Method for conditional handover

Abstract

The present disclosure describes method for Non Terrestrial Networks (NTN) conditional and RACH-less handover comprising the steps: Performing UE mobility prediction and group UEs, whereby a determination of different suitable CHO configurations and / or sequence of multiple CHO candidates is done, pre-allocating UL grants, considering UE's QoS requirements and mobility characteristics.

Description

[0001] TITLE

[0002] Method for conditional handover

[0003] TECHNNICAL FIELD

[0004] The 3rd Generation Partnership Project (3GPP) is a standards organization which develops protocols for mobile telephony and is known for the development and maintenance of various standards including second generation (2G), third generation (3G), fourth generation (4G), Long Term Evolution (LTE), and fifth generation (5G) standards.

[0005] The 5G network has been designed as a Service Based Architecture (SBA) or, in other words, a system architecture in which the system functionality is achieved by a set of network functions providing services to other authorized network functions to access their services. The 5G network may comprise a plurality of base stations (e.g., Next generation NodeB (gNB), etc.) that serve multiple cells across a particular area.

[0006] As a User Equipment (UE) moves through the particular area cell changes, known as handovers in the connected mode, occur to maintain connectivity between the UE and the serving Radio Access Network (RAN). Moreover, cells transmit and receive data via multiple beams. Handover procedures may be triggered as a result of rotation of the UE or as a result of obstructions between the UE and base stations e.g., a wall, etc.

[0007] Conditional Handover (CHO) allows a source cell to prepare a UE with multiple target cells for future handover procedures. The preparation for the CHO occurs during good radio conditions between the source cell and the UE before the handover is required to maintain communication. The UE determines that a CHO is necessary based on detection of a configured condition. Upon detection of conditions necessitating the CHO, the UE executes the prepared CHO to one of the target cells. The CHO is more likely to happen because of preparation during good radio conditions and the handover between cells is triggered during poorer radio conditions.

[0008] BACKGROUND

[0009] Specify NTN-TN and NTN-NTN measurement / mobility and service continuity enhancements are defined. For NTN-NTN mobility, specify cell reselection enhancements for earth moving cell, the timing based and location-based cell reselection for quasi-earth fixed cell in Rel-17 can be considered as the starting point. Specify NTN-NTN handover enhancement for RRC_CONNECTED UEs in the quasi- earth-fixed cell and earth-moving cell to reduce the signaling overhead. Specify cell reselection enhancements for RRCJDLE / INACTIVE UEs to reduce UE power consumption are about to be defined and NTN-TN mobility is prioritized.

[0010] At least for pre-allocated grant, for the confirmation of RACH-less HO completion a reuse of LTE approach is known, i.e., UE Contention Resolution Identity MAC CE is used but UE ignores the content of this field. FFS is taken into account if anything else is needed for dynamic grant. Considering to support combining RACH-less HO with time-based CHO for NTN, taking into account the validity of pre-allocated grant and potential waste of reserved resource; when / how to provide dynamic grant in PDCCH.

[0011] In NTN RACH-less handover, NW either indicates NTA in the target cell is identical to the source cell, or the NTA explicitly provided by the NW is 0. RACH-less handover will be limited to NTNs at same orbit and speed. The synchronization among source and target cells is not an issue in NTN RACH-less HO. Release pre-allocated UL grant after RACH-less HO completion. The LTE approach of confirming the HO completion is reused for both pre-allocated grant and dynamic grant. FFS any enhancement to the confirmation of RACH-less HO completion, e.g. the NW does not send the UE Contention Resolution Identity MAC CE, and sends PDCCH / PDSCH addressed to C-RNTI. Remove “FFS how to perform RACH-less UL synchronization to NTN target cell”, the UL sync handling in the target cell is the same in RACH- based HO and RACH-less HO, except how to acquire NTA, FFS on the spec impact, if any.

[0012] At least the scenario of intra-satellite HO within the same gNB is possible, and the scenarios of intra-satellite HO between gNBs, inter-satellite HO within the same gNB and inter-satellite HO between gNBs may also be possible, as long as UE uplink transmission synchronization can be maintained by applying correct Timing Advance (TA) pre-com pensation in the target cell. Based on the above reply the are some approaches in supporting RACH-less HO in NTN.

[0013] US 2021282061 A1 describes methods, systems, and devices for wireless communications for management of conditional handover (CHO) configurations. A source base station may configure a user equipment (UE) with one or more CHO configurations for multiple target base stations. The CHO configurations may provide, for each target base station, one or more associated conditions that may trigger the UE to initiate a handover to the particular target base station, or to deconfigure a CHO configuration, such as based on a measurement threshold of one or more target base station measurements, one or more source base station measurements, or combinations thereof. The CHO configurations may also include failure handling information for initiating one or more subsequent handovers responsive to a failure of an initial handover attempt.

[0014] US 2022030483 A1 discloses a user equipment (UE) may determine to perform a conditional handover procedure to transfer from a source cell to a target cell of a plurality of candidate target cells. The UE may transmit, to the source cell, a conditional handover execution message to indicate the conditional handover procedure to transfer from the source cell to the target cell based at least at least in part on determining to perform the conditional handover procedure. The UE may communicate with the target cell to transfer to the target cell based at least in part on determining to perform the conditional handover procedure. Numerous other aspects are provided. US 2022240138 A1 relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE). According to embodiments, a method performed by a user equipment (UE) in a wireless communication system, the method comprises: receiving, from a base station, a radio resource control (RRC) reconfiguration message including conditional configuration information, wherein the conditional configuration information includes: identification information for a candidate cell; and a configuration of the candidate cell; and performing one or more operations for a conditional handover based on RRC reconfiguration message.

[0015] US 2022167220 A1 discloses a handover configuration method including: receiving target handover configuration information and handover configuration valid information, the handover configuration valid information including valid area information and / or valid timer information, the valid area information being used for indicating a valid area of at least part of the target handover configuration information, the valid timer information being used for indicating a valid duration of at least part of the target handover configuration information; keeping at least part of the target handover configuration information valid in a case that a current cell of the terminal device is located in the valid area, in a case that a current moment is within the valid duration, or in a case that a current cell of the terminal device is located in the valid area and a current moment is within the valid duration.

[0016] US 2022361055 A1 is describing a method comprising: checking if an indication indicates that a target cell is configured to store concurrently first and second configurations of a terminal, wherein the first configuration is based on a first conditional handover request, and the second configuration data set is based on a second conditional handover request; monitoring if the source cell intends performing a radio reconfiguration of the terminal after the source cell configured the terminal for the first conditional handover; canceling the first conditional handover if the source cell intends performing the radio reconfiguration and the indication does not indicate the concurrently storing; instructing the source cell to request the second conditional handover from the target cell if the source cell intends performing the radio reconfiguration and the indication indicates the concurrently storing.

[0017] US 2022264397 A1 describes a method by a wireless device includes receiving, from a network node, an indication identifying at least a first configuration identifier for modification. The first configuration identifier is associated with a conditional reconfiguration. The wireless device replaces at least a portion of the conditional reconfiguration based on the indication. The wireless devices determines that the first configuration identifier is associated with at least a first trigger condition for performing a conditional handover and stops monitoring for the first trigger condition.

[0018] US 2022078684 A1 describes a user equipment supports conditional handovers to one or more cells of a cellular network. The user equipment is configured to receive configuration data from the cellular network. The configuration data indicates for a plurality of target cells of the cellular network, conditions to trigger a conditional handover to any of the target cells. The user equipment is further configured to check the conditions with respect to appliance, and, in case of appliance, trigger the conditional handover.

[0019] US 2020154326 A1 describes a wireless transmit / receive unit (WTRU) may receive, from a serving cell based on the measurement report, a conditional reconfiguration message that includes a trigger condition and configuration information for handover to a target cell based on the trigger condition. The conditional reconfiguration message may be stored and the WTRU monitors trigger quantities of the serving cell and the target cell for the trigger condition being met. When the trigger condition is met within a validity period, then the WTRU applies the received configuration information and starts the handover to the target cell.

[0020] US 2021051537 A1 discloses apparatus and methods are provided for handover robustness. The UE receives a conditional handover (CHO) command from a source gNB containing a set of candidate cells with corresponding triggering conditions; detects a handover conditions for a target gNB belonging to the set of candidate cells; and performs HO procedure towards the target gNB. In one embodiment, the conditional HO command further configures a validity timer that controls a validity of handover conditions for the set of candidate cells. The validity timer is started upon receiving the conditional HO command, the validity timer is stopped upon detecting at least one events comprising a handover condition is met and a normal handover command is received, and the conditional HO command is set to be invalid upon the expiration of the validity timer.

[0021] US 2021360495 A1 is a disclosure relates to techniques for performing conditional handovers and cell re-selections along known routes. A cellular base station may select a conditional handover set for a wireless device. The conditional handover set may include information for multiple conditional handovers. The wireless device may receive the conditional handover set. The wireless device may perform conditional handover to at least a first cell indicated in the conditional handover set based at least in part on the conditional handover set.

[0022] US 2022377633 A1 describes a user equipment receives multiple conditional reconfigurations associated with respective conditions. The user equipment is to execute a conditional configuration upon fulfillment of an associated condition. The user equipment accordingly executes one of the multiple conditional configurations upon fulfillment of an associated condition. The user equipment transmits, to a target radio network node, an indication that indicates which one of the multiple conditional reconfigurations the user equipment executed.

[0023] US 2022338076 A1 provides handover method and apparatus. The handover method includes: A terminal device sends path information used to determine a first cell to a network device; and the terminal device receives conditional handover CHO configuration information that is corresponding to the first cell and that is sent by the network device, and determines a target cell based on the CHO configuration information corresponding to the first cell. According to the technical solutions provided in this application, a handover success rate can be improved when the terminal device performs cell handover. US 2016345222 A1 describes a handover procedure is described where a user equipment, UE, is pre-configured by a network node of a source cell with one or more target cells and associated conditions to be fulfilled for the UE to autonomously decide when to execute the handover. The UE may be pre-configured while in good radio conditions, being connected to the source cell, and hence the UE does not risk going out of source cell coverage before being handed over to a target cell.

[0024] US 2019387440 A1 provides methods, systems, and storage media for exiting conditional handovers and for estimating a user equipment mobility state. Other embodiments may be described and / or claimed.

[0025] US 2021051534 A1 discloses techniques for performing consecutive conditional handovers. A cellular base station may provide conditional handover information for multiple conditional handovers to a wireless device. The conditional handover information may include information for performing a conditional handover from a cell provided by the cellular base station to at least one cell, and information for performing a conditional handover from one or more of those cells to at least one cell. The wireless device may perform multiple consecutive conditional handovers using the conditional handover information.

[0026] US 2022408323 A1 describes a wireless terminal comprises receiver circuitry and processor circuitry. The receiver circuitry is configured to receive a message. The message comprises one or more conditional handover configurations; at least one indication; and, at least one triggering condition; each of the one or more conditional handover configurations comprising at least one identity of a candidate target cell, the at least one indication indicating whether or not the message is provided as full configuration. The processor circuitry is configured to: store the one or more conditional handover configurations and the at least one indication; perform a handover to a target cell; and determine validity of the one or more conditional handover configurations based on the indication upon or after performing the handover. 3GPP Rel. 17, indication of cell type / freq. / priority, cell reference location, distanceThresh, time stamp / validity. Furthermore UE autonomous estimation of service time is well known. Also that the Network provides conditional handover config is well described.

[0027] Earth-moving NTN cells at very high velocity (i.e., UE mobility is negligible). One satellite can operate multiple cells / beams. Depending on NTN constellation and beam footprints, a high number of UEs will recurringly perform conditional and / or RACH-less handover, which results in recurring high network signaling load and overhead and service continuity challenges.

[0028] Problem to be solved is that UE releases CHO config, after successful CHO.

[0029] Hence, the new source gNB needs to provide full CHO config, every time. As a result, the signaling overhead of new source gNB would increase unnecessarily.

[0030] The solution of that described problem is that’s UE maintains CHO configuration after performed CHO. If source gNB determines the same CHO candidates, it will avoid sending CHO configuration. If source gNB determines changes in CHO candidates, source gNB will provide updated CHO configuration.

[0031] The proposed idea is relevant to wireless communications of mobile devices communicating, especially for Conditional handover, configuration and mobility prediction.

[0032] Beneficially, UE mobility prediction will help to enhance CHO configurations, and ultimately, improve service continuity. More efficient network signaling, and overall, less handover messages.

[0033] The presented problem is solved by a method for conditional handover in a wireless communication system comprising the steps, performing UE mobility prediction and group UEs, whereby a determination of different suitable CHO configurations and / or sequence of multiple CHO candidates is done, pre-allocating UL grants, considering UE’s QoS requirements and mobility characteristics. The presented problem is also solved by a method for conditional handover in a wireless communication system comprising the steps, whereby the User Equipment (UE) maintains Conditional Handover (CHO) configuration after performed CHO and If source gNB determines the same CHO candidates, source gNB isn't sending Conditional Handover(CHO) configuration and for determining Conditional Handover (CHO) candidates, the gNB performs UE mobility prediction based on UE measurement reports or configure the UE to provide mobility assistance information, whereby if source gNB determines changes in Conditional Handover (CHO) candidates, source gNB is providing updated CHO configuration.

[0034] In some embodiments of the method according to the first aspect, the method is characterized by, that Uplink (UL) grants are pre-allocated in a recurring and / or semi- persistent way.

[0035] In some embodiments of the method according to the first aspect, the method is characterized by, that gNBs will use CHO config. ID for preparing / reserving multiple CHO candidate target cells, each CHO config. ID represents a set / sequence of N neigboring CHO candidate cells, which are known by each gNB neighbor and enable more efficient signaling between gNBs.

[0036] In some embodiments of the method according to the first aspect the method is characterized by that gNBs will use CHO config. ID for preparing / reserving multiple CHO candidate target cells, each CHO config ID represents a set / sequence of / V neigboring CHO candidate cells, which are known by each gNB neighbor and enable more efficient signaling between gNBs. A CHO config, ID in combination with UE mobility info is used to potentially update UE-specific CHO configurations as well as request / release handover / grant resources from potential target cells.

[0037] In some embodiments of the method according to the first aspect the method is characterized by that the CHO config. ID in combination with UE mobility information is used to update User Equipment (UE) specific Conditional Handover (CHO) configurations are request and / or release handover and / or grant resources from potential target cells are used for the update. In some embodiments of the method according to the first aspect the method is characterized by that, the wireless communication system is a Non Terrestrial Network (NTN).

[0038] According to a second aspect, the present disclosure relates to an Apparatus for Non Terrestrial Networks (NTN) conditional and RACH-less handover a wireless transceiver, a processor coupled with a memory in which computer program instructions are stored, said instructions being configured to implement steps according to any one of the embodiments of the first aspect.

[0039] According to a third aspect, the present disclosure relates to an User Equipment (UE) comprising an apparatus according to any one of the embodiments of the first aspect, whereby UE maintains CHO configuration after performed CHO and delivers UE measurement reports and determines and reports UE mobility info, whereby this is determines the measurement report.

[0040] According to a fourth aspect, the present disclosure relates to an base station gNB, which is configures as a source gNB, comprising an apparatus according to a second aspect, whereby if source gNB determines the same CHO candidates, it is avoiding sending CHO configuration and for determining CHO candidates, the gNB can perform UE mobility prediction based on UE measurement reports or configure the UE to provide mobility assistance information and if source gNB determines changes in CHO candidates, source gNB will provide updated CHO configuration.

[0041] According to a fifth aspect, the present disclosure relates toa a wireless communication system, wherein the gNB, 1stTarget gNB, Other Target gNBs, source gNB according to according to fourth aspect comprises a processor coupled with a memory in which computer program instructions are stored, said instructions being configured to implement steps according to first aspect, wherein the user equipment (UE) according to the third aspect a processor coupled with a memory in which computer program instructions are stored, said instructions being configured to implement steps according to the first aspect and that the wireless communication System is a Non Terrestrial Network (NTN). The present disclosure describes also a method for Non Terrestrial Networks (NTN) conditional and RACH-less handover comprising the steps: Performing UE mobility prediction and group UEs, whereby a determination of different suitable CHO configurations and / or sequence of multiple CHO candidates is done, pre-allocating UL grants, considering UE’s QoS requirements and mobility characteristics.

[0042] BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Fig. 1 shows timing advance from gNB to UE that enables the UE to adjust its uplink transmission;

[0044] Fig. 2 shows Timing Advance and Frequency Pre-com pensation;

[0045] Fig. 3 shows NTN cells broadcast (SIB19)

[0046] Fig. 4 shows the Conditional Handover (CHO);

[0047] Fig. 5 shows the scenario of Random Access / Handover for a very large Number of UEs;

[0048] Fig. 6 shows Conditional Handover with the handover cancel signaling.

[0049] Fig. 7 shows the scenario of NTN with satellites ;

[0050] Fig. 8a / b shows the Earth-Moving Cell Scenario with indicating the distance threshold

[0051] Fig. 9a / b shows Earth-Moving Cell Scenario with CHO candidates;

[0052] Fig. 10 shows CHO Configuration;

[0053] Fig. 11 shows Conditional and RACH-less Handover in RRC CONNECTED MODE;

[0054] Fig. 12 shows Conditional and RACH-less Handover in Admission Control of the first target gNB RRC CONNECTED MODE;.

[0055] Fig. 13 shows Conditional and RACH-less Handover with UE evaluates CHO conditions;

[0056] Fig. 14 shows the flowchart on UE-side;

[0057] Fig. 15 shows the flowchart on gNH-side;

[0058] Fig. 16 shows an embodiment with indicated Value Rand und Cell ID . DETAILED DESCRIPTION

[0059] The detailed description set forth below, with reference to annexed drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In particular, although terminology from 3GPP 5G NR may be used in this disclosure to exemplify embodiments herein, this should not be seen as limiting the scope of the invention.

[0060] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0061] Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and / or is implied from the context in which it is used. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and / or where it is implicit that a step must follow or precede another step. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate. Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following description. In some embodiments, a more general term “network node” may be used and may correspond to any type of radio network node or any network node, which communicates with a UE (directly or via another node) and / or with another network node. Examples of network nodes are NodeB, MeNB, ENB, a network node belonging to MCG or SCG, base station (BS), multi-standard radio (MSR) radio node such as MSR BS, eNodeB, gNodeB, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, RRU, RRH, nodes in distributed antenna system (DAS), core network node (e.g. Mobile Switching Center (MSC), Mobility Management Entity (MME), etc), Operations & Maintenance (O&M), Operations Support System (OSS), Self Optimized Network (SON), positioning node (e.g. Evolved- Serving Mobile Location Centre (E-SMLC)), Minimization of Drive Tests (MDT), test equipment (physical node or software), etc.

[0062] In some embodiments, the non-limiting term user equipment (UE) or wireless device may be used and may refer to any type of wireless device communicating with a network node and / or with another UE in a cellular or mobile communication system. Examples of UE are target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine (M2M) communication, PDA, PAD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, UE category Ml, UE category M2, ProSe UE, V2V UE, V2X UE, etc.

[0063] Additionally, terminologies such as base station / gNodeB and UE should be considered non-limiting and do in particular not imply a certain hierarchical relation between the two; in general, “gNodeB” could be considered as device 1 and “UE” could be considered as device 2 and these two devices communicate with each other over some radio channel. And in the following the transmitter or receiver could be either gNodeB (gNB), or UE.

[0064] As will be appreciated by one skilled in the art, aspects of the embodiments may be embodied as a system, apparatus, method, or program product. Accordingly, embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects.

[0065] For example, the disclosed embodiments may be implemented as a hardware circuit comprising custom very-large-scale integration (“VLSI”) circuits or gate arrays, off- the-shelf semiconductors such as logic chips, transistors, or other discrete components. The disclosed embodiments may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices, or the like. As another example, the disclosed embodiments may include one or more physical or logical blocks of executable code which may, for instance, be organized as an object, procedure, or function.

[0066] Furthermore, embodiments may take the form of a program product embodied in one or more computer readable storage devices storing machine readable code, computer readable code, and / or program code, referred hereafter as code. The storage devices may be tangible, non- transitory, and / or non-transmission. The storage devices may not embody signals. In a certain embodiment, the storage devices only employ signals for accessing code.

[0067] Any combination of one or more computer readable medium may be utilized. The computer readable medium may be a computer readable storage medium. The computer readable storage medium may be a storage device storing the code. The storage device may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.

[0068] More specific examples (a non-exhaustive list) of the storage device would include the following: 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), a portable compact disc readonly memory (“CD-ROM”), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[0069] Code for carrying out operations for embodiments may be any number of lines and may be written in any combination of one or more programming languages including an object- oriented programming language such as Python, Ruby, Java, Smalltalk, C++, or the like, and conventional procedural programming languages, such as the “C” programming language, or the like, and / or machine languages such as assembly languages. The code may execute entirely on the user’s computer, partly on the user’s computer, as a stand-alone software package, partly on the user’s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user’s computer through any type of network, including a local area network (“LAN”), wireless LAN (“WLAN”), or a wide area network (“WAN”), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider (“ISP”)).

[0070] Furthermore, the described features, structures, or characteristics of the embodiments may be combined in any suitable manner. In the following description, numerous specific details are provided, such as examples of programming, software modules, user selections, network transactions, database queries, database structures, hardware modules, hardware circuits, hardware chips, etc., to provide a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that embodiments may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of an embodiment. Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment, but mean “one or more but not all embodiments” unless expressly specified otherwise. The terms “including,” “comprising,” “having,” and variations thereof mean “including but not limited to,” unless expressly specified otherwise. An enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms “a,” “an,” and “the” also refer to “one or more” unless expressly specified otherwise.

[0071] Aspects of the embodiments are described below with reference to schematic flowchart diagrams and / or schematic block diagrams of methods, apparatuses, systems, and program products according to embodiments. It will be understood that each block of the schematic flowchart diagrams and / or schematic block diagrams, and combinations of blocks in the schematic flowchart diagrams and / or schematic block diagrams, can be implemented by code. This code may be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart diagrams and / or block diagrams.

[0072] The code may also be stored in a storage device that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the storage device produce an article of manufacture including instructions which implement the function / act specified in the flowchart diagrams and / or block diagrams.

[0073] The code may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus, or other devices to produce a computer implemented process such that the code which execute on the computer or other programmable apparatus provide processes for implementing the functions / acts specified in the flowchart diagrams and / or block diagrams. The flowchart diagrams and / or block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of apparatuses, systems, methods, and program products according to various embodiments. In this regard, each block in the flowchart diagrams and / or block diagrams may represent a module, segment, or portion of code, which includes one or more executable instructions of the code for implementing the specified logical function(s).

[0074] It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more blocks, or portions thereof, of the illustrated Figures.

[0075] Although various arrow types and line types may be employed in the flowchart and / or block diagrams, they are understood not to limit the scope of the corresponding embodiments. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the depicted embodiment. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted embodiment. It will also be noted that each block of the block diagrams and / or flowchart diagrams, and combinations of blocks in the block diagrams and / or flowchart diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and code.

[0076] The description of elements in each figure may refer to elements of proceeding figures. Like numbers refer to like elements in all figures, including alternate embodiments of like elements.

[0077] The detailed description set forth below, with reference to annexed drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. Although terminology from 3GPP 5G NR may be used in this disclosure to exemplify embodiments herein, this should not be seen as limiting the scope of the invention.

[0078] The disclosure is related to wireless communication system, which may be for example a 5G NR wireless communication system. More specifically, it represents a RAN of the wireless communication system, which is used exchange data with UEs via radio signals. For example, the RAN may send data to the UEs (downlink, DL), for instance data received from a core network (CN). The RAN may also receive data from the UEs (uplink, UL), which data may be forwarded to the CN.

[0079] In the examples illustrated, the RAN comprises one base station, BS. Of course, the RAN may comprise more than one BS to increase the coverage of the wireless communication system. Each of these BSs may be referred to as NB, eNodeB (or eNB), gNodeB (or gNB, in the case of a 5G NR wireless communication system), an access point or the like, depending on the wireless communication standard(s) implemented.

[0080] The UEs are located in a coverage of the BS. The coverage of the BS corresponds for example to the area in which UEs can decode a PDCCH transmitted by the BS.

[0081] An example of a wireless device suitable for implementing any method, discussed in the present disclosure, performed at a UE corresponds to an apparatus that provides wireless connectivity with the RAN of the wireless communication system, and that can be used to exchange data with said RAN. Such a wireless device may be included in a UE. The UE may for instance be a cellular phone, a wireless modem, a wireless communication device, a handheld device, a laptop computer, or the like. The UE may also be an Internet of Things (loT) equipment, like a wireless camera, a smart sensor, a smart meter, smart glasses, a vehicle (manned or unmanned), a global positioning system device, etc., or any other equipment that may run applications that need to exchange data with remote recipients, via the wireless device.

[0082] The wireless device comprises one or more processors and one or more memories. The one or more processors may include for instance a central processing unit (CPU), a digital signal processor (DSP), a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc. The one or more memories may include any type of computer readable volatile and non-volatile memories (magnetic hard disk, solid-state disk, optical disk, electronic memory, etc.). The one or more memories may store a computer program product, in the form of a set of programcode instructions to be executed by the one or more processors to implement all or part of the steps of a method for exchanging data, performed at a UE’s side, according to any one of the embodiments disclosed herein.

[0083] The wireless device can comprise also a main radio, MR, unit. The MR unit corresponds to a main wireless communication unit of the wireless device, used for exchanging data with BSs of the RAN using radio signals. The MR unit may implement one or more wireless communication protocols, and may for instance be a 3G, 4G, 5G, NR, WiFi, WiMax, etc. transceiver or the like. In preferred embodiments, the MR unit corresponds to a 5G NR wireless communication unit.

[0084] Every gNB can be configured as a source gNB, a gNB, 1stTarget gNB, Other Target gNBs.

[0085] Fig. 1 shows timing advance from gNB to UE that enables the UE to adjust its uplink transmission; Timing Advance is a special command (notification) from gNB to UE that enables the UE to adjust its uplink transmission as shown here: This UL adjustment applies to PUSCH, PUCCH and SRS. For NTN, the long propagation delay requires timing relationship adaptations and UE pre-com pensation - e.g., GEO with x100s ms and LEO with x10s ms Round Trip Delays.

[0086] To accommodate the propagation delay in NTNs, several timing relationships are enhanced by a Common Timing Advance (Common TA) and two scheduling offsets K_offset and k_mac Common TA is a configured offset that corresponds to the RTT between the Reference Point (RP) and the NTN payload.

[0087] K_offset is a configured scheduling offset that need to be larger or equal to the sum of the service link RTT and the Common TA. k_mac is a configured offset that need to be larger or equal to the RTT between the RP and the gNB.

[0088] DL and UL are frame aligned at the uplink time synchronization reference point (RP) with an offset given by NTA, offset which is disclosed in clause 4.3 of TS 38.211. The offset k_mac is used to delay the application of a downlink configuration indicated by a MAC CE command on PDSCH, see TS 38.213, and estimation of UE-gNB RTT, see TS 38.321. It may be provided by the network when downlink and uplink frame timing are not aligned at gNB. The k_mac is also used in the random access procedure, to determine the start time of RAR window / MsgB window after a Msg1 / MsgA transmission which is disclosed in TS 38.213. NTA: reception of the random access response or absolute timing advance command (MAC CE)

[0089] Fig. 2 shows Timing Advance and Frequency Pre-compensation. For the serving cell, the network broadcast valid ephemeris information and Common TA parameters. The UE shall have valid GNSS position as well as ephemeris and Common TA before connecting to an NTN cell. To achieve synchronisation, before and during connection to an NTN cell, the UE shall compute the RTT between UE and the RP based on the GNSS position, the ephemeris, and the Common TA parameters (see clause 4.2 in TS 38.213

[0038] ), and autonomously pre-compensate the TTA for the RTT between UE and the RP as illustrated in Figure 16.14.2.1-1 (see clause 4.3 of TS 38.211 ). In connected mode, the UE shall be able to continuously update the Timing Advance and frequency pre-compensation. The UE may be configured to report Timing Advance during Random Access procedures or in connected mode. In connected mode, event-triggered reporting of the Timing Advance is supported.

[0090] Fig. 3 shows NTN cells broadcast (SIB19), whereby. ntn-Config-r17 menas ephemeris data, common TA parameters, k_offset, validity duration for UL sync information and epoch, referenceLocation-r17 means Reference location of the serving cell, e.g., used for measurement initiation in IDLE / INACTIVE mode, distanceThresh-r17 means distance from the serving cell reference location t-Service-r17 indicates the time information on when a cell provided via NTN quasiEarth fixed system is going to stop serving the area it is currently covering, ntn-NeighCellConfigList-r17 is a list of NTN neighbour cells including their ntn-Config, carrier frequency and PhysCellld. This set includes all elements of ntn- NeighCellConfigList and all elements of ntn-NeighCellConfigListExt. If ntn-Config is absent for an entry in ntn-NeighCellConfigListExt, the ntn-Config provided in the entry at the same position in ntn-NeighCellConfigList applies. Cell reference location, if cell beam points straight to ground, it coincides with sub-satellite point.

[0091] Fig.4 shows the Conditional Handover (CHO). A Conditional Handover (CHO) is defined as a handover that is executed by the UE when one or more handover execution conditions are met. The UE starts evaluating the execution condition(s) upon receiving the CHO configuration and stops evaluating the execution condition(s) once a handover is executed. Up to 8 CHO candidate cells can be configured, which is indicated by the CHO circle in Fig. 4.

[0092] Fig. 5 shows the scenario of Random Access / Handover for a very large Number of UEs; Considering the large cell size of non-terrestrial networks, many devices may be served within a single cell. Depending on constellation assumptions (e.g., propagation delay and satellite speed) and UE density, a potentially very large number of UEs may need to perform HO at a given time, leading to possibly large signaling overhead and service continuity challenges. Mitigate peak load during RA procedure by means of RACH-less handover and further enhance by combining with Conditional Handover at the cost of increased signaling load during the handover preparation phase.

[0093] HO signaling concentration can be briefly mitigated by distributing the signaling of HO command and HO execution timing of UEs. Network can provide configuration of target cell by CHO configuration in advance. Furthermore, time-based CHO can be utilized to trigger CHO at intended time. For example, the network configures various entering condition of time-based conditional event, i.e., CondEvent TI among UEs. In addition, the network also configures RRM-based conditional event, e.g., CondEvent A4 to be satisfied at configured entering condition of CondEvent T1 for each UE. By combining two conditions, UE automatically performs CHO at configured timing leading to distributed HO execution among UEs. Consequently, CHO-based preconfiguration can reduce the number of HO signaling by skipping triggering indication and alleviates RACH congestion thanks to distributed HO execution.

[0094] During a conditional handover, the ephemeris data of the satellite serving the candidate target cell, as well as the associated Common TA parameters and Kmac, are part of the essential configuration a UE needs to initiate Random Access to an NTN candidate target cell. These are commonly included in the Handover Command (RRCReconfiguration). However, the CHO configuration may be stored a non- negligible time in the UE before the CHO is executed, and the validity time of the ephemeris data and Common TA parameters may expire.

[0095] Multiple sets of ephemeris and Common TA parameters, each with its own epoch (increasingly further into the future) and validity time can be transmitted in the CHO configuration message (RRCReconfiguration). Fig. 6 shows Conditional Handover with the handover cancel signaling. A Conditional Handover (CHO) is defined as a handover that is executed by the UE when one or more handover execution conditions are met. The UE starts evaluating the execution condition(s) upon receiving the CHO configuration and stops evaluating the execution condition(s) once a handover is executed.

[0096] Up to 8 CHO candidate cells can be configured.

[0097] 0 / 1 . Same as step 0, 1

[0098] 2. The source gNB decides to use CHO.

[0099] 3. The source gNB requests CHO for one or more candidate cells belonging to one or more candidate gNBs. A CHO request message is sent for each candidate cell.

[0100] 4. Same as step 4 in Figure 9.2.3.2.1 -1 of clause 9.2.3.2.1 .

[0101] 5. The candidate gNB(s) sends CHO response (HO REQUEST ACKNOWLEDGE) including configuration of CHO candidate cell(s) to the source gNB. The CHO response message is sent for each candidate cell.

[0102] 6. The source gNB sends an RRCReconfiguration message to the UE, containing the configuration of CHO candidate cell(s) and CHO execution condition(s).

[0103] 7. The UE sends an RRCReconfigurationComplete message to the source gNB.

[0104] 7a If early data forwarding is applied, the source gNB sends the EARLY STATUS TRANSFER message.

[0105] 8. The UE maintains connection with the source gNB after receiving CHO configuration, and starts evaluating the CHO execution conditions for the candidate cell(s). If at least one CHO candidate cell satisfies the corresponding CHO execution condition, the UE detaches from the source gNB, applies the stored corresponding configuration for that selected candidate cell, synchronises to that candidate cell and completes the RRC handover procedure by sending RRCReconfigurationComplete message to the target gNB. The UE releases stored CHO configurations after successful completion of RRC handover procedure.

[0106] 8a / b The target gNB sends the HANDOVER SUCCESS message to the source gNB to inform that the UE has successfully accessed the target cell. In return, the source gNB sends the SN STATUS TRANSFER message following the principles described in step 7 of Intra-AMF / UPF Handover in clause 9.2.3.2.1. 8c. The source gNB sends the HANDOVER CANCEL message toward the other signalling connections or other candidate target gNBs, if any, to cancel CHO for the UE.

[0107] Fig. 7 shows the scenario of NTN with satellites with PCI 1 to PCI 14.

[0108] The source gNB sends the HANDOVER CANCEL message toward the other signaling connections or other candidate target gNBs, if any, to cancel CHO for the UE. Hence, all resource reservations will be canceled, although UEs will be arriving after the 1stCHO to other configured target cell. One Solutionis defined by the 1stoption: when UL grant is configured, a timer is allocated by target cell (during admission control), Timer starts, when UE receives RRC reconfiguration message (6.) or sends HO complete (7.) Timer stops, when UE uses UL grant. If timer expires, UE will release UL grant.

[0109] The other option is after CHO procedure, this is defined by further variation: if congestion is determined in any target cell, target cell will indicate to source cell to release configured UL grant resources (update CHO config.) -> any grant-related validity timer is over-written and stopped. Source cell to provide indication in different ways: RRC, MAC CE, PDCCH.

[0110] Benefit is that the target cell does not reserve grant resources infinitely but can flexibly revoke allocated grants.

[0111] Leverage the fact that satellite movements are deterministic and recurring.

[0112] Either network or UE perform UE mobility prediction:

[0113] Network performs UE mobility prediction based on consecutive UE measurement reports (e.g., RSRP values of serving and neighboring cells).

[0114] UE determines and reports distance to serving cell’s referencePoint (SIB19) and angle w.r.t. reference vector and own mobility vector (UE mobility info).

[0115] Network groups UEs and determine different suitable CHO configurations (set / sequence of multiple CHO candidates; pre-defined catalogue (almanac) of CHO config. ID, where each ID represent suitable, location-specific sequence of CHO candidates), e.g., depending on NTN ephemeris, UE measurements and / or UE mobility info.

[0116] UE only discards CHO candidate cell, if no measurements could be obtained for the last / V times or new / updated CHO configuration is provided.

[0117] The source gNB sends the HANDOVER CANCEL message toward the other signaling connections or other candidate target gNBs, if any, which based on CHO config ID and UE mobility predictions will not become target gNBs, to cancel CHO for the UE i.e. , to free pre-allocated resources.

[0118] Network uses UE’s QoS requirements and mobility characteristics for determining and pre-allocating UL grants, e.g., in a recurring / semi-persistent manner.

[0119] If network predicts significant cell load increase, target cell will indicate to source cell to release configured UL grant resources (update CHO config.), and thus, over- write / stop any running grant-related validity timer.

[0120] If network predicts significant cell load increase, network may configure additional randomization in CHO trigger timer of corresponding candidate cell(s) (e.g., based on UE’s QoS requirements and mobility characteristics), which is signaled via delta configuration.

[0121] Fig. 8a / b shows the Earth-Moving Cell Scenario with indicating the distance threshold. UE determines and reports distance to referencePoint and angle w.r.t. reference vector (pre-defined, e.g., latitudinal direction) and own mobility vector -> enable UE mobility prediction CHO candidate sequence: {cell #1 , cell #2, cell #3}

[0122] Fig. 9 shows Earth-Moving Cell Scenario with CHO candidates with cell #4 with CHO candidate sequence: {cell #1 , cell #2, cell #4} in Fig. 9a and Beam-ZSSB-specific grant in Fig. 9b Fig. 10 shows CHO Configuration.

[0123] The network is aware of NTN constellation characteristics, where cell neighborhood relationships are pre-defined and deterministic. Thus, an almanac of possible CHO configurations that is based on cell neighborhood relationships and possible UE movement directions can be created. gNBs will use CHO config. ID for preparing / reserving multiple CHO candidate target cells. Each CHO config ID represents a set / sequence of / V neigboring CHO candidate cells, which are known by each gNB neighbor and enable more efficient signaling between gNBs. A CHO config. ID in combination with UE mobility info is used to potentially update UE- specific CHO configurations as well as request / release handover / grant resources from potential target cells. Highly mobile UEs may receive several CHO configs, with different CHO IDs. For example: 1string 6 neighbors, 2ndring 12 neighbors -> almanac of 6*12 possible configurations for configuring 2 subsequent CHOs.

[0124] Fig. 11 shows Conditional and RACH-less Handover in RRC CONNECTED MODE;

[0125] UE and Serving gNB are in RRC_CONNECTED. UE uses SIB19 to determine own mobility vector w.r.t. NTN movements. Ue send Measurement Report (UE mobility vector) to Serving gNB. Serving gNB groups UEs by using QoS requirements, UE mobility and available further metainformation and determines set / sequence of suitable CHO target candidates (using ephemeris data). Serving gNB defines CHO Decision. Serving gNB sends Handover Request (incl. QoS, mobility info, CHO ID) to the 1stTarget gNB. And sends a Handover Request(s) (incl. QoS, mobility info, CHO ID) to Other Target gNBs.

[0126] Fig. 12 shows Conditional and RACH-less Handover in Admission Control of the first target gNB has Admission Control. 1stTarget gNB and Other Target gNB have Admission Control. 1stTarget gNB sends a andover Request Acknowledge incl. preallocated UL grants + validity timer, NTA + validity timer, cell load status to Serving gNB. Other Target gNBs send Handover Request(s) Acknowledge incl. pre-allocated UL grants + validity timer, NTA + validity timer, cell load status to Serving gNB. Serving gNB determines CHO config, incl. set of CHO cell / beam candidates, UL grants + validity, NTA + validity, additional back-off. Serving gNB sends RRCReconfiguration (CHO config.) to UE. UE send RRCReconfigurationComplete back to Serving gNB.

[0127] Fig. 13 shows Conditional and RACH-less Handover with UE evaluates CHO conditions; UE evaluates CHO conditions, Detach from old cell, synchronize with new cell and send RRCReconfigurationComplete (incl. CHO ID) to 1stTarget gNB. Serving gNB sends Early Status Transfer to Other Target gNBs before UE has send RRCReconfigurationComplete (incl. CHO ID) to 1stTarget gNB. 1stTarget gNB uses CHO ID and future UE mobility info for updating CHO (delta) configuration and sends Handover Success (incl. CHO ID) to Serving gNB. Serving gNB sends Status Transfer to 1stTarget gNB. Serving gNB determines (using CHO ID) which handover / resource reservations to cancel. Serving gNB sends Handover Cancel (unfeasible target gNBs) to other Target gNBs.

[0128] Fig. 14 shows the flowchart on UE-side; UE receives SIB19 from serving cell, determines and reports UE mobility info (measurement report), receives CHO (delta) configuration, Evaluates CHO condition, CHO conditions met? If they are met perform CHO and report used CHO ID and terminate the flow. If they are not met Evaluates CHO condition.

[0129] Fig. 15 shows the flowchart on gNB - side; gNB configures measurement reporting (incl. UE mobility info), receives UE measurement report (incl. UE mobility info), uses UE QoS requirements and / or UE mobility info for grouping UEs, uses NTN ephemeris data (of neighbor NTN cells / nodes) as well as beam characteristics to determine set / sequence of CHO candidate cells / beams, request handover and allocation of UL grants from identified neighbor NTN cells / nodes, receive handover ACK incl. UL grants + validity times, NTAs + validity times, and load status from neighbor NTN cells / nodes, creates and sends (delta) CHO config, (incl. CHO candidates, NTAs + validity times, UL grants + validity times, and additional back-off timers (determined based on neighbor cell load), receive CHO complete message (incl. CHO ID), determine which handover / resource reservations to cancel and the flow ends. Fig. 16 shows an embodiment with indicated Value Rand und Cell ID. For NTN cells, high and recurring occurrence of handovers is expected. High number of UEs that try to perform CHO may create significant congestion in the target cell. Serving gNB contacts potential CHO target cell candidates for requesting / reserving handover and grant resources. Based on pre-defined load threshold, target cell may request to introduce additional back-off timer to delay CHO execution or provide a mapping to select CHO target cell. Mapping is pre-determined by network / target cell.

[0130] In Fig. 16 the situation is issued by Cell #7:

[0131] The proposed idea is relevant to wireless communications of mobile or loT devices communicating via NTN. UE mobility prediction will help to enhance CHO configurations, and ultimately, improve service continuity. Less network signaling: in the best-case full CHO configuration (incl. sequence of N suitable candidate cells needs to provided once, in the future, after N CHOs, only delta configuration updates will be provided). If CHO configurations are based on pre-defined catalogue of CHO configuration IDs (similar to almanac of satellite ephemeris data). Signaling of CHO config ID will be sufficient. Accounting for UE’s requirements when pre-allocation UL grants will improve QoS (e.g., minimize handover interruption time).

[0132] Introducing additional randomization in CHO triggering can help to mitigate network congestion.

[0133] UE mobility prediction will help to enhance CHO configurations, and ultimately, improve service continuity. Less network signaling is achieved. In the best case full CHO configuration incl. sequence of N suitable candidate cells needs to provided once, in the future, after N CHOs, only delta configuration updates will be provided. If UE does not remove but maintains CHO configuration after successful CHO, further signaling can be saved.

[0134] Abbreviations:

[0135] BWP Bandwidth part

[0136] CBG Code block group

[0137] CHO Conditional Handover

[0138] CLI Cross Link Interference

[0139] CP Cyclic prefix

[0140] CQI Channel quality indicator

[0141] CPU CSI processing unit

[0142] CRB Common resource block

[0143] CRC Cyclic redundancy check

[0144] CRI CSI-RS Resource Indicator

[0145] CSI Channel state information

[0146] CSI-RS Channel state information reference signal

[0147] CSI-RSRP CSI reference signal received power

[0148] CSI-RSRQ CSI reference signal received quality

[0149] CSI-SINR CSI signal-to-noise and interference ratio

[0150] CW Codeword

[0151] DCI Downlink control information

[0152] DL Downlink

[0153] DM-RS Demodulation reference signals

[0154] DRX Discontinuous Reception

[0155] EPRE Energy per resource element

[0156] IAB-MT Integrated Access and Backhaul - Mobile Terminal

[0157] L1 -RSRP Layer 1 reference signal received power

[0158] LI Layer Indicator

[0159] MCS Modulation and coding scheme

[0160] PDCCH Physical downlink control channel

[0161] PDSCH Physical downlink shared channel

[0162] PSS Primary Synchronisation signal

[0163] PUCCH Physical uplink control channel

[0164] QCL Quasi co-location

[0165] PMI Precoding Matrix Indicator PRB Physical resource block PRG Precoding resource block group PRS Positioning reference signal PT-RS Phase-tracking reference signal RB Resource block RBG Resource block group Rl Rank Indicator RIV Resource indicator value RS Reference signal SCI Sidelink control information SLIV Start and length indicator value SR Scheduling Request SRS Sounding reference signal SS Synchronisation signal SSS Secondary Synchronisation signal SS-RSRP SS reference signal received power SS-RSRQ SS reference signal received quality SS-SINR SS signal-to-noise and interference ratio

[0166] TB Transport Block TCI Transmission Configuration Indicator TDM Time division multiplexing UE User equipment UL Uplink

Claims

CLAIMS1. Method for conditional handover in a wireless communication system comprising the steps:• Performing UE mobility prediction and group UEs, whereby a determination of different suitable CHO configurations and / or sequence of multiple CHO candidates is done, pre-allocating UL grants,• considering UE’s QoS requirements and mobility characteristics.

2. Method according claim 1 , comprising the steps:• User Equipment (UE) maintains Conditional Handover (CHO) configuration after performed CHO and If source gNB determines the same CHO candidates, source gNB isn't sending Conditional Handover(CHO) configuration,• for determining Conditional Handover (CHO) candidates, the gNB performs UE mobility prediction based on UE measurement reports or configure the UE to provide mobility assistance information, whereby if source gNB determines changes in Conditional Handover (CHO) candidates, source gNB is providing updated CHO configuration.

3. The method according to any of the previous claims, wherein Uplink (UL) grants are pre-allocated in a recurring and / or semi-persistent way.

4. The method according to any of the previous claims, wherein gNBs will use CHO config. ID for preparing / reserving multiple CHO candidate target cells, each CHO config. ID represents a set / sequence of / V neigboring CHO candidate cells, which are known by each gNB neighbor and enable more efficient signaling between gNBs.

5. The method according to any of the previous claims, wherein the CHO config. ID in combination with UE mobility information is used to update User Equipment (UE) specific Conditional Handover (CHO) configurations are request and / orrelease handover and / or grant resources from potential target cells are used for the update.

6. The method according to any of the previous claims, wherein the wireless communication system is a Non Terrestrial Networks (NTN).

7. Apparatus for Non Terrestrial Networks (NTN) conditional and RACH-less handover a wireless transceiver, a processor coupled with a memory in which computer program instructions are stored, said instructions being configured to implement steps of the claims 1 to 5.

8. User Equipment (UE) comprising an apparatus according to claim 6, whereby UE UE maintains CHO configuration after performed CHO and delivers UE measurement reports and determines and reports UE mobility info, whereby this is determines the measurement report.

9. Base station gNB, which is configures as a source gNB, comprising an apparatus according to claim 6, whereby if source gNB determines the same CHO candidates, it is avoiding sending CHO configuration and for determining CHO candidates, the gNB can perform UE mobility prediction based on UE measurement reports or configure the UE to provide mobility assistance information and if source gNB determines changes in CHO candidates, source gNB will provide updated CHO configuration.

10. Wireless communication system, wherein the gNB, 1stTarget gNB, Other Target gNBs, source gNB according to claim 7 comprises a processor coupled with a memory in which computer program instructions are stored, said instructions being configured to implement steps of claims 1 to 5: wherein the user equipment (UE) according to claim 7 comprises a processor coupled with a memory in which computer program instructions are stored, said instructions being configured to implement steps of the claims 1 to 5 and that the wireless communication system is a and that the wireless communication System is a Non Terrestrial Network (NTN).

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