Apparatus, methods and computer readable media

Abstract

There is provided an apparatus comprising means for receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit, means for determining whether a target cell is known at the user equipment based on the indication and means for configuring the user equipment based on the determining.

Description

[0001] Title

[0002] APPARATUS, METHODS AND COMPUTER READABLE MEDIA

[0003] Field

[0004] The present application relates to a method, apparatus, system and computer program and in particular but not exclusively to Lower Layer Triggered Mobility (LTM) cell switching.

[0005] Background

[0006] A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and / or other nodes by providing carriers between the various entities involved in the communications path. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia and / or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

[0007] In a wireless communication system at least a part of a communication session between at least two stations occurs over a wireless link. Examples of wireless systems comprise public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). Some wireless systems can be divided into cells, and are therefore often referred to as cellular systems.

[0008] A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user may be referred to as user equipment (UE) or user device. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access a carrier provided by a station, for example a base station of a cell, and transmit and / or receive communications on the carrier. The communication system and associated 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. Communication protocols and / or parameters which shall be used for the connection are also typically defined. One example of a communications system is Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) (3G radio). Other examples of communication systems are the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology and so-called 5G or New Radio (NR) networks. NR is being standardized by the 3rd Generation Partnership Project (3GPP). Other examples of communication systems include 5G-Advanced (NR Rel-18 and beyond) and 6G.

[0009] Summary

[0010] In a first aspect there is provided an apparatus comprising means for receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit, means for determining whether a target cell is known at the user equipment based on the indication and means for configuring the user equipment based on the determining.

[0011] The apparatus may comprise means for receiving the indication from a centralised unit.

[0012] The indication may comprise identifiers associated with the cells known at the user equipment.

[0013] The indication may comprise measurements associated with the cells known at the user equipment.

[0014] The measurements may comprise L3 measurements.

[0015] The indication may comprise a timestamp.

[0016] The apparatus may comprise means for receiving the indication from the user equipment.

[0017] The apparatus may comprise means for receiving the indication from the user equipment in a measurement report. The measurement report may comprise an L1 measurement report.

[0018] The apparatus may comprise means for providing a request to the user equipment for the indication.

[0019] In a second aspect there is provided an apparatus comprising means for receiving, at a centralised unit, a measurement report from a user equipment, means for determining, based on the measurement report, whether a cell is known at the user equipment and means for providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

[0020] The indication may comprise identifiers associated with the cells known at the user equipment.

[0021] The indication may comprise measurements associated with the cells known at the user equipment.

[0022] The measurements may comprise L3 measurements.

[0023] The indication may comprise a timestamp.

[0024] The measurement report may comprise an L3 measurement report.

[0025] In a third aspect there is provided an apparatus comprising means for providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

[0026] The apparatus may comprise means for providing the indication from the user equipment in a measurement report.

[0027] The measurement report may comprise an L1 measurement report.

[0028] The apparatus may comprise means for receiving a request from the distributed unit for the indication.

[0029] In a fourth aspect there is provided a method comprising receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit, determining whether a target cell is known at the user equipment based on the indication and configuring the user equipment based on the determining.

[0030] The method may comprise receiving the indication from a centralised unit.

[0031] The indication may comprise identifiers associated with the cells known at the user equipment.

[0032] The indication may comprise measurements associated with the cells known at the user equipment.

[0033] The measurements may comprise L3 measurements.

[0034] The indication may comprise a timestamp.

[0035] The method may comprise receiving the indication from the user equipment.

[0036] The method may comprise receiving the indication from the user equipment in a measurement report.

[0037] The measurement report may comprise an L1 measurement report.

[0038] The method may comprise providing a request to the user equipment for the indication.

[0039] In a fifth aspect there is provided a method comprising receiving, at a centralised unit, a measurement report from a user equipment, determining, based on the measurement report, whether a cell is known at the user equipment and providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

[0040] The indication may comprise identifiers associated with the cells known at the user equipment.

[0041] The indication may comprise measurements associated with the cells known at the user equipment.

[0042] The measurements may comprise L3 measurements. The indication may comprise a timestamp.

[0043] The measurement report may comprise an L3 measurement report.

[0044] In a sixth aspect there is provided a method comprising providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

[0045] The method may comprise providing the indication from the user equipment in a measurement report.

[0046] The measurement report may comprise an L1 measurement report.

[0047] The method may comprise receiving a request from the distributed unit for the indication.

[0048] In a seventh aspect there is provided an apparatus comprising at least one processor, and at least one memory including 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 at least to receive, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit, determine whether a target cell is known at the user equipment based on the indication and configure the user equipment based on the determining.

[0049] The apparatus may be caused to receive the indication from a centralised unit.

[0050] The indication may comprise identifiers associated with the cells known at the user equipment.

[0051] The indication may comprise measurements associated with the cells known at the user equipment.

[0052] The measurements may comprise L3 measurements.

[0053] The indication may comprise a timestamp.

[0054] The apparatus may be caused to receive the indication from the user equipment. The apparatus may be caused to receive the indication from the user equipment in a measurement report.

[0055] The measurement report may comprise an L1 measurement report.

[0056] The apparatus may be caused to provide a request to the user equipment for the indication.

[0057] In an eighth aspect there is provided an apparatus comprising at least one processor, and at least one memory including 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 at least to receive, at a centralised unit, a measurement report from a user equipment, determine, based on the measurement report, whether a cell is known at the user equipment and provide from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

[0058] The indication may comprise identifiers associated with the cells known at the user equipment.

[0059] The indication may comprise measurements associated with the cells known at the user equipment.

[0060] The measurements may comprise L3 measurements.

[0061] The indication may comprise a timestamp.

[0062] The measurement report may comprise an L3 measurement report.

[0063] In a ninth aspect there is provided an apparatus comprising at least one processor, and at least one memory including 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 at least to provide, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

[0064] The apparatus may be caused to provide the indication from the user equipment in a measurement report.

[0065] The measurement report may comprise an L1 measurement report. The apparatus may be caused to receive a request from the distributed unit for the indication.

[0066] In a tenth aspect there is provided a computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit, determining whether a target cell is known at the user equipment based on the indication and configuring the user equipment based on the determining.

[0067] The apparatus may be caused to perform receiving the indication from a centralised unit.

[0068] The indication may comprise identifiers associated with the cells known at the user equipment.

[0069] The indication may comprise measurements associated with the cells known at the user equipment.

[0070] The measurements may comprise L3 measurements.

[0071] The indication may comprise a timestamp.

[0072] The apparatus may be caused to perform receiving the indication from the user equipment.

[0073] The apparatus may be caused to perform receiving the indication from the user equipment in a measurement report.

[0074] The measurement report may comprise an L1 measurement report.

[0075] The apparatus may be caused to perform providing a request to the user equipment for the indication.

[0076] In an eleventh aspect there is provided a computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, at a centralised unit, a measurement report from a user equipment, determining, based on the measurement report, whether a cell is known at the user equipment and providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

[0077] The indication may comprise identifiers associated with the cells known at the user equipment.

[0078] The indication may comprise measurements associated with the cells known at the user equipment.

[0079] The measurements may comprise L3 measurements.

[0080] The indication may comprise a timestamp.

[0081] The measurement report may comprise an L3 measurement report.

[0082] In a twelfth aspect there is provided a computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

[0083] The apparatus may be caused to perform providing the indication from the user equipment in a measurement report.

[0084] The measurement report may comprise an L1 measurement report.

[0085] The apparatus may be caused to perform receiving a request from the distributed unit for the indication.

[0086] In a thirteenth aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to the third or fourth aspect.

[0087] In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above. Description of Figures

[0088] Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

[0089] Figure 1 shows a schematic diagram of an example 5GS communication system;

[0090] Figure 2 shows a schematic diagram of an example mobile communication device;

[0091] Figure 3 shows a schematic diagram of an example control apparatus;

[0092] Figure 4 shows a signalling flow of a LTM procedure;

[0093] Figure 5 shows a flowchart of a method according to an example embodiment;

[0094] Figure 6 shows a flowchart of a method according to an example embodiment;

[0095] Figure 7 shows a flowchart of a method according to an example embodiment;

[0096] Figure 8 shows a signalling flow according to an example embodiment;

[0097] Figure 9 shows a signalling flow according to an example embodiment.

[0098] Detailed description

[0099] Before explaining in detail the examples, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figure 1 , Figure 2 and Figure 3 to assist in understanding the technology underlying the described examples.

[0100] An example of a suitable communications system is the 5G or NR concept. Network architecture in NR may be similar to that of LTE-advanced. Base stations of NR systems may be known as next generation NodeBs (gNBs). Changes to the network architecture may depend on the need to support various radio technologies and finer Quality of Service (QoS) support, and some on-demand requirements for e.g. QoS levels to support Quality of Experience (QoE) for a user. Also network aware services and applications, and service and application aware networks may bring changes to the architecture. Those are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use Multiple Input - Multiple Output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

[0101] Future networks may utilise network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into “building blocks” or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0102] Figure 1 shows a schematic representation of a 5G system (5GS) 100. The 5GS may comprise a user equipment (UE) 102 (which may also be referred to as a communication device or a terminal), a 5G radio access network (5GRAN) 104, a 5G core network (5GCN) 106, one or more internal or external application functions (AF) 108 and one or more data networks (DN) 1 10.

[0103] An example 5G core network (CN) comprises functional entities. The 5GCN 106 may comprise one or more Access and mobility Management Functions (AMF) 112, one or more session management functions (SMF) 1 14, an authentication server function (AUSF) 1 16, a Unified Data Management (UDM) 118, one or more user plane functions (UPF) 120, a Unified Data Repository (UDR) 122 and / or a Network Exposure Function (NEF) 124. The UPF is controlled by the SMF (Session Management Function) that receives policies from a PCF (Policy Control Function).

[0104] The CN is connected to a UE via the Radio Access Network (RAN). The 5GRAN may comprise one or more gNodeB (gNB) Distributed Unit (DU) functions connected to one or more gNodeB (gNB) Centralized Unit (CU) functions. The RAN may comprise one or more access nodes. A User Plane Function (UPF) referred to as PDU Session Anchor (PSA) may be responsible for forwarding frames back and forth between the DN and the tunnels established over the 5G towards the UE(s) exchanging traffic with the DN.

[0105] A possible mobile communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, voice over IP (VoIP) phones, portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart devices, wireless customer-premises equipment (CPE), or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts, and other information.

[0106] A mobile device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant components can be provided on an appropriate circuit board and / or in chipsets. This feature is denoted by reference 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and / or for connecting external accessories, for example hands-free equipment, thereto.

[0107] The mobile device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

[0108] Figure 3 shows an example of a control apparatus 300 for a communication system, for example to be coupled to and / or for controlling a station of an access system, such as a RAN node, e.g. a base station, eNB or gNB, a relay node or a core network node such as an MME or Serving Gateway (S-GW) or Packet Data Network Gateway (P-GW), or a core network function such as AMF / SMF, or a server or host. The method may be implemented in a single control apparatus or across more than one control apparatus. The control apparatus may be integrated with or external to a node or module of a core network or RAN. In some embodiments, base stations comprise a separate control apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input / output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and / or the transmitter may be implemented as a radio front end or a remote radio head.

[0109] The following relates to Lower Layer Triggered Mobility (LTM), for example the selection of candidate target cells in case of inter-cell beam management and inter-cell multi-TRP scenarios.

[0110] Lower Layer Triggered Mobility (LTM) is a procedure in which a network receives L1 measurement reports from UEs and, on the basis of the received L1 measurement reports, the network changes the UEs’ serving cell(s) through MAC control element (MAC CE), or other physical layer control information (e.g., Downlink Control Information (DCI)). The network prepares one or multiple candidate cells and provides the candidate cell configurations to the UE through, e.g., RRC message. The LTM cell switch is then triggered, by selecting one of the candidate configurations as a target configuration for LTM by the network. The candidate cell configurations are added, modified and released by the network via RRC signaling. LTM may provide a fast reaction time to radio link degradation in the serving link, which may result in reducing in the number of radio link failures compared to baseline handover.

[0111] In the context of the present description, the protocol layers L1 , L2, L3 follow the same meaning as in the 3GPP standard specifications. L1 (Layer 1 ) refers to the physical layer, L2 (Layer 2) refers to the medium access control (MAC), the radio link control (RLC), and the packet data convergence protocol (PDCP) layers, and L3 (Layer 3) refers to the radio resource control (RRC) layer. LTM may thus be understood as a lower layer handover procedure where a handover command is triggered on a protocol layer below L3 (the RRC layer), e.g. on the L1 or L2.

[0112] In LTM, L1 measurement reports are sent either via physical layer signalling or the MAC protocol layer in periodic (or semi-static or aperiodic) fashion. The configuration for those reports may be delivered to the UE via an LTM specific RRC message “CSI- ReportConfig”, or LTM-CSI-ReportConfig.

[0113] Currently, the LTM procedure is the subject of active discussion. Figure 4 shows a message flow chart between a UE, a source DU, a target DU and a CU.

[0114] In steps 1 and 2, the UE sends L3 measurement report to CU via the source DU.

[0115] In step 3, CU decides about the preparation of new cells and in step 4, the CU requests the DU preparation of a candidate target cell(s) controlled by Target DU by sending UE Context Setup Request message to the Target DU.

[0116] In step 5, the target DU provides the configuration of the UE in UE Context Setup Response message containing a container from DU to CU. The same steps 4 / 5 are performed with other Target DUs in order to prepare target cell(s).

[0117] Having received the UE configurations for the candidate target cell(s), the CU generates an RRC Reconfiguration that is sent to the UE in step 6. Among other information, the RRC Reconfiguration message contains: measurement reporting configuration (e.g., LTM-CSI- ReportConfig) for L1 / L2 handover and configuration of the prepared candidate cell(s) which the LIE needs to execute when it receives a MAC CE command to change the serving cell (perform handover)

[0118] In steps 7 to 10 of Figure 4, the configurations are provided to the UE which also acknowledges the reception and reconfiguration.

[0119] In step 1 1 , the UE reports L1 measurement.

[0120] At step 12, the source DU determines that there is a target candidate cell having a better radio link / beam measurement than the serving cell (step 12), e.g., L1 -RSRP (Layer 1 Reference Signal Received Power) of target cell beam measurement > L1 -RSRP of serving cell beam measurement + Offset for an amount of time e.g., Time -to-Trigger (TTT)

[0121] In step 13, the serving cell sends a MAC Control Element (MAC CE) or a L1 message to the UE to trigger the cell change to the target candidate cell.

[0122] The handover from serving cell to target cell is executed by the UE in steps 14 to 17. Both RACH and RACH-less based cell change are considered.

[0123] In step 18 the Target DU provides to the CU the RRC Reconfiguration Complete which indicates to the latter that the UE is now served from the target DU.

[0124] The UE context is released from the source DU in steps 19 and 20.

[0125] Steps 1 to 10 in Figure 4 may be referred to as the preparation phase, in which the candidate cells are prepared based on L3 measurement report at CU. Such configurations are sent to UE in step 8 via a RRC reconfiguration message. Steps 1 1 to 20 are the execution phase, when the target cell will be switched to target DU based on L1 measurement reports.

[0126] After step 10, there may be early synchronisation (DL / UL synchronisation with candidate cells). L1 measurements maybe needed for this step.

[0127] Service interruption time and processing delay are a consideration in RAN. Whether the prepared candidate cells from step 1 to 10 are known to UE may play a role in determining service interruption time and processing delay later during the execution phase (steps 11 to 20). For a UE to perform L1 measurement which lead to the triggering of cell change is that the cell shall be known to the UE. In LTM, a DU could trigger the L1 measurement, therefore, DU should know which cell is known to UE.

[0128] Whether a cell is known or not from a UE perspective, is currently defined in TS 38.133, and therefore a UE knows if a cell is known or not. The exact conditions in which a LTM cell is considered to be known at a UE are still under discussion. For cells to be known to a UE the following example condition has been defined. For L1 -RSRP measurement of a cell with different Physical Cell ID (PCI) than the serving cell, it may be specified the UE has sent a valid L3 measurement report during the a given time period (e.g., the last 5 seconds). It may be required that the Synchronization Signal Block (SSB) from the cell with different PCI remains detectable according to cell identification requirements. Otherwise, the cell is unknown to the UE.

[0129] The two phases (preparation phase and execution phase) shown in Figure 4 have different reports as the triggering reference and are at different entities (CU and DU) at the network side. At the network side, the CU may know whether a cell is visible to a UE, because the CU receives L3 measurement reports for the cell from the UE. The CU configures the UE for L1 measurements based on the received L3 measurements. The list of configured candidate cells may contain cells which are not yet known at the UE.

[0130] One assumption for LTM is that the LTM decision on the network side is made on the MAC layer (DU-level in some deployments). The DU may activate the L1 measurement via a MAC CE, indicating the candidate cells to be measured by the UE. However, L3- measurements are processed at RRC-layer.

[0131] The DU may activate the L1 measurement via a MAC CE, indicating the candidate cells to be measured by the UE. The network may be unaware of whether the candidate target cells are known to the UE at the execution phase. A cell that is known to the UE during the preparation phase is not guaranteed to be known during the execution phase at a DU given the known condition defined above.

[0132] If a candidate cell is not known to the UE, the interruption time may increase by a delay Tsearch during DL synchronization, wherein Tsearch is the time required to search the target cell and may be up to 60ms. In previous proposals, a DU has the knowledge about the beam and reference signal information of the configured cells by receiving Channel State Information (CSI) resource configuration and Transmission Configuration Indicator (TCI) states information from CU but this information does not indicate which cells are known to UE at the time of preparation. Further, when the UE is moving, and a new L3 measurement report is received at CU, unknown cells become known cells. Again, the DU is not aware of this. If the last L3 Measurement report was received 5 seconds ago and no new L3 measurement report is received, the known cells become unknown. Hence, a UE may stop reporting these cells to DU. Even if the same cells become known again later because UE triggers a L3 measurement report, the DU is unaware.

[0133] Figure 5 shows a flowchart of a method according to an example embodiment. The method may be performed at a distributed unit (DU) of a base station (e.g., gNB). The distributed unit may be associated with a serving cell of a UE. The DU may be referred to as a source DU.

[0134] In 501 , the method comprises receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit.

[0135] In 502, the method comprises determining whether a target cell is known at the user equipment based on the indication.

[0136] In 503, the method comprises configuring the user equipment based on the determining.

[0137] Figure 6 shows a flowchart of a method according to an example embodiment. The method may be performed at a centralised unit of a base station (e.g., gNB). The centralised unit may be associated with a serving cell of a UE.

[0138] In 601 , the method comprises receiving, at a centralised unit, a measurement report from a user equipment.

[0139] In 602, the method comprises determining, based on the measurement report, whether a cell is known at the user equipment.

[0140] In 603, the method comprises providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells. The indication may comprise identifiers associated with the cells known at the user equipment.

[0141] The indication may comprise measurements associated with the cells known at the user equipment. The measurements may be L3 measurements.

[0142] The indication may comprise a timestamp.

[0143] Figure 7 shows a flowchart of a method according to an example embodiment. The method may be performed at a user equipment.

[0144] In 701 , the method comprises providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

[0145] The distributed unit may be associated with the serving cell of the UE.

[0146] The method described with reference to Figure 7 may comprise providing the indication from the user equipment in a measurement report. The measurement report may be an L1 measurement report. The method may comprise receiving a request from the distributed unit for the indication.

[0147] From the definition of known condition above, if a UE has sent valid L3 measurement reports, and the measurement report contains valid SSB measurement (e.g., as defined in 3GPP standards), the cells are considered to be known at the UE.

[0148] In an example embodiment, the RRC-processing layer (e.g., CU) receives an L3 measurement report from UE, and decodes the measurement report. Hence, the CU knows if the cells are known to UE when CU receives the L3 measurement report. This is an example of receiving, at a centralised unit, a measurement report from a user equipment and determining, based on the measurement report, whether a cell is known at the user equipment

[0149] In an example embodiment, the CU extracts the information regarding the known cells from the L3-measurement report that the UE transmits, and transmits this information to the DU. This is an example of the CU providing an indication of cells known at a user equipment to the DU. The DU then has this information available without the need to process L3-measurement report, or without receiving L1 -measurements. The information about known cells may be further used for down selection process (reducing the number of candidate / target cells UE is required to perform L1 -RSRP measurements). This is an example of configuring the user equipment based on the determining.

[0150] In an example embodiment, the CU informs DU about the prepared candidate cells once a valid L3 measurement report is received. The CU may inform the DU about the prepared candidate cells in the preparation phase as described above with reference to Figure 4 or in a subsequent L3 measurement update.

[0151] The CU may provide the DU with information to read L3 measurement (e.g., measurements associated with the cells known at the user equipment) or forwards the prepared candidate cell IDs or the cell IDs contained in the L3 measurement report (e.g., identifiers associated with the cells known at the user equipment).

[0152] In addition to the information indicating if a cell is known by the UE or not, the indication may include a time stamp. The time stamp may indicate the age of the L3 measurements.

[0153] In an example embodiment, that CU forwards known cells to the DU. The DU may assume all cells are known until receiving update from the CU.

[0154] In an alternative embodiment, the UE may be configured to send an indication to the DU (e.g., through RRC or MAC-CE) indicating the known / unknown conditions. This is an example in which the DU provides a request (e.g., through RRC or MAC-CE) to the user equipment for the indication. The UE may provide the indication in a measurement report (e.g., L1 measurement report sent to the DU).

[0155] Figure 8 shows a message signalling flow according to an example embodiment.

[0156] Steps 1 to 5 are as in Figure 4.

[0157] In Step 6, the message may contain one or more of the following: a list of cell IDs into a message, L3 measurement reports or timestamp indicating the age of the measurement. The message container may, for instance, be “CU-to-DU-RRC-Information” IE in the LIE CONTEXT MODIFICATION REQUEST message to source DU

[0158] In another embodiment CU may include a candidate exclude list into a message, indicating which LTM candidate cells were not included in the message, or which candidate cells should be disabled.

[0159] In step 7, the source DU responds with UE CONTEXT MODIFICATION RESPONSE message.

[0160] These two steps may be repeated when CU received a valid L3 measurement report, see steps 22 to 23.

[0161] Steps 8 to 12 correspond to steps 6 to 10 as shown in Figure 4.

[0162] In steps 13 to 17 of Figure 8, UE performs early DL sync and UL sync if configured.

[0163] As shown in step 18, the UE starts to report periodically the L1 beam measurement of serving and candidate target cell(s). In steps 19-20, UE reports periodically L3 measurements to CU, regardless of if LTM is triggered or not.

[0164] In step 21 , upon receiving periodic L3 measurements report, CU decodes the report, and obtains the list of known cells to UE, and compares that with the prepared cells for LTM in step 8.

[0165] In step 22 and 23, (as in step 6 and step 7), CU will update the list of known cells to UE to DU.

[0166] Steps 24 to 32 correspond to steps 11 to 20 as shown in Figure 4 except that the source DU is aware that the target cell is known at the UE.

[0167] In step 33, a path switch is performed to the new serving DU.

[0168] Figure 9 shows a message signalling flow according to an example embodiment.

[0169] Steps 1 to 7 are as in Figure 8. In steps 9 to 12 the configurations are provided to the UE which also acknowledges the reception and reconfiguration. In step 10, the network configures the UE to provide known condition indication in the L1 measurement report. This configuration may come from DU or CU.

[0170] Steps 13 to 17 are as shown in Figure 8.

[0171] In steps 18 to 19, the UE starts to report periodically the L1 beam measurement of serving and candidate target cell(s). UE will append the list to known cells to UE at the end of L1 measurement report to DU. This list includes all the cells known to UE, instead of only those which are associated with the current L1 -measurements. For instance, UE reports 1 cell with L1 -RSRP measurements to the network and includes the cells which are known to UE also in the report.

[0172] Steps 20 to 28 correspond to steps 25 to 33 of Figure 8.

[0173] This information about the prepared cells, which are known to the UE, may be used for gNB UL scheduling. The DU having the information about whether the prepared cells are known to the UE may enable the gNB to make more precise activation of measurement in subsequent cell switch.

[0174] A benefit of a DU knowing if the cell is known to the UE side during the execution phase is that gNB can schedule the corresponding UL resources more efficiently, thus enhancing the efficiency of LTM handover.

[0175] It is possible to indicate to the DU if a cell is known on UE side or not. This way DL synchronization will not be delayed by Tsearch and the RAN2 requirements for the case in which DU activates the L1 measurement can be fulfilled.

[0176] An apparatus may comprise means for receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit, means for determining whether a target cell is known at the user equipment based on the indication and means for configuring the user equipment based on the determining.

[0177] The apparatus may comprise a network node, such as a gNB or a DU of a gNB, be the network node or be comprised in the network node or a chipset for performing at least some actions of / for the network node. Alternatively, or in addition, an apparatus may comprise means for receiving, at a centralised unit, a measurement report from a user equipment, means for determining, based on the measurement report, whether a cell is known at the user equipment and means for providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

[0178] The apparatus may comprise a network node, such as a gNB or a CU of a gNB, be the network node or be comprised in the network node or a chipset for performing at least some actions of / for the network node.

[0179] Alternatively, or in addition, an apparatus may comprise means for providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

[0180] The apparatus may comprise the user equipment, such as a mobile phone, be the user equipment or be comprised in the user equipment or a chipset for performing at least some actions of / for the user equipment.

[0181] It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and / or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0182] It is noted that whilst some embodiments have been described in relation to 5G networks, similar principles can be applied in relation to other networks and communication systems such as 6G networks or 5G-Advanced networks. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

[0183] It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention. As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0184] In general, the various embodiments may be implemented in hardware or special purpose circuitry, software, logic or any combination thereof. Some aspects of the disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0185] As used in this application, the term “circuitry” may refer to one or more or all of the following:

[0186] (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and

[0187] (b) combinations of hardware circuits and software, such as (as applicable):

[0188] (i) a combination of analog and / or digital hardware circuit(s) with software / fi rmware and

[0189] (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

[0190] I hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.”

[0191] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. The embodiments of this disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and / or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computerexecutable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0192] Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0193] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

[0194] Embodiments of the disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0195] The scope of protection sought for various embodiments of the disclosure is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the disclosure.

[0196] The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this disclosure will still fall within the scope of this invention as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

Claims1 . An apparatus comprising: means for receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit; means for determining whether a target cell is known at the user equipment based on the indication; and means for configuring the user equipment based on the determining.

2. The apparatus according to claim 1 , comprising means for receiving the indication from a centralised unit.

3. The apparatus according to claim 2, wherein the indication comprises identifiers associated with the cells known at the user equipment.

4. The apparatus according to claim 2 or claim 3, wherein the indication comprises measurements associated with the cells known at the user equipment.

5. The apparatus according to claim 4, wherein the measurements comprise L3 measurements.

6. The apparatus according to any of claims 2 to 5, wherein the indication comprises a timestamp.

7. The apparatus according to claim 1 , comprising means for receiving the indication from the user equipment.

8. The apparatus according to claim 7, comprising means for receiving the indication from the user equipment in a measurement report.

9. The apparatus according to claim 8, wherein the measurement report comprises an L1 measurement report.

10. The apparatus according to any of claims 7 to 9, comprising means for providing a request to the user equipment for the indication.

11. An apparatus comprising: means for receiving, at a centralised unit, a measurement report from a user equipment; means for determining, based on the measurement report, whether a cell is known at the user equipment; and means for providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

12. The apparatus according to claim 11 , wherein the indication comprises identifiers associated with the cells known at the user equipment.

13. The apparatus according to claim 11 or claim 12, wherein the indication comprises measurements associated with the cells known at the user equipment.

14. The apparatus according to claim 13, wherein the measurements comprise L3 measurements.

15. The apparatus according to any of claims 11 to 14, wherein the indication comprises a timestamp.

16. The apparatus according to any of claims 11 to 15, wherein the measurement report comprises an L3 measurement report.

17. An apparatus comprising: means for providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

18. The apparatus according to claim 17, comprising means for providing the indication from the user equipment in a measurement report.

19. The apparatus according to claim 18, wherein the measurement report comprises an L1 measurement report.

20. The apparatus according to any of claims 17 to 19, comprising means for receiving a request from the distributed unit for the indication.21 . An apparatus comprising: at least one processor, and at least one memory including 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 at least to: receive, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit; determine whether a target cell is known at the user equipment based on the indication; and configure the user equipment based on the determining.

22. An apparatus comprising: at least one processor, and at least one memory including 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 at least to: receive, at a centralised unit, a measurement report from a user equipment; determine, based on the measurement report, whether a cell is known at the user equipment; and provide from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

23. An apparatus comprising: at least one processor, and at least one memory including 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 at least to: provide, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

24. A method comprising: receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit; determining whether a target cell is known at the user equipment based on the indication; and configuring the user equipment based on the determining.

25. A method comprising: receiving, at a centralised unit, a measurement report from a user equipment; determining, based on the measurement report, whether a cell is known at the user equipment; and providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

26. A method comprising: providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

27. A computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, at a distributed unit, an indication of cells known at a user equipment associated with the distributed unit; determining whether a target cell is known at the user equipment based on the indication; and configuring the user equipment based on the determining.

28. A computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, at a centralised unit, a measurement report from a user equipment; determining, based on the measurement report, whether a cell is known at the user equipment; and providing from the centralised unit to a distribution unit associated with the user equipment, an indication of the determined cells.

29. A computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: providing, from a user equipment to a distributed unit associated with the user equipment, an indication of cells known at the user equipment.

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