Method and apparatus for improving in and relating to RACH-less timing advance management

Abstract

The disclosure provides a method or an apparatus for RACH-less timing advance management, wherein the method performed by a terminal comprises: receiving, from a first base station, a first message comprising information on a random access channel (RACH)-less handover; and transmitting, to a second base station, a second message for completing a handover procedure based on the information on the RACH-less handover, wherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported, and wherein the information on the RACH-less handover comprises at least one of information on a beam that the terminal uses in a target cell to monitor physical downlink control channel (PDCCH) for initial uplink transmission and information on a timing advance value which the terminal uses for a handover.

Description

METHOD AND APPARATUS FOR IMPROVING IN AND RELATING TO RACH-LESS TIMING ADVANCE MANAGEMENT

[0001] The disclosure relates to operations of a base station, a user equipment, and a core network in a mobile communication system.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] An embodiment of the disclosure provides a method and an apparatus for RACH-less Timing advance management.

[0009] The technical subjects pursued in the disclosure may not be limited to the above-mentioned technical subjects, and other technical subjects which are not mentioned may be clearly understood, through the following descriptions, by those skilled in the art to which the disclosure pertains.

[0010] To solve the above-described problem, a method performed by a terminal in a wireless communication system according to an embodiment of the disclosure may include receiving, from a first base station, a first message comprising information on a random access channel (RACH)-less handover; and transmitting, to a second base station, a second message for completing a handover procedure based on the information on the RACH-less handover, wherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.

[0011] In an embodiment, information on the RACH-less handover comprises at least one of information on a beam that the terminal uses in a target cell to monitor physical downlink control channel (PDCCH) for initial uplink transmission and information on a timing advance value which the terminal uses for a handover.

[0012] In an embodiment, the first message comprises information on an uplink grant for transmitting the first message or information for monitoring an uplink grant from the second base station

[0013] In an embodiment, the transmitting the second message comprises: in case that the first message comprises the information for monitoring the uplink grant from the second base station, receiving, from the second base station, a physical downlink control channel (PDCCH) for the uplink grant based on the information on the RACH-less handover; and transmitting, to the second base station, the second message based on the uplink grant.

[0014] In an embodiment, the first message comprises a message to modify an radio resource control (RRC) connection.

[0015] To solve the above-described problem, a method performed by a first base station in a wireless communication system according to an embodiment of the disclosure may include transmitting, to a second base station, a handover request message; receiving, from the second base station, a handover request acknowledge message; and transmitting, to a terminal, a first message comprising information on a random access channel (RACH)-less handover, wherein a second message for complete a handover procedure is transmitted to the second base station, based on the information on the RACH-less handover, and wherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.

[0016] To solve the above-described problem, a terminal in a wireless communication system according to an embodiment of the disclosure may include a transceiver; and a controller coupled with the transceiver and configured to: receive, from a first base station, a first message comprising information on a random access channel (RACH)-less handover, and transmit, to a second base station, a second message for completing a handover procedure based on the information on the RACH-less handover, wherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.

[0017] To solve the above-described problem, a first base station in a wireless communication system according to an embodiment of the disclosure may include a transceiver; and a controller coupled with the transceiver and configured to: transmit, to a second base station, a handover request message, receive, from the second base station, a handover request acknowledge message, and transmit, to a terminal, a first message comprising information on a random access channel (RACH)-less handover, wherein a second message for complete a handover procedure is transmitted to the second base station, based on the information on the RACH-less handover, and wherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.

[0018] An embodiment of the disclosure provides a method and an apparatus for RACH-less Timing advance management.

[0019] Advantageous effects obtainable from the disclosure may not be limited to the above - mentioned effects, and other effects which are not mentioned may be clearly understood from the following descriptions by those skilled in the art to which the disclosure pertains.

[0020] Figures 1a illustrates RACH-less handover where the UE is configured with uplink grants.

[0021] Figure 1b illustrates the case where the UE is configured to monitor PDCCH of target cell.

[0022] Figure 2 illustrates SCG addition procedures (from UE perspective).

[0023] Figure 3 illustrates EN-DC SCG addition procedures.

[0024] Figure 4a illustrates timing advance from a cell of SCS=30 kHz used in a cell of SCS=15 kHz and a timing advance command is later used;

[0025] Figure 4b illustrates rounding down the TA using in SCS=30 kHz to an a value that would be used in SCS=15 kHz;

[0026] Figure 5a illustrates SCG establishment using N_TA translation for EN-DC; and

[0027] Figure 5b illustrates SCG establishment using N_TA translation for NE-DC.

[0028] Figure 6 illustrates a configuration of a UE according to an embodiment of the disclosure.

[0029] Figure 7 illustrates a configuration of a base station according to an embodiment of the disclosure.

[0030] In describing the disclosure below, a detailed description of known functions or configurations incorporated herein will be omitted when it is determined that the description may make the subject matter of the disclosure unnecessarily unclear. Hereinafter, embodiments of the disclosure will be described with reference to the accompanying drawings.

[0031] Hereinafter, the operation principle of the disclosure will be described in detail in conjunction with the accompanying drawings. The terms which will be described below are terms defined in consideration of the functions in the disclosure. They may be different according to users, intentions of the users, or customs, and therefore, the definitions of the terms should be made based on the contents throughout the specification.

[0032] For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically illustrated. Furthermore, the size of each element does not completely reflect the actual size. In the respective drawings, the same or corresponding elements are assigned the same reference numerals.

[0033] The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described below in detail in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth below, but may be implemented in various different forms. The following embodiments are provided only to completely disclose the disclosure and inform those skilled in the art of the scope of the disclosure, and the disclosure is defined only by the scope of the appended claims. Throughout the disclosure, the same or like reference numerals designate the same or like elements.

[0034] Herein, it will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions can 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 specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.

[0035] Furthermore, each block in the flowchart illustrations may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. 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.

[0036] As used in embodiments of the disclosure, the term "unit" refers to a software element or a hardware element, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), and the "unit" may perform certain functions. However, the "unit" does not always have a meaning limited to software or hardware. The "unit" may be constructed either to be stored in an addressable storage medium or to execute one or more processors. Therefore, the "unit" includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, properties, procedures, sub-routines, segments of a program code, drivers, firmware, micro-codes, circuits, data, database, data structures, tables, arrays, and parameters. The elements and functions provided by the "unit" may be either combined into a smaller number of elements, or a "unit", or divided into a larger number of elements, or a "unit". Moreover, the elements and "units" may be implemented to reproduce one or more CPUs within a device or a security multimedia card.

[0037] Particular terms as used in the following description are merely provided to help understanding pf the disclosure, and other types of terms may be used without departing from the scope of the technical idea of the disclosure.

[0038] As used herein, terms referring to network entities, terms referring to messages, terms referring to identification information, and the like are illustratively used for the sake of descriptive convenience. Therefore, the disclosure is not limited by the terms as described below, and other terms referring to subjects having equivalent technical meanings may also be used.

[0039] In the following description, the disclosure will be described using terms and names defined in the 5G system standards for the sake of descriptive convenience, but the disclosure is not limited by these terms and names and may be applied in the same way to systems that conform other standards.

[0040] Random Access Channel, RACH, is an essential part of wireless communication systems, including Fifth Generation, 5G, (or New Radio, NR), Fourth Generation, 4G, (or Long-Term Evolution, LTE) and even Third Generation, 3G. It plays a significant role in establishing an initial connection (Initial Access) between a device and a network. It also significant in handing over a User Equipment, UE, from one cell to another.

[0041] RACH-less is a handover method introduced in Evolved Universal Terrestrial Radio Access Network, E-UTRAN, Release 14. It enables a UE to skip performing random access during a handover. This is to improve the delay of handovers in some certain cases.

[0042] RACH-less can be performed in certain cases related to the Timing Advance (TA):

[0043] ● When TA to the target cell is equal to zero

[0044] ● When TA to the target cell is equal to the TA of the source cell

[0045] Figures 1a illustrates RACH-less handover where the UE is configured with uplink grants; and Figure 1b illustrates the case where the UE is configured to monitor PDCCH of target cell.

[0046] RACH-less can be considered to comprise two different methods:

[0047] - Consecutive Uplink Grants are configured to be used by the UE to send the first message after the handover, which is the RRCReconfigurationComplete and optionally any data. For this case, the UE is configurated with an uplink grant (ul-Grant), the scheduling interval (ul-SchedInterval) as well as how many occasions that are configured (numberOfConfUL-Processes)

[0048] - The UE is scheduled to synchronize with a cell without sending any messages to the target cell. Instead, the UE starts monitoring PDCCH for assignments from the target cell. The assignments may be for downlink PDSCH transmissions or UL grants for the UE to send PUSCH.

[0049] The following fields are configured with RACH-less:

[0050] ● targetTA

[0051] ● numberOfConfUL-Processes

[0052] ● ul-SchedInterval

[0053] ● ul-StartSubframe

[0054] ● ul-Grant

[0055] For the target TA, there are a number of options of what to apply in the target cell for the timing advance. The UE can either set NTA=0 or NTAequal to another serving cell that the UE is already connected to, for instance the PCell or the SCell.

[0056] Not only was RACH-less introduced for the purpose of handovers, but also for the establishment of a secondary eNB, i.e a SeNB. The establishment of a SeNB is normally done via random access procedure.

[0057] Carrier Aggregation, CA, is key technique for modern cellular connectivity that was introduced for LTE in Rel-10. It was made native with the first 5G NR release and is an important technique to ensure higher rates.

[0058] Carrier aggregation, as the name implies, allows for the aggregation of multiple carriers for a single base station, gNB. In addition to the main cell where the UE is RRC-connected to, i.e the PCell or PSCell, the gNB also configures secondary cells, SCells. Each carrier is sometimes referred to as a Component Carrier.

[0059] Dual Connectivity, DC, is another important technique that was introduced for LTE in Rel-12 and made native to 5G NR. It is implemented in a number of different ways, such as E-UTRAN-NR DC, NR-E-UTRAN DC and NR DC. Dual connectivity allows a UE to simultaneously connect to a Main Node, MN, and Secondary Node, SN, i.e two different gNBs.

[0060] In NR, the MN will have an associated Master Cell Group (MCG) and the SN will have an associated Secondary Cell Group (SCG), allowing for Dual Connectivity and Carrier Aggregation to co-exist. A cell group refers to either an MCG or an SCG. The Primary Cell (PCell) refers to the non-secondary cell of the MCG, and the Primary SCG Cell (PSCell) refers to the non-secondary cell of the SCG. Special Cell (SpCell) refers to either the PCell or the PSCell. These gNBs may or may not be collocated and each node may have multiple SCells, i.e carriers. In 5G NR a common use case is that the MN / MCG is at Frequency Range 1, FR1 and SN / SCG is at FR2.

[0061] Compared to Carrier Aggregation, in Dual Connectivity the MN and SN will act a lot more independently whereby the MN and SN can configure the UE, for instance, with separate measurements at each Cell Group.

[0062] Figure 2 illustrates SCG addition procedures (from UE perspective).

[0063] SCG addition, also known as SN addition, SCG establishment or DC establishment is the procedure used to establish Dual Connectivity by adding another SCG. The procedure to add the SCG from the perspective of the UE can be seen in Figure 2.

[0064] The steps set out in Figure 2 are:

[0065] Step 1: First the decision to attempt to establish an SCG is made.

[0066] Step 2: The MN initiates the SCG addition by sending the S-Node Addition Request to the SN. If the SN is able to accommodate the UE and the SCG role, the SN generates the SCG RRC configuration and replies with S-Node Addition Request Acknowledge, containing RRC configuration of the SCG that the UE shall apply.

[0067] Step 3: RRCReconfiguration is sent to the UE to configure the SCG. For NR SCG addition, the mrdc-SecondaryCellGroupConfig is set to nr-SCG and the gNB includes the field CellGroupConfig.

[0068] Step 4: RRCReconfigurationComplete may be generated before or after having performed the random access to SN.

[0069] Step 5: Perform random access to the SgNB.

[0070] The RRC message SCGFailureInformation is used in order to indicate to a MN that the UE has experienced a failure on the SCG link. This can, for instance, be due to radio link failure, failure to synchronize on the SCG or SCG configuration failure. The SCGFailureInformation contains a field FailureReportSCG, which may contain the failure type, possible UE measurements, location info, previously visited cells etc.

[0071] Figure 3 illustrates EN-DC SCG addition procedures.

[0072] In connection with EN-DC SCG addition, Figure 3 shows the procedure to add the NR SCG from E-UTRAN MN from the perspective of the UE.

[0073] The steps set out in Figure 3 are:

[0074] Step 1: First the decision to attempt to establish an SCG is made.

[0075] Step 2: The MN initiates the SCG addition by sending the SGNB Addition Request to the SN. If the SN is able to accommodate the UE and the SCG role, the SN generates the SCG RRC configuration and replies with SGNB Addition Request Acknowledge, containing RRC configuration of the SCG that the UE shall apply.

[0076] Step 3: RRCConnectionReconfiguration is sent to the UE to configure the SCG. For NR SCG addition, the nr-SecondaryCellGroupConfig with a transparent NR RRC container, containing the configuration to use in the NR SCG.

[0077] Step 4: RRCReconfigurationComplete may be generated before or after having performed the random access to SN.

[0078] Step 5: Perform random access to the SgNB.

[0079] It is instructive to understand more about how Timing Advance functions in NR and LTE.

[0080] In LTE, the full timing advance of a UE, TTAis defined as [Math Figure 1]:

[0081]

[0082] Where the individual components are:

[0083] ● Ts= basic time unit 1 / (15000 x 2048) = 1 / 30720000

[0084] ● NTA= TAx 16

[0085] ● are Non-Terrestrial Networks, NTN, specific

[0086] In NR, TTA, which is the full and absolute Timing Advance of a UE, is defined as [Math Figure 2]:

[0087]

[0088] Where the individual components are:

[0089] ● Tcis the basic time unit for NR = 1 / (480x103x 4096) = 1 / 1966080000

[0090] ● The NTA, which is the MAC-signalled timing advance is calculated as:

[0091] ○ , which is how to calculate the timing advance when receiving the TA in Random Access response

[0092] ○ , calculated when receiving the TAin a Timing Advance MAC CE

[0093] ● is the subcarrier spacing configuration, which can take the values [0, 1, 2, 3, 4, 5, 6] which corresponds to the Subcarrier Spacing (SCS) [15, 30, 60, 120, 240, 480, 960] kHz. In general, the higher the frequency, the higher the subcarrier spacing.

[0094] ● are NTN specific

[0095] What can be seen from the above is that in NR the granularity of NTAvalues changes with the subcarrier spacing. For instance for SCS = 15 kHz, the values of the timing advance changes that the UE applies are the values NTA= [...-4096, -3072, -2048, -1024, 0, 1024, 2048, ...]. For SCS = 60 kHz, the UE applies the values NTA= [..., -1024, -768, -512, -256, 0, 256, 512, 768, 1024, ...].

[0096] A difference between LTE and NR is that in LTE, the SCS is always the same and that in LTE, the basic time unit is much smaller.

[0097] When performing RACH-less handovers between different cells or using RACH-less for establishment of new cells in LTE, the UE can either apply the same Timing Advance in the target cell as the source cell, or use Timing Advance equal to zero. Applying the same timing advance is specified as reusing the same NTA.

[0098] In NR, the adjustments of the Timing Advance changes as the subcarrier spacing changes (which is often configured to be correlated to the frequency).

[0099] This may cause issues when either performing RACH-less handovers between different cells at different frequency or establishing another cell or Radio Access Technology, RAT, of another frequency.

[0100] For LTE, the option of using RACH-less to perform SN addition was introduced in Rel-14 in addition to being introduced for mobility purposes.

[0101] Now that RACH-less is being introduced for NR for mobility purposes, it would also be beneficial to introduce RACH-less for SN addition. However, the number and variety of Dual Connectivity scenarios in 5G are greater than compared to what was the case in LTE. As an example, the following are different:

[0102] ● The range of frequency bands of NR are a lot wider compared to LTE, affecting how Dual Connectivity functions;

[0103] ● In addition to NR-DC, where both legs in DC are NR, there are also EN-DC and NE DC scenarios.

[0104] As an example of an issue, LTE RACH-less has some options on how to deal with the Timing Advance of the target cell / target SN. One option is that NTA=0 is used in the target cell, NTAof one of the already established cells, such as the PCell or any SCells is used in the target cell. However, if the NTAof an LTE cell is used in NR, there is a need to ensure that the NTAcan truly be applied in an NR cell.

[0105] According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

[0106] According to a first aspect of the present invention, there is provided a method of operating a telecommunication network to perform RACH-less handover between a source cell and a target cell, comprising the steps of:

[0107] a) determining whether to configure an operably connected User Equipment, UE, for RACH-less handover according to a predetermined condition;

[0108] b) if so determined, sending a handover command to the UE to perform RACH-less handover, wherein the predetermined condition is one of:

[0109] (i) the target cell is not on a different Sub-Carrier Spacing, SCS, compared to source cell;

[0110] (ii) the target cell is not on a different frequency compared to source cell;

[0111] (iii) the target cell is on a different frequency compared to source cell and the timing advance is configured to be zero;

[0112] (iv) the target cell is on a different SCS compared to source cell and the timing advance is configured to be zero; and

[0113] (v) the target cell is on a different SCS compared to source cell and the timing advance is adjusted according to the SCS in the target and source cell.

[0114] In an embodiment, the handover command comprises a configuration of the timing advance comprising one of:

[0115] ● the timing advance is configured to be zero if the target cell is on a different SCS compared to the source cell;

[0116] ● the timing advance is configured to be zero if the target cell is on a different frequency compared to source cell; and

[0117] ● the timing advance is configured to be the same as that of the target cell if the SCS of the target cell is adjusted according to a difference in the target cell SCS and the source cell SCS

[0118] In an embodiment, if the predetermined condition is (v) the target cell is on a different SCS compared to source cell and the timing advance is adjusted according to the SCS in the target and source cell, then the adjustment is made by either rounding down to the nearest NTAor rounding up to the nearest NTA.

[0119] In an embodiment, if the timing advance is adjusted by rounding down, then a flooring function is utilised such that a minimum value is assigned.

[0120] In an embodiment, if the timing advance is adjusted by rounding up, then a ceiling function is utilised such that a maximum value is assigned.

[0121] In an embodiment, if the predetermined condition is (v) the target cell is on a different SCS compared to source cell and the timing advance is adjusted according to the SCS in the target and source cell, then

[0122] In an embodiment, rounding is performed if one or more of:

[0123] ● the target cell SCS is smaller than the source cell SCS;

[0124] ● the target cell frequency is smaller than the source cell frequency;

[0125] ● the handover is an inter-frequency handover.

[0126] In an embodiment, in the case that target cell frequency is smaller than the source cell frequency, the handover is from Frequency Range 2, FR2, to FR1.

[0127] In an embodiment, an explicit instruction to perform rounding is included in a RACH-less configuration message.

[0128] In an embodiment, in certain cases, regardless of any determination, a RACH-less handover may not be performed, such certain cases including inter-SCS or inter-frequency handovers.

[0129] In an embodiment, inter-SCS, inter-frequency RACH-less handovers or RACH-less establishment, may only be performed if Timing Advance=0 is configured.

[0130] According to a second aspect of the present invention, there is provided method of operating a User Equipment, UE, arranged for RACH-less handover, wherein the UE has been configured for conditional RACH-less handover by an operably connected telecommunication network.

[0131] In an embodiment, the conditional RACH-less handover is performed on the basis of one of:

[0132] (i) a target cell is not on a different Sub-Carrier Spacing, SCS, compared to a source cell;

[0133] (ii) a target cell is not on a different frequency compared to a source cell;

[0134] (iii) a target cell is on a different frequency compared to a source cell and the timing advance is configured to be zero;

[0135] (iv) a target cell is on a different SCS compared to a source cell and the timing advance is configured to be zero; and

[0136] (v) a target cell is on a different SCS compared to source cell and the timing advance is adjusted according to the SCS in the target and source cell.

[0137] According to a third aspect of the present invention, there is provided telecommunication network arranged to perform the method of the first aspect.

[0138] According to a fourth aspect of the present invention, there is provided User Equipment arranged to perform the method of the second aspect.

[0139] A key idea in an embodiment of this invention revolves around methods for managing the Timing advance during a RACH-less handover or a RACH-less cell establishment when it is signalled that the UE shall use the timing advance of the source cell in the target cell.

[0140] Embodiments describe the RACH-less handover using what is known as the configured or the pre-configured uplink grant, but this is only one option. The other option of configuring the UE to monitor PDCCH and then the target eNB sends PDCCHs containing UL grant is also applicable.

[0141] Embodiments are mostly described using gNBs (4G E-UTRAN), but may equally apply to eNBs or NG-RAN (5G NR). Embodiments may also apply to a eMTC / LTE-M UE, or 5G NR UE, or E-UTRAN UE.

[0142] When performing a RACH-less handover or RACH-less establishment, the source cell may a PCell, or a PSCell, or a SpCell. Similarly, the target cell may become the PCell, or a PSCell or a SpCell.

[0143] Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0144] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

[0145] Figure 1a shows a RACH-less handover with uplink grants configured;

[0146] Figure 1b shows a RACH-less handover where the UE is configured to monitor PDCCH of target cell;

[0147] Figure 2 shows SCG addition procedures;

[0148] Figure 3 shows EN-DC SCG addition procedures;

[0149] Figure 4a shows timing advance from a cell of SCS=30 kHz used in a cell of SCS=15 kHz and a timing advance command is later used;

[0150] Figure 4b shows rounding down the TA using in SCS=30 kHz to an a value that would be used in SCS=15 kHz;

[0151] Figure 5a shows SCG establishment using N_TA translation for EN-DC; and

[0152] Figure 5b shows SCG establishment using N_TA translation for NE-DC.

[0153] In order to perform a RACH-less handover or RACH-less SgNB addition, there needs to be some management of the Timing Advance. For instance, when performing RACH-less handover from a first cell to a second cell with lower SCS, the NTAthat is used in the first cell may not be suitable in the second cell. This is because the NTAmay be in-between the configurable NTAvalues for the second cells.

[0154] For instance, the NTAvalue from the first cell with SCS = 60 kHZ can be 3 x 16 x 64 / 23= 384, while in the second cell, granularity of the NTAare in multiples of 1024.

[0155] Thus, in one embodiment of the invention, when performing inter-SCS RACH-less handovers, inter-frequency RACH-less handover or RACH-less establishment, the NTAused from the first cell is rounded up or rounded down to a value that is consistent with the specific SCS of the cell.

[0156] If rounded down, a flooring function is used, similar to the following [Math Figure 3]:

[0157]

[0158] If rounded up, a ceiling function is used, similar to the following [Math Figure 4]:

[0159]

[0160] In the above, the is the NTAto apply in the target cell when calculating the full timing advance. The is the value that is used in the source cell.

[0161] In the above, the condition to apply may be one or a combination of the below:

[0162] ● The target cell SCS is smaller than the source cell SCS

[0163] ● The target cell frequency is smaller than the source cell frequency

[0164] ○ For instance it can be FR2 to FR1

[0165] ● Condition may be that it is an inter-frequency handover.

[0166] The above can be applied by implicit indication or explicit indication. By implicit indication, the above is applied when one of the above conditions are fulfilled, i.e. when the UE is indicated to apply source TA in target cell during RACH-less handover and the target cell has a lower SCS than the source cell. By explicit indication, a bit in the RACH-less configuration may indicate that rounding shall be performed. In a refinement, two bits are used, with 00 indicating no rounding, 01 indicating rounding up, 10 indicating rounding down, and 11 being unused.

[0167] In one embodiment of the invention, there are restrictions on when RACH-less handovers may be performed. For instance, for inter-SCS, inter-frequency (such as between FR1 and FR2) RACH-less handovers may not be performed. For instance, for inter-SCS or inter-frequency RACH-less handovers or RACH-less establishment, it may only be performed if TA=0 is configured. This can be seen in Example #1. In a further refinement, RACH-less handover to a lower SCS can only be performed using TA=0 or, RACH-less handover or RACH-less establishment may only be performed when the SCS values are adjacent, for instance 120kHz -> 60 kHz, 60 kHz -> 30 kHz, 30 kHz -> 15 kHz. In another refinement, RACH-less handover or RACH-less establishment may only be performed when the difference between and is below a certain pre-defined or configurable threshold.

[0168] In one embodiment of the invention, the same methods can be used when performing a handover from a first cell, where the UE is configured to operate on the first cell with a Bandwidth Part (BWP) with a specific SCS, to a second cell with a different SCS from the configuration in first cell. This means that even though the first cell and second cell may operate with the same SCS, the UE may be dedicatedly configured with BWP that has a different SCS from any of the two cells. In other words, the change of the SCS may occur even though the common configuration suggests that the cells have the same SCS.

[0169] Some of the above may, for instance, mean that RACH-less handover or SCG establishment may only be performed within the same Frequency Range (FR1->FR1, FR2->FR2, FR2-1->FR2-1, etc.).

[0170] In the above, there may be a need to round to the nearest multiple of the Timing Advance, i.e , where is the SCS number. This can be seen in Figure 4a, which shows timing advance from a cell of SCS=30 kHz used in a cell of SCS=15 kHz and a timing advance command is later used.

[0171] In another embodiment of the invention, it can be configurable whether the UE shall round up / down to the nearest multiple of the Timing Advance. This can be seen in Figure 4b, where it is rounded down. More particularly, the TA is rounded down from a value used in SCS=30 kHz to a value that would be used in SCS=15 kHz.

[0172] The following relates to EN-DC and NE-DC RACH-less SCG establishment. As the absolute timing in advance is defined based on NTAin both NR and LTE, but the steps involved in establishing the NTAare different in each case, one feature of embodiments of this invention, relates to a translation of the NTAwhen performing EN-DC and NE-DC RACH-less SCG establishment.

[0173] In one embodiment of the invention, when performing EN-DC RACH-less SCG establishment and the MN eNB signals that the target TA should depend on an already serving cell, there is a translation from LTE to NR NTA:

[0174]

[0175] Thus, the NTAto apply in a target NR cell from the source E-UTRAN cell, is the target E-UTRAN NTAmultiplied by the factor that is the difference between the LTE and NR basic timing unit.

[0176] The condition to apply the above translation may for instance be that one or more of the following conditions shall be true:

[0177] ● Target cell or SN is NR

[0178] ● Source cell or MN is E-UTRAN

[0179] ● A part ofnr-SecondaryCellGroupConfigin LTE RRC messageRRCConnectionReconfiguration.

[0180] Similarly, when performing NE-DC RACH-less SCG establishment and the MN gNB signals that target TA should depend on an already serving cell, there is a translation from NR to LTE NTA:

[0181]

[0182] The condition to apply the above translation may, for instance, be that one or more of the following conditions shall be true:

[0183] ● Target cell or SN is E-UTRAN

[0184] ● Source cell or MN is NR

[0185] ● Signalled as part ofrach-SkipSCG

[0186] ● A part ofeutran-scgin NR RRC messageRRCReconfiguration.

[0187] The above will be applied regardless of the serving cell that the network signals that the UE use the timing advance from (i.e PCell or any SCell).

[0188] These two examples can be seen later in this application as "Example #2" and "Example #3" as well as in Figures 5a and 5b, which show SCG establishment using N_TA translation for EN-DC, and SCG establishment using N_TA translation for NE-DC, respectively.

[0189] As the number of scenarios for RACH-less SCG establishment are many, in some cases, there can be reasons why RACH-less SCG establishment may not be performed. Thus, there may be conditions when RACH-less can be performed or not. Or in other cases, these restrictions may be related to UE capabilities.

[0190] In one embodiment of this invention, when a failure occurs when trying to establish an SCG and using RACH-less, this is reported in the SCGFailureInformation. This can for instance be a flag in the SCGFailureInformation RRC message that RACH-less was used. It can also be indicated the NTAthat was used in for RACH-less.

[0191] In the following part of the description, implementation examples are present in ASN.1 format.

[0192] Example #1

[0193] ---------------- Example based on TS38.331 V18.0.0 --------------------

[0194] -CellGroupConfig

[0195] TheCellGroupConfigIE is used to configure a master cell group (MCG) or secondary cell group (SCG). A cell group comprises of one MAC entity, a set of logical channels with associated RLC entities and of a primary cell (SpCell) and one or more secondary cells (SCells). For an NCR-MT, theCellGroupConfigIE is also used to provide the configuration of side control information for the NCR-Fwd access link.

[0196] CellGroupConfiginformation element-- ASN1START-- TAG-CELLGROUPCONFIG-START-- Configuration of one Cell-Group:CellGroupConfig ::= SEQUENCE {cellGroupId CellGroupId,rlc-BearerToAddModList SEQUENCE (SIZE(1..maxLC-ID)) OF RLC-BearerConfig OPTIONAL, -- Need Nrlc-BearerToReleaseList SEQUENCE (SIZE(1..maxLC-ID)) OF LogicalChannelIdentity OPTIONAL, -- Need Nmac-CellGroupConfig MAC-CellGroupConfig OPTIONAL, -- Need MphysicalCellGroupConfig PhysicalCellGroupConfig OPTIONAL, -- Need MspCellConfig SpCellConfig OPTIONAL, -- Need MsCellToAddModList SEQUENCE (SIZE (1..maxNrofSCells)) OF SCellConfig OPTIONAL, -- Need NsCellToReleaseList SEQUENCE (SIZE (1..maxNrofSCells)) OF SCellIndex OPTIONAL, -- Need N...,[[reportUplinkTxDirectCurrent ENUMERATED {true} OPTIONAL -- Cond BWP-Reconfig]],. . . OMITTED . . .}-- Serving cell specific MAC and PHY parameters for a SpCell:SpCellConfig ::= SEQUENCE {servCellIndex ServCellIndex OPTIONAL, -- Cond SCGreconfigurationWithSync ReconfigurationWithSync OPTIONAL, -- Cond ReconfWithSyncrlf-TimersAndConstants SetupRelease { RLF-TimersAndConstants } OPTIONAL, -- Need MrlmInSyncOutOfSyncThreshold ENUMERATED {n1} OPTIONAL, -- Need SspCellConfigDedicated ServingCellConfig OPTIONAL, -- Need M...,[[lowMobilityEvaluationConnected-r17 SEQUENCE {s-SearchDeltaP-Connected-r17 ENUMERATED {dB3, dB6, dB9, dB12, dB15, spare3, spare2, spare1},t-SearchDeltaP-Connected-r17 ENUMERATED {s5, s10, s20, s30, s60, s120, s180, s240, s300, spare7, spare6, spare5,spare4, spare3, spare2, spare1}} OPTIONAL, -- NeedgoodServingCellEvaluationRLM-r17 GoodServingCellEvaluation-r17 OPTIONAL, -- Need RgoodServingCellEvaluationBFD-r17 GoodServingCellEvaluation-r17 OPTIONAL, -- Need RdeactivatedSCG-Config-r17 SetupRelease { DeactivatedSCG-Config-r17 } OPTIONAL -- Cond SCG-Opt]]}ReconfigurationWithSync ::= SEQUENCE {spCellConfigCommon ServingCellConfigCommon OPTIONAL, -- Need MnewUE-Identity RNTI-Value,t304 ENUMERATED {ms50, ms100, ms150, ms200, ms500, ms1000, ms2000, ms10000},rach-ConfigDedicated CHOICE {uplink RACH-ConfigDedicated,supplementaryUplink RACH-ConfigDedicated} OPTIONAL, -- Need N...,[[smtc SSB-MTC OPTIONAL -- Need S]],[[daps-UplinkPowerConfig-r16 DAPS-UplinkPowerConfig-r16 OPTIONAL -- Need N]],[[sl-PathSwitchConfig-r17 SL-PathSwitchConfig-r17 OPTIONAL -- Cond DirectToIndirect-PathSwitch]],[[rach-LessHO-r18 RACH-LessHO-r18 OPTIONAL -- Need N]]}. . . OMITTED . . .RACH-LessHO-r18 ::= SEQUENCE {targetNTA-r18 ENUMERATED {zero, source} OPTIONAL, -- Need Rtci-StateID-r18 TCI-StateId OPTIONAL, -- Cond MobileIABdg-beam-r18 SSB-Index OPTIONAL, -- Cond DG-RACH-LessHO...}. . . OMITTED . . .-- TAG-CELLGROUPCONFIG-STOP-- ASN1STOP

[0197] RACH-LessHO field descriptionsdg-beamThis field indicates a beam that the UE should use in the target cell to monitor PDCCH for initial uplink transmission, see TS 38.321 [3].targetNTAThis field refers to the timing adjustment, see TS 38.213

[0013] and TS 38.321 [3], indicating the NTAvalue which the UE shall use for the target PTAG of handover. Only value source is configured by the network in case source cell is a mobile IAB cell. If the SCS of the target cell is smaller than the source cell, the UE rounds NTAvalue applied is Floor (N_TA_source / (16 * 64 / 2u)) * 16 * 64 / 2uwhere u is the target cell SCS.tci-StateIDThis field indicates a beam that the UE should use in the target cell to monitor PDCCH for initial uplink transmission. This field is always present in case this cell is a mobile IAB cell.

[0198] ReconfigurationWithSync field descriptionsrach-ConfigDedicatedRandom access configuration to be used for the reconfiguration with sync (e.g. handover). The UE performs the RA according to these parameters in the firstActiveUplinkBWP (see UplinkConfig).smtcThe SSB periodicity / offset / duration configuration of target cell for NR PSCell change and NR PCell change. The network sets the periodicityAndOffset to indicate the same periodicity as ssb-periodicityServingCell in spCellConfigCommon or sets to the same periodicity as ssb-Periodicity-r17 in nonCellDefiningSSB-r17 if the first active DL BWP included in this RRC message is configured with nonCellDefiningSSB-r17.For case of NR PCell change, the smtc is based on the timing reference of (source) PCell. For case of NR PSCell change, it is based on the timing reference of source PSCell.If both this field and targetCellSMTC-SCG are absent, the UE uses the SMTC in the measObjectNR having the same SSB frequency and subcarrier spacing, as configured before the reception of the RRC message. If the first active DL BWP included in this RRC message is configured with nonCellDefiningSSB-r17, this field corresponds to the NCD-SSB indicated by nonCellDefiningSSB-r17, otherwise, this field corresponds to the CD-SSB indicated by absoluteFrequencySSB in frequencyInfoDL.

[0199] Example #2

[0200] --------------- Example based on TS38.331 V18.0.0 ------------------

[0201] -CellGroupConfig

[0202] TheCellGroupConfigIE is used to configure a master cell group (MCG) or secondary cell group (SCG). A cell group comprises of one MAC entity, a set of logical channels with associated RLC entities and of a primary cell (SpCell) and one or more secondary cells (SCells). For an NCR-MT, theCellGroupConfigIE is also used to provide the configuration of side control information for the NCR-Fwd access link.

[0203] CellGroupConfiginformation element-- ASN1START-- TAG-CELLGROUPCONFIG-START-- Configuration of one Cell-Group:CellGroupConfig ::= SEQUENCE {cellGroupId CellGroupId,rlc-BearerToAddModList SEQUENCE (SIZE(1..maxLC-ID)) OF RLC-BearerConfig OPTIONAL, -- Need Nrlc-BearerToReleaseList SEQUENCE (SIZE(1..maxLC-ID)) OF LogicalChannelIdentity OPTIONAL, -- Need Nmac-CellGroupConfig MAC-CellGroupConfig OPTIONAL, -- Need MphysicalCellGroupConfig PhysicalCellGroupConfig OPTIONAL, -- Need MspCellConfig SpCellConfig OPTIONAL, -- Need MsCellToAddModList SEQUENCE (SIZE (1..maxNrofSCells)) OF SCellConfig OPTIONAL, -- Need NsCellToReleaseList SEQUENCE (SIZE (1..maxNrofSCells)) OF SCellIndex OPTIONAL, -- Need N...,[[reportUplinkTxDirectCurrent ENUMERATED {true} OPTIONAL -- Cond BWP-Reconfig]],. . . OMITTED . . .}-- Serving cell specific MAC and PHY parameters for a SpCell:SpCellConfig ::= SEQUENCE {servCellIndex ServCellIndex OPTIONAL, -- Cond SCGreconfigurationWithSync ReconfigurationWithSync OPTIONAL, -- Cond ReconfWithSyncrlf-TimersAndConstants SetupRelease { RLF-TimersAndConstants } OPTIONAL, -- Need MrlmInSyncOutOfSyncThreshold ENUMERATED {n1} OPTIONAL, -- Need SspCellConfigDedicated ServingCellConfig OPTIONAL, -- Need M...,[[lowMobilityEvaluationConnected-r17 SEQUENCE {s-SearchDeltaP-Connected-r17 ENUMERATED {dB3, dB6, dB9, dB12, dB15, spare3, spare2, spare1},t-SearchDeltaP-Connected-r17 ENUMERATED {s5, s10, s20, s30, s60, s120, s180, s240, s300, spare7, spare6, spare5,spare4, spare3, spare2, spare1}} OPTIONAL, -- NeedgoodServingCellEvaluationRLM-r17 GoodServingCellEvaluation-r17 OPTIONAL, -- Need RgoodServingCellEvaluationBFD-r17 GoodServingCellEvaluation-r17 OPTIONAL, -- Need RdeactivatedSCG-Config-r17 SetupRelease { DeactivatedSCG-Config-r17 } OPTIONAL -- Cond SCG-Opt]]}ReconfigurationWithSync ::= SEQUENCE {spCellConfigCommon ServingCellConfigCommon OPTIONAL, -- Need MnewUE-Identity RNTI-Value,t304 ENUMERATED {ms50, ms100, ms150, ms200, ms500, ms1000, ms2000, ms10000},rach-ConfigDedicated CHOICE {uplink RACH-ConfigDedicated,supplementaryUplink RACH-ConfigDedicated} OPTIONAL, -- Need N...,[[smtc SSB-MTC OPTIONAL -- Need S]],[[daps-UplinkPowerConfig-r16 DAPS-UplinkPowerConfig-r16 OPTIONAL -- Need N]],[[sl-PathSwitchConfig-r17 SL-PathSwitchConfig-r17 OPTIONAL -- Cond DirectToIndirect-PathSwitch]],[[rach-LessHO-r18 RACH-LessHO-r18 OPTIONAL -- Need N]]}. . . OMITTED . . .RACH-LessHO-r18 ::= SEQUENCE {targetNTA-r18 ENUMERATED {zero, source} OPTIONAL, -- Need Rtci-StateID-r18 TCI-StateId OPTIONAL, -- Cond MobileIABdg-beam-r18 SSB-Index OPTIONAL, -- Cond DG-RACH-LessHO...}. . . OMITTED . . .-- TAG-CELLGROUPCONFIG-STOP-- ASN1STOP

[0204] RACH-LessHO field descriptionsdg-beamThis field indicates a beam that the UE should use in the target cell to monitor PDCCH for initial uplink transmission, see TS 38.321 [3].targetNTAThis field refers to the timing adjustment, see TS 38.213

[0013] and TS 38.321 [3], indicating the NTAvalue which the UE shall use for the target PTAG of handover. Only value source is configured by the network in case source cell is a mobile IAB cell. If signalled as part of nr-SecondaryCellGroupConfig, see TS 36.331

[0010] , for establishment of NR SCG, the NTAapplied in NR SCG NTA_new= NTA_oldx 64, where the NTA_oldis the NTAfrom E-UTRAN PCell.tci-StateIDThis field indicates a beam that the UE should use in the target cell to monitor PDCCH for initial uplink transmission. This field is always present in case this cell is a mobile IAB cell.

[0205] ReconfigurationWithSync field descriptionsrach-ConfigDedicatedRandom access configuration to be used for the reconfiguration with sync (e.g. handover). The UE performs the RA according to these parameters in the firstActiveUplinkBWP (see UplinkConfig).smtcThe SSB periodicity / offset / duration configuration of target cell for NR PSCell change and NR PCell change. The network sets the periodicityAndOffset to indicate the same periodicity as ssb-periodicityServingCell in spCellConfigCommon or sets to the same periodicity as ssb-Periodicity-r17 in nonCellDefiningSSB-r17 if the first active DL BWP included in this RRC message is configured with nonCellDefiningSSB-r17.For case of NR PCell change, the smtc is based on the timing reference of (source) PCell. For case of NR PSCell change, it is based on the timing reference of source PSCell.If both this field and targetCellSMTC-SCG are absent, the UE uses the SMTC in the measObjectNR having the same SSB frequency and subcarrier spacing, as configured before the reception of the RRC message. If the first active DL BWP included in this RRC message is configured with nonCellDefiningSSB-r17, this field corresponds to the NCD-SSB indicated by nonCellDefiningSSB-r17, otherwise, this field corresponds to the CD-SSB indicated by absoluteFrequencySSB in frequencyInfoDL.

[0206] Example #3

[0207] ------------------------ TS36.331 V18.0.0 --------------------------

[0208] -MobilityControlInfo

[0209] The IEMobilityControlInfoincludes parameters relevant for network controlled mobility to / within E-UTRA.

[0210] MobilityControlInfoinformation element-- ASN1STARTMobilityControlInfo ::= SEQUENCE {targetPhysCellId PhysCellId,carrierFreq CarrierFreqEUTRA OPTIONAL, -- Cond HO-toEUTRA2carrierBandwidth CarrierBandwidthEUTRA OPTIONAL, -- Cond HO-toEUTRAadditionalSpectrumEmission AdditionalSpectrumEmission OPTIONAL, -- Cond HO-toEUTRAt304 ENUMERATED {ms50, ms100, ms150, ms200, ms500, ms1000,ms2000, ms10000-v1310},newUE-Identity C-RNTI,radioResourceConfigCommon RadioResourceConfigCommon,rach-ConfigDedicated RACH-ConfigDedicated OPTIONAL, -- Need OP...,[[ carrierFreq-v9e0 CarrierFreqEUTRA-v9e0 OPTIONAL -- Need ON]],[[ drb-ContinueROHC-r11 ENUMERATED {true} OPTIONAL -- Cond HO]],[[ mobilityControlInfoV2X-r14 MobilityControlInfoV2X-r14 OPTIONAL, -- Need ONhandoverWithoutWT-Change-r14 ENUMERATED {keepLWA-Config, sendEndMarker} OPTIONAL, -- Cond HOmakeBeforeBreak-r14 ENUMERATED {true} OPTIONAL, -- Need ORrach-Skip-r14 RACH-Skip-r14 OPTIONAL, -- Need ORsameSFN-Indication-r14 ENUMERATED {true} OPTIONAL -- Cond HO-SFNsynced]],[[mib-RepetitionStatus-r14 BOOLEAN OPTIONAL, -- Need ORschedulingInfoSIB1-BR-r14 INTEGER (0..31) OPTIONAL -- Cond HO-SFNsynced]],[[ daps-Config-r16 DAPS-Config-r16 OPTIONAL -- Cond NotFullConfigHO]],[[ gnss-PositionFixDurationReporting-r18 ENUMERATED {true} OPTIONAL -- Need OR]]}. . . OMITTED . . .RACH-Skip-r14 ::= SEQUENCE {targetTA-r14 CHOICE {ta0-r14 NULL,mcg-PTAG-r14 NULL,scg-PTAG-r14 NULL,mcg-STAG-r14 STAG-Id-r11,scg-STAG-r14 STAG-Id-r11},ul-ConfigInfo-r14 SEQUENCE {numberOfConfUL-Processes-r14 INTEGER (1..8),ul-SchedInterval-r14 ENUMERATED {sf2, sf5, sf10},ul-StartSubframe-r14 INTEGER (0..9),ul-Grant-r14 BIT STRING (SIZE (16))} OPTIONAL -- Need OR}-- ASN1STOP

[0211] MobilityControlInfo field descriptionsrach-SkipThis field indicates whether random access procedure for the target PCell is skipped.rach-SkipSCGThis field indicates whether random access procedure for the target PSCell is skipped....targetTAThis field refers to the timing adjustment indication, see TS 36.213

[0023] , indicating the NTAvalue which the UE shall use for the target PTAG of handover or the target PSTAG of SCG change. If signalled as part of rach-SkipSCG and MCG is NR, the NTAapplied in E-UTRAN SCG is NTA_new= NTA_old / 64, where the NTA_oldis the NTAfrom NR MCG. ta0 corresponds to NTA=0. mcg-PTAG corresponds to the latest NTAvalue of the PTAG associated with MCG. scg-PTAG corresponds to the latest NTAvalue of the PTAG associated with SCG. mcg-STAG corresponds to the latest NTAvalue of a MCG STAG indicated by the STAG-Id. scg-STAG corresponds to the latest NTAvalue of a SCG STAG indicated by the STAG-Id....

[0212] Figure 6 illustrates a configuration of a UE (terminal) according to an embodiment of the disclosure.

[0213] Referring to Figure 6, a UE according to an embodiment of the disclosure may include a transceiver 620 and a controller 610 for controlling the overall operation of the UE. In addition, the transceiver 620 may include a transmitter 625 and a receiver 623. In addition, the UE may include one of a remote user equipment (remote UE) and a remote user equipment (remote UE).

[0214] The transceiver 620 may transmit or receive a signal to or from other network entities.

[0215] The controller 610 may control the UE to perform one operation among the above-described embodiments. The controller 610 and the transceiver 620 are not necessarily implemented as separate modules, and may be implemented by one element in the form such as a single chip. In addition, the controller 610 and the transceiver 620 may be electrically connected. For example, the controller 610 may be a circuit, an application-specific circuit, or at least one processor. In addition, the operations of the UE may be implemented by including, in an arbitrary element in the UE, a memory device having a corresponding program code stored therein.

[0216] Figure 7 illustrates a configuration of a base station according to an embodiment of the disclosure.

[0217] Referring to Figure 7, a base station according to an embodiment of the disclosure may include a transceiver 720 and a controller 710 for controlling the overall operation of the base station. In addition, the transceiver 720 may include a transmitter 725 and a receiver 723.

[0218] The transceiver 720 may transmit or receive a signal to or from other network entities.

[0219] The controller 710 may control the base station to perform one operation among the above-described embodiments. The controller 710 and the transceiver 720 are not necessarily implemented as separate modules, and may be implemented by one element in the form such as a single chip. In addition, the controller 710 and the transceiver 720 may be electrically connected. For example, the controller 710 may be a circuit, an application-specific circuit, or at least one processor. In addition, the operations of the base station may be implemented by including, in an arbitrary element in the base station, a memory device having a corresponding program code stored therein.

[0220] The base station may mean a mater base station, a secondary base station, a source base station, a target base station, the MCG, the SCG, a master node, or a secondary node.

[0221] It should be noted that the configuration diagrams, illustrative diagrams of control / data signal transmission methods, illustrative diagrams of operation procedures, and structural diagrams as illustrated in Figure 1a to Figure 7 are not intended to limit the scope of protection of the disclosure. That is, all the constituent units, entities, or operation steps shown in Figure 1a to Figure 7 should not be construed as essential elements for implementing the disclosure, and even when including only some of the elements, the disclosure may be implemented without impairing the true nature of the disclosure.

[0222] The above-described operations of a base station or a terminal may be implemented by providing a memory device storing corresponding program codes in a bast station or terminal device. That is, a controller of the base station or terminal device may perform the above-described operations by reading and executing the program codes stored in the memory device by means of a processor or central processing unit (CPU).

[0223] Various units or modules of a network entity, a base station device, or a terminal device may be operated using hardware circuits such as complementary metal oxide semiconductor-based logic circuits, firmware, or hardware circuits such as combinations of software and / or hardware and firmware and / or software embedded in a machine-readable medium. For example, various electrical structures and methods may be implemented using transistors, logic gates, and electrical circuits such as application-specific integrated circuits.

[0224] Although specific embodiments have been described in the detailed description of the disclosure, it will be apparent that various modifications and changes may be made thereto without departing from the scope of the disclosure. Therefore, the scope of the disclosure should not be defined as being limited to the embodiments set forth herein, but should be defined by the appended claims and equivalents thereof.

[0225] At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as 'component', 'module' or 'unit' used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of others.

[0226] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0227] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0228] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0229] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1.A method performed by a terminal in a wireless communication system, the method comprising:receiving, from a first base station, a first message comprising information on a random access channel (RACH)-less handover; andtransmitting, to a second base station, a second message for completing a handover procedure based on the information on the RACH-less handover,wherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.2.The method of claim 1,wherein the information on the RACH-less handover comprises at least one of information on a beam that the terminal uses in a target cell to monitor physical downlink control channel (PDCCH) for initial uplink transmission and information on a timing advance value which the terminal uses for a handover.3.The method of claim 1,wherein the first message comprises information on an uplink grant for transmitting the first message or information for monitoring an uplink grant from the second base station, andwherein the transmitting the second message comprises:in case that the first message comprises the information for monitoring the uplink grant from the second base station, receiving, from the second base station, a physical downlink control channel (PDCCH) for the uplink grant based on the information on the RACH-less handover; andtransmitting, to the second base station, the second message based on the uplink grant.4.The method of claim 1,wherein the first message comprises a message to modify an radio resource control (RRC) connection.5.A method performed by a first base station in a wireless communication system, the method comprising:transmitting, to a second base station, a handover request message;receiving, from the second base station, a handover request acknowledge message; andtransmitting, to a terminal, a first message comprising information on a random access channel (RACH)-less handover,wherein a second message for complete a handover procedure is transmitted to the second base station, based on the information on the RACH-less handover, andwherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.6.The method of claim 5,wherein the information on the RACH-less handover comprises at least one of information on a beam that the terminal uses in a target cell to monitor physical downlink control channel (PDCCH) for initial uplink transmission and information on a timing advance value which the terminal uses for a handover.7.The method of claim 5,wherein the first message comprises information on an uplink grant for transmitting the first message or information for monitoring an uplink grant from the second base station.8.The method of claim 5,wherein the first message comprises a message to modify an radio resource control (RRC) connection.9.A terminal in a wireless communication system, the terminal comprising:a transceiver; anda controller coupled with the transceiver and configured to:receive, from a first base station, a first message comprising information on a random access channel (RACH)-less handover, andtransmit, to a second base station, a second message for completing a handover procedure based on the information on the RACH-less handover,wherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.10.The terminal of claim 9,wherein the information on the RACH-less handover comprises at least one of information on a beam that the terminal uses in a target cell to monitor physical downlink control channel (PDCCH) for initial uplink transmission and information on a timing advance value which the terminal uses for a handover.11.The terminal of claim 9,wherein the first message comprises information on an uplink grant for transmitting the first message or information for monitoring an uplink grant from the second base station, andwherein the controller is further configured to:in case that the first message comprises the information for monitoring the uplink grant from the second base station, receive, from the second base station, a physical downlink control channel (PDCCH) for the uplink grant based on the information on the RACH-less handover; andtransmit, to the second base station, the second message based on the uplink grant.12.The terminal of claim 9,wherein the first message comprises a message to modify an radio resource control (RRC) connection.13.A first base station in a wireless communication system, the first base station comprising:a transceiver; anda controller coupled with the transceiver and configured to:transmit, to a second base station, a handover request message,receive, from the second base station, a handover request acknowledge message, andtransmit, to a terminal, a first message comprising information on a random access channel (RACH)-less handover,wherein a second message for complete a handover procedure is transmitted to the second base station, based on the information on the RACH-less handover, andwherein a frequency range 1 (FR1)-FR2 RACH-less handover is not supported.14.The first base station of claim 13,wherein the information on the RACH-less handover comprises at least one of information on a beam that the terminal uses in a target cell to monitor physical downlink control channel (PDCCH) for initial uplink transmission and information on a timing advance value which the terminal uses for a handover, andwherein the first message comprises a message to modify an radio resource control (RRC) connection.15.The first base station of claim 13,wherein the first message comprises information on an uplink grant for transmitting the first message or information for monitoring an uplink grant from the second base station.

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