WO2025091327A1

WO2025091327A1 - Physical downlink control channel (pdcch) order-based random access channel (rach) triggering across lower layer triggered mobility (ltm) candidate cells

Info

Publication number: WO2025091327A1
Application number: PCT/CN2023/129074
Authority: WO
Inventors: Qiming Li; Yang Tang; Dawei Zhang; Jie Cui; Yuqin Chen; Hong He
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2023-11-01
Filing date: 2023-11-01
Publication date: 2025-05-08
Anticipated expiration: 2026-05-01

Abstract

Techniques and devices for timing advances in early UL synchronization are disclosed. The techniques may be used in Lower Layer Triggered Mobility (LTM) cell switching scenarios, such as a handover. The techniques include a network device transmitting a PDCCH order. A wireless device in a source cell receives the PDCCH order, and the wireless device performs an early RACH procedure using a timing advance in candidate cell based on the PDCCH order. The timing advance may be established in accordance with the network settings or included in the PDCCH order.

Description

Physical Downlink Control Channel (PDCCH) order-based Random Access Channel (RACH) Triggering across Lower Layer Triggered Mobility (LTM) Candidate Cells

FIELD

The present application relates to wireless devices and wireless networks including devices, computer-readable media, and methods for performing Physical Downlink Control Channel (PDCCH) order-based Random Access Channel (RACH) triggering procedures that may be used, for example, across Lower layer Triggered Mobility (LTM) Candidate Cells.

BACKGROUND

Wireless communication systems are rapidly growing in usage. In recent years, wireless devices such as smart phones and tablet computers have become increasingly sophisticated. In addition to supporting telephone calls, many mobile devices now provide access to the internet, email, text messaging, and navigation using the global positioning system (GPS) , and are capable of operating sophisticated applications that utilize these functionalities. Additionally, there exist numerous different wireless communication technologies and standards. Some examples of wireless communication standards include GSM, UMTS (associated with, for example, WCDMA or TD-SCDMA air interfaces) , LTE, LTE Advanced (LTE-A) , HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD) , IEEE 802.11 (WLAN or Wi-Fi) , BLUETOOTH^TM, etc.

The ever increasing number of features and functionality introduced in wireless communication devices also creates a continuous need for improvement in both the wireless communications and the wireless communication devices. To increase coverage and better serve the increasing demand and range of envisioned uses of wireless communication, in addition to the communication standards mentioned above, there are further wireless communication technologies under development, including fifth generation (5G) new radio (NR) communication. Accordingly, improvements in the field in support of such development and design are desired.

One such improvement may be the reduction of latency when connecting, or reconnecting, a device to a network. For example, under certain conditions, an early phase synchronization may be employed to reduce latency of connection switching between network cells.

SUMMARY

In general, embodiments are directed to devices, systems, and methods for synchronization in an early phase synchronization, prior to establishing a connected state between a device and a network. More specifically, embodiments relate to uplink (UL) synchronization in an early phase synchronization using a PDCCH order that directs the device to perform a RACH procedure towards an LTM candidate cell.

In one aspect, embodiments are directed to a method for early UL synchronization that includes a network device transmitting a PDCCH order. A wireless device in a source cell receives the PDCCH order, and the wireless device performs an early RACH procedure using a timing advance in candidate cell based on the PDCCH order. The timing advance is established in accordance with network procedures or included in the PDCCH order as described herein.

In another aspect, embodiments are directed to a method for LTM cell selection that includes a User Equipment (UE) in an Radio Resource Control (RRC) connected state in a source cell transmitting to a base station a measurement report that includes measurements associated with one or more target cells. The UE receives from the base station a PDCCH order that includes configuration information of one or more candidate cells from the one or more target cells. The UE performs a RACH procedure using a timing advance in one of the one or more candidate cells based on the PDCCH order. The method further includes the UE receiving from the base station a cell switch command that commands the UE to switch to one of the one or more candidate cells. After receiving the cell switch command, the UE performs a second RACH procedure in the one of the one or more candidate cells based on the cell switch command. The timing advance in the RACH procedure is established in accordance with the network procedures or included in the PDCCH order as described herein.

The techniques described herein may be implemented in and/or used with a number of different types of devices, including but not limited to cellular phones, wireless devices, tablet computers, wearable computing devices, portable media players, and any of various other computing devices.

This Summary is intended to provide a brief overview of some of the subject matter described in this document. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF DRAWINGS

A better understanding of the present subject matter can be obtained when the following detailed description of various aspects is considered in conjunction with the following drawings.

Figure 1 illustrates an example wireless communication system, according to some aspects.

Figure 2 illustrates an example block diagram of a UE, according to some aspects.

Figure 3 illustrates a base station (BS) in communication with a UE device, according to some aspects.

Figure 4 illustrates a general process that utilizes an early phase synchronization, according to some aspects.

Figure 5 illustrates timing associated with an LTM cell switch delay, according to some aspects.

Figure 6 illustrates methods for early uplink synchronization, according to some aspects.

While the features described herein may be susceptible to various modifications and alternative forms, specific aspects thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to be limiting to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION

In Lower Layer (L1/L2) Triggered Mobility (LTM) , an early synchronization phase is supported in order to help reduce cell switch latency in 5G NR. The early synchronization may include both downlink (DL) and UL synchronizations. Such a DL synchronization is based on an L3 and L1 measurement performed by the device. The UL synchronization may be based on a Timing Advance (TA) estimation made by the device based on propagation delays; however, because a UE may be configured with multiple LTM candidate cells at a time, performing pre-decoding and validity checks on each such candidate cell may over-burden the device, given the computation power, memory, and number of measurements/determinations that would be needed for each such candidate cell.

In accordance with embodiments, the UL synchronization may also be based on a PDCCH order-based RACH triggering procedure. In the PDCCH order-based RACH triggering procedure, a PDCCH order is received by the device in a first cell (e.g., a source cell) , and the device performs a RACH procedure towards a second cell, (e.g., a candidate/target cell) . The second cell may then estimate a suitable TA, and the second cell transmits the TA through the network to the first cell. Accordingly, when the device is later issued a command to switch from the first cell to the second cell, the command may include an appropriate TA to be used by the device.

However, in order to perform the RACH procedure towards the second cell, the device needs to know the related parameters for the RACH, such as the RACH preamble index, Synchronization Signal (SS) /Physical Broadcast Channel (PBCH) index, Physical Random Access Channel (PRACH) mask, etc. These parameters are typically included in the PDCCH order.

One parameter that has previously not been included in such orders is a TA, e.g., an NTA-Offset or n-TimingAdvanceOffset. This is a TA that is applied for all uplink transmissions on a particular cell. Such parameters are typically included in the RRC parameters of a serving cell, but are not considered by a device until a full connection being established. For example, in 5G NR, TA commands are typically received via a Medium Access Control (MAC) -Control Element (CE) , as part of the serving cell RRC procedures.

That is, in previous systems, the NTA-Offset or TA of a connection is known to the device because such information is part of the serving cell RRC parameters. However, for neighboring cells, the device will not decode and check the validity of all the RRC parameters until a cell switch command is received. Given that multiple candidate cells (e.g., LTM candidate cells) may be configured for a device, multiple pre-decoding and validity checks for all candidate cells is undesirable in terms of complexity and available memory size.

Further, without an appropriate TA, the network may not detect a RACH preamble transmitted by the device. Given that NTA-Offsets can be multiple times greater than a Cyclic Prefix (CP) duration, and different for different Subcarrier Spacing (SCS) , there are conditions in which a network may not detect the RACH preamble transmitted by the device in the RACH procedure.

In view of the above, without an appropriate TA, the RACH procedure by the device towards the second connection may increase the cell switch delay. A higher cell switch delay decreases the reliability and latency of the system. This could influence initial connections used in Ultra-Reliable and Low Latency Communications (URLLC) in 5G NR.

Embodiments disclosed herein address the issues described above by introducing methods for establishing the TA in an uplink (UL) synchronization in an early phase synchronization during LTM candidate cell switching, prior to establishing an RRC connection with the candidate cell.

The following is a glossary of terms that may be used in this disclosure:

Memory Medium –Any of various types of non-transitory memory devices or storage devices. The term “memory medium” is intended to include an installation medium, e.g., a CD-ROM, floppy disks, or tape device; a computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc. ; a non-volatile memory such as a Flash, magnetic media, e.g., a hard drive, or optical storage; registers, or other similar types of memory elements, etc. The memory medium may include other types of non-transitory memory as well or combinations thereof. In addition, the memory medium may be located in a first computer system in which the programs are executed, or may be located in a second different computer system which connects to the first computer system over a network, such as the Internet. In the latter instance, the second computer system may provide program instructions to the first computer for execution. The term “memory medium” may include two or more memory mediums which may reside in different locations, e.g., in different computer systems that are connected over a network. The memory medium may store program instructions (e.g., embodied as computer programs) that may be executed by one or more processors.

Carrier Medium –a memory medium as described above, as well as a physical transmission medium, such as a bus, network, and/or other physical transmission medium that conveys signals such as electrical, electromagnetic, or digital signals.

Programmable Hardware Element -includes various hardware devices comprising multiple programmable function blocks connected via a programmable interconnect. Examples include FPGAs (Field Programmable Gate Arrays) , PLDs (Programmable Logic Devices) , FPOAs (Field Programmable Object Arrays) , and CPLDs (Complex PLDs) . The programmable function blocks may range from fine grained (combinatorial logic or look up tables) to coarse grained (arithmetic logic units or processor cores) . A programmable hardware element may also be referred to as “reconfigurable logic. ”

Computer System –any of various types of computing or processing systems, including a personal computer system (PC) , mainframe computer system, workstation, network appliance, Internet appliance, personal digital assistant (PDA) , television system, grid computing system, or other device or combinations of devices. In general, the term “computer system” can be broadly defined to encompass any device (or combination of devices) having at least one processor that executes instructions from a memory medium.

User Equipment (UE) (also “User Device” or “UE Device” ) –any of various types of computer systems or devices that are mobile or portable and that perform wireless communications. Examples of UE devices include mobile telephones or smart phones (e.g., iPhone^TM, Android^TM-based phones) , portable gaming devices (e.g., Nintendo DS^TM, PlayStation Portable^TM, Gameboy Advance^TM, iPhone^TM) , laptops, wearable devices (e.g., smart watch, smart glasses) , PDAs, portable Internet devices, music players, data storage devices, other handheld devices, in-vehicle infotainment (IVI) , in-car entertainment (ICE) devices, an instrument cluster, head-up display (HUD) devices, onboard diagnostic (OBD) devices, dashtop mobile equipment (DME) , mobile data terminals (MDTs) , Electronic Engine Management System (EEMS) , electronic/engine control units (ECUs) , electronic/engine control modules (ECMs) , embedded systems, microcontrollers, control modules, engine management systems (EMS) , networked or “smart” appliances, machine type communications (MTC) devices, machine-to-machine (M2M) , internet of things (IoT) devices, etc. In general, the term “UE” or “UE device” can be broadly defined to encompass any electronic, computing, and/or telecommunications device (or combination of devices) which is transportable by a user and capable of wireless communication.

Wireless Device –any of various types of computer systems or devices that perform wireless communications. A wireless device can be portable (or mobile) or may be stationary or fixed at a certain location. A UE is an example of a wireless device.

Communication Device –any of various types of computer systems or devices that perform communications, where the communications can be wired or wireless. A communication device can be portable (or mobile) or may be stationary or fixed at a certain location. A wireless device is an example of a communication device. A UE is another example of a communication device.

Base Station –The term “base station” or “wireless station” has the full breadth of its ordinary meaning, and at least includes a wireless communication station installed at a fixed location and used to communicate as part of a wireless telephone system or radio system. For example, if the base station is implemented in the context of LTE, it may alternately be referred to as an ‘eNodeB’ or ‘eNB’ . If the base station is implemented in the context of 5G NR, it may alternately be referred to as a ‘gNodeB’ or ‘gNB’ . Although certain aspects are described in the context of LTE or 5G NR, references to “eNB, ” “gNB, ” “nodeB, ” “base station, ” “NB, ” etc., may refer to one or more wireless nodes that service a cell to provide a wireless connection between user devices and a wider network generally and that the concepts discussed are not limited to any particular wireless technology. Although certain aspects are described in the context of LTE or 5G NR, references to “eNB, ” “gNB, ” “nodeB, ” “base station, ” “NB, ” etc., are not intended to limit the concepts discussed herein to any particular wireless technology and the concepts discussed may be applied in any wireless system.

Node –The term “node, ” or “wireless node” as used herein, may refer to one more apparatus associated with a cell that provide a wireless connection between user devices and a wired network generally.

Processing Element (or Processor) –refers to various elements or combinations of elements that are capable of performing a function in a device, such as a user equipment or a cellular network device. Processing elements may include, for example: processors and associated memory, portions or circuits of individual processor cores, entire processor cores, individual processors, processor arrays, circuits such as an ASIC (Application Specific Integrated Circuit) , programmable hardware elements such as a field programmable gate array (FPGA) , as well any of various combinations of the above.

Channel -a medium used to convey information from a sender (transmitter) to a receiver. It should be noted that since characteristics of the term “channel” may differ according to different wireless protocols, the term “channel” as used herein may be considered as being used in a manner that is consistent with the standard of the type of device with reference to which the term is used. In some standards, channel widths may be variable (e.g., depending on device capability, band conditions, etc. ) . For example, LTE may support scalable channel bandwidths from 1.4 MHz to 20MHz. In contrast, WLAN channels may be 22MHz wide while Bluetooth channels may be 1Mhz wide. Other protocols and standards may include different definitions of channels. Furthermore, some standards may define and use multiple types of channels, e.g., different channels for uplink or downlink and/or different channels for different uses such as data, control information, etc.

Band -The term “band” has the full breadth of its ordinary meaning, and at least includes a section of spectrum (e.g., radio frequency spectrum) in which channels are used or set aside for the same purpose.

Automatically –refers to an action or operation performed by a computer system (e.g., software executed by the computer system) or device (e.g., circuitry, programmable hardware elements, ASICs, etc. ) , without user input directly specifying or performing the action or operation. Thus the term “automatically” is in contrast to an operation being manually performed or specified by the user, where the user provides input to directly perform the operation. An automatic procedure may be initiated by input provided by the user, but the subsequent actions that are performed “automatically” are not specified by the user, i.e., are not performed “manually” , where the user specifies each action to perform. For example, a user filling out an electronic form by selecting each field and providing input specifying information (e.g., by typing information, selecting check boxes, radio selections, etc. ) is filling out the form manually, even though the computer system must update the form in response to the user actions. The form may be automatically filled out by the computer system where the computer system (e.g., software executing on the computer system) analyzes the fields of the form and fills in the form without any user input specifying the answers to the fields. As indicated above, the user may invoke the automatic filling of the form, but is not involved in the actual filling of the form (e.g., the user is not manually specifying answers to fields but rather they are being automatically completed) . The present specification provides various examples of operations being automatically performed in response to actions the user has taken.

Approximately -refers to a value that is almost correct or exact. For example, approximately may refer to a value that is within 1 to 10 percent of the exact (or desired) value. It should be noted, however, that the actual threshold value (or tolerance) may be application dependent. For example, in some aspects, “approximately” may mean within 0.1%of some specified or desired value, while in various other aspects, the threshold may be, for example, 2%, 3%, 5%, and so forth, as desired or as required by the particular application.

Concurrent –refers to parallel execution or performance, where tasks, processes, or programs are performed in an at least partially overlapping manner. For example, concurrency may be implemented using “strong” or strict parallelism, where tasks are performed (at least partially) in parallel on respective computational elements, or using “weak parallelism” , where the tasks are performed in an interleaved manner, e.g., by time multiplexing of execution threads.

Configured to -Various components may be described as “configured to” perform a task or tasks. In such contexts, “configured to” is a broad recitation generally meaning “having structure that” performs the task or tasks during operation. As such, the component can be configured to perform the task even when the component is not currently performing that task (e.g., a set of electrical conductors may be configured to electrically connect a module to another module, even when the two modules are not connected) . In some contexts, “configured to” may be a broad recitation of structure generally meaning “having circuitry that” performs the task or tasks during operation. As such, the component can be configured to perform the task even when the component is not currently on. In general, the circuitry that forms the structure corresponding to “configured to”may include hardware circuits.

Various components may be described as performing a task or tasks, for convenience in the description. Such descriptions should be interpreted as including the phrase “configured to. ” Reciting a component that is configured to perform one or more tasks is expressly intended not to invoke 35 U.S.C. § 112 (f) interpretation for that component.

Example Wireless Communication System

Turning now to Figure 1, a simplified example of a wireless communication system is illustrated, according to some aspects. It is noted that the system of Figure 1 is a non-limiting example of a possible system, and that features of this disclosure may be implemented in any of various systems, as desired.

As shown, the example wireless communication system includes a base station 102A, which communicates over a transmission medium with one or more user devices 106A and 106B, through 106Z. Each of the user devices may be referred to herein as a “user equipment” (UE) . Thus, the user devices 106 are referred to as UEs or UE devices.

The base station (BS) 102A may be a base transceiver station (BTS) or cell site (e.g., a “cellular base station” ) and may include hardware that enables wireless communication with the UEs 106A through 106Z.

The communication area (or coverage area) of the base station may be referred to as a “cell. ” The base station 102A and the UEs 106 may be configured to communicate over the transmission medium using any of various radio access technologies (RATs) , also referred to as wireless communication technologies, or telecommunication standards, such as GSM, UMTS (associated with, for example, WCDMA or TD-SCDMA air interfaces) , LTE, LTE-A, 5G NR, HSPA, 3GPP2 CDMA2000. Note that if the base station 102A is implemented in the context of LTE, it may alternately be referred to as an ‘eNodeB’ or ‘eNB’ . Note that if the base station 102A is implemented in the context of 5G NR, it may alternately be referred to as a ‘gNodeB’ or ‘gNB’ .

In some aspects, the UEs 106 may be IoT UEs, which may comprise a network access layer designed for low-power IoT applications utilizing short-lived UE connections. An IoT UE may utilize technologies such as M2M or MTC for exchanging data with an MTC server or device via a public land mobile network (PLMN) , proximity service (ProSe) or device-to-device (D2D) communication, sensor networks, or IoT networks. The M2M or MTC exchange of data may be a machine-initiated exchange of data. An IoT network describes interconnecting IoT UEs, which may include uniquely identifiable embedded computing devices (within the Internet infrastructure) , with short-lived connections. As an example, vehicles to everything (V2X) may utilize ProSe features using a PC5 interface for direct communications between devices. The IoT UEs may also execute background applications (e.g., keep-alive messages, status updates, and the like) to facilitate the connections of the IoT network.

As shown in Figure 1, the UEs 106, such as UE 106A and UE 106B, may directly exchange communication data via a PC5 interface 108A. Also, the UEs 106C, 106N, and 106Z, may collectively exchange communication data via a PC5 interfaces 108B, 108C, and 108D. In general, such PC5 interfaces are referred to as SL connections.

The PC5 interface 108 may comprise one or more physical channels, including but not limited to a Physical Sidelink Shared Channel (PSSCH) , a Physical Sidelink Control Channel (PSCCH) , a Physical Sidelink Broadcast Channel (PSBCH) , and a Physical Sidelink Feedback Channel (PSFCH) . The PC5 interface 108 may be responsible for direct communication between devices (unicast) , group messaging among select devices (groupcast) , and broadcast messaging in accordance with embodiments disclosed herein.

In V2X scenarios, one or more of the base stations 102 may be or act as Road Side Units (RSUs) . The term RSU may refer to any transportation infrastructure entity used for V2X communications. An RSU may be implemented in or by a suitable wireless node or a stationary (or relatively stationary) UE, where an RSU implemented in or by a UE , eNB, or by a gNB. For example, an RSU is a computing device coupled with radio frequency circuitry located on a roadside that provides connectivity support to passing vehicle UEs.

As shown, the base station 102A may also be equipped to communicate with a network 100 (e.g., a core network of a cellular service provider, a telecommunication network such as a public switched telephone network (PSTN) , and/or the Internet, among various possibilities) . Thus, the base station 102A may facilitate communication between the user devices and/or between the user devices and the network 100. In particular, the cellular base station 102A may provide UEs 106 with various telecommunication capabilities, such as voice, SMS and/or data services.

Base station 102A and other similar base stations (such as base stations 102B through 102N) operating according to the same or a different cellular communication standard may thus be provided as a network of cells, which may provide continuous or nearly continuous overlapping service to UEs 106A-106Z and similar devices over a geographic area via one or more cellular communication standards.

Thus, while base station 102A may act as a “serving cell” for UEs 106A-106Z as illustrated in Figure 1, each UE 106 may also be capable of receiving signals from (and possibly within communication range of) one or more other cells (which may be provided by base stations 102B-102Z and/or any other base stations) , which may be referred to as “neighboring cells. ” Such cells may also be capable of facilitating communication between user devices and/or between user devices and the network 100. Such cells may include “macro” cells, “micro” cells, “pico” cells, and/or cells which provide any of various other granularities of service area size. For example, base stations 102A and 102B illustrated in Figure 1 may be macro cells, while base station 102Z may be a micro cell. Other configurations are also possible.

In some aspects, base station 102A may be a next generation base station, (e.g., a 5G New Radio (5G NR) base station, or “gNB” ) . In some aspects, a gNB may be connected to a legacy evolved packet core (EPC) network and/or to a NR core (NRC) /5G core (5GC) network. In addition, a gNB cell may include one or more transition and reception points (TRPs) . In addition, a UE capable of operating according to 5G NR may be connected to one or more TRPs within one or more gNBs. For example, it may be possible that that the base station 102A and one or more other base stations 102 support joint transmission, such that UE 106 may be able to receive transmissions from multiple base stations (and/or multiple TRPs provided by the same base station) . For example, as illustrated in Figure 1, both base station 102A and base station 102C are shown as serving UE 106A.

Note that a UE 106 may be capable of communicating using multiple wireless communication standards. For example, the UE 106 may be configured to communicate using a wireless networking (e.g., Wi-Fi) and/or peer-to-peer wireless communication protocol (e.g., Bluetooth, Wi-Fi peer-to-peer, and the like) in addition to some of the cellular communication protocols discussed herein. The UE 106 may also or alternatively be configured to communicate using one or more global navigational satellite systems (GNSS) (e.g., GPS or GLONASS) , one or more mobile television broadcasting standards (e.g., ATSC-M/H) , and/or any other wireless communication protocol, if desired. Other combinations of wireless communication standards (including more than two wireless communication standards) are also possible.

In one or more embodiments, the UE 106 may be a device with cellular communication capability such as a mobile phone, a hand-held device, a computer, a laptop, a tablet, a smart watch, or other wearable device, or virtually any type of wireless device.

The UE 106 may include a processor (processing element) that is configured to execute program instructions stored in memory. The UE 106 may perform any of the method aspects described herein by executing such stored instructions. Alternatively, or in addition, the UE 106 may include a programmable hardware element such as an FPGA (field-programmable gate array) , an integrated circuit, and/or any of various other possible hardware components that are configured to perform (e.g., individually or in combination) any of the method aspects described herein, or any portion of any of the method aspects described herein.

The UE 106 may include one or more antennas for communicating using one or more wireless communication protocols or technologies. In some aspects, the UE 106 may be configured to communicate using, for example, NR or LTE using at least some shared radio components. As additional possibilities, the UE 106 could be configured to communicate using CDMA2000 (1xRTT /1xEV-DO /HRPD /eHRPD) or LTE using a single shared radio and/or GSM or LTE using the single shared radio. The shared radio may couple to a single antenna, or may couple to multiple antennas (e.g., for a multiple-input multiple output (MIMO) configuration) for performing wireless communications. In general, a radio may include any combination of a baseband processor, analog RF signal processing circuitry (e.g., including filters, mixers, oscillators, amplifiers, and the like) , or digital processing circuitry (e.g., for digital modulation as well as other digital processing) . Similarly, the radio may implement one or more receive and transmit chains using the aforementioned hardware. For example, the UE 106 may share one or more parts of a receive and/or transmit chain between multiple wireless communication technologies, such as those discussed above.

In some aspects, the UE 106 may include separate transmit and/or receive chains (e.g., including separate antennas and other radio components) for each wireless communication protocol with which it is configured to communicate. As a further possibility, the UE 106 may include one or more radios which are shared between multiple wireless communication protocols, and one or more radios which are used exclusively by a single wireless communication protocol. For example, the UE 106 might include a shared radio for communicating using either of LTE or 5G NR (or either of LTE or 1xRTT, or either of LTE or GSM, among various possibilities) , and separate radios for communicating using each of Wi-Fi and Bluetooth. Other configurations are also possible.

In some aspects, a downlink resource grid may be used for downlink transmissions from any of the base stations 102 to the UEs 106, while uplink transmissions may utilize similar techniques. The grid may be a time-frequency grid, called a resource grid or time-frequency resource grid, which is the physical resource in the downlink in each slot. Such a time-frequency plane representation is a common practice for Orthogonal Frequency Division Multiplexing (OFDM) systems, which makes it intuitive for radio resource allocation. Each column and each row of the resource grid corresponds to one OFDM symbol and one OFDM subcarrier, respectively. The duration of the resource grid in the time domain corresponds to one slot in a radio frame. The smallest time-frequency unit in a resource grid is denoted as a resource element. Each resource grid may comprise a number of resource blocks, which describe the mapping of certain physical channels to resource elements. Each resource block comprises a set of resource elements. There are several different physical downlink channels that are conveyed using such resource blocks.

One such channel is the physical downlink shared channel (PDSCH) that may carry user data and higher layer signaling to the UEs 106. The PDCCH may carry information about the transport format and resource allocations related to the PDSCH channel, among other things. It may also inform the UEs 106 about the transport format, resource allocation, and HARQ (Hybrid Automatic Repeat Request) information related to the uplink shared channel. Typically, downlink scheduling (assigning control and shared channel resource blocks to the UE 102 within a cell) may be performed at any of the base stations 102 based on channel quality information fed back from any of the UEs 106. The downlink resource assignment information may be sent on the PDCCH used for (e.g., assigned to) each of the UEs.

The PDCCH may use control channel elements (CCEs) to convey the control information. Before being mapped to resource elements, the PDCCH complex-valued symbols may first be organized into quadruplets, which may then be permuted using a sub-block interleaver for rate matching. Each PDCCH may be transmitted using one or more of these CCEs, where each CCE may correspond to nine sets of four physical resource elements known as resource element groups (REGs) . Four Quadrature Phase Shift Keying (QPSK) symbols may be mapped to each REG. The PDCCH may be transmitted using one or more CCEs, depending on the size of the Downlink Control Information (DCI) and the channel condition. There may be four or more different PDCCH formats defined in LTE with different numbers of CCEs (e.g., aggregation level, L=1, 2, 4, or 8) .

Example Communication Device

Figure 2 illustrates user equipment 106 (e.g., one of the devices 106A through 106N) in communication with a base station 102 or other user equipment 106, according to some aspects. The UE 106 may be a device with cellular communication capability such as a mobile phone, a hand-held device, a computer, a laptop, a tablet, a smart watch or other wearable device, or virtually any type of wireless device.

The UE 106 may include one or more antennas for communicating using one or more wireless communication protocols or technologies. In some aspects, the UE 106 may be configured to communicate using, for example, NR or LTE using at least some shared radio components. As additional possibilities, the UE 106 could be configured to communicate using CDMA2000 (1xRTT /1xEV-DO /HRPD /eHRPD) or LTE using a single shared radio and/or GSM or LTE using the single shared radio. The shared radio may couple to a single antenna, or may couple to multiple antennas (e.g., for MIMO) for performing wireless communications. In general, a radio may include any combination of a baseband processor, analog RF signal processing circuitry (e.g., including filters, mixers, oscillators, amplifiers, etc. ) , or digital processing circuitry (e.g., for digital modulation as well as other digital processing) . Similarly, the radio may implement one or more receive and transmit chains using the aforementioned hardware. For example, the UE 106 may share one or more parts of a receive and/or transmit chain between multiple wireless communication technologies, such as those discussed above.

In some aspects, a downlink resource grid can be used for downlink transmissions from any of the base stations 102 to the UEs 106, while uplink transmissions can utilize similar techniques. The grid can be a time-frequency grid, called a resource grid or time-frequency resource grid, which is the physical resource in the downlink in each slot. Such a time-frequency plane representation is a common practice for OFDM systems, which makes it intuitive for radio resource allocation. Each column and each row of the resource grid corresponds to one OFDM symbol and one OFDM subcarrier, respectively. The duration of the resource grid in the time domain corresponds to one slot in a radio frame. The smallest time-frequency unit in a resource grid is denoted as a resource element. Each resource grid may comprise a number of resource blocks, which describe the mapping of certain physical channels to resource elements. Each resource block comprises a collection of resource elements. There are several different physical downlink channels that are conveyed using such resource blocks.

The PDSCH may carry user data and higher-layer signaling to the UEs 106. The PDCCH may carry information about the transport format and resource allocations related to the PDSCH channel, among other things. It may also inform the UEs 106 about the transport format, resource allocation, and H-ARQ (Hybrid Automatic Repeat Request) information related to the uplink shared channel. Typically, downlink scheduling (assigning control and shared channel resource blocks to the UE 102 within a cell) may be performed at any of the base stations 102 based on channel quality information fed back from any of the UEs 106. The downlink resource assignment information may be sent on the PDCCH used for (e.g., assigned to) each of the UEs.

The PDCCH may use control channel elements (CCEs) to convey the control information. Before being mapped to resource elements, the PDCCH complex-valued symbols may first be organized into quadruplets, which may then be permuted using a sub-block interleaver for rate matching. Each PDCCH may be transmitted using one or more of these CCEs, where each CCE may correspond to nine sets of four physical resource elements known as resource element groups (REGs) . Four Quadrature Phase Shift Keying (QPSK) symbols may be mapped to each REG. The PDCCH can be transmitted using one or more CCEs, depending on the size of the downlink control information (DCI) and the channel condition. There can be four or more different PDCCH formats defined in LTE with different numbers of CCEs (e.g., aggregation level, L=1, 2, 4, or 8) .

Figure 2 illustrates an example simplified block diagram of a communication device 106, according to some aspects. It is noted that the block diagram of the communication device of Figure 2 is only one example of a possible communication device. According to aspects, communication device 106 may be a user equipment (UE) device, a mobile device or mobile station, a wireless device or wireless station, a desktop computer or computing device, a mobile computing device (e.g., a laptop, notebook, or portable computing device) , a tablet, and/or a combination of devices, among other devices. As shown, the communication device 106 may include a set of components 200 configured to perform core functions. For example, this set of components may be implemented as a system on chip (SOC) , which may include portions for various purposes. Alternatively, this set of components 200 may be implemented as separate components or groups of components for the various purposes. The set of components 200 may be coupled (e.g., communicatively; directly or indirectly) to various other circuits of the communication device 106.

For example, the communication device 106 may include various types of memory (e.g., including NAND flash 210) , an input/output interface such as connector I/F 220 (e.g., for connecting to a computer system; dock; charging station; input devices, such as a microphone, camera, keyboard; output devices, such as speakers; etc. ) , the display 260, which may be integrated with or external to the communication device 106, and wireless communication circuitry 230 (e.g., for LTE, LTE-A, NR, UMTS, GSM, CDMA2000, Bluetooth, Wi-Fi, NFC, GPS, etc. ) . In some aspects, communication device 106 may include wired communication circuitry (not shown) , such as a network interface card, e.g., for Ethernet.

The wireless communication circuitry 230 may couple (e.g., communicatively; directly or indirectly) to one or more antennas, such as antenna (s) 335 as shown. The wireless communication circuitry 230 may include cellular communication circuitry and/or short to medium range wireless communication circuitry, and may include multiple receive chains and/or multiple transmit chains for receiving and/or transmitting multiple spatial streams, such as in a multiple-input multiple output (MIMO) configuration.

In some aspects, as further described below, cellular communication circuitry 230 may include one or more receive chains (including and/or coupled to (e.g., communicatively; directly or indirectly) dedicated processors and/or radios) for multiple RATs (e.g., a first receive chain for LTE and a second receive chain for 5G NR) . In addition, in some aspects, cellular communication circuitry 230 may include a single transmit chain that may be switched between radios dedicated to specific RATs. For example, a first radio may be dedicated to a first RAT, e.g., LTE, and may be in communication with a dedicated receive chain and a transmit chain shared with a second radio. The second radio may be dedicated to a second RAT, e.g., 5G NR, and may be in communication with a dedicated receive chain and the shared transmit chain. In some aspects, the second RAT may operate at mmWave frequencies. As mmWave systems operate in higher frequencies than typically found in LTE systems, signals in the mmWave frequency range are heavily attenuated by environmental factors. To help address this attenuating, mmWave systems often utilize beamforming and include more antennas as compared LTE systems. These antennas may be organized into antenna arrays or panels made up of individual antenna elements. These antenna arrays may be coupled to the radio chains.

The communication device 106 may also include and/or be configured for use with one or more user interface elements. The user interface elements may include any of various elements, such as display 260 (which may be a touchscreen display) , a keyboard (which may be a discrete keyboard or may be implemented as part of a touchscreen display) , a mouse, a microphone and/or speakers, one or more cameras, one or more buttons, and/or any of various other elements capable of providing information to a user and/or receiving or interpreting user input.

The communication device 106 may further include one or more smart cards 245 that include SIM (Subscriber Identity Module) functionality, such as one or more UICC (s) (Universal Integrated Circuit Card (s) ) cards 245.

As shown, the SOC 200 may include processor (s) 202, which may execute program instructions for the communication device 106 and display circuitry 204, which may perform graphics processing and provide display signals to the display 260. The processor (s) 202 may also be coupled to memory management unit (MMU) 240, which may be configured to receive addresses from the processor (s) 202 and translate those addresses to locations in memory (e.g., memory 206, read only memory (ROM) 250, NAND flash memory 210) and/or to other circuits or devices, such as the display circuitry 204, wireless communication circuitry 230, connector I/F 220, and/or display 260. The MMU 240 may be configured to perform memory protection and page table translation or set up. In some aspects, the MMU 240 may be included as a portion of the processor (s) 202.

As noted above, the communication device 106 may be configured to communicate using wireless and/or wired communication circuitry. As described herein, the communication device 106 may include hardware and software components for implementing any of the various features and techniques described herein. The processor 202 of the communication device 106 may be configured to implement part or all of the features described herein, e.g., by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium) . Alternatively (or in addition) , processor 202 may be configured as a programmable hardware element, such as an FPGA (Field Programmable Gate Array) , or as an ASIC (Application Specific Integrated Circuit) . Alternatively (or in addition) the processor 202 of the communication device 106, in conjunction with one or more of the other components 200, 204, 206, 210, 220, 230, 240, 245, 250, 260 may be configured to implement part or all of the features described herein.

In addition, as described herein, processor 202 may include one or more processing elements. Thus, processor 202 may include one or more integrated circuits (ICs) that are configured to perform the functions of processor 202. In addition, each integrated circuit may include circuitry (e.g., first circuitry, second circuitry, etc. ) configured to perform the functions of processor (s) 202.

Further, as described herein, wireless communication circuitry 230 may include one or more processing elements. In other words, one or more processing elements may be included in wireless communication circuitry 230. Thus, wireless communication circuitry 230 may include one or more integrated circuits (ICs) that are configured to perform the functions of wireless communication circuitry 230. In addition, each integrated circuit may include circuitry (e.g., first circuitry, second circuitry, etc. ) configured to perform the functions of wireless communication circuitry 230.

Example Base Station

Figure 3 illustrates an example block diagram of a base station 102, according to some aspects. It is noted that the base station of Figure 3 is merely one example of a possible base station. As shown, the base station 102 may include processor (s) 304 which may execute program instructions for the base station 102. The processor (s) 304 may also be coupled to memory management unit (MMU) 340, which may be configured to receive addresses from the processor (s) 304 and translate those addresses to locations in memory (e.g., memory 360 and read only memory (ROM) 350) or to other circuits or devices.

The base station 102 may include at least one network port 370. The network port 370 may be configured to couple to a telephone network and provide a plurality of devices, such as UE devices 106, access to the telephone network as described above in Figures 1 and 2.

The network port 370 (or an additional network port) may also or alternatively be configured to couple to a cellular network, e.g., a core network of a cellular service provider. The core network may provide mobility related services and/or other services to a plurality of devices, such as UE devices 106. In some cases, the network port 370 may couple to a telephone network via the core network, and/or the core network may provide a telephone network (e.g., among other UE devices serviced by the cellular service provider) .

In some aspects, base station 102 may be a next generation base station, e.g., a 5G New Radio (5G NR) base station, or “gNB. ” In such aspects, base station 102 may be connected to a legacy evolved packet core (EPC) network and/or to a NR core (NRC) /5G core (5GC) network. In addition, base station 102 may be considered a 5G NR cell and may include one or more transition and reception points (TRPs) . In addition, a UE capable of operating according to 5G NR may be connected to one or more TRPs within one or more gNBs.

The base station 102 may include at least one antenna 334, and possibly multiple antennas. The at least one antenna 334 may be configured to operate as a wireless transceiver and may be further configured to communicate with UE devices 106 via radio 330. The antenna 334 communicates with the radio 330 via communication chain 332. Communication chain 332 may be a receive chain, a transmit chain or both. The radio 330 may be configured to communicate via various wireless communication standards, including, but not limited to, 5G NR, LTE, LTE-A, GSM, UMTS, CDMA2000, Wi-Fi, etc.

The base station 102 may be configured to communicate wirelessly using multiple wireless communication standards. In some instances, the base station 102 may include multiple radios, which may enable the base station 102 to communicate according to multiple wireless communication technologies. For example, as one possibility, the base station 102 may include an LTE radio for performing communication according to LTE as well as a 5G NR radio for performing communication according to 5G NR. In such a case, the base station 102 may be capable of operating as both an LTE base station and a 5G NR base station. When the base station 102 supports mmWave, the 5G NR radio may be coupled to one or more mmWave antenna arrays or panels. As another possibility, the base station 102 may include a multi-mode radio, which is capable of performing communications according to any of multiple wireless communication technologies (e.g., 5G NR and LTE, 5G NR and Wi-Fi, LTE and Wi-Fi, LTE and UMTS, LTE and CDMA2000, UMTS and GSM, etc. ) .

As described further subsequently herein, the BS 102 may include hardware and software components for implementing or supporting implementation of features described herein. The processor 304 of the base station 102 may be configured to implement or support implementation of part or all of the methods described herein, e.g., by executing program instructions stored on a memory medium (e.g., a non-transitory computer readable memory medium) . Alternatively, the processor 304 may be configured as a programmable hardware element, such as an FPGA (Field Programmable Gate Array) , or as an ASIC (Application Specific Integrated Circuit) , or a combination thereof. Alternatively (or in addition) the processor 304 of the BS 102, in conjunction with one or more of the other components 330, 332, 334, 340, 350, 360, 370 may be configured to implement or support implementation of part or all of the features described herein.

In addition, as described herein, processor (s) 304 may include one or more processing elements. Thus, processor (s) 304 may include one or more integrated circuits (ICs) that are configured to perform the functions of processor (s) 304. In addition, each integrated circuit may include circuitry (e.g., first circuitry, second circuitry, etc. ) configured to perform the functions of processor (s) 304.

Further, as described herein, radio 330 may include one or more processing elements. Thus, radio 330 may include one or more integrated circuits (ICs) that are configured to perform the functions of radio 330. In addition, each integrated circuit may include circuitry (e.g., first circuitry, second circuitry, etc. ) configured to perform the functions of radio 330.

In previous cell selection operations, such as a handover, a serving cell change is triggered by Layer 3 (L3) measurements and through RRC signaling. Handovers may require reconfiguration of the upper layers (e.g., RRC or PDCP) and/or the resetting of the lower layers (e.g., MAC and/or PHY) . All this reconfiguring can lead to longer latency, larger overhead, and longer interruption time than beam level mobility.

Lower layer (L1/L2) based mobility, or LTM, allows a serving cell to change via L1/L2 signaling, while maintaining the configurations of the upper layers and/or minimizing changes to the lower layers. This helps to reduce the latency, overhead, and interruption time during handover.

Figure 4 illustrates a general process that utilizes an early phase synchronization, in accordance with embodiments disclosed herein. More specifically, Figure 4 shows a general process for an LTM handover in 5G NR that includes an LTM preparation phase (Steps 1–3) , an early synchronization phase (Steps 4a-4b) , an LTM execution phase (Steps 5–7) , and an LTM completion phase (Step 8) .

In the LTM preparation phase, a UE sends an L3 Measurement Report message to a base station (gNB) in Step 1. Based on the measurement report, the network, or gNB, decides to use LTM, and the gNB initiates LTM candidate preparation. Such candidate preparation includes the gNB selecting one or more cells to be LTM candidate cells based on the received measurement report. For example, the gNB may select four of the eight neighbor cells as candidate cells for the LTM cell switch. In Step 2, the gNB transmits an RRCReconfiguration message to the UE that includes configurations of one or more LTM candidate cells. The UE stores the configurations of the LTM candidate cells, and the UE transmits a RRCReconfigurationComplete message to the gNB in Step 3.

In the early synchronization phase, the UE performs an early synchronization with the candidate cell. The early synchronization may include a DL synchronization (Step 4a) and an UL synchronization (Step 4b) . In Step 4a, the DL synchronization is based on L3 and L1 measurements performed by the UE.

The UL synchronization in Step 4b may be based on a TA estimation made by the UE from propagation delays; however, such techniques may over-burden the device, given the computation power and number of measurements needed.

In accordance with embodiments, the UL synchronization in Step 4b may be based on a PDCCH order based RACH procedure. As described further below, in the PDCCH order based RACH, a PDCCH order is received by the UE from the gNB, and the UE performs a RACH procedure towards a candidate cell based on the PDCCH order.

In the LTM execution phase, the UE performs L1 measurements on the configured LTM candidate cell (s) . The UE then transmits the lower-layer measurement reports to the gNB in Step 5. The gNB then decides to execute an LTM cell switch to a candidate cell, and the gNB transmits a cell switch command (i.e., a MAC control element (MAC-CE) ) triggering the LTM cell switch in Step 6. The UE then switches to the configuration of the LTM candidate target cell. In some processes, the UE may then perform a RACH procedure towards the target cell in Step 7. In the LTM completion phase, the UE indicates successful completion of the LTM cell switch towards the target cell in Step 8. This may include a partial or full MAC reset, re-establishment of radio link control (RLC) , and data recovery using packet data convergence protocol (PDCP) from the cell switch.

Returning to Step 4b, in a PDCCH order-based RACH triggering, the source cell sends a PDCCH order to the UE and, then, the UE performs RACH toward the target candidate cell. The target cell may estimate a suitable TA from the RACH procedure to be used after cell switch and forward the TA info to the source cell. The source cell may then include the TA info in the cell switch command in Step 6.

In order to perform the RACH procedure transmission to the target candidate cell in Step 4b, the UE needs to know the related parameters, such as the RACH preamble index, SS/PBCH index, PRACH mask and so on. These parameters are included in the PDCCH order; however, such parameters fail to include the NTA-Offset or n-TimingAdvanceOffset for the candidate cell. Historically, such PDCCH order RACH procedures were only used in a serving cell, so the TA offset was already known from the serving cell RRC parameters. That is, the UE only considers the TA for uplink transmissions on a particular cell when a connection is pursued.

Without an appropriate TA, the network may not detect a RACH preamble transmitted by the device. For example, Table 1 illustrates different timing adjustments (N_TA offset) that may occur for different frequency ranges and bands used for UL transmissions. Given that the values in Table 1 may be 5-6 times greater than a CP duration even with an SCS at 15 kHz, there is a chance that the network may detect the RACH preamble successfully. For a larger SCS, this issue is further exacerbated.

Table 1

Even if the network is able to detect the RACH preamble successfully, the process may contribute to the LTM cell switch delay. The LTM cell switch delay (D_LTM) is the delay from the end of the last Transmission Time Interval (TTI) containing the MAC-CE command for the cell switch until the time the UE transmits the first UL message on the target cell. When the target cell and the target joint UL/DL TCI states (or separate UL and DL TCI states) in the MAC-CE LTM cell switch command are known, the LTM cell switch delay may be expressed by the following Equation (1) :
D_LTM= T_cmd [+ T_{LTM-RRC processing} or T_{execution_time}] + T_LTM-interupt (1) .

In Equation (1) , T_cmd is equal to T_HARQ + 3ms, where T_HARQ is the timing between the cell switch command and the acknowledgement (see, e.g., TS 38.213) . T_{LTM-RRC-processing} or T_{execution_time} is the time for early ASN. 1 decoding and validity/compliance checks for the RRC configuration of the LTM target cell indicated in the LTM cell switch command, as described herein.

[T_{LTM-RRC-processing} or T_{execution_time}] may equal zero if a UE has performed early ASN. 1 decoding and validity/compliance check of the complete LTM candidate cell configuration prior to the cell switch command for the LTM candidate cell indicated in the cell switch command.

The T_LTM-interupt is the delay from the end of the last TTI containing the MAC-CE cell switch command for the LTM cell switch until the time the UE transmits the first UL message on the target cell, excluding the T_cmd and T_{LTM-RRC-processing} [or T_{execution_time}] contributions.

Figure 5 illustrates timing associated with an LTM cell switch delay, according to some aspects. At 501, the candidate configuration is received for the UE reconfiguration and the time for RRC processing (T_RRC) and processing (T_{PROCESSING, 1}) passes. At 502, a potential target cell is acquired, and time is consumed acquiring measurements (T_MEAS) .

At time 503, an early downlink synchronization occurs (in accordance with Step 4a of Figure 4) . The DL synchronization at 503 includes the time to search (T_SEARCH) , time for measurements (T_Δ) , and time for processing (T_MARGIN) .

In accordance with embodiments, at time 504, an early uplink synchronization occurs (in accordance with Step 4b of Figure 4) . During the time 504, at time 504A, a RACH preamble is transmitted towards the candidate cell.

At some later time 505, a cell switch command (i.e., a MAC-CE) triggering the LTM cell switch is received. This is followed by an Interruption, in accordance with the LTM cell switch delay (T_LTM-interupt) as described above. The Interruption includes T_{processing, 2}, which may be associated with T_LTM-interupt.

However, as previously explained, during the time 504, the UE may not be aware of the TA offset for the candidate cell, and the network may not detect the preamble at 504A. As such, the overall timing of the LTM cell switch process in may be increased.

Figure 6 illustrates methods for early UL synchronization, according to some aspects. The method 6000 provides general guidelines for an early UL synchronization that may be performed prior to establishing a connection with a candidate cell, e.g., during an LTM cell switching scenario. In Step 6002, a network device transmits a PDCCH order that includes information about a candidate cell. The network device includes a base station (gNodeB, Transmission Reception Point (TRP) , etc. ) The PDCCH order may include information on multiple candidate cells.

In Step 6004, a wireless device (e.g., UE) that is connected to a source cell receives the PDCCH order. The wireless device may be in an RRC CONNECTED state with the network device in the source cell. The wireless device performs an early RACH procedure towards the candidate cell based on the PDCCH order in Step 6006. The early RACH procedure is performed using a TA offset in accordance with embodiments herein.

In accordance with embodiments, the TA offset used may be based on a relationship between the source and candidate cells. For example, in one scenario, the candidate cell is an intra-frequency neighbor cell to the source cell. The intra-frequency neighbor cell may be on the Primary Component Carrier (PCC) , Primary Serving Component Carrier (PSCC) , or Secondary Component Carrier (SCC) in accordance with embodiments. In such embodiments, the network guarantees that the TA offset (e.g., n-TimingAdvanceOffset) across all the LTM candidate cells on the same carrier are same. This allows the wireless device to assume that the TA offset for the candidate cell is same as that configured in the serving cell on the same carrier frequency. The wireless device may then obtain the TA offset from the configuration of the source cell. For example, n-TimingAdvanceOffset may be obtained from the ServingCellConfigCommon parameters associated with the RRC connection in the source cell in 5G NR.

In another scenario, the target candidate cell is an intra-band, inter-frequency neighbor cell. For example, there exists at least one candidate cell on the same band as the source cell. In such embodiments, the network may guarantee that the TA offset (e.g., n-TimingAdvanceOffset) across all the LTM candidate cells on the same band are the same. Therefore, the wireless device may assume the TA offset from existing RRC parameters, as in the previous scenario.

Continuing this scenario, as another option, embodiments may introduce a new component in the PDCCH order that indicates a TA offset to be used for the LTM candidate cell. For example, the PDCCH order may include one or two bits to indicate the TA offset for the candidate cell to use in the early UL synchronization. More specifically, two bits may be used to indicate a TA offset, or a one bit flag may be used to indicate that the wireless device should use the same TA offset as in the source cell.

In a final scenario, the target candidate cell is an inter-band, inter-frequency neighbor cell to the source cell. That is, there is no candidate cell available on the same band. Similar to the above, embodiments may introduce a new element definition in the PDCCH order for RACH to the LTM candidate cell. That is, two bits may be added to the PDCCH order to indicate the TA offset for a candidate cell. In these embodiments, the network may still guarantee that the TA offset is the same across all LTM candidate cells on the same band. In such embodiments, the wireless device uses the indicated TA offset for the early RACH procedure in the candidate cell.

Returning to Figure 6, following the early UL synchronization, in Step 6008, the network device transmits an LTM cell switch command. As previous explained, the LTM switch command may be in the form of an MAC-CE. In Step 6010, the wireless device then connects to the candidate cell as per the cell switch command. In embodiments, the RRC connection established in the candidate cell may include a second RACH procedure to establish the connection.

Embodiments disclosed herein provide techniques for an early UL synchronization prior to establishing a connection in a candidate cell. Thus, embodiments may provide for the reduction of latency when connecting, or reconnecting, a device to a network.

Aspects of the present disclosure may be realized in any of various forms. For example, some aspects may be realized as a computer-implemented method, a computer-readable memory medium, or a computer system. Other aspects may be realized using one or more custom-designed hardware devices such as ASICs. Still other aspects may be realized using one or more programmable hardware elements such as FPGAs.

In some aspects, a non-transitory computer-readable memory medium may be configured so that it stores program instructions and/or data, where the program instructions, if executed by a computer system, cause the computer system to perform a method, e.g., any of a method aspects described herein, or, any combination of the method aspects described herein, or, any subset of any of the method aspects described herein, or, any combination of such subsets.

In some aspects, a device (e.g., a UE 106, a BS 102) may be configured to include a processor (or a set of processors) and a memory medium, where the memory medium stores program instructions, where the processor is configured to read and execute the program instructions from the memory medium, where the program instructions are executable to implement any of the various method aspects described herein (or, any combination of the method aspects described herein, or, any subset of any of the method aspects described herein, or, any combination of such subsets) . The device may be realized in any of various forms.

Although the aspects above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Claims

A method for early uplink (UL) synchronization, the method comprising:

receiving, by a wireless device in a source cell from a network device, a Physical Downlink Control Channel (PDCCH) order;

performing, by the wireless device, a Random Access Channel (RACH) procedure using a timing advance offset in an Lower layer Triggered Mobility (LTM) candidate cell based on the PDCCH order.
The method of claim 1, wherein a timing advance offset of the source cell is used as the timing advance in the LTM candidate cell.
The method of claim 1, wherein an n-TimingAdvanceOffset is the same across LTM candidate cells on a same band.
The method of claim 1, 2 or 3, wherein the source cell is an intra-frequency neighbor cell to the candidate cell.
The method of claim 1, 2 or 3, wherein the source cell is an intra-band, inter-frequency neighbor cell to the candidate cell.
The method of claim 1, 2 or 3, wherein the source cell is an inter-band, inter-frequency neighbor cell to the candidate cell.
The method of claim 1, wherein the PDCCH order comprises an indication of the timing advance offset of the candidate cell for the RACH procedure.
The method of claim 7, wherein the indication is one-bit that indicates whether to use a timing advance offset of the source cell as the timing advance in the candidate cell.
A method for Lower layer Triggered Mobility (LTM) cell selection, the method comprising:

transmitting to a base station, by a User Equipment (UE) in a Radio Resource Control (RRC) connected state in a source cell, a measurement report comprising measurements associated with one or more target cells;

receiving, by the UE from the base station, a Physical Downlink Control Channel (PDCCH) order comprising configuration information of one or more candidate cells of the one or more target cells;

performing, by the UE, a Random Access Channel (RACH) procedure using a timing advance offset in one of the one or more candidate cells based on the PDCCH order.

receiving, by the UE from the base station, a cell switch command that commands the UE to switch to one of the one or more candidate cells.

performing, by the UE, a second RACH procedure in the one of the one or more candidate cells based on the cell switch command.
The method of claim 9, wherein a timing advance offset of the source cell is used as the timing advance offset in the one of the one or more candidate cells.
The method of claim 1, wherein an n-TimingAdvanceOffset is the same across the one or more candidate cells on a same band.
The method of any of claims 9 to 11, wherein the source cell is an intra-frequency neighbor cell to the one of the one or more candidate cells.
The method of any of claims 9 to 11, wherein the source cell is an intra-band, inter-frequency neighbor cell to the one of the one or more candidate cells.
The method of any of claims 9 to 11, wherein the source cell is an inter-band, inter-frequency neighbor cell to the one of the one or more candidate cells.
The method of claim 9, wherein the PDCCH order comprises an indication of the timing advance offset of the one or more candidate cells for the RACH procedure.
The method of claim 15, wherein the indication is one-bit that indicates whether to use a timing advance offset of the source cell as the timing advance in a candidate cell of the one or more candidate cells.
A wireless device configured to perform the methods of any of claims 1–16.
A non-transitory computer readable medium configured to store and execute instructions to perform the methods of any of claims 1–16.