WO2016020013A1

WO2016020013A1 - Uplink prioritisation

Info

Publication number: WO2016020013A1
Application number: PCT/EP2014/067078
Authority: WO
Inventors: Benoist Pierre Sebire; Tero Henttonen
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2014-08-08
Filing date: 2014-08-08
Publication date: 2016-02-11

Abstract

A method is disclosed comprising defining (401), in a network node for a terminal device, a split bearer reconfiguration in a dual connectivity mode, The network node causes (402) transmission of a control message to the terminal device, the control message comprising at least one information element indicating the split bearer reconfiguration including a release of a secondary cell group SCG part of a split data radio bearer DRB for the terminal device. The network node determines (406) for the terminal device, a reconfigured prioritised bit rate PBR based on the prioritised bit rate of a logical channel corresponding to the split data radio bearer DRB.

Description

DESCRI PTION

TITLE

UPLINK PRIORITISATION TECHNICAL FIELD

The invention relates to the field of cellular communication systems and, particularly, uplink prioritisation. BACKGROUND

A communication system may be seen as a facility that enables communication sessions between two or more nodes such as fixed or mobile communication devices, access points such as nodes, base stations, servers, hosts, machine type servers, routers, and so on. A communication system and compatible communicating devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols may define the manner how communication devices communicate with the access points, how various aspects of the communications are implemented and how the devices and functionalities thereof are configured.

An example of cellular communication systems is an architecture that is being

standardized by the 3rd generation partnership project (3GPP). A recent development in this field is often referred to as the long-term evolution (LTE) or long-term evolution advanced (LTE advanced) of the universal mobile telecommunications system (UMTS) radio-access technology. In LTE, base stations providing the cells are commonly referred to as enhanced node-Bs (eNB). eNBs may provide coverage for an entire cell or similar radio service area.

BRIEF DESCRIPTION

The invention is defined by the independent claims. Embodiments are defined in the dependent claims.

Although the various aspects, embodiments and features of the invention are recited independently, it should be appreciated that all combinations of the various aspects, embodiments and features of the invention are possible and within the scope of the present invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 illustrates a wireless communication system to which embodiments of the invention may be applied;

Figure 2 illustrates user plane architectures in dual connectivity;

Figure 3 illustrates bearer types in dual connectivity; Figure 4 illustrates a signalling diagram of a procedure for uplink prioritisation according to an embodiment of the invention;

Figures 5 and 6 illustrate processes for uplink prioritisation according to an embodiment of the invention;

Figures 7 and 8 illustrate blocks diagrams of apparatuses according to some

embodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The following embodiments are exemplary. 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 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 102 arranged to provide terminal devices 104, 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 100 may be deployed to provide terminal devices 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.

In LTE, a radio bearer is the service access point at PDCP layer and a logical channel is the service access point at MAC layer. There is a one-to-one mapping between these two to guarantee one data path when processing packets trough the sub-layers of layer-2. In order to control how UE fills the uplink grants it receives from eNB, a prioritized bit rate (PBR) is configured per bearer, i.e. per logical channel (LCH). PBR ensures that high priority LCHs are scheduled first while avoiding starvation of lower priority LCHs. In other words, PBR guarantees QoS that the bearer experiences in uplink (uplink prioritisation). PBR is used by token bucket mechanisms in logical channel prioritisation (LCP) in MAC. Regarding small cell enhancements in 3GPP, in order to decrease signalling load towards the core network as well as benefiting from flexible resource usage across eNBs, dual connectivity (DC) has been investigated. In DC, UE is simultaneously connected to both a master eNB (MeNB) and a secondary eNB (SeNB). MeNB and SeNB are assumed to be connected to each other via an X2 interface. In DC, the X2 interface is a non-ideal backhaul link: transmission delays in the range of -20 ms may occur, and the bit rate is limited. Two different user plane architectures are to be supported: architectures 1 A and 3C as illustrated in Figure 2.

The cells from MeNB are defined as a master cell group (MCG), and the cells from SeNB as a secondary cell group (SCG). Architectures 1 A and 3C are realised by a different RRC configuration which leads to three different types of bearers: bearers served by MeNB alone = an MCG bearer - PDCP 1 , RLC 1 in Figure 3; bearers served by MeNB and SeNB = a split bearer - PDCP 2, RLC 2 in Figure 3; bearers served by SeNB alone = a SCG bearer - PDCP 3, RLC 3 in Figure 3.

The split bearer therefore refers to an ability to send PDCP PDUs to both MCG and SCG. While the support of the split bearer in downlink is currently agreed, the uplink direction is still being debated. Nonetheless, because two RLC entities are needed in the downlink anyway (one RLC entity for MeNB/MCG and one RLC entity for SeNB/SCG), two logical channels are required in both DL and UL (one for MeNB/MCG, and one RLC entity for SeNB/SCG) so that the RLC entities are able to communicate (for instance, to send status reports in uplink). Those logical channels are separately handled in the two MAC entities which are configured in DC: one for MCG and one for SCG.

For uplink prioritisation, the two LCP of the two MAC entities are kept independent: each uplink logical channel of the DL split bearer is configured with a separate PBR and is separately handled in LCP of the MAC entity to which it belongs.

When the split bearer is reconfigured into the MCG bearer, for instance, when SCG is removed, PBR to be used for the MCG bearer needs to be updated in order to maintain QoS of the bearer. This requires explicit reconfiguration of the whole data radio bearer (DRB), even though only some of the parameters require updating.

With independent MAC entities assumed for DC, logical channel prioritization runs per logical channel.

In MAC, the logical channel prioritization procedure is applied when a new transmission is performed. RRC controls the scheduling of uplink data by signalling for each logical channel: priority where an increasing priority value indicates a lower priority level, prioritisedBitRate which sets the prioritized bit rate (PBR), bucketSizeDuration which sets bucket size duration (BSD). UE maintains a variable Bj for each logical channel j. Bj is initialized to zero when the related logical channel is established, and incremented by a product PBR ^χ TTI duration for each TTI, where PBR is the prioritized bit rate of the logical channel j. However, the value of Bj never exceeds the bucket size and if the value of Bj is larger than the bucket size of logical channel j, it is set to the bucket size. The bucket size of the logical channel is equal to PBR ^χ BSD, where PBR and BSD are configured by upper layers. UE performs the following logical channel prioritization procedure when the new transmission is performed, wherein UE allocates resources to the logical channels in the following steps: Step 1 : the logical channels with Bj > 0 are allocated resources in a decreasing priority order. If PBR of the radio bearer is set to "infinity", UE allocates resources for the data that is available for transmission on the radio bearer before meeting PBR of the lower priority radio bearer(s). Step 2: UE decrements Bj by the total size of MAC SDUs served to the logical channel j in Step 1 . The value of Bj may also be negative. Step 3: if any resources remain, the logical channels are served in a strict decreasing priority order (regardless of the value of Bj) until either the data for that logical channel or the UL grant is exhausted, whichever occurs first. Logical channels configured with equal priority are served equally.

If it is relied that RRC reconfigures the MCG part of the split bearer every time in order to take into account the fact that the SCG part changes or disappears, while only PBR is likely to require an update, the logical channel prioritization seems too heavy a procedure to change one parameter. This also has no effect on the bucket value Bj.

Modern cellular communication systems are wideband systems where a large bandwidth may be scheduled to a single terminal device for the transmission of data. The scheduled resources may be indicated in terms of physical resource blocks or frequency resource blocks. Each frequency resource block has a determined bandwidth and a centre frequency and one or more frequency resource blocks may be scheduled to the terminal device at a time. The frequency resource blocks scheduled to the terminal device may be contiguous and, thus, form a continuous scheduled band for the terminal device. However, the resource blocks may be non-contiguous in which case the form a non-contiguous band fragmented into a plurality of smaller bands.

Let us now describe an embodiment of the invention for determining and signalling system frame number offset parameters with reference to Figure 4.

Figure 4 illustrates a signalling diagram illustrating a method for signalling uplink prioritisation parameters between a base station of a cellular communication system, e.g. base station 100 and 102, and a terminal device of the cellular communication system, e.g. the terminal device 104 or 106. In another embodiment, the procedure of Figure 4 may be carried out between the terminal device and an access node or, more generally, a network node. The network node may be 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. 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 4, the base station and/or the terminal device may perform following operations when the split bearer reconfiguration occurs. The base station decides on a split bearer reconfiguration (e.g. due to a SCG release) for the terminal device in a dual connectivity mode (block 401 ). The base station signals an RRC reconfiguration including the release of SCG part of a split DRB to the terminal device (step 402). The terminal device receives the reconfiguration including the release of the SCG part of the split DRB from the base station (block 403). The terminal device determines a new PBR for a (non- split) DRB, by combining PBR from the MCG and SCG part as the new PBR for the (non- split) DRB (block 404). The terminal device determines a sum of Bj values of the MCG and SCG parts of the split bearer as a new Bj value for the (non-split) DRB (block 405). The base station determines a new (i.e. reconfigured) PBR based a logical channel corresponding to the split data radio bearer DRB (block 406). The base station may consider that the new PBR is a combination of MCG and SCG PBR.

In an embodiment, the base station considers the combination of MCG and SCG PBR to be a sum of the PBR values.

In an embodiment, the base station considers the combination of MCG and SCG PBR to be the maximum of the PBR values.

In an embodiment, the base station considers the combination of MCG and SCG PBR to be a double of the MCG PBR value. In an embodiment, the terminal device combines PBR from the MCG and SCG part as the new PBR for the (non-split) DRB such that the combination is the sum of the PBR values.

In an embodiment, the terminal device combines PBR from the MCG and SCG part as the new PBR for the (non-split) DRB such that the combination is the maximum of the PBR values. In an embodiment, the terminal device combines PBR from the MCG and SCG part as the new PBR for the (non-split) DRB such that the combination is the double of the MCG PBR value.

In an embodiment, when one of the two components of the split bearer is removed (the MCG part or the SCG part), the corresponding PBR and the token bucket value are carried over to the remaining component. For instance, when the SCG part of the split bearer is removed, PBR of the logical channel of MCG is increased by PBR of the logical channel of SCG that disappears, and the bucket of the logical channel of MCG is increased by the bucket of the logical channel of SCG.

In an embodiment, a possible exception to the PBR principle described above may occur if PBR is set to infinity in one of the components to be removed, in which case PBR of the remaining component may remain the same, i.e. it is not changed. In an embodiment, QoS of the bearer is maintained during reconfiguration. Relying on rules instead of explicit signalling speeds up the reconfiguration and reduces overhead (having to reconfigure MAC of MCG just to update one PBR of one logical channel may be considered as a waste). In an embodiment, the RRC reconfiguration of SCG DRBs is defined by using a RRC reconfiguration procedure involving a DRB release procedure. The terminal device receives an RRC reconfiguration message that releases, for each drb-ldentity value included in a drb-ToReleaseList that is part of a current UE configuration (DRB release), or for each drb-identity value that is to be released as the result of a full configuration option, the PDCP entity, the RLC entity or entities, and the DTCH logical channel. For each drb-ldentity value included in the drb-ToReleaseList that is part of the split DRB (split DRB release), the terminal device combines the value of the prioritisedBitrate in the LogicalChannelConfig of the SCG DRB to the prioritisedBitrate in the

LogicalChannelConfig of the corresponding MCG DRB, and indicates to the MAC layer that Bj of the SCG part of the split DRB is to be added to Bj for the MCG part of the split DRB. If the procedure is triggered due to handover, the terminal device indicates the release of DRB(s) and the eps-Bearerldentity of the released DRB(s) to upper layers after a successful handover. Else the terminal device indicates the release of the DRB(s) and the eps-Bearerldentity of the released DRB(s) to the upper layers immediately. UE does not consider the message as erroneous if the drb-ToReleaseList includes any drb-ldentity value that is not part of the current UE configuration.

In an embodiment, the RRC reconfiguration of SCG DRBs is de-fined using a RRC reconfiguration involving a DRB modification procedure. When the terminal device receives an RRC reconfiguration message that modifies, for each drb-ldentity value included in a drb-ToAddModl_ist that is part of a current UE configuration (DRB

modification). For each drb-ldentity value included in the drb-ToAddModl_ist that is part of the split DRB and is to be released to only MCG DRB (split DRB release), the terminal device combines the value of the prioritisedBitrate in the LogicalChannelConfig of the SCG DRB to the prioritisedBitrate in the LogicalChannelConfig of the corresponding MCG DRB, and indicates to the MAC layer that Bj of the SCG part of the split DRB is to be added to Bj for the MCG part of the split DRB. If the procedure is triggered due to handover, the terminal device indicates the release of DRB(s) and the eps-Bearerldentity of the released DRB(s) to upper layers after a successful handover.

In an embodiment, the combining of the PBR values may be done in different ways, including e.g. summing MCG and SCG PBRs and round the result up to the next allowed value. For example, in case PBR=64kbps for MCG and PBR=32 kbps for SCG, the sum is 96 kbps but the next rounded-up value is PBR=128 kbps. If either value is "infinity", the new value is also "infinity" (since the sum also returns "infinity") or the new value is set to the 2nd value that is not infinity.

In an embodiment, the combining of the PBR values is done e.g. by the maximum of MCG and SCG PBRs becoming the new PBR. This saves signalling in case SCG PBR is larger than MCG PBR.

In an embodiment, the combining of the PBR values is done e.g. by doubling MCG PBR and by rounding up the result. This operates on an assumption that DRB is split evenly between MCG and SCG. In an embodiment, for the Bj value, the MCG and SCG parts are summed up since they depict the situation at UE.

Let us now describe some embodiments with reference to Figures 5-6.

Referring to Figure 5, the base station may perform following operations when the split bearer reconfiguration occurs. The base station decides on a split bearer reconfiguration (e.g. due to a SCG release) for the terminal device in a dual connectivity mode (block 501 ). The base station signals an RRC reconfiguration including the release of SCG part of a split DRB to the terminal device (block 502). The base station determines a new PBR by considering that the new PBR is a combination of MCG and SCG PBR (block 503).

Referring to Figure 6, the terminal device may perform following operations when the split bearer reconfiguration occurs. The terminal device acquires the RRC reconfiguration including the release of the SCG part of the split DRB from the base station (block 601 ). The terminal device determines a new PBR for a (non-split) DRB, by combining PBR from the MCG and SCG part as the new PBR for the (non-split) DRB (block 602). The terminal device determines a sum of Bj values of the MCG and SCG parts of the split bearer as a new Bj value for the (non-split) DRB (block 603).

In an embodiment, the embodiments of Figures 5 to 6 may be combined. In a

modification, the processes of any of Figures 5 to 6 may be exclusive to small area cell base stations, e.g. the base station 100 may carry out the embodiments of Figure 4 to 6 but the macro base station 102 may not. 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 7 illustrates a block diagram of a structure of such an apparatus. The apparatus may be comprised in the base station or the network node, e.g. the apparatus may form a chipset or a circuitry in the base station or 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 an PBR determination circuitry 16 configured to determine, a prioritised bit rate for the terminal device. A split bearer reconfiguration selector 18 may be configured to define for the terminal device a split bearer reconfiguration in a dual connectivity mode. Upon determining the split bearer reconfiguration, the split bearer reconfiguration selector 18 may output a signal indicating the split bearer reconfiguration to a control message generator 12 configured to generate the control message indicating the determined split bearer reconfiguration to the terminal device for which the split bearer reconfiguration is determined.

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 further store a database 26 comprising definitions for the selection of the link adaptation scheme, 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 the transmitter and/or the receiver, as described above in connection with Figures 1 to 6. 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 22 may carry out only some of radio frequency signal processing or no radio frequency signal processing at all. The connection between the communication interface 22 and the remote radio head may be an analogue connection or a digital connection. 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 8 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 communication controller circuitry 54 configured to extract control messages received from a serving base station, to acquire the split bearer reconfiguration determined for the terminal device, and to control the terminal device to transmit or receive data between the base station in the scheduled communication resources. The apparatus may further comprise a PBR determination circuitry 52 configured to determine a reconfigured prioritised bit rate PBR for a non-split data radio bearer, based on the prioritised bit rate of a master cell group MCG and the prioritised bit rate of a secondary cell group SCG. The apparatus may further comprise a Bj determination circuitry 56 configured to determine reconfigured Bj value for the non-split data radio bearer, based on a Bj value of a master cell group MCG and optionally a Bj value of a secondary cell group SCG. The processing circuitry 50 may comprise the circuitries 52, 54, 56 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 the transmitter and/or the receiver, as described above in connection with Figures 1 to 7.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardware- only circuit implementations such as implementations in only analogue 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 processes or methods described above in connection with Figures 1 to 8 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 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

DC dual connectivity

LCP logical channel prioritisation

MeNB master eNB

MCG master cell group

PBR prioritised bit rate

SeNB secondary eNB

SCG secondary cell group

UE user equipment

Bj the number of tokens in the bucket of a logical channel j

Claims

1 . A method comprising: defining, in a network node for a terminal device of a cellular communication system, a split bearer reconfiguration in a dual connectivity mode; causing, in the network node, transmission of a control message to the terminal device, the control message comprising at least one information element indicating the split bearer reconfiguration including a release of a secondary cell group SCG part of a split data radio bearer DRB for the terminal device; determining, in the network node for the terminal device, a reconfigured prioritised bit rate PBR based on the prioritised bit rate of a logical channel corresponding to the split data radio bearer DRB.

2. A method comprising: acquiring, in a terminal device of a cellular communication system, a control message from a network node, the control message comprising at least one information element indicating a split bearer reconfiguration including a release of a secondary cell group SCG part of a split data radio bearer DRB for the terminal device; determining, in the terminal device, a reconfigured prioritised bit rate PBR for a non-split data radio bearer, based on the prioritised bit rate of a master cell group MCG and the prioritised bit rate of a secondary cell group SCG; determining, in the terminal device, a reconfigured Bj value for the non-split data radio bearer, based on a Bj value of a master cell group MCG and optionally a Bj value of a secondary cell group SCG.

3. The method of claims 1 or 2, wherein the reconfigured prioritised bit rate PBR is determined as a combination of the prioritised bit rate of the master cell group MCG and the prioritised bit rate of the secondary cell group SCG, wherein the combination is a sum of a prioritised bit rate value of the master cell group MCG and a prioritised bit rate value of the secondary cell group SCG.

4. The method of claim 1 or 2, wherein if the prioritised bit rate PBR is set to infinity in the MCG part or the SCG part of the split data radio bearer, the prioritised bit rate PBR of the remaining component remains the same.

5. The method of claim 1 or 2, wherein the reconfigured prioritised bit rate PBR is determined as a combination of the prioritised bit rate of the master cell group MCG and the prioritised bit rate of the secondary cell group SCG, wherein the combination is a maximum of a prioritised bit rate value of the master cell group MCG and a prioritised bit rate value of the secondary cell group SCG.

6. The method of claim 1 or 2, wherein the reconfigured prioritised bit rate PBR is determined as a double of a prioritised bit rate value of the master cell group MCG.

7. The method of any of claims 1 -6, wherein if the MCG part or the SCG part of the split bearer is removed, the corresponding prioritised bit rate PBR and token bucket value are added to the remaining component.

8. The method of any of claims 1 -7, wherein if the SCG part of the split bearer is removed, the prioritised bit rate PBR of the logical channel of MCG is increased by the prioritised bit rate PBR of the logical channel of SCG, and the token bucket value of the logical channel of MCG is increased by the token bucket value of the logical channel of SCG.

9. 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: define, for a terminal device, a split bearer reconfiguration in a dual connectivity mode; cause transmission of a control message to the terminal device, the control message comprising at least one information element indicating the split bearer reconfiguration including a release of a secondary cell group SCG part of a split data radio bearer DRB for the terminal device; determine, for the terminal device, a reconfigured prioritised bit rate PBR based on the prioritised bit rate of a logical channel corresponding to the split data radio bearer DRB.

10. 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: acquire from a network node, a control message comprising at least one information element indicating a split bearer reconfiguration including a release of a secondary cell group SCG part of a split data radio bearer DRB for a terminal device; determine a reconfigured prioritised bit rate PBR for a non-split data radio bearer, based on the prioritised bit rate of a master cell group MCG and the prioritised bit rate of a secondary cell group SCG; determine a reconfigured Bj value for the non-split data radio bearer, based on a Bj value of a master cell group MCG and optionally a Bj value of a secondary cell group SCG.

1 1 . The apparatus of claim 9 or 10, 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 the reconfigured prioritised bit rate PBR as a combination of the prioritised bit rate of the master cell group MCG and the prioritised bit rate of the secondary cell group SCG, wherein the combination is a sum of a prioritised bit rate value of the master cell group MCG and a prioritised bit rate value of the secondary cell group SCG.

12. The apparatus of claim 9 or 10, wherein if the prioritised bit rate PBR is set to infinity in the MCG part or the SCG part of the split data radio bearer, the prioritised bit rate PBR of the remaining component remains the same.

13. The apparatus of claim 9 or 10, 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 the reconfigured prioritised bit rate PBR as a combination of the prioritised bit rate of the master cell group MCG and the prioritised bit rate of the secondary cell group SCG, wherein the combination is a maximum of a prioritised bit rate value of the master cell group MCG and a prioritised bit rate value of the secondary cell group SCG.

14. The apparatus of claim 9 or 10, 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 the reconfigured prioritised bit rate PBR as a double of a prioritised bit rate value of the master cell group MCG.

15. The apparatus of any of claims 9-14, wherein if the MCG part or the SCG part of the split bearer is removed, the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to add the corresponding prioritised bit rate PBR and token bucket value to the remaining component.

16. The method of any of claims 9-15, wherein if the SCG part of the split bearer is removed, the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to increase the prioritised bit rate PBR of the logical channel of MCG by the prioritised bit rate PBR of the logical channel of SCG, and increase the token bucket value of the logical channel of MCG by the token bucket value of the logical channel of SCG.

17. 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: the method steps of any preceding claim 1 to 8.