WO2025199768A1

WO2025199768A1 - Devices and methods for communication

Info

Publication number: WO2025199768A1
Application number: PCT/CN2024/083919
Authority: WO
Inventors: Yingchao MAO; Gang Wang
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2024-03-26
Filing date: 2024-03-26
Publication date: 2025-10-02
Anticipated expiration: 2026-09-26

Abstract

Embodiments of the present disclosure provide a solution for mobility procedure. In a solution, a terminal device initiates a mobility procedure from a source cell to a target cell; in response to that the mobility procedure fails, reverts back to a set of user equipment (UE) variables used in the source cell, wherein the set of UE variables comprises at least one of: a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information.

Description

DEVICES AND METHODS FOR COMMUNICATION

FIELDS

Example embodiments of the present disclosure generally relate to the field of communication techniques and in particular, to devices and methods for mobility procedure.

BACKGROUND

L1/L2 Triggered Mobility (LTM) is a procedure in which a gNB receives L1 measurement report (s) from a user equipment (UE) , and on their basis the gNB changes UE’s serving cell by a cell switch command signaled via a MAC CE. The cell switch command indicates an LTM candidate cell configuration that the gNB previously prepared and provided to the UE through RRC signaling. Then the UE switches to the target cell according to the cell switch command. The LTM procedure can be used to reduce the mobility latency.

Further, random access channel-less (RACH-less) is supported in mobility procedures like LTM cell switch and handover. In particular, random access (RA) procedure can be skipped for handover procedure to reduce handover latency, interruption time and signalling overhead for several scenarios. For example, if UE-based TA measurement is configured, UE performs RACH-less mobility upon receiving the cell switch command. Alternatively, UE determines whether to access the target cell with the RA procedure depending on whether a TA value is provided in the cell switch command or handover command. For RACH-less mobility, the UE may access the target cell via configured grant or dynamic grant. For example, for RACH-less LTM, the UE may access the target cell via a configured grant provided in the LTM candidate cell configuration and select the configured grant occasion associated with the beam indicated in the cell switch command, or the UE may monitor physical downlink control channel (PDCCH) for dynamic scheduling from the target cell upon LTM cell switch.

SUMMARY

In general, embodiments of the present disclosure provide a solution on mobility.

In a first aspect, there is provided a terminal device. The terminal device comprises: a processor, configured to cause the terminal device to: initiate a mobility procedure from a source cell to a target cell; in response to that the mobility procedure fails, revert back to a set of user equipment (UE) variables used in the source cell, wherein the set of UE variables comprises at least one of: a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information.

In a second aspect, there is provided a terminal device. The terminal device comprises: a processor, configured to cause the terminal device to: determine that a random access channel (RACH) less mobility procedure is triggered; determine a carrier for the RACH-less mobility procedure; and in response to at least one condition being satisfied, initiate a RACH-based mobility procedure, wherein the at least one condition comprises that the carrier is not configured with a configured grant.

In a third aspect, there is provided a terminal device. The terminal device comprises: a processor, configured to cause the terminal device to: receive, from a network device, a configuration of a measurement gap; and transmit, to the network device, a first physical uplink shared channel (PUSCH) transmission during a RACH-less mobility procedure regardless of the measurement gap.

In a fourth aspect, there is provided a terminal device. The terminal device comprises: a processor, configured to cause the terminal device to: receive, from a network device, a mobility procedure command; and determine a timing advance group to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity in the mobility procedure command.

In a fifth aspect, there is provided a communication method performed by a terminal device. The method comprises: initiating a mobility procedure from a source cell to a target cell; in response to that the mobility procedure fails, reverting back to a set of user equipment (UE) variables used in the source cell, wherein the set of UE variables comprises at least one of: a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information.

In a sixth aspect, there is provided a communication method performed by a terminal device. The method comprises: determining that a random access channel (RACH) less mobility procedure is triggered; determining a carrier for the RACH-less mobility procedure; and in response to at least one condition being satisfied, initiating a RACH-based mobility procedure, wherein the at least one condition comprises that the carrier is not configured with a configured grant.

In a seventh aspect, there is provided a communication method performed by a terminal device. The method comprises: receiving, from a network device, a configuration of a measurement gap; and transmitting, to the network device, a first physical uplink shared channel (PUSCH) transmission during a RACH-less mobility procedure regardless of the measurement gap.

In an eighth aspect, there is provided a communication method performed by a terminal device. The method comprises: receiving, from a network device, a mobility procedure command; and determining a timing advance group to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity in the mobility procedure command.

In a ninth aspect, there is provided a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to carry out the method according to the fifth, sixth, seventh, or eighth aspect.

Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some example embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:

FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

FIG. 2 illustrates a signaling flow of handling mobility procedure failure in accordance with some embodiments of the present disclosure;

FIG. 3 illustrates a signaling flow of RACH-less mobility fallback to RACH-based mobility in accordance with some embodiments of the present disclosure;

FIG. 4 illustrates a signaling flow of RACH-less PUSCH transmission during measurement gap in accordance with some embodiments of the present disclosure;

FIG. 5A illustrates a signaling flow of indicting timing advance group (TAG) in accordance with some embodiments of the present disclosure;

FIG. 5B illustrates a signaling flow of mobility procedure termination in accordance with some embodiments of the present disclosure;

FIG. 6 illustrates a flowchart of a communication method implemented at a terminal device according to some example embodiments of the present disclosure;

FIG. 7 illustrates a flowchart of a communication method implemented at a terminal device according to some example embodiments of the present disclosure;

FIG. 8 illustrates a flowchart of a communication method implemented at a terminal device according to some example embodiments of the present disclosure;

FIG. 9 illustrates a flowchart of a communication method implemented at a terminal device according to some example embodiments of the present disclosure; and

FIG. 10 illustrates a simplified block diagram of an apparatus that is suitable for implementing example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein, the term ‘terminal device’ refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, internet of things (IoT) devices, Ultra-reliable and Low Latency Communications (URLLC) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, devices on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, devices for Integrated Access and Backhaul (IAB) , Space borne vehicles or Air borne vehicles in Non-terrestrial networks (NTN) including Satellites and High Altitude Platforms (HAPs) encompassing Unmanned Aircraft Systems (UAS) , eXtended Reality (XR) devices including different types of realities such as Augmented Reality (AR) , Mixed Reality (MR) and Virtual Reality (VR) , the unmanned aerial vehicle (UAV) commonly known as a drone which is an aircraft without any human pilot, devices on high speed train (HST) , or image capture devices such as digital cameras, sensors, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. The ‘terminal device’ can further has ‘multicast/broadcast’ feature, to support public safety and mission critical, V2X applications, transparent IPv4/IPv6 multicast delivery, IPTV, smart TV, radio services, software delivery over wireless, group communications and IoT applications. It may also incorporate one or multiple Subscriber Identity Module (SIM) as known as Multi-SIM. The term “terminal device” can be used interchangeably with a UE, a mobile station, a subscriber station, a mobile terminal, a user terminal or a wireless device.

The term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a next generation NodeB (gNB) , a transmission reception point (TRP) , a remote radio unit (RRU) , a radio head (RH) , a remote radio head (RRH) , an IAB node, a low power node such as a femto node, a pico node, a reconfigurable intelligent surface (RIS) , and the like.

The terminal device or the network device may have Artificial intelligence (AI) or Machine learning capability. It generally includes a model which has been trained from numerous collected data for a specific function, and can be used to predict some information.

The terminal or the network device may work on several frequency ranges, e.g., FR1 (e.g., 450 MHz to 6000 MHz) , FR2 (e.g., 24.25GHz to 52.6GHz) , frequency band larger than 100 GHz as well as Tera Hertz (THz) . It can further work on licensed/unlicensed/shared spectrum. The terminal device may have more than one connection with the network devices under Multi-Radio Dual Connectivity (MR-DC) application scenario. The terminal device or the network device can work on full duplex, flexible duplex and cross division duplex modes.

The embodiments of the present disclosure may be performed in test equipment, e.g., signal generator, signal analyzer, spectrum analyzer, network analyzer, test terminal device, test network device, channel emulator. In some embodiments, the terminal device may be connected with a first network device and a second network device. One of the first network device and the second network device may be a master node and the other one may be a secondary node. The first network device and the second network device may use different radio access technologies (RATs) . In some embodiments, the first network device may be a first RAT device and the second network device may be a second RAT device. In some embodiments, the first RAT device is eNB and the second RAT device is gNB. Information related with different RATs may be transmitted to the terminal device from at least one of the first network device or the second network device. In some embodiments, first information may be transmitted to the terminal device from the first network device and second information may be transmitted to the terminal device from the second network device directly or via the first network device. In some embodiments, information related with configuration for the terminal device configured by the second network device may be transmitted from the second network device via the first network device. Information related with reconfiguration for the terminal device configured by the second network device may be transmitted to the terminal device from the second network device directly or via the first network device.

As used herein, the singular forms ‘a’ , ‘an’ and ‘the’ are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term ‘includes’ and its variants are to be read as open terms that mean ‘includes, but is not limited to. ’ The term ‘based on’ is to be read as ‘at least in part based on. ’ The term ‘one embodiment’ and ‘an embodiment’ are to be read as ‘at least one embodiment. ’ The term ‘another embodiment’ is to be read as ‘at least one other embodiment. ’ The terms ‘first, ’ ‘second, ’ and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below.

In some examples, values, procedures, or apparatus are referred to as ‘best, ’ ‘lowest, ’ ‘highest, ’ ‘minimum, ’ ‘maximum, ’ or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, higher, or otherwise preferable to other selections.

As used herein, the term “resource, ” “transmission resource, ” “uplink resource, ” or “downlink resource” may refer to any resource for performing a communication, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

As used herein, the term “random access channel (RACH) ” used herein may refer to an uplink transmission channel used in a wireless communication system to allow a terminal device for setting up a connection with the network. The term “random access procedure” used herein may refer to a procedure where a terminal device establishes the connection with a network device. There may be a contention based random access procedure and a contention free random access procedure. The term “RACH-less mobility procedure” used herein may refer to a mobility procedure that is performed without RACH. The RACH-less mobility may include one or more of: an RACH-less LTM procedure, an RACH-less handover procedure, an RACH-less (non-terrestrial network) NTN procedure, or an RACH-less integrated access and backhaul, IAB. The term “RACH-based mobility procedure” used herein may refer to a mobility procedure that is performed based on a random access procedure. The RACH-based mobility may include one or more of: an RACH-based LTM procedure, an RACH-based handover procedure, an RACH-based (non-terrestrial network) NTN procedure, or an RACH-less integrated access and backhaul, IAB.

The term “configured grant (CG) ” used herein may refer to a mechanism for scheduling for uplink (UL) transmissions that eliminates the need to request and assign resources for each packet transmission by pre-allocating resources to the UE. Two types of transmission without dynamic grant. Configured grant Type 1 where an uplink grant is provided by RRC, and stored as configured uplink grant. For configured grant Type 1, once it is configured by RRC, it considers to be active. Configured grant Type 2 where an uplink grant is provided by PDCCH, and stored or cleared as configured uplink grant based on L1 signaling indicating configured uplink grant activation or deactivation. Configured grant Type 1 can be configured for LTM or handover.

The term “handover (HO) ” used herein may refer to a procedure that a serving cell of UE is changed from a current cell (i.e., a source cell) to another cell (i.e., a target cell) . In some embodiments, the handover may refer to layer 3 handover procedure. For example, the handover command may refer to RRC Reconfiguration message or reconfigurationwithsync signaling. The term “cell switch” used herein may refer to a procedure that the UE switches between cells. In some embodiments, the cell switch may refer to layer1/layer2 triggered mobility (LTM) cell switch.

The term “hybrid automatic repeat request (HARQ) ” used herein may refer to a combination of high-rate forward error correction (FEC) and automatic repeat request (ARQ) error-control, which is implemented to correct the erroneous packets coming from physical layer. The term “HARQ process” may refer to a stop-and-wait process that is used to transmit data. Each HARQ process has an independent HARQ buffer. The term “buffer flushing” used herein may refer to a mechanism that delete data stored in a buffer.

The term “radio link control (RLC) ” used herein may refer to a layer 2 protocol used on an air interface. The RLC layer can provide a full reliable transport service for selected transmissions. The term “packet data convergence protocol (PDCP) ” used herein may refer to a layer that lies between a radio resource control (RRC) on upper side and radio link control (RLC) on lower side of a control protocol stack. PDCP layer provides services to the upper layers that are, RRC or service data adaptation protocol (SDAP) and takes services and inputs from the RLC layer, medium access control (MAC) layer, and physical (PHY) layer.

In some solutions, LTM and layer 3 (L3) handover can be co-existence. For LTM, parameters ltm-servingCellNoResetID and/or ltm-NoResetID can be used by the terminal device 110 to determine on whether L2 reset should be performed when an LTM cell switch procedure is triggered towards an LTM candidate cell. However, the network cannot configure this after the L3 HO, which may result the UE performs the L2 behavior incorrectly for the subsequent LTM after the L3 HO or LTM fast recovery after L3 HO failure, resulting LTM or handover failure. Similarly, for UE based TA measurement, the parameters or field ltm-ServingCellUE-MeasuredTA-ID and/or ltm-MeasuredTA-ID can be used by the UE to determine whether UE-based TA measurements should be performed towards a mobility target cell or candidate cell. However, if the network not configure this after handover, e.g., L3 handover, which may result the UE performs the UE based TA measurement behavior incorrectly for the subsequent LTM or LTM fast recovery procedure, resulting LTM or handover failure.

In some solutions, if the LTM or HO failure, the UE revert back to the UE configuration used in the source PCell, the UE configuration includes state variables and parameters of each radio bearer. But the UE variable is not included in the UE configuration. If UE performs the LTM fast recovery, it may result the UE performs the L2 behavior incorrectly.

In some other solutions, for RACH-less LTM cell switch or handover procedure, the configured grant may be configured on normal uplink (NUL) and/or supplementary uplink (SUL) . However, UE may select the carrier which is not configured with CG. In this case, the UE can only wait for DG and/or until the LTM or handover supervisor timer (e.g., t304 or t304a) expired trigger the RRC reestablishment. This may result the latency increment or failure for mobility procedure.

In some further solutions, if a random access procedure is skipped for mobility procedures (i.e. RACH-less) like LTM cell switch or handover, the configured UL grant can be used for first PUSCH transmission for mobility procedure if it is configured. However, if the UE is configured with measurement gap, the UE is not able to transmit UL-SCH except msg3 or MSGA during the measurement gap period, i.e., the first PUSCH transmission can not be transmitted during the measurement gap. This results in latency increment for LTM cell switch.

Therefore, solutions on mobility procedures are proposed. Principles and implementations of the present disclosure will be described in detail below with reference to the figures.

FIG. 1 illustrates a schematic diagram of an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, a plurality of communication devices, including a terminal device 110 and a network device 120, can communicate with each other.

In the example of FIG. 1, the terminal device 110 may be a UE and the network device 120 may be a base station serving the UE. The serving area of the network device 120 may be called a cell 101. In some embodiments, the terminal device 110 may perform a mobility procedure from the cell 101 to another cell (for example, the cell 102) . For example, the mobility procedure may include at least one of: an LTM cell switch procedure, a conditional LTM cell switch procedure, a handover procedure, or a conditional handover procedure.

It is to be understood that the number of devices and their connections shown in FIG. 1 are only for the purpose of illustration without suggesting any limitation. The communication environment 100 may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices may be located in the cell 102, and one or more additional cells may be deployed in the communication environment 100. It is noted that although illustrated as a network device, the network device 120 may be another device than a network device. Although illustrated as a terminal device, the terminal device 110 may be other device than a terminal device.

In the following, for the purpose of illustration, some example embodiments are described with the terminal device 110 operating as a UE and the network device 120 operating as a base station. However, in some example embodiments, operations described in connection with a terminal device may be implemented at a network device or other device, and operations described in connection with a network device may be implemented at a terminal device or other device.

In some example embodiments, if the terminal device 110 is a terminal device and the network device 120 is a network device, a link from the network device 120 to the terminal device 110 is referred to as a downlink (DL) , while a link from the terminal device 110 to the network device 120 is referred to as an uplink (UL) . In DL, the network device 120 is a transmitting (TX) device (or a transmitter) and the terminal device 110 is a receiving (RX) device (or a receiver) . In UL, the terminal device 110 is a TX device (or a transmitter) and the network device 120 is a RX device (or a receiver) .

The communications in the communication environment 100 may conform to any suitable standards including, but not limited to, Global System for Mobile Communications (GSM) , Long Term Evolution (LTE) , LTE-Evolution, LTE-Advanced (LTE-A) , New Radio (NR) , Wideband Code Division Multiple Access (WCDMA) , Code Division Multiple Access (CDMA) , GSM EDGE Radio Access Network (GERAN) , Machine Type Communication (MTC) and the like. The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-Advanced networks, or the sixth generation (6G) networks.

Reference is made to FIG. 2, which illustrates a signaling flow 200 of handling mobility procedure failure in accordance with some embodiments of the present disclosure. For the purposes of discussion, the signaling flow 200 will be discussed with reference to FIG. 1, for example, by using the terminal device 110 and the network device 120.

The terminal device 110 initiates (2020) a mobility procedure from a source cell to a target cell. For example, the mobility procedure may be from the cell 101 (i.e., sourc cell) to the cell 102 (i.e., target cell) . In some embodiments, the source cell may be a source primary cell (Pcell) . Alternatively, the source cell may be a source primary secondary cell (PScell) . Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

In some embodiments, the mobility procedure may be a handover from the cell 101 to the cell 102. In some other embodiments, the mobility procedure may be a cell switch from the cell 101 to the cell 102. For example, the cell switch may refer to a LTM cell switch. In some embodiments, the mobility procedure may be triggered by the network device 120. Alternatively, the mobility procedure may be triggered by the terminal device, if a condition is satisfied.

The terminal device 110 may determine (2025) whether the mobility procedure fails. For example, if a timer (such as T304) expires or reconfiguration with sync failure during the mobility handover, the terminal device 110 may determine that the mobility procedure fails.

If the mobility procedure fails, the terminal device 110 reverts (2030) back to a set of UE variables used in the source cell. In other words, the terminal device 110 reverts back to the set of UE variables related to the source cell. The set of UE variables includes one or more of: a UE variable related to layer 2 (L2) reset information or a UE variable related to timing advance (TA) measurement information. In this way, it can ensure the UE correctly execution of L2 reset and/or UE based TA measurement, to ensure successful LTM cell switch or HO or fast recovery.

In some embodiments, the layer 2 reset information can be used by the terminal device 110 to determine on whether L2 reset or how the L2 reset should be performed when a mobility procedure is triggered. In some embodiments, the layer 2 reset information may include a serving cell layer 2 no reset identity which is used to determine whether the RLC re-establish and PDCP data recovery should be performed during the mobility procedure. Alternatively, or in addition, the layer 2 reset information may include a first identity, e.g., a serving cell layer 2 full reset identity, which is used to determine whether the RLC re-establish and PDCP re-establish should be performed during the mobility procedure. For example, the L2 reset information may include the intra-central unit (CU) L2 reset or inter-CU L2 reset information. For intra-CU L2 reset, the layer 2 reset information may include MAC reset and RLC reestablishment and PDCP data recovery, or include only MAC reset. For inter-CU L2 reset, including MAC reset, the layer 2 reset information may RLC re-establish and PDCP re-establish. By way of example, the L2 reset information may include ltm-ServingCellNoResetID and/or ltm-ServingCellFullResetID, or L2 reset information may include ltm-NoResetID and/or ltm-FullResetID.

In some embodiments, if the L2 reset information include a serving cell layer 2 no reset identity in UE variable is same as the L2 reset information in target cell during the mobility procedure, the terminal device 110 skips performing the RLC reestablish and PDCP recovery. If the L2 reset information include a serving cell layer 2 no reset identity in UE variable is different from the L2 reset information in target cell during the mobility procedure, the terminal device 110 performs the RLC reestablish and PDCP recovery. In addition, the terminal device 110 performs the MAC reset during the mobility procedure. For example, if the ltm-ServingCellNoResetID in UE variable is different from the ltm-NoResetID in target cell, the terminal device 110performs the RLC reestablish and PDCP recovery. In some embodiments, if the L2 reset information include a first identity (e.g., a serving cell layer 2 full reset identity) in UE variable is different from the identity in target cell, the terminal device 110 mayperform the RLC reestablish and PDCP reestablish. Alternatively, if the first identity in UE variable is same as the identity in target cell, the terminal device 110 further performs the L2 reset based on the serving cell layer 2 no reset identity. For example, if the ltm-ServingCellFullResetID in UE variable is same as the ltm-FullResetID in target cell, and the ltm-ServingCellNoResetID in UE variable is different from the ltm-NoResetID in target cell, the terminal device 110 performs the RLC reestablish and PDCP recovery.

In some other embodiments, the TA measurement information can be used by the terminal device 110 to determine whether UE-based TA measurements should be performed towards a mobility target cell or candidate cell. For example, the TA measurement information comprises a serving cell measurement TA identity. If the serving cell measurement TA identity in target cell same as the serving cell measurement TA identity in UE variable, the terminal device 110 may perform the UE based TA measurement for this target cell. By way of example, the UE based TA measurement information may include ltm-ServingCellUE-MeasuredTA-ID or ltm-UE-MeasuredTA-ID.

In an example embodiment, the set of UE variables may include an information element (IE) VarLTM-ServingCellNoResetID that is used to store the serving cell ID based on which the terminal device 110 determines whether a L2 reset is needed or not upon an LTM cell switch procedure. Alternatively, or in addition, the set of UE variables may include an IE VarLTM-ServingCellUE-MeasuredTA-ID which is used to store the serving cell ID based on which the terminal device 110 determines whether UE-based TA measurements are needed or not upon an LTM cell switch procedure. The set of UE variables may include an IE VarLTM-ServingCellFullResetID which is used to store the serving cell ID based on which the terminal device 110 determines whether a L2 full reset is needed or not upon an LTM cell switch procedure. In some example embodiment, L2 full reset may include RLC reestablish and PDCP reestablish.

In some embodiments, if the mobility procedure fails, the terminal device 110 reverts (2030) back to the UE variable VarLTM-ServingCellNoResetID and/or VarLTM- ServingCellFullResetID and/or VarLTM-ServingCellUE-MeasuredTA-ID used in the source cell. In other words, the terminal device 110 reverts back to the UE variable VarLTM-ServingCellNoResetID and/or VarLTM-ServingCellFullResetID and/or VarLTM-ServingCellUE-MeasuredTA-ID related to the source cell.

In some embodiments, if the mobility procedure fails, the terminal device 110 may revert back UE configuration used in the source cell. The set of UE variables may be part of the UE configuration used in the source cell. For example, the UE configuration includes the variables of VarLTM-ServingCellNoResetID, VarLTM-ServingCellFullResetID, or VarLTM-ServingCellUE-MeasuredTA-ID.

Table 1 below shows an example procedure of reverting back to UE variables.

Table 1

In some embodiments, the layer 2 reset information and/or TA measurement information may be mandatory present, if the network device 120 transmits (2010) a RRC reconfiguration which includes at least one LTM candidate configuration to the terminal device 110. In this way, it can the correct execution of layer 2 reset and/or TA measurement.

In some embodiments, if the mobility procedure is an LTM cell switch procedure, at least one of: the layer 2 reset information or the TA measurement information may be present in a LTM configuration included in a RRC reconfiguration under a certain condition. In other words, the layer 2 reset information and/or the TA measurement information may be mandatory present in the LTM configuration included in the RRC reconfiguration under a certain condition. For example, the condition may include one or more of: the RRC reconfiguration message includes the LTM configuration with at least one LTM candidate configuration, the RRC reconfiguration message is used to configure a handover candidate cell or target cell and the terminal device is configured with a LTM candidate cell, or the RRC reconfiguration message is used to configure a handover and values of layer 2 reset information or TA measurement information for the source and target cells are different if the terminal device is configured with LTM candidate cell. By way of example, the field including the layer 2 reset information and/or the TA measurement information is mandatory present in the LTM-Config in the RRC Reconfiguration message which first includes the LTM-config with at least one LTM candidate configuration. Alternatively, the filed may be mandatory present in the RRC Reconfiguration which is used to configure (L3) handover/conditional handover candidate cell and the LTM-Config set to “setup” (or if the terminal device 110 is configured with LTM candidate cell and/or LTM candidate is not released) . Otherwise, the field is absent or optional. In some other embodiments, the filed may be mandatory present in RRC Reconfiguration which is used to configure (L3) handover and the value of this field for source and (L3) handover target/candidate cell is different in case the terminal device 110 is configured with LTM candidate. Table 2 shows an example of LTM-Config IE. It is noted that Table 2 is only an example not limitation. Table 3 shows an example of the present condition “Cond LTM” .

Table 2

Table 3

Alternatively, or in addition, if the mobility procedure is an LTM cell switch procedure, the layer 2 reset information and/or the TA measurement information may be present in the RRC reconfiguration message under a certain condition. Examples of the condition are described above, which are omitted here. In some embodiments, the field including the layer 2 reset information and/or the TA measurement information is mandatory present in RRC Reconfiguration message which first include the LTM-config with at least one LTM candidate configuration. Alternatively, the filed may be mandatory present in RRC Reconfiguration which is used to configure (L3) handover/conditional handover candidate cell and the LTM-Config set to “setup” (or if the terminal device 110is configured with LTM candidate cell and/or LTM candidate is not released) . Otherwise, the field is absent or optional. Table 4 shows an example of RRC reconfiguration message. It is noted that Table 4 is only an example not limitation. Table 5 shows an example of the present condition LTM.

Table 4

Table 5

In some embodiments, the above mentioned RRC reconfiguration message be a handover command. In some other embodiments, the RRC reconfiguration may be an L3 handover command.

In some embodiments, if the RRC reconfiguration message includes L2 reset information, the terminal device 110 may replace a value of L2 reset information in the set of UE variables with a value of L2 reset information in the RRC reconfiguration message. Alternatively, the terminal device 110 may store the L2 reset information in the set of UE variables. For example, if the RRC Reconfiguration includes the L2 reset information, the terminal device 110 may replace the value of L2 reset information in UE variable with the value of L2 reset information in RRC Reconfiguration message or store the L2 reset information in the UE variable. In other words, if the terminal device 110 is configured with LTM candidate cell or if the RRC Reconfiguration includes the ltm-Config is set to setup, if the RRC Reconfiguration includes the L2 reset information, the terminal device 110 may replace the value of L2 reset information in UE variable with the value of L2 reset information in RRC Reconfiguration or store the L2 reset information in the UE variable. Otherwise, the terminal device 110 may ignore the L2 reset information in RRC Reconfiguration.

In some embodiments, if the RRC reconfiguration message includes TA measurement information, the terminal device 110 may replace a value of TA measurement information in the set of UE variables with a value of TA measurement information in RRC reconfiguration message. Alternatively, the terminal device 110 may store the value of TA measurement information in the set of UE variables. For example, if the RRC Reconfiguration includes the UE based TA measurement information, the terminal device 110 may replace the value of UE based TA measurement information in UE variable with the value of UE based TA measurement information in RRC Reconfiguration or store the UE based TA measurement information in the UE variable. In other words, if the terminal device 110 is configured with LTM candidate cell or if the RRC Reconfiguration includes the ltm-Config is set to setup, if the RRC Reconfiguration includes the TA measurement information, the terminal device 110 may replace the value of TA measurement information in UE variable with the value of TA measurement information in RRC Reconfiguration or store the TA measurement information in the UE variable. Otherwise, the terminal device 110 may ignore the TA measurement information in RRC Reconfiguration.

Reference is made to FIG. 3, which illustrates a signaling flow 300 of RACH-less mobility fallback to RACH-based mobility in accordance with some embodiments of the present disclosure. For the purposes of discussion, the signaling flow 300 will be discussed with reference to FIG. 1, for example, by using the terminal device 110 and the network device 120.

The network device 120 may transmit (3005) a mobility command to the terminal device 110. For example, the mobility command may be a command for LTM or handover procedure.

The terminal device 110 determines (3010) a RACH-less mobility procedure from a source cell to a target cell is triggered. Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

In some embodiments, the network device 120 may transmit (3005) a mobility command to the terminal device 110. In this case, the terminal device 110 may determine that the RACH-less mobility procedure is triggered based on the reception (3005) of the mobility command. Alternatively, or in addition, if the terminal device 110 has a valid timing advance for a target cell (for example, the cell 102) , the terminal device 110 may determine that the RACH-less mobility procedure is triggered. In some other embodiments, if a condition for RACH-less mobility is satisfied, the terminal device 110 determines that the RACH-less mobility procedure is triggered.

In some embodiments, upon the reception of the mobility command, such as LTM cell switch command or handover command, if the timing advance or timing advance command or rach-less indication is included in the mobility command, or if the valid TA is measured by UE based TA measurement, the terminal device 110 may determine that the RACH-less mobility procedure is triggered.

The terminal device 110 determines (3020) a carrier for the RACH-less mobility procedure. In some embodiments, the terminal device 110 may reuse the rsrp-rsrp- ThresholdSSB-SUL for carrier selection for RACH-less LTM or handover. Alternatively, in some example embodiments, the S/U field in LTM cell switch common may indicate which UL carrier to transmit the first PUSCH of the RACH-less LTM on configured uplink grant. In this case, if the value of this field is set to 1, SUL may be used. Otherwise, NUL may be used. The length of the field may be 1 bit. If the MAC entity receives the LTM Cell Switch Command MAC CE or RRC handover command, the carrier may be determined or selected based on the rsrp-rsrp-ThresholdSSB-SUL threshold or indication in LTM command MAC CE. In some embodiments, for RACH-less LTM or RACH-less handover procedure, the terminal device 110 or a MAC entity of the terminal device 110 may select the SSB and determine whether the configured uplink grant is valid on the selected carrier.

In some embodiments, a timer may be used to control a time duration regarding the fallback from the RACH-less mobility procedure to a RACH-based mobility procedure. In some embodiments, the terminal device 110 may start the timer after or upon the reception of the mobility procedure command. For example, the terminal device 110 may determine (3020) the carrier after reception of the mobility command or after starting the timer. If the carrier is configured with CG, the terminal device may stop the timer. Alternatively, if the terminal device 110 receives downlink control information (DCI) for dynamic grant, the terminal device 110 may stop the timer. For example, if a physical downlink control channel (PDCCH) addressed to the MAC entity's cell-radio network temporary identity (C-RNTI) has been received and the timer is running, the terminal device 110 may stop the timer.

Alternatively, after determining (3020) the carrier, the terminal device 110 may start the timer, if the carrier is not configured with the configured grant. In this case, in some embodiments, if the terminal device 110 receives the DCI for dynamic grant, the timer is stopped.

The terminal device 110 determines (3030) whether at least one condition is satisfied. The at least one condition includes that the carrier is not configured with a configured grant. In some embodiments, if the timer is used to control the time duration regarding the fallback from the RACH-less mobility procedure to a RACH-based mobility procedure, the at least one condition may include an expiration of a timer. Alternatively, if the RACH-less mobility procedure is a conditional mobility procedure, the at least one condition may include no synchronization signal block (SSB) with reference signal received power (RSRP) being above a threshold.

The terminal device 110 initiates (3040) a RACH-based mobility procedure, if the at least one condition is satisfied. In this way, it can improve the success rate of cell switch or handover and reduce latency of cell switch or handover.

In some embodiments, if the timer expires, the terminal device 110 may initiate the RACH-based mobility procedure. Alternatively, if the carrier is not configured with the configured grant or no SSB with RSRP being above the threshold, the terminal device 110 may initiate the RACH-based mobility procedure. In some other embodiments, if the carrier is configured with the configured grant and the terminal device 110 has a valid timing advance, the terminal device 110 may initiate the RACH-less mobility procedure. In some example embodiments, if the evaluation condition for conditional mobility is satisfied, and if the configured grant is configured on the selected carrier, if the terminal device 110 has the valid TA for target cell, the terminal device 110 may consider the conditional RACH-less LTM or conditional handover is on-going. Otherwise, the terminal device 110 may trigger the RACH-based conditional LTM or handover. In other words, if the selected carrier is not configured with configured grant, the terminal device 110 fallback to or initiate RACH-based mobility procedure. In some embodiments, if the RACH-less mobility is triggered or on-going, if there is no SSB with RSRP above the threshold, the terminal device 110 fallback to RACH-based procedure.

Reference is made to FIG. 4, which illustrates a signaling flow 400 of first PUSCH transmission of RACH-less mobility procedure during measurement gap in accordance with some embodiments of the present disclosure. For the purposes of discussion, the signaling flow 400 will be discussed with reference to FIG. 1, for example, by using the terminal device 110 and the network device 120.

The network device 120 transmits (4010) a configuration of a measurement gap to the terminal device 110. For example, the configuration of the measurement gap may indicate a start time and a length of the measurement gap, or further indicate the periodicity of the measurement. Alternatively, the configuration of the measurement gap may indicate a start time and ending time of the measurement gap.

The network device 120 transmits (4020) a first PUSCH transmission of a RACH-less mobility procedure regardless of the measurement gap. For example, the RACH-less mobility procedure may be a RACH-less LTM cell switch procedure or a RACH-less conditional LTM cell switch procedure. Alternatively, the RACH-less mobility procedure may be a RACH-less handover procedure or a RACH-less conditional handover procedure. In some example embodiments, during the measurement gaps, the terminal device 110 can transmit the first PUSCH payload if there is on-going RACH-less LTM or RACH-less handover or conditional RACH-less LTM or conditional handover. In this way, it can shorten the latency of LTM cell switch.

The RACH-less mobility may be from a source cell to a target cell. Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

In some embodiments, the terminal device 110 may skip PUSCH transmission within the measurement gap except for one or more of: a PUSCH transmission during a random access procedure or the first PUSCH transmission during the RACH-less mobility procedure. In other words, the terminal device 110 may not transmit on UL-SCH except for Msg3 or MSGA payload or first PUSCH payload of the on-going RACH-less mobility procedure. For example, the terminal device 110 may not transmit on UL-SCH except for Msg3 or MSGA payload or first PUSCH payload during the on-going RACH-less LTM or RACH-less handover or conditional RACH-less LTM or conditional handover. Table 6 shows an example procedure of handling measurement gaps.

Table 6

In some embodiments, if a medium access control (MAC) protocol data unit (PDU) is related to the first PUSCH transmission of the RACH-less mobility procedure, the terminal device 110 may generate a transmission according to a stored uplink grant. For example, to generate a transmission for a transport block (TB) , if the MAC PDU is related to the first PUSCH payload or transmission for RACH-less mobility procedure, the HARQ process of the terminal device 110 may instruct the physical layer to generate a transmission according to the stored uplink grant. For example, to generate a transmission for a transport block (TB) , if the MAC PDU was obtained from the Multiplexing and assembly entity, and the MAC PDU is related to the first PUSCH transmission at RACH-less LTM cell switch or RACH-less handover, the HARQ process of the terminal device 110 may instruct the physical layer to generate a transmission according to the stored uplink grant. Table 7 shows an example of HARQ process.

Table 7

Reference is made to FIG. 5A, which illustrates a signaling flow 500 of indicating timing advance group (TAG) in accordance with some embodiments of the present disclosure. For the purposes of discussion, the signaling flow 500 will be discussed with reference to FIG. 1, for example, by using the terminal device 110 and the network device 120.

The network device 120 transmits (5010) a mobility procedure command to the terminal device 110. For example, the mobility procedure may be a LTM cell switch procedure or a conditional LTM cell switch procedure. Alternatively, the mobility procedure may be a handover procedure or a conditional handover procedure. In some embodiments, the mobility procedure command may be a LTM cell switch MAC CE or a handover command. The mobility procedure may be from a source cell to a target cell. Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

The terminal device 110 determines (5020) a TAG to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity (ID) in the mobility procedure command. For example, the terminal device 110 may determine the TAG from the TCI state information associated with TCI state ID in mobility procedure command. The mobility procedure command may include a TCI state ID which is associated with TCI state information. In some embodiments, the TCI state information may include one or more of: a first value of an indication in the TCI state information indicating that the measured timing advance is for a first timing advance group; or a second value of the indication in the TCI state information indicating that the measured timing advance is for a second timing advance group. In some embodiments, the TCI state information may refer to TCI state configuration. For example, if tag-Id-ptr is configured for the TCI state indicated by the TCI state ID field in the LTM Cell switch command MAC CE and tag-Id-ptr is set to value n1, the Timing Advance measured by UE is for the TAG indicated by the tag2-id of LTM target cell; Otherwise, the Timing Advance measured by UE is for the TAG indicated by the tag-id of the LTM target cell.

In some embodiments, the measured timing advance may be measured by the terminal device 110. Alternatively, the terminal device 110 may obtain the measured timing advance from the network device 120.

In some embodiments, the terminal device 110 may apply the measured timing advance according to the TCI state identity indicated in the mobility procedure command, start or restart the timeAlignmentTimer associated with the PTAG corresponding to the TCI state ID indicated by the LTM Cell Switch Command MAC CE. In some embodiments, when an LTM Cell Switch Command MAC CE is received and the UE has successfully measured the Timing Advance, the terminal device 110 may apply the measured timing advance indicated by LTM Cell Switch Command MAC CE, start or restart the timeAlignmentTimer associated with the PTAG indicated by LTM Cell Switch Command MAC CE. Table 8 shows an example of applying the measured timing advance.

Table 8

Reference is made to FIG. 5B, which illustrates a signaling flow 510 of mobility procedure termination in accordance with some embodiments of the present disclosure. For the purposes of discussion, the signaling flow 510 will be discussed with reference to FIG. 1, for example, by using the terminal device 110 and the network device 120.

The terminal device 110 determines (5120) a mobility procedure is triggered. For example, in some embodiments, if the network device 120 transmits (5110) a mobility procedure command to the terminal device 110, the mobility procedure is triggered. For example, the mobility procedure may be a LTM cell switch procedure or a conditional LTM cell switch procedure. Alternatively, the mobility procedure may be a handover procedure or a conditional handover procedure. In some embodiments, the mobility procedure command may be a LTM cell switch MAC CE or a handover command. The mobility procedure may be from a source cell to a target cell. Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

For an uplink grant configured for configured grant Type 1 for RACH-less handover, when RACH-less handover is triggered and not terminated or when there is an on-going RACH-less HO procedure, for each configured uplink grant valid according to technical specification (TS) 38.214 for which the above formula is satisfied, a MAC entity of the terminal device 110 may determine whether the configured grant is valid.

In some embodiments, after the initial transmission of RACH-less handover has been performed and the PDCCH addressed to the MAC entity's C-RNTI has not been received, if the SSB corresponding to the configured UL grant has the same SSB index as the SSB selected for the initial transmission of RACH-less handover, the terminal device 110 may consider this configured uplink grant as valid. Alternatively, or in addition, if at least one SSB corresponding to the configured uplink grant with SS-RSRP above rach-less-RSRP-ThresholdSSB is available, the terminal device 110 may select an SSB with SS-RSRP above rach-less-RSRP-ThresholdSSB amongst the SSB (s) associated with the configured uplink grant for RACH-less HO, and consider this configured uplink grant as valid.

In some other embodiments, for configured grant configured for RACH-less HO, if no SSB configured for RACH-less HO with the SS-RSRP above rach-less-RSRP-ThresholdSSB is available, the terminal device 110 may consider this configured uplink grant as not valid. In addition, the terminal device 110 may initiate the Random Access procedure, and consider that the RACH-less HO is not on-going or consider that the RACH-less HO is terminated.

In some embodiment, for RACH-less HO, when rach-LessHO is configured, the terminal device 110 may consider the RACH-less HO procedure to be ongoing. In some embodiment, for RACH-less HO, upon the reception of the handover command, and the rach-LessHO is configured, the terminal device 110 may consider the RACH-less HO procedure to be ongoing.

In some embodiment, RACH-less HO being not on-going or RACH-less HO being terminated includes at least one of: RACH-less HO being triggered and successfully completed, or RACH-less handover failure. For example, after the initial transmission of RACH-less handover has been performed and PDCCH addressed to the MAC entity's C-RNTI has been received, or if the t304 expire, the terminal device 110 consider the RACH-less HO is not on-going or RACH-less HO is terminated.

According to embodiments described with reference to FIG. 5B, when there is no SSB above a threshold and the terminal device initiates a random access procedure, the terminal device considers that the RACH-less is terminated or not on-going. In this way, after completing the mobility procedure, the terminal device can reselect the SSB and perform the determination of configured grant valid, thereby avoiding unnecessary UE behaviors. In addition, it can also save UE power and/or reduce handover latency. Table 9 shows an example of mobility procedure termination.

Table 9

It is noted that embodiments described with reference to FIG. 2 to FIG. 5B may be combined in any suitable manner. Alternatively, embodiments described with reference to FIG. 2 to FIG. 5B may be implemented independently.

FIG. 6 illustrates a flowchart of a communication method 600 implemented at a terminal device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the terminal device 110 in FIG. 1.

At block 610, the terminal device 110 initiates a mobility procedure from a source cell to a target cell. Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

At block 620, in response to that the mobility procedure fails, the terminal device 110 revert back to a set of user equipment (UE) variables used in the source celL. the set of UE variables comprises at least one of: a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information.

In some example embodiments, the mobility procedure comprises a handover from the source cell to the target cell, or wherein the mobility procedure comprises a cell switch from the source cell to the target cell.

In some example embodiments, the layer 2 reset information is used by the terminal device to determine on whether L2 reset should be performed when a mobility procedure is triggered, and wherein the layer 2 reset information comprises at least one of:a serving cell layer 2 no reset identity, or a serving cell layer 2 full reset identity.

In some example embodiments, the TA measurement information is used by the terminal device to determine whether UE-based TA measurements should be performed towards a mobility target cell or candidate cell, and wherein the TA measurement information comprises a serving cell measurement TA identity.

In some example embodiments, the set of UE variables are part of UE configuration used in the source cell.

In some example embodiments, in case of the mobility procedure is a layer 1/layer 2 triggered mobility (LTM) cell switch procedure, wherein at least one of layer 2 reset information or TA measurement information is present in a LTM configuration included in a radio resource control (RRC) reconfiguration message, or wherein at least one of layer 2 reset information or the TA measurement information is present in a radio resource control reconfiguration message, under at least one of the following conditions: the radio resource control reconfiguration message includes the LTM configuration with at least one LTM candidate configuration, the radio resource control reconfiguration message is used to configure a handover candidate cell or target cell and the terminal device is configured with a LTM candidate cell, or the radio resource control reconfiguration message is used to configure a handover and values of layer 2 reset information or TA measurement information for the source and target cells are different if the terminal device is configured with LTM candidate cell.

In some example embodiments, the method 600 further comprises in response to the RRC reconfiguration message including L2 reset information, replacing a value of L2 reset information in the set of UE variables with a value of L2 reset information in the RRC reconfiguration message; or storing the L2 reset information in the set of UE variables.

In some example embodiments, the method 600 further comprises in response to the RRC reconfiguration message including TA measurement information, replacing a value of TA measurement information in the set of UE variables with a value of TA measurement information in RRC reconfiguration message; or storing the value of TA measurement information in the set of UE variables.

FIG. 7 illustrates a flowchart of a communication method 700 implemented at a terminal device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 700 will be described from the perspective of the terminal device 110in FIG. 1.

At block 710, the terminal device 110 determines that a random access channel (RACH) less mobility procedure is triggered. The RACH-less mobiliyt procedure may be from a Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

At block 720, the terminal device 110 determines a carrier for the RACH-less mobility procedure.

At block 730, in response to at least one condition being satisfied, the terminal device 110 initiates a RACH-based mobility procedure. The at least one condition comprises that the carrier is not configured with a configured grant.

In some example embodiments, the method 700 further comprises determining that the RACH-less mobility procedure is triggered based on at least one of: reception of a mobility procedure command from a network device, or the terminal device has a valid timing advance for target cell.

In some example embodiments, the method 700 further comprises starting a timer after the reception of the mobility procedure command; or in response to the carrier being configured with the configured grant or a reception of downlink control information for dynamic grant, stopping the timer.

In some example embodiments, the method 700 further comprises selecting the carrier for the RACH-less mobility procedure based on the reception of the mobility procedure command; in response to the carrier being not configured with the configured grant, starting a timer; or in response to a reception of downlink control information for dynamic grant, stopping the timer.

In some example embodiments, the at least one condition further comprises an expiration of the timer, and wherein the terminal device is caused to: in response to the expiration of the timer, initiate the RACH-based mobility procedure.

In some example embodiments, the method 700 further comprises determining that the RACH-less mobility procedure is triggered based on a condition for initiating RACH-less mobility procedure is satisfied.

In some example embodiments, the at least one condition further comprises no synchronization signal block (SSB) with reference signal received power (RSRP) being above a threshold, and wherein the method 700 further comprises in response to the carrier being not configured with the configured grant or no SSB with RSRP being above the threshold, initiating the RACH-based mobility procedure.

In some example embodiments, the method 700 further comprises in response to the carrier being configured with the configured grant and a valid timing advance, initiating the RACH-less mobility procedure.

FIG. 8 illustrates a flowchart of a communication method 800 implemented at a terminal device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 800 will be described from the perspective of the terminal device 110 in FIG. 1.

At block 810, the terminal device 110 receives, from a network device, a configuration of a measurement gap.

At block 820, the terminal device 110 transmits, to the network device, a first physical uplink shared channel (PUSCH) transmission during a RACH-less mobility procedure regardless of the measurement gap. The RACH-less mobility may be from a source cell to a target cell. Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

In some example embodiments, the method 800 further comprises skipping uplink shared channel transmission within the measurement gap except for at least one of: a message 3 during a four-step random access procedure, a message A during a two-step random access procedure, or the first PUSCH transmission during the RACH-less mobility procedure.

In some example embodiments, the method 800 further comprises in response to that a medium access control (MAC) protocol data unit (PDU) is related to the first PUSCH transmission of the RACH-less mobility procedure, generating a transmission according to a stored uplink grant.

FIG. 9 illustrates a flowchart of a communication method 900 implemented at a terminal device in accordance with some embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the terminal device 110 in FIG. 1.

At block 910, the terminal device 110 receives, from a network device, a mobility procedure command.

At block 920, the terminal device 110 determines a timing advance group to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity in the mobility procedure command. The mobility procedure may be from a source cell to a target cell. Target cell may be a candidate cell configured for mobility. In some embodiments, the network device 120 sends the mobility command to terminal device 110, and the mobility command may indicate one of the candidate cells as the target cell of the mobility. Alternatively, in some embodiments, the terminal device 110 evaluates the one or more conditions of candidate cell for mobility, and in case the one or more conditions are satisfied for a candidate cell, the terminal device 110 may trigger the mobility procedure and this candidate cell is considered as target cell.

In some example embodiments, the TCI state identity is associated with TCI state information, and wherein the TCI state information is comprise: a first value of an indication in the TCI state information indicating that the measured timing advance is for a first timing advance group; or a second value of the indication in the TCI state information indicating that the measured timing advance is for a second timing advance group.

In some example embodiments, the method 900 further comprises applying the measured timing advance according to the TCI state identity indicated in the mobility procedure command.

In some example embodiments, the mobility procedure comprises at least one of:an LTM cell switch procedure, a conditional LTM cell switch procedure, a handover procedure, or a conditional handover procedure.

FIG. 10 is a simplified block diagram of a device 1000 that is suitable for implementing embodiments of the present disclosure. The device 1000 can be considered as a further example implementation of any of the devices as shown in FIG. 1. Accordingly, the device 1000 can be implemented at or as at least a part of the terminal device 110 or the network device 120.

As shown, the device 1000 includes a processor 1010, a memory 1020 coupled to the processor 1010, a suitable transceiver 1040 coupled to the processor 1010, and a communication interface coupled to the transceiver 1040. The memory 1020 stores at least a part of a program 1030. The transceiver 1040 may be for bidirectional communications or a unidirectional communication based on requirements. The transceiver 1040 may include at least one of a transmitter 1042 and a receiver 1044. The transmitter 1042 and the receiver 1044 may be functional modules or physical entities. The transceiver 1040 has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2/Xn interface for bidirectional communications between eNBs/gNBs, S1/NG interface for communication between a Mobility Management Entity (MME) /Access and Mobility Management Function (AMF) /SGW/UPF and the eNB/gNB, Un interface for communication between the eNB/gNB and a relay node (RN) , or Uu interface for communication between the eNB/gNB and a terminal device.

The program 1030 is assumed to include program instructions that, when executed by the associated processor 1010, enable the device 1000 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to FIGS. 1 to 10. The embodiments herein may be implemented by computer software executable by the processor 1010 of the device 1000, or by hardware, or by a combination of software and hardware. The processor 1010 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1010 and memory 1020 may form processing means 1050 adapted to implement various embodiments of the present disclosure.

The memory 1020 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1020 is shown in the device 1000, there may be several physically distinct memory modules in the device 1000. The processor 1010 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1000 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

According to embodiments of the present disclosure, a terminal device comprising a circuitry is provided. The circuitry is configured to: initiate a mobility procedure from a source cell to a target cell; in response to that the mobility procedure fails, revert back to a set of user equipment (UE) variables used in the source cell, wherein the set of UE variables comprises at least one of: a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the terminal device as discussed above.

According to embodiments of the present disclosure, a terminal device comprising a circuitry is provided. The circuitry is configured to: determine that a random access channel (RACH) less mobility procedure is triggered; determine a carrier for the RACH-less mobility procedure; and in response to at least one condition being satisfied, initiate a RACH-based mobility procedure, wherein the at least one condition comprises that the carrier is not configured with a configured grant. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the terminal device as discussed above.

According to embodiments of the present disclosure, a terminal device comprising a circuitry is provided. The circuitry is configured to: receive, from a network device, a configuration of a measurement gap; and transmit, to the network device, a first physical uplink shared channel (PUSCH) transmission during a RACH-less mobility procedure regardless of the measurement gap. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the terminal device as discussed above.

According to embodiments of the present disclosure, a terminal device comprising a circuitry is provided. The circuitry is configured to: receive, from a network device, a mobility procedure command; and determine a timing advance group to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity in the mobility procedure command. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the terminal device as discussed above.

The term “circuitry” used herein may refer to hardware circuits and/or combinations of hardware circuits and software. For example, the circuitry may be a combination of analog and/or digital hardware circuits with software/firmware. As a further example, the circuitry may be any portions of hardware processors with software including digital signal processor (s) , software, and memory (ies) that work together to cause an apparatus, such as a terminal device or a network device, to perform various functions. In a still further example, the circuitry may be hardware circuits and or processors, such as a microprocessor or a portion of a microprocessor, that requires software/firmware for operation, but the software may not be present when it is not needed for operation. As used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (s) or a portion of a hardware circuit or processor (s) and its (or their) accompanying software and/or firmware.

According to embodiments of the present disclosure, a terminal apparatus is provided. The terminal apparatus comprises means for initiating a mobility procedure from a source cell to a target cell; in response to that the mobility procedure fails, means for reverting back to a set of user equipment (UE) variables used in the source cell, wherein the set of UE variables comprises at least one of: a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information. In some embodiments, the first apparatus may comprise means for performing the respective operations of the method 600. In some example embodiments, the first apparatus may further comprise means for performing other operations in some example embodiments of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a terminal apparatus is provided. The terminal apparatus comprises means for determining that a random access channel (RACH) less mobility procedure is triggered; means for determining a carrier for the RACH-less mobility procedure; and in response to at least one condition being satisfied, means for initiating a RACH-based mobility procedure, wherein the at least one condition comprises that the carrier is not configured with a configured grant. In some embodiments, the second apparatus may comprise means for performing the respective operations of the method 700. In some example embodiments, the second apparatus may further comprise means for performing other operations in some example embodiments of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a terminal apparatus is provided. The terminal apparatus comprises means for receiving, from a network device, a configuration of a measurement gap; and means for transmitting, to the network device, a first physical uplink shared channel (PUSCH) transmission during a RACH-less mobility procedure regardless of the measurement gap. In some embodiments, the third apparatus may comprise means for performing the respective operations of the method 800. In some example embodiments, the third apparatus may further comprise means for performing other operations in some example embodiments of the method 800. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a terminal apparatus is provided. The terminal apparatus comprises means for receiving, from a network device, a mobility procedure command; and means for determining a timing advance group to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity in the mobility procedure command. In some embodiments, the fourth apparatus may comprise means for performing the respective operations of the method 900. In some example embodiments, the fourth apparatus may further comprise means for performing other operations in some example embodiments of the method 900. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In summary, embodiments of the present disclosure provide the following aspects.

In an aspect, it is proposed a terminal device, comprising: a processor, configured to cause the terminal device to: initiate a mobility procedure from a source cell to a target cell; in response to that the mobility procedure fails, revert back to a set of user equipment (UE) variables used in the source cell, wherein the set of UE variables comprises at least one of: a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information.

In some embodiments, the mobility procedure comprises a handover from the source cell to the target cell, or wherein the mobility procedure comprises a cell switch from the source cell to the target cell.

In some embodiments, the layer 2 reset information is used by the terminal device to determine on whether L2 reset should be performed when a mobility procedure is triggered, and wherein the layer 2 reset information comprises at least one of: a serving cell layer 2 no reset identity, or a serving cell layer 2 full reset identity.

In some embodiments, the TA measurement information is used by the terminal device to determine whether UE-based TA measurements should be performed towards a mobility target cell or candidate cell, and wherein the TA measurement information comprises a serving cell measurement TA identity.

In some embodiments, the set of UE variables are part of UE configuration used in the source cell.

In some embodiments, in case of the mobility procedure is a layer 1/layer 2 triggered mobility (LTM) cell switch procedure, wherein at least one of layer 2 reset information or TA measurement information is present in a LTM configuration included in a radio resource control (RRC) reconfiguration message, or wherein at least one of layer 2 reset information or the TA measurement information is present in a radio resource control reconfiguration message, under at least one of the following conditions: the radio resource control reconfiguration message includes the LTM configuration with at least one LTM candidate configuration, the radio resource control reconfiguration message is used to configure a handover candidate cell or target cell and the terminal device is configured with a LTM candidate cell, or the radio resource control reconfiguration message is used to configure a handover and values of layer 2 reset information or TA measurement information for the source and target cells are different if the terminal device is configured with LTM candidate cell.

In some embodiments, the terminal device is caused to: in response to the RRC reconfiguration message including L2 reset information, replace a value of L2 reset information in the set of UE variables with a value of L2 reset information in the RRC reconfiguration message; or store the L2 reset information in the set of UE variables.

In some embodiments, the terminal device is caused to: in response to the RRC reconfiguration message including TA measurement information, replace a value of TA measurement information in the set of UE variables with a value of TA measurement information in RRC reconfiguration message; or store the value of TA measurement information in the set of UE variables.

In an aspect, it is proposed a terminal device, comprising: a processor, configured to cause the terminal device to: determine that a random access channel (RACH) less mobility procedure is triggered; determine a carrier for the RACH-less mobility procedure; and in response to at least one condition being satisfied, initiate a RACH-based mobility procedure, wherein the at least one condition comprises that the carrier is not configured with a configured grant.

In some embodiments, the terminal device is caused to: determine that the RACH-less mobility procedure is triggered based on at least one of: reception of a mobility procedure command from a network device, or the terminal device has a valid timing advance for target cell.

In some embodiments, the terminal device is caused to: start a timer after the reception of the mobility procedure command; or in response to the carrier being configured with the configured grant or a reception of downlink control information for dynamic grant, stop the timer.

In some embodiments, the terminal device is caused to: select the carrier for the RACH-less mobility procedure based on the reception of the mobility procedure command; in response to the carrier being not configured with the configured grant, start a timer; or in response to a reception of downlink control information for dynamic grant, stop the timer.

In some embodiments, the at least one condition further comprises an expiration of the timer, and wherein the terminal device is caused to: in response to the expiration of the timer, initiate the RACH-based mobility procedure.

In some embodiments, the terminal device is caused to: determine that the RACH-less mobility procedure is triggered based on a condition for initiating RACH-less mobility procedure is satisfied.

In some embodiments, the at least one condition further comprises no synchronization signal block (SSB) with reference signal received power (RSRP) being above a threshold, and wherein the terminal device is caused to: in response to the carrier being not configured with the configured grant or no SSB with RSRP being above the threshold, initiate the RACH-based mobility procedure.

In some embodiments, the terminal device is further caused to: in response to the carrier being configured with the configured grant and a valid timing advance, initiate the RACH-less mobility procedure.

In an aspect, it is proposed a terminal device, comprising: a processor, configured to cause the terminal device to: receive, from a network device, a configuration of a measurement gap; and transmit, to the network device, a first physical uplink shared channel (PUSCH) transmission during a RACH-less mobility procedure regardless of the measurement gap.

In some embodiments, the terminal device is caused to: skip uplink shared channel transmission within the measurement gap except for at least one of: a message 3 during a four-step random access procedure, a message A during a two-step random access procedure, or the first PUSCH transmission during the RACH-less mobility procedure.

In some embodiments, the terminal device is caused to: in response to that a medium access control (MAC) protocol data unit (PDU) is related to the first PUSCH transmission of the RACH-less mobility procedure, generate a transmission according to a stored uplink grant.

In an aspect, it is proposed a terminal device, comprising: a processor, configured to cause the terminal device to: receive, from a network device, a mobility procedure command; and determine a timing advance group to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity in the mobility procedure command.

In some embodiments, the TCI state identity is associated with TCI state information, and wherein the TCI state information is comprise: a first value of an indication in the TCI state information indicating that the measured timing advance is for a first timing advance group; or a second value of the indication in the TCI state information indicating that the measured timing advance is for a second timing advance group.

In some embodiments, the terminal device is caused to: apply the measured timing advance according to the TCI state identity indicated in the mobility procedure command.

In some embodiments, the mobility procedure comprises at least one of: an LTM cell switch procedure, a conditional LTM cell switch procedure, a handover procedure, or a conditional handover procedure.

In an aspect, a terminal device comprises: at least one processor; and at least one memory coupled to the at least one processor and storing instructions thereon, the instructions, when executed by the at least one processor, causing the device to perform the method implemented by the terminal device discussed above.

In an aspect, a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the terminal device discussed above.

In an aspect, a computer program comprising instructions, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the terminal device discussed above.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to FIGS. 1 to 10. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A terminal device, comprising:

a processor, configured to cause the terminal device to:

initiate a mobility procedure from a source cell to a target cell;

in response to that the mobility procedure fails, revert back to a set of user equipment (UE) variables used in the source cell, wherein the set of UE variables comprises at least one of:a UE variable related to layer 2 reset information or a UE variable related to timing advance (TA) measurement information.
The terminal device of claim 1, wherein the mobility procedure comprises a handover from the source cell to the target cell, or

wherein the mobility procedure comprises a cell switch from the source cell to the target cell.
The terminal device of claim 1 or 2, wherein the layer 2 reset information is used by the terminal device to determine on whether L2 reset should be performed when a mobility procedure is triggered, and

wherein the layer 2 reset information comprises at least one of:

a serving cell layer 2 no reset identity, or

a serving cell layer 2 full reset identity.
The terminal device of any of claims 1-3, wherein the TA measurement information is used by the terminal device to determine whether UE-based TA measurements should be performed towards a mobility target cell or candidate cell, and

wherein the TA measurement information comprises a serving cell measurement TA identity.
The terminal device of any of claims 1-4, wherein the set of UE variables are part of UE configuration used in the source cell.
A terminal device, comprising:

a processor, configured to cause the terminal device to:

determine that a random access channel (RACH) less mobility procedure is triggered;

determine a carrier for the RACH-less mobility procedure; and

in response to at least one condition being satisfied, initiate a RACH-based mobility procedure, wherein the at least one condition comprises that the carrier is not configured with a configured grant.
The terminal device of claim 6, wherein the terminal device is caused to:

determine that the RACH-less mobility procedure is triggered based on at least one of:

reception of a mobility procedure command from a network device, or

the terminal device has a valid timing advance for target cell.
The terminal device of claim 6 or 7, wherein the terminal device is caused to:

start a timer after the reception of the mobility procedure command; or

in response to the carrier being configured with the configured grant or a reception of downlink control information for dynamic grant, stop the timer.
The terminal device of claim 6 or 7, wherein the terminal device is caused to:

select the carrier for the RACH-less mobility procedure based on the reception of the mobility procedure command;

in response to the carrier being not configured with the configured grant, start a timer; or

in response to a reception of downlink control information for dynamic grant, stop the timer.
The terminal device of any claim of 6-9, wherein the at least one condition further comprises an expiration of the timer, and wherein the terminal device is caused to:

in response to the expiration of the timer, initiate the RACH-based mobility procedure.
The terminal device of claim 6, wherein the terminal device is caused to:

determine that the RACH-less mobility procedure is triggered based on a condition for initiating RACH-less mobility procedure is satisfied.
The terminal device of claim 11, wherein the at least one condition further comprises no synchronization signal block (SSB) with reference signal received power (RSRP) being above a threshold, and wherein the terminal device is caused to:

in response to the carrier being not configured with the configured grant or no SSB with RSRP being above the threshold, initiate the RACH-based mobility procedure.
The terminal device of claim 11, wherein the terminal device is further caused to:

in response to the carrier being configured with the configured grant and a valid timing advance, initiate the RACH-less mobility procedure.
A terminal device, comprising:

a processor, configured to cause the terminal device to:

receive, from a network device, a configuration of a measurement gap; and

transmit, to the network device, a first physical uplink shared channel (PUSCH) transmission during a RACH-less mobility procedure regardless of the measurement gap.
The terminal device of claim 14, wherein the terminal device is caused to:

skip uplink shared channel transmission within the measurement gap except for at least one of:

a message 3 during a four-step random access procedure,

a message A during a two-step random access procedure, or

the first PUSCH transmission during the RACH-less mobility procedure.
The terminal device of claim 14, wherein the terminal device is caused to:

in response to that a medium access control (MAC) protocol data unit (PDU) is related to the first PUSCH transmission of the RACH-less mobility procedure, generate a transmission according to a stored uplink grant.
A terminal device, comprising:

a processor, configured to cause the terminal device to:

receive, from a network device, a mobility procedure command; and

determine a timing advance group to which a measured timing advance belongs based on a transmission configuration indicator (TCI) state identity in the mobility procedure command.
The terminal device of claim 17, wherein the TCI state identity is associated with TCI state information, and wherein the TCI state information comprise:

a first value of an indication in the TCI state information indicating that the measured timing advance is for a first timing advance group; or

a second value of the indication in the TCI state information indicating that the measured timing advance is for a second timing advance group.
The terminal device of claim 17 or 18, wherein the terminal device is caused to:

apply the measured timing advance according to the TCI state identity indicated in the mobility procedure command.
The terminal device of any of claims 1-19, wherein the mobility procedure comprises at least one of:

an LTM cell switch procedure,

a conditional LTM cell switch procedure,

a handover procedure, or

a conditional handover procedure.