Method and user equipment for reporting accessibility measurements in a wireless communication system

Abstract

The present disclosure relates to a 5G (5th generation) or pre-5G communication system provided to support higher data rates after a 4G (4th Generation) communication system such as LTE (Long Term Evolution). An embodiment of the present specification discloses a method for reporting an accessibility measurement by a UE 100 based on an RRC connection establishment failure in a wireless communication system. The method includes detecting an RRC connection establishment failure and logging parameters selected during the failed RRC connection establishment attempt, the logged parameters being referred to as an accessibility measurement. Furthermore, the method includes a step of indicating the presence of a connection establishment failure report to the base station 200 in response to receiving a request from the base station 200 and a step of reporting the connection establishment failure report to the base station 200, the failure report may include accessibility measurements including at least one of SSB information selected by the UE during cell access and thereafter during the occurrence of an RRC connection establishment failure and uplink carrier information selected by the UE during cell access and thereafter during the occurrence of an RRC connection establishment failure.

Description

[Technical Field]

[0001] The present disclosure relates to wireless communication systems, and more particularly to a method and user equipment (UE) for accessibility measurement based on radio resource control (RRC) connection failure in a wireless communication system. This application claims priority to Indian Patent Application No. 201941017815, filed on May 3, 2019, the disclosure of which is incorporated herein by reference. [Background technology]

[0002] 4G(4 th Since the commercialization of the 5G (5th generation) communication system, improved 5G (5G) technology has been developed to meet the increasing demand for wireless data traffic. th Efforts are being made to develop 5G (Next Generation) or pre-5G communication systems. For this reason, 5G or pre-5G communication systems are called "Beyond 4G Network communication systems" or "Post-LTE (Long Term Evolution) systems."

[0003] To achieve high data transmission rates, 5G communication systems are being considered for implementation in ultra-high frequency (mmWave) bands (e.g., 60 GHz bands). To mitigate the path loss of radio waves in the ultra-high frequency bands and increase the transmission distance of radio waves, technologies such as beamforming, massive MIMO, full dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and large scale antennas are being discussed for 5G communication systems.

[0004] Additionally, to improve the system network, 5G communication systems are undergoing technological development, including advanced small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device-to-device communication (D2D), wireless backhaul, moving networks, cooperative communication, CoMP (Coordinated Multi-Points), and receiver interference cancellation.

[0005] For 5G systems, advanced coding modulation (ACM) methods such as FSK (Hybrid Frequency Shift Keying), FQAM (Quadrature Amplitude Modulation), and SWSC (Sliding Window Superposition Coding) are being developed, as well as advanced access technologies such as FBMC (Filter Bank Multi Carrier), NOMA (Non Orthogonal Multiple Access), and SCMA (Sparse Code Multiple Access).

[0006] The fifth-generation (5G) communication system (NR (New Radio)) is being developed to meet the demand for high bandwidth through enhanced mobile broadband (eMBB) and to support new use cases such as ultra-reliable low latency communication (URLLC) and massive machine-type communication (mMTC). NR is an air interface based on orthogonal frequency-division multiplexing (OFDM) designed to support diverse 5G device types, services, deployments, and spectrum variants. A base station 200 monitors device activity and provides the necessary resources to a UE (e.g., a mobile phone) to perform any required tasks (data uplink or downlink, call, etc.). The signal strength and quality experienced by a UE varies depending on the proximity of the UE to the gNB. UEs located near a cell are expected to have better signal conditions than those located farther from the gNB, i.e., cell edge conditions.

[0007] In LTE, the base station 200 RAN node (i.e., gNodeB) in the NR / eNB constantly maintains context for UEs in an active RRC connection with it. At any point, the gNB can hand over the UE from its control (i.e., source cell) to another gNB or another cell (i.e., target cell) and convey the entire context of the particular UE to the target cell. This decision is taken by the base station 200 selectively based on assistance received from the UE with the help of measurement reports for neighboring cells (i.e., the gNB configures the UE to measure the signal conditions of the serving cell to which it belongs and neighboring cells that may belong to other gNBs). There are specific measurement criteria and specific reporting criteria, both of which are configured by the serving gNB. For various reasons, such as weak signal conditions or overloading of the serving gNB, the serving gNB can hand over the device to a neighboring cell or target gNB, and this can be done based on assistance received from the UE in the form of measurement reports.

[0008] The UE continuously monitors the quality of the radio link to ensure that the link is in a good enough state to successfully receive transmissions from and transmit to the base station. When the UE determines that the link quality has weakened, the radio resource management (RRM) function, which performs radio link monitoring (RLM) at the PHY layer, transmits an out-of-synchronization indication to the upper layer (i.e., the RRC layer) to indicate the degradation of the radio link quality. When the link degradation condition reaches an acceptable limit, i.e., a configured threshold condition, the UE enters an outage state, which is poor radio conditions in which the UE experiences Qout (no radio resource manager synchronization indication) due to a high block error rate. The current specification specifies the use of a configured T310 timer in this state. The UE declares a radio link failure (RLF) when timer T310 expires and initiates a cell selection procedure to attempt recovery.

[0009] In a basic handover in NR (and similarly in LTE), the source node (i.e., eNB in ​​LTE and gNB in ​​NR) triggers handover by transmitting an HO request to the target node. After receiving an ACK from the target node, the source node initiates handover by transmitting an HO command along with the target cell configuration. The UE applies RRC reconfiguration to the received target cell configuration and then transmits a PRACH to the target cell. 3GPP is currently working to improve handover interruptions and handover reliability. The proposed invention relates to improvements to existing handover mechanisms in LTE and NR to improve interruption time and reliability during handover. It would therefore be desirable to overcome the above-mentioned shortcomings or at least provide a useful alternative. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a method and user equipment for controlling improved mobility in LTE and NR.

[0011] Another object of the present invention is to provide a method and a user equipment for performing a handover in a wireless communication system. [Means for solving the problem]

[0012] Therefore, this embodiment discloses a method for reporting accessibility measurements of a terminal based on an RRC connection establishment failure in a wireless communication system. The method includes detecting an RRC connection establishment failure by a UE. The method also includes logging, by the UE, parameters selected during the failed RRC connection establishment attempt, where the logged parameters are accessibility measurements. The method also includes indicating, by the UE, the existence of a connection establishment failure report to a base station, and reporting, by the UE, the connection establishment failure report to the base station in response to receiving a request from the base station, where the failure report includes accessibility measurements. The accessibility measurements include at least one of synchronization signal block (SSB) information selected during cell access and the subsequent RRC connection establishment failure of the UE, and uplink carrier information selected during cell access and the subsequent RRC connection establishment failure of the UE. The accessibility measurements also enable the base station to accurately evaluate resources used by the UE during the RRC connection establishment failure.

[0013] In one embodiment, the failure report is one of a 5G NR new-radio radio resource control (RRC) configuration failure report and a 5G NR RRC resumption failure report.

[0014] In one embodiment, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection resumption failure.

[0015] In one embodiment, the carrier information is one of a Supplementary Uplink (SUL) carrier and a Normal Uplink (NUL) carrier, which is selected during cell access and subsequently logged by the UE when the UE experiences an RRC connection establishment failure.

[0016] In one embodiment, the logged values ​​of the uplink carrier information are included in the connection establishment report in response to receiving a request from the base station.

[0017] In one embodiment, the SSB information is an SSB index selected during access and subsequently logged by the UE when it experiences an RRC connection establishment failure.

[0018] In one embodiment, the logged value of the SSB index is included in the connection establishment report in response to receiving a request from the base station.

[0019] Thus, a UE for accessibility measurement based on RRC connection establishment failure in a wireless communication system is disclosed.

[0020] Thus, according to an embodiment of the present disclosure, a UE includes a processor coupled to a memory. The processor detects an RRC connection failure and logs parameters selected during the failed RRC connection establishment attempt. The logged parameters are accessibility measurements. The processor is also configured to indicate the existence of a connection establishment failure report to a base station and to receive a request from the base station corresponding to the connection establishment failure report. In response to receiving the request from the base station, the processor is configured to report the connection establishment failure report to the base station in a wireless communication system. The connection establishment failure report includes accessibility measurements, the accessibility measurements including at least one of synchronization signal block (SSB) information selected during cell access and the subsequent time the UE experienced the RRC connection establishment failure and uplink carrier information selected during cell access and the subsequent time the UE experienced the RRC connection establishment failure.

[0021] The present invention also discloses a method for a terminal performing a handover in a wireless communication system. The method includes receiving, by a UE, from a source cell, a handover configuration including an execution condition associated with at least one candidate target cell from a plurality of candidate target cells and a configuration associated with the at least one candidate target cell from the plurality of candidate target cells. The method also includes evaluating, by the UE, the execution condition associated with the at least one candidate target cell. The method also includes determining, by the UE, whether the execution condition for the target cell from the plurality of candidate target cells is satisfied. The method also includes performing, by the UE, a handover to the target cell based on the determination.

[0022] Accordingly, disclosed herein is a UE for performing a handover in a wireless communication system. The UE includes a processor coupled to a memory. The processor is configured to receive from a source cell a handover configuration including an execution condition associated with at least one candidate target cell from a plurality of candidate target cells and a configuration associated with at least one candidate target cell from the plurality of candidate target cells. The processor is also configured to evaluate the execution condition associated with the at least one candidate target cell. The processor is also configured to determine whether the execution condition for the target cell is satisfied. The processor is also configured to perform a handover to the target cell based on the determination.

[0023] These and other aspects will be more readily appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments and numerous specific details, is given by way of illustration and not limitation. Numerous changes and modifications may be made within the scope of this disclosure without departing from the spirit thereof, and all such modifications may be included. [Brief explanation of the drawings]

[0024] The above methods and systems are illustrated in the accompanying drawings, in which like reference characters throughout refer to corresponding parts in the various drawings. Embodiments herein can be more readily understood from the following description with reference to the drawings, in which: [Figure 1] 1 is a schematic diagram of a wireless communication system for accessibility measurement based on RRC connection failure, according to embodiments disclosed herein; [Figure 2A] 1 is a flowchart illustrating a method for reporting accessibility measurements based on the RRC connection failure in a wireless communication system, according to embodiments disclosed herein. [Figure 2B] 1 is a flowchart illustrating a method for performing a handover in a wireless communication system according to embodiments disclosed herein. [Figure 3A] FIG. 1 is a sequence diagram illustrating a simplified model of a Release 15 handover according to the current Release 15 specification. [Figure 3B] 10 is a sequence diagram of a source cell initiating transmission of data forwarding and SN status transmission to a target cell indicated in a measurement report that triggers CHO execution in the UE, according to an embodiment disclosed herein. [Figure 4A] FIG. 10 is a sequence diagram illustrating a process in which a source cell ignores a handover ACK received for normal handover preparation if the source cell has already received a measurement report from the UE indicating CHO execution, according to an embodiment disclosed in this specification. [Figure 4B] FIG. 10 is a sequence diagram illustrating a UE canceling CHO execution and issuing a normal HO command if a normal HO command is received from a source cell before receiving an L2 ACK or HARQ ACK for a CHO measurement report transmission according to an embodiment disclosed in this specification. [Figure 5]1 illustrates a base station configuring a UE with multiple CHO conditions to enable the UE to evaluate candidate target cells for performing CHO, according to embodiments disclosed herein. [Figure 6] FIG. 10 is a sequence diagram illustrating a case where the source cell continues to serve the UE after providing a handover command until a timer equivalent to the T304 timer for configuring the UE in the source cell expires, or when the UE receives a CONTEXT RELEASE message from the target cell upon successful completion of the path change, according to an embodiment disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0025] The embodiments and various features and advantageous details of the present specification are described in detail in the following description and more fully with reference to non-limiting embodiments illustrated in the accompanying drawings. Descriptions of well-known components and processing techniques are omitted so as not to unnecessarily obscure the embodiments of the present specification. In addition, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments may be combined with one or more other embodiments to form new embodiments. As used herein, the term "or" indicates non-exclusion unless otherwise indicated. The examples used herein are merely intended to facilitate understanding of the manner in which the embodiments of the present specification may be implemented and to enable those skilled in the art to implement the embodiments of the present specification. Therefore, the examples should not be construed as limiting the scope of the embodiments.

[0026] As is common in the art, embodiments may be described and illustrated in terms of described functions or blocks performing functions. These blocks, which may be referred to herein as processors, units, modules, hardware components, etc., may be physically implemented with analog and / or digital circuitry, such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuitry, etc., and may optionally be driven by firmware and software. Circuits may be implemented, for example, on one or more semiconductor chips or on a substrate support such as a printed circuit board. The circuits constituting a block may be implemented with dedicated hardware or processors (e.g., one or more programmed microprocessors and associated circuitry), or a combination of dedicated hardware performing some of the block's functions and processors performing other functions. Each block of an embodiment may be physically separated into two or more interacting individual blocks without departing from the scope of the present disclosure. Similarly, the blocks of an embodiment may be physically combined into a more complex block without departing from the scope of the present disclosure.

[0027] The terms handover command and reconfiguration with synchronization are used interchangeably in this disclosure and both refer to messages that trigger a handover execution procedure in a UE.

[0028] Accordingly, embodiments herein disclose a method for reporting accessibility measurements by a UE based on an RRC connection establishment failure in a wireless communication system. The method includes detecting an RRC connection establishment failure by the UE. The method also includes logging, by the UE, parameters selected during the failed RRC connection establishment attempt, where the logged parameters are referred to as accessibility measurements. The method also includes indicating, by the UE, the existence of a connection establishment failure report to a base station, and reporting, by the UE, the connection establishment failure report to the base station in response to receiving a request from the base station, where the failure report comprises accessibility measurements. The accessibility measurements include at least one of synchronization signal block (SSB) information selected during cell access and the subsequent time the UE experienced the RRC connection establishment failure and uplink carrier information selected during cell access and the subsequent time the UE experienced the RRC connection establishment failure.

[0029] The accessibility measurements also allow the base station to accurately assess the resources used by the UE during an RRC connection establishment failure.

[0030] Unlike conventional methods and systems, the method can be used to control enhanced mobility in LTE and NR. The method can be used to initiate data forwarding in conditional handover based on an indication from the UE. The method can be used to avoid duplicate handover commands to the UE. The method can be used to configure CHO execution conditions to identify conditions for suspending transmission in the source cell during eMBB-based handover.

[0031] The above method can be used to indicate a beam ID in logged MDT accessibility measurements. The above method can be used to indicate a UL carrier ID in logged MDT accessibility measurements. The above method can be used to provide an indication from the UE as to the type(s) of make before break handover that the UE supports. In the proposed method, base station 200 provisions make before break handover based on one of multiple handover types supported by the UE.

[0032] The proposed method can be used to reduce interruption time during handover and improve reliability even when the UE is in a conventional handover mechanism in LTE and NR systems. The above method can be used to correctly estimate the resources used when the UE faces a connection establishment failure and needs to indicate the SSB that the UE has selected to access the cell.

[0033] The method can be used to correctly evaluate resources used when a UE experiences a connection resumption failure and needs to indicate the SSB selected by the UE to access a cell. The method can be used to correctly evaluate resources used when a UE experiences a connection establishment failure and needs to indicate the UL carrier selected by the UE to access a cell. The method can be used to correctly evaluate resources used when a UE experiences a connection resumption failure and needs to indicate the UL carrier selected by the UE to access a cell.

[0034] In the proposed method, beam information (e.g., attempted beam index) can be indicated as part of the RACH information, i.e., attempted SSB index can be indicated as part of the RACH failure information.

[0035] In the proposed method, the 5G NR RRC connection failure report includes the SSB indexes of the downlink beams of both the serving cell and the neighboring cell, the corresponding measurement results, and the SUL / NUL carrier information.

[0036] As discussed in the drawings, and more particularly in FIGS. 1-6, where like reference characters indicate corresponding features consistently throughout the drawings, preferred embodiments are illustrated.

[0037] 1 is a schematic diagram of a wireless communication system 1000 for accessibility measurement based on RRC connection failures, according to an embodiment disclosed herein. In one embodiment, the wireless communication system 1000 includes a UE 100 and a base station 200. The UE 100 may be, for example, a mobile phone, tablet, smartphone, laptop, personal digital assistant (PDA), global positioning system (GPS), multimedia device, video device, Internet of Things (IoT) device, smart watch, game console, smartwatch, foldable display device, unmanned aerial vehicle (UAV), airplane, etc. The UE 100 may also be referred to by those skilled in the art as a mobile station, subscriber station, mobile unit, subscriber unit, radio unit, remote unit, mobile device, wireless device, wireless communication device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, handset, user agent, mobile client, etc. The base station 200 may also be referred to as a base transceiver station, radio base station, radio transceiver, transceiver function, basic service set (BSS), enhanced service set (ESS), eNB, gNB, etc.

[0038] In one embodiment, the UE 100 includes a processor 110, a communication unit 120, and a memory 130. The processor 110 is coupled to the memory 130 and the communication unit 120. The processor 110 includes an accessibility measurement based RRC connection establishment failure decision engine 110a and a CHO engine 110b. The processor 110 is configured to execute instructions stored in the memory 130 and perform various processes. The communication unit 120 is configured to communicate internally between internal hardware components and external devices via one or more networks.

[0039] The memory 130 stores instructions executed by the processor 140. The memory 130 may include non-volatile storage elements. Examples of such non-volatile storage elements may include a magnetic hard disk, an optical disk, a floppy disk, a flash memory, or an electrically programmable memory (EPROM) or electronic device. The memory 130 may also be considered a non-transitory storage medium in some instances. The term "non-transitory" may indicate that the storage medium is not implemented as a carrier wave or a propagated signal. However, the term "non-transitory" should not be interpreted as meaning that the memory 130 is non-removable. In some instances, the memory 130 may be configured to store more information than a memory. In certain instances, the non-transitory storage medium may store data that may change over time (e.g., a random access memory (RAM) or a cache).

[0040] The accessibility measurement based RRC connection establishment failure decision engine 110a is configured to detect RRC connection failures and log selected parameters during failed RRC connection establishment attempts. The logged parameters are referred to as accessibility measurements. In one embodiment, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection resumption failure.

[0041] Additionally, the accessibility measurement based RRC connection establishment failure decision engine 110a is configured to indicate the existence of the connection establishment failure report to the base station 200 and to receive a request corresponding to the connection establishment failure report from the base station 200. In one embodiment, the connection establishment failure report is one of a 5G New Generation Radio Resource Control (5G NR RRC) setup failure report and a 5G NR RRC resume failure report.

[0042] In response to receiving a request from the base station 200, the accessibility measurement based RRC connection establishment failure decision engine 110a is configured to report a connection establishment failure report to the base station in the wireless communication system, the connection establishment failure report including accessibility measurements, the accessibility measurements including at least one of synchronization signal block (SSB) information selected during cell access and thereafter when the UE experiences an RRC connection establishment failure and uplink carrier information selected during cell access and thereafter when the UE experiences an RRC connection establishment failure.

[0043] In one embodiment, the accessibility measurement is performed by the base station 200 assessing the resources used by the UE 100 during the RRC connection establishment failure.

[0044] In one embodiment, the uplink carrier information is one of a supplementary uplink (SUL) carrier and a normal uplink (NUL) carrier, and the SUL carrier or NUL carrier is selected during cell access and subsequently logged by the UE 100 when encountering an RRC connection establishment failure.

[0045] In one embodiment, the SSB information includes at least one SSB index, which is selected during cell access and subsequently logged by the UE 100 when an RRC connection establishment failure is experienced.

[0046] In one embodiment, the logged value of the SSB index is included in a connection establishment report in response to receiving a request from base station 200 .

[0047] In one embodiment, the logged values ​​of the uplink carrier information are included in a connection establishment failure report in response to receiving a request from base station 200 .

[0048] In one embodiment, the CHO engine 110b is configured to receive from the source cell a handover configuration including an execution condition associated with at least one candidate target cell from the plurality of candidate target cells and a configuration associated with at least one candidate target cell from the plurality of candidate target cells.

[0049] In one embodiment, the execution condition is a measurement ID that links the measurement object and a single reporting configuration or one of two reporting configurations.

[0050] In one embodiment, if two reporting configurations are included in an execution, the first reporting configuration in the execution condition indicates a measurement event with one of the following: An A3 event or an A5 event, and a trigger quantity that is one of the following: RSRP (reference signals received power) or RSRQ (reference signal received quality) or SINR (signal-to-interference-plus-noise ratio), The second reporting structure indicates the measurement event as one of the following: A3 event, A5 event, or A4 event, and RSRP, RSRQ, or SINR, and a trigger quantity that is one of the following: the trigger quantity of the first reporting configuration is different from the trigger quantity of the second reporting configuration, and the reference signal type of the first reporting configuration is the same as the reference signal type of the second reporting configuration.

[0051] The CHO engine 110b is also configured to evaluate execution conditions associated with at least one candidate target cell. In one embodiment, evaluating the execution conditions associated with the at least one candidate target cell includes identifying a completion of an event indicated in the first reporting structure and a completion of an event indicated in the second reporting structure.

[0052] The CHO engine 110b is also configured to determine whether an execution condition for the target cell is met. In one embodiment, determining whether an execution condition for the candidate target cell is met includes indicating a joint completion of an event in the first reporting configuration and the second reporting configuration. The CHO engine 110b is also configured to perform a handover to a candidate target cell based on the determination. In one embodiment, performing a handover to a candidate target cell is performed by selecting a target cell from the plurality of candidate target cells for which a joint completion of the event is determined, and applying a target cell configuration associated with the selected target cell from the received handover configuration.

[0053] 1 illustrates various hardware components of wireless communication system 1000, it should be understood that other embodiments are not so limited. In other embodiments, wireless communication system 1000 includes fewer or more components. Also, the labels or names of the components are used for illustrative purposes only and do not limit the scope of the invention. One or more components may be coupled together to perform the same or substantially similar functions, such as for processing accessibility measurements based on RRC connection failures.

[0054] According to various embodiments, the present invention provides a user equipment UE 100 for reporting accessibility measurements in a wireless communication system 1000, comprising: memory 130; and The processor 110 connected to the memory Detecting a radio resource control (RRC) connection establishment failure; log parameters selected during the failed RRC connection establishment attempt, the logged parameters being accessibility measurements; The method is configured to report a connection establishment failure report to a base station in the wireless communication system based on the log.

[0055] According to various embodiments, the step of reporting the connection establishment failure report to the base station in the wireless communication system based on the log comprises: instructing the base station 200 to fail the RRC connection establishment; receiving a request corresponding to the indicated RRC connection establishment failure from the base station; and reporting the connection establishment failure report to the base station in a wireless communication system based on the request.

[0056] According to various embodiments, the connection establishment failure report includes the accessibility measurements, and the accessibility measurements include at least one of SSB information and uplink carrier information. According to various embodiments, the connection establishment failure report is one of a 5G NR RRC setup failure report and a 5G NR RRC resume report.

[0057] According to various embodiments, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection resumption failure.

[0058] According to various embodiments, the uplink carrier information is one of a supplementary uplink (SUL) carrier and a normal uplink (NUL) carrier, and the SUL carrier or the NUL carrier is selected during cell access and subsequently logged by the UE 100 when encountering the RRC connection establishment failure.

[0059] According to various embodiments, the SSB information includes at least one SSB index selected during cell access and subsequently logged by the UE 100 when experiencing an RRC connection establishment failure.

[0060] According to various embodiments, the logged value of the SSB index is included in the connection establishment report in response to receiving a request from the base station 200 .

[0061] According to various embodiments, the logged value of the uplink carrier information is included in the connection establishment report in response to receiving a request from the base station 200 .

[0062] 2A is a flow chart S200a illustrating a method for reporting accessibility measurements based on the RRC connection establishment failure in the wireless communication system 1000, according to an embodiment disclosed herein. The operations (S202a to S210a) are performed by the processor 110.

[0063] At 202a, the method includes detecting the RRC connection establishment failure. At 204a, the method includes logging parameters selected during the failed RRC connection establishment attempt, the logged parameters being the accessibility measurements.

[0064] At 206a, the method includes indicating the presence of a connection establishment failure report to the base station 200. At 208a, the method includes receiving a request from the base station 200 corresponding to the connection establishment failure report.

[0065] At 210a, the method includes reporting the connection establishment failure report to the base station 200 in the wireless communication system 1000 in response to receiving a request from the base station 200. The connection establishment failure report includes the accessibility measurements, the accessibility measurements including at least one of SSB information selected during cell access and thereafter when the UE 100 experiences an RRC connection establishment failure and uplink carrier information (SUL or NUL) selected during cell access and thereafter when the UE 100 experiences an RRC connection establishment failure.

[0066] 2B is a flowchart S200b illustrating a method for performing a handover in the wireless communication system 1000 according to an embodiment disclosed herein. The operations (S202a through S208b) are performed by the processor 110.

[0067] At S202b, the method includes receiving from the source cell a handover configuration including an execution condition associated with at least one candidate target cell from a plurality of candidate target cells and a configuration associated with at least one candidate target cell from the plurality of candidate target cells. At S204b, the method includes evaluating an execution condition associated with the at least one candidate target cell. At S206b, the method includes evaluating whether the execution condition is satisfied for a target cell from the plurality of target cells. At S208b, the method includes performing the handover to the target cell based on the determination.

[0068] According to various embodiments of the present disclosure, the present invention provides a method for reporting accessibility measurements in a wireless communication system 1000, the method comprising: detecting an RRC connection establishment failure by a user equipment (UE); Logging, by the UE 100, selected parameters during the failed RRC connection establishment attempt, the logged parameters being accessibility measurements, and reporting, by the UE 100, a connection establishment failure report to the base station 200 in the wireless communication system 1000 based on the logging.

[0069] According to various embodiments of the present disclosure, the step of reporting the connection establishment failure report to the base station 200 in the wireless communication system 1000 based on the logging by the UE 100 includes: the UE 100 instructing the base station 200 to fail the RRC connection establishment; receiving, by the UE 100, from the base station 200, a request corresponding to the indicated RRC connection establishment failure report; and reporting the connection establishment failure report to the base station 200 in the wireless communication system 1000 based on the request.

[0070] According to various embodiments, the connection establishment failure report includes the accessibility measurements, the accessibility measurements including at least one of SSB information or uplink carrier information. According to various embodiments, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection resumption failure.

[0071] According to various embodiments, the uplink carrier information is one of an SUL carrier and a NUL carrier, and the SUL carrier or the NUL carrier is selected during cell access and subsequently logged by the UE 100 when encountering an RRC connection establishment failure. According to various embodiments, the SSB information includes at least one SSB index selected during cell access and subsequently logged by the UE 100 when experiencing an RRC connection establishment failure.

[0072] According to various embodiments, the logged value of the SSB index corresponding to receiving a request from the base station 200 is included in the connection establishment report.

[0073] According to various embodiments, the logged value of the uplink carrier in response to receiving a request from the base station 200 is included in the connection establishment failure report.

[0074] FIG. 3A is a sequence diagram illustrating a simplified model of a Release 15 handover, according to embodiments disclosed herein.

[0075] Upon receiving a handover command (or reconfiguration with synchronization) from the base station 200 during a mobility procedure currently available in the general LTE HO and NR Release 15 specifications, the UE 100 suspends operation with the source eNB / gNB, tunes to the target frequency (i.e., DL synchronization), and performs random access to the target cell. After successful completion of random access to the target cell, data exchange with the target cell resumes. There is a visible interruption while suspending operation with the source eNB / gNB and resuming operation with the target eNB / gNB. Furthermore, conventional handover models rely on measurement reports sent by the UE 100 to the base station 200, so that the base station 200 becomes aware of the weak source cell and one or more neighboring cell(s) that are superior to the source cell. RF and coverage planning for the base station 200 is performed in a way that neighboring cells have minimal overlap at the cell edges. The overlap is sufficient to facilitate handovers between these cells and does not create significant interference during transmissions from the cells. Provision is made to provide such a coverage footprint to reduce deployment costs. Consequently, the area in which the UE 100 identifies neighboring cells as being stronger than the current serving cell is called a handover region based on a trigger condition called a measurement event. The UE 100 triggers a measurement report and transmits it to the source eNB / gNB when the measurement event is triggered. The source node immediately prepares one or more target cell(s) indicated in the measurement report for handover. Once admission control for the UE 100 is completed at the potential target node, a handover confirmation is provided to the source cell. The source cell determines the target cell and provides a handover command to the UE 100 with the necessary configuration to access the target cell.

[0076] In this case, the time it takes for the base station 200 to prepare the target cell for handover may be longer than the time the UE 100 can maintain connection with the source cell. This leads to cases where the UE 100 cannot successfully receive a handover command from the source cell due to more degraded signal conditions. This is particularly common in high mobility scenarios or when the handover area is subject to high interference. As a result, in Release 16, both LTE and NR introduce a new handover model in which the target cell prepares the handover in advance, and the UE 100 can autonomously perform handover to the target cell based on the condition(s) provided by the base station 200. This handover model is called conditional handover. Conditional handover, which is partially under the control of the base station and deviates from the traditional handover model in which the base station is fully in control, requires some changes compared to traditional handover.

[0077] In one embodiment, the method can be used to initiate data forwarding in a conditional handover based on an indication from the UE 100. Once admission control is successful at the target node, the UE 100 transmits a handover confirmation to the source node. During this time, the user plane connection to the core network 500 (i.e., rerouting) remains at the source node and is not redirected to the target node. Rerouting from the source cell to the target cell can only occur once the handover to the target cell has been successfully completed. The source node immediately transmits SN transmission status to the target node to identify the sequence numbers (SNs) to apply to transmissions on the downlink (DL) and uplink (UL) and perform data forwarding. Data forwarding is the process of transmitting all packets pending at the source from the source node to the target node. This is accomplished by the source cell suspending communication with the UE 100 as soon as it receives a handover confirmation from the target cell and transmits a handover command (reconfiguration with synchronization) to the UE 100. Thereafter, if the handover is successful, that is, if the random access is successfully completed in the target cell, the forwarded packets are transmitted to the UE 100 by the target cell.

[0078] In Release 15 handover, based on a measurement report received from the UE 100, the source typically determines a target cell from one or more target cell(s) reported by the UE 100. Only one target cell may be prepared for handover by the source cell. Therefore, upon receiving a handover confirmation from the target cell, data forwarding and SN status transfer to the target may be performed immediately. However, in conditional handover, the UE 100 evaluates the handover conditions at a later stage and cannot know in advance which target cell satisfies the handover conditions. Therefore, multiple cells may be prepared for potential handover of the UE 100. Because the source cell cannot accurately predict in advance the target cell to which the UE 100 should perform handover, multiple target cells are prepared. Performing SN status transfer and data forwarding for all prepared cells causes overload on the X2 interface of the base station 200, resulting in a huge waste of resources. Thus, traditional timing and triggering for data forwarding from the source node to the target node as soon as the target cell is prepared for handover cannot be employed in conditional handover.

[0079] Then, new trigger conditions for data forwarding need to be defined in CHO (Conditional Handover). In CHO, the target cell configuration is transmitted to the UE 100 in advance, and the actual handover execution is performed after the handover condition, i.e., the measurement event, is triggered. The execution of handover to the target cell is controlled by the conditions set in the UE 100 together with the CHO configuration. In the above method, when the conditions for performing CHO are met, the UE 100 sends an indication to the source cell. In theory, measurement objects including serving cell and target cell evaluation (e.g., Event A3, Event A5) are used to assist the base station 200 in initiating handover of the UE 100 to a neighboring cell. This serves as a mechanism to inform the base station 200 that the UE 100 is leaving its own coverage area and approaching the coverage area of ​​a neighboring cell. To facilitate conditional handover, the target cell has already prepared for the handover, so there is no need to send a measurement report to the source cell. However, the source cell must be informed of the target cell to which the UE 100 will perform handover. This allows the source cell to trigger an SN transmission state and forward data only to that target cell. When the UE 100 successfully completes random access to the target cell, the forwarded data is already available in the target cell. Therefore, this mechanism forwards data to only one target cell, preventing resource waste on the X2 interface, and reducing interruption time during handover because the target cell already has data to transmit to the UE 100 when the target cell is successfully accessed. In one embodiment, the UE 100 reports a measurement report to the source cell to trigger execution of CHO for the target cell. In one embodiment, the UE 100 indicates a target cell identifier for which CHO execution is triggered. The target cell identifier is one of a physical cell identifier (PCI) and DL-ARFCN (i.e., DL frequency) for the target cell or a global cell identifier and DL-Absolute Radio Frequency Channel Number (ARFCN) of the target cell.

[0080] This information for the target cell may be indicated in the measurement report together with the measurement results or in another new RRC message.

[0081] In traditional base station 200-controlled handover, most handover failures occur because the UE 100 fails to receive the handover command in time. The delay between transmitting a measurement report containing detailed information about neighboring cells to the base station 200 and receiving a handover command containing the target cell configuration from the base station 200 is caused by the time it takes to prepare the target cell for handover. Until the target cell is successfully prepared for handover, the source cell signal conditions may further deteriorate, making it impossible for the UE 100 to successfully receive downlink transmissions. However, the probability of receiving a measurement report from the UE 100 indicating measurement results for one or more neighboring cell(s) is lower than the probability of receiving a handover command from the source until the target cell is prepared. The measurement conditions configured to trigger CHO execution are expected to have a similar configuration to the measurement report used in traditional handover to indicate the source cell for the UE 100 moving to the neighboring cell. Therefore, the probability of successfully receiving the measurement report at the source node is high. Receipt of a measurement report from the source node serves as a trigger to start data forwarding to the target cell indicated in the measurement report.

[0082] 3A, at S302a, UE 100 transmits a measurement report to SgNB 300. At S304a, based on the measurement report, SgNB 300 transmits a handover request to TgNB 400. At S306a, based on the handover request, TgNB 400 performs an admission control procedure. At S308a, based on the admission control procedure, TgNB 400 transmits a handover request confirmation message to SgNB 300. After receiving the handover request confirmation message from TgNB 400, at S310a, SgNB 300 transmits an HO Command / Reconfig with sync message to UE 100. At S312a, based on the HO Command / Reconfig with sync message, UE 100 detaches from the source cell and tunes to the target cell. At S314a, the SgNB 300 transmits an SN status transfer message to the TgNB 400, and at S316a, the SgNB 300 transmits data forwarding to the TgNB 400. At S318a, RAN handover completion occurs between the UE 100 and the TgNB 400. At S320a, the TgNB 400 transmits a route change request to the CN 500. At S322a, the CN 500 transmits a route change request confirmation message to the TgNB 400. At S324a, the TgNB 400 transmits a UE context release to the SgNB 300.

[0083] 3B illustrates a sequence diagram in which a source cell initiates an SN status transmission and data forwarding transmission to a target cell indicated in a measurement report that triggers CHO execution at the UE 100, according to an embodiment disclosed herein. In another embodiment, the source cell initiates an SN status transmission and data forwarding transmission to a target cell indicated in a measurement report that triggers CHO execution at the UE 100.

[0084] When the conditions for performing CHO are met, the UE 100 transmits a measurement report to the source indicating the target cell identifier. Since the measurement report is transmitted using RLC AM, if the measurement report is successfully received, an RLC ACK is sent from the source cell. When the UE 100 receives the RLC ACK, it performs handover-related operations (i.e., HO execution) and tunes to the target cell frequency (i.e., DL synchronization). This may include suspending transmission and reception operations of the source cell depending on the handover type for handovers that do not support simultaneous connection with the source cell and the target cell. In the case of handovers that allow continued activity with the source cell even after handover execution is triggered (i.e., make-before-break HO), the UE 100 does not suspend transmission / reception operations with respect to the source cell while tuning to the target cell frequency. To ensure that data forwarding to the target cell is initiated by the source cell, the UE 100 may wait until it receives a Layer 2 acknowledgment (i.e., RLC ACK) from the source cell for the measurement report it transmitted. Therefore, in another embodiment, the UE 100 may cease operation towards the source cell or wait for an L2 ACK (ie, an RLC ACK) for the transmitted measurement report before initiating an HO execution towards the target cell.

[0085] It is possible that the signal conditions may deteriorate and the UE 100 may not be able to successfully decode the PDSCH (Physical Downlink Shared Channel) until the L2 ACK (i.e., RLC ACK) is received by the UE 100. To handle such cases, a timer (predefined or configurable) can be used. The timer starts when a measurement report that triggers CHO execution is sent to the base station 200. The timer is stopped when the L2 ACK for the measurement report is received. When the timer expires, the UE 100 stops source cell monitoring for the L2 ACK and attempts handover to the target cell. That is, HO execution is triggered in the target cell.

[0086] If the signal condition can deteriorate very quickly (e.g., deep fading in a higher frequency range), the measurement report transmitted to the source cell may not be successfully received. However, the UE 100 may still proceed with CHO to the target cell even if the CHO condition is met and the timer for receiving the RLC ACK has expired. In this case, if the UE 100 successfully completes random access at the target cell and the target cell determines that a data forwarding path has not been established / no SN status transmission has been received from the source cell, the target cell may request SN status transmission and data forwarding from the source cell. In one embodiment, the target cell requests SN status transmission and data forwarding from the source cell if it has not been notified by the source cell until the UE 100 successfully completes random access to the target cell.

[0087] At S302b, the UE 100 transmits a measurement report to the SgNB 300. At S304b, based on the measurement report, the SgNB 300 transmits a handover request to the first TgNB 400a. Based on the handover request, at S306b, the first TgNB 400a performs an admission control procedure. Based on the admission control procedure, at S308b, the first TgNB 400a transmits a handover request confirmation message to the SgNB 300.

[0088] After receiving the handover request confirmation message from the first TgNB 400a, the SgNB 300 transmits a handover request to the second TgNB 400b at S310b. Based on the handover request, the second TgNB 400b performs an admission control procedure at S312b. Based on the admission control procedure, the second TgNB 400b transmits a handover request confirmation message to the SgNB 300 at S314b. At S316b, the SgNB 300 transmits the CHO configuration to the UE 100. At S318b, the UE 100 performs a CHO candidate evaluation, and at S320b, the UE 100 triggers a CHO event to the first TgNB 400a. At S322b, the UE 100 identifies an MR that instructs the first TgNB 400a to perform CHO. At 324b, the UE 100 detaches from the source cell and tunes to the target cell. At S326b, the SgNB 300 transmits an SN status transfer message to the first TgNB 400a, and at 328b, the SgNB 300 transmits data forwarding to the first TgNB 400a. At 330b, RAN handover completion occurs between the UE 100 and the first TgNB 400a. At S332b, the first TgNB 400a transmits a route change request to the CN 500. At S334b, the CN 500 transmits a route change request confirmation message to the TgNB 400. At S336b, the first TgNB 400a transmits a UE context release to the SgNB 300.

[0089] FIG. 4A illustrates a sequence diagram in which the source cell ignores a handover ACK received for normal handover preparation if the source cell has already received a measurement report indicating CHO execution from UE 100, according to an embodiment disclosed herein.

[0090] In one embodiment, the above method can be used to avoid duplicate handover commands to the UE 100. In CHO, the UE 100 is pre-configured with potential candidate cells for handover. However, the UE mobility may be to other neighboring cells that are not part of the CHO candidates. In such a case, the base station 200 configures a regular handover based on measurement reports from the UE 100. The handover command has a higher priority than the received CHO configuration and therefore takes precedence if a CHO condition is not triggered.

[0091] In another scenario, UE 100 may transmit a measurement report for a neighboring cell (e.g., the second TgNB in ​​FIG. 4A) that is not a CHO candidate. The neighboring cell (the second TgNB) is prepared for handover, and a handover ACK is transmitted to the source cell. During the HO preparation phase for the second TgNB, UE 100 satisfies the CHO execution conditions for the candidate cell in the CHO configuration (the first TgNB in ​​FIG. 4A) and sends the related measurement report to the source cell. At this point, the source cell has two target cells prepared for handover. One is the target cell (the second TgNB) based on general handover preparation, and the other is the target cell (the first TgNB) based on CHO preparation. However, when the source cell receives the measurement report for the first TgNB, it has not yet received the HO request ACK from the second TgNB. The UE 100 can only perform handover to one of them, and the source cell must perform SN status transmission and data forwarding to the same target cell (i.e., the first TgNB) to which the UE 100 is attempting handover. In one embodiment, the source cell ignores the handover ACK received for normal handover preparation if it has already received a measurement report indicating CHO execution from the UE, as shown in Figure 4A.

[0092] At S402a, the UE 100 transmits a measurement report to the SgNB 300. At S404a, based on the measurement report, the SgNB 300 transmits a handover request for CHO to the first TgNB 400a. Based on the handover request, at S406a, the first TgNB 400a performs an admission control procedure. Based on the admission control procedure, at S408a, the first TgNB 400a transmits a handover request confirmation message to the SgNB 300.

[0093] At S410a, the UE 100 transmits an MR indicating normal HO to the second TgNB 400b. At 412a, the SgNB 300 transmits a handover request for normal HO to the second TgNB 400b. At 414a, the UE 100 transmits an MR instructing the first TgNB 400a to perform CHO. Based on the handover request, at 416b, the second TgNB 400b performs an admission control procedure. Based on the admission control procedure, at S418b, the second TgNB 400b transmits a handover request confirmation message to the SgNB 300. At S420a, the SgNB 300 performs the CHO execution instruction received from the second TgNB before the ACK, ignores the normal HO ACK, and forwards data to the CHO candidate.

[0094] At S422a, the UE 100 detaches from the source cell and tunes to the target cell. At S424a, the SgNB 300 transmits an SN status transfer message to the first TgNB 400a, and at S426a, the SgNB 300 transmits data forwarding to the first TgNB 400a. At S428a, RAN handover completion occurs between the UE 100 and the first TgNB 400a. At S430a, the first TgNB 400a transmits a path change request to the CN 500. At S432a, the CN 500 transmits a path change request confirmation message to the first TgNB 400a. At S434a, the first TgNB 400a transmits a UE context release to the SgNB 300.

[0095] FIG. 4B shows a sequence diagram in which UE 100 according to an embodiment of the present disclosure cancels CHO execution and performs a normal HO command if it has received a normal HO command from the source cell before receiving an L2 ACK or HARQ ACK for CHO measurement report transmission.

[0096] Similarly, it is possible that UE 100 transmits a CHO triggering measurement report to base station 200, at which time UE 100 receives an HO command for normal handover. In another scenario, UE 100 may transmit a measurement report for a neighboring cell (e.g., the second TgNB in ​​FIG. 4B) that is not a CHO candidate. The neighboring cell (the second TgNB) is prepared for handover, and a handover ACK is transmitted to the source cell. Once the HO preparation phase for the second TgNB is completed, UE 100 can satisfy the conditions for CHO execution for the candidate cell (the first TgNB in ​​FIG. 4B) in the CHO configuration, and UE 100 transmits the related measurement report to the source cell.

[0097] At this point, the source cell has two target cells prepared for handover. One is a target cell (second TgNB) based on normal handover preparation, and the other is a target cell (first TgNB) based on CHO preparation. However, the source cell received an HO request ACK from the second TgNB before receiving a measurement report for the first TgNB. UE 100 can only perform handover to one of them, and the source cell must transmit SN status and forward data to the same target cell (i.e., second TgNB) to which the UE is attempting handover.

[0098] In one embodiment, as shown in FIG. 4B, if the UE 100 receives a normal HO command from the source cell before receiving an L2 ACK (i.e., RLC ACK) or HARQ ACK for the CHO measurement report transmission, the UE 100 cancels the CHO execution and performs a normal HO execution. As a result, the details of the handover execution are received by the source cell. That is, in the case of a measurement report for CHO or an HO preparation AKC for normal HO, the source node processes the first message received and ignores messages that arrive later. As a result, if the UE 100 receives an HO command after the transmission of the CHO MR (before the L2 ACK of the CHO MR), the UE 100 performs a normal handover. This is because the normal HO command arrived at the source cell earlier than the CHO triggering measurement report, and the UE 100 must know that the source cell provided a normal HO command. Therefore, data forwarding is initiated by the source cell to the target cell from which the handover indication was first received by the source cell.

[0099] In one embodiment, the above method can be used to configure the CHO execution condition. The UE 100 reports event A1 only when the serving cell signal condition is good. That is, A1 is reported when the serving cell signal condition is better than a network-configured threshold. When the base station 200 (i.e., the source gNB) receives event A1 from the UE 100, it can reconfigure / add / remove other measurement IDs, for example, configure A2 to identify when the UE's signal condition begins to drop below a configured value. Therefore, the A1 event is not suitable for triggering a handover to a neighboring cell.

[0100] The UE 100 reports event A2 only when the serving cell signal condition is poor and does not inform the base station 200 about potential neighboring cells with good signal conditions. That is, it reports A2 when the serving cell signal condition is weaker than a network-configured threshold. Upon receiving event A2, the source gNB can reconfigure / add / remove measurement IDs. For example, the source gNB can configure A1 to identify when the UE signal condition improves, or configure A3 / A5 to identify whether a neighboring cell has suitable signal conditions to serve the UE 100. Alternatively, the source gNB can perform blind preparation of the target cell and provide a handover command to the UE. However, this does not guarantee a good handover success rate because the UE proximity to such neighboring cells is unknown to the source gNB. Blind handover based on event A2 may be useful only when there are two collocated cells, one belonging to a low frequency band and the other to a high frequency band, and the coverage of these cells overlaps and overlays. In such a case, a UE 100 connected to a higher frequency cell may be handed over to a cell operating at a lower frequency (the lower frequency cell has a larger coverage footprint) without knowledge of the target cell's signal conditions. This is a very restrictive scenario and may not be widely applied in practical deployments. Event A2 can be used to trigger a handover, but event A2 alone cannot perform a reliable handover. The UE 100 reports event A4 only if the neighboring cell signal condition is good; i.e., A4 is reported if the neighboring cell signal condition is better than a network-configured threshold.

[0101] Upon receiving event A4, the source gNB can reconfigure / add / remove other measurement IDs. For example, the source gNB configures events A3 / A5 to understand neighboring cell signal conditions compared to the serving cell signal conditions. Alternatively, the source gNB can provide a handover command to the neighboring cell reported in event A4 to the UE 100. A handover to the target cell may be successful because the target cell has good signal conditions, but there is no guarantee that the target cell is better than the source cell. The signal conditions and QoS provided by the target cell may be worse than those of the source cell. Event A4 can be used to trigger a handover, but event A4 alone cannot ensure a reliable handover. To provide a reliable handover to a neighboring cell, the source gNB should recognize that the neighboring cell can provide better service to the UE 100 than the current serving cell. Events A3 and A5 provide both the serving cell and neighboring cell signal conditions to the base station 200. A3 is reported when the neighboring cell signal conditions are better than the serving cell by at least the configured offset. A5 is reported when the serving cell signal condition is weaker than a configured threshold and the neighboring cell signal condition is better than other network-configured thresholds. Therefore, if a neighboring cell can provide better service, the source gNB is in a position to understand this. However, in some cases, more than one event is required to reliably trigger a handover.

[0102] In a traditional handover, the base station 200 configures several measurement events for the UE 100. The base station 200 does not need to prepare a target cell based on each associated measurement report from the UE 100. The base station 200 can decide whether to provide a handover command to the UE 100 based on multiple measurement reports from the UE 100 or the order of the measurement reports. It is also possible for the source node to be aware of the load conditions of neighboring / target nodes. Even if the measurement results indicate that a neighboring cell has better signal conditions, the target cell can only be prepared for handover if the load conditions are within an acceptable level. As a result, sometimes handover is not offered to the best cell reported to the base station 200 in the measurement reports.

[0103] However, in the case of conditional handover, the conditions for performing handover are set in the UE 100, and the UE 100 autonomously performs handover based on the conditions. Therefore, CHO is partially under the control of the base station 200. Unlike that of the base station 200 in conventional handover, the UE 100 does not have the intelligence when performing CHO to the target, so the base station 200 carefully decides to handover the UE 100 to a neighboring target based on the intelligence of the base station 200 (e.g., the load status of the target).

[0104] In conventional handover, the serving cell provides a handover command to the UE 100 when neighboring signal conditions are good and the load of the neighboring cell is suitable for serving additional UEs 100. However, in conditional handover, the conditions for triggering CHO execution are provided much earlier. During this time, the target cell load may be low enough to allow more UEs 100 to access the cell. However, the actual CHO execution occurs later, and the load of the target cell may change until that time. However, when CHO is triggered and the UE 100 performs handover to the target cell, the load at the target increases. In such a scenario, the service provided by the target cell may be worse / weaker than the service provided by the source cell.

[0105] To overcome this, it is necessary to inject some intelligence into the UE 100 in its decision-making regarding CHO execution. This can be done by introducing a requirement for the UE 100 to satisfy the multiple reporting configuration. For example, the UE 100 can be configured with event A3 with the trigger amount set to RSRP. To overcome this, it is necessary to inject some intelligence into the UE 100 in its decision-making regarding CHO execution. This can be done by introducing a requirement for the UE 100 to satisfy the multiple reporting configuration. For example, the UE 100 can be configured with event A3 with the trigger amount set to RSRP. When A3 is successfully satisfied by the UE 100, it recognizes that the signal strength of the neighboring cell is superior to the serving cell / is suitable to serve the UE 100. However, it is unaware of the load and quality of the neighboring cell. To enable the UE 100 to intelligently evaluate the target cell, the base station 200 can configure event A4 with the trigger amount set to RSRQ. The RSRQ measurement provides an indication of the load on the target cell. At the same time, A3 based on RSRP indicates that the target cell signal condition is good, and A4 based on RSRQ indicates that the target cell load is acceptable. Therefore, handover is not more reliable than when CHO is performed based on a single condition / trigger.

[0106] In another example, in a normal handover, the source cell has several options for deciding on a handover (based on different reporting configurations and different trigger quantities). a. UE assisted handover based on A3 / A5 where strong neighbors are indicated by the MR; or b. UE assisted handover based on A4 where the neighbor is visible in the MR, but the source cell may still be in sustainable signal conditions (or may not meet the entry conditions for A3 / A5). c. Blind HO based on A2 where no neighbors are visible in MR. d. UE Assisted Handover Based on Multiple or Series of Measurement Reports from UE 100 (for Different Reporting Configurations)

[0107] To manage and assist the HO decision, the source cell can configure multiple measurement reporting configurations for the same MO, ultimately determining the HO decision based on the MR received from the UE 100. The MR does not always need to be A3 / A5, but can also be A2 / A4. In the above example, Beam Failure Recovery (BFR) was shown as one of the possible outcomes of a sudden cell degradation (in FR2). Typical values ​​for the Time-to-Trigger (TTT) configured in LTE deployments vary between 256 ms and 1024 ms. When BFR is triggered by a sudden drop in beam quality in a mobility scenario, considering that the PRACH resource is configured every 10 ms (including the RAR monitoring time), a new preamble is transmitted every 10 ms if no RAR is received. An RA failure may occur before the TTT is completed based on preambleTransMax, which may lead to RLF even in the case of CHO configuration.

[0108] The above examples are for illustrative purposes only and are not limiting. The combinations of reporting configurations for CHO evaluation can be any combination or same / different reporting configurations using the same / different trigger quantities, the same / different RS types, etc. In one embodiment, base station 200 can configure multiple CHO conditions for a UE.

[0109] Referring to FIG. 4B, at S402b, the UE 100 transmits a measurement report to the SgNB 300. At S404b, based on the measurement report, the SgNB 300 transmits a handover request for CHO to the first TgNB 400a. At S406b, based on the handover request, the first TgNB 400a performs an admission control procedure. At S408b, based on the admission control procedure, the first TgNB 400a transmits a handover request confirmation message to the SgNB 300. At S410b, the SgNB 300 conveys a CHO configuration to the UE 100, and at S412b, the UE 100 performs CHO candidate evaluation. At S414b, the UE 100 transmits an MR instructing normal HO to the second TgNB 400b via the SgNB 300.

[0110] At S416b, the SgNB 300 transmits a handover request for normal HO to the second TgNB 400b. At S418b, the UE 100 transmits an MR instructing the first TgNB 400a to perform CHO via the SgNB 300. Based on the handover request, at S420b, the second TgNB 400b performs an admission control procedure. Based on the admission control procedure, at S422b, the second TgNB 400b transmits a handover request confirmation message to the SgNB 300.

[0111] At S424b, the SgNB 300 transmits a normal HO command to the UE 100, and at S426b, the SgNB 300 first receives a normal HO execution instruction and ignores the CHO instruction from the UE 100. At 430b, the UE 100 detaches from the source cell and tunes to the target cell. At S428b, the SgNB 300 transmits an SN status transfer message to the first TgNB 400a, and at 432b, the SgNB 300 forwards data to the first TgNB 400a. At S434b, RAN handover completion occurs between the UE 100 and the first TgNB 400a. At S436b, the first TgNB 400a transmits a route change request to the CN 500. At S438b, the CN 500 transmits a route change request confirmation message to the TgNB 400. At S440b, the first TgNB 400a transmits a UE context release to the SgNB 300.

[0112] FIG. 5 illustrates that, according to an embodiment disclosed herein, base station 200 can configure UE 100 with a one-bit indication (multipleConditionTrigger) along with the CHO condition configuration to provide UE 100 with more freedom in decision-making. To provide UE 100 with smarter control decisions, base station 200 can configure UE 100 with a one-bit indication (multipleConditionTrigger in FIG. 5) along with the CHO condition configuration. If an indication is configured in the CHO configuration, it means that there are multiple reporting configurations, and CHO is performed only if all reporting configurations are satisfied. If the field is absent, it means that only one reporting configuration is provided, or multiple reporting conditions are provided, but CHO can be performed if any one of the configured reporting configurations is satisfied. FIG. 5 also illustrates that the network configures a UE with multiple CHO conditions so that the UE can evaluate candidate target cells for CHO.

[0113] FIG. 6 is a sequence diagram illustrating a case where, according to the disclosed embodiment, even after providing a handover command, the source cell continues to serve the UE until a timer corresponding to the T304 timer configured in the UE 100 for handover expires or a UE CONTEXT RELEASE message is received from the target cell where the route change has been successfully completed.

[0114] Referring to Figure 6, at S602, UE 100 transmits a measurement report to SgNB 300. At S604, based on the measurement report, SgNB 300 transmits a handover request to TgNB 400. Based on the handover request, TgNB 400 performs an admission control procedure at S606. Based on the admission control procedure, TgNB 400 transmits a handover request confirmation message to SgNB 300 at S608. After receiving the handover request confirmation message from TgNB 400, SgNB 300 transmits an HO Command / Reconfig with sync message to UE 100 at S610. Based on the HO Command / Reconfig with sync message, UE 100 continues to tune to the target cell at S312a. At S614, SgNB 300 continues the data path to UE 100 and starts timer T304.

[0115] At S616, the SgNB 300 transmits an SN status transfer message to the TgNB 400, and at S618, the SgNB 300 forwards the data to the TgNB 400. At S620, RAN handover completion occurs between the UE 100 and the TgNB 400. At S622, the TgNB 400 transmits a route change request to the CN 500. At S624, the CN 500 transmits a route change request confirmation message to the TgNB 400. At S626, the TgNB 400 transmits a UE context release to the SgNB 300.

[0116] In one embodiment, the above method can be used to identify conditions for ceasing transmission on the source cell during an eMBB-based handover. In Release 14, make before break handover LTE, the UE 100 continues to receive on the source cell after receiving a handover command from the base station 200. However, the base station 200 does not know how long the UE 100 will continue monitoring the DL channel from the source cell. This is because the UE 100 is assumed to have a single receive chain (single Rx) and cannot receive from both the source and target simultaneously. Therefore, the source cannot accurately estimate how long it will take for the UE 100 to tune to the target cell and perform random access. As a result, the time it takes for the UE 100 to receive data from the source cell and for the source to continue DL transmission is left to the implementation.

[0117] In Release 16, both LTE and NR are working to improve the MBB procedure, which expects the UE 100 to have two receive chains. Therefore, the UE 100 can simultaneously receive from both the source cell and the target cell. As a result, the source can continue transmitting from the source cell, and the UE 100 can receive from the source cell until it successfully accesses the target cell. Therefore, it is possible to accurately identify the point at which the source cell can suspend transmission to the UE 100. One method is for the UE 100 to indicate to the source cell via MAC CE or other uplink signaling methods when the UE 100 wants to release the source cell connection and operate only on the target cell. However, this method is unreliable because the signal conditions for the source cell are expected to be very poor and the probability of successfully sending an indication to the source cell is very low.

[0118] Another way to indicate the release of the source cell is for the target cell to indicate to the source cell that the UE 100 has successfully accessed the target cell (completed handover to the target cell). However, this method introduces additional overhead of introducing new signaling from the target cell to the source cell, requesting the source to suspend activity from the source cell, and may cause delays in indicating to the source cell.

[0119] In another embodiment, the method may be used such that the source cell continues to operate after providing a handover command to the UE 100 until a timer expires or an event occurs. In one embodiment, the source cell continues to serve the UE after providing the handover command until a timer corresponding to a T304 timer configured in the UE 100 for handover expires, or until a UE CONTEXT RELEASE message is received from the target cell for which the route change has been successfully completed. This is illustrated in the case of FIG. 6. In another embodiment, the source cell may continue to serve the UE 100 until a portion of the T304 timer expires.

[0120] In one embodiment, the above method can be used to indicate the beam ID in the accessibility measurement in a logged Minimization of Drive Test (MDT). In LTE, the accessibility measurement includes the number of preambles transmitted during a failed connection establishment attempt and location information, among other parameters. In a beamformed system such as NR, the UE 100 can be within the coverage of one or more beams. The UE 100 selects a beam for random access based on a threshold configured in the system information. Thus, different UEs at the same location receiving signals from the same set of beams can attempt connection establishment based on PRACH resources associated with different beams. As a result, to accurately evaluate the resources used when the UE 100 experiences a connection establishment failure, the UE 100 needs to indicate the SSB selected to access the cell. In one embodiment, the SSB ID on which the UE 100 experiences a connection establishment failure is indicated to the base station 200 in the accessibility measurement as follows:

[0121] ConnEstFailReportNR ::= SEQUENCE { failedCellId CellIdNR, locationInfo LocationInfo-r10 OPTIONAL, measResultFailedCell SEQUENCE { rsrpResult RSRP-Range, rsrqResult RSRQ-Range, sinrResult SINR-Range OPTIONAL }, measResultNeighCells SEQUENCE { measResultListNR MeasResultListNR OPTIONAL, measResultListEUTRA MeasResultList2EUTRA OPTIONAL, } OPTIONAL, numberOfPreamblesSent NumberOfPreamblesSent contentionDetected BOOLEAN, maxTxPowerReached BOOLEAN, timeSinceFailure TimeSinceFailure, measResultListNR MeasResultListNR OPTIONAL, measResultFailedCell RSRQ-Range OPTIONAL, failedCellRSRQ-Type RSRQ-Type-r12 OPTIONAL, SSBid SSB-Index, }

[0122] In LTE, accessibility measurements include the number of preambles transmitted during a failed connection establishment attempt and location information, among other parameters, which can be reused for NR resumption failure reporting. In a beamforming system such as NR, the UE 100 can be within the coverage of one or more beams. The UE 100 selects a beam for random access based on a threshold configured in the system information. Thus, different UEs at the same location receiving signals from the same set of beams can attempt connection resumption based on PRACH resources associated with different beams. As a result, to accurately evaluate the resources used when the UE 100 experiences a connection resumption failure, the UE 100 needs to indicate the SSB selected to access the cell. In another embodiment, the SSB ID on which the UE 100 experiences a connection resumption failure is indicated to the base station 200 in the accessibility measurement, as described below.

[0123] ConnResumeFailReportNR ::= SEQUENCE { failedCellId CellIdNR, locationInfo LocationInfo-r10 OPTIONAL, measResultFailedCell SEQUENCE { rsrpResult RSRP-Range, rsrqResult RSRQ-Range, sinrResult SINR-Range OPTIONAL }, measResultNeighCells SEQUENCE { measResultListNR MeasResultListNR OPTIONAL, measResultListEUTRA MeasResultList2EUTRA OPTIONAL, } OPTIONAL, numberOfPreamblesSent NumberOfPreamblesSent contentionDetected BOOLEAN, maxTxPowerReached BOOLEAN, timeSinceFailure TimeSinceFailure, measResultListNR MeasResultListNR OPTIONAL, measResultFailedCell RSRQ-Range OPTIONAL, failedCellRSRQ-Type RSRQ-Type-r12 OPTIONAL, SSBid SSB-Index, }

[0124] In another embodiment, the above method can be used to indicate the UL carrier ID in the accessibility measurement in the logged MDT. Unlike LTE, NR can have two uplink carriers (normal UL and SUL) configured to access a cell. Therefore, random access for connection establishment can be performed on the normal UL or SUL PRACH resource. The carrier on which the RACH is performed varies depending on the DL path loss criteria. As a result, depending on RF performance and channel variations, all UEs in the same location may not perform the RACH on the same UL carrier. Therefore, in order to accurately evaluate the resources used when the UE 100 experiences a connection establishment failure, the UE 100 needs to indicate the UL carrier selected to access the cell. In one embodiment, the uplink carrier on which the UE 100 experiences a connection establishment failure is indicated to the base station 200 in the accessibility measurement as follows:

[0125] ConnEstFailReportNR ::= SEQUENCE { failedCellId CellIdNR, locationInfo LocationInfo-r10 OPTIONAL, measResultFailedCell SEQUENCE { rsrpResult RSRP-Range, rsrqResult RSRQ-Range, sinrResult SINR-Range OPTIONAL }, measResultNeighCells SEQUENCE { measResultListNR MeasResultListNR OPTIONAL, measResultListEUTRA MeasResultList2EUTRA OPTIONAL, } OPTIONAL, numberOfPreamblesSent NumberOfPreamblesSent contentionDetected BOOLEAN, maxTxPowerReached BOOLEAN, timeSinceFailure TimeSinceFailure, measResultListNR MeasResultListNR OPTIONAL, measResultFailedCell RSRQ-Range OPTIONAL, failedCellRSRQ-Type RSRQ-Type-r12 OPTIONAL, ulCarrierIndex ULCarrierIndex, } ULCarrierIndex ::= ENUMERATED {NormalUL, SUL}

[0126] Unlike LTE, NR can have two uplink carriers (normal UL and SUL) configured to access a cell. Therefore, random access for connection resumption can be performed on either the normal UL or SUL PRACH resource. The carrier on which RACH is performed varies depending on the DL path loss criteria. As a result, depending on RF performance and channel variations, all UEs in the same location may not perform RACH on the same UL carrier. Therefore, in order to accurately evaluate the resources used when the UE 100 experiences a connection resumption failure, the UE 100 needs to indicate the UL carrier selected to access the cell. In another embodiment, the uplink carrier on which the UE 100 experiences a connection resumption failure is indicated to the base station 200 in the accessibility measurement.

[0127] ConnResumeFailReportNR ::= SEQUENCE { failedCellId CellIdNR, locationInfo LocationInfo-r10 OPTIONAL, measResultFailedCell SEQUENCE { rsrpResult RSRP-Range, rsrqResult RSRQ-Range, sinrResult SINR-Range OPTIONAL }, measResultNeighCells SEQUENCE { measResultListNR MeasResultListNR OPTIONAL, measResultListEUTRA MeasResultList2EUTRA OPTIONAL, } OPTIONAL, numberOfPreamblesSent NumberOfPreamblesSent contentionDetected BOOLEAN, maxTxPowerReached BOOLEAN, timeSinceFailure TimeSinceFailure, measResultListNR MeasResultListNR OPTIONAL, measResultFailedCell RSRQ-Range OPTIONAL, failedCellRSRQ-Type RSRQ-Type-r12 OPTIONAL, ulCarrierIndex ULCarrierIndex, } ULCarrierIndex ::= ENUMERATED {NormalUL, SUL}

[0128] In another embodiment, the above method can be used to indicate UE capability to support different enhanced mobility procedures for handover. There are many ways to reduce mobility interruption time based on make-before-break type handover methods. UE 100 can support one or more types of MBB / enhanced MBB-based handover depending on the scenario and UE capability. Therefore, UE 100 needs to indicate to base station 200 its capability and supported methods for performing MBB-based handover. This should be displayed as part of UE capability. In one embodiment, UE 100 has capability to support one or both of single-stack based enhanced MBB HO and dual-stack based enhanced MBB HO.

[0129] In a single-stack based mobile broadband (MBB) solution, only one protocol stack is fully active at a given time, and the other protocol stacks are not fully activated. For example, upon receiving a single-stack based eMBB handover command from base station 200, UE 100 maintains the full stack on the source cell and continues to operate on the source until a specific time. During this time, the target stack may be partially or not activated at all, depending on UE capabilities. Upon successful access to the target cell, UE 100 releases the protocol stack associated with the source cell and functions using only the protocol stack associated with the target.

[0130] In a dual-stack based MBB solution, the UE 100 can simultaneously activate a protocol stack associated with a source cell and a protocol stack associated with a target cell. The two stacks are simultaneously activated for a short period of time to facilitate resource / packet transfer from the source cell to the target cell. Examples of UE capabilities indicating support for mobility types are provided below.

[0131] MeasAndMobParameters ::= SEQUENCE { measAndMobParametersCommon MeasAndMobParametersCommon OPTIONAL, measAndMobParametersXDD-Diff MeasAndMobParametersXDD-Diff OPTIONAL, measAndMobParametersFRX-Diff MeasAndMobParametersFRX-Diff OPTIONAL } MeasAndMobParametersCommon ::= SEQUENCE { supportedGapPattern BIT STRING (SIZE (22)) OPTIONAL, ssb-RLM ENUMERATED {supported} OPTIONAL, ssb-AndCSI-RS-RLM ENUMERATED {supported} OPTIONAL, ..., [[ eventB-MeasAndReport ENUMERATED {supported} OPTIONAL, handoverFDD-TDD ENUMERATED {supported} OPTIONAL, eutra-CGI-Reporting ENUMERATED {supported} OPTIONAL, nr-CGI-Reporting ENUMERATED {supported} OPTIONAL ]], [[ independentGapConfig ENUMERATED {supported} OPTIONAL, periodicEUTRA-MeasAndReport ENUMERATED {supported} OPTIONAL, handoverFR1-FR2 ENUMERATED {supported} OPTIONAL, maxNumberCSI-RS-RRM-RS-SINR ENUMERATED {n4, n8, n16, n32, n64, n96} OPTIONAL ]], [[ nr-CGI-Reporting-ENDC ENUMERATED {supported} OPTIONAL ]], [[ enhancedMBBSupport-R16 ENUMERATED {singleStack, dualStack, both} OPTIONAL ]] }

[0132] In another embodiment, the above method can be used to indicate that an MBB type UE should apply a configured handover. The UE 100 can support one or more MBB-based handovers, i.e., single-stack and dual-stack based MBB HO. When the UE 100 is provided with a reconfiguration with synchronization, the type of handover to be performed needs to be indicated. Thus, the base station 200 provides the MBB type to be used for the current handover based on several factors, which may include UE capabilities, interruption requirements for ongoing services, deployment scenario, etc. In one embodiment, the serving PCell instructs the UE 100 on the MBB type to be used for the current handover.

[0133] The indication can be provided as part of the reconfiguration with synchronization in several ways. One way is to always provide the mobility type in the reconfig sync / handover command. The indication explicitly informs the UE 100 of the MBB type that should be applied as follows:

[0134] ReconfigurationWithSync ::= SEQUENCE { spCellConfigCommon ServingCellConfigCommon OPTIONAL, -- Need M newUE-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 ]], [[ enhancedMbbType-r16 ENUMERATED {singleStack, dualStack} OPTIONAL Need N ]] }

[0135] In other embodiments, the method may optionally include an indication that if handover is included, the MBB HO should be dual-stack based, and if no indication is included (or vice versa), the MBB HO should be single-stack based.

[0136] ReconfigurationWithSync ::= SEQUENCE { spCellConfigCommon ServingCellConfigCommon OPTIONAL, -- Need M newUE-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 ]], [[ enhancedMbbType-r16 ENUMERATED {dualStack} OPTIONAL Need N ]] }

[0137] Embodiments herein are applicable to LTE, NR, and other cellular communication technologies, and any reference herein to any one of these technologies is for illustrative purposes only and is not intended to be limiting.

[0138] The embodiments disclosed herein may be implemented using at least one software program running on at least one hardware device and performing network management functions to control the elements.

[0139] The various operations, acts, blocks, steps, etc. of the flowcharts (S200a and S200b) may be performed in the order presented, in a different order, or simultaneously. Also, in some embodiments, some of the operations, acts, blocks, steps, etc. may be omitted, added, modified, skipped, etc. without departing from the scope of the present invention.

[0140] The foregoing description of specific embodiments fully illustrates the general features of the embodiments herein so that others, applying their current knowledge, can easily modify and / or adapt such specific embodiments to various applications without departing from the general concept, and therefore, such adaptations and modifications should be understood and intended to be within the meaning and range of equivalents of the disclosed embodiments. The words or terms used herein are for the purpose of description and not of limitation.

[0141] Thus, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments described herein. [Explanation of symbols]

[0142] 100 User Device 110 processors 120 Communications Department 130 memory 200 base stations

Claims

1. 1. A method performed by a user equipment (UE) in a wireless communication system, comprising: receiving a first message for reconfiguration with synchronization from a base station (BS), the first message including information related to a dual stack based handover; detecting a radio resource control (RRC) connection establishment failure for the dual stack based handover; generating first information including a synchronization signal block (SSB) index associated with a random access performed for an RRC connection, second information associated with an uplink carrier for the random access performed for the RRC connection, and third information indicating whether contention is detected in the random access; a step of transmitting a second message to the base station to report the RRC connection establishment failure, the second message including the first information, the second information, and the third information.

2. The method of claim 1 , wherein the uplink carrier comprises a normal uplink (NUL) carrier or a supplementary uplink (SUL) carrier.

3. The method comprises: receiving, from the base station, a third message for requesting a report of the RRC connection establishment failure; The method of claim 1 , wherein the second message is sent in response to the third message.

4. 1. A method performed by a base station (BS) in a wireless communication system, comprising: transmitting a first message for reconfiguration with synchronization in a user equipment (UE), the first message including information related to a dual stack based handover; receiving, from the user equipment, a second message for reporting a radio resource control (RRC) connection establishment failure for the dual stack based handover; identifying the RRC connection establishment failure based on first information, second information, and third information included in the second message; The first information includes an SSB (synchronization signal block) index associated with a random access performed for an RRC connection; the second information is associated with an uplink carrier for random access performed for the RRC connection; The third information indicates whether contention is detected in the random access.

5. The method of claim 4 , wherein the uplink carrier comprises a normal uplink (NUL) carrier or a supplementary uplink (SUL) carrier.

6. The method comprises: transmitting, by the user equipment, a third message for requesting a report of the RRC connection establishment failure; 5. The method of claim 4, wherein the second message is received in response to the third message.

7. In a user equipment (UE) of a wireless communication system, a transceiver; a control unit connected to the transceiver unit, The control unit receiving a first message for reconfiguration with synchronization from a base station (BS), the first message including information related to a dual stack based handover; Identifying a radio resource control (RRC) connection establishment failure for the dual stack based handover; generating first information including a synchronization signal block (SSB) index associated with a random access performed for an RRC connection, second information associated with an uplink carrier for the random access performed for the RRC connection, and third information indicating whether contention is detected in the random access; A user equipment configured to transmit a second message to the base station for reporting the RRC connection establishment failure, the second message including the first information, the second information, and the third information.

8. The user equipment (10) of claim 7, wherein the uplink carrier (10) comprises a normal uplink (NUL) carrier or a supplementary uplink (SUL) carrier.

9. the control unit is further configured to receive a third message from the base station to request a report of the RRC connection establishment failure; 8. The user device of claim 7, wherein the second message is sent in response to the third message.

10. In a base station (BS) of a wireless communication system, a transceiver; a control unit connected to the transceiver unit, The control unit transmitting a first message for reconfiguration with synchronization in a user equipment (UE), the first message including information related to a dual stack based handover; receiving, from the user equipment, a second message for reporting a radio resource control (RRC) connection establishment failure for the dual stack based handover; configured to identify the RRC connection establishment failure based on first information, second information, and third information included in the second message; The first information includes an SSB (synchronization signal block) index associated with a random access performed for an RRC connection; the second information is associated with an uplink carrier for random access performed for the RRC connection; The third information is a base station indicating whether contention is detected in the random access.

11. The base station according to claim 10 , wherein the uplink carrier comprises a normal uplink (NUL) carrier or a supplementary uplink (SUL) carrier.

12. the control unit is further configured to send a third message to the user equipment to request a report of the RRC connection establishment failure; 11. The base station of claim 10, wherein the second message is received in response to the third message.

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