description lang="EN" 
FIELD OF THE INVENTION 

[0001] The invention relates to methods for scheduling of uplink transmission and generating transport blocks according to multiple received uplink resource assignments. Furthermore, the invention is also related to the implementation/performance of these methods in/by hardware, i.e. apparatuses, and their implementation in software. 

 TECHNICAL BACKGROUND 

 Long Term Evolution (LTE) 

[0002] Third-generation mobile systems (3G) based on WCDMA radio-access technology are being deployed on a broad scale all around the world. A first step in enhancing or evolving this technology entails introducing High-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, also referred to as High Speed Uplink Packet Access (HSUPA), giving a radio-access technology that is highly competitive. 

[0003] In order to be prepared for further increasing user demands and to be competitive against new radio access technologies 3GPP introduced a new mobile communication system which is called Long Term Evolution (LTE). LTE is designed to meet the carrier needs for high speed data and media transport as well as high capacity voice support to the next decade. The ability to provide high bit rates is a key measure for LTE. 

[0004] The work item (WI) specification on Long-Term Evolution (LTE) called Evolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN) is to be finalized as Release 8 (LTE Rel. 8). The LTE system represents efficient packet-based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. The detailed system requirements are given in. In LTE, scalable multiple transmission bandwidths are specified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieve flexible system deployment using a given spectrum. In the downlink, Orthogonal Frequency Division Multiplexing (OFDM) based radio access was adopted because of its inherent immunity to multipath interference (MPI) due to a low symbol rate, the use of a cyclic prefix (CP), and its affinity to different transmission bandwidth arrangements. Single-carrier frequency division multiple access (SC-FDMA) based radio access was adopted in the uplink, since provisioning of wide area coverage was prioritized over improvement in the peak data rate considering the restricted transmit power of the user equipment (UE). Many key packet radio access techniques are employed including multiple-input multiple-output (MIMO) channel transmission techniques, and a highly efficient control signaling structure is achieved in LTE Rel. 8. 

 LTE architecture 

[0005] The overall architecture is shown in Fig. 1 and a more detailed representation of the E-UTRAN architecture is given in Fig. 2 . The E-UTRAN consists of eNode B, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the user equipment (UE). The eNode B (eNB) hosts the Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of downlink/uplink user plane packet headers. The eNode Bs are interconnected with each other by means of the X2 interface. 

[0006] The eNode Bs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (SGW) by means of the S1-U. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNode Bs. The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNode B handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW). For idle state user equipments, the SGW terminates the downlink data path and triggers paging when downlink data arrives for the user equipment. It manages and stores user equipment contexts, e.g. parameters of the IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception. 

[0007] The MME is the key control-node for the LTE access-network. It is responsible for idle mode user equipment tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation process and is also responsible for choosing the SGW for a user equipment at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation. It is responsible for authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to user equipments. It checks the authorization of the user equipment to camp on the service provider's Public Land Mobile Network (PLMN) and enforces user equipment roaming restrictions. The MME is the termination point in the network for ciphering/integrity protection for NAS signaling and handles the security key management. Lawful interception of signaling is also supported by the MME. The MME also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME from the SGSN. The MME also terminates the S6a interface towards the home HSS for roaming user equipments. 

 QoS control 

[0008] Efficient Quality of Service (QoS) support is seen as a basic requirement by operators for LTE. In order to allow best in class user experience, while on the other hand optimizing the network resource utilization, enhanced QoS support should be integral part of the new system. 

[0009] Aspects of QoS support is currently being under discussion within 3GPP working groups. Essentially, the QoS design for System Architecture Evolution (SAE)/LTE is based on the QoS design of the current UMTS system reflected in 3GPP TR 25.814, "Physical layer aspects for evolved Universal Terrestrial Radio Access (UTRA)", v.7.1.0 (available at http://www.3gpp.org and incorporated herein by reference). The agreed SAE Bearer Service architecture is depicted in Fig. 5 . The definition of a bearer service as given in 3GPP TR 25.814 may still be applicable:
"A bearer service includes all aspects to enable the provision of a contracted QoS. These aspects are among others the control signaling, user plane transport and QoS management functionality".

[0010] In the new SAE/LTE architecture the following new bearers have been defined: the SAE Bearer service between the mobile terminal (User Equipment - UE) and the serving gateway, the SAE Radio Bearer on the radio access network interface between mobile terminal and eNode B as well as the SAE Access Bearer between the eNode B and the serving gateway. 

[0011] The SAE Bearer Service provides:
QoS-wise aggregation of IP end-to-end-service flows;
IP header compression (and provision of related information to UE);
User Plane (UP) encryption (and provision of related information to UE);
if prioritized treatment of end-to-end-service signaling packets is required an additional SAE Bearer Service can be added to the default IP service;
provision of mapping/multiplexing information to the UE;
provision of accepted QoS information to the UE.

[0012] The SAE Radio Bearer Service provides:
transport of the SAE Bearer Service data units between eNode B and UE according to the required QoS;
linking of the SAE Radio Bearer Service to the respective SAE Bearer Service.

[0013] The SAE Access Bearer Service provides:
transport of the SAE Bearer Service data units between serving gateway and eNode B according to the required QoS;
provision of aggregate QoS description of the SAE Bearer Service towards the eNode B;
linking of the SAE Access Bearer Service to the respective SAE Bearer Service.

[0014] In 3GPP TR 25.814 a one-to-one mapping between an SAE Bearer and an SAE Radio Bearer. Furthermore there is a one-to-one mapping between a radio bearer (RB) and a logical channel. From that definition it follows that a SAE Bearer, i.e. the corresponding SAE Radio Bearer and SAE Access Bearer, is the level of granularity for QoS control in an SAE/LTE access system. Packet flows mapped to the same SAE Bearer receive the same treatment. 

[0015] For LTE there will be two different SAE bearer types: the default SAE bearer with a default QoS profile, which is configured during initial access and the dedicated SAE bearer (SAE bearers may also be referred to as SAE bearer services) which is established for services requiring a QoS profile which is different from the default one. 

[0016] The default SAE bearer is an "always on" SAE bearer that can be used immediately after L TE_IDLE to LTE_ACTIVE state transition. It carries all flows which have not been signaled a Traffic Flow Template (TFT). The Traffic Flow Template is used by serving gateway to discriminate between different user payloads. The Traffic Flow Template incorporates packet filters such as QoS. Using the packet filters the serving gateway maps the incoming data into the correct PDP Context (Packet Data Protocol Context). For the default SAE bearer, several service data flows can be multiplexed. Unlike the Default SAE Bearer, the Dedicated SAE Bearers are aimed at supporting identified services in a dedicated manner, typically to provide a guaranteed bit-rate. Dedicated SAE bearers are established by the serving gateway based on the QoS information received in Policy and Charging Control (PCC) rules from evolved packet core when a new service is requested. A dedicated SAE bearer is associated with packet filters where the filters match only certain packets. A default SAE bearer is associated with "match all" packet filters for uplink and downlink. For uplink handling the serving gateway builds the Traffic Flow Template filters for the dedicated SAE bearers. The UE maps service data flows to the correct bearer based on the Traffic Flow Template, which has been signaled during bearer establishment. As for the default SAE Bearer, also for the dedicated SAE Bearer several service data flows can be multiplexed. 

[0017] The QoS Profile of the SAE bearer is signaled from the serving gateway to the eNode B during the SAE bearer setup procedure. This profile is then used by the eNode B to derive a set of Layer 2 QoS parameters, which will determine the QoS handling on the air interface. The Layer 2 QoS parameters are input the scheduling functionality. The parameters included in the QoS profile signaled on S1 interface from serving gateway to eNode B are currently under discussion. Most likely the following QoS profile parameters are signaled for each SAE bearer: Traffic Handling Priority, Maximum Bit-rate, Guaranteed Bit-rate. In addition, the serving gateway signals to the eNode B the Allocation and Retention Priority for each user during initial access. 

 Uplink Access scheme for LTE 

[0018] For uplink transmission, power-efficient user-terminal transmission is necessary to maximize coverage. Single-carrier transmission combined with FDMA (Frequency Division Multiple Access) with dynamic bandwidth allocation has been chosen as the evolved UTRA uplink transmission scheme. The main reason for the preference for single-carrier transmission is the lower peak-to-average power ratio (PAPR), compared to multi-carrier signals (OFDMA - Orthogonal Frequency Division Multiple Access), and the corresponding improved power-amplifier efficiency and assumed improved coverage (higher data rates for a given terminal peak power). During each time interval, eNode B assigns users a unique time/frequency resource for transmitting user data thereby ensuring intra-cell orthogonality. An orthogonal access in the uplink promises increased spectral efficiency by eliminating intra-cell interference. Interference due to multipath propagation is handled at the base station (eNode B), aided by insertion of a cyclic prefix in the transmitted signal. 

[0019] The basic physical resource used for data transmission consists of a frequency resource of size BWgrantduring one time interval, e.g. a sub-frame of 0.5 ms, onto which coded information bits are mapped. It should be noted that a sub-frame, also referred to as transmission time interval (TTI), is the smallest time interval for user data transmission. It is however possible to assign a frequency resource BWgrantover a longer time period than one TTl to a user by concatenation of sub-frames. 

[0020] The frequency resource can either be in a localized or distributed spectrum as illustrated in Fig. 3 and Fig. 4 . As can be seen from Fig. 3 , localized single-carrier is characterized by the transmitted signal having a continuous spectrum that occupies a part of the total available spectrum. Different symbol rates (corresponding to different data rates) of the transmitted signal imply different bandwidths of a localized single-carrier signal. 

[0021] On the other hand, as shown in Fig. 4 , distributed single-carrier is characterized by the transmitted signal having a non-continuous ("comb-shaped") spectrum that is distributed over system bandwidth. Note that, although the distributed single-carrier signal is distributed over the system bandwidth, the total amount of occupied spectrum is, in essence, the same as that of localized single-carrier. Furthermore, for higher/lower symbol rate, the number of "comb-fingers" is increased/reduced, while the "bandwidth" of each "comb finger" remains the same. 

[0022] At first glance, the spectrum in Fig. 4 may give the impression of a multi-carrier signal where each comb-finger corresponds to a "sub-carrier". However, from the time-domain signal-generation of a distributed single-carrier signal, it should be clear that what is being generated is a true single-carrier signal with a corresponding low peak-to-average power ratio. The key difference between a distributed single-carrier signal versus a multi-carrier signal, such as e.g. OFDM (Orthogonal Frequency Division Multiplex), is that, in the former case, each "sub-carrier" or "comb finger" does not carry a single modulation symbol. Instead each "comb-finger" carries information about all modulation symbols. This creates a dependency between the different comb-fingers that leads to the low-PAPR characteristics. It is the same dependency between the "comb fingers" that leads to a need for equalization unless the channel is frequency-non-selective over the entire transmission bandwidth. In contrast, for OFDM equalization is not needed as long as the channel is frequency-non-selective over the sub-carrier bandwidth. 

[0023] Distributed transmission can provide a larger frequency diversity gain than localized transmission, while localized transmission more easily allows for channel-dependent scheduling. Note that, in many cases the scheduling decision may decide to give the whole bandwidth to a single user equipment to achieve high data rates. 

 Uplink Scheduling scheme for LTE 

[0024] The uplink scheme allows for both scheduled access, i.e. controlled by eNodeB, and contention-based access. 

[0025] In case of scheduled access the user equipment is allocated a certain frequency resource for a certain time (i.e. a time/frequency resource) for uplink data transmission. However, some time/frequency resources can be allocated for contention-based access. Within these time/frequency resources, user equipments can transmit without first being scheduled. One scenario where user equipment is making a contention-based access is for example the random access, i.e. when user equipment is performing initial access to a cell or for requesting uplink resources. 

[0026] For the scheduled access eNode B scheduler assigns a user a unique frequency/time resource for uplink data transmission. More specifically the scheduler determines
which user equipment(s) that is (are) allowed to transmit,
which physical channel resources (frequency),
Transport format (Transport Block Size (TBS) and Modulation Coding Scheme (MCS)) to be used by the mobile terminal for transmission

[0027] The allocation information is signaled to the user equipment via a scheduling grant, sent on the so-called L1/L2 control channel. For simplicity, this downlink channel is referred to the "uplink grant channel" in the following. 

[0028] A scheduling grant message (also referred to as an resource assignment herein) contains at least information which part of the frequency band the user equipment is allowed to use, the validity period of the grant, and the transport format the user equipment has to use for the upcoming uplink transmission. The shortest validity period is one sub-frame. Additional information may also be included in the grant message, depending on the selected scheme. Only "per user equipment" grants are used to grant the right to transmit on the Uplink Shared Channel UL-SCH (i.e. there are no "per user equipment per RB" grants). Therefore the user equipment needs to distribute the allocated resources among the radio bearers according to some rules, which will be explained in detail in the next section. 

[0029] Unlike in HSUPA there is no user equipment based transport format selection. The base station (eNodeB) decides the transport format based on some information, e.g. reported scheduling information and QoS information, and user equipment has to follow the selected transport format. In HSUPA eNodeB assigns the maximum uplink resource and user equipment selects accordingly the actual transport format for the data transmissions. 

[0030] Uplink data transmissions are only allowed to use the time-frequency resources assigned to the user equipment through the scheduling grant. If the user equipment does not have a valid grant, it is not allowed to transmit any uplink data. Unlike in HSUPA, where each user equipment is always allocated a dedicated channel there is only one uplink data channel shared by multiple users (UL-SCH) for data transmissions. 

[0031] To request resources, the user equipment transmits a resource request message to the eNodeB. This resources request message could for example contain information on the buffer status, the power status of the user equipment and some Quality of Services (QoS) related information. This information, which will be referred to as scheduling information, allows eNodeB to make an appropriate resource allocation. Throughout the document it's assumed that the buffer status is reported for a group of radio bearers. Of course other configurations for the buffer status reporting are also possible. Since the scheduling of radio resources is the most important function in a shared channel access network for determining Quality of Service, there are a number of requirements that should be fulfilled by the uplink scheduling scheme for LTE in order to allow for an efficient QoS management (see 3GPP RAN WG#2 Tdoc. R2- R2-062606, "QoS operator requirements/use cases for services sharing the same bearer", by T-Mobile, NTT DoCoMo, Vodafone, Orange, KPN; available at http://www.3gpp.org / and incorporated herein by reference):
Starvation of low priority services should be avoided
Clear QoS differentiation for radio bearers/services should be supported by the scheduling scheme
The uplink reporting should allow fine granular buffer reports (e.g. per radio bearer or per radio bearer group) in order to allow the eNode B scheduler to identify for which Radio Bearer/service data is to be sent.
It should be possible to make clear QoS differentiation between services of different users
It should be possible to provide a minimum bit-rate per radio bearer

[0032] As can be seen from above list one essential aspect of the LTE scheduling scheme is to provide mechanisms with which the operator can control the partitioning of its aggregate cell capacity between the radio bearers of the different QoS classes. The QoS class of a radio bearer is identified by the QoS profile of the corresponding SAE bearer signaled from serving gateway to eNode B as described before. An operator can then allocate a certain amount of its aggregate cell capacity to the aggregate traffic associated with radio bearers of a certain QoS class. 

[0033] The main goal of employing this class-based approach is to be able to differentiate the treatment of packets depending on the QoS class they belong to. For example, as the load in a cell increases, it should be possible for an operator to handle this by throttling traffic belonging to a low-priority QoS class. At this stage, the high-priority traffic can still experience a low-loaded situation, since the aggregate resources allocated to this traffic is sufficient to serve it. This should be possible in both uplink and downlink direction. 

[0034] One benefit of employing this approach is to give the operator full control of the policies that govern the partitioning of the bandwidth. For example, one operator's policy could be to, even at extremely high loads, avoid starvation of traffic belonging to its lowest priority QoS Class. The avoidance of starvation of low priority traffic is one of the main requirements for the uplink scheduling scheme in LTE. In current UMTS Release 6 (HSUPA) scheduling mechanism the absolute prioritization scheme may lead to starvation of low priority applications. E-TFC selection (Enhanced Transport Format Combination selection) is done only in accordance to absolute logical channel priorities, i.e. the transmission of high priority data is maximized, which means that low priority data is possibly starved by high priority data. In order to avoid starvation the eNode B scheduler must have means to control from which radio bearers a user equipment transmits data. This mainly influences the design and use of the scheduling grants transmitted on the L1/L2 control channel in downlink. In the following the details of the uplink rate control procedure in LTE is outlined. 

 Medium Access Control (MAC) and MAC Control Elements 

[0035] The MAC layer is the lowest sub-layer in the Layer 2 architecture of the LTE radio protocol stack (see 3GPP TS 36.321, "Medium Access Control (MAC) protocol specification", version 8.7.0, in particular sections 4.2, 4.3, 5.4.3 and 6, available at http//www.3gpp.org and incorporated in its entirety herein by reference). The connection to the physical layer below is through transport channels, and the connection to the RLC layer above is through logical channels. The MAC layer performs multiplexing and demultiplexing between logical channels and transport channels. The MAC layer in the transmitting side (in the following examples the user equipment) constructs MAC PDUs, also referred to as transport blocks, from MAC SDUs received through logical channels, and the MAC layer in the receiving side recovers MAC SDUs from MAC PDUs received through transport channels. 

[0036] In the multiplexing and demultiplexing entity, data from several logical channels can be (de)multiplexed into/from one transport channel. The multiplexing entity generates MAC PDUs from MAC SDUs when radio resources are available for a new transmission. This process includes prioritizing the data from the logical channels to decide how much data and from which logical channel(s) should be included in each MAC PDU. Please note that the process of generating MAC PDUs in the user equipment is also referred to a logical channel prioritization (LCP) in the 3GPP terminology. 

[0037] The demultiplexing entity reassembles the MAC SDUs from MAC PDUs and distributes them to the appropriate RLC entities. In addition, for peer-to-peer communication between the MAC layers, control messages called 'MAC Control Elements' can be included in the MAC PDU. 

[0038] A MAC PDU primarily consists of the MAC header and the MAC payload (see 3GPP TS 36.321, section 6). The MAC header is further composed of MAC subheaders, while the MAC payload is composed of MAC Control Elements, MAC SDUs and padding. Each MAC subheader consists of a Logical Channel ID (LCID) and a Length (L) field. The LCID indicates whether the corresponding part of the MAC payload is a MAC Control Element, and if not, to which logical channel the related MAC SDU belongs. The L field indicates the size of the related MAC SDU or MAC Control Element. As already mentioned above, MAC Control Elements are used for MAC-level peer-to-peer signaling, including delivery of BSR information and reports of the UE's available power in the uplink, and in the downlink DRX commands and timing advance commands. For each type of MAC Control Element, one special LCID is allocated. An example for a MAC PDU is shown in Fig. 6 . 

 Power Control 

[0039] Uplink transmitter power control in a mobile communication system serves the purpose of balancing the need for sufficient transmitter energy per bit to achieve the required QoS against the need to minimize interference to other users of the system and to maximize the battery life of the user equipment. 

[0040] In achieving this, the uplink power control has to adapt to the characteristics of the radio propagation channel, including path loss, shadowing and fast fading, as well as overcoming interference from other users within the same cell and neighboring cells. 

[0041] The power control scheme provided in LTE Rel. 8 employs a combination of open-loop and closed-loop control. A mode of operation involves setting a coarse operating point for the transmission power density spectrum by open-loop means based on path-loss estimation. Faster operation can then be applied around the open-loop operating point by closed-loop power control. This controls interference and fine-tunes the power settings to suit the channel conditions including fast fading. 

[0042] With this combination of mechanisms, the power control scheme in LTE Rel. 8 provides support for more than one mode of operation. It can be seen as a toolkit for different power control strategies depending on the deployment scenario, the system load and operator preference. 

 Power Headroom Reporting 

[0043] In order to assist the eNodeB to schedule the uplink transmission resources to different user equipments in an appropriate way, it is important that the user equipment can report its available power headroom to eNodeB. 

[0044] The eNodeB can use the power headroom reports to determine how much more uplink bandwidth per sub-frame a user equipment is capable of using. This helps to avoid allocating uplink transmission resources to user equipment s which are unable to use them in order to avoid a waste of resources. 

[0045] The range of the power headroom report is from +40 to -23 dB (see 3GPP TS 36.133, "Requirements for support of radio resource management", version 8.7.0, section 9.1.8.4, available at http//www.3gpp.org and incorporated in its entirety herein by reference). The negative part of the range enables the user equipment to signal to the eNodeB the extent to which it has received an UL grant which would require more transmission power than the UE has available. This would enable the eNodeB to reduce the size of a subsequent grant, thus freeing up transmission resources to allocate to other UEs. 

[0046] A power headroom report can only be sent in sub-frames in which a UE has an UL grant. The report relates to the sub-frame in which it is sent. A number of criteria are defined to trigger a power headroom report. These include:
A significant change in estimated path loss since the last power headroom report
More than a configured time has elapsed since the previous power headroom report
More than a configured number of closed-loop TPC commands have been implemented by the UE

[0047] The eNodeB can configure parameters to control each of these triggers depending on the system loading and the requirements of its scheduling algorithm. To be more specific, RRC controls power headroom reporting by configuring the two timersperiodicPHR-Timer and prohibitPHR-Timer,and by signallingdl-PathlossChangewhich sets the change in measured downlink pathloss to trigger a power headroom report. 

[0048] The power headroom report is send as a MAC Control Element. It conssits of a single octet where the two highest bits are reserved and the six lowest bits represent the dB values mentioned above in 1 dB steps. The structure of the MAC Control Element is shown in Fig. 7 . 

 Further Advancements for LTE (LTE-A) 

[0049] The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07) last November [4 ]. Although the overall frequency spectrum for IMT-Advanced was decided, the actual available frequency bandwidth is different according to each region or country. Following the decision on the available frequency spectrum outline, however, standardization of a radio interface started in the 3rd Generation Partnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the Study Item description on "Further Advancements for E-UTRA (LTE-Advanced)" was approved. The study item covers technology components to be considered for the evolution of E-UTRA, e.g. to fulfill the requirements on IMT-Advanced. Two major technology components which are currently under consideration for LTE-A are described in the following. 

 LTE-A Support of wider bandwidth 

[0050] Carrier aggregation, where two or more component carriers are aggregated, is considered for LTE-Advanced in order to support wider transmission bandwidths e.g. up to 100 MHz and for spectrum aggregation. 

[0051] A terminal may simultaneously receive or transmit on one or multiple component carriers depending on its capabilities:
An LTE-Advanced terminal with reception and/or transmission capabilities for carrier aggregation can simultaneously receive and/or transmit on multiple component carriers. There is one Transport Block (in absence of spatial multiplexing) and one HARQ entity per component carrier.
An LTE Rel. 8 terminal can receive and transmit on a single component carrier only, provided that the structure of the component carrier follows the Rel. 8 specifications.

[0052] It shall be possible to configure all component carriers LTE Release 8 compatible, at least when the aggregated numbers of component carriers in the uplink and the downlink are same. Consideration of non-backward-compatible configurations of LTE-A component carriers is not precluded 

 LTE-A Support of Relaying functionality 

[0053] Relaying is considered for LTE-Advanced as a tool to improve e.g. the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and/or to provide coverage in new areas. 

[0054] The relay node is wirelessly connected to radio-access network via a donor cell. The connection can be
inband, in which case the network-to-relay link share the same band with direct network-to-user equipment links within the donor cell. Rel. 8 user equipments should be able to connect to the donor cell in this case.
outband, in which case the network-to-relay link does not operate in the same band as direct network-to-user equipment links within the donor cell

[0055] With respect to the knowledge in the user equipment, relays can be classified into
transparent, in which case the user equipment is not aware of whether or not it communicates with the network via the relay.
non-transparent, in which case the user equipment is aware of whether or not it is communicating with the network via the relay.

[0056] Depending on the relaying strategy, a relay may
be part of the donor cell
control cells of its own

[0057] In the case the relay is part of the donor cell, the relay does not have a cell identity of its own (but may still have a relay ID). At least part of the RRM is controlled by the eNodeB to which the donor cell belongs, while parts of the RRM may be located in the relay. In this case, a relay should preferably support also LTE Rel. 8 user equipments. Smart repeaters, decode-and-forward relays and different types of Layer 2 relays are examples of this type of relaying. 

[0058] In the case the relay is in control of cells of its own, the relay controls one or several cells and a unique physical-layer cell identity is provided in each of the cells controlled by the relay. The same RRM mechanisms are available and from a user equipment perspective there is no difference in accessing cells controlled by a relay and cells controlled by a "normal" eNodeB. The cells controlled by the relay should support also LTE Rel. 8 user equipments. Self-backhauling (Layer 3 relay) uses this type of relaying. 

[0059] As indicated above, one of the major changes from LTE Rel. 8 to LTE-A is that instead of receiving and transmitting only on a single component carrier, a LTE-A UE can aggregate several component carriers for uplink transmission and downlink reception. Therefore, a LTE-A user equipment can simultaneously receive and/or transmit on multiple component carriers. When transmitting on several component carriers in the uplink within the same sub-frame the user equipment is sending individual transport blocks on each of the assigned component carriers. 

[0060] Regarding these uplink transmissions on each of the component carriers that received an uplink grant within the same sub-frame, in order to conduct an efficient uplink transmission for each of the component carriers, there is a need of a power control loop per component carrier. This is because the power needed for a transmission on a specific component carrier is independent of other component carriers where the user equipment conducts simultaneous UL transmission as each of the component carriers aggregated by one UE can experience an individual path loss as well as interference (since it might terminate at a different geographical source). Therefore the propagation conditions between the transmitting UE and the receiving eNodeB are not the same for all component carriers. 

[0061] As each component carrier can be assumed to have its own power control loop and each transport block on each component carrier is transmitted with a power individually set for the component carrier, also the power headroom reporting should be performed per component carrier. Since carrier aggregation can be seen as a multiplication of several LTE Rel. 8 (component) carriers, it can be assumed that also the power headroom reporting on the individual component carriers will reuse the LTE Rel. 8 power headroom reporting procedures. 

[0062] Hence each UE transmits power headroom reports for each component carrier on that component carrier. This means that each component carrier that has an UL transmission in a specific sub-frame could also transmit a power headroom report given that the conditions for sending such a report are fulfilled. 

[0063] Power headroom reporting as know form LTE Rel. 8 is controlled, respectively triggered on a component carrier basis (by employing different timers). Applying this concept to the individual component carriers of a system utilizing carrier aggregation, this means that it almost never happens that within one sub-frame each of the component carriers with an uplink transmission is transmitting a power headroom report. Hence, even if the timers relating to power headroom reporting (the periodicPHR timer and the prohibitPHR timer) are set to the same values for all component carriers, synchronous power headroom reports on all component carriers within a sub-frame will only happen by chance. 

[0064] However, since the transmit power available for uplink transmissions in a UE is not set per component carrier, but per UE, this implies that two or even more component carriers on which transmissions have been scheduled for a sub-frame have to share the transmit power of one power amplifier. As a consequence the power setting in one component carrier has influence on the power setting in another component carrier. The overall transmit power spent by the UE for all uplink transmissions within a sub-frame is only known to the eNodeB, if the UE is including power headroom reports for all the component carriers within the sub-frame. If UE includes only power headroom reports of some of the assigned component carriers, the eNodeB cannot determine how much power was actually spent by the UE for transmitting the sub-frame and if UE still has power available to a transmission with increased power (i.e. there is a power headroom) in one of the following sub-frames or if there were already problems and the UE reached it's power limit, hence already transmitting on some of the component carriers with less power than was demanded by eNodeB. 

[0065] The UE reaching its power limit means that the UE is utilizing the maximum transmit power it has available for uplink transmission. This "maximum available transmit power" is defined by a maximum power value which is set by preconfigured UE capability classes (e.g. standardization typically defines a maximum transit power the UEs are allowed to radiate at maximum). This maximum power value can optionally be lowered individually per UE by eNodeB using RRC signaling. 

[0066] Fig. 10 shows exemplary power headroom reporting in a LTE-A system, assuming that the power headroom reporting of LTE Rel. 8 is applied to each of the exemplary three component carriers (CoCa1 to CoCa3). AtT1, there is an uplink assignment on all three component carriers and an uplink transport block, respectively MAC PDU, including a power headroom report for the respective component carrier is sent on each component carrier. As there is a per-component carrier (per-CC) power headroom report for each component carrier, the eNodeB is informed on the user equipment's power status. Furthermore, the respective timersperiodicPHR-TimerandprohibitPHR-Timerare restarted for each component carrier. For component carriers CoCa2 and CoCa3, it is assumed that after expiry of theperiodicPHR-Timerthere is no uplink allocation in the next sub-frame, so that no periodic power headroom report can be sent immediately. Hence atT2'the user equipment transmits a transport block/MAC PDU with a power headroom report only on component carrier CoCa1. As there is only a resource assignment on component carrier CoCa1, the eNodeB may again conclude on the user equipment's power status from the per-CC power headroom report atT2. 

[0067] However atT3 , T4 ,andT5 ,only some transport blocks/PDUs of the component carriers within a sub-frame carry a power headroom report. Regarding the power headroom report on component carrier CoCa3 atT5. a path-loss change on component carrier CoCa3 is assumed to trigger the power headroom report, but at the time of the path-loss change none of the component carriers with uplink transmissions (i.e. component carriers CoCa1 and CoCa2) have a power headroom report included. Therefore,T3 , T4 ,andT5, the eNodeB is not aware of the actual transmit power spend on the uplink transmissions within the respective sub-frames. 

 SUMMARY OF THE INVENTION 

[0068] One object of the invention is to propose procedures that allow the eNodeB to recognize the power usage status of a user equipment in a mobile communication system using carrier aggregation. 

[0069] The object is solved by the subject matter of the independent claims. Advantageous embodiments are subject to the dependent claims. 

[0070] One aspect of the invention is to enable to UE to indicate to the eNodeB when it is potentially becoming power limited or is power limited, i.e. when being close to using its maximum available transmit power or the resource allocations and power control commands of the eNodeB would require using a transmit power exceeding the user equipment's maximum available transmit power. This is achieved by defining a new MAC control element that is inserted by the user equipment to one or more protocol data units transmitted on respective (assigned) component carriers within a single sub-frame that is providing the eNodeB with a corresponding indication. 

[0071] Furthermore, in addition to the indication of the user equipment approaching its maximum available transmit power, the control element inserted to the protocol data units may further indicate a per-user equipment (per-UE) power headroom. For example, the per-user equipment power headroom indicates the transmit power unused by the user equipment when transmitting the protocol data units (including the MAC control element) within the sub-frame relative to the user equipment's maximum available transmit power. 

[0072] The MAC control element may be inserted to the protocol data units of a sub-frame. For example, the MAC control element may be inserted into one of the protocol data units transmitted by the user equipment within the sub-frame or all of the protocol data units transmitted by the user equipment within the sub-frame. 

[0073] In an alternative solution, according to another aspect of the invention, the object is solved by the user equipment sending per-component carrier power headroom reports for all assigned component carriers within a single sub-frame when the user equipment is potentially becoming power limited or is power limited, i.e. when being close to using its maximum available transmit power or the resource allocations and power control commands of the eNodeB would require using a transmit power exceeding the user equipment's maximum available transmit power. 

[0074] One embodiment of the present invention provides a method for informing an eNodeB on the power status of a user equipment in a mobile communication system using component carrier aggregation. The user equipment determines whether an estimated transmit power required for transmitting protocol data units on respective component carriers within a sub-frame will exceed a threshold value relative to a maximum available transmit power of the user equipment. If the threshold value is exceeded, the user equipment multiplexes a MAC control element to the protocol data units and transmits the protocol data units including the MAC control element to the eNodeB within the sub-frame. The MAC control element indicates to the eNodeB that the transmit power spent by the user equipment for transmitting the generated protocol data units on uplink exceeded the threshold value, i.e. is reporting the power headroom per-user equipment. The threshold value may be for example defined as a percentage of the maximum the user equipment is allowed to use. 

[0075] According to a further embodiment of the invention, the MAC control element provides the eNodeB with a per-user equipment power headroom relative to all uplink protocol data units transmitted in the sub-frame. For example, in a 3GPP-based communication system such as LTE-Advanced, the per-user equipment power headroom could account for all transmissions on a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH) within the sub-frame. 

[0076] In another embodiment of the invention, at least one uplink resource assignment is received, wherein each uplink resource assignment is assigning resources for the transmission of one of the protocol data units on one of the plural component carriers to the user equipment. For each received uplink resource assignment a protocol data unit is generated for transmission on the respective assigned component carrier. Each protocol data unit is transmitted via a corresponding one of the component carriers according to one of the received resource assignments. 

[0077] According another embodiment of the invention, generating for each received uplink resource assignment a protocol data unit comprises said multiplexing of the MAC control element to at least one of said protocol data units. In an further embodiment of the invention the MAC control element is multiplexed to one of the protocol data units or to each of the protocol data units. The protocol data units may be for example generated by executing a joint logical channel prioritization procedure. 

[0078] According to an advantageous embodiment of the invention, the component carriers each have a priority, and the MAC control element is multiplexed to the protocol data unit to be transmitted on the highest priority component carrier for which a resource assignment has been received. 

[0079] In an alternative embodiment of the invention, the component carriers each have a priority, and the MAC control element is multiplexed to the protocol data unit to be transmitted on the component carrier achieving the lowest block error rate, having the largest power headroom or experiencing the best channel quality, and for which a resource assignment has been received. 

[0080] With regard to a further embodiment of the invention, the estimated transmit power is estimated based on the resource assignments for the protocol data units to be transmitted in the sub-frame and the status of a transmit power control function. 

[0081] According to further embodiment of the invention radio resource control signaling is received from the eNodeB indicating said threshold value as a percentage of the maximum the user equipment is allowed to use. The threshold value is configured according to the indicated percentage. 

[0082] Another embodiment of the invention provides another alternative method for informing an eNodeB on the power status of a user equipment in a mobile communication system using component carrier aggregation. Protocol data units are transmitted in each of a predetermined number of successive sub-frames (monitoring period) from the user equipment to the eNodeB. At the user equipment a MAC control element is multiplexed to the protocol data units of the last sub-frame of said predetermined number of successive sub-frames transmitted by the user equipment, if one of the following conditions is met:
the transmit power required for transmitting the protocol data units in each of the successive sub-frames exceeds a threshold value relative to the user equipment's maximum available transmit power, or
the transmit power required for transmitting protocol data units in a subset of sub-frames of said successive sub-frames exceeds a threshold value relative to the user equipment's maximum available transmit power, or
the average transmit power required for transmitting the protocol data units in said successive sub-frames exceeds a threshold value relative to the user equipment's maximum available transmit power.

[0083] The MAC control element thus indicates to the eNodeB that the respective condition was met. 

[0084] In a further embodiment of the invention the number of sub-frames of said subset is configured by RRC control signaling received at the user equipment from the eNodeB or is predefined. 

[0085] According to another embodiment of the invention, a MAC control element for transmission from a user equipment to a eNodeB in a mobile communication system using component carrier aggregation is provided. The MAC control element comprises a power headroom field consisting of a predetermined number of bits for comprising a per-user equipment power headroom with respect to all uplink transmissions of the user equipment on a plurality of component carriers within a sub-frame containing the MAC control element, relative to the maximum available transmit power of the user equipment. 

[0086] In a further advantageous embodiment of the invention, the MAC control element comprises a component carrier indicator field for indicating
the number of component carrier for which the user equipment has received resource assignments, or
a bitmap indicating the component carriers for which the user equipment has received resource assignments.

[0087] In another embodiment of the invention, the power headroom field comprises either said per-user equipment power headroom or a per-component carrier power headroom. The MAC control element comprises a component carrier indicator field that is indicating whether the power headroom field comprises said per-user equipment power headroom or said per-component carrier power headroom. 

[0088] An additional embodiment of the invention provides a MAC protocol data unit for transmission from a user equipment to a eNodeB in a mobile communication system using component carrier aggregation. The MAC protocol data unit comprises a MAC subheader and a MAC control element according to one of the embodiments thereof described herein. The MAC subheader comprises a logical channel identifier (LCID) that is indicating the content and format of said MAC control element. 

[0089] According to another embodiment of the invention, a user equipment is provided for informing a eNodeB on the power status of a user equipment in a mobile communication system using component carrier aggregation. An determining section of the user equipment determines whether an estimated transmit power required for transmitting protocol data units on respective component carriers within a sub-frame will exceed a threshold value relative to a maximum available transmit power of the user equipment. A protocol data unit generation section of the user equipment multiplexes a MAC control element to the protocol data units, if the threshold value is exceeded. A transmitting section of the user equipment transmits the protocol data units including the MAC control element to the eNodeB within the sub-frame. The MAC control element indicates to the eNodeB that the transmit power spent by the user equipment for transmitting the generated protocol data units on uplink exceeded the threshold value. 

[0090] In an advantageous embodiment of the invention the MAC control element provides the eNodeB with a per-user equipment power headroom relative to all uplink protocol data units transmitted in the sub-frame. 

[0091] For another embodiment of the invention a receiving section of the user equipment receives at least one uplink resource assignment. Each uplink resource assignment is assigning resources for the transmission of one of the protocol data units on one of the plural component carriers to the user equipment. A protocol data unit generation section of the user equipment generates for each received uplink resource assignment a protocol data unit for transmission on the respective assigned component carrier. The transmitting section transmits each protocol data unit via a corresponding one of the component carriers according to one of the received resource assignments. 

[0092] According to a further embodiment of the invention, the component carriers each have a priority, and a protocol data unit generation section of the user equipment multiplexes the MAC control element to the protocol data unit to be transmitted on the highest priority component carrier for which a resource assignment has been received. 

[0093] With regard to another embodiment of the invention, the component carriers each have a priority, and a protocol data unit generation section of the user equipment multiplexes the MAC control element to the protocol data unit to be transmitted on the component carrier achieving the lowest block error rate, having the largest power headroom or experiencing the best channel quality, and for which a resource assignment has been received. 

[0094] In a further embodiment of the invention a power control section of the user equipment performs power control, and the determining section determines the estimated transmit power based on the resource assignment for the protocol data units to be transmitted in the sub-frame and the status of a transmission power control section. 

[0095] According to an advantageous embodiment of the invention, a receiving section of the user equipment receives radio resource control signaling from the eNodeB indicating said threshold value as a percentage of the maximum the user equipment is allowed to use. A configuration section of the user equipment configures the threshold value according to the indicated percentage. 

[0096] A further embodiment of the invention provides a computer readable medium storing instructions that, when executed by a processor of a user equipment, cause the user equipment to inform am eNodeB on the power status of a user equipment in a mobile communication system using component carrier aggregation. This is done as follows. It is determined whether an estimated transmit power required for transmitting protocol data units on respective component carriers within a sub-frame will exceed a threshold value relative to a maximum available transmit power of the user equipment. If the threshold value is exceeded, a MAC control element is multiplexed to the protocol data units. The protocol data units including the MAC control element are transmitted to the eNodeB within the sub-frame. The MAC control element indicates to the eNodeB that the transmit power spent by the user equipment for transmitting the generated protocol data units on uplink exceeded the threshold value. 

 BRIEF DESCRIPTION OF THE FIGURES 

[0097] 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.
Fig. 1 : shows an exemplary architecture of a 3GPP LTE system,
Fig. 2 : shows an exemplary overview of the overall E-UTRAN architecture of LTE,
Fig. 3 and 4 : show an exemplary localized allocation and distributed allocation of the uplink bandwidth in a single carrier FDMA scheme,
Fig. 5 : shows an exemplary SAE Bearer Architecture,
Fig. 6 : shows the format of an exemplary MAC PDU,
Fig. 7 : shows the format of a MAC control element for reporting a per- component carrier power headroom (PH),
Fig. 8 : shows a flow chart of an exemplary operation of a user equipment according to one embodiment of the invention in line with the first aspect of the invention,
Fig. 9 : shows a flow chart of an exemplary operation of a user equipment according to one embodiment of the invention in line with the second aspect of the invention,
Fig. 11 : shows power headroom reporting in a LTE-A system, where the known power headroom reporting of LTE Rel. 8 is employed for each component carrier individually,
Fig. 11 : shows power headroom reporting in a LTE-A system according to an embodiment of the invention, where the exemplary operation of a user equipment according to Fig. 8 is employed,
Fig. 12 : shows an exemplary power headroom reporting in a LTE-A system according to an embodiment of the invention, where the exemplary operation of a user equipment according to Fig. 9 is employed,
Fig. 13 : shows another exemplary power headroom reporting in a LTE-A system according to a further embodiment of the invention, where the exemplary operation of a user equipment according to Fig. 9 is employed,
Fig. 14 to 16 : show different formats of a power-limit MAC CE according to different embodiments of the invention in line with the first aspect of the invention,
Fig. 17 : shows an exemplary structure of a MAC PDU according to an embodiment of the invention, wherein the MAC PDU contains three PHR MAC CEs and corresponding subheaders reporting on the power headroom of three assigned component carriers within a single sub- frame, and
Fig. 18 : show an exemplary MAC CE format ("multiple PHR MAC CE") according to an embodiment of the invention in line with the second aspect of the invention, allowing to report multiple power headroom reports in a single MAC CE.

 DETAILED DESCRIPTION OF THE INVENTION 

[0098] 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 the LTE-Advanced mobile communication system discussed in the Technical Background section above. It should be noted that the invention may be advantageously used for example in connection with a mobile communication system such as the LTE-Advanced communication system previously described, but the invention is not limited to its use in this particular exemplary communication network. 

[0099] The explanations given in the Technical Background section above are intended to better understand the mostly LTE-Advanced 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. Nevertheless, the improvements proposed herein may be readily applied in the architectures/systems described in the Technical Background section and may in some embodiments of the invention also make use of standard and improved procedures of theses architectures/systems. 

[0100] One aspect of the invention is to enable to UE to indicate to the eNodeB when it is potentially becoming power limited or is power limited, i.e. when being close to using its maximum available transmit power or the resource allocations and power control commands of the eNodeB would require using a transmit power exceeding the user equipment's maximum available transmit power. This is achieved by defining a new MAC control element that is inserted by the user equipment to one or more protocol data units transmitted on respective (assigned) component carriers within a single sub-frame that is providing the eNodeB with a corresponding indication. 

[0101] Please note that in this document, the transmission of protocol data units in a sub-frame means that there has been a resource allocation for a respective one of the protocol data units on a respective one of the component carriers usable by the user equipment. Usable means that the user equipment can be assigned resources on each of these component carriers ― however, the component carriers on which the user equipment is allowed to transmit data (in form of protocol data units) within a given sub-frame is decided by the scheduler (e.g. implemented in the eNodeB) and is controlled by the resource assignments to the user equipment. Accordingly, a transmission on an "assigned component carrier" refers to a transmission of a protocol data unit on a component carrier for which the user equipment has received a resource assignment (also referred to as scheduling grant, grant (for short) or PDCCH). 

[0102] The MAC control element may be inserted to the protocol data units of a sub-frame. For example, the MAC control element may inserted into one of the protocol data units transmitted by the user equipment within the sub-frame or all of the protocol data units transmitted by the user equipment within the sub-frame. 

[0103] Furthermore, in addition to the indication of the user equipment approaching its maximum available transmit power, the control element inserted to the protocol data units may further indicate a per-user equipment (per-UE) power headroom. For example, the per-user equipment power headroom indicates the transmit power unused by the user equipment when transmitting the protocol data units (including the MAC control element) within the sub-frame relative to the user equipment's maximum available transmit power. Unlike the power headroom indicated in LTE Rel. 8 that is per-component carrier, the power headroom indicated in the MAC control element is considering the transmissions (protocol data units) on all assigned component carriers (i.e. more than one component carrier) within the sub-frame and is therefore not per-component carrier, but per-user equipment. 

[0104] In one exemplary embodiment of the invention, this per-user equipment power headroom is not only taking into account the transmit power required for the transmission of protocol data units via physical uplink data channels, but also the transmit power required for the transmission of control signaling via physical control channels. In one more detailed implementation is thus accounting for the transmit power required for transmitting user data and control data (protocol data units) on the assigned component carriers via the physical uplink shared channel (PUSCH) and the physical uplink control channel (PUCCH). 

[0105] In an alternative solution, according to another aspect of the invention, the object is solved by the user equipment sending per-component carrier power headroom reports for all assigned component carriers within a single sub-frame when the user equipment is potentially becoming power limited or is power limited, i.e. when being close to using its maximum available transmit power or the resource allocations and power control commands of the eNodeB would require using a transmit power exceeding the user equipment's maximum available transmit power. 

[0106] Please note that in one implementation according to an exemplary embodiment of the invention, the per-component carrier power headroom reports for all assigned component carriers are transmitted on the respective assigned component carriers to which they refer. In this exemplary implementation, a potentially employed prohibit timer controlling the power headroom reporting on a respective one of the assigned component carrier is overwriften/ignored. In an alternative exemplary embodiment of the invention, the per-component carrier power headroom reports are transmitted within a single protocol data unit on one of the assigned component carriers. In this example, the respective component carrier to which a respective per-component carrier power headroom report refers may be for example identified by including a component carrier identifier into the power headroom reports. Alternatively, there may be a new MAC control element defined ("all component carrier power headroom report") that is indicating the power headrooms of the assigned component carriers ordered according to the priority of the component carriers to which they refer. 

[0107] Furthermore, please note that in both aspect of the invention, the decision of whether the user equipment is approaching (or is in) a power limit situation may be determined in different fashions. In one exemplary implementation, the user equipment determines (or more correctly estimates) the transmit power it will have to spend for transmitting the protocol data units on the assigned component carriers within a sub-frame and compares the determined (or estimated) transmit power to a threshold. This threshold may be for example a certain percentage (e.g. in the range 80% to 100%) of the maximum available transmit power. In other exemplary implementations, the user equipment determines (or more correctly estimates) the transmit power it will have to spend for transmitting the protocol data units on the assigned component carriers within a sub-frame for a given number of successive sub-frames (i.e. a monitoring time period) and decides based on criteria further outlined below, whether to include a MAC control element to indicate a power limit situation to the protocol data units of the last sub-frame of said monitoring time period. 

[0108] In the following different embodiments of the invention will be outlined. It is assumed in these embodiments that the user equipment is operated in a mobile communication system that is using carrier aggregation and that the user equipment is configured with plural component carriers, i.e. is capable of transmitting uplink data on plural component carriers simultaneously within individually sub-frames according to resource assignments of a scheduler. The scheduler is for example implemented in the eNode B. Furthermore, it should be noted that the scheduler may assign one or more (up to all) of the plurality of configured component carriers for a given sub-frame and the user equipment is transmitting a respective transport block/protocol data unit on each assigned component carrier, i.e. each component carrier for which a resource assignment has been received. Using the 3GPP terminology, the resource assignments may also be referred to as grants or PDCCH. In addition, the there may be a respective transmit power loop implemented per component carrier configured for the user equipment, i.e. the transmit power control function implemented in the user equipment and the eNodeB perform transmit power control for each component carrier individually. 

[0109] Moreover, in a further exemplary embodiment of the invention, a joint logical channel prioritization procedure may be used for to the generation of the protocol data units for transmission within a sub-frame. Different exemplary implementations of such joint logical channel prioritization procedure are described in the co-pending European patent application no. 09005727.4 of the same applicant (attorney's docket no. EP64934DKFH) and the co-pending European patent application with the title "Logical Channel Prioritization Procedure for generating Multiple Uplink Transport Blocks" of the same applicant filed October 29, 2009 (attorney's docket no. EP649341DKFH). The two European patent applications will be referred to as Application 1 and Application 2 in the following where appropriate. 

[0110] Fig. 8 shows a flow chart of an exemplary operation of a user equipment according to one embodiment of the invention in line with the first aspect of the invention. The user equipment receives 801 plural resource assignments for a given sub-frame and estimates 802 the transmit power (ETP) required for uplink transmissions on assigned component carriers according to received resource assignments. In one exemplary embodiment of the invention, the transmit power is estimated by the user equipment based on the received resource assignments for the protocol data units to be transmitted in the sub-frame and the status of a transmit power control function of the user equipment. For example, the user equipment may estimate the transmit power needed for each of the resource blocks depending on which component carrier they are located on and based on the state of the transmit power function of the component carrier. The estimated transmit power is then the sum of the individual transmit power for all assigned resource blocks. 

[0111] Next, the user equipment determines 803, whether the estimated transmit power (ETP) is exceeding a certain threshold value. In the example of Fig. 8 , this threshold is defined as a certain percentage P of the maximum available transmit power (MATP) of the user equipment. Please note that this would be equivalent to determining whether the ratio of the estimated transmit power (ETP) and the maximum available transmit power (MATP), is exceeding a threshold value, that would be equivalent to the percentage P, i.e. ETP MATP > P .
<img class="EMIRef" id="464623252-ib0001" />


[0112] If the threshold value is not exceeded, the user equipment is not in a power limit situation, so that report thereon needs to be signaled to the eNodeB. Accordingly, the user equipment will next generate 804 the protocol data units for transmission on the respective assigned component carriers and transmits 805 the protocol data units (which are referred to as transport blocks in the Physical layer) to the eNodeB via the assigned component carriers. Please note that the generation of the protocol data units can be for example implemented as described in Application 1 or Application 2. 

[0113] If the If the threshold value is exceeded, the user equipment determines 806 the per-user equipment power headroom for all transmissions according to the resource assignments. As outlined above, this per-user power headroom is determined for all protocol data units to be transmitted within the given sub-frame on the assigned component carriers. The per-user equipment power headroom essentially indicates how much transmit power on top of what is to be used for transmitting the protocol data units in the sub-frame (estimated transmit power) is remaining relative to the maximum available transmit power of the user equipment. Simplified, the power headroom (PH) indicates the difference between maximum available transmit power of the user equipment and the estimated transmit power, i.e.PH = MATP - ETP .

[0114] The user equipment further generates 807 a MAC control element that is comprising the determined per-user equipment power headroom ("per-UE power headroom MAC CE") and provides the per-UE power headroom MAC CE to a protocol data generation section that generates 808 the protocol data units for transmission according to the resource assignments, similar to step 804. However, in step 808 the per-UE power headroom MAC CE is included in this generation process, so that depending on the implementation per-UE power headroom MAC CE is included in one of the protocol data units or all of the protocol data units. Subsequently the generated protocol data units including the per-UE power headroom MAC CE are transmitted 809 to the eNodeB on the assigned resources. 

[0115] Fig. 11 shows power headroom reporting in a LTE-A system according to an embodiment of the invention, where the exemplary operation of a user equipment according to Fig. 8 is employed. In most situations, the operation is corresponding to the operation of the user equipment as has been outlined with respect to Fig. 10 previously herein. In contrast to Fig. 10 , it is assumed that at T6the user equipment has received three resources assignments for all three component carriers for the sub-frame at T6, however the transmit power control function has is yielding a gain factor for the transmission that high that given the resource allocation, the estimated transmit power exceeds the maximum available transmit power (see step 803 of Fig. 8 ). Accordingly, in this case the user equipment determines the per-UE power headroom and multiplexes the per-UE power headroom MAC CE (also referred to as power-limit MAC CE in the following) to the protocol data unit transmitted on component carrier CoCa1. The scheduler in the eNodeB receiving the uplink transmission can now detect based on the per-UE power headroom MAC CE that the user equipment is in a power limit situation and can adapt the further scheduling and/or power control of the user equipment accordingly. 

[0116] As apparent from the above, per-UE power headroom MAC CE may basically have two functions. The first and most important function is that the sole reception of the per-UE power headroom MAC CE by eNodeB already informs eNodeB that a problem with the transmit power for the uplink transmissions existed in the sub-frame. Secondly, the per-UE power headroom MAC CE may also be reporting the per-user equipment power headroom of the user equipment, thus yielding more detailed information on the exact power situation in the user equipment to the eNodeB. 

[0117] In one alternative exemplary implementation according to another embodiment of the invention, the user equipment is not immediately including a power-limit MAC CE to the protocol data units transmitted on the uplink if the estimated transmit power exceeds the threshold. For example when the threshold is exceeded, instead of transmitting the power-limit MAC CE immediately, the user equipment start monitoring the estimated transmit power for a certain number of sub-frames, i.e. for a given monitoring period of sub-frames. Having monitored the given number of sub-frames, the user equipment decides whether or not a power-limit MAC CE is to be included to the protocol data units to be transmitted in the next sub-frame following certain criteria. Please note that the power-limit MAC CE may for example be transmitted in the last sub-frame transmitted in the monitoring period, if the user equipment decides to insert same. 

[0118] These criterions may be for example:
Estimated transmit power of the uplink transmissions in each of the sub-frames within the monitoring period was above a threshold value.
Estimated transmit power of the uplink transmission in some of the sub-frames within the monitoring period was above the threshold. The number of sub-frame required for sending the power-limit MAC CE at the end of the monitoring period is configured by eNodeB per UE through RRC signaling or alternatively can be set to a fixed value defined in the specifications.
The average estimated transmit power of the uplink transmissions in the sub-frames within the monitoring period was above the threshold.

[0119] The monitoring of the estimated transmit power for a given time period, i.e. a certain number for sub-frames, has the advantage that the power-limit MAC CE is not reported immediately when the threshold is crossed, which may avoid unnecessary reporting of a power-limit situation to the eNodeB if the threshold is exceeded only sporadically. However, since the power-limit MAC CE is indicating an emergency situation to the eNodeB and countermeasures should be taken by eNodeB after receiving the power-limit MAC CE, the drawback of introducing a monitoring period is the delay in the transmission of the power-limit MAC CE, once user equipment's transmit power has crossed the threshold. 

[0120] In a further alternative embodiment of the invention, the user equipment is configured with two thresholds. Also the second, "additional" threshold may be for example set by the eNodeB by RRC signaling. This second threshold may for example also be a fraction of the maximum available transmit power of the user equipment, but is preferably higher than the first threshold. Similar to the exemplary embodiments discussed above, the user equipment again determines for each sub-frame whether the estimated transmit power of a sub-frame exceeds the first threshold. If this is the case, i.e. the first threshold is exceeded for a sub-frame, the user equipment starts monitoring the estimated transmit power as described in the paragraphs above, for example for a given monitoring period. If the second threshold is exceeded by the estimated transmit power of a sub-frame within the monitoring period, the user equipment transmits a power-limit MAC CE within that sub-frame for which the estimated transmit power exceeded the second threshold was crossed. 

[0121] In another alternative embodiment of the invention, the user equipment is multiplexing the power-limit MAC CE to each of the protocol data units sent in the sub-frame via the assigned component carriers. This may be advantageous in that the reliability of the reception of the control element by eNodeB is increased. 

 Reporting Format of the per-UE power headroom MAC CE 

[0122] The format for the per-UE power headroom MAC CE indicating a potential power limitation of the user equipment ("power-limit MAC CE") could be based on the LTE Rel. 8 MAC CE format used for power headroom reporting as exemplified in Fig. 7 . The power headroom MAC CE consists of 8 bits, i.e. one octet, The first two bits are reserved bits, and the remaining 6 bits indicate the power headroom. In one embodiment of the invention, the format is maintained, but the 6 bit-field PH of the MAC CE format shown in Fig. 7 includes the a per-UE power headroom determined by the user equipment (see for example step 806 of Fig. 8 ). Optionally, in one embodiment of the invention, the per-UE power headroom does not only transmissions on the PUSCH but also transmissions on the PUCCH is taken into account while calculating the per-UE power headroom. 

[0123] In order to distinguish the power-limit MAC CE from a LTE Rel. 8 power headroom MAC CE, one of the two reserved bits (R) of the octet shown in Fig. 8 , e.g. the highest bit in the octet, is used to differentiate power headroom MAC CEs and power-limit MAC CEs (i.e. the per-UE power headroom CEs). For example, if the highest bit in the octet is set to 0, the MAC CE represents a power headroom report for that component carrier, i.e. a per-component carrier MAC CE reporting a power headroom for the given component carrier - the per-component carrier MAC CE reporting on the power headroom is thus a component carrier-specific MAC control element. If the bit is set to 1, the reported power headroom is the per-UE power headroom of the power-limit MAC CE. Please note that the power-limit MAC CE (i.e. the per-UE power headroom CE can be considered to be UE specific, so that the power-limit MAC CE can be considered a UE-specific MAC control element. 

[0124] Please note that the differentiation of UE-specific and component carrier-specific MAC control elements may lead to a different treatment and multiplexing of the MAC control element to the transport block (MAC protocol data units) as explained in Application 2. 

[0125] When user equipment is sending a power-limit MAC CE, it may be of additional value to the eNodeB to acquire knowledge for which component carriers the user equipment actually received resource assignments (uplink grants) in order to know, if the user equipment obeyed all uplink grants correctly, or if it missed one or more of the uplink grants. This information allows the eNodeB to determine, if the power-limit situation exists already for a situation where the user equipment did not even transmit on all the granted resources due having missed one or more of the uplink grants. 

[0126] Therefore, in another embodiment of the invention, the another exemplary format for the power-limit MAC CE is proposed which is including information on the component carriers for which uplink grants have been received, respectively on the number of received uplink grants. 

[0127] An exemplary format of the power-limit MAC CE according to another embodiment of the invention is shown in Fig. 14 . This power-limit MAC CE consists of two fields, a first field CCI (Component Carrier Indicator field) and a second field PH (Power Headroom) for indicating the per-UE power headroom. The power-limit MAC CE is again one octet long. 

[0128] Assuming that there are five component carriers configured for the user equipment, a total of 2<5>= 32 combinations of resource assignments are possible. As the user equipment already indicates by sending data (including the power-limit MAC CE) via one of the five component carriers, it is apparent that the user equipment has received an uplink grant for this component carrier. Hence, 2<4>=16 combinations of resource assignments remain for the four other configured component carriers, i.e. the CCI field would consist of 4 bits for signaling all combinations (for example by indicating by means of a bitmap, for which of the four other component carriers further uplink grants have been received). Hence, the remaining four bits of the MAC CE format are left for the PH field, allowing differentiating 16 per-UE power headroom values. The component carriers other than the one on which the MAC CE is signaled, for which an uplink grant has been received may be for example indicated by means of a bitmap. The actual mapping of which bit in the bitmap represents which component carrier could be for example configured by eNodeB through RRC signaling or can be determined by a priority order of the component carriers, as for example outlined in Application 1 and Application 2. 

[0129] In another embodiment, another MAC CE format shown in Fig. 15 is suggested. The CCI field is only 3 bits in size, while the PH field has 5 bits. This format may be considered a modification of the LTE Rel. 8 power headroom report MAC CE format in Fig. 7 in that the two reserved bits (R) and one additional bit from the PH field are reused as the CCI field. This implies of course reducing the granularity of the per-UE power headroom values that can be reported from 6 to 5 bits. 

[0130] As highlighted in Fig. 16 and as will be shown in Table 1 below, the MAC CE format for reporting a per-UE power headroom as shown in Fig. 15 allows for indicating the number of component carriers for which the user equipment received an uplink assignment while also indicating the whether the MAC control element is a LTE Rel. 8 power headroom MAC CE or a per-UE power headroom MAC CE, without requiring the assignment of a new logical channel identifier (LCID) to the new per-UE power headroom MAC CE but being able to also use the same LCID for a LTE Rel. 8 power headroom MAC CE and per-UE power headroom MAC CE . The eNodeB would have to evaluate the first two bits of the control element to determine whether a LTE Rel. 8 power headroom MAC CE or a per-UE power headroom MAC CE.
Table 1 
<tb>00Highest bit of 6bit-PH fieldLTE Rel. 8 power headroom report
<tb>010Per-UE power headroom report; UE has received 1 uplink grant
<tb>100Per-UE power headroom report; UE has received 2 uplink grants
<tb>101Per-UE power headroom report; UE has received 3 uplink grants
<tb>110Per-UE power headroom report; UE has received 4 uplink grant
<tb>111Per-UE power headroom report; UE has received 5 uplink grants

[0131] If the first two bits are both set to 0, i.e. the reserved bits as shown in Fig. 7 are set to zero, the MAC control element is a LTE Rel. 8 power headroom report as shown in Fig. 7 . 

[0132] In any other case, the MAC control element is a per-UE power headroom MAC CE. If the first two bits are not set to 0, the eNodeB needs to also evaluate the third bit within the octet, as the first three bits yield the number of uplink grants received by the user equipment. The remaining five bits (see Fig. 15 ) - the PH field - indicate the per-UE power headroom value. 

[0133] When user equipment has a power limit situation, one way the eNodeB may react to the reporting thereof by a power-limit MAC CE is to reduce the number of the component carriers on which the user equipment is simultaneously scheduled. It would be advantageous, if the user equipment assists the eNodeB in choosing on which of the component carriers resources should be scheduled to the UE. Accordingly, in another embodiment of the invention, the power-limit MAC CE may be used to not only signal the per-UE power headroom in a PH field, but to also suggest to the eNodeB for which component carriers the eNodeB should further send resource assignments. In one example, this is implemented in a similar fashion as described previously herein with respect to Fig. 14 . Instead of indicating the component carriers for which a uplink grant has been received, the four bits of the CCI field may be used to signal a bitmap that indicates on which the component carriers (other than the one on which the power-limit MAC CE is received), the eNodeB should continue to give grants on. Alternatively, the bitmap could represent the component carriers the eNodeB should stop giving grants on. 

[0134] In a further embodiment of the invention, the MAC CE as shown in Fig. 7 is used for the per-UE power headroom reporting. One of the two reserved bits, e.g. the first reserved bit shown in Fig. 7 is used to identify whether the MAC CE is a LTE Rel. 8 power headroom MAC CE or a per-UE power headroom MAC CE. In both cases the PH field may be 6 bits and indicates a per-component carrier headroom as in LTE Rel. 8 or the per-UE power headroom. Furthermore, if the MAC control element is a per-UE power headroom MAC CE, the component carrier on which the control element has been transmitted is the component carrier the user equipment is suggesting to the eNodeB for further resource assignments thereon. 

[0135] As indicated above, the MAC control element formats discussed above with respect to Fig. 7 , and Fig. 14 to 16 have the advantage that ― in comparison to LTE Rel. 8 - no new logical channel identifier needs to be assigned for the per-UE power headroom reports. As shown in Fig. 6 , a MAC PDU yields the format of the MAC control elements included in the MAC PDU payload by respective logical channel identifiers in the subheader of the respective MAC control elements. In another embodiment of the invention a new logical channel identifier (LCID) is defined for indicating a per-UE power headroom MAC CE. Hence this embodiment of the invention provides a MAC PDU comprising a subheader ("per-UE power headroom MAC CE subheader") and the related MAC CE. The per-UE power headroom MAC CE subheader comprises a LCID that is identifying the related MAC CE being a per-UE power headroom MAC CE. 

[0136] The format of the per-UE power headroom MAC CE may be again that described in one of the embodiments relating to Fig. 7 , Fig. 14 or Fig. 15 above, however, no indicating of a LTE Rel. 8 power headroom MAC CE may need to be included in the format definition any more, as the differentiation of the LTE Rel. 8 power headroom MAC CE and per-UE power headroom MAC CE is now achieved by means of the LCID in the subheader of the MAC PDU. 

 Setting of the Threshold Value 

[0137] In each sub-frame where user equipment has been assigned resources for uplink transmission in at least one of it's aggregated component carriers, the user equipment may calculate the transmit power needed to fulfill all uplink grants (resource assignments) in that sub-frame, i.e. determines the estimated transmit power required in this sub-frame. As explained above (see step 803 of Fig. 8 ) a threshold is configured relative to the maximum available transmit power which essentially indicates the maximum transmit power the user equipment is allowed to (or able to) spend on all uplink transmissions on the assigned component carriers in the specific sub-frame. 

[0138] The threshold may be, for example, configured by the eNodeB in relation to the maximum available transmit power. The threshold may be, for example, set by eNodeB for each user equipment individually and the value of the threshold could be, for example, conveyed to respective user equipments via RRC signaling. The threshold may be for example a fractional value of (or percentage P) of the maximum available transmit power. As outlined previously, in case the user equipment would need more power for all uplink transmissions on all assigned component carriers than defined by the threshold value, the power-limit MAC CE is included in the uplink transmissions of the sub-frame. 

[0139] It should be noted that the user equipment's estimated transmit power might not only cross the configured threshold but may be even above the maximum available power available to the user equipment. In the latter case user equipment is already in a severe power-limited situation and cannot fulfill all uplink resource assignments as demanded by eNodeB. 

 Selection of the Component Carrier for transmitting the per-UE power headroom MAC CE 

[0140] When user equipment include the power-limit MAC CE into the protocol data units transmitted in the given sub-frame, the transmit power that is available for UL transmissions is already critical. Therefore the transport block of the most reliable component carrier needs to be chosen for the inclusion of the power-limit MAC control element. 

[0141] The criterion for the selection of the most reliable component carrier can be based on the following conditions. One option would be to choose the component carrier which is the "special cell", i.e. the component carrier where the UE camps on and reads system information from. Another option would be to choose from the set of component carriers with UL transmissions the one with the best physical parameters. Parameters could be for example the target BLER or the actual power headroom of a component carrier. Furthermore, if a priority ranking of the component carriers is already known to UE the UE could send the power-limit MAC CE always on the component carrier with the highest priority. 

 Synchronous per-CC Power Headroom Reports in one Sub-frame 

[0142] In line with the second aspect of the invention, another alternative mechanism for informing the eNode B on a power-limit situation of the user equipment is proposed in the following. Instead of using a new power-limit MAC control element as discussed above, the user equipment sends a per-component carrier (per-CC) power headroom report for each assigned component carrier of the sub-frame to inform the eNode B on a situation where the user equipment is close to using its maximum available transmit power or the resource allocations and power control commands of the eNodeB would require using a transmit power exceeding the user equipment's maximum available transmit power. 

[0143] In this exemplary embodiment, the user equipment could re-use the power headroom reporting mechanism (including the user of the timersperiodicPHR-TimerandprohibitPHR-Timer)and their format as shown in Fig. 7 know from LTE Rel. 8 for each respective report sent in the sub-frame. When the user equipment is in a situation where it is close to using its maximum available transmit power or the resource allocations and power control commands of the eNodeB would require using a transmit power exceeding the user equipment's maximum available transmit power, the user equipment will send on each assigned component carrier a per-CC power headroom report as known from LTE Rel. 8 for the respective component carrier. In doing so the user equipment ignores the timerprohibitPHR-Timer,if running. Subsequent to the transmission of the multiple per-CC power headroom reports, the timersperiodicPHR-TimerandprohibitPHR-Timermay be restarted. 

[0144] Upon reception of all power headroom reports in the sub-frame, the eNodeB has the full picture of the total power situation of the user equipment. 

[0145] In a further exemplary implementation according to another embodiment of the invention, the per-CC power headroom reports on all assigned component carriers could be send in only one MAC PDU on one of the assigned component carriers. The selection of this component carrier on which the power headroom reports are to be sent can be implemented as described previously herein (seeinter aliasection Selection of the Component Carrier for transmitting the per-UE power headroom MAC CE). 

[0146] In one exemplary implementation of this embodiment, the multiple per-CC power headroom reports could be included into one MAC PDU. An exemplary format of a MAC PDU containing multiple PHR MAC CEs is shown in Fig. 17 , where a report of three power headroom reports on assigned component carriers CoCa1, CoCa3 and CoCa4 is exemplified. 

[0147] The MAC PDU comprises first the component carrier-specific logical channel identifiers (LCIDS) within respective subheaders field that allow the identification of the component carriers reported on and indicate that the MAC PDU's payload section comprises three PHR MAC CEs. Each subheader (indicating the LCID) is 8 bits long (one octet), wherein the first two bits of the octet (R) are reserved bits, and the third bit (E) indicates whether the next octet in the MAC PDU is another subheader of the MAC PDU header or whether the payload section of the MAC PDU is following the octet (i.e. whether the next octet is PHR MAC CE in this example), and the last 5 bits are the LCID. 

[0148] For example, if the E bit is set (e.g. 1), another subheader is present in the next octet of the MAC PDU; if the E bit is not set (e.g. 0), the next octet is part of the payload section of the MAC PDU that is assumed to start with the first PHR MAC CE. 

[0149] In another alternative implementation, the power headroom reports on multiple component carriers may also be included into a single MAC control element ("multiple PHR MAC CE"). 

[0150] The multiple PHR MAC CE comprises in its first octet a bitmap of 5 bits indicating for which component carrier a PHR field is included in the multiple PHR MAC CE. A priority order of the component carriers, as described in Application 1 and Application 2, may define the meaning of the individual positions of bits within the bitmap. Generally, a bit set (e.g. 1) at a certain position of the bitmap means that there is a PHR field for the associated component carrier including in the MAC CE. Following the octet comprising the component carrier bitmap, the respective PHR field(s) with the power headroom value for the component carrier is/are included. The PHR field may for example have the same format as shown in Fig. 7 and reports the power headroom (PH) for a component carrier. An example of a multiple PHR MAC CE, where a report of three power headroom reports on assigned component carriers CoCa1, CoCa3 and CoCa4 is exemplified in Fig. 18 . 

[0151] Please note that for this alternative implementation, LTE Rel. 8 power headroom reports and the multiple PHR MAC CE could use the same logical channel identifier, and the two formats may be distinguished by setting or not setting the first or second reserved bit in the first octet of the control element. Of course, the multiple PHR MAC CE may also be assigned its own logical channel identifier (LCID) in the MAC PDU header. 

[0152] The multiple PHR MAC CE may be further assigned its own logical channel identifier, so that it can be identified by a corresponding subheaders in the MAC PDU's header (see Fig. 6 ). 

[0153] Fig. 9 shows a flow chart of an exemplary operation of a user equipment according to one embodiment of the invention in line with the second aspect of the invention. Similar to Fig. 8 , the user equipment receives 801 plural resource assignments for a given sub-frame and estimates 802 the transmit power (ETP) required for uplink transmissions on assigned component carriers according to received resource assignments. Next, the user equipment determines 803, whether the estimated transmit power (ETP) is exceeding a certain threshold value. If the threshold value is not exceeded, the user equipment is not in a power limit situation, so that report thereon needs to be signaled to the eNodeB. Accordingly, the user equipment will next generate 804 the protocol data units for transmission on the respective assigned component carriers and transmits 805 the protocol data units (which are referred to as transport blocks in the Physical layer) to the eNodeB via the assigned component carriers. Please note that the generation of the protocol data units can be for example implemented as described in Application 1 or Application 2. 

[0154] If the user equipment is in a power limit situation as determined in step 803, the user equipment determines 906 for each component carrier for which a resource assignment has been received a per-CC power headroom. This per-CC power headroom may be for example determined as described in 3GPP TS 36.213, "Physical layer procedures", version 8.8.0, section 5.1.1, the document being available at http://www.3gpp.org and being incorporated herein by reference. 

[0155] Next, the user equipment may generate 907 for each assigned component carrier an individual per-CC power headroom MAC CE (for example using the format shown in Fig. 7 ) and further generates 908 the MAC PDUs including each the corresponding per-CC power headroom MAC CE according to the resource assignments. Subsequently the user equipment transmits the PDUs including per-CC power headroom MAC CEs on the assigned component carriers to the eNode B. 

[0156] Please note that alternatively to steps 907 and 908, there could also be a single multiple PHR MAC CE formed and transmitted in one of the MAC PDUs, as outlined above. 

[0157] Fig. 12 shows power headroom reporting in a LTE-A system according to an embodiment of the invention, where the exemplary operation of a user equipment according to Fig. 9 is employed. In most situations, the operation is corresponding to the operation of the user equipment as has been outlined with respect to Fig. 10 previously herein. In contrast to Fig. 10 , it is assumed that at T6the user equipment has received three resources assignments for all three component carriers for the sub-frame at T6, however the transmit power control function has is yielding a gain factor for the transmission that high that given the resource allocation, the estimated transmit power exceeds the maximum available transmit power (see step 803 of Fig. 9 ). Accordingly, in this case the user equipment determines the per-CC power headroom values for all three component carriers and sends PDUs each comprising a per-CC power headroom report for the respective component carrier in the uplink. As can be recognized from Fig. 12 , the theprohibitPHR-Timeris running at T6for the component carrier CoCa3, but is ignored by the user equipment. Upon sending the per-CC power headroom reports the respective timers are restarted for each component carrier. 

[0158] Fig. 13 shows another exemplary power headroom reporting in a LTE-A system according to an embodiment of the invention, where the exemplary operation of a user equipment according to Fig. 9 is employed. The example shown therein is the same as in Fig. 12 , except for the user equipment having been assigned only resources on component carriers CoCa1 and CoCa3 for the sub-frame atT6. Similar to Fig. 12 , the user equipment still is in a power limit situation for this sub-frame, but sends a single multiple PHR MAC CE in the PDU transmitted on component carrier CoCa1 that reports the power headrooms for component carriers CoCa1 and CoCa3. Thereupon the timersperiodicPHR-TimerandprohibitPHR-Timerare restarted for the component carriers for which a per-CC power headroom report has been sent, i.e. component carriers CoCa1 and CoCa3 in this example. 

[0159] Another embodiment of the invention relates to the implementation of the above described various embodiments using hardware and software. It is 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. 

[0160] 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. 

[0161] 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. 

[0162] 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. 

