WO2016119882A1

WO2016119882A1 - Carrier aggregation with cross-carrier scheduling

Info

Publication number: WO2016119882A1
Application number: PCT/EP2015/051943
Authority: WO
Inventors: Chunli Wu; Esa Malkamäki; Klaus Hugl; Lars Lindh
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2015-01-30
Filing date: 2015-01-30
Publication date: 2016-08-04
Also published as: TW201632027A

Abstract

A solution comprising determining for a terminal device of a cellular communication system, a configuration for carrier aggregation with at least one serving cell configured to be scheduled by means of cross- carrier scheduling; determining, a mapping between a serving cell index of the configured serving cell to be scheduled by means of cross-carrier scheduling and a scheduling cell-specific carrier indicator field value; causing, in the network node, transmission of a configuration message to the terminal device for the carrier aggregation, the configuration message comprising at least one information element indicating at least one cell to be scheduled by means of the cross-carrier scheduling and transmitting control information to the terminal device, the control information comprising a carrier indicator field, wherein the carrier indicator field value is based on said mapping between the serving cell index and the scheduling cell-specific carrier indicator field.

Description

DESCRIPTION

TITLE

CARRIER AGGREGATION WITH CROSS-CARRIER SCHEDULING

TECHNICAL FIELD

The invention relates to communications. BACKGROUND

3GPP LTE-A (long term evolution advanced) involves the concept of a primary cell (PCell) and a secondary cell (SCell) for supporting carrier aggregation. Carrier aggregation is introduced in LTE-A in order to provide an increased bandwidth and thereby an increased bitrate. Each aggregated carrier is referred to as a component carrier (CC) or alternatively as a cell or a serving cell. When carrier aggregation is applied, a number of serving cells are provided, one for each component carrier. The coverage of the serving cells may differ, for example, due to differences in experienced pathloss. One of the serving cells is called a primary serving cell, served by a primary component carrier (DL and UL PCC). Other component carriers are referred to as secondary component carriers (DL and UL SCC), serving secondary serving cells.

BRIEF DESCRIPTION

According to an aspect, there is provided the subject matter of the independent claims.

Embodiments are defined in the dependent claims.

One or more examples of implementations are set forth in more detail in the

accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

In the following, the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 illustrates an example of a wireless communication system to which

embodiments of the invention may be applied; Figure 2 illustrates an example of carrier aggregation;

Figure 3 illustrates an example of self-scheduling; Figure 4 illustrates an example of cross-carrier scheduling;

Figure 5 is an exemplifying signalling diagram of a procedure for carrier aggregation according to an embodiment of the invention;

Figures 6 and 7 illustrate example of processes for carrier aggregation according to an embodiment of the invention;

Figures 8 and 9 illustrate example block diagrams of an apparatus according to an embodiment of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The following embodiments are exemplifying. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may contain also features/structures that have not been specifically mentioned.

Figure 1 illustrates an example of a wireless communication scenario to which

embodiments of the invention may be applied. Referring to Figure 1 , a cellular

communication system may comprise a radio access network comprising base stations disposed to provide radio coverage in a determined geographical area. The base stations may comprise macro cell base stations (eNB) 102 arranged to provide terminal devices (UE) 106 with the radio coverage over a relatively large area spanning even over several square miles, for example. In densely populated hotspots where improved capacity is required, small area cell base stations (eNB) 100 may be deployed to provide terminal devices (UE) 104 with high data rate services. Such small area cell base stations may be called micro cell base stations, pico cell base stations, or femto cell base stations. The small area cell base stations typically have significantly smaller coverage area than the macro base stations 102. The cellular communication system may operate according to specifications of the 3rd generation partnership project (3GPP) long-term evolution (LTE) advanced or its evolution version (such as 5G).

When carrier aggregation is applied, UE is served by more than one component carrier. These component carriers may be in the same location (e.g. both in the macro cell) or in different locations (e.g. one in the macro cell and the other(s) in the small cell). Carrier aggregation may be arranged by using contiguous component carriers within the same operating frequency band. This may not be possible e.g. due to operator frequency allocation scenarios. Non-contiguous allocation may either be intra-band, i.e. the component carriers belong to the same operating frequency band, but have a gap, or gaps, in between, or it may be inter-band, in which case the component carriers belong to different operating frequency bands. Figure 2 illustrates carrier aggregation. Regarding scheduling there are two main alternatives for carrier aggregation, either resources are scheduled on the same carrier as the grant is received (i.e. self-scheduling), or cross- carrier scheduling may be used where the downlink control information containing the scheduling grant for a carrier is received on a different carrier. For cross-carrier scheduling, a scheduling cell also carries the scheduling grants of other cells which are then to be denoted as (cross-carrier) scheduled cells. Figure 3 illustrates self-scheduling, and Figure 4 illustrates cross-carrier scheduling.

Cross-carrier scheduling according to Rel-10 uses a field in a UL/DL scheduling grant, denoted as a carrier indicator field (CIF). In Rel-10, CIF is limited to 3 bits, which is sufficient to enable cross-carrier scheduling of up to 5 component carriers as supported by LTE specifications. The carrier indicator field is part of the scheduling UL/DL grant procedure, and is transmitted within downlink control information (DCI).

Cross-carrier scheduling for carrier aggregation is a UE capability. The cross-carrier scheduling for the carrier aggregation is configured for UE separately for each configured component carrier.

In 3GPP LTE Rel-10, CIF carried in DCI is limited to 3 bits, and the value of CIF equals to a serving cell index. The CIF value defines a carrier for which the scheduling UL/DL grant is, and the CIF value also has an effect on a downlink control channel user-specific search space position for which UE is searching. The respective search space formulation dependent on the CIF value (0...7) may be as follows. The set of physical downlink control channel (PDCCH) candidates to monitor are defined in terms of search spaces, where the search space at an aggregation level is defined by a set of PDCCH candidates. For each serving cell on which PDCCH is monitored, control channel elements (CCE)

corresponding to the PDCCH candidate of the search space are defined. The following may be taken into account: a common search space, a PDCCH (or enhanced physical downlink control channel (EPDCCH)) UE-specific search space, whether or not the monitoring UE is configured with the carrier indicator field, the serving cell on which PDCCH/EPDCCH is monitored, and/or the number of PDCCH/EPDCCH candidates to monitor in the given search space. The carrier indicator field value is the same as the serving cell index. The configuration of the cross-carrier scheduling is defined as follows. A cif-Presence-r10 in PhysicalConfigDedicated (PCell configuration) indicates whether CIF is present in PDCCH downlink control information (DCI) of PCell. A CIF value of 0 indicates PCell, while another SCell may be addressed with a ServCelllndex parameter, i.e. the CIF value is the same as the ServCelllndex parameter. Accordingly, each SCell may be configured with the cross-carrier scheduling as part of SCell addition or modification. The configuring of SCell with the cross-carrier scheduling as part of the SCell addition or modification is carried out by means of a CrossCarrierSchedulingConfig parameter which is part of a PhysicalConfigDedicatedSCell parameter. Rel-13 on carrier aggregation enhancements states that scheduling of up to 32 component carriers is supported. Mechanisms are specified to enable the LTE carrier aggregation of up to 32 component carriers for downlink (DL) and uplink (UL), including enhancements to DL control signalling for up to 32 component carriers including both self- scheduling and cross-carrier scheduling, if any. A SchedulingCelllnfo parameter, specified along with Rel-10 LTE carrier aggregation, under the CrossCarrierSchedulingConfig parameter indicates whether cross-carrier scheduling is enabled or not. The SchedulingCelllnfo parameter indicating "own" means that SCell transmits its own PDCCH, i.e. the cross-carrier scheduling is not enabled. Whether or not SCell is a scheduling cell that cross-schedules another cell, may be indicated by cif-Presence-10 (it is also possible to have SCell as the scheduling cell that cross-schedules another SCell in Rel-10). On the other hand, if cross-carrier scheduling is enabled (i.e. SCell is cross-scheduled by another cell), then the SchedulingCelllnfo parameter indicates "other", which means that some "other" serving cell transmits PDCCH DCI. A SchedulingCellld parameter informs UE on which cell signals downlink allocations and uplink grants for SCell in question. Extending this operation to 32 component carriers (i.e. 32 serving cells) means, from the UE point of view, that the serving cell index needs to be increased from [0,..,7] to [0,..,31 ]. This may also affect the cross-carrier scheduling operation. The cross-carrier scheduling principle may be extended by increasing the CIF length from

3 bits to 5 bits, in order to enable the cross-carrier scheduling of up to 32 component carriers. However, this requires larger DCI formats, causing higher probability for missed detection of DCI (i.e. a higher coding rate with the same aggregation level). Moreover, there is a larger probability for having DCIs with the same size and an additional need to add bits at the end of DCI (to prevent ambiguity), which further increases the DCI block error rates. If two DCIs have the same size, zeros may be added at the end to generate a different size.

Let us now describe example embodiments for carrier aggregation with reference to Figure 5. Figure 5 illustrates a signalling diagram illustrating a method for communicating cross-carrier scheduling parameters between network elements of the cellular

communication system. The network element may be a network node, an access node, a base station, a terminal device, a server computer or a host computer. For example, the server computer or the host computer may generate a virtual network through which the host computer communicates with the terminal device. In general, virtual networking may involve a process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network. In another embodiment, the network node may be a terminal device. Network virtualization may involve platform virtualization, often combined with resource virtualization. Network virtualization may be categorized as external virtual networking which combines many networks, or parts of networks, into the server computer or the host computer. External network virtualization is targeted to optimized network sharing. Another category is internal virtual networking which provides network-like functionality to the software containers on a single system. Virtual networking may also be used for testing the terminal device. Referring to Figure 5, in item 501 , a network node determines for a terminal device a configuration for carrier aggregation with at least one cell configured to be scheduled by means of cross-carrier scheduling. In an embodiment, the configuration comprises more than 8 serving cells for carrier aggregation. However, embodiments of the invention are not limited to this number which is here used as an example. In an example embodiment, the network node may determine a mapping between the serving cell index of the configured serving cell to be scheduled by means of cross-carrier scheduling and a scheduling cell-specific carrier indicator field value.

In item 502, based on the determining, the network node causes transmission of a configuration message to the terminal device for the carrier aggregation, the configuration message comprising at least one information element indicating at least one cell to be scheduled by means of the cross-carrier scheduling. In item 503, the terminal device receives the configuration message from the network node for the carrier aggregation. In an embodiment, in item 504 the network node may apply the mapping. In item 505, the network node causes transmission of control information (e.g. DCI) to the terminal device, the control information comprising a carrier indicator field, wherein the carrier indicator field value is based on said mapping between the serving cell index and the scheduling cell-specific carrier indicator field.

In an embodiment, the mapping may be based on a mapping rule wherein the serving cell indexes of the serving cells to be scheduled by means of cross carrier scheduling are mapped to the scheduling cell-specific carrier indicator field values for example in ascending or descending order.

In item 506, the terminal device receives the control information from the network node.

In another example embodiment with regard to Figure 5, in item 501 , a network node determines for a terminal device a configuration of for carrier aggregation and at least one cell to be scheduled by means of cross-carrier scheduling, such that the number of cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is 8 cells or less even though the overall number of configured cells for carrier aggregation may be more than 8 cells. In item 502, based on the determining, the network node causes transmission of a configuration message to the terminal device for the carrier aggregation. The configuration message comprising at least one information element indicating at least one cell to be scheduled from a single scheduling cell by means of the cross-carrier scheduling such that the number of the cells to be scheduled by means of the cross-carrier scheduling is 8 cells or less. In item 503, the terminal device receives the configuration message from the network node for the carrier aggregation. In item 504, the network node performs a mapping of the serving cell to a scheduling cell-specific carrier indicator value.

In item 505, the network node causes transmission of downlink control information to the terminal device, on cross-carrier scheduled serving cells via a scheduling cell, the downlink control information comprising a carrier indicator field. The carrier indicator field value is based on a mapping 504 of a serving cell to a scheduling cell-specific carrier indicator field value. In item 506, the terminal device receives the downlink control information from the network node, wherein the terminal device applies the inverse scheduling cell specific mapping from carrier indicator field to serving cell in order to obtain the control information for a schedule cell. In an embodiment, the mapping between serving cell and a scheduling cell-specific carrier indicator field value in the network in 504 and vice versa (i.e. inverse mapping) in the UE in 506, are according to the same mapping rule. This mapping rule may be according on a pre-defined mapping rule. Alternatively, the eNB may determine a mapping between serving cell and a scheduling cell-specific carrier indicator field value by itself and informs the intended UE about the mapping rule. The UE may in this case utilize 506 mapping between the scheduling cell- specific CIF and a serving cell based on RRC signaling. RRC signaling is either signaled explicitly, i.e. the configuration message 502 may also indicate CIF to be used for a given SCell, or implicitly where the RRC signalling (i.e. the configuration message 502) configures SCell and indicates which cell is the scheduling cell and the mapping is then utilized 506 based on a predefined mapping rule. DCI carries CIF, wherein based on the mapping, UE knows which SCell is being scheduled. The terminal device and the network node may maintain predefined mapping rules (e.g. mapping tables or some other data structures) for mapping between serving cell indexes, corresponding scheduling cell identifiers and carrier indicator field. Alternatively, appropriate mapping rule information may be determined 501 in the network node and provided to the terminal device from the network node e.g. by using the RRC signalling 502.

In an example embodiment, the number of scheduled cells from a single scheduling cell may be restricted to be in the range of 8 cells or less. Thus the interpretation and mapping of the CIF value in DCI does not require increasing the 3-bit CIF length to support more than 8 serving cells. The restriction does not affect the cross-carrier scheduling operation, as with a large number of scheduled cells from a single scheduling cell there is

PDCCH/EPDCCH blocking (i.e. too many DCIs need to be transmitted from

PDCCH/EPDCCH of the single scheduling cell).

In an embodiment, serving cell index to CIF mapping may be carried out so that CIF only indicates the serving cell indexes of the configured cells for the single scheduling cell in an increasing order, which enables even with a 3bit CIF being limited to values of 0 to 7 to serve cells with a serving cell index larger than 7..

The serving cell index CIF mapping may be performed as follows. For example, assuming that UE is configured with carrier aggregation of 14 cells/carriers and the configuration defines two scheduling cells which are used for (cross-carrier) each of the 14 cells. For these 14 cells, the scheduling cell for each of the cells according to a higher layer configuration is as shown in Table 1 . Table 1

In this example, two scheduling cells are considered here, having SchedulingCellld #0 and SchedulingCellld #1 . As ServCelllndex for PCell is 0 each time, the first scheduling cell in this example is PCell, and the second scheduling cell the SCell with the ServingCelllndex 1 . From the 14 cells (ServCelllndex-r13 is [0,...,13]), 5 cells are configured for the cross- carrier scheduling from PCell, in addition to self-scheduling from PCell (cells # 3, 4, 5, 6, 10), and a first scheduling SCell (with ServingCelllndex 1 ) is configured to schedule cell #1 (i.e. self-scheduling), and for the cross-carrier scheduling of cells # 2, 7, 8, 9, 1 1 , 12, 13. For PCell, the serving cell index of the cells to be scheduled is sorted according to the increasing order of the serving cell indexes as described above, and a related CIF is assigned (i.e. mapping is defined) for the cross-carrier scheduling as shown in Table 2.

Table 2

Therefore, CIF=2 in DCI on PCell maps to the cell with ServCelllndex_r13 of 4, and CIF=5 indicates ServCelllndex_r13 of 10. Accordingly, for the second scheduling cell, the same mapping rule is applied as described above (see Table 3). Table 3

Thus, the CIF value for the cell is determined by the place of the serving cell index of the cell sorted in the increasing order for each cell scheduled by the same cell. The UE implementation may maintain such a mapping table based on the configuration.

In another example, assuming there are 14 carriers (with ServCelllndexes 0..13) of which 7 are cross-carrier scheduled e.g. from PCell (servCell Index = 0). Let us assume that even-numbered cells are cross-scheduled from PCell, then a mapping between CIF = 0..7 and serving cell indexes = 0,2,4,6,8,1 0, 12 is needed. Two alternatives are provided for determining the mapping, including predefined mapping rules and explicit RRC signaling. Based on a rule, a mapping CIF=0 corresponds to ServCell lndex=0, CIF=1 to

ServCelllndex=2, CIF=6 to ServCelllndex=12 (in ascending order). This is similar to Table 2 above.With explicit RRC signaling any mapping is possible, e.g. the mapping may be:

CIF ServCelllndex 0 0

3 1 2 4 1 0

6 8 This may be implemented into RRC specification as follows. When SCell is added it is given a sCelllndex value (which equals to ServCelllndex):

SCellToAddMod-n O ::= SEQUENCE { sCelllndex-r10 SCelllndex-r10, cellldentification-r10 SEQUENCE { physCellld-r10 PhysCellld, dl-CarrierFreq-r10 ARFCN-ValueEUTRA

} OPTIONAL, - Cond SCellAdd radioResourceConfigCommonSCell-r10 RadioResourceConfigCommonSCell-r10 OPTIONAL, -- Cond SCellAdd radioResourceConfigDedicatedSCell-r10 RadioResourceConfigDedicatedSCell-r10 OPTIONAL, -- Cond SCellAdd2

[[ dl-CarrierFreq-v1090 ARFCN-ValueEUTRA-v9eO OPTIONAL -- Cond

EARFCN-max

]]

}

Inside RadioResourceConfigDedicatedSCell there is PhysicalConfigDedicatedSCell which includes a cross-carrier scheduling configuration:

CrossCarrierSchedulingConfig-r10 ::= SEQUENCE { schedulingCelllnfo-r10 CHOICE { own-r10 SEQUENCE { - No cross carrier scheduling cif-Presence-r10 BOOLEAN

} .

other-r10 SEQUENCE { - Cross carrier scheduling schedulingCellld-r10 ServCelllndex-r10, pdsch-Start-r10 INTEGER (1 ..4)

}

This tells (among other things) the scheduling cell (ServCelllndex of the scheduling cell) from where the configured SCell is to be scheduled. The CIF value to be used may be added for this SCell (see ciflnSchedulingCell-r13 ... INTEGER (0..7) below) (for instance, when configuring SCell with sCelllndex=6, setting may be CIF=1 ):

CrossCarrierSchedulingConfig-r13 ::= SEQUENCE { schedulingCelllnfo-r13 CHOICE { own-r13 SEQUENCE { - No cross carrier scheduling cif-Presence-r13 BOOLEAN

} .

other-r13 SEQUENCE { - Cross carrier scheduling schedulingCellld-r13 ServCelllndex-r13, pdsch-Start-r13 INTEGER (1 ..4), ciflnSchedulingCell-r13 INTEGER (0..7)

} } }

In an embodiment, it is possible to schedule up to 8 component carriers from a scheduling cell, and to extend the cross-carrier scheduling operation without the need to increase the CIF size in downlink control information formats to support more than 8 serving cells.

In another embodiment, the ServCelllndexes may be sorted in a decreasing order, and/or any other appropriate ServCell Index sorting rule may be defined and applied. The defining of the rule enables that no extra RRC signaling is needed for the mapping.

In another embodiment, the mapping may be configurable, i.e. the RRC signaling may explicitly indicate the mapping between CIF and ServCelllndex, e.g. when adding SCell to be scheduled by a given cell. If ServCelllndex of the added SCell is in between

ServCelllndexes of existing SCells, the mapping of the earlier SCells may be kept, i.e. the addition of SCell to be scheduled does not change the mapping of other CIFs. This may be implemented in RRC, for instance, by adding in CrossCarrierSchedulingConfig a parameter such as cifValuelnSchedulingCell. Regarding Table 2 and Table 3, the mapping for the two scheduling cells is in this example directly given by higher layer signalling in this case.

The CIF value may also have an effect on the user-specific search space definition on PDCCH and EPDCCH, where the CIF value gives the offset of the search spaces for each of the scheduled cells. This may be extended to accommodate the mapping

table/procedure as follows. 1 ) The CIF value may be used instead of ServingCellld in the search space definition; in this case, the search space remains rather compact, with a maximum offset of M^*7, but may be slightly different compared to the case where the CIF value (as an alternative solution for the CIF mapping) is defined. In this case, n CIF is the CIF value of the mapping table. 2) Alternatively, ServingCellld may be used in the

PDCCH/EPDCCH user specific search space definition; in this case, exactly the same search space is defined as in case of extending CIF to 5 bits, with a maximum offset of M^*31 . In this case, the definition for n CIF is ServingCellld. Herein, M refers to the number of PDCCH candidates to be monitored in a given search space. An embodiment enables enhancing cross-carrier scheduling capabilities. The cross-carrier scheduling from up to 32 component carriers is enabled without the need to increase the CIF size. For 32 component carriers, 4 or more scheduling cells may be configured, each scheduling cell being limited to schedule 8 cells or less. Thereby, the cross-carrier scheduling is extended up to 32 cells without enlarging the CIF length in the DCI formats. DCI decoding performance is not negatively affected, and there is a smaller probability of having DCIs with same size. CIF vs. ServingCellld mapping for each scheduling cell is implemented, where the mapping may be given by a simple rule (increasing, decreasing order, etc.) or by higher layer signalling (e.g. RRC signalling). Up to 8 carriers may be scheduled from the single scheduling cell.

In an embodiment, a scheduling cell-specific carrier indicator field value derived based on the mapping rule may be used in the downlink control information for identifying a corresponding scheduled serving cell. 33. In an embodiment, a scheduling cell-specific carrier indicator field value derived based on the mapping rule may be used for identifying a search space of a corresponding cross-carrier scheduled serving cell.

Let us now describe embodiments of the cross-carrier scheduling in greater detail with reference to Figures 6 and 7. Referring to Figure 6, in item 601 , a network node determines for a terminal device a configuration for carrier aggregation with at least one cell configured to be scheduled by means of cross-carrier scheduling. In an embodiment, the configuration comprises of more than 8 serving cells for carrier aggregation. .

However, embodiments of the invention are not limited to this number which is here used as an example. In an example embodiment, the network node may determine a mapping between the serving cell index of the configured serving cell to be scheduled by means of cross-carrier scheduling and a scheduling cell-specific carrier indicator field value. In item 602, based on the determining, the network node causes transmission of a configuration message to the terminal device for the carrier aggregation, the configuration message comprising at least one information element indicating at least one cell to be scheduled by means of the cross-carrier scheduling.

In an embodiment, in item 603 the network node may apply the mapping. In item 604, the network node causes transmission of control information (e.g. DCI) to the terminal device, the control information comprising a carrier indicator field, wherein the carrier indicator field value is based on said mapping between the serving cell index and the scheduling cell-specific carrier indicator field. In an embodiment, the mapping may be based on a mapping rule wherein the serving cell indexes of the serving cells to be scheduled by means of cross carrier scheduling are mapped to the scheduling cell- specific carrier indicator field values for example in ascending or descending order.

Referring to Figure 7, in item 701 , a terminal device receives from a network node, a configuration message for carrier aggregation. The configuration message comprises at least one information element indicating at least one cell to be scheduled by means of cross-carrier scheduling.

In item 702, the terminal device receives from the network node, control information on cross-carrier scheduled serving cells via a scheduling cell. The control information comprises a carrier indicator field, wherein the carrier indicator field value is based on mapping between a serving cell index and a scheduling cell-specific carrier indicator field value.

In item 703, the terminal device may utilize the mapping between serving cell index, corresponding scheduling cell identifiers and carrier indicator field. The terminal device may maintain predefined mapping rules (e.g. mapping tables) for mapping between serving cell indexes, corresponding scheduling cell identifiers and carrier indicator field. Alternatively, appropriate mapping rule information may be determined in the network node and received 701 in the terminal device from the network node e.g. in the configuration message. An embodiment provides an apparatus comprising at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to carry out the procedures of the above-described base station or the network node. The at least one processor, the at least one memory, and the computer program code may thus be considered as an embodiment of means for executing the above- described procedures of the base station or the network node. Figure 8 illustrates a block diagram of a structure of such an apparatus. The apparatus may be comprised in the base station or in the network node, e.g. the apparatus may form a chipset or a circuitry in the base station or in the network node. In some embodiments, the apparatus is the base station or the network node. The apparatus comprises a processing circuitry 10 comprising the at least one processor. The processing circuitry 10 may comprise a configuration circuitry 12 configured to determine for a terminal device a configuration of more than 8 serving cells for carrier aggregation and at least one cell configured to be scheduled by means of cross-carrier scheduling, such that the number of cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is 8 cells or less. The configuration circuitry 12 may be configured to determine the configuration, as described above, and output the information to a configuration message generator 18. The configuration message generator 18 is configured to cause transmission of a configuration message to the terminal device for the carrier aggregation. The configuration message comprises at least one information element indicating at least one cell to be scheduled by means of the cross-carrier scheduling such that the number of the cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is 8 cells or less. A mapping circuitry 16 is configured to maintain predefined mapping rules (e.g. mapping tables) for mapping between serving cell indexes and corresponding scheduling cell identifiers and carrier indicator field. Alternatively, the mapping circuitry 16 is configured to determine appropriate mapping rule information. The mapping circuitry 16 may be configured to provide the predefined mapping rules to the terminal device (e.g. by using RRC signalling). A control message generator 14 is configured to cause

transmission of control information (e.g. DCI) to the terminal device, on cross-carrier scheduled serving cells via a scheduling cell, the control information comprising a carrier indicator field. The processing circuitry 10 may comprise the circuitries 12 to 18 as sub- circuitries, or they may be considered as computer program modules executed by the same physical processing circuitry. The memory 20 may store one or more computer program products 24 comprising program instructions that specify the operation of the circuitries 12 to 18. The memory 20 may fur-their store a database 26 comprising definitions for carrier aggregation, for example. The apparatus may further comprise a communication interface 22 providing the apparatus with radio communication capability with the terminal devices. The communication interface 22 may comprise a radio communication circuitry enabling wireless communications and comprise a radio frequency signal processing circuitry and a baseband signal processing circuitry. The baseband signal processing circuitry may be configured to carry out the functions of a transmitter and/or a receiver. In some embodiments, the communication interface may be connected to a remote radio head comprising at least an antenna and, in some embodiments, radio frequency signal processing in a remote location with respect to the base station. In such embodiments, the communication interface may carry out only some of radio frequency signal processing or no radio frequency signal processing at all. The connection between the communication interface and the remote radio head may be an analogue connection or a digital connection. In some embodiments, the communication interface may comprise a fixed communication circuitry enabling wired communications.

An embodiment provides another apparatus comprising at least one processor and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to carry out the procedures of the above-described terminal device. The at least one processor, the at least one memory, and the computer program code may thus be considered as an embodiment of means for executing the above-described procedures of the terminal device. Figure 9 illustrates a block diagram of a structure of such an apparatus. The apparatus may be comprised in the terminal device, e.g. it may form a chipset or a circuitry in the terminal device. In some embodiments, the apparatus is the terminal device. The apparatus comprises a processing circuitry 50 comprising the at least one processor. The processing circuitry 50 may comprise a TX/RX controller 54 configured to receive from a network node, a configuration message for carrier

aggregation. The configuration message comprises at least one information element indicating at least one cell to be scheduled by means of cross-carrier scheduling such that the number of the cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is 8 cells or less. The TX/RX controller 54 is further configured to receive from the network node, control information on cross-carrier scheduled serving cells via a scheduling cell. The control information comprises a carrier indicator field. The TX/RX controller 54 is configured to receive the control information as described above and output the information to a mapping circuitry 52. The mapping circuitry 52 is configured to utilize mapping between serving cell indexes, corresponding scheduling cell identifiers and carrier indicator field. Predefined mapping rules (e.g. mapping tables) may be maintained in the memory 60 for mapping between serving cell indexes, corresponding scheduling cell identifiers and carrier indicator field. Alternatively, appropriate mapping information may be received in the TX/RX controller 54 from the network node (e.g. in the configuration message).The processing circuitry 50 may comprise the circuitries 52, 54 as sub-circuitries, or they may be considered as computer program modules executed by the same physical processing circuitry. The memory 60 may store one or more computer program products 64 comprising program instructions that specify the operation of the circuitries 52, 54. The apparatus may further comprise a communication interface 62 providing the apparatus with radio communication capability with base stations of one or more cellular communication networks. The communication interface 62 may comprise a radio communication circuitry enabling wireless communications and comprise a radio frequency signal processing circuitry and a baseband signal processing circuitry. The baseband signal processing circuitry may be configured to carry out the functions of a transmitter and/or a receiver. In some embodiments, the communication interface 62 may comprise a fixed communication circuitry enabling wired communications.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware- only circuit implementations such as implementations in only analog and/or digital circuitry; (b) combinations of circuits and software and/or firmware, such as (as

applicable): (i) a combination of processor(s) or processor cores; or (ii) portions of processor(s)/software including digital signal processor(s), software, and at least one memory that work together to cause an apparatus to perform specific functions; and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term in this application. As a further example, as used in this application, the term "circuitry" would also cover an

implementation of merely a processor (or multiple processors) or portion of a processor, e.g. one core of a multi-core processor, and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular element, a baseband integrated circuit, an application-specific integrated circuit (ASIC), and/or a field-programmable grid array (FPGA) circuit for the apparatus according to an embodiment of the invention.

The techniques described herein may be implemented by various means so that an apparatus implementing one or more functions of a corresponding mobile entity described with an embodiment comprises not only prior art means, but also means for implementing the one or more functions of a corresponding apparatus described with an embodiment and it may comprise separate means for each separate function, or means may be configured to perform two or more functions.

The processes or methods described above in connection with Figures 1 to 9 may also be carried out in the form of one or more computer process defined by one or more computer programs. The computer program shall be considered to encompass also a module of a computer programs, e.g. the above-described processes may be carried out as a program module of a larger algorithm or a computer process. The computer program(s) may be in source code form, object code form, or in some intermediate form, and it may be stored in a carrier, which may be any entity or device capable of carrying the program. Such carriers include transitory and/or non-transitory computer media, e.g. a record medium, computer memory, read-only memory, electrical carrier signal, telecommunications signal, and software distribution package. Depending on the processing power needed, the computer program may be executed in a single electronic digital processing unit or it may be distributed amongst a number of processing units.

The present invention is applicable to cellular or mobile communication systems defined above but also to other suitable communication systems. The protocols used, the specifications of cellular communication systems, their network elements, and terminal devices develop rapidly. Such development may require extra changes to the described embodiments. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its

embodiments are not limited to the examples described above but may vary within the scope of the claims. List of abbreviations

CIF carrier indicator field

DCI downlink control information

PDCCH physical downlink control channel

EPDCCH enhanced physical downlink control channel

UE user equipment

ID identifier

PCell primary cell

SCell secondary cell

5G 5^th generation

UL uplink

DL downlink

CCE control channel element

Claims

1 . A method comprising: determining, in a network node for a terminal device of a cellular communication system, a configuration for carrier aggregation with at least one serving cell configured to be scheduled by means of cross-carrier scheduling; determining, in the network node, a mapping between a serving cell index of the configured serving cell to be scheduled by means of cross-carrier scheduling and a scheduling cell-specific carrier indicator field value; causing, in the network node, transmission of a configuration message to the terminal device for the carrier aggregation, the configuration message comprising at least one information element indicating at least one cell to be scheduled by means of the cross- carrier scheduling: causing, in the network node, transmission of control information to the terminal device, the control information comprising a carrier indicator field, wherein the carrier indicator field value is based on said mapping between the serving cell index and the scheduling cell-specific carrier indicator field.

2. The method of claim 1 , wherein the mapping is based on a mapping rule wherein the serving cell indexes of the serving cells to be scheduled by means of cross carrier scheduling are mapped to the scheduling cell-specific carrier indicator field values in ascending or descending order.

3. The method of any preceding claim, wherein the mapping is transmitted to the terminal device in the configuration message.

4. The method of any preceding claim, wherein the configuration comprises more than eight serving cells for carrier aggregation.

5. The method of any preceding claim, wherein the number of cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is eight cells or less.

6. The method of any preceding claim, further comprising in the network node maintaining information on a predefined mapping rule for mapping between the serving cells and the scheduling cell-specific carrier indicator field value.

7. The method of any preceding claim, wherein the scheduling cell-specific carrier indicator field value is used for identifying the search space of the corresponding scheduled serving cell.

8. A method comprising: receiving, in a terminal device of a cellular communication system from a network node, a configuration message for carrier aggregation, the configuration message comprising at least one information element indicating at least one cell to be scheduled by means of cross-carrier scheduling; receiving, in the terminal device from the network node, control information, the control information comprising a carrier indicator field, wherein the carrier indicator field value is based on mapping between a serving cell index and a scheduling cell-specific carrier indicator field value.

9. The method of claim 8, wherein the mapping is based on a mapping rule wherein the serving cell indexes of the serving cells to be scheduled by means of cross carrier scheduling are mapped to the scheduling cell-specific carrier indicator field values in ascending or descending order.

10. The method of claim 8 or 9, wherein the mapping is transmitted to the terminal device in the configuration message.

1 1 . The method of any preceding claim 8 to1 0, further comprising in the terminal device maintaining information on a predefined mapping rule for mapping between the serving cells and the scheduling cell-specific carrier indicator field value.

12. The method of claim 1 1 , wherein the mapping rule indicates a mapping between the serving cell indexes of the cross-carrier scheduled cells, the corresponding scheduling cell identifiers and the corresponding carrier indicator field.

13. The method of any preceding claim 8 to 1 2, comprising a configuration of more than eight serving cells for carrier aggregation.

14. The method of any preceding claim 8 to 1 3, wherein the number of cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is eight cells or less.

15. The method of any preceding claim 8 to 14, wherein the scheduling cell-specific carrier indicator field value is used for identifying the search space of the corresponding scheduled serving cell.

16. An apparatus comprising: at least one processor; and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: determine for a terminal device of a cellular communication system, a configuration for carrier aggregation with at least one serving cell configured to be scheduled by means of cross-carrier scheduling; determine a mapping between a serving cell index of the configured serving cell to be scheduled by means of cross-carrier scheduling and a scheduling cell-specific carrier indicator field value; cause transmission of a configuration message to the terminal device for the carrier aggregation, the configuration message comprising at least one information element indicating at least one cell to be scheduled by means of the cross-carrier scheduling: cause transmission of control information to the terminal device, the control information comprising a carrier indicator field, wherein the carrier indicator field value is based on said mapping between the serving cell index and the scheduling cell-specific carrier indicator field.

17. The apparatus of claim 16, wherein the mapping is based on a mapping rule wherein the serving cell indexes of the serving cells to be scheduled by means of cross carrier scheduling are mapped to the scheduling cell-specific carrier indicator field values in ascending or descending order.

18. The apparatus of claim 16 or 17, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to transmit the mapping to the terminal device in the configuration message.

19. The apparatus of any preceding claim 16 to 18, wherein wherein the configuration comprises more than eight serving cells for carrier aggregation.

20. The apparatus of any preceding claim 16 to 19, wherein the number of cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is eight cells or less.

21 . The apparatus of any preceding claim 16 to 20, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to maintaining information on a predefined mapping rule for mapping between the serving cells and the scheduling cell-specific carrier indicator field value.

22. The apparatus of any preceding claim 1 6 to 21 , wherein the scheduling cell-specific carrier indicator field value is used for identifying the search space of the corresponding scheduled serving cell.

23. An apparatus comprising: at least one processor; and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to: receive from a network node, a configuration message for carrier aggregation the configuration message comprising at least one information element indicating at least one cell to be scheduled by means of cross-carrier scheduling; receive from the network node, control information, the control information comprising a carrier indicator field, wherein the carrier indicator field value is based on mapping between a serving cell index and a scheduling cell-specific carrier indicator field value.

24. The apparatus of claim 23, wherein the mapping is based on a mapping rule wherein the serving cell indexes of the serving cells to be scheduled by means of cross carrier scheduling are mapped to the scheduling cell-specific carrier indicator field values in ascending or descending order.

25. The apparatus of claim 23 or 24, wherein the mapping is transmitted to the terminal device in the configuration message.

26. The apparatus of any preceding claim 23 to 25, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to maintain information on a predefined mapping rule for mapping between the serving cells and the scheduling cell-specific carrier indicator field value.

27. The apparatus of claim 23 or 26, wherein the mapping rule indicates a mapping between the serving cell indexes of the cross-carrier scheduled cells, the corresponding scheduling cell identifiers and the corresponding carrier indicator field.

28. The apparatus of any preceding claim 23 to 27, wherein the number of cells to be scheduled from a single scheduling cell by means of the cross-carrier scheduling is eight cells or less.

29. The apparatus of any preceding claim 23 to 28, wherein the scheduling cell-specific carrier indicator field value is used for identifying the search space of the corresponding scheduled serving cell.

30. An apparatus comprising means for carrying out the steps of the method according to any preceding claim 1 to 1 5.

31 . A computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute the method according to any preceding claim 1 to 15.

32. A computer program product embodied on a non-transitory distribution medium readable by a computer and comprising program instructions which, when loaded into the computer, execute a computer process comprising any of the method steps of claims 1 to 15.