WO2015108253A1

WO2015108253A1 - Processing limitations with distributed scheduling

Info

Publication number: WO2015108253A1
Application number: PCT/KR2014/005064
Authority: WO
Inventors: Gert Jan Van Lieshout; Boon Loong Ng; Thomas David NOVLAN; Soeng-Hun Kim; Himke Van Der Velde
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2014-01-17
Filing date: 2014-06-10
Publication date: 2015-07-23
Also published as: GB201400817D0

Abstract

A method of operating a UE in a LTE compliant mobile communications network. The network further comprises first and second eNBs in communication with the UE. The method comprises: detecting downlink scheduling information in respect of the first and second eNBs for a single TTI, the scheduling information specifying a TB including a number of TB bits to be received by the UE from each eNB during that TTI; and calculating whether the cumulative scheduled number of TB bits within that TTI exceeds a UE capability to process downlink data.

Description

PROCESSING LIMITATIONS WITH DISTRIBUTED SCHEDULING

The present invention relates to techniques for addressing processing limitations in terminals (also referred to herein as User Equipment, UE) within distributed scheduling environments. In particular, certain embodiments of the present invention relate to services supporting dual connectivity in a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) or LTE Advanced compliant mobile communications network comprising a UEs and network equipment.

Wireless or mobile (cellular) communications networks in which a UE, such as a mobile handset, communicates via a radio link to a network of base stations or other wireless access points connected to a telecommunications network, have undergone rapid development through a number of generations. The initial deployment of systems using analogue signalling has been superseded by Second Generation (2G) digital systems such as Global System for Mobile communications (GSM), which typically use a radio access technology known as GSM Enhanced Data rates for GSM Evolution Radio Access Network (GERAN), combined with an improved core network.

Second generation systems have themselves been largely replaced, or augmented, by Third Generation (3G) digital systems such as the Universal Mobile Telecommunications System (UMTS), which uses a Universal Terrestrial Radio Access Network (UTRAN) radio access technology and a similar core network to GSM. UMTS is specified in standards produced by 3GPP. Third generation standards provide for a greater throughput of data than is provided by second generation systems. This trend is continued with the move towards Fourth Generation (4G) systems.

3GPP design, specify and standardise technologies for mobile wireless communications networks. Specifically, 3GPP produces a series of Technical Reports (TR) and Technical Specifications (TS) that define 3GPP technologies. The focus of 3GPP is currently the specification of standards beyond 3G, and in particular an Evolved Packet System (EPS) offering enhancements over 3G networks, including higher data rates. The set of specifications for the EPS comprises two work items: Systems Architecture Evolution (SAE, concerning the core network) and LTE concerning the air interface. The first set of EPS specifications were released as 3GPP Release 8 in December 2008. LTE uses an improved radio access technology known as Evolved UTRAN (E-UTRAN), which offers potentially greater capacity and additional features compared with previous standards. SAE provides an improved core network technology referred to as the Evolved Packet Core (EPC). Despite LTE strictly referring only to the air interface, LTE is commonly used to refer to the whole of the EPS, including by 3GPP themselves. LTE is used in this sense in the remainder of this specification, including when referring to LTE enhancements, such as LTE Advanced. LTE is an evolution of UMTS and shares certain high level components and protocols with UMTS. LTE Advanced offers still higher data rates compared to LTE and is defined by 3GPP standards releases from 3GPP Release 10 up to and including 3GPP Release 12. LTE Advanced is considered to be a 4G mobile communication system by the International Telecommunication Union (ITU).

Certain embodiments of the present invention are implemented within an LTE mobile network. Therefore, an overview of an LTE network is shown in Figure 1. The LTE system comprises three high level components: at least one UE 102, the E-UTRAN 104 and the EPC 106. The EPC 106 communicates with Packet Data Networks (PDNs) and servers 108 in the outside world and is responsible transferring data between the EUTRAN 104 and the outside world, as well various signalling functions that are outside the scope of the present specification. The EPC 106 may also be referred to as the Core Network (CN). Figure 1 shows the key component parts of the EPC 106. It will be appreciated that Figure 1 is a simplification and a typical implementation of LTE will include further components. In Figure 1 interfaces between different parts of the LTE system are shown. The double ended arrow indicates the air interface between the UE 102 and the E-UTRAN 104. For the remaining interfaces user data is represented by solid lines and signalling is represented by dashed lines.

The E-UTRAN 104 comprises at least one base station referred to variously as an E-UTRAN node B or an eNB. As is discussed in greater detail below, when an LTE network includes dual connectivity, the E-UTRAN includes two types of component: the Main eNB (MeNB) and the Secondary eNB (SeNB). The eNB is responsible for handling radio communications between the UE 102 and the EPC 106 across the air interface. An eNB controls UEs 102 in at least one cell. Typically there is a plurality of eNBs within an LTE system. In general, a UE in LTE communicates with one eNB through one cell at a time. However, in some circumstances an eNB can communicate with two eNBs, as described below.

Key components of the EPC 106 are shown in Figure 1. It will be appreciated that in an LTE network there may be more than one of each component according to the number of UEs 102, the geographical area of the network and the volume of data to be transported across the network. Data traffic is passed between each eNB and a corresponding Serving Gateway (S-GW) 110 which routes data between the eNB and a PDN Gateway (P-GW) 112. The P-GW 112 is responsible for connecting a UE to one or more servers or PDNs 108 in the outside world. The Mobility Management Entity (MME) 114 controls the high-level operation of the UE 102 through signalling messages exchanged with the UE 102 through the E-UTRAN 104. Each UE is registered with a single MME. There is no direct signalling pathway between the MME 114 and the UE 102(communication with the UE 102 being across the air interface via the E-UTRAN 104). Signalling messages between the MME 114 and the UE 102 comprise EPS Session Management (ESM) protocol messages controlling the flow of data from the UE to the outside world and EPS Mobility Management (EMM) protocol messages controlling the rerouting of signalling and data flows when the UE 102 moves between eNBs within the E10 UTRAN. The MME 114 exchanges signalling traffic with the S-GW 110 to assist with routing data traffic. The MME 114 also communicates with a Home Subscriber Server (HSS) 116 which stores information about users registered with the network.

The LTE architecture uses an Orthogonal Frequency Division Multiple Access (OFDMA) based interface for the radio downlink and a Single Carrier Frequency Division Multiple Access (SC-FDMA) based interface for the radio uplink. Multiple access systems allow signalling to be arranged in so-called radio frames, distributing synchronisation, control and user data in time and subcarrier frequency. LTE downlink and uplink radio frames transmitted from an eNB or a UE last 10 ms. A frame is made up of 10 subframes each of which are composed of two slots. Each subframe comprises a predetermined number of symbols which are transmitted over a 1ms period: this period is known as the Transmission Time Interval (TTI). Certain slots in each subframe are arranged to carry control data; certain other slots of particular subframes within each radio frame carry synchronisation data. User data is distributed in symbols within those slots of the radio frame not occupied by control or synchronisation data.

In LTE, the UE transmits/receives bits of data in so called Transport Blocks (TB), with each TB being sent within a single subframe (per TTI). There may be one or more TBs sent or received in each subframe. These TBs are processed into codewords, which are then transported as symbols over the radio interface. The generation of codewords includes the attachment of a Cyclic Redundancy Check (CRC) checksum to allow a receiver to verify correct reception.

LTE contemplates configurations of transmitters and receivers where one or more transmitter is provided in a transmitter arrangement and one or more receiver is provided in a receiver arrangement. Propagation channels between transmitter arrangement and receiver arrangement can therefore be configured to use multiple inputs (transmitters) and multiple outputs (receivers) . so-called Multiple Input Multiple Output (MIMO). Alternative configurations include Single Input Multiple Outputs (SIMO). MIMO and SIMO are examples of “receive diversity” configurations.

If the UE is only receiving data from one cell and a receive diversity configuration is not used, the UE will only receive one TB per TTI. If, however, the UE is configured to receive data from multiple cells, or is configured with MIMO in one or more cells, it is possible for the UE to receive more than 1 TB in a TTI.

Each UE has limitations with respect to the amount of data it can effectively process. UEs are classified into categories, which broadly characterise their capabilities, including their capability for processing received data. In LTE, each UE of a given category is configured to comply with limitations described in 3GPP TS 36.306. Specifically, tables 4.1-1 and 4.1-2 respectively indicate downlink and uplink parameters set by the field ue-Category. For the downlink, this includes the maximum number of bits of a Downlink Shared Channel (DL-SCH) TB the UE can receive per TTI and the maximum number of DL-SCH TB bits aggregated across two or more TBs that the UE can receive per TTI. For instance, a UE that declares that it belongs to category 3 is only required to receive a maximum of 75376 bits per TB and 102048 TB bits per TTI. For the uplink, the parameters include the maximum number of bits of an Uplink Shared Channel (UL-SCH) TB that the UE can transmit within a TTI and the maximum number of US-SCH TB bits aggregated across two or more TBs that the UE can transmit within a TTI. For a category 3 UE the corresponding figure is 51024 bits for both parameters.

For downlink data transmission the data scheduling is performed by an eNB. Scheduling is performed one subframe (one TTI) at a time. The eNB sends the UE a scheduling command using Downlink Control Information (DCI) transmitted on a Physical Downlink Control Channel (PDCCH). The scheduling command informs the UE of a forthcoming data transmission and provides parameters defining the transmission, including the size of each TB in that TTI. The data is then sent to the UE in one or more TBs on a Downlink Shared Channel (DL-SCH) and a Physical Downlink Shared Channel (PDSCH). In response the UE sends a Hybrid Automatic Repeat Request (HARQ) acknowledgement (ACK) or a negative acknowledgement (NACK) according to whether the data is correctly received. This determines whether retransmission from the eNB is required, for instance due to a poor radio environment.

For uplink data transmission the process is similar, and again is performed one subframe at a time. It begins with the eNB sending the UE a scheduling grant on the PDCCH. This grants permission for the mobile to transmit, and states all of the required transmission parameters, including TB size. In response the UE performs the data transmission on an Uplink Shared Channel (UL-SCH) and a Physical Uplink Shared Channel (PUSCH). The eNB returns an ACK or a NACK according to whether the data is correctly received, which again determines whether retransmission from the UE is required.

As long as there is one central entity (a single eNB) scheduling downlink and uplink data transmission for a UE, that entity can ensure, by controlling the total downlink TB bit allocations and uplink grants given to the UE, that the UE capabilities as indicated by the category are not exceeded (that is, a downlink or uplink bit over allocation does not occur).

A 3GPP Radio Access Network (RAN) workgroup has worked on a Study Item (SI) called “Small Cell Enhancements”. The technical outcome of this SI is documented in 3GPP TR 36.842 “Evolved Universal Terrestrial Radio Access (E-UTRA)”; Study on Small Cell enhancements for E-UTRA and E-UTRAN . Higher layer aspects (Release 12); v0.4.0. 3GPP TR 36.842 concerns the radio access aspects of the SI and impacts upon both the UE and the eNB. Small cell enhancements are applicable, for instance, where 15 there is a macro cell and a small cell (within the coverage area of the macro cell) operating on the same carrier frequency.

As a result of the SI documented in 3GPP TR 36.842 it has been agreed that the RAN will in the future support so called “dual connectivity” functionality. It is anticipated that this may be introduced as part of Release 12. Dual connectivity refers to an operation where a given UE consumes radio resources provided by at least two different network points (MeNBs and SeNBs). When operating in a dual connectivity mode control plane data between the UE and the CN is always transferred between the MeNB and a MME within the EPC. However, user plane data handled by the SeNB may either be directly transferred between the S-GW and the SeNB or it may be transferred indirectly via the MeNB. The MeNB may control one or more cells communicating with the UE: a Master Cell Group (MCG) also referred to as a Primary Cell Group (PCG). Similarly, the SeNB may control one or more cells communicating with the UE: a Secondary Cell Group (SCG). The MeNB and the SeNB are typically connected with a non-ideal backhaul while the UE is active within the network (in an RRC_CONNECTED - Radio Resource Control Connected. state). Dual connectivity permits a greater data rate to be achieved between the UE and the eNB, with scheduling being distributed between two eNBs at the same time.

Figure 2, drawn from 3GPP TS 36.842 shows a scenario in which a macro cell 200 controlled by a MeNB 202 (represented by a transmitter) transmits user-plane (Uplane) data to a UE 204 on a first carrier frequency (F1) and a small cell 206 controlled by a SeNB 208 (represented by a transmitter) transmits U-plane data to a UE on a second carrier frequency (F2). 3GPP TS 36.842 defines certain aspects of inter-node radio resource aggregation. The SeNB 208 may either communicate with the core network (not shown) via the MeNB 202, or it may be separately connected. Figure 2 shows a non-ideal backhaul connection 210 between the MeNB 202 and the SeNB 208 across the X2 interface 210. The x2 interface 210 may be used to communicate Layer 1 (L1 . physical layer) and higher layer data connection aspects between the

eNBs

202, 208.

It will appreciated in the scenario of Figure 2 that both the MeNB 202 and the SeNB 208 are responsible for scheduling downlink data and uplink data per TTI. That is, Figure 2 illustrates a distributed scheduling environment. There is no standardised mechanism for coordinating distributed scheduling. For a UE with a limited capability to 10 process received data (defined according the UE category in 3GPP TS 36.306 as described above) the cumulative data transmitted by two eNBs in a dual connectivity mode may exceed that capability. As noted above, each eNB schedules data transmission to the UE per TTI (1 ms). Conversely, inter eNB coordination (for instance, which carriers to use) is on a relatively slow time scale. A conventional approach to inter eNB coordination is inadequate for coordinating distributed scheduling.

It is an aim of certain embodiments of the present invention to provide improved methods for distributed scheduling to avoid exceeding a UE capability to process received or transmitted data, or to mitigate the effects of exceeding that capability.

According to a first aspect of the present invention there is provided a method of operating a User Equipment, UE, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising first and second Universal Terrestrial Radio Access Network Node Bs, eNBs, in communication with the UE, the method comprising: detecting downlink scheduling information in respect of the first and second eNBs for a single Transmission Time Interval, TTI, the scheduling information specifying a Transport Block, TB, including a number of TB bits to be received by the UE from each eNB during that TTI; and calculating whether the cumulative scheduled number of TB bits within that TTI exceeds a UE capability to process downlink data; wherein if the UE capability to process data is exceeded, the method further comprises determining not to process a TB received from one of the eNBs.

The method may further comprises: detecting uplink scheduling grants in respect of the first and second eNBs for a single TTI, each scheduling grant specifying a TB including a number of TB bits to be transmitted by the UE to each eNB during that TTI; andcalculating whether the cumulative granted number of TB bits within that TTI exceeds a UE capability to process uplink data; wherein if the UE capability to transmit data is exceeded, the method further comprises determining not to process a TB for transmission to one of the eNBs.

The method may further comprise: determining to process a TB received from one of the eNBs; and sending an acknowledgement to an eNB associated with a TB which it is determined to process.

If it is determined not to process a TB then the method may further comprise: sending a negative acknowledgement to the eNB associated with the TB which it is determined not to process. The negative acknowledgement may indicate to the eNB that the TB has not been processed due to the UE capability to process downlink data having been exceeded.

If it is determined not to process a TB then the method may further comprise: sending an indication to the eNB associated with the TB which it is determined not to process to indicate that the TB is not transmitted due to the UE capability to process uplink data having been exceeded.

The method may further comprise: sending a report message to at least one of the eNBs containing information on TBs that have not been processed.

The report message may indicate at least one of: the number of TBs that have not been processed in a certain period of time; the frequency with which TBs are not processed; or a proportion of TBs that have not been processed.

If it is determined not to process a TB then the method may further comprise: determining a TB not to process; wherein the determination a TB not to process may comprise: determining to not process a TB received from or for transmission to the first eNB; if one eNB comprises a Master eNB, MeNB, and the other eNB comprises a Secondary eNB, SeNB, determining not to process a TB received from or for transmission to the SeNB; receiving a Radio Resource Control, RRC, message from one of the eNBs indicating whether the UE should select a TB received from or for transmission to either the first or second eNB if it is determined not to process a TB; determining the content type of each TB and determining a TB not to process according to the content of each TB; determining whether each TB comprises a retransmitted TB, and if a first TB, but not a second TB, is a retransmitted TB then determining not to process the second TB; determining the relative size of each TB and determining not to process a smaller TB; or determining the relative priority of the content of each TB, and determining not to process a lower priority TB.

According to a second aspect of the present invention there is provided a User Equipment, UE, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising first and second Universal Terrestrial Radio Access Network Node Bs, eNBs, in communication with the UE, the UE being arranged to: detect downlink scheduling information in respect of the first and second eNBs for a single Transmission Time Interval, TTI, the scheduling information specifying a Transport Block, TB, including a number of TB bits to be received by the UE from each eNB during that TTI; and calculate whether the cumulative scheduled number of TB bits within that TTI exceeds a UE capability to process downlink data; wherein if the UE capability to process data is exceeded, the UE is further arranged to determine not to process a TB received from one of the eNBs.

The UE may be further arranged to: detect uplink scheduling grants in respect of the first and second eNBs for a single TTI, each scheduling grant specifying a TB including a number of TB bits to be transmitted by the UE to each eNB during that TTI; and calculate whether the cumulative granted number of TB bits within that TTI exceeds a UE capability to process uplink data; wherein if the UE capability to transmit data is exceeded, the UE is further arranged to determine not to process a TB for transmission to one of the eNBs.

According to a third aspect of the present invention there is provided a method of operating a first Universal Terrestrial Radio Access Network Node B, eNB, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising a second eNB and a User Equipment, UE, the first and second eNBs being in communication with the UE, the method comprising: receiving a parameter indicating the capability of the UE to process received Transport Block, TB, bits in a single Transmission Time Interval, TTI; and calculating a first maximum number of TB bits that can be scheduled by the first eNB for downlink data transmission to the UE; wherein the first maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to process received TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to process received TB bits in a single TTI will not be exceeded.

The method may further comprise: receiving a parameter indicating the capability of the UE to transmit TB bits in a single TTI; and calculating a second maximum number of TB bits that can be granted by the first eNB to the UE for uplink data transmission to the first eNB; wherein the second maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to transmit TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to transmit TB bits in a single TTI will not be exceeded.

The data transmission parameter may comprise a Layer 1, L1, data transmission parameter or a higher layer data transmission parameter.

The data transmission parameter may comprise at least one of: bandwidth; Multiple Input Multiple Output, MIMO, capability; traffic volume; or configured guaranteed bit rate.

According to a fourth aspect of the present invention there is provided a first Universal Terrestrial Radio Access Network Node B, eNB, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising a second eNB and a User Equipment, UE, the first and second eNBs being in communication with the UE, the first eNB being arranged to: receive a parameter indicating the capability of the UE to process received Transport Block, TB, bits in a single Transmission Time Interval, TTI; and calculate a first maximum number of TB bits that can be scheduled by the first eNB for downlink data transmission to the UE; wherein the first maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to process received TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to process received TB bits in a single TTI will not be exceeded.

The first eNB may be further arranged to: receive a parameter indicating the capability of the UE to transmit TB bits in a single TTI; and calculate a second maximum number of TB bits that can be granted by the first eNB to the UE for uplink data transmission to the first eNB; wherein the second maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to transmit TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to transmit TB bits in a single TTI will not be exceeded.

Another aspect of the invention provides a computer program comprising instructions arranged, when executed, to implement a method and/or apparatus in accordance with any one of the above-described aspects. A further aspect provides machine-readable storage storing such a program.

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 schematically illustrates an overview of an LTE mobile communication network;

Figure 2 illustrates dual connectivity in a LTE system in which two eNBs transmit U-plane data to a single UE;

Figure 3 is a flowchart illustrating processing at a UE to determine which TB to drop in the event that a UE data processing limitation is exceeded; and

Figure 4 illustrates a method of signalling between a UE, a MeNB and a SeNB in the event that a UE data processing limitation is exceeded, in accordance with an embodiment of the present invention.

Embodiments of the invention will now be described in the context of an LTE compliant mobile wireless communications network operating in accordance with Release-11 and beyond of the 3GPP LTE standards. However, it will be understood that this is by way of example only and that other embodiments may involve other wireless networks, operating at least partially in compliance with other releases and other standards.

In accordance with embodiments of the present invention, there will now be described two separate approaches to addressing the problem of limited UE processing capability in a distributed scheduling environment. The first approach concerns solutions which enable the network to ensure that the UE capability is not exceeded, and may thus be referred to as network centric. The second approach concerns solutions which in principle allow each network entity to use the full UE processing capability and specify the UE behaviour in the event that the capability is exceeded, and may thus be referred to as UE centric.

Network Centric Approach

As noted above, the first approach enables the network to ensure it does not exceed the UE capability to process received or transmitted TB bits. From the perspective of the UE there remains a single processing limitation for the number of bits that can be processed per TTI. The UE capability is split into a part that can be used by one entity (for instance, a MeNB), and a part that can be used by another entity (for instance, a SeNB). The split may be semi-static, in the sense that it may remain constant for two or more TTI, but need not be permanent. The UE may be unaware that the UE processing capability has been split in order to avoid the UE processing capability being exceeded. The splitting of the UE capability is applicable to both the downlink and the uplink, though in certain embodiments of the invention a different split may be calculated for each split. This splitting is achieved without requiring explicit signalling between eNBs to communicate or coordinate the bit allocations for TBs in downlink or uplink data communications. Instead, the UE capability split is implicitly derived from other parameters according to a predefined rule, which may be communicated between the eNBs, for instance across the X2 interface, periodically. Such parameters are typically shared between the eNBs for other purposes.

In accordance with a first embodiment of the invention the UE capability split is derived from Layer 1 (L1 . physical layer) data transmission configuration aspects. In accordance with a second embodiment of the invention the UE capability split is derived from higher layer aspects. In both embodiments the number of bits per TTI that are allocated to a MeNB and a SeNB can be calculated by each eNB, which cumulatively are less than the maximum number of bits per TTI that can be accommodated by the UE (the UE capability). It will be appreciated that while the two embodiments are described separately, they may in fact be applied in combination (that is, a single rule may take account of L1 configuration aspects and also higher layer aspects).

Network Centric Approach - L1 Configuration Aspects

In this embodiment the eNBs do not explicitly coordinate the number of bits each of them can use in downlink or uplink, but instead each eNB can derive the amount of bits that it can allocate based on some other L1 configuration aspects, for instance Bandwidth (BW) or MIMO configuration, known by each eNB for itself and the other eNB. The BW or MIMO information may be communicated between the eNBs. In the following examples UEcap refers to the UE processing limitation for downlink or uplink as appropriate, specifically the maximum number of TB bits per TTI.

As an example based on bandwidth, where for instance BW_MCG indicates the total bandwidth of a Master Cell Group controlled by an MeNB:

Bits available for MCG = total BW_MCG cells / (total BW_MCG + BW_SCG cells) * UEcap; Bits available for SCG = total BW_SCG cells / (total BW_MCG + BW_SCG cells) * UEcap.

An example based on MIMO capability:

Maximum number of supported layers for spatial multiplexing in downlink for MeNB on F1 = 2

Maximum number of supported layers for spatial multiplexing in downlink for 30 SeNB on F2 = 4

Bits available for MCG = 2 / (2+4) * UEcap

Bits available for MCG = 4 / (2+4) * UEcap

Network Centric Approach - Higher Layer Aspects

In this embodiment, rather than looking at the L1 configuration that the two eNBs are using towards the UE, the allocation of bits per TTI is based on higher layer aspects of the data communication, for instance bearer or service characteristics.

As an example, the split could be based on what services each eNB is handling for the UE, for instance expected traffic volume to be handled by services over the MCG and over the SCG or a configured guaranteed bit rate of bearers handled over MCG and over SCG. The calculation of the bits available for the MCG or the SCG is numerically the same as for the examples given above, which is by using the higher layer data to calculate a proportionate split of available TB bits per TTI.

Depending on the network architecture, if one eNB (for instance the MeNB) maintains the connection to the core network for both eNBs then the above split may be implicitly derived by the MeNB and SeNB without the need for further communication between the eNBs. In case of independent links to the core network for the MeNB and SeNB, periodic signalling about the metric used for determining the capability split may be needed to determine if further refinement of the capability split should be negotiated. For instance, the MeNB may not know the volume of traffic currently handled by the SeNB.

It will be appreciated that whether the maximum number of bits available to each eNB may be calculated proportionately according to L1 or higher layer aspects, the split need not be proportionate. As just one example, the eNB with the higher bandwidth may be allocated 0.75 of the UE capability. It is sufficient that the parameters forming the basis of the calculation are available to both eNBs and that both eNBs follow the same predetermined rule.

UE Centric Approach As noted above, the second approach does not rely on a calculated split between the eNBs of the UE capability to process uplink or downlink TB bits per TTI. In principle, the second approach allows each eNB to use the full UE capability. This approach does not enable the network to ensure it does not exceed the UE capability in every TTI. Instead, UE behaviour is specified to accommodate a situation in which UE capabilities are exceeded, thus ensuring overall acceptable performance. According to a UE centric approach, a TB may be dropped if the UE capability for processing uplink or downlink data is exceeded in any given TTI, and so this may be referred to as a “TB dropping solution”. By “dropping” it is meant that the TB is not processed for transmission (in the uplink) and is not received or is not processed or fully processed (in the downlink). According to certain embodiments of the present invention the UE is able to determine certain parameters including which TB or which TBs to drop, whether and how the transmitting UE should be notified that a TB has been dropped, and, in the case of the uplink, how to avoid unnecessary data loss.

In accordance with a UE centric embodiment of the present invention, the UE can determine that UE capability to process is exceeded via the following steps. An example for downlink is given. Firstly, the UE determines if a PDCCH or an Enhanced PDCCH (EPDCCH) for downlink assignment is detected for an MCG for a given subframe and a PDCCH/EPDCCH for downlink assignment is detected for an SCG for the same subframe.

If so, the UE determines the TB size for the MCG and the TB size for the SCG from respective Modulation and Coding Scheme (MCS) fields in the DCI. If the sum of the TB size for the MCG and the TB size for the SCG is greater than the maximum number of bits supported according to the UE capability this indicates that UE capability is exceeded (an over allocation situation has occurred). A similar method can be used for uplink, the only difference being that it is uplink scheduling grants that are checked to determine if the total number of transmit TB bits granted in a given TTI exceeds the UE capability to process that data. If it is determined that the UE capability is exceeded, then in accordance with a UE centric embodiment of the present invention the UE must then determine which TB to drop in that TTI. This determination is applicable to both the downlink and the uplink and refers respectively to the decision which TB to drop from a pair of TBs transmitted by a pair of eNBs in the downlink and which TB to not send to an eNB in the uplink. By “drop” in the downlink, it is meant that the UE sends a NACK to indicate that the TB was not received. As will be described in greater detail below, in certain embodiments in fact a TB may be physically received and buffered, but the UE temporarily does not have the capacity to process the data. The result may be that the TB data is received twice as the respective eNB will retransmit a TB for which it receives a NACK. There are a number of options for determining which TB to drop in accordance with certain embodiments of the invention, some of which will now be described. Each option may be referred to as a dropping rule, which may be either preset or dynamically configured by a network entity, for instance the MeNB. In certain embodiments of the present invention the dropping rule is communicated from an eNB (for instance the MeNB) to the UE. In accordance with a first option, the decision whether to drop a TB of the MCG or the SCG is left to the discretion of the UE (and may be preconfigured by a UE manufacturer). This first option may be acceptable if it is expected that the UE capability will not be frequently exceeded. In accordance with a second option, if the UE capability is exceeded the UE may always drop a TB of the SCG. This second option may be appropriate on the assumption that in general MCG TBs are likely to be more important as they may correspond to RRC messages or delay sensitive messages. Of course, in a further option it may always be an MCG TB that is dropped.

In accordance with a third option, the network (and specifically an eNB, for instance the MeNB) can semi-statically configure through RRC which TB to drop. For instance the network can configure whether to drop TBs from MCG or SCG.

The network decision can be based on L1 configuration aspects, higher layer aspects or radio link conditions (or some combination of two or more aspects).

In accordance with a fourth option, the UE may avoid dropping TBs which contain certain information. The UE receives control information through a control channel which is separate from the data and so the UE can determine which is the higher priority TB in a TTI. For instance, the UE may avoid dropping uplink TBs that contain Uplink Control Information (UCI). For the downlink, the UE may avoid dropping TBs that contain system information, paging information or random access response information. If both uplink TBs to be transmitted to a MCG and a SCG contain UCI, then a priority rule based on another option, for instance as listed above, can be used.

In accordance with a fifth option, the UE may avoid dropping TBs that correspond to retransmissions of a packet over a new transmission. This may be desirable to avoid retransmissions of packets where energy has already been expended. In addition, this can also assist in minimising further delay to information in a TB that has already been transmitted. If both TBs correspond to new transmissions, then a priority rule based on another option, for instance as listed above, can be used. If both TBs correspond to retransmissions, then the TB that has been retransmitted least may be dropped. If both have been dropped the same number of times then a priority rule based on another option, for instance as listed above, can be used.

With reference to Figure 3, this illustrates in the form of a flowchart an embodiment of the present invention in accordance with the fifth option. At step 300 a UE receives two TBs: TB1 from a MeNB and TB2 from a SeNB. At step 302 the UE determines if the total size of the TBs exceeds its processing capability. If the capability is 30 not exceeded then at step 304 the UE processes both TBs and will acknowledge each with a respective ACK.

If at step 302 it is determined that the capability has been exceeded, then at step 306 the UE determines if TB1 has been retransmitted. If so, then at step 308 TB1 is processed normally and a respective ACK is sent to the MeNB. At step 310 TB2 is 35 dropped and a respect NACK is sent to the SeNB.

If at step 306 it is determined that TB1 has not been retransmitted then at step 312 it is determined if TB2 has been retransmitted. If TB2 has not been retransmitted then processing passes to

steps

308 and 310. If TB2 has been retransmitted, at step 314 TB2 is processed normally and a respective ACK is sent to the SeNB. At step 316 TB1 is 5 dropped and a respect NACK is sent to the MeNB.

In accordance with a sixth option, the UE may always drop the smaller TB. This is beneficial to minimize throughput loss. If both TBs from a MCG and a SCG have the same size, then a priority rule based on another option, for instance as listed above, can be used.

In accordance with a seventh option, the UE may drop TBs that contain or are expected to contain data with the lowest priority. It is known for each uplink logical channel to be configured with a priority. Alternatively, the UE could anticipate the priority of the data that is contained in the TB (in the case of downlink) or would be contained in the TB (in the case of uplink). As an example for uplink, if in a TTI there is high priority data available (for instance RRC signalling or voice data) to be transmitted to the MeNB, and only lower priority data that has to be transmitted to the SeNB, the UE should transmit the TB which will contain the higher priority data. In accordance with a further option, the dropping rule applied for downlink may differ from that applied to uplink.

As noted above, in accordance with certain embodiments of the present invention, for the downlink, if a UE determines to drop a TB then it sends a NACK to the eNB associated with the dropped TB. Since the UE is able to receive the control information related to the TB transmission (for instance over PDCCH/EPDCCH) even if the UE does not have sufficient processing capability to immediately handle the TB, the UE can still transmit a NACK to the eNB to inform the eNB that the UE was not able to successfully receive the TB. Although, the TB is “dropped” by the UE, the control information is still handled correctly. The NACK triggers a retransmission at the eNB thus ensuring that the TB is not actually lost. In certain embodiments the eNB may track the number of times that a TB is retransmitted and after a predetermined number of attempts the eNB may discontinue further retransmission of the TB. The missing data may then be handled at the RLC layer. The NACK may be a single bit sent within a control channel in connection with each received TB.

The network may be not be able to derive from the normal NACK described above whether the UE was not able to receive the TB correctly because of bad radio conditions, or because the total amount of TB bits transmitted to the UE in that TTI exceeded the UE capability to process TB bits. In accordance with certain embodiments of the invention the NACK may be modified in the event of dropping a TB due to the UE capability being exceeded in order to inform the network about the over allocation (particularly if this is a repeated event). This could be based on L1 signalling (for instance, a special Channel Quality Indicator (CQI) or a special NACK), MAC signalling (for instance, a new MAC Control Element (CE) or based on RRC signalling. Special NACK signalling is described in greater detail below.

In certain embodiments, different forms of signalling may be used to indicate to the network that the UE capability has been exceed. The selected form of signalling may depend on what type of TB is dropped. For instance, instantaneous L1 signalling such as a special NACK may be used when an important TB (for instance, control information, UCI or high Quality of Service . QoS data) is dropped.

Additionally, or alternatively, less frequent feedback may be supplied to one or both eNBs if less important traffic is dropped. In one example, the UE reports statistics of TB dropping due to the UE’s capability being exceeded (for instance, the number of TBs dropped within a given reporting time window). The period for sending the feedback may be configurable. Alternatively, a report about TB dropping may be triggered periodically or aperiodically by control signalling from the MeNB or the SeNB. As a further alternative, reporting about TB dropping may be triggered based on a configurable metric. For example, a UE may provide signalling (L1, MAC or RRC) only after X TBs are dropped within a window comprising Y TTIs. The values of X and Y may be preconfigured or signalled to the UE upon dual connectivity setup.

In the case of eNB triggered reporting, in one alternative the MeNB or the SeNB may request the UE to report dropping statistics based on a count kept by the UE of the number of TBs dropped for the MeNB and the SeNB. The MeNB or the SeNB may request the UE to begin counting for a predetermined amount of time or until the UE receives a second request by the eNB to provide a report.

In another reporting alternative the dropping reporting may be instantaneous informing the eNB about every dropped TB due to the UE capability being exceeded. For instance, this could be achieved by using the L1 special NACK signalling noted above.

In a first example, special NACK signalling is carried on a Physical Uplink Control Channel (PUCCH) resource which is separate from the conventional PUCCH resource for a conventional HARQ-ACK. For instance, it is described in 3GPP TS 36.213 (section 10.1.2.1) for Frequency Division Duplex (FDD) that for a PDSCH transmission indicated by the detection of a corresponding PDCCH in subframe n-4 , or for a PDCCH indicating 35 downlink Semi Persistent Scheduling (SPS) release in subframe n-4 , to send an ACK the UE shall use

for antenna port p0 , where n_CCE is the number of the first Control Channel Element (CCE), (the lowest CCE index used to construct the PDCCH) used for transmission of the corresponding DCI assignment and

is configured by higher layers. In contrast, in accordance with one embodiment the special NACK can be transmitted using a separate PUCCH resource defined as

can be higher layer configured.

In a second example, the special NACK signalling is carried on a new PUCCH format (for instance, Format 1x) which provides bits for HARQ ACK and NACK with or without a Scheduling Request (SR) and an additional bit indicating the reason for NACK. The additional bit may indicate either a normal TB reception error or TB dropping due to L1 capability over allocation.

In a third example, special NACK L1 signalling may be achieved by the MeNB and/or the SeNB reserving specific PUCCH Resource Blocks (RBs) or regions for the associated special NACK PUCCH message. For example an eNB may indicate to the UE that PUCCH region x (for example consisting of RB y and RB NRB 15 UL . z) should be used for UCI transmission only if the message is a PUCCH carrying a special NACK indication due to L1 capability over allocation. The format of the PUCCH transmitted in the reserved region may be an existing format or a new format.

In a fourth example, special NACK L1 signalling may be achieved by the MeNB and/or SeNB reserving specific orthogonal spreading codes or cyclic time shifts to be used in transmitting a PUCCH control message. For example when UEs need to transmit a NACK due to L1 capability over allocation, they may apply a time shift x1 to the waveform out of a set of possible time shifts X. Instead or in addition to the cyclic time shift the UE may apply an orthogonal spreading code to the transmitted symbols of the message which are reserved for this purpose and allow the eNB to interpret the received NACK as corresponding to a L1 capability over allocation situation.

In further alternatives, dropping reports may be separately provided to the MeNB and the SeNB, or they may be combined into a single report provided to only one eNB (for instance, the MeNB). This may be beneficial in the case that excessive dropping results in a reconfiguration of the UE capability split.

The UE behaviour regarding L1 capability over allocation reporting may be configurable by the network. This may be beneficial to provide the network with flexibility in reserving the necessary resources for reporting (in case of L1 message feedback) and to allow adaptation based on scenarios where reporting may be most beneficial (e.g. limited UE L1 processing capability and large sized traffic bearers at the MeNB and SeNB), and where reporting may be infrequent (for instance, where there is a very large L1 UE processing capability and small or very bursty data traffic bearers at the MeNB and SeNB).

In one alternative the UE reporting is configured based on a RRC message provided upon initiation of dual connectivity at the UE and may be periodically reconfigured by additional RRC messages. The parameters that can be configured may include whether or not over allocation/TB dropping feedback is on or off, the granularity of the feedback, the periodicity of the feedback, and L1 resources to be used for transmitting feedback messages.

Referring now to Figure 4, this illustrates signalling between a UE, a MeNB and a SeNB for distributed downlink scheduling in accordance with a UE centric embodiment of the present invention. At step 400 the UE indicates to the MeNB its capability for receiving downlink bits per TTI. At step 402 the MeNB forwards this information to the SeNB. In alternative embodiments the UE may separately provide this information to the SeNB. At step 404 the MeNB sends a dropping rule configuration to the UE through a RRC layer message. The dropping rule may be defined according to one or more of the options described above. Alternatively, step 404 may be omitted, for instance if the UE is preconfigured with a dropping rule. The UE may alternatively receive the dropping rule from another network entity.

At

steps

406 and 408 both the MeNB and the SeNB transmit TBs (TB 1 and TB 2) to the UE in the same TTI (TTI x). At step 410 the UE determines if the two TBs exceed its capability to process received bits within a single TTI. At step 412 the dropping rule is applied, which for instance is that TBs from the MeNB take precedence over TBs from the SeNB. On the assumption that the capability is exceeded at step 414, an ACK is sent to the MeNB in respect of TB 1 and at step 416 a NACK (which may be a special NACK as described above) is sent to the SeNB in respect of the dropped TB 2.

At step 418, which may not immediately follow step 416, a dropping report is triggered, for instance due to the number of dropped TBs exceeding a predetermined number in a predetermined period of time. If the dropping report is a MAC level report then it is sent to SeNB (as the affected eNB) at step 420. If, however, the dropping report is a RRC level report then it would instead be sent to the MeNB which may choose to forward some or all of the report to the SeNB (not illustrated).

The above discussion of dropping TBs relates to all forms of dropping TBs when a UE capability to receive or transmit data is exceeded. However, a distinction may be made between different types of UE capabilities being exceeded. For instance, a TB may be dropped due to the UE capability being instantaneously exceeded, or due to the average UE capability being exceeded. Further distinguishable cases may include a HARQ buffer limit being reached or a L2 buffer limit being reached.

For downlink, the situation may arise that even if an instantaneous UE processing capability is exceeded and the UE cannot fully process a TB upon receiving the TB, the UE might still be able to store the TB temporarily and process the TB later if the overload situation does not continue. The result of this may be that initially the UE would send a NACK to the originating eNB for that TB (since the UE cannot confirm correct reception yet to the network). However, the UE may later be able to process that TB. The later retransmission of the TB may simply be ignored. It will therefore be appreciated that where in the present specification reference is made to dropping a TB in the downlink this may mean either that the TB is not fully received or not received at all, or that the TB is received but cannot be processed at that time and so must be treated as if it has not be received.

In respect of handling a UE capability limitation for the uplink, if the UE determines using the TB grants from a MeNB and a SeNB that a TB must be dropped for that TTI (that is, one or other of the TBs is not able to be transmitted), in general the considerations set out above for the downlink generally apply. A further consideration is whether the MAC layer should request data from the RLC for a TB that will not be transmitted. According to a first option, the MAC layer does request data from the RLC layer for a TB that it will not transmit. Preferably, according to a second option, when theUE MAC receives uplink allocations for TBs with a total size exceeding the UE transmission capability, rather than the MAC asking the RLC for data to fill TBs that the L1 cannot process (which would result in lost data), the MAC entity will not ask the RLC entity for new data for those TBs.

Furthermore, for the uplink, rather than the eNB detecting that it cannot receive an uplink TB transmission (which could also be due to bad radio conditions rather than the UE not having performed the transmission), in accordance with certain embodiments of the invention the UE informs the network explicitly about which TBs have been transmitted (or which have been dropped) through uplink signalling. This signalling may comprise L1 signalling, MAC signalling (for instance, in a Power Headroom Report, PHR report) or RRC signalling. It is noted that RRC signalling would result in slower reporting of dropping status.

It will be appreciated that embodiments of the present invention can be realized in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium, for example, a CD, DVD, magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing apparatus or a method as claimed in any one of the claims of this specification and a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium including a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers or characteristics described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. It will be also be appreciated that, throughout the description and claims of this specification, language in the general form of “X for Y”(where Y is some action, activity or step and X is some means for carrying out that action, activity or step) encompasses means X adapted or arranged specifically, but not exclusively, to do Y. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

A method of operating a User Equipment, UE, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising first and second Universal Terrestrial Radio Access Network Node Bs, eNBs, in communication with the UE, the method comprising:

detecting downlink scheduling information in respect of the first and second eNBs for a single Transmission Time Interval, TTI, the scheduling information specifying a Transport Block, TB, including a number of TB bits to be received by the UE from each eNB during that TTI; and calculating whether the cumulative scheduled number of TB bits within that TTI exceeds a UE capability to process downlink data;

wherein if the UE capability to process data is exceeded, the method further comprises determining not to process a TB received from one of the eNBs.
A method according to claim 1, the method further comprising:

detecting uplink scheduling grants in respect of the first and second eNBs for a single TTI, each scheduling grant specifying a TB including a number of TB bits to be transmitted by the UE to each eNB during that TTI; and

calculating whether the cumulative granted number of TB bits within that TTI exceeds a UE capability to process uplink data;

wherein if the UE capability to transmit data is exceeded, the method further comprises determining not to process a TB for transmission to one of the eNBs.
A method according to claim 1, further comprising:

determining to process a TB received from one of the eNBs; and

sending an acknowledgement to an eNB associated with a TB which it is

determined to process.
A method according to claim 1 or claim 3, wherein if it is determined not to process a TB then the method further comprises:

sending a negative acknowledgement to the eNB associated with the TB which it is determined not to process.
A method according to claim 4, wherein the negative acknowledgement indicates to the eNB that the TB has not been processed due to the UE capability to process downlink data having been exceeded.
A method according to claim 2, wherein if it is determined not to process a TB then the method further comprises:

sending an indication to the eNB associated with the TB which it is determined not to process to indicate that the TB is not transmitted due to the UE capability to process uplink data having been exceeded.
A method according to any one of the preceding claims, further comprising:

sending a report message to at least one of the eNBs containing information on TBs that have not been processed.
A method according to claim 7, wherein the report message indicates at least one of:

the number of TBs that have not been processed in a certain period of time;

the frequency with which TBs are not processed; or

a proportion of TBs that have not been processed.
A method according to any one of the preceding claims, wherein if it is determined not to process a TB then the method further comprises:

determining a TB not to process;

wherein the determination a TB not to process may comprise:

determining to not process a TB received from or for transmission to the first eNB;

if one eNB comprises a Master eNB, MeNB, and the other eNB comprises a Secondary eNB, SeNB, determining not to process a TB received from or for transmission to the SeNB;

receiving a Radio Resource Control, RRC, message from one of the eNBs indicating whether the UE should select a TB received from or for transmission to either the first or second eNB if it is determined not to process a TB;

determining the content type of each TB and determining a TB not to process according to the content of each TB;

determining whether each TB comprises a retransmitted TB, and if a first TB, but not a second TB, is a retransmitted TB then determining not to process the second TB;

determining the relative size of each TB and determining not to process a smaller TB; or

determining the relative priority of the content of each TB, and determining not to process a lower priority TB.
A User Equipment, UE, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising first and second Universal Terrestrial Radio Access Network Node Bs, eNBs, in communication with the UE, the UE being arranged to:

detect downlink scheduling information in respect of the first and second eNBs for a single Transmission Time Interval, TTI, the scheduling information specifying a Transport Block, TB, including a number of TB bits to be received by the UE from each eNB during that TTI; and

calculate whether the cumulative scheduled number of TB bits within that TTI exceeds a UE capability to process downlink data;

wherein if the UE capability to process data is exceeded, the UE is further arranged to determine not to process a TB received from one of the eNBs.
A UE according to claim 10, the UE being further arranged to:

detect uplink scheduling grants in respect of the first and second eNBs for a single TTI, each scheduling grant specifying a TB including a number of TB bits to be transmitted by the UE to each eNB during that TTI; and

calculate whether the cumulative granted number of TB bits within that TTI exceeds a UE capability to process uplink data;

wherein if the UE capability to transmit data is exceeded, the UE is further arranged to determine not to process a TB for transmission to one of the eNBs.
A method of operating a first Universal Terrestrial Radio Access Network Node B, eNB, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising a second eNB and a User Equipment, UE, the first and second eNBs being in communication with the UE, the method comprising:

receiving a parameter indicating the capability of the UE to process received Transport Block, TB, bits in a single Transmission Time Interval, TTI; and

calculating a first maximum number of TB bits that can be scheduled by the first eNB for downlink data transmission to the UE;

wherein the first maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to process received TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to process received TB bits in a single TTI will not be exceeded.
A method according to claim 12, the method further comprising:

receiving a parameter indicating the capability of the UE to transmit TB bits in a single TTI; and

calculating a second maximum number of TB bits that can be granted by the first eNB to the UE for uplink data transmission to the first eNB;

wherein the second maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to transmit TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to transmit TB bits in a single TTI will not be exceeded.
A method according to claim 12 or claim 13, wherein the data transmission parameter comprises a Layer 1, L1, data transmission parameter or a higher layer data transmission parameter.
A method according to claim 14, wherein the data transmission parameter

comprises at least one of:

bandwidth;

Multiple Input Multiple Output, MIMO, capability;

traffic volume; or

configured guaranteed bit rate.
A first Universal Terrestrial Radio Access Network Node B, eNB, in a Long Term Evolution, LTE, compliant mobile communications network, the network further comprising a second eNB and a User Equipment, UE, the first and second eNBs being in communication with the UE, the first eNB being arranged to:

receive a parameter indicating the capability of the UE to process received Transport Block, TB, bits in a single Transmission Time Interval, TTI; and

calculate a first maximum number of TB bits that can be scheduled by the first eNB for downlink data transmission to the UE;

wherein the first maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to process received TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to process received TB bits in a single TTI will not be exceeded.
A first eNB according to claim 16, the first eNB being further arranged to:

receive a parameter indicating the capability of the UE to transmit TB bits in a single TTI; and

calculate a second maximum number of TB bits that can be granted by the first eNB to the UE for uplink data transmission to the first eNB;

wherein the second maximum number of TB bits in a single TTI is calculated according to a predetermined rule based on a parameter indicating the capability of the UE to transmit TB bits in a single TTI and a data transmission parameter for both eNBs known to both eNBs, such that if the second eNB follows the same predetermined rule the capability of the UE to transmit TB bits in a single TTI will not be exceeded.