RACH transmission in candidate cells for l1 and l2 mobility

Abstract

The present disclosure provides a system, method, and apparatus, including a computer program encoded on a computer storage medium, for a user equipment (UE) to initiate a layer 1 or layer 2 mobility procedure. The UE receives a random access channel (RACH) configuration including a RACH occasion for a candidate cell. The UE determines that conditions for a layer 1 or layer 2 mobility procedure to the candidate cell are met. The UE transmits a physical RACH (PRACH) message to the candidate cell to initiate the layer 1 or layer 2 mobility procedure.

Description

[Technical Field]

[0001] The present disclosure relates to wireless communications, including random access channel (RACH) transmissions in candidate cells for Layer 1 and Layer 2 mobility. [Background technology]

[0002] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. 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, and time division synchronous code division multiple access (TD-SCDMA) systems.

[0003] These multiple access technologies have been adopted in various telecommunications standards to provide common protocols that enable different wireless devices to communicate at city, national, regional, or even global levels. An exemplary telecommunications standard is 5G New Radio (NR). 5G NR is part of the ongoing mobile broadband evolution promulgated by the 3rd Generation Partnership Project (3GPP®) to meet new requirements associated with latency, reliability, security, scalability (e.g., with the Internet of Things (IoT)), and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra-reliable low latency communications (URLLC). Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. Summary of the Invention [Problem to be solved by the invention]

[0004] The systems, methods, and devices of the present disclosure each have several innovative aspects, no single aspect of which is solely responsible for the desirable attributes disclosed herein.

[0005] One innovative aspect of the subject matter described in this disclosure can be embodied in a method for initiating a L1 / L2 mobility procedure. The method includes receiving a random access channel (RACH) configuration including a RACH occasion for a candidate cell. The method includes determining that conditions for a Layer 1 or Layer 2 mobility procedure for the candidate cell are met. The method includes transmitting a physical RACH (PRACH) message to the candidate cell to initiate the Layer 1 or Layer 2 mobility procedure.

[0006] The present disclosure also provides an apparatus (e.g., a UE) including a memory that stores computer-executable instructions and at least one processor that is configured to execute the computer-executable instructions to perform at least one of the above methods; an apparatus that includes means for performing at least one of the above methods; and a non-transitory computer-readable medium that stores computer-executable instructions for performing at least one of the above methods.

[0007] One inventive aspect of the subject matter described in this disclosure can be embodied in a method for controlling L1 / L2 mobility, the method including transmitting a RACH configuration including a RACH occasion for a candidate cell, and receiving a PRACH message at the candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for the UE from an active serving cell to the candidate cell.

[0008] The present disclosure also provides an apparatus (e.g., a BS) including a memory that stores computer-executable instructions and at least one processor that is configured to execute the computer-executable instructions to perform at least one of the above methods; an apparatus including means for performing at least one of the above methods; and a non-transitory computer-readable medium that stores computer-executable instructions for performing at least one of the above methods.

[0009] The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. It should be noted that the relative dimensions of the following figures may not be drawn to scale. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates an example of a wireless communication system including an access network. [Figure 2A] FIG. 2 is a diagram illustrating an example of a first frame. [Figure 2B] FIG. 1 is a diagram illustrating an example of a DL channel within a subframe. [Figure 2C] FIG. 10 is a diagram illustrating an example of a second frame. [Figure 2D] FIG. 2 is a diagram illustrating an example of a subframe. [Figure 3] FIG. 1 illustrates an example of a base station (BS) and user equipment (UE) in an access network. [Figure 4] FIG. 1 illustrates an exemplary disaggregated base station architecture. [Figure 5] FIG. 1 illustrates an example of a Layer 1 or Layer 2 (L1 / L2) mobility scenario. [Figure 6] FIG. 1 illustrates the transmission of synchronization signal blocks (SSBs) for both intra-frequency and inter-frequency mobility. [Figure 7] 7 is a message diagram 700 illustrating various messages for initiating an L1 / L2 mobility procedure. [Figure 8] FIG. 2 is a conceptual data flow diagram illustrating data flow between different means / components in an exemplary BS. [Figure 9] FIG. 2 is a conceptual data flow diagram illustrating data flow between different means / components in an exemplary UE. [Figure 10]10 is a flowchart of an example of a method for a UE to perform PRACH transmission for L1 / L2 mobility. [Figure 11] 1 is a flowchart of an example method for a network node to support L2 / L2 mobility.

[0011] Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following description is directed to several implementations for the purpose of describing the inventive aspects of the present disclosure. However, those skilled in the art will readily recognize that the teachings herein can be applied in many different ways. Some of the examples in this disclosure are based on wireless and wired local area network (LAN) communications according to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 wireless standard, the IEEE 802.3 Ethernet standard, and the IEEE 1901 Powerline communication (PLC) standard.However, the described implementations may be based on any of the IEEE 802.11 standards, the Bluetooth® 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 Rev A, EV-DO Rev B, High Speed ​​Packet Access (HSPA), High Speed ​​Downlink Packet Access (HSDPA), High Speed ​​Uplink Packet Access (HSP), High Speed ​​Packet Access (HSDPA), High Speed ​​Packet Access (HSP ... The present invention may be implemented in any device, system, or network capable of transmitting and receiving RF signals according to any of the wireless communication standards, including High-Speed ​​Packet Access (HSUPA), Evolved High Speed ​​Packet Access (HSPA+), Long Term Evolution (LTE), AMPS, or other known signals used to communicate within wireless, cellular, or Internet of Things (IoT) networks, such as systems utilizing 3G, 4G, or 5G technologies, or further implementations thereof.

[0013] Traditionally, in wireless communication networks such as 5G NR networks, mobility procedures are performed at Layer 3 (L3) using radio resource control (RRC) messaging. Mobility procedures allow a user equipment (UE) to move from a source cell to a target cell. In some scenarios, L3 mobility procedures may involve interruptions or gaps in communication as the UE establishes an RRC connection with the target cell. Mobility procedures at Layer 1 or Layer 2 (L1 / L2) offer the potential to improve mobility speed over L3 mobility procedures. However, L1 and L2 offer less flexibility regarding the type and content of messages that can be transmitted.

[0014] In one aspect, the present disclosure provides a random access channel (RACH) transmission in a candidate cell for L1 / L2 mobility. A PRACH transmission from a UE in a candidate cell may provide the candidate cell with uplink information about the UE that can be used to initiate an L1 / L2 mobility procedure. The UE may identify the candidate cell (both intra-frequency and inter-frequency) and the candidate cell's RACH opportunity for PRACH transmission. For example, the UE may receive a RACH configuration for the candidate cell as a synchronization signal block (SSB), which may be transmitted by the active serving cell or the candidate cell depending on whether the candidate cell is an intra-frequency cell or an inter-frequency cell. The UE may determine when an L1 / L2 mobility condition is met. For example, the condition may be evaluated by the UE based on a rule, or the UE may receive a trigger signal indicating that the condition is met. In response to the condition being met, the UE may transmit a physical RACH (PRACH) message on the appropriate RACH occasion of the candidate cell to initiate an L1 / L2 mobility procedure.

[0015] Particular implementations of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages: L1 / L2 mobility procedures may improve mobility latency, thereby reducing communication interruptions during mobility. The use of PRACH to initiate L1 / L2 mobility procedures may provide flexibility in various scenarios, such as mobility to intra-frequency and inter-frequency candidate cells. L1 / L2 mobility may use less signaling overhead than other mobility procedures.

[0016] Certain aspects of telecommunications systems are presented herein with reference to various apparatus and methods. These apparatus and methods are described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as "elements"). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0017] As an example, an element, or any portion of an element, or any combination of elements, may be implemented as a "processing system" including one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gate logic, discrete hardware circuits, and other suitable hardware configured to perform various functionality described throughout this disclosure. A processor may include or be coupled to an interface that can acquire or output signals. The processor may acquire signals via the interface and output signals via the interface. In some implementations, the interface may be a printed circuit board (PCB) transmission line. In some other implementations, the interface may include a wireless transmitter, a wireless transceiver, or a combination thereof. For example, the interface may include a radio frequency (RF) transceiver that may be implemented to receive or transmit signals, or both. One or more processors in the processing system may execute software.Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0018] Thus, in one or more exemplary implementations, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media, which may be referred to as non-transitory computer-readable media. Non-transitory computer-readable media may exclude transitory signals. 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 random-access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the above types of computer-readable media, or any other medium that can be used to store computer-executable code in the form of instructions or data structures that can be accessed by a computer.

[0019] 1 illustrates an example wireless communication system and access network 100. The wireless communication system (also referred to as a wireless wide area network (WWAN)) includes a base station 102, a UE 104, an Evolved Packet Core (EPC) 160, and another core network 190 (such as 5G Core (5GC)). The base station 102 may include a macrocell (a high-power cellular base station) or a small cell (a low-power cellular base station). A macrocell includes a base station. Small cells include femtocells, picocells, and microcells. Small cells include femtocells, picocells, and microcells. The base station 102 may be configured with a disaggregated RAN (D-RAN) or open RAN (O-RAN) architecture, in which functionality is divided among multiple units, such as a central unit (CU), one or more distributed units (DUs), or a radio unit (RU). Such an architecture may be configured to utilize a protocol stack that is logically divided among one or more units (e.g., one or more CUs and one or more DUs). The base station 102 may be referred to as a network node or network entity. In some aspects, the CU may be implemented within an edge RAN node, and in some aspects, one or more DUs may be co-located with the CU or geographically distributed throughout one or more RAN nodes. A DU may be implemented to communicate with one or more RUs.

[0020] In some implementations, one or more of the UEs 104 may include a mobility component 140 that performs L1 / L2 mobility procedures. The mobility component 140 may include a random access channel (RACH) configuration component 142 configured to receive a RACH configuration including RACH occasions for a candidate cell. The mobility component 140 may include a condition component 144 configured to determine that conditions are met for a Layer 1 or Layer 2 mobility procedure for the candidate cell. The mobility component 140 may include a physical RACH (PRACH) component 146 configured to transmit a PRACH message to the candidate cell to initiate a Layer 1 or Layer 2 mobility procedure.

[0021] In some implementations, one or more of the base stations 102 (or network nodes) may include a mobility control component 120 configured to manage L1 / L2 mobility procedures for the UE. The mobility control component 120 may include a configuration Tx component 122 configured to transmit a random access channel (PRACH) configuration including a RACH occasion for a candidate cell. The mobility control component 120 may include a PRACH Rx component 124 configured to receive a PRACH message at a candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for the UE. In some implementations, the mobility control component 120 may optionally include a trigger component 126 configured to transmit a trigger signal from an active serving cell to trigger the UE to transmit a PRACH message.

[0022] A base station 102 configured for 4G LTE (collectively referred to as the Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC 160 through a first backhaul link 132 (e.g., an S1 interface), which may be wired or wireless. A base station 102 configured for 5G NR (collectively referred to as the Next Generation RAN (NG-RAN)) may interface with the core network 190 through a second backhaul link 184, which may be wired or wireless. In addition to other functions, the base stations 102 may perform one or more of the following functions: forwarding user data, encryption and decryption of radio channels, integrity protection, header compression, mobility control functions (such as handover and dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment tracing, RAN information management (RIM), paging, positioning, and delivery of alert messages. The base stations 102 may communicate with each other directly or indirectly (such as through the EPC 160 or the core network 190) via a third backhaul link 134 (such as an X2 interface). The third backhaul link 134 may be wired or wireless.

[0023] The base stations 102 may communicate wirelessly with the UE 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. Overlapping geographic coverage areas 110 may exist. For example, a small cell 102' may have a coverage area 110' that overlaps with the coverage area 110 of one or more macro base stations 102. A network including both small cells and macro cells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (Home eNBs, HeNBs), which may serve restricted groups called closed subscriber groups (CSGs). The communication link 112 between the base station 102 and the UE 104 may include UL (also called reverse link) transmissions from the UE 104 to the base station 102 or DL ​​(also called forward link) transmissions from the base station 102 to the UE 104. The communication link 112 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, or transmit diversity. The communication link may be over one or more carriers. The base station 102 / UE 104 may use spectrum with a bandwidth of up to Y MHz per carrier (5, 10, 15, 20, 100, 400 MHz, etc.) allocated in carrier aggregation with up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. The carrier allocation may be asymmetric with respect to DL and UL (such that more or fewer carriers may be allocated for DL ​​than for UL). The component carriers may include a primary component carrier and one or more secondary component carriers. The primary component carrier may be referred to as a primary cell (PCell), and the secondary component carrier may be referred to as a secondary cell (SCell).

[0024] Particular UEs 104 may communicate with each other using device-to-device (D2D) communication links 158. The D2D communication links 158 may use the DL / UL WWAN spectrum. The D2D communication links 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH). The D2D communication may be over various wireless D2D communication systems, such as FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

[0025] The wireless communication system may further include a Wi-Fi access point (AP) 150 communicating with Wi-Fi stations (STAs) 152 via communication links 154 in the 5 GHz unlicensed frequency spectrum. When communicating in the unlicensed frequency spectrum, the STAs 152 / AP 150 may perform clear channel assessment (CCA) prior to communication to determine whether a channel is available.

[0026] The small cell 102' may operate in a licensed or unlicensed frequency spectrum. When operating in the unlicensed frequency spectrum, the small cell 102' may employ NR and use the same 5 GHz unlicensed frequency spectrum used by the Wi-Fi AP 150. A small cell 102' employing NR in the unlicensed frequency spectrum may boost coverage to or increase capacity of the access network.

[0027] The base stations 102, whether small cells 102' or large cells (such as macro base stations), may include eNBs, gNodeBs (gNBs), or other types of base stations. Some base stations, such as the gNB 180, may operate within one or more frequency bands in the electromagnetic spectrum.

[0028] The electromagnetic spectrum is often subdivided into various classes, bands, channels, etc. based on frequency / wavelength. In 5G NR, two initial operating bands have been identified, designated frequency ranges FR1 (410 MHz to 7.125 GHz) and FR2 (24.25 GHz to 52.6 GHz). Frequencies between FR1 and FR2 are often referred to as mid-band frequencies. Although portions of FR1 are higher than 6 GHz, FR1 is often referred to (interchangeably) as the “sub-6 GHz” band in various documents and papers. Similar nomenclature issues may arise with FR2, which is often referred to (interchangeably) as the “millimeter wave” (mmW) band in documents and papers, even though it differs from the extremely high frequency (EHF) band (30 GHz to 300 GHz) identified as the “millimeter wave” band by the International Telecommunications Union (ITU).

[0029] With the above aspects in mind, it should be understood that, unless specifically stated otherwise, terms such as "sub-6 GHz," when used herein, may broadly refer to frequencies that may be below 6 GHz, may be within FR1, or may include mid-band frequencies. Furthermore, it should be understood that, unless specifically stated otherwise, terms such as "millimeter wave," when used herein, may broadly refer to frequencies that may include mid-band frequencies, may be within FR2, or may be within the EHF band. Communications using the mmW radio frequency band have significant path loss and short distances. The mmW base station 180 may utilize beamforming 182 with the UE 104 to compensate for the path loss and short distances.

[0030] The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may communicate with a Home Subscriber Server (HSS) 174. The MME 162 is a control node that handles signaling between the UE 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet Protocol (IP) packets are forwarded through the Serving Gateway 166, which is itself connected to the PDN Gateway 172. The PDN Gateway 172 provides IP address allocation for the UE as well as other functions. The PDN gateway 172 and the BM-SC 170 are connected to IP services 176, which may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), PS streaming services, or other IP services. The BM-SC 170 may provide functionality related to the provisioning and delivery of MBMS user services. The BM-SC 170 may serve as an entry point for content providers' MBMS transmissions and may be used to authorize and initiate MBMS bearer services within the public land mobile network (PLMN) and to schedule MBMS transmissions.The MBMS gateway 168 can be used to distribute MBMS traffic to base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and is responsible for session management (start / stop) and collection of eMBMS-related billing information.

[0031] The core network 190 may include an Access and Mobility Management Function (AMF) 192, other AMFs 193, a Session Management Function (SMF) 194, and a User Plane Function (UPF) 195. The AMF 192 may communicate with a Unified Data Management (UDM) 196. The AMF 192 is a control node that handles signaling between the UE 104 and the core network 190. Generally, the AMF 192 provides QoS flow and session management. All user Internet Protocol (IP) packets are forwarded through the UPF 195. The UPF 195 provides IP address allocation for the UE as well as other functions. The UPF 195 is connected to IP services 197. The IP services 197 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), PS streaming services, or other IP services.

[0032] A base station 102 may include or be referred to as a gNB, Node B, eNB, network node, network entity, access point, base transceiver station, radio base station, radio transceiver, transceiver function, basic service set (BSS), extended service set (ESS), transmit reception point (TRP), or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or core network 190 for the UE 104. Examples of the UE 104 include a cellular phone, a smartphone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (such as an MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electricity meter, a gas pump, a large or small cooking appliance, a healthcare device, an implant, a sensor / actuator, a display, or any other similarly functional device. Some of the UEs 104 may be referred to as IoT devices (such as parking meters, gas pumps, toasters, vehicles, heart monitors, etc.) The UEs 104 may also be referred to as stations, mobile stations, subscriber stations, mobile units, subscriber units, wireless units, remote units, mobile devices, wireless devices, wireless communication devices, remote devices, mobile subscriber stations, access terminals, mobile terminals, wireless terminals, remote terminals, handsets, user agents, mobile clients, clients, or some other suitable terminology.

[0033] The following description may focus on 5G NR, but the concepts described herein may be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies, including future 6G technologies.

[0034] FIG. 2A is a diagram 200 illustrating an example of a first frame. FIG. 2B is a diagram 230 illustrating an example of a DL channel within a subframe. FIG. 2C is a diagram 250 illustrating an example of a second frame. FIG. 2D is a diagram 280 illustrating an example of a subframe. The 5G NR frame structure can be FDD, where for a specific set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated to either DL or UL, or TDD, where for a specific set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated to both DL and UL. A subset of the total cell bandwidth of a cell is called a Bandwidth Part (BWP), and bandwidth adaptation is achieved by configuring a UE with BWP(s) and informing the UE which of the configured BWPs is currently active. In one aspect, a narrow bandwidth part (NBWP) refers to a BWP with a bandwidth less than or equal to the maximum configurable bandwidth of the BWP. The bandwidth of the NBWP is smaller than the carrier system bandwidth.

[0035] In the examples provided by FIGS. 2A and 2C, the 5G NR frame structure is assumed to be TDD, subframe 4 is configured with slot format 28 (with mostly DL), where D is DL, U is UL, and X is flexible with respect to use between DL / UL, and subframe 3 is configured with slot format 34 (with mostly UL). While subframes 3 and 4 are shown with slot formats 34 and 28, respectively, any particular subframe may be configured with any of the various available slot formats 0 through 61. Slot formats 0 and 1 are all DL and all UL, respectively. The other slot formats 2 through 61 contain a mix of DL symbols, UL symbols, and flexible symbols. The UE is configured with a slot format through a received slot format indicator (SFI) (either dynamically through DL control information (DCI) or semi-statically / statically through radio resource control (RRC) signaling). Please note that the following description also applies to the 5G NR frame structure, which is TDD.

[0036] Other wireless communication technologies may have different frame structures or different channels. A frame (10 milliseconds (ms)) may be divided into 10 equal-sized subframes (1 ms). Each subframe may include one or more time slots. A subframe may also include a minislot, which may include 7, 4, or 2 symbols. Each slot may include 7 or 14 symbols depending on the slot configuration. In slot configuration 0, each slot may include 14 symbols, and in slot configuration 1, each slot may include 7 symbols. Symbols on the DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. The symbols on the UL can be CP-OFDM symbols (for high-throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also called single-carrier frequency division multiple access (SC-FDMA) symbols) (for power-limited scenarios, i.e., when limited to single-stream transmission). The number of slots in a subframe is based on the slot configuration and numerology. For slot configuration 0, different numerologies μ 0-5 allow 1, 2, 4, 8, 16, and 32 slots per subframe, respectively. For slot configuration 1, different numerologies 0-2 allow 2, 4, and 8 slots per subframe, respectively. Thus, for slot configuration 0 and numerology μ, there are 14 symbols / slot and 2 μ There are slots / subframes. The subcarrier spacing and symbol length / duration are functions of numerology. The subcarrier spacing is 2 μ* μ can be equal to 15 kHz, where μ is a numerology from 0 to 5. Therefore, numerology μ=0 has a subcarrier spacing of 15 kHz, and numerology μ=5 has a subcarrier spacing of 480 kHz. Symbol length / duration is inversely proportional to the subcarrier spacing. Figures 2A-2D provide an example of slot configuration 0 with 14 symbols per slot and numerology μ=2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 microseconds (μs).

[0037] A resource grid may be used to represent the frame structure. Each time slot contains resource blocks (RBs) (also called physical RBs (PRBs)), spanning 12 consecutive subcarriers. The resource grid is divided into multiple resource elements (REs). The number of bits carried by each RE depends on the modulation scheme.

[0038] As shown in FIG. 2A, some of the REs carry reference (pilot) signals (RS) for the UE. The RSs are demodulation RSs (DM-RSs) (in one particular configuration, R x where 100x is the port number, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RS). The RSs may also include beam measurement RSs (BRS), beam refinement RSs (BRRS), and phase tracking RSs (PT-RS).

[0039] FIG. 2B shows an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs), each of which includes nine RE groups (REGs), with each REG including four consecutive REs within one OFDM symbol. A primary synchronization signal (PSS) may be present within symbol 2 of a particular subframe of the frame. The PSS is used by the UE 104 to determine the subframe / symbol timing and the L1 identity. A secondary synchronization signal (SSS) may be present within symbol 4 of a particular subframe of the frame. The SSS is used by the UE to determine the group number of the L1 cell identity and the timing of the radio frame. Based on the L1 identity and the group number of the L1 cell identity, the UE can determine the physical cell identifier (PCI). Based on the PCI, the UE can determine the location of the above-mentioned DM-RS. The physical broadcast channel (PBCH), which carries the master information block (MIB), may be logically grouped with the PSS and SSS to form a synchronization signal (SS) / PBCH block (SSB). The MIB provides the number of RBs in the system bandwidth and the system frame number (SFN). The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted over the PBCH, such as system information blocks (SIBs), and paging messages.

[0040] As shown in FIG. 2C , some of the REs carry DM-RS (denoted as R for one particular configuration, but other DM-RS configurations are possible) for channel estimation at the base station. The UE may transmit DM-RS for the physical uplink control channel (PUCCH) and DM-RS for the physical uplink shared channel (PUSCH). The PUSCH DM-RS may be transmitted within the first one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations depending on whether a short or long PUCCH is transmitted and the particular PUCCH format used. The UE may transmit sounding reference signals (SRS). The SRS may be transmitted within the last symbol of a subframe. The SRS may have a comb structure, and the UE may transmit the SRS in one of the combs. The SRS may be used by the base station for channel quality estimation to enable frequency-dependent scheduling on the UL.

[0041] 2D shows an example of various UL channels within a subframe of a frame. The PUCCH, in one configuration, may be arranged as shown. The PUCCH carries uplink control information (UCI), such as scheduling requests, channel quality indicators (CQI), precoding matrix indicators (PMI), rank indicators (RI), and HARQ ACK / NACK feedback. The PUSCH carries data and may additionally be used to carry buffer status reports (BSR), power headroom reports (PHR), or UCI.

[0042] 3 is a diagram of an example of a base station 310 and a UE 350 in an access network. In the DL, IP packets from the EPC 160 may be provided to a controller / processor 375. The controller / processor 375 implements Layer 3 and Layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and Layer 2 includes a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller / processor 375 includes RRC layer functionality associated with broadcasting system information (MIBs, SIBs, etc.), RRC connection control (such as RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter-radio access technology (RAT) mobility, and measurement configurations for UE measurement reporting; PDCP layer functionality associated with header compression / decompression, security (encryption, decryption, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with forwarding higher layer packet data units (PDUs), error correction via ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and mapping of logical channels to transport channels, multiplexing MAC SDUs onto transport blocks (TBs), and MAC SDUs from TBs. It provides MAC layer functionality associated with demultiplexing of SDUs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

[0043] The transmit (TX) processor 316 and receive (RX) processor 370 implement Layer 1 functionality associated with various signal processing functions. Layer 1, including the physical (PHY) layer, may include error detection on transport channels, forward error correction (FEC) coding / decoding of transport channels, interleaving, rate matching, mapping onto physical channels, modulation / demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM), etc.). The coded and modulated symbols may be split into parallel streams. Each stream may be mapped to an OFDM subcarrier, multiplexed with a reference signal (such as a pilot) in the time or frequency domain, and combined together using an Inverse Fast Fourier Transform (IFFT) to generate a physical channel carrying a time-domain OFDM symbol stream. This OFDM stream is spatially precoded to generate multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation scheme and for spatial processing. The channel estimates may be derived from a reference signal or channel condition feedback transmitted by the UE 350. Each spatial stream may be provided to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX may modulate an RF carrier with the respective spatial stream for transmission.

[0044] At the UE 350, each receiver 354RX receives signals through its respective antenna 352. Each receiver 354RX recovers information modulated onto an RF carrier and provides the information to a receive (RX) processor 356. The TX processor 368 and RX processor 356 implement Layer 1 functionality associated with various signal processing functions. The RX processor 356 can perform spatial processing on the information to recover any spatial streams destined for the UE 350. If multiple spatial streams are destined for the UE 350, the RX processor 356 can combine them into a single OFDM symbol stream. The RX processor 356 converts the OFDM symbol stream from the time domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency-domain signal includes a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, as well as the reference signal, are recovered and demodulated by determining the most likely signal constellation point transmitted by the base station 310. These soft decisions may be based on channel estimates calculated by a channel estimator 358. The soft decisions are decoded and deinterleaved to recover the data and control signals originally transmitted by the base station 310 on the physical channel. The data and control signals are provided to a controller / processor 359, which implements Layer 3 and Layer 2 functionality.

[0045] The controller / processor 359 can be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller / processor 359 provides demultiplexing between transport and logical channels, packet reassembly, decryption, header decompression, and control signal processing to recover IP packets from the EPC 160. The controller / processor 359 is also responsible for error detection using an ACK or NACK protocol to support HARQ operations.

[0046] Similar to the functionality described in connection with DL transmissions by base station 310, controller / processor 359 provides RRC layer functionality associated with system information (such as MIBs, SIBs), RRC connection, and measurement reporting; PDCP layer functionality associated with header compression / decompression and security (encryption, decryption, integrity protection, integrity verification); RLC layer functionality associated with forwarding of upper layer PDUs, error correction via ARQ, concatenation, segmentation, and reassembly of RLC SDUs, resegmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping of logical channels to transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority handling, and logical channel prioritization.

[0047] Channel estimates derived by the channel estimator 358 from a reference signal or feedback transmitted by the base station 310 may be used by the TX processor 368 to select an appropriate coding and modulation scheme and to facilitate spatial processing. The spatial streams generated by the TX processor 368 may be provided to different antennas 352 via separate transmitters 354TX. Each transmitter 354TX may modulate an RF carrier with a respective spatial stream for transmission.

[0048] The UL transmissions are processed at the base station 310 in a manner similar to that described for the receiver functions at the UE 350. Each receiver 318RX receives a signal through its corresponding antenna 320. Each receiver 318RX recovers the information modulated onto the RF carrier and provides the information to the RX processor 370.

[0049] The controller / processor 375 can be associated with a memory 376 that stores program codes and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller / processor 375 provides demultiplexing between transport and logical channels, packet reassembly, decryption, header decompression, and control signal processing to recover IP packets from the UE 350. The IP packets from the controller / processor 375 may be provided to the EPC 160. The controller / processor 375 is also responsible for error detection using an ACK or NACK protocol to support HARQ operations.

[0050] At least one of the TX processor 368, the RX processor 356, and the controller / processor 359 may be configured to perform aspects associated with the mobility component 140 of FIG. 1. For example, the memory 360 may include executable instructions that define the mobility component 140. The TX processor 368, the RX processor 356, and / or the controller / processor 359 may be configured to execute the mobility component 140.

[0051] At least one of the TX processor 316, the RX processor 370, and the controller / processor 375 may be configured to perform aspects associated with the mobility control component 120 of FIG. 1. For example, the memory 376 may include executable instructions that define the mobility control component 120. The TX processor 316, the RX processor 370, and / or the controller / processor 375 may be configured to execute the mobility control component 120.

[0052] 4 illustrates the architecture of an exemplary disaggregated base station 400. The disaggregated base station 400 architecture may include one or more central units (CUs) 410 that can communicate directly with a core network 420 via a backhaul link or indirectly with the core network 420 through one or more disaggregated base station units (e.g., a near-real-time (Near-RT) RAN Intelligent Controller (RIC) 425 via an E2 link, or a non-real-time (Non-RT) RIC 415 associated with a Service Management and Orchestration (SMO) framework 405, or both). The CUs 410 can communicate with one or more distributed units (DUs) 430 via respective midhaul links, such as an F1 interface. The DUs 430 can communicate with one or more radio units (RUs) 440 via respective fronthaul links. The RUs 440 may communicate with each UE 104 via one or more radio frequency (RF) access links. In some implementations, a UE 104 may be served by multiple RUs 440 simultaneously.

[0053] Each of the units, i.e., CU 410, DU 430, RU 440, quasi-RT RIC 425, non-RT RIC 415, and SMO framework 405, may include or be coupled to one or more interfaces configured to receive or transmit signals, data, or information (collectively, signals) over a wired or wireless transmission medium. Each of the units, or an associated processor or controller that provides instructions to the unit's communication interface, may be configured to communicate with one or more of the other units over a transmission medium. For example, a unit may include a wired interface configured to receive signals from or transmit signals to one or more of the other units over a wired transmission medium. Furthermore, the units may include a wireless interface, which may include a receiver, transmitter, or transceiver (such as a radio frequency (RF) transceiver) configured to receive, transmit, or transmit signals over a wireless transmission medium to one or more of the other units.

[0054] In some aspects, the CU 410 may host one or more upper layer control functions. Such control functions may include Radio Resource Control (RRC), Packet Data Convergence Protocol (PDCP), Service Data Adaptation Protocol (SDAP), etc. Each control function may be implemented with an interface configured to communicate signals with other control functions hosted by the CU 410. The CU 410 may be configured to handle user plane functionality (i.e., Central Unit-User Plane (CU-UP)), control plane functionality (i.e., Central Unit-Control Plane (CU-Control Plane (CU-CP))), or a combination thereof. In some implementations, the CU 410 may be logically divided into one or more CU-UP units and one or more CU-CP units. The CU-UP units, when implemented in an O-RAN configuration, may communicate bidirectionally with the CU-CP units via an interface, such as an E1 interface. The CU 410 may be implemented to communicate with the DU 430 as needed for network control and signaling.

[0055] The DU 430 may correspond to a logical unit including one or more base station functions for controlling the operation of one or more RUs 440. In some aspects, the DU 430 may host one or more of a radio link control (RLC) layer, a medium access control (MAC) layer, and one or more upper physical (PHY) layers (e.g., modules for forward error correction (FEC) encoding and decoding, scrambling, modulation and demodulation, etc.), at least in part according to a functional division such as that defined by the 3rd Generation Partnership Project (3GPP). In some aspects, the DU 430 may further host one or more lower PHY layers. Each layer (or module) may be implemented with an interface configured to communicate signals with other layers (and modules) hosted by the DU 430 or with control functions hosted by the CU 410.

[0056] The lower layer functionality can be implemented by one or more RUs 440. In some deployments, the RUs 440 controlled by the DU 430 may correspond to logical nodes hosting RF processing functions, lower PHY layer functions (such as performing fast Fourier transforms (FFTs), inverse FFTs (iFFTs), digital beamforming, physical random access channel (PRACH) extraction and filtering, etc.), or both, based at least in part on a functional division, such as a lower layer functional division. In such an architecture, the RU(s) 440 can be implemented to handle over-the-air (OTA) communications with one or more UEs 104. In some implementations, real-time and non-real-time aspects of control and user plane communications with the RU(s) 440 can be controlled by the corresponding DU 430. In some scenarios, this configuration can enable the DU(s) 430 and CU 410 to be implemented in a cloud-based RAN architecture, such as a vRAN architecture.

[0057] The SMO framework 405 may be configured to support RAN deployment and provisioning of non-virtualized and virtualized network elements. For non-virtualized network elements, the SMO framework 405 may be configured to support deployment of dedicated physical resources for RAN coverage requirements, which may be managed via an operations and maintenance interface (e.g., an O1 interface). For virtualized network elements, the SMO framework 405 may be configured to interact with a cloud computing platform (e.g., an open cloud (O-cloud) 490) to perform network element lifecycle management (e.g., instantiate virtualized network elements) via a cloud computing platform interface (e.g., an O2 interface). Such virtualized network elements may include, but are not limited to, the CU 410, the DU 430, the RU 440, and the quasi-RT RIC 425. In some implementations, the SMO framework 405 may communicate with hardware aspects of a 4G RAN, such as an open eNB (O-eNB) 411, via the O1 interface. Additionally, in some implementations, the SMO framework 405 can communicate directly with one or more RUs 440 via an O1 interface. The SMO framework 405 can also include a non-RT RIC 415 configured to support the functionality of the SMO framework 405.

[0058] The non-RT RIC 415 may be configured to include logic functions that enable non-real-time control and optimization of RAN elements and resources, artificial intelligence / machine learning (AI / ML) workflows including model training and updates, or policy-based guidance of applications / features in the quasi-RT RIC 425. The non-RT RIC 415 may be coupled to or in communication with the quasi-RT RIC 425 (e.g., via an A1 interface). The quasi-RT RIC 425 may be configured to include logic functions that enable near-real-time control and optimization of RAN elements and resources through data collection and action via one or more CUs 410, one or more DUs 430, or both, and interfaces connecting the O-eNB to the quasi-RT RIC 425 (e.g., via an E2 interface).

[0059] In some implementations, the non-RT RIC 415 may receive parameters or external enrichment information from an external server to generate AI / ML models that are deployed to the quasi-RT RIC 425. Such information may be utilized by the quasi-RT RIC 425 and may be received at the SMO framework 405 or non-RT RIC 415 from non-network data sources or from network functions. In some examples, the non-RT RIC 415 or quasi-RT RIC 425 may be configured to adjust RAN behavior or performance. For example, the non-RT RIC 415 may employ AI / ML models to monitor long-term trends and patterns in performance and take corrective action through the SMO framework 405 (e.g., reconfiguration via O1) or through the creation of RAN management policies (e.g., A1 policies).

[0060] 5 illustrates an example of an L1 / L2 mobility scenario 500. A UE 104 may initially be served by an active serving cell 510, sometimes referred to as a special cell (SpCell). L1 / L2 mobility may allow the SpCell to be updated via L1 / L2 signaling based on L1 measurements. Scenario 500 may apply to a single SpCell change without carrier aggregation (CA). L1 / L2 mobility may apply to both intra-frequency and inter-frequency mobility.

[0061] During the L1 / L2 mobility procedure, the UE 104 may determine a target candidate cell 520a from a set of candidate cells 520. For example, the set of candidate cells 520 may include candidate cells 520a, 520b, and 520c. The target candidate cell 520a may be selected based on, for example, L1 measurements.

[0062] L1 / L2 mobility may include L1 / L2-based inter-cell mobility mechanisms and procedures for mobility latency reduction. For example, configuration and maintenance for multiple candidate cells may enable fast application of configuration for candidate cell 520. A dynamic switching mechanism between candidate serving cells (including SpCell cells and secondary cells (SCells)) may satisfy multiple potential applicable scenarios based on L1 / L2 signaling. L1 extensions for inter-cell beam management, including L1 measurement and reporting and beam direction, may facilitate L1 / L2 mobility. Timing advance management for candidate cells may facilitate L1 / L2 mobility. CU-DU interface signaling to support L1 / L2 mobility may be applicable in a distributed architecture. Exemplary L1 / L2 mobility scenarios include standalone, CA, and NR-DC cases with serving cell change within one cell group (CG), intra-DU and intra-CU inter-DU cases (applicable to standalone and CA), both intra-frequency and inter-frequency mobility, both FR1 and FR2 frequency ranges, and when the source and target cells are synchronous or asynchronous.

[0063] FIG. 6 is a diagram 600 illustrating synchronization signal block (SSB) transmission for both intra-frequency and inter-frequency mobility. The active serving cell 510 may transmit the SSB 610 on a center frequency within a configured active bandwidth portion (BWP) 606 within a carrier bandwidth 602. The intra-frequency candidate cell 520d may be a candidate cell operating on the same carrier bandwidth 602, active BWP 606, center frequency, and having the same subcarrier spacing (SCS) as the active serving cell 510. In some implementations, the active serving cell 510 may transmit the SSB 620 associated with the physical cell identifier (PCI) of the intra-frequency candidate cell 520d. For example, the intra-frequency candidate cell 520d may be inactive until selected for mobility. In some implementations, the intra-frequency candidate cell 520d may transmit the SSB 620 on a center frequency within the active BWP 606 on the carrier bandwidth 602. The inter-frequency candidate cell 520e may be a candidate SpCell whose center frequency, SCS, active BWP, or carrier bandwidth 602 is different from that of the active serving cell 510. For example, the inter-frequency candidate cell 520e may transmit the SSB 630 within the active BWP 606 of the active serving cell 510 but using a different center frequency or SCS than the SSB 610 of the active serving cell 510. As another example, the inter-frequency candidate cell 520e may transmit the SSB 640 outside the active BWP 606 of the active serving cell 510 but within the configured carrier bandwidth 602 of the active serving cell 510. As another example, the inter-frequency candidate cell 520e may transmit the SSB 650 outside the configured carrier bandwidth 602 of the active serving cell 510 (e.g., in the carrier bandwidth 604).

[0064] FIG. 7 is a message diagram 700 illustrating various messages for initiating an L1 / L2 mobility procedure.

[0065] In one aspect, the active serving cell 510 may transmit SSB 710, which may correspond to SSB 610. The SSB 710 may provide information about the active serving cell 510 and may be used by the UE 104 to measure the signal quality (e.g., L1 RSRP) of the active serving cell 510. The active serving cell 510 and / or the candidate SpCell 520 may transmit SSB 720, which may correspond to SSB 620. The SSB 720 may be associated with the PCI of the candidate cell 520 (e.g., intra-frequency cell 520d). The SSB 720 may be included in the RACH configuration for the candidate cell 520. For example, the SSB 720 may identify or be associated with a RACH occasion on which the UE 104 may transmit a PRACH message based on the SSB 720. The UE 104 may also measure the signal quality of the candidate cell 520 based on the SSB 720. The candidate cell 520 may transmit SSB 730, which may correspond to any of SSBs 630, 640, or 650. The SSB 730 may be associated with the PCI of the candidate cell 520 (e.g., inter-frequency candidate cell 520e). The SSB 730 may include a RACH configuration for the candidate cell 520. For example, the SSB 730 may identify a RACH occasion on which the UE 104 may transmit a PRACH message based on the SSB 730. The UE 104 may also measure the signal quality of the candidate cell 520 based on the SSB 730. In some implementations, the UE 104 may be configured with an L1 measurement gap to measure the SSB 730.

[0066] In some implementations, the active serving cell 510 may transmit a candidate cell indication 740. For example, the candidate cell indication 740 may be an RRC configuration message, a MAC-CE, or a DCI that configures the UE 104 with one or more candidate cells 520. For example, the candidate cell indication 740 may include one or more PCIs and / or frequencies of the candidate cells 520. The UE 104 may receive appropriate SSBs 720, 730 to obtain RACH configurations and measurements for the configured or indicated candidate cells 520.

[0067] In some implementations, at block 750, the UE 104 may determine that conditions are met for a Layer 1 or Layer 2 mobility procedure for a candidate cell by evaluating a rule for selecting a candidate cell. For example, the rule may be specified in a standard document or regulation and / or configured by the active serving cell 510. For example, the active serving cell 510 may provide an RRC configuration message having parameters for the rule. In some implementations, the rule indicates a candidate cell when cell-level measurements or beam-level measurements for the candidate cell are greater than a threshold value for the candidate cell. In some implementations, the rule indicates a candidate cell when cell-level measurements or beam-level measurements for the candidate cell have changed by at least a threshold amount for the candidate cell. In some implementations, the rule is based on a timing advance miss-alignment timer for the candidate cell. For example, the UE 104 may determine that conditions are met for a Layer 1 or Layer 2 mobility procedure for the candidate cell by determining that a timing advance miss-alignment timer for the candidate cell has expired (e.g., timing may not be synchronized).

[0068] In some implementations, the active serving cell 510 and / or the candidate cell 520 may transmit a trigger signal 760, 762 that triggers transmitting a PRACH message. For example, the trigger signal 760 may be downlink control information (DCI) from the active serving cell 510 including a physical downlink control channel (PDCCH) command for the PRACH on the candidate cell 520. As another example, the trigger signal 762 may be a DCI from the candidate cell 520 including a PDCCH command for the PRACH message on the candidate cell 520. In another example, the trigger signal 760 may be a media access control (MAC) control element (CE) transmitted by the active serving cell 510. When the trigger signal 760 is a MAC-CE, the UE 104 may wait for a period 764 from the MAC-CE or an acknowledgment of the MAC-CE before transmitting a PRACH message 770. In some implementations, the trigger signal 760 is a radio resource control (RRC) configuration or reconfiguration of the candidate cell 520.

[0069] In some implementations, the trigger signals 760, 762 indicate a single SSB for the PRACH message 770. The UE 104 may transmit the PRACH message 770 based on the single SSB. In some implementations, the trigger signals indicate multiple SSBs for the PRACH message 770. The UE 104 may select one SSB of the multiple SSBs for the PRACH message 770. In some implementations, the trigger signals do not indicate an SSB for the PRACH message. The UE 104 may select a received SSB of any of the candidate cells for the PRACH message 770.

[0070] The PRACH message 770 may enable the candidate cell 520 to obtain uplink information regarding the UE 104. For example, in block 780, the candidate cell 520 may perform uplink measurements. For example, the candidate cell 520 may determine uplink timing and uplink transmit power. In some implementations, the L1 / L2 mobility procedure may include transmitting a timing advance 782 from the candidate cell 520 to the UE 104. In some implementations, the L1 / L2 mobility procedure may include an L1 / L2 handover command from either the candidate cell 520 or the active serving cell 510.

[0071] 8 is a conceptual data flow diagram 800 illustrating data flow between different means / components in an exemplary base station 802 (e.g., a network node), which may be an example of a base station 102 that includes a mobility control component 120. The mobility control component 120 may be implemented by the memory 376, and the TX processor 316, the RX processor 370, and / or the controller / processor 375 of FIG. 3. For example, the memory 376 may store executable instructions that define the mobility control component 120, and the TX processor 316, the RX processor 370, and / or the controller / processor 375 may execute the instructions.

[0072] The base station 102 may include a receiver component 870, which may include, for example, a radio frequency (RF) receiver for receiving signals described herein. The base station 102 may include a transmitter component 872, which may include, for example, an RF transmitter for transmitting signals described herein. In one aspect, the receiver component 870 and the transmitter component 872 may be co-located within a transceiver such as illustrated by TX / RX 318 in FIG. 3 .

[0073] 1, the mobility control component 120 may include a configure Tx component 122 and an active PRACH Rx component 124. The mobility control component 120 may optionally include a trigger component 126 or an indication component 810.

[0074] The receiver component 870 may receive UL signals including UL communications from the UE 104. In some implementations, the receiver component 870 may optionally receive PRACH messages 770. The receiver component 870 may provide the PRACH messages to the PRACH Rx component 124.

[0075] The configure Tx component 122 may be configured to transmit a RACH configuration including RACH occasions for the candidate cell. For example, the configure Tx component 122 may transmit any of SSBs 710, 720, or 730 depending on the cell configuration supported by the base station 802 and / or the transition control component 120. The configure Tx component 122 may generate a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) associated with the PCI of the candidate cell. The configure Tx component 122 may generate system information including a broadcast channel (BCH) and / or cell access parameters. For example, the configure Tx component 122 may generate a RACH configuration defining RACH occasions for the UE to transmit the PRACH. The configure Tx component 122 may output an SSB including the PSS, SSS, and BCH for transmission via the transmitter component 872.

[0076] The optional indication component 810 may be configured to transmit an indication from the active serving cell indicating transmission of a PRACH message for the candidate cell. The indication component 810 may obtain information about the candidate cell via a backhaul. The indication component 810 may receive information about the UE, such as uplink channel state information and measurements, via the receiver component 870. The indication component 810 may generate an indication 740 of one or more candidate cells for the UE. For example, the indication may include a PCI and / or frequency for each candidate cell. The indication component 810 may output the indication 740 for transmission via the transmitter component 872.

[0077] The optional trigger component 126 may be configured to transmit a trigger signal from the active serving cell that triggers the UE to transmit a PRACH message. The trigger component 126 may be configured to evaluate various conditions for the UE's mobility. For example, the conditions may be based on reported channel measurements, such as L1 RSRP. The trigger component 126 may transmit the trigger signal in response to determining that the mobility condition is met. The trigger signal may have various forms, such as an RRC configuration, a MAC-CE, or a DCI including a PDCCH command. The trigger component 126 may output the trigger signal for transmission via the transmitter component 872.

[0078] The PRACH Rx component 124 may be configured to receive a PRACH message 770 at a candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for the UE from the active serving cell to the candidate cell. For example, the PRACH Rx component 124 may obtain the PRACH message 770 via the receiver component 870. The PRACH Rx component 124 may identify a PRACH preamble in the PRACH message 770. The PRACH Rx component 124 may measure various uplink properties of the UE 104, such as uplink timing and uplink transmit power, based on the PRACH message 770. In some implementations, the PRACH Rx component 124 may initiate the L1 / L2 mobility procedure by transmitting an L1 / L2 message, such as a timing advance 782 or an L1 / L2 handover command 784.

[0079] 9 is a conceptual data flow diagram 900 illustrating data flow between different means / components in an exemplary UE 904, which may be an example of a UE 104 and may include a mobility component 140. The mobility component 140 may be implemented by a memory 360, a TX processor 368, an RX processor 356, and / or a controller / processor 359. For example, the memory 360 may store executable instructions that define the mobility component 140, and the TX processor 368, the RX processor 356, and / or the controller / processor 359 may execute the instructions.

[0080] The UE 104 may include a receiver component 970, which may include, for example, an RF receiver for receiving signals described herein. The UE 104 may include a transmitter component 972, which may include, for example, an RF transmitter for transmitting signals described herein. In one aspect, the receiver component 970 and the transmitter component 972 may be co-located within a transceiver, such as the TX / RX 352 of FIG. 3.

[0081] As discussed with respect to FIG. 1, the mobility component 140 may include a RACH configuration component 142, a condition component 144, and a PRACH component 146.

[0082] The receiver component 970 may receive DL signals described herein, such as the SSBs 710, 720, or 730, the indications 740, the trigger signals 760 or 762, the timing advance 782, or the L1 / L2 handover commands 784. The receiver component 970 may provide the SSBs 710, 720, or 730 to the RACH configuration component 142. The receiver component 970 provides the indications 740 and / or the trigger signals 760, 762 to the condition component 144. The receiver component 970 may provide the timing advance 782 or the L1 / L2 handover commands 784 to the mobility component 140.

[0083] The RACH configuration component 142 may be configured to receive a RACH configuration including RACH occasions for the candidate cells. For example, the RACH configuration component 142 may receive the SSBs 710, 720, and 730 via the receiver component 970. The RACH configuration component 142 may decode the SSBs 710, 720, and 730 to determine the PCI of each candidate cell. The RACH configuration component 142 may decode the BCH portion of the SSBs 710, 720, and 730 to determine the RACH configuration of each candidate cell. The RACH configuration component 142 may output the RACH occasions to the PRACH component 146.

[0084] The condition component 144 can be configured to determine that a condition for a Layer 1 or Layer 2 mobility procedure for a candidate cell is met. In some implementations, the condition component 144 can receive the indication 740 via the receiver component 970. The condition component 144 can decode the indication to determine the candidate cell.

[0085] In some implementations, the condition component 144 may determine that a condition for a Layer 1 or Layer 2 mobility procedure for a candidate cell is met by evaluating a rule for selecting a candidate cell. For example, the rule may indicate a candidate cell when a cell-level measurement or a beam-level measurement for the candidate cell is greater than a threshold value for the candidate cell. The condition component 144 may obtain measurements, e.g., L1 RSRP based on SSBs 710, 720, 730, via the receiver component 970. The condition component 144 may compare the cell-level measurement or the beam-level measurement to a threshold value. In some implementations, the rule indicates a candidate cell when the cell-level measurement or the beam-level measurement for the candidate cell changes by at least a threshold amount for the candidate cell. The condition component 144 may determine the change in the cell-level measurement or the beam-level measurement and compare it to the threshold value.

[0086] In some implementations, the condition component 144 may determine that the conditions for a Layer 1 or Layer 2 mobility procedure for a candidate cell are met when a timing advance miss alignment timer for the candidate cell has expired. The condition component 144 may maintain a timing advance miss alignment timer for each candidate cell. The condition component 144 may reset the respective timer each time the UE receives a timing advance 782 from the respective candidate cell. The condition component 144 may identify a candidate cell when the timing advance miss alignment timer has expired.

[0087] In some implementations, the condition component 144 may receive a trigger signal from the active serving cell that triggers transmitting a PRACH message. The condition component 144 may determine that the condition is met upon receiving the trigger signal 760, 762. For example, the trigger signal 760, 762 may be an RRC configuration or reconfiguration of the candidate cell, a MAC-CE, or a DCI including a PDCCH command. When the trigger signal 760, 762 is a MAC-CE, the condition component 144 may determine a period 764 to wait after the MAC-CE or its acknowledgment before transmitting the PRACH. In some implementations, the trigger signal may indicate zero or more SSBs for the PRACH. The condition component 144 may decode the trigger signal to indicate whether the trigger signal indicates an SSB. The condition component 144 may output an indication that the condition is met to the PRACH component 146. In some implementations, the condition component 144 may output an indication of an SSB to the PRACH component 146.

[0088] The PRACH component 146 may be configured to transmit a PRACH message to a candidate cell to initiate a Layer 1 or Layer 2 mobility procedure. The PRACH component 146 may obtain a PRACH occasion for the candidate cell from the RACH configuration component 142. The PRACH component 146 may receive an indication that a condition is met from the condition component 144. In some implementations, the PRACH component 146 may receive an indication of an SSB to use for the PRACH message 770. In other implementations, the PRACH component 146 may select an SSB (e.g., based on measurements). The PRACH component 146 may select a RACH occasion and a preamble for transmission (e.g., based on the SSB). The PRACH component 146 may output the PRACH message 770 for transmission via the transmitter component 972.

[0089] 10 is a flowchart of an example method 1000 for a UE to initiate an L1 / L2 mobility procedure. The method 1000 may be performed by the UE (e.g., the UE 104, which may include the memory 360 and may be the UE 104 in its entirety or a component of the UE 104, such as the mobility component 140, the TX processor 368, the RX processor 356, or the controller / processor 359). The method 1000 may be performed by the mobility component 140 in communication with the mobility control component 120 of the base station 102. Optional blocks are indicated by dashed lines.

[0090] In block 1010, the method 1000 may include receiving a configuration of a RACH including a RACH occasion for the candidate cell. In some implementations, for example, the UE 104, the RX processor 356, or the controller / processor 359 may execute the mobility component 140 or the RACH configuration component 142 to receive a configuration of a RACH (e.g., SSBs 710, 720, 730) including a RACH occasion for the candidate cell 520. In some implementations, in subblock 1012, the block 1010 may optionally include receiving an SSB 720 transmitted by the active serving cell 510 and associated with a physical cell identifier of the candidate cell 520. The candidate cell may be an intra-frequency candidate cell 520d having the same frequency, subcarrier spacing, and bandwidth portion as the active serving cell 510. In some implementations, in subblock 1014, the block 1010 may optionally include receiving an SSB 730 transmitted by the candidate cell 520. The candidate cell 520 may be an inter-frequency candidate cell 520e. The inter-frequency candidate cell 520e may transmit an SSB 650 outside the configured bandwidth 602 of the active serving cell 510. The inter-frequency candidate cell 520e may transmit an SSB 640 outside the active bandwidth portion 606 of the active serving cell 510 but within the configured bandwidth 602 of the active serving cell 510. The inter-frequency candidate cell 520e may transmit an SSB 630 within the active bandwidth portion 606 of the active serving cell but using a different center frequency or subcarrier spacing than the SSB 610 of the active serving cell 510. Thus, the UE 104, RX processor 356, or controller / processor 359 running the mobility component 140 or the RACH configuration component 142 may provide means for receiving a RACH configuration including RACH occasions for the candidate cell.

[0091] At block 1020, the method 1000 may include determining that a condition for a Layer 1 or Layer 2 mobility procedure for the candidate cell is met. In some implementations, for example, the UE 104, the RX processor 356, or the controller / processor 359 may execute the mobility component 140 or the condition component 144 to determine that a condition for a Layer 1 or Layer 2 mobility procedure for the candidate cell is met. In some implementations, at sub-block 1022, the block 1020 may optionally include receiving an indication 740 from the active serving cell 510 indicating transmission of a PRACH message 770 for the candidate cell 520. In some implementations, at sub-block 1024, the block 1020 may optionally include evaluating a rule for selecting the candidate cell 520. For example, the rule may indicate the candidate cell 520 when a cell-level measurement or a beam-level measurement for the candidate cell is greater than a threshold for the candidate cell. As another example, the rule may indicate a candidate cell when cell-level measurements or beam-level measurements for the candidate cell change by at least a threshold amount for the candidate cell. In some implementations, in sub-block 1026, block 1020 may optionally include determining that a timing advance misalignment timer for the candidate cell 520 has expired. In some implementations, in sub-block 1028, block 1020 may optionally include receiving a trigger signal 760 from the active serving cell 510 or the candidate cell 520 that triggers transmitting a PRACH message. For example, the trigger signal may be a DCI from the active serving cell 510 that includes a PDCCH command for a PRACH message 770 on the candidate cell 520. As another example, the trigger signal may be a DCI from the candidate cell that includes a PDCCH command for a PRACH message 770 on the candidate cell 520. As yet another example, the trigger signal may be a MAC-CE transmitted by the active serving cell 510. As yet another example, the trigger signal may be an RRC configuration or reconfiguration of the candidate cell 520 .In some implementations, the trigger signal indicates a single SSB, multiple SSBs, or no SSBs for the PRACH message 770. Thus, the UE 104, the RX processor 356, or the controller / processor 359 executing the mobility component 140 or the condition component 144 may provide a means for determining that the conditions for a Layer 1 or Layer 2 mobility procedure to a candidate cell are met.

[0092] In block 1030, method 1000 includes transmitting a PRACH message to a candidate cell to initiate a Layer 1 or Layer 2 mobility procedure. In some implementations, for example, UE 104, TX processor 368, or controller / processor 359 may execute mobility component 140 or PRACH component 146 to transmit a PRACH message to a candidate cell to initiate a Layer 1 or Layer 2 mobility procedure. In some implementations, in sub-block 1032, block 1030 may optionally include: transmitting the PRACH message based on a single SSB when the trigger signal indicates a single SSB for the PRACH message. In some implementations, in sub-block 1034, block 1030 may optionally include: transmitting the PRACH message based on a single SSB when the trigger signal indicates a single SSB for the PRACH message. In some implementations, in sub-block 1036, block 1030 may optionally include selecting a received SSB of the candidate cell for the PRACH message when the trigger signal does not indicate an SSB for the PRACH message. In some implementations (e.g., when the trigger signal is MAC-CE), in sub-block 1038, block 1030 may optionally include transmitting a PRACH message on a RACH occasion for the candidate cell that is at least a threshold time period after the MAC-CE or after an acknowledgment of the MAC-CE. Thus, the UE 104 running the mobility component 140 or the PRACH component 146, the TX processor 368, or the controller / processor 359 may provide a means for transmitting a PRACH message to a candidate cell to initiate a Layer 1 or Layer 2 mobility procedure.

[0093] 11 is a flowchart of an example method 1100 for a network node to support L1 / L2 mobility procedures for a UE. The method 1100 may be performed by a network node (such as a base station 102, which may include memory 376 and may be the entire base station 102 or a component of the base station 102, such as the mobility control component 120, the TX processor 316, the RX processor 370, or the controller / processor 375). The method 1100 may be performed by the mobility control component 120 in communication with the mobility component 140 of the UE 104.

[0094] In block 1110, the method 1100 includes transmitting a RACH configuration including a RACH occasion for the candidate cell. In some implementations, for example, the base station 102, the TX processor 316, or the controller / processor 375 may execute the mobility control component 120 or the configure Tx component 122 to transmit the RACH configuration including the RACH occasion for the candidate cell. In some implementations, in subblock 1112, block 1110 may optionally include transmitting, in the active serving cell, an SSB associated with the physical cell identifier of the candidate cell. The candidate cell may be an intra-frequency candidate cell 520d having the same frequency, subcarrier spacing, and bandwidth portion as the active serving cell 510. In some implementations, in subblock 1114, block 1110 may optionally include transmitting an SSB 730 from the candidate cell, where the candidate cell is an inter-frequency candidate cell. The candidate cell 520 may be an inter-frequency candidate cell 520e. The inter-frequency candidate cell 520e may transmit SSB 650 outside the configured bandwidth 602 of the active serving cell 510. The inter-frequency candidate cell 520e may transmit SSB 640 outside the active bandwidth portion 606 of the active serving cell 510, but within the configured bandwidth 602 of the active serving cell 510. The inter-frequency candidate cell 520e may transmit SSB 630 within the active bandwidth portion 606 of the active serving cell, but using a different center frequency or subcarrier spacing than the SSB 610 of the active serving cell 510. Thus, the base station 102, TX processor 316, or controller / processor 375 executing the mobility control component 120 or the configuring Tx component 122 may provide a means for transmitting a RACH configuration including RACH occasions for the candidate cell.

[0095] At block 1120, the method 1100 may optionally include transmitting an indication from the active serving cell indicating transmission of a PRACH message for the candidate cell. In some implementations, for example, the base station 102, the TX processor 316, or the controller / processor 375 may execute the mobility control component 120 or the indication component 810 to transmit the indication from the active serving cell indicating transmission of a PRACH message for the candidate cell. Thus, the base station 102, the TX processor 316, or the controller / processor 375 executing the mobility control component 120 or the indication component 810 may provide a means for transmitting the indication from the active serving cell indicating transmission of a PRACH message for the candidate cell.

[0096] At block 1130, the method 1100 may optionally include transmitting a trigger signal from the active serving cell that triggers the UE to transmit a PRACH message. In some implementations, for example, the base station 102, the RX processor 370, or the controller / processor 375 may execute the mobility control component 120 or the trigger component 126 to transmit a trigger signal 760, 762 from the active serving cell 510 or the candidate cell 520 that triggers the UE 104 to transmit a PRACH message 770. For example, the trigger signal may be a DCI from the active serving cell 510 that includes a PDCCH command for the PRACH message 770 on the candidate cell 520. As another example, the trigger signal may be a DCI from the candidate cell that includes a PDCCH command for the PRACH message 770 on the candidate cell 520. As yet another example, the trigger signal may be a MAC-CE transmitted by the active serving cell 510. As yet another example, the trigger signal may be an RRC configuration or reconfiguration of the candidate cell 520. In some implementations, the trigger signal indicates a single SSB, multiple SSBs, or no SSBs for the PRACH message 770. Thus, the base station 102, RX processor 370, or controller / processor 375 executing the mobility control component 120 or the trigger component 126 may provide a means for transmitting a trigger signal from the active serving cell that triggers the UE to transmit a PRACH message.

[0097] In block 1140, method 1100 includes receiving a PRACH message at a candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for the UE from the active serving cell to the candidate cell. In some implementations, for example, the base station 102, the RX processor 370, or the controller / processor 375 may execute the mobility control component 120 or the PRACH Rx component 124 to receive a PRACH message at the candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for the UE from the active serving cell to the candidate cell. In some implementations (e.g., if the trigger signal 760, 762 is MAC-CE), in sub-block 1142, block 1140 may optionally include receiving a PRACH message on a RACH occasion for the candidate cell that is at least a threshold period after the MAC-CE or after an acknowledgment of the MAC-CE. In some implementations, in sub-block 1144, block 1140 may optionally include receiving a PRACH message based on a single SSB. In some implementations, in sub-block 1146, block 1140 may optionally include receiving a PRACH message based on a selected one of the plurality of SSBs. In some implementations, in sub-block 1148, block 1140 may optionally include receiving a PRACH message based on transmitted SSBs of the candidate cell. Thus, the base station 102, RX processor 370, or controller / processor 375 executing the mobility control component 120 or the PRACH Rx component 124 may provide means for receiving a PRACH message at the candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for the UE from the active serving cell to the candidate cell.

[0098] The following numbered clauses provide a summary of aspects of the disclosure.

[0099] Aspect 1: A method of wireless communication in a user equipment (UE), comprising: receiving a random access channel (RACH) configuration including a RACH occasion for a candidate cell; determining that conditions for a layer 1 or layer 2 mobility procedure for the candidate cell are met; and transmitting a physical RACH (PRACH) message to the candidate cell to initiate the layer 1 or layer 2 mobility procedure.

[0100] Aspect 2: The method of aspect 1, wherein receiving the configuration of the RACH includes receiving a synchronization signal block (SSB) transmitted by an active serving cell and associated with a physical cell identifier of the candidate cell.

[0101] Aspect 3: The method of aspect 2, wherein the candidate cell has the same frequency, subcarrier spacing, and bandwidth portion as the active serving cell.

[0102] Aspect 4: The method of aspect 1, wherein receiving the configuration of the RACH includes receiving an SSB being transmitted by a candidate cell, and the candidate cell is an inter-frequency candidate cell.

[0103] Aspect 5: The method of aspect 4, wherein the inter-frequency candidate cell transmits SSBs outside the active bandwidth portion of the active serving cell but within the configured bandwidth of the active serving cell.

[0104] Aspect 6: The method of aspect 4, wherein the inter-frequency candidate cell transmits SSBs outside the configured bandwidth of the active serving cell.

[0105] Aspect 7: The method of aspect 4, wherein the inter-frequency candidate cell transmits an SSB within the active bandwidth portion of the active serving cell but using a different center frequency or subcarrier spacing than the SSB of the active serving cell.

[0106] Aspect 8: A method according to any one of aspects 1 to 7, wherein determining that conditions for a Layer 1 or Layer 2 mobility procedure for the candidate cell are met includes receiving an indication from an active serving cell indicating transmission of a PRACH message for the candidate cell.

[0107] Aspect 9: The method of any one of aspects 1 to 8, wherein determining that the conditions for a Layer 1 or Layer 2 mobility procedure for the candidate cell are met includes evaluating rules for selecting the candidate cell.

[0108] Aspect 10: The method of aspect 9, wherein the rule indicates a candidate cell when a cell level measurement or a beam level measurement for the candidate cell is greater than a threshold value for the candidate cell.

[0109] Aspect 11: The method of aspect 9, wherein the rule indicates a candidate cell when a cell-level measurement or a beam-level measurement for the candidate cell changes by at least a threshold amount for the candidate cell.

[0110] Aspect 12: A method as described in any one of aspects 1 to 8, wherein determining that the conditions for a Layer 1 or Layer 2 mobility procedure for the candidate cell are met includes determining that a timing advance miss alignment timer for the candidate cell has expired.

[0111] Aspect 13: A method according to any one of aspects 1 to 8, wherein determining that conditions for a Layer 1 or Layer 2 mobility procedure for the candidate cell are met includes receiving a trigger signal from the active serving cell or the candidate cell that triggers transmitting a PRACH message.

[0112] Aspect 14: The method of aspect 13, wherein the trigger signal is downlink control information (DCI) from an active serving cell that includes a physical downlink control channel (PDCCH) command for a PRACH message on the candidate cell.

[0113] Aspect 15: The method of aspect 13, wherein the trigger signal is downlink control information (DCI) from the candidate cell including a physical downlink control channel (PDCCH) command for a PRACH message on the candidate cell.

[0114] Aspect 16: The method of aspect 13, wherein the trigger signal is a Medium Access Control (MAC) Control Element (CE) transmitted by the active serving cell, and transmitting the PRACH message includes transmitting the PRACH message on a RACH occasion for the candidate cell that is at least a threshold period after the MAC-CE or after an acknowledgment of the MAC-CE.

[0115] Aspect 17: The method of aspect 13, wherein the trigger signal is a radio resource control (RRC) configuration or reconfiguration of the candidate cell.

[0116] Example 18: The method of any one of Examples 13 to 17, wherein the trigger signal indicates a single SSB for the PRACH message, and transmitting the PRACH message includes transmitting the PRACH message based on the single SSB.

[0117] Aspect 19: The method of any one of aspects 13 to 17, wherein the trigger signal indicates a plurality of SSBs for the PRACH message, and transmitting the PRACH message includes selecting one SSB from the plurality of SSBs for the PRACH message.

[0118] Aspect 20: The method of any of aspects 13 to 17, wherein the trigger signal does not indicate an SSB for the PRACH message, and transmitting the PRACH message includes selecting a received SSB of the candidate cell for the PRACH message.

[0119] Aspect 21: A method of wireless communication in a network, comprising: transmitting a random access channel (RACH) configuration including a RACH occasion for a candidate cell; and receiving a physical RACH (PRACH) message at the candidate cell to initiate a layer 1 or layer 2 mobility procedure for a user equipment (UE) from an active serving cell to the candidate cell.

[0120] Aspect 22: The method of aspect 21, wherein transmitting the configuration of the RACH includes transmitting, in the active serving cell, a synchronization signal block (SSB) associated with a physical cell identifier of the candidate cell.

[0121] Aspect 23: The method of aspect 22, wherein the candidate cell has the same frequency, subcarrier spacing, and bandwidth portion as the active serving cell.

[0122] Aspect 24: The method of aspect 21, wherein transmitting the configuration of the RACH includes transmitting an SSB from a candidate cell, the candidate cell being an inter-frequency candidate cell.

[0123] Aspect 25: The method of aspect 24, wherein the inter-frequency candidate cell transmits SSBs outside the active bandwidth portion of the active serving cell but within the configured bandwidth of the active serving cell.

[0124] Aspect 26: The method of aspect 24, wherein the inter-frequency candidate cell transmits SSBs outside the configured bandwidth of the active serving cell.

[0125] Aspect 27: The method of aspect 24, wherein the inter-frequency candidate cell transmits an SSB within the active bandwidth portion of the active serving cell but using a different center frequency or subcarrier spacing than the SSB of the active serving cell.

[0126] Example 28: The method of any one of Examples 21 to 27, further comprising: transmitting, from the active serving cell, an indication indicating transmission of a PRACH message for the candidate cell.

[0127] Example 29: The method of any one of Examples 21 to 28, further comprising: transmitting, from the active serving cell, a trigger signal that triggers the UE to transmit a PRACH message.

[0128] Aspect 30: The method of aspect 29, wherein the trigger signal is downlink control information (DCI) from an active serving cell that includes a physical downlink control channel (PDCCH) command for the PRACH on the candidate cell.

[0129] Aspect 31: The method of aspect 29, wherein the trigger signal is downlink control information (DCI) from the candidate cell including a physical downlink control channel (PDCCH) command for a PRACH message on the candidate cell.

[0130] Aspect 32: The method of aspect 29, wherein the trigger signal is a Medium Access Control (MAC) Control Element (CE) transmitted by the active serving cell, and receiving the PRACH message includes receiving the PRACH message on a RACH occasion for the candidate cell that is at least a threshold period after the MAC-CE or after an acknowledgment of the MAC-CE.

[0131] Aspect 33: The method of aspect 29, wherein the trigger signal is a radio resource control (RRC) configuration or reconfiguration of the candidate cell.

[0132] Example 34: The method of any of examples 29 to 33, wherein the trigger signal indicates a single SSB for the PRACH message, and receiving the PRACH message includes receiving the PRACH message based on the single SSB.

[0133] Aspect 35: The method of any of aspects 29 to 33, wherein the trigger signal indicates a plurality of SSBs for the PRACH message, and receiving the PRACH message includes receiving the PRACH message based on a selected one SSB of the plurality of SSBs.

[0134] Aspect 36: The method of any of aspects 29 to 33, wherein the trigger signal does not indicate an SSB for the PRACH message, and receiving the PRACH message includes receiving the PRACH message based on a transmitted SSB of the candidate cell.

[0135] Aspect 37: An apparatus for wireless communication, comprising: a transceiver; a memory that stores computer-executable instructions; and a processor coupled to the transceiver and the memory, wherein the processor is configured to execute the computer-executable instructions to perform instructions for performing a method described in any of aspects 1 to 20.

[0136] Aspect 38: An apparatus for wireless communication, comprising: a transceiver; a memory that stores computer-executable instructions; and a processor coupled to the transceiver and the memory, wherein the processor is configured to execute the computer-executable instructions to perform a method described in any of aspects 21 to 36.

[0137] Embodiment 39: An apparatus for wireless communication, comprising the method of any one of embodiments 1 to 20.

[0138] Aspect 40: An apparatus for wireless communication, comprising means for performing the method according to any one of aspects 21 to 36.

[0139] Aspect 41: A non-transitory computer-readable medium storing computer-executable instructions that, when executed by a processor of a user equipment (UE), cause the UE to perform a method described in any of aspects 1-20.

[0140] Aspect 42: A non-transitory computer-readable medium storing computer-executable instructions that, when executed by a processor of a network node, cause the network node to perform a method described in any of aspects 21-36.

[0141] 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. As an example, "at least one of a, b, or c" is intended to encompass a, b, c, ab, ac, bc, and abc.

[0142] The various exemplary logic, logic blocks, modules, circuits, and algorithmic processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software, or a combination of both. The interchangeability of hardware and software has been generally described in terms of functionality and illustrated in the various exemplary components, blocks, modules, circuits, and processes above. Whether such functionality is implemented in hardware or software depends on the particular application and design constraints imposed on the overall system.

[0143] The hardware and data processing devices used to implement the various example logic, logic blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed using general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, 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. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, specific processes and methods may be performed by circuitry specific to a given function.

[0144] In one or more aspects, the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware, or any combination thereof, including the structures disclosed herein and their structural equivalents. Implementations of the subject matter described herein may also be implemented as one or more computer programs, i.e., as one or more modules of computer program instructions encoded on a computer storage medium for execution by or to control the operation of a data processing apparatus.

[0145] If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. The processes of a method or algorithm disclosed herein may be implemented in a processor-executable software module, which may reside on a computer-readable medium. Computer-readable media includes both computer storage media and communication media, including any medium that can enable transfer of a computer program from one place to another. A storage medium 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, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection may be properly termed a computer-readable medium. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc, where disks typically reproduce data magnetically while discs reproduce data optically using lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, operations of a method or algorithm may reside on machine-readable and computer-readable media, which may be embodied in a computer program product as one or any combination or set of code and instructions.

[0146] Various modifications to the implementations described in this disclosure will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other implementations without departing from the spirit or scope of the disclosure. Thus, the scope of the claims is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with this disclosure, the principles and novel features disclosed herein.

[0147] Additionally, those skilled in the art will readily appreciate that the terms "upper" and "lower" may be used to facilitate description of the figures and refer to relative positions corresponding to the orientation of the figure on a properly oriented page, and may not reflect the proper orientation of any device in which it may be implemented.

[0148] Some features described herein in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Furthermore, while features may be described above as working in several combinations and may even initially be claimed as such, one or more features from a claimed combination may, in some cases, be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination.

[0149] Similarly, while operations are illustrated in the figures in a particular order, this should not be understood as requiring that such operations be performed in the particular order or sequential order shown, or that all of the operations shown be performed, to achieve desirable results. Furthermore, the figures may generally depict one or more exemplary processes in flow diagram form. However, other operations not shown may be incorporated into the generally depicted exemplary process. For example, one or more additional operations may be performed before, after, simultaneously with, or between any of the depicted operations. In some situations, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

Claims

1. 1. An apparatus for wireless communication in a user equipment (UE), comprising: A transceiver; a memory storing computer-executable instructions; a processor coupled to the transceiver and the memory; wherein the processor executes the computer-executable instructions to receiving, via the transceiver, a random access channel (RACH) configuration including RACH occasions for candidate cells; determining that a condition is met for a Layer 1 or Layer 2 mobility procedure for the candidate cell; transmitting, via the transceiver, a physical RACH (PRACH) message to the candidate cell to initiate the layer 1 or layer 2 mobility procedure; The apparatus is configured to:

2. 2. The apparatus of claim 1, wherein the configuration of the RACH is a synchronization signal block (SSB) transmitted by an active serving cell and associated with a physical cell identifier of the candidate cell.

3. The apparatus of claim 2 , wherein the candidate cell has the same frequency, subcarrier spacing, and bandwidth portion as the active serving cell.

4. 2. The apparatus of claim 1, wherein the configuration of the RACH is an SSB being transmitted by the candidate cell, and the candidate cell is an inter-frequency candidate cell.

5. 5. The apparatus of claim 4, wherein the inter-frequency candidate cell transmits the SSB outside an active bandwidth portion of an active serving cell but within a configured bandwidth of the active serving cell.

6. The apparatus of claim 4 , wherein the inter-frequency candidate cell transmits the SSB outside a configured bandwidth of an active serving cell.

7. 5. The apparatus of claim 4, wherein the inter-frequency candidate cell transmits the SSB within an active bandwidth portion of an active serving cell but using a different center frequency or subcarrier spacing than the SSB of the active serving cell.

8. 2. The apparatus of claim 1, wherein the processor is configured to receive an indication from an active serving cell indicating transmission of the PRACH message for the candidate cell to determine that conditions for a Layer 1 or Layer 2 mobility procedure for the candidate cell are met.

9. 2. The apparatus of claim 1, wherein the processor is configured to evaluate rules for selecting the candidate cell to determine that conditions for a layer 1 or layer 2 mobility procedure for the candidate cell are met.

10. The apparatus of claim 9 , wherein the rule indicates a candidate cell when a cell-level measurement or a beam-level measurement for the candidate cell is greater than a threshold for the candidate cell.

11. 10. The apparatus of claim 9, wherein the rule indicates a candidate cell when a cell-level measurement or a beam-level measurement for the candidate cell has changed by at least a threshold amount for the candidate cell.

12. 2. The apparatus of claim 1, wherein the processor is configured to determine that a timing advance misalignment timer for the candidate cell has expired to determine that conditions for a layer 1 or layer 2 mobility procedure for the candidate cell are met.

13. 2. The apparatus of claim 1, wherein the processor is configured to receive a trigger signal from an active serving cell or the candidate cell that triggers transmitting the PRACH message to determine that conditions for a Layer 1 or Layer 2 mobility procedure for the candidate cell are met.

14. 14. The apparatus of claim 13, wherein the trigger signal is downlink control information (DCI) from the active serving cell that includes a physical downlink control channel (PDCCH) command for the PRACH message on the candidate cell.

15. 14. The apparatus of claim 13, wherein the trigger signal is downlink control information (DCI) from the candidate cell that includes a physical downlink control channel (PDCCH) command for the PRACH message on the candidate cell.

16. 14. The apparatus of claim 13, wherein the trigger signal is a Medium Access Control (MAC) Control Element (CE) transmitted by the active serving cell, and transmitting the PRACH message includes transmitting the PRACH message on a RACH occasion for the candidate cell that is at least a threshold time period after the MAC-CE or after an acknowledgment of the MAC-CE.

17. The apparatus of claim 13 , wherein the trigger signal is a radio resource control (RRC) configuration or reconfiguration of the candidate cell.

18. 14. The apparatus of claim 13, wherein the trigger signal indicates a single SSB for the PRACH message, and the processor is configured to transmit the PRACH message based on the single SSB.

19. 14. The apparatus of claim 13, wherein the trigger signal indicates a plurality of SSBs for the PRACH message, and the processor is configured to select one SSB from the plurality of SSBs for the PRACH message.

20. 14. The apparatus of claim 13, wherein the trigger signal does not indicate an SSB for the PRACH message, and the processor is configured to select a received SSB of the candidate cell for the PRACH message.

21. 1. An apparatus for wireless communication in a network node, comprising: A transceiver; a memory storing computer-executable instructions; a processor coupled to the transceiver and the memory; wherein the processor executes the computer-executable instructions to Transmitting a random access channel (RACH) configuration including RACH occasions for the candidate cells; receiving a physical RACH (PRACH) message at the candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for a user equipment (UE) from an active serving cell to the candidate cell; The apparatus is configured to:

22. 22. The apparatus of claim 21, wherein to transmit the configuration of the RACH, the processor is configured to transmit, in the active serving cell, a synchronization signal block (SSB) associated with a physical cell identifier of the candidate cell, the candidate cell having the same frequency, subcarrier spacing, and bandwidth portion as the active serving cell.

23. 22. The apparatus of claim 21, wherein the processor is configured to transmit an SSB from the candidate cell to transmit the configuration of the RACH, the candidate cell being an inter-frequency candidate cell.

24. 22. The apparatus of claim 21, wherein the processor is configured to transmit an indication from the active serving cell indicating transmission of the PRACH message for the candidate cell.

25. 22. The apparatus of claim 21, wherein the processor is configured to transmit a trigger signal from the active serving cell that triggers the UE to transmit the PRACH message.

26. The trigger signal is Downlink control information (DCI) from the active serving cell, including physical downlink control channel (PDCCH) instructions for the PRACH message on the candidate cell; DCI from the candidate cell, the DCI including a PDCCH command for the PRACH message on the candidate cell; a Medium Access Control (MAC) Control Element (CE) transmitted by the active serving cell; or a radio resource control (RRC) configuration or reconfiguration of the candidate cell; 26. The device of claim 25, wherein the

27. 1. A method of wireless communication in a user equipment (UE), comprising: receiving a random access channel (RACH) configuration including RACH occasions for the candidate cell; determining that a condition is met for a layer 1 or layer 2 mobility procedure for the candidate cell; and sending a Physical RACH (PRACH) message to the candidate cell to initiate the Layer 1 or Layer 2 mobility procedure; A method comprising:

28. receiving the configuration of the RACH is a synchronization signal block (SSB), transmitted by the active serving cell and associated with the physical cell identifier of the intra-frequency candidate cell, or being transmitted by an inter-frequency candidate cell, 28. The method of claim 27, comprising receiving an SSB.

29. determining that a condition is met for a Layer 1 or Layer 2 mobility procedure for the candidate cell; evaluating rules for selecting the candidate cells; determining that a timing advance misalignment timer for the candidate cell has expired; or receiving a trigger signal from an active serving cell or the candidate cell that triggers transmitting the PRACH message; 28. The method of claim 27, comprising one of:

30. 1. A method of wireless communication in a network node, comprising: transmitting a random access channel (RACH) configuration including RACH occasions for the candidate cells; receiving a physical RACH (PRACH) message at the candidate cell to initiate a Layer 1 or Layer 2 mobility procedure for a user equipment (UE) from an active serving cell to the candidate cell; A method comprising:

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