Method and device for TA acquisition

Abstract

Embodiments of the present application relate to a method and apparatus for timing advance (TA) acquisition in a 3rd Generation Partnership Project (3GPP) 5G system or the like. In accordance with an embodiment of the present application, a candidate distributed unit (DU) of a base station (BS) includes a transceiver, and a processor coupled to the transceiver, where the processor is configured to receive, via the transceiver, a signal from a user equipment (UE) for timing advance (TA) acquisition associated with a candidate cell; transmitting a TA value associated with the candidate unit to a source DU of the BS via the transceiver via a CU of the BS, or transmitting the TA value to the UE via a Random Access Response (RAR) message; and one of the candidate DU, the CU, the source DU, and the UE determines whether the TA value associated with the candidate cell is valid.

Description

Technical Field

[0001] Embodiments of the present application generally relate to wireless communication technologies, and more particularly, to methods and devices for timing advance (TA) acquisition. Background Art

[0002] Wireless communication systems are widely used to provide various telecommunication services such as telephony, video, data, messaging, broadcasting, etc. A wireless communication system may employ a multiple access technology capable of supporting communication with multiple users by sharing available system resources such as time, frequency, and power. Examples of wireless communication systems may include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, as well as fifth generation (5G) systems that may also be referred to as New Radio (NR) systems.

[0003] Currently, details regarding the handling of TA values during or after TA acquisition have not been addressed in 3GPP 5G technologies. Summary of the Invention

[0004] Some embodiments of the present application provide a candidate distributed unit (DU) of a base station (BS). The candidate DU includes a transceiver, and a processor coupled to the transceiver; and the processor is configured to receive, via the transceiver, a signal for timing advance (TA) acquisition associated with a candidate cell from a user equipment (UE); transmit, via the transceiver, a TA value associated with the candidate cell to a source DU of the BS or the UE; and determine whether the TA value associated with the candidate cell is valid.

[0005] In some embodiments, the signal is at least one of the following: a preamble; or a sounding reference signal (SRS).

[0006] In some embodiments, the processor of the candidate DU is configured to calculate the TA value based on the received signal, and the TA value is transmitted to the source DU via a centralized unit (CU) of the BS.

[0007] In some embodiments, the processor of the candidate DU is configured to transmit, via the CU, at least one of the following to the source DU: identifier (ID) information of the candidate cell; or ID information of the UE.

[0008] In some embodiments, based on the received signal, the TA value is transmitted to the UE in a random access response (RAR) message.

[0009] In some embodiments, it is determined whether the TA value is valid based on conditions, where the conditions based on which the TA value is determined to be invalid include at least one of the following: expiration of an early TA timer; or a difference between a first reference signal received power (RSRP) value and a second RSRP value being greater than or equal to a threshold associated with an RSRP change.

[0010] In some embodiments, the processor of the candidate DU is configured to receive, via the transceiver, configuration information regarding the conditions from the CU, and the configuration information includes at least one of the following: the value of the early TA timer; or the threshold associated with an RSRP change.

[0011] In some embodiments, the processor of the candidate DU is configured to start the early TA timer when receiving the signal or when calculating the TA value.

[0012] In some embodiments, the first RSRP value is the RSRP value when the candidate DU receives the signal or when the candidate DU calculates the TA value, and the second RSRP value is the RSRP value received from the CU or the source DU.

[0013] In some embodiments, the processor of the candidate DU is configured to receive, via the transceiver, at least one of the following: layer 1 (L1) measurement results of the UE from the source DU; or layer 3 (L3) measurement results of the UE from the CU, where the second RSRP value is included in at least one of the L1 measurement results or the L3 measurement results.

[0014] In some embodiments, in response to determining that the TA value is invalid, the processor of the candidate DU is configured to transmit, via the CU and via the transceiver, information indicating that the TA value is invalid to the source DU.

[0015] In some embodiments, the processor of the candidate DU is configured to transmit, via the CU and via the transceiver, configuration information regarding random access channel (RACH) resources for TA acquisition associated with the candidate cell to the source DU.

[0016] Some embodiments of the present application provide a centralized unit (CU) of a base station (BS). The CU includes a transceiver and a processor coupled to the transceiver; and the processor is configured to receive, via the transceiver, a timing advance (TA) value associated with a candidate cell from a candidate distributed unit (DU) of the BS; and transmit, via the transceiver, the TA value associated with the candidate cell to a source DU of the BS.

[0017] In some embodiments, the processor of the CU is configured to: receive, via the transceiver, identifier (ID) information of the candidate cell and ID information of a user equipment (UE) from the candidate DU; and transmit, via the transceiver, the ID information of the candidate cell and the ID information of the UE to the source DU.

[0018] In some embodiments, the processor of the CU is configured to determine whether the TA value associated with the candidate cell is valid.

[0019] In some embodiments, the processor of the CU is configured to determine that the TA value is invalid if the difference between a first reference signal received power (RSRP) value and a second RSRP value is greater than or equal to a threshold.

[0020] In some embodiments, the first RSRP value is the RSRP value when the CU receives the TA value, and the second RSRP value is the RSRP value received from the UE via the source DU.

[0021] In some embodiments, in response to determining that the TA value is invalid, the processor of the CU is configured to transmit, via the transceiver, an indication of TA acquisition associated with the candidate cell to the source DU.

[0022] In some embodiments, in response to determining that the TA value is invalid, the processor of the CU is configured to transmit, via the transceiver, information indicating that the TA value is invalid or a request for random access channel (RACH) resources for TA acquisition associated with the candidate cell to the candidate DU.

[0023] In some embodiments, the processor of the CU is configured to transmit, via the transceiver, configuration information about conditions associated with determining the validity of the TA value to at least one of the candidate DU or the source DU.

[0024] In some embodiments, the configuration information includes at least one of: the value of an early TA timer; or a threshold related to an RSRP change.

[0025] Some embodiments of the present application provide a source distributed unit (DU) of a base station (BS). The source DU includes a transceiver and a processor coupled to the transceiver; and the processor is configured to transmit, via the transceiver, a first indication for timing advance (TA) acquisition associated with a candidate cell to a user equipment (UE); and transmit, via the transceiver, a second indication of TA acquisition associated with the candidate cell to the UE.

[0026] In some embodiments, at least one of the first indication or the second indication is included in at least one of the following: downlink control information (DCI); medium access control (MAC) control element (CE); or radio resource control (RRC) signaling.

[0027] In an embodiment, after transmitting the first indication, the processor of the source DU is configured to receive from the CU at least one of the following: a first TA value associated with the candidate cell; identifier (ID) information of the candidate cell; ID information of the UE; or configuration information regarding a condition for determining whether the first TA value associated with the candidate cell is valid.

[0028] In an embodiment, the condition based on which the first TA value is determined to be invalid includes at least one of the following: expiration of an early TA timer; or a difference between a first reference signal received power (RSRP) value and a second RSRP value being greater than or equal to a threshold related to RSRP change.

[0029] In an embodiment, the configuration information regarding the condition includes at least one of the following: a value of the early TA timer; or the threshold related to RSRP change.

[0030] In an embodiment, the first RSRP value is the RSRP value when the source DU transmits the first indication or when the source DU receives the first TA value, and the second RSRP value is the RSRP value received from the UE.

[0031] In an embodiment, the processor of the source DU is configured to receive, via the transceiver, layer 1 (L1) measurement results of the UE, where the second RSRP value is included in the L1 measurement results.

[0032] In an embodiment, the processor of the source DU is configured to determine whether the first TA value associated with the candidate cell is valid based on the condition.

[0033] In an embodiment, the second indication is transmitted in response to determining that the first TA value is invalid.

[0034] In an embodiment, after transmitting the second indication, the processor of the source DU is configured to release configuration information regarding a random access channel (RACH) resource or a sounding reference signal (SRS) resource used to obtain the first TA value.

[0035] In an embodiment, the RACH resource includes at least one of the following: a preamble; or a time-frequency domain resource.

[0036] Some embodiments of the present application provide a user equipment (UE). The UE includes a transceiver and a processor coupled to the transceiver; and the processor is configured to receive, via the transceiver, a first indication of timing advance (TA) associated with a candidate cell from a source distributed unit (DU) of a base station (BS); transmit, based on the first indication, a first signal for TA acquisition to a candidate distributed unit (DU) of the BS via the transceiver; receive, via the transceiver, a second indication of TA acquisition associated with the candidate cell from the source DU; and transmit, based on the second indication, a second signal for TA acquisition to the candidate DU via the transceiver.

[0037] In an embodiment, at least one of the first indication or the second indication is included in at least one of the following: downlink control information (DCI); medium access control (MAC) control element (CE); or radio resource control (RRC) signaling.

[0038] In an embodiment, at least one of the first signal or the second signal is at least one of the following: a preamble; or a sounding reference signal (SRS).

[0039] In an embodiment, the processor of the UE is configured to: receive, via the transceiver, a first TA value associated with the candidate cell from the candidate DU after transmitting the first signal; and determine whether the first TA value associated with the candidate cell is valid.

[0040] In an embodiment, the first TA value is included in: a cell handover command; or a random access response (RAR) message before the cell handover command.

[0041] In an embodiment, the processor of the UE is configured to determine that the first TA value is invalid based on a condition, and the condition includes at least one of the following: expiration of an early TA timer; or a difference between a first reference signal received power (RSRP) value and a second RSRP value is greater than or equal to a threshold related to RSRP change.

[0042] In an embodiment, the processor of the UE is configured to receive, via the transceiver, configuration information about the condition from a central unit (CU), and the configuration information is configured by the CU or the candidate DU.

[0043] In an embodiment, the configuration information includes at least one of the following: a value of the early TA timer; or the threshold related to RSRP change.

[0044] In an embodiment, the processor of the UE is configured to start the early TA timer when the UE receives the first indication or when the UE receives the first TA value.

[0045] In an embodiment, the first RSRP value is the RSRP value when the UE transmits the first signal, and the second RSRP value is the RSRP value measured by the UE after the UE receives the first TA value.

[0046] In an embodiment, the second signal is transmitted in response to determining that the first TA value is invalid.

[0047] In an embodiment, in response to determining that the first TA value is invalid, the processor of the UE is configured to transmit, via the transceiver, information indicating that the first TA value is invalid to the source DU of the BS.

[0048] Some embodiments of the present application provide a method performed by a candidate distributed unit (DU) of a base station (BS). The method includes: receiving, from a user equipment (UE), a signal for timing advance (TA) acquisition associated with a candidate cell; transmitting, to the source DU of the BS or the UE, a TA value associated with the candidate cell; and determining whether the TA value associated with the candidate cell is valid.

[0049] Some embodiments of the present application provide a method performed by a centralized unit (CU) of a base station (BS). The method includes: receiving, from a candidate distributed unit (DU) of the BS, a timing advance (TA) value associated with a candidate cell; and transmitting, to the source DU of the BS, the TA value associated with the candidate cell.

[0050] Some embodiments of the present application provide a method performed by a source distributed unit (DU) of a base station (BS). The method includes: transmitting, to a user equipment (UE), a first indication for timing advance (TA) acquisition associated with a candidate cell; and transmitting, to the UE, a second indication for TA acquisition associated with the candidate cell.

[0051] Some embodiments of the present application provide a method performed by a UE. The method includes: receiving, from a source distributed unit (DU) of a base station (BS), a first indication of timing advance (TA) associated with a candidate cell; transmitting, based on the first indication, a first signal for TA acquisition to a candidate distributed unit (DU) of the BS; receiving, from the source DU, a second indication for TA acquisition associated with the candidate cell; and transmitting, based on the second indication, a second signal for TA acquisition to the candidate DU.

[0052] Some embodiments of the present application provide a device for wireless communication. The device includes: a non-transitory computer-readable medium having computer-executable instructions stored thereon; a receiving circuit system; a transmitting circuit system; and a processor coupled to the non-transitory computer-readable medium, the receiving circuit system, and the transmitting circuit system, wherein the computer-executable instructions cause the processor to implement the methods mentioned above performed by a UE or a network node (e.g., a base station (BS), a CU, or a DU).

[0053] Details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] To describe the manner in which the advantages and features of the present application can be obtained, the description of the present application is presented by reference to specific embodiments of the present application illustrated in the accompanying drawings. These figures only depict example embodiments of the present application and should not be considered as limiting its scope.

[0055] Figure 1 Schematic diagram illustrating a wireless communication system according to some embodiments of the present application.

[0056] Figure 2 Schematic diagram illustrating inter-cell layer 1 / layer 2 (L1 / L2) mobility according to some embodiments of the present application.

[0057] Figures 3 to 6 Schematic flow chart illustrating an exemplary process associated with TA acquisition according to some embodiments of the present application.

[0058] Figures 7 to 10 Schematic flow chart illustrating exemplary TA acquisition according to some embodiments of the present application.

[0059] Figure 11 Block diagram illustrating an exemplary device according to some embodiments of the present application. DETAILED DESCRIPTION

[0060] The detailed description of the drawings is intended as a description of the preferred embodiments of the present application and is not intended to represent the only form in which the present application can be practiced. It should be understood that the same or equivalent functions can be achieved by different embodiments that are intended to be covered within the spirit and scope of the present application.

[0061] Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. For the sake of facilitation of understanding, the embodiments are provided under specific network architectures and new service scenarios (such as 3GPP 5G, 3GPP LTE Release 8, etc.). It is contemplated that, with the development of the network architecture and new service scenarios, all embodiments in the present application are also applicable to similar technical problems; and furthermore, the terms enumerated in the present application may change, which should not affect the principles of the present application.

[0062] Figure 1 Schematic diagram illustrating a wireless communication system according to some embodiments of the present application. As shown in Figure 1 what is shown, the wireless communication system 100 includes at least one base station (BS) 101 and at least one user equipment (UE) 102. Specifically, for illustrative purposes, the radio communication system 100 includes one BS 101 and two UEs 102 (e.g., UE 102a and UE 102b). Although, for simplicity, Figure 1 a specific number of BSs and UEs are illustrated, it is contemplated that in some other embodiments of the present application, the wireless communication system 100 may include more or fewer BSs and UEs.

[0063] The wireless communication system 100 is compatible with any type of network capable of transmitting and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular phone network, a time division multiple access (TDMA)-based network, a code division multiple access (CDMA)-based network, an orthogonal frequency division multiple access (OFDMA)-based network, an LTE network, a 3GPP-based network, a 3GPP 5G network, a satellite communication network, a high altitude platform network, and / or other communication networks.

[0064] The BS 101 may communicate with a core network (CN) node (not shown) via an interface, such CN nodes as a mobility management entity (MME) or a serving gateway (S-GW), an access and mobility management function (AMF) or a user plane function (UPF), etc. The BS may also be referred to as an access point, an access terminal, a base, a macro cell, a Node B, an evolved Node B (eNB), a gNB, a home Node B, a relay node, or a device, or described using other terms used in the art. In 5G NR, the BS may also refer to a RAN node or a network device. Each BS may serve several UEs within a service area (e.g., a cell or a cell sector) via a wireless communication link. Neighboring BSs may communicate with each other as needed, for example, during a handover procedure of a UE.

[0065] The UE 102 (e.g., UE 102a and UE 102b) should be understood as any type of terminal device, which may include a computing device such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smart TV (e.g., a TV connected to the Internet), a set-top box, a game console, a security system (including security cameras), an in-vehicle computer, a network device (e.g., a router, a switch, and a modem), or the like. According to an embodiment of the present application, the UE 102 may include a portable wireless communication device, a smart phone, a cellular phone, a flip phone, a device with a subscriber identity module, a personal computer, a selective call receiver, or any other device capable of transmitting and receiving communication signals over a wireless network. In some embodiments, the UE 102 includes a wearable device such as a smart watch, a fitness bracelet, an optical head-mounted display, or the like. Additionally, the UE 102 may be referred to as a subscriber unit, a mobile device, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, or a device, or other terms used in the art to describe. The UE 102 may communicate directly with the BS 101 via an uplink (UL) communication signal.

[0066] In 3GPP Release 18, support for inter-cell mobility based on layer 1 / layer 2 (L1 / L2) signaling has been discussed. Specifically, the UE may be pre-provided with configurations from multiple cells, and the BS (e.g., gNB) may use L1 / L2 signaling to switch the UE to a new cell considering the received physical layer measurement results. According to the 3GPP standard document, the BS may be composed of a BS central unit (CU) and one or more BS distributed units (DU). The BS-CU and the BS-DU are connected via an F1 interface as a logical interface. One BS-DU is connected to only one BS-CU.

[0067] Figure 2 A schematic diagram illustrating inter-cell layer 1 / layer 2 (L1 / L2) mobility according to some embodiments of the present application. As shown in Figure 2 As shown, the CU may communicate with two DUs (i.e., DU1 or DU2) via the F1 interface. Figure 2 The CU in Figure 2 may implement legacy mobility decisions based on layer 3 (L3) measurement results.

[0068] Compared with legacy L3 mobility, L1 / L2 mobility is considered faster with less processing delay and signaling delay. In legacy L3 mobility, the CU (e.g., as in Figure 2The CU shown in makes mobility decisions based on the received radio resource management (RRM) measurement reports. Different from legacy L3 mobility, in L1 / L2 mobility, the DU (e.g., DU1 or DU2 as shown in ) makes mobility decisions based on physical layer measurement results carried in, for example, channel state information (CSI) reports. In addition, in legacy L3 mobility, the handover command is sent from the SN CU to the UE via RRC signaling, while in L1 / L2 mobility, the "handover" command is sent from the DU to the UE via L1 / L2 signaling (e.g., downlink control information (DCI) or medium access control (MAC) control element (CE)). The "handover" command in L1 / L2 mobility can be for cell activation or deactivation, such as activating a new serving PCell while deactivating the old serving PCell. Figure 2 The DU shown in or DU2) makes mobility decisions based on physical layer measurement results carried in, for example, channel state information (CSI) reports. In addition, in legacy L3 mobility, the handover command is sent from the SN CU to the UE via RRC signaling, while in L1 / L2 mobility, the "handover" command is sent from the DU to the UE via L1 / L2 signaling (e.g., downlink control information (DCI) or medium access control (MAC) control element (CE)). The "handover" command in L1 / L2 mobility can be for cell activation or deactivation, such as activating a new serving PCell while deactivating the old serving PCell.

[0069] Currently, the problem of how to handle the TA value during or after TA acquisition in the case of lower layer-based mobility has not been solved. Embodiments of this application aim to solve such problems. For example, in some embodiments of this application, after the target DU successfully calculates the TA value, the target DU can transmit it to the source DU via the CU. However, the TA value is not always valid. Once the TA value is invalid, TA acquisition can be triggered again. Some embodiments of this application aim to design a mechanism for determining whether the acquired TA value is invalid and how to obtain or acquire the TA value again after the acquired TA value of the candidate cell is determined to be invalid by the candidate DU, CU, source DU, or UE.

[0070] In an embodiment of this application, TA acquisition or early TA acquisition means that it is desired for the UE to perform a TA acquisition procedure before the cell handover procedure. TA reacquisition or early TA reacquisition means that it is desired for the UE to perform a TA reacquisition procedure before the cell handover procedure. TA acquisition, early TA acquisition, TA reacquisition, or early TA reacquisition can be triggered by receiving an indication from the serving BS, such as a PDCCH command as DCI.

[0071] Some embodiments of the present application may be applicable to cases of "lower layer triggered mobility" or "L1 / L2 triggered mobility", and the abbreviation of at least one of them may be "LTM". In the LTM case, the UE may access the serving BS (e.g., serving gNB). The UE may report layer 3 (L3) measurement results based on the configuration from the serving gNB. If the serving gNB (e.g., the CU of the serving gNB) decides to hand over the UE to a candidate cell based on the measurement results, the serving gNB may request the target DU to prepare the configuration for one or more candidate cells. After receiving the candidate cell configuration from the target DU of the serving gNB, the serving gNB may transmit an RRC reconfiguration message containing the ID information of one or more candidate cells to the UE. For example, the CU may transmit the RRC reconfiguration message to the UE via the source DU of the serving gNB. The UE may transmit an RRC reconfiguration complete message to the serving gNB (e.g., CU) via the source DU. The UE may ensure UL synchronization or DL synchronization before receiving the cell handover command. For example, the UE may obtain or acquire the TA value via random access (RA) or preamble transmission. The UE may report layer 1 (L1) measurement results for dynamic handover purposes. The serving gNB (e.g., source DU) may transmit a cell handover command, such as MAC CE or DCI. The UE may apply the RRC reconfiguration message and start a timer when receiving the lower layer command.

[0072] Specifically, in the Figures 3 to 11 embodiments of the present application, both inter-DU mobility scenarios and intra-DU mobility scenarios are considered, such as LTM between gNB-DUs or LTM within a gNB-DU. Inter-DU mobility means that the connection to the CU remains unchanged, while the UE may change from the source cell associated with the source DU to the target cell associated with the target DU due to mobility, and both the source DU and the target DU are managed by the CU. Intra-DU mobility means that the connection to the CU remains unchanged, while the UE may change from the source cell to the target cell associated with the same DU due to mobility. More details will be described below in conjunction with the drawings.

[0073] Figure 3 Illustrate an exemplary flowchart associated with TA acquisition according to some embodiments of the present application. Figure 3 The exemplary flowchart 300 in the Figure 2 or Figure 7 embodiments may be executed by a candidate DU (e.g., Figure 3 or Figure 3 DU1 or DU2 or candidate DU 703 shown and described in Figure 3The details described in the embodiments of Figure 1 , 2 and all embodiments from 4 to 11. Figure 3 Specific examples of the embodiments of Figure 7 are described as follows in the embodiments of

[0074] In exemplary flow chart 300, at operation 301, a candidate DU of the BS (e.g., Figure 7 the candidate DU 703 shown and described in Figure 7 ) may receive a signal for TA acquisition associated with a candidate cell from a UE (e.g.,

[0075] the UE 701 shown and described in Figure 7 ). In some embodiments, the signal is a sequence. For example, the signal is a preamble and / or a sounding reference signal (SRS).

[0076] At operation 302, the candidate DU may transmit a TA value associated with the candidate cell to a source DU of the BS (e.g., Figure 7 the source DU 702 shown and described in

[0077] or the UE.

[0078] In some embodiments, the candidate DU may calculate a TA value associated with the candidate cell based on the signal received at operation 301 and transmit the TA value to the source DU via a CU of the BS (e.g.,

[0079] the CU 704 shown and described in

[0080] (2) The difference between the RSRP value (denoted as RSRP#1 for simplicity) and another RSRP value (denoted as RSRP#2) is greater than or equal to the threshold associated with the RSRP change (denoted as threshold#1). In some embodiments, RSRP#1 is the RSRP value when the candidate DU receives the signal in operation 301 or when the candidate DU calculates the TA value, and RSRP#2 is the RSRP value received from the CU or the source DU.

[0081] In some embodiments, the candidate DU may receive configuration information about the condition from the CU, and the configuration information includes the value of the early TA timer and / or the threshold associated with the RSRP change (e.g., threshold#1).

[0082] In some embodiments, the candidate DU may receive at least one of the following: (1) the layer 1 (L1) measurement result of the UE from the source DU; or (2) the layer 3 (L3) measurement result of the UE from the CU. RSRP#2 may be included in the L1 measurement result and / or the L3 measurement result.

[0083] In some embodiments, in response to determining that the TA value is invalid, the candidate DU may transmit information indicating that the TA value is invalid to the source DU via the CU.

[0084] In some embodiments, the candidate DU may transmit configuration information about the RACH resource for TA acquisition associated with the candidate cell to the source DU via the CU.

[0085] Figure 4 Illustrate another exemplary flowchart associated with TA acquisition according to some embodiments of the present application. Figure 4 The exemplary flowchart 400 in the embodiments of may be executed by the CU (e.g., Figure 2 or Figure 8 the CU or CU 804 shown and described in. Although described with respect to the CU, it should be understood that other devices may be configured to execute a flowchart similar to the Figure 4 flowchart. The details described in all other embodiments of the present application apply to the embodiments in Figure 4 In addition, the details described in the embodiments in Figure 4 apply to Figures 1 to 3 and all embodiments of 5 to 11. Figure 4 A specific example of the embodiments of is described as follows in the embodiments of Figure 8 the embodiments of.

[0086] In Figure 4 the exemplary flowchart 400 shown in, in operation 401, the CU (e.g., Figure 8 the CU 804 shown and described in) may receive from a candidate DU of the BS (e.g., Figure 8The candidate DU 803) shown and described therein receives the TA value associated with the candidate cell. In operation 402, the CU may transmit the TA value associated with the candidate cell to the source DU to the BS (e.g., Figure 8 the source DU 802) shown and described therein.

[0087] In some embodiments, the CU may receive the ID information of the candidate cell and the ID information of the UE (e.g., Figure 8 the UE 801) shown and described therein from the candidate DU, and transmit the ID information of the candidate cell and the ID information of the UE to the source DU.

[0088] In some embodiments, the CU may determine whether the TA value associated with the candidate cell is valid. In an embodiment, if the difference between the RSRP value (represented as RSRP#3 for simplicity) and another RSRP value (represented as RSRP#4 for simplicity) is greater than or equal to a threshold (e.g., the threshold associated with the RSRP change, represented as threshold#2), then the CU may determine that the TA value is invalid. For example, RSRP#3 is the RSRP value when the CU receives the TA value, and RSRP#4 is the RSRP value received from the UE via the source DU.

[0089] In some embodiments, in response to determining that the TA value is invalid, the CU may transmit an "indication of TA acquisition associated with the candidate cell" to the source DU.

[0090] In some embodiments, in response to determining that the TA value is invalid, the CU may transmit "information indicating that the TA value is invalid" or "a request for RACH resources for TA acquisition associated with the candidate cell" to the candidate DU.

[0091] In some embodiments, the CU may transmit "configuration information regarding the conditions associated with determining the validity of the TA value" to the candidate DU and / or the source DU. In an embodiment, the configuration information includes the value of the early TA timer and / or the threshold associated with the RSRP change (e.g., threshold#2).

[0092] Figure 5 Illustrate another exemplary flowchart associated with TA acquisition according to some embodiments of the present application. Figure 5 The exemplary flowchart 500 in the embodiment of Figure 2 or Figure 9 the DU2 or DU1 or the source DU 902) shown and described therein may be executed by the source DU. Although described with respect to the source DU, it should be understood that other devices may be configured to execute a flowchart similar to the Figure 5 flowchart. The details described in all other embodiments of the present application are applicable to the embodiments in Figure 5 In addition, in Figure 5The details described in the embodiments of Figures 1 to 4 apply to all embodiments from Figure 5 6 to 11. Figure 9 Specific examples of the embodiments of

[0093] are described below in the embodiments of Figure 5 In the exemplary flowchart 500 shown in Figure 9 source DU (e.g., source DU 902 shown and described in Figure 9 ) may transmit an indication of TA acquisition associated with a candidate cell (denoted as indication #1 for simplicity) to UE (e.g., UE 901 shown and described in

[0094] In operation 502, the source DU may transmit another indication of TA acquisition associated with the candidate cell (denoted as indication #2) to the UE.

[0095] In some embodiments, indication #1 and / or indication #2 may be included in at least one of the following: DCI; MAC CE; or RRC signaling.

[0096] In some embodiments, after transmitting indication #1, the source DU may receive at least one of the following from the CU: (1) a TA value associated with the candidate cell; (2) ID information of the candidate cell; ID information of the UE; or (3) configuration information regarding conditions for determining whether the TA value associated with the candidate cell is valid.

[0097] In some embodiments, the conditions based on which the TA value is determined to be invalid include at least one of the following: (1) expiration of an early TA timer; or (2) the difference between an RSRP value (denoted as RSRP#5) and another RSRP value (denoted as RSRP#6) is greater than or equal to a threshold associated with RSRP change (denoted as threshold #3).

[0098] In some embodiments, the configuration information regarding the conditions includes the value of the early TA timer and / or the threshold associated with RSRP change (e.g., threshold #3).

[0099] In some embodiments, RSRP#5 is the RSRP value when the source DU transmits indication #1 or when the source DU receives the TA value, and RSRP#6 is the RSRP value received from the UE.

[0100] In some embodiments, the source DU may receive the layer 1 (L1) measurement results of the UE, where RSRP#6 is included in the L1 measurement results.

[0101] In some embodiments, the source DU may determine whether the TA value associated with the candidate cell is valid based on the conditions.

[0102] In some embodiments, an indication #2 is transmitted in response to determining that the TA value is invalid.

[0103] In some embodiments, after transmitting indication #2, the source DU may release the configuration information regarding the RACH resource or SRS resource used to obtain the TA value. In an embodiment, the RACH resource includes a preamble and / or time-frequency domain resources.

[0104] Figure 6 Illustrate another exemplary flowchart associated with TA acquisition according to some embodiments of the present application. Figure 6 The exemplary flowchart 600 in the embodiments of may be executed by a UE (e.g., Figure 1 or Figure 10 the UE 102 or UE1001 shown and described in). Although described with respect to a UE, it should be understood that other devices may be configured to execute a flowchart similar to the Figure 6 flowchart. The details described in all other embodiments of the present application apply to the embodiments in Figure 6 In addition, the details described in the embodiments of Figure 6 apply to Figures 1 to 5 and all embodiments of 7 to 11. Figure 6 A specific example of the embodiments of is described as follows in the embodiments of Figure 10 In the embodiments of.

[0105] In Figure 6 In the exemplary flowchart 600 shown in, in operation 601, the UE ( Figure 10 the UE 1001 shown and described in) may receive an indication of the TA associated with the candidate cell from the source DU of the BS (e.g., Figure 10 the source DU 1002 shown and described in). In operation 602, the UE may transmit a signal for TA acquisition (denoted as signal #1) to the candidate DU of the BS (e.g., Figure 10 the candidate DU 1003 shown and described in) based on indication #3.

[0106] In operation 603, the UE may receive another indication of TA acquisition associated with the candidate cell from the source DU (denoted as indication #4). In operation 604, the UE may transmit another signal for TA acquisition (denoted as signal #2) to the candidate DU based on indication #4.

[0107] In some embodiments, indication #3 and / or indication #4 is included in at least one of the following: DCI; MAC CE; or RRC signaling.

[0108] In some embodiments, signal # and / or signal #2 is a sequence, such as a preamble and / or SRS.

[0109] In some embodiments, the UE may receive a TA value associated with a candidate cell from a candidate DU after transmitting Signal #1; and determine whether the TA value associated with the candidate cell is valid.

[0110] In some embodiments, the TA value is included in one of the following: a cell handover command (e.g., a MAC CE command); or a RAR message before the cell handover command.

[0111] In some embodiments, the UE may determine that the TA value is invalid based on a condition, and the condition includes at least one of the following: (1) expiration of an early TA timer; or (2) the difference between an RSRP value (denoted as RSRP#7) and another RSRP value (denoted as RSRP#8) is greater than or equal to a threshold associated with an RSRP change (denoted as Threshold #4).

[0112] In some embodiments, the UE may receive configuration information about the condition from the CU, and the configuration information is configured by the CU or the candidate DU. In an embodiment, the configuration information includes at least one of the following: (1) the value of the early TA timer; or (2) the threshold associated with the RSRP change (e.g., Threshold #4).

[0113] In some embodiments, the UE may start the early TA timer when the UE receives Indication #3 or when the UE receives the TA value.

[0114] In some embodiments, RSRP#7 is the RSRP value when the UE transmits Signal #1, and RSRP#8 is the RSRP value measured by the UE after receiving the TA value.

[0115] In some embodiments, Signal #2 is transmitted in response to determining that the TA value is invalid.

[0116] In some embodiments, in response to determining that the TA value is invalid, the UE may transmit information indicating that the TA value is invalid to the source DU.

[0117] The following text describes Figures 3 to 6 specific embodiments of the flowcharts shown and described in any of the following. Those skilled in the art will understand that, without departing from the spirit and scope of the present disclosure, Figures 7 to 10 the sequence of operations in any of the exemplary flowcharts 700, 800, 900, and 1000 may be changed, and some of the operations in any of the exemplary flowcharts 700, 800, 900, and 1000 may be eliminated or modified. Figures 7 to 10 in any of the exemplary flowcharts 700, 800, 900, and 1000.

[0118] Figure 7 An exemplary flowchart illustrating TA acquisition according to some embodiments of the present application.Figure 7 The embodiment relates to a scenario of TA re-acquisition triggered by a candidate cell, where the candidate DU determines whether the TA value is valid. The details described in all other embodiments of this application are applicable to the embodiment shown in Figure 7 .

[0119] As shown in Figure 7 , BS 705 is in a CU-DU architecture and includes CU 704, source DU 702, and candidate DU 703. In the embodiment of Figure 7 , the cell handover operation performed by UE 701 may refer to an intra-DU situation where the source cell and the target cell are in the same DU, or an inter-DU situation where the source cell and the target cell are located at different DUs. For example, for illustrative purposes, Figure 7 the flowchart 700 shown in only shows the cell handover operation in the inter-DU situation. If the source DU 702 and the candidate DU 703 are the same DU, then the flowchart 700 can also be applied to the intra-DU situation.

[0120] In Figure 7 the exemplary flowchart 700 shown in, in operation 711, UE 701 may access the serving BS (e.g., gNB) and send a measurement report to the serving BS (e.g., BS 705). The serving BS may include a CU (e.g., gNB-CU) and one or more DUs (e.g., gNB-DU). The serving cell is associated with the CU and the DU. There is an F1 interface between the DU and the CU. For example, as Figure 7 shown in, BS 705 includes CU 704, source DU 702, and candidate DU 703. BS 705 may include one or more other candidate DUs ( Figure 7 not shown in).

[0121] In operation 712, CU 704 may determine to initiate L1 / L2-based inter-cell mobility configuration and transmit a request message, such as a UE CONTEXTSETUP REQUEST message, to one or more candidate DUs (e.g., candidate DU 703) associated with one or more candidate cells. In some embodiments, the conditions for determining the TA value from CU 704 may be sent to candidate DU 703. The conditions may be the value of an early TA timer or a threshold related to RSRP change (e.g., Figure 3 the threshold #1 described in the embodiment of).

[0122] In operation 713, if candidate DU 703 decides to accept the request for LTM configuration, then candidate DU 703 may generate lower layer RRC configurations for one or more of the accepted candidate cells and send a response message containing the generated lower layer RRC configurations to CU 704. The response message may be a UE CONTEXT SETUP REQUEST message.

[0123] In operation 714, CU 704 may generate an RRCReconfiguration message based on the configurations of the accepted candidate cells received from candidate DU 703 and transmit the RRCReconfiguration message associated with the candidate cells for LTM configuration to UE 701 via source DU 702.

[0124] In operation 715, UE 701 may receive information from source DU 702 to trigger TA acquisition for the candidate cells within the candidate cell. In some embodiments, the information may be DCI, MAC CE, or RRC signaling. If the information is DCI, then it may be a PDCCH command.

[0125] In some embodiments, after source DU 702 transmits information (e.g., a PDCCH command) to UE 701 to trigger TA acquisition associated with the candidate cell, source DU 702 may release the dedicated RACH configuration for TA acquisition, such as a dedicated preamble and / or dedicated time-frequency domain resources. In some other embodiments, source DU 702 may retain the dedicated RACH resources for TA acquisition.

[0126] In operation 716, UE 701 may transmit a signal for TA acquisition (e.g., a sequence, e.g., a dedicated preamble or SRS) to candidate DU 703.

[0127] In operation 717, after candidate DU 703 successfully receives the signal for TA acquisition, candidate DU 703 may calculate or generate a TA value associated with the candidate cell.

[0128] In operation 718, candidate DU 703 may transmit a message via the F1 interface to CU 704, the message containing the calculated TA value, ID information of the corresponding candidate cell, and / or ID information of UE 701. The F1 message may be an UL RRC MESSAGETRANSFER message or a UE Context Modification Request message.

[0129] In operation 719, after the CU 704 receives the TA value, the CU 704 transmits the received TA value to the source DU 702. In some embodiments, the CU 704 will transmit the TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 701 to the source DU 702 via the F1 interface.

[0130] In operation 720, after the source DU 702 receives the TA value, the source DU 702 stores the TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 701. In some embodiments, if the source DU 702 receives the TA value of the same candidate cell and UE 701, then the source DU 702 stores the latest TA value.

[0131] In operation 721, the candidate DU 703 determines whether the current TA value associated with the candidate cell is invalid. In some embodiments, the candidate DU 703 may determine whether the TA value associated with the candidate cell is valid based on conditions, for example, until it is determined that the TA value is invalid.

[0132] In an embodiment, RSRP#1 is the RSRP value when the candidate DU 703 receives a preamble (or SRS) in operation 716 or when the candidate DU 703 calculates or generates a TA value in operation 717. RSRP#2 is the RSRP value received from the CU 704 or the source DU 702. In an embodiment, the source DU 702 may receive a measurement report, such as an L1 measurement result, which will be transmitted to the candidate DU 703 via the CU 704. Additionally, the CU 704 may transmit L3 measurement results to the candidate DU 703. RSRP#2 may be included in the L1 measurement result and / or the L3 measurement result. For example, if the RSRP change (RSRP#2 - RSRP#1) is equal to or greater than a threshold (e.g., threshold #1), then the TA value is considered invalid. Once the RSRP change (RSRP#2 - RSRP#1) is greater than or equal to the threshold, the candidate DU 703 determines that the TA value is invalid.

[0133] In another embodiment, a timer (e.g., an early TA timer) is used to determine whether the TA value is invalid. The candidate DU 703 may start the timer when it receives a TA acquisition signal (e.g., a preamble or SRS) in operation 716 or when it calculates the TA value in operation 717. The value of the timer may be configured by the CU 704. If the timer expires, then the TA value is considered invalid. Once the timer expires, the candidate DU 703 determines that the TA value is invalid.

[0134] In operation 722, if the candidate DU 703 determines that the current TA value is invalid based on L1 or L3 measurement results, the candidate DU 703 will indicate this to the source DU 702 via the CU 704. For example, the candidate DU 703 transmits an indication indicating that the current TA value is invalid. A new RACH resource may also be transmitted to the source DU 702.

[0135] In operation 723, the source DU 702 may transmit information (e.g., a PDCCH command) to the UE 701 again to trigger TA acquisition associated with the candidate cell to obtain the latest TA value of the candidate cell.

[0136] Figure 8 Another exemplary flowchart illustrating TA acquisition according to some embodiments of the present application. Figure 8 Embodiments relate to a CU-triggered TA re-acquisition scenario, where the CU determines whether the TA value is valid. The details described in all other embodiments of the present application apply to the embodiments shown in Figure 8

[0137] As shown in Figure 8 BS 805 is in a CU-DU architecture and includes a CU 804, a source DU 802, and a candidate DU 803. In the embodiments of Figure 8 a cell handover operation performed by the UE 801 may refer to a DU-internal scenario where the source cell and the target cell are in the same DU, or a DU-inter scenario where the source cell and the target cell are located at different DUs. For example, for illustrative purposes, Figure 8 the flowchart 800 shown in

[0138] only shows the cell handover operation in the DU-inter scenario. If the source DU 802 and the candidate DU 803 are the same DU, the flowchart 800 may also be applied to the DU-internal scenario. Figure 8 In the exemplary flowchart 800 shown in Figure 8 in operation 811, the UE 801 may access the serving BS (e.g., a gNB) and send a measurement report to the serving BS (e.g., BS 805). The serving BS may include a CU (e.g., a gNB-CU) and one or more DUs (e.g., gNB-DUs). The serving cell is associated with the CU and the DU. There is an F1 interface between the DU and the CU. For example, as shown in Figure 8 BS 805 includes a CU 804, a source DU 802, and a candidate DU 803. BS 805 may include one or more other candidate DUs (

[0139] In operation 812, the CU 804 may determine to initiate an L1 / L2-based inter-cell mobility configuration and transmit a request message, such as a UE CONTEXTSETUP REQUEST message, to one or more candidate DUs (e.g., candidate DU 803) associated with one or more candidate cells.

[0140] In operation 813, if the candidate DU 803 decides to accept the request for the LTM configuration, then the candidate DU 803 may generate a lower-layer RRC configuration for the accepted one or more candidate cells and send a response message containing the generated lower-layer RRC configuration to the CU 804. The response message may be a UE CONTEXT SETUP REQUEST message.

[0141] In operation 814, the CU 804 may generate an RRCReconfiguration message based on the configuration of the accepted candidate cells from the candidate DU 803 and transmit the RRCReconfiguration message associated with the candidate cells for the LTM configuration to the UE 801 via the source DU 802.

[0142] In operation 815, the UE 801 receives information for triggering TA acquisition for candidate cells within a candidate cell. In some embodiments, the information may be DCI, MAC CE, or RRC signaling. If the information is DCI, it may be a PDCCH command.

[0143] In some embodiments, after the source DU 802 transmits information (e.g., a PDCCH command) to the UE 801 to trigger TA acquisition associated with a candidate cell, the source DU 802 may release or store dedicated RACH resources (e.g., dedicated preambles and / or dedicated time-frequency domain resources) or dedicated SRS resources for TA acquisition.

[0144] In operation 816, the UE 801 may transmit a signal for TA acquisition (e.g., a sequence, e.g., a dedicated preamble or SRS) to the candidate DU 803.

[0145] In operation 817, after the candidate DU 803 successfully receives the signal for TA acquisition, the candidate DU 803 may calculate or generate a TA value associated with the candidate cell.

[0146] In operation 818, the candidate DU 803 may transmit a message via the F1 interface to the CU 804, the message containing the calculated TA value, ID information of the corresponding candidate cell, and / or ID information of the UE 801. The F1 message may be an UL RRC MESSAGETRANSFER message or a UE Context Modification Request message.

[0147] In operation 819, after the CU 804 receives the TA value, the CU 804 transmits the received TA value to the source DU 802. In some embodiments, the CU 804 will transmit the TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 801 to the source DU 802 via the F1 interface.

[0148] In operation 820, after the source DU 802 receives the TA value, the source DU 802 stores the TA value, the ID information of the corresponding candidate cell, and / or the ID information of the UE 801.

[0149] In operation 821, the CU 804 determines whether the current TA value associated with the candidate cell is valid. In some embodiments, the CU 804 may determine whether the TA value associated with the candidate cell is valid based on conditions, for example, until it is determined that the TA value is invalid.

[0150] In some embodiments, the CU 804 may determine whether the current TA value is valid based on the L3 measurement results. In an embodiment, the CU 804 determines whether the change in RSRP is greater than or equal to a threshold associated with the change in RSRP. For example, for instance, RSRP#3 is the RSRP value when the CU 804 receives the TA value, and RSRP#4 is the RSRP value included in the L3 measurement results received by the CU 804 from the UE 801 via the source DU 802. If the change in RSRP (RSRP#4 - RSRP#3) is equal to or greater than or equal to the threshold (for example, Figure 4 the threshold #2 described in the embodiments of), then the TA value is considered invalid. Once the change in RSRP (RSRP#4 - RSRP#3) is greater than or equal to the threshold, the CU 804 determines that the TA value is invalid.

[0151] In operation 822, once the CU determines that the TA is invalid, the CU 804 transmits an indication of TA re - acquisition to the source DU 802. Before the CU 804 transmits the indication to the source DU 802, the CU 804 may request the latest RACH resources from the candidate DU 803.

[0152] In operation 823, the source DU 802 may transmit again to the UE 801 the information (e.g., PDCCH command) for triggering the TA acquisition associated with the candidate cell to obtain the latest TA value of the candidate cell.

[0153] Figure 9 Another exemplary flowchart of TA acquisition according to some embodiments of the present application is illustrated. Figure 9The embodiment relates to a source DU-triggered TA re-acquisition scenario, where the source DU determines whether the TA value is valid. The details described in all other embodiments of this application apply to the embodiment shown in Figure 9 .

[0154] As shown in Figure 9 , BS 905 is in a CU-DU architecture and includes CU 904, source DU 902, and candidate DU 903. In the embodiment of Figure 9 , a cell change of UE 901 may refer to a DU-internal situation where the source cell and the target cell are in the same DU, or a DU-inter situation where the source cell and the target cell are located at different DUs. For example, for illustrative purposes, Figure 9 the flowchart 900 shown in only shows the cell change in the DU-inter situation. If the source DU 902 and the candidate DU 903 are the same DU, then the flowchart 900 can be applied to the DU-internal situation.

[0155] In Figure 9 the exemplary flowchart 900 shown, in operation 911, UE 901 may access the serving BS (e.g., gNB) and send a measurement report to the serving BS (e.g., BS 905). The serving BS may include a CU (e.g., gNB-CU) and one or more DUs (e.g., gNB-DU). The serving cell is associated with the CU and the DUs. There is an F1 interface between the DU and the CU. For example, as Figure 9 shown, BS 905 includes CU 904, source DU 902, and candidate DU 903. BS 905 may include one or more other candidate DUs ( Figure 9 not shown in).

[0156] In operation 912, CU 904 may determine to initiate L1 / L2-based inter-cell mobility configuration and transmit a request message, such as a UE CONTEXT SETUP REQUEST message, to one or more candidate DUs (e.g., candidate DU 903) associated with one or more candidate cells.

[0157] In operation 913, if candidate DU 903 decides to accept the request for LTM configuration, then candidate DU 903 may generate a lower-layer RRC configuration for the accepted one or more candidate cells and send a response message containing the generated lower-layer RRC configuration to CU 804. The response message may have a UE CONTEXT SETUP REQUEST message.

[0158] In operation 914, CU 904 generates an RRCReconfiguration message based on the configuration of the accepted candidate cell from candidate DU 903, and transmits the RRCReconfiguration message associated with the candidate cell for LTM configuration to UE 901 via source DU 902.

[0159] In operation 915, UE 901 may receive information (e.g., indication #1 described in the embodiments of Figure 5 ) from source DU 902 for triggering TA acquisition for the candidate cell within the candidate cell. In some embodiments, the information may be DCI, MACCE, or RRC signaling. If the information is DCI, it may be a PDCCH command.

[0160] In some embodiments, after source DU 902 transmits information (e.g., a PDCCH command) to UE 901 to trigger TA acquisition associated with the candidate cell, source DU 902 may release or store dedicated RACH resources (e.g., dedicated preambles and / or dedicated time-frequency domain resources) or dedicated SRS resources for TA acquisition.

[0161] In operation 916, UE 901 may transmit a TA acquisition signal (e.g., a sequence, e.g., a dedicated preamble or SRS) to candidate DU 903.

[0162] In operation 917, after candidate DU 903 successfully receives the TA acquisition signal, candidate DU 903 calculates or generates a TA value associated with the candidate cell.

[0163] In operation 918, candidate DU 903 transmits a message to CU 904 via the F1 interface, the message including the calculated TA value, ID information of the corresponding candidate cell, and / or ID information of UE 901. The F1 message may be a UL RRC MESSAGE TRANSFER message or a UE Context Modification Request message.

[0164] In operation 919, after CU 904 receives the TA value, CU 904 transmits the received TA value to source DU 902. In some embodiments, CU 904 may transmit the TA value, ID information of the corresponding candidate cell, and / or ID information of UE 901 to source DU 902 via the F1 interface.

[0165] In operation 920, after source DU 902 receives the TA value, source DU 902 stores the TA value, ID information of the corresponding candidate cell, and / or ID information of UE 901.

[0166] In operation 921, the source DU 902 determines whether the current TA value associated with the candidate cell is valid. In some embodiments, the source DU 902 may determine whether the TA value associated with the candidate cell is valid based on conditions, for example, until it is determined that the TA value is invalid.

[0167] In some embodiments, the source DU 902 may maintain configuration information regarding the conditions for determining whether the TA value is valid. The configuration information may include the value of the early TA timer and / or a threshold related to the RSRP change. The configuration information may be provided to the source DU 902 by the CU 904 or the candidate DU 903.

[0168] In an embodiment, regarding the RSRP change, RSRP#5 may be the RSRP when the source DU 902 transmits information (e.g., a PDCCH command) to trigger TA acquisition in operation 915, or may be the RSRP when the source DU 902 receives the TA value from the candidate DU 903. RSRP#6 is the RSRP value received from the UE 901. In an embodiment, the source DU 902 may receive the layer 1 (L1) measurement results of the UE 901 from the UE 901, where RSRP#6 is included in the L1 measurement results. For example, if the RSRP change (RSRP#6 - RSRP#5) is equal to or greater than or equal to a threshold (e.g., Figure 5 the threshold #3 described in the embodiment of), then the TA value is considered invalid. Once the RSRP change (RSRP#6 - RSRP#5) is greater than or equal to the threshold, the source DU 902 determines that the TA value is invalid.

[0169] In another embodiment, a timer (e.g., an early TA timer) is used to determine whether the TA value is invalid. In operation 915, when the source DU 902 transmits information (e.g., a PDCCH command) to trigger TA acquisition associated with the candidate cell, the source DU 902 may start the timer. The value of the timer may be configured by the CU 904. If the timer expires, then the TA value is considered invalid. Once the timer expires, the source DU 902 determines that the TA value is invalid.

[0170] In operation 922, once the source DU 902 determines that the TA value of the candidate cell is invalid, the source DU 902 transmits information (e.g., Figure 5 the indication #2 described in the embodiment of) (e.g., a PDCCH command) to the UE 901 again to trigger TA acquisition associated with the candidate cell to obtain the latest TA value of the candidate cell. In some embodiments, before the source DU 902 transmits information to the UE 901 to trigger TA acquisition, the source DU 902 may request the latest RACH resources from the candidate DU 903.

[0171] Figure 10Another exemplary flowchart illustrating TA acquisition according to some embodiments of the present application. Figure 10 Embodiments relate to a UE-triggered TA re-acquisition scenario in which the UE determines whether the TA value is valid. Details described in all other embodiments of the present application apply to the embodiments shown in Figure 10 herein.

[0172] As shown in Figure 10 herein, BS1005 is in a CU-DU architecture and includes CU 1004, source DU 1002, and candidate DU 1003. In Figure 10 embodiments, a cell change of UE 1001 may refer to an intra-DU situation where the source cell and the target cell are in the same DU, or an inter-DU situation where the source cell and the target cell are at different DUs. For example, for illustrative purposes, Figure 10 flowchart 1000 shown herein only shows cell changes in the inter-DU situation. If source DU 1002 and candidate DU 1003 are the same DU, then flowchart 1000 can be applied to the intra-DU situation.

[0173] In Figure 10 the exemplary flowchart 1000 shown herein, in operation 1011, UE 1001 may access a serving BS (e.g., gNB) and send a measurement report to the serving BS (e.g., BS1005). The serving BS may include a CU (e.g., gNB-CU) and one or more DUs (e.g., gNB-DU). The serving cell is associated with the CU and the DUs. There is an F1 interface between the DU and the CU. For example, as Figure 10 shown herein, BS1005 includes CU 1004, source DU 1002, and candidate DU 1003. BS1005 may include one or more other candidate DUs ( Figure 10 not shown herein).

[0174] In operation 1012, CU 1004 may determine to initiate L1 / L2-based inter-cell mobility configuration and transmit a request message, such as a UE CONTEXT SETUP REQUEST message, to one or more candidate DUs (e.g., candidate DU 1003) associated with one or more candidate cells.

[0175] In operation 1013, if candidate DU 1003 decides to accept the request for the LTM configuration, then candidate DU 1003 may generate lower-layer RRC configuration for the accepted one or more candidate cells and send a response message containing the generated lower-layer RRC configuration to CU 1004. The response message may have a UE CONTEXT SETUP REQUEST message.

[0176] In operation 1014, CU 1004 may generate an RRCReconfiguration message based on the configuration of the accepted candidate cells from candidate DU 1003, and transmit the RRCReconfiguration message associated with the candidate cells for LTM configuration to UE 1001 via source DU 1002.

[0177] In operation 1015, UE 1001 may receive information for triggering TA acquisition for candidate cells within the candidate cell (e.g., indication #3 described in the embodiments of Figure 6 ). In some embodiments, the information may be DCI, MAC CE, or RRC signaling. If the information is DCI, it may be a PDCCH command.

[0178] In some embodiments, after source DU 1002 transmits information (e.g., a PDCCH command) for triggering TA acquisition associated with the candidate cell to UE 1001, source DU 1002 may release or store dedicated RACH resources (e.g., dedicated preambles and / or dedicated time-frequency domain resources) or dedicated SRS resources for TA acquisition.

[0179] In operation 1016, UE 1001 may transmit a TA acquisition signal (e.g., a sequence, such as a dedicated preamble or SRS) to candidate DU 1003 (e.g., signal #1 described in the embodiments of Figure 6 ).

[0180] In operation 1017, after candidate DU 1003 successfully receives the TA acquisition signal, candidate DU 1003 may calculate or generate a TA value associated with the candidate cell.

[0181] In operation 1018, candidate DU 1003 may transmit a message via the F1 interface to CU 1004, the message including the calculated TA value, ID information of the corresponding candidate cell, and / or ID information of UE 801. The F1 message may be a UL RRC MESSAGETRANSFER message or a UE Context Modification Request message.

[0182] In operation 1019, there may be two cases in different embodiments, namely Case 1 and Case 2 as follows. (1) Case 1: In operation 1019, UE 1001 may receive the TA value included in a cell handover command (e.g., a MAC CE command). In Case 1, UE 1001 does not receive a RAR message. It is not expected that UE 1001 maintains the TA value before cell handover.

[0183] (2) Case 2: In operation 1019, UE 1001 will receive a RAR message containing a TA value before cell handover.

[0184] In Case 2, UE 1001 needs to maintain the TA value before cell handover.

[0185] In operation 1020, UE 1001 may determine whether the current TA value associated with the candidate cell is valid. In some embodiments, UE 1001 may determine whether the TA value associated with the candidate cell is valid based on conditions, for example, until it is determined that the TA value is invalid.

[0186] In some embodiments, UE 1001 may maintain configuration information regarding the conditions for determining whether the TA value is valid. The configuration information may include the value of an early TA timer and / or a threshold related to RSRP change. The configuration information may be provided by CU 1004 or candidate DU 1003.

[0187] In an embodiment, in operation 1020, once UE 1001 receives information (e.g., a PDCCH command) for triggering TA acquisition in operation 1015 or receives a TA value in operation 1019, UE 1001 starts a timer (e.g., an early TA timer). The value of the timer may be configured by CU 904. If the timer expires, the TA value is considered invalid. Once the timer expires, UE 1001 determines that the TA value is invalid.

[0188] In another embodiment, regarding RSRP change, RSRP#7 may be the RSRP when UE 1001 transmits a TA acquisition signal (e.g., a dedicated preamble or SRS) in operation 1016. RSRP#8 is the RSRP value measured by the UE after the UE receives the TA value. For example, if the RSRP change (RSRP#8 - RSRP#7) is equal to or greater than a threshold (e.g., Figure 6 the threshold #4 described in the embodiment of), then the TA value is considered invalid. Once the RSRP change (RSRP#8 - RSRP#7) is greater than or equal to the threshold, UE1001 determines that the TA value is invalid.

[0189] After UE 1001 determines that the TA value is invalid, there may be the following two options in different embodiments, namely Option 1 and Option 2 as follows.

[0190] (1) Option 1: After the UE 1001 receives information (e.g., PDCCH command) for triggering TA acquisition in operation 1015, the UE 1001 transmits a TA acquisition signal (e.g., dedicated preamble or SRS) (e.g., signal #1) to the candidate DU 1003 in operation 1016. In operation 1021A (optional), once the UE 1001 determines that the TA value of the candidate cell is invalid, the UE 1001 is triggered again to transmit a TA acquisition signal (e.g., dedicated preamble or SRS) (e.g., Figure 6 signal #2 as described in the embodiment of

[0191] (2) Option 2: In operation 1021B (optional), once the UE 1001 determines that the TA value of the candidate cell is invalid, the UE 1001

[0192] transmits information indicating the invalid TA value to the network (e.g., source DU 1002). In operation 1022B (optional), the source DU 1002 may transmit information (e.g., Figure 6 indication #4 as described in the embodiment of

[0193] to trigger TA acquisition associated with the candidate cell again (e.g., PDCCH command). In operation 1022B, there may be the following two options in different embodiments, namely Option A and Option B as follows.

[0194] a) Option A: In the inter-DU scenario, once the source DU 1002 receives information indicating the invalid TA value from the UE 1001, the source DU 1002 transmits information indicating the valid TA value to the candidate DU 1003 via the CU 1004. Then, the candidate DU 1003 transmits RACH resources (e.g., dedicated preamble or dedicated time-frequency resources) to the source DU 1002 via the CU 1004. Finally, the source DU 1002 transmits information (e.g., indication #4, e.g., PDCCH command) to the UE 1001 to trigger TA re-acquisition.

[0194] b) Option B: In the intra-DU scenario, once the source DU 1002 receives information for indicating the invalid TA value from the UE 1001, the source DU 1002 transmits information (e.g., indication #4,

[0195] e.g., PDCCH command) to the UE 1001 based on the RACH resources to trigger TA acquisition.

[0196] Figure 11 A block diagram of an exemplary device 1100 according to some embodiments of the present application is illustrated. As in Figure 11As shown, device 1100 may include at least one processor 1106 and at least one transceiver 1102 coupled to processor 1106. Although in this figure, elements such as at least one transceiver 1102 and processor 1106 are described in the singular, plural may be contemplated unless explicitly limited to the singular. In some embodiments of the present application, transceiver 1102 may be divided into two devices, such as a receiving circuit system and a transmitting circuit system. In some embodiments of the present application, device 1100 may further include an input device, a memory, and / or other components.

[0197] In some embodiments of the present application, device 1100 may be a UE or a network node (e.g., a BS, a CU, or a DU). Transceiver 1102 and processor 1106 may interact with each other to perform operations regarding the UE or the network node as described above, for example, in Figures 1 to 10 any of the above.

[0198] In some embodiments of the present application, device 1100 may further include at least one non-transitory computer-readable medium. For example, in some embodiments of the present disclosure, the non-transitory computer-readable medium may store computer-executable instructions thereon to cause processor 1106 to implement a method regarding the UE or the network node (e.g., a BS, a CU, or a DU) as described above. For example, when the computer-executable instructions are executed, they cause processor 1106 to interact with transceiver 1102 to perform Figures 1 to 10 operations regarding the UE or the network node as described above.

[0199] Those of ordinary skill in the art will understand that the operations or steps of the methods described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of both. The software module may reside in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Additionally, in some aspects, the operations or steps of the methods may reside on a non-transitory computer-readable medium as one or any combination or group of codes and / or instructions that may be incorporated into a computer program product.

[0200] In this document, the term "includes" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a series of elements includes not only those elements but also other elements not expressly listed or inherent to the process, method, article, or apparatus. Without further limitation, an element preceded by "a" or the like does not exclude the presence of additional equivalent elements in the process, method, article, or apparatus that includes the element. Additionally, the term "another" is defined as at least second or more. The terms "has" and the like as used herein are defined as "includes". For example, an expression such as "A and / or B" or "at least one of A and B" can include any and all combinations of the words enumerated with the expression. For example, the expression "A and / or B" or "at least one of A and B" can include A, B, or both A and B. The terms "first", "second", or the like are used only to clearly illustrate embodiments of the present application but do not limit the substance of the present application.

Claims

1. A candidate distributed unit (DU) of a base station (BS), comprising: A transceiver; And A processor coupled to the transceiver, wherein the processor is configured to: Receive, via the transceiver, a signal from a user equipment (UE) for timing advance (TA) acquisition associated with a candidate cell; Transmit, via the transceiver, a TA value associated with the candidate cell to a source DU of the BS or to the UE; And Determine whether the TA value associated with the candidate cell is valid.

2. The candidate DU according to claim 1, wherein the signal is at least one of the following: A preamble; or A sounding reference signal (SRS).

3. The candidate DU according to claim 1, wherein the processor of the candidate DU is configured to calculate the TA value based on the received signal, and the TA value is transmitted to the source DU via a centralized unit (CU) of the BS.

4. The candidate DU according to claim 3, wherein the processor of the candidate DU is configured to transmit, via the CU, at least one of the following to the source DU: Identifier (ID) information of the candidate cell; or ID information of the UE.

5. The candidate DU according to claim 1, wherein based on the received signal, the TA value is transmitted to the UE in a random access response (RAR) message.

6. The candidate DU according to claim 1, wherein it is determined whether the TA value is valid based on conditions, and the conditions based on which the TA value is determined to be invalid include at least one of the following: Expiration of an early TA timer; or The difference between a first reference signal received power (RSRP) value and a second RSRP value is greater than or equal to a threshold related to RSRP change.

7. The candidate DU according to claim 6, wherein the processor of the candidate DU is configured to receive, via the transceiver, configuration information about the conditions from the CU, and the configuration information includes at least one of the following: The value of the early TA timer; or The threshold related to RSRP change.

8. The candidate DU according to claim 6, wherein the processor of the candidate DU is configured to start the early TA timer when the signal is received or when the TA value is calculated.

9. The candidate DU according to claim 6, wherein the first RSRP value is the RSRP value when the candidate DU receives the signal or when the candidate DU calculates the TA value, and the second RSRP value is the RSRP value received from the CU or the source DU.

10. The candidate DU according to any one of claims 1, 6, and 9, wherein the processor of the candidate DU is configured to receive, via the transceiver, at least one of the following: Layer 1 (L1) measurement results of the UE from the source DU; or Layer 3 (L3) measurement results of the UE from the CU, wherein the second RSRP value is included in at least one of the L1 measurement results or the L3 measurement results.

11. The candidate DU according to claim 1 or claim 6, in response to determining that the TA value is invalid, the processor of the candidate DU is configured to transmit, via the CU and via the transceiver, information indicating that the TA value is invalid to the source DU.

12. The candidate DU according to claim 11, wherein the processor of the candidate DU is configured to transmit, via the CU and via the transceiver, configuration information about a random access channel RACH resource for TA acquisition associated with the candidate cell to the source DU.

13. A central unit CU of a base station BS, comprising: A transceiver; And A processor coupled to the transceiver, wherein the processor is configured to: Receive, via the transceiver, a timing advance TA value associated with a candidate cell from a candidate distributed unit DU of the BS; And Transmit, via the transceiver, the TA value associated with the candidate cell to a source DU of the BS.

14. A source distributed unit DU of a base station BS, comprising: A transceiver; And A processor coupled to the transceiver, wherein the processor is configured to: Transmit, via the transceiver, a first indication for timing advance TA acquisition associated with a candidate cell to a user equipment UE; and Transmit, via the transceiver, a second indication of TA acquisition associated with the candidate cell to the UE.

15. A user equipment UE, comprising: A transceiver; And A processor coupled to the transceiver, wherein the processor is configured to: Receive, via the transceiver, a first indication of timing advance TA associated with a candidate cell from a source distributed unit DU of a base station BS; Based on the first indication, transmit, via the transceiver, a first signal for TA acquisition to a candidate distributed unit DU of the BS; Receive, via the transceiver, a second indication of TA acquisition associated with the candidate cell from the source DU; And Based on the second indication, transmit, via the transceiver, a second signal for TA acquisition to the candidate DU.

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