WO2025118199A1

WO2025118199A1 - Devices and methods of communication

Info

Publication number: WO2025118199A1
Application number: PCT/CN2023/136883
Authority: WO
Inventors: Da Wang; Gang Wang
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2023-12-06
Filing date: 2023-12-06
Publication date: 2025-06-12
Anticipated expiration: 2026-06-06

Abstract

Embodiments of the present disclosure relate to devices and methods of communication. In one aspect, a CU may determine a problem in an LTM cell switch of a terminal device from a source cell to a target cell, and transmit information of the problem to a DU providing the source cell. Based on the information of the problem, the DU may determine that the problem is detected in the LTM cell switch. In this way, a DU may be aware of a problem of an LTM cell switch procedure, and may further improve implementation for the LTM cell switch procedure.

Description

DEVICES AND METHODS OF COMMUNICATION

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication, and in particular, to devices and methods of communication for mobility robustness optimization (MRO) for layer 1 (L1) or layer 2 (L2) triggered mobility (LTM) .

BACKGROUND

Self-organizing networks (SON) , which encompasses solutions for network self-configuration and self-optimization, has been introduced to support deployment of system and performance optimization. MRO is one of SON functions. One of functions of MRO is to detect connection failures that occur due to a too early mobility or a mobility to a wrong cell. Another function of MRO is to detect a ping-pong problem or a “too short time to stay” problem of a mobility procedure. With introduction of LTM as a new mobility procedure, the MRO functions for SON need to be further enhanced for better LTM performance.

SUMMARY

In general, embodiments of the present disclosure provide methods, devices and computer storage media of communication for MRO for LTM.

In a first aspect, there is provided a central unit (CU) of a network device. The CU comprises a processor. The processor is configured to cause the CU to: determine a problem in an LTM cell switch of a terminal device from a source cell to a target cell, the source cell being provided by a DU of the network device; and transmit information of the problem to the DU.

In a second aspect, there is provided a distributed unit (DU) of a network device. The DU comprises a processor. The processor is configured to cause the DU to: receive, from a CU of the network device, information of a problem in an LTM cell switch of a terminal device from a source cell to a target cell, the source cell being provided by the DU; and determine that the problem is detected in the LTM cell switch.

In a third aspect, there is provided a CU of a network device. The CU comprises a processor. The processor is configured to cause the CU to: determine history information of a terminal device; and transmit the history information of the terminal device to a first DU of the network device.

In a fourth aspect, there is provided a method of communication. The method comprises: determining, at a CU, a problem in an LTM cell switch of a terminal device from a source cell to a target cell, the source cell being provided by a DU of the network device; and transmitting information of the problem to the DU.

In a fifth aspect, there is provided a method of communication. The method comprises: receiving, at a DU of a network device and from a CU of the network device, information of a problem in an LTM cell switch of a terminal device from a source cell to a target cell, the source cell being provided by the DU; and determining that the problem is detected in the LTM cell switch.

In a sixth aspect, there is provided a method of communication. The method comprises: determining, at a CU of a network device, history information of a terminal device; and transmitting the history information of the terminal device to a first DU of the network device.

In a seventh aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor, cause the at least one processor to perform the method according to any of the fourth to sixth aspects of the present disclosure.

Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:

FIG. 1 illustrates an example communication network in which some embodiments of the present disclosure can be implemented;

FIG. 2 illustrates a signaling chart illustrating an example process of communication according to embodiments of the present disclosure;

FIG. 3 illustrates a signaling chart illustrating another example process of communication according to embodiments of the present disclosure;

FIG. 4 illustrates a flowchart of an example method of communication implemented at a CU of a network device in accordance with some embodiments of the present disclosure;

FIG. 5 illustrates a flowchart of an example method of communication implemented at a DU of a network device in accordance with some embodiments of the present disclosure;

FIG. 6 illustrates a flowchart of another example method of communication implemented at a CU of a network device in accordance with some embodiments of the present disclosure; and

FIG. 7 illustrates a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein, the term ‘terminal device’ refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, internet of things (IoT) devices, Ultra-reliable and Low Latency Communications (URLLC) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, device on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, devices for Integrated Access and Backhaul (IAB) , Space borne vehicles or Air borne vehicles in Non-terrestrial networks (NTN) including Satellites and High Altitude Platforms (HAPs) encompassing Unmanned Aircraft Systems (UAS) , eXtended Reality (XR) devices including different types of realities such as Augmented Reality (AR) , Mixed Reality (MR) and Virtual Reality (VR) , the unmanned aerial vehicle (UAV) commonly known as a drone which is an aircraft without any human pilot, devices on high speed train (HST) , or image capture devices such as digital cameras, sensors, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. The ‘terminal device’ can further has “multicast/broadcast” feature, to support public safety and mission critical, V2X applications, transparent IPv4/IPv6 multicast delivery, IPTV, smart TV, radio services, software delivery over wireless, group communications and IoT applications. It may also incorporate one or multiple Subscriber Identity Module (SIM) as known as Multi-SIM. The term “terminal device” can be used interchangeably with a UE, a mobile station, a subscriber station, a mobile terminal, a user terminal or a wireless device.

The term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a next generation NodeB (gNB) , a transmission reception point (TRP) , a remote radio unit (RRU) , a radio head (RH) , a remote radio head (RRH) , an IAB node, a low power node such as a femto node, a pico node, a reconfigurable intelligent surface (RIS) , and the like.

The terminal device or the network device may have artificial intelligence (AI) or machine learning (ML) capability. It generally includes a model which has been trained from numerous collected data for a specific function, and can be used to predict some information.

The terminal device or the network device may work on several frequency ranges, e.g. FR1 (410 MHz to 7125 MHz) , FR2 (24.25GHz to 71GHz) , frequency band larger than 100GHz as well as Tera Hertz (THz) . It can further work on licensed/unlicensed/shared spectrum. The terminal device may have more than one connections with the network devices under multi-radio dual connectivity (MR-DC) application scenario. The terminal device or the network device can work on full duplex, flexible duplex and cross division duplex modes.

The embodiments of the present disclosure may be performed in test equipment, e.g. signal generator, signal analyzer, spectrum analyzer, network analyzer, test terminal device, test network device, channel emulator.

In one embodiment, the terminal device may be connected with a first network device and a second network device. One of the first network device and the second network device may be a master node and the other one may be a secondary node. The first network device and the second network device may use different radio access technologies (RATs) . In one embodiment, the first network device may be a first RAT device and the second network device may be a second RAT device. In one embodiment, the first RAT device is eNB and the second RAT device is gNB. Information related with different RATs may be transmitted to the terminal device from at least one of the first network device or the second network device. In one embodiment, first information may be transmitted to the terminal device from the first network device and second information may be transmitted to the terminal device from the second network device directly or via the first network device. In one embodiment, information related with configuration for the terminal device configured by the second network device may be transmitted from the second network device via the first network device. Information related with reconfiguration for the terminal device configured by the second network device may be transmitted to the terminal device from the second network device directly or via the first network device.

As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes, but is not limited to. ” The term “based on” is to be read as “at least in part based on. ” The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” The terms “first, ” “second, ” and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below.

In some examples, values, procedures, or apparatus are referred to as “best, ” “lowest, ” “highest, ” “minimum, ” “maximum, ” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, higher, or otherwise preferable to other selections.

In the context of the present disclosure, the term “aconnected state” may be interchangeably used with “an RRC_CONNECTED state” , the term “an idle state” may be interchangeably used with “an RRC_IDLE state” , and the term “an inactive state” may be interchangeably used with “an RRC_INACTIVE state” . In the context of the present disclosure, the term “above” herein may be interchangeably used with “higher than or equal to” or “greater than or equal to” . The term “below” herein may be interchangeably used with “lower than or equal to” or “smaller than or equal to” .

In the context of the present disclosure, the term “acell switch” may be interchangeably used with “reconfiguration with sync for secondary cell group (SCG) or master cell group (MCG) ” or “acell change” . The term “PSCell” refers to a special cell (SpCell) of a SCG, the term “primary cell (PCell) ” refers to a SpCell of an MCG, and the term “SpCell” refers to a primary cell of an SCG or MCG. The term “secondary cell (SCell) ” refers to a secondary cell. The term “lower-layer signaling” may be interchangeably used with “L1/L2 signaling” . The term “radio resource control (RRC) reconfiguration” may be interchangeably used with “RRC reconfiguration message” . The term “candidate cell” may be interchangeably used with “LTM candidate cell” or “candidate cell allowing LTM” . The term “target cell” may be interchangeably used with “target candidate cell” , “candidate target cell” , or “LTM target candidate cell” .

When a terminal device moves from a coverage area of one cell to another cell, a serving cell change may need to be performed at some point. Conventionally, a serving cell change is triggered by layer 3 (L3) measurements and is done by an RRC signaling triggered reconfiguration with synchronization for change of PCell and PSCell. All these cases involve complete L2 (and L1) resets, leading to longer latency, larger overhead and longer interruption time than beam switch mobility. A goal of LTM is to enable a serving cell change via L1/L2 signaling, in order to reduce the latency, overhead and interruption time.

LTM is a procedure in which a network device (e.g., gNB) receives L1 measurement report (s) from a terminal device (e.g., UE) , and on their basis the network device changes the terminal device’s serving cell by a cell switch command signaled via a MAC CE. The cell switch command indicates an LTM candidate cell configuration that the network device previously prepared and provided to the terminal device through an RRC signaling. Then the terminal device switches to a target cell according to the cell switch command.

The network device indicates in the cell switch command whether the terminal device accesses the target cell with a random access (RA) procedure if a timing advance (TA) value is not provided or with a physical uplink shared channel (PUSCH) transmission using an indicated TA value. For random access channel (RACH) -less LTM, the terminal device may access the target cell via a configured grant (CG) provided in the RRC signaling and selects a CG occasion associated with a beam indicated in the cell switch command. If the terminal device does not receive the CG in the RRC signaling, the terminal device may monitor a physical downlink control channel (PDCCH) for dynamic scheduling from the target cell upon LTM cell switch.

For the LTM cell switch, an MRO function for SON needs to be further enhanced for better performance of the LTM cell switch.

Embodiments of the present disclosure provide solutions of communication for MRO for LTM. In one aspect, a CU of a network device may determine a problem in an LTM cell switch of a terminal device from a source cell to a target cell, and transmit information of the problem to a DU of the network device providing the source cell. Based on the information of the problem, the DU may determine that the problem is detected in the LTM cell switch. In this way, a DU may be aware of a problem of an LTM cell switch procedure, and may further improve implementation for the LTM cell switch procedure.

In another aspect, a CU of a network device may determine history information of a terminal device; and transmit the history information of the terminal device to a DU of the network device. The history information may be related to a set of LTM cell switch procedures. The DU may store the history information for use in MRO for LTM. In this way, a DU may collect history information of a terminal device, and use the history information to improve future LTM cell switch preparations.

Principles and implementations of the present disclosure will be described in detail below with reference to the figures.

EXAMPLE OF COMMUNICATION NETWORK

FIG. 1 illustrates a schematic diagram of an example communication network 100 in which some embodiments of the present disclosure can be implemented. As shown in FIG. 1, the communication network 100 may include a terminal device 110 and network devices 120 and 130. The network device 120 may provide one or more cells (cells 122-1, 122-2, 123-1, and 123-2 as shown) to serve one or more terminal devices. The network device 130 may also provide one or more cells (not shown) to serve one or more terminal devices.

As shown in FIG. 1, the network device 120 may comprise a CU 121 and DUs 122 and 123. The CU 121 may communicate with the DUs 122 and 123. It is to be understood that the two DUs 122 and 123 are shown only for illustration, and more or less DUs may also be provided for implementation of embodiments of the present disclosure.

As shown in FIG. 1, the DU 122 provides the cells 122-1 and 122-2 and the DU 123 provides the cells 123-1 and 123-2. It is to be understood that this is merely an example, and any of the DUs 122 and 123 may provide more or less cells. The terminal device 110 may communicate with any of these cells. In this example, the terminal device 110 is located in the cell 123-1 and served by the network device 120.

Although not shown, the network device 130 may comprise a CU and one or more DUs as described in connection with the network device 120. Alternatively, the network device 130 may not be implemented in a CU-DU architecture, and may be implemented in an integrated architecture as shown.

The CU 121 may communicate with the network device 130. In some embodiments where the network device 130 comprises a CU and one or more DUs, the CU 121 may communicate with the CU of the network device 130.

As shown in FIG. 1, the communication network 100 may further include a core network (CN) 135. The terminal device 110 may communicate with the CN 135 via the network device 120 and/or the network device 130. In this example, the terminal device 110 may communicate with the CU 121 via the DU 123 and the CU 121 may further communicate with the CN 135.

It is to be understood that the number of devices or cells or CUs or DUs in FIG. 1 is given for the purpose of illustration without suggesting any limitations to the present disclosure. The communication network 100 may include any suitable number of network devices and/or terminal devices and/or cells and/or CUs and/or DUs adapted for implementing implementations of the present disclosure.

A CU (e.g., the CU 121) may be responsible for accomplishing functionalities of RRC, service data application protocol (SDAP) and packet data convergence protocol (PDCP) entities, and a DU (e.g., the DU 122 or 123 may be responsible for accomplishing functionalities of radio link control (RLC) , medium access control (MAC) and physical (PHY) entities. In some embodiments, a CU and a DU may be implemented in separate devices. In some embodiments, a CU and a DU may be implemented in the same device. In some embodiments, different DUs may be implemented in separate devices. In some embodiments, different CUs are implemented in separate devices.

In the context of the present disclosure, a CU (also referred to as a gNB-CU herein) is a logic node hosting RRC, SDAP and PDCP protocols of a gNB or RRC and PDCP protocols of an en-gNB that controls operation of one or more DUs (also referred to as gNB-DUs herein) . The gNB-CU terminates an F1 interface connected with the gNB-DU. A DU is a logical node hosting RLC, MAC and PHY layers of the gNB or en-gNB, and its operation is partly controlled by gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates an F1 interface connected with the gNB-CU.

The communications in the communication network 100 may conform to any suitable standards including, but not limited to, global system for mobile communications (GSM) , long term evolution (LTE) , LTE-evolution, LTE-advanced (LTE-A) , new radio (NR) , wideband code division multiple access (WCDMA) , code division multiple access (CDMA) , GSM EDGE radio access network (GERAN) , machine type communication (MTC) and the like. The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-advanced networks, or the sixth generation (6G) networks.

Continuing to refer to FIG. 1, in some embodiments, the terminal device 110 may be located within the coverage of the cell 123-1, and the terminal device 110 may communicate with the DU 123 of the network device 120 based on a network configuration. In this case, the cell 123-1 may be referred to as a serving cell of the terminal device 110. Other cells such as the cells 122-1, 122-2 and 123-2 may be referred to as candidate cells of the terminal device 110.

In some embodiments, the terminal device 110 may establish a dual connection (i.e., simultaneous connection) with the network device 120 and the network device 130. In some embodiments, the network device 120 may serve as a master node (MN) . In these embodiments, the terminal device 110 may communicate with the network device 120 via a set of serving cells. The set of serving cells form an MCG, and a primary cell in the MCG is called as PCell. In some scenarios, the PCell may be changed from the cell 123-1 to the cell 131. This is called as a handover (HO) . In some embodiments, the network device 120 may serve as a secondary node (SN) . In these embodiments, the set of serving cells provided by the network device 120 form an SCG, and a primary cell in the SCG is called as PSCell. In some scenarios, the PSCell may be changed from the cell 123-1 to the cell 131. This is called as a PSCell change.

In some scenarios, the network device 120 may receive L1 measurement reports from the terminal device 110. Based on the L1 measurement reports, the network device 120 may change a serving cell of the terminal device 110 through a MAC CE. This procedure is called as LTM. The network device 120 may prepare one or multiple candidate cells and provides candidate cell configurations to the terminal device 110 through an RRC message. Then an LTM cell switch procedure is triggered by selecting one of the candidate cell configurations as a target configuration for LTM by the network device 120.

In some scenarios, an LTM cell switch from a source cell (e.g., the cell 122-1) to a target cell (e.g., the cell 123-1) is successfully completed. However, a radio link failure (RLF) occurs in the target cell (i.e., the cell 123-1) following (e.g., immediately following) the successful completion of the LTM cell switch, and the terminal device 110 attempts RRC re-establishment or re-connection at the source cell (i.e., the cell 122-1) . In these scenarios, the LTM cell switch is regarded as a too early cell switch. That is, the LTM cell switch is too early.

In some scenarios, an LTM cell switch from a source cell (e.g., the cell 122-1) to a target cell (e.g., the cell 123-1) is successfully completed. However, an RLF occurs in the target cell (i.e., the cell 123-1) following (e.g., immediately following) the successful completion of the LTM cell switch, and the terminal device 110 attempts RRC re-establishment or re-connection at a further cell (e.g., the cell 123-2) different from the source and target cells. In these scenarios, the LTM cell switch is regarded as a cell switch to a wrong cell. That is, the LTM cell switch to a wrong cell is performed.

In some scenarios, an LTM cell switch from a source cell (e.g., the cell 122-1) to a target cell (e.g., the cell 123-1) is successfully completed. However, after the successful completion of the LTM cell switch, the terminal device 110 switches back to the source cell (i.e., the cell 122-1) from the target cell (i.e., the cell 123-1) . And the time spent at the target cell is very short (e.g., below a threshold) . In these scenarios, a ping-pong problem occurs for the LTM cell switch.

In some scenarios, an LTM cell switch from a source cell (e.g., the cell 122-1) to a target cell (e.g., the cell 123-1) is successfully completed. However, after the successful completion of the LTM cell switch, the terminal device 110 switches to a further cell (i.e., the cell 123-2) from the target cell (i.e., the cell 123-1) . And the time spent at the target cell is very short (e.g., below a threshold) . In these scenarios, a too short time to stay problem occurs for the LTM cell switch. That is, time to stay is too short.

Currently, MRO for the above problems in the LTM cell switch is still incomplete and needs to be further enhanced for better performance of an LTM cell switch procedure.

Embodiments of the present disclosure provide solutions of communication for MRO for LTM. More details will be described with reference to FIGs. 2 and 3 below.

EXAMPLE IMPLEMENTATION OF DETECTION OF PROBLEM IN LTM CELL SWITCH

For a conventional mobility procedure, e.g., HO, it is a gNB-CU to determine when to trigger the mobility procedure, and it is the gNB-CU to determine whether there is a problem in the mobility procedure, e.g., too early HO or HO to a wrong cell, based on an RLF report from UE. However, for an LTM cell switch, it is a gNB-DU to determine when to trigger the LTM cell switch. It is still unclear how the gNB-DU identifies a too early cell switch and cell switch to a wrong cell.

In addition, for a conventional mobility procedure, e.g., HO and PSCell change, a gNB-CU identifies a ping-pong issue or too short of time to stay issue based on UE history information collected by the gNB-CU. However, for LTM cell switch, it is a gNB-DU makes decision on when and whether to trigger the LTM cell switch. It is still unclear how the gNB-DU identifies ping-pong and too short of time to stay occurs for the LTM cell switch.

Thus, embodiments of the present disclosure provide a solution of detecting a problem in an LTM cell switch. The solution will be described in connection with FIG. 2 below.

FIG. 2 illustrates a signaling chart illustrating an example process 200 of communication according to embodiments of the present disclosure. For the purpose of discussion, the process 200 will be described with reference to FIG. 1. The process 200 may involve the terminal device 110 and the CU 121 and one of DUs (e.g., the DU 122) of the network device 120 as illustrated in FIG. 1. In this example, the network device 120 provides a serving cell for the terminal device 110 and also provides one or more candidate cells for the terminal device 110. The serving cell may be SpCell, PCell or PSCell of the terminal device 110. The DU 122 may be an LTM candidate DU or serving DU.

As shown in FIG. 2, the CU 121 may determine a problem in an LTM cell switch from a source cell (e.g., the cell 122-1) to a target cell (e.g., the cell 123-1) . In other words, the CU 121 may detect the problem in the LTM cell switch.

In some embodiments, if an RLF occurs in the target cell following successful completion of the LTM cell switch and the terminal device 110 attempts RRC re-establishment or re-connection at the source cell, the CU 121 may determine that the LTM cell switch is a too early cell switch.

In some embodiments, if an RLF occurs in the target cell following successful completion of the LTM cell switch and the terminal device 110 attempts RRC re-establishment or re-connection at a further cell (e.g., the cell 123-2) , the CU 121 may determine that the LTM cell switch is a cell switch to a wrong cell.

In some embodiments, if the terminal device 110 switches back to the source cell from the target cell after successful completion of the LTM cell switch, and time spent at the target cell is very short (e.g., below a threshold, for convenience, also referred to as a first threshold herein) , the CU 121 may determine that a ping-pong problem occurs for the LTM cell switch.

In some embodiments, if the terminal device 110 switches to a further cell (e.g., the cell 123-2) after successful completion of the LTM cell switch, and the time spent at the target cell is very short (e.g., below a threshold, for convenience, also referred to as a second threshold herein) , the CU 121 may determine that time to stay is too short for the LTM cell switch.

Continuing to refer to FIG. 2, in some embodiments, the DU 122 may transmit 211, to the terminal device 110, an LTM cell switch command triggering the LTM cell switch. After triggering the terminal device 110 to perform the LTM cell switch from the source cell of the DU 122, the DU 122 may transmit 212 cell switch information to the CU 121.

In some embodiments, the cell switch information may comprise a bit string. The bit string indicates information associated with the LTM cell switch or is associated with the information associated with the LTM cell switch. The cell switch information may be used to enable later analysis of conditions that led to too early cell switch, cell switch to wrong cell, ping-pong cell switch, or too short of stay time for the cell switch.

In some embodiments, the DU 122 may also transmit, to the CU 121, a cell-radio network temporary identity (C-RNTI) of the terminal device 110 in the source cell, i.e., source cell C-RNTI of the terminal device 110.

In some embodiments, the DU 122 may transmit the cell switch information and source cell C-RNTI of the terminal device 110 in an F1AP message such as a DU-CU CELL SWITCH NOTIFICATION message or any other messages existing or to be developed in future.

With reference to FIG. 2, upon reception of the cell switch information and source cell C-RNTI of the terminal device 110, the CU 121 may store 213 the cell switch information and source cell C-RNTI of the terminal device 110, e.g., for determination of the problem in the LTM cell switch.

Continuing to refer to FIG. 2, upon determination of the problem in the LTM cell switch, the CU 121 may transmit 220 information of the problem to the DU 122. In some embodiments, the CU 121 may transmit the information of the problem via a non-UE associated signaling. It is to be understood that a UE associated signaling may also be feasible. In some embodiments, the CU 121 may transmit the information of the problem via an F1AP message such as a CU-DU CELL SWITCH NOTIFICATION message or any other messages existing or to be developed in future. For the information of the problem, some example embodiments will be described in connection with Embodiments 1 and 2 below.

Embodiment 1

In this embodiment, the problem in the LTM cell switch is that the LTM cell switch is the too early cell switch or the cell switch to the wrong cell.

In some embodiments, the information of the problem may comprise a type (also referred to as cell switch report type herein) of the problem in the LTM cell switch. In some embodiments, the type of the problem may indicate that the LTM cell switch is too early, e.g., the type of the problem is set to “cell switch too early” . In some embodiments, the type of the problem may indicate that the LTM cell switch to a wrong cell is performed, e.g., the type of the problem is set to “cell switch to wrong cell” .

In some embodiments, if the type of the problem is set to “cell switch too early” , it means that gNB-CU (i.e., CU 121) indicates to gNB-DU (i.e., DU 122) that, following a successful cell switch from a cell of gNB-DU, a radio link failure occurred and UE attempted RRC re-establishment or re-connected at the original cell of gNB-DU. If the type of the problem is set to “cell switch to wrong cell” , it means that gNB-CU indicates to gNB-DU that, following a successful cell switch from a source cell of the gNB-DUto a target cell, a radio link failure occurred and UE attempted RRC re-establishment or re-connected at another cell (different from the source cell and the target cell) .

In some embodiments, the information of the problem may comprise the cell switch information received from the DU 122. In some embodiments, the information of the problem may comprise the source cell C-RNTI of the terminal device 110 received from the DU 122.

In some embodiments, the information of the problem may comprise an identity (ID) of the source cell (i.e., the source cell of the LTM cell switch procedure) . For example, the source cell ID may be a cell global identifier (CGI) of the source cell. It is to be understood that the source cell ID may be in any other suitable forms.

In some embodiments, the information of the problem may comprise an ID of the target cell (i.e., the target cell of the LTM cell switch procedure) . For example, the target cell ID may be a CGI of the target cell. It is to be understood that the target cell ID may be in any other suitable forms.

In some embodiments, the information of the problem may comprise an ID of the further cell (i.e., the re-establishment or re-connected cell after the RLF) . For example, the ID of the further cell may be a CGI of the further cell. It is to be understood that the ID of the further cell may be in any other suitable forms.

In some embodiments, the information of the problem may comprise a report (also referred to as UE RLF report herein) of the RLF from the terminal device 110.

It is to be understood that one or more of the above information of the problem may be transmitted from the CU 121 to the DU 122. Of course, more information of the problem may also be feasible.

Embodiment 2

In this embodiment, the problem in the LTM cell switch is the ping-pong problem or “too short of time to stay” problem.

In some embodiments, the information of the problem may comprise a type (e.g., a cell switch type) of the problem in the LTM cell switch, e.g., an indication of occurrence of ping-pong or “too short of time to stay” for the LTM cell switch. In some embodiments, the type of the problem may indicate that the ping-pong problem occurs for the LTM cell switch, e.g., the indication of occurrence of ping-pong may be a cell switch type set as “ping-pong” . In some embodiments, the type of the problem may indicate that the “too short of time to stay” problem occurs for the LTM cell switch, e.g., the indication of occurrence of too short of time to stay may be a cell switch type set as “too short of time to stay” .

In some embodiments, if the type of the problem is set to “ping-pong” , it means that gNB-CU (i.e., CU 121) indicates to gNB-DU (i.e., DU 122) that, following a successful cell switch from a source cell of the gNB-DU, the terminal device 110 switches back to the source cell from the target cell after successful completion of the LTM cell switch, and time spent at the target cell is very short (e.g., below the first threshold) . If the type of the problem is set to “too short of time to stay” , it means that gNB-CU indicates to gNB-DU that, following a successful cell switch from a source cell of the gNB-DU to a target cell, the terminal device 110 switches to a further cell after successful completion of the LTM cell switch, and the time spent at the target cell is very short (e.g., below the second threshold) .

In some embodiments, the information of the problem may comprise the time spent in the target cell (i.e., the cell 123-1) .

In some embodiments, the information of the problem may comprise an ID of the source cell (i.e., the cell 122-1, the source cell of the LTM cell switch procedure) . For example, the source cell ID may be a CGI of the source cell. It is to be understood that the source cell ID may be in any other suitable forms.

In some embodiments, the information of the problem may comprise an ID of the target cell (i.e., the cell 123-1, the target cell of the LTM cell switch procedure) . For example, the target cell ID may be a CGI of the target cell. It is to be understood that the target cell ID may be in any other suitable forms.

So far, the information of the problem is described in connection with Embodiments 1 and 2. Continuing to refer to FIG. 2, upon reception of the information of the problem, the DU 122 may determine 230 that the problem is detected in the LTM cell switch.

As such, a DU may be aware of a problem of an LTM cell switch procedure, and may further improve implementation for the LTM cell switch procedure.

EXAMPLE IMPLEMENTATION OF COLLECTION OF HISTORY INFORMATION

Embodiments of the present disclosure also provide a solution of collecting history information of a terminal device. The solution will be described in connection with FIG. 3 below.

FIG. 3 illustrates a signaling chart illustrating another example process 300 of communication according to embodiments of the present disclosure. For the purpose of discussion, the process 300 will be described with reference to FIG. 1. The process 300 may involve the terminal device 110 and the CU 121 and one of DUs (e.g., the DU 122) of the network device 120 as illustrated in FIG. 1. In this example, the network device 120 provides a serving cell for the terminal device 110 and also provides one or more candidate cells for the terminal device 110. The serving cell may be SpCell, PCell or PSCell of the terminal device 110. The DU 122 may be an LTM candidate DU or serving DU.

As shown in FIG. 3, the CU 121 may determine 310 history information (also referred to as UE history information herein) of the terminal device 110. In some embodiments, the history information may be related to a set of LTM cell switch procedures (i.e., one or more cell switch procedures) . In some embodiments, an LTM cell switch of the set of LTM cell switch procedures may be a successfully completed cell switch procedure. In some embodiments, an LTM cell switch of the set of LTM cell switch procedures may be a failed cell switch procedure. In some embodiments, the history information may comprise a list of “ID (e.g., CGI) of the last visit cell and a duration of time the terminal device 110 stayed in the cell” .

With reference to FIG. 3, in some embodiments, the CU 121 may collect 311 the history information by itself.

In some embodiments, the CU 121 may receive 312 the history information of the terminal device 110 from a further DU. In some embodiments, the further DU may be a DU (e.g., the DU 123) providing a target cell or source cell of the LTM cell switch procedure. It is to be understood that the further DU may be any other DUs different from the DU 122. For convenience, the further DU is shown as the DU 123 in this example. It is to be understood that the present disclosure is not limited to this.

In some embodiments, the further DU (e.g., the DU 123) may transmit the history information of the terminal device 110 to the CU 121 in an LTM cell switch execution procedure. For example, the further DU may transmit the history information of the terminal device 110 via a DU-CU CELL SWITCH NOTIFICATION message. It is to be understood that any other suitable F1AP messages may also be feasible.

In some embodiments, the further DU (e.g., the DU 123) may transmit the history information of the terminal device 110 to the CU 121 in an LTM configuration preparation procedure. For example, the further DU may transmit the history information of the terminal device 110 via a UE CONTEXT MODIFCATION RESPONSE message. It is to be understood that any other suitable F1AP messages may also be feasible.

In some embodiments, the further DU (e.g., the DU 123) may transmit the history information of the terminal device 110 to the CU 121 in a UE context release procedure. For example, the further DU may transmit the history information of the terminal device 110 via a UE CONTEXT RELEASE REQUEST message. It is to be understood that any other suitable F1AP messages may also be feasible.

In some embodiments, the CU 121 may receive 313 the history information of the terminal device 110 from the terminal device 110. In some embodiments, the CU 121 may receive the history information of the terminal device 110 in an information element (IE) mobilityHistoryReport or visitedCellInfoList or visitedPSCellInfoList by an RRC signaling. It is to be understood that the CU 121 may receive the history information of the terminal device 110 via any suitable RRC messages.

Continuing to refer to FIG. 3, the CU 121 may transmit 320 the history information of the terminal device 110 to the DU 122.

In some embodiments, the CU 121 may transmit the history information of the terminal device 110 to the DU 122 in an LTM configuration preparation procedure. For example, the CU 121 may transmit the history information of the terminal device 110 via a UE CONTEXT SETUP REQUEST message, UE CONTEXT MODIFCATION REQUEST message, UE CONTEXT MODIFICATION CONFIRM message, or any other suitable F1AP messages.

In some embodiments, the CU 121 may transmit the history information of the terminal device 110 to the DU 122 in an LTM cell switch execution procedure. For example, the CU 121 may transmit the history information of the terminal device 110 via a CU-DU CELL SWITCH NOTIFICATION message or any other suitable F1AP messages.

Continuing to refer to FIG. 3, upon reception of the history information of the terminal device 110, the DU 122 may collect 330 information of the terminal device 110 based on the history information of the terminal device 110. For example, as long as the terminal device 110 stays in one of cells of the DU 122, the DU 122 may collect the history information of the terminal device 110. The DU 122 may store the collected information of the terminal device 110 and use the collected information for future LTM cell switch preparations. In some embodiments, the DU 122 may identify occurrence of “ping-pong” or “too short of time to stay” for the cell switch procedures using the UE history information by itself. The DU 122 may also use the UE history information for better cell switch performance, e.g., for load balance.

As such, a DU may collect history information of a terminal device, and use the history information to improve future LTM cell switch preparations.

It is to be understood that operations of the processes 200 and/or 300 may be carried out separately or in any suitable combination.

EXAMPLE IMPLEMENTATION OF METHODS

Accordingly, embodiments of the present disclosure provide methods of communication implemented at a DU and a CU of a network device. These methods will be described below with reference to FIGs. 4 to 6.

FIG. 4 illustrates a flowchart of an example method 400 of communication implemented at a CU of a network device in accordance with some embodiments of the present disclosure. For example, the method 400 may be performed at the CU 121 as shown in FIG. 1. For the purpose of discussion, in the following, the method 400 will be described with reference to FIG. 1. It is to be understood that the method 400 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard.

At block 410, the CU 121 of the network device 120 may determine a problem in an LTM cell switch of the terminal device 110 from a source cell (e.g., the cell 122-1) to a target cell (e.g., the cell 123-1) . The source cell is provided by a DU (e.g., the DU 122) of the network device 120.

At block 420, the CU 121 may transmit information of the problem to the DU 122.

In some embodiments, the problem may be one of the following: a radio link failure occurs in the target cell following successful completion of the LTM cell switch and the terminal device attempts RRC re-establishment or re-connection at the source cell; or the radio link failure occurs in the target cell following successful completion of the LTM cell switch and the terminal device attempts RRC re-establishment or re-connection at a further cell. In some embodiments, the information of the problem may comprise at least one of the following: a type of the problem in the LTM cell switch; cell switch information of the LTM cell switch; a C-RNTI of the terminal device 110 in the source cell; an identity of the source cell; an identity of the target cell; an identity of the further cell; or a report of the radio link failure from the terminal device 110. In some embodiments, the type of the problem may indicate one of the following: the LTM cell switch is too early; or the LTM cell switch to a wrong cell is performed.

In some embodiments, the problem may be one of the following: the terminal device 110 switches back to the source cell from the target cell after successful completion of the LTM cell switch, and time spent at the target cell is very short (e.g., below a first threshold) ; or the terminal device 110 switches to a further cell after successful completion of the LTM cell switch, and the time spent at the target cell is very short (e.g., below a second threshold) . In some embodiments, the information of the problem may comprise at least one of the following: a type of the problem in the LTM cell switch; the time spent at the target cell; an identity of the source cell; an identity of the target cell; cell switch information of the LTM cell switch; or a C-RNTI of the terminal device 110 in the source cell. In some embodiments, the type of the problem may indicate one of the following: a ping-pong problem occurs; or time to stay is too short.

In some embodiments, the CU 121 may receive, from the DU 122, at least one of the following: the cell switch information; or the C-RNTI of the terminal device 110 in the source cell. In some embodiments, the cell switch information may comprise a bit string indicating information associated with the LTM cell switch.

With the method 400, a CU may indicate a problem of an LTM cell switch procedure to a DU for improvement of the LTM cell switch procedure.

FIG. 5 illustrates a flowchart of an example method 500 of communication implemented at a DU of a network device in accordance with some embodiments of the present disclosure. For example, the method 500 may be performed at the DU 122 as shown in FIG. 1. For the purpose of discussion, in the following, the method 500 will be described with reference to FIG. 1. It is to be understood that the method 500 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard.

At block 510, the DU 122 of the network device 120 may receive, from the CU 121 of the network device 120, information of a problem in an LTM cell switch of the terminal device 110 from a source cell (e.g., the cell 122-1) to a target cell (e.g., the cell 123-1) . The source cell is provided by the DU 122.

At block 520, the DU 122 may determine that the problem is detected in the LTM cell switch.

In some embodiments, the DU 122 may transmit, to the CU 121, at least one of the following: the cell switch information; or the C-RNTI of the terminal device 110 in the source cell. In some embodiments, the cell switch information may comprise a bit string indicating information associated with the LTM cell switch.

With the method 500, a DU may be aware of a problem of an LTM cell switch procedure, and may further improve implementation for the LTM cell switch procedure.

FIG. 6 illustrates a flowchart of another example method 600 of communication implemented at a CU of a network device in accordance with some embodiments of the present disclosure. For example, the method 600 may be performed at the CU 121 as shown in FIG. 1. For the purpose of discussion, in the following, the method 600 will be described with reference to FIG. 1. It is to be understood that the method 600 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard.

At block 610, the CU 121 of the network device 120 may determine history information of the terminal device 110. In some embodiments, the history information may be related to a set of LTM cell switch procedures.

At block 620, the CU 121 may transmit the history information of the terminal device 110 to a DU (e.g., the DU 122) of the network device 120. The DU may provide a source cell of an LTM cell switch procedure in the set of LTM cell switch procedures.

In some embodiments, the CU 121 may collect the history information of the terminal device 110. In some embodiments, the CU 121 may receive the history information of the terminal device 110 from a further DU (e.g., the DU 123) . In some embodiments, the further DU may provide a target cell or source cell of the LTM cell switch procedure in the set of LTM cell switch procedures. In some embodiments, the CU 121 may receive, from the terminal device 110, the history information of the terminal device 110.

With the method 600, a DU may collect history information of a terminal device, and use the history information to improve future LTM cell switch preparations.

It is to be understood that the operations of methods 400 to 600 correspond to that described in connection with FIGs. 2 and 3, and thus other details are not repeated here for conciseness.

EXAMPLE IMPLEMENTATION OF DEVICES

FIG. 7 is a simplified block diagram of a device 700 that is suitable for implementing embodiments of the present disclosure. The device 700 can be considered as a further example implementation of the terminal device 110 or a DU or CU of the network device 120 as shown in FIG. 1. Accordingly, the device 700 can be implemented at or as at least a part of the terminal device 110 or a DU or CU of the network device 120.

As shown, the device 700 includes a processor 710, a memory 720 coupled to the processor 710, a suitable transceiver 740 coupled to the processor 710, and a communication interface coupled to the transceiver 740. The memory 710 stores at least a part of a program 730. The transceiver 740 may be for bidirectional communications or a unidirectional communication based on requirements. The transceiver 740 may include at least one of a transmitter 742 or a receiver 744. The transmitter 742 and the receiver 744 may be functional modules or physical entities. The transceiver 740 has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2/Xn interface for bidirectional communications between eNBs/gNBs, S1/NG interface for communication between a mobility management entity (MME) /access and mobility management function (AMF) /SGW/UPF and the eNB/gNB, Un interface for communication between the eNB/gNB and a relay node (RN) , or Uu interface for communication between the eNB/gNB and a terminal device.

The program 730 is assumed to include program instructions that, when executed by the associated processor 710, enable the device 700 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to FIGs. 1 to 6. The embodiments herein may be implemented by computer software executable by the processor 710 of the device 700, or by hardware, or by a combination of software and hardware. The processor 710 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 710 and memory 720 may form processing means 750 adapted to implement various embodiments of the present disclosure.

The memory 720 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 720 is shown in the device 700, there may be several physically distinct memory modules in the device 700. The processor 710 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 700 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

In some embodiments, a CU of a network device comprises a circuitry configured to: determine a problem in an LTM cell switch of a terminal device from a source cell to a target cell, the source cell being provided by a DU of the network device; and transmit information of the problem to the DU.

In some embodiments, a DU of a network device comprises a circuitry configured to:receive, from a CU of the network device, information of a problem in an LTM cell switch of a terminal device from a source cell to a target cell, the source cell being provided by the DU; and determine that the problem is detected in the LTM cell switch.

In some embodiments, a CU of a network device comprises a circuitry configured to:determine history information of a terminal device; and transmit the history information of the terminal device to a first DU of the network device.

The term “circuitry” used herein may refer to hardware circuits and/or combinations of hardware circuits and software. For example, the circuitry may be a combination of analog and/or digital hardware circuits with software/firmware. As a further example, the circuitry may be any portions of hardware processors with software including digital signal processor (s) , software, and memory (ies) that work together to cause an apparatus, such as a terminal device or a network device, to perform various functions. In a still further example, the circuitry may be hardware circuits and or processors, such as a microprocessor or a portion of a microprocessor, that requires software/firmware for operation, but the software may not be present when it is not needed for operation. As used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (s) or a portion of a hardware circuit or processor (s) and its (or their) accompanying software and/or firmware.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects 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. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the 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.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to FIGs. 1 to 6. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A central unit (CU) of a network device, comprising:

a processor configured to cause the CU to:

determine a problem in a layer 1 or layer 2 triggered mobility (LTM) cell switch of a terminal device from a source cell to a target cell, the source cell being provided by a distributed unit (DU) of the network device; and

transmit information of the problem to the DU.
The CU of claim 1, wherein the problem is one of the following:

a radio link failure occurs in the target cell following successful completion of the LTM cell switch and the terminal device attempts radio resource control (RRC) re-establishment or re-connection at the source cell; or

the radio link failure occurs in the target cell following successful completion of the LTM cell switch and the terminal device attempts RRC re-establishment or re-connection at a further cell.
The CU of claim 2, wherein the information of the problem comprises at least one of the following:

a type of the problem in the LTM cell switch;

cell switch information of the LTM cell switch;

a cell-radio network temporary identity (C-RNTI) of the terminal device in the source cell;

an identity of the source cell;

an identity of the target cell;

an identity of the further cell; or

a report of the radio link failure from the terminal device.
The CU of claim 3, wherein the type of the problem indicates one of the following:

the LTM cell switch is too early; or

the LTM cell switch to a wrong cell is performed.
The CU of claim 1, wherein the problem is one of the following:

the terminal device switches back to the source cell from the target cell after successful completion of the LTM cell switch, and time spent at the target cell is below a first threshold; or

the terminal device switches to a further cell after successful completion of the LTM cell switch, and the time spent at the target cell is below a second threshold.
The CU of claim 5, wherein the information of the problem comprises at least one of the following:

a type of the problem in the LTM cell switch;

the time spent at the target cell;

an identity of the source cell;

an identity of the target cell;

cell switch information of the LTM cell switch; or

a cell-radio network temporary identity (C-RNTI) of the terminal device in the source cell.
The CU of claim 6, wherein the type of the problem indicates one of the following:

a ping-pong problem occurs; or

time to stay is too short.
The CU of claim 3 or 6, wherein the CU is further caused to:

receive, from the DU, at least one of the following:

the cell switch information; or

the C-RNTI of the terminal device in the source cell.
The CU of claim 3 or 6, wherein the cell switch information comprises a bit string indicating information associated with the LTM cell switch.
A distributed unit (DU) of a network device, comprising:

a processor configured to cause the DU to:

receive, from a central unit (CU) of the network device, information of a problem in a layer 1 or layer 2 triggered mobility (LTM) cell switch of a terminal device from a source cell to a target cell, the source cell being provided by the DU; and

determine that the problem is detected in the LTM cell switch.
The DU of claim 10, wherein the problem is one of the following:

a radio link failure occurs in the target cell following successful completion of the LTM cell switch and the terminal device attempts radio resource control (RRC) re-establishment or re-connection at the source cell; or

the radio link failure occurs in the target cell following successful completion of the LTM cell switch and the terminal device attempts RRC re-establishment or re-connection at a further cell.
The DU of claim 11, wherein the information of the problem comprises at least one of the following:

a type of the problem in the LTM cell switch;

cell switch information of the LTM cell switch;

a cell-radio network temporary identity (C-RNTI) of the terminal device in the source cell;

an identity of the source cell;

an identity of the target cell;

an identity of the further cell; or

a report of the radio link failure from the terminal device.
The DU of claim 12, wherein the type of the problem indicates one of the following:

the LTM cell switch is too early; or

the LTM cell switch to a wrong cell is performed.
The DU of claim 10, wherein the problem is one of the following:

the terminal device switches back to the source cell from the target cell after successful completion of the LTM cell switch, and time spent at the target cell is below a first threshold; or

the terminal device switches to a further cell after successful completion of the LTM cell switch, and the time spent at the target cell is below a second threshold.
The DU of claim 14, wherein the information of the problem comprises at least one of the following:

a type of the problem in the LTM cell switch;

the time spent at the target cell;

an identity of the source cell;

an identity of the target cell;

cell switch information of the LTM cell switch; or

a cell-radio network temporary identity (C-RNTI) of the terminal device in the source cell.
The DU of claim 15, wherein the type of the problem indicates one of the following:

a ping-pong problem occurs; or

time to stay is too short.
The DU of claim 12 or 15, wherein the DU is further caused to:

transmit, to the CU, at least one of the following:

the cell switch information; or

the C-RNTI of the terminal device in the source cell.
The DU of claim 12 or 15, wherein the cell switch information comprises a bit string indicating information associated with the LTM cell switch.
A central unit (CU) of a network device, comprising:

a processor configured to cause the CU to:

determine history information of a terminal device; and

transmit the history information of the terminal device to a distributed unit (DU) of the network device.
The CU of claim 19, wherein the CU is caused to determine the history information by at least one of the following:

collecting the history information of the terminal device;

receiving the history information of the terminal device from a further DU; or

receiving, from the terminal device, the history information of the terminal device.