WO2024087675A1

WO2024087675A1 - Methods and apparatuses for ta acquisition and calculation

Info

Publication number: WO2024087675A1
Application number: PCT/CN2023/101833
Authority: WO
Inventors: Lianhai WU; Mingzeng Dai; Congchi ZHANG; Shuigen Yang
Original assignee: Lenovo (Beijing) Limited
Priority date: 2023-06-21
Filing date: 2023-06-21
Publication date: 2024-05-02

Abstract

Various aspects of the present disclosure relate to methods and apparatuses for timing advance (TA) acquisition and/or TA calculation during wireless communications. According to an embodiment of the present disclosure, a user equipment (UE) includes at least one memory and at least one processor coupled to the at least one memory and configured to cause the UE to: receive a radio resource control (RRC) reconfiguration message from a base station (BS), wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells related to lower layer triggered mobility (LTM); receive a cell switching command from the BS, wherein the cell switching command includes identifier (ID) information related to a candidate cell within the set of candidate cells; and perform cell switching towards the candidate cell based on the cell switching command.

Description

METHODS AND APPARATUSES FOR TA ACQUISITION AND CALCULATION

TECHNICAL FIELD

The present disclosure relates to wireless communications, and more specifically to methods and apparatuses for timing advance (TA) acquisition and/or TA calculation during wireless communications.

BACKGROUND

A wireless communications system may include one or multiple network communication devices, such as base stations, which may support wireless communications for one or multiple user communication devices, which may be otherwise known as user equipment (UE) , or other suitable terminology. The wireless communications system may support wireless communications with one or multiple user communication devices by utilizing resources of the wireless communication system (e.g., time resources (e.g., symbols, slots, subframes, frames, or the like) or frequency resources (e.g., subcarriers, carriers, or the like) . Additionally, the wireless communications system may support wireless communications across various radio access technologies including third generation (3G) radio access technology, fourth generation (4G) radio access technology, fifth generation (5G) radio access technology, among other suitable radio access technologies beyond 5G (e.g., sixth generation (6G) ) .

SUMMARY

An article “a” before an element is unrestricted and understood to refer to “at least one” of those elements or “one or more” of those elements. The terms “a, ” “at least one, ” “one or more, ” and “at least one of one or more” may be interchangeable. As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of” or “one or more of” or “one or both of” ) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) . Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on. Further, as used herein, including in the claims, a “set” may include one or more elements.

Some implementations of the present disclosure provide a user equipment (UE) . The UE includes at least one memory; and at least one processor coupled to the at least one memory and configured to cause the UE to: receive a radio resource control (RRC) reconfiguration message from a base station (BS) , wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells; receive a cell switching command from the BS, wherein the cell switching command includes identifier (ID) information related to a first candidate cell within the set of candidate cells; and perform cell switching towards the first candidate cell based on the cell switching command.

In some implementations of the UE described herein, the cell switching command includes at least one of the following: index information of candidate cell configuration of the first candidate cell; a first timing advance (TA) value for the first candidate cell; or a timer length of a timing advance timer (TAT) associated with the first TA value.

In some implementations of the UE described herein, the processor is configured to cause the UE to: if the UE fails to access the first candidate cell, initiate a reestablishment procedure; and if first information indicating that the set of candidate cells can be used for recovery has been configured to the UE, keep first configuration, wherein the first configuration at least includes configuration for a primary cell of a master or secondary cell group (SpCell) , configuration for one or more master cell group (MCG) secondary cells (SCell) s, multi-radio dual connectivity (MR-DC) configuration, overheating assistance configuration, and In-Device Coexistence (IDC) assistance configuration; or if the first information is not configured to the UE, release the first configuration.

In some implementations of the UE described herein, the processor is configured to cause the UE to: select a second candidate cell for an RRC reestablishment procedure; determine whether the second candidate cell is one candidate cell within the set of candidate cells or not; and if the second candidate cell is the one candidate cell within the set of candidate cells, apply cell switching configuration for the second candidate cell and perform cell switching to the second candidate cell; or if the second candidate cell is not the one candidate cell within the set of candidate cells and if the first information has been configured to the UE, release the first configuration.

In some implementations of the UE described herein, the processor is configured to cause the UE to: transmit an RRC reconfiguration complete message associated with the second candidate cell to the CU, wherein the RRC reconfiguration complete message includes identifier (ID) information related to the second candidate cell.

In some implementations of the UE described herein, the RRC reconfiguration message includes second information indicating the UE to calculate at least one of the following: a first TA value for the first candidate cell; or a second TA value for a second candidate cell.

In some implementations of the UE described herein, whether the UE is to calculate a TA value or not is determined by a centralized unit (CU) of the BS, one or more candidate DUs of the BS, or a source distributed unit (DU) of the BS.

In some implementations of the UE described herein, the processor is configured to cause the UE to: in response to receiving the second information including ID information of the first candidate cell, consider that the first TA value for the first candidate cell is not included in the cell switching command for the first candidate cell.

In some implementations of the UE described herein, the processor is configured to cause the UE to: after receiving the second information including ID information of both the first candidate cell and the second candidate cell, calculate the first TA value for the first candidate cell and the second TA value for the second candidate cell.

In some implementations of the UE described herein, the first or second TA value is calculated based on at least one of the following: a receiving timing difference between a source cell of the UE and the first or second candidate cell; or a TA value for the source cell.

In some implementations of the UE described herein, the processor is configured to cause the UE to: if a physical downlink control channel (PDCCH) order for a TA acquisition procedure for the first candidate cell is received: discard the first TA value for the first candidate cell; or keep the first TA value for the first candidate cell before receiving a third TA value for the first candidate cell from a source distributed unit (DU) of the BS, and discarding the first TA value for the first candidate cell after receiving the third TA value from the source DU; or if the cell switching command includes the third TA value, discard the first TA value for the first candidate cell, and perform cell switching to the first candidate cell using the third TA value.

In some implementations of the UE described herein, the processor is configured to cause the UE to: release or store the second TA value for the second candidate cell after UE switches to the first candidate cell.

In some implementations of the UE described herein, the processor is configured to cause the UE to: in response to storing the second TA value for the second candidate cell, determine whether the second TA value is valid or not based on a timing advance timer (TAT) associated with the second TA value.

In some implementations of the UE described herein, the processor is configured to cause the UE to: release or store the first TA value for the first candidate cell after UE switches to the first candidate cell.

In some implementations of the UE described herein, the processor is configured to cause the UE to: in response to storing the first TA value for the first candidate cell, report the first TA value via an RRC message or a medium access control (MAC) control element (CE) to a candidate DU associated with the first candidate cell.

In some implementations of the UE described herein, the processor is configured to cause the UE to: receive a delta value used for updating the first TA value from the candidate DU associated with the first candidate cell.

In some implementations of the UE described herein, the processor is configured to cause the UE to: in response to storing the first TA value for the first candidate cell, receive an absolute TA value for the first candidate cell from a candidate DU associated with the first candidate cell; release the first TA value; and store the absolute TA value for the first candidate cell.

In some implementations of the UE described herein, the processor is configured to cause the UE to: continue updating the first TA value before receiving the delta value or the absolute TA value from the candidate DU associated with the first candidate cell.

In some implementations of the UE described herein, to continue updating the first TA value, the processor is configured to cause the UE to: store a TA value of a source cell of the UE; receive a timer length of a first timing advance timer (TAT) associated with the TA value of the source cell; continue updating the first TA value based on the TA value of the source cell before expiry of the first TAT; and consider the first TA value as invalid upon the expiry of the first TAT.

In some implementations of the UE described herein, the processor is configured to cause the UE to: in response to considering the first TA value as invalid, trigger a random access channel (RACH) procedure for uplink (UL) synchronization.

Some implementations of the present disclosure provide a method performed by a user equipment (UE) . The method includes: receiving a radio resource control (RRC) reconfiguration message from a base station (BS) , wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells; receiving a cell switching command from the BS, wherein the cell switching command includes identifier (ID) information related to a first candidate cell within the set of candidate cells; and performing cell switching towards the first candidate cell based on the cell switching command.

Some implementations of the present disclosure provide a processor for wireless communication, comprising at least one controller coupled with at least one memory and configured to cause the processor to: receive a radio resource control (RRC) reconfiguration message from a base station (BS) , wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells; receive a cell switching command from the BS, wherein the cell switching command includes identifier (ID) information related to a first candidate cell within the set of candidate cells; and perform cell switching towards the first candidate cell based on the cell switching command.

Some implementations of the present disclosure provide a source distributed unit (DU) of a base station (BS) . The source DU includes at least one memory; and at least one processor coupled to the at least one memory and configured to cause the source DU to: receive a first timing advance (TA) value list for a set of candidate cells from a centralized unit (CU) of the BS, wherein the first TA value list includes a first TA value for a first candidate cell within the set of candidate cells; and transmit a cell switching command to a user equipment (UE) , wherein the cell switching command includes identifier (ID) information related to the first candidate cell.

In some implementations of the source DU described herein, the cell switching command includes at least one of the following: the first TA value for the first candidate cell; or a timer length of a timing advance timer (TAT) associated with the first TA value.

In some implementations of the source DU described herein, the first TA value list further includes a second TA value for a second candidate cell within the set of candidate cells.

In some implementations of the source DU described herein, the processor is configured to cause the source DU to: after transmitting the cell switching command, transmit at least one of the following via the CU to a candidate distributed unit (DU) of the BS associated with the first candidate cell: a second TA value list; or additional information associated with the second TA value list.

In some implementations of the source DU described herein, the second TA value list includes all TA values within the first TA value list, or includes all TA values within the first TA value list except the first TA value for the first candidate cell included in cell switching command.

In some implementations of the source DU described herein, the additional information associated with a TA value within the TA value list includes at least one of the following: absolute time when receiving the TA value; time elapsed since receiving the TA value; or a remaining valid period of the TA value.

Some implementations of the present disclosure provide a method performed by a source distributed unit (DU) of a base station (BS) . The method includes: receiving a first timing advance (TA) value list for a set of candidate cells from a centralized unit (CU) of the BS, wherein the first TA value list includes a first TA value for a first candidate cell within the set of candidate cells; and transmitting a cell switching command to a user equipment (UE) , wherein the cell switching command includes identifier (ID) information related to the first candidate cell.

Some implementations of the present disclosure provide a processor for wireless communication, comprising at least one controller coupled with at least one memory and configured to cause the processor to: receive a first timing advance (TA) value list for a set of candidate cells from a centralized unit (CU) of the BS, wherein the first TA value list includes a first TA value for a first candidate cell within the set of candidate cells; and transmit a cell switching command to a user equipment (UE) , wherein the cell switching command includes identifier (ID) information related to the first candidate cell.

Some implementations of the present disclosure provide a centralized unit (CU) of a base station (BS) . The CU includes at least one memory; and at least one processor coupled to the at least one memory and configured to cause the CU to: transmit a request for cell switching configuration for a set of candidate cells to one or more candidate distributed units (DU) s of the BS; receive a response corresponding to the request from the one or more candidate DUs, wherein the response includes the cell switching configuration for the set of candidate cells; and transmit the cell switching configuration for the set of candidate cells to a user equipment (UE) via a source DU of the BS based on the response.

In some implementations of the CU described herein, the processor is configured to cause the CU to receive a radio resource control (RRC) reconfiguration complete message associated with a second candidate cell within the set of candidate cells from the UE after the UE fails to switch to a first candidate cell, wherein the RRC reconfiguration complete message includes identifier (ID) information related to the second candidate cell.

In some implementations of the CU described herein, the processor is configured to cause the CU to transmit at least one of the following to a candidate DU associated with the second candidate cell after receiving the RRC reconfiguration complete message: a TA value list; or additional information associated with the TA value list.

In some implementations of the CU described herein, the processor is configured to cause the CU to receive at least one of the following from the source DU after the source DU transmits a cell switching command including identifier (ID) information related to a first candidate cell: a TA value list; or additional information associated with the TA value list.

In some implementations of the CU described herein, the additional information associated with a TA value within the TA value list includes at least one of the following: absolute time when receiving the TA value; time elapsed since receiving the TA value; or a remaining valid period of the TA value.

In some implementations of the CU described herein, the processor is configured to cause the CU to transmit at least one of the TA value list or the additional information to the second candidate cell.

In some implementations of the CU described herein, the request for cell switching configuration includes first information indicating that the UE is to calculate a TA value for a candidate cell.

In some implementations of the CU described herein, the processor is configured to cause the CU to: receive at least one of the following from the one or more candidate DUs: second information indicating the UE to calculate one or more TA values for the set of candidate cells; or reference signal (RS) configuration information configured to the UE.

In some implementations of the CU described herein, the second information is included in the cell switching configuration to the UE.

Some implementations of the present disclosure provide a method performed by a centralized unit (CU) of a base station (BS) . The method includes: transmitting a request for cell switching configuration for a set of candidate cells to one or more candidate distributed units (DU) s of the BS; receiving a response corresponding to the request from the one or more candidate DUs, wherein the response includes the cell switching configuration for the set of candidate cells; and transmitting the cell switching configuration for the set of candidate cells to a user equipment (UE) via a source DU of the BS based on the response.

Some implementations of the present disclosure provide a processor for wireless communication, comprising at least one controller coupled with at least one memory and configured to cause the processor to: transmit a request for cell switching configuration for a set of candidate cells to one or more candidate distributed units (DU) s of the BS; receive a response corresponding to the request from the one or more candidate DUs, wherein the response includes the cell switching configuration for the set of candidate cells; and transmit the cell switching configuration for the set of candidate cells to a user equipment (UE) via a source DU of the BS based on the response.

Some implementations of the present disclosure provide a candidate distributed unit (DU) of a base station (BS) . The candidate DU includes at least one memory; and at least one processor coupled to the at least one memory and configured to cause the candidate DU to: receive a request for cell switching configuration for a set of candidate cells for a user equipment (UE) from a centralized unit (CU) of the BS; and transmit a response to the CU based on the request, wherein the response includes configuration related to the set of candidate cells for the UE, and wherein the set of candidate cells includes a first candidate cell.

In some implementations of the candidate DU described herein, the processor is configured to cause the candidate DU to: receive at least one of the following from the CU: a timing advance (TA) value list for the set of candidate cells; the TA value list except a first TA value for the first candidate cell, wherein the UE is configured to switch to the first candidate cell; or additional information associated with the TA value list.

In some implementations of the candidate DU described herein, the additional information associated with a TA value within the TA value list includes at least one of the following: absolute time when receiving the TA value; time elapsed since receiving the TA value; or a remaining valid period of the TA value.

In some implementations of the candidate DU described herein, the processor is configured to cause the candidate DU to transmit at least one of the following to the CU: second information indicating the UE to calculate one or more TA values for the set of candidate cells; or reference signal (RS) configuration information configured to the UE.

In some implementations of the candidate DU described herein, the processor is configured to cause the candidate DU to determine whether the UE is to calculate the one or more TA values or not.

In some implementations of the candidate DU described herein, the processor is configured to cause the candidate DU to receive a first TA value for the first candidate cell via the CU from the UE, wherein the UE is configured to switch to the first candidate cell.

In some implementations of the candidate DU described herein, the processor is configured to cause the candidate DU to transmit a delta value used for updating the first TA value via the CU to the UE.

In some implementations of the candidate DU described herein, the processor is configured to cause the candidate DU to transmit an absolute TA value for the first candidate cell via the CU to the UE.

Some implementations of the present disclosure provide a method performed by a candidate distributed unit (DU) of a base station (BS) . The method includes: receiving a request for cell switching configuration for a set of candidate cells for a user equipment (UE) from a centralized unit (CU) of the BS; and transmitting a response to the CU based on the request, wherein the response includes configuration related to the set of candidate cells for the UE, and wherein the set of candidate cells includes a first candidate cell.

Some implementations of the present disclosure provide a processor for wireless communication, comprising at least one controller coupled with at least one memory and configured to cause the processor to: receive a request for cell switching configuration for a set of candidate cells for a user equipment (UE) from a centralized unit (CU) of the BS; and transmit a response to the CU based on the request, wherein the response includes configuration related to the set of candidate cells for the UE, and wherein the set of candidate cells includes a first candidate cell.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an example of a wireless communications system in accordance with aspects of the present disclosure.

Figure 2 illustrates an example of a user equipment (UE) 200 in accordance with aspects of the present disclosure.

Figure 3 illustrates an example of a processor 300 in accordance with aspects of the present disclosure.

Figure 4 illustrates an example of a network equipment (NE) 400 in accordance with aspects of the present disclosure.

Figure 5 illustrates a schematic diagram of inter-cell Layer1/Layer2 (L1/L2) mobility in accordance with aspects of the present disclosure.

Figure 6 illustrates a flowchart of method performed by a UE in accordance with aspects of the present disclosure.

Figure 7 illustrates a flowchart of method performed by a source DU in accordance with aspects of the present disclosure.

Figure 8 illustrates a flowchart of method performed by a CU in accordance with aspects of the present disclosure.

Figure 9 illustrates a flowchart of method performed by a candidate DU in accordance with aspects of the present disclosure.

Figure 10 illustrates an example of performing cell switching in accordance with aspects of the present disclosure.

Figure 11 illustrates another example of performing cell switching in accordance with aspects of the present disclosure.

Figure 12 illustrates an example of TA calculation in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Some implementations of the present disclosure may be applicable for a case of “lower layer triggered mobility” or “L1/L2 triggered mobility” , and the abbreviation of at least one of them may be “LTM” . In an LTM case, a UE may access a serving BS (e.g., a serving gNB) . The UE may report Layer3 (L3) measurement result (s) based on the configuration from the serving gNB. If the serving gNB, e.g., a CU of the serving gNB, decides to switch the UE to a candidate cell based on the measurement result (s) , the serving gNB may request target DU (s) to prepare the configuration for one or more candidate cells. After receiving the candidate cell configuration from a target DU of the serving gNB, the serving gNB may transmit an RRC reconfiguration message including 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 a 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 a cell switching command. For example, the UE may get or acquire a TA value via a random access (RA) or preamble transmission. The UE may report Layer1 (L1) measurement result (s) for a dynamic switching purpose. The serving gNB, e.g., the source DU, may transmit a cell switching command, e.g., a MAC CE or downlink control information (DCI) . The UE can apply the RRC reconfiguration message and start a timer upon receiving the lower layer command.

Currently, issues regarding TA acquisition and/or TA calculation in a lower layer-based mobility (LTM) case in different scenarios have not been solved. Embodiments of the present disclosure aim to solve such issues. For instance, there may be a PDCCH order based early TA acquisition without a random access response (RAR) scenario. In some implementations of the present disclosure, in this scenario, a source DU stores some TA values for some candidate cells for LTM. Some implementations of the present disclosure study the maintenance for the TA values stored in the source DU for a successful LTM case and a LTM based recovery case. In some implementations of the present disclosure, information related to TA value validity determination could be transferred. For example, a source DU or a CU may transmit information related to TA value validity determination.

For instance, there may be a scenario in which a UE may calculate or compute a TA value for a candidate cell on its own, rather than acquiring or obtaining a TA value for a candidate cell (e.g., TA acquisition or early TA acquisition) from a NE or a network. This scenario may also be named as “a UE-based TA measurement scenario” or “a UE-based TA calculation scenario” or the like. UE-based TA measurement means that a UE calculates or computes a TA value on its own, e.g., based on “Rx timing difference between the current serving cell of the UE and a candidate cell” as well as “a TA value for the current serving cell of the UE” . In this scenario, some implementations of the present disclosure discuss the coexistence of UE-based TA measurement and early TA acquisition, for example, the maintenance of the calculated TA value is discussed. Some implementations of the present disclosure solves an issue of whether should a UE continue keeping the calculated TA value. If kept, a network may need to know the TA value for updating purpose. The UE itself may continue updating the stored TA before receiving update from a target cell. Some implementations of the present disclosure solves an issue of which node is responsible for determining to use UE-based TA measurement. Some implementations of the present disclosure introduces F1 interface enhancement for the abovementioned scenario.

In the embodiments of the present disclosure, TA acquisition or early TA acquisition means that a UE is expected to perform a TA acquisition procedure before a cell switching procedure. TA re-acquisition or early TA re-acquisition means that the UE is expected to perform a TA re-acquisition procedure before a cell switching procedure. TA acquisition, early TA acquisition, TA re-acquisition, or early TA re-acquisition may be triggered by the reception of an indication from the serving BS, e.g., a PDCCH order which is DCI.

In particular, in embodiments of Figures 6-12 of the present disclosure, both inter-DU mobility scenario and intra-DU mobility scenario are considered, e.g., inter-gNB-DU LTM or intra-gNB-DU LTM. Inter-DU mobility means that a connection to a CU remains the same, while a UE may change from a source cell related to a source DU to a target cell related to a target DU due to mobility, while both the source DU and the target DU are managed by the CU. Intra-DU mobility means that a connection to a CU remains the same, while a UE may change from a source cell to a target cell related to the same DU due to mobility. Aspects of the present disclosure are described in the context of a wireless communications system.

Figure 1 illustrates an example of a wireless communications system 100 in accordance with aspects of the present disclosure. The wireless communications system 100 may include one or more NE 102, one or more UE 104, and a core network (CN) 106. The wireless communications system 100 may support various radio access technologies. In some implementations, the wireless communications system 100 may be a 4G network, such as an LTE network or an LTE-Advanced (LTE-A) network. In some other implementations, the wireless communications system 100 may be a NR network, such as a 5G network, a 5G-Advanced (5G-A) network, or a 5G ultrawideband (5G-UWB) network. In other implementations, the wireless communications system 100 may be a combination of a 4G network and a 5G network, or other suitable radio access technology including Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20. The wireless communications system 100 may support radio access technologies beyond 5G, for example, 6G. Additionally, the wireless communications system 100 may support technologies, such as time division multiple access (TDMA) , frequency division multiple access (FDMA) , or code division multiple access (CDMA) , etc.

The one or more NE 102 may be dispersed throughout a geographic region to form the wireless communications system 100. One or more of the NE 102 described herein may be or include or may be referred to as a network node, a base station, a network element, a network function, a network entity, a radio access network (RAN) , a NodeB, an eNodeB (eNB) , a next-generation NodeB (gNB) , or other suitable terminology. An NE 102 and a UE 104 may communicate via a communication link, which may be a wireless or wired connection. For example, an NE 102 and a UE 104 may perform wireless communication (e.g., receive signaling, transmit signaling) over a Uu interface.

An NE 102 may provide a geographic coverage area for which the NE 102 may support services for one or more UEs 104 within the geographic coverage area. For example, an NE 102 and a UE 104 may support wireless communication of signals related to services (e.g., voice, video, packet data, messaging, broadcast, etc. ) according to one or multiple radio access technologies. In some implementations, an NE 102 may be moveable, for example, a satellite associated with a non-terrestrial network (NTN) . In some implementations, different geographic coverage areas 112 associated with the same or different radio access technologies may overlap, but the different geographic coverage areas may be associated with different NE 102.

The one or more UE 104 may be dispersed throughout a geographic region of the wireless communications system 100. A UE 104 may include or may be referred to as a remote unit, a mobile device, a wireless device, a remote device, a subscriber device, a transmitter device, a receiver device, or some other suitable terminology. In some implementations, the UE 104 may be referred to as a unit, a station, a terminal, or a client, among other examples. Additionally, or alternatively, the UE 104 may be referred to as an Internet-of-Things (IoT) device, an Internet-of-Everything (IoE) device, or machine-type communication (MTC) device, among other examples.

A UE 104 may be able to support wireless communication directly with other UEs 104 over a communication link. For example, a UE 104 may support wireless communication directly with another UE 104 over a device-to-device (D2D) communication link. In some implementations, such as vehicle-to-vehicle (V2V) deployments, vehicle-to-everything (V2X) deployments, or cellular-V2X deployments, the communication link 114 may be referred to as a sidelink. For example, a UE 104 may support wireless communication directly with another UE 104 over a PC5 interface.

An NE 102 may support communications with the CN 106, or with another NE 102, or both. For example, an NE 102 may interface with other NE 102 or the CN 106 through one or more backhaul links (e.g., S1, N2, N2, or network interface) . In some implementations, the NE 102 may communicate with each other directly. In some other implementations, the NE 102 may communicate with each other or indirectly (e.g., via the CN 106. In some implementations, one or more NE 102 may include subcomponents, such as an access network entity, which may be an example of an access node controller (ANC) . An ANC may communicate with the one or more UEs 104 through one or more other access network transmission entities, which may be referred to as a radio heads, smart radio heads, or transmission-reception points (TRPs) .

The CN 106 may support user authentication, access authorization, tracking, connectivity, and other access, routing, or mobility functions. The CN 106 may be an evolved packet core (EPC) , or a 5G core (5GC) , which may include a control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management functions (AMF) ) and a user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a Packet Data Network (PDN) gateway (P-GW) , or a user plane function (UPF) ) . In some implementations, the control plane entity may manage non-access stratum (NAS) functions, such as mobility, authentication, and bearer management (e.g., data bearers, signal bearers, etc. ) for the one or more UEs 104 served by the one or more NE 102 associated with the CN 106.

The CN 106 may communicate with a packet data network over one or more backhaul links (e.g., via an S1, N2, N2, or another network interface) . The packet data network may include an application server. In some implementations, one or more UEs 104 may communicate with the application server. A UE 104 may establish a session (e.g., a protocol data unit (PDU) session, or the like) with the CN 106 via an NE 102. The CN 106 may route traffic (e.g., control information, data, and the like) between the UE 104 and the application server using the established session (e.g., the established PDU session) . The PDU session may be an example of a logical connection between the UE 104 and the CN 106 (e.g., one or more network functions of the CN 106) .

In the wireless communications system 100, the NEs 102 and the UEs 104 may use resources of the wireless communications system 100 (e.g., time resources (e.g., symbols, slots, subframes, frames, or the like) or frequency resources (e.g., subcarriers, carriers) ) to perform various operations (e.g., wireless communications) . In some implementations, the NEs 102 and the UEs 104 may support different resource structures. For example, the NEs 102 and the UEs 104 may support different frame structures. In some implementations, such as in 4G, the NEs 102 and the UEs 104 may support a single frame structure. In some other implementations, such as in 5G and among other suitable radio access technologies, the NEs 102 and the UEs 104 may support various frame structures (i.e., multiple frame structures) . The NEs 102 and the UEs 104 may support various frame structures based on one or more numerologies.

One or more numerologies may be supported in the wireless communications system 100, and a numerology may include a subcarrier spacing and a cyclic prefix. A first numerology (e.g., μ=0) may be associated with a first subcarrier spacing (e.g., 15 kHz) and a normal cyclic prefix. In some implementations, the first numerology (e.g., μ=0) associated with the first subcarrier spacing (e.g., 15 kHz) may utilize one slot per subframe. A second numerology (e.g., μ=1) may be associated with a second subcarrier spacing (e.g., 30 kHz) and a normal cyclic prefix. A third numerology (e.g., μ=2) may be associated with a third subcarrier spacing (e.g., 60 kHz) and a normal cyclic prefix or an extended cyclic prefix. A fourth numerology (e.g., μ=3) may be associated with a fourth subcarrier spacing (e.g., 120 kHz) and a normal cyclic prefix. A fifth numerology (e.g., μ=4) may be associated with a fifth subcarrier spacing (e.g., 240 kHz) and a normal cyclic prefix.

A time interval of a resource (e.g., a communication resource) may be organized according to frames (also referred to as radio frames) . Each frame may have a duration, for example, a 10 millisecond (ms) duration. In some implementations, each frame may include multiple subframes. For example, each frame may include 10 subframes, and each subframe may have a duration, for example, a 1 ms duration. In some implementations, each frame may have the same duration. In some implementations, each subframe of a frame may have the same duration.

Additionally or alternatively, a time interval of a resource (e.g., a communication resource) may be organized according to slots. For example, a subframe may include a number (e.g., quantity) of slots. The number of slots in each subframe may also depend on the one or more numerologies supported in the wireless communications system 100. For instance, the first, second, third, fourth, and fifth numerologies (i.e., μ=0, μ=1, μ=2, μ=3, μ=4) associated with respective subcarrier spacings of 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz may utilize a single slot per subframe, two slots per subframe, four slots per subframe, eight slots per subframe, and 16 slots per subframe, respectively. Each slot may include a number (e.g., quantity) of symbols (e.g., OFDM symbols) . In some implementations, the number (e.g., quantity) of slots for a subframe may depend on a numerology. For a normal cyclic prefix, a slot may include 14 symbols. For an extended cyclic prefix (e.g., applicable for 60 kHz subcarrier spacing) , a slot may include 12 symbols. The relationship between the number of symbols per slot, the number of slots per subframe, and the number of slots per frame for a normal cyclic prefix and an extended cyclic prefix may depend on a numerology. It should be understood that reference to a first numerology (e.g., μ=0) associated with a first subcarrier spacing (e.g., 15 kHz) may be used interchangeably between subframes and slots.

In the wireless communications system 100, an electromagnetic (EM) spectrum may be split, based on frequency or wavelength, into various classes, frequency bands, frequency channels, etc. By way of example, the wireless communications system 100 may support one or multiple operating frequency bands, such as frequency range designations FR1 (410 MHz –7.125 GHz) , FR2 (24.25 GHz –52.6 GHz) , FR3 (7.125 GHz –24.25 GHz) , FR4 (52.6 GHz –114.25 GHz) , FR4a or FR4-1 (52.6 GHz –71 GHz) , and FR5 (114.25 GHz –300 GHz) . In some implementations, the NEs 102 and the UEs 104 may perform wireless communications over one or more of the operating frequency bands. In some implementations, FR1 may be used by the NEs 102 and the UEs 104, among other equipment or devices for cellular communications traffic (e.g., control information, data) . In some implementations, FR2 may be used by the NEs 102 and the UEs 104, among other equipment or devices for short-range, high data rate capabilities.

FR1 may be associated with one or multiple numerologies (e.g., at least three numerologies) . For example, FR1 may be associated with a first numerology (e.g., μ=0) , which includes 15 kHz subcarrier spacing; a second numerology (e.g., μ=1) , which includes 30 kHz subcarrier spacing; and a third numerology (e.g., μ=2) , which includes 60 kHz subcarrier spacing. FR2 may be associated with one or multiple numerologies (e.g., at least 2 numerologies) . For example, FR2 may be associated with a third numerology (e.g., μ=2) , which includes 60 kHz subcarrier spacing; and a fourth numerology (e.g., μ=3) , which includes 120 kHz subcarrier spacing.

Figure 2 illustrates an example of a UE 200 in accordance with aspects of the present disclosure. The UE 200 may include a processor 202, a memory 204, a controller 206, and a transceiver 208. The processor 202, the memory 204, the controller 206, or the transceiver 208, or various combinations thereof or various components thereof may be examples of means for performing various aspects of the present disclosure as described herein. These components may be coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more interfaces.

The processor 202, the memory 204, the controller 206, or the transceiver 208, or various combinations or components thereof may be implemented in hardware (e.g., circuitry) . The hardware may include a processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , or other programmable logic device, or any combination thereof configured as or otherwise supporting a means for performing the functions described in the present disclosure.

The processor 202 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, an ASIC, an FPGA, or any combination thereof) . In some implementations, the processor 202 may be configured to operate the memory 204. In some other implementations, the memory 204 may be integrated into the processor 202. The processor 202 may be configured to execute computer-readable instructions stored in the memory 204 to cause the UE 200 to perform various functions of the present disclosure.

The memory 204 may include volatile or non-volatile memory. The memory 204 may store computer-readable, computer-executable code including instructions when executed by the processor 202 cause the UE 200 to perform various functions described herein. The code may be stored in a non-transitory computer-readable medium such the memory 204 or another type of memory. Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special-purpose computer.

In some implementations, the processor 202 and the memory 204 coupled with the processor 202 may be configured to cause the UE 200 to perform one or more of the functions described herein (e.g., executing, by the processor 202, instructions stored in the memory 204) . For example, the processor 202 may support wireless communication at the UE 200 in accordance with examples as disclosed herein. The UE 200 may be configured to support: a means for receiving an RRC reconfiguration message from a BS, wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells; a means for receiving a cell switching command from the BS, wherein the cell switching command includes ID information related to a candidate cell within the set of candidate cells; and a means for performing cell switching towards the candidate cell based on the cell switching command.

The controller 206 may manage input and output signals for the UE 200. The controller 206 may also manage peripherals not integrated into the UE 200. In some implementations, the controller 206 may utilize an operating system such as or other operating systems. In some implementations, the controller 206 may be implemented as part of the processor 202.

In some implementations, the UE 200 may include at least one transceiver 208. In some other implementations, the UE 200 may have more than one transceiver 208. The transceiver 208 may represent a wireless transceiver. The transceiver 208 may include one or more receiver chains 210, one or more transmitter chains 212, or a combination thereof. The means for receiving abovementioned in the processor 202 or the means for transmitting in the processor 202 may be implemented via at least one transceiver 208.

A receiver chain 210 may be configured to receive signals (e.g., control information, data, packets) over a wireless medium. For example, the receiver chain 210 may include one or more antennas for receive the signal over the air or wireless medium. The receiver chain 210 may include at least one amplifier (e.g., a low-noise amplifier (LNA) ) configured to amplify the received signal. The receiver chain 210 may include at least one demodulator configured to demodulate the receive signal and obtain the transmitted data by reversing the modulation technique applied during transmission of the signal. The receiver chain 210 may include at least one decoder for decoding the processing the demodulated signal to receive the transmitted data.

A transmitter chain 212 may be configured to generate and transmit signals (e.g., control information, data, packets) . The transmitter chain 212 may include at least one modulator for modulating data onto a carrier signal, preparing the signal for transmission over a wireless medium. The at least one modulator may be configured to support one or more techniques such as amplitude modulation (AM) , frequency modulation (FM) , or digital modulation schemes like phase-shift keying (PSK) or quadrature amplitude modulation (QAM) . The transmitter chain 212 may also include at least one power amplifier configured to amplify the modulated signal to an appropriate power level suitable for transmission over the wireless medium. The transmitter chain 212 may also include one or more antennas for transmitting the amplified signal into the air or wireless medium.

Figure 3 illustrates an example of a processor 300 in accordance with aspects of the present disclosure. The processor 300 may be an example of a processor configured to perform various operations in accordance with examples as described herein. The processor 300 may include a controller 302 configured to perform various operations in accordance with examples as described herein. The processor 300 may optionally include at least one memory 304, which may be, for example, an L1/L2/L3 cache. Additionally, or alternatively, the processor 300 may optionally include one or more arithmetic-logic units (ALUs) 306. One or more of these components may be in electronic communication or otherwise coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more interfaces (e.g., buses) .

The processor 300 may be a processor chipset and include a protocol stack (e.g., a software stack) executed by the processor chipset to perform various operations (e.g., receiving, obtaining, retrieving, transmitting, outputting, forwarding, storing, determining, identifying, accessing, writing, reading) in accordance with examples as described herein. The processor chipset may include one or more cores, one or more caches (e.g., memory local to or included in the processor chipset (e.g., the processor 300) or other memory (e.g., random access memory (RAM) , read-only memory (ROM) , dynamic RAM (DRAM) , synchronous dynamic RAM (SDRAM) , static RAM (SRAM) , ferroelectric RAM (FeRAM) , magnetic RAM (MRAM) , resistive RAM (RRAM) , flash memory, phase change memory (PCM) , and others) .

The controller 302 may be configured to manage and coordinate various operations (e.g., signaling, receiving, obtaining, retrieving, transmitting, outputting, forwarding, storing, determining, identifying, accessing, writing, reading) of the processor 300 to cause the processor 300 to support various operations in accordance with examples as described herein. For example, the controller 302 may operate as a control unit of the processor 300, generating control signals that manage the operation of various components of the processor 300. These control signals include enabling or disabling functional units, selecting data paths, initiating memory access, and coordinating timing of operations.

The controller 302 may be configured to fetch (e.g., obtain, retrieve, receive) instructions from the memory 304 and determine subsequent instruction (s) to be executed to cause the processor 300 to support various operations in accordance with examples as described herein. The controller 302 may be configured to track memory address of instructions associated with the memory 304. The controller 302 may be configured to decode instructions to determine the operation to be performed and the operands involved. For example, the controller 302 may be configured to interpret the instruction and determine control signals to be output to other components of the processor 300 to cause the processor 300 to support various operations in accordance with examples as described herein. Additionally, or alternatively, the controller 302 may be configured to manage flow of data within the processor 300. The controller 302 may be configured to control transfer of data between registers, arithmetic logic units (ALUs) , and other functional units of the processor 300.

The memory 304 may include one or more caches (e.g., memory local to or included in the processor 300 or other memory, such RAM, ROM, DRAM, SDRAM, SRAM, MRAM, flash memory, etc. In some implementations, the memory 304 may reside within or on a processor chipset (e.g., local to the processor 300) . In some other implementations, the memory 304 may reside external to the processor chipset (e.g., remote to the processor 300) .

The memory 304 may store computer-readable, computer-executable code including instructions that, when executed by the processor 300, cause the processor 300 to perform various functions described herein. The code may be stored in a non-transitory computer-readable medium such as system memory or another type of memory. The controller 302 and/or the processor 300 may be configured to execute computer-readable instructions stored in the memory 304 to cause the processor 300 to perform various functions. For example, the processor 300 and/or the controller 302 may be coupled with or to the memory 304, the processor 300, the controller 302, and the memory 304 may be configured to perform various functions described herein. In some examples, the processor 300 may include multiple processors and the memory 304 may include multiple memories. One or more of the multiple processors may be coupled with one or more of the multiple memories, which may, individually or collectively, be configured to perform various functions herein.

The one or more ALUs 306 may be configured to support various operations in accordance with examples as described herein. In some implementations, the one or more ALUs 306 may reside within or on a processor chipset (e.g., the processor 300) . In some other implementations, the one or more ALUs 306 may reside external to the processor chipset (e.g., the processor 300) . One or more ALUs 306 may perform one or more computations such as addition, subtraction, multiplication, and division on data. For example, one or more ALUs 306 may receive input operands and an operation code, which determines an operation to be executed. One or more ALUs 306 be configured with a variety of logical and arithmetic circuits, including adders, subtractors, shifters, and logic gates, to process and manipulate the data according to the operation. Additionally, or alternatively, the one or more ALUs 306 may support logical operations such as AND, OR, exclusive-OR (XOR) , not-OR (NOR) , and not-AND (NAND) , enabling the one or more ALUs 306 to handle conditional operations, comparisons, and bitwise operations.

The processor 300 may support wireless communication in accordance with examples as disclosed herein.

In some implementations, the processor 300 may be configured to support means for performing operations as described with respect to Figure 6. For example, the processor 300 may be configured to or operable to support: a means for receiving an RRC reconfiguration message from a BS, wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells; a means for receiving a cell switching command from the BS, wherein the cell switching command includes ID information related to a candidate cell within the set of candidate cells; and a means for performing cell switching towards the candidate cell based on the cell switching command.

In some further implementations, the processor 300 may be configured to support means for performing operations as described with respect to Figure 7. For example, the processor 300 may be configured to or operable to support: a means for receiving a first timing advance (TA) value list for a set of candidate cells from a centralized unit (CU) of the BS, wherein the first TA value list includes a first TA value for a first candidate cell within the set of candidate cells; and a means for transmitting a cell switching command to a user equipment (UE) , wherein the cell switching command includes identifier (ID) information related to the first candidate cell.

In some additional implementations, the processor 300 may be configured to support means for performing operations as described with respect to Figure 8. For example, the processor 300 may be configured to or operable to support: a means for transmitting a request for cell switching configuration for a set of candidate cells to one or more candidate distributed units (DU) s of the BS; a means for receiving a response corresponding to the request from the one or more candidate DUs, wherein the response includes the cell switching configuration for the set of candidate cells; and a means for transmitting the cell switching configuration for the set of candidate cells to a user equipment (UE) via a source DU of the BS based on the response.

In yet some additional implementations, the processor 300 may be configured to support means for performing operations as described with respect to Figure 9. For example, the processor 300 may be configured to or operable to support: a means for receive a request for cell switching configuration for a set of candidate cells for a user equipment (UE) from a centralized unit (CU) of the BS; and a means for transmitting a response to the CU based on the request, wherein the response includes configuration related to the set of candidate cells for the UE, and wherein the set of candidate cells includes a first candidate cell.

It should be appreciated by persons skilled in the art that the components in exemplary processor 300 may be changed, for example, some of the components in exemplary processor 300 may be omitted or modified or new component (s) may be added to exemplary processor 300, without departing from the spirit and scope of the disclosure. For example, in some embodiments, the processor 300 may not include the ALUs 306.

Figure 4 illustrates an example of a NE 400 in accordance with aspects of the present disclosure. The NE 400 may include a processor 402, a memory 404, a controller 406, and a transceiver 408. The processor 402, the memory 404, the controller 406, or the transceiver 408, or various combinations thereof or various components thereof may be examples of means for performing various aspects of the present disclosure as described herein. These components may be coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more interfaces.

The processor 402, the memory 404, the controller 406, or the transceiver 408, or various combinations or components thereof may be implemented in hardware (e.g., circuitry) . The hardware may include a processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , or other programmable logic device, or any combination thereof configured as or otherwise supporting a means for performing the functions described in the present disclosure.

The processor 402 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, an ASIC, an FPGA, or any combination thereof) . In some implementations, the processor 402 may be configured to operate the memory 404. In some other implementations, the memory 404 may be integrated into the processor 402. The processor 402 may be configured to execute computer-readable instructions stored in the memory 404 to cause the NE 400 to perform various functions of the present disclosure.

The memory 404 may include volatile or non-volatile memory. The memory 404 may store computer-readable, computer-executable code including instructions when executed by the processor 402 cause the NE 400 to perform various functions described herein. The code may be stored in a non-transitory computer-readable medium such the memory 404 or another type of memory. Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special-purpose computer.

In some implementations, the processor 402 and the memory 404 coupled with the processor 402 may be configured to cause the NE 400 to perform one or more of the functions described herein (e.g., executing, by the processor 402, instructions stored in the memory 404) . For example, the processor 402 may support wireless communication at the NE 400 in accordance with examples as disclosed herein. For example, the NE 400 may be configured to support means for performing the operations as described with respect to Figures 7-9.

In some implementations, the NE 400 may be a source DU and configured to support: a means for receiving a TA value list for a set of candidate cells from a CU of the BS, wherein the TA value list includes a TA value for a candidate cell within the set of candidate cells; and a means for transmitting a cell switching command to a UE, wherein the cell switching command includes ID information related to the candidate cell.

In some implementations, the NE 400 may be a CU and configured to support: a means for transmitting a request for cell switching configuration for a set of candidate cells to one or more candidate DUs of the BS; a means for receiving a response corresponding to the request from the one or more candidate DUs, wherein the response includes the cell switching configuration for the set of candidate cells; and a means for transmitting the cell switching configuration for the set of candidate cells to a UE via a source DU of the BS based on the response.

In some implementations, the NE 400 may be a candidate DU and configured to support: a means for receiving a request for cell switching configuration for a set of candidate cells for a UE from a CU of the BS; and a means for transmitting a response to the CU based on the request, wherein the response includes configuration related to the set of candidate cells for the UE, and wherein the set of candidate cells includes a first candidate cell.

The controller 406 may manage input and output signals for the NE 400. The controller 406 may also manage peripherals not integrated into the NE 400. In some implementations, the controller 406 may utilize an operating system such as or other operating systems. In some implementations, the controller 406 may be implemented as part of the processor 402.

In some implementations, the NE 400 may include at least one transceiver 408. In some other implementations, the NE 400 may have more than one transceiver 408. The transceiver 408 may represent a wireless transceiver. The transceiver 408 may include one or more receiver chains 410, one or more transmitter chains 412, or a combination thereof. The means for receiving or the means for transmitting abovementioned in the processor 402 may be implemented via at least one transceiver 408.

A receiver chain 410 may be configured to receive signals (e.g., control information, data, packets) over a wireless medium. For example, the receiver chain 410 may include one or more antennas for receive the signal over the air or wireless medium. The receiver chain 410 may include at least one amplifier (e.g., a low-noise amplifier (LNA) ) configured to amplify the received signal. The receiver chain 410 may include at least one demodulator configured to demodulate the receive signal and obtain the transmitted data by reversing the modulation technique applied during transmission of the signal. The receiver chain 410 may include at least one decoder for decoding the processing the demodulated signal to receive the transmitted data.

A transmitter chain 412 may be configured to generate and transmit signals (e.g., control information, data, packets) . The transmitter chain 412 may include at least one modulator for modulating data onto a carrier signal, preparing the signal for transmission over a wireless medium. The at least one modulator may be configured to support one or more techniques such as amplitude modulation (AM) , frequency modulation (FM) , or digital modulation schemes like phase-shift keying (PSK) or quadrature amplitude modulation (QAM) . The transmitter chain 412 may also include at least one power amplifier configured to amplify the modulated signal to an appropriate power level suitable for transmission over the wireless medium. The transmitter chain 412 may also include one or more antennas for transmitting the amplified signal into the air or wireless medium.

It should be appreciated by persons skilled in the art that the components in exemplary NE 400 may be changed, for example, some of the components in exemplary NE 400 may be omitted or modified or new component (s) may be added to exemplary NE 400, without departing from the spirit and scope of the disclosure. For example, in some embodiments, the NE 400 may not include the controller 406.

Figure 5 illustrates a schematic diagram of inter-cell Layer1/Layer2 (L1/L2) mobility in accordance with aspects of the present disclosure. As shown in Figure 5, CU may communicate with two DUs, i.e., DU1 or DU2, via F1 interfaces. CU in Figure 5 may implement legacy mobility decision based on Layer 3 (L3) measurement result. DU1 or DU2 in Figure 5 may implement L1/L2 mobility decision based on physical layer measurement result (s) .

Compared to legacy L3 mobility, L1/L2 mobility is considered faster with less processing delay and signaling delay. In legacy L3 mobility, a CU (e.g., CU as shown in Figure 5) makes the mobility decision based on received radio resource management (RRM) measurement report. Different than legacy L3 mobility, in L1/L2 mobility, a DU (e.g., DU1 or DU2 as shown in Figure 5) makes the mobility decision based on physical layer measurement result, e.g., carried in a channel state information (CSI) report. Besides, in legacy L3 mobility, the handover command is sent via an RRC message from the SN CU to a UE, while in L1/L2 mobility, the “handover” command is sent via L1/L2 signaling (e.g., downlink control information (DCI) or a medium access control (MAC) control element (CE) ) from the DU to a UE. The “handover” command in L1/L2 mobility can be about cell activation or deactivation, e.g., activate a new serving PCell while deactivate the old serving PCell.

Figure 6 illustrates a flowchart of a method in accordance with aspects of the present disclosure. The operations of the method may be implemented by a UE as described herein. In some implementations, the UE may execute a set of instructions to control the function elements of the UE to perform the described functions. In some implementations, aspects of operations 602, 604, and 606 may be performed by UE 200 as described with reference to Figure 2. Each of operations 602, 604, and 606 may be performed in accordance with examples as described herein.

At operation 602, the method may include receiving an RRC reconfiguration message by a UE from a BS, and the RRC reconfiguration message includes cell switching configuration for a set of candidate cells.

At operation 604, the method may include receiving a cell switching command by the UE from the BS, e.g., from a source DU of the BS. The cell switching command includes ID information related to a candidate cell (denoted as cell#1 for simplicity) within the set of candidate cells. For instance, the ID information may be a candidate cell configuration index for the candidate cell, e.g., LTM configuration ID for candidate cell.

At operation 606, the method may include performing cell switching towards cell#1 by the UE based on the cell switching command. Namely, cell#1 is a target cell of cell switching. In some implementations of the method described herein, the cell switching command includes at least one of the following:

(1) index information of candidate cell configuration of cell#1 (e.g., LTM configuration ID cell#1) ;

(2) a TA value for cell#1; or

(3) a timer length of a TAT associated with the TA value or cell#1.

In some implementations of the method described herein, the UE may further perform the following operations:

(1) if the UE fails to access cell#1, e.g., timer T304 expiry, the UE may initiate a reestablishment procedure; and

(2) if “information indicating that the set of candidate cells can be used for recovery” (denoted as information#1) has been configured to the UE, the UE may keep the related configuration (denoted as configuration#1) ; for instance, information#1 may be an attempt LTM configuration information element (IE) ; or

(3) if information#1 is not configured to the UE, the UE may release configuration#1.

In an implementation of the method described herein, configuration#1 may at least include configuration for SpCell, configuration for one or more MCG SCells, MR-DC configuration, overheating assistance configuration, and IDC assistance configuration. A specific example is described in Figure 11 as follows.

In an implementation of the method described herein, if the UE fails to access cell#1 and initiates a reestablishment procedure, the UE may further:

(1) select another candidate cell (denoted as cell#2) for an RRC reestablishment procedure;

(2) determine whether cell#2 is one candidate cell within the set of candidate cells or not;

(3) if cell#2 is one candidate cell within the set of candidate cells, apply cell switching configuration for cell#2 and perform cell switching to cell#2; or

(4) if cell#2 is not one candidate cell within the set of candidate cells and if information#1 has been configured to the UE, release configuration#1.

For example, configuration#1 may include at least one of the following:

(1) reset MAC;

(2) release configuration for SpCell e.g spCellConfig, if configured;

(3) suspend all RBs, and BH RLC channels for IAB-MT, and Uu Relay RLC channels for L2 U2N Relay UE, except SRB0 and broadcast MRBs

(4) release the MCG SCell (s) , if configured;

(5) release MR-DC configuration.

(6) release delayBudgetReportingConfig, if configured and stop timer T342, if running;

(7) release overheatingAssistanceConfig, if configured and stop timer T345, if running;

(8) release idc-AssistanceConfig, if configured;

(9) release btNameList, if configured;

(10) release wlanNameList, if configured; or

(11) release sensorNameList, if configured.

In some implementations of the method described herein, the UE may further transmit an RRC reconfiguration complete message associated with cell#2 to the CU, if the UE switches to cell#2. The RRC reconfiguration complete message includes ID information related to cell#2 (e.g., a cell ID, cell#2 configuration index or LTM configuration ID for cell#2) . The cell ID could be a physical cell identifier (PCI) or a NR cell globe index (NCGI) .

In some implementations of the method described herein, the RRC reconfiguration message at operation 602 includes information (denoted as information#2) which indicates the UE to calculate a TA value for a candidate cell. Information#2 may include ID information of the candidate cell. For example, information#2 indicates the UE to calculate a TA value (denoted as TA#1) for cell#1 and/or a TA value (denoted as TA#2) for another candidate cell (e.g., cell#2) . Information#2 includes ID information of cell#1 and/or cell#2.

In some implementations of the method described herein, whether the UE is to calculate a TA value or not is determined by a CU of the BS, one or more candidate DUs of the BS, or a source DU of the BS.

In an implementation, in response to receiving information#2 including ID information of cell#1, the UE may further consider that TA#1 for cell#1 is not included in the cell switching command for cell#1. Namely, the UE considers that TA#1 for cell#1 is not included in the cell switching command for cell#1 based on that the received information#2 includes ID information of cell#1. Then, the UE may calculate TA#1 for cell#1 on its own.

In another implementation, after receiving information#2 including ID information of both cell#1 and cell#2, the UE may further calculate TA#1 for cell#1 and TA#2 for cell#2. Namely, based on that the received information#2 includes ID information of both cell#1 and cell#2, the UE calculates TA#1 for cell#1 and TA#2 for cell#2 on its own.

For instance, TA#1 for cell#1 may be calculated based on:

(1) a receiving timing difference between a source cell of the UE and cell#1 (e.g., a RS signal receiving timing difference between two cells) , and/or

(2) a TA value for the source cell.

For instance, TA#2 for cell#2 may be calculated based on:

(1) a receiving timing difference between a source cell of the UE and cell#2 (e.g., a RS signal receiving timing difference between two cells) , and/or

(2) a TA value for the source cell. A specific example is described in Figure 12 as follows.

In some implementations of the method described herein, the UE may further:

(1) if a PDCCH order for a TA acquisition procedure for cell#1 is received:

a) discard TA#1 for cell#1; or

b) keep TA#1 for cell#1 before receiving another TA value (denoted as TA#3) for cell#1 from a source DU of the BS, and discard TA#1 for cell#1 after receiving TA#3 from the source DU; or

(2) if the cell switching command includes TA#3, discard TA#1 for cell#1, and perform cell switching to cell#1 using TA#3.

In some implementations of the method described herein, the UE may further release or store TA#2 for cell#2 after UE switches to cell#1. In an implementation, in response to storing TA#2 for cell#2, the UE may further determine whether TA#2 is valid or not based on a TAT associated with TA#2.

In some implementations of the method described herein, the UE may further release or store TA#1 for cell#1 after UE switches to cell#1.

In an implementation, in response to storing TA#1 for cell#1, the UE may further report TA#1 via an RRC message or a MAC CE to a candidate DU associated with cell#1. In this implementation, the UE may further receive a delta value used for updating TA#1 from the candidate DU associated with cell#1. For example, the UE updates TA#1 for cell#1 by applying the received delta value to TA#1.

In another implementation, in response to storing TA#1 for cell#1, the UE may further: receive an absolute TA value for cell#1 from a candidate DU associated with cell#1; release TA#1 for cell#1; and store the absolute TA value for cell#1. For example, the UE uses the received absolute TA value as the current TA value for cell#1 and releases TA#1 for cell#1.

In some implementations, the UE may continue updating TA#1 for cell#1 before receiving the delta value or the absolute TA value from the candidate DU associated with cell#1. For example, the UE continues updating and/or calculating TA#1 for cell#1 on its own, before it receives the delta value or the absolute TA value for updating.

In an implementation, to continue updating TA#1, the UE may further: store a TA value of a source cell of the UE; receive a timer length of a TAT (denoted as TAT#1) associated with the TA value of the source cell; continue updating TA#1 based on the TA value of the source cell before expiry of TAT#1; and consider TA#1 as invalid upon the expiry of TAT#1.

In some implementations of the method described herein, in response to considering TA#1 as invalid, the UE may further trigger a RACH procedure for UL synchronization. A specific example is described in Figure 12 as follows.

It should be noted that the method described in Figure 6 describes possible implementations, and that the operations and the steps may be rearranged or otherwise eliminated or modified and that other implementations are possible, without departing from the spirit and scope of the disclosure.

Figure 7 illustrates a flowchart of a method in accordance with aspects of the present disclosure. The operations of the method may be implemented by a source DU of a BS (e.g., a source DU of a NE) as described herein. In some implementations, the source DU may execute a set of instructions to control the function elements of the source DU to perform the described functions. In some implementations, aspects of operations 702 and 704 may be performed by DU1 as described with reference to Figure 4. Each of operations 702 and 704 may be performed in accordance with examples as described herein.

At operation 702, the method may include receiving a TA value list for a set of candidate cells by a source DU of a BS from a CU of the BS. The TA value list (denoted as list#1) refers to one or more TA values or a set of TA values. List#1 may include a TA value for a candidate cell (e.g., TA#1 for cell#1 described or illustrated in the method in Figure 6) within the set of candidate cells. In some implementations, list#1 further includes another TA value for another candidate cell (e.g., TA#2 for cell#2 described or illustrated in the method in Figure 6) within the set of candidate cells.

At operation 704, the method may include transmitting a cell switching command by the source DU to a UE. For example, the cell switching command includes ID information related to cell#1 (i.e., a target candidate cell) . In some implementations, the cell switching command includes at least one of (1) TA#1 for cell#1 or (2) a TAT associated with TA#1.

In some implementations of the method described herein, after transmitting the cell switching command, the source DU may further transmit at least one of the following via the CU to a candidate DU of the BS associated with cell#1 (i.e., the target candidate cell) :

(1) Another TA value list (denoted as list#2) , which refers to one or more TA values or a set of TA values. In an implementation, list#2 includes all TA values within list#1. In another implementation, list#2 includes all TA values within list#1 except TA#1 for cell#1 included in the cell switching command.

(2) Additional information associated with list#2, which may be used for determining whether list#2 is invalid or not. In an implementation, the additional information associated with a TA value within list#2 includes at least one of the following:

(1) absolute time (e.g., a time stamp) when receiving the TA value;

(2) time elapsed since receiving the TA value; or

(3) a remaining valid period of the TA value.

In some implementations of the method described herein, the source DU may further transmit list#2 and/or the additional information associated with list#2 to the CU. Specific examples are described in Figures 10 and 11 as follows.

It should be noted that the method described in Figure 7 describes possible implementations, and that the operations and the steps may be rearranged or otherwise eliminated or modified and that other implementations are possible, without departing from the spirit and scope of the disclosure.

Figure 8 illustrates a flowchart of a method in accordance with aspects of the present disclosure. The operations of the method may be implemented by a CU of a BS (e.g., a CU of a NE) as described herein. In some implementations, the CU may execute a set of instructions to control the function elements of the CU to perform the described functions. In some implementations, aspects of operations 802, 804, and 806 may be performed by CU as described with reference to Figure 5. Each of operations 802, 804, and 806 may be performed in accordance with examples as described herein.

At operation 802, the method may include transmitting a request for cell switching configuration for a set of candidate cells by a CU of a BS to one or more candidate DUs of the BS.

At operation 804, the method may include receiving a response corresponding to the request by the CU from the one or more candidate DUs. The response includes the cell switching configuration for the set of candidate cells (e.g., LTM configuration related to the set of candidate cells) . The one or more candidate DUs may be in an Inter-DU case or an intra-DU case.

At operation 806, the method may include transmitting the cell switching configuration for the set of candidate cells to a UE via a source DU of the BS based on the response.

In some implementations of the method described herein, the CU may further receive an RRC reconfiguration complete message associated with another candidate cell (i.e., a target cell to which the UE switches) within the set of candidate cells from the UE, after the UE fails to switch to a candidate cell. For example, in the method described or illustrated in Figure 6, after the UE fails to switch to cell#1, the CU may receive an RRC reconfiguration complete message associated with cell#2 from the UE. The RRC reconfiguration complete message may include ID information related to cell#2.

In some implementations of the method described herein, the CU may further transmit at least one of the following to a candidate DU associated with cell#2 after receiving the RRC reconfiguration complete message:

(1) A TA value list (denoted as list#3) , which refers to one or more TA values or a set of TA values. In an implementation, list#3 includes all TA values within a TA value list for all candidate cells configured with TA acquisition (e.g., list#1 described or illustrated in the method in Figure 6) . In another implementation, list#3 includes all TA values within list#1 except a TA value for a target cell included in the RRC reconfiguration complete message (e.g., TA#2 for cell#2) .

(2) Additional information associated with list#3, which may be used for determining whether list#3 is invalid or not. In an implementation, the additional information associated with a TA value within list#3 includes at least one of the following: absolute time when receiving the TA value; time elapsed since receiving the TA value; or a remaining valid period of the TA value.

In some implementations of the method described herein, the CU may receive at least one of the following from the source DU after the source DU transmits a cell switching command including ID information related to a candidate cell (e.g., cell#1 described or illustrated in the method in Figure 6) :

(1) a TA value list (e.g., list#2 described or illustrated in the method in Figure 6) ; or

(2) additional information associated with list#2, which may be used for determining whether list#2 is invalid or not. In an implementation, the additional information associated with a TA value within list#2 includes at least one of the following: absolute time when receiving the TA value; time elapsed since receiving the TA value; or a remaining valid period of the TA value.

In some implementations of the method described herein, the CU may further transmit list#2 and/or the additional information associated with list#2 to a candidate DU of the BS associated with the target cell, e.g., cell#2. Specific examples are described in Figures 10 and 11 as follows.

In some implementations of the method described herein, the request for cell switching configuration at operation 802 includes information (denoted as information#3) indicating that the UE is to calculate a TA value for a candidate cell.

In some implementations of the method described herein, the CU may further receive at least one of the following (e.g., in the response at operation 804) from the one or more candidate DUs:

(1) information (denoted as information#4) indicating the UE to calculate one or more TA values for the set of candidate cells. The information may be included in the cell switching configuration to the UE.

(2) reference signal (RS) configuration information configured to the UE. A specific example is described in Figure 12 as follows.

It should be noted that the method described in Figure 8 describes possible implementations, and that the operations and the steps may be rearranged or otherwise eliminated or modified and that other implementations are possible, without departing from the spirit and scope of the disclosure.

Figure 9 illustrates a flowchart of a method in accordance with aspects of the present disclosure. The operations of the method may be implemented by a candidate DU of a BS (e.g., a candidate DU of a NE) as described herein. In some implementations, the NE may execute a set of instructions to control the function elements of the NE to perform the described functions. In some implementations, aspects of operations 902 and 904 may be performed by DU2 as described with reference to Figure 4. Each of operations 902 and 904 may be performed in accordance with examples as described herein.

At operation 902, the method may include receiving a request for cell switching configuration for a set of candidate cells for a UE by a candidate DU of a BS from a CU of the BS.

At operation 904, the method may include transmitting a response by the candidate DU to the CU based on the request. The response includes configuration related to the set of candidate cells for the UE, and the set of candidate cells includes a candidate cell (e.g., cell#1 or cell#2 described or illustrated in the method in Figure 6) .

In some implementations of the method described herein, the candidate DU may receive at least one of the following from the CU:

(1) A TA value list for the set of candidate cells.

(2) The TA value list except a TA value for a candidate cell (e.g., cell#1 or cell#2 to which the UE is configured to switch) .

(3) Additional information associated with the TA value list, which may be used to determining whether TA value (s) within the TA value list is invalid or not. In an implementation, the additional information associated with a TA value within the TA value list includes at least one of: (1) absolute time when receiving the TA value; (2) time elapsed since receiving the TA value; or (3) a remaining valid period of the TA value.

For example, in case that the CU is responsible for maintenance or storing of TA value (s) (e.g., after receiving them from a source DU or a candidate DU) and that the source DU transmits a cell switching command to cell#1, the candidate DU may receive a TA value (denoted as list#4) from the CU. In an implementation, list#4 includes all TA values within a TA value list for all candidate cells (e.g., list#1 described or illustrated in the method in Figure 6) . In another implementation, list#4 includes all TA values within list#1 except a TA value for cell#1 included in the cell switching command.

For example, in case that the CU receives the RRC reconfiguration complete message from the UE after the UE switches to cell#2, the candidate DU may receive list#3 described or illustrated in the method in Figure 8 from the CU. In an implementation, list#3 includes all TA values within a TA value list for all candidate cells (e.g., list#1 described or illustrated in the method in Figure 6) . In another implementation, list#3 includes all TA values within list#1 except a TA value for a target cell included in the RRC reconfiguration complete message (e.g., TA#2 for cell#2) .

In some implementations of the method described herein, the candidate DU may transmit at least one of (1) information indicating the UE to calculate one or more TA values for the set of candidate cells or (2) RS configuration information configured to the UE. For example, in the method described or illustrated in Figure 8, the candidate DU may transmit information#4 and/or the RS configuration information configured to the UE to the CU.

In some implementations, the candidate DU may further determine whether the UE is to calculate the one or more TA values or not.

In some implementations, the candidate DU may further receive a TA value for cell#1 via the CU from the UE, and the UE is configured to switch to cell#1. In an implementation, the candidate DU may transmit a delta value used for updating the TA value for cell#1 via the CU to the UE. For example, the UE may update the TA value for cell#1 by applying the received delta value.

In some implementations, the candidate DU may further transmit an absolute TA value for cell#1 via the CU to the UE. For example, the UE may use the received absolute TA value as the current TA value for cell#1 and releases its stored TA value for cell#1. A specific example is described in Figure 12 as follows.

It should be noted that the method described in Figure 9 describes possible implementations, and that the operations and the steps may be rearranged or otherwise eliminated or modified and that other implementations are possible, without departing from the spirit and scope of the disclosure.

Figure 10 illustrates an example of performing cell switching in accordance with aspects of the present disclosure. Details described in all other embodiments of the present disclosure are applicable for the embodiments shown in Figure 10.

As shown in Figure 10, BS 1005 is in CU-DU architecture, and includes CU 1004, source DU 1002, and candidate DU 1003. In the embodiments of Figure 10, a cell switching operation performed by UE 1001 may refer to an Intra-DU case in which a source cell and a target cell in the same DU or refer to an Inter-DU case in which a source cell and a target cell are located at different DUs. For instance, the flowchart 1000 as shown in Figure 10 only shows a cell switching operation in an Inter-DU case for the exemplary purpose. The flowchart 1000 also can be applied to an intra-DU case if source DU 1002 and candidate DU 1003 are the same DU.

In the exemplary flowchart 1000 as shown in Figure 10, in operation 1011, UE 1001 may access the serving BS (e.g., gNB) and send a measurement report to the serving BS, for example, BS 1005. The serving BS may include a CU (e.g., gNB-CU) and one or more DUs (e.g., gNB-DUs) . A serving cell is associated with a CU and a DU. There is an F1 interface between the DU and the CU. For example, as shown in Figure 10, BS 1005 includes CU 1004, source DU 1002, and candidate DU 1003. BS 1005 may include one or more other candidate DUs (not shown in Figure 10) . In some implementations, UE 1001 may send the measurement report to CU 1004 via source DU 1002.

In operation 1012, CU 1004 may determine to initiate a L1/L2 based inter-cell mobility configuration procedure, i.e., making a L1/L2 based inter-cell mobility configuration decision.

In operation 1013, CU 1004 may send a request message, which contains ID information of the candidate cells, to candidate DU 1003 via an F1 interface. In Inter-DU case, the request message may be a UE CONTEXT SETUP REQUEST message. In Intra-DU case, the request message may be a UE CONTEXT MODIFICATION REQUEST message.

In operation 1014, if candidate DU 1003 decides to accept the request of LTM configuration related to candidate cell (s) , candidate DU 1003 may transmit a response message, which includes the RRC configuration (s) for the accepted target candidate cell (s) , to CU 1004 via an F1 interface. In Inter-DU case, the response message may be a UE CONTEXT SETUP RESPONSE message. In Intra-DU case, the response message may be a UE CONTEXT MODIFICATION RESPONSE message.

In some implementations, the response message may include the lower layer RRC configuration (s) for the candidate cell (s) , which is named as “lower layer RRC configuration for LTM” , “L1/L2 RRC configuration information for LTM” , “RRC configuration for LTM” , “LTM configuration information” or the like. In some implementations, RACH resource (s) for early TA acquisition may be included in the response message transmitted to CU 1004. The candidate cell (s) may be named as “candidate cell (s) for LTM” or the like.

In operation 1015, CU 1004 will transmit the configuration (s) to source DU 1002. In some implementations, CU 1004 may transmit the configuration (s) , e.g., RACH resource (s) for early TA acquisition, to source DU. CU 1004 may further indicate whether early TA acquisition should be triggered.

In some implementations, CU 1004 may generate an RRC reconfiguration message based on the configuration (s) from the candidate cell (s) and transmit the RRC reconfiguration message to source DU 1002. For instance, the RRC reconfiguration message includes candidate cell configuration (s) for LTM and/or RACH resource (s) for early TA acquisition.

In operation 1016, UE 1001 may receive the RRC reconfiguration message associated with one or more candidate cells for LTM configuration from source DU 1002.

In operation 1017, UE 1001 may receive a PDCCH order for triggering TA acquisition to a particular candidate cell, e.g., a candidate cell associated with candidate DU 1003.

In operation 1018, UE 1001 may transmit the preamble for TA acquisition to candidate DU 1003. In some implementations, if candidate DU 1003 can calculate a TA value for the particular candidate cell based on the received preamble, candidate DU 1003 may transmit the preamble and corresponding RACH occasion, a beam indication, an ID of UE 1001, RA-RNTI, ID information of the candidate cell ID (i.e., target cell ID) , TCI State index for the candidate cell or similar information, and/or the calculated TA value to source DU 1002 via CU 1004. In some implementations, candidate DU 1003 may store the calculated TA value. In operation 1018, after CU 1004 receives the information from candidate DU 1003, CU 1004 will transfer the information, e.g., the calculated TA value, to source DU 1002 via F1 interface.

In operation 1019, source DU 1002 may transmit a cell switching command for a candidate cell to UE 1001. The candidate cell may also be named as “atarget candidate cell” or the like. For example, the candidate cell is associated with candidate DU 1003 (e.g., cell#1 described or illustrated in the method in Figure 6) . In some implementations, source DU 1002 transmits an indication of cell switching towards the candidate cell to CU 1004 in operation 1019. In some implementations, the cell switching command includes at least one of: (1) candidate cell configuration index of the candidate cell; (2) a TA value for the candidate cell; or (3) a timer length of a TAT associated with the TA value.

In some implementations, the cell switching command includes at least one of: a candidate cell configuration index of the candidate cell; a TA value for the candidate cell; or a timer length of a TAT associated with the TA value. In some embodiments, after receiving the cell switching command including the TA value for the candidate cell or the timer length of the TAT, UE 1001 may continue to keep the received the TA value for the candidate cell and/or the timer length of the TAT.

In operation 1020, UE 1001 performs cell switching to the corresponding candidate cell (e.g., cell#1) of candidate DU 1003 in response to receiving the cell switching command.

In operation 1020, candidate DU 1003 (i.e., target DU) may receive, from CU 1004, information which includes at least one of the following:

(1) A cell switching indication, e.g., including ID information of the corresponding candidate cell (e.g., cell#1) .

(2) A TA value list, e.g., list#3 described or illustrated in the method in Figure 8. In an implementation, list#3 includes all TA values within a TA value list for all candidate cells (e.g., list#1 described or illustrated in the method in Figure 6) . In another implementation, list#3 includes all TA values within list#1 except the TA value for cell#1.

(3) Additional information associated with the TA value list, which may be used to determining whether TA value (s) within the TA value list is invalid or not.

There may be following three options in different embodiments of operation 1020, i.e., Option#1, Option#2, or Option#3 as below.

(1) Option#1: source DU 1002 needs to forward the stored TA value (s) (e.g., a TA value list) and/or additional information which may be used to determining whether TA value (s) is invalid or not. For example, the additional information associated with a TA value could include at least one of: (1) absolute time (e.g., a time stamp) of receiving the TA value, (2) the elapsed time of since receiving the TA value, or (3) a remaining valid period of the TA value. The remaining valid period of the TA value is a difference between the timer length of the TAT and the elapsed time of since receiving the TA value.

- In an embodiment, source DU 1002 forwards all the stored TA value (s) and the related additional information to candidate DU 1003 via CU 1004. In other words, source DU 1002 forwards TA value (s) related to all candidate cell (s) including the target cell and/or the related additional information to candidate DU 1003.

- In another embodiment, source DU 1002 forwards all the stored TA value (s) except a TA value of the candidate cell associated with candidate DU 1003 (i.e., the target cell) and/or the related additional information to candidate DU 1003 (i.e., target DU) via CU 1004. In other words, source DU 1002 forwards TA value (s) related to all candidate cell (s) except the target cell and/or the related additional information to candidate DU 1003.

(2) Option#2: CU 1004 may be responsible for maintenance or storing of TA value (s) , e.g., in the case that CU 1004 stores TA value (s) after receiving them from source DU 1002. In such embodiment, CU 1004 may provide a TA value list (e.g., list#4 described or illustrated in the method in Figure 9) and/or additional information, which may be used to determining whether TA value (s) in the TA value list is invalid or not, to candidate DU 1003 (i.e., target DU) . For example, the additional information associated with a TA value within the TA value list could include at least one of: absolute time (e.g., a time stamp) of receiving the TA value, the elapsed time of since receiving the TA value, or the remaining valid period of the TA value.

(3) Option#3: CU 1004 may be not responsible for maintenance or storing of TA value (s) . In such embodiment, CU 1004 may transmit a request to source DU 1002 to ask TA value (s) and/or the additional information which may be used to determining whether the TA value (s) is invalid or not. Then, CU 1004 may transmit a TA value list (e.g., list#2 described or illustrated in the method in Figure 7) and/or the related additional information, which are received from source DU 1002, to candidate DU 1003 (i.e., target DU) . For example, the additional information associated with a TA value within the TA value list could include at least one of: (1) absolute time (e.g., a time stamp) of receiving the TA value, (2) the elapsed time of since receiving the TA value, or (3) the remaining valid period of the TA value.

Figure 11 illustrates another example of performing cell switching in accordance with aspects of the present disclosure. Details described in all other embodiments of the present disclosure are applicable for the embodiments shown in Figure 11.

As shown in Figure 11, BS 1105 is in CU-DU architecture, and includes CU 1104, source DU 1102, and candidate DU 1103. In the embodiments of Figure 11, a cell switching operation performed by UE 1101 may refer to an Intra-DU case in which a source cell and a target cell in the same DU or refer to an Inter-DU case in which a source cell and a target cell are located at different DUs. For instance, the flowchart 1110 as shown in Figure 11 only shows a cell switching operation in an Inter-DU case for the exemplary purpose. The flowchart 1110 also can be applied to an intra-DU case if source DU 1102 and candidate DU 1103 are the same DU.

In the exemplary flowchart 1110 as shown in Figure 11, in operation 1111, UE 1101 may access the serving BS (e.g., gNB) and send a measurement report to the serving BS, for example, BS 1105. The serving BS may include a CU (e.g., gNB-CU) and one or more DUs (e.g., gNB-DUs) . A serving cell is associated with a CU and a DU. There is an F1 interface between the DU and the CU. For example, as shown in Figure 11, BS 1105 includes CU 1104, source DU 1102, and candidate DU 1103. BS 1105 may include one or more other candidate DUs (e.g., candidate DU 1106 shown in Figure 11) . In some implementations, UE 1101 may send the measurement report to CU 1104 via source DU 1102.

In operation 1112, CU 1104 may determine to initiate a L1/L2 based inter-cell mobility configuration procedure, i.e., making a L1/L2 based inter-cell mobility configuration decision.

In operation 1113, CU 1104 may send a request message, which contains ID information of the candidate cells, to candidate DU 1103 via an F1 interface. In Inter-DU case, the request message may be a UE CONTEXT SETUP REQUEST message. In Intra-DU case, the request message may be a UE CONTEXT MODIFICATION REQUEST message.

In operation 1114, if candidate DU 1103 decides to accept the request of LTM configuration related to candidate cell (s) , candidate DU 1103 may transmit a response message, which includes the RRC configuration (s) for the accepted target candidate cell (s) , to CU 1104 via an F1 interface. In Inter-DU case, the response message may be a UE CONTEXT SETUP RESPONSE message. In Intra-DU case, the response message may be a UE CONTEXT MODIFICATION RESPONSE message.

In some implementations, the response message may include the lower layer RRC configuration (s) for the candidate cell (s) , which is named as “lower layer RRC configuration for LTM” , “L1/L2 RRC configuration information for LTM” , “RRC configuration for LTM” , “LTM configuration information” or the like. In some implementations, RACH resource (s) for early TA acquisition may be included in the response message transmitted to CU 1104. The candidate cell (s) may be named as “candidate cell (s) for LTM” or the like.

In operation 1115, CU 1104 will transmit the received configuration (s) to source DU 1102. In some implementations, CU 1104 may transmit the received configuration (s) , e.g., RACH resource (s) for early TA acquisition, to source DU 1102. CU 1104 may further indicate to source DU 1102 whether early TA acquisition should be triggered.

In some implementations, CU 1104 may generate an RRC reconfiguration message based on the configuration (s) received from candidate DU 1106 and transmit the RRC reconfiguration message to source DU 1102. For instance, the RRC reconfiguration message includes candidate cell configuration (s) for LTM and/or RACH resource (s) for early TA acquisition.

In operation 1116, UE 1101 may receive the RRC reconfiguration message associated with one or more candidate cells (i.e., candidate cells for LTM) for LTM configuration from source DU 1102.

In operation 1117, UE 1101 may receive a PDCCH order for triggering TA acquisition to a particular candidate cell, e.g., a candidate cell associated with candidate DU 1103.

In operation 1118, UE 1101 may transmit the preamble for TA acquisition to candidate DU 1103. In some implementations, if candidate DU 1103 can calculate a TA value for the candidate cell based on the received preamble, candidate DU 1103 may transmit the preamble and corresponding RACH occasion, a beam indication, an ID of UE 1101, RA-RNTI, ID information of the candidate cell ID (i.e., target cell ID) , TCI State index for the candidate cell or similar information to source DU 1102 via CU 1104. In some implementations, candidate DU 1103 may store the calculated TA value. In operation 1118, after CU 1104 receives the information from candidate DU 1103, CU 1104 will transfer the received information, e.g., one or more TA values, to source DU 1102 via F1 interface.

In operation 1119, source DU 1102 transmits a cell switching command for a candidate cell (i.e., a target candidate cell) to UE 1101. For example, the candidate cell is associated with candidate DU 1003 (e.g., cell#1 described or illustrated in the method in Figure 6) . In some implementations, source DU 1102 may transmit an indication of cell switching towards the candidate cell to CU 1104 in operation 1119. In some implementations, the cell switching command includes at least one of: (1) candidate cell configuration index of the candidate cell; (2) a TA value for the candidate cell; or (3) a timer length of a TAT associated with the TA value.

In operation 1119, there may be following two cases in different embodiment:

(1) Case#1: UE 1101 receives the cell switching command. In operation 1120 (which is optional marked as a dotted line) , UE 1101 performs cell switching to the corresponding candidate cell of candidate DU 1103 (i.e., target DU) in response to receiving the cell switching command. In some implementations, UE 1101 starts a LTM timer upon receiving the cell switching command. In operation 1120, candidate DU 1103 (i.e., target DU) may receive the information from CU 1104, which includes a cell switching indication, ID information of the corresponding candidate cell, a TA value list, and/or the related additional information.

(2) Case#2: a radio link failure (RLF) on source DU 1102 occurs before UE 1101 receiving the cell switching command (operation 1119 is thus marked as a dotted line) .

In operation 1121, once the LTM timer expires in Case#1 or the RLF on source DU 1102 occurs before receiving UE 1101 the cell switching command in Case#2, UE 1101 may initiate a reestablishment procedure.

In operation 1121, if “an indication to indicate that a LTM candidate cell can be used for recovery” (for example, information#1 described or illustrated in the method in Figure 6, e.g., attempt LTM configuration IE) is not configured to UE 1101, UE 1101 may release the related configuration (e.g., configuration#1 described or illustrated in the method in Figure 6) . Otherwise, if “an indication to indicate that a LTM candidate cell can be used for recovery” is configured to UE 1101, UE 1101 may keep the related configuration. For example, the related configuration (e.g., configuration#1) may include at least one of the following:

(1) reset MAC;

(2) release configuration for SpCell, e.g., spCellConfig, if configured;

(3) suspend all RBs, and BH RLC channels for IAB-MT, and Uu Relay RLC channels for L2 U2N Relay UE, except SRB0 and broadcast MRBs;

(4) release the MCG SCell (s) , if configured;

(5) release MR-DC configuration;

(8) release idc-AssistanceConfig, if configured;

(9) release btNameList, if configured;

(10) release wlanNameList, if configured; or

(11) release sensorNameList, if configured.

For instance, in operation 1121, once UE 1101 selects a suitable cell (e.g., a cell of candidate DU 1106) , if “an indication to indicate that a LTM candidate cell can be used for recovery” has been configured to UE 1101 and the selected cell is one of the candidate cells for LTM, UE 1101 may apply the LTM configuration for the selected candidate cell. If “an indication to indicate that a LTM candidate cell can be used for recovery” is not configured to UE 1101or the selected cell is not one of the candidate cells for LTM, UE 1101 may release the configuration (e.g., configuration#1) .

In operation 1122, UE 1101 accesses the selected cell (e.g., a cell of candidate DU 1106) via the stored TA value (s) or RACH resource (s) .

In operation 1123, UE 1101 will transmit an RRC reconfiguration complete message to the selected cell (via CU 1104) . The ID information of cell switching configuration related to a candidate cell (e.g., a candidate cell configuration index or a LTM configuration ID for candidate cell) should be added in the RRC reconfiguration complete message. For instance, the RRC reconfiguration complete message includes the following contents:

After operation 1123, there may be following two options in different embodiments, i.e., Option#A and Option#B.

(1) Option#A: in operation 1124, once CU 1104 receives the RRC reconfiguration complete message, CU 1104 may transmit a TA value list and the additional information associated with the TA value list to the new serving DU, e.g., candidate DU 1106. In addition, CU 1104 may indicate candidate DU 1103 related to the candidate cell indicated in the cell switching command that UE 1101 accesses another cell (i.e., the selected cell of candidate DU 1106) .

(2) Option#B: once CU 1104 receives the RRC reconfiguration complete message, CU 1104 may request source DU 1102 to provide a TA value list upon receiving the RRC reconfiguration complete message from UE 1101 or corresponding F1AP message including cell switching from source DU 1102. Then, in operation 1124, CU 1104 may forward a TA value list and the additional information associated with the TA value list (which are received from source DU 1102) to candidate DU 1106.

Figure 12 illustrates an example of TA calculation in accordance with aspects of the present disclosure. Details described in all other embodiments of the present disclosure are applicable for the embodiments shown in Figure 12.

As shown in Figure 12, BS 1205 is in CU-DU architecture, and includes CU 1204, source DU 1202, and candidate DU 1203. In the embodiments of Figure 12, a cell switching operation performed by UE 1201 may refer to an Intra-DU case in which a source cell and a target cell in the same DU or refer to an Inter-DU case in which a source cell and a target cell are located at different DUs. For instance, the flowchart 1200 as shown in Figure 12 only shows a cell switching operation in an Inter-DU case for the exemplary purpose. The flowchart 1200 also can be applied to an intra-DU case if source DU 1202 and candidate DU 1203 are the same DU.

In the exemplary flowchart 1200 as shown in Figure 12, in operation 1211, UE 1201 may access the serving BS (e.g., gNB) and send a measurement report to the serving BS, for example, BS 1205. The serving BS may include a CU (e.g., gNB-CU) and one or more DUs (e.g., gNB-DUs) . A serving cell is associated with a CU and a DU. There is an F1 interface between the DU and the CU. For example, as shown in Figure 12, BS 1205 includes CU 1204, source DU 1202, and candidate DU 1203. BS 1205 may include one or more other candidate DUs (not shown in Figure 12) . In some implementations, UE 1201 may send the measurement report to CU 1204 via source DU 1202.

In operation 1212, CU 1204 may determine to initiate a L1/L2 based inter-cell mobility configuration procedure, i.e., making a L1/L2 based inter-cell mobility configuration decision.

In operation 1213, CU 1204 may send a request message, which contains ID information of the candidate cells, to candidate DU 1203 via an F1 interface. In Inter-DU case, the request message may be a UE CONTEXT SETUP REQUEST message. In Intra-DU case, the request message may be a UE CONTEXT MODIFICATION REQUEST message.

In some implementations, optionally, the request message in operation 1213 may include an indication (e.g., information#3 as described or illustrated in the method in Figure 8) indicating that UE 1201 is to calculate TA value (s) for candidate cell (s) . This indication may be named as “an indication of UE-based TA measurement for a candidate cell” or the like. UE-based TA measurement means that a UE calculates or computes a TA value on its own, e.g., based on “Rx timing difference between the current serving cell of the UE and a candidate cell” as well as “aTA value for the current serving cell of the UE” .

In operation 1214, if candidate DU 1203 decides to accept the request of LTM configuration related to candidate cell (s) , candidate DU 1203 may transmit a response message, which includes the RRC configuration for the accepted target candidate cell (s) , to CU 1204 via an F1 interface. In Inter-DU case, the response message may be a UE CONTEXT SETUP RESPONSE message. In Intra-DU case, the response message may be a UE CONTEXT MODIFICATION RESPONSE message.

In some implementations, the response message may include the lower layer RRC configuration for the candidate cell (s) , which is named as “lower layer RRC configuration for LTM” , “L1/L2 RRC configuration information for LTM” , “RRC configuration for LTM” , “LTM configuration information” , “candidate cell configuration for LTM” or the like. In some implementations, RACH resource (s) for early TA acquisition may be included in the response message transmitted to CU 1204. The candidate cell (s) may be named as “candidate cell (s) for LTM” or the like.

In some implementations, candidate DU 1203 may configure UE-based TA measurement for a candidate cell. For example, the response message may include an indication (e.g., information#4 as described or illustrated in the method in Figure 8) to indicate UE 1201 to perform UE-based TA measurement for the candidate cell (s) . In addition, the response message may also include corresponding RS configuration (s) which is configured to UE 1201. The RS configuration (s) is external to the lower layer RRC configuration for the candidate cell (s) (i.e., candidate cell configuration (s) for LTM) .

In operation 1215, CU 1204 will transmit the received configuration (s) to source DU 1202. In some implementations, CU 1204 may transmit RACH resource (s) for early TA acquisition and/or the corresponding RS configuration (s) to source DU 1202. CU 1204 may also transmit information indicating whether early TA acquisition should be triggered.

In some implementations, CU 1204 may generate an RRC reconfiguration message based on the configuration (s) from the candidate cell (s) and transmit the RRC reconfiguration message to source DU 1202. For instance, the RRC reconfiguration message includes the candidate cell configuration (s) for LTM and/or the RACH resource (s) for early TA acquisition.

In operation 1216, UE 1201 may receive the RRC reconfiguration message associated with the candidate cell (s) for LTM configuration from source DU 1202. In the RRC reconfiguration message, for which cell UE 1201 should calculate a TA value may be configured. For example, UE 1201 is configured to perform UE-based TA measurement for cell#1 and cell#2 as described or illustrated in the method in Figure 6. In case of asynchronization between the serving cell and the candidate cell of UE 1201, a system frame number (SFN) offset between the serving cell and the candidate cell may be included in the RRC reconfiguration message for UE 1201.

In some implementations, if CU 1204 determines whether UE 1201 is to calculate a TA value for a candidate cell or not, an indication of UE-based TA measurement for the candidate cell (e.g., information#2 as described or illustrated in the method in Figure 6) can be configured via an RRC reconfiguration message to UE 1201.

In operation 1217, UE 1201 calculates TA value (s) for one or more candidate cells, e.g., for both cell#1 and cell#2. After UE 1201 successfully calculates the TA value (s) via UE-based TA measurement, UE 1201 may transmit an indication of success calculation or report the calculated TA value (s) to the serving cell of UE 1201.

In operation 1218, source DU 1202 transmits a cell switching command, which includes a candidate cell configuration index of a candidate cell (e.g., a target candidate cell associated with candidate DU 1203) , to UE 1201. There may be following two options in different embodiments, i.e., Option#M or Option#N as below.

(1) Option#M: If UE-based TA measurement for a candidate cell is configured to UE 1201 and if the cell switching command for a target candidate cell (e.g., cell#1) is received, UE 1201 expects that a TA value for the target candidate cell (i.e., cell#1) will not be included in the cell switching command.

(2) Option#N: After UE 1201 calculates a TA value (e.g., TA#1 as described or illustrated in the method in Figure 6) for cell#1 based on the configuration for UE-based TA measurement:

a) If UE 1201 receives a PDCCH order for early TA acquisition for the same cell#1, UE 1201 may discard the calculated TA value for cell#1, e.g., after receiving another TA value for cell#1 (e.g., TA#3 as described or illustrated in the method in Figure 6) from the source DU.

b) If UE 1201 receives the cell switching command including a TA value (e.g., TA#3) for cell#1, UE 1201 may discard the calculated TA value for cell#1. The TA value (i.e., TA#3) for cell#1included in the cell switching command will be used for cell switching.

In operation 1219, UE 1201 performs cell switching to the corresponding target candidate cell of candidate DU 1203 after receiving the cell switching command from source DU 1202.

In operation 1220, UE 1201 may perform at least one of the following operations in different implementations.

Regarding the calculated TA value for the target candidate cell (e.g., cell#1) , there may be following two options in different embodiments, i.e., Option#V or Option#W as below.

(1) Option#V: UE 1201 may release the calculated TA value for cell#1.

(2) Option#W: after UE 1201 performs cell switching using the TA value for cell#1 calculated by UE-based TA measurement, UE 1201 may store the calculated TA value for cell#1 (i.e., the target cell) .

In Option#W, if UE 1201 stores the calculated TA value for cell#1, UE 1201 may need to report the stored TA value to the network node. Then, the network node can configure a delta value on top of the stored TA value, to update the TA value for cell#1. The delta value may be included in a MAC CE. If UE 1201 is not expected to report the stored TA to the network node, the network node can configure an absolute TA value to UE 1201. Once UE 1201 receives the absolute TA value, UE 1201 may use the absolute TA value instead of the calculated TA value, as the current TA value for cell#1. A MAC CE can be used to inform the absolute TA value to UE 1201. For instance, the absolute TA value may be included in an absolute timing advance command MAC CE, e.g., Absolute Timing Advance Command MAC CE.

Before receiving update information of a TA value (e.g., the delta value or the absolute TA value) from the target cell (i.e., cell#1) , UE 1201 itself may continue updating the TA value for the target cell. That means that UE 1201 stores the TA value based on UE-based TA measurement, a TA value of the source cell and A TAT associated with the source cell’s TA value (e.g., TAT#1 as described or illustrated in the method in Figure 6) . Before the TAT associated with the source cell’s TA value expires, UE 1201 can continue updating the TA value for the target cell based on the source cell’s TA value. After the corresponding TAT expires (before receiving the update information of TA value from the target cell) , UE 1201 may consider the TA value for the target cell as invalid. Then, UE 1201 may trigger a RACH procedure for UL synchronization.

Regarding the calculated TA value (s) for other candidate cell (s) (not the target cell to which UE 1201 switches) , there may be following two options in different embodiments, i.e., Option#X or Option#Y as below.

(1) Option#X: UE 1201 should release the calculated TA value (s) for other candidate cell (s) (e.g., cell#2) after UE 1201 switches to the target cell (e.g., cell#1) .

(2) Option#Y: UE 1201 keeps the calculated TA value (s) for other candidate cell (s) . If so, the corresponding TAT (s) for determining whether the calculated TA value (s) invalid or not may be configured to UE 1201.

The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

A user equipment (UE) , comprising:

at least one memory; and

at least one processor coupled to the at least one memory and configured to cause the UE to:

receive a radio resource control (RRC) reconfiguration message from a base station (BS) , wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells;

receive a cell switching command from the BS, wherein the cell switching command includes identifier (ID) information related to a first candidate cell within the set of candidate cells; and

perform cell switching towards the first candidate cell based on the cell switching command.
The UE of Claim 1, wherein the cell switching command includes at least one of the following:

index information of candidate cell configuration of the first candidate cell;

a first timing advance (TA) value for the first candidate cell; or

a timer length of a timing advance timer (TAT) associated with the first TA value.
The UE of Claim 1, wherein the processor is configured to cause the UE to:

if the UE fails to access the first candidate cell, initiate a reestablishment procedure; and

if first information indicating that the set of candidate cells can be used for recovery has been configured to the UE, keep first configuration, wherein the first configuration at least includes configuration for a primary cell of a master or secondary cell group (SpCell) , configuration for one or more master cell group (MCG) secondary cells (SCell) s, multi-radio dual connectivity (MR-DC) configuration, overheating assistance configuration, and In-Device Coexistence (IDC) assistance configuration ; or

if the first information is not configured to the UE, release the first configuration.
The UE of Claim 3, wherein the processor is further configured to cause the UE to:

select a second candidate cell for an RRC reestablishment procedure;

determine whether the second candidate cell is one candidate cell within the set of candidate cells or not; and

if the second candidate cell is the one candidate cell within the set of candidate cells, apply cell switching configuration for the second candidate cell and perform cell switching to the second candidate cell; or

if the second candidate cell is not the one candidate cell within the set of candidate cells and if the first information has been configured to the UE, release the first configuration.
The UE of Claim 4, wherein the processor is configured to cause the UE to transmit an RRC reconfiguration complete message associated with the second candidate cell to the CU, and wherein the RRC reconfiguration complete message includes identifier (ID) information related to the second candidate cell.
The UE of Claim 1, wherein the RRC reconfiguration message includes second information indicating the UE to calculate at least one of the following:

a first timing advance (TA) value for the first candidate cell; or

a second TA value for a second candidate cell.
The UE of Claim 6, after receiving the second information including ID information of both the first candidate cell and the second candidate cell, the processor is configured to cause the UE to calculate the first TA value for the first candidate cell and the second TA value for the second candidate cell.
The UE of Claim 6, wherein the first or second TA value is calculated based on at least one of the following:

a receiving timing difference between a source cell of the UE and the first or second candidate cell; or

a TA value for the source cell.
The UE of Claim 6 or Claim 7, wherein the processor is configured to cause the UE to release or store the second TA value for the second candidate cell after UE switches to the first candidate cell.
The UE of Claim 9, in response to storing the second TA value for the second candidate cell, the processor is configured to cause the UE to determine whether the second TA value is valid or not based on a timing advance timer (TAT) associated with the second TA value.
The UE of Claim 6 or Claim 7, wherein the processor is configured to cause the UE to release or store the first TA value for the first candidate cell after UE switches to the first candidate cell.
The UE of Claim 11, in response to storing the first TA value for the first candidate cell, the processor is configured to cause the UE to report the first TA value via an RRC message or a medium access control (MAC) control element (CE) to a candidate DU associated with the first candidate cell.
A source distributed unit (DU) of a base station (BS) , comprising:

at least one memory; and

at least one processor coupled to the at least one memory and configured to cause the source DU to:

receive a first timing advance (TA) value list for a set of candidate cells from a centralized unit (CU) of the BS, wherein the first TA value list includes a first TA value for a first candidate cell within the set of candidate cells; and

transmit a cell switching command to a user equipment (UE) , wherein the cell switching command includes identifier (ID) information related to the first candidate cell.
The source DU of Claim 13, wherein the cell switching command includes at least one of the following:

the first TA value for the first candidate cell; or

a timer length of a timing advance timer (TAT) associated with the first TA value.
The source DU of Claim 13, wherein the first TA value list further includes a second TA value for a second candidate cell within the set of candidate cells.
The source DU of Claim 13, after transmitting the cell switching command, the processor is configured to cause the source DU to transmit at least one of the following via the CU to a candidate distributed unit (DU) of the BS associated with the first candidate cell:

a second TA value list; or

additional information associated with the second TA value list.
The source DU of Claim 16, wherein the second TA value list includes all TA values within the first TA value list, or includes all TA values within the first TA value list except the first TA value for the first candidate cell included in cell switching command.
The source DU of Claim 16, wherein the additional information associated with a TA value within the TA value list includes at least one of the following:

absolute time when receiving the TA value;

time elapsed since receiving the TA value; or

a remaining valid period of the TA value.
A centralized unit (CU) of a base station (BS) , comprising:

at least one memory; and

at least one processor coupled to the at least one memory and configured to cause the CU to:

transmit a request for cell switching configuration for a set of candidate cells to one or more candidate distributed units (DU) sof the BS;

receive a response corresponding to the request from the one or more candidate DUs, wherein the response includes the cell switching configuration for the set of candidate cells; and

transmit the cell switching configuration for the set of candidate cells to a user equipment (UE) via a source DU of the BS based on the response.
A processor for wireless communication, comprising:

at least one controller coupled with at least one memory and configured to cause the processor to:

receive a radio resource control (RRC) reconfiguration message from a base station (BS) , wherein the RRC reconfiguration message includes cell switching configuration for a set of candidate cells;

receive a cell switching command from the BS, wherein the cell switching command includes identifier (ID) information related to a first candidate cell within the set of candidate cells; and

perform cell switching towards the first candidate cell based on the cell switching command.