Maintenance of uplink time alignment in conditional mobility

Abstract

The present disclosure is related to maintenance of uplink time alignment in conditional mobility in wireless communications. According to an embodiment of the present disclosure, a method performed by a user equipment (UE) comprises: receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; receiving uplink timing information for the candidate cell; applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; and transmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled, wherein the uplink signal comprises information for elapsed status of the timer.

Description

MAINTENANCE OF UPLINK TIME ALIGNMENT IN CONDITIONAL MOBILITY

[0001] The present disclosure is related to maintenance of uplink time alignment in conditional mobility in wireless communications.

[0002] 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

[0003] Work has started in International Telecommunication Union (ITU) and 3GPP to develop requirements and specifications for New Radio (NR) systems. 3GPP has to identify and develop the technology components needed for successfully standardizing the new RAT timely satisfying both the urgent market needs, and the more long-term requirements set forth by the ITU Radio communication sector (ITU-R) International Mobile Telecommunications (IMT)-2020 process. Further, the NR should be able to use any spectrum band ranging at least up to 100 GHz that may be made available for wireless communications even in a more distant future.

[0004] The NR targets a single technical framework addressing all usage scenarios, requirements and deployment scenarios including enhanced Mobile BroadBand (eMBB), massive Machine Type Communications (mMTC), Ultra-Reliable and Low Latency Communications (URLLC), etc. The NR shall be inherently forward compatible.

[0005] In a wireless communication system, several　Conditional Mobility　procedures have been introduced to enhance handover robustness and reduce interruption time. These include　Conditional Handover (CHO),　Conditional PSCell Change (CPC),　Conditional PSCell Addition (CPA), and　Conditional L1 / L2-Triggered Mobility (CLTM).

[0006] Traditionally, when a User Equipment (UE) moves between cells, it must perform a Random Access (RA) procedure to achieve UL time alignment with a target cell. However, in　Conditional Mobility, the UE is configured with one or more candidate cells and evaluates mobility execution conditions (e.g., Signal-to-Interference-plus-Noise Ratio (SINR) or Reference Signal Received Power (RSRP) thresholds) before performing the mobility execution.

[0007] A significant challenge in these procedures is the　maintenance of uplink (UL) time alignment　for candidate cells prior to the actual mobility execution. To minimize the latency during a cell switch, it is often　recommended that the UE maintains a valid Timing Advance (TA) for potential target cells.

[0008] An aspect of the present disclosure is to provide method and apparatus for maintenance of uplink time alignment in conditional mobility in a wireless communication system.

[0009] According to an embodiment of the present disclosure, a method performed by a user equipment (UE) comprises: receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; receiving uplink timing information for the candidate cell; applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; and transmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled, wherein the uplink signal comprises information for elapsed status of the timer.

[0010] According to an embodiment of the present disclosure, a method performed by a network node comprises: transmitting, to a user equipment (UE), a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; and transmitting, to the UE, uplink timing information for the candidate cell, wherein the UE is configured to perform operations comprising: applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; and transmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled, wherein the uplink signal comprises information for elapsed status of the timer.

[0011] According to various embodiments, apparatuses to implement the above methods are provided.

[0012] The present disclosure may have various advantageous effects.

[0013] For example, the UE reports the candidate TA information associated with the target cell during RACH-less conditional mobility execution toward the target cell. By doing so, the target cell and the UE can continuously maintain valid UL synchronization without interruption. Consequently, it has the effect of reducing UE interruptions by reducing the occurrence probability of subsequent procedures (e.g., random access - scheduling request - buffer status report) that may occur when UL synchronization between UE and network is lost.

[0014] Advantageous effects which can be obtained through specific embodiments of the present disclosure are not limited to the advantageous effects listed above. For example, there may be a variety of technical effects that a person having ordinary skill in the related art can understand and / or derive from the present disclosure. Accordingly, the specific effects of the present disclosure are not limited to those explicitly described herein, but may include various effects that may be understood or derived from the technical features of the present disclosure.

[0015] FIG. 1 shows an example of a communication system to which implementations of the present disclosure is applied.

[0016] FIG. 2 shows an example of wireless devices to which implementations of the present disclosure is applied.

[0017] FIG. 3 shows an example of UE to which implementations of the present disclosure is applied.

[0018] FIGs. 4 and 5 show an example of protocol stacks in a 3GPP based wireless communication system to which implementations of the present disclosure is applied.

[0019] FIG. 6 shows a frame structure in a 3GPP based wireless communication system to which implementations of the present disclosure is applied.

[0020] FIG. 7 shows a data flow example in the 3GPP NR system to which implementations of the present disclosure is applied.

[0021] FIG. 8 shows an example of a timing difference between a downlink frame and an uplink frame.

[0022] FIG. 9 shows an example of a signalling procedure for LTM.

[0023] FIG. 10 shows an example of a signalling procedure for CLTM.

[0024] FIG. 11 shows an example of a method performed by a UE for maintenance of uplink time alignment in conditional mobility according to various embodiments of the present disclosure.

[0025] FIG. 12 shows an example of a signal flow between UE and network for maintenance of uplink time alignment in conditional mobility according to various embodiments of the present disclosure.

[0026] FIG. 13 illustrates a first example of reporting candidate TA information.

[0027] FIG. 14 illustrates a second example of reporting candidate TA information.

[0028] The following techniques, apparatuses, and systems may be applied to a variety of wireless multiple access systems. Examples of the multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, a Single Carrier Frequency Division Multiple Access (SC-FDMA) system, and a Multi Carrier Frequency Division Multiple Access (MC-FDMA) system. CDMA may be embodied through radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be embodied through radio technology such as Global System for Mobile communications (GSM), General Packet Radio Service (GPRS), or Enhanced Data rates for GSM Evolution (EDGE). OFDMA may be embodied through radio technology such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is a part of a Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) is a part of Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA in downlink (DL) and SC-FDMA in uplink (UL). Evolution of 3GPP LTE includes LTE-Advanced (LTE-A), LTE-A Pro, and / or 5G New Radio (NR).

[0029] For convenience of description, implementations of the present disclosure are mainly described in regards to a 3GPP based wireless communication system. However, the technical features of the present disclosure are not limited thereto. For example, although the following detailed description is given based on a mobile communication system corresponding to a 3GPP based wireless communication system, aspects of the present disclosure that are not limited to 3GPP based wireless communication system are applicable to other mobile communication systems.

[0030] For terms and technologies which are not specifically described among the terms of and technologies employed in the present disclosure, the wireless communication standard documents published before the present disclosure may be referenced.

[0031] In the present disclosure, "A or B" may mean "only A", "only B", or "both A and B". In other words, "A or B" in the present disclosure may be interpreted as "A and / or B". For example, "A, B or C" in the present disclosure may mean "only A", "only B", "only C", or "any combination of A, B and C".

[0032] In the present disclosure, slash ( / ) or comma (,) may mean "and / or". For example, "A / B" may mean "A and / or B". Accordingly, "A / B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B or C".

[0033] In the present disclosure, "at least one of A and B" may mean "only A", "only B" or "both A and B". In addition, the expression "at least one of A or B" or "at least one of A and / or B" in the present disclosure may be interpreted as same as "at least one of A and B".

[0034] In addition, in the present disclosure, "at least one of A, B and C" may mean "only A", "only B", "only C", or "any combination of A, B and C". In addition, "at least one of A, B or C" or "at least one of A, B and / or C" may mean "at least one of A, B and C".

[0035] Also, parentheses used in the present disclosure may mean "for example". In detail, when it is shown as "control information (PDCCH)", "PDCCH" may be proposed as an example of "control information". In other words, "control information" in the present disclosure is not limited to "PDCCH", and "PDCCH" may be proposed as an example of "control information". In addition, even when shown as "control information (i.e., PDCCH)", "PDCCH" may be proposed as an example of "control information".

[0036] Technical features that are separately described in one drawing in the present disclosure may be implemented separately or simultaneously.

[0037] Although not limited thereto, various descriptions, functions, procedures, suggestions, methods and / or operational flowcharts of the present disclosure disclosed herein can be applied to various fields requiring wireless communication and / or connection (e.g., 5G) between devices.

[0038] Hereinafter, the present disclosure will be described in more detail with reference to drawings. The same reference numerals in the following drawings and / or descriptions may refer to the same and / or corresponding hardware blocks, software blocks, and / or functional blocks unless otherwise indicated.

[0039] FIG. 1 shows an example of a communication system to which implementations of the present disclosure is applied.

[0040] The 5G usage scenarios shown in FIG. 1 are only exemplary, and the technical features of the present disclosure can be applied to other 5G usage scenarios which are not shown in FIG. 1.

[0041] Three main requirement categories for 5G include (1) a category of enhanced Mobile BroadBand (eMBB), (2) a category of massive Machine Type Communication (mMTC), and (3) a category of Ultra-Reliable and Low Latency Communications (URLLC).

[0042] Referring to FIG. 1, the communication system 1 includes wireless devices 100a to 100f, Base Stations (BSs) 200, and a network 300. Although FIG. 1 illustrates a 5G network as an example of the network of the communication system 1, the implementations of the present disclosure are not limited to the 5G system, and can be applied to the future communication system beyond the 5G system.

[0043] The BSs 200 and the network 300 may be implemented as wireless devices and a specific wireless device may operate as a BS / network node with respect to other wireless devices.

[0044] The wireless devices 100a to 100f represent devices performing communication using Radio Access Technology (RAT) (e.g., 5G NR or LTE) and may be referred to as communication / radio / 5G devices. The wireless devices 100a to 100f may include, without being limited to, a robot 100a, vehicles 100b-1 and 100b-2, an eXtended Reality (XR) device 100c, a hand-held device 100d, a home appliance 100e, an Internet-of-Things (IoT) device 100f, and an Artificial Intelligence (AI) device / server 400. For example, the vehicles may include a vehicle having a wireless communication function, an autonomous driving vehicle, and a vehicle capable of performing communication between vehicles. The vehicles may include an Unmanned Aerial Vehicle (UAV) (e.g., a drone). The XR device may include an Augmented Reality (AR) / Virtual Reality (VR) / Mixed Reality (MR) device and may be implemented in the form of a Head-Mounted Device (HMD), a Head-Up Display (HUD) mounted in a vehicle, a television, a smartphone, a computer, a wearable device, a home appliance device, a digital signage, a vehicle, a robot, etc. The hand-held device may include a smartphone, a smartpad, a wearable device (e.g., a smartwatch or a smartglasses), and a computer (e.g., a notebook). The home appliance may include a TV, a refrigerator, and a washing machine. The IoT device may include a sensor and a smartmeter.

[0045] In the present disclosure, the wireless devices 100a to 100f may be called User Equipments (UEs). A UE may include, for example, a cellular phone, a smartphone, a laptop computer, a digital broadcast terminal, a Personal Digital Assistant (PDA), a Portable Multimedia Player (PMP), a navigation system, a slate Personal Computer (PC), a tablet PC, an ultrabook, a vehicle, a vehicle having an autonomous traveling function, a connected car, an UAV, an AI module, a robot, an AR device, a VR device, an MR device, a hologram device, a public safety device, an MTC device, an IoT device, a medical device, a FinTech device (or a financial device), a security device, a weather / environment device, a device related to a 5G service, or a device related to a fourth industrial revolution field.

[0046] The wireless devices 100a to 100f may be connected to the network 300 via the BSs 200. An AI technology may be applied to the wireless devices 100a to 100f and the wireless devices 100a to 100f may be connected to the AI server 400 via the network 300. The network 300 may be configured using a 3G network, a 4G (e.g., LTE) network, a 5G (e.g., NR) network, and a beyond-5G network. Although the wireless devices 100a to 100f may communicate with each other through the BSs 200 / network 300, the wireless devices 100a to 100f may perform direct communication (e.g., sidelink communication) with each other without passing through the BSs 200 / network 300. For example, the vehicles 100b-1 and 100b-2 may perform direct communication (e.g., Vehicle-to-Vehicle (V2V) / Vehicle-to-everything (V2X) communication). The IoT device (e.g., a sensor) may perform direct communication with other IoT devices (e.g., sensors) or other wireless devices 100a to 100f.

[0047] Wireless communication / connections 150a, 150b and 150c may be established between the wireless devices 100a to 100f and / or between wireless device 100a to 100f and BS 200 and / or between BSs 200. Herein, the wireless communication / connections may be established through various RATs (e.g., 5G NR) such as uplink / downlink communication 150a, sidelink communication (or Device-to-Device (D2D) communication) 150b, inter-base station communication 150c (e.g., relay, Integrated Access and Backhaul (IAB)), etc. The wireless devices 100a to 100f and the BSs 200 / the wireless devices 100a to 100f may transmit / receive radio signals to / from each other through the wireless communication / connections 150a, 150b and 150c. For example, the wireless communication / connections 150a, 150b and 150c may transmit / receive signals through various physical channels. To this end, at least a part of various configuration information configuring processes, various signal processing processes (e.g., channel encoding / decoding, modulation / demodulation, and resource mapping / de-mapping), and resource allocating processes, for transmitting / receiving radio signals, may be performed based on the various proposals of the present disclosure.

[0048] NR supports multiples numerologies (and / or multiple Sub-Carrier Spacings (SCS)) to support various 5G services. For example, if SCS is 15 kHz, wide area can be supported in traditional cellular bands, and if SCS is 30 kHz / 60 kHz, dense-urban, lower latency, and wider carrier bandwidth can be supported. If SCS is 60 kHz or higher, bandwidths greater than 24.25 GHz can be supported to overcome phase noise.

[0049] The NR frequency band may be defined as two types of frequency range, i.e., Frequency Range 1 (FR1) and Frequency Range 2 (FR2). The numerical value of the frequency range may be changed. For example, the frequency ranges of the two types (FR1 and FR2) may be as shown in Table 1 below. For ease of explanation, in the frequency ranges used in the NR system, FR1 may mean "sub 6 GHz range", FR2 may mean "above 6 GHz range," and may be referred to as millimeter Wave (mmW).

[0050] Frequency Range designationCorresponding frequency rangeSubcarrier SpacingFR1450MHz - 6000MHz15, 30, 60kHzFR224250MHz - 52600MHz60, 120, 240kHz

[0051] As mentioned above, the numerical value of the frequency range of the NR system may be changed. For example, FR1 may include a frequency band of 410MHz to 7125MHz as shown in Table 2 below. That is, FR1 may include a frequency band of 6GHz (or 5850, 5900, 5925 MHz, etc.) or more. For example, a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more included in FR1 may include an unlicensed band. Unlicensed bands may be used for a variety of purposes, for example for communication for vehicles (e.g., autonomous driving).

[0052] Frequency Range designationCorresponding frequency rangeSubcarrier SpacingFR1410MHz - 7125MHz15, 30, 60kHzFR224250MHz - 52600MHz60, 120, 240kHz

[0053] Here, the radio communication technologies implemented in the wireless devices in the present disclosure may include NarrowBand IoT (NB-IoT) technology for low-power communication as well as LTE, NR and 6G. For example, NB-IoT technology may be an example of Low Power Wide Area Network (LPWAN) technology, may be implemented in specifications such as LTE Cat NB1 and / or LTE Cat NB2, and may not be limited to the above-mentioned names. Additionally and / or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may communicate based on LTE-M technology. For example, LTE-M technology may be an example of LPWAN technology and be called by various names such as enhanced MTC (eMTC). For example, LTE-M technology may be implemented in at least one of the various specifications, such as 1) LTE Cat 0, 2) LTE Cat M1, 3) LTE Cat M2, 4) LTE non-bandwidth limited (non-BL), 5) LTE-MTC, 6) LTE Machine Type Communication, and / or 7) LTE M, and may not be limited to the above-mentioned names. Additionally and / or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may include at least one of ZigBee, Bluetooth, and / or LPWAN which take into account low-power communication, and may not be limited to the above-mentioned names. For example, ZigBee technology may generate Personal Area Networks (PANs) associated with small / low-power digital communication based on various specifications such as IEEE 802.15.4 and may be called various names.FIG. 2 shows an example of wireless devices to which implementations of the present disclosure is applied.

[0054] In FIG. 2, The first wireless device 100 and / or the second wireless device 200 may be implemented in various forms according to use cases / services. For example, {the first wireless device 100 and the second wireless device 200} may correspond to at least one of {the wireless device 100a to 100f and the BS 200}, {the wireless device 100a to 100f and the wireless device 100a to 100f} and / or {the BS 200 and the BS 200} of FIG. 1. The first wireless device 100 and / or the second wireless device 200 may be configured by various elements, devices / parts, and / or modules.

[0055] The first wireless device 100 may include at least one transceiver, such as a transceiver 106, at least one processing chip, such as a processing chip 101, and / or one or more antennas 108.

[0056] The processing chip 101 may include at least one processor, such a processor 102, and at least one memory, such as a memory 104. Additional and / or alternatively, the memory 104 may be placed outside of the processing chip 101.

[0057] The processor 102 may control the memory 104 and / or the transceiver 106 and may be adapted to implement the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts described in the present disclosure. For example, the processor 102 may process information within the memory 104 to generate first information / signals and then transmit radio signals including the first information / signals through the transceiver 106. The processor 102 may receive radio signals including second information / signals through the transceiver 106 and then store information obtained by processing the second information / signals in the memory 104.

[0058] The memory 104 may be operably connectable to the processor 102. The memory 104 may store various types of information and / or instructions. The memory 104 may store a firmware and / or a software code 105 which implements codes, commands, and / or a set of commands that, when executed by the processor 102, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 105 may implement instructions that, when executed by the processor 102, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 105 may control the processor 102 to perform one or more protocols. For example, the firmware and / or the software code 105 may control the processor 102 to perform one or more layers of the radio interface protocol.

[0059] Herein, the processor 102 and the memory 104 may be a part of a communication modem / circuit / chip designed to implement RAT (e.g., LTE or NR). The transceiver 106 may be connected to the processor 102 and transmit and / or receive radio signals through one or more antennas 108. Each of the transceiver 106 may include a transmitter and / or a receiver. The transceiver 106 may be interchangeably used with Radio Frequency (RF) unit(s). In the present disclosure, the first wireless device 100 may represent a communication modem / circuit / chip.

[0060] The second wireless device 200 may include at least one transceiver, such as a transceiver 206, at least one processing chip, such as a processing chip 201, and / or one or more antennas 208.

[0061] The processing chip 201 may include at least one processor, such a processor 202, and at least one memory, such as a memory 204. Additional and / or alternatively, the memory 204 may be placed outside of the processing chip 201.

[0062] The processor 202 may control the memory 204 and / or the transceiver 206 and may be adapted to implement the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts described in the present disclosure. For example, the processor 202 may process information within the memory 204 to generate third information / signals and then transmit radio signals including the third information / signals through the transceiver 206. The processor 202 may receive radio signals including fourth information / signals through the transceiver 106 and then store information obtained by processing the fourth information / signals in the memory 204.

[0063] The memory 204 may be operably connectable to the processor 202. The memory 204 may store various types of information and / or instructions. The memory 204 may store a firmware and / or a software code 205 which implements codes, commands, and / or a set of commands that, when executed by the processor 202, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 205 may implement instructions that, when executed by the processor 202, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 205 may control the processor 202 to perform one or more protocols. For example, the firmware and / or the software code 205 may control the processor 202 to perform one or more layers of the radio interface protocol.

[0064] Herein, the processor 202 and the memory 204 may be a part of a communication modem / circuit / chip designed to implement RAT (e.g., LTE or NR). The transceiver 206 may be connected to the processor 202 and transmit and / or receive radio signals through one or more antennas 208. Each of the transceiver 206 may include a transmitter and / or a receiver. The transceiver 206 may be interchangeably used with RF unit. In the present disclosure, the second wireless device 200 may represent a communication modem / circuit / chip.

[0065] Hereinafter, hardware elements of the wireless devices 100 and 200 will be described more specifically. One or more protocol layers may be implemented by, without being limited to, one or more processors 102 and 202. For example, the one or more processors 102 and 202 may implement one or more layers (e.g., functional layers such as Physical (PHY) layer, Media Access Control (MAC) layer, Radio Link Control (RLC) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Resource Control (RRC) layer, and Service Data Adaptation Protocol (SDAP) layer). The one or more processors 102 and 202 may generate one or more Protocol Data Units (PDUs), one or more Service Data Unit (SDUs), messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. The one or more processors 102 and 202 may generate signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure and provide the generated signals to the one or more transceivers 106 and 206. The one or more processors 102 and 202 may receive the signals (e.g., baseband signals) from the one or more transceivers 106 and 206 and acquire the PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure.

[0066] The one or more processors 102 and 202 may be referred to as controllers, microcontrollers, microprocessors, or microcomputers. The one or more processors 102 and 202 may be implemented by hardware, firmware, software, or a combination thereof. As an example, one or more Application Specific Integrated Circuits (ASICs), one or more Digital Signal Processors (DSPs), one or more Digital Signal Processing Devices (DSPDs), one or more Programmable Logic Devices (PLDs), or one or more Field Programmable Gate Arrays (FPGAs) may be included in the one or more processors 102 and 202. For example, the one or more processors 102 and 202 may be configured by a set of a communication control processor, an Application Processor (AP), an Electronic Control Unit (ECU), a Central Processing Unit (CPU), a Graphic Processing Unit (GPU), and a memory control processor.

[0067] The one or more memories 104 and 204 may be connected to the one or more processors 102 and 202 and store various types of data, signals, messages, information, programs, code, instructions, and / or commands. The one or more memories 104 and 204 may be configured by Random Access Memory (RAM), Dynamic RAM (DRAM), Read-Only Memory (ROM), electrically Erasable Programmable Read-Only Memory (EPROM), flash memory, volatile memory, non-volatile memory, hard drive, register, cash memory, computer-readable storage medium, and / or combinations thereof. The one or more memories 104 and 204 may be located at the interior and / or exterior of the one or more processors 102 and 202. The one or more memories 104 and 204 may be connected to the one or more processors 102 and 202 through various technologies such as wired or wireless connection.

[0068] The one or more transceivers 106 and 206 may transmit user data, control information, and / or radio signals / channels, mentioned in the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure, to one or more other devices. The one or more transceivers 106 and 206 may receive user data, control information, and / or radio signals / channels, mentioned in the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure, from one or more other devices. For example, the one or more transceivers 106 and 206 may be connected to the one or more processors 102 and 202 and transmit and receive radio signals. For example, the one or more processors 102 and 202 may perform control so that the one or more transceivers 106 and 206 may transmit user data, control information, or radio signals to one or more other devices. The one or more processors 102 and 202 may perform control so that the one or more transceivers 106 and 206 may receive user data, control information, or radio signals from one or more other devices.

[0069] The one or more transceivers 106 and 206 may be connected to the one or more antennas 108 and 208. Additionally and / or alternatively, the one or more transceivers 106 and 206 may include one or more antennas 108 and 208. The one or more transceivers 106 and 206 may be adapted to transmit and receive user data, control information, and / or radio signals / channels, mentioned in the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure, through the one or more antennas 108 and 208. In the present disclosure, the one or more antennas 108 and 208 may be a plurality of physical antennas or a plurality of logical antennas (e.g., antenna ports).

[0070] The one or more transceivers 106 and 206 may convert received user data, control information, radio signals / channels, etc., from RF band signals into baseband signals in order to process received user data, control information, radio signals / channels, etc., using the one or more processors 102 and 202. The one or more transceivers 106 and 206 may convert the user data, control information, radio signals / channels, etc., processed using the one or more processors 102 and 202 from the base band signals into the RF band signals. To this end, the one or more transceivers 106 and 206 may include (analog) oscillators and / or filters. For example, the one or more transceivers 106 and 206 can up-convert OFDM baseband signals to OFDM signals by their (analog) oscillators and / or filters under the control of the one or more processors 102 and 202 and transmit the up-converted OFDM signals at the carrier frequency. The one or more transceivers 106 and 206 may receive OFDM signals at a carrier frequency and down-convert the OFDM signals into OFDM baseband signals by their (analog) oscillators and / or filters under the control of the one or more processors 102 and 202.

[0071] Although not shown in FIG. 2, the wireless devices 100 and 200 may further include additional components. The additional components 140 may be variously configured according to types of the wireless devices 100 and 200. For example, the additional components 140 may include at least one of a power unit / battery, an Input / Output (I / O) device (e.g., audio I / O port, video I / O port), a driving device, and a computing device. The additional components 140 may be coupled to the one or more processors 102 and 202 via various technologies, such as a wired or wireless connection.

[0072] In the implementations of the present disclosure, a UE may operate as a transmitting device in Uplink (UL) and as a receiving device in Downlink (DL). In the implementations of the present disclosure, a BS may operate as a receiving device in UL and as a transmitting device in DL. Hereinafter, for convenience of description, it is mainly assumed that the first wireless device 100 acts as the UE, and the second wireless device 200 acts as the BS. For example, the processor(s) 102 connected to, mounted on or launched in the first wireless device 100 may be adapted to perform the UE behavior according to an implementation of the present disclosure or control the transceiver(s) 106 to perform the UE behavior according to an implementation of the present disclosure. The processor(s) 202 connected to, mounted on or launched in the second wireless device 200 may be adapted to perform the BS behavior according to an implementation of the present disclosure or control the transceiver(s) 206 to perform the BS behavior according to an implementation of the present disclosure.

[0073] In the present disclosure, a BS is also referred to as a node B (NB), an eNode B (eNB), or a gNB.

[0074] FIG. 3 shows an example of UE to which implementations of the present disclosure is applied.

[0075] Referring to FIG. 3, a UE 100 may correspond to the first wireless device 100 of FIG. 2.

[0076] A UE 100 includes a processor 102, a memory 104, a transceiver 106, one or more antennas 108, a power management module 141, a battery 142, a display 143, a keypad 144, a Subscriber Identification Module (SIM) card 145, a speaker 146, and a microphone 147.

[0077] The processor 102 may be adapted to implement the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. The processor 102 may be adapted to control one or more other components of the UE 100 to implement the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. Layers of the radio interface protocol may be implemented in the processor 102. The processor 102 may include ASIC, other chipset, logic circuit and / or data processing device. The processor 102 may be an application processor. The processor 102 may include at least one of DSP, CPU, GPU, a modem (modulator and demodulator). An example of the processor 102 may be found in SNAPDRAGONTMseries of processors made by Qualcomm®, EXYNOSTMseries of processors made by Samsung®, A series of processors made by Apple®, HELIOTMseries of processors made by MediaTek®, ATOMTMseries of processors made by Intel®or a corresponding next generation processor.

[0078] The memory 104 is operatively coupled with the processor 102 and stores a variety of information to operate the processor 102. The memory 104 may include ROM, RAM, flash memory, memory card, storage medium and / or other storage device. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, etc.) that perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. The modules can be stored in the memory 104 and executed by the processor 102. The memory 104 can be implemented within the processor 102 or external to the processor 102 in which case those can be communicatively coupled to the processor 102 via various means as is known in the art.

[0079] The transceiver 106 is operatively coupled with the processor 102, and transmits and / or receives a radio signal. The transceiver 106 includes a transmitter and a receiver. The transceiver 106 may include baseband circuitry to process radio frequency signals. The transceiver 106 controls the one or more antennas 108 to transmit and / or receive a radio signal.

[0080] The power management module 141 manages power for the processor 102 and / or the transceiver 106. The battery 142 supplies power to the power management module 141.

[0081] The display 143 outputs results processed by the processor 102. The keypad 144 receives inputs to be used by the processor 102. The keypad 144 may be shown on the display 143.

[0082] The SIM card 145 is an　integrated circuit　that is intended to　securely store the　International Mobile Subscriber Identity　(IMSI) number and its related　key, which are used to identify and authenticate subscribers on　mobile telephony　devices (such as　mobile phones　and　computers). It is also possible to store contact information on many SIM cards.

[0083] The speaker 146 outputs sound-related results processed by the processor 102. The microphone 147 receives sound-related inputs to be used by the processor 102.

[0084] FIGs. 4 and 5 show an example of protocol stacks in a 3GPP based wireless communication system to which implementations of the present disclosure is applied.

[0085] In particular, FIG. 4 illustrates an example of a radio interface user plane protocol stack between a UE and a BS and FIG. 5 illustrates an example of a radio interface control plane protocol stack between a UE and a BS. The control plane refers to a path through which control messages used to manage call by a UE and a network are transported. The user plane refers to a path through which data generated in an application layer, for example, voice data or Internet packet data are transported. Referring to FIG. 4, the user plane protocol stack may be divided into Layer 1 (L1, for example PHY layer) and Layer 2 (L2, for example MAC / RLC / PDCP layer). Referring to FIG. 5, the control plane protocol stack may be divided into Layer 1 (L1, for example PHY layer), Layer 2 (L2, for example MAC / RLC / PDCP layer), Layer 3 (L3, for example an RRC layer), and a non-access stratum (NAS) layer. Layer 1, Layer 2 and Layer 3 are referred to as an access stratum (AS).

[0086] In the 3GPP LTE system, the Layer 2 is split into the following sublayers: MAC, RLC, and PDCP. In the 3GPP NR system, the Layer 2 is split into the following sublayers: MAC, RLC, PDCP and SDAP. The PHY layer offers to the MAC sublayer transport channels, the MAC sublayer offers to the RLC sublayer logical channels, the RLC sublayer offers to the PDCP sublayer RLC channels, the PDCP sublayer offers to the SDAP sublayer radio bearers. The SDAP sublayer offers to 5G core network quality of service (QoS) flows.

[0087] In the 3GPP NR system, the main services and functions of the MAC sublayer include: mapping between logical channels and transport channels; multiplexing / de-multiplexing of MAC SDUs belonging to one or different logical channels into / from transport blocks (TB) delivered to / from the physical layer on transport channels; scheduling information reporting; error correction through hybrid automatic repeat request (HARQ) (one HARQ entity per cell in case of carrier aggregation (CA)); priority handling between UEs by means of dynamic scheduling; priority handling between logical channels of one UE by means of logical channel prioritization; padding. A single MAC entity may support multiple numerologies, transmission timings and cells. Mapping restrictions in logical channel prioritization control which numerology(ies), cell(s), and transmission timing(s) a logical channel can use.

[0088] Different kinds of data transfer services are offered by MAC. To accommodate different kinds of data transfer services, multiple types of logical channels are defined, i.e., each supporting transfer of a particular type of information. Each logical channel type is defined by what type of information is transferred. Logical channels are classified into two groups: control channels and traffic channels. Control channels are used for the transfer of control plane information only, and traffic channels are used for the transfer of user plane information only. Broadcast control channel (BCCH) is a downlink logical channel for broadcasting system control information, paging control channel (PCCH) is a downlink logical channel that transfers paging information, system information change notifications and indications of ongoing public warning service (PWS) broadcasts, common control channel (CCCH) is a logical channel for transmitting control information between UEs and network and used for UEs having no RRC connection with the network, and dedicated control channel (DCCH) is a point-to-point bi-directional logical channel that transmits dedicated control information between a UE and the network and used by UEs having an RRC connection. Dedicated traffic channel (DTCH) is a point-to-point logical channel, dedicated to one UE, for the transfer of user information. A DTCH can exist in both uplink and downlink. In downlink, the following connections between logical channels and transport channels exist: BCCH can be mapped to broadcast channel (BCH); BCCH can be mapped to downlink shared channel (DL-SCH); PCCH can be mapped to paging channel (PCH); CCCH can be mapped to DL-SCH; DCCH can be mapped to DL-SCH; and DTCH can be mapped to DL-SCH. In uplink, the following connections between logical channels and transport channels exist: CCCH can be mapped to uplink shared channel (UL-SCH); DCCH can be mapped to UL-SCH; and DTCH can be mapped to UL-SCH.

[0089] The RLC sublayer supports three transmission modes: transparent mode (TM), unacknowledged mode (UM), and acknowledged node (AM). The RLC configuration is per logical channel with no dependency on numerologies and / or transmission durations. In the 3GPP NR system, the main services and functions of the RLC sublayer depend on the transmission mode and include: transfer of upper layer PDUs; sequence numbering independent of the one in PDCP (UM and AM); error correction through ARQ (AM only); segmentation (AM and UM) and re-segmentation (AM only) of RLC SDUs; reassembly of SDU (AM and UM); duplicate detection (AM only); RLC SDU discard (AM and UM); RLC re-establishment; protocol error detection (AM only).

[0090] In the 3GPP NR system, the main services and functions of the PDCP sublayer for the user plane include: sequence numbering; header compression and decompression using robust header compression (ROHC); transfer of user data; reordering and duplicate detection; in-order delivery; PDCP PDU routing (in case of split bearers); retransmission of PDCP SDUs; ciphering, deciphering and integrity protection; PDCP SDU discard; PDCP re-establishment and data recovery for RLC AM; PDCP status reporting for RLC AM; duplication of PDCP PDUs and duplicate discard indication to lower layers. The main services and functions of the PDCP sublayer for the control plane include: sequence numbering; ciphering, deciphering and integrity protection; transfer of control plane data; reordering and duplicate detection; in-order delivery; duplication of PDCP PDUs and duplicate discard indication to lower layers.

[0091] In the 3GPP NR system, the main services and functions of SDAP include: mapping between a QoS flow and a data radio bearer; marking QoS flow ID (QFI) in both DL and UL packets. A single protocol entity of SDAP is configured for each individual PDU session.

[0092] In the 3GPP NR system, the main services and functions of the RRC sublayer include: broadcast of system information related to AS and NAS; paging initiated by 5GC or NG-RAN; establishment, maintenance and release of an RRC connection between the UE and NG-RAN; security functions including key management; establishment, configuration, maintenance and release of signalling radio bearers (SRBs) and data radio bearers (DRBs); mobility functions (including: handover and context transfer, UE cell selection and reselection and control of cell selection and reselection, inter-RAT mobility); QoS management functions; UE measurement reporting and control of the reporting; detection of and recovery from radio link failure; NAS message transfer to / from NAS from / to UE.

[0093] FIG. 6 shows a frame structure in a 3GPP based wireless communication system to which implementations of the present disclosure is applied.

[0094] The frame structure shown in FIG. 6 is purely exemplary and the number of subframes, the number of slots, and / or the number of symbols in a frame may be variously changed. In the 3GPP based wireless communication system, OFDM numerologies (e.g., subcarrier spacing (SCS), transmission time interval (TTI) duration) may be differently configured between a plurality of cells aggregated for one UE. For example, if a UE is configured with different SCSs for cells aggregated for the cell, an (absolute time) duration of a time resource (e.g., a subframe, a slot, or a TTI) including the same number of symbols may be different among the aggregated cells. Herein, symbols may include OFDM symbols (or CP-OFDM symbols), SC-FDMA symbols (or discrete Fourier transform-spread-OFDM (DFT-s-OFDM) symbols).

[0095] Referring to FIG. 6, downlink and uplink transmissions are organized into frames. Each frame has Tf= 10ms duration. Each frame is divided into two half-frames, where each of the half-frames has 5ms duration. Each half-frame consists of 5 subframes, where the duration Tsfper subframe is 1ms. Each subframe is divided into slots and the number of slots in a subframe depends on a subcarrier spacing. Each slot includes 14 or 12 OFDM symbols based on a cyclic prefix (CP). In a normal CP, each slot includes 14 OFDM symbols and, in an extended CP, each slot includes 12 OFDM symbols. The numerology is based on exponentially scalable subcarrier spacing f = 2u*15 kHz.

[0096] Table 3 shows the number of OFDM symbols per slot Nslotsymb, the number of slots per frameNframe,uslot, and the number of slots per subframe Nsubframe,uslotfor the normal CP, according to the subcarrier spacing f = 2u*15 kHz.

[0097] uNslotsymbNframe,uslotNsubframe,uslot01410111420221440431480841416016

[0098] Table 4 shows the number of OFDM symbols per slot Nslotsymb, the number of slots per frameNframe,uslot, and the number of slots per subframe Nsubframe,uslotfor the extended CP, according to the subcarrier spacing f = 2u*15 kHz.

[0099] uNslotsymbNframe,uslotNsubframe,uslot212404

[0100] A slot includes plural symbols (e.g., 14 or 12 symbols) in the time domain. For each numerology (e.g., subcarrier spacing) and carrier, a resource grid ofNsize,ugrid,x*NRBscsubcarriers andNsubframe,usymbOFDM symbols is defined, starting at common resource block (CRB)Nstart,ugridindicated by higher-layer signalling (e.g., RRC signalling), whereNsize,ugrid,xis the number of resource blocks (RBs) in the resource grid and the subscript x is DL for downlink and UL for uplink.NRBscis the number of subcarriers per RB. In the 3GPP based wireless communication system,NRBscis 12 generally. There is one resource grid for a given antenna portp, subcarrier spacing configurationu, and transmission direction (DL or UL). The carrier bandwidthNsize,ugridfor subcarrier spacing configurationuis given by the higher-layer parameter (e.g., RRC parameter). Each element in the resource grid for the antenna portpand the subcarrier spacing configurationuis referred to as a resource element (RE) and one complex symbol may be mapped to each RE. Each RE in the resource grid is uniquely identified by an indexkin the frequency domain and an indexlrepresenting a symbol location relative to a reference point in the time domain. In the 3GPP based wireless communication system, an RB is defined by 12 consecutive subcarriers in the frequency domain. As shown in FIG. 6, as SCS doubles, the slot length and symbol length are halved. For example, when SCS is 15kHz, the slot length is 1ms, which is the same as the subframe length. When SCS is 30kHz, the slot length is 0.5ms (=500us), and the symbol length is half of that when the SCS is 15kHz. When SCS is 60kHz, the slot length is 0.25ms (=250us), and the symbol length is half of that when the SCS is 30kHz. When SCS is 120kHz, the slot length is 0.125ms (=125us), and the symbol length is half of that when the SCS is 60kHz. When SCS is 240kHz, the slot length is 0.0625ms (=62.5us), and the symbol length is half of that when the SCS is 120kHz.

[0101] In the 3GPP NR system, RBs are classified into CRBs and physical resource blocks (PRBs). CRBs are numbered from 0 and upwards in the frequency domain for subcarrier spacing configurationu. The center of subcarrier 0 of CRB 0 for subcarrier spacing configurationucoincides with 'point A' which serves as a common reference point for resource block grids. In the 3GPP NR system, PRBs are defined within a bandwidth part (BWP) and numbered from 0 toNsizeBWP,i-1, where i is the number of the bandwidth part. The relation between the physical resource block nPRBin the bandwidth part i and the common resource block nCRBis as follows: nPRB= nCRB+NsizeBWP,i, whereNsizeBWP,iis the common resource block where bandwidth part starts relative to CRB 0. The BWP includes a plurality of consecutive RBs. A carrier may include a maximum of N (e.g., 5) BWPs. A UE may be configured with one or more BWPs on a given component carrier. Only one BWP among BWPs configured to the UE can active at a time. The active BWP defines the UE's operating bandwidth within the cell's operating bandwidth.

[0102] In the present disclosure, the term "cell" may refer to a geographic area to which one or more nodes provide a communication system, or refer to radio resources. A "cell" as a geographic area may be understood as coverage within which a node can provide service using a carrier and a "cell" as radio resources (e.g., time-frequency resources) is associated with bandwidth which is a frequency range configured by the carrier. The "cell" associated with the radio resources is defined by a combination of downlink resources and uplink resources, for example, a combination of a DL component carrier (CC) and a UL CC. The cell may be configured by downlink resources only, or may be configured by downlink resources and uplink resources. Since DL coverage, which is a range within which the node is capable of transmitting a valid signal, and UL coverage, which is a range within which the node is capable of receiving the valid signal from the UE, depends upon a carrier carrying the signal, the coverage of the node may be associated with coverage of the "cell" of radio resources used by the node. Accordingly, the term "cell" may be used to represent service coverage of the node sometimes, radio resources at other times, or a range that signals using the radio resources can reach with valid strength at other times.

[0103] In CA, two or more CCs are aggregated. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities. CA is supported for both contiguous and non-contiguous CCs. When CA is configured, the UE only has one RRC connection with the network. At RRC connection establishment / re-establishment / handover, one serving cell provides the NAS mobility information, and at RRC connection re-establishment / handover, one serving cell provides the security input. This cell is referred to as the primary cell (PCell). The PCell is a cell, operating on the primary frequency, in which the UE either performs the initial connection establishment procedure or initiates the connection re-establishment procedure. Depending on UE capabilities, secondary cells (SCells) can be configured to form together with the PCell a set of serving cells. An SCell is a cell providing additional radio resources on top of special cell (SpCell). The configured set of serving cells for a UE therefore always consists of one PCell and one or more SCells. For dual connectivity (DC) operation, the term SpCell refers to the PCell of the master cell group (MCG) or the primary SCell (PSCell) of the secondary cell group (SCG). An SpCell supports PUCCH transmission and contention-based random access, and is always activated. The MCG is a group of serving cells associated with a master node, comprised of the SpCell (PCell) and optionally one or more SCells. The SCG is the subset of serving cells associated with a secondary node, comprised of the PSCell and zero or more SCells, for a UE configured with DC. For a UE in RRC_CONNECTED not configured with CA / DC, there is only one serving cell comprised of the PCell. For a UE in RRC_CONNECTED configured with CA / DC, the term "serving cells" is used to denote the set of cells comprised of the SpCell(s) and all SCells. In DC, two MAC entities are configured in a UE: one for the MCG and one for the SCG.

[0104] FIG. 7 shows a data flow example in the 3GPP NR system to which implementations of the present disclosure is applied.

[0105] Referring to FIG. 7, "RB" denotes a radio bearer, and "H" denotes a header. Radio bearers are categorized into two groups: DRBs for user plane data and SRBs for control plane data. The MAC PDU is transmitted / received using radio resources through the PHY layer to / from an external device. The MAC PDU arrives to the PHY layer in the form of a transport block.

[0106] In the PHY layer, the uplink transport channels UL-SCH and random access channel (RACH) are mapped to their physical channels physical uplink shared channel (PUSCH) and physical random access channel (PRACH), respectively, and the downlink transport channels DL-SCH, BCH and PCH are mapped to physical downlink shared channel (PDSCH), physical broadcast channel (PBCH) and PDSCH, respectively. In the PHY layer, uplink control information (UCI) is mapped to physical uplink control channel (PUCCH), and downlink control information (DCI) is mapped to physical downlink control channel (PDCCH). A MAC PDU related to UL-SCH is transmitted by a UE via a PUSCH based on an UL grant, and a MAC PDU related to DL-SCH is transmitted by a BS via a PDSCH based on a DL assignment.

[0107] Hereinafter, contents regarding timing advance (TA) are described.

[0108] FIG. 8 shows an example of a timing difference between a downlink frame and an uplink frame.

[0109] Referring to FIG. 8, there is a timing difference of between a downlink frame and an uplink frame. TA may be used to adjust the uplink frame timing related to the downlink frame timing.

[0110] The refers to a timing advance between downlink and uplink. The may be determined based on a timing advance command (TAC) value (or, timing advance value, ).

[0111] In some implementations, the TAC value may be included in a random access response (RAR) or an absolute TAC MAC CE. In this case, , where is a subcarrier spacing configuration for subcarrier spacing [kHz].

[0112] In some implementations, the TAC value may be included in a TAC MAC CE. In this case, .

[0113] The refers to a fixed offset used to calculate the timing advance. The may be determined based on a frequency range and / or a band of a cell used for uplink transmission.

[0114] The refers to a basic time unit, where .

[0115] In RRC_CONNECTED, the RAN node may be responsible for maintaining the timing advance to keep the L1 uplink synchronized. Serving cells having UL to which the same timing advance applies and using the same timing reference cell may be grouped in a timing advance group (TAG). Each TAG may contain at least one serving cell with configured uplink, and the mapping of each serving cell to a TAG may be configured by RRC.

[0116] For the primary TAG, the UE may use the PCell as timing reference, except with shared spectrum channel access where an SCell can also be used as timing reference in certain cases. In a secondary TAG, the UE may use any of the activated SCells of this TAG as a timing reference cell, but should not change the timing reference cell unless necessary.

[0117] Timing advance updates (i.e., TAC value / timing advance value) may be signalled by the RAN node to the UE via MAC CE commands (e.g., TAC and / or RAR). Such commands may restart a TAG-specific timer (e.g.,TimeAlignmentTimer) which indicates whether the L1 uplink can be synchronized or not: when the timer is running, the L1 uplink is considered synchronized, otherwise, the L1 uplink is considered non-synchronized (in which case uplink transmission can only take place through MSG1 / MSGA).

[0118] RRC configures, for the maintenance of UL time alignment,timeAlignmentTimer(per TAG) which controls how long the MAC entity considers the Serving Cells belonging to the associated TAG to be uplink time aligned.

[0119] The MAC entity of the UE shall:

[0120] 1> when a Timing Advance Command MAC CE is received, and if an has been maintained with the indicated TAG:

[0121] 2> apply the Timing Advance Command for the indicated TAG;

[0122] 2> start or restart thetimeAlignmentTimerassociated with the indicated TAG.

[0123] 1> when a Timing Advance Command is received in a Random Access Response message for a Serving Cell belonging to a TAG or in a MSGB for an SpCell:

[0124] 2> if the Random Access Preamble was not selected by the MAC entity among the contention-based Random Access Preamble:

[0125] 3> apply the Timing Advance Command for this TAG;

[0126] 3> start or restart thetimeAlignmentTimerassociated with this TAG.

[0127] 2> else if thetimeAlignmentTimerassociated with this TAG is not running:

[0128] 3> apply the Timing Advance Command for this TAG;

[0129] 3> start thetimeAlignmentTimerassociated with this TAG;

[0130] 3> when the Contention Resolution is considered not successful; or

[0131] 3> when the Contention Resolution is considered successful for SI request, after transmitting HARQ feedback for MAC PDU including UE Contention Resolution Identity MAC CE:

[0132] 4> stoptimeAlignmentTimerassociated with this TAG.

[0133] 2> else:

[0134] 3> ignore the received Timing Advance Command.

[0135] 1> when an Absolute Timing Advance Command is received in response to a MSGA transmission including C-RNTI MAC CE:

[0136] 2> apply the Timing Advance Command for PTAG;

[0137] 2> start or restart thetimeAlignmentTimerassociated with PTAG.

[0138] 1> when atimeAlignmentTimerexpires:

[0139] 2> if thetimeAlignmentTimeris associated with the PTAG:

[0140] 3> flush all HARQ buffers for all Serving Cells;

[0141] 3> notify RRC to release PUCCH for all Serving Cells, if configured;

[0142] 3> notify RRC to release SRS for all Serving Cells, if configured;

[0143] 3> clear any configured downlink assignments and configured uplink grants;

[0144] 3> clear any PUSCH resource for semi-persistent CSI reporting;

[0145] 3> consider all runningtimeAlignmentTimers as expired;

[0146] 3> maintain of all TAGs.

[0147] 2> else if thetimeAlignmentTimeris associated with an STAG, then for all Serving Cells belonging to this TAG:

[0148] 3> flush all HARQ buffers;

[0149] 3> notify RRC to release PUCCH, if configured;

[0150] 3> notify RRC to release SRS, if configured;

[0151] 3> clear any configured downlink assignments and configured uplink grants;

[0152] 3> clear any PUSCH resource for semi-persistent CSI reporting;

[0153] 3> maintain of this TAG.

[0154] When the MAC entity stops uplink transmissions for an SCell due to the fact that the maximum uplink transmission timing difference between TAGs of the MAC entity or the maximum uplink transmission timing difference between TAGs of any MAC entity of the UE is exceeded, the MAC entity considers thetimeAlignmentTimerassociated with the SCell as expired.

[0155] The MAC entity shall not perform any uplink transmission on a Serving Cell except the Random Access Preamble and MSGA transmission when thetimeAlignmentTimerassociated with the TAG to which this Serving Cell belongs is not running. Furthermore, when thetimeAlignmentTimerassociated with the PTAG is not running, the MAC entity shall not perform any uplink transmission on any Serving Cell except the Random Access Preamble and MSGA transmission on the SpCell.

[0156] Hereinafter, a description will be given of mobility.

[0157] The mobility may comprise PCell change, PSCell change (or, secondary node (SN) change), and / or PSCell addition (or, SN addition).

[0158] In the present disclosure, the term "handover (HO)" may mean PCell change, or may be a broad concept that includes not only PCell change but also PSCell change / addition.

[0159] In the present disclosure, the terms "handover" and "mobility" can be used interchangeably.

[0160] In the present disclosure, the description regarding handover can also be applied to other mobility procedures (e.g., PSCell change / addition).

[0161] For example, there may be a mobility called L1 / L2-triggered mobility (LTM)(or, cell switch).

[0162] LTM is a procedure in which a gNB receives L1 or L3 measurement report(s) from a UE, and on their basis the gNB may change UE serving cell by a cell switch command signalled via a MAC CE. The cell switch command indicates an LTM candidate configuration that the gNB previously prepared and provided to the UE through RRC signalling. Then the UE switches to the target configuration according to the cell switch command. The LTM procedure can be used to reduce the mobility latency.

[0163] When configured by the network, it is possible to activate TCI states of one or multiple cells that are different from the current serving cell. For instance, the TCI states of the LTM candidate cells can be activated in advance before any of those cells become the serving cell. This allows the UE to be DL synchronized with those cells, thereby facilitating a faster cell switch to one of those cells when cell switch is triggered. All the activated TCI states except those received in the cell switch command are deactivated upon LTM cell switch execution.

[0164] When configured by the network, it is possible to initiate UL TA acquisition (called early TA) procedure of one or multiple cells that are different from the current serving cells. If the cell has the same NTA as the current serving cells or NTA=0, early TA acquisition procedure is not required. The network may request the UE to perform early TA acquisition of a candidate cell before a cell switch. The early TA acquisition procedure is triggered by PDCCH order or realized through UE-based TA measurement as configured by RRC. In the former case, the gNB / gNB-DU to which the candidate cell belongs calculates the TA value and sends it to the gNB / gNB-DU to which the serving cell belongs via gNB-CU. The serving cell sends the TA value in the LTM cell switch command MAC CE when triggering LTM cell switch. In the latter case, the UE performs TA measurement for the candidate cells after being configured by RRC but the exact time the UE performs TA measurement is up to UE implementation. The UE applies the TA value measured by itself and performs RACH-less LTM upon receiving the cell switch command, if it does not include any valid TA value. The network may also send a TA value in the LTM cell switch command MAC CE without early TA acquisition.

[0165] When two TAG IDs are configured for an LTM candidate cell, the gNB-DU to which the LTM candidate cell belongs assigns the same TAG ID pointer value for each TRP to be used by the UEs.

[0166] Depending on the availability of a valid TA value, the UE performs either a RACH-less LTM or RACH-based LTM cell switch. If the valid TA value is provided in the cell switch command, the UE applies the TA value as instructed by the network. In the case where UE-based TA measurement is configured, but no valid TA value is provided in the cell switch command, the UE applies the valid TA value by itself if available. The UE performs RACH-less LTM cell switch upon receiving the cell switch command whenever a valid TA value is available. If no valid TA value is available, the UE performs RACH-based LTM cell switch.

[0167] Regardless of whether the UE is configured for UE-based TA measurement for a certain candidate cell, it will still follow the PDCCH order, which includes performing a random access procedure towards one or more candidate cells.

[0168] This also applies to the candidate cells for which the UE is capable of deriving TA values by itself. Additionally, regardless of whether the UE has already performed a random access procedure towards the candidate cells, it will still follow the UE-based measurement configuration if configured by the network.

[0169] For RACH-less LTM, the UE accesses the target cell using either a configured grant or a dynamic grant. The configured grant is provided in the LTM candidate configuration, and the UE selects the configured grant occasion associated with the beam indicated in the cell switch command. Upon initiation of LTM cell switch to the target cell, the UE starts to monitor PDCCH on the target cell for dynamic scheduling. Before RACH-less LTM procedure completion, the UE shall not trigger random access procedure if it does not have a valid PUCCH resource for triggered SRs.

[0170] The following principles apply to LTM:

[0171] - Security keys are maintained upon an LTM cell switch;

[0172] - Subsequent LTM is supported.

[0173] LTM supports both intra-gNB-DU and inter-gNB-DU mobility within the same gNB-CU. LTM supports both intra-frequency and inter-frequency mobility, including mobility to inter-frequency cell that is not a current serving cell.

[0174] LTM is supported only for licensed spectrum. The following scenarios are supported:

[0175] - PCell change in non-CA scenario and non-DC scenario;

[0176] - PCell and SCell(s) change in CA scenario;

[0177] - Dual connectivity scenario: including PCell and MCG SCell(s) change and intra-SN PSCell and SCG SCell(s) change without MN involvement. LTM for simultaneous PCell and PSCell change is not supported.

[0178] While the UE has stored LTM candidate configurations the UE can also execute any L3 handover except for DAPS handover. In the RRC message which the UE applies for any L3 handover (except DAPS), LTM candidate configurations can be added / modified / released by the target cell.

[0179] Cell switch command is conveyed in a MAC CE, which contains the necessary information to perform the LTM cell switch.

[0180] The overall procedure for LTM is shown in FIG. 9 below. Subsequent LTM is done by repeating the early synchronization, LTM cell switch execution, and LTM cell switch completion steps without the need to release, reconfigure or add other LTM candidate configurations after each LTM cell switch completion.　The general procedure over the air interface may also be applicable to SCG LTM.

[0181] FIG. 9 shows an example of a signalling procedure for LTM.

[0182] Referring to FIG. 9, in step S901, the UE may send aMeasurementReportmessage to the gNB. The gNB decides to configure LTM and initiates LTM preparation.

[0183] In step S903, the gNB may transmit anRRCReconfigurationmessage to the UE including the LTM candidate cell configurations of one or multiple candidate cells. TheRRCReconfigurationmessage comprise an LTM configuration / cell switch configuration (e.g.,LTM-Config) comprising a list of LTM candidate configurations (e.g.,ltm-CandidateToAddModList) comprising one or more LTM candidate configurations (e.g.,ltm-Candidate). Each LTM candidate configuration may comprise a configuration of a corresponding candidate cell (e.g.,ltm-CandidateConfigcontainingRRCReconfiguration). That is, the network may configure the UE with one or more LTM candidate configurations within theLTM-ConfigIE.

[0184] In step S905, the UE may store the LTM configuration / cell switch configuration comprising the list of LTM candidate configurations, and transmit anRRCReconfigurationCompletemessage to the gNB.

[0185] In step S907, the UE may perform DL / UL synchronization with the LTM candidate cell(s) before receiving the cell switch command.

[0186] In some implementations, the UE may perform DL synchronization with the LTM candidate cell(s) before receiving the cell switch command. The UE may activate and deactivate TCI states of LTM candidate cell(s), as triggered by the gNB.

[0187] In some implementations, the UE may perform UL synchronization with LTM candidate cell(s) before receiving the cell switch command, by using UE-based timing advance (TA) measurement, if configured, and / or by transmitting a preamble towards the candidate cell, as triggered by the gNB. When UE-based TA measurement is configured, UE acquires the TA value(s) of the candidate cell(s) by measurement. UE performs early TA acquisition with the candidate cell(s) as requested by the network before receiving the cell switch command. This is done via CFRA triggered by a PDCCH order from the source cell, following which the UE sends preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE does not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. The UE does not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.

[0188] In step S9010, the UE may perform L1 measurements on the configured LTM candidate cell(s) and transmit L1 measurement reports to the gNB. L1 measurement should be performed as long as RRC reconfiguration (step S903) is applicable. The UE can also perform L3 measurement reporting to the gNB, including beam level measurement results on cell(s) which are configured as LTM candidate cell(s) according to the received network configuration.

[0189] In step S911, the gNB may decide to execute cell switch to a target cell and transmit an LTM cell switch command MAC CE triggering cell switch by including a target configuration ID which indicates the index of the candidate configuration of the target cell (e.g.,ltm-CandidateId), a beam indicated with a TCI state or beams indicated with DL and UL TCI states, and a timing advance command for the target cell, if available. The UE switches to the target cell and applies the candidate configuration (e.g.,ltm-CandidateConfig) indicated by the target configuration ID.

[0190] In step S913, the UE may perform the random access procedure towards the target cell, if UE does not have valid TA of the target cell. If UE has valid TA of the target cell, the UE may skip the random access procedure towards the target cell (i.e., RACH-less LTM).

[0191] When performing the random access procedure / RACH procedure: i) the UE may perform a contention-free random access (CFRA) if CFRA resources / dedicated RACH configuration is available to the UE; and ii) the UE may perform a contention-based random access (CBRA) if CFRA resources / dedicated RACH configuration is not available to the UE.

[0192] For the CBRA, the UE may transmit a random access preamble in uplink, to a RAN node. The UE may transmit a message 1 (MSG1) comprising the random access preamble to the RAN node. The random access preamble may be associated with a random access - radio resource temporary identifier (RA-RNTI). The random access preamble may be selected based on the selected RACH resources, and transmitted through a time / frequency resources identified by the selected RACH resources.

[0193] For the CFRA, the UE may transmit a dedicated random access preamble in uplink, to a RAN node. The UE may transmit an MSG1 comprising the dedicated random access preamble to the RAN node. The dedicated random access preamble may be associated with a RA-RNTI. The dedicated random access preamble may be selected based on the CFRA resources / dedicated RACH configuration, and transmitted through a time / frequency resources identified by the CFRA resources / dedicated RACH configuration.

[0194] In step S915, the UE may complete the LTM cell switch procedure by sendingRRCReconfigurationCompletemessage to target cell. If the UE has performed a RA procedure in step S913, the UE considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first UL data.

[0195] The steps S907 to S915 can be performed multiple times for subsequent LTM cell switch executions using the LTM candidate configuration(s) provided in step S903.

[0196] The procedure over the air interface described in FIG. 9 is applicable to both intra-gNB-CU / DU LTM and inter-gNB-CU / DU LTM.

[0197] Further, LTM may be executed conditionally, which may be referred to as　conditional LTM (CLTM). In CLTM, the UE may execute LTM without reception of an execution command (e.g., LTM cell switch command) from the network. Thus, for the execution of CLTM, when one or more L1 measurement event conditions (or, one or more L1 conditions) are configured, the UE may perform CLTM to a candidate cell based on at least one beam from a beam set configured for the candidate cell satisfying at least one of the one or more L1 measurement event conditions. For example, the L1 condition may comprise at least one of event LTM2, event LTM3, event LTM4, or event LTM5.

[0198] The overall procedure for CLTM is as shown in FIG. 10.

[0199] FIG. 10 shows an example of a signalling procedure for CLTM.

[0200] Referring to FIG. 10, in step S1001, the UE sends aMeasurementReportmessage to the gNB. The gNB decides to configure CLTM and initiates CLTM preparation.

[0201] In step S1003, the source gNB can request the candidate cells to provide conditional execution configurations and the candidate cells provide the conditional configuration including their own execution conditions, to be used in subsequent CLTM.

[0202] In step S1005, the source gNB sends anRRCReconfigurationmessage to the UE and this includes the CLTM configurations of candidate cells as well as the execution condition for the CLTM. TheRRCReconfigurationmessage may comprise an LTM configuration / cell switch configuration (e.g.,LTM-Config) comprising a list of LTM candidate configurations (e.g.,ltm-CandidateToAddModList) comprising one or more LTM candidate configurations (e.g.,ltm-Candidate). Each LTM candidate configuration may comprise a configuration of a corresponding candidate cell (e.g.,ltm-CandidateConfigcontainingRRCReconfiguration). That is, the network may configure the UE with one or more CLTM candidate configurations within theLTM-Config.

[0203] Each LTM candidate configuration may comprise a list of execution conditions for CLTM (e.g.,LTM-ExecutionConditionList) comprising one or more execution conditions for CLTM (e.g.,LTM-ExecutionCondition). Alternatively, each LTM candidate configuration may be included in the LTM configuration / cell switch configuration comprising the list of execution conditions for CLTM (e.g.,LTM-ExecutionConditionList, which is also referred to asltm-ServingCellExecutionConditionin this case). These LTM candidate configuration may be referred to as CLTM (candidate) configuration.

[0204] In step S1007, the UE stores the CLTM candidate configurations and transmits anRRCReconfigurationCompletemessage to the gNB. The UE starts evaluating the execution conditions based on the provided configuration.

[0205] In step S1009, the source gNB can trigger early synchronization (for example, based on the L1 or L3 measurement reports from the UE, if configured) to the UE and step S907 in FIG. 9 is applicable here as well. In addition, the source gNB can provide the TA value for each of the candidate cells the UE has performed UL synchronization with.

[0206] For example, the source gNB may provide the TA value for each CLTM candidate cell to the UE via LTM Candidate Timing Advance Command MAC CE. The LTM Candidate Timing Advance Command MAC CE may comprise at least one of:

[0207] - Candidate Config ID: This field indicates the index of the CLTM candidate configuration, corresponding toltm-CandidateIDminus 1. The length of the field is 3 bits;

[0208] - TI: If two TAGs are configured for the CLTM candidate cell indicated by Candidate Config ID, this field indicates one of the two TAGs to which the Timing Advance Command is applied. The field set to 0 indicates thetag2-Idand the field set to 1 indicates thetag-Idof the CLTM candidate cell. If two TAGs are not configured for the CLTM candidate cell indicated by the PDCCH order related to the received MAC CE, the reserved bit is present instead; or

[0209] - Timing Advance Command: This field indicates the index valueTAused to control the amount of timing adjustment that MAC entity has to apply when the UE switches to the candidate cell during CLTM. The length of the field is 12 bits.

[0210] The UE (or, MAC entity of the UE) shall for each CLTM candidate cell:

[0211] 1> when an LTM Candidate Timing Advance Command MAC CE is received:

[0212] 2> if two TAGs are configured for the CLTM candidate cell:

[0213] 3> store the TA value in the LTM Candidate Timing Advance Command MAC CE for the indicated CLTM candidate cell for the indicated TAG;

[0214] 3> start or restart theltm-TimeAlignmentTimerorltm-TimeAlignmentTimerTag2associated with the indicated LTM candidate cell for the indicated TAG;

[0215] 2> else:

[0216] 3> store the TA value in the LTM Candidate Timing Advance Command MAC CE for the indicated CLTM candidate cell;

[0217] 3> start or restart theltm-TimeAlignmentTimerassociated with the indicated LTM candidate cell.

[0218] If the UE receives more TA values than it can store, it is up to the UE implementation which TA values to store or discard.

[0219] 1> when the CLTM candidate configuration(s) or all execution condition(s) for a CLTM candidate configuration is released:

[0220] 2> stop the runningltm-TimeAlignmentTimerandltm-TimeAlignmentTimerTag2associated with the corresponding CLTM candidate cell(s), if any;

[0221] 2> release the stored TA value for the corresponding CLTM candidate cell(s), if any.

[0222] In step S1011, the CLTM execution condition (e.g.,ltm-ExecutionCondition) is satisfied at the UE and on the satisfied candidate LTM cell, the UE performs the CLTM switch by applying the configuration (e.g.,ltm-CandidateConfig / RRCReconfiguration) of the satisfied LTM candidate cell. If the UE has valid TA as part of the UL early synchronization from step S1009, the UE skips RACH. Otherwise, RACH is performed as part of the CLTM switch.

[0223] In step S1013, the UE completes the CLTM cell switch procedure by sendingRRCReconfigurationCompletemessage to the switched LTM cell as in step S915 from FIG. 9. The UE does not release any valid TA value(s) of LTM candidate cells with CLTM configuration.

[0224] The steps S1009 to S1013 can be performed multiple times for subsequent CLTM cell switch executions using the CLTM candidate configuration(s) provided in step S1005.

[0225] The following principles apply to CLTM:

[0226] - CLTM is supported for intra-gNB LTM and / or inter-gNB LTM;

[0227] - CLTM can be RACH-based or RACH-less. RACH-based CLTM includes CFRA and CBRA, and only CG based RACH-less CLTM is supported;

[0228] - Since there is no LTM cell switch command MAC CE reception for CLTM, the UE performs MAC reset as part of the CLTM execution.

[0229] Further, LTM may be executed subsequently, which may be referred to as subsequent LTM. The subsequent LTM may comprise repeating LTM execution / completion after each LTM execution / completion based on a corresponding candidate configuration without releasing the candidate configuration and / or other candidate configurations. That is, the subsequent LTM may refer to LTM that is performed without reconfiguration and / or re-initialization of the LTM preparation from a network after a previous LTM. For example, when a UE has received a plurality of candidate configurations, after the UE performs LTM based on a corresponding candidate configuration, the UE does not release the candidate configuration and / or other candidate configurations, and may perform a subsequent LTM based on a corresponding candidate configuration among the already received / configured candidate configurations without reconfiguration and / or re-initialization of the LTM preparation from the network (or, without receiving new candidate configurations from the network). This results in a reduction of the signalling overhead and / or interrupting time for LTM. The subsequent　LTM　can also be applied to　CLTM, which may be referred to as　subsequent CLTM.

[0230] The IEs in the LTM configuration / cell switch configuration (e.g.,LTM-Config) are shown in table 5:

[0231] LTM-Config-r18 ::= SEQUENCE {ltm-ReferenceConfiguration-r18 SetupRelease {ReferenceConfiguration-r18} OPTIONAL, -- Cond NR-DCltm-CandidateToReleaseList-r18 SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF LTM-CandidateId-r18 OPTIONAL, -- Need Nltm-CandidateToAddModList-r18 SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF LTM-Candidate-r18 OPTIONAL, -- Need Nltm-ServingCellNoResetID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need Nltm-CSI-ResourceConfigToAddModList-r18 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ResourceConfigurations-r18)) OF LTM-CSI-ResourceConfig-r18OPTIONAL, -- Need Nltm-CSI-ResourceConfigToReleaseList-r18 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ResourceConfigurations-r18)) OF LTM-CSI-ResourceConfigId-r18OPTIONAL, -- Need NattemptLTM-Switch-r18 ENUMERATED {true} OPTIONAL, -- Cond LTM-MCGltm-ServingCellUE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need N...,[[ltm-ServingCellNoSecurityChangeID-r19 LTM-NoSecurityChangeId-r19 OPTIONAL, -- Need Nltm-ServingCellExecutionCondition-r19 SetupRelease {LTM-ExecutionConditionList-r19} OPTIONAL -- Need M]]}

[0232] In table 5:

[0233] -ltm-ReferenceConfiguration: LTM reference configuration used to provide a configuration that is common, within the same cell group, to all configured non-complete LTM candidate configurations;

[0234] -ltm-CandidateToAddModList: a list of LTM candidate configurations (e.g.,LTM-Candidate(s)) related to candidate SpCells to be added or modified for LTM;

[0235] -ltm-CandidateToReleaseList: a list of LTM candidate configuration IDs (e.g.,LTM-CandidateId(s)) related to candidate SpCells to be removed;

[0236] -ltm-ServingCellNoResetID: serving cell ID based on which the UE determines whether a L2 reset is needed or not upon an LTM cell switch procedure;

[0237] -ltm-ServingCellUE-MeasuredTA-ID: serving cell ID based on which the UE determines whether UE-based TA measurements are needed or not;

[0238] -ltm-ServingCellNoSecurityChangeID: ID associated with the serving cell based on which the UE determines whether a security change is needed or not upon an LTM cell switch procedure.

[0239] -ltm-ServingCellExecutionCondition: This field can only be included within anltm-Configassociated with the MCG.

[0240] The IEs in the LTM configuration / cell switch configuration for NR-DC (e.g.,LTM-ConfigNRDC) are shown in table 6:

[0241] LTM-ConfigNRDC-r19 ::= SEQUENCE {ltm-ConfigurationSCG-r19 SetupRelease {LTM-Config-r18} OPTIONAL, -- Need Mltm-SK-CounterConfigToAddModList-r19 SEQUENCE (SIZE (1..maxSecurityCellSet-r18)) OF SK-CounterConfigLTM-r19 OPTIONAL, -- Need Nltm-SK-CounterConfigToReleaseList-r19 SEQUENCE (SIZE (1..maxSecurityCellSet-r18)) OF LTM-NoSecurityChangeId-r19 OPTIONAL, -- Need N...}

[0242] In table 6:

[0243] -ltm-ConfigurationSCG: the network does not configure this field in anRRCReconfigurationmessage within anLTM-ConfigIE andConditionalReconfigurationIE. The network does not configure this field in anRRCReconfigurationmessage contained innr-SCGor transmitted on SRB3.

[0244] The LTM candidate configuration / candidate configuration / candidate cell configuration (e.g.,LTE-Candidate) may be related to a candidate (target) cell. The IEs in the LTM candidate configuration / candidate configuration / candidate cell configuration (e.g.,LTE-Candidate) are shown in table 7:

[0245] LTM-Candidate-r18 ::= SEQUENCE {ltm-CandidateId-r18 LTM-CandidateId-r18,ltm-CandidatePCI-r18 PhysCellId OPTIONAL, -- Need Mltm-SSB-Config-r18 LTM-SSB-Config-r18 OPTIONAL, -- Need Mltm-CandidateConfig-r18 OCTET STRING (CONTAINING RRCReconfiguration) OPTIONAL, -- Need Mltm-ConfigComplete-r18 ENUMERATED {true} OPTIONAL, -- Need Rltm-EarlyUL-SyncConfig-r18 OCTET STRING (CONTAINING EarlyUL-SyncConfig-r18) OPTIONAL, -- Need Rltm-EarlyUL-SyncConfigSUL-r18 OCTET STRING (CONTAINING EarlyUL-SyncConfig-r18) OPTIONAL, -- Need Rltm-TCI-Info-r18 LTM-TCI-Info-r18 OPTIONAL, -- Need Mltm-NoResetID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need Mltm-UE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need M...,[[ltm-NoSecurityChangeID-r19 LTM-NoSecurityChangeId-r19 OPTIONAL, -- Need Mltm-ExecutionCondition-r19 SetupRelease {LTM-ExecutionConditionList-r19} OPTIONAL, -- Need Mltm-NZP-CSI-RS-ResourceToAddModList-r19 SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-Resources)) OF NZP-CSI-RS-ResourceOPTIONAL, -- Need Nltm-NZP-CSI-RS-ResourceToReleaseList-r19 SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-Resources)) OF NZP-CSI-RS-ResourceIdOPTIONAL, -- Need Nltm-NZP-CSI-RS-ResourceSetToAddModList-r19 SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourceSets)) OF NZP-CSI-RS-ResourceSetOPTIONAL, -- Need Nltm-NZP-CSI-RS-ResourceSetToReleaseList-r19 SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourceSets)) OF NZP-CSI-RS-ResourceSetIdOPTIONAL, -- Need Nltm-CSI-ReportConfigToAddModList-r19 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ReportConfigurations-r18)) OF LTM-CSI-ReportConfig-r18OPTIONAL, -- Need Nltm-CSI-ReportConfigToReleaseList-r19 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ReportConfigurations-r18)) OF LTM-CSI-ReportConfigId-r18OPTIONAL -- Need Nltm-CSI-IM-ResourceSetToAddModList-r19 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ReportConfigurations-r18)) OF CSI-IM-ResourceSetOPTIONAL, -- Need Nltm-CSI-IM-ResourceSetToReleaseList-r19 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ReportConfigurations-r18)) OF CSI-IM-ResourceSetIdOPTIONAL -- Need N]]}LTM-SSB-Config-r18 ::= SEQUENCE {ssb-Frequency-r18 ARFCN-ValueNR,subcarrierSpacing-r18 SubcarrierSpacing,ssb-Periodicity-r18 ENUMERATED {ms5, ms10, ms20, ms40, ms80, ms160, spare2, spare1} OPTIONAL, -- Need Rssb-PositionsInBurst-r18 CHOICE {shortBitmap BIT STRING (SIZE (4)),mediumBitmap BIT STRING (SIZE (8)),longBitmap BIT STRING (SIZE (64))} OPTIONAL, -- Need Rss-PBCH-BlockPower-r18 INTEGER (-60..50) OPTIONAL, -- Need R...}LTM-NoSecurityChangeId-r19 ::= INTEGER (1..maxNrofLTM-Configs-plus1-r18)

[0246] In table 7:

[0247] -ltm-CandidateId: an ID used to identify an LTM candidate configuration;

[0248] -ltm-CandidateConfig: a configuration of the related candidate cell for LTM, comprisingRRCReconfigurationmessage to be applied when LTM / cell switch is executed;

[0249] -ltm-ConfigComplete: if included in theLTM-Candidate, the UE may consider that the relatedltm-CandidateConfigis a complete configuration of the related candidate cell for LTM;

[0250] -ltm-NoResetID: if this field is equal toltm-ServingCellNoResetID, UE may determine that L2 reset is needed upon an LTM cell switch procedure;

[0251] -ltm-NoSecurityChangeID: ID associated with the corresponding candidate cell based on which the UE determines whether a security change is needed or not upon an LTM cell switch procedure. If the network configures this field for one LTM candidate configuration, the network configures also for all LTM candidate configurations withinltm-CandidateToAddModListinLTM-Configand ensures that the UE has stored a value forltm-ServingCellNoSecurityChangeIDwithinVarLTM-ServingCellNoSecurityChange.

[0252] -ltm-UE-MeasuredTA-ID: if this field is equal toltm-ServingCellNoResetID, UE may determine that the UE-based TA measurements are needed;

[0253] -ltmExecutionCondition: this field can only be included within anltm-Configassociated with the MCG;

[0254] -ltm-NZP-CSI-RS-ResourceToAddModList: pool of CSI-RS resources sets which can be referred to inNZP-CSI-RS-ResourceSet;

[0255] -ltm-NZP-CSI-RS-ResourceSetToAddModList: pool of CSI-RS resource set which can be referred to inLTM-CSI-RS-ResourceConfig; and

[0256] -ltm-CSI-ReportConfigToAddModList: configured CSI report settings for LTM.

[0257] The IEEarlyUL-SyncConfigmay be used to configure random access resources for the early UL synchronization procedure, and comprises IEs as shown in table 8:

[0258] EarlyUL-SyncConfig-r18 ::= SEQUENCE {frequencyInfoUL-r18 FrequencyInfoUL,rach-ConfigGeneric-r18 RACH-ConfigGeneric,bwp-GenericParameters-r18 BWP,ssb-PerRACH-Occasion-r18 ENUMERATED {oneEighth, oneFourth, oneHalf, one, two, four, eight, sixteen} OPTIONAL, -- Need Rprach-RootSequenceIndex-r18 CHOICE {l839 INTEGER (0..837),l139 INTEGER (0..137)} OPTIONAL, -- Need Rltm-PRACH-SubcarrierSpacing-r18 SubcarrierSpacing n-TimingAdvanceOffset-r18 ENUMERATED { n0, n25600, n39936, spare1 } OPTIONAL, -- Cond L139OPTIONAL, -- Need R...,[[ltm-tdd-UL-DL-ConfigurationCommon-r18 TDD-UL-DL-ConfigCommon ltm-restrictedSetConfig-r18 ENUMERATED {unrestrictedSet, restrictedSetTypeA, restrictedSetTypeB} OPTIONAL -- Need ROPTIONAL, -- Cond TDD]],[[ltm-TimeAlignmentTimer-r19 TimeAlignmentTimer ltm-TimeAlignmentTimerTag2-r19 TimeAlignmentTimer OPTIONAL, -- Need ROPTIONAL -- Cond 2TA]]}

[0259] In table 8:

[0260] -frequencyInfoUL: This field provides basic parameters of an uplink carrier for PRACH transmission on a candidate cell;

[0261] -ltm-PRACH-SubcarrierSpacing: Indicates subcarrier spacing of PRACH for LTM. The values are applicable depending on the used frequency. If absent, the UE applies the SCS as derived from theprach-ConfigurationIndexinRACH-ConfigGeneric;

[0262] -n-TimingAdvanceOffset: The to be applied for all uplink transmissions on a candidate cell;

[0263] -rach-ConfigGeneric: RACH parameters for performing a random access procedure on a candidate cell;

[0264] -ssb-PerRACH-Occasion: This field indicated the number of SSBs for RACH occasion; and / or

[0265] -ltm-TimeAlignmentTimerTag2: The TAT value for TAG with IDtag2-Id.

[0266] The IELTM-ExecutionConditionListmay be used to configure LTM cell switch conditions, and comprises IEs as shown in table 9:

[0267] LTM-ExecutionConditionList-r19 ::= SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF LTM-ExecutionCondition-r19LTM-ExecutionCondition-r19 ::= SEQUENCE {ltm-CandidateId-r19 LTM-CandidateId-r18,executionCondition-r19 CHOICE {l1-Conditions-r19 LTM-CSI-ReportConfigId-r18,l3-Conditions-r19 SEQUENCE (SIZE (1..2)) OF MeasId} OPTIONAL, -- Need R...}

[0268] For example, when one or more L1 conditions (e.g.,l1-Conditions) are configured, the UE may perform CLTM to a candidate cell based on a beam-level measurement result of at least one beam from a beam set configured for the candidate cell satisfying at least one of the one or more L1 conditions. The one or more L1 conditions may comprise at least one of LTM2 condition (or, event LTM2), LTM3 condition (or, event LTM3), LTM4 condition (or, event LTM4), or LTM5 condition (or, event LTM5).

[0269] The LTM2 condition　(e.g., Beam of SpCell becomes worse than absolute threshold) may include at least one of the following:

[0270] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of at least one beam from a beam set for the　SpCell　(or a serving cell)　becomes lower than a configured threshold; and / or

[0271] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0272] The　LTM3 condition　(e.g., Beam of candidate cell becomes amount of offset better than the beam of) may include at least one of the following:

[0273] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of at least one beam from a beam set for a　candidate cell　related to the corresponding　measurement object　is better that that of the SpCell by a predefined offset; and / or

[0274] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0275] The　LTM4 condition　(e.g., Beam of candidate cell becomes better than absolute threshold) may include at least one of the following:

[0276] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of at least one beam from a beam set for a　candidate cell　related to the corresponding　measurement object　is better than a configured threshold; and / or

[0277] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0278] The　LTM5 condition　(e.g., Beam of SpCell becomes worse than absolute threshold1 AND Beam of candidate cell becomes better than another absolute threshold2) may include at least one of the following:

[0279] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of at least one beam from a beam set for the SpCell becomes lower than threshold1, and a measurement result of at least one beam from a beam set for a　candidate cell　related to the corresponding　measurement object　is better than threshold2; and / or

[0280] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0281] For example, when one or more L3 conditions (e.g.,l3-Conditions) are configured, the UE may perform CLTM to a candidate cell based on a cell-level measurement result obtained by applying filtering on measurement results of multiple beams from a beam set configured for the candidate cell satisfying at least one of the one or more L3 conditions.

[0282] The one or more L3 conditions may comprise at least one of A2 condition (or, event A2), A3 condition (or, event A3), A4 condition (or, event A4) or A5 condition (or, event A5).

[0283] The A2 condition　(e.g., Serving becomes worse than threshold) may include at least one of the following:

[0284] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of the　SpCell　(or a serving cell) related to the corresponding　measurement object　becomes lower than a configured threshold; and / or

[0285] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0286] The　A3 condition　(e.g., Neighbor becomes offset better than SpCell) may include at least one of the following:

[0287] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of a　candidate cell　related to the corresponding　measurement object　is better than the SpCell by a predefined offset; and / or

[0288] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0289] The　A4 condition　(e.g., Neighbor becomes better than threshold) may include at least one of the following:

[0290] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of a　candidate cell　related to the corresponding　measurement object　is better than a configured threshold; and / or

[0291] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0292] The　A5 condition　(e.g., SpCell becomes worse than threshold1 and Neighbor becomes better than threshold2) may include at least one of the following:

[0293] - a measurement result (e.g., reference signal received power (RSRP) / reference signal received quality (RSRQ)) of the SpCell becomes lower than threshold1, and a measurement result of a　candidate cell　related to the corresponding　measurement object　is better than threshold2; and / or

[0294] - the above-mentioned condition persists for at least a　time-to-trigger (TTT).

[0295] The　SpCell　may be a serving cell including at least one of a　PCell　or a　PSCell.

[0296] Meanwhile, UE can execute a CLTM cell switch toward a candidate cell without random access procedure, based on performing an early TA acquisition procedure. In this regard, at least one of the followings may be applied:

[0297] - time alignment timer (TAT i.e.,timeAlignmentTimer) for LTM / CLTM associated with a candidate cell may be started / re-started when UE receives TA value for the candidate cell sent by the MAC CE from the current serving cell.

[0298] - If the TAT for LTM / CLTM associated with a candidate cell is running, UE may consider the TA for the candidate cell is valid; if the TAT for LTM / CLTM associated with a candidate cell expires, UE may consider the TA for the candidate cell is invalid.

[0299] - If UE has valid TA value at the time of CLTM execution, UE may perform RACH-less CLTM; otherwise, UE performs RACH-based CLTM.

[0300] - The TAT for LTM / CLTM may be per-candidate configuration.

[0301] - The received TA values for LTM / CLTM associated with other candidate cells may be released or still valid at UE side upon CLTM execution.

[0302] - Absolute TA value may be included in the MAC CE for early TA acquisition procedure in LTM / CLTM.

[0303] - The candidate configuration ID (e.g.,ltm-CandidateId) may be included in the MAC CE for early TA acquisition procedure in LTM / CLTM. There may be one candidate configuration ID for one TA in one MAC CE.

[0304] For example, the source cell may order UE to transmit a random access (RA) preamble to a candidate cell and then the UE may transmit an RA preamble to the candidate cell. Upon receiving the RA preamble from the UE, the candidate cell may calculate uplink timing information (i.e., Timing Advance (TA)) and then forward the calculated uplink timing information to the source cell via network interfaces (e.g., F1AP, Xn). The candidate cell may not know which UE the calculated TA value is associated with. The source cell may transmit to the UE the TA value of the candidate cell via e.g., LTM Candidate TA Command MAC CE. Upon receiving the TA value of the candidate cell, the UE may start the corresponding TAT. The UE may execute RACH-less CLTM cell switch toward the candidate cell if the TAT for the candidate cell is running (i.e., TAT has not expired) when the corresponding execution condition(s) is met.

[0305] As described above, the target cell (or, candidate cell) may not know whether the TA is still valid at UE upon CLTM cell switch execution, whereas the UE maintains the TA of the target cell based on the TAT. This means that there may exist misalignment of the remaining time of TAT and / or TA validity between the UE and the target cell upon CLTM cell switch execution. Since the target cell does not have the remaining time of TAT and / or TA validity at UE side, the target cell may not provide to the UE a new TA command even if the remaining time of TAT and / or TA validity is too small. Consequently, the UE may need to initiate the random access procedure if uplink data occurs after the TAT expires, which can result in the UE interruption.

[0306] Therefore, the present disclosure provides various embodiments for maintenance of uplink time alignment in conditional mobility.

[0307] FIG. 11 shows an example of a method performed by a UE for maintenance of uplink time alignment in conditional mobility according to various embodiments of the present disclosure.

[0308] Referring to FIG. 11, in step S1101, the UE may receive a candidate configuration for cell switch related to a candidate cell. The candidate configuration may comprise one or more execution conditions for cell switch towards the candidate cell.

[0309] In step S1103, the UE may receive uplink timing information for the candidate cell.

[0310] In step S1105, the UE may apply the uplink timing information for the candidate cell and start a timer related to a validity of the uplink timing information.

[0311] In step S1107, the UE may transmit an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled. The uplink signal may comprise information for elapsed status of the timer (e.g., remaining TAT information).

[0312] According to various embodiments, the candidate configuration may comprise a timer value of the timer related to a time period during which the uplink timing information is valid.

[0313] According to various embodiments, the candidate configuration may comprise a threshold time within a time period of the timer. The information for elapsed status of the timer may comprise information informing that a condition related to the threshold time is satisfied. The condition related to the threshold time may comprise at least one of: a condition that the timer has elapsed more than or equal to the threshold time; or a condition that a remaining time of the timer is less than or equal to a duration from the threshold time until the timer expires.

[0314] According to various embodiments, the uplink signal comprising the information for elapsed status of the timer may be transmitted based on the condition related to the threshold time being satisfied.

[0315] According to various embodiments, the threshold time may be related to a threshold percentage of a timer value of the timer.

[0316] According to various embodiments, the information for elapsed status of the timer may comprise information for a remaining time of the timer.

[0317] According to various embodiments, the remaining time may be a duration from when at least one of the one or more execution conditions is fulfilled until the timer expires.

[0318] According to various embodiments, the remaining time may be a duration from when the uplink signal is transmitted until the timer expires.

[0319] According to various embodiments, the UE may receive, from a source cell, a command comprising information for a random access preamble. The UE may transmit, to the candidate cell, the random access preamble. The uplink timing information may comprise a TA value calculated based on the random access preamble.

[0320] According to various embodiments, the uplink timing information may be received from a source cell via a MAC CE (e.g., LTM Candidate Timing Advance Command MAC CE).

[0321] According to various embodiments, after transmitting the uplink signal comprising the information for elapsed status of the timer, the UE may receive, from the candidate cell, information for a TA value. The UE may apply the TA value for the candidate cell and restarting the timer related to a validity of the TA value.

[0322] According to various embodiments, the UE may apply an RRC reconfiguration for the candidate cell for executing cell switch to the candidate cell based on at least one of the one or more execution conditions being fulfilled. The RRC reconfiguration for the candidate cell may be included in the candidate configuration related to the candidate cell. The uplink signal may be an RRC reconfiguration complete message that is transmitted after the RRC reconfiguration is applied.

[0323] FIG. 12 shows an example of a signal flow between UE and network for maintenance of uplink time alignment in conditional mobility according to various embodiments of the present disclosure.

[0324] Referring to FIG. 12, in step S1201, a network node related to a source cell may transmit, to the UE, a candidate configuration for cell switch related to a candidate cell. The candidate configuration may comprise one or more execution conditions for cell switch towards the candidate cell.

[0325] In step S1203, the network node may transmit, to the UE, uplink timing information for the candidate cell.

[0326] In step S1205, the UE may apply the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information.

[0327] In step S1207, the UE may transmit an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled. The uplink signal may comprise information for elapsed status of the timer (e.g., remaining TAT information).

[0328] Hereinafter, detailed implementations regarding maintenance of uplink time alignment in conditional mobility are described.

[0329] According various embodiments of the present disclosure, UE may report candidate TA information associated with a target cell in conditional mobility (e.g., CLTM). For example, the UE may report the candidate TA information associated with the target cell during RACH-less conditional mobility execution (e.g., CLTM execution) toward the target cell. For example, the candidate TA information associated with the target cell may comprise at least one of the absolute TA value, the remaining TAT value, or a flag indicating that the remaining TAT value satisfies a condition (e.g., threshold-based condition). For UE reporting, the network may configure the UE with a threshold value for reporting. For example, when the UE is configured with a threshold as 80% of the TAT value until expiry (i.e., 80% of the TAT has elapsed toward expiry) for reporting the candidate TA information associated with the target cell, the UE may report the candidate TA information associated with the target cell to the target cell if the TAT has elapsed more than or equal to 80% of the TAT value until expiry.

[0330] The UE may receive a conditional mobility configuration (e.g.,LTM-Config) comprising one or more candidate configurations for conditional mobility (e.g.,LTM-Candidate). Each candidate configuration may comprise at least one of:

[0331] - Configuration for early uplink synchronization procedure (e.g.,EarlyUL-SyncConfig);

[0332] - Configuration for early downlink synchronization procedure (e.g.,LTM-SSB-Config);

[0333] - One or more execution conditions (e.g.,LTM-ExecutionConditionList); or

[0334] - Candidate TA related configuration.

[0335] For example, the candidate TA related configuration comprise at least one of:

[0336] - TAT value;

[0337] - Threshold for determining whether to report candidate TA information associated with a candidate cell / target cell during RACH-less conditional mobility execution. For example, UE may report the candidate TA information if the threshold-based condition is satisfied; or

[0338] - Flag indicating whether to report candidate TA information associated with a target cell during RACH-less conditional mobility execution. For example, UE may report the candidate TA information if the flag is true.

[0339] The candidate TA information associated with a target cell (to be reported to the target cell during RACH-less conditional mobility execution) may comprise at least one of:

[0340] - Candidate cell identifier;

[0341] - Absolute candidate TA value associated with the target cell; or

[0342] - Remaining TAT information.

[0343] For example, the remaining TAT information may comprise at least one of a remaining TAT value (e.g., in milli-seconds), or a flag indicating that the remaining TAT value satisfied a condition if the condition is configured.

[0344] UE may transmit the candidate TA information viaRRCReconfigurationCompletemessage or an uplink MAC CE.

[0345] In some implementations, when UE is configured with a threshold as 80% of the TAT value until expiry (i.e., 80% of the TAT has elapsed toward expiry) for reporting candidate TA information associated with a target cell, the UE may report the candidate TA information associated with the target cell to the target cell if the TAT has elapsed more than or equal to 80% of the TAT value until expiry. FIG. 13 illustrates this example.

[0346] FIG. 13 illustrates a first example of reporting candidate TA information.

[0347] Referring to FIG. 13, in step S1301, UE may be configured with CLTM. That is, UE may receive anRRCReconfigurationmessage comprising LTM configuration, where the LTM configuration may comprise one or more candidate configurations with LTM execution condition(s). The candidate configuration may include candidate TA relevant information (or, candidate TA related configuration) comprising a TAT value and / or a threshold for reporting candidate TA information toward a corresponding candidate / target cell during RACH-less CLTM cell switch. For example, the TAT value may be 10 msec and the threshold may be 80% of the TAT value until expiry (i.e., 80% of the TAT has elapsed toward expiry).

[0348] In step S1303, the UE may acquire a TA value of the candidate / target cell via RA-based early TA acquisition procedure. For example, the UE may receive, from the source cell, a PDCCH order for acquiring (early) TA of the candidate / target cell. Then, the UE may transmit, to the candidate / target cell, a message 1 (MSG1) comprising RA preamble indicated by the PDCCH order. The candidate / target cell may calculate the TA value based on the RA preamble, and indicate the calculated TA value to the source cell via central unit (CU). The source cell may transmit (LTM) candidate TA command MAC CE comprising the TA value to the UE.

[0349] In step S1305, upon receiving the TA value of the candidate / target cell, the UE may start the TAT based on the candidate configuration provided in step S1301. For example, the UE may start the TAT having the TAT value included in the candidate TA relevant information within the candidate configuration for the candidate / target cell.

[0350] In step S1307, the UE may detect / identify that an execution condition for the candidate / target cell is met 9 msec after the TAT is started.

[0351] In step S1309, the UE may send anRRCReconfigurationCompletemessage comprising candidate TA information to the candidate / target cell. For example, the candidate TA information may comprise a flag indicating that the TAT has elapsed more than or equal to 80% of the TAT value until expiry.

[0352] In step S1311, the candidate / target cell may send TA command MAC CE comprising a TA value to the UE in order to update the TA between the UE and the candidate / target cell.

[0353] In some implementations, the UE may report the remaining TAT value when RACH-less CLTM cell switch is performed.

[0354] FIG. 14 illustrates a second example of reporting candidate TA information.

[0355] Referring to FIG. 14, in step S1401, UE may be configured with CLTM. That is, UE may receive anRRCReconfigurationmessage comprising LTM configuration, where the LTM configuration may comprise one or more candidate configurations with LTM execution condition(s). The candidate configuration may include candidate TA relevant information (or, candidate TA related configuration) comprising a TAT value. For example, the TAT value may be 10 msec.

[0356] In step S1403, the UE may acquire a TA value of the candidate / target cell via RA-based early TA acquisition procedure. For example, the UE may receive, from the source cell, a PDCCH order for acquiring (early) TA of the candidate / target cell. Then, the UE may transmit, to the candidate / target cell, a message 1 (MSG1) comprising RA preamble indicated by the PDCCH order. The candidate / target cell may calculate the TA value based on the RA preamble, and indicate the calculated TA value to the source cell via central unit (CU). The source cell may transmit (LTM) candidate TA command MAC CE comprising the TA value to the UE.

[0357] In step S1405, upon receiving the TA value of the candidate / target cell, the UE may start the TAT based on the candidate configuration provided in step S1301. For example, the UE may start the TAT having the TAT value included in the candidate TA relevant information within the candidate configuration for the candidate / target cell.

[0358] In step S1407, the UE may detect / identify that an execution condition for the candidate / target cell is met 9 msec after the TAT is started.

[0359] In step S1409, the UE may send anRRCReconfigurationCompletemessage comprising candidate TA information to the candidate / target cell. For example, the candidate TA information may comprise the remaining TAT value (e.g., 1 msec).

[0360] In step S1411, the candidate / target cell may send TA command MAC CE comprising a TA value to the UE in order to update the TA between the UE and the candidate / target cell.

[0361] According to various embodiments, the UE may receive a configuration for one or more execution conditions for a first candidate cell. The UE may receive uplink timing information for the first candidate cell. The UE may start a timer for the uplink timing information for the first candidate cell. The UE may transmit an uplink signal for the cell switch toward the first candidate cell if an execution condition for the first candidate cell is met and if the timer for the uplink timing information for the first candidate cell is running. The uplink signal may comprise the remaining value of the timer for the uplink timing information for the first candidate cell.

[0362] Furthermore, the method in perspective of the communication device / UE described in the present disclosure (e.g., in FIG. 11) may be performed by the first wireless device 100 shown in FIG. 2 and / or the UE 100 shown in FIG. 3.

[0363] More specifically, the communication device / UE comprises at least one transceiver, at least processor, and at least one computer memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations.

[0364] The operations comprise: receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; receiving uplink timing information for the candidate cell; applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; and transmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled, wherein the uplink signal comprises information for elapsed status of the timer.

[0365] Furthermore, the method in perspective of the communication device / UE described in the present disclosure (e.g., in FIG. 11) may be performed by a software code 105 stored in the memory 104 included in the first wireless device 100 shown in FIG. 2.

[0366] More specifically, at least one computer readable medium (CRM) stores instructions that, based on being executed by at least one processor, perform operations comprising: receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; receiving uplink timing information for the candidate cell; applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; and transmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled, wherein the uplink signal comprises information for elapsed status of the timer.

[0367] Furthermore, the method in perspective of the communication device / UE described in the present disclosure (e.g., in FIG. 11) may be performed by control of the processor 102 included in the first wireless device 100 shown in FIG. 2 and / or by control of the processor 102 included in the UE 100 shown in FIG. 3.

[0368] More specifically, an apparatus configured to / adapted to operate in a wireless communication system (e.g., communication device / UE) comprises at least processor, and at least one computer memory operably connectable to the at least one processor. The at least one processor is configured to / adapted to perform operations comprising: receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; receiving uplink timing information for the candidate cell; applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; and transmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled, wherein the uplink signal comprises information for elapsed status of the timer.

[0369] Furthermore, the method in perspective of a network node described in the present disclosure (e.g., in FIG. 12) may be performed by the second wireless device 200 shown in FIG. 2. The network node may be related to a serving cell.

[0370] More specifically, the network node comprises at least one transceiver, at least processor, and at least one computer memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations.

[0371] The operations comprise: transmitting, to a user equipment (UE), a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; and transmitting, to the UE, uplink timing information for the candidate cell, wherein the UE is configured to perform operations comprising: applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; and transmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled, wherein the uplink signal comprises information for elapsed status of the timer.

[0372] The present disclosure may have various advantageous effects.

[0373] For example, the UE reports the candidate TA information associated with the target cell during RACH-less conditional mobility execution toward the target cell. By doing so, the target cell and the UE can continuously maintain valid UL synchronization without interruption. Consequently, it has the effect of reducing UE interruptions by reducing the occurrence probability of subsequent procedures (e.g., random access - scheduling request - buffer status report) that may occur when UL synchronization between UE and network is lost.

[0374] Advantageous effects which can be obtained through specific embodiments of the present disclosure are not limited to the advantageous effects listed above. For example, there may be a variety of technical effects that a person having ordinary skill in the related art can understand and / or derive from the present disclosure. Accordingly, the specific effects of the present disclosure are not limited to those explicitly described herein, but may include various effects that may be understood or derived from the technical features of the present disclosure.

[0375] Claims in the present disclosure can be combined in a various way. For instance, technical features in method claims of the present disclosure can be combined to be implemented or performed in an apparatus, and technical features in apparatus claims can be combined to be implemented or performed in a method. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in an apparatus. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in a method. Other implementations are within the scope of the following claims.

Claims

1.A method comprising:receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell;receiving uplink timing information for the candidate cell;applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; andtransmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled,wherein the uplink signal comprises information for elapsed status of the timer.2.The method of claim 1, wherein the candidate configuration comprises a timer value of the timer related to a time period during which the uplink timing information is valid.3.The method of claim 1, wherein the candidate configuration comprises a threshold time within a time period of the timer,wherein the information for elapsed status of the timer comprises information informing that a condition related to the threshold time is satisfied,wherein the condition related to the threshold time comprises at least one of:a condition that the timer has elapsed more than or equal to the threshold time; ora condition that a remaining time of the timer is less than or equal to a duration from the threshold time until the timer expires.4.The method of claim 3, the uplink signal comprising the information for elapsed status of the timer is transmitted based on the condition related to the threshold time being satisfied.5.The method of claim 3, wherein the threshold time is related to a threshold percentage of a timer value of the timer.6.The method of claim 1, wherein the information for elapsed status of the timer comprises information for a remaining time of the timer.7.The method of claim 6, wherein the remaining time is a duration from when at least one of the one or more execution conditions is fulfilled until the timer expires.8.The method of claim 6, wherein the remaining time is a duration from when the uplink signal is transmitted until the timer expires.9.The method of claim 1, further comprising:receiving, from a source cell, a command comprising information for a random access preamble;transmitting, to the candidate cell, the random access preamble,wherein the uplink timing information comprises a timing advance (TA) value calculated based on the random access preamble.10.The method of claim 1, wherein the uplink timing information is received from a source cell via a media access control (MAC) control element (CE).11.The method of claim 1, further comprising:after transmitting the uplink signal comprising the information for elapsed status of the timer, receiving, from the candidate cell, information for a timing advance (TA) value; andapplying the TA value for the candidate cell and restarting the timer related to a validity of the TA value.12.The method of claim 1, further comprising:applying a radio resource control (RRC) reconfiguration for the candidate cell for executing cell switch to the candidate cell based on at least one of the one or more execution conditions being fulfilled,wherein the RRC reconfiguration for the candidate cell is included in the candidate configuration related to the candidate cell, andwherein the uplink signal is an RRC reconfiguration complete message that is transmitted after the RRC reconfiguration is applied.13.The method of claims 1, wherein the UE is in communication with at least one of a mobile device, a network, or autonomous vehicles.14.A user equipment (UE) comprising:at least one transceiver;at least one processor; andat least one memory operatively coupled to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell;receiving uplink timing information for the candidate cell;applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; andtransmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled,wherein the uplink signal comprises information for elapsed status of the timer.15.An apparatus comprising:at least processor; andat least one memory operatively coupled to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell;receiving uplink timing information for the candidate cell;applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; andtransmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled,wherein the uplink signal comprises information for elapsed status of the timer.16.A non-transitory computer readable medium (CRM) having stored thereon a program code implementing instructions that, based on being executed by at least one processor, perform operations comprising:receiving a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell;receiving uplink timing information for the candidate cell;applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; andtransmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled,wherein the uplink signal comprises information for elapsed status of the timer.17.A method comprising:transmitting, to a user equipment (UE), a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; andtransmitting, to the UE, uplink timing information for the candidate cell,wherein the UE is configured to perform operations comprising:applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; andtransmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled,wherein the uplink signal comprises information for elapsed status of the timer.18.A network node comprising:at least one transceiver;at least one processor; andat least one memory operatively coupled to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising:transmitting, to a user equipment (UE), a candidate configuration for cell switch related to a candidate cell, wherein the candidate configuration comprises one or more execution conditions for cell switch towards the candidate cell; andtransmitting, to the UE, uplink timing information for the candidate cell,wherein the UE is configured to perform operations comprising:applying the uplink timing information for the candidate cell and starting a timer related to a validity of the uplink timing information; andtransmitting an uplink signal to the candidate cell, based on at least one of the one or more execution conditions being fulfilled,wherein the uplink signal comprises information for elapsed status of the timer.

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