Timing advance configuration for multiple uplink component carriers

Abstract

The invention relates methods for time aligning uplink transmissions by a mobile terminal in a mobile communication system, and to methods for performing a handover of a mobile terminal to a target aggregation access point. The invention is also providing apparatus and system for performing these methods, and computer readable media the instructions of which cause the apparatus and system to perform the methods described herein. In order to allow for aligning the timing of uplink transmissions on uplink component carriers, where different propagation delays are imposed on the transmissions on the uplink component carriers, the inventions suggests to time align the uplink component carriers based on a reference time alignment of a reference cell and a reception time difference or propagation delay difference between the downlink transmissions in the reference cell and the other radio cells, the uplink component carriers of which need to be time aligned.

Claims

1. A method, comprising: configuring a mobile terminal with a time-aligned uplink reference cell; measuring, by the mobile terminal, downlink reception time difference information between a beginning of a first downlink subframe on a target cell that is a non-time-aligned uplink target cell and a beginning of a second downlink subframe on the reference cell, wherein the first downlink subframe and the second downlink subframe refer to a same subframe number; determining, by the mobile terminal, a first target timing advance based on at least the measured reception time difference information and on a reference timing advance used for uplink transmissions on the time-aligned reference cell; time-aligning, by the mobile terminal, the uplink target cell by adjusting a timing for uplink transmissions on the uplink target cell based on the determined first target timing advance; and performing a handover of the mobile terminal to the target cell based on the measurement results and the first target timing advance.

2. The method according to claim 1, comprising: determining by the mobile terminal a reception transmission time difference between the target and reference cell, by measuring a time difference between a time when the mobile terminal transmits an uplink radio frame on the reference cell and a time when the mobile terminal receives a downlink radio frame on the target cell, wherein the uplink radio frame and the downlink radio frame relate to the same radio frame, and the measurement results comprise the reception transmission time difference between the target and reference cell.

3. The method according to claim 2, comprising: determining a downlink reception time difference between the target cell and the reference cell by subtracting the reception transmission time difference from the timing advance of the reference cell.

4. The method according to claim 1, wherein the time-aligning the target cell comprises at least one of: setting the transmission of uplink radio frames on the uplink target cell relative to the beginning of downlink radio frames received via the downlink target cell, using the first target timing advance determined considering that the setting of the transmission of the uplink radio frames on the uplink target cell will be relative to the beginning of downlink radio frames received via the downlink target cell, respectively; setting the transmission of uplink radio frames on the uplink target cell relative to the beginning of downlink radio frames received via the downlink reference cell, using the first target timing advance determined considering that the setting of the transmission of the uplink radio frames on the uplink target cell will be relative to the beginning of downlink radio frames received via the downlink reference cell; and setting the transmission of uplink radio frames on the uplink target cell relative to the beginning of uplink radio frames transmitted via the uplink reference cell, using the first target timing advance determined considering that the setting of the transmission of the uplink radio frames on the uplink target cell will be relative to the beginning of uplink radio frames transmitted via the uplink reference cell.

5. The method according to claim 1, wherein the measuring the downlink reception time difference information, determining a first target timing advance by the mobile terminal and performing a handover of the mobile terminal based on the measurement results and the first target timing advance are triggered by at least one of: a periodical event and a non-periodical determined event.

6. The method according to claim 5, wherein the non-periodical determined event is at least one of the measurement results exceeding a determined threshold and expiration of a timer.

7. A mobile terminal, comprising: a receiver, which, in operation, receives a first downlink subframe and a second downlink subframe; and processing circuitry, which, in operation: configures the mobile terminal with a time-aligned uplink reference cell; measures downlink reception time difference information between a beginning of the first downlink subframe on a target cell that is a non-time-aligned uplink target cell and a beginning of the second downlink subframe on the reference cell, wherein the first downlink subframe and the second downlink subframe refer to a same subframe number; determines a first target timing advance based on at least the measured reception time difference information and on a reference timing advance used for uplink transmissions on the time-aligned reference cell; time-aligns the uplink target cell by adjusting a timing for uplink transmissions on the uplink target cell based on the determined first target timing advance, and performs a handover of the mobile terminal to the target cell based on the measurement results and the first target timing advance.

8. The mobile terminal according to claim 7, wherein the processing circuitry, in operation: determines a reception transmission time difference between the target and reference cell, by measuring a time difference between a time when the mobile terminal transmits an uplink radio frame on the reference cell and a time when the mobile terminal receives a downlink radio frame on the target cell, wherein the uplink radio frame and the downlink radio frame relate to the same radio frame, and the measurement results comprise the reception transmission time difference between the target and reference cell.

9. The mobile terminal according to claim 8, wherein the processing circuitry, in operation, determines a downlink reception time difference between the target cell and the reference cell by subtracting the reception transmission time difference from the timing advance for the reference cell.

10. The mobile terminal according to claim 7, wherein the processing circuitry, in operation, implements at least one of: setting the transmission of uplink radio frames on the uplink target cell relative to the beginning of downlink radio frames received via the downlink target cell, using the first target timing advance determined considering that the setting of the transmission of the uplink radio frames on the uplink target cell will be relative to the beginning of downlink radio frames received via the downlink target cell, respectively; setting the transmission of uplink radio frames on the uplink target cell relative to the beginning of downlink radio frames received via the downlink reference cell, using the first target timing advance determined considering that the setting of the transmission of the uplink radio frames on the uplink target cell will be relative to the beginning of downlink radio frames received via the downlink reference cell; and setting the transmission of uplink radio frames on the uplink target cell relative to the beginning of uplink radio frames transmitted via the uplink reference cell, using the first target timing advance determined considering that the setting of the transmission of the uplink radio frames on the uplink target cell will be relative to the beginning of uplink radio frames transmitted via the uplink reference cell.

11. The mobile terminal according to claim 7, wherein the processing circuitry, in operation, measures the downlink reception time difference information, determines a first target timing advance by the mobile terminal, and performs a handover of the mobile terminal based on the measurement results and the first target timing advance when triggered by at least one of: a periodical event, and a non-periodical determined event.

12. The mobile terminal according to claim 11, wherein the non-periodical determined event is at least one of the measurement results exceeding a determined threshold and expiration of a timer.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) In the following the invention is described in more detail in reference to the attached figures and drawings. Similar or corresponding details in the figures are marked with the same reference numerals.

(2) FIG. 1 shows an exemplary architecture of a 3GPP LTE system,

(3) FIG. 2 shows an exemplary overview of the overall E-UTRAN architecture of 3GPP LTE,

(4) FIG. 3 shows an exemplary sub-frame boundaries on a downlink component carrier as defined for 3GPP LTE (Release 8/9),

(5) FIG. 4 shows an exemplary downlink resource grid of a downlink slot as defined for 3GPP LTE (Release 8/9),

(6) FIGS. 5 & 6 show the 3GPP LTE-A (Release 10) Layer 2 structure with activated carrier aggregation for the downlink and uplink, respectively,

(7) FIG. 7 shows a RACH procedures as defined for 3GPP LTE (Release 8/9) in which contentions may occur, and

(8) FIG. 8 shows a contention-free RACH procedure as defined for 3GPP LTE (Release 8/9),

(9) FIG. 9 exemplifies the time alignment of an uplink component carrier relative to a downlink component carrier by means of a timing advance as defined for 3GPP LTE (Release 8/9),

(10) FIGS. 10 & 11 exemplify the interruption time during a non-synchronized and synchronized handover, respectively, due to time alignment of multiple uplink component carriers,

(11) FIG. 12 exemplifies the reduction of the interruption time caused by a synchronous handover, when employing the time alignment calculation of uplink component carriers according to one of the various embodiments described herein,

(12) FIG. 13 shows an exemplary scenario in which a user equipments aggregates two radio cells, one radio cell originating from an eNodeB, and the other radio cell originating from a Remote Radio Head (RRH),

(13) FIG. 14 shows an exemplary scenario in which a user equipments aggregates two radio cells, one radio cell originating from an eNodeB, and the other radio cell originating from a Frequency Selective Repeater (FSR),

(14) FIGS. 15 to 17 show a exemplary procedures according to different exemplary embodiments of the invention allowing the user equipment to determine the correct time alignment for non-time aligned uplink component carriers in other radio cells than the reference cell,

(15) FIG. 18 shows an exemplifies the structure of a sub-frame according to one exemplary embodiment of the invention, and the transmissions thereof via three component carriers,

(16) FIG. 19 exemplifies the time alignment of three uplink transmissions for a single sub-frame using different timing advance values, so as to time align their reception at an aggregation access point,

(17) FIG. 20 shows the format of an activation/deactivation MAC control element, being a command for activating or deactivating one or more SCells,

(18) FIG. 21 shows the format of an Extended Power Headroom MAC control element, when Type 2 PHR is reported,

(19) FIG. 22 illustrates the disadvantage of using a PRACH transmission on a component carrier to be uplink-time-aligned, and in particular, the differences in the uplink timing between PRACH on one component carrier and PUSCH/PUCCH on the another component carrier,

(20) FIG. 23 is a signaling diagram illustrating an uplink-time-alignment procedure according to one embodiment of the invention,

(21) FIG. 24 presents the network scenario assumed for one particular embodiment of the invention,

(22) FIG. 25 shows a signaling diagram illustrating an uplink-time-alignment procedure according to another embodiment of the invention,

(23) FIG. 26 shows a timing diagram of transmissions exchanged between the UE and the eNodeB, including uplink-time-aligned uplink transmission according to one embodiment of the invention,

(24) FIG. 27 shows a timing diagram of transmissions exchanged between the UE and the eNodeB, including uplink-time-aligned uplink transmissions according to another embodiment of the invention, wherein the PCell and SCell downlink transmission are time-delayed,

(25) FIG. 28 is a flowchart diagram illustrating an uplink-time-alignment procedure according to a further embodiment of the invention,

(26) FIG. 29 shows a format of a MAC control element for transmitting the measurement results from the mobile terminal to the eNodeB, the measurement results being the downlink reception time differences between the PCell and all the SCells,

(27) FIG. 30 shows a format of a MAC control element for transmitting the measurement results from the mobile terminal to the eNodeB, the measurement results being the reception transmission time differences between the PCell and all the SCells,

(28) FIG. 31 illustrates the uplink time alignment process performed at the mobile terminal, in case the timing advance command received from the eNodeB is calculated relative to the beginning of an uplink radio frame of the PCell, according to one embodiment of the invention,

(29) FIG. 32 illustrates the uplink time alignment process performed at the mobile terminal, in case the timing advance command received from the eNodeB is calculated relative to the beginning of a downlink radio frame of the PCell, according to one embodiment of the invention, and

(30) FIG. 33 shows the format of a timing advance command according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(31) The following paragraphs will describe various embodiments of the invention. For exemplary purposes only, most of the embodiments are outlined in relation to an orthogonal single-carrier uplink radio access scheme according to 3GPP LTE (Release 8/9) and LTE-A (Release 10) mobile communication systems discussed in the Technical Background section above. It should be noted that the invention may be advantageously used for example in a mobile communication system such as 3GPP LTE (Release 8/9) and LTE-A (Release 10) communication systems as described in the Technical Background section above, but the invention is not limited to its use in this particular exemplary communication network. The invention may be broadly used in communication systems where time alignment of uplink transmissions on multiple carriers (having different propagation delays) is desired.

(32) The explanations given in the Technical Background section above are intended to better understand the mostly 3GPP LTE (Release 8/9) and LTE-A (Release 10) specific exemplary embodiments described herein and should not be understood as limiting the invention to the described specific implementations of processes and functions in the mobile communication network.

(33) One aspect of the invention is to time align a non-time aligned uplink component carrier of a radio cell relative to a reference cell in which a (reference) uplink component carrier is already time aligned. The timing advance for time alignment of the non-time aligned uplink component carrier of the radio cell is determined based on the timing advance for the uplink component carrier of the reference cell and the time difference of the reception times (or propagation delay difference) for corresponding downlink transmissions via the downlink component carriers of the reference cell and the radio cell comprising the non-time aligned uplink component carrier. The time alignment mechanism may be used for time aligning transmissions on uplink component carriers that are newly configured or activated by a mobile terminal or that may require reestablishment of the time alignment (e.g. after loosing same). As will be outlined below, the new configuration of uplink component carriers may for example result from a handover of the mobile terminal to a target access point or an operation of configuring or activating an additional uplink component carrier at the mobile terminal.

(34) Corresponding downlink transmissions may for example denote transmissions that are sent simultaneously by an access point via the downlink component carrier of the reference cell and via the radio cell comprising the non-time aligned uplink component carrier (e.g. transmissions of a given sub-frame sent via the two downlink component carriers). In this case the reception time difference is also the time difference of the propagation delay of the transmission sent via the downlink component carrier of the reference cell and propagation delay of the transmission sent via the downlink component carrier of the radio cell comprising the non-time aligned uplink component carrier (also referred to as “propagation delay difference” in the following). Hence, in this case the determination of the timing advance for time alignment of the non-time aligned uplink component carrier of the radio cell is determined based on the timing advance for the (uplink component carrier of the) reference cell and the propagation delay difference of downlink transmissions via the downlink component carriers of the reference cell and the radio cell comprising the non-time aligned uplink component carrier.

(35) For the purpose of time alignment, it is—strictly speaking—not necessary that the reference cell is configured an uplink component carrier. It would be sufficient that the mobile terminal is provided with a reference timing advance value to be used, and further there is downlink component carrier received through the reference cell, based on which the reception time difference (or propagation delay difference) can be determined for time aligning the other radio cells. However, for most practical implementations it may be advantageous is the reference cell is configured with a downlink component carrier and a (time aligned) uplink component carrier.

(36) Furthermore, in one embodiment of the invention, the reference cell relative to which the timing of the non-time aligned uplink component carrier(s) is a radio cell comprising a time-aligned uplink component carrier between the user equipment and the aggregation access point. However, the reference cell may also be a radio cell comprising a time-aligned uplink component carrier between the user equipment and another access point than the aggregation access point. The term aggregation access point (for example a base station or eNodeB) is used to denote location in the access network, i.e. a node, at which the uplink transmissions of the user equipment on the different uplink component carriers are aggregated. Aggregation refers to a simultaneous reception of the radio signals corresponding to transmissions (e.g. respective sub-frames) on the different uplink component carriers from the user equipment, i.e. on the physical layer, for joint physical layer processing (e.g. joint demodulation (e.g. including utilization of one IFFT (Inverse Fast Fourier Transform) for the processing of the received sub-frame in an OFDM system) and/or joint decoding of coded transport block(s), etc.) by the aggregation access point;

(37) and/or a processing of protocol data units received in the transmissions (e.g. respective sub-frames) on the different uplink component carriers from the user equipment in a protocol entity of the aggregation access point.

(38) The conjoint processing of protocol data units received in the transmissions on the different uplink component carriers from the user equipment may be—in one exemplary implementation—the conjoint processing of PDUs obtained from the transmissions on the different uplink component carriers in the MAC layer or RLC layer of the aggregation access point, e.g. for the purpose of PDU reordering.

(39) In other words, in one exemplary embodiment of the invention, the aggregation access point denotes the network node which is to receive the radio signals corresponding to transmissions (e.g. respective sub-frames) on the different uplink component carriers, i.e. on the physical layer, from the user equipment for joint processing (e.g. demodulation and/or decoding) by the aggregation access point. In another exemplary embodiment of the invention, the aggregation access point denotes the network node which should processes protocol data units received in the transmissions (e.g. respective sub-frames) via the different uplink component carriers from the user equipment. In one exemplary implementation, the aggregation access point is a base station or eNodeB.

(40) In line with this first aspect of the invention and according to an exemplary embodiment of the invention a method for time aligning uplink transmissions by a mobile terminal in a mobile communication system is provided. The mobile terminal is configured with a first radio cell comprising a downlink component carrier and a time aligned uplink component carrier, and a second radio cell comprising a downlink component carrier and a non-time aligned uplink component carrier. The mobile terminal determines a reception time difference (or propagation delay difference) for downlink transmissions from an aggregation access point to the mobile terminal via the downlink component carrier of the first radio cell and via the downlink component carrier of the second radio cell, respectively, and time aligns the uplink component carrier of the second radio cell by adjusting a timing advance for uplink transmissions on the uplink component carrier of the second radio cell based on the timing advance for uplink transmissions on the time aligned uplink component carrier of the first radio cell and the determined reception time difference (or propagation delay difference), so that uplink transmissions transmitted from the mobile terminal to the aggregation access point via the uplink component carrier of the first radio cell and the uplink component carrier of the second radio cell arrives at the aggregation access point simultaneously. Hence, no RACH procedure is needed for time alignment of the uplink component carrier in the second radio cell.

(41) In this document, simultaneously or at the same point in time means at the same point in time plus/minus some deviation, which is in the μs range. For example, minor differences between uplink and downlink propagation delays in a given radio cell as well as the granularity of timing advance values imply that there is no perfect time alignment of the uplink transmissions on uplink component carriers. In any case simultaneous arrival of uplink transmissions is ensured to the extent that the uplink transmissions by a mobile terminal via distinct uplink component carriers (having different propagation delays) can be processed together by the receiving aggregation access point. For example, different transmissions of one given sub-frame on the uplink component carriers are time aligned such that they are received in a manner allowing the aggregation access point to process all transmissions of the sub-frame together (joint processing).

(42) Furthermore, it should also be noted that time alignment of uplink component carriers that are configured for a mobile terminal is of course also applicable, where the mobile terminal has to time align more than one uplink component carrier. Basically, an arbitrary number of uplink component carriers can be time aligned by the procedures described herein, as long as there is one reference time advance for an uplink component carrier.

(43) Moreover, it should be noted that a single radio cell may comprise one or more uplink component carrier and one or more downlink component carriers. In one radio cell it may be the case that the propagation delay of all uplink and downlink component carriers can be assumed identical. Accordingly, the uplink component carriers of a radio cell can be considered to form a group of uplink component carriers that experience the same propagation delay and that may be associated to a single timing advance value. Of course, if the propagation delays of the uplink component carriers differ from each other within a radio cell (e.g. due to using a FSR), then a timing advance value for each experienced propagation delay should be provided.

(44) Another second aspect of the invention is to suggest a procedure for time alignment of uplink component carriers for use in a handover procedure of a mobile terminal. Procedures are provided for synchronous and non-synchronous handover. The time alignment procedure as discussed above may be also used for time aligning uplink component carriers in radio cells controlled by the target (aggregation) access point to which the mobile terminal is handed over. According to this aspect, the timing advance for one of the uplink component carriers in a radio cell (i.e. the reference cell) of the target (aggregation) access point may be either provided to the mobile terminal (synchronized handover) or may be determined by the mobile terminal (non-synchronized handover), e.g. by means of performing a random access procedure. The other uplink component carrier(s) of the other radio cell(s) to be used by the mobile terminal may then be time aligned relative to the reference cell as described previously herein.

(45) In case a mobile terminal, also denoted user equipment in the 3GPP terminology, is aggregating component carriers that stem from sources in different bands and physical locations, due to different propagation conditions these component carriers all might have different propagations delay.

(46) Under the premises that an aggregation access point (e.g. eNodeB) is processing the uplink transmissions via all configured component carriers of a given mobile terminal, the uplink transmissions from the mobile terminal should arrive simultaneously (at the point in time) at the aggregation access point even though the propagation delays on the component carriers are different. Hence the aggregation access point could configure the mobile terminal with a different timing advance for each uplink component carrier depending on it's specific propagation delay. The propagation delay is likely to be the same for component carriers that lie in the same frequency band and that are terminated at the same location (i.e. by one access point). Hence it may be suitable to group certain component carries into timing advance groups where all the member component carriers of a given group transmit with the same timing advance specific to this group in the uplink.

(47) When considering for example a state-of-the-art 3GPP communications system setting several timing advances for one user equipment would imply that several RACH procedures, one RACH procedure for each timing advance group, would need to be performed. Thus the eNodeB can determine the propagation delay for each component carrier group in the uplink based the RACH preamble 701, 802 and would then set the appropriate timing advance for each component carrier group needed using the Random Access Response message 702, 802 (see FIG. 7 and FIG. 8). This would imply a significant delay caused by executing several RACH procedures assuming that a user equipment can only perform a single RACH procedure at a time.

(48) Likewise, upon a handover, a user equipment would have to acquire a timing advance value for the component carriers in the target cell through RACH procedures, which would mean that there is an increased interruption time between the “RRC connection reconfiguration” message and the “RRC connection reconfiguration completed” message, where UE cannot receive or transmit data. FIG. 10 exemplifies the steps within a conventional non-synchronized handover of a user equipment from a source eNodeB to a target eNodeB. After the user equipment receiving a RRC connection reconfiguration message from the source eNodeB the user equipment acquires downlink synchronization in the target primary cell (PCell) first and performs a random access procedure (RACH procedure) resulting in a time alignment of the uplink component carrier(s) of the primary cell. Furthermore, in case the user equipment is configured with additional component carriers by the target eNodeB (in this example, component carriers of two component carrier groups (CoCa Group 1 and 2)) that experience different propagation delays then the user equipment would need to perform additional RACH procedures (in this example, a RACH procedure of CoCa Group 1 and another RACH procedure of CoCa Group 2) that contribute to the handover delay. Upon having time aligned all configured uplink carriers, the user equipment finishes the non-synchronized handover by sending a RRC connection reconfiguration complete message.

(49) As highlighted in FIG. 11, in case of a synchronous handover the user equipment would be provided with the timing advance value for the primary cell of the target eNodeB which would allow avoiding the RACH procedure for the primary cell (PCell). However, still the RACH procedures for uplink component carriers of all other timing advance groups (CoCa Group 1 and 2) would need to be performed to appropriately establish the timing advances for the respective uplink component carriers.

(50) Assuming for exemplary purposes that there is an aggregation access point in the network and that there are at least two component carriers that stem from at least two different physical locations (e.g. due to involvement of a remote radio head, RRH), respectively, that are experiencing different propagation delays (e.g. because the signal path is through a frequency selective repeater) and further assuming that the mobile terminal has at least one uplink component carrier which is time aligned (i.e. the uplink component carrier of the reference cell), the mobile terminal can derive the necessary timing advance for the non-aligned component carrier(s) from one reference timing advance, i.e. the timing advance of the already time aligned uplink component carrier in the reference cell. Furthermore, it should be noted that this is true as long as the uplink propagation delay is the same as the downlink propagation delay for the uplink component carrier and the downlink component carrier of a given radio cell.

(51) The timing advance for a given non-time aligned uplink component carrier of a radio cell is determined based on the timing advance (for the uplink component carrier) in the reference cell and a reception time difference or propagation delay difference of transmissions receiving through a downlink component carrier of the reference cell and through a downlink component carrier of the radio cell comprising the non-time aligned uplink component carrier.

(52) In the following the procedure for determining the timing advance for non-timer aligned uplink component carrier according to exemplary embodiments of the invention will be described with reference to a 3GPP based system for exemplary purposes only. In the following examples, the aggregation access point is corresponding to an eNodeB, while a further access point is formed by a Remote Radio Head (RRH) or a Frequency Selective Repeater (FSR).

(53) For exemplary purposes the uplink and downlink component carriers are assumed to have a slotted structure, i.e. transmissions in the uplink and downlink are transmitted in sub-frames. In the downlink, a sub-frame structure as exemplarily shown in FIG. 3 and FIG. 4 can be used, but the invention is not limited thereto. Similarly, in the uplink, a sub-frame structure as exemplified in FIG. 3 and FIG. 4 can be used, but the invention in not limited thereto. The number of subcarriers (i.e. the bandwidth) for an uplink component carrier may be different from the number of subcarriers (i.e. the bandwidth) of a downlink component carrier. The uplink component carriers may have different bandwidths. Likewise the downlink component carriers may have different bandwidths.

(54) Furthermore, in the uplink, a single sub-frame is assumed to span the entire bandwidth (i.e. all subcarriers (or sub-bands)) of all uplink component carriers aggregated by an access point (e.g. eNodeB). From the perspective of a user equipment, a single sub-frame is spanning the entire bandwidth (i.e. all subcarriers (or sub-bands)) of all component carriers configured by the mobile terminal in the uplink or downlink, respectively. Hence, the data sent within in one sub-frame is transmitted as an individual transmission of modulated symbols (e.g. OFDM symbols) on each component carrier configured in the uplink or downlink, respectively. Therefore, order to process a given single sub-frame that is transmitted in the downlink or uplink the mobile terminal (e.g. the user equipment) or the access point (e.g. the base station or eNodeB) needs to receive all transmissions of the sub-frame on the respective downlink component carriers configured by the mobile terminal, respectively, all uplink component carriers received by the (aggregation) access point (e.g. eNodeB).

(55) FIG. 18 exemplarily shows a sub-frame that is to be transmitted via three component carriers in the uplink. Assuming for example an OFDM-based communications system, a sub-fame can be defined as a set of N.sub.sub-frame consecutive OFDM symbols (for example 12 or 14 OFDM symbols) in the time domain and a set of sub carriers corresponding to the—here three—difference component carriers in the frequency domain. For exemplary purposes, three component carriers CoCa 1, CoCa 2 and CoCa 3 are shown that comprise each N.sub.CoCa1, N.sub.Coca2, and N.sub.CoCa3 subcarriers respectively. The subcarriers of the component carriers may also be grouped into individual sub-bands. Further, strictly speaking, the sub-frame does not necessarily span a continuous region of subcarriers in the frequency domain; the different subcarriers of the component carriers may also be spaced in the frequency domain. Similarly, the number of the subcarriers of the individual component carriers (i.e. their bandwidth) may or may not be the same for the different component carriers. E.g. component carriers CoCa 1 and CoCa 2 could be component carriers providing each a bandwidth of 5 MHz, while component carrier CoCa 3 has a bandwidth of 10 MHz.

(56) The modulation symbols of a respective OFDM symbol that are located on the subcarriers of a given component carrier are considered a transmission of the sub-frame. Hence, in the example shown in FIG. 18, a single sub-frame is transmitted by means of three transmissions on the three component carriers CoCa 1, CoCa 2 and CoCa 3.

(57) In this connection, time alignment of the transmissions on an uplink component carrier means that the mobile terminal shifts (in time) the sub-frame structure of the respective uplink component carrier relative to the boundaries of the sub-frames received in the downlink (e.g. the sub-frame boundaries of the downlink component carrier of the reference cell or the radio cell to which the uplink component carrier to be time-aligned belongs). The timing advance (value) indicates the shift in time to be applied relative to the beginning/timing of the sub-frames in the reference sub-frame structure received in the downlink by the mobile terminal. In case of appropriately configuring the timing advance for the uplink component carriers (of different radio cells with different propagation delays and/or of different mobile terminals) the access point can ensure that the uplink sub-frame boundaries are aligned for all uplink component carriers.

(58) FIG. 19 exemplarily shows the transmission of three consecutive sub-frames (numbered 1, 2 and 3) via three uplink component carriers (as shown in FIG. 18). Due to the user equipment UE using individual timing advance values for the three component carriers CoCa 1, CoCa 2 and CoCa 3, which are assumed to have different propagation delays for exemplary purposes, the individual transmissions of the respective single sub-frames become time aligned with respect to their reception at the eNodeB. This facilitates, for example, that the physical layer entity of the eNodeB can a single IFFT operation when processing the individual sub-frames.

(59) In one exemplary embodiment of the invention, the timing advance value TA.sub.AP2 of a (non-time aligned) uplink component carrier of a radio cell is calculated at the mobile terminal based on the known timing advance value TA.sub.AP1 of the (time-aligned) uplink component carrier of the reference cell, and further based reception time difference (or propagation delay difference) ΔT.sub.prop, as follows:
TA.sub.AP2=TA.sub.AP1+2.Math.ΔT.sub.prop  (Equation 1)

(60) The timing advance value TA.sub.AP1 of the (time-aligned) uplink component carrier of the reference cell may have been for example obtained by the mobile terminal by performing a RACH procedure as outlined with respect to FIGS. 7 to 9 before, or the timing advance value TA.sub.AP1 may have also been calculated earlier by the user equipment as described herein with reference to another reference cell.

(61) Furthermore, in one exemplary implementation the time alignment of the reference cell and hence the value of TA.sub.AP1 may be (constantly) updated by the access point of the reference cell. Hence, in case the timing advance of the reference cell is updated the mobile terminal may also update the timing advance values calculated relative thereto. The update of the timing advance for the uplink component carrier(s) based on the updated timing advance of the uplink component carrier in the reference cell may also include a new measurement of the reception time difference (or propagation delay difference) ΔT.sub.prop since the this time difference may also be subject to changes, e.g. due to movement of the mobile terminal.

(62) Alternatively, the update of the time alignment of the reference cell may not cause an update of the timing advance value(s) for the uplink component carrier(s) of the other radio cell(s). Instead, the aggregation access point (e.g. the eNodeB) could send update commands for the timing advance values of the respective uplink component carriers or the respective uplink component carrier groups. The update commands may for example indicate a correction of the presently set timing advance values. The update commands may be sent for example by MAC control signalling, e.g. within MAC control elements that are multiplexed to the downlink transmissions.

(63) It is assumed in Equation 1 that the timing advance value TA.sub.AP2 is defining the timing advance relative to the reception timing of the downlink component carrier (or to be more precise relative to the reception timing of the beginning of sub-frames transmitted via the downlink component carrier) of the radio cell the uplink component carrier of which is to be time aligned.

(64) The reception time difference (or propagation delay difference) ΔT.sub.prop can be assumed to be defined as:
ΔT.sub.prop=T.sub.DL-TCell−T.sub.DL-RCell  (Equation 2)

(65) where T.sub.DL-TCell denotes the point in time at which the beginning of a sub-frame is detected by the mobile terminal within a transmission via the target cell (TCell), i.e. the radio cell the uplink component carrier of which is to be time aligned, and T.sub.DL-RCell denotes the point in time at which the beginning of the same sub-frame is detected by the mobile terminal within a transmission via the reference cell (RCell).

(66) In case the timing advance value TA.sub.AP2 is defining the timing advance relative to the reception timing of the downlink component carrier of the reference cell, the timing advance value TA.sub.AP2 is calculated as follows:
TA.sub.AP2=TA.sub.AP1+ΔT.sub.prop  (Equation 3)

(67) However, defining the timing advance value TA.sub.AP2 as in Equation 3 may have the disadvantage that in case the reference cell is “dropped”, i.e. the component carrier(s) of the reference cell are deactivated or no longer configured (e.g. due to handover), the mobile terminal may need to recalculate all timing advance values. This is true in case the loss of the (time alignment in the) reference cell is also implying a loss of the time alignment of all other radio cells that are time aligned relative thereto. However, it may also be the case that after initial time alignment relative to the reference cells, the time alignment of the individual radio cells (i.e. uplink component carriers) is individually or group-wise updated by the aggregation access point, so that a loss of the reference cell does not necessarily require a new time alignment of the other radio cells configured by the mobile terminal.

(68) In the following the determination of the timing advance for non-time aligned uplink component carriers (non-time aligned radio cells) will be outlined in further detail and reference to some exemplary scenarios. In the exemplary scenario shown in FIG. 13, it is assumed that a user equipments aggregates two radio cells, one radio cell originating from a first location, e.g. an eNodeB, and the other radio cell originating from a different location, e.g. a Remote Radio Head (RRH). A RRH denotes a radio equipment that is connected to and remote to an access point, such as a base station (e.g. a eNodeB in 3GPP based systems) which is controlling the RRH. The interface between the access point and the RRH may be for example use the Common Public Radio Interface (CPRI) standard—see www.cpri.info. The RRH and its controlling access point may be for example interconnected via a fiber optic cable.

(69) Transmissions via the uplink component carriers of the two radio cells are processed in the same aggregation node, i.e. the eNodeB in this example, and the propagation delay of the downlink component carrier and the uplink component carrier of each radio cell is the same. The radio cell comprising the uplink component carrier UL CoCa 1 and the downlink component carrier DL CoCa 1 between the mobile terminal UE and the eNodeB is denoted the primary radio cell (e.g. the PCell of the user equipment), while the radio cell comprising the uplink component carrier UL CoCa 2 and the downlink component carrier DL CoCa 2 between the mobile terminal UE and the RRH is denoted secondary radio cell (e.g. a SCell of the user equipment). All transmissions sent from the user equipment via the secondary cell are received by the transceiver of the RRH and a forwarded to the eNodeB via the interface between RRH and eNodeB. Similarly, when transmitting data via the RRH, the eNodeB transmits the data to the RRH e.g. using CPRI protocols and the RRH forwards the data to the user equipment via the downlink component carrier of the secondary cell.

(70) The primary radio cell may be considered to be the PCell of the user equipment in this example and is the reference cell for time alignment. However, also any other radio cell that the user equipment aggregates and which is currently timing aligned can serve as a reference cell. For example, the time alignment of the uplink component carrier UL CoCa1 in the primary radio cell may have been set by the eNodeB through a RACH procedure performed in the primary radio cell.

(71) FIG. 15 is showing a procedure according to an exemplary embodiment of the invention allowing the user equipment to determine the correct time alignment for non-time aligned uplink component carriers in other radio cells than the reference cell. For exemplary purposes, it is assumed that the eNodeB is the aggregation access point and that the RRH servers as an additional access point, as outlined with respect to FIG. 13 above. The eNodeB transmits sub-frames in the downlink to the user equipment via the primary and secondary radio cell, respectively. For exemplary purposes, it is assumed that the eNodeB transmits all transmissions of a single sub-frame (corresponding transmissions) simultaneously. Corresponding transmissions of a given sub-frame are indicated by the same number in FIG. 15. Since the transmissions of a given sub-frame take different propagation paths, the respective transmissions of the given sub-frame are received at different points in time at the user equipment, as highlighted in the upper part of FIG. 15.

(72) The time shift between the transmission of a sub-frame by the eNodeB and the RRH is for example due to the transmission of the sub-frame via the RRH being forwarded by the eNodeB via the interface to the RRH (propagation delay TPD.sub.eNB-RRH) and from the RRH to the user equipment (propagation delay TPD.sub.RRH-UE). Furthermore, there may be also a non-neglectable processing delay TPROC.sub.RRH of the sub-frames at the RRH, which may need to be taken into account. The propagation delay of the transmission of a sub-frame from the eNodeB to the user equipment via the primary cell is denoted TPD.sub.eNB-UE.

(73) The user equipment measures the time difference ΔT.sub.prop between the reception of corresponding transmissions of a sub-frame. In more detail, the user equipment determines the difference between the reception times of a transmission of a sub-frame #i via a downlink component carrier of the radio cell in which the uplink component carrier is to be time aligned, and a transmission of the sub-frame #i via a downlink component carrier of the reference radio cell. In the example shown in FIG. 15, where the primary radio cell of the eNodeB is the reference cell for time alignment, the user equipment determines at what point in time the beginning of a sub-frame transmitted via a downlink component carrier of the reference cell is received, and at what point in time the beginning of the of the very same sub-frame via downlink component carrier of the radio cell of the RRH is received, and calculates the time difference ΔT.sub.prop of these two reception times.

(74) Time difference ΔT.sub.prop between the reception of corresponding transmissions of a sub-frame assuming a scenario as shown in FIG. 13 is defined as
ΔT.sub.prop=(TPD.sub.eNB-RRH+TPROC.sub.RRH+TPD.sub.RRH-UE)−TPD.sub.eNB-UE  (Equation 4)
where the term TPROC.sub.RRH may be omitted. Since the eNodeB sends all transmissions of the sub-frame simultaneously, ΔT.sub.prop actually denotes the propagation delay difference of the transmission of the sub-frames via the reference cell (primary radio cell) and the secondary radio cell as shown in FIG. 13.

(75) In order to ensure that corresponding transmissions of a sub-frame arrive simultaneously at the eNodeB when sending them through different uplink component carries experiencing different propagation delays, the user equipment needs to compensate the measured propagation delay difference and advance the transmissions further (relative to the uplink transmission on the uplink component carrier of the reference cell). Hence, in the exemplary scenario of FIG. 13, the transmissions of sub-frames on uplink component carrier UL CoCa 2 via the RRH is to be advanced by the reference timing advance TA.sub.eNodeB (which is known to the user equipment) and two times the time difference ΔT.sub.prop measured by the user equipment. Thus the correct timing advance to be applied for the uplink transmissions of the sub-frames sent via the RRH can be calculated as
TA.sub.RRH=TA.sub.eNodeB+2.Math.ΔT.sub.prop  (Equation 5)

(76) As mentioned earlier, the timing advance value TA.sub.eNodeB of the reference cell/reference uplink component carrier UL CoCa 1 may have been learned by the user equipment from a RACH procedure with the eNodeB or may have been determined in the manner described above based on the known timing advance from another/previous reference cell.

(77) The eNodeB controlling the reference cell in the scenario of FIG. 13 may constantly adjust the time alignment of the uplink component carrier UL CoCa 1 by sending continuous updates of the timing advance value TA.sub.eNodeB. The updates of the timing advance may be for example sent via MAC signalling, e.g. using MAC control elements multiplexed into a downlink transmission sent to the user equipment.

(78) In one further exemplary embodiment of the invention, the time alignment of an uplink component carrier could be controlled by means of a timer. A separate timer may be maintained by the mobile terminal for each timing advance value (each associated to either an individual uplink component carrier or a uplink component carrier group). The mobile terminal resets and starts the timer each time it receives an update command for a given timing advance value (respectively, plink component carrier or a uplink component carrier group). Whenever the timer expires, i.e. timing alignment is considered to be lost, time alignment can be reestablished by the mobile terminal using the mechanisms described herein, e.g. the mobile terminal can recalculate the timing advance value based on the reference cell and a new measurement of the reception time difference (or propagation delay difference) or the user equipment could alternatively perform a RACH procedure to reestablish time alignment.

(79) Thus an uplink—in practice—can be considered to be timing aligned as long as the user equipment maintains a reference timing alignment on another radio cell's uplink.

(80) As exemplified in FIG. 16, the timing advance value TA.sub.RRH may also be calculated relative to the reception timing of the downlink sub-frame boundaries on a downlink component carrier with the reference cell, i.e. downlink component carrier DL CoCa 1 of the primary radio cell as shown in FIG. 13. Accordingly, the equation for calculating the timing advance value TA.sub.RRH for the uplink component carrier UL CoCa 2 in the secondary radio cell would be changed to:
TA.sub.RRH=TA.sub.eNodeB+ΔT.sub.prop  (Equation 6)
where the values TA.sub.eNodeB and ΔT.sub.prop remain unchanged in comparison to Equation 5.

(81) Furthermore, in the examples of FIG. 15 and FIG. 16, the timing advance values TA.sub.RRH and TA.sub.eNodeB have been chosen to not only align the uplink transmissions on the uplink component carriers with respect to the sub-frame boundaries, but also to aligned the sub-frame boundaries in the uplink and downlink component carriers. However, this is not mandatory.

(82) As exemplified in FIG. 17, the timing advance values for the uplink component carriers may be also chosen so that the sub-frame boundaries in the uplink and downlink component carriers are not aligned. This may be for example achieved in case the reference timing advance value (denoted TA.sub.AP1 or TA.sub.eNodeB in the examples above) is configured by the aggregation access point (e.g. eNodeB) so as to not correspond to two times the propagation delay between the aggregation access point and the mobile terminal, as for example shown in FIG. 9. The timing advance values for non-aligned uplink component carrier(s) may be then still determined as outlined above with respect to FIGS. 15 and 16 based on this reference timing advance value. However, the timing advance value(s) calculated on such reference timing advance value will then still align the sub-frame boundaries on the uplink component carriers, but not the sub-frame boundaries of uplink and downlink component carriers.

(83) The same assumptions and calculations that are described above may also be used in scenarios where the over-the-air signal between mobile terminal and aggregation access point, and vice versa, is passing through a Frequency Selective Repeater (FSR). A FSR may also be referred to as a bi-directional amplifier (BDA). The FSR is an apparatus that used for boosting the radio signals of a wireless system in a local area by receiving the radio signal by means of a reception antenna, amplifying the received radio signal with a signal amplifier and broadcasting the amplified radio signal via an internal antenna. The operation of the FSR is commonly transparent to the other network nodes, i.e. the access points and mobile terminals. The FSR may be assumed to boost the radio signals of one or more component carriers in the downlink and uplink. In case only a subset of the configured component carriers is amplified by a FSR, the radio signals of the different component carriers may experience different propagation delays, similar to the situation discussed previously herein with respect to FIG. 13.

(84) One difference between the usage of a RRH or a FSR is the location of reception of the physical layer. Physical layer reception of the uplink transmissions for the radio cells that originate at the location of the aggregation access point (e.g. eNodeB) takes place at the aggregation access point, while for the radio cells originating from the location of the RRH for physical layer reception takes place at the RRH. Inherently, the method of time alignment described above for the scenario shown in FIG. 13 adjusts the uplink timing for the radio cells being received at the RRH in manner that all uplink transmissions of all mobile terminal arrive at the same time at the RRH, which is important for interference-free reception of all uplink radio signals arriving from all mobile terminals at the RRH. Furthermore, since processing delay in the RRH and propagation delay from RRH to aggregation access point (e.g. eNodeB) can be assumed to be the same for all uplink radio signals received at the RRH, all uplink data forwarded by the RRH arrive at the aggregation access point at the same time as well, which is beneficial for further processing in higher layers.

(85) For the case that a Frequency Selective Repeater is used, all uplink radio signals are received at the location of the aggregation access point (e.g. the eNodeB). Hence, the physical radio signals of all uplink transmissions for all radio cells should advantageously arrive at the same time instance, in order to ensure interference-free physical layer processing.

(86) FIG. 14 exemplifies a scenario, where a FSR is used to boost the downlink and uplink component carriers (DL/UL CoCa 2) of a secondary radio cell, while the radio signals of the downlink and uplink component carriers (DL/UL CoCa 1) of a primary radio cell are not amplified by the FSR. In this scenario it is assumed that the uplink and downlink component carriers of the secondary radio cell are boosted by the FSR and that the user equipment is not receiving the uplink and downlink carriers of the secondary radio cell from the directly eNodeB. Hence, in this scenario it can be again assumed that the propagation delay of uplink and downlink component carriers within the secondary radio cell is different from the propagation delay of uplink and downlink component carriers within the primary radio cell. Furthermore, there is no propagation delay difference between the uplink and downlink component carriers within the secondary radio cell.

(87) In case it is further assumed that the timing advance value TA.sub.eNodeB for the uplink component carrier UL CoCa 1 in the primary radio cell is known, the user equipment can time align the transmissions on the uplink component carrier UL CoCa 2 in the secondary radio cell based on this reference time alignment TA.sub.eNodeB and the reception time difference (or propagation delay difference) between the downlink component carrier transmissions in the primary and secondary radio cells in a manner described above. Basically the same equations above can be reused, where replacing the term TA.sub.RRH with the term TA.sub.FSR denoting the timing advance value for the uplink component carrier UL CoCa 2 in the secondary radio cell.

(88) Since the utilization of a FSR may not be known to the mobile terminal—as it is operating in a transparent fashion—the aggregation access point (e.g. eNodeB) may inform the mobile terminal(s) whether it (they) are allowed to calculate timing advance values based on a reference cell or not. The aggregation access point (e.g. eNodeB) may be aware of the network configuration and thus also about the use and configuration of FSR(s) in its vicinity.

(89) Configuration of Timing Advance method by Aggregation Access Point

(90) As already indicated above the mobile terminal (e.g. user equipment) may be unaware of the location the different radio cells it is aggregating are stemming from. Hence, in this case, the mobile terminal is also unaware of the actual propagation delay it's uplink transmissions experience. Since mobile terminal may also not know whether both uplink and downlink of a radio cell are transmitted from the same location, in one further embodiment of the invention the methods for time aligning the uplink component carriers depending on a reference cell may for example be applied only in case the aggregation access point is authorizing this procedure. For example, in a 3GPP based mobile communications system, only the eNodeB knows if the user equipment's uplink transmissions experience the same propagation delay as the downlink signals received by the user equipment, since network topology and exact location of nodes (access points) and location of transmission and reception antennas is known to eNodeB.

(91) Taking the above into account for each cell that is configured in the mobile terminal (e.g. user equipment), the aggregation access point (e.g. eNodeB) for example signal the uplink time alignment configuration mode, i.e. whether the calculation of timing advance as discussed previously herein can be applied for an uplink component carrier or uplink component carrier group, or whether initial timing advance for an uplink component carrier or uplink component carrier group is to be set through the RACH procedure.

(92) The signalling can be for example achieved by introducing a flag indicating whether the RACH procedure is to be used for to get time aligned or whether the mobile terminal can calculate the timing advance based on the reference timing advance. The flag may be signalled for each individual radio cell or for a group of radio cells the component carriers of which experience an equal propagation delay.

(93) The information on how to time align an uplink component carrier of a given radio cell should be available to the mobile terminal before transmission and reception on the radio cell can start. Therefore, in one exemplary implementation, the flag to signal the time alignment configuration mode may be conveyed to the mobile terminal via RRC signalling when the radio cells are configured. For example, the signalling information of the flag (e.g. one bit) to indicate the time alignment configuration mode may be for example included in a Radioresource Configuration Message of the RRC protocol.

(94) Synchronized and Non-Synchronized Handover

(95) The methods described above are also usable in a handover scenario, where the mobile terminal is to aggregate new uplink component carriers in one or more target cells. Instead of performing RACH procedure for a target radio cell, the mobile terminal can determine the uplink time alignment of the uplink component carriers relative to a reference cell controlled by the target aggregation node (or base station/eNodeB).

(96) Once reference timing advance has been established in a target radio cell, further radio cells that are configured from the target aggregation access point (e.g. eNodeB) for the mobile terminal (e.g. user equipment) can be time aligned without using further RACH procedures. Hence, a handover where mobile terminal shall retain several aggregated radio cells under control of the target aggregation access point will commence by using only a single RACH procedure for the case of a non-synchronized handover instead of using one RACH procedure for every timing advance to be set for the radio cells in the new target aggregation access point.

(97) The time alignment of the new reference cell under control of the target aggregation access point can be either obtained trough a RACH procedure (for non-synchronized handover), as mentioned above, or by configuring the timing advance value for one of the target radio cells through the source aggregation access point (i.e. the access point, e.g. eNodeB, from which the mobile terminal is handed over to the new/target access point) when using a synchronized handover. In the latter case no RACH procedure may be required at all in the target cells.

(98) In one exemplary embodiment of the invention referring to a 3GPP based mobile communications network, such as 3GPP LTE-A, the source eNodeB (serving as an aggregation access point) is initiating the handover by sending a RRC connection reconfiguration message to the user equipment, which is instructing the user equipment to perform a handover. The RRC connection reconfiguration message informs the user equipment on the new eNodeB (serving as the new aggregation access point) controlling the target radio cells which are to be configured by the user equipment. Furthermore, the RRC connection reconfiguration message indicates the radio cells to be configured by the user equipment. Optionally, i.e. in case of a synchronized handover, the RRC connection reconfiguration message also comprises a timing advance value for setting the timing advance for an uplink component carrier (or uplink component carrier group) under control of the target eNodeB.

(99) In case of a non-synchronized handover, the user equipment establishes downlink synchronization in the target radio cells and performs a RACH procedure on one of the uplink component carriers to establish time alignment for this the uplink component carrier (or the uplink component carrier group to which the uplink component carrier belongs). Once the time alignment is established, i.e. a timing advance value is set, the other uplink component carriers configured by the user equipment may be time aligned by the methods outlined herein above. Hence, in case of a non-synchronized handover, the user equipment only needs to perform one single RACH procedure, but can time align all uplink component carriers.

(100) In case the eNodeB does not allow for calculating the timing advance values based on a reference cell (e.g. by means of RRC control signaling), the user equipment may need to perform more than one RACH procedure to time align uplink component carriers for which the timing advance value may not be configured based on the timing advance in a reference cell. For example, the RRC connection reconfiguration message could indicate for which target radio cells the user equipment may calculate the timing advance based on a reference cell.

(101) In case of a synchronized handover no RACH procedure at all is needed. An initial reference timing advance for a target radio cell serving as the reference is provided to the user equipment by the source eNodeB. All remaining radio cells controlled by the target eNodeB can then be time aligned using the methods described above (e.g. in case the eNodeB allow the time align the respective radio cell based on a reference timing advance). As shown in FIG. 12, the handover delay is minimized. The user equipment establishes downlink synchronization in one of the target cells (which will service as the reference cell) and configures the timing advance as provided by the eNodeB in the RRC connection reconfiguration message. Then the user equipment only needs calculate the timing advance values for the other uplink component carrier(s) or component carrier groups, and can then send the RRC connection reconfiguration complete message back to the new eNodeB to finish the handover.

(102) Hence, the calculation of the timing advance(s) for the time alignment of uplink component carriers relative to a reference cell may significantly reduce the handover delay and thus reducing the latency and delay associated with this procedure when compared to the prior art methods for both, synchronized and non-synchronized handover.

(103) Another aspect of the invention is to time-align a non-time-aligned uplink of a serving cell and to transmit timing information used for time-aligning the non-time-aligned uplink of the serving cell to the aggregation access point.

(104) The following specific scenario is assumed, however should not be understood as limiting the invention, but as an example for describing the invention's principles. It is assumed that the reference cell is the PCell, and the target cell is the SCell. The aggregation access point is assumed to be the eNodeB.

(105) FIG. 23 discloses a signaling diagram illustrating the various steps performed by the mobile terminal UE and the eNodeB, and the messages exchanged between them to allow the time-alignment procedure according to one embodiment of the invention.

(106) The mobile terminal UE has configured a PCell over which it exchanges data with the eNodeB. The PCell of the mobile terminal UE is already time-aligned in the uplink, i.e. the uplink transmissions made by the mobile terminal UE over the PCell are performed by the mobile terminal UE at a timing such that their reception at the eNodeB is synchronized with the receptions of uplink transmissions of other mobile terminals UE on this cell. The PCell was uplink-time-aligned initially by performing a RACH procedure as explained in the background section, be it contention based or non-contention based (see FIGS. 7 and 8).

(107) Though it seems less advantageous, it would be theoretically possible to initially synchronize the PCell using the principles of the present invention, assuming that the reference is an uplink-time-aligned SCell. The following description, however, assumes that the PCell is initially synchronized in the uplink using the RACH procedure, since the PCell will always be uplink synchronized for the case that the UE aggregates multiple serving cells, e.g. PUCCH is transmitted on PCell, and will have the “best” uplink-time-alignment (due to the RACH procedure being more accurate).

(108) The mobile terminal UE is now configured with a Secondary Cell, SCell, which however is not yet time-aligned in the uplink. For instance, the SCell has just been configured, or the SCell, having been previously uplink-time-aligned, has lost its uplink synchronization (e.g. timing advance timer expires). In any case, the mobile terminal UE has now to achieve uplink time alignment in order to be able to transmit uplink data to the eNodeB through the SCell. The following steps are performed as exemplified by FIG. 23.

(109) 1. The mobile terminal UE performs measurements to determine specific timing information of transmissions/receptions in the PCell and/or SCell. There is various timing information which can be determined at the mobile terminal UE, as will be explained in detail further below. The timing information which the terminal measures is such that it allows the terminal to determine the timing advance for the SCell by considering the uplink time alignment of the PCell, which is already time-aligned and thus serves as a reference for the time-alignment of the SCell.

(110) With regard to steps 4a, 4b or 4c, it is important to note that the information of the measurements, which may be transmitted to the eNodeB, is such that it isn't already known in the eNodeB, thus, relating to timings which are unknown in the eNodeB, such as to transmission and/or reception timing information of signal exchange performed on the PCell and/or SCell between the mobile terminal UE and the eNodeB.

(111) 2. The mobile terminal UE uses the information of the measurement to determine a timing advance for the SCell. The determination is based on the information of the measurement and on information referring to the uplink time alignment of the PCell. There are various possibilities how to achieve this, and the following description will discuss them in more detail.

(112) This timing advance for the SCell will be preferably determined by the mobile terminal UE as an absolute value, i.e. similar to the initial timing advance value known from the standard, which is applied by the mobile terminal UE with respect to the time of arrival of a downlink transmission from the eNodeB on the SCell. Alternatively, the determined timing advance may also be relative to the timing advance used for the PCell, thus allowing the mobile terminal UE to apply the value with respect to the time of transmission of an uplink transmission by the mobile terminal UE to the eNodeB on the time-aligned PCell, or with respect to the time of arrival of a downlink transmission from the eNodeB on the PCell.

(113) With regard to steps 4a, 4b or 4c, the timing advance determined by the mobile terminal UE for uplink transmissions on the SCell is also not known by the eNodeB except for the case when the mobile terminal UE performs a RACH procedure on the SCell or receives a TA command to be applied for uplink transmissions on the SCell.

(114) In theory, the eNodeB could determine a timing advance by measuring a relative time difference between of uplink transmissions on the PCell and on the SCell, once uplink transmission are performed on the PCell and SCell. However, such measurements would require that UE is transmitting with the wrong timing advance on the SCell creating interference with other uplink transmissions on the same SCell. Such interference shall, in general, be avoided. Apart from the unbearable interference, the measurement would not be very precise. In other words, even though there exists a theoretical possibility for the eNodeB to measure a timing advance for use by the mobile terminal UE, the time difference measurements, in practice, do not allow for an exact determination of the timing advance on the SCell.

(115) In contrast thereto, a time alignment based on a random access procedure avoid the interference with other uplink transmissions on the SCell. It should be noted that the RACH preamble has some specific characteristics as explained in the background section in order to allow some good detection at the eNodeB side.

(116) In other words, even though there exists a theoretical possibility for the eNodeB to measure a timing advance for use by the mobile terminal UE, the time difference measurements, in practice, do not allow for an exact determination of the timing advance on the SCell.

(117) However, with the mobile terminal providing the information of the measurements to the eNodeB (as in step 1), the eNodeB can calculate a timing advance for the SCell similar to that determined by the mobile terminal UE in step 2. It will be later explained that the transmitted information of the measurements and/or the timing advance for the SCell enable the eNodeB to controlling the time-aligning process in the SCell. For now it is important to note that the eNodeB can also determine a timing advance for the SCell similarly to the mobile terminal UE, namely based on the information of the measurement and on information referring to the uplink time alignment of the PCell.

(118) 3. Using the determined timing advance for the SCell, the mobile terminal UE can time-align the uplink transmission timing of the SCell. How exactly the uplink transmission timing is adjusted depends on the particular type of the determined timing advance. In case the determined timing advance information is an absolute value of the timing advance to be applied, the mobile terminal UE sets its uplink transmission timing relative to the beginning of the downlink subframes received over the SCell by the amount of time indicated in the timing advance information. Alternatively, in case the timing advance is determined by the mobile terminal UE relative to the timing advance of the PCell, the mobile terminal UE sets its uplink transmission timing relative to the beginning of the uplink subframes transmitted over the time-aligned PCell by the amount of time indicated in the time advance information, or relative to a downlink transmission on the PCell.

(119) Thus, the mobile terminal UE time-aligns its uplink of the SCell, and can then start transmitting scheduled uplink transmissions based on received uplink grant.

(120) 4a, 4b or 4c. The mobile terminal UE transmits the information on the measurement of step 1 and/or the timing advance of step 2 to the eNodeB to enable the eNodeB to better control the timing alignment of the SCell.

(121) Transmitting information of the measurements and/or the determined timing advance is not necessarily performed after the mobile terminal UE applying the determined timing advance for time-aligning uplink transmission on the SCell (i.e. as step 4c). Alternatively, the mobile terminal UE may transmit the information on the measurement of step 1 to the eNodeB directly after the measurement thereof in step 1 (i.e. step 4a in FIG. 23) or after the determination step 2 (i.e. step 4b) or after time-alignment of the uplink transmissions on the SCell in step 3 (i.e. step 4c). According to another alternative, the mobile terminal may transmit the determined timing advance of step 2 to the eNodeB directly after the determination thereof in step 2 (i.e. step 4b in FIG. 23) or after time-aligning the uplink transmission on the SCell of step 3 (i.e. step 4c). In general the timing of the reporting of the timing measurements performed by the mobile terminal can be manifold as explained later: either periodically or event-triggered or requested by eNodeB.

(122) As explained earlier, the eNodeB can also determine, based on the transmitted information of the measurement in step 4a, a similar timing advance for the SCell to that determined by the mobile terminal UE in step 2. With the eNodeB capable of converting between both transmitted information, the above described alternative may be considered equal alternatives with respect to the transmitted information.

(123) There are various advantages provided by the present invention as explained above. First, a procedure is implemented to apply different timing advances on different component carriers, i.e. cells. Therefore, in situations where the propagation of the SCell is different to the PCell, the uplink timing can be adjusted for each cell separately when possible. Further, performing a random access procedure in the SCell may be avoided. Further, the prevention of RACH procedures circumvents several problems, such as complicated prioritization rules for the power limitation, or problems with the power amplifier.

(124) Additionally, the uplink synchronization process for the present invention is faster compared to where a RACH procedure is performed. As will be shown later in detail this is, in particular, important for the activation of an uplink non time-aligned SCell. Furthermore, the transmission, to the eNodeB, of the information of the measurement and/or of a timing advance value for the SCell enables the eNodeB to track changes in the timing advance of the SCell and the eNodeB to control time aligning uplink transmissions on the SCell in the mobile communication system.

(125) In the following a more specific embodiment of the invention will be explained with reference to FIGS. 24 and 25.

(126) FIG. 24 shows a scenario in which a PCell, SCell1 and SCell2 are served by the eNodeB to different UEs, namely UE1, UE2, UE3. A Frequency Selective Repeater (FSR) is provided, being configured for the frequencies used by SCell 1 and SCell2, such that it amplifies signals transmitted/received on the secondary serving cells SCell1 and SCell2, however not those signals transmitted/received on the PCell. As illustrated by FIG. 24, the coverage of the PCell is greater than the one of the SCells.

(127) In the lower part of FIG. 24 the downlink reception time difference at the mobile terminal between the SCells1 or 2 and the PCell (Δ.sub.Scell-PCellRx.sub.DL) is plotted against the position of a UE in the cell.

(128) The downlink reception time difference is the difference between the point in time when the UE receives a downlink subframe from the eNodeB over the SCell and a point in time when the UE receives a downlink subframe from the eNodeB over the PCell.

(129) In this particular scenario, the need for different uplink timing advances for PCell, SCell 1 and SCell2 changes depending on the location of the UE. In more detail, three UEs are depicted in FIG. 24, UE1 is located at A, within the coverage of PCell, SCell 1 and SCell2; UE2 is located at B, at the overlapping area of the coverage for SCell1/SCell2 provided by the eNodeB and the coverage for SCell1/SCell2 provided by the FSR; UE3 is located at C, outside coverage for SCell1/SCell2 provided by eNodeB, but inside the coverage for SCell1/SCell2 provided by the F SR.

(130) From location A to location B, the PCell, SCell 1 and SCell2 are provided by the same transmission node, e.g. eNodeB to the UEs. Therefore, the propagation delays for the three cells should be substantially the same, and thus the downlink reception time difference should be negligible. As a result, the same timing advance can be used for the PCell, SCell1 and SCell2. On the other hand, at location B it is assumed that the signal for SCell1/SCell2 from FSR is stronger than the one for SCell1/SCell2 from eNodeB, and correspondingly, the UE2 at location B receives signals over PCell from the eNodeB and signals over SCell1/SCell2 from the FSR. Consequently, the propagation between PCell signals and SCell1/SCell2 signals is different, which results in different downlink reception timings between PCell and SCell1/SCell2. As apparent from the lower part of FIG. 24, the plotted downlink reception time difference measured by the UE2 between PCell and SCell1/SCell2 suddenly jumps to a particular value, at the moment when UE2 switches from one reception path (from eNodeB) to another (from FSR).

(131) At location B the downlink reception time difference is at its maximum since the path length difference between the PCell path and the SCell1/SCell2 path is at its maximum too in this exemplary scenario. The downlink reception time difference decreases as the UE moves further towards the FSR, and is minimum directly at the FSR, the downlink reception time difference mainly being the time of the FSR for receiving, processing and transmitting the amplified signal for SCell1/SCell2. When moving away again from the FSR, the downlink reception time difference increases again.

(132) Accordingly, UE2 and UE3 cannot use the same timing advance for SCell1/SCell2 as used for the PCell, but would have to configure separate uplink timing advances for them. However, the same timing advance could be used for SCell1 and SCell2, since in the present scenario the propagation delays for SCell1 and SCell2 are the same.

(133) One of the main ideas of the invention is to determine the timing advance for the SCell relative to the uplink timing of the uplink-time-aligned PCell. In particular, the timing advance used by UE3 to synchronize the uplink transmissions in the SCell is defined in relation to the uplink timing of the uplink-time-aligned PCell. The following timing relations apply for a timing advance for the SCell, TA.sub.SCell, in relation to the timing advance of the PCell, TA.sub.PCell, and other parameters.
TA.sub.PCell=PD.sub.UL.sub._.sub.PCell+PD.sub.DL.sub._.sub.PCell  (equation 7)
TA.sub.SCell=PD.sub.UL.sub._.sub.SCell+PD.sub.DL.sub._.sub.SCell=PD.sub.UL.sub._.sub.PCell+PD.sub.DL.sub._.sub.PCell+(Δ.sub.SCell-PCellPD.sub.DL+Δ.sub.SCell-PCellPD.sub.UL)=TA.sub.PCell+(Δ.sub.SCell-PCellPD.sub.DL+Δ.sub.SCell-PCellPD.sub.UL)
wherein Δ.sub.SCell-PCellPD.sub.DL is the difference between the propagation delays in the downlink of the PCell and the SCell; and wherein Δ.sub.SCell-PCellPD.sub.UL is the difference between the propagation delays in the uplink of the PCell and the SCell.

(134) The following substitution:
Δ.sub.SCell-PCellPD.sub.UL=Δ.sub.SCell-PCellPD.sub.DL+Δ.sub.SCellPD.sub.UL-DL  (equation 8)
where Δ.sub.SCellPD.sub.UL-DL is the difference between the propagation delays of the uplink and downlink for the SCell, leads to the equation:
TA.sub.SCell=TA.sub.PCell+2.Math.Δ.sub.SCell-PCellPD.sub.DL−Δ.sub.SCellPD.sub.UL-DL  (equation 9)
The following substitution:
Δ.sub.SCell-PCellPD.sub.DL=Δ.sub.SCell-PCellRx.sub.DL−Δ.sub.SCell-PCellTx.sub.DL  (equation 10)
where Δ.sub.SCell-PCellRx.sub.DL is the downlink reception time difference between the PCell and the SCell, i.e. the difference in time between the reception in the UE3 of a downlink transmission from the eNodeB on the PCell and the reception in the UE3 of a downlink transmission from the eNodeB on the SCell, and
where Δ.sub.SCell-PCellTx.sub.DL is the downlink transmission time difference between the PCell and the SCell, i.e. the difference in time between the transmission in the eNodeB of a downlink transmission to UE3 on the PCell and the transmission in the eNodeB of a downlink transmission to UE3 on the SCell, leads to the equation:
TA.sub.SCell=TA.sub.PCell+2.Math.(Δ.sub.SCell-PCellRx.sub.DL−Δ.sub.SCell-PCellTx.sub.DL)−Δ.sub.SCellPD.sub.UL-DL  (equation 11)
=TA.sub.PCell+2.Math.Δ.sub.SCell-PCellRx.sub.DL−2.Math.Δ.sub.SCell-PCellTx.sub.DL−Δ.sub.SCellPD.sub.UL-DL  (equation 12)

(135) Put differently, the timing advance of the SCell can be calculated based on: the timing advance of the PCell the downlink reception time difference between the PCell and the SCell the downlink transmission time difference between the PCell and the SCell the propagation delay difference between the uplink and the downlink on the SCell

(136) The timing advance of the PCell is basically both known to the eNodeB and UE3.

(137) The downlink reception time difference between the PCell and the SCell (Δ.sub.SCell-PCellRx.sub.DL) is not known in the eNodeB, but can be measured at UE side.

(138) The downlink transmission time difference between the PCell and the SCell Δ.sub.SCell-PCellTx.sub.DL is known only by the eNodeB, however not to UE3, as will become more clear in connection with FIG. 27. In the particular embodiment of FIG. 26, the downlink transmission time difference between the PCell and the SCell (Δ.sub.SCell-PCellTx.sub.DL) is zero; for the embodiment of FIG. 27 explained later the downlink transmission time difference between the PCell and the SCell (Δ.sub.SCell-PCellTx.sub.DL) is not zero.

(139) In relation to the examples of FIGS. 15, 16 and 17, the definition of the timing advance TA.sub.SCell of equation 11 and equation 12 additionally considers the downlink transmission time difference between the PCell and the SCell (Δ.sub.SCell-PCellTx.sub.DL) and the propagation delay difference between the uplink and the downlink on the SCell (Δ.sub.SCellPD.sub.UL-DL) and is, hence, more precise. In other words, in a mobile communication system configured to operate without a transmission time difference between the PCell and the SCell (Δ.sub.SCell-PCellTx.sub.DL=0) and without a propagation delay difference between the uplink and the downlink on the SCell (Δ.sub.SCellPD.sub.UL-DL=0), as considered with respect to FIG. 26, the equation 12 corresponds to that of the examples of FIGS. 15, 16 and 17.

(140) The propagation delay difference between the uplink and the downlink of a serving cell, SCell, is assumed to be negligible for the purposes of the invention. More specifically, it is assumed that the propagation delay for the uplink and downlink direction is the same for each carrier. Simulation done by 3GPP WG RAN4 provided results of the simulated propagation delay differences for inter-band carrier aggregation case which show that for the same reception node (i.e. the eNodeB), propagation timing difference will be less than one TA step (˜0.5 us) in 97˜98% case and less than five TA steps in 100% case. Following this for the SIB-2 linked DL and UL carrier pairs, where the frequency gap between uplink and downlink will be even smaller than that between different frequency bands, resulting in that the propagation timing difference between the UL direction and the DL direction for a given cell will be even less and, hence, negligible for the present invention.

(141) Assuming the above and considering that the mobile terminal UE shall calculate a timing advance of the SCell, the mobile terminal UE may approximate the timing advance for uplink transmissions on the SCell, as defined by equation 13 below, namely based on the timing advance of the PCell (TA.sub.PCcell) and the downlink reception time difference between the PCell and the SCell (Δ.sub.SCell-PCellRx.sub.DL). In case of a mobile communication system as exemplified in FIG. 27 having different uplink timing advances for PCell and Scell1/SCell2, it has to be noted that the, by the mobile terminal, determined timing advance only approximates an accurate timing advance for the SCell1/SCell2.

(142) In future releases, a mobile terminal UE may perform uplink transmissions to plural different eNodeBs at a same time i.e. cooperative multi-point (COMP) transmissions in the uplink. Since two different eNodeBs are not required to use a same downlink timing, the transmission time difference between a first eNodeB1 providing a PCell and a second eNodeB2 providing a SCell (Δ.sub.SCell-PCellTx.sub.DL) needs to be considered when time aligning uplink transmissions on an SCell. Without this value, a mobile terminal can also only approximate the timing advance for uplink transmissions on the SCell

(143) Consequently, based on the information of measurements performed by the mobile terminal and/or the uplink time alignment for the SCell determined by the mobile terminal, only the eNodeB can ensure an accurate time alignment of uplink transmissions performed by the mobile terminal on the SCell. In other words, transmitting this timing information by the mobile terminal to the eNodeB enables the eNodeB to accurately control the time alignment process for an SCell at the mobile terminal, e.g. in case of cooperative multi-point (COMP) transmissions. Resulting from the above considerations, a more detailed embodiment of the invention for uplink-time-alignment of SCell for UE3 will be presented below with reference to FIG. 25.

(144) In step 1 of FIG. 25, the UE3 measures the downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL and in particular the time difference between the time when the UE3 receives the start of one subframe from the PCell and the time when the UE3 receives the corresponding start of one subframe from the SCell that is closest in time to the subframe received from the PCell. Correspondingly, UE3 performs the measurements for each of the two SCells, resulting in Δ.sub.SCell1-PCellRx.sub.DL and Δ.sub.SCell2-PcellRx.sub.DL. In the present scenario the downlink reception time difference will be substantially the same for SCell1 and SCell2. The downlink reception time difference for one SCell can be seen in FIG. 26.

(145) In step 2, the UE3 uses the measurements results to calculate the timing advance for the SCells. Since the downlink reception time difference is the same for both SCells, the UE3 will only calculate one timing advance that may be used by the UE3 to uplink-time-align both SCells. Considering the assumptions of the present embodiment, equation 12 discussed above can be written in a simplified manner as:
TA.sub.SCell=TA.sub.PCell+2.Math.Δ.sub.SCell-PCellRx.sub.DL  (equation 13)
since both Δ.sub.SCell-PCellTx.sub.DL and Δ.sub.SCellPD.sub.UL-DL may be considered zero.

(146) The mobile terminal thus uses the received downlink reception time difference(s) Δ.sub.SCell1-PCellRx.sub.DL/Δ.sub.SCell2-PCellRx.sub.DL and the known time advance for the PCell to calculate the time advance for the SCell1 and SCell2 TA.sub.SCell1/SCell2 according to equation 13.

(147) In step 4b of FIG. 25, the UE3 transmits the results of the measurements, i.e. the downlink reception time difference Δ.sub.SCell1-PCellRx.sub.DL and/or Δ.sub.SCell2-PCellRx.sub.DL and/or the calculated timing advances for the SCells TA.sub.SCell1/SCell2 to the eNodeB, preferably by using the PUSCH of the PCell. Alternatively, since both downlink reception time differences are the same, the UE3 may transmit only one of the two measurements and/or one of the calculated timing advances.

(148) In step 3, the UE3 applies the calculated timing advance TA.sub.SCell1/SCell2 relative to the beginning of the downlink radio frame of the SCell1 and SCell2, similar to the way in which a standard initial timing advance is applied by a UE.

(149) In this way, the UE3 can uplink-time-align the SCell1 and SCell2, and start uplink transmissions thereon according to received uplink scheduling grants. The first uplink grant is usually part of the RAR message within the standard RACH procedure. Since in the invention no RACH procedure is performed on an SCell, the first uplink grant for the SCells can be transmitted at any time in any way to the UE3 via the PDCCH.

(150) The UE3 uses an uplink grant on SCell1 and SCell2 to transmit an uplink transmission to the eNodeB. This is illustrated in FIG. 25 for one SCell. The UE3 sets the time of transmission of an uplink radio frame for the SCell T.sub.UL.sub._.sub.TX.sub._.sub.SCell relative to the time of reception of a downlink radio frame for the SCell T.sub.DL.sub._.sub.RX.sub._.sub.SCell, by “shifting” by the timing advance value T.sub.SCell1/SCell2.

(151) Such a time-aligned uplink transmission on the SCell is received at T.sub.UL.sub._.sub.RX.sub._.sub.SCell in the eNodeB, after the propagation delay PD.sub.UL.sub._.sub.SCell.

(152) Having received in step 4b from the UE3 information on the downlink reception time difference Δ.sub.SCell1-PCellRx.sub.DL and/or Δ.sub.SCell2-PCellRx.sub.DL and/or the calculated timing advances for the SCells TA.sub.SCell1/SCell2, the eNodeB is enabled to control time alignment of uplink transmissions on the SCells (step 7).

(153) In particular, as described before, the UE3 transmits the downlink reception time difference and/or the calculated timing advance to the eNodeB and provides the eNodeB with information it cannot measure or derive by itself. Based on the received information on the downlink reception time difference Δ.sub.SCell1-PCellRx.sub.DL and/or Δ.sub.SCell2-PCellRx.sub.DL and/or the calculated timing advances for the SCells TA.sub.SCell1/SCell2 the eNodeB can determine if the time advance to be used with the SCells allows for accurately time aligned uplink transmissions by the UE3 on the SCells.

(154) Exemplary, for determining if the received timing advances for the SCells TA.sub.SCell1/SCell2 (which is calculated by the UE3 in step 2) allows for a sufficient time alignment of uplink transmission on the SCells, the eNodeB can compare the received value with a timing advance value for the SCells it determines based on the three values: the timing advance of the PCell, the downlink reception time difference between the PCell and the SCell and the downlink transmission time difference between the PCell and the SCell according to equation 12. In case the difference between the received and the determined timing advance for an SCell is larger than a threshold, the eNodeB determines that the timing advance to be used with the SCells does not allow for accurately time aligned uplink transmissions by the UE3 on the SCells.

(155) This exemplary determination of whether the timing advance calculated by the UE3 is sufficient for time aligning uplink transmissions on the SCell can be made before actual uplink transmissions are performed by the UE3 on the SCell.

(156) Alternatively, for determining if the received timing advances for the SCells TA.sub.SCell1/SCell2 (which is calculated by the UE3 in step 2) allows for an accurate time alignment of uplink transmission on the SCells, the eNodeB can determine, based on its knowledge of the deployment of the radio cells of the mobile communication system, if the by the UE3 measured downlink reception time difference between the PCell and the SCell appears correct or not, and based on a threshold distinguish if the received timing advance is sufficient for time aligning uplink transmissions by the UE3 on the SCells. This determination of whether the timing advance calculated by the UE3 is sufficient for time aligning uplink transmissions on the SCell can also in this case be made before actual uplink transmissions are performed by the UE3 on the SCell.

(157) Furthermore, other exemplary implementations for the eNodeB to determine whether the timing advance calculated by the UE3 is sufficient for time aligning uplink transmissions on the SCells depend on the mobile terminal performing actual uplink transmission on the SCells having applied the calculated timing advance for the SCells TA.sub.SCell1/SCell2 (of step 2). In case of uplink transmissions by the mobile terminal on the SCells, the eNodeB may compare a reception time of uplink transmissions on the uplink of the SCells with a predefined reference time for uplink transmission on the uplink of the SCells, or compare a reception time of uplink transmissions on the uplink of the SCells with a transmission time of downlink transmissions on the corresponding downlink of the SCells.

(158) In case the eNodeB determines in step 7, that the calculated timing advance for the SCells TA.sub.SCell1/SCell2 does not allow for accurately time-aligned uplink transmissions by the UE3, the eNodeB transmits in step 8 information, instructing the UE3, that the calculated and transmitted timing advance TA.sub.SCell1/SCell2 cannot be used by the UE3 for time aligning the uplink transmissions on the SCells i.e. that it does not allow for accurately time-aligned uplink transmissions on the SCells.

(159) According to one example, the information may include a RACH order triggering the mobile terminal, upon reception of the RACH order message, to perform a random access procedure on at least one of the SCells (step 9). As part of the random access procedure, the UE3 receives an accurate timing advance for the SCell(s) and time-aligns the SCell(s) by adjusting a timing for uplink transmissions on the uplink target cell based on the received timing advance within the random access procedure.

(160) According to another example, the information may include a timing advance command with a timing advance for use with the SCell triggering the mobile terminal, upon reception of the timing advance, to time-align the uplink SCell(s) by adjusting a timing for uplink transmissions on the uplink target cell based on the received timing advance (step 9).

(161) According to further example, the information may include a timing advance update command triggering the mobile terminal, upon reception of the timing advance update command, to determine a timing advance for use with the uplink of the SCell(s) based on the included target timing advance update value and on the timing advance used for uplink transmissions on the uplink of the SCell(s), and the SCell(s) by adjusting a timing for uplink transmissions on the uplink target cell based on the determined timing advance (step 9).

(162) FIG. 27 illustrates a timing diagram according to another embodiment of the invention. Compared to the timing diagram of FIG. 26, the difference is that the PCell and the SCell perform a downlink transmission at different times, i.e. the downlink subframe timing is not synchronized between PCell and SCell. Furthermore, it is assumed that the SCell1 and SCell2 have the same downlink transmission timing. In other words, there is a downlink transmission time difference between the PCell and the SCell Δ.sub.SCell-PCellTx.sub.DL which is not zero but is the same for SCell1 and SCell2.

(163) The uplink-time-alignment procedure, explained before in connection with FIG. 25, can be similarly applied to the scenario exemplified in FIG. 27, considering the following changes in procedure.

(164) The UE3 can measure the downlink reception time differences Δ.sub.SCell1-PCellRx.sub.DL and/or Δ.sub.SCell2-PCellRx.sub.DL, which are the same for SCell1 and SCell2 (step 1 in FIG. 25). It should be noted that the downlink reception time difference not only considers the propagation delay differences between PCell and SCell (as in FIG. 26), but in this case also the downlink transmission time difference Δ.sub.SCell-PCellTx.sub.DL.

(165) In this particular embodiment of the invention, the measured downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL is longer than the difference of the propagation delays between PCell and SCell, i.e. longer by the downlink transmission time difference between the PCell and the SCell Δ.sub.SCell-PCellTx.sub.DL.

(166) However, since the downlink transmission time difference between the PCell and the SCell Δ.sub.SCell-PCellTx.sub.DL is unknown, i.e. transparent, to the UE3, it will calculate timing advance for uplink transmissions on the SCell based on equation 13 (step 2 in FIG. 25). In particular, the UE3 will assume that the timing advance can be determined based on the timing advance of the PCell (TA.sub.PCell) and the downlink reception time difference between the PCell and the SCell (Δ.sub.SCell-PCellRx.sub.DL).

(167) Exemplary, the UE3 then transmits the results of the measurements, i.e. the downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL and/or the calculated timing advances for the SCell TA.sub.SCell to the eNodeB, preferably by using the PUSCH of the PCell (step 4a in FIG. 25).

(168) Receiving this value, the eNodeB can compare by subtraction the value with a timing advance value for the SCell it determines based on the three values: the timing advance of the PCell, the downlink reception time difference between the PCell and the SCell and the downlink transmission time difference between the PCell and the SCell. Since the, from the UE3 received value does not account for the downlink transmission time difference between the PCell and the SCell (Δ.sub.SCell-PCellTx.sub.DL), the difference is larger than a threshold.

(169) Hence, the eNodeB can determine that the by the UE3 calculated timing advance for use with the SCells does not allow for accurately time-aligned uplink transmissions on the SCells (step 7 in FIG. 25) and then uses the following equation 14 for alignment of uplink transmissions by the UE3 on the SCells. Namely, only Δ.sub.SCellPD.sub.UL-DL is set to zero for the reasons explained before.
TA.sub.SCell=TA.sub.PCell+2.Math.Δ.sub.SCell-PCellRx.sub.DL−2.Math.Δ.sub.SCell-PCellTx.sub.DL  (equation 14)

(170) Exemplary, the eNodeB transmits the determined timing advance TA.sub.SCell to the UE3 according to step 8, illustrated in FIG. 25. Accordingly, the UE3 uses the received timing advance value TA.sub.SCell for time aligning the uplink transmissions on the SCell1 and SCell2 with respect to the beginning of the downlink radio frames on the respective SCell1 and SCell2 (step 9 in FIG. 25). Alternatively, the eNodeB transmits a RACH order or a timing advance update command as explained earlier.

(171) It should be noted that even though the eNodeB knows the timing advance used by the UE for uplink transmission on PCell, the UE autonomous change of the uplink timing according to TS36.133 section 7.1.2 causes some deviation from the timing advance value of the PCell signalled by the eNodeB to the UE, except only just after the PRACH transmission took place. Therefore, according to another alternative embodiment the UE also reports the used difference between DL radio frames received on the PCell and UL radio frames transmitted on the PCell to the eNodeB in addition to the downlink reception time difference measurements.

(172) FIG. 28 discloses a flowchart diagram illustrating the various steps performed by the mobile terminal UE to allow for time-aligned uplink transmissions in line with the time-alignment procedure according to an exemplary embodiment of the invention.

(173) It should be noted that in the time-alignment procedure according to this exemplary embodiment of the invention, the eNodeB respectively aggregation access point is the node that controls the uplink timing used by the mobile terminal for transmission on the uplink of the cells. Even though the mobile terminal may calculate autonomously the timing advance for a target cell (e.g. SCell or group of SCells), the aggregation access point can at any time override this self-calculated timing advance and direct the mobile terminal to use another timing advance that has been determined and signalled by the aggregation access point. The mobile terminal will in this case use the timing advance signalled from the aggregation access point. Put in other words, the timing advance signalled by the aggregation access point takes precedence over the timing advance calculated autonomously by the mobile terminal.

(174) In the following, variants and additional steps for the above-described embodiments will be presented with reference to FIG. 28.

(175) Triggering of the Step of Reporting by the UE

(176) In the previous embodiments it has been left open when the UE starts the measurements (step 1a) and the reporting of the measurement results and/or of the calculated timing advance (step 1c). Measurements may be for example performed periodically.

(177) The reporting/signalling can be performed either periodically or event-triggered.

(178) For instance, in step 1) in FIG. 28 the periodical triggering of the reporting may be similar to mobility or power headroom or buffer status report reporting. The advantage of periodical reports is that the eNodeB gets with a certain frequency up-to-date information on the measurement results and/or the calculated timing advance. The eNodeB is thus enabled at periodical intervals to determine if the, by the UE calculated timing advance is sufficient for time alignment of uplink transmissions on the SCell, and thus can continuously control the timing advance of the UE when necessary.

(179) Event-triggered reporting is in step 1) in FIG. 28, however, beneficial too and may be necessary in order to allow the eNodeB to react quickly so as to prevent from e.g. interference due to wrong uplink time alignment. Some events are described in the following.

(180) The configuration of an SCell can be used as a trigger for the UE to start reporting (step 1c) of the measurement results and/or of the calculated timing advance to the eNodeB (step 1b is optional). The measurement and reporting is done according to one exemplary embodiment for configured and deactivated Scell(s). Providing the measurement results and/or of the calculated timing advance to the eNodeB everytime a new SCell is configured, has additional benefits (step 1c).

(181) In more detail, the eNodeB is given the opportunity to check whether a different timing advance (multi-TA) is required for the newly configured SCell. Furthermore and in response thereto, the eNodeB can optionally calculate an accurate timing advance for the UE to be used with the SCell and optionally signal it to the UE (step 4 in FIG. 28). In other words, even though the SCell is deactivated (i.e. not used for transmission), the UE already knows which timing advance to use for this SCell.

(182) Thus, when the SCell is activated, the UE can immediately apply the previously-received timing advance for the SCell, and already transmit with the correct uplink time alignment (step 4a). Therefore, the activation of an SCell would be faster, for example, when compared to the approach where RACH needs to be performed on a newly activated SCell so as to achieve uplink synchronization. Essentially, the activation delay for an SCell, when using the present invention, would be the same as for Rel-10, where SCells have the same timing advance as the PCell.

(183) Alternatively, the activation of an SCell can be used as a trigger by the UE to start measurements (step 1a) and reporting (step 1c) of the measurement results and/or of the calculated timing advance (step 1b is optional). The advantage of using the activation as a trigger is that, when the eNodeB activates an SCell it also intends to schedule transmissions on the SCell. In order to determine the correct timing advance used for the uplink transmissions on the activated SCell, it is beneficial to provide the eNodeB with up-to-date measurement results and/or of the calculated timing advance.

(184) Another option to be used as trigger is that the mobile terminal receives from the eNodeB a specific request to report the measurement results and/or of the calculated timing advance to the eNodeB. This would allow the eNodeB to decide case-by-case whether the reporting of the measurement results and/or of the calculated timing advance is necessary or not.

(185) There are several possibilities how to transmit this request from the eNodeB to the mobile terminal. For instance, a flag within the RRC messages which configure the SCell, e.g. RRC connection reconfiguration message, could explicitly request for measurement result reporting.

(186) Or, the activation/deactivation command (MAC CE) as illustrated in FIG. 29 could contain a flag which explicitly indicates the need for timing info reporting, i.e. the eNodeB explicitly request the mobile terminal to report the measurement results and/or of the calculated timing advance.

(187) The flag could be signalled by using the free “reserved bit” in the activation/deactivation MAC control element. Since the activation of an already activated SCell is supported (also referred to as reactivation), the activation/deactivation MAC control element could be sent by the eNodeB at any time for requesting reporting of measurement results, without the need to actually activate or deactivate any of the SCells.

(188) Another possibility would be to re-use the so-called “RACH order” message corresponding to the message 801 in FIG. 8, which is a physical layer signalling (PDCCH with DCI format 1A). Some predefined codepoints or combination of field codepoints within a RACH order for an SCell could be used as a request for reporting. For example, a RACH order for an SCell with ra-Preambellndex set to “000000” (i.e. normally indicating that the UE should make a contention-based RACH) could be redefined to request the reporting. Or, a predefined carrier indicator (CI) codepoint for the case of cross-scheduling can be used as request. The advantage would be that the uplink resource allocation where the mobile terminal shall transmit the measurement results and/or of the calculated timing advance can be sent together with the request for measuring and/or reporting, hence reducing the reporting delay.

(189) Another trigger event for reporting (step 1c) the measurement results and/or of the calculated timing advance (step 1b optional) could be that the measurement results performed in connection with the uplink-time-alignment of the SCell exceed a certain preconfigured threshold.

(190) Such a reporting by the UE is especially beneficial in cases where the eNodeB is not aware of the necessity of using a timing advance for the SCell different to the one of the PCell. The eNodeB may not always have sufficient knowledge from e.g. an OAM (Operation, Administration and Maintenance usually providing cell deployment info like presence of repeaters or RRHs).

(191) Also, the need for multi-timing-advance depends on the position of the UE (see FIG. 26 and corresponding description). Thus, e.g. a frequency-selective repeater may be transparent to the eNodeB, and is only made visible to the eNodeB by the UE reporting on a high downlink reception time difference. Or even if the eNodeB is aware of the FSR, it does not know when exactly the UE will receive the SCell not anymore from the eNodeB but via the FSR.

(192) Triggering of the Step of Time-Aligning by the UE

(193) Similarly to the previous embodiments, the mobile terminal UE as illustrated in FIG. 28 measures (step 2a) the downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL between the SCell and PCell and calculates (step 2b) a timing advance TA.sub.SCell for uplink transmissions on the SCell based on the reception time difference Δ.sub.SCell-PCellRx.sub.DL between the SCell and PCell and the timing advance used for uplink transmissions on the PCell. Then, the mobile terminal UE time-aligns (step 2c) uplink transmissions on the SCell based on the calculated timing advance for the uplink SCell.

(194) However, in the previous embodiments, it has always been left open when the UE time-aligns uplink transmission on the SCell and how the timing-alignment is updated for the SCell over time.

(195) The time-alignment for the SCell can be performed either periodically or event-triggered. In particular, an event-triggered time-alignment procedure is advantageous with respect to an initial time-alignment of uplink transmissions of an SCell. Periodically triggered time-alignment ensures that the uplink-transmissions performed by the mobile terminal UE remain time-aligned even at times when the timing advance of the SCell is not controlled by the eNodeB.

(196) For an event-triggered timing-alignment of uplink-transmissions on the SCell, the same trigger mechanisms as described with respect to event-triggered reporting can be used. In particular, the UE may be configured to use the configuration of an SCell as a trigger for starting the timing-alignment procedure of the SCell. Alternatively, the activation of an SCell can be used as a trigger by the UE for starting the timing-alignment procedure of the SCell. Another alternative for triggering the timing-alignment procedure of the SCell is when the mobile terminal UE receives from the eNodeB a specific message requesting the start of the time-alignment procedure of the SCell.

(197) Due to the similarities between the measurements for reporting (step 1a) and the measurements for time-alignment (step 2a) and the similarities between the calculation of the timing advance for reporting (step 1b) and the calculation of the timing advance for time-alignment (step 2b), the mobile terminal may, according to another exemplary implementation, simultaneously perform the steps for reporting of the measurements results and/or the calculated timing advance for the SCell (step 1c) and the steps for time-aligning uplink transmissions on the SCell (step 2c) and, hence, would only require one event-trigger.

(198) A periodically performed time-alignment procedure is exemplified in FIG. 28.

(199) In FIG. 28, the mobile terminal UE ensures that uplink transmissions remain time-aligned by means of a timer. A separated timer may be maintained by the mobile terminal for each timing advance value (each associated to either an individual uplink cell or a group of uplink cells).

(200) The mobile terminal resets and starts the timer each time it (i) applies a calculated timing advance (step 2d) or (ii) performs a RACH procedure (step 3c) or (iii) applies a received timing advance value for uplink transmissions on the respective PCell or SCell for which the timer is maintained. In this respect, as long as the timer is running, the mobile terminal UE considers itself as being uplink synchronized.

(201) Whenever the timer expires (step 2), i.e. timing alignment is considered to be lost, the mobile terminal uses the mechanisms described herein to reestablish a time alignment for uplink transmissions on an SCell.

(202) For example, the mobile terminal may use a newly determined timing advance for the SCell to time-align the uplink transmission timing of the SCell (step 2c).

(203) Upon having reestablished timing alignment for the SCell, the mobile terminal resets and starts the timer (step 2d) since the mobile terminal UE considers itself as being uplink synchronized.

(204) Determining the Timing Advance for the SCell

(205) As described with reference to FIGS. 26 and 27, the mobile terminal may (re-)establish a time alignment on an SCell by calculating a timing advance value based on the measured downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL and the timing advance used for uplink transmissions on the PCell.

(206) Alternatively or in addition, the mobile terminal can measure and report a reception transmission time difference between the PCell and the SCell Δ.sub.SCell-PCellRx.sub.DL−Tx.sub.UL and/or a timing advance calculated based thereon and on the timing advance used for uplink transmissions on the PCell.
Δ.sub.SCell-PCellRx.sub.DL−Tx.sub.UL=T.sub.DL.sub._.sub.RX.sub._.sub.SCell−T.sub.UL.sub._.sub.TX.sub._.sub.PCell
as is also depicted in FIG. 26 or 27.

(207) Put into words, the reception transmission time difference between the PCell and SCell is the time difference between the time when the mobile terminal transmits an uplink radio frame on the PCell and the time when the mobile terminal receives a downlink radio frame on the SCell. The uplink radio frame and downlink radio frame shall refer to the same radio frame number.

(208) As can be seen from either FIG. 26 or 27, the downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL can be calculated based on the reception transmission time difference Δ.sub.SCell-PCellRx.sub.DL−Tx.sub.UL and the timing advance of the PCell TA.sub.PCell, in particular by:
Δ.sub.SCell-PCellRx.sub.DL=Δ.sub.SCell-PCellRx.sub.DL−Tx.sub.UL−TA.sub.PCell  (equation 15)
where TA.sub.PCell could also be substituted by the time measured between T.sub.UL.sub._.sub.TX.sub._.sub.PCell and T.sub.DL.sub._.sub.RX.sub._.sub.Pcell. The measured time between T.sub.UL.sub._.sub.TX.sub._.sub.PCell and T.sub.DL.sub._.sub.RX.sub._.sub.PCell could also be reported to the eNodeB along with the reception transmission time difference.

(209) Measuring and reporting the reception transmission time difference instead of or additionally to the downlink reception time difference is beneficial, since for future techniques like cooperative multi-point (COMP) transmissions in the uplink, the reception transmission time difference could be used to control the uplink transmission timing. Furthermore, it might be more preferably from the implementation point of view.

(210) The reception transmission time difference Δ.sub.SCell-PCellRx.sub.DL−Tx.sub.UL is then used to calculate the timing advance for the SCell by the mobile terminal UE and/or reported to the eNodeB, which then also uses equation 15 to calculate the downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL. Based on the calculated downlink reception time difference, the mobile terminal and/or eNodeB can calculate the timing advance for the SCell as explained before and in more detail later.

(211) It should be noted that the mobile terminal may for example count the number of samples as a way of determining the time difference. For example, in order to determine the downlink reception time difference, the mobile terminal would count the number of samples between the reception time of a downlink subframe in the PCell and the reception time of a downlink subframe in the SCell. For instance, the downlink subframes may refer to common reference signals (CRS).

(212) Reporting of the Measurement Results

(213) The mobile terminal, after performing the measurements (step 1a), transmits the results to the eNodeB. As explained before, the measurements may refer to the downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL and/or to the reception transmission time difference Δ.sub.SCell-PCellRx.sub.DL−Tx.sub.UL between the PCell and SCell. (step 1c)

(214) The reporting itself could be implemented in principle on several layers, e.g. RRC layer or MAC layer. Other measurements like mobility or positioning measurements are signaled on the RRC layer too. Since the timing advance commands are generated by the MAC layer, it could be beneficial from an implementation point of view, to also implement the reporting of the measurement results on the MAC layer.

(215) FIGS. 29 and 30 illustrate the format of a MAC control element which can be used to transmit the measurement results from the mobile terminal to the eNodeB. As apparent, the structure of the MAC CEs is similar to the extended power headroom MAC CE. The size depends on the number of configured or configured and activated SCells, i.e. on the number of SCells for which measuring and reporting is to be performed.

(216) In more detail, FIG. 29 shows a MAC control element to transmit the downlink reception time difference between the PCell and all the available SCells 1-n.

(217) On the other hand, FIG. 30 illustrates the MAC control element to transmit the reception transmission time difference between the PCell and all the available SCells 1-n. Since the time between T.sub.UL.sub._.sub.TX.sub._.sub.PCell and T.sub.DL.sub._.sub.RX.sub._.sub.PCell corresponds to TA.sub.PCell, and hence should be actually known by the eNodeB, in an alternative embodiment this information must not be reported to the eNodeB.

(218) Instead of reporting the downlink reception time difference and/or the reception transmission time difference for all SCells, the mobile terminal may only report them for the particular SCell which is to be time-aligned.

(219) Further, instead of reporting the downlink reception time difference and/or the reception transmission time difference for all SCells, the mobile terminal may report the calculated timing advance for the SCell to be time-aligned based on the calculated timing advance value as described earlier.

(220) Furthermore, the time differences could be encoded and indicated in the number of samples, i.e. the mobile reports a particular number of samples, and the eNodeB can then use the number of samples and a sample time to derive the actual time differences.

(221) As already mentioned previously, the measurement results are preferably transmitted on the physical uplink shared channel, PUSCH, of the PCell.

(222) Determining the Timing Advance for the SCell

(223) In the previous embodiments of the invention, it was assumed that the mobile terminal and/or the eNodeB calculates a timing advance value as known from the standard RACH procedure, i.e.

(224) a timing advance that is applied by the mobile terminal relative to the beginning of downlink radio frames received via the downlink SCell, as exemplified in FIGS. 26 and 27 (see arrow TA.sub.SCell).

(225) This may be termed as an absolute value, since the timing advance value is of the same type as the timing advance defined by the standard, not to be defined relative to the PCell but relative to the downlink reception of radio frames in the SCell.

(226) There are however other alternatives too. The timing advance calculated by the mobile terminal and/or the eNodeB and applied by the mobile terminal UE does not need to be relative to the beginning of downlink radio frames received via the downlink SCell; other references can be chosen.

(227) For example, the calculated and applied timing advance can be relative to the beginning of downlink radio frames received via the PCell T.sub.DL.sub._.sub.RX.sub._.sub.PCell, or relative to the beginning of uplink radio frames transmitted via the PCell T.sub.UL.sub._.sub.TX.sub._.sub.PCell.

(228) In case the timing advance is calculated relative to the beginning of uplink radio frames transmitted via the PCell, it basically refers to the difference of the timing advance between the PCell and SCell ΔTA.sub.PCell-SCell.

(229) where considering equation 12:
ΔTA.sub.PCell-SCell=+2.Math.Δ.sub.SCell-PCellRx.sub.DL−2.Math.Δ.sub.SCell-PCellTx.sub.DL−Δ.sub.SCellPD.sub.UL-DL

(230) Thus, the timing advance determined by the mobile terminal UE and/or eNodeB is ΔTA.sub.PCell-SCell.

(231) As described with reference to FIGS. 26 and 27, the mobile terminal does not know about the downlink transmission time difference between the PCell and the SCell (Δ.sub.SCell-PCellTx.sub.DL) and the propagation delay difference between the uplink and the downlink on the SCell (Δ.sub.SCellPD.sub.UL-DL) and, hence, determines the timing advance ΔTA.sub.PCell-SCell assuming both values Δ.sub.SCell-PCellTx.sub.DL and Δ.sub.SCellPD.sub.UL-DL to be zero.

(232) In contrast, in case the eNodeB determine a timing advance ΔTA.sub.PCell-SCell, e.g. for checking if the measurement performed by the mobile terminal UE allows for a sufficient time alignment of uplink transmission on the SCell, the eNodeB may determine the timing advance ΔTA.sub.PCell-SCell based on its additional knowledge of the downlink transmission time difference between the PCell and the SCell (Δ.sub.SCell-PCellTx.sub.DL) and the propagation delay difference between the uplink and the downlink on the SCell (Δ.sub.SCellPD.sub.UL-DL).

(233) The mobile terminal in turn applies this value relative to the beginning of uplink radio frames received via the PCell, to determine the uplink timing for uplink transmissions performed on the SCell. This is exemplified in FIG. 31, where the timing advance is indicated by the number of samples N.sub.TA, and is then multiplied with the sample time T.sub.S to acquire the actual difference in time to apply for uplink transmissions in the SCell compared to the uplink transmissions in the PCell.

(234) In case the timing advance is calculated relative to the beginning of downlink radio frames received via the downlink PCell, the timing advance value is
TA.sub.SCell+Δ.sub.SCell-PCellRx.sub.DL
as can be deduced from FIG. 26 and FIG. 27.

(235) Thus, the mobile terminal first derives the current timing advance value TA.sub.SCell and subtracts therefrom the downlink reception time difference Δ.sub.SCell-PCellRx.sub.DL.

(236) The calculation result is used to set the timing of uplink transmissions on the SCell based on the received timing advance relative to the beginning of the downlink radio frame received by the mobile terminal in the PCell.

(237) This is exemplified in FIG. 32, where the timing advance is indicated by the number of samples N.sub.TA, and is then multiplied with the sample time T.sub.S to acquire the actual difference in time to apply for uplink transmissions in the SCell.

(238) Reception of a Random Access Channel, RACH, Order

(239) As described with respect to the previous embodiments, the mobile terminal transmits timing information to the eNodeB, enabling the eNodeB to control the time-aligning process for the uplink of an SCell or group of SCells.

(240) In connection with FIG. 25, it has been described that the eNodeB may determine, upon reception of measurement results and/or a calculated timing advance from the mobile terminal, if the transmitted information allows for an accurate time alignment of uplink transmissions on the SCell (e.g. in case of a non-zero downlink transmission time difference between the PCell and the SCell).

(241) Alternatively, the eNodeB may also determine (i.e. without reference to the received timing information) that the time-alignment of the PCell used by the mobile terminal UE does not allow for an accurate time alignment of uplink transmissions on the SCell.

(242) For example, when the eNodeB detects that the time-alignment of uplink transmission by the mobile terminal on the PCell is not accurate, the eNodeB may according to an example, immediately transmit a random access channel, RACH, order message to the mobile terminal UE. In other words, in case the mobile terminal would use a timing advance for the SCell which was, for example, based on a borderline timing advance of the uplink of the PCell, the eNodeB can prevent from interference between uplink transmissions on the SCell by immediately transmitting a RACH order message to the mobile terminal. Errors in a timing advance of uplink transmissions on the PCell (i.e. reference cell) propagate to the calculated timing advance for uplink transmissions on the SCell to-be time-aligned.

(243) As another example, the configuration of the PCell and the SCell may also trigger the eNodeB to immediately transmit a random access channel, RACH, order message to the mobile terminal UE. Based on particular configurations of the PCell and the SCell, the eNodeB may assume that the calculation of a timing advance for an SCell by the mobile terminal does not allow for an accurate time alignment of uplink transmissions on the SCell. For instance, if the PCell and the SCell are configured on widely separated frequency bands, the eNodeB may determine that the mobile terminal cannot calculate an accurate timing advance for the SCell.

(244) Should the eNodeB determines that the mobile terminal UE is not able to calculate a timing advance which would accurately time-align uplink transmission on the SCell, the eNodeB may, in one example, immediately transmit a random access channel, RACH, order message to the mobile terminal. In other words with the RACH order message the eNodeB ensures a robust time-alignment of uplink transmissions on the SCell and avoids an un-controllable uplink timing advance drift.

(245) The RACH order message preferably corresponds to message 801 in FIG. 8, which is a physical layer signalling (PDCCH with DCI format 1A).

(246) In step 3 in FIG. 28, when the mobile terminal receives a RACH order message, the mobile terminal performs a random access procedure as described with reference to FIG. 8.

(247) As part of the random access procedure (i.e. step 802), the mobile terminal receives an accurate timing advance for the SCell. The mobile terminal then time-aligns the SCell by setting a time advance for uplink transmissions on the uplink target cell based on the timing advance received within the random access procedure (step 3b in FIG. 28).

(248) Thereafter, the mobile terminal resets and restarts the respective timing advance timer for the SCell or group of SCells on which the random access procedure has been performed (step 3c in FIG. 28).

(249) Reception of a Timing Advance Command

(250) Another alternative for the eNodeB to control the time-aligning process uplink for the uplink of an SCell or group of SCells is the transmission of a timing advance command.

(251) As described with respect to the previous embodiments, the mobile terminal UE transmit timing information to the eNodeB, enabling the eNodeB to calculate a timing advance for uplink transmissions on a particular SCell or group of SCells in a similar manner to the calculation of the timing advance by the mobile terminal.

(252) In some situations, as described earlier, only the eNodeB is able to calculate a timing advance which allows for an accurate time alignment of uplink transmissions on the particular SCell or group of SCells (e.g. in case of a non-zero downlink transmission time difference between the PCell and the SCell).

(253) In such a situation, the calculated timing advance can be transmitted to the mobile terminal e.g. using the downlink shared channel of the SCell to which the timing advance shall be applied.

(254) FIG. 33 shows the format of a timing advance command to be used for transmitting the calculated timing advance from the eNodeB to the mobile terminal, according to one particular embodiment of the invention. If the timing advance information calculated and transmitted to the mobile terminal is the TA.sub.SCell (and not some of the relative values mentioned above in connection with FIGS. 31 and 32), 11 bits are preferably used to transmit the timing advance for the SCell to achieve the necessary granularity (same as for the initial TA command known from the standard).

(255) On the other hand, less bits suffice if the timing advance is smaller, due to being relative to another timing.

(256) One example is using a new MAC control element to convey the timing advance information with e.g. 8 bits. Alternatively, the timing advance update command, known from Release 8 of LTE, can be used, having a format as shown in FIG. 33. One of the free R-bits could be used to distinguish between an actual timing advance update command as known from the standard, and the timing advance information according to one of the various embodiments of the invention.

(257) Since some embodiments use a relative timing advance (see description in connection with FIGS. 31 and 32), the six bits provided by the timing advance update command may provide sufficient granularity.

(258) Another alternative would be that the eNodeB sends timing advance information not only for one SCell but for all configured respectively configured and activated SCells. In case the UE reports timing information for all configured respectively configured and activated SCells according to a previous embodiment, it could make sense to also report all the calculated TA in response.

(259) In step 4 in FIG. 28, when the mobile terminal UE receives a timing advance command from the eNodeB using the downlink shared channel of a SCell or of one of group of SCells to which the timing advance shall be applied, the mobile terminal UE time aligns uplink transmissions using the conveyed timing advance value on the SCell or group of SCells (step 4a of FIG. 28).

(260) Thereafter, the mobile terminal resets and restarts the respective timing advance timer for the SCell or group of SCells on which the time advance has been applied (step 4b in FIG. 28).

(261) Grouping of SCells

(262) In the scenario assumed for FIGS. 24, 25 and 26, SCell1 and SCell2 have the same timing advance in the uplink since the propagation delay for SCell1 and SCell2 is the same. In said case, the SCell1 and SCell2 can be said to form a timing advance group.

(263) Further to this scenario, there may be several respectively configured and activated SCells, forming different timing advance groups, depending on whether the SCells can be uplink-time-aligned using the same timing advance value. As already explained, there are several reasons leading to the need for different timing advances between various SCells of a same mobile terminal. An example is one or more frequency-selective repeater, amplifying the signals of only some of the SCells.

(264) In any case, if the mobile terminal stores a mapping of SCells to specific timing advance groups, when having to time-align an SCell1, belonging to a timing advance group with a time-aligned SCell2, the mobile terminal can immediately apply the timing advance previously used for the time-aligned SCell2, to time-align the uplink transmissions of SCell1 too. Thus, there would be no need to perform all the steps of the invention.

(265) The mapping of SCells to timing advance groups can be configured and updated by the eNodeB only.

(266) Hardware and Software Implementation of the Invention

(267) Another embodiment of the invention relates to the implementation of the above described various embodiments using hardware and software. In this connection the invention provides a user equipment (mobile terminal) and a eNodeB (base station). The user equipment is adapted to perform the methods described herein. Furthermore, the eNodeB comprises means that enable the eNodeB to determine the power status of respective user equipments from the power status information received from the user equipments and to consider the power status of the different user equipments in the scheduling of the different user equipments by its scheduler.

(268) It is further recognized that the various embodiments of the invention may be implemented or performed using computing devices (processors). A computing device or processor may for example be general purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, etc. The various embodiments of the invention may also be performed or embodied by a combination of these devices.

(269) Further, the various embodiments of the invention may also be implemented by means of software modules, which are executed by a processor or directly in hardware. Also a combination of software modules and a hardware implementation may be possible. The software modules may be stored on any kind of computer readable storage media, for example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc.

(270) It should be further noted that the individual features of the different embodiments of the invention may individually or in arbitrary combination be subject matter to another invention.

(271) It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.