Low-latency switching between secondary nodes

Abstract

The present disclosure provides systems, methods, and apparatus for low-latency handover between secondary nodes (SNs). In one aspect, a user equipment (UE) may receive a configuration for a plurality of SNs, receive a command for communicating via a SN in the plurality of SNs, and determine a handover procedure to be used to establish a connection with the SN. The handover procedure may be a random access channel (RACH)-free procedure or a two-step RACH procedure, and the handover procedure is determined to be used based on determining to establish uplink time synchronization with the SN.

Description

Technical Field

[0001]

[0006] Generally speaking, aspects of the present disclosure relate to wireless communications and, more particularly, to techniques for low-latency handoffs between secondary nodes. Background Art

[0002] Wireless communication systems are widely deployed to provide a variety of telecommunication services, such as telephony, video, data, messaging, and broadcasting. Typical wireless communication systems may employ multiple access technologies that can support communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single carrier frequency division multiple access (SC-FDMA) systems, time division synchronous code division multiple access (TD-SCDMA) systems, and long term evolution (LTE). LTE / LTE-Advanced is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by the Third Generation Partnership Project (3GPP).

[0003] A wireless communication network may include multiple base stations (BSs), which can support communications for multiple user equipments (UEs). User equipments (UEs) can communicate with base stations (BSs) via downlinks (DL) and uplinks (UL). DL (or forward link) refers to the communication link from the BS to the UE, while UL (or reverse link) refers to the communication link from the UE to the BS. As will be described in more detail herein, a BS may be referred to as a Node B, an LTE Evolved Node B (eNB), a gNB, an access point (AP), a radio head, a transmit receive point (TRP), a new radio (NR) BS, a 5G Node B, and the like.

[0004] The above multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different UEs to communicate at urban, national, regional, and even global levels. NR (which may also be referred to as 5G) is an enhancement set of the LTE mobile standard released by the Third Generation Partnership Project (3GPP). NR is designed to better support mobile broadband Internet access by improving spectrum efficiency, reducing costs, improving services, making full use of new spectrum, using orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) on DL, using CP-OFDM or SC-FDM (e.g., also known as discrete Fourier transform spread OFDM (DFT-s-OFDM) on UL), and supporting beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation to better integrate with other open standards. Summary of the invention

[0005] The systems, methods and devices of the disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0006] One innovative aspect of the subject matter described in the present disclosure may be implemented in a wireless communication method performed by a user equipment (UE). The method may include: receiving a configuration for a plurality of secondary nodes (SNs); receiving a command for communicating via an SN in the plurality of SNs; determining a handover procedure to be used to establish a connection with the SN; and performing the handover procedure to establish a connection with the SN.

[0007] In some aspects, multiple SNs are candidates for providing dual connectivity with the primary node.

[0008] In some aspects, the handover procedure is a random access channel-less procedure, and a determination to use the handover procedure is based on a determination to establish uplink time synchronization with the SN.

[0009] In some aspects, a configuration identifies one or more TCI states for each respective SN of a plurality of SNs. In some aspects, performing a handover procedure includes: selecting a TCI state from the one or more TCI states identified for the SN in the configuration; and sending a message indicating a handover to the SN for dual connectivity with a primary node, using a beam indicated by the TCI state, to the SN. In some aspects, the TCI state identifies information associated with a reference signal, and the TCI state is selected based on the information associated with the reference signal.

[0010] In some aspects, the method may include sending a request to activate the SN, wherein the request identifies a specific beam of the SN and the command for communicating via the SN is based on the request. In some aspects, the command identifies an activated TCI state for the SN. In some aspects, the method may include monitoring a physical downlink control channel of the SN to obtain uplink grant information based on the activated TCI state; and sending a message to the SN and based on the uplink grant information indicating a handover to the SN for dual connectivity with the primary node.

[0011] In some aspects, the handover procedure is a two-step RACH procedure, and the determination to use the handover procedure is based on determining that uplink time synchronization is not established with the SN. In some aspects, performing the handover procedure includes: sending a message indicating a handover to the SN for dual connectivity with the primary node in a msgA communication of the two-step RACH procedure; and receiving information identifying a timing advance for communication with the SN in a msgB communication of the two-step RACH procedure. In some aspects, a first RACH opportunity in the msgA communication identifies a specific beam of the SN.

[0012] In some aspects, the handover procedure is a four-step RACH procedure, and the handover procedure is determined to be used based on determining that transmission of the msgA communication of the two-step RACH procedure failed.

[0013] Another innovative aspect of the subject matter described in the present disclosure may be implemented in a UE for wireless communication. The UE may include a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to: receive a configuration for a plurality of SNs; receive a command for communicating via an SN in the plurality of SNs; determine a handover procedure to be used to establish a connection with the SN; and perform the handover procedure to establish a connection with the SN.

[0014] Another innovative aspect of the subject matter described in the present disclosure may be implemented in a non-transitory computer-readable medium. The non-transitory computer-readable medium may store one or more instructions for wireless communication. When the one or more instructions are executed by one or more processors of the UE, the one or more processors may perform the following operations: receiving configurations for multiple SNs; receiving commands for communicating via SNs in the multiple SNs; determining a handover procedure to be used to establish a connection with the SN; and performing a handover procedure to establish a connection with the SN.

[0015] Another innovative aspect of the subject matter described in the present disclosure can be implemented in an apparatus for wireless communication. The apparatus for wireless communication can include: a unit for receiving a configuration for a plurality of SNs; a unit for receiving a command for communicating via an SN in the plurality of SNs; a unit for determining a handover procedure to be used to establish a connection with the SN; and a unit for performing the handover procedure to establish a connection with the SN.

[0016] Another innovative aspect of the subject matter described in the present disclosure can be implemented in an apparatus for wireless communication. The apparatus for wireless communication can include: a first interface for receiving a configuration for a plurality of SNs; a second interface for receiving a command for communicating via an SN in the plurality of SNs; a third interface for determining a handover procedure to be used to establish a connection with the SN; and a fourth interface for performing a handover procedure to establish a connection with the SN.

[0017] Aspects generally include methods, apparatus, systems, computer program products, non-transitory computer-readable media, user equipment, base stations, wireless communication devices and / or processing systems as fully described herein with reference to and as illustrated by the accompanying drawings and description.

[0018] Details of one or more implementations of the subject matter described in the present disclosure are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will be apparent from the description, drawings, and claims. It should be noted that the relative sizes of the drawings may not be depicted to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a block diagram conceptually illustrating an example of a wireless network.

[0020] Figure 2 is a block diagram conceptually illustrating an example of a base station communicating with a user equipment (UE) in a wireless network.

[0021] Figure 3-5 is a schematic diagram showing an example of low-latency switching between secondary nodes.

[0022] Figure 6 is a schematic diagram illustrating an example process performed, for example, by a UE.

[0023] Like reference numbers and designations in the various drawings represent like elements. DETAILED DESCRIPTION

[0024] To describe the innovative aspects of the present disclosure, the following description is directed to certain implementations. However, those skilled in the art will readily recognize that the teachings herein may be applied in a variety of different ways. Some examples in the present disclosure are based on wireless and wired local area network (LAN) communications in accordance with the following standards: Institute of Electrical and Electronics Engineers (IEEE) 802.11 wireless standards, IEEE 802.3 Ethernet standards, and IEEE 1901 power line communications (PLC) standards. However, the described implementations may be implemented in any device, system, or network capable of sending and receiving radio frequency signals in accordance with any wireless communication standard, including any of the following standards: IEEE 802.11 standards, IEEE 802.3 Ethernet standards, and IEEE 1901 power line communications (PLC) standards. Standard, Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), GSM / General Packet Radio Service (GPRS), Enhanced Data GSM Environment (EDGE), Terrestrial Trunked Radio (TETRA), Wideband CDMA (W-CDMA), Evolution Data Optimized (EV-DO), 1xEV-DO, EV-DO Release A, EV-DO Release B, High Speed ​​Packet Access (HSPA), High Speed ​​Downlink Packet Access (HSDPA), High Speed ​​Uplink Packet Access (HSUPA), Evolved High Speed ​​Packet Access (HSPA+), Long Term Evolution (LTE), AMPS or other known signals for communication within wireless, cellular or Internet of Things (IoT), such as systems utilizing 3G, 4G or 5G or further implementations thereof.

[0025] In order to synchronize the connection in the uplink direction, the user equipment (UE) and the base station can perform a random access (RACH) process. In some aspects, the UE and the base station can perform a four-step RACH process. In the four-step RACH process, the UE and the base station can exchange four main RACH communications. The UE can send a first message (i.e., msg1 communication) to the base station. The msg1 communication may include a RACH preamble communication. The base station may respond to the msg1 communication with a second message (i.e., msg2 communication), and the second message may include a random access response (RAR) communication. The UE may respond to the msg2 communication with a third message (i.e., msg3 communication), and the third message may include a radio resource control (RRC) connection request communication. The base station may respond to the msg3 communication with a fourth message (i.e., msg4 communication), and the fourth message may include a media access control (MAC) control element (MAC-CE) contention resolution identifier communication.

[0026] In some cases, the four-step RACH process may not meet the low latency requirements of the NR wireless system. Therefore, the UE and the base station can use a two-step RACH process to reduce the latency when synchronizing the connection in the uplink direction. In the two-step RACH process, the UE can combine msg1 communication and msg3 communication into a communication set called msgA communication. The msg1 communication can be called the preamble of the msgA communication, and the msg3 communication can be called the payload of the msgA communication. In this way, the UE sends msg1 communication and msg3 communication sequentially or simultaneously with each other before receiving msg2 communication and msg4 communication. The base station can receive msgA communication and can send msgB communication, which can include msg2 communication and msg4 communication.

[0027] The RACH process (such as the four-step RACH process) may increase the switching delay in the dual-connectivity communication, thereby reducing the throughput of the dual-connectivity communication.

[0028] Specific implementations of the subject matter described in the present disclosure may be implemented to achieve one or more of the following potential advantages. In some aspects, the techniques and apparatus described herein provide a RACH-free process and a two-step RACH process for switching in dual-connection communications, thereby reducing the latency of dual-connection communications relative to a four-step RACH process. In addition, the techniques and apparatus described herein provide a mechanism for selecting between a RACH-free process and a two-step RACH process, thereby enabling efficient selection of a low-latency switching process. In addition, the techniques and apparatus described herein facilitate selection and use of specific beams for dual-connection communications, thereby improving the reliability, speed, and throughput of dual-connection communications after switching.

[0029] Figure 1 1 is a block diagram conceptually illustrating an example of a wireless network 100. The wireless network 100 may be an LTE network or some other wireless network (such as a 5G or NR network). The wireless network 100 may include multiple BSs 110 (shown as BS 110a, BS 110b, BS 110c, and BS 110d) and other network entities. A BS is an entity that communicates with a UE and may also be referred to as a base station, NR BS, Node B, gNB, 5G Node B (NB), access point, transmit receive point (TRP), and the like. Each BS may provide communication coverage for a specific geographic area. In 3GPP, the term "cell" may refer to a coverage area of ​​a BS, a BS subsystem serving the coverage area, or a combination thereof, depending on the context in which the term "cell" is used.

[0030] A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, another type of cell, or a combination thereof. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions. A femto cell may cover a relatively small geographic area (e.g., a residence) and may allow restricted access by UEs associated with the femto cell (e.g., UEs in a closed subscriber group (CSG)). A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In Figure 1In the example shown in , BS 110a may be a macro BS for macro cell 102a, BS 110b may be a pico BS for pico cell 102b, and BS 110c may be a femto BS for femto cell 102c. A BS may support one or more (e.g., three) cells. The terms "eNB", "base station", "NR BS", "gNB", "TRP", "AP", "Node B", "5G NB", and "cell" may be used interchangeably.

[0031] In some examples, the cells may not necessarily be stationary, and the geographic area of ​​the cells may move depending on the location of the mobile BS. In some examples, the BSs may be interconnected to each other and to one or more other BSs or network nodes (not shown) in the wireless network 100 through various types of backhaul interfaces (such as direct physical connections, virtual networks, or combinations thereof) using any appropriate transport network.

[0032] The wireless network 100 may also include a relay station. A relay station is an entity that can receive transmissions of data from an upstream station (e.g., a BS or a UE) and send transmissions of data to a downstream station (e.g., a UE or a BS). A relay station may also be a UE that is capable of relaying transmissions for other UEs. Figure 1 In the example shown in FIG. 1 , a relay station 110 d may communicate with a macro BS 110 a and a UE 120 d to facilitate communication between the BS 110 a and the UE 120 d. A relay station may also be referred to as a relay BS, a relay base station, a relay, or the like.

[0033] The wireless network 100 may be a heterogeneous network including different types of BSs (e.g., macro BSs, pico BSs, femto BSs, relay BSs, etc.). These different types of BSs may have different transmit power levels, different coverage areas, and different effects on interference in the wireless network 100. For example, a macro BS may have a high transmit power level (e.g., 5 to 40 watts), while a pico BS, a femto BS, and a relay BS may have a lower transmit power level (e.g., 0.1 to 2 watts).

[0034] The network controller 130 may be coupled to a set of BSs and provide coordination and control for these BSs. The network controller 130 may communicate with the BSs via a backhaul. The BSs may also communicate with each other, for example, directly or indirectly via a wireless backhaul or a wired backhaul.

[0035] UE 120 (e.g., 120a, 120b, 120c) can be dispersed throughout the wireless network 100, and each UE can be stationary or mobile. UE can also be referred to as an access terminal, terminal, mobile station, subscriber unit, station, etc. UE can be a cellular phone (e.g., a smart phone), a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet device, a camera, a gaming device, a netbook, a smartbook, an ultrabook, a medical device or equipment, a biosensor / device, a wearable device (smart watch, smart clothing, smart glasses, smart wristband, smart jewelry (e.g., smart ring, smart bracelet)), an entertainment device (e.g., a music or video device, or a satellite radio unit), a vehicle component or sensor, a smart meter / sensor, an industrial manufacturing device, a global positioning system device, or any other suitable device configured to communicate via a wireless medium or a wired medium.

[0036] Some UEs may be considered machine type communication (MTC) UEs or evolved or enhanced machine type communication (eMTC) UEs. For example, MTC and eMTC UEs include robots, drones, remote devices, sensors, meters, monitors, location tags, etc. that can communicate with a base station, another device (e.g., a remote device), or some other entity. A wireless node may provide, for example, a connection to a network or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered Internet of Things (IoT) devices, or may be implemented as NB-IoT (narrowband Internet of Things) devices. Some UEs may be considered customer premises equipment (CPE). UE 120 may be included in a housing that houses components of UE 120 (e.g., a processor component, a memory component, a similar component, or a combination thereof).

[0037] Generally, any number of wireless networks can be deployed in a given geographic area. Each wireless network can support a specific RAT and can operate on one or more frequencies. RAT can also be referred to as radio technology, air interface, etc. Frequency can also be referred to as carrier, frequency channel, etc. Each frequency can support a single RAT in a given geographic area to avoid interference between wireless networks of different RATs. In some cases, NR or 5G RAT networks can be deployed.

[0038] In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station) allocates resources for communication between some or all devices and equipment within a service area or cell of the scheduling entity. Within the present disclosure, as further discussed below, a scheduling entity may be responsible for scheduling, allocating, reconfiguring, and releasing resources for one or more dependent entities. That is, for scheduled communications, the dependent entities utilize resources allocated by the scheduling entity.

[0039] The base station is not the only entity that can be used as a scheduling entity. That is, in some examples, the UE can act as a scheduling entity to schedule resources for one or more subordinate entities (e.g., one or more other UEs). In this example, the UE acts as a scheduling entity, and other UEs use the resources scheduled by the UE for wireless communication. The UE can act as a scheduling entity in a peer-to-peer (P2P) network, a mesh network, or other types of networks. In the mesh network example, in addition to communicating with the scheduling entity, the UEs can also optionally communicate directly with each other.

[0040] Thus, in a wireless communication network having scheduled access to time-frequency resources and having a cellular configuration, a P2P configuration, and a mesh configuration, a scheduling entity and one or more slave entities may communicate using the scheduled resources.

[0041] In some aspects, two or more UEs 120 (e.g., shown as UE 120a and UE 120e) may communicate directly (e.g., without using base station 110 as an intermediary for communicating with each other) using one or more sidelink channels. For example, UE 120 may communicate using peer-to-peer (P2P) communication, device-to-device (D2D) communication, vehicle-to-everything (V2X) protocol (which may include vehicle-to-vehicle (V2V) protocol, vehicle-to-infrastructure (V2I) protocol, or similar protocol), mesh network, or similar network, or a combination thereof. In this case, UE 120 may perform scheduling operations, resource selection operations, and other operations described elsewhere herein as being performed by base station 110.

[0042] Figure 2 1 is a block diagram conceptually illustrating an example 200 of a base station 110 communicating with a UE 120. In some aspects, the base station 110 and the UE 120 may be respectively Figure 1 A base station in a base station and a UE in a UE in the wireless network 100. The base station 110 may be equipped with T antennas 234a through 234t, and the UE 120 may be equipped with R antennas 252a through 252r, where in general T≥1 and R≥1.

[0043] At the base station 110, the transmit processor 220 may receive data for one or more UEs from the data source 212, select one or more modulation and coding schemes (MCS) for each UE based at least in part on a channel quality indicator (CQI) received from the UE, process (e.g., encode and modulate) the data for the UE based at least in part on the MCS selected for each UE, and provide data symbols for all UEs. The transmit processor 220 may also process system information (e.g., for semi-static resource partitioning information (SRPI), etc.) and control information (e.g., CQI requests, grants, upper layer signaling, etc.), and provide overhead symbols and control symbols. The transmit processor 220 may also generate reference symbols for reference signals (e.g., cell-specific reference signals (CRS)) and synchronization signals (e.g., primary synchronization signals (PSS) and secondary synchronization signals (SSS)). The transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (if applicable) (e.g., precoding) on ​​data symbols, control symbols, overhead symbols, or reference symbols, and provide T output symbol streams to T modulators (MOD) 232a to 232t. Each modulator 232 may process a corresponding output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and up-convert) the output sample stream to obtain a downlink signal. The T downlink signals from modulators 232a to 232t may be transmitted via T antennas 234a to 234t, respectively. According to various aspects described in more detail below, position coding may be used to generate synchronization signals to convey additional information.

[0044] At UE 120, antennas 252a to 252r may receive downlink signals from base station 110 or other base stations, and may provide received signals to demodulators (DEMODs) 254a to 254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) the received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all R demodulators 254a to 254r, perform MIMO detection on the received symbols (if applicable), and provide detected symbols. A receive processor 258 may process (e.g., demodulate and decode) the detected symbols, provide decoded data for UE 120 to a data sink 260, and provide decoded control information and system information to a controller or processor (controller / processor) 280. The channel processor may determine reference signal received power (RSRP), received signal strength indicator (RSSI), reference signal received quality (RSRQ), channel quality indicator (CQI), etc. In some aspects, one or more components of UE 120 may be included in a housing.

[0045] On the uplink, at the UE 120, a transmit processor 264 may receive and process data from a data source 262 and control information from a controller / processor 280 (e.g., for reports including RSRP, RSSI, RSRQ, CQI, etc.). The transmit processor 264 may also generate reference symbols for one or more reference signals. The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266 (if applicable), further processed by modulators 254a through 254r (e.g., for DFT-s-OFDM, CP-OFDM, etc.), and transmitted to the base station 110. At the base station 110, uplink signals from the UE 120 and other UEs may be received by the antenna 234, processed by the demodulator 232, detected by the MIMO detector 236 (if applicable), and further processed by the receive processor 238 to obtain decoded data and control information sent by the UE 120. The receive processor 238 may provide the decoded data to a data sink 239 and provide the decoded control information to a controller or processor (i.e., controller / processor) 240. The base station 110 may include a communication unit 244 and communicate with the network controller 130 via the communication unit 244. The network controller 130 may include a communication unit 294, a controller or processor (i.e., controller / processor) 290, and a memory 292.

[0046] The controller / processor 240 of the base station 110, the controller / processor 280 of the UE 120, or Figure 2 Any other component of the UE 120 may perform one or more techniques associated with low latency handover between secondary nodes (SNs), as described in more detail elsewhere herein. For example, the controller / processor 240 of the base station 110, the controller / processor 280 of the UE 120, or Figure 2 Any other component (or combination of components) may perform or direct, for example, Figure 6 The operations of process 600, or other processes as described herein, may be performed. Memories 242 and 282 may store data and program codes for base station 110 and UE 120, respectively.

[0047] The stored program code, when executed by the controller / processor 280 or other processors and modules at the UE 120, may cause the UE 120 to perform operations related to Figure 6 The operations described in process 600 or other processes as described herein. The scheduler 246 may schedule UEs for data transmission on the downlink, uplink, or a combination thereof.

[0048] In some aspects, the UE 120 may include: means for receiving a configuration for a plurality of SNs; means for receiving a command for communicating via an SN in the plurality of SNs; means for determining a handover procedure to be used to establish a connection with the SN; means for performing a handover procedure to establish a connection with the SN; or a combination thereof. In some aspects, such means may include a combination of Figure 2 One or more components of the described UE 120. For example, the UE 120 may include: a first interface that provides a unit for receiving a configuration for a plurality of SNs; a second interface that provides a unit for receiving a command for communicating via an SN in the plurality of SNs; a third interface that provides a unit for determining a handover procedure to be used to establish a connection with the SN; a fourth interface that provides a unit for performing a handover procedure to establish a connection with the SN; or a combination thereof.

[0049] Although in Figure 2 The blocks in the figure are shown as different components, but the functions described above with respect to the blocks may be implemented in a single hardware, software, or combined component, or various combinations of components. For example, the functions described with respect to the transmit processor 264, the receive processor 258, the TX MIMO processor 266, or another processor may be performed by the controller / processor 280 or under the control of the controller / processor 280.

[0050] Figure 3 is a schematic diagram illustrating an example 300 of low-latency handover between SNs. In some aspects, as Figure 3 As shown in , the handover process for low-latency handover between SNs can be a RACH-free process. Figure 3 As shown in FIG. 1 , a master node (MN) 310 may configure a UE 120 for dual connectivity to a network via the MN 310 and one of a plurality of SNs 320. In some aspects, the MN 310 and one or more of the plurality of SNs 310 may be a base station (such as a base station 110). For example, the MN 310 may be a first base station 110, and the SN 320 may be a second base station 110.

[0051] As in Figure 3 As shown in the figure and by reference numeral 330, the MN 310 may send (e.g., via an RRCReconfiguration message) and the UE 120 may receive, configurations for multiple SNs 320 (e.g., configurations for secondary cell groups (SCGs) respectively associated with the multiple SNs 320). For example, the multiple SNs 320 may be configured to provide dual connectivity with the MN 310, and the MN 310 may thereafter send the configurations for the multiple SNs 320 to the UE 120. The configuration may identify the multiple SNs 320 as candidates for providing dual connectivity with the MN 310. The configuration may include information identifying the SNs 320 (e.g., information identifying configured data radio bearers of the SNs 320). The UE 120 may retain the configurations for the multiple SNs 320 during dual connectivity communications involving the MN 310 so as to implement switching between the multiple SNs based on the configurations.

[0052] In some aspects, the configuration may identify one or more transmission configuration indication (TCI) states for each SN 320 in the plurality of SNs 320. For example, the configuration may identify one or more first TCI states for a first SN 320 in the plurality of SNs 320 (e.g., a primary secondary cell (PSCell) for the first SN) and one or more second TCI states for a second SN 320 in the plurality of SNs 320 (e.g., a PSCell for the second SN). In some aspects, the TCI states identified by the configuration may be associated with an uplink grant reserved for the UE 120.

[0053] As indicated by reference numeral 340, the MN 310 may send an activation request (e.g., a 5G assisted next generation Node B (SgNB) activation request) to a target SN 320 of the plurality of SNs 320 identified in a configuration provided to the UE 120, resulting in activation of the SN 320 for dual connectivity with the MN 310. The MN 310 may send the activation request to the target SN 320 based on one or more measurements (e.g., RRM measurements) related to the plurality of SNs 320 obtained by the UE 120. For example, the one or more measurements may indicate an SN 320 (e.g., the target SN 320) of the plurality of SNs 320 that provides the strongest signal to the UE 120. In some aspects, the UE 120 may monitor the one or more measurements related to the plurality of SNs 320 to detect satisfaction of a measurement condition (e.g., a measurement condition specifying a threshold value for signal strength) by a SN 320 of the plurality of SNs 320. In this case, based on determining that the measurement condition is satisfied, UE 120 may send and MN 310 may receive a request for activating target SN 320, thereby causing MN 310 to send an activation request to target SN 320. In some aspects, MN 310 may also send a deactivation request to a source SN 320 among the multiple SNs 320, thereby causing an SN switching from the source SN 320 to the target SN 320.

[0054] As shown by reference numeral 350, the MN 310 may send, and the UE 120 may receive, a command for communicating via the activated target SN 320. As shown by reference numeral 360, the UE 120 may determine a handover procedure to be used to establish a connection with the activated target SN 320. For example, the UE 120 may establish a connection using a no-RACH procedure, a two-step RACH procedure, or a four-step RACH procedure. In some aspects, the UE 120 may determine whether to use a no-RACH procedure or a two-step RACH procedure based on whether uplink time synchronization is established with the activated target SN 320. For example, when uplink time synchronization is established with the activated target SN 320, the UE 120 may determine to use a no-RACH procedure. As another example, when uplink time synchronization is not established with the activated target SN 320, the UE 120 may determine to use a two-step RACH procedure.

[0055] In some aspects, the UE 120 may determine to perform the RACH-free procedure based on determining that uplink time synchronization is established with the activated target SN 320. When the timing advance of the activated target SN 320 is equal to 0, the UE 120 may determine that uplink time synchronization is established with the activated target SN 320. Additionally or alternatively, when the source SN 320 and the activated target SN 320 are time synchronized (e.g., the timing advances associated with the source SN 320 and the activated target SN 320 are the same), the UE 120 may determine that uplink time synchronization is established with the activated target SN 320.

[0056] As indicated by reference numeral 370, the UE 120 may perform the determined handover procedure. In some aspects, the UE 120 may perform a RACH-free procedure. The UE 120 may perform the RACH-free procedure by selecting a TCI state associated with the activated target SN 320. For example, the UE 120 may select a TCI state from one or more TCI states configured for the activated target SN 320 (identified in the configuration for the multiple SNs 320). In some aspects, the UE 120 may select a TCI state from one or more TCI states based on a reference signal associated with the TCI state (e.g., a channel state information reference signal (CSI-RS) or a synchronization signal block (SSB)). For example, the UE 120 may select a TCI state associated with a reference signal that satisfies a threshold value (e.g., a threshold power level or a threshold quality level of the reference signal).

[0057] After selecting the TCI state, the UE 120 may further perform a RACH-free procedure by sending a message (e.g., an RRCReconfigurationComplete message) indicating that the UE 120 has switched to the activated target SN 320 for dual connectivity with the MN 310. The TCI state may provide an indication of a specific beam of the activated target SN 320. Therefore, the UE 120 may send the message to the activated target SN 320 based on the uplink grant associated with the selected TCI state and using a beam corresponding to the specific beam indicated by the selected TCI state. In this way, the UE 120 may establish a connection with the activated target SN 320 without sending a RACH preamble to the activated target SN 320, thereby reducing the delay associated with switching to the activated target SN 320.

[0058] Figure 4 4 is a schematic diagram illustrating an example 400 of low-latency switching between SNs. In some aspects, as Figure 4 As shown in , the handover process for low-latency handover between SNs can be a RACH-free process. Figure 4 As shown in , the MN 310 may configure the UE 120 to have dual connectivity to the network via the MN 310 and one of the multiple SNs 320.

[0059] like Figure 4 As shown in FIG. 4 and by reference numeral 410, the MN 310 may send (e.g., via an RRCReconfiguration message) and the UE 120 may receive, configurations for the plurality of SNs 320 (e.g., configurations for secondary cell groups (SCGs) respectively associated with the plurality of SNs 320), as described above in conjunction with Figure 3 In some aspects, the configuration may not identify one or more TCI states for multiple SNs 320. In this way, resources associated with the TCI states for uplink grants may be saved.

[0060] As indicated by reference numeral 420, UE 120 may send, and MN 310 may receive, a request to switch SNs to provide dual connectivity with MN 310. UE 120 may send (e.g., in a physical uplink shared channel) the request to switch SNs via a MAC-CE or via a release auxiliary indication. In some aspects, UE 120 may send the request to switch SNs based on determining that a target SN 320 among a plurality of SNs 320 configured for UE 120 satisfies a measurement condition (e.g., a measurement condition specifying a threshold value for signal strength). Thus, the request to switch SNs may identify the target SN 320.

[0061] In some aspects, the request for switching SNs may identify a specific beam of the target SN 320 (e.g., by a beam index). The specific beam may be a beam of the target SN 320 that provides the strongest signal to the UE 120, or a beam of the target SN 320 that has a signal strength that meets a threshold. In some aspects, the request for switching SNs may also provide one or more measurements related to the target SN 320 (e.g., a reference signal received power (RSRP) measurement, a reference signal received quality (RSRQ) measurement, a signal-to-noise ratio (SNR) measurement, a signal-to-interference-plus-noise ratio (SINR) measurement).

[0062] As indicated by reference numeral 430, the MN 310 may send an activation request (eg, an SgNB activation request) to an SN 320 of the plurality of SNs 320 configured for the UE 120, as described above in conjunction with Figure 3For example, MN 310 may send an activation request to a target SN 320 identified in a request for switching SN sent by UE 120, thereby resulting in activation of the target SN 320 for dual connectivity with MN 310. In some aspects, the activation request may include information associated with a specific beam indicated in the request for switching SN, or with one or more measurements provided in the request for switching SN. In this way, the activation request may enable the target SN 320 to determine and activate the TCI state for UE 320.

[0063] As indicated by reference numeral 440, the MN 310 may send, and the UE 120 may receive, a command to communicate via the activated target SN 320. In some aspects, the command to communicate may identify a TCI state that has been activated for the UE 120 (e.g., a TCI state that has been activated based on a particular beam or one or more measurements indicated by the UE 120).

[0064] As indicated by reference numeral 450, UE 120 may determine a handover procedure to be used to establish a connection with the activated target SN 320, as described above in conjunction with Figure 3 In some aspects, the UE 120 may determine to perform a RACH-free procedure based on determining that uplink synchronization has been established with the activated target SN 320, as described above in conjunction with Figure 3 Described in more detail.

[0065] As indicated by reference numeral 460, the UE 120 may monitor a physical downlink control channel (PDCCH) of the activated target SN 320 according to the activated TCI state. That is, the UE 120 may monitor the PDCCH according to the beam indicated by the activated TCI state. The UE 120 may monitor the PDCCH to obtain uplink grant information for PUSCH communication.

[0066] As indicated by reference numeral 470, UE 120 may perform the determined handover procedure. In some aspects, UE 120 may perform a RACH-free procedure. UE 120 may perform a RACH-free procedure by sending a message (e.g., an RRCReconfigurationComplete message) indicating that UE 120 has switched to the activated target SN 320 for dual connectivity with MN 310. UE 120 may send the message to the activated target SN 320 based on the uplink grant and using a specific beam indicated by the activated TCI state. In this manner, UE 120 may establish a connection with the activated target SN 320 without sending a RACH preamble to the activated target SN 320, thereby reducing the latency associated with switching to SN 320.

[0067] Figure 5 is a schematic diagram illustrating an example 500 of low-latency switching between SNs. In some aspects, as Figure 5 As shown in , the handover process for low-latency handover between SNs can be a two-step RACH process. Figure 5 As shown in , the MN 310 may configure the UE 120 to have dual connectivity to the network via the MN 310 and one of the multiple SNs 320.

[0068] like Figure 5 As shown in FIG. 1 and by reference numeral 510, the MN 310 may send (e.g., via an RRCReconfiguration message) and the UE 120 may receive, configurations for the plurality of SNs 320 (e.g., configurations for secondary cell groups (SCGs) respectively associated with the plurality of SNs 320), as described above in conjunction with Figure 3 and Figure 4 As indicated by reference numeral 520, the MN 310 may send an activation request (e.g., an SgNB activation request) to a target SN 320 among the plurality of SNs 320 identified in the configuration provided to the UE 120, as described above in conjunction with Figure 3 and Figure 4 As indicated by reference numeral 530, the MN 310 may send, and the UE 120 may receive, a command for communicating via the activated target SN 320, as described above in connection with Figure 3 and Figure 4 Described in more detail.

[0069] As indicated by reference numeral 540, UE 120 may determine a handover procedure to be used to establish a connection with activated target SN 320. For example, UE 120 may determine whether to use a RACH-free procedure or a two-step RACH procedure based on whether uplink synchronization is established with activated target SN 320, as described above in conjunction with Figure 3 Described in more detail.

[0070] like Figure 5 As shown in , UE 120 may determine to perform a two-step RACH procedure based on determining that uplink synchronization is not established with the activated target SN 320. When the timing advance of the activated target SN 320 is not equal to zero, UE 120 may determine that uplink synchronization is not established with the activated target SN 320. Additionally or alternatively, when the source SN 320 and the activated target SN 320 are not time synchronized (e.g., the timing advances associated with the source SN 320 and the activated target SN 320 are different), UE 120 may determine that uplink synchronization is not established with the activated target SN 320.

[0071] As indicated by reference numeral 550, UE 120 may perform the determined handover procedure. Figure 5 As shown in FIG. 5 , UE 120 may perform a two-step RACH procedure. UE 120 may perform a two-step RACH procedure by sending msgA communication 550a to activated target SN 320 and receiving msgB communication 550b from activated target SN 320.

[0072] In some aspects, the msgA communication may include a RACH preamble and a PUSCH transmission. According to the two-step RACH process, the UE 120 may send a message (e.g., an RRCReconfigurationComplete message) in a PUSCH transmission indicating that the UE 120 has switched to the activated target SN 320 for dual connectivity with the MN 310. In addition, the UE 120 may send information identifying the data radio bearers configured for the UE 120 by the activated target SN 320 in a PUSCH transmission. In some aspects, the msgA communication may be sent by the UE 120 before receiving a RAR message from the activated target SN 320. In some aspects, the UE 120 may use the first RACH opportunity in the msgA communication to identify a specific beam of the activated target SN 320. The specific beam may be a beam of the activated target SN 320 that provides the strongest signal to the UE 120, or a beam of the activated target SN 320 that has a signal strength that meets a threshold.

[0073] Thereafter, the activated target SN 320 may send, and the UE 120 may receive, a msgB communication. The msgB communication may indicate a timing advance that the UE 120 will use to communicate with the activated target SN 320. In this manner, the UE 120 may establish a connection with the activated target SN 320 using a two-step RACH procedure, thereby reducing latency associated with a handover relative to a four-step RACH procedure.

[0074] In some aspects, msgA communications to the activated target SN 320 may fail. For example, the UE 120 may attempt to send msgA communications to the activated target SN 320 within a specific time period, and the msgA communications to the activated target SN 320 may fail (which may be indicated by the absence of msgB communications from the activated target SN 320). In such a case, the UE may determine to perform the four-step RACH procedure based on determining that the specific time period for sending msgA communications has expired. According to the four-step RACH procedure, the UE 120 may send a message (e.g., an RRCReconfigurationComplete message) in a msg3 communication of the four-step RACH procedure indicating that the UE 120 has switched to the activated target SN 320 for dual connectivity with the MN 310.

[0075] Figure 6 6 is a diagram illustrating an example process 600, performed, for example, by a UE, in accordance with various aspects of the present disclosure. Example process 600 illustrates a UE, such as UE 120, performing operations associated with low-latency handover between secondary nodes.

[0076] like Figure 6 As shown in , in some aspects, process 600 may include: receiving a configuration for multiple SNs (block 610). For example, the UE may receive a configuration for multiple SNs (e.g., using receive processor 258, controller / processor 280, memory 282), as described above.

[0077] like Figure 6 As shown in , in some aspects, process 600 may include: receiving a command for communicating via a SN in a plurality of SNs (block 620). For example, the UE may receive (e.g., using receive processor 258, controller / processor 280, memory 282) a command for communicating via a SN in a plurality of SNs, as described above.

[0078] like Figure 6As shown in , in some aspects, process 600 may include: determining a handover procedure to be used to establish a connection with the SN (block 630). For example, the UE may determine (e.g., using controller / processor 280, memory 282, etc.) a handover procedure to be used to establish a connection with the SN, as described above.

[0079] like Figure 6 As further shown in FIG. 6 , in some aspects, process 600 may include performing a handover procedure to establish a connection with the SN (block 640). For example, the UE may (e.g., using receive processor 258, transmit processor 264, controller / processor 280, memory 282) perform a handover procedure to establish a connection with the SN, as described above.

[0080] Process 600 may include additional aspects, such as any single aspect or any combination of the aspects described below and / or in combination with one or more other processes described elsewhere herein.

[0081] In a first aspect, a plurality of SNs are candidates for providing dual connectivity with a master node.

[0082] In a second aspect, either alone or in combination with the first aspect, the handover procedure is a procedure without a random access channel, and the handover procedure is determined to be used based on determining to establish uplink time synchronization with the SN.

[0083] In a third aspect, either alone or in combination with one or more of the first and second aspects, a configuration identifies one or more TCI states for each corresponding SN in a plurality of SNs. In a fourth aspect, either alone or in combination with one or more of the first to third aspects, performing a switching process includes: selecting a TCI state from one or more TCI states identified for the SN in the configuration; and sending a message indicating a switch to the SN to perform a dual connection with a master node, using a beam indicated by the TCI state, to the SN. In a fifth aspect, either alone or in combination with one or more of the first to fourth aspects, the TCI state identifies information associated with a reference signal, and the TCI state is selected based on the information associated with the reference signal.

[0084] In a sixth aspect, either alone or in combination with one or more of the first to fifth aspects, process 600 further comprises: sending a request for activating the SN, wherein the request identifies a specific beam of the SN, and a command for communicating via the SN is based on the request. In a seventh aspect, either alone or in combination with one or more of the first to sixth aspects, the command identifies an activated TCI state for the SN. In an eighth aspect, either alone or in combination with one or more of the first to seventh aspects, process 600 further comprises: monitoring a physical downlink control channel of the SN according to the activated TCI state to obtain uplink grant information; and sending a message to the SN and according to the uplink grant information indicating a switch to the SN for dual connection with the master node.

[0085] In the ninth aspect, either alone or in combination with one or more of the first to eighth aspects, the switching process is a two-step random access channel process, and the use of the switching process is determined based on determining that uplink time synchronization with the SN is not established. In the tenth aspect, either alone or in combination with one or more of the first to ninth aspects, executing the switching process includes: sending a message indicating a switch to the SN in the msgA communication of the two-step RACH process to perform a dual connection with the master node; in the msgB communication of the two-step RACH process, receiving information identifying the timing advance used for communication with the SN. In the eleventh aspect, either alone or in combination with one or more of the first to tenth aspects, the first RACH opportunity in the msgA communication identifies a specific beam of the SN.

[0086] In a twelfth aspect, alone or in combination with one or more of the first to eleventh aspects, the handover procedure is a four-step RACH procedure, and the handover procedure is determined to be used based on determining that transmission failure of msgA communication of the two-step RACH procedure has occurred.

[0087] Although Figure 6 Example blocks of process 600 are shown, but in some aspects, the same Figure 6 Process 600 may include additional blocks, fewer blocks, different blocks, or blocks in a different arrangement than those described in . Additionally or alternatively, two or more of the blocks of process 600 may be performed in parallel.

[0088] The above disclosure provides illustration and description, but is not intended to be exhaustive or to limit the various aspects to the precise forms disclosed. Modifications and variations may be made based on the above disclosure, or may be acquired from practice of the various aspects.

[0089] As used herein, the term "component" is intended to be broadly interpreted as hardware, firmware, or a combination of hardware and software. As used herein, a processor is implemented with hardware, firmware, or a combination of hardware and software. As used herein, the phrase "based on" is intended to be broadly interpreted to mean "based at least in part on."

[0090] Some aspects are described herein in conjunction with thresholds. As used herein, satisfying a threshold may refer to a value being greater than a threshold, greater than or equal to a threshold, less than a threshold, less than or equal to a threshold, equal to a threshold, not equal to a threshold, and the like.

[0091] As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items, including single members. For example, "at least one of a, b, or c" is intended to cover: a, b, c, ab, ac, bc, and abc.

[0092] The various illustrative logics, logic blocks, modules, circuits, and algorithmic processes described in conjunction with the various aspects disclosed herein may be implemented as electronic hardware, computer software, or a combination of the two. The interchangeability of hardware and software has been generally described around functionality and shown in the various illustrative components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented in hardware or software depends on the specific application and the design constraints imposed on the overall system.

[0093] The various illustrative logics, logic blocks, modules, and circuits described in conjunction with the various aspects disclosed herein may be implemented or executed using a general purpose single-chip or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, a combination of one or more microprocessors and a DSP core, or any other such configuration. In some aspects, specific processes and methods may be performed by circuits specific to a given function.

[0094] In one or more aspects, the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware (including the structures disclosed in this specification and their structural equivalents), or any combination thereof. Aspects of the subject matter described in this specification may also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a computer storage medium, to be executed by a data processing apparatus or to control the operation of the data processing apparatus.

[0095] When implemented in software, the functions may be stored as one or more instructions or codes on a computer-readable medium or transmitted via a computer-readable medium. The processing of the method or algorithm disclosed herein may be implemented in a processor executable software module located on a computer-readable medium. Computer-readable media include computer storage media and communication media, and communication media include any medium that is enabled to transmit a computer program from one place to another. Storage media may be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage device, or any other medium that can be used to store a desired program code in the form of an instruction or data structure and can be accessed by a computer. In addition, any connection may be appropriately referred to as a computer-readable medium. As used herein, disks and discs include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks and blue-ray discs, wherein disks usually copy data magnetically, while optical discs use lasers to optically copy data. The above combination should also be included in the scope of computer-readable media. In addition, the operations of a method or algorithm may be located as a code and instruction set, or any combination of code and instruction sets, on a machine-readable medium and a computer-readable medium, which may be incorporated into a computer program product.

[0096] Various modifications to the various aspects described in this disclosure may be apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the spirit or scope of the disclosure. Therefore, the claims are not intended to be limited to the various aspects shown herein, but are to be given the broadest scope consistent with the disclosure, principles, and novel features disclosed herein.

[0097] In addition, those skilled in the art will readily appreciate that the terms "upper" and "lower" are sometimes used for convenience in describing the drawings and indicate relative positions corresponding to the orientation of the graphics on a properly oriented page, and may not reflect the correct orientation of any device as implemented.

[0098] Certain features described in this specification in the context of different aspects may also be implemented in combination in a single aspect. Conversely, various features described in the context of a single aspect may also be implemented in multiple aspects individually or in any suitable subcombination in multiple aspects. Furthermore, while features may be described above as operating in certain combinations and even initially claimed as such, in some cases one or more features from a claimed combination may be deleted from the combination, and a claimed combination may be directed to a subcombination or a variation of a subcombination.

[0099] Similarly, although the operations are described in a specific order in the accompanying drawings, this should not be understood as: in order to obtain the desired result, it is necessary to perform such operations in the specific order shown or in a serial order, or it is necessary to perform all the operations shown. In addition, the accompanying drawings can schematically depict one or more example processes in the form of a flow chart. However, other operations not depicted can be incorporated into the example processes schematically illustrated. For example, one or more other operations can be performed before, after, at the same time, or between any of the operations shown. In some environments, multitasking and parallel processing may be advantageous. In addition, the separation of the various system components in the various aspects described above should not be understood as requiring such separation in all aspects, and it should be understood that the described program components and systems can generally be integrated together into a single software product, or encapsulated into multiple software products. In addition, other aspects are within the scope of the appended claims. In some cases, the actions stated in the claims can be performed in different orders and still achieve the desired results.

Claims

1. A method of wireless communication performed by a user equipment (UE), comprising: receiving a configuration for a plurality of secondary nodes (SNs); receiving a command for communicating via an SN of the plurality of SNs; determining a handover procedure to be used to establish a connection with the SN; as well as The switching process is performed to establish the connection with the SN, and the switching process includes: selecting a TCI state from one or more TCI states identified for the SN in the configuration, and sending a message indicating switching to the SN to perform a dual connection with the master node to the SN and using a beam indicated by the TCI state.

2. The method according to claim 1, wherein: The multiple SNs are candidates for providing dual connectivity with the master node.

3. The method according to claim 1, wherein: The handover procedure is a procedure without a random access channel, and is determined to be used based on determining to establish uplink time synchronization with the SN.

4. The method according to claim 1, wherein: The configuration identifier is used for one or more transmission configuration indication (TCI) states of each corresponding SN in the plurality of SNs.

5. The method according to claim 1, wherein: The TCI state identifies information associated with a reference signal, and wherein the TCI state is selected based on the information associated with the reference signal.

6. The method according to claim 1, further comprising: A request is sent to activate the SN, wherein the request identifies a specific beam of the SN, and wherein the command to communicate via the SN is based on the request.

7. The method according to claim 6, wherein: The command identifies an activated transmission configuration indication (TCI) state for the SN.

8. The method according to claim 7, further comprising: monitoring a physical downlink control channel of the SN according to the activated TCI state to obtain uplink grant information; as well as Wherein, sending the message indicating the switching to the SN to perform dual connectivity with the primary node is based on the uplink grant information.

9. The method according to claim 1, wherein: The handover procedure is a two-step random access channel procedure, and is determined to be used based on a determination that uplink time synchronization is not established with the SN.

10. The method according to claim 1, wherein: Performing the handover process further comprises: sending the message indicating the handover to the SN for dual connectivity with the primary node in a msgA communication of a two-step random access channel (RACH) process; and In a msgB communication of the two-step RACH procedure, information identifying a timing advance for communication with the SN is received.

11. The method according to claim 10, wherein: The first RACH opportunity in the msgA communication identifies a specific beam of the SN.

12. The method according to claim 1, wherein: The handover procedure is a four-step random access channel (RACH) procedure, and is determined to be used based on determining that a transmission failure of the msgA communication of the two-step RACH procedure occurs.

13. A user equipment (UE) for wireless communication, comprising: Memory; as well as one or more processors operably coupled to the memory, the memory and the one or more processors being configured to: receiving a configuration for a plurality of secondary nodes (SNs); receiving a command for communicating via an SN of the plurality of SNs; determining a handover procedure to be used to establish a connection with the SN; as well as The switching process is performed to establish the connection with the SN, and the switching process includes: selecting a TCI state from one or more TCI states identified for the SN in the configuration, and sending a message indicating switching to the SN to perform a dual connection with the master node to the SN and using a beam indicated by the TCI state.

14. The UE according to claim 13, wherein: The multiple SNs are candidates for providing dual connectivity with the master node.

15. The UE according to claim 13, wherein: The handover procedure is a procedure without a random access channel, and is determined to be used based on determining to establish uplink time synchronization with the SN.

16. The UE according to claim 13, wherein: The configuration identifier is used for one or more transmission configuration indication (TCI) states of each corresponding SN in the plurality of SNs.

17. The UE according to claim 13, wherein: The TCI state identifies information associated with a reference signal, and wherein the TCI state is selected based on the information associated with the reference signal.

18. The UE according to claim 13, wherein: The memory and the one or more processors are further configured to send a request to activate the SN, wherein the request identifies a specific beam of the SN, and wherein the command to communicate via the SN is based on the request.

19. The UE according to claim 18, wherein: The command identifies an activated transmission configuration indication (TCI) state for the SN.

20. The UE according to claim 19, wherein: The memory and the one or more processors are further configured to: monitoring a physical downlink control channel of the SN according to the activated TCI state to obtain uplink grant information; as well as Wherein, sending the message indicating the switching to the SN to perform dual connectivity with the primary node is based on the uplink grant information.

21. The UE according to claim 13, wherein: The handover procedure is a two-step random access channel procedure, and is determined to be used based on a determination that uplink time synchronization is not established with the SN.

22. The UE according to claim 13, wherein: In order to perform the switching process, the memory and the one or more processors are further configured to: sending said message indicating a handover to said SN for dual connectivity with a primary node in a msgA communication of a two-step random access channel (RACH) procedure; as well as In a msgB communication of the two-step RACH procedure, information identifying a timing advance for communication with the SN is received.

23. The UE according to claim 22, wherein: The first RACH opportunity in the msgA communication identifies a specific beam of the SN.

24. The UE according to claim 13, wherein: The handover procedure is a four-step random access channel (RACH) procedure, and is determined to be used based on determining that a transmission failure of the msgA communication of the two-step RACH procedure occurs.

25. A non-transitory computer-readable medium storing one or more instructions for wireless communication, the one or more instructions comprising: One or more instructions that, when executed by one or more processors of a user equipment (UE), cause the one or more processors to: receiving a configuration for a plurality of secondary nodes (SNs); receiving a command for communicating via an SN of the plurality of SNs; determining a handover procedure to be used to establish a connection with the SN; as well as The switching process is performed to establish the connection with the SN, and the switching process includes: selecting a TCI state from one or more TCI states identified for the SN in the configuration, and sending a message indicating switching to the SN to perform a dual connection with the master node to the SN and using a beam indicated by the TCI state.

26. The non-transitory computer readable medium of claim 25, wherein: The handover procedure is a procedure without a random access channel, and is determined to be used based on determining to establish uplink time synchronization with the SN.

27. An apparatus for wireless communication, comprising: means for receiving a configuration for a plurality of secondary nodes (SN); means for receiving a command for communicating via an SN of the plurality of SNs; means for determining a handover procedure to be used to establish a connection with the SN; as well as A unit for performing the switching process to establish the connection with the SN, the switching process comprising: selecting a TCI state from one or more TCI states identified for the SN in the configuration, and sending a message indicating switching to the SN to perform a dual connection with a primary node to the SN and using a beam indicated by the TCI state.

28. The device according to claim 27, wherein The handover procedure is a procedure without a random access channel, and is determined to be used based on determining to establish uplink time synchronization with the SN.

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