reported uplink time difference between uplink signals on uplink serving cells, T_diff.

For example, if the network node has an interference mitigation receiver and the radio environment is non-dispersive or mildly dispersive (e.g., a delay spread < 0.5 με), then the network node may select a larger value of T_diff_max, e.g., 35 microseconds or more. Similarly if the drift in downlink transmit timing is more frequent or larger (e.g., each drift is 2 microseconds or more), then the network node may select a larger value of T_diff_max. This is because the autonomous adjustment by the UE is based on downlink changes in timing, and a larger drift in downlink timing will lead to a larger difference in uplink timing at the UE.

The network node, when configuring the UE with a configurable T_diff_max, may also take into account the capability of the UE in terms of its supported T_diff_max_. For example, different UEs may support different values that are larger than the pre-defined value of 32.5 microseconds. Some UEs may not support a value larger than pre-defined value of 32.5 microseconds. Therefore, the network node may receive the UE capability in terms of T_diff_max and use it in addition to other criteria (e.g., as listed above) for selecting the most appropriate value of the T_diff_max for that UE. For example, the T_diff_max should not exceed the T_diff_max value supported by the UE according to its indicated capability.

The UE may also report the actual value of uplink time difference between uplink signals transmitted in uplink serving cells (T diff). The network node may also take into account the actual value of T diff as a criterion for selecting the T_diff_max value. For example, if the current value is large (e.g., 30 microseconds), then the network node may select a

T_diff_max larger (e.g., 33 microseconds) than this value. This is because it may be expected that the actual value may exceed the maximum pre-defined limit.

After selecting the T_diff_max value based on one or more criteria, the network node may configure the UE to use the indicated value for one or more operations as described in preceding sections. In some embodiments, the network node deactivates or de-configures one or more serving cells of the UE based on the maximum uplink time difference (T diff) at the UE (i.e., the transmission timing difference between TAGs) and one or more criteria as described below.

The network node, in some of these embodiments, performs the following steps:

determines the current value of the maximum UL time difference at the UE (T diff) i.e., the transmission timing difference between TAGs and compare it with a threshold (Γ). The network node is aware of TA values so it can determine the TA difference between the TAGs;

if the T diff exceeds the threshold (Γ), then the network node evaluates one or more of the criteria 1 -7 listed in the preceding section above.

deactivates or deconfigures one or more serving cells based on the above evaluations, e.g., o if the network node does not have a robust receiver and/or radio

environment is more dispersive (e.g., delay spread is more than 1 microsecond) then the network node may deactivate at least one SCell.

All UEs may not be capable of performing autonomous deactivation of UL SCell when the transmit difference between TAGs exceed the threshold. Similarly, all UEs may not be capable of reporting or indicating to the network the reason of autonomous deactivation (or reactivation) of the UL SCell (i.e., when transmit difference between TAGs exceeds the threshold). Therefore, according to some embodiments the UE signals capability information associated with the embodiments disclosed in preceding sections to the network node (e.g., eNB, MME, core network node, base station, etc.).

For example, the UE may indicate that it is capable of autonomous activation, deactivation, configuration, de-configuration of uplink SCell, according to one or more of the techniques described above, but that it cannot indicate this explicitly to the network node.

In another example the UE may indicate that it is capable of autonomous activation, deactivation, configuration, de-configuration of uplink SCell and it is also capable of explicitly indicating to the network node when any of this occurs.

The UE may also indicate the above capability for all types of carrier aggregation or for a certain specific type of carrier aggregation that the UE supports, e.g., intra-band contiguous, inter-band carrier aggregation, etc. The UE may signal this capability to the network node via RRC signaling, for example. This may be done when requested by the network node, in some embodiments, or autonomously, such as during the initial setup.

The acquired capability information may be used by the receiving network node for taking one or more radio operation tasks or radio resource management actions. Examples of radio operation tasks are:

a decision whether to configure the UE with one or more UL SCells or not;

a decision regarding whether to autonomously detect that the UE has deactivated or de-configured the UL SCell due to a maximum time difference between TAGs exceeding a threshold;

forwarding the received UE capability information to another network node which may use it after cell change of the UE e.g. from serving eNodeB to neighboring eNodeB over X2, from core network node (e.g., MME) to eNodeB, etc.; the network node may store the received capability information and use it in future, e.g., when the same UE is configured with one or more UL SCells.

Embodiments of the techniques and apparatus disclosed herein include methods for handling timing advance, in a mobile terminal or in a network node. One example method, suitable for implementation in a UE or other wireless device that is adapted for carrier aggregation operation in a wireless network, is illustrated in Figure 7. As seen in the figure, the illustrated method begins, as shown at block 710, with the UE identifying (i.e., determining) that an autonomous uplink transmission timing modification should be performed. As shown at block 720, the UE then checks to determine whether performing the timing modification would result in T diff being larger or smaller than

T_diff_max. T_diff_max may be a static parameter in the UE, in some embodiments, or a network-configured value, in others.

If T diff is smaller than T_diff_max, the UE should have no problem handling a subsequent uplink transmission, and the method simply repeats. If T diff is larger than T_diff_max, on the other hand, the UE needs to take some action with respect to one or more carriers or carrier groups. In the example shown in Figure 7, the UE selects a TAG, as shown at block 730 (e.g., based on an evaluation of performance, or based on a priority indication provided by the network, or based on a predetermined order of priority), and deactivates the uplink cells in the selected TAG, as shown at block 740. The UE also stops the time alignment timer for the selected TAG, as shown at block 750.

It should be appreciated that other methods consistent with the above-described techniques and the example embodiments listed below are possible. Figure 8, for example, illustrates a generalized method for handling uplink timing alignment, again as implemented in a mobile terminal adapted for carrier aggregation in a wireless communication network.

As shown at block 830, the illustrated method includes the step of determining that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold. In response, the mobile terminal then takes an action with respect to at least one uplink carrier, as shown at block 840, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions. In some embodiments or instances, the action comprises deactivating one or more uplink serving cells. In others, the action comprises de-configuring one or more uplink serving cells. In some of these and in other embodiments or instances, taking an action comprises stopping a time alignment timer for one or more uplink serving cells. Alternatively, the action in some embodiments or instances may comprise considering a time alignment timer for one or more uplink serving cells to be expired.

In some embodiments, the action comprises indicating to the wireless communication network that a handover should be performed. In still others, the action may include triggering a Radio Link Failure.

In some embodiments, the at least one carrier for which action is to be taken is selected based on an evaluation of quality for the at least one carrier. In some embodiments or instances, the action is taken with respect to all of two or more carriers in a timing alignment group. In some embodiments, the method further includes sending, to the wireless communication network, an indication that the action has been taken. This is shown at block 850. In some embodiments, the indication identifies a carrier or carrier group for which the action has been taken. In some embodiments, the method still further includes reversing the action for one or more of the at least one carrier, subsequent to taking the action. This is shown at block 860.

In some embodiments, the method includes, prior to taking the action, receiving, from the wireless communication network, information indicating that one or more carriers are to be prioritized for the action. This is shown at block 810. Similarly, in some embodiments, the mobile terminal receives an indication of the value of the timing difference threshold, as shown at block 820. These blocks are shown with a dashed outline, indicating that they are "optional" in the sense that they don't appear in every embodiment or instance of the illustrated method.

Figure 9 shows an example method as might be implemented in a network node of a wireless communication network. This example method begins, as shown at block 910, with determining that a difference in uplink transmit timing for the mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold. As shown at block 920, the method continues with, in response to the determining shown in block 910, taking an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions. Taking an action may comprise, for instance, deactivating one or more uplink serving cells for the mobile terminal. Likewise, taking an action may comprise de-configuring one or more uplink serving cells for the mobile terminal. In some embodiments, the taking of the action is further based on an evaluation of one or more of: an amount of degradation in the UL signal quality that the network node can tolerate; a type of uplink receiver in the network node; a robustness level of the uplink receiver in the network node; the radio environment; an amount and/or frequency of the drift in downlink transmission timing of downlink signals that are received or that are expected to be received by the mobile terminal; a mobile capability in terms of maximum supported T_diff_max_.; a mobile terminal-reported uplink time difference between uplink signals on uplink serving cells, T diff.

It will be appreciated that the methods shown in Figures 7-9 are illustrative examples only, and that variations of these methods, in accordance with the various techniques detailed above, are possible.

Several of the techniques and methods described herein may be implemented using radio circuitry, electronic data processing circuitry, and other electronic hardware provided in a mobile terminal. Figure 10 illustrates features of an example mobile terminal 1000 according to several embodiments of the present invention. Mobile terminal 1000, which may be a UE configured for operation with an LTE wireless communication network (E-UTRAN), for example, as well as for operation in a device-to-device mode, comprises a radio transceiver circuit 1020 configured to communicate with one or more base stations as well as a processing circuit 1010 configured to process the signals transmitted and received by the radio transceiver circuit 1020. Transceiver circuit 1020 includes a transmitter 1025 coupled to one or more transmit antennas 1028 and receiver 1030 coupled to one or more receiver antennas 1033. The same antenna(s) 1028 and 1033 may be used for both transmission and reception.

Receiver 1030 and transmitter 1025 use known radio processing and signal processing components and techniques, typically according to a particular telecommunications standard such as the 3GPP standards for LTE. Note also that transmitter circuit 1020 may comprise separate radio and/or baseband circuitry for each of two or more different types of radio access network, in some embodiments. The same applies to the antennas - while in some cases one or more antennas may be used for accessing multiple types of networks, in other cases one or more antennas may be specifically adapted to a particular radio access network or networks. Because the various details and engineering tradeoffs associated with the design and implementation of such circuitry are well known and are unnecessary to a full understanding of the invention, additional details are not shown here. Processing circuit 1010 comprises one or more processors 1040 coupled to one or more memory devices 1050 that make up a data storage memory 1055 and a program storage memory 1060. Processor 1040, identified as CPU 1040 in Figure 10, may be a

microprocessor, microcontroller, or digital signal processor, in some embodiments. More generally, processing circuit 1010 may comprise a processor/firmware combination, or specialized digital hardware, or a combination thereof. Memory 1050 may comprise one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. Because terminal 1000 may support multiple radio access networks, including, for example, a wide-area RAN such as LTE as well as a wireless local-area network (WLAN), processing circuit 1010 may include separate processing resources dedicated to one or several radio access technologies, in some embodiments. Again, because the various details and engineering tradeoffs associated with the design of baseband processing circuitry for mobile devices are well known and are unnecessary to a full understanding of the invention, additional details are not shown here.

Typical functions of the processing circuit 1010 include modulation and coding of transmitted signals and the demodulation and decoding of received signals. In several embodiments of the present invention, processing circuit 1010 is adapted, using suitable program code stored in program storage memory 1060, for example, to carry out one of the techniques specifically described herein, and variants thereof. Of course, it will be appreciated that not all of the steps of these techniques are necessarily performed in a single microprocessor or even in a single module.

Mobile terminal 1000 may further include one or more additional interface circuits, depending on the specific application for the unit. Typically, mobile terminal 1070 includes connector interface circuitry 1070. In some embodiments, connector interface circuitry 1070 may consist of no more than electrical terminals and associated hardware to support charging of an on-board battery (not shown) or to provide direct-current (DC) power to the illustrated circuits. More often, connector interface circuitry 1070 further includes a wired

communication and/or control interface, which may operate according to proprietary signaling and message formats in some embodiments, or according to a standardized interface definition, in others. For example, connector interface 1070 may comprise electrical terminals and associated hardware for support of the well-known Universal Serial Bus (USB) interface. It will be appreciated that while connector interface circuitry 1070 includes at least the necessary receiver and driver circuits to support such an interface and may further comprise specialized hardware/firmware, part of the interface functionality may be provided by CPU 1040, configured with appropriate firmware and/or software in memory 1050, in some embodiments.

Mobile terminal 1000 may further comprise local-area network (LAN) interface circuitry 680, in some embodiments. In some embodiments, for example, LAN interface circuitry 1080 may provide support for wireless LAN (WLAN) functionality, such as according to the well- known Wi-Fi standards. In some such embodiments, LAN interface circuitry 1080 may include an appropriate antenna or antennas. In other embodiments, LAN interface circuitry 1080 may make use of one or more common antenna structures that provide reception and/or transmission of WLAN signals as well as wide-area RAN signals. In some embodiments, LAN interface circuitry 1080 may be relatively self-contained, in that it includes all of the necessary hardware, firmware, and/or software to carry out the LAN functionality, including the associated protocol stacks. In other embodiments, at least parts of the LAN functionality may be carried out by processing circuit 1010.

Still further, mobile terminal 1000 may include user-interface circuitry 1090, which may include, for example, circuitry and/or associated hardware for one or more switches, pushbuttons, keypads, touch screens, and the like, for user input, as well as one or more speakers and/or displays for output. Of course, some mobile terminals, such as those developed for machine-to-machine applications or for insertion into another device (e.g., a laptop computer) may have only a subset of these input/output devices, or none at all. Although the described solutions may be implemented in any appropriate type of telecommunication system supporting any suitable communication standards and using any suitable components, network-based embodiments of the solutions and techniques described above may be implemented in one or more nodes of a radio access network (RAN), such as a base station (eNB) in an LTE network. The network in which these techniques are implemented may further include any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device (such as a landline telephone). Although the illustrated network nodes may represent a network communication device that includes any suitable combination of hardware and/or software, these network nodes may, in particular embodiments, represent a device such as the example network node 1 100 illustrated in greater detail by Figure 1 1 . Similarly, although the illustrated base station nodes (e.g., an eNB) may represent network nodes that include any suitable combination of hardware and/or software, these network nodes may, in particular embodiments, represent devices such as the example network node 1200 illustrated in greater detail by Figure 12. As shown in Figure 1 1 , the example network node 1 100 includes processing circuitry 1 120, a memory 1 130, and network interface circuitry 1 1 10. In particular embodiments, some or all of the functionality described above that is provided by a core network node or a node in a RAN may be provided by the processing circuitry 1 120 executing instructions stored on a computer-readable medium, such as the memory 1 130 shown in Figure 1 1 . Alternative embodiments of the network node 1 100 may include additional components beyond those shown in Figure 1 1 that may be responsible for providing certain aspects of the node's functionality, including any of the functionality described above and/or any functionality necessary to support the solutions described above. As shown in Figure 12, an example base station 1200 includes processing circuitry 1220, a memory 1230, radio circuitry 1210, and at least one antenna. The base station 1200 further includes a network interface circuit 1240, which is configured to provide connectivity to one or more other nodes in the wireless network, such as one or more other radio base stations, one or more core network nodes, a radio network controller, etc. The processing circuitry 1220 may comprise RF circuitry and baseband processing circuitry (not shown). In particular embodiments, some or all of the functionality described above as being provided by a mobile base station, a radio network controller, a base station controller, a relay node, a NodeB, an enhanced NodeB, and/or any other type of mobile communications node may be provided by the processing circuitry 1220 executing instructions stored on a computer-readable medium, such as the memory 1230 shown in Figure 12. Alternative embodiments of the base station 1200 may include additional components responsible for providing additional functionality, including any of the functionality identified above and/or any functionality necessary to support the solution described above.

It will further be appreciated that various aspects of the above-described embodiments can be understood as being carried out by functional "modules" corresponding to the method steps illustrated in Figures 7-9. These functional modules may be program instructions executing on an appropriate processor circuit, hard-coded digital circuitry and/or analog circuitry, or appropriate combinations thereof, e.g., in network nodes and wireless devices having hardware configurations like those shown in Figure 2 and 3. For example, Figure 13 is a block diagram illustrating another view of the example wireless device 1000 shown in Figure 10, but where the processing circuit is illustrated according to this functional view. In Figure 13, processing circuitry 1310 includes a timing determination module 1310 for determining that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold, and also includes an action-taking module 1320 for taking an action with respect to at least one uplink carrier, in response to the determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

Similarly, Figure 14 is a block diagram illustrating another view of the example base station 300 depicted in Figure 12, but where the processing circuit of base station 1200 is illustrated according to a functional view. In Figure 14, a processing circuit 1410 comprises a timing determination module 1410 for determining that a difference in uplink transmit timing for the mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold, and further comprises an action-taking module 1420 for taking an action with respect to at least one uplink carrier, in response to the determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

Advantages of some of the disclosed techniques include:

The maximum UL time difference can be flexibly adjusted based on various criteria, e.g., base station receiver ability to cope with received signals with larger transmit time difference, UE capability in terms of supported maximum uplink timing difference between TAGs, etc.

The base station receiver performance is not degraded, by avoiding unnecessarily large differences in uplink transmission timings between uplink serving cells (e.g., between pTAG and sTAG).

A fast procedure is provided in the UE to autonomously deactivate or de-configure one or more serving cells, to avoid degradation at the base station due to large differences in uplink transmit timings between uplink TAGs. Some aspects of the inventive techniques and apparatus disclosed herein may be summarized by the following example embodiments:

(a) A method of handling uplink timing advance in a mobile terminal adapted for carrier aggregation in a wireless communication network, the method comprising:

determining that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and, in response to said determining, taking an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

(b) The method of embodiment (a), wherein taking an action comprises deactivating one or more uplink serving cells.

(c) The method of embodiment (a), wherein taking an action comprises de-configuring one or more uplink serving cells. (d) The method of any of embodiments (a)-(c), wherein taking an action comprises stopping a time alignment timer for one or more uplink serving cells.

(e) The method of any of embodiments (a)-(c), wherein taking an action comprises considering a time alignment timer for one or more uplink serving cells to be expired.

(f) The method of embodiment (a), wherein taking an action comprises indicating to the wireless communication network that a handover should be performed.

(g) The method of embodiment (a), wherein taking an action comprises triggering a Radio Link Failure.

(h) The method of any of embodiments (a)-(f), further comprising selecting the at least one carrier for which action is to be taken based on an evaluation of quality for the at least one carrier.

(i) The method of any of embodiments (a)-(h), wherein said action is taken with respect to all of two or more carriers in a timing alignment group.

(j) The method of any of embodiments (a)-(i), further comprising sending, to the wireless communication network, an indication that the action has been taken. (k) The method of embodiment (j), wherein the indication identifies a carrier or carrier group for which the action has been taken.

(I) The method of any of embodiments (a)-(k), further comprising, prior to taking the action, receiving, from the wireless communication network, information indicating that one or more carriers are to be prioritized for the action. (m) The method of any of embodiments (a)-(l), further comprising, prior to taking the action, receiving, from the wireless communication network, an indication of the value of the timing difference threshold.

(n) The method of any of embodiments (a)-(m), further comprising, subsequent to taking the action, reversing the action for one or more of the at least one carrier.

(o) A mobile terminal apparatus comprising one or more processing circuits adapted to carry out one or more of the methods of example embodiments (a)-(n).

(p) A mobile terminal apparatus comprising:

means for determining that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and

means for taking an action with respect to at least one uplink carrier, in response to said determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

(q) A mobile terminal apparatus comprising:

a determining unit for determining that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and

an action unit for taking an action with respect to at least one uplink carrier, in response to said determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions. (r) A method, in a network node, of handling uplink timing advance in a mobile terminal adapted for carrier aggregation in a wireless communication network, the method comprising:

determining that a difference in uplink transmit timing for the mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and,

in response to said determining, taking an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions. (s) The method of embodiment (r), wherein taking an action comprises deactivating one or more uplink serving cells for the mobile terminal.

(t) The method of embodiment (r), wherein taking an action comprises de-configuring one or more uplink serving cells for the mobile terminal. (u) The method of any of embodiments (r)-(t), wherein taking the action is further based on an evaluation of one or more of:

an amount of degradation in the UL signal quality that the network node can tolerate; a type of uplink receiver in the network node;

a robustness level of the uplink receiver in the network node;

the radio environment;

an amount and/or frequency of the drift in downlink transmission timing of downlink signals that are received or that are expected to be received by the mobile terminal; a mobile capability in terms of maximum supported T_diff_max_.;

a mobile terminal-reported uplink time difference between uplink signals on uplink serving cells, T diff.

(v) A network node apparatus comprising one or more processing circuits adapted to carry out one or more of the methods of example embodiments (r)-(u).

(w) A network node apparatus comprising:

means for determining that a difference in uplink transmit timing for the mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and,

in response to said determining, taking an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions. (x) A network node apparatus comprising:

a determining unit for determining that a difference in uplink transmit timing for the mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold and

an action unit for taking an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions. (y) A mobile terminal apparatus adapted to aggregate carriers in a wireless communication network, the mobile terminal apparatus comprising:

a radio transceiver circuit configured to communicate with one or more base stations; and

a processing circuit configured to process the signals transmitted and received by the radio transceiver circuit and to:

determine that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and

take an action with respect to at least one uplink carrier, in response to said determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

(z) A network node apparatus adapted for use in a wireless communication network supporting aggregation of carriers, the network node apparatus comprising a processing circuit configured to:

determine that a difference in uplink transmit timing for a mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and,

in response to said determining, take an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention. For example, although embodiments of the present invention have been described with examples that reference a communication system compliant to the 3GPP-specified LTE standards, it should be noted that the solutions presented may be equally well applicable to other networks. The specific embodiments described above should therefore be considered exemplary rather than limiting the scope of the invention. Because it is not possible, of course, to describe every conceivable combination of components or techniques, those skilled in the art will appreciate that the present invention can be implemented in other ways than those specifically set forth herein, without departing from essential characteristics of the invention. The present embodiments are thus to be considered in all respects as illustrative and not restrictive.

When an element is referred to as being "connected", "coupled", "responsive", or variants thereof to another element, it can be directly connected, coupled, or responsive to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected", "directly coupled", "directly responsive", or variants thereof to another element, there are no intervening elements present. Like numbers refer to like elements throughout. Furthermore, "coupled", "connected", "responsive", or variants thereof as used herein may include wirelessly coupled, connected, or responsive. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Well-known functions or constructions may not be described in detail for brevity and/or clarity. The term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood that although the terms first, second, third, etc. may be used herein to describe various elements/operations, these elements/operations should not be limited by these terms. These terms are only used to distinguish one element/operation from another element/operation. Thus a first element/operation in some embodiments could be termed a second element/operation in other embodiments without departing from the teachings of present inventive concepts. The same reference numerals or the same reference designators denote the same or similar elements throughout the specification.

As used herein, the terms "comprise", "comprising", "comprises", "include", "including", "includes", "have", "has", "having", or variants thereof are open-ended, and include one or more stated features, integers, elements, steps, components or functions but does not preclude the presence or addition of one or more other features, integers, elements, steps, components, functions or groups thereof. Furthermore, as used herein, the common abbreviation "e.g.", which derives from the Latin phrase "exempli gratia," may be used to introduce or specify a general example or examples of a previously mentioned item, and is not intended to be limiting of such item. The common abbreviation "i.e.", which derives from the Latin phrase "id est," may be used to specify a particular item from a more general recitation.

Example embodiments have been described herein, with reference to block diagrams and/or flowchart illustrations of computer-implemented methods, apparatus (systems and/or devices) and/or computer program products. It is understood that a block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by computer program instructions that are performed by one or more computer circuits. These computer program instructions may be provided to a processor circuit of a general purpose computer circuit, special purpose computer circuit, and/or other programmable data processing circuit to produce a machine, such that the instructions, which execute via the processor of the computer and/or other programmable data processing apparatus, transform and control transistors, values stored in memory locations, and other hardware components within such circuitry to implement the functions/acts specified in the block diagrams and/or flowchart block or blocks, and thereby create means (functionality) and/or structure for implementing the functions/acts specified in the block diagrams and/or flowchart block(s).

These computer program instructions may also be stored in a tangible computer-readable medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of manufacture including instructions which implement the functions/acts specified in the block diagrams and/or flowchart block or blocks. Accordingly, embodiments of present inventive concepts may be embodied in hardware and/or in software (including firmware, resident software, micro-code, etc.) running on a processor such as a digital signal processor, which may collectively be referred to as "circuitry," "a module" or variants thereof. It should also be noted that in some alternate implementations, the functions/acts noted in the blocks may occur out of the order noted in the flowcharts. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Moreover, the functionality of a given block of the flowcharts and/or block diagrams may be separated into multiple blocks and/or the functionality of two or more blocks of the flowcharts and/or block diagrams may be at least partially integrated. Finally, other blocks may be added/inserted between the blocks that are illustrated, and/or blocks/operations may be omitted without departing from the scope of inventive concepts. Moreover, although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.

Many variations and modifications can be made to the embodiments without substantially departing from the principles of the present inventive concepts. All such variations and modifications are intended to be included herein within the scope of present inventive concepts. Accordingly, the above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended examples of embodiments are intended to cover all such modifications, enhancements, and other embodiments, which fall within the spirit and scope of present inventive concepts. Thus, to the maximum extent allowed by law, the scope of present inventive concepts are to be determined by the broadest permissible interpretation of the present disclosure, and shall not be restricted or limited by the foregoing detailed description.

ABBREVIATIONS

cc Component Carrier

LTE Long term evolution

3GPP 3^rd generation partnership project

DL Downlink

UL Uplink

PCell Primary cell/Primary serving cell

SCell Secondary Cell/Secondary serving cell

RRC Radio Resource Control

eNB evolved Node B

UE User Equipment (3GPP Term for terminal)

MAC Medium Access Control

CE Control Element

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

CP Cyclic Prefix

DFT Discrete Fourier Transform

FFT Fast Fourier Transform

DL-SCH Downlink Shared Channel

HARQ Hybrid Automatic-Repeat-Request

ACK Acknowledgment

NACK Negative Acknowledgement

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

UL-SCH Uplink Shared Channel

TA Timing Advance/Time Advance

TAG Timing Advance Group

NW Network

SRS Sounding Reference Signal PRACH Physical Random Access Channel

RAN Radio Access Network

RNTI Radio Network Temporary Identification

C-RNTI Cell-RNTI

RA-RNTI Random Access-RNTI

TC-RNTI Temporary C-RNTI

CRC Cyclic Redundancy Check

RACH Random Access Channel

HO Handover

TAC Timing Advance Command

Claims

CLAIMS What is claimed is:

1 . A method in a mobile terminal adapted for aggregating carriers in a wireless

communication network, the method comprising:

determining (830) that a difference in uplink transmit timing between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and,

in response to said determining, taking (840) an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

2. The method of claim 1 , wherein taking (840) an action comprises deactivating one or more uplink serving cells.

3. The method of claim 1 , wherein taking (840) an action comprises de-configuring one or more uplink serving cells.

4. The method of any of claims 1 -3, wherein taking (840) an action comprises stopping a time alignment timer for one or more uplink serving cells.

5. The method of any of claims 1 -3, wherein taking (840) an action comprises considering a time alignment timer for one or more uplink serving cells to be expired.

6. The method of claim 1 , wherein taking (840) an action comprises indicating to the wireless communication network that a handover should be performed.

7. The method of claim 1 , wherein taking (840) an action comprises triggering a Radio Link Failure.

8. The method of any of claims 1 -6, further comprising selecting the at least one carrier for which action is to be taken based on an evaluation of quality for the at least one carrier.

9. The method of any of claims 1 -8, wherein said action is taken with respect to all of two or more carriers in a timing advance group.

10. The method of any of claims 1 -9, further comprising sending (850), to the wireless communication network, an indication that the action has been taken.

1 1 . The method of claim 10, wherein the indication identifies a carrier or carrier group for which the action has been taken.

12. The method of any of claims 1 -1 1 , further comprising, prior to taking (840) the action, receiving (810), from the wireless communication network, information indicating that one or more carriers are to be prioritized for the action.

13. The method of any of claims 1 -12, further comprising, prior to taking (840) the action, receiving (820), from the wireless communication network, an indication of the value of the timing difference threshold.

14. The method of any of claims 1 -13, further comprising, subsequent to taking (840) the action, reversing (860) the action for one or more of the at least one carrier.

15. A mobile terminal apparatus (1000) adapted to aggregate carriers in a wireless communication network and to:

take an action with respect to at least one uplink carrier, in response to said

determining, so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

16. The mobile terminal apparatus (1000) of claim 15, wherein the mobile terminal apparatus (1000) is adapted to deactivate one or more uplink serving cells, in response to said determining.

17. The mobile terminal apparatus (1000) of claim 15, wherein the mobile terminal apparatus (1000) is adapted to de-configure one or more uplink serving cells, in response to said determining.

18. The mobile terminal apparatus (1000) of any of claims 15-17, wherein the mobile terminal apparatus (1000) is adapted to stop a time alignment timer for one or more uplink serving cells, in response to said determining.

19. The mobile terminal apparatus (1000) of any of claims 15-17, wherein the mobile terminal apparatus (1000) is adapted to consider a time alignment timer for one or more uplink serving cells to be expired, in response to said determining.

20. The mobile terminal apparatus (1000) of claim 15, wherein the mobile terminal apparatus (1000) is adapted to indicate to the wireless communication network that a handover should be performed, in response to said determining.

21 . The mobile terminal apparatus (1000) of claim 15, wherein the mobile terminal apparatus (1000) is adapted to trigger a Radio Link Failure, in response to said determining.

22. The mobile terminal apparatus (1000) of any of claims 15-20, wherein the mobile terminal apparatus (1000) is further adapted to select the at least one carrier for which action is to be taken based on an evaluation of quality for the at least one carrier.

23. The mobile terminal apparatus (1000) of any of claims 15-22, wherein the mobile terminal apparatus (1000) is adapted to take said action with respect to all of two or more carriers in a timing advance group.

24. The mobile terminal apparatus (1000) of any of claims 15-23, wherein the mobile terminal apparatus (1000) is further adapted to send, to the wireless communication network, an indication that the action has been taken.

25. The mobile terminal apparatus (1000) of claim 24, wherein the indication identifies a carrier or carrier group for which the action has been taken.

26. The mobile terminal apparatus (1000) of any of claims 15-25, wherein the mobile terminal apparatus (1000) is further configured to receive from the wireless communication network, prior to taking the action, information indicating that one or more carriers are to be prioritized for the action.

27. The mobile terminal apparatus (1000) of any of claims 15-26, wherein the mobile terminal apparatus (1000) is further configured to receive from the wireless communication network, prior to taking the action, an indication of the value of the timing difference threshold.

28. The mobile terminal apparatus (1000) of any of claims 15-27, wherein the mobile terminal apparatus (1000) is further configured to reverse the action for one or more of the at least one carrier, subsequent to taking the action.

29. A method, in a network node, of handling a mobile terminal adapted for aggregating carriers in a wireless communication network, the method comprising: determining (910) that a difference in uplink transmit timing for the mobile terminal between a first carrier or group and a second carrier or group is or will be greater than a timing difference threshold; and,

in response to said determining, taking (920) an action with respect to at least one uplink carrier so as to avoid that the timing difference threshold is exceeded by uplink transmit timing differences for one or more subsequent uplink transmissions.

30. The method of claim 29, wherein taking (920) an action comprises deactivating one or more uplink serving cells for the mobile terminal.

31 . The method of claim 29, wherein taking (920) an action comprises de-configuring one or more uplink serving cells for the mobile terminal.

32. The method of any of claims 29-31 , wherein taking (920) the action is further based on an evaluation of one or more of:

a robustness level of the uplink receiver in the network node;

the radio environment;

an amount and/or frequency of the drift in downlink transmission timing of downlink signals that are received or that are expected to be received by the mobile terminal;

a mobile capability in terms of maximum supported T_diff_max_.;

33. A network node apparatus (1 100, 1200) for use in a wireless communication network supporting aggregation of carriers, wherein the network node apparatus (1 100, 1200) is adapted to:

34. The network node apparatus (1 100, 1200) of claim 33, wherein the network node apparatus is adapted to deactivate one or more uplink serving cells for the mobile terminal, in response to said determining.

35. The network node apparatus (1 100, 1200) of claim 33, wherein the network node apparatus is adapted to de-configure one or more uplink serving cells for the mobile terminal, in response to said determining.

36. The network node apparatus (1 100, 1200) of any of claims 33-35, wherein the network node apparatus is configured to take the action based further on an evaluation of one or more of:

a robustness level of the uplink receiver in the network node;

the radio environment;

a mobile capability in terms of maximum supported T_diff_max_.;

37. A mobile terminal apparatus (1000) adapted to aggregate carriers in a wireless communication network, the mobile terminal apparatus (1000) comprising:

a radio transceiver circuit (1020) configured to communicate with one or more base stations; and

a processing circuit (1010) configured to process the signals transmitted and

received by the radio transceiver circuit (1020) and to:

38. A network node apparatus (1 100, 1200) adapted for use in a wireless communication network supporting aggregation of carriers, the network node apparatus (1 100, 1200) comprising a processing circuit (1 120,1220) configured to: