Interworking of beam failure recovery (BFR) and cell handover

Abstract

Example embodiments of the present disclosure are directed to interworking of beam failure recovery (BFR) and cell handover. A method includes during an on-going BFR procedure for a first cell, transmitting, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during the on-going BFR procedure; receiving, from the network entity of the second cell, a response message at least comprising and an indication of the uplink resource of the second cell; and based on a determination of whether the BFR procedure is successfully completed or failed, performing a beam switch in the first cell or performing a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

Description

INTERWORKING OF BEAM FAILURE RECOVERY (BFR) AND CELL HANDOVERFIELD

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for interworking of beam failure recovery (BFR) and cell handover.BACKGROUND

[0002] The Layer 1 or Layer 2 (L1 / L2) triggered mobility (LTM) mechanism is provided for cell handover of a terminal device (e.g., UE) from a source cell to a target cell. The LTM procedure is based on a measurement report of the terminal device.

[0003] Beam failure recovery (BFR) is a mechanism in the communication networks designed to ensure seamless connectivity and reliability. The network may configure the terminal device with specific reference signals, e.g., channel state information reference signal (CSI-RS) or synchronization signal blocks (SSBs), for beam failure detection. Upon detecting a beam failure on a serving cell, the terminal device triggers a recovery procedure and selects a suitable candidate beam for recovery. If the beam failure recovery succeeds, the terminal device may maintain in the serving. Otherwise, the terminal device may decide to perform a handover from the current source cell to a target cell.SUMMARY

[0004] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: during an on-going beam failure recovery procedure for a first cell, transmit, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during the on-going beam failure recovery procedure; receive, from the network entity of the second cell, a response message at least comprising an indication of the uplink resource of the second cell; and based on a determination of whether the beam failure recovery procedure is successfully completed or failed, perform a beam switch inthe first cell or perform a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0005] In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus providing a second cell at least to: receive, from a terminal device, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device; transmit, to the terminal device, a response message at least comprising an indication of the uplink resource of the second cell; and determine release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

[0006] In a third aspect of the present disclosure, there is provided a method. The method comprises: during an on-going beam failure recovery procedure for a first cell, transmitting, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during the on-going beam failure recovery procedure; receiving, from the network entity of the second cell, a response message at least comprising an indication of the uplink resource of the second cell; and based on a determination of whether the beam failure recovery procedure is successfully completed or failed, performing a beam switch in the first cell or performing a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0007] In a fourth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a terminal device, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device; transmitting, to the terminal device, a response message at least comprising an indication of the uplink resource of the second cell; and determining release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

[0008] In a fifth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for during an on-going beam failure recovery procedurefor a first cell, transmitting, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during the on-going beam failure recovery procedure; means for receiving, from the network entity of the second cell, a response message at least comprising an indication of the uplink resource of the second cell; and means for based on a determination of whether the beam failure recovery procedure is successfully completed or failed, performing a beam switch in the first cell or performing a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0009] In a sixth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for receiving, from a terminal device, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device; means for transmitting, to the terminal device, a response message at least comprising an indication of the uplink resource of the second cell; and means for determining release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

[0010] In a seventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the third aspect.

[0011] In an eighth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourth aspect.

[0012] It is to be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0014] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0015] FIG. 2 illustrates a signaling flow showing problems due to BFR failure and incomplete BFR procedure with triggered random access channel (RACH)-based recovery in a communication system;

[0016] FIG. 3A illustrates a signaling flow for interworking of beam failure recovery (BFR) and cell handover according to some example embodiments of the present disclosure;

[0017] FIG. 3B illustrates a signaling flow for interworking of beam failure recovery (BFR) and cell handover according to some further example embodiments of the present disclosure;

[0018] FIG. 3C illustrates a signaling flow for interworking of beam failure recovery (BFR) and cell handover according to some yet further example embodiments of the present disclosure;

[0019] FIG. 4A illustrates a signaling flow for LTM preparation according to some example embodiments of the present disclosure;

[0020] FIG. 4B illustrates a signaling flow for interworking of beam failure recovery (BFR) and cell handover in a first scenario according to some example embodiments of the present disclosure;

[0021] FIG. 4C illustrates a signaling flow for interworking of beam failure recovery (BFR) and cell handover in a second scenario according to some example embodiments of the present disclosure;

[0022] FIG. 4D illustrates a signaling flow for interworking of beam failure recovery (BFR) and cell handover in a third scenario according to some example embodiments of the present disclosure;

[0023] FIG. 5A illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0024] FIG. 5B illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0025] FIG. 6A illustrates a flowchart of a method implemented at a first apparatus inaccordance with some further example embodiments of the present disclosure;

[0026] FIG. 6B illustrates a flowchart of a method implemented at a second apparatus in accordance with some further example embodiments of the present disclosure;

[0027] FIG. 7A illustrates a flowchart of a method implemented at a first apparatus in accordance with some yet further example embodiments of the present disclosure;

[0028] FIG. 7B illustrates a flowchart of a method implemented at a second apparatus in accordance with some yet further example embodiments of the present disclosure;

[0029] FIG. 8 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0030] FIG. 9 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0031] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0032] The 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.

[0033] 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.

[0034] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0035] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0036] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0037] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting example embodiments. 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. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0039] As used in this application, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0040] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0041] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, 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), 5.5G, the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0042] As used herein, the term “network device” refers to a node in a communicationnetwork via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0043] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0044] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, 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 combination of the time, frequency, space and / or code domain 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.

[0045] FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. As shown in FIG. 1, the communication environment 100 comprises one or more network devices, such as a network device 110-1, a network device 110-2, and one or more terminal devices such as a terminal device 120. For the purpose of discussion, the network device 110-1 and network device 110-2 are collectively or individually referred to as network devices 110 or RAN network devices.

[0046] In some example embodiments, the network device 110-1 may be a RAN network device of a serving cell 140, for example, a gNB of the serving cell 140 for the terminal device 120. The network device 110-2 may be a RAN network device of a neighbor cell 150, for example, a gNB of the cell 150. In some embodiments, the cell 150 may be a candidate for LTM of the terminal device 120. The terminal device 120, for example, may be a UE served by the serving cell 140. The cell 150 may be a potential candidate to become a new serving cell for the terminal device 120.

[0047] In some example embodiments, a network device of a serving cell for a terminal device may include one or more distributed units (DUs), e.g., one or more gNB-DUs, and one or more central units (CUs), e.g., one or more gNB-CUs. For example, the network device 110 may include a CU 112-1, and one or more DUs 114-1, 114-2. The network device 110-2 may include a CU 112-2, and one or more DUs DU 114-3, 114-4. The CU 112-1 and CU 112-2 are collectively or individually referred to as CUs 112. The DU 114-1, 114-2, 114-3, 114-4 are collectively or individually referred to as DUs 114.

[0048] In some example embodiments, a DU may be connected to the terminal device 120, and each DU may serve one or more cells. Depending on whether the serving cell and a candidate target cell are associated with the same CU, the LTM procedure may include an intra-CU LTM procedure or an inter-CU LTM procedure. If the candidate target cell(s) and the serving cell are associated with the same CU, the intra-CU LTM procedure is applied. If the candidate target cell(s) and the serving cell are associated with different CUs, the inter-CU LTM procedure is applied.

[0049] In the following, for the purpose of illustration, some example embodiments may be described with the network device 110-1 or the network device 110-2 operating as a network device. 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.

[0050] In some example embodiments, a communication direction from a network device 110 to the terminal device 120 is referred to as a downlink (DL), and a communication direction from the terminal device 120 to a network device 110 is referred to as an uplink (UL). In DL, the network device 110 is a transmitting (TX) device (or a transmitter) and the terminal device 120 is a receiving (RX) device (or a receiver). In UL, the terminal device 120 is a TX device (or a transmitter) and the network device 110 is a RX device (or a receiver).

[0051] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0052] Layer 1 or Layer 2 (L1 / L2) triggered mobility (LTM) is a cell switch procedure, where a serving cell (primary cell (PCell) or primary secondary cell (PSCell)) is switched by the network by sending an LTM cell switch command. An LTM cell switch decision is based on measurements (for example LI measurements) that are performed and reported (for example LI measurement report) by the terminal device. Measurements and reporting are based on an LTM candidate cell configuration provided by the network for one or more LTM candidate cells. An LTM candidate cell may be a neighboring cell or a UE’s current serving cell (e.g., SCell). LTM measurements on a neighboring candidate cell are performed using synchronization signal and physical broadcast channel (PBCH) blocks (SSBs) transmitted by the candidate cell for which the SSB configuration is provided to the UE. This is being extended to channel state information-reference signal (CSI-RS) based measurements.

[0053] The primary advantage of L1 / L2 triggered mobility (LTM) is to reduce the interruption time and flexibility towards random access channel (RACH)-less implementation. However, in the frequency band, the measurements involved for LTM cell switch execution will become more beam specific than cell specific. As part of beam level enhancements, the beam failure detection and beam failure recovery procedure is available.

[0054] One of the procedures to prevent radio link failure (RLF) is early beam failure detection (BFD) based on the measurements of the received reference signal, e.g., channel state information reference signal (CSI-RS) or synchronization signal blocks (SSBs) from the media access control (MAC) layer of the serving cell. A beam failure may be identified by counting beam failure instance (BFI) indication from the lower layers to the MAC entity. If a BFI is not identified for a certain amount of time (i.e., Beam Failure Detection Timer), the BFI counter will be reset. In case the BFI counter reaches a maximum number, as configured in RRC, the terminal device will declare a beam failure and it will start the beam failure recovery (BFR) procedure.

[0055] During the BFR procedure, the terminal device will perform new beam search, and it will identify the best beam from the serving cell to recover. In case the BFR procedure fails, the terminal device will declare a radio link failure (RLF) and it will start searching candidate beams for connection re-establishment. These beams may come from the serving cell or a non-serving cell. However, declaring RLF and initiating connection re-establishment increases the interruption time. The resources to perform BFR areconfigured to the terminal device in RRC configuration. The beams to perform BFR are configured in the BFR- S SB -Resource or in the BFR-CSI-RS-Resource, where specific RACH resources are allocated to enable the terminal device to access the configured beams. If no specific RACH resources are allocated, then the terminal device will perform contention-based access using the recovery beam.

[0056] FIG. 2 illustrates a signaling flow 200 showing problems due to BFR failure and incomplete BFR procedure with triggered RACH-based recovery in a communication system.

[0057] In the signaling flow 200, steps 1 to 16 are related to an LTM preparation process, where the UE may obtain configuration of cells that are prepared as candidate cells for handover. The signaling flow 200 is related to an intra-CU scenario where the candidate cells and the serving cell (or source cell) are provided by different DUs under the same CU.

[0058] If the UE detects beam failure over the serving cell provided by the source DU, it might eventually lead to radio link failure. Then the UE may trigger a BFR procedure in the serving cell. According to the legacy procedures, BFR failure may lead to increased interruption time. Specifically, in case the BFR fails, UE will declare RLF. In that case, the UE can either go for RRC re-establishment or may perform a RACH-based recovery procedure to the best candidate cell. If the best candidate cell is LTM prepared, then the UE may initiate a RACH-based procedure with the LTM-prepared best candidate cell. However, this recovery process is RACH-based procedure which may increase the interruption time because the UE may need to obtain uplink synchronization with the target cell while executing a handover. Currently, there is no option for a RACH-less recovery.

[0059] Another possible solution is that the UE triggers a RACH-based recovery procedure without completing the BFR procedure. For example, if the UE anticipates an imminent RLF, it may trigger a RACH-based recovery to handover to a target cell while the BFR procedure for the serving cell is ongoing or just before the completion of the BFR procedure. However, there is a possibility that the entire BFR procedure will become redundant. If the BFR procedure could succeed eventually, the UE is not getting a chance to recover at the serving cell itself. On one hand, the signal quality at the serving cell could have been better than the chosen candidate cell, if the beam is recovered in theserving cell. On the other hand, the unnecessary cell handovers may lead to additional delay overheads.

[0060] Example embodiments of the present disclosure, some solutions are proposed for the interworking of the BFR procedure and the cell handover. In some example embodiments, during an on-going BFR procedure for a first cell, a terminal device transmits, towards a second cell, a request for an uplink resource of the second cell. In some example embodiments, the request may include a random access request, including a random access preamble. Then, the terminal device obtains an indication of the uplink resource of a second cell as a response. In some examples, the terminal device, if not configured with timing advance (TA) information of the second cell, may also request for the TA information. The TA information and the indication of the uplink resource may be transmitted to the terminal device via a random access response (RAR). By preemptively obtaining the uplink resource of the second cell (and further the TA information in some examples), even if the beam failure recovery procedure is failed, the terminal device can perform a RACH-less recovery towards the second cell, which reduces the interruption time. In this way, the terminal device may be prevented from triggering a RACH-based recovery procedure while the BFR procedure is on-going. The signaling overhead may be reduced, and latency may be reduced.

[0061] In some example embodiments, if the BFR procedure for the first cell is successfully completed, the terminal device transmits an indication of successful completion of the BFR procedure towards the second cell. By receiving such an indication, the second cell can determine that the terminal device will continue to stay in the first cell and thus may release the uplink resource that is allocated to the terminal device. In this way, unnecessary handovers may be prevented from executing, the resources of the second cell may be saved, and additional delays may be prevented.

[0062] In some other example embodiments, during the on-going BFR procedure for a first cell, the terminal device transmits towards the second cell the request message together with an indication indicating early resource acquisition during the on-going BFR procedure. Then, the terminal device obtains a response that includes at least an indication of an uplink resource of the second cell. In some examples, the response may further include TA information of the second cell. The network entity of the second cell, upon reception of the indication from the terminal device, may be aware that the request of the terminal device for the uplink resource is triggered due to preemptive recoverywhile the on-going BFR procedure for a currently serving cell of the terminal device. If the network entity of the second cell cannot receive a trigger of cell handover from the terminal device later, the network entity may automatically release the uplink resource allocated to the terminal device. In this case, the terminal device may not need to additionally transmit an indication to indicate the successful BFR completion when the BFR procedure turns out to be successful.

[0063] The example embodiments propose UE behaviour which reduces the interruption time by preventing the terminal device from triggering a RACH-based recovery procedure while the BFR is ongoing. It may enable the terminal device to have RACH-less recovery even after failure of the BFR procedure. It may happen that the UE sends the preamble only after detecting that BFR has failed, which requires additional time. Performing the preamble transmission and TA + UL grant reception already during BFR process ensures that in case the BFR fails, the UE is already aware of the TA + UL grant and can proceed directly to the establishing connection to the target cell by utilizing the TA and UL grant. To achieve this, enhancements are proposed in terms of signalling and new behaviour of the termina device and network entities.

[0064] It would be appreciated that although some example embodiments of the present disclosure are described in the intra-CU LTM scenario, the present disclosure may be similarly applied to other scenario for handover, such as the inter-CU LTM scenario where DUs of the serving cell and target cells are in the control of two different CUs, a scenario involving RAN network nodes without a distribution of DU and CU, or the conditional handover (CHO) scenario. The CHO mechanism is introduced to ensure robustness of the handover procedure. In the CHO procedure, the terminal device is configured with a CHO command containing the target cell configuration and a condition to execute the handover for one or multiple target cells. The condition is based on radio measurements of the neighboring cells. The terminal device is allowed to perform cell handover when the condition is satisfied.

[0065] FIG. 3 A illustrates a signaling flow 300A for interworking of BFR and cell handover according to some example embodiments of the present disclosure. As shown in FIG. 3, the signaling flow 300 A involves a terminal device 310, a network entity 320, and a network entity 330. The network entity 320 may provide at least a first cell, which may be a serving cell (or source cell) of the terminal device 310. Herein the first cell, the serving cell, and the source cell may be used interchangeably. The network entity 330may provide at least a second cell, which may be a candidate cell or target cell for handover of the terminal device 310. The second cell, the candidate cell, and the target cell may be used interchangeably. The terminal device 310 is currently served in the first cell.

[0066] In some example embodiments, the network entity 320 of the first cell may include a source DU, and the network entity 330 of the second cell may include a target DU. The signaling flow 300 A may be related to an intra-CU scenario where the source DU and the target DU may be under the management of the same CU. Alternatively and / or additionally, the signaling flow 300 A may be related to an inter-CU scenario where the source DU and the target DU may belong to different CUs. In some example embodiments where the RAN network device is not constructed with a distribution of DU and CU, the network entity 320 and the network device 330 may include different RAN network devices, e.g., gNB or the like.

[0067] In the signaling flow 300A (and the signaling flows 300B and 330C to be discussed in the following), it is assumed that the terminal device 310 served by the first cell detects beam failure and initiates an BFR procedure for the first cell. For example, if the terminal device 310 detects a beam failure due to reasons such as rapid changes in the environment leading to obstructions or interference, or misalignments in the beam direction due to mobility, the terminal device 310 may trigger a BFR procedure for the serving cell.

[0068] Based on an on-going BFR procedure for the first cell, the terminal device 310 transmits (305) a request message to the network entity 330 of the second cell, to request for at least an uplink resource of the second cell. In some example embodiments, if TA information of the second cell is available at the terminal device 310, it may not need to request for TA information of the second cell. For example, the terminal device 310 may be configured with UE -based TA estimation and thus may be able to determine or estimate the TA information of the second cell. If the TA information of the second cell is not available at the terminal device 310, in some example embodiments, the request message may be used to request for both TA information and an uplink resource of the second cell.

[0069] In the following, even though example embodiments are described so that both TA information and uplink resource of the second cell are requested and received, it would be appreciated that in some other embodiments only the uplink resource is requested andreceived and the TA information is already known by the terminal device.

[0070] In some example embodiments, the second cell may be determined from a set of candidate cells or neighbor cells for the terminal device 330. In some example embodiments, the candidate cells or neighbor cells may be prepared in the LTM procedure. The terminal device 31 may receive a list of candidate cells within an LTM configuration (which may be transmitted via RRC reconfiguration) and may select the best candidate cell from the list to transmit the random access request. In some other example embodiments, the second cell may be any other cell that can be determined as a candidate for cell handover.

[0071] In some example embodiments, the terminal device 310 may initiate a random access request towards the network entity 330 of the second cell. In some example embodiments, the random access request may include a random access preamble. In some example embodiments, the random access request may include a physical random access channel (PRACH) preamble. In some example embodiments, the random access request may include a dedicated random access preamble which is selected from a set of dedicated random access preambles. The set of dedicated random access preambles may be configured for contention-free random access (CFRA). Since dedicated random access preambles are used, the time required to retrieve the TA information and uplink resource may be minimized as much as possible.

[0072] In some example embodiments, the terminal device 310 may at least obtain the random access configuration (e.g., physical random access channel, PRACH, configuration) of the second cell and downlink control configuration (e.g., physical downlink control channel, PDCCH, configuration) of the second cell and thus may be able to trigger the random access request towards the second cell. The terminal device 130 may obtain the random access configuration and the downlink control configuration of the second cell during a handover preparation procedure, where the random access and downlink control configurations of at least one candidate cell including the second cell may be configured to the terminal device 130, e.g., via the CU.

[0073] In some example embodiments, the terminal device 310 may be configured to enable transmitting the request message for TA information and / or UL resource of the second cell during the on-going BFR procedure for the serving cell. During the connection with the network entity 320 of the serving cell, the network entity 320 may transmit(301 A), to the terminal device 310, an indication of enabling early timing advance acquisition of a candidate cell during the BFR procedure in the serving cell. For example, during a scenario where the network entity 320 needs to transmit the radio resource control configuration of the terminal device 310, the network entity 320 may transmit this indication in a RRC reconfiguration message to the terminal device 310. The indication may be enabled that when the terminal device 310 detects beam failure in the serving cell and triggers BFR, the terminal device 310 is allowed or enabled to obtain timing advance (TA) information and an uplink resource from the candidate cell in advance. Such an indication from the network may be referred to as a “preemptive recovery indication”, “preemptive RACH-less recovery indication” or a “preemptive LTM recovery indication” (in the example where the candidate cell is prepared in an LTM procedure).

[0074] The terminal device 310 may receive (303 A) the indication from the network entity 320. Based on the indication from the network entity 320, upon detecting beam failure and subsequently triggering the beam failure recovery procedure, and if the best candidate cell is above a first specific threshold and serving cell is below a second specific threshold configured by the network, the network entity 320 may temporarily apply the PRACH configuration. If the best candidate cell is an LTM prepared cell, the terminal device 310 may proactively transmit PRACH preamble towards the best candidate cell. Then, the terminal device 310 may apply the PDCCH configuration to receive the timing advance (TA) information and timing alignment timer (TAT) along with physical uplink shared channel (PUSCH) resource configuration over the response message, e.g., the random access response (RAR) message. Once the response message of the network entity 330 is received, the terminal device 310 may revert to the serving cell configuration to continue with the beam failure recovery procedure.

[0075] In some example embodiments, once the terminal device 310 has acquired the RAR (which includes the TA and PUSCH grant), it will not immediately trigger the RACH-less LTM recovery procedure. The terminal device 310 may wait for the ongoing BFR outcome for a certain period of time. If BFR fails, the terminal device 310 may trigger recovery, e.g., re-apply the best candidate cell configuration and transmit RRC Reconfiguration Complete to the candidate cell by utilizing the TA and the PUSCH resource obtained earlier.

[0076] In some example embodiments, in addition to reception the indication of enabling early timing advance and / or resource acquisition of a candidate cell during the BFRprocedure in the serving cell, the terminal device 310 may further determine whether a condition is satisfied before triggering the request towards the second cell. In some examples, the terminal device 310 may determine the cell strength of the first cell and the cell strength of the second cell. If the cell strength of the first cell and the cell strength of the second cell satisfy corresponding requirements, the terminal device 310 may transmit the request for the uplink resource and / or TA information to the network entity 330 of the second cell. For example, when the terminal device 310 determines that the cell strength of the second cell is above a second cell strength threshold and a cell strength of the first cell is less than a first cell strength threshold, the terminal device 310 may transmit the request to the network entity 320 of the second cell.

[0077] In some example embodiments, the terminal device 310 may temporarily apply random access configuration related to the second cell, e.g., the PRACH configuration to transmit the random access request towards the second cell. The random access configuration may be obtained, e.g., during a handover preparation procedure such as the LTM preparation procedure for the second cell.

[0078] The network entity 330 providing the second cell receives (307 A) the request message, e.g., the random access request from the terminal device 310. Then, the network entity 330 transmits (309A) a response message towards the terminal device 310. The response message includes at least an indication of the uplink resource of the second cell. In some example embodiments, the response message may further include TA information of the second cell. In some example embodiments, the response message may include a RAR as a response to the random access request received from the terminal device 310. The TA information may include TA value, TAT, and the like which are used for time synchronization in the second cell. The indication of the uplink resource may include corresponding uplink resource configurations, e.g., UL grant, physical uplink shared channel (PUSCH) configuration or resource, PUSCH grant, etc.

[0079] In some example embodiments, the network entity 330, when receiving the request from the terminal device 310 while the on-going BFR procedure, may determine the UL resource to be allocated to the terminal device as it knows that the terminal device 310 may not have an uplink transmission towards the second cell until the BFR procedure is completed. In some example embodiments, the network side including the network entity 330 may have already been configured with the BFR timer duration which was shared to the terminal device along with the RRC reconfiguration. When the networkentity 330 of the second cell receives the random access preamble (e.g., a dedicated access preamble), the network entity 330 may determine that BFR has been triggered at the terminal device. Now based on this information that BFR has been triggered and the maximum value of the BFR timer, the network entity 330 may decide on which uplink resource it can allocate the UL grant. In some examples, the uplink resource may be in the same time slot by a certain time instant after the BFR timer expiry or may be just before the BFR timer expiry.

[0080] The terminal device 310 receives (311 A) the response message from the network entity 330. In some example embodiments, the terminal device 310 may temporarily apply a downlink control configuration related to the second cell, and then monitor the response from the network entity 330. For example, the downlink control configuration may include PDCCH configuration, which is obtained, e.g., during the handover preparation procedure for the second cell.

[0081] In some embodiments, although it is illustrated in FIG. 3A that the response message is transmitted directly from the network entity 330 to the terminal device 310, the response message may also be received from the network entity 320, e.g., after the BFR procedure is resumed. While the terminal device 310 transmits the request (e.g., the random access request) to the network entity 330, the terminal device 310 has already applied the PDCCH configuration to receive the TA information and the uplink resource of the second cell. Thus, in some example embodiments, the TA information and the indication of the uplink resource of the second cell is received via the RAR from the network entity 330 of the second cell directly.

[0082] In some other example embodiments, instead of being provided in the RAR, the TA information and the indication of the uplink resource may be received by the terminal device via a MAC CE or any other information from the network entity of the second cell 330, or even from the network entity 320 of the first cell. For the latter case, there may be a long route whereby the network entity 330 of the second cell may share the TA information and the indication of the uplink resource of the second cell to a CU which controls the network entity 320 of the first cell. Then the CU forwards the TA information and the indication of the uplink resource of the second cell to the serving DU of the first cell, which may correspond to the network entity 330 of the first cell. The serving DU stores the TA information and the indication of the uplink resource of the second cell and when the BFR procedure for the first cell is once again resumed at the terminal device,the network entity 330 (e.g., the serving DU) may attempt to transmit the TA and the indication of the uplink resource of the second cell to the terminal device 310.

[0083] In some cases, since beam failure recovery is already ongoing with the first cell, the connectivity between the terminal device 310 and the serving-DU (serving cell) may not be very reliable. Therefore, in some examples, the network entity 320 may either send the early TA information and the indication of the uplink resource over all the configured serving cell beams or selectively over a few beams for which the terminal device 310 has reported signal strength above a pre-defined threshold earlier. The TA information and the indication of the uplink resource for the second cell may be carried in a MAC CE from the network entity 320 to the terminal device 310. As a result, the TA information and the uplink resource of the second cell may still be successfully delivered to the terminal device 310 by the serving cell before the terminal device 310 receives any beam recovery indication for the serving cell.

[0084] It would be appreciated that the above-mentioned example embodiments of providing TA information and uplink resource of the second cell to the terminal device may similarly applied to the example embodiments of FIG. 3B-3C which are to be described in the following.

[0085] In some example embodiments, before the terminal device 310 transmits the request for TA information and uplink resource to the network entity 330 of the second cell, the on-going BFR procedure for the first cell needs to be suspended. After reception of the response from the network entity 330 of the second cell, the suspended BFR procedure for the first cell may be resumed.

[0086] In some example embodiments, once terminal device 310 has obtained the response message of the second cell, it may not directly trigger the handover procedure from the first cell to the second cell, it may wait for the outcome of the on-going BFR procedure. In some example embodiments, if the BFR procedure is successfully completed, the terminal device 310 performs (313 A) the beam switch in the first cell, e.g., to switch to the recovered beam(s) and thus may continue staying in the first cell.

[0087] There may be various ways used by the terminal device to perform a BFR procedure for a cell. A basic four-step BFR procedure may include a first step of detecting beam failure, e.g., a measurement result on a specific reference signal for the connected beam goes below a certain limit, and a second step of searching for another candidatebeam with good quality. Then in a third step, if a predefined number of beam failure is detected, the terminal device triggers a beam failure recovery process with the candidate beam in the serving cell. For example, the terminal device may send PRACH preamble (which is used for BFR purpose) over the candidate beam. In a fourth step, the network entity in the serving cell may reply to beam failure recovery request (e.g., a RACH response). If the beam failure recovery response indicates that the candidate beam is good enough, then the BFR procedure is successfully completed. Otherwise, the terminal device will repeat the third step to re-transmit the PRACH preamble to the network entity of the serving cell.

[0088] In some example embodiments, the terminal device 310 may be configured with a BFR timer. Upon the BFR procedure is triggered, the BFR timer starts counting. Once this BFR timer expires, and the terminal device 310 still does not receive any beam recovery indication from the serving cell, the terminal device 310 may determine that the BFR procedure is failed.

[0089] In some example embodiments, the terminal device may suspend the BFR procedure between the third step and the four step, to request for the TA information and the uplink resource of the second cell. Once the response is received from the second cell, the terminal device may resume the BFR procedure and wait for the beam recovery response (e.g., the RACH Response) from the first cell.

[0090] If the BFR procedure is determined to be failed, the terminal device 310 performs (313 A) the cell handover from the first cell to the second cell based at least on the uplink resource of the second cell. In some examples, the cell handover may be performed further based on the TA information of the second cell, which is already known to the terminal device 310 or is acquired together with the uplink resource during the on-going BFR procedure. Since the terminal device 310 was prepared with the early acquired TA and configured uplink resources just in case the BFR failed, the terminal device 310 may have initiated a RACH-less recovery process without an interruption in the BFR failure case. In some example embodiments, if the BFR procedure is failed, the terminal device 310 may perform handover to the second cell by transmitting a message indicating successful completion of cell handover to the second cell.

[0091] In some example embodiments, to perform the cell handover to the second cell, the terminal device 310 may re-apply the (PDCCH) configuration of the second cell (e.g.,the best LTM candidate cell configuration). Then, when the terminal device 310 has successfully completed the RACH-less recovery towards the best candidate cell, the terminal device 310 may transmit a RRC reconfiguration complete message to the second cell via the PUSCH transmission, indicating that the terminal device 310 has successfully completed the RACH-less recovery towards the best candidate cell using the TA information and the uplink resource (which are received during the BFR procedure). The PUSCH transmission may be considered as the first PUSCH transmission of the terminal device 310 in the second cell. In some example embodiments, the cell handover towards the second cell may be performed over non-serving cell beams where no failures have been detected by the terminal device 310.

[0092] In some example embodiments, if the BFR procedure is successfully completed, the terminal device 310 may discard the uplink resource of the second cell. In some example embodiments, based on the implementation of the terminal device 310, the terminal device 310 may discard the uplink resource of the second cell after a predetermined time period. For example, the terminal device 310 may set a timer upon receiving the uplink resource of the second cell. When the timer expires, the terminal device 310 may discard the uplink resource of the second cell. The time duration of the timer may be preconfigured or prespecified.

[0093] FIG. 3B illustrates a signaling flow 300B for interworking of beam failure recovery (BFR) and cell handover according to some further example embodiments of the present disclosure. As shown in FIG. 3B, the signaling flow 300B involves the terminal device 310, the network entity 320, and the network entity 330.

[0094] The terminal device 310 performs (307B) an early resource acquisition procedure with a network entity of a second cell, to obtain at least an uplink resource of the second cell. The early acquisition procedure may sometimes also be referred to as an early timing advance acquisition procedure if TA information as well as the uplink resource is acquired from the second cell. The early timing advance and / or resource acquisition procedure may include that, during the on-going beam failure recovery procedure, the terminal device 310 transmits a request message to the network entity 330 providing the second cell, to request for TA information and uplink resource of the second cell. The request message, as mentioned above, may include a random access request (e.g., a random access preamble such as PRACH preamble). The terminal device 310 may then receive the TA information and an indication of the allocated uplink resource of the second cell from the networkentity 330 directly or forwarded by the network entity 320. The TA information and the indication of the allocated uplink resource may be conveyed in the RAR as a response to the random access request or may be included in any other signaling or information such as via a MAC CE. The details of the early resource acquisition procedure may be referred to FIG. 3 A, which will not be repeated here.

[0095] In some example embodiments, once the terminal device 310 has obtained the TA information and the uplink resource of the second cell, it may not directly trigger the handover procedure from the first cell to the second cell, it may wait for the outcome of the on-going BFR procedure. If the BFR procedure is successfully completed, the terminal device 310 performs (309B) the beam switch in the first cell, e.g., to switch to the recovered beam(s) and thus may continue staying in the first cell.

[0096] In some example embodiments, after the terminal device 310 has switched to the recovered beam(s) in the first cell, the terminal device 310 transmits (31 IB) an indication of successful completion of the beam failure recovery procedure towards the network entity 330. In some example embodiments, rather than directly transmitting the indication to the network entity 330, the terminal device 310 may transmit the indication to the network entity 320 via the recovered beam of the first cell. Then the network entity 320 may forward the indication to the network entity 330.

[0097] In some example embodiments, during a handover preparation procedure for the terminal device 310, the network entity 320 may transmit (301B) a configuration to the terminal device 310. The configuration may configure the terminal device 310 to transmit the indication of successful completion upon the BFR procedure is successfully completed. The terminal device 310 may receive (303B) the configuration from the network entity 320. When the terminal device 310 detects a beam failure, the terminal device 310 initiates (305B) a beam failure recovery procedure for the first cell.

[0098] Based on reception of the indication, the network device 330 may determine that the BFR procedure of the terminal device 310 succeeds and deduces that the terminal device 310 may maintain in the first cell instead of handover towards the second cell. In this case, the network device 330 may revoke or release the uplink resource allocated to the terminal device 310 in the uplink resource configuration.

[0099] In some example embodiments, the network entity 330 may release the uplink resource allocated to the terminal device 310. For example, when the network entity 330determines that no cell handover towards the second cell is triggered by the terminal device 310, the network entity 330 may release the uplink resource allocated to the terminal device 310. In some example embodiments, the network entity 330 may maintain a timer and as long as the timer is active, the uplink resource (e.g., PUSCH resources) which was allocated to the terminal device 310 is valid for the terminal device 310. As the timer expires and if a cell switch is not triggered by the terminal device 310 to the second cell, the network entity 330 may revoke the PUSCH resources it granted to the terminal device 310.

[0100] In some other example embodiments, to allow the network entity 330 timely releasing the uplink resource allocated to the terminal device in the case that the BFR procedure is successfully completed, the terminal device 310 may be configured to transmit an indication in an early stage. FIG. 3C illustrates a signaling flow 300C for interworking of beam failure recovery (BFR) and cell handover according to such example embodiments of the present disclosure. As shown in FIG. 3C, the signaling flow 300B involves the terminal device 310, the network entity 320, and the network entity 330.

[0101] In the signaling flow 300C, when the terminal device 310 detects the beam failure, and initiates the BFR, the terminal device 310 transmits (305C) a request message to the network entity 330, to request for at least an uplink resource of the second cell, and optionally request for TA information of the second cell. The request message may further include an indication indicating early timing advance and / or resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device 310.

[0102] In some example embodiments, the request message may include a random access preamble, and the indication may be a separate flag in addition to the random access preamble in the request message. In some example embodiments, the indication may be included in the random access preamble configured to indicate the early timing advance and / or resource acquisition during the on-going beam failure recovery procedure. For example, there may be one or more random access preambles that are configured as specified preambles to indicate the early timing advance and / or resource acquisition during the on-going beam failure recovery procedure. The terminal device 310, when initiating the request message to the second cell, may select one of those preambles for transmission towards the second cell.

[0103] In some example embodiments, during the handover preparation procedure, thenetwork entity 320 may transmit, to the terminal device 310, a configuration of transmitting the indication in association with the request message (e.g., with the random access preamble) towards a network entity of a candidate cell during an on-going BFR procedure for a serving cell. As an example, the network entity 320 may transmit this configuration in the RRC reconfiguration message to the terminal device 310. The terminal device 310 may receive (303C) the configuration from the network entity 320. Upon receiving this configuration, the terminal device 310 may be enabled to transmit the indication in association with the request message towards the second cell.

[0104] The network entity 330 receives (307C) the request message including the indication from the terminal device 310. When the network entity 330 receives the request message and determines the indication included therein, the network entity 330 determines that the terminal device 310 requests for the uplink resource of the second cell (and optionally, the TA information) for a preemptive recovery procedure. The network entity 330 transmits (309C) the RAR to the terminal device 310. In some example embodiments, the network entity 330 may transmit the RAR to the network entity 320, and the network entity 320 may transmit the RAR to the terminal device 310. The terminal device 310 receives (311C) the RAR from the network entity 330. The transmission of the RAR and the information included in the RAR may be similar to those discussed above.

[0105] In some example embodiments, if the BFR procedure is successfully completed, the terminal device 310 performs (313C) the beam switch in the first cell, e.g., to switch to the recovered beam(s) and thus may continue staying in the first cell. If the BFR procedure fails, the terminal device 310 performs (313C) the cell handover from the first cell to the second cell based at least on the uplink resource of the second cell. In some examples, the cell handover may be performed further based on the TA information of the second cell.

[0106] In some example embodiments, after transmitting the RAR, the network entity 330 determines (315C) whether to release the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time. In some example embodiments, if no cell handover towards the second cell is triggered by the terminal device 310 within a predetermined period of time, the network entity 330 may release the uplink resource of the second cell.

[0107] Based on the received request message and the indication, the network entity 330may be aware that the acquisition of the TA information and the uplink resource is triggered by the terminal device 310 due to its preemptive RACH-less recovery procedure, and may thus start a timer to monitor the handover triggered by the terminal device towards it. In some example embodiments, the terminal device 310 may not need to additionally transmit the indication of successful BFR completion when the BFR procedure succeeds.

[0108] In some example embodiments, when the network entity 330 receives the indication indicating early timing advance and / or resource acquisition during the on-going BFR procedure_for a first cell, it may start a timer with the predetermined period of time. As long as the timer is active, the uplink resource (e.g., PUSCH resource) which was allocated by the network entity 330 in order to perform the preemptive RACH-less recovery is valid for the terminal device 310. As the timer expires and if a cell switch is not triggered by the terminal device 310 to the second cell, in that case the network entity 330 may release the uplink resource of the second cell it granted to the terminal device 310. In some examples, the value of the timer may be determined based on the BFR timer configured to the network entity 330. In some other examples, the value of the timer may be determined or configured as any other suitable values.

[0109] In some example embodiments, the network entity 330 may detect a cell handover towards the second cell triggered by the terminal device 310 while the timer is running. If the cell handover is triggered while the timer is running, the network entity 330 may terminate the timer. In this case, if the BFR procedure for the first cell fails, the terminal device 310 may determine to hand over to the second cell based on the already acquired or available TA information and the uplink resource of the second cell. Upon the trigger of the cell handover by the terminal device 310, the network entity 330 of the second cell may not need to monitor the release of the uplink resource using the running timer.

[0110] FIG. 4A illustrates a signaling flow 400A for LTM preparation according to some example embodiments of the present disclosure. The signaling flow 400A (as well as the signaling flows 400B-400D described below) involves a terminal device 491, a source DU 492, a target DU 493, and a CU 494.[OHl] The signaling flow 400A illustrates an intra-CU LTM scenario. It is assumed that the source DU 492 provides a serving cell for the UE 491, and the target DU 493 provides a target cell that is prepared for the cell handover of the UE 491. It would be appreciatedthat the operations performed by the source DU 492 and the target DU 493 may be similarly applied to the intra-CU LTM scenario, a CHO procedure, or a scenario involving RAN network nodes without a distribution of DU and CU.

[0112] At Step 401: the terminal device 491 transmits the L3 measurement report to the source DU 492 which provides a serving or source cell for the terminal device 492. The L3 measurement report may include measurement information about the serving cell and one or mor neighbor cells.

[0113] At Step 402: the source DU 492 forwards the L3 measurements to the source CU 494, e.g., through UL RRC message transfer.

[0114] At Step 403: the source CU 494 determines to configure one or more candidate cell(s) for L1 / L2 triggered mobility for intra-CU LTM.

[0115] At Step 404 and at Step 405: the source CU 494 sends the UE context set-up request to the candidate cell(s) belonging to the candidate DU which is different from the source DU 492 but under the same CU (e.g., a gNB). The source CU 494 then receives the UE Context Set-up Response from the candidate DU.

[0116] At Step 406: the source CU 494 sends the UE context modification request to the source DU 492 which contains the CSI resource configuration request for LTM reporting configuration for the selected list of candidate IDs.

[0117] At Step 407: the source DU 492 then send the UE context modification response to the source CU 494.

[0118] At Step 408: the source CU 494 now prepares the RRC reconfiguration message which contains the LTM configuration of the selected candidate cell(s) including the conditional-LTM execution conditions which it has received from the serving DU and transmit it to the serving-DU as a transparent container.

[0119] In some example embodiments of the present disclosure, the RRC reconfiguration message may also contain the indication of enabling early timing advance and / or resource acquisition of a candidate cell during the BFR procedure in the serving cell, e.g., the preemptive LTM recovery indication. As discussed above, this indication may indicate that the early timing advance and / or resource acquisition is enabled upon beam failure detection and BFR triggered by the terminal device 491.

[0120] In some example embodiments of the present disclosure, the RRC reconfiguration message may further contain a configuration of transmitting an indication of successful completion of the BFR procedure by the terminal device. As discussed above, this configuration may configure the terminal device to transmit an indication of successful completion of the BFR procedure towards the cell of the target DU 493 if the BRF procedure is successfully completed.

[0121] In some example embodiments of the present disclosure, the RRC reconfiguration message may further contain a configuration for transmitting an indication indicating early timing advance and / or resource acquisition during an on-going BFR procedure. As discussed above, this configuration may configure the terminal device to transmit this indication together with the request message towards the target cell of the target DU 493.

[0122] At Step 409 and at Step 410: the source DU 492 upon receiving the transparent container containing the RRC reconfiguration message and the proposed preemptive LTM recovery indication and the proposed configuration(s), forwards the same to the terminal device 491.

[0123] It would be appreciated that although it is shown as being included in the same RRC message, the preemptive LTM recovery indication and the proposed configuration(s) may be transmitted in separate messages to the terminal device 491.

[0124] At Step 411: the terminal device 491 reads the RRC reconfiguration along with the proposed preemptive LTM recovery indication and optionally, the proposed configuration(s). The terminal device 491 upon reading this indication is aware of the behavior which describes a set of actions that the terminal device 491 needs to perform in case if beam failure is detected by the terminal device 491 over the serving cell (beam failure detection) and in case the terminal device 491 initiates the beam failure recovery. The details of the terminal device 491 behavior triggered by the indication are described in the above.

[0125] At Step 412 and At Step 413: the terminal device 491 sends the RRC reconfiguration complete message to the CU 494 via the source DU 492.

[0126] At Step 414: the terminal device 491 detects beam failure over the serving cell, e.g., based on the out-of-synchronization (OoS) indications and in- synchronization (IS) indications.

[0127] If the OoS indications exceed the corresponding BFD threshold over the serving cell or if the IS indications exceed the corresponding BFD threshold over the serving cell, then at Step 415, the terminal device 491 triggers abeam failure recovery (BFR) procedure for the serving cell.

[0128] At Step 416: the terminal device 491 determines a candidate cell which is LTM prepared whose signal strength is better than a given threshold and at the same time the signal strength of the serving cell is below a certain threshold. Then the terminal device 491 may operate in some manners as discussed in FIGS. 4B-4D.

[0129] FIG. 4B illustrates a signaling flow 400B for interworking of beam failure recovery (BFR) and cell handover in a first scenario according to some example embodiments of the present disclosure. The signaling flow 400B may follow the steps of the signaling flow 400 A after the terminal device 491 triggers a BFR procedure and determines that a candidate cell strength is better than a specified threshold and the serving cell strength is lower than a specified threshold. The signaling flow 400B may be considered as some example embodiments of the signaling flow 300A.

[0130] At Step 417: As per the terminal device 491 behavior indicated in the preemptive recovery Indication, the terminal device 491 initiates the preemptive recovery procedure and applies the PRACH configuration of the candidate cell temporarily. This will temporarily halt the ongoing BFR procedure.

[0131] At Step 418: the terminal device 491 sends the PRACH preamble to the best candidate or target cell which is LTM prepared to obtain the TA information and uplink resource of the candidate or target cell.

[0132] At Step 419: the terminal device 491 temporarily applies the PDCCH configuration to detect the RAR from the target DU 493.

[0133] At Step 420: the target DU 493 sends the RAR message containing the TA and an indication of the uplink resource of the target cell (e.g., the PUSCH resources). The terminal device 491 receives the RAR message to achieve early acquisition of TA and uplink resource of the target cell.

[0134] At Step 421: the terminal device 491 determines for how long it can hold the uplink resources assigned by the target cell. The time period may be determined by the terminal device 491 or may be configured by the network.

[0135] At Step 422: upon reception of the TA information and the uplink resource of the target cell, the terminal device 491 reverts back to the serving cell configuration and restarts the BFR procedure. The terminal device 419 may not trigger immediately the RACH-less recovery towards the target cell of the target DU 493 but will wait for the outcome of the BFR procedure for the serving cell.

[0136] At Step 423-1: the terminal device 491 determines that the BFR procedure has failed, for example, the BFR timer has expired, and the terminal device 491 has not yet received any beam recovery indication from the serving cell.

[0137] At Step 424-1: the terminal device 491 applies the best LTM candidate cell configuration. At Step 425-1 and at Step 426-1: the terminal device 491 sends the RRC reconfiguration complete message to the candidate cell as the first PUSCH transmission which indicates successful completion of RACH-less recovery towards the target cell using the TA and uplink resource which was acquired during the preemptive recovery during at Step 417 to Step 420. In this case, the successful completion of RACH-less LTM recovery phase may be achieved with no additional interruptions caused due to the triggering of BFR procedure by the terminal device and eventual BFR failure.

[0138] FIG. 4C illustrates a signaling flow 400C for interworking of beam failure recovery (BFR) and cell handover in a second scenario according to some example embodiments of the present disclosure. The signaling flow 400C may follow the steps of the signaling flow 400 A after the terminal device 491 triggers a BFR procedure and determines that a candidate cell strength is better than a specified threshold and the serving cell strength is lower than a specified threshold. The signaling flow 400C may be considered as some example embodiments of the signaling flow 300B.

[0139] In the signaling flow 400C, Step 417 to Step 422 may be similar as those in the signaling flow 400B.

[0140] At Step 423-2: the terminal device 491 determines that the BFR has successfully completed, and the terminal device 491 has received the Beam Recovery indication from the serving cell before the beam recovery timer expiry.

[0141] At Step 424-2: the terminal device 491 determines to continue with the serving cell as the BFR procedure succeeds.

[0142] At Step 425-2, at Step 426-2 and at Step 427-2: the terminal device 491determines to send the successful BFR completion indication to the target DU 493 through the source DU 492 and the CU 494, or directly to the target DU 493. In some example embodiments, the terminal device 491 may be configured, e.g., in the RRC configuration message, to transmit the successful BFR completion indication when the BFR procedure is successful. In some example embodiments, the terminal device 491 may be preconfigured or prespecified to transmit the successful BFR completion indication, and thus no explicit configuration from the network side is needed.

[0143] At Step 428-2: the target DU 493, upon receiving the successful BFR completion indication is now aware the terminal device 491 will not perform handover and will continue to remain with its current serving cell, Therefore, the target DU 493 would now revoke the UL grants (PUSCH configuration) which it assigned to the terminal device 491 during the preemptive recovery procedure.

[0144] FIG. 4D illustrates a signaling flow 400D for interworking of beam failure recovery (BFR) and cell handover in a third scenario according to some example embodiments of the present disclosure. The signaling flow 400C may follow the steps of the signaling flow 400 A after the terminal device 491 triggers a BFR procedure and determines that a candidate cell strength is better than a specified threshold and the serving cell strength is lower than a specified threshold. The signaling flow 400D may be considered as some example embodiments of the signaling flow 300C.

[0145] In the signaling flow 400C, Step 417 may be similar as Step 417 in the signaling flow 400B.

[0146] At Step 418-2: the terminal device 491 sends the PRACH preamble to the best candidate or target cell which is LTM prepared to obtain the TA information and uplink resource of the candidate or target cell. In addition, the terminal device 491 may transmit an indication of early timing advance and / or resource acquisition during the on-going BFR procedure in association with the PRACH preamble.

[0147] In some example embodiments, the terminal device 491 may be configured, e.g., in the RRC configuration message, to transmit the indication of early timing advance and / or resource acquisition during the on-going BFR procedure. In some example embodiments, the terminal device 491 may be preconfigured or prespecified to transmit the indication in association with the preamble, and thus no explicit configuration from the network side is needed.

[0148] The following Step 419 to Step 422 may be similar as those in the signaling flow 400B.

[0149] At Step 423-3 : the terminal device 491 may determine whether the BFR procedure is successfully completed or failed. At Step 424-3: the terminal device 491 determines to continue with the serving cell if the BFR procedure succeeds or to perform cell handover to the target cell if the BFR procedure fails. In either case, the terminal device 491 may not need to further indicate the outcome of the BFR procedure to the target cell.

[0150] At the side of the target DU, upon reception of the indication of the early timing advance and / or resource acquisition from the terminal device 491, at Step 429, the target DU 493 starts a timer to monitor cell handover triggered by the terminal device 491. The value of the timer may be determined based on the BFR timer configured to the target DU, or as any other suitable predetermined or preconfigured values.

[0151] At step 430, if no cell handover is triggered by the termina device 491, the target DU 493 may release the PUSCH configuration or the allocated uplink resource for the terminal device 491; if handover is triggered by the terminal device 491, the handover may be performed using the TA information and the PUSCH configuration.

[0152] FIG. 5 A illustrates a flowchart of a method 500 A implemented at a first apparatus in accordance with some example embodiments of the present disclosure. The first apparatus may be or may be included in a terminal device, such as the terminal device 120 in FIG. 1. For the purpose of discussion, the method 500A will be described from the perspective of the first apparatus.

[0153] At block 510, based on an on-going beam failure recovery procedure for a first cell, the first apparatus transmits to a network entity of a second cell, a request message for an uplink resource of the second cell.

[0154] At block 520, the first apparatus receives a response message from the network entity of the second cell, the response message at least including an indication of the uplink resource of the second cell.

[0155] At block 530, based on a determination of whether the beam failure recovery procedure is successfully completed or failed, the first apparatus performs a beam switch in the first cell or perform a cell handover from the first cell to the second cell based at least on and the uplink resource of the second cell.

[0156] In some example embodiments, the method 500A may further include: in accordance with a determination that the beam failure recovery procedure is successfully completed, performing the beam switch in the first cell.

[0157] In some example embodiments, the method 500A may further include: in accordance with a determination that the beam failure recovery procedure is failed, performing the cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0158] In some example embodiments, the response message further comprises timing advance information of the second cell. In some example embodiments, the method 500A may further include: in accordance with a determination that the beam failure recovery procedure is failed, performing the cell handover from the first cell to the second cell based on the timing advance information and the uplink resource of the second cell.

[0159] In some example embodiments, the method 500A may further include: receiving, from a network entity of the first cell, an indication of enabling early resource acquisition of a candidate cell during a beam failure recovery procedure in a serving cell; and based on the reception of the indication, transmitting the request message to the network entity of the second cell during the on-going beam failure recovery procedure for the first cell.

[0160] In some example embodiments, the method 500A may further include: based on the on-going beam failure recovery procedure for the first cell and further based on a determination that a cell strength of the second cell is above a second cell strength threshold and a cell strength of the first cell is less than a first cell strength threshold, transmitting the request message to the network entity of the second cell.

[0161] In some example embodiments, the method 500A may further include: before transmitting the request message to the network entity of the second cell, suspending the on-going beam failure recovery procedure; and resuming the suspended beam failure recovery procedure after reception of the response message from the network entity of the second cell.

[0162] In some example embodiments, the response message from the network entity of the second cell may be forwarded by the network entity of the first cell after the beam failure recovery procedure is resumed.

[0163] In some example embodiments, the method 500A may further include: discardingthe uplink resource configuration of the second cell after a predetermined time period or based on a determination that the beam failure recovery procedure is successfully completed.

[0164] In some example embodiments, performing the cell handover from the first cell to the second cell may include: based on a determination that the beam failure recovery procedure is failed, transmitting, to the network entity of the second cell based at least on the uplink resource of the second cell, a message indicating successful completion of cell handover to the second cell.

[0165] In some example embodiments, the request message may include a random access preamble selected from a set of dedicated random access preambles, and the response message may include a random access response to the random access preamble.

[0166] In some example embodiments, the first apparatus may be or may be comprised in a terminal device, and / or a network entity of the first cell may include a first distributed unit, DU, associated with a first centralized unit, CU, and the network entity of the second cell may include a second DU associated with the first CU or associated with a second CU.

[0167] In some example embodiments, a first apparatus capable of performing any of the method 500A (for example, the terminal device 120 in FIG. 1) may include means for performing the respective operations of the method 500A. In some example embodiments, the first apparatus includes means for based on an on-going beam failure recovery procedure for a first cell, transmitting to a network entity of a second cell, a request message for an uplink resource of the second cell; means for receiving a response message from the network entity of the second cell, the response message including the timing advance information and an indication of the uplink resource of the second cell; and means for based on a determination of whether the beam failure recovery procedure is successfully completed or failed, performing a beam switch in the first cell or performing a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0168] In some example embodiments, the first apparatus may further include means for performing any of the described one or more example embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or includedin the terminal device 120 in FIG. 1 or the terminal device 310 in FIGS. 3A-3C, or the terminal device 491 in FIGS. 4A-4D.

[0169] FIG. 5B illustrates a flowchart of a method 500B implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 500B will be described from the perspective of the second apparatus.

[0170] At block 540, the second apparatus receives, from a terminal device, a request message for an uplink resource of the second cell during an on-going beam failure recovery procedure for a first cell at the terminal device.

[0171] At block 550, the second apparatus transmits, to the terminal device, a response message, the response message at least including an indication of the uplink resource of the second cell.

[0172] In some example embodiments, the method 500B may further include: receiving, from the terminal device, a message indicating successful completion of cell handover to the second cell based at least on the uplink resource of the second cell.

[0173] In some example embodiments, the response message further comprises timing advance information of the second cell. In some example embodiments, the method 500B may further include: receiving, from the terminal device, a message indicating successful completion of cell handover to the second cell based at least on the timing advance information and the uplink resource of the second cell.

[0174] In some example embodiments, the method 500B may further include: based on determining that no cell handover towards the second cell is triggered by the terminal device, releasing the uplink resource allocated to the terminal device.

[0175] In some example embodiments, the request message may include a random access preamble selected from a set of dedicated random access preambles, and the response message may include a random access response to the random access preamble.

[0176] In some example embodiments, a second apparatus capable of performing any of the method 500B may include means for performing the respective operations of the method 500B. In some example embodiments, the second apparatus includes means for receiving, from a terminal device, a request message for an uplink resource of the second cell during an on-going beam failure recovery procedure for a first cell at the terminaldevice; and means for transmitting, to the terminal device, a response message, the response message at least including an indication of the uplink resource of the second cell.

[0177] In some example embodiments, the second apparatus may further include means for performing any of the described one or more example embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the network entity 330 in FIGS. 3A-3C, or the target DU 493 in FIGS.4A-4D.

[0178] FIG. 6A illustrates a flowchart of a method 600A implemented at a first apparatus in accordance with some further example embodiments of the present disclosure. The first apparatus may be or may be included in a terminal device, such as the terminal device 120 in FIG. 1. For the purpose of discussion, the method 600A will be described from the perspective of the first apparatus.

[0179] At block 610, the first apparatus initiates a beam failure recovery procedure for a first cell.

[0180] At block 620, during the on-going beam failure recovery procedure, the first apparatus performs an early timing advance acquisition procedure with a network entity of a second cell, to obtain at least an indication of an uplink resource of the second cell.

[0181] At block 630, based on a determination that the beam failure recovery procedure is successfully completed, the first apparatus transmits an indication of successful completion of the beam failure recovery procedure towards the network entity of the second cell.

[0182] In some example embodiments, the method 600A may further include: receiving, from a network entity of the first cell, a configuration to configure the first apparatus to transmit the indication of successful completion upon the beam failure recovery procedure is successfully completed; and based on the configuration and based on a determination that the beam failure recovery procedure is successfully completed, transmitting the indication of successful completion of the beam failure recovery procedure towards the network entity of the second cell.

[0183] In some example embodiments, the configuration may be received in a radio resource control configuration during a handover preparation procedure.

[0184] In some example embodiments, the method 600 A may further include: transmitting the indication to a network entity of the first cell via a recovered beam of the first cell, to cause the network entity of the first cell to forward the indication to the network entity of the second cell.

[0185] In some example embodiments, the method 600 A may further include: during the on-going beam failure recovery procedure, performing an early resource acquisition procedure with the network entity of the second cell, to obtain timing advance information and an indication of an uplink resource of the second cell.

[0186] In some example embodiments, performing the early resource acquisition procedure may include: during the on-going beam failure recovery procedure, transmitting a random access request to the network entity of the second cell; and receiving a random access response from the network entity of the second cell, the random access response at least including the indication of the uplink resource of the second cell.

[0187] In some example embodiments, the random access request may include a random access preamble selected from a set of dedicated random access preambles.

[0188] In some example embodiments, the method 600A may further include: in accordance with a determination that the beam failure recovery procedure is failed, performing the cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0189] In some example embodiments, the first apparatus may further be caused to: discard the uplink resource of the second cell after a predetermined time period or based on a determination that the beam failure recovery procedure is successfully completed.

[0190] In some example embodiments, the first apparatus may be or may be included in a terminal device, and / or a network entity of the first cell may include a first distributed unit, DU, associated with a first centralized unit, CU, and the network entity of the second cell may include a second DU associated with the first CU or associated with a second CU.

[0191] In some example embodiments, a first apparatus capable of performing any of the method 600A (for example, the terminal device 120 in FIG. 1) may include means for performing the respective operations of the method 600A. In some example embodiments, the first apparatus includes means for initiating a beam failure recovery procedure for afirst cell; means for during the on-going beam failure recovery procedure, performing an early resource acquisition procedure with a network entity of a second cell, to obtain at least an indication of an uplink resource of the second cell; and means for based on a determination that the beam failure recovery procedure is successfully completed, transmitting an indication of successful completion of the beam failure recovery procedure towards the network entity of the second cell.

[0192] In some example embodiments, the first apparatus may further include means for performing any of the described one or more example embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the terminal device 120 in FIG. 1 or the terminal device 310 in FIGS. 3A-3C, or the terminal device 491 in FIGS. 4A-4D.

[0193] FIG. 6B illustrates a flowchart of a method 600B implemented at a second apparatus in accordance with some further example embodiments of the present disclosure. For the purpose of discussion, the method 600B will be described from the perspective of the second apparatus.

[0194] At block 640, the second apparatus performs an early resource acquisition procedure with a terminal device during an on-going beam failure recovery procedure for a first cell at the terminal device, to provide the terminal device with at least an indication of an uplink resource of the second cell.

[0195] At block 650, the second apparatus receives, from the terminal device, an indication of successful completion of the beam failure recovery procedure for the first cell by the terminal device.

[0196] In some example embodiments, the method 600B may further include: based on reception of the indication, releasing the uplink resource allocated to the terminal device.

[0197] In some example embodiments, the method 600B may further include: performing an early resource acquisition procedure with a terminal device during an on-going beam failure recovery procedure for a first cell at the terminal device, to provide the terminal device with timing advance information and an indication of an uplink resource of the second cell.

[0198] In some example embodiments, the second apparatus may be caused to performthe early resource acquisition procedure by: receiving a random access request from a terminal device during the on-going beam failure recovery procedure; and transmitting a random access response to the terminal device, the random access response at least including the indication of the uplink resource of the second cell.

[0199] In some example embodiments, the second apparatus may be further caused to perform the early resource acquisition procedure by: receiving a random access request from the terminal device during the on-going beam failure recovery procedure for the first cell at the terminal device; and transmitting a random access response towards the terminal device, the random access response at least including the indication of the uplink resource of the second cell.

[0200] In some example embodiments, a second apparatus capable of performing any of the method 600B may include means for performing the respective operations of the method 500B. In some example embodiments, the second apparatus includes means for performing an early resource acquisition procedure with a terminal device during an ongoing beam failure recovery procedure for a first cell at the terminal device, to provide the terminal device with at least an indication of an uplink resource of the second cell; and means for receiving, from the terminal device, an indication of successful completion of the beam failure recovery procedure for the first cell by the terminal device.

[0201] In some example embodiments, the second apparatus may further include means for performing any of the described one or more example embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the network entity 330 in FIGS. 3A-3C, or the target DU 493 in FIGS.4A-4D.

[0202] FIG. 7 A illustrates a flowchart of a method 700 A implemented at a first apparatus in accordance with some yet further example embodiments of the present disclosure. The first apparatus may be or may be included in a terminal device, such as the terminal device 120 in FIG. 1. For the purpose of discussion, the method 700A will be described from the perspective of the first apparatus.

[0203] At block 710, during an on -going beam failure recovery procedure for a first cell, the first apparatus transmits, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message including a first indicationindicating early resource acquisition during the on-going beam failure recovery procedure.

[0204] At block 720, the first apparatus receives, from the network entity of the second cell, a response message at least including an indication of the uplink resource of the second cell.

[0205] At block 730, based on a determination of whether the beam failure recovery procedure is successfully completed or failed, the first apparatus performs a beam switch in the first cell or perform a cell handover from the first cell to the second cell based at least on and the uplink resource of the second cell.

[0206] In some example embodiments, the request message may include a random access preamble in addition to the first indication.

[0207] In some example embodiments, the request message may include a random access preamble, and the first indication may be included in the random access preamble configured to indicate the early resource acquisition during the on-going beam failure recovery procedure.

[0208] In some example embodiments, the request message may include a random access preamble selected from a set of dedicated random access preambles, and the response message may include a random access response to the random access preamble.

[0209] In some example embodiments, the response message further comprises timing advance information of the second cell. In some example embodiments, the method 700A further include: in accordance with a determination that the beam failure recovery procedure is failed, performing the cell handover from the first cell to the second cell based on the timing advance information and the uplink resource of the second cell.

[0210] In some example embodiments, the method 700A may further include: receiving, from a network entity of the first cell, a configuration of transmitting the first indication in association with the random access preamble towards the network entity of the second cell during the on-going beam failure recovery procedure.

[0211] In some example embodiments, the method 700 A may further include: starting a first timer for maintaining the uplink resource of the second cell; and based on expiry of the first timer, discarding the uplink resource of the second cell.

[0212] In some example embodiments, the method 700A may further include: receiving,from a network entity of the first cell, a second indication of enabling early resource acquisition of a candidate cell during the beam failure recovery procedure for the first cell; and based on the reception of the second indication, transmitting the request message to the network entity of the second cell during the on-going beam failure recovery procedure for the first cell.

[0213] In some example embodiments, the method 700A may further include: in accordance with a determination that the beam failure recovery procedure is successfully completed, performing the beam switch in the first cell; and in accordance with a determination that the beam failure recovery procedure is failed, performing the cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0214] In some example embodiments, the first apparatus may be or may be included in a terminal device, and / or wherein a network entity of the first cell may include a first distributed unit, DU, associated with a first centralized unit, CU, and the network entity of the second cell may include a second DU associated with the first CU or associated with a second CU.

[0215] In some example embodiments, a first apparatus capable of performing any of the method 700A (for example, the terminal device 120 in FIG. 1) may include means for performing the respective operations of the method 700A. In some example embodiments, the first apparatus includes means for during an on-going beam failure recovery procedure for a first cell, transmitting, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message including a first indication indicating early resource acquisition during the on-going beam failure recovery procedure; means for receiving, from the network entity of the second cell, a response message at least including an indication of the uplink resource of the second cell; and means for based on a determination of whether the beam failure recovery procedure is successfully completed or failed, performing a beam switch in the first cell or performing a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

[0216] In some example embodiments, the first apparatus may further include means for performing any of the described one or more example embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implementedin a circuitry or software module. The first apparatus may be implemented as or included in the terminal device 120 in FIG. 1 or the terminal device 310 in FIGS. 3A-3C, or the terminal device 491 in FIGS. 4A-4D.

[0217] FIG. 7B illustrates a flowchart of a method 700B implemented at a second apparatus in accordance with some yet further example embodiments of the present disclosure. For the purpose of discussion, the method 700B will be described from the perspective of the second apparatus.

[0218] At block 740, the second apparatus receives, from a terminal device, a request message for an uplink resource of the second cell, the request message including a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device.

[0219] At block 750, the second apparatus transmits, to the terminal device, a response message at least including an indication of the uplink resource of the second cell.

[0220] At block 760, the second apparatus determines release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

[0221] In some example embodiments, the method 700B may further include: releasing the uplink resource of the second cell based on reception of the first indication and further based on determining that no cell handover towards the second cell is triggered by the terminal device within a predetermined period of time.

[0222] In some example embodiments, the method 700B may further include: based on reception of the first indication, starting a timer with the predetermined period of time; and upon expiry of the timer, release the uplink resource of the second cell based on determining that no cell handover towards the second cell is triggered by the terminal device.

[0223] In some example embodiments, the method 700B may further include: detecting a cell handover towards to the second cell triggered by the terminal device while the timer is running; and terminating the timer based on the triggered cell handover.

[0224] In some example embodiments, the response message further comprises timing advance information of the second cell. In some example embodiments, the method 700B may further include: receiving, from the terminal device, a message indicating successfulcompletion of cell handover to the second cell based at least on the timing advance information and the uplink resource of the second cell.

[0225] In some example embodiments, the method 700B may further include: receiving, from the terminal device, a message indicating successful completion of cell handover to the second cell based at least on the uplink resource of the second cell.

[0226] In some example embodiments, the request message may include a random access preamble selected from a set of dedicated random access preambles, and the response message may include a random access response to the random access preamble.

[0227] In some example embodiments, a second apparatus capable of performing any of the method 700B may include means for means for receiving, from a terminal device, a request message for an uplink resource of the second cell, the request message including a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device; means for transmitting, to the terminal device, a response message at least including an indication of the uplink resource of the second cell; and means for determining release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

[0228] In some example embodiments, the second apparatus may further include means for performing any of the described one or more example embodiments thereof. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the network entity 330 in FIGS. 3A-3C, or the target DU 493 in FIGS.4A-4D.

[0229] FIG. 8 is a simplified block diagram of a device 800 that is suitable for implementing example embodiments of the present disclosure. The device 800 may be provided to implement a communication device, for example, the terminal device 120, the network device 110, or the DU 114 or DU 112 as shown in FIG. 1. As shown, the device 800 includes one or more processors 810, one or more memories 820 coupled to the processor 810, and one or more communication modules 840 coupled to the processor 810.

[0230] The communication module 840 is for bidirectional communications. The communication module 840 has one or more communication interfaces to facilitatecommunication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 840 may include at least one antenna.

[0231] The processor 810 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 800 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.

[0232] The memory 820 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 824, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random-access memory (RAM) 822 and other volatile memories that will not last in the power-down duration.

[0233] A computer program 830 includes computer executable instructions that are executed by the associated processor 810. The instructions of the program 830 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 830 may be stored in the memory, e.g., the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

[0234] The example embodiments of the present disclosure may be implemented by means of the program 830 so that the device 800 may perform any process of the disclosure as discussed with reference to FIG. 3 A to FIG. 7C. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0235] In some example embodiments, the program 830 may be tangibly contained in a computer readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer readable medium to the RAM 822 forexecution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0236] FIG. 9 shows an example of the computer readable medium 900 which may be in the form of CD, DVD or other optical storage disk. The computer readable medium 900 has the program 830 stored thereon.

[0237] 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, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method 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.

[0238] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computerexecutable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. 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.

[0239] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may beprovided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, 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 be executed 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.

[0240] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0241] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer 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 computer 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.

[0242] Further, although 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, although 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. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0243] Although the present disclosure has been described in languages 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

WHAT IS CLAIMED IS1. A first apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to:during an on-going beam failure recovery procedure for a first cell, transmit, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during the on-going beam failure recovery procedure;receive, from the network entity of the second cell, a response message comprising at least an indication of the uplink resource of the second cell; and based on a determination of whether the beam failure recovery procedure is successfully completed or failed, perform a beam switch in the first cell or perform a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

2. The first apparatus of claim 1, wherein the request message comprises a random access preamble in addition to the first indication.

3. The first apparatus of claim 1, wherein the request message comprises a random access preamble, and the first indication is comprised in the random access preamble configured to indicate the early resource acquisition during the on-going beam failure recovery procedure.

4. The first apparatus of any of claims 1 to 3, wherein the request message comprises a random access preamble selected from a set of dedicated random access preambles, and wherein the response message comprises a random access response to the random access preamble.

5. The first apparatus of any of claims 1 to 4, wherein the response message further comprises timing advance information of the second cell, and wherein the first apparatus is caused to:in accordance with a determination that the beam failure recovery procedure is failed,perform the cell handover from the first cell to the second cell based on the timing advance information and the uplink resource of the second cell.

6. The first apparatus of any of claims 1 to 5, wherein the first apparatus is caused to: receive, from a network entity of the first cell, a configuration of transmitting the first indication in association with the random access preamble towards the network entity of the second cell during the on-going beam failure recovery procedure.

7. The first apparatus of any of claims 1 to 6, wherein the first apparatus is further caused to:start a first timer for maintaining the uplink resource of the second cell; andbased on expiry of the first timer, discard the uplink resource of the second cell.

8. The first apparatus of any of claims 1 to 7, wherein the first apparatus is further caused to:receive, from a network entity of the first cell, a second indication of enabling early resource acquisition of a candidate cell during the beam failure recovery procedure for the first cell; andbased on the reception of the second indication, transmit the request message to the network entity of the second cell during the on-going beam failure recovery procedure for the first cell.

9. The first apparatus of any of claims 1 to 8, wherein the first apparatus is caused to: in accordance with a determination that the beam failure recovery procedure is successfully completed, perform the beam switch in the first cell; andin accordance with a determination that the beam failure recovery procedure is failed, perform the cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

10. The first apparatus of any of claims 1 to 9, wherein the first apparatus is or is comprised in a terminal device, and / orwherein a network entity of the first cell comprises a first distributed unit, DU, associated with a first centralized unit, CU, and the network entity of the second cell comprises a second DU associated with the first CU or associated with a second CU.

11. A second apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus providing a second cell at least to:receive, from a terminal device, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device;transmit, to the terminal device, a response message at least comprising an indication of the uplink resource of the second cell; anddetermine release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

12. The second apparatus of claim 11, wherein the second apparatus is caused to: release the uplink resource of the second cell based on reception of the first indication and further based on determining that no cell handover towards the second cell is triggered by the terminal device within a predetermined period of time.

13. The second apparatus of claim 11 or 12, wherein the second apparatus is caused to: based on reception of the first indication, start a timer with the predetermined period of time; andupon expiry of the timer, release the uplink resource of the second cell based on determining that no cell handover towards the second cell is triggered by the terminal device.

14. The second apparatus of claim 13, wherein the second apparatus is caused to: detect a cell handover towards to the second cell triggered by the terminal device while the timer is running; andterminate the timer based on the triggered cell handover.

15. The second apparatus of any of claims 11 to 14, wherein the response message further comprises timing advance information of the second cell, and wherein the second apparatus is caused to:receive, from the terminal device, a message indicating successful completion of cellhandover to the second cell based at least on the timing advance information and the uplink resource of the second cell.

16. The second apparatus of any of claims 11 to 15, wherein the second apparatus is further caused:receive, from the terminal device, a message indicating successful completion of cell handover to the second cell based at least on the uplink resource of the second cell.

17. The second apparatus of any of claims 11 to 16, wherein the request message comprises a random access preamble selected from a set of dedicated random access preambles, andwherein the response message comprises a random access response to the random access preamble.

18. A method comprising:during an on-going beam failure recovery procedure for a first cell, transmitting, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during the on-going beam failure recovery procedure;receiving, from the network entity of the second cell, a response message at least comprising an indication of the uplink resource of the second cell; andbased on a determination of whether the beam failure recovery procedure is successfully completed or failed, performing a beam switch in the first cell or performing a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

19. A method comprising:receiving, from a terminal device, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device;transmitting, to the terminal device, a response message at least comprising an indication of the uplink resource of the second cell; anddetermining release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

20. A first apparatus, comprising:means for, during an on-going beam failure recovery procedure for a first cell, transmitting, to a network entity of a second cell, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during the on-going beam failure recovery procedure;means for receiving, from the network entity of the second cell, a response message at least comprising an indication of the uplink resource of the second cell; and means for, based on a determination of whether the beam failure recovery procedure is successfully completed or failed, performing a beam switch in the first cell or performing a cell handover from the first cell to the second cell based at least on the uplink resource of the second cell.

21. A second apparatus, comprising:means for receiving, from a terminal device, a request message for an uplink resource of the second cell, the request message comprising a first indication indicating early resource acquisition during an on-going beam failure recovery procedure for a first cell at the terminal device;means for transmitting, to the terminal device, a response message at least comprising and an indication of the uplink resource of the second cell; andmeans for determining release of the uplink resource based on a determination of whether a cell handover is triggered by the terminal device within a predetermined period of time.

22. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of claim 18 or the method of claim 19.

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