Small data transmission

Abstract

In accordance with an example aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions, the instructions, when executed by the at least one processing core, cause the apparatus to at least: determine that a small data transmission (SDT) procedure with a user equipment in a radio resource control inactive state is ongoing, and send assistance information to a control plane entity of a centralized unit of the base station.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to wireless communication. BACKGROUND

[0002] A user equipment, UE, of a cellular communication network can be in one of a number of possible radio resource control, RRC, states, depending on how active the UE is in communicating with the network.

[0003] Switching from one RRC state to another involves some signaling in the network, in particular between a base station and the UE. For example, when the UE is in an idle state, it can request a switch to a connected state by sending a request using a random access procedure. SUMMARY

[0004] According to some aspects, the subject matter of the independent claims is provided. Some embodiments are defined in the dependent claims. The independent claims define the scope of the various embodiments of the invention for which protection is sought. Embodiments and features described in the present specification that are not part of the independent claims, if any, are to be interpreted as examples useful for understanding the various embodiments of the invention.

[0005] According to a first aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to determine that a small data transmission, SDT, procedure is ongoing with a user equipment in a radio resource control inactive state, and to send assistance information to a control plane entity of a centralized unit of a base station.

[0006] According to a second aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to, in a control plane entity for a centralized unit of a base station, receive, from a radio access node, assistance information for an ongoing small data transmission, SDT, procedure with a user equipment, UE, the base station comprising the centralized unit and a distributed unit, and to determine, based at least partly on the received assistance information, whether to switch a radio resource control, RRC, state of the UE.

[0007] According to a third aspect of the present disclosure, there is provided a method comprising determining that a small data transmission, SDT, procedure is ongoing with a user equipment in a radio resource control inactive state, and sending assistance information to a control plane entity of a centralized unit of a base station.

[0008] According to a fourth aspect of the disclosure, there is provided a method comprising, in a control plane entity of a centralized unit of a base station, receiving assistance information from a radio access node for an ongoing small data transmission, SDT, procedure with a user equipment, UE, the base station comprising the centralized unit and a distributed unit, and determining, based at least in part on the received assistance information, whether to switch a radio resource control, RRC, state of the UE.

[0009] According to a fifth aspect of the disclosure, there is provided an apparatus comprising means for: determining that a small data transmission, SDT, procedure with a user equipment in a radio resource control inactive state is ongoing, and sending assistance information to a control plane entity of a centralized unit of a base station.

[0010] According to a sixth aspect of the disclosure, there is provided an apparatus comprising means for: in a control plane entity of a centralized unit of a base station, receiving assistance information from a radio access node for an ongoing small data transmission, SDT, procedure with a user equipment, UE, the base station comprising the centralized unit and a distributed unit, and determining, based at least in part on the received assistance information, whether to switch a radio resource control, RRC, state of the UE.

[0011] According to a seventh aspect of the disclosure, there is provided a non-transitory computer readable medium having stored thereon a computer readable instruction set that, when executed by at least one processor, causes an apparatus to at least: determine that a small data transmission, SDT, procedure with a user equipment in a radio resource control inactive state is ongoing, and send assistance information to a control plane entity of a centralized unit of a base station.

[0012] According to an eighth aspect of the disclosure, there is provided a non-transitory computer readable medium having stored thereon a computer readable instruction set that, when executed by at least one processor, causes an apparatus to at least: in a control plane entity of a centralized unit of a base station, receive assistance information from a radio access node for an ongoing small data transmission, SDT, procedure with a user equipment, UE, the base station comprising the centralized unit and a distributed unit, and determine, based at least in part on the received assistance information, whether to switch a radio resource control, RRC, state of the UE. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 Figures illustrate example systems according to at least some embodiments;

[0014] Figure 2 Figures illustrate signaling examples according to at least some embodiments;

[0015] Figure 3 Figures illustrate signaling examples according to at least some embodiments;

[0016] Figure 4 Figure illustrates a signaling example according to at least some embodiments;

[0017] Figure 5 Figure illustrates an example apparatus capable of supporting at least some embodiments, and

[0018] Figure 6 is a flowchart of a method according to at least some embodiments. DETAILED DESCRIPTION

[0019] Disclosed herein are methods of facilitating data transmission in a case where a user equipment is in a radio resource control, RRC, inactive state and has an active data transmission context, such as a small data transmission, SDT. Small data transmission or small data transmission context is one example of a data transmission context. To avoid losing data when a data transmission context, such as an SDT, expires, the UE can be switched to an RRC active state to send data from at least one buffer. Additionally or alternatively, the UE can be switched to an RRC active state to send data if the amount of data in the buffer exceeds a data amount threshold. This can occur if the amount of data is large enough to warrant an RRC active state, rather than using an SDT in an RRC inactive state.

[0020] Figure 1 Figure illustrates an example system according to at least some embodiments. A base station 110 controls at least one cell of a cellular communications system. The base station 110 is connected with a node 140, which can comprise, for example, a core network node or a radio access network controller. Examples of suitable core network nodes include an access and mobility management function, AMF, and a mobility management entity, MME. The core network node can be a physical and / or a logical node.

[0021] The base station 110 can be a single base station or a distributed base station. A distributed base station comprises a central unit, CU, and one or more distributed units, DUs. The DUs are equipped with radio parts and can handle, for example, radio link control, RLC, and medium access control, MAC, functions, while the CU can be configured to handle radio resource control, RRC, and packet data convergence protocol, PDCP, functions. In a realistic physical network, the number of base stations can be hundreds, or even thousands, rather than Figure 1A CU can have a number of logical nodes, as shown. A CU can also have a logical node CU-UP for handling the user plane and a logical node CU-CP for handling the control plane. The CU-UP and the CU-CP can run on the same physical computing substrate, for example, or on separate computing substrates. For example, the CU-CP can be configured to run the control plane part of the RRC, and the control plane part of the PDCP protocol, while the CU-UP can be configured to run the user plane part of the PDCP protocol and the service data adaptation protocol, SDAP. In a network based on the Third Generation Partnership Project, 3GPP, standards, the E1 interface can connect the CP-CP to the CP-UP, while the F1-C interface can connect the CP-CP to the DU(s).

[0022] The UEs 120, 130 are in contact with the base station 110 at least intermittently via radio links 112 and 113, respectively. For example, the UE 120 can be in an RRC_Inactive state in which the base station 110 does not provide the UE with reserved radio interface resources, and both the UE 120 and the base station 110 store a UE context for the UE 120, e.g. an access stratum, AS, context for the UE 120. Storing the UE context can enable faster transition to an RRC_Connected state. In an active RRC state, such as RRC_Connected, the UE is provided with reserved radio interface resources. In the RRC_Inactive state, the RRC connection between the UE and the base station is suspended, while in the RRC_Idle state, there is no RRC connection between the base station and the UE, and no UE context is stored in the base station for the UE. In the RRC_Idle state, the UE is not registered in a particular cell, and has no reserved radio interface resources. The UE 130 can be in an RRC_Connected state, e.g. if it is in the middle of a data transfer session with a peer node via the base station 110.

[0023] The UE 120 in the RRC_Inactive state can have an ongoing data transfer context, such as a small data transfer, SDT. Hereinafter, the SDT will be used as an example of a data transfer context. The SDT is a framework that can be used to transfer small amounts of, e.g. mobile originated, user plane data between the UE and the network without the need to switch the UE to an RRC active state, such as RRC_Connected. The data transfer of the SDT can be conducted using, e.g. random access and / or uplink configured grant procedures, while keeping the UE in the RRC_Inactive state. Keeping the UE in the RRC_Inactive state is efficient in terms of signaling, as switching to the RRC_Connected state and then switching back to the RRC_Inactive would involve a large amount of signaling with the base station.

[0024] For example, an ongoing SDT can end by the UE transitioning to the RRC_Idle state after the purpose of the SDT has been achieved. After the SDT expires, the UE can also stay in the RRC_Inactive state. Further, the SDT can end if the SDT timer expires. In response to the SDT timer expiring, the UE can switch to the RRC_Idle state.

[0025] However, the SDT or more generally the data transmission context also comes with some challenges. From a radio capacity perspective, the RRC_Inactive state with SDT uplink and / or downlink transmission is not optimized for transmitting large amounts of data, as in the RRC_Inactive state no channel quality information, CQI, beam, sounding reference signal, SRS, and other typical reporting of the RRC_Connected state is used between the UE and the base station. Further, in the RRC_Inactive state, the UE energy usage is not optimal, as the UE can need to continuously monitor the physical downlink control channel, PDCCH, for possible downlink SDT transmission during the SDT procedure. Thus, the base station cannot optimally estimate the radio link quality for the UE, which has a negative impact on the modulation and coding used. Therefore, for data transmission, in the SDT, a lower modulation coding scheme and more physical radio resource blocks can be used compared to communicating in the RRC_Connected mode to avoid a large number of retransmissions in the SDT. Further, due to supporting better link adaptation procedures, such as channel state information, CSI, reporting, scheduling in the RRC_Connected mode is more efficient for large amounts of data than in the SDT.

[0026] Therefore, if a relatively large amount of data is to be transmitted using the SDT, it can be more useful to do this in the RRC_Connected state even considering the signaling needed to switch the UE to the RRC_Connected state.

[0027] Further, if the SDT expires and there is still data to be transmitted in at least one uplink or downlink buffer, this data can be discarded when the UE switches to the RRC_Idle state. For example, there can be data in the uplink buffer in the UE and / or in the downlink buffer in the base station. For example, the SDT can expire when the SDT timer expires. Such a timer can be initialized to an initial value when the SDT starts.

[0028] To overcome such challenges, procedures are disclosed herein for switching a UE from an RRC_Inactive state to an active state, such as an RRC_Connected state, in response to one or more determinations. First, it can be determined that, during an SDT procedure, the amount of data to be transmitted during the SDT procedure exceeds a data amount threshold. The data amount threshold can be expressed in terms of an amount of data, such as in kilobytes or megabytes, or in terms of a number of bits. In response to the amount of data in a transmit buffer in the UE and / or base station exceeding the data amount threshold while the UE is in the SDT, the UE can be triggered to switch to an RRC active state, as will be discussed in greater detail below. Second, as an alternative or in addition to the determination based on the amount of data to be transmitted, it can be determined that, during the SDT procedure, the remaining length of time of the duration of the SDT procedure is less than a threshold duration, and there is still data to be transmitted in the uplink or downlink during the SDT procedure.

[0029] Figure 2 A signaling example is illustrated in accordance with at least some embodiments. A UE 120 and a base station 110 are provided on a vertical axis, with the same numbering denoting the same structures as in Figure 1

[0030] Phase 201 represents an ongoing SDT between the UE 120 and the base station 110, with the UE in an RRC_Inactive state. The SDT can be a mobile originated or mobile terminated SDT. During this SDT context, the UE provides data amounts 210 and 220 to the base station 110. However, in phase 230, the base station determines that the UE 110 should switch to an RRC_Connected state, and phase 240 represents the triggering of an RRC state switch from RRC_Inactive to RRC_Connected. The signaling procedures related to the switching of the UE 120 from RRC_Inactive to RRC_Connected are schematically represented as phase 250, after which the UE is in an RRC_Connected state, and the SDT 201 ends. In phase 260, communication between the UE and the base station occurs in the RRC_Connected state. The determination of phase 230 can be based on the amount of data to be transmitted during the SDT procedure, or the SDT timer is close to expiring and there is still data to be transmitted, for example.

[0031] ​In relation to the end of the SDT 201, data in the buffer related to the SDT transmission is kept, rather than discarded. Such data can be transferred in phase 260. In case the base station is distributed, in phase 230, the DU or CU-UP can determine that the RRC_Connected state is more appropriate. The DU or CU-UP can then inform the CU-CP of this, and the CU-CP can trigger the message of phase 240. In case the base station is not distributed, the CU-CP can determine that the RRC_Connected state is more appropriate, and can trigger the message of phase 240. Figure 2 In one variant of embodiments, each time the DU receives a buffer status report, BSR, from the UE 120, the DU informs the CU-CP of the UL data volume. Alternatively, the CU-CP can perform the determination of phase 230. In general, the DU and / or CU-UP can be configured to provide assistance information to the CU-CP, which the CU-CP can base on in deciding in phase 230 that the RRC_Connected state is preferred. The assistance information can be, for example, at least one buffer status report (indicating UL data volume), a downlink data volume, or an indication that the data volume (UL and / or DL) exceeds a data volume threshold, or an indication that the SDT timer is about to expire and there is still data to send. The message of phase 240 is a message about switching the user equipment to a radio resource control active state, such as the RRC Connected state.

[0032] Figure 3 Figures illustrate signaling examples according to at least some embodiments. On the vertical axis, the UE 120 is on the left side and the base station 110 is on the right side, where the same numbering denotes the same structures as in Figure 2 Figure 3 The base station of is distributed, comprising a DU, a CU-CP and a CU-UP, as described above.

[0033] As in the case of Figure 2 There is an active SDT 201. Initially, in phase 310, SDT data transmission occurs in the SDT context 201, as in conjunction with Figure 2 ​The DU determines, in stage 320, that the amount of data to be transmitted in the SDT exceeds a data volume threshold and / or that the remaining length of time of the duration of the SDT is less than a threshold duration while there is still data to be transmitted using the SDT. In other words, the DU can perform a determination based on the amount of data or a determination based on the timer and the presence of data to be transmitted. Stage 320 can include determining to send assistance information to the CU-CP as a response to the determination based on the amount of data or the determination based on the timer and the presence of data to be transmitted. The determination that the amount of data to be transmitted over the SDT exceeds the data volume threshold can be based at least in part on, for example, a buffer status report, BSR, from the UE or on the DL data volume buffer(s). The determination based on the amount of data can be based on a cumulative data threshold across all logical channel groups, LCGs, in the buffer status report, BSR, or on separate LCG-specific data volume thresholds, that is, if the buffer status indicated for a particular LCG exceeds a threshold level, the DU can determine that the amount of data exceeds at least one data volume threshold.

[0034] For example, the indication of the data volume threshold or the threshold duration can be provided from the CU-CP to the DU. The CU-CP can use the FlAP UE Context Setup Request or UE Context Modification Request message to indicate the data volume threshold or the threshold duration to the DU. Alternatively, the data volume threshold or the threshold duration can be configured in the DU from an operations and maintenance system. Further, the data volume threshold or the threshold duration can be one or more constant thresholds specified at the time of manufacture of the DU. Further, the initial value of the SDT timer can be indicated to the DU from the CU-CP, an operations and maintenance system, or as a constant specified at the time of manufacture, for example, as described above for the data volume threshold and the threshold duration. The SDT timer can be referred to as the SDT Maximum Duration, SMD, timer.

[0035] In stage 330, the DU signals to the CU-CP to indicate the result of the determination of stage 320 and / or that the switching of the UE 120 to an active RRC state, such as RRC_Connected, would be appropriate. The signal of stage 330 can indicate that the SMD (SDT Maximum Duration) timer is approaching expiration and there is still data to be transmitted through the SDT procedure, or the message of stage 330 can indicate that the amount of data to be transmitted over the SDT 201 exceeds the data volume threshold. The message of stage 330 can be, for example, a FlAP UE Context Modification Required message. In the case that the determination is based on the amount of data, the message of stage 330 can inform the CU-CP that the sum of all UL data reported in the BSR exceeds the data volume threshold, or it can inform that the UL data of one particular LCG exceeds the data volume threshold as reported by the UE.

[0036] In stage 340, in response to stage 330, the CU-CP determines that UE 120 is to be handed over to the RRC_Connected state, and in stage 350, a signal to trigger this change is sent to the DU. The message of stage 350 can be, for example, a UE Context Modification Confirm message including an RRC resume. As part of the base station 110 that is in wireless communication with UE 120, the DU reacts in stage 360 by transmitting an RRC resume message to the UE, which results in RRC procedure 370 handing over UE 120 to the RRC_Connected state and ending SDT 201. The messages of stages 330, 350, and 360 are messages regarding handover of the user equipment to a radio resource control active state. The message of stage 330 includes the assistance information. The DU can be configured to generate the assistance information.

[0037] After the end of SDT 201, in stage 380, UE 120 and base station 110 can communicate in the RRC_Connected mode. For example, data that was in at least one SDT transmission buffer in stage 320 can be transmitted in stage 380. In the case of a determination in stage 320 based on the SDT timer, this provides the benefit that the data is successfully transmitted rather than being discarded upon expiration of the SDT timer. Alternatively, if the determination of stage 320 is based on the amount of data to be transmitted, the benefit can be obtained that less energy is used to effect transmission of the data, as described above.

[0038] Figure 4 Signaling is illustrated in accordance with at least some embodiments. On the vertical axis, UE 120 is on the left and base station 110 is on the right, with the same numbering as in Figure 2 and Figure 3 denotes the same structure. Figure 4 The base station of

[0039] As in Figure 2 and Figure 3As in the case of FIG. 4, there is an active SDT 201. Initially, at stage 410, SDT data transmission occurs in the SDT context 201. In stage 420, the CU-UP determines that the amount of data to be transmitted through the SDT procedure exceeds a data volume threshold and / or the remaining length of time of the duration of the SDT procedure is less than a threshold duration while there is still data to be transmitted using the SDT. In other words, the CU-UP can perform a determination based on the amount of data or a determination based on the timer and the presence of data to be transmitted. The determination that the amount of data to be transmitted through the SDT exceeds the data volume threshold can be based on, for example, the status of data buffers in the CU-UP. The CU-UP buffer status can be related to downlink data. Stage 420 can include determining to send assistance information to the CU-CP in response to the determination based on the amount of data or in response to the determination based on the timer and the presence of data to be transmitted. The CU-UP can be configured to generate the assistance information. The data volume threshold can be related to the sum of UL and DL data in all buffers of the SDT bearer or it can be related to the UL and DL data of the buffer of one particular SDT bearer, such that the CU-UP determines that the amount of data to be transmitted through the SDT procedure exceeds the threshold if at least one of the UL and DL data buffer status to be transmitted exceeds the data volume threshold.

[0040] For example, the data volume threshold or the threshold duration can be provided from the CU-CP to the CU-UP. For example, the CU-CP can indicate the data volume threshold or the threshold duration to the CP-UP using an El AP Bearer Context Setup Request or an El AP Bearer Context Modification Request message. Alternatively, the data volume threshold or the threshold duration can be configured in the CU-UP from an operations and maintenance system. Further, the data volume threshold or the threshold duration can be one or more constant thresholds specified at manufacture of the CU-UP. Further, the initial value of the SDT timer can be indicated to the CU-UP from the CU-CP, an operations and maintenance system, or as a constant specified at manufacture, for example, as described above for the data volume threshold and the threshold duration. The SDT timer can be referred to as an SDT Maximum Duration, SMD, timer.

[0041] In stage 430, the CU-UP signals to the CU-CP to indicate the result of the determination of stage 420 and / or that a switch of the UE 120 to an active RRC state, such as RRC_Connected, would be appropriate. The signal of stage 430 can indicate that the SMD timer is approaching expiration and there is still data to be transmitted through the SDT or the message of stage 430 can indicate that the amount of data to be transmitted through the SDT 201 exceeds the data volume threshold. The message of stage 430 can be, for example, an El AP DL Data Notification message.

[0042] In stage 440, in response to stage 430, the CU-CP determines to handover the UE 120 to the RRC_Connected stage. Subsequent stages 450-480 correspond to stages 350-380 of Figure 3 . The messages of stages 430, 450, and 460 are messages regarding handover of the user equipment to the radio resource control active state. The message of stage 430 includes assistance information.

[0043] Figure 5 An example apparatus capable of supporting at least some embodiments is illustrated. Illustrated is a device 500, which can comprise, for example, a base station, a DU, or a CU. Included in the device 500 is a processor 510, which can comprise, for example, a single-core or multi-core processor, where a single-core processor includes one processing core and a multi-core processor includes more than one processing core. The processor 510 can generally include control of the device. The processor 510 can comprise more than one processor. When the processor 510 comprises more than one processor, the device 500 can be a distributed device, where processing of tasks occurs in more than one physical unit. The processor 510 can be a control device. For example, a processing core can comprise, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Zen processing core designed by Advanced Micro Devices Corporation. The processor 510 can comprise at least one Qualcomm Snapdragon and / or Intel Atom processor. The processor 510 can comprise at least one application-specific integrated circuit ASIC. The processor 510 can comprise at least one field-programmable gate array FPGA. The processor 510 can be a means for performing method steps in the device 500, such as determining, triggering, performing, receiving, sending, and communicating. The processor 510 can be configured, at least in part, by computer instructions to perform actions.

[0044] The processor can comprise circuitry, or be structured as one or more circuitries, configured to perform the stages of the method according to embodiments described herein. As used in this application, the term “circuitry” can refer to one or more or all of: (a) hardware-only circuitry such as only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as: (i) combinations of analog and / or digital hardware circuit(s) with software / firmware, as applicable, (ii) portions of hardware processor(s) with software, software, and memory(ies) that work together to cause an apparatus, such as a base station, a DU, or a CU, to perform various functions described herein, and (c) hardware circuit(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but software that can not be present when it is not needed for operation.

[0045] This definition of circuitry applies to all uses of this term in this application, including in any claims. As another example, as used in this application, the term circuitry also encompasses implementations of only hardware circuitry or a processor (or processors) or a portion of a hardware circuitry or processor with its accompanying software and / or firmware. For example, if applicable to a particular claim element, the term circuitry also encompasses a baseband integrated circuit or processor integrated circuit for a mobile device, or a similar integrated circuit in a server, cellular network device, or other computing or network device.

[0046] The device 500 can comprise a memory 520. The memory 520 can comprise a random access memory and / or a persistent memory. The memory 520 can comprise at least one RAM chip. The memory 520 can comprise, for example, solid-state, magnetic, optical, and / or holographic memory. The memory 520 can be at least partially accessible to the processor 510. The memory 520 can be at least partially included in the processor 510. The memory 520 can be a component for storing information. The memory 520 can comprise computer instructions that the processor 510 is configured to execute. When computer instructions configured to cause the processor 510 to perform certain actions are stored in the memory 520, and the device 500 as a whole is configured to run using the computer instructions from the memory 520 under the direction of the processor 510, the processor 510 and / or at least one processing core thereof can be seen as configured to perform the certain actions described above. The memory 520 can be at least partially included in the processor 510. The memory 520 can be at least partially located outside the device 500, but accessible to the device 500. The memory 520 can be non-transitory. The term “non-transitory” as used herein is a limitation on the medium itself (i.e., tangible, rather than a signal) and not a limitation on the durability of the data storage (e.g., RAM versus ROM).

[0047] The device 500 can comprise a transmitter 530. The device 500 can comprise a receiver 540. The transmitter 530 and the receiver 540 can be configured to transmit and receive information, respectively, according to at least one cellular or non-cellular standard. The transmitter 530 can comprise more than one transmitter. The receiver 540 can comprise more than one receiver. The transmitter 530 and / or the receiver 540 can be configured to operate according to Global System for Mobile Communications, GSM, Wideband Code Division Multiple Access, WCDMA, 5G, 6G, Long Term Evolution, LTE, IS-95, Wireless Local Area Network, WLAN, Ethernet, and / or Worldwide Interoperability for Microwave Access, WiMAX, standards, among others.

[0048] The device 500 can comprise a user interface, UI, 560. The UI 560 can comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing the device 500 to vibrate, a loudspeaker, and a microphone. A user can be able to operate the device 500 via the UI 560, for example, to configure communication context parameters or thresholds.

[0049] The processor 510 can be provided with a transmitter arranged to output information from the processor 510 to other devices comprised in the device 500 via electrical leads inside the device 500. Such a transmitter can comprise a serial bus transmitter arranged to output information, e.g. to the memory 520 for storage therein, via at least one electrical lead. As an alternative to a serial bus, the transmitter can comprise a parallel bus transmitter. Likewise, the processor 510 can comprise a receiver arranged to receive information in the processor 510 from other devices comprised in the device 500 via electrical leads inside the device 500. Such a receiver can comprise a serial bus receiver arranged to receive information, e.g. from the receiver 540, via at least one electrical lead, for processing in the processor 510. As an alternative to a serial bus, the receiver can comprise a parallel bus receiver.

[0050] The device 500 can comprise other devices not shown in the figure. In some embodiments, the device 500 lacks at least one of the above-described devices. Figure 5 The device 500 can comprise other devices not shown in the figure. In some embodiments, the device 500 lacks at least one of the above-described devices.

[0051] The processor 510, the memory 520, the transmitter 530, the receiver 540 and / or the UI 560 can be interconnected in various different ways by electrical leads inside the device 500. For example, each of the above-described devices can be individually connected to a main bus inside the device 500 to allow the devices to exchange information. However, the skilled person will understand that this is only one example and that various ways of interconnecting at least two of the above-described devices can be chosen according to the embodiment without leaving the scope of the invention.

[0052] Figure 6 is a flowchart of a method according to at least some embodiments. For example, the stages of the illustrated method can be performed in a base station 110, or in a control device configured to control the functionality of the base station 110 when installed therein.

[0053] Stage 610 comprises determining that a small data transmission, SDT, procedure is ongoing with a user equipment in a radio resource control inactive state. Stage 620 comprises sending assistance information to a control plane entity of a centralized unit of the base station. As described above, determining that assistance information is to be sent can be based on an amount of data to be sent exceeding a data amount threshold related to the small data transmission procedure. Alternatively or additionally, determining that assistance information is to be sent can be based on a remaining length of time of a duration of the SDT procedure being less than a threshold duration, and there being remaining data to be sent using the SDT. More generally, as a specific alternative to the SDT, a data transmission context can be employed. The sending of a message to switch the user equipment to a radio resource control active state can be done by the base station, the DU or the CU-CP. The above is described herein in connection with Figure 2 ,Figure 3 and Figure 4 Examples of such messages are described.

[0054] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein but are amenable to equivalents and / or substitutions without departing from the spirit and scope of the invention. It is also to be understood that the terminology herein is used by way of example.

[0055] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. The appearances of the phrase in one embodiment in various places in the specification are not necessarily all referring to the same embodiment.

[0056] As used herein, a plurality of items, structural elements, compositional elements, and / or materials can be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list without explicit indication to the contrary. In addition, various embodiments and examples of the present invention can be referred to herein as "alternative embodiments" or "alternative examples". However, it will be appreciated that those terms are not mutually exclusive, and that the various embodiments and examples of the present invention can be combined with each other without losing the intended scope of the invention.

[0057] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details were provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of the invention.

[0058] While the forgoing examples are illustrative of the principles of the invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications can be made of the details, methods, and examples, without departing from the principles and concepts of the application. Accordingly, the invention is not to be restricted except by the following claims.

[0059] In this document, the verbs “comprise” and “include” are used as open-ended

[0060] Industrial applicability

[0061] At least some embodiments of the invention find industrial application in the management of wireless communications.

[0062] List of acronyms

[0063] 3GPP: Third Generation Partnership Project

[0064] 5G: Fifth Generation

[0065] 6G: Sixth Generation

[0066] AMF: Access and Mobility Management Function

[0067] CU: Centralized Unit

[0068] CU-CP: Centralized Unit Control Plane node

[0069] CU-UP: Centralized Unit User Plane node

[0070] CQI: Channel Quality Information

[0071] DL: Downlink

[0072] LTE: Long Term Evolution

[0073] MAC: Medium Access Control

[0074] MME: Mobility Management Entity

[0075] PDCCH: Physical Downlink Control Channel

[0076] PDCP: Packet Data Convergence Protocol

[0077] RLC: Radio Link Control

[0078] RRC: Radio Resource Control

[0079] SDAP: Service Data Adaptation Protocol

[0080] SDT: Small Data Transmission

[0081] SMD: SDT Maximum Duration

[0082] SRS: Sounding Reference Signal

[0083] UE: User Equipment

[0084] UL: Uplink

[0085] WCDMA: Wideband Code Division Multiple Access

[0086] WiMAX: Worldwide Interoperability for Microwave Access

[0087] WLAN: Wireless Local Area Network

[0088] List of reference signs

[0089] 110 Base station 120、130 UE 112、113 Radio link 140 Core network node 201 Small data transmission 210-260 Figure 2 phases of the signaling procedure 310-380 Figure 3 phases of the signaling procedure 410-480 Figure 4 phases of the signaling procedure 500-560 Figure 5 Structure of the device of the application 610-630 Stages of the method of Figure 6 ​

[0090] Technical clause:

[0091] Clause 1. A method comprising:

[0092] - determining, in an apparatus, that a small data transmission, SDT, procedure with a user equipment in a radio resource control inactive state is ongoing, and

[0093] - transmitting assistance information to a control plane entity of a centralized unit of a base station.

[0094] Clause 2. The method according to clause 1, wherein the method comprises performing the determination of transmitting the assistance information based on at least one of:

[0095] - determining that an amount of data to be transmitted in the SDT procedure exceeds at least one data volume threshold related to the small data transmission, and

[0096] - determining that a remaining duration of a timer associated with the ongoing SDT procedure is less than a threshold duration while still having data to transmit.

[0097] Clause 3. The method according to clause 1 or 2, wherein the assistance information comprises at least one of:

[0098] - an indication of an amount of data to be transmitted,

[0099] - a UE buffer status report,

[0100] - an indication that the amount of data to be transmitted in the SDT procedure has exceeded the at least one data volume threshold,

[0101] - an indication of a time or duration related to the SDT procedure,

[0102] - an indication that the remaining duration of the timer is less than a threshold duration,

[0103] - a recommendation or preference to switch a radio resource control state of the UE,

[0104] - a recommendation or preference of the radio resource control state of the UE.

[0105] Clause 4. The method of any one of clauses 2-3, wherein the method comprises receiving the at least one data volume threshold, the threshold time duration, or an initial value for the timer from an operation and maintenance system or from signaling received in the apparatus from the control plane entity of the centralized unit.

[0106] Clause 5. The method of clause 4, wherein the signaling from the control plane entity of the centralized unit is related to a context for the user equipment stored in the apparatus or to be created in the apparatus.

[0107] Clause 6. The method of any one of the preceding clauses, wherein the apparatus is a distributed unit for a base station, the base station comprising the distributed unit and the centralized unit.

[0108] Clause 7. The method of clause 6 as dependent on clause 2, wherein the method comprises performing, by the distributed unit, the determining that the amount of data exceeds the at least one data volume threshold based on at least one buffer status report associated with the SDT.

[0109] Clause 8. The method of clause 6, wherein the at least one data volume threshold is specific to at least one of the UE and a logical channel group.

[0110] Clause 9. The method of any one of the preceding clauses, wherein the method comprises sending the assistance information to the control plane entity of the centralized unit in an FlAP UE Context Modification Required message.

[0111] Clause 10. The method of any one of clauses 1-5, wherein the apparatus is a user plane entity of the centralized unit.

[0112] Clause 11. The method of clause 10, wherein the method comprises receiving, from the control plane entity of the centralized unit, signaling related to a context for the user equipment stored in the apparatus or to be created in the apparatus, the signaling comprising an ElAP Bearer Context Setup / Modification Request message.

[0113] Clause 12. The method of any one of clauses 11-12, wherein the method comprises sending the assistance information to the control plane entity of the centralized unit in an ElAP DL Data Notification message.

[0114] Clause 13. A method comprising:

[0115] - in a control plane entity of a centralized unit for a base station, the base station comprising a centralized unit and a distributed unit, receiving assistance information from a radio access node for an ongoing small data transmission, SDT, procedure with a user equipment, UE, and

[0116] - determining, based at least partly on the received assistance information, whether to switch a radio resource control, RRC, state of the UE.

[0117] Clause 14. The method of clause 13, wherein the method comprises:

[0118] - determining, based on the assistance information, that the UE is to be switched to an RRC connected state, and

[0119] - sending an RRC message to switch the UE to the RRC connected state.

[0120] Clause 15. The method of clause 13 or 14, wherein the assistance information comprises at least one of:

[0121] - an indication of a data volume,

[0122] - a UE buffer status report,

[0123] - an indication that a data volume has exceeded at least one data volume threshold,

[0124] - an indication of a value of a timer related to the SDT procedure,

[0125] - an indication that a remaining duration of the timer is less than a threshold duration,

[0126] - a recommendation or preference to switch a radio resource control state of the UE,

[0127] - a recommendation or preference of the radio resource control state of the UE.

[0128] Clause 16. The method of any of clauses 13 to 15, further comprising:

[0129] - signalling at least one of a data volume threshold or an initial SDT timer value to the radio access node,

[0130] - receiving the assistance information from the radio access node in response to the signalling.

[0131] Clause 17. The method of clauses 13 to 16, wherein the radio access node is, or is comprised in, a distributed unit of the base station.

[0132] Clause 18. The method of clause 17, wherein the method comprises receiving the assistance information in a FlAP UE Context Modification Request message or an ElAP DL Data Notification message.

[0133] Clause 19. The method of any one of clauses 13-16, wherein the radio access node is a user plane entity of the central unit of the base station.

[0134] Clause 20. The method of clause 15 when dependent on clause 14, wherein the determining whether to switch the RRC state of the UE is based on a determination that an amount of data to be transmitted exceeds the at least one data volume threshold, the amount of data to be transmitted being based on the buffer status report.

[0135] Clause 21. The method of clause 16, wherein the method comprises performing the signaling of the at least one of the at least one data volume threshold or the initial SDT timer value in a FlAP UE Context Setup Request message or a FlAP UE Context Modification Request message or an ElAP Bearer Context Setup Request message or an ElAP Bearer Context Modification Request message.

[0136] Clause Al: An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus (the apparatus comprising a base station apparatus) at least:

[0137] - determining that a small data transmission, SDT, is ongoing with a user equipment in a radio resource control, RRC, inactive state, and

[0138] - transmitting a message about switching the user equipment to a RRC active state.

[0139] Clause A2: The apparatus of clause Al, further configured to:

[0140] - determine that an amount of data to be transmitted exceeds a data volume threshold related to the small data transmission, and

[0141] - based on the determination that the data volume threshold is exceeded, perform the transmitting of the message about switching the user equipment to the RRC active state.

[0142] Clause A3: The apparatus of clause Al, further configured to:

[0143] - determine that a remaining length of time of a timer of the small data transmission is less than a threshold duration while there is still data to be transmitted using the small data transmission, and

[0144] - performing the sending of the message about switching the user equipment to the radio resource control active state based on determining that the remaining length of time of the timer of the small data transmission is less than the threshold duration and there is still data to send using the small data transmission.

[0145] Clause A4: A method comprising:

[0146] - determining that a small data transmission, SDT, with a user equipment in a radio resource control inactive state is ongoing, and

[0147] - sending a message about switching the user equipment to a radio resource control active state.

[0148] Clause A5: An apparatus comprising means for:

[0149] - determining that a small data transmission, SDT, with a user equipment in a radio resource control inactive state is ongoing, and

[0150] - sending a message about switching the user equipment to a radio resource control active state.

[0151] Clause A6: A non-transitory computer-readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least:

[0152] - determining that a small data transmission, SDT, with a user equipment in a radio resource control inactive state is ongoing, and

[0153] - sending a message about switching the user equipment to a radio resource control active state.

Claims

1. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to: - determine that a small data transmission, SDT, procedure with a user equipment in a radio resource control inactive state is ongoing, and - send assistance information to a control plane entity of a centralized unit of a base station.

2. The apparatus of claim 1, wherein the apparatus is configured to send the assistance information based on at least one of: - determining that a quantity of data to be transmitted in the SDT procedure exceeds at least one data volume threshold related to the small data transmission, and - determining that a remaining duration of a timer associated with the ongoing SDT procedure is less than a threshold duration while there is still data to be transmitted.

3. The apparatus of claim 1 or 2, wherein the assistance information comprises at least one of: - an indication of a quantity of data to be transmitted, - a UE buffer status report, - an indication that the quantity of data to be transmitted in the SDT procedure has exceeded the at least one data volume threshold, - an indication of a time or duration related to the SDT procedure, - an indication that the remaining duration of the timer is less than a threshold duration, - a recommendation or preference to switch a radio resource control state of the UE, - a recommendation or preference of the radio resource control state of the UE.

4. The apparatus of any one of claims 2 to 3, wherein the apparatus is configured to receive the at least one data volume threshold, the threshold duration, or an initial value for the timer from an operation and maintenance system or from the control plane entity of the centralized unit.

5. The apparatus of claim 4, wherein the signaling from the control plane entity of the centralized unit is related to a context for the user equipment that is stored in or to be created in the apparatus.

6. The apparatus of any one of the preceding claims, wherein the apparatus is a distributed unit for a base station that comprises the distributed unit and the centralized unit.

7. The apparatus of claim 6 when depending on claim 2, wherein the distributed unit is configured to perform the determination that the quantity of data exceeds the at least one data volume threshold based on at least one buffer status report associated with the SDT.

8. The apparatus of claim 7, wherein the at least one data volume threshold is specific to at least one of the UE or a logical channel group.

9. The apparatus of any one of the preceding claims, wherein the apparatus is configured to send the assistance information to the control plane entity of the centralized unit in an FlAP UE context modification required message.

10. The apparatus of any one of claims 1 to 5, wherein the apparatus is a user plane entity of the centralized unit. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 11. The apparatus of claim 10, wherein the apparatus is configured to receive, from the control plane entity of the centralized unit, signaling related to a context of the user equipment stored in or to be created in the apparatus, the signaling comprising an El AP Bearer Context Setup / Modify Request message.

12. The apparatus of any one of claims 10 to 11, wherein the apparatus is configured to send the assistance information to the control plane entity of the centralized unit in an El AP DL Data Notification message.

13. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to: - receive, in a control plane entity of a centralized unit for a base station comprising the centralized unit and a distributed unit, assistance information from a radio access node for an ongoing small data transmission, SDT, procedure with a user equipment, UE, and - determine, based at least in part on the received assistance information, whether to switch a radio resource control, RRC, state of the UE.

14. The apparatus of claim 13, wherein the apparatus is configured to: - determine, based on the assistance information, to switch the UE to an RRC connected state, and - send an RRC message to switch the UE to the RRC connected state.

15. The apparatus of claim 13 or 14, wherein the assistance information comprises at least one of: - an indication of a data volume, - a UE buffer status report, - an indication that a data volume has exceeded at least one data volume threshold, - an indication of a value of a timer related to the SDT procedure, - an indication that a remaining duration of the timer is less than a threshold duration, - a recommendation or preference to switch the radio resource control state of the UE, - a recommendation or preference of the radio resource control state of the UE.

16. The apparatus of any one of claims 13 to 15, further configured to: - signal at least one of a data volume threshold or an initial SDT timer value to the radio access node, - receive the assistance information from the radio access node in response to the signaling.

17. The apparatus of any one of claims 13 to 16, wherein the radio access node is the distributed unit or is comprised in the distributed unit.

18. The apparatus of claim 17, wherein the apparatus is configured to receive the assistance information in an Fl AP UE Context Modification Required message or an El AP DL Data Notification message.

19. The apparatus of any one of clauses 13 to 16, wherein the radio access node is a user plane entity of the central unit of the base station.

20. The apparatus of clause 15 when dependent on claim 14, wherein the apparatus is configured to perform the determining whether to switch the RRC state of the UE based at least in part on determining that an amount of data to be transmitted exceeds the at least one data volume threshold, the amount of data to be transmitted determined based on the buffer status report.

21. The apparatus of claim 16, wherein the apparatus is configured to perform the signaling the at least one of the at least one data volume threshold or the initial SDT timer value in a FlAP UE Context Setup Request message or a FlAP UE Context Modification Request message or an ElAP Bearer Context Setup Request message or an ElAP Bearer Context Modification Request message.

22. A method comprising: - determining that a small data transmission, SDT, procedure with a user equipment in a radio resource control inactive state is ongoing, and - sending assistance information to a control plane entity of a centralized unit of a base station.

23. A method comprising: - receiving, in a control plane entity of a centralized unit for a base station, assistance information for a small data transmission, SDT, procedure ongoing with a user equipment, UE, from a radio access node, the base station comprising the centralized unit and a distributed unit, and - determining whether to switch the radio resource control, RRC, state of the UE based at least in part on the received assistance information.

24. An apparatus comprising means for: - determining that a small data transmission, SDT, procedure with a user equipment in a radio resource control inactive state is ongoing, and - sending assistance information to a control plane entity of a centralized unit of a base station.

25. An apparatus comprising means for: - receiving, in a control plane entity of a centralized unit for a base station, assistance information for a small data transmission, SDT, procedure ongoing with a user equipment, UE, from a radio access node, the base station comprising the centralized unit and a distributed unit, and - determining whether to switch the radio resource control, RRC, state of the UE based at least in part on the received assistance information.

26. A non-transitory computer-readable medium having stored thereon a set of computer-readable instructions that, when executed by at least one processor, cause an apparatus to at least: - determine that a small data transmission, SDT, procedure with a user equipment in a radio resource control inactive state is ongoing, and - send assistance information to a control plane entity of a centralized unit of a base station.

27. A non-transitory computer-readable medium having stored thereon a set of computer-readable instructions that, when executed by at least one processor, cause an apparatus to at least: - receive, in a control plane entity of a centralized unit for a base station, assistance information for a small data transmission, SDT, procedure ongoing with a user equipment, UE, from a radio access node, the base station comprising the centralized unit and a distributed unit, and - determining, based at least in part on the received assistance information, whether to switch the radio resource control, RRC, state of the UE.

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