GB2493707A - Using common time alignment timer for time advance values from multiple base stations with similar rates of change - Google Patents

Abstract

Time Advance (TA) values are used to compensate for the time of flight propagation delay in the uplink from a user equipment (UE) to a node (eg. e-NodeB or repeater). The TA will be valid for a limited time due to movement of the UE. This validity period is monitored using a Timing Alignment Timer (TAT) which determines when the TA needs to be updated/refreshed. In situations where the UE 16 communicates with multiple nodes 10,12 each air link will have its own propagation delay and TA. Movement of the UE may be such that it travels tangentially to one node 12 but radially to another 10. Hence the rate of change of the two TAs will be different and separate TATs will be required, however if the motion is such that the changes to the TA are correlated a single TAT would suffice. The invention monitors changes in the TA values to check for correlations, and rationalises the number of TATs where correlation is found.

Description

Timing Advance Timer Management

Field of the invention

The present invention relates to developments in timing advance timer management, and particularly to mobile telecommunication networks utilizing same. More particularly, the present invention relates to uplink timing synchronization of a user equipment involved in multi-cell carner aggregation, with the said cells belonging to different timing advance groups, as applicable in the context of the 3GPP Long Temi Evolution (LTE) -Advanced.

Back2round art Wireless transmissions in LTE networks require synchronization, similarly to other digital communication solutions. Due to the mobility of user equipment (UE). such as mobile phones it is possible that the distances between a Base Station (eNB) aiid UEs in the Base Station's cdl are different. Therefore the time of arrival at the Base station of the transmitted signals from the UEs will be different. To maintain synchronization in the uplink these differences should be compensated in time. This is achieved using timing advance (TA). The higher eNB-UE distance, the higher time compensation is needed and therefore the TA value will be higher. The granularity of TA is based on the reference time, Ts = 1730720000 s.

The timing advance for a UE must be changed according to the movements of the UR.

Moreover, a TA value will only be valid for a given period of time if the UE is moving. To manage the amount of time for which an assigned TA is valid, a parameter called a Time Alignment Timer (TAT) is used.

The TAT is used to control how long the UE is considered uplink time aligned. The TAT value is expressed in number of sub-frames (the duration of a sub-frame equals I ms). The number of values is limited to a tight set which is the following: 500, 750, 1280, 1920, 2560, 5120, 10240 sub-frames or infinity.

A UE can receive a TA Command in two ways: 1. In a MAC control element: 11 a UE receives a TA Command in a MAC control element it shall apply the TA Command and start or restart TAT; and 2. a TA Command is received in a Random Access Response message: If the Random Access Preamble was not selected by UE MAC, the UE shall apply the TA Command and start or restart the TAT; or * if the TAT is not running, the UP shall apply the TA Command, start TAT and when the contention resolution is considered not successful, it shall stop the TAT.

Otherwise, the UP ignores the received TA Command.

When the TAT expires, all HARQ buffers should be flushed, RRC should be notified to release PUCCH/SRS and any configured downlink assignments and uplink grants should be cleared. (When a new cycle is started the RRC should be notified to set up PUCCH/SRS and perform all necessary processes.)

Disclosure of the invention

According to the present invention there is provided a wireless communications network comprising: a first node; a second node; a user equipment (UE), wherein the UE is operable to communicate simultaneously with each of the first node and the second node, such that said communications use respective first and second timing advance (TA) values for uplink synchronisation. wherein the first node is operable to determine a con-elation between the first and second timing advance values and, based on said correlation, determine whether or not a single timing advance timer (TAT) may be used for the UE's communication with both the first node and the second node.

Preferably the network comprises further nodes, such that UE is operable to communicate simultaneously with each of the first and second nodes and the further nodes, wherein the first node is operable to determine the minimum number of required timing advance timers required based on a con-elation between the timing advance values of the nodes in the network.

The present invention is operable to function in alTangements in which cells are in separate physical locations when multi-cell carrier aggregation is used, whether this is when two nodes are utilized, or a greater number.

It is prefelTed that the first node is operable to continually monitor timing advance values for each node so as to adaptively control the number of required timing advance timers.

Depending upon the speed of movement of a UE, the TA values required may change rapidly.

This in turn affects the TATs. As such the first node continually monitors the relationship between the TA values to ensure that the appropriate number of TATs are implemented.

Preferably the first node is configured to reduce the number of timing advance timers to the lowest viable number. Such an arrangement is advantageous to save network resources.

It is preferred that the first node is an eNodeB. Mso, it is preferred that the second node is a repeater node or remote radio head. The further nodes may be eNodeBs, repeaters/remote radio heads or other types of relay node.

Preferably the correlation between the timing advance values is based upon their rate of change over time.

Preferably the first node calculates the time derivate of each timing advance value, and further calculates a ratio of the time derivative values to determine the required number of timing advance timers.

Preferably the first node continually monitors the ratio of the time derivative values and dynamically adapts the number of timing advance timers based on the current value of the ratio of the time derivative values. This arrangement provides the network with a parameter that the network can use to determine the required number of TATs. When the parameter is within certain values, the eNodeB can reduce the required number of TATs. If the UE is using can-icr aggregation with just two groups of nodes, each requinng different TA, this would mean reverting from two TATs to a single TAT, or to revert to using two TATs instead of a single TAT.

According to a second aspect of the present invention there is provided a method of synchronizing uphnk timing for a user equipment (UE), said UE communicating with multiple nodes, including an eNodeB, in carrier aggregation, wherein the eNodeB is operable to determine the minimum number of timing advance timers required.

A further aspect of the present invention relates to an eNodeB operable to implement the above mentioned method.

It is preferred that this eNodeB is operable to dynamically adapt the number of timing advance timers based upon the change of timing advance values for the UE to each of the multiple nodes. Particularly, the eNodeB may be operable to determine whether or not the relative change in mobility of the UE to the multiple nodes is effectively the same or not.

Preferably, if the relative change in mobility of the UE to the multiple nodes is effectively the same, said eNodeB is operable to implement the same timing advance timer for each of the UE's timing advances. Also, if the relative change in mobility of the LIE to the multiple nodes is not the same, the eNodeB implements a separate timing advance timer for each of the UP's timing advances.

A further aspect, linked with the other aspects, is to provide a method of dynamically adapting the number of time advance timers (TATs) in a network by monitoring the relative change between timing advances used by a LIE in multi-cell carrier aggregation.

In order that the present invention be more readily understood, specific embodiments thereof will now be described with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 shows an example of part of a wirekss communication network.

Figure 2 shows a flow chart indicating the operation of a time advance timer Figure 3 is a working example showing a UE in wireless communication with a pair of nodes.

Figure 4a shows a relationship between timing advance values and distance for the arrangement of figure 3.

Figure 4b shows the time derivative of the graph of figure 4a.

Figure 5 shows a graph of a variable that is achieved by taking the ratio of the plots from figure 4b.

Description of Preferred Embodiments

Figure 1 shows a diagrammatical example of part of a wireless communications system.

There is provided a first node, which is a Base Station 10. In LTE systems this is termed an eNodeB (sometimes abbreviated to eNB). There is also provided a second node, which is a repeater relay 12, which may a'so be termed a remote radio head. Repeaters/remote radio heads are used in wireless networks to extend the coverage of a Base Station. They do not generally possess significant functionality, but are used to receive and/or transmit a signal. A received signal is passed on to the Base Station. The signal is processed at the Base Station, with the return signal being sent to the UE via the repeater/remote radio head 12. Both the Base Station 10 and the repeater 12 may generally be termed nodes. This general tern-i covers any device that is operable to support a wireless communication sessions with a user equipment (UE) -such as a mobile phone. Each node supports an area in which it is operable to support wireless sessions. This area is typically termed a cell. When a user equipment leaves a cell, the node is no longer operable to support wireless communication with that UE.

In this case, it is necessary for the UE to connect with another node closer by. In the example provided by figure 1. eNodeB 10 supports cell 18. whilst remote radio head 12 supports cell 20.

It will be appreciated that further nodes may be included within the network (these are not shown in the figures). These further nodes may be additional eNBs, repeaters, RRI-ls or other relay nodes.

The wireless communications system of figure 1 also includes two user equipments (UEs) 14, 16. UE 14 is in wireless communication with eNodeB 10. The connection from the UE 14 to the eNodeB JO is often termed the uplink. The reciprocal connection, from the eNodeB 10 to the UE 14 is usually termed the downlink.

UE 16 is located within cell 18 supported by the eNodeB and cell 20 supported by the repeater 12. In this case UE 16 may uplink to either the eNB 10 or the repeater (or with both nodes, if cell 20 is configured to be in carrier aggregation with cell 18 -see below). In this case, the wireless communication signal from UE 16 will be passed on from the repeater 12 to the eNodeB 10. The downlink signal will likewise pass through the repeater 12.

LTE systems have defined a frame and subframe structure for carrying data. For an LTE system, a time frame, or frame, in a wireless communication system has an overall length of lOms. This frame is split into 10 sub-frames, each ims in length.

To ensure that the system maintains uplink synchronisation it is important that all signals being received by an eNodeB are received at the beginning of a sub-frame. If this does not occur, signals from different liEs which are allocated specific resources (i.e. frequency and time frames) may interfere with one another.

To achieve this uplink synchronisation, the wireless communications network uses a mechanism termed timing advance. Each LIE in communication with a Base Station will be instructed by the network to adjust its transmission timing using a timing advance, which is a time value that is used to alter the time when the UE starts to transmit wireless data to the Base Station. The timing advance thus corresponds to the length of time a signal takes to reach the Base Station from the liE. Whilst the radio waves used by the wireless communication system travel at the speed of light, they still take a finite time to travel from the liE to the Base Station. This time will vary depending upon how far the UE is from the Base Station.

In LTE systems the timing advance is first calculated during the initial connection between the UP and the Base Station. When a UF wishes to establish an RRC connection with an eNodeB. it transmits a Random Access Preatnbie, the uNodeB estimates the transmission timing of the tennEna based on this signal. The eNodeB responds by transmittin a Random Access Response whlch consists of timing advance command, and based on this command the (,JE adjusts its transmission timing.

More details of the LTE networks, and the detailed works of the timing advance mechanisms may be found at [1] Physical Channels and Modulation, Tech. Specification 3GPP TS 36.211 V10.2.0. June 2011; [2] Physical Layer Measurements, Tech. Specification 3GPP TS 36.214 Vl0.l.0, Mar 2011; [3] Physical Layer Procedures, Tech. Specification 3GPP TS 36.213 Vi 0.2.0, Jun. 2011; and [4] Medium Access Control (MAC) Protocol Specification, Tech.

Specification 3GPP TS 36.321 Vl0.2.0, June. 2011, details of which are incorporated herewith by reference.

Referring back to figure I, it will be appreciated that UE 14 will have a certain timing advance in its connection with eNodeB 10. UE 16 will likely have a greater timing advance to eNodeB 10, because its signal needs to pass through remote radio head 12 before reaching the eNodeB 10.

It will be appreciated that the timing advance for a UE will not change if the UE is effectively stationary. However, UEs are typically mobile with respect to the Base Station. The term mobility is often used to cover a UE's speed and direction of movement. A UE with high mobility maybe travelling fast, whereas a IJE with low mobility may be travelling slowly.

I

A UE with high mobility may require regular updates to its timing advance. In the most extreme example. when the liE travels with high speed directly towards or away from the Base Station, the distance between the UE and the Base Station will rapidly change, and thus maintaining the same timing advance will result in a lack of synchronisation with the network, and hence inteiference between radio signals from different UEs.

The network thus uses a mechanism called a time advance timer (TAT). TATs denote how often the TA is updated. If transmission delay changes quickly, the TAT would be low (since the TAT denotes the period of the refresh, or, in other words, indicates that TA updates should arrive more frequently). The ideal TAT value (as the integer multiples of Tsubframe = 1 ms) is to be inversely proportional to one over the time derivate of the timing advance.

Carrier aggregation was introduced to meet LTEAdvartced requirements, which requires support of v,ider transmission bandwidths than the 20 MI-k. bandwidth specified in 3GPP Release 819. Carrier aggregation allows the expansion cf effective bandwidth delivered to a F. through concurrent utiLization ot radio resources across ntu Itipie carriers. Multiple component carriers are aggregated to form a lareer overall transmission bandwidth. Ji the present release of LTE (release ii), UEs can use carrier aggregation by communicating directly with multiple nodes. Thus, referring to figure 1, it is possible for UE 16 to communicate directly with both eNodeB 10 and repeater 12 (because it is within the cell of each node). This mechanism allows for greater flexibility and improved resource efficiency.

It should be noted that UE 14 could not use this type of calTier aggregation as it is only within the cell of one node. Generally, different TA values are needed for different groups of cells, or, put another way, a UE may require a first TA for a first node and a second TA for a second node. Given the mobility of a UE. the TAT for each different TA group may be different.

For example. referring again to figure 1, UE 16 may be travelling directly away from eNodeB 10, and parallel to repeater 12. As such, the distance between the UE 16 and the two nodes is changing at a different rate. Therefore the timing advance required to communicate with the two nodes will also change at a different rate.

The present arrangement is applicable to any group of cells (and therefore nodes) within which a UE is communicating with different Timing Advance (TA). As stated earlier, Timing Advance denotes how much earlier (in advance) the transmitter of the UE should start the transmission to have all signals received at the Base Station synchronized. Advance transmission should compensate the transmission delay (i.e. the delay between the Base Station and the receiver). Thus, it will be appreciated that TAs vary according to the transmission delays between a given IJE and a given Base Station.

Broadly speaking, the present invention proposes ways to more effectively manage uplink synchronization for a UE that is in wireless communication with nodes from multiple cells.

Particularly. the present alTangement is operable to deteimine the minimum required number of time alignment timers (TAT), typically depending on the mobility (movement) of the UE with respect to the particular group of cells.

The present arrangement also seeks to define mechanisms to switch between single or multiple TATs, based on the change in the TA parameters of different groups of cells.

In 3GPP LTE-Advanced (Release 11) different TAs can be applied on given carriers or carrier TA groups (carrier TA group can be a set of carriers that require the same TA value). In this case it is also possible that the validity of TA values and the necessary refresh rate for each carrier or carrier groups are also different as well.

Figure 2 shows a flow chart illustrating typical (known) time alignment time!' operation. As can be seen, the TAT counter can be started, restarted or stopped during the operation according to incoming TA Commands. Thus, if UE is implementing a given TAT value, and a new value is sent by the eNodeB. the new value will take precedence. In other words, the first TAT does not count down to zero; the new TAT is implemented immediately.

When a UE is communicating simultaneously with multiple cells, for example in carrier aggregation with cells belonging to multiple TA groups, the node(s) for each TA group will require independent TA values, which change according to the relative position and mobility (the speed and direction of movement) of the UE.

Therefore, the same TAT for all node(s)/TA groups may not always be effective, as node(s) in each TA group may require separate TAT for satisfactory/enhanced performance. However, calculating multiple TATs may waste resources. It would thus be advantageous to maintain a single TAT, where appropriate, but also have the flexibility to revert to multiple TATs if required.

To achieve this aim, there is provided a network with a first node (an eNB) and a second node (a repeater). The network will also comprise a UE. The UE is operable to communicate simultaneously with each of the first node and the second node (for example using carrier aggregation). such that said communications use respective first and second TA values for uplink synchronisation to the network. The eNodeB (first node) is operable to determine a correlation between the first and second TA values and, based on said correlation, determine whether or not a single timing advance timer (TAT) may be used for the US's communication with both the first node and the second node.

It will be appreciated that the network may comprise further nodes. In this case it may be that the UE is operable to communicate simultaneously with each of the eNB and the repeater and the further nodes. In this case the eNB will determine the minimum number of required timing advance timers required based on a correlation between the timing advance values of each of the nodes or TA groups in the network (ie each of the nodes or TA groups which the UE is using in carrier aggregation).

An example of how to determine the suitability of single or multiple TATs will now be provided with reference to figure 3. Assume there are two cells: the node of the first cell (eNBl) is located at position (xl,1) and is an eNodeB, the node of the second cell is at (x2,y2). The node of the second cell is a repeater, or a remote radio head (RRH) of the eNodeB. The system also comprises a UF. hi this scenario the delay from the RRH is larger than the delay from the eNodeB. Two distinct TA values must be used for the two nodes. The TA of the eNodeB is denoted by TAI aiid the TA of the repeater is denoted by 1A2 (as stated, 142> 141).

Since the rotation of the coordinate system could be done without the loss of generality, assume that the UE is travelling along the axis x. The UE has a constant velocity v and at time it = 0 it starts from the origin. For any time e, the UE is located at (v I,0). The distance between the UE and eNodeB is denoted by dl, whereas the distance between UE and repeater is denoted by d2. Finally, c13 represents the distance between the two Base Stations. Thus: =/tx dy.Y:.-Supposing that radio signals travel at speed c, and that line of sight propagation exists in the system, the delay (which must be equal to the half of the TA) on the two paths can be calculated as: r 2 -to twnI biu&o atat;-on and 1 :F-, :{c MFcond basvy JtaxM-i wh&fto T tepn.stiua the fl.3ckuj tnte nI th ixtmtt/RR1--Nowletu- inickly fAa cnmgen tirfln. We pnduce the firM dnñvatlve accyord lug to ithie. k

-U -t k.-: and

--C 71 F

YW tvC)trodtice a t-tew vartd)k-. fl t-vhic 1110 t Liton 01 the above. taco de1\tes.

\S' k1 :JT:TiI1 T"7 tO If the change in the TA values are more or less the same, q is close to one. If I, there is no need for more than one TAT. Separate TAT values are needed if q deviates remarkably from 1, That is,

CTTTT

or vica versa.

S From the above, it can be seen that the decision on single or multiple TATs can be made using this parameter q. It will be noted that the eNodeB (first node) is operable to continually monitor timing advance values for each node or TA group that the UE is communicating with so as to adaptively control the number of required timing advance timers. It is configured to reduce the number of timing advance timers to the lowest viable number. However, when it is not appropriate to maintain a single (or reduced) number of TATs, the eNodeB will implement multiple TATs -upto one per TA group, if necessary.

To aid understanding an illustrative embodiment will now be provided. In this connection, consider figure 3, and the scenario when a UE moves towards the eNB, while the repeatertRRH is disposed to the eft-hand side of the UE. Assume that the repeater/RRH is ocated at (R/2. R12) position and the eNB is at (R,0). For the sake of simplicity, assume that R = RI = R2 = 1000 meters. To aid understanding, it will be assumed that the processing time of the repeaterlRRH is equal to zero (ie TP = 0). The following example will investigate how the TA and their derivates behaves as the UE moves from the origin (where the coverage area of the eNB starts) to (3+l) R/2 (where the coverage of the repeater/RRFI diminishes).

Figures 4a and 4b illustrates how the TA1 and TA2 parameters change on this exemplary path. It will be noted that TA2 changes differently compared to TA I as the UE passes by, and that TA1 linearly decreases and increases as the UE approaches and leaves the Base Station.

Note the remarkable gap between TA I and TA2. Ahhough processing time is discounted (1'? is assumed zero), due to the fact that radio signal must be transmitted to the repeater/RRH from the eNB, the delay of the repeater/RRH-eNB link appears as the minimum gap between the two curves. There is no way to circumvent this gap. The gap depends on the distance between the repeater/RRH and the eNB.

Figure 5 shows the behaviour of. Parameter q starts from a value close to one, and it tends to infinity as the slope of the TA2 curve gets closer to zero. As the slope of Th2 changes its sign (after the local minimum of 1>12), i becomes negative. As the UE arrives under the eNB, the slope of TAI changes its sign: 1 becomes positive again and tends to one from the light. If the coverage radii of the cells were infinite, would get infinitely close to one. It should be realised that the positive or negative value of is not relevant, only the absolute value is important. The only parameter that is necessary is the rapidity of change in TA value(s) (i.e. the delay).

From the above it will be seen that Parameter 1 shows the relative mobility of a UE to the two network nodes, or, put another way, shows whether or not the timing advance for the two nodes is chaiging at the same rate. Here, it would be appropriate for the network to implement a single TAT from at least Diii to 20Gm and 100Gm to i 40Dm, and probably from 80Dm to 140Gm. Obviously, this example is only mentioned for illustrative purposes.

Thus, for a mobile UE. if there is a similar pattern of change for both TATs, a UE can rely on a single TAT for its communication with two network nodes. Only if the pattern of change is different will it be required to implement multiple TATs. Also, even if the system implements multiple TATs per UE throughout, (ie., not changing adaptively by using single TAT or multiple TATs) as a mechanism to manage UL synchronization. then the above mentioned method can be used to decide whether same TAT value can be assigned to multiple TATs.

It will thus be appreciated that the correlation between the timing advance values is based upon their rate of change over time, and that the eNodeB (first node) calculates the time derivate of each timing advance value, and further calculates a ratio of the time derivative values to determine the required number of timing advance timers. To achieve efficiencies in resource management the eNodeB continually monitors the ratio of the time derivative values and dynamically adapts the number of timing advance timers based on the current value of the ratio of the time derivative values.

Whilst it is believed that all of the foregoing will be well understood by a skilled person, various technical definitions -taken from 3GPP TR 21.905: "Vocabt.dary for 3GPP Specifications" version 10.3.0, Mar 2011 -are provided below.

An eNodeB (or eNB) is shorthand for E-UTRAN NodeB. This is further defined as: Node B: A logical node responsible for radio transmission / reception in one or more cells to/from the User Equipment..

Evolved UTRA: Evolved UTRA is an evolution of the 3G UMTS radio-access technology towards a high-data-rate. low-latency and packet-optimized radio-access technology.

Evolved UTRAN: Evolved UTRAN is an evolution of the 3G UMTS radio-access network towards a high-data-rate. low-latency and packet-optimized radio-access network.

Canier: The modulated waveform conveying the E-UTRA, UTRA or GSM/EDGE physical channels Cell: Radio network object that can be uniquely identified by a User Equipment from a (cell) identification that is broadcasted over a geographical area from one UTRAN Access Point. A Cell is either FDD or TDD mode.

Repeater: A device that receives, amplifies and transmits the radiated or conducted RE carrier both in the down-link direction (from the base station to the mobile area) and in the up-link direction (from the mobile to the base station) A Remote Radio I-lead is an equipment used in wireless telecom systems. This type of equipment may be used in wireless technologies such as LTE. As this equipment is remote to the eNodeB, it is called a Remote Radio Head. These equipments typically used to extend the coverage of a BTS/NodeB/eNodeB like rural areas or tunnels.

It is to be understood that the above embodiments are described for reference and understanding and should not be used to limit the scope of the present invention, which is define by the appended claims.

Claims (1)

1. <claim-text>Claims I. A wireless communications network comprising: a first node; a second node; a user equipment (UE), wherein the UE is operable to communicate simultaneously with each of the first node and the second node, such that said communications use respective first and second timing advance (TA) values for uplink synchronisation, wherein the first node is operable to determine a colTelation between the first and second timing advance values and, based on said corrdation, determine whether or not a single timing advance timer (TAT) may be used for the US's communication with both the first node and the second node.</claim-text> <claim-text>2. A wireless communications network according to claim 1, wherein the network comprises further nodes, such that UE is operable to communicate simultaneously with each of the first and second nodes and the further nodes, wherein the first node is operable to determine the minimum number of required TATs required based on a correlation between the TA values of the nodes in the network.</claim-text> <claim-text>3. A wireless communications network according to claim 1 or 2, wherein the first node is operable to continually monitor timing advance values for each node so as to adaptively control the number of required timing advance timers.</claim-text> <claim-text>4. A wireless communications network according to claim 3. wherein the first node is configured to reduce the number of TATs to the lowest viable number.</claim-text> <claim-text>5. A wireless communications network according to any preceding claim, wherein the first node is an eNodeB.</claim-text> <claim-text>6. A wireless communications network according to any preceding claim, wherein the second node is a repeater node or remote radio head.</claim-text> <claim-text>7. A wireless communications network according to any preceding claim, wherein the correlation between the TA values is based upon their rate of change over time.</claim-text> <claim-text>8. A wireless communications network according to claim 7, wherein the first node calculates the time derivate of each TA value, and further calculates a ratio of the time derivative values to determine the required number of TATs.</claim-text> <claim-text>IS 9. A wireless communications network according to claim 8, wherein the first node continually monitors the ratio of the time derivative values and dynamically adapts the number of TATs based on the culTent value of the ratio of the time denvative values.</claim-text> <claim-text>10. A node operable to implement the functionality of the first node in the wireless communications network of any of claims 1 to 9.</claim-text> <claim-text>11. A user equipment operable to implement the functionality of the TIE in the wireless communications network of any of claims 1 to 9.</claim-text> <claim-text>12. A method of synchronizing uplink timing for a user equipment (UE), said UE communicating with multiple nodes, including an eNodeB, in carl-icr aggregation, wherein the eNodeB is operable to determine the minimum number of TATs required.</claim-text> <claim-text>13. An eNodeB operable to implement the method of claim 12.</claim-text> <claim-text>14. An eNodeB of claim 13, operable to dynamically adapt the number of TATs based upon the change of TA values for the UE to each of the multiple nodes.</claim-text> <claim-text>15. An eNodeB of claim 13. operable to determine whether or not the relative change in mobility of the TIE to the multiple nodes is effectively the same or not.</claim-text> <claim-text>16. An eNodeB of claim 15. wherein if the relative change in mobility of the TIE to the multiple nodes is effectively the same, said eNodeB is operable to implement the same TAT for each of the UE's timing advances.</claim-text> <claim-text>17. An eNodeB of claim 15, wherein if the relative change in mobility of the UE to the multiple nodes is not the same, the eNodeB implements a separate TAT for each of the UE's TAs.</claim-text> <claim-text>18. A method of dynamically adapting the number of time advance timers (TATs) in a network by monitoring the relative change between timing advances used by a TIE in multi-cell carrier aggregation.</claim-text> <claim-text>19. A wireless commuications system operable to implement multipk timing advance timers per UE as a mechanism to manage uplink synchronization, wherein the system is operable to determine whether the same TAT value can be assigned to multiple TATs.</claim-text>