Method and UE for reporting accessibility measurements in wireless communication system

Abstract

The present disclosure relates to a pre-fifth generation (5G) or 5G communication system provided to support higher data rates beyond fourth generation (4G) communication systems (such as long term evolution (LTE)). Embodiments herein disclose a method for reporting accessibility measurements by a user equipment (100) based on an RRC connection establishment failure in a wireless communication system. The method includes detecting an RRC connection establishment failure and logging a parameter selected when attempting a failed RRC connection establishment, wherein the logged parameter is referred to as an accessibility measurement. In addition, the method includes indicating the presence of a connection establishment failure report to a base station (200), and in response to receiving a request from the base station (200), reporting the connection establishment failure report to the base station (200), wherein the failure report includes an accessibility measurement, the accessibility measurement including at least one of SSB information selected during cell access and on which the UE subsequently encounters an RRC connection establishment failure and uplink carrier information selected during cell access and on which the UE subsequently encounters an establishment failure.

Description

Technical Field

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

[0002] In order to meet the increased demand for wireless data traffic since the deployment of the fourth generation (4G) communication system, efforts have been made to develop improved fifth generation (5G) or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also referred to as "beyond 4G networks" or "post-Long Term Evolution (LTE) systems".

[0003] 5G communication systems are considered to be implemented in higher frequency (millimeter wave) bands (e.g., 60 GHz bands) in order to achieve higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple-input multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technologies are discussed in 5G communication systems.

[0004] In addition, in the 5G communication system, system network improvements are being developed based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, collaborative communications, coordinated multi-point (CoMP), receiving-end interference cancellation, etc.

[0005] In 5G systems, hybrid frequency shift keying (FSK) and quadrature amplitude modulation (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coded modulation (ACM), as well as filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0006] Fifth generation (5G) communication systems (New Radio (NR)) are being developed to meet the growing demand for broadband through enhanced mobile broadband (eMBB), while also supporting new use cases such as ultra-reliable low latency communications (URLLC) and massive machine type communications (mMTC). NR is an orthogonal frequency division multiplexing (OFDM) based air interface designed to support the wide variety of 5G device types, services, deployments and spectrum. The base station (200) monitors device behavior and provides the necessary resources to the UE (e.g., mobile phone, etc.) to perform any operations required by it (data - uplink or downlink, call, etc.). The signal strength and quality experienced by the UE varies depending on the proximity of the UE to the gNB. UEs near the cell are expected to have better signal conditions than UEs far away from the gNB (i.e., cell edge situation).

[0007] The base station (200) RAN node (i.e. gNodeB) in NR / eNB in ​​LTE always maintains a context on the UE with which it is in an active RRC connection. At any point in time, the gNB can hand over the UE from its control (i.e. source cell) to another gNB or another cell (i.e. target cell), thereby transferring the entire context of the particular UE to the target cell. The decision is made by the base station (200) optionally based on assistance received from the UE with the help of measurement reports about neighboring cells (i.e. the gNB configures the UE to measure the signal conditions of the serving cell and neighboring cells that may belong to different gNBs). There are specific measurement criteria and specific reporting criteria, both of which are configured by the serving gNB. Due to various reasons like weak signal conditions, heavy load on the serving gNB, etc., the serving gNB may hand over the device to a neighboring cell or a target gNB, which may be done based on assistance in the form of measurement reports received from the UE.

[0008] The UE continuously monitors the quality of its radio link to ensure that the link is in a good enough condition to successfully receive any transmission from the base station and successfully transmit to the base station. When the UE recognizes that the link quality has weakened, the radio resource management (RRM) function that performs radio link monitoring (RLM) at the PHY layer sends an out of sync indication to the upper layer (i.e., the RRC layer), thereby indicating to the upper layer that the radio link quality has deteriorated. Once the link degradation condition reaches the allowed limit, i.e., the configured threshold condition, the UE enters the outage state, i.e., a poor radio condition in which the UE experiences Qout (out of sync indication from the radio resource manager) due to a high block error rate. The current specification specifies the use of a configured T310 timer in this state. When the timer T310 expires, the UE declares a radio link failure (RLF) and initiates a cell selection process to attempt recovery.

[0009] In basic handover in NR (and LTE), the source node (i.e., eNB for LTE and gNB for NR) triggers the handover by sending a HO request to the target node, and after receiving an ACK from the target node, the source node initiates the handover by sending a HO command along with the target cell configuration. After applying the RRC reconfiguration with the received target cell configuration, the UE sends a PRACH to the target cell. Work is ongoing in 3GPP to improve the outage due to handover and to improve the reliability of handover. The proposed invention relates to enhancements to the existing handover mechanisms in LTE and NR to improve the outage time and reliability during handover.

[0010] It would therefore be desirable to address the above-mentioned shortcomings or at least provide a useful alternative. Summary of the invention

[0011] Technical issues

[0012] The present invention provides a method and UE for controlling enhanced mobility in LTE and NR.

[0013] Furthermore, the present invention provides a method and UE for performing handover in a wireless communication system.

[0014] Solution to the problem

[0015] Therefore, the embodiment of this article discloses a method for reporting accessibility measurement based on RRC connection establishment failure by UE in a wireless communication system. The method includes detecting RRC connection establishment failure by UE. In addition, the method includes logging parameters selected when attempting to establish a failed RRC connection by UE, wherein the parameters of the log record are called accessibility measurement. In addition, the method includes indicating the existence of a connection establishment failure report to the base station by UE, and in response to receiving a request from the base station, reporting the connection establishment failure report to the base station by UE, wherein the failure report includes accessibility measurement. Accessibility measurement includes synchronization signal block (SSB) information selected during cell access and subsequently on which UE encounters RRC connection establishment failure and uplink carrier information selected during cell access and subsequently on which UE encounters RRC connection establishment failure. In addition, accessibility measurement enables the base station to accurately evaluate the resources used by the UE during the RRC connection establishment failure.

[0016] In an embodiment, the failure report is one of a fifth generation new radio radio resource control (5G NR RRC) setup failure report and a 5G NR RRC resume failure report.

[0017] In an embodiment, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection resume failure.

[0018] In an embodiment, the carrier information is one of a Supplementary Uplink (SUL) carrier and a Normal Uplink (NUL) carrier selected during cell access and subsequently logged by the UE when an RRC connection establishment failure is encountered.

[0019] In an embodiment, in response to receiving a request from the base station, the logged value of the uplink carrier information is included in the connection establishment report.

[0020] In an embodiment, the SSB information is an SSB index selected during cell access and subsequently logged by the UE when an RRC connection establishment failure is encountered.

[0021] In an embodiment, in response to receiving a request from the base station, the logged value of the SSB index is included in the connection establishment report.

[0022] Accordingly, an embodiment of the present invention discloses a UE for accessibility measurement based on RRC connection establishment failure in a wireless communication system. The UE includes a processor coupled to a memory. The processor is configured to detect an RRC connection failure and log the parameters selected when attempting to establish a failed RRC connection, wherein the parameters of the log record are referred to as accessibility measurements. In addition, the processor is configured to indicate the existence of a connection establishment failure report to a base station and receive a request corresponding to the connection establishment failure report from the base station. In response to receiving a request from the base station, the processor is configured to report a connection establishment failure report to a base station in the wireless communication system. The connection establishment failure report includes an accessibility measurement, wherein the accessibility measurement includes a synchronization signal block (SSB) information selected during cell access and subsequently on which the UE encounters an RRC connection establishment failure and at least one of the uplink carrier information selected during cell access and subsequently on which the UE encounters an RRC connection establishment failure.

[0023] Accordingly, an embodiment of the present invention discloses a method for performing a handover by a UE in a wireless communication system. The method includes receiving a handover configuration by the UE from a source cell, the 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 a plurality of candidate target cells. In addition, the method includes evaluating, by the UE, an execution condition associated with at least one candidate target cell. In addition, the method includes determining, by the UE, that a target cell from a plurality of candidate target cells satisfies the execution condition. In addition, the method includes performing a handover to the target cell based on the determination by the UE.

[0024] Accordingly, an embodiment of the present invention discloses 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 a handover configuration from a source cell, the 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 a plurality of candidate target cells. In addition, the processor is configured to evaluate the execution condition associated with at least one candidate target cell. In addition, the processor is configured to determine that the execution condition is satisfied for the target cell. In addition, the processor is configured to perform a handover to the target cell based on the determination.

[0025] When considered in conjunction with the following description and the accompanying drawings, these and other aspects of the embodiments herein will be better appreciated and understood. However, it should be understood that the following description, although indicating preferred embodiments and many specific details thereof, is provided in an illustrative and non-limiting manner. Without departing from the spirit of the embodiments herein, many changes and modifications may be made within the scope of the embodiments herein, and the embodiments herein include all of these modifications.

[0026] Advantageous Effects of the Invention

[0027] The beneficial effect of the present invention is to provide a method and UE for performing accessibility measurement based on RRC connection establishment failure in a wireless communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The method and system are illustrated in the accompanying drawings, in which the same reference numerals represent corresponding parts in the various drawings. The embodiments of the present invention will be better understood from the following description with reference to the accompanying drawings, in which:

[0029] Figure 1 is a schematic diagram of a wireless communication system for performing accessibility measurement based on RRC connection failure according to an embodiment disclosed herein;

[0030] Figure 2Ais a flow chart illustrating a method for reporting accessibility measurements based on RRC connection establishment failure in a wireless communication system according to an embodiment disclosed herein;

[0031] Figure 2B is a flow chart illustrating a method for performing handover in a wireless communication system according to an embodiment disclosed herein;

[0032] Figure 3A shows a sequence diagram according to the current Release 15 specification in which a simplified model of Release 15 handover is depicted;

[0033] Figure 3B A sequence diagram showing transmission of SN state transfer and data forwarding in which a source cell initiates transmission of SN state transfer and data forwarding to a target cell indicated in a measurement report triggering CHO execution at a UE according to an embodiment disclosed herein;

[0034] Figure 4A A sequence diagram showing a source cell ignoring a handover ACK received for normal handover preparation if the source cell has received a measurement report indicating CHO execution from a UE according to an embodiment disclosed herein;

[0035] Figure 4B A sequence diagram showing a sequence diagram in which, if a normal HO command is received from a source cell before an L2 ACK or HARQ ACK for a CHO measurement report transmission is received, the UE cancels the CHO execution and performs a normal HO execution according to an embodiment disclosed herein;

[0036] Figure 5 It is shown that according to the embodiments disclosed herein, the base station configures multiple CHO conditions to the UE so that the UE can evaluate candidate target cells for performing CHO; and

[0037] Figure 6 A sequence diagram according to an embodiment disclosed herein is shown, in which the source cell continues to serve the UE even after providing a handover command until a timer at the source cell (which is equivalent to the T304 timer configured for the UE for handover) expires, or in the event of receiving a UE CONTEXT RELEASE message from the target cell upon successful completion of the path switch. DETAILED DESCRIPTION

[0038] The embodiments of the present invention and their various features and advantageous details are explained more fully with reference to the non-limiting embodiments shown in the accompanying drawings and described in detail in the following description. The description of known components and processing techniques is omitted so as not to unnecessarily obscure the embodiments of the present invention. In addition, the various embodiments described herein are not necessarily mutually exclusive, because some embodiments can be combined with one or more other embodiments to form new embodiments. Unless otherwise indicated, the term "or" used herein refers to a non-exclusive or. The examples used herein are merely to facilitate understanding of the manner in which the embodiments of the present invention can be practiced, and further enable those skilled in the art to practice the embodiments of the present invention. Therefore, these examples should not be interpreted as limiting the scope of the embodiments of the present invention.

[0039] As is conventional in the art, embodiments may be described and illustrated in terms of blocks that perform one or more functions described. These blocks may be referred to herein as managers, units, modules, hardware components, etc., which are physically implemented by analog and / or digital circuits (such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hard-wired circuits, etc.), and may be optionally driven by firmware and software. For example, the circuit may be embodied in one or more semiconductor chips, or embodied on a substrate support such as a printed circuit board. The circuits that constitute the blocks may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuits), or by a combination of dedicated hardware that performs some functions of the blocks and a processor that performs other functions of the blocks. Without departing from the scope of the present disclosure, each block of the embodiment may be physically divided into two or more discrete blocks that interact with each other. Similarly, without departing from the scope of the present disclosure, the blocks of the embodiment may be physically combined into more complex blocks.

[0040] The terms handover command and synchronous reconfiguration are used interchangeably in this disclosure, and both refer to messages that trigger a handover execution procedure at a UE.

[0041] Therefore, the embodiment of the present invention discloses a method for reporting accessibility measurement based on RRC connection establishment failure by UE in a wireless communication system. The method includes detecting RRC connection establishment failure by UE. In addition, the method includes recording parameters selected by UE log when attempting to establish a failed RRC connection, wherein the parameters recorded in the log are called accessibility measurement. In addition, the method includes indicating the existence of a connection establishment failure report to the base station by the UE, and reporting the connection establishment failure report to the base station by the UE in response to receiving a request from the base station, wherein the failure report includes accessibility measurement. The accessibility measurement includes synchronization signal block (SSB) information selected during cell access and subsequently on which the UE encounters RRC connection establishment failure and uplink carrier information selected during cell access and subsequently on which the UE encounters RRC connection establishment failure. At least one of the failure. In addition, the accessibility measurement enables the base station to accurately evaluate the resources used by the UE during the RRC connection establishment failure.

[0042] Unlike conventional methods and systems, the method may be used to control enhanced mobility in LTE and NR. The method may be used to initiate data forwarding in conditional handover based on an indication from a UE. The method may be used to avoid repeated handover commands to a UE. The method may be used to configure CHO execution conditions to identify conditions for stopping transmission on a source cell during an eMBB-based handover.

[0043] The method may be used to indicate the beam ID in accessibility measurements in logged MDT. The method may be used to indicate the UL carrier id in accessibility measurements in logged MDT. The method may be used to indicate from a UE the type(s) of make before break handover it supports. In the proposed method, a base station (200) specifies a make before break handover based on one of a plurality of handover types supported by the UE.

[0044] The proposed method can be used to reduce the outage time and improve the reliability during handover, even if the UE is in the existing handover mechanism in LTE and NR systems.

[0045] This method can be used to correctly evaluate the resources used when the UE encounters a connection establishment failure and the UE needs to indicate the SSB it selects to access the cell.

[0046] The method can be used to correctly evaluate the resources used when the UE encounters a connection recovery failure and the UE needs to indicate the SSB it selects to access the cell. The method can be used to correctly evaluate the resources used when the UE encounters a connection establishment failure and the UE needs to indicate the UL carrier it selects to access the cell. The method can be used to correctly evaluate the resources used when the UE encounters a connection recovery failure and the UE needs to indicate the UL carrier it selects to access the cell.

[0047] In the proposed method, beam information (e.g., attempted beam index) may be indicated as part of RACH information. In other words, attempted SSB index may be indicated as part of RACH failure information.

[0048] In the proposed method, the SSB indices of the downlink beams of both the serving cell and the neighboring cell as well as the corresponding measurement results and SUL / NUL carrier information should be included in the 5G NR RRC connection failure report.

[0049] Referring now to the drawings, and more particularly to the Figures 1 to 6 , wherein like reference numerals indicate corresponding features consistently throughout the drawings, there is shown a preferred embodiment.

[0050] Figure 1 1 is a schematic diagram of a wireless communication system (1000) for performing accessibility measurement based on RRC connection failure according to an embodiment disclosed herein. In an embodiment, the wireless communication system (1000) includes a UE (100) and a base station (200). The UE (100) can be, for example, but not limited to, a cellular phone, a tablet computer, a smart phone, a laptop computer, a personal digital assistant (PDA), a global positioning system, a multimedia device, a video device, an Internet of Things (IoT) device, a smart watch, a game console, a smart watch, a foldable display device, an unmanned aerial vehicle (UAV), an airplane, etc. Those skilled in the art may also refer to the UE (100) as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communication device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a mobile phone, a user agent, a mobile client, etc. The base station (200) may also be referred to as a base station transceiver, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an eNB, a gNB, etc.

[0051] In an embodiment, a UE (100) includes a processor (110), a communicator (120) and a memory (130). The processor (110) is coupled to the memory (130) and the communicator (120). The processor (110) includes an RRC connection establishment failure determination engine (110a) and a CHO engine (110b) based on accessibility measurement. The processor (110) is configured to execute instructions stored in the memory (130) and perform various processes. The communicator (120) is configured to communicate internally between internal hardware components and with external devices via one or more networks.

[0052] The memory (130) stores instructions to be executed by the processor 140. The memory (130) may include a non-volatile storage element. Examples of such non-volatile storage elements may include a magnetic hard disk, an optical disk, a floppy disk, a flash memory, or various forms of electrically programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). In addition, in some examples, the memory (130) may be considered a non-transitory storage medium. The term "non-transitory" may mean that the storage medium is not embodied in a carrier or propagating signal. However, the term "non-transitory" should not be interpreted as the memory (130) being non-removable. In some examples, the memory (130) may be configured to store a larger amount of information than internal memory. In some examples, a non-transitory storage medium may store data that may change over time (e.g., in a random access memory (RAM) or a cache).

[0053] The RRC connection establishment failure determination engine (110a) based on accessibility measurement is configured to detect RRC connection failure and log the parameters selected when attempting a failed RRC connection establishment. The parameters logged are called accessibility measurements. In an embodiment, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection recovery failure.

[0054] In addition, the RRC connection establishment failure determination engine (110a) based on accessibility measurement is configured to indicate the presence of a connection establishment failure report to the base station (200) and receive a request corresponding to the connection establishment failure report from the base station (200). In an embodiment, the connection establishment failure report is one of a fifth generation new radio radio resource control (5G NR RRC) setup failure report and a 5G NR RRC recovery failure report.

[0055] In response to receiving a request from a base station (200), an RRC connection establishment failure determination engine (110a) based on accessibility measurement is configured to report a connection establishment failure report to a base station in a wireless communication system. The connection establishment failure report includes accessibility measurement, wherein the accessibility measurement includes at least one of synchronization signal block (SSB) information selected during cell access and on which the UE (100) subsequently encounters an RRC connection establishment failure and uplink carrier information selected during cell access and on which the UE (100) subsequently encounters an RRC connection establishment failure.

[0056] In an embodiment, accessibility measurements enable a base station (200) to evaluate resources used by a UE (100) during an RRC connection establishment failure.

[0057] In an embodiment, the uplink carrier information is one of a supplementary uplink (SUL) carrier and a normal uplink (NUL) carrier, wherein the SUL carrier or the NUL carrier is selected during cell access and subsequently logged by the UE (100) when an RRC connection establishment failure is encountered.

[0058] In an embodiment, the SSB information includes at least one of the SSB indices selected during cell access and subsequently logged by the UE (100) when an RRC connection establishment failure is encountered.

[0059] In an embodiment, in response to receiving a request from the base station (200), the logged value of the SSB index is included in the connection establishment report.

[0060] In an embodiment, in response to receiving a request from the base station (200), the logged value of the uplink carrier information is included in the connection establishment failure report.

[0061] In an embodiment, the CHO engine (110b) is configured to receive a handover configuration from a source cell, the handover configuration comprising 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.

[0062] In an embodiment, the execution condition comprises a measurement identity linking the measurement object and one of: a single reporting configuration or a two reporting configuration.

[0063] In an embodiment, if two reporting configurations are included in the execution condition, the first reporting configuration indicates the measurement event as one of the A3 event or the A5 event, and indicates the trigger amount as one of the reference signal received power (RSRP) or the reference signal received quality (RSRQ) or the signal to interference and noise ratio (SINR), and the second reporting configuration indicates the measurement event as one of the A3 event or the A5 event or the A4 event, and indicates the trigger amount as one of the RSRP or the RSRQ or the SINR, and wherein the trigger amount in the first reporting configuration is different from the trigger amount in the second reporting configuration. In addition, the reference signal type in the first reporting configuration and the reference signal type in the second reporting configuration are the same.

[0064] Furthermore, the CHO engine (110b) is configured to evaluate an execution condition associated with at least one candidate target cell. In an embodiment, evaluating the execution condition associated with at least one target cell comprises identifying the realization of an event indicated in the first reporting configuration and the realization of an event indicated in the second reporting configuration.

[0065] Furthermore, the CHO engine (110b) is configured to determine that an execution condition is satisfied for the target cell.In an embodiment, determining that an execution condition is satisfied for the candidate target cell comprises indicating a joint implementation of events in the first reporting configuration and the second reporting configuration.

[0066] In addition, the CHO engine (110b) is configured to perform a handover to a candidate target cell based on the determination. In an embodiment, the handover to the candidate target cell is performed when a target cell is selected from a plurality of candidate target cells for which a joint realization of an event is determined and a target cell configuration associated with the selected target cell is applied from a received handover configuration.

[0067] although Figure 1 Various hardware components of the wireless communication system (1000) are shown, but it should be understood that other embodiments are not limited thereto. In other embodiments, the wireless communication system (1000) may include fewer or more components. In addition, the labels or names of the components are for illustrative purposes only and do not limit the scope of the present invention. One or more components may be combined to perform the same or substantially similar functions of processing accessibility measurements based on RRC connection failure.

[0068] According to various embodiments, the present invention provides a user equipment (UE) (100) for reporting accessibility measurements in a wireless communication system (1000), comprising:

[0069] Memory (130); and

[0070] The processor (110), coupled to the memory (130), is configured to:

[0071] Detecting a radio resource control (RRC) connection establishment failure;

[0072] Logging parameters selected when attempting a failed RRC connection establishment, wherein the logged parameters are referred to as accessibility measurements;

[0073] A connection establishment failure report is reported to a base station (200) in a wireless communication system (1000) based on the log record.

[0074] According to various embodiments, reporting a connection establishment failure report to a base station (200) in a wireless communication system (1000) based on a log record includes:

[0075] Indicating to the base station (200) that the RRC connection establishment has failed;

[0076] receiving a request corresponding to the indicated RRC connection establishment failure report from a base station (200); and

[0077] A connection establishment failure report is reported to a base station (200) in a wireless communication system (1000) based on the request.

[0078] According to various embodiments, wherein the connection establishment failure report includes accessibility measurements, wherein the accessibility measurements include at least one of synchronization signal block (SSB) information and uplink carrier information.

[0079] According to various embodiments, the connection establishment failure report is one of a fifth generation new radio radio resource control (5GNR RRC) setup failure report and a 5G NR RRC recovery failure report.

[0080] According to various embodiments, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection recovery failure.

[0081] According to various embodiments, the uplink carrier information is one of a supplementary uplink (SUL) carrier and a normal uplink (NUL) carrier, wherein the SUL carrier or the NUL carrier is selected during cell access and subsequently logged by the UE (100) when an RRC connection establishment failure is encountered.

[0082] According to various embodiments, the SSB information includes at least one of the SSB indices selected during cell access and subsequently logged by the UE (100) when an RRC connection establishment failure is encountered.

[0083] According to various embodiments, wherein in response to receiving a request from a base station (200), a logged value of the SSB index is included in a connection establishment report.

[0084] According to various embodiments, wherein the logged value of the uplink carrier information is included in the connection establishment failure report in response to receiving a request from the base station (200).

[0085] Figure 2A The invention is a flowchart (S200a) showing a method for reporting accessibility measurements based on RRC connection establishment failure in a wireless communication system (1000) according to an embodiment disclosed herein. The operations (S202a to S210a) are performed by a processor (110).

[0086] At 202a, the method includes detecting an RRC connection establishment failure. At 204a, the method includes logging parameters selected when attempting a failed RRC connection establishment, wherein the logged parameters are referred to as accessibility measurements.

[0087] 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 corresponding to the connection establishment failure report from the base station (200).

[0088] At 210a, the method includes reporting a connection establishment failure report to a base station (200) in a wireless communication system (1000) in response to receiving a request from the base station (200). The connection establishment failure report includes accessibility measurements, wherein the accessibility measurements include at least one of synchronization signal block (SSB) information selected during cell access and on which the UE (100) subsequently encounters an RRC connection establishment failure and uplink carrier information (SUL or NUL) selected during cell access and on which the UE (100) subsequently encounters an RRC connection establishment failure.

[0089] Figure 2B is a flow chart (S200b) showing a method for performing handover in a wireless communication system (1000) according to an embodiment disclosed herein. Operations (S202b to S208b) are performed by a processor (110).

[0090] At S202b, the method includes receiving a handover configuration from a source cell, the 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 the execution condition associated with at least one candidate target cell. At S206b, the method includes determining that the execution condition is satisfied for a target cell from the plurality of target cells. At S208b, the method includes performing a handover to the target cell based on the determination.

[0091] According to various embodiments, the present invention provides a method for reporting accessibility measurements in a wireless communication system (1000), comprising:

[0092] Detecting, by a user equipment (UE) (100), a radio resource control (RRC) connection establishment failure;

[0093] logging, by the UE (100), parameters selected when attempting a failed RRC connection establishment, wherein the logged parameters are referred to as accessibility measurements; and

[0094] A connection establishment failure report is reported by a UE (100) to a base station (200) in a wireless communication system (1000) based on the log record.

[0095] According to various embodiments, reporting, by the UE (100), a connection establishment failure report to a base station (200) in the wireless communication system (1000) based on log records includes:

[0096] The UE (100) indicates to the base station (200) that the RRC connection establishment has failed;

[0097] Receiving, by the UE (100) from the base station (200), a request corresponding to the indicated RRC connection establishment failure report; and

[0098] The UE (100) reports a connection establishment failure report to a base station (200) in the wireless communication system (1000) based on the request.

[0099] According to various embodiments, wherein the connection establishment failure report includes accessibility measurements, wherein the accessibility measurements include at least one of synchronization signal block (SSB) information and uplink carrier information.

[0100] According to various embodiments, the RRC connection establishment failure is one of an RRC connection setup failure and an RRC connection recovery failure.

[0101] According to various embodiments, the uplink carrier information is one of a supplementary uplink (SUL) carrier and a normal uplink (NUL) carrier, wherein the SUL carrier or the NUL carrier is selected during cell access and subsequently logged by the UE (100) when an RRC connection establishment failure is encountered.

[0102] According to various embodiments, the SSB information includes at least one of the SSB indices selected during cell access and subsequently logged by the UE (100) when an RRC connection establishment failure is encountered.

[0103] According to various embodiments, wherein in response to receiving a request from a base station (200), a logged value of the SSB index is included in a connection establishment report.

[0104] According to various embodiments, wherein the logged value of the uplink carrier information is included in the connection establishment failure report in response to receiving a request from the base station (200).

[0105] Figure 3A A sequence diagram is shown in which a simplified model of Release 15 handover is depicted according to embodiments disclosed herein.

[0106] During normal LTE HO and mobility procedures currently available in NR Release 15 specifications, upon receiving a handover command (or synchronization reconfiguration) from the base station (200), the UE (100) suspends operations on the source eNB / gNB, tunes to the target frequency (i.e., DL synchronization), and performs random access on the target cell. After successful completion of random access on the target cell, data exchange with the target cell is resumed. There is a visible interruption between suspending operations on the source eNB / gNB and resuming operations on the target eNB / gNB. In addition, existing handover models rely on measurement reports sent by the UE (100) to the base station (200) so that the base station (200) knows that the source cell is weak and one or more neighboring cells are better than the source cell. The RF and coverage planning of the base station (200) is done in such a way that the neighboring cells have minimal overlap at the cell edges. The overlap is sufficient to facilitate handover between these cells without causing significant interference between transmissions from the cells. They are configured to provide this form of coverage footprint to reduce deployment costs altogether. As a result, the area referred to as the handover area where the UE (100) identifies the neighboring cell to become stronger than the current serving cell is based on a trigger condition referred to as a measurement event. When the measurement event is triggered, the UE (100) triggers a measurement report and sends it to the source eNB / gNB. The source node now prepares one or more target cells indicated in the measurement report for handover. Once the admission control of the UE (100) is completed on the potential target node, a handover confirmation is provided to the source cell. The source cell decides on the target cell and provides the UE (100) with a handover command, as well as the necessary configuration to access the target cell.

[0107] Sometimes, 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 a connection with the source cell. This leads to a situation where the UE (100) does not successfully receive a handover command from the source cell due to further deteriorating signal conditions. This is particularly common in high mobility scenarios or if the handover area is subject to high interference. As a result, in Release 16, both LTE and NR introduced a new handover model in which the target cell is prepared in advance for handover, and the UE (100) can autonomously perform a handover to the target cell based on (multiple) conditions provided by the base station (200). This handover model is called conditional handover. Because it is separated from the traditional handover model under full base station control, conditional handover under partial base station control requires certain changes compared to traditional handover.

[0108] In an embodiment, the method can be used to initiate data forwarding in a conditional handover based on an indication from a UE (100). Once the admission control succeeds at the target node, the UE (100) sends a handover confirmation to the source node. During this period, the user plane connection (i.e., path switch) to the core network (500) is still at the source node and has not yet been switched to the target node. The path switch from the source cell to the target cell can only be performed when the handover to the target cell is successfully completed. The source node now sends the SN transfer status to the target node to let the target node know the sequence number (SN) that it must apply to its transmission in the downlink (DL) and uplink (UL), and performs data forwarding. Data forwarding is the process of forwarding all to-be-sent packets from the source node to the target node. This is done because once the source cell receives the handover confirmation from the target cell and sends a handover command (synchronous reconfiguration) to the UE (100), the source cell stops communicating with the UE (100). Once the handover is successful, that is, once the random access is successfully completed in the target cell, the forwarded packets are delivered to the UE (100) via the target cell.

[0109] In Release 15 handover, based on measurement reports received from the UE (100), the source typically decides the target cell from one or more target cells reported by the UE (100). There may be only one target cell ready for handover by the source cell. Therefore, once the handover confirmation is received from the target cell, data forwarding and SN status transfer to the target can be performed. However, in conditional handover, since the UE (100) evaluates the handover conditions at a later stage and it does not know a priori which target cell satisfies the handover conditions, there may be multiple cells ready for potential handover of the UE (100). Multiple target cells are prepared because the source cell cannot accurately predict in advance the target cell to which the UE (100) may have to perform a handover. Performing SN status transfer and data forwarding for all prepared cells would introduce a heavy load on the X2 interface of the base station (200) and thus cause a huge waste of resources. Therefore, it is necessary that the traditional timing and triggering of data forwarding from the source node to the target node once the target cell is ready for handover cannot be adopted in conditional handover.

[0110] Then new trigger conditions for data forwarding in conditional handover (CHO) need to be defined. In CHO, the target cell configuration is sent to the UE (100) in advance, and the actual handover execution is performed at a later point in time when the handover conditions are met (i.e. when a measurement event is triggered). The handover execution to the target cell is controlled by the conditions configured to the UE (100) together with the CHO configuration.

[0111] In the method, when the conditions for performing CHO are met, the UE (100) sends an indication to the source cell. In theory, measurement objects (such as event A3, event A5) involving the evaluation of the serving cell and the target cell are used to help the base station (200) initiate the handover of the UE (100) to the neighboring cell. It is used as a mechanism to indicate to the base station (200) that the UE (100) is leaving its coverage area and approaching the coverage area of ​​the neighboring cell. In order to facilitate conditional handover, there is no need to send a measurement report to the source cell because the target cell is already ready for handover. However, it is necessary to inform the source cell of the target cell to which the UE (100) is performing handover. This will allow the source cell to trigger SN transfer status and data forwarding only to the target cell, and when the UE (100) successfully completes random access to the target cell, the forwarded data is already available at the target cell. Therefore, in this mechanism, data forwarding is performed only to one target cell, thereby avoiding resource waste on the X2 interface and allowing less interruption time during handover because when the UE (100) successfully accesses the target cell, the target cell already has data to be forwarded to the UE (100). In an embodiment, the UE (100) reports a measurement report to the source cell that triggers the CHO execution on the target cell. In an embodiment, the UE (100) indicates the target cell identifier that triggers the CHO execution. The target cell identifier is one of the physical cell identifier (PCI) and DL-ARFCN (i.e., DL frequency) of the target cell, or one of the global cell identifier and DL-Absolute Radio Frequency Channel Number (ARFCN) of the target cell. This information about the target cell can be indicated in the measurement report together with the measurement result or in any other new RRC message.

[0112] In a conventional base station (200) controlled HO, most handover failures occur due to the UE (100) not receiving the handover command in time. The delay from sending a measurement report with neighboring cell details to the base station (200) and receiving a handover command with the target cell configuration from the base station (200) is caused by the time taken to prepare the target cell for handover. When the target cell is successfully prepared for handover, the source cell signal condition may further deteriorate, making it unlikely that the UE (100) will successfully receive downlink transmissions. However, the probability of receiving a measurement report indicating measurement results of one or more neighboring cells from the UE (100) is high compared to the probability of receiving a handover command from the source when the target cell is ready. The measurement conditions configured to trigger CHO execution are expected to have a configuration similar to the measurement report used in conventional handovers to indicate to the source cell that the UE (100) is moving to a neighboring cell. Therefore, the probability of the source node successfully receiving the measurement report is high. The reception of the measurement report by the source node acts as a trigger to initiate data forwarding to the target cell indicated in the measurement report.

[0113] like Figure 3A As shown, at S302a, the UE (100) sends a measurement report to the SgNB (300). At S304a, based on the measurement report, the SgNB (300) sends a handover request to the TgNB (400). Based on the handover request, at S306a, the TgNB (400) performs a grant control process. Based on the grant control process, at S308a, the TgNB (400) sends a handover request confirmation message to the SgNB (300). After receiving the handover request confirmation message from the TgNB (400), at S310a, the SgNB (300) sends a HO command / synchronization reconfiguration message to the UE (100). Based on the HO command / synchronization reconfiguration message, at S312a, the UE (100) detaches from the source cell and tunes to the target cell. At S314a, the SgNB (300) sends an SN status transfer message to the TgNB (400), and at S316a, the SgNB (300) sends a data forwarding to the TgNB (400). At S318a, a RAN handover completion occurs between the UE (100) and the TgNB (400). At S320a, the TgNB (400) sends a path switch request to the CN (500). At S322a, the CN (500) sends a path switch request confirmation message to the TgNB (400). At S324a, the TgNB (400) sends a UE context release to the SgNB (300).

[0114] Figure 3B A sequence diagram is shown in which a source cell initiates transmission of SN state transfer and data forwarding to a target cell indicated in a measurement report that triggers CHO execution at a UE (100) according to an embodiment disclosed herein. In another embodiment, the source cell initiates transmission of SN state transfer and data forwarding to a target cell indicated in a measurement report that triggers CHO execution at a UE (100).

[0115] Once the conditions for performing CHO are met, a measurement report is sent by the UE (100) to the source, indicating the target cell identifier. The measurement report is sent using RLC AM, so if the source cell successfully receives the measurement report, there is an RLC ACK from the source cell. When the UE (100) receives the RLC ACK, it performs handover related actions (i.e., HO execution) and tunes to the target cell frequency (i.e., DL synchronization). This may involve suspending transmit / receive operations on the source cell depending on the handover type - for handovers that do not support simultaneous connections with the source cell and the target cell. For handovers that allow continued activity on the source cell even after handover execution is triggered (i.e., a make-before-leave type of HO), when the UE (100) tunes to the target cell frequency, it does not suspend transmit / receive operations on the source cell. In order to ensure data forwarding initiated by the source cell to the target cell, the UE (100) may wait until it receives a layer 2 acknowledgement (i.e., RLC ACK) from the source cell for the measurement report it has sent. Therefore, in another embodiment, the UE (100) waits for an L2 ACK (ie, RLC ACK) for the sent measurement report before suspending operation on the source cell or initiating HO execution to the target cell.

[0116] It is possible that when the UE (100) receives the L2 ACK (i.e., RLC ACK), the signal condition has deteriorated and the UE (100) cannot successfully decode the physical downlink shared channel (PDSCH). To handle this situation, a timer (predefined or configurable) can be used. The timer is started when a measurement report is sent to the base station (200) to trigger CHO execution. The timer is stopped when the L2 ACK for the measurement report is received. When the timer expires, the UE (100) stops monitoring the L2 ACK of the source cell and attempts to perform a handover on the target cell, i.e., triggering HO execution on the target cell.

[0117] In situations where signal conditions may deteriorate at a very fast rate (e.g., deep fading in the higher frequency range), measurement reports sent to the source cell may not be successfully received. However, when the CHO conditions are met and the timer for receiving the RLC ACK expires, the UE (100) may still perform a CHO to the target cell. In this case, when the UE (100) successfully completes random access in the target cell, and the target cell determines that no data forwarding path has been established / no SN status transfer has been received from the source cell, the target cell may request the source cell to perform SN status transfer and data forwarding. In an embodiment, if the source cell does not initiate SN status transfer and data forwarding when the UE (100) successfully completes random access on the target cell, the target cell requests the source cell to perform SN status transfer and data forwarding.

[0118] At S302b, UE (100) sends a measurement report to SgNB (300). At S304b, based on the measurement report, SgNB (300) sends a handover request to TgNB1 (400a). Based on the handover request, at S306b, TgNB1 (400a) performs a grant control process. Based on the grant control process, at S308b, TgNB1 (400a) sends a handover request confirmation message to SgNB (300).

[0119] After receiving the handover request confirmation message from TgNB1 (400a), at S310b, SgNB (300) sends a handover request to TgNB2 (400b). Based on the handover request, at S312b, TgNB2 (400b) performs a grant control process. Based on the grant control process, at S314b, TgNB2 (400b) sends a handover request confirmation message to SgNB (300).

[0120] At S316b, the SgNB (300) sends a CHO configuration to the UE (100). At S318b, the UE (100) performs a CHO candidate evaluation, and at S320b, the UE (100) performs a CHO event triggered for TgNB1 (400a). At S322b, the UE (100) specifies an MR indicating CHO execution to TgNB1 (400a). At 324b, the UE (100) detaches from the source cell and tunes to the target cell. At S326b, the SgNB (300) sends an SN status transfer message to TgNB1 (400a), and at 328b, the SgNB (300) sends a data forwarding to TgNB1 (400a). At 330b, a RAN handover completion occurs between the UE (100) and TgNB1 (400a). At S332b, TgNB1 (400a) sends a path switch request to CN (500). At S334b, CN (500) sends a path switch request confirmation message to TgNB (400). At S336b, TgNB1 (400a) sends a UE context release to SgNB (300).

[0121] Figure 4A A sequence diagram is shown in which a source cell ignores a handover ACK received for normal handover preparation if the source cell has received a measurement report indicating CHO execution from a UE (100) according to an embodiment disclosed herein.

[0122] In an embodiment, the method can be used to avoid repeated handover commands to the UE (100). In CHO, the UE (100) is pre-configured with potential candidate cells for handover. However, it is possible that the UE's mobility is towards other neighboring cells that are not part of the CHO candidates. In this case, the base station (200) configures a regular handover based on measurement reports from the UE (100). This handover command has a higher priority than the received CHO configuration and therefore takes precedence if the CHO condition is not triggered.

[0123] In another scenario, the UE (100) may send a request for a neighboring cell that is not a CHO candidate (e.g., Figure 4A The neighboring cell (TgNB-2) is prepared for handover and a handover ACK is sent to the source cell. It is possible that during the HO preparation phase for TgNB-2, the UE (100) meets the requirements for the candidate cell ( Figure 4A The source cell determines the conditions for CHO execution of TgNB-1 (TgNB-1 in the handover) and sends the relevant measurement report to the source cell. At this time, the source cell has 2 target cells prepared for handover - one is the target cell based on normal handover preparation (TgNB-2), and the other is the target cell based on CHO preparation (TgNB-1). However, when the source cell receives the measurement report for TgNB-1, it has not yet received the HO request ACK from TgNB-2. The UE (100) can only perform handover to one of them, and the source cell must perform SN status transfer and data forwarding to the same target cell (i.e., TgNB-1) to which the UE (100) attempts to switch. In an embodiment, if the source cell has received a measurement report indicating CHO execution from the UE, the source cell ignores the handover ACK received for normal handover preparation, such as Figure 4A shown.

[0124] At S402a, the UE (100) sends a measurement report to the SgNB (300). At S404a, based on the measurement report, the SgNB (300) sends a handover request for CHO to the TgNB1 (400a). Based on the handover request, at S406a, the TgNB1 (400a) performs a grant control procedure. Based on the grant control procedure, at S408a, the TgNB1 (400a) sends a handover request confirmation message to the SgNB (300).

[0125] At S410a, the UE (100) sends an MR indicating a normal HO to TgNB-2 (400b). At 412a, the SgNB (300) sends a handover request for normal HO to TgNB2 (400b). At 414a, the UE (100) sends an MR indicating a CHO execution to TgNB1 (400a). Based on the handover request, at 416b, TgNB2 (400b) performs a grant control process. Based on the grant control process, at S418b, TgNB2 (400b) sends a handover request confirmation message to SgNB (300). At S420a, the SgNB (300) executes the CHO execution indication received before the ACK from TgNB-2, ignores the normal HO ACK, and forwards the data to the CHO candidate.

[0126] At S422a, the UE (100) detaches from the source cell and tunes to the target cell. At S424a, the SgNB (300) sends an SN status transfer message to TgNB1 (400a), and at S426a, the SgNB (300) sends a data forwarding to TgNB1 (400a). At S428a, a RAN handover completion occurs between the UE (100) and TgNB1 (400a). At S430a, TgNB1 (400a) sends a path switch request to CN (500). At S432a, CN (500) sends a path switch request confirmation message to TgNB1 (400a). At S434a, TgNB1 (400a) sends a UE context release to SgNB (300).

[0127] Figure 4B A sequence diagram is shown in which, 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, the UE (100) cancels the CHO execution and performs a normal HO execution according to an embodiment disclosed herein.

[0128] Similarly, it is possible that the UE (100) sends a CHO triggered measurement report to the base station (200), and then receives a HO command for normal handover at the UE (100). In another scenario, the UE (100) may send a CHO triggered measurement report for a neighboring cell that is not a CHO candidate (e.g., Figure 4B The neighboring cell (TgNB-2) is prepared for handover and a handover ACK is sent to the source cell. It is possible that after completing the HO preparation phase for TgNB-2, the UE (100) meets the requirements for the candidate cell ( Figure 4BThe source cell (100) meets the conditions for CHO execution of TgNB-1 in the source cell, and the UE (100) sends a relevant measurement report to the source cell. At this time, the source cell has 2 target cells prepared for handover - one is the target cell based on normal handover preparation (TgNB-2), and the other is the target cell based on CHO preparation (TgNB-1). However, before receiving the measurement report for TgNB-1, the source has received the HO request ACK from TgNB-2. The UE (100) can only perform handover to one of them, and the source cell must perform SN status transfer and data forwarding to the same target cell (i.e., TgNB-2) to which the UE is attempting to switch.

[0129] In an embodiment, Figure 4B As shown, if a normal HO command is received from the source cell before receiving the L2 ACK (i.e., RLCACK) or HARQ ACK for the CHO measurement report transmission, the UE (100) cancels the CHO execution and performs a normal HO execution. As a corollary, once the handover execution details (i.e., the measurement report for CHO or the HO preparation ACK for normal HO) are received at the source cell, the source node processes the first message it receives and ignores the messages that arrive subsequently. As a result, if the UE (100) receives the HO command after transmitting the CHO MR (before the L2 ACK of the CHO MR), the UE (100) will perform a normal handover. This is done because the UE (100) should know that the source cell provides a normal HO command because the normal HO command arrives at the source cell earlier in time than the CHO trigger measurement report. Therefore, data forwarding is initiated by the source cell to the target cell for which the handover indication is received earliest at the source cell.

[0130] In an embodiment, the method may be used to configure CHO execution conditions. The UE (100) reports event A1 only when the serving cell signal condition is good, i.e., reports A1 when the serving cell signal condition is better than a threshold configured by the network. The base station (200) (i.e., source gNB), upon receiving event A1 from the UE (100), may reconfigure / add / remove other measurement IDs, for example, to configure A2 to identify when the UE's signal condition begins to deteriorate below a configured value. Therefore, event A1 is not suitable for triggering a handover to a neighboring cell.

[0131] The UE (100) reports event A2 only when the serving cell signal condition is poor, and does not indicate potential neighboring cells in good signal conditions to the base station (200), i.e., A2 is reported when the serving cell signal condition is weaker than a network configured threshold. The source gNB may reconfigure / add / remove measurement ids upon receiving event A2, for example, the source gNB configures A1 to identify when the UE signal condition improves, or configures A3 / A5 to identify whether the neighboring cell is in suitable signal conditions to serve the UE (100). Alternatively, the source gNB may 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 source gNB is not aware of the UE's proximity to these neighboring cells. Blind handover based on event A2 may only be useful in cases where there are two collocated cells, one of which belongs to a low frequency and the other to a high frequency, and the coverage of these cells is overlapping and superimposed. In these cases, the UE (100) connected to the higher frequency cell may be handed over to a cell operating on a lower frequency without knowing the signal condition of the target cell (the cell on the lower frequency has a larger coverage footprint). This is a very limited scenario and may not be widely used in actual deployments. Although event A2 can be used to trigger a switch, event A2 alone cannot be used to perform reliable switchover.

[0132] The UE (100) reports event A4 only when the neighbor cell signal condition is good, that is, when the neighbor cell signal condition is better than the network configured threshold. The source gNB may reconfigure / add / remove other measurement IDs upon receiving event A4, for example, the source gNB configures event A3 / A5 to understand the neighbor cell signal condition compared to the serving cell signal condition. Alternatively, the source gNB may provide a handover command to the UE (100) to the neighbor cell reported in event A4. Although the handover to the target cell may be successful due to the good signal condition of the target cell, it does not ensure that the target cell is better than the source cell. The signal condition and QoS provided by the target cell may be poor compared to the source cell. Although event A4 can be used to trigger a handover, event A4 cannot be used alone to perform a reliable handover.

[0133] In order to provide reliable handover to a neighboring cell, the source gNB should know that the neighboring cell can provide better service to the UE (100) than the current serving cell. Events A3 and A5 provide the base station (200) with both the serving cell signal condition and the neighboring cell signal condition. A3 is reported when the neighboring cell signal condition is better than the serving cell by at least one 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 another network configured threshold. Thus, the source gNB is able to understand whether the neighboring cell can provide better service. However, in some cases, more than one event is needed to reliably trigger a handover.

[0134] In a conventional handover, the base station (200) configures several measurement events to the UE (100). The base station (200) does not have to prepare a target cell based on each relevant measurement report from the UE (100). The base station (200) may take a decision to provide a handover command to the UE (100) based on multiple measurement reports or a sequence of measurement reports from the UE (100). The source node may also know the load conditions of neighboring nodes / target nodes. The target cell can be prepared for handover only when the load conditions are within an acceptable level, even if the measurement results indicate that the neighboring cell is in better signal conditions. As a result, sometimes the handover is not offered to the best cell reported to the base station (200) in the measurement report.

[0135] However, in the case of conditional handover, the conditions for performing the handover are configured to the UE (100), and the UE (100) autonomously performs the handover based on the conditions. Therefore, CHO is under the control of part of the base station (200). When the UE (100) performs CHO towards the target, there is no intelligence at the UE (100), which is different from the intelligence of the base station (200) in traditional handover, in which the base station (200) wisely decides the handover of the UE (100) to the adjacent target cell based on such base station (200) intelligence (e.g., the load condition of the target). In traditional handover, if the adjacent signal conditions are good and the load of the adjacent cell is acceptable to serve the additional UE (100), the serving cell provides a handover command to the UE (100). However, in conditional handover, the conditions that trigger the execution of CHO are provided much earlier in time. It is possible that during this period, the target cell load is low enough to allow more UEs (100) to access the cell. However, the actual CHO execution takes place at a later time, by which time the load on the target cell may have changed. However, when CHO is triggered and the UE (100) performs a handover to the target cell, the load in the target has already increased. In this scenario, the service provided on the target cell may be worse / weaker than the service on the source cell.

[0136] To overcome this, it is necessary to instill some intelligence into the UE (100) for making decisions on CHO execution. This can be achieved by introducing the requirement that multiple reporting configurations be met by the UE (100). For example, the UE (100) can be configured with event A3 where the trigger quantity is set to RSRP. When the UE (100) successfully meets A3, it knows that the signal strength of the neighboring cell is better than the serving cell / suitable for serving the UE (100). However, it does not know the load and quality of the neighboring cells. In order to enable the UE (100) to make an intelligent assessment of the target cell, the base station (200) can configure event A4 where the trigger quantity is set to RSRQ. The RSRQ measurement provides an indication of the load on the target cell. Together, A3 based on RSRP indicates that the target cell signal condition is good, and A4 based on RSRQ indicates that the load on the target cell is acceptable. Therefore, the handover will not be more reliable than if CHO is performed based on a single condition / trigger.

[0137] In another example, in a regular handover, the source cell has several options to decide the handover (based on different reporting configurations and different triggering amounts).

[0138] a. UE-assisted handover based on A3 / A5, where the stronger neighbor is indicated in the MR, or

[0139] b. UE-assisted handover based on A4, where neighbors are indicated in the MR. However, the source cell may still be in tolerable signal conditions (or the entry conditions of A3 / A5 may not be met).

[0140] c. A2-based blind HO, where neighbors are not indicated in the MR.

[0141] d. UE-assisted handover based on multiple measurement reports or measurement report sequences from the UE (100) (for different reporting configurations)

[0142] To manage and assist the HO decision, the source cell may configure multiple measurement report configurations for the same MO and ultimately make a decision based on the MR it receives from the UE (100). The MR is not necessarily always A3 / A5, but may also be A2 / A4. In the above example, beam failure recovery (BFR) is indicated as one of the possible results of a sudden cell degradation (in FR2). Typical values ​​of the time-to-trigger (TTT) configured in LTE deployments often vary between 256ms and 1024ms. If BFR is triggered due to a sudden drop in beam quality in a mobile scenario, considering that PRACH resources are configured every 10ms (including the time for monitoring RAR), a new RA preamble is sent every 10ms if no RAR is received. Based on preambleTransMax, RA failure may occur before TTT is completed, and may even lead to RLF in the case of CHO configuration.

[0143] The above examples are for illustration purposes only, and the present application is not limited to this illustration. This combination of report configurations for CHO evaluation can be done in any combination or with the same / different report configurations with the same / different trigger amounts, the same / different RS types, etc. In an embodiment, the base station (200) can configure multiple CHO conditions to the UE.

[0144] like Figure 4B As shown, at S402b, the UE (100) sends a measurement report to the SgNB (300). At S404b, based on the measurement report, the SgNB (300) sends a handover request for CHO to TgNB1 (400a). Based on the handover request, at S406b, TgNB1 (400a) performs a grant control process. Based on the grant control process, at S408b, TgNB1 (400a) sends a handover request confirmation message to the SgNB (300). At S410b, the SgNB (300) sends a CHO configuration to the UE (100), and at S412b, the UE (100) performs a CHO candidate evaluation. At S414b, the UE (100) sends an MR indicating a normal HO to TgNB-2 (400b) through the SgNB (300).

[0145] At S416b, SgNB (300) sends a handover request for normal HO to TgNB2 (400b). At S418b, UE (100) sends an MR indicating CHO execution to TgNB-1 (400a) through SgNB (300). Based on the handover request, at S420b, TgNB2 (400b) performs a grant control process. Based on the grant control process, at S422b, TgNB2 (400b) sends a handover request confirmation message to SgNB (300).

[0146] At S424b, the SgNB (300) sends a normal HO command to the UE (100), and at S426b, in the SgNB (300), a normal HO execution indication is first received and the CHO indication from the UE (100) is ignored. At 430b, the UE (100) detaches from the source cell and tunes to the target cell. At S428b, the SgNB (300) sends an SN status transfer message to TgNB1 (400a), and at 432b, the SgNB (300) sends a data forwarding to TgNB1 (400a). At S434b, a RAN handover completion occurs between the UE (100) and TgNB1 (400a). At S436b, TgNB1 (400a) sends a path switch request to the CN (500). At S438b, CN (500) sends a path switch request confirmation message to TgNB (400). At S440b, TgNB1 (400a) sends a UE context release to SgNB (300).

[0147] Figure 5 It is shown that according to the embodiments disclosed herein, the base station (200) can configure a 1-bit indication (multipleConditionTrigger) and a CHO condition configuration to the UE (100) to provide more decision freedom to the UE (100). In order to provide a more intelligent decision control to the UE (100), the base station (200) can configure a 1-bit indication (multipleConditionTrigger) and a CHO condition configuration to the UE (100) to provide more decision freedom to the UE (100). Figure 5 multipleConditionTrigger in the CHO configuration) and the CHO condition configuration. If this indication is configured in the CHO configuration, it means that there are multiple report configurations, provided that CHO will only be executed if all report configurations are met. If this field is not present, it means that only one report configuration is provided, or it means that multiple report conditions are provided, but CHO can be performed if any of the configured report configurations are met. Figure 5 It is also shown that the network is configuring multiple CHO conditions to the UE to enable the UE to evaluate candidate target cells for performing CHO.

[0148] Figure 6 A sequence diagram according to an embodiment disclosed herein is shown, wherein the source cell continues to serve the UE (100) even after providing a handover command, until a timer at the source cell (which timer is equivalent to the T304 timer configured to the UE (100) for handover) expires, or in the event of receiving a UE CONTEXT RELEASE message from the target cell upon successful completion of the path switch.

[0149] like Figure 6As shown, at S602, the UE (100) sends a measurement report to the SgNB (300). At S604, based on the measurement report, the SgNB (300) sends a handover request to the TgNB (400). Based on the handover request, at S606, the TgNB (400) performs a grant control process. Based on the grant control process, at S608, the TgNB (400) sends a handover request confirmation message to the SgNB (300). After receiving the handover request confirmation message from the TgNB (400), at S610, the SgNB (300) sends a HO command / synchronization reconfiguration message to the UE (100). Based on the HO command / synchronization reconfiguration message, at S312a, the UE (100) continues on the source cell and tunes to the target cell. At S614, the SgNB (300) continues the data path to the UE (100) and starts timer T304.

[0150] At S616, the SgNB (300) sends an SN status transfer message to the TgNB (400), and at S618, the SgNB (300) sends a data forwarding to the TgNB (400). At S620, a RAN handover completion occurs between the UE (100) and the TgNB (400). At S622, the TgNB (400) sends a path switch request to the CN (500). At S624, the CN (500) sends a path switch request confirmation message to the TgNB (400). At S626, the TgNB (400) sends a UE context release to the SgNB (300).

[0151] In an embodiment, the method can be used to identify conditions for stopping transmission on the source cell during an eMBB-based handover. In a connect-before-leave handover of Release 14 in LTE, the UE (100) continues to receive on the source cell even after receiving a handover command from the base station (200). However, the base station (200) does not know the time until the UE (100) continues to monitor the DL channel from the source cell. This is because it is assumed that the UE (100) has a single receive chain (single Rx) and cannot receive from both the source and the target at the same time. Therefore, it is impossible for the source to correctly estimate the time required for the UE (100) to tune to the target cell and perform random access. As a result, the time until the UE (100) receives data from the source cell and the time until the source continues DL transmission are left to implementation.

[0152] In Release 16, both LTE and NR are committed to enhancing MBB procedures, where the UE (100) is expected to have 2 receive chains. Therefore, the UE (100) can receive from both the source cell and the target cell at the same time. As a result, the source can continue transmission on the source cell, and the UE (100) can receive on the source cell until successfully accessing the target cell. Therefore, it is possible to correctly identify when the source cell can stop transmitting to the UE (100). One way is that when the UE (100) releases the source cell connection and performs actions only on the target cell, the UE (100) indicates to the source cell via MAC CE or other uplink signaling methods. However, this method is unreliable because the signal conditions to the source cell are expected to be very poor and the probability of successfully sending an indication to the source cell is very small.

[0153] Another way to indicate the release of the source cell is for the target cell to indicate to the source cell once the UE (100) successfully accesses the target cell (the handover on the target cell is completed). However, this approach may result in a delay in indicating to the source cell, as well as the introduction of additional overhead of new signaling from the target cell to the source cell requesting the source to suspend activities from the source cell.

[0154] In another embodiment, the method may be used for the source cell to continue to be active after providing a handover command to the UE (100) until a timer expires or an event occurs. In an embodiment, even after providing a handover command, the source cell continues to serve the UE (100) until a timer at the source cell (which timer is equivalent to the T304 timer configured to the UE (100) for handover) expires, or in the event of receiving a UE CONTEXT RELEASE message from the target cell when the path switch is successfully completed. This is Figure 6 In another embodiment, the source cell may continue to serve the UE (100) until a portion of the T304 timer.

[0155] In an embodiment, the method can be used to indicate the beam ID in the accessibility measurement in the minimization of driving test (MDT) recorded in the log. In LTE, the accessibility measurement contains the number and location information of the preamble codes sent during the failed connection establishment attempt and other parameters. In a beamforming system like NR, the UE (100) may be within the coverage of more than one beam. The UE (100) selects the beam for random access based on the threshold configured in the system information. Therefore, different UEs receiving signals from the same beam set at the same location can attempt connection establishment based on PRACH resources associated with different beams. As a result, in order to correctly evaluate the resources used when the UE (100) encounters a connection establishment failure, the UE (100) needs to indicate the SSB it selects to access the cell. In an embodiment, the SSB ID on which the UE (100) encountered the connection establishment failure is indicated to the base station (200) in the accessibility measurement, as shown below:

[0156]

[0157] In LTE, accessibility measurements contain information about the number and location of preambles sent during failed connection establishment attempts, as well as other parameters, and these can be reused for NR recovery failure reporting. In a beamforming system like NR, a UE (100) may be within the coverage of more than one beam. The UE (100) selects a beam for random access based on a threshold configured in the system information. Therefore, different UEs receiving signals from the same beam set at the same location may attempt connection recovery based on PRACH resources associated with different beams. As a result, in order to correctly evaluate the resources used when the UE (100) encounters a connection recovery failure, the UE (100) needs to indicate the SSB it selected to access the cell. In another embodiment, the SSB id on which the UE (100) encountered a connection recovery failure is indicated to the base station (200) in the accessibility measurement, as shown below:

[0158]

[0159] In another embodiment, the method can be used to indicate the UL carrier id in the accessibility measurement in the logged MDT. Unlike LTE, NR can have 2 uplink carriers (normal UL and SUL) configured for accessing the cell. Therefore, random access for connection establishment can be performed on normal UL or SUL PRACH resources. The carrier on which the RACH is performed depends on the DL path loss reference. As a result, due to RF performance and channel variations, not all UEs in the same location can perform RACH on the same UL carrier. Therefore, in order to correctly evaluate the resources used when the UE (100) encounters a connection establishment failure, the UE (100) needs to indicate the UL carrier it selects to access the cell. In an embodiment, the uplink carrier on which the UE (100) encountered the connection establishment failure is indicated to the base station (200) in the accessibility measurement:

[0160]

[0161]

[0162] Unlike LTE, NR can have 2 uplink carriers (normal UL and SUL) configured for accessing a cell. Therefore, random access for connection recovery can be performed on either normal UL or SUL PRACH resources. The carrier on which the RACH is performed depends on the DL path loss reference. As a result, due to RF performance and channel variations, not all UEs in the same location can perform RACH on the same UL carrier. Therefore, in order to correctly evaluate the resources used when the UE (100) encounters a connection recovery failure, the UE (100) needs to indicate the UL carrier it selected to access the cell. In another embodiment, the uplink carrier on which the UE (100) encountered a connection recovery failure is indicated to the base station (200) in the accessibility measurement:

[0163]

[0164]

[0165] In another embodiment, the method can be used to indicate the UE capability of supporting different enhanced mobility procedures for handover. There are multiple ways to reduce mobility interruption time based on a connect-before-leave type of handover. Depending on the scenario and UE capabilities, the UE (100) may support more than one type of MBB / enhanced MBB-based handover. Therefore, the UE (100) is required to indicate to the base station (200) its ability to perform MBB-based handover and the supported methods. This must be indicated as part of the UE capabilities. In an embodiment, the UE (100) has the ability to support one or both of a single-stack-based enhanced MBB HO or a dual-stack-based enhanced MBB HO.

[0166] In a single stack based mobile broadband (MBB) solution, only one protocol stack is fully activated at a given time, while the other protocol stacks are not fully activated. For example, upon receiving a single stack based eMBB handover command from a base station (200), the UE (100) maintains a full stack on the source cell and continues to operate on the source until a specific time. During this period, based on UE capabilities, the target stack may be partially active or not active at all. Once access to the target cell is successful, the UE (100) releases the protocol stack associated with the source cell and operates only using the protocol stack associated with the target.

[0167] In a dual-stack MBB solution, the UE (100) may simultaneously activate a protocol stack associated with a source cell and a protocol stack associated with a target cell. The two stacks are only active simultaneously for a short period of time to facilitate the transfer of resources / packets from the source cell to the target cell. The description of the UE capability indicating the supported mobility type is as follows:

[0168]

[0169]

[0170] In another embodiment, the method may be used to indicate the MBB type that the UE should apply to the configured handover. Since the UE (100) may support more than one type of MBB-based handover, namely single-stack-based MBB HO and dual-stack-based MBB HO, it is necessary to indicate to the UE (100) the type of handover that must be performed when providing synchronous reconfiguration to it. Therefore, the base station (200) provides the MBB type that needs to be used for the current handover based on several factors, which may include UE capabilities, interruption requirements of ongoing services, deployment scenarios, etc. In an embodiment, the serving PCell indicates to the UE (100) the MBB type that it must apply to the current handover.

[0171] This indication can be provided as part of the synchronous reconfiguration in several ways. One way is to always provide the mobility type in the synchronous reconfiguration / handover command. This indication will explicitly inform the UE (100) of the MBB type it needs to apply, as shown below:

[0172]

[0173] In another embodiment, the method may optionally include an indication, wherein if the indication is included, the handover must be based on a dual-stack MBB HO, and if the indication is not included (or vice versa), the handover must be based on a single-stack MBB HO, as shown below:

[0174]

[0175] The embodiments herein are applicable to LTE, NR and other cellular communication technologies, and reference to any one of these technologies in the present invention is for illustrative purposes only and is not limited thereto.

[0176] 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.

[0177] The various actions, actions, blocks, steps, etc. in the flow chart (S200a and S200b) can be performed in the order presented, in a different order, or simultaneously. In addition, in some embodiments, some actions, actions, blocks, steps, etc. can be omitted, added, modified, skipped, etc. without departing from the scope of the present invention.

[0178] The foregoing description of specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, easily modify and / or adapt various applications of such specific embodiments without departing from the general concepts, and therefore, such adaptations and modifications should and are intended to be understood to be within the meaning and range of equivalents of the disclosed embodiments. It should be understood that the wording or terminology employed herein is for descriptive purposes and not for limitation. Therefore, although the embodiments herein have been described according to preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications within the spirit and scope of the embodiments described herein.

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: receiving a first message for configuring synchronization reconfiguration from a base station, the first message including information related to dual stack based handover; Identifying a failure to establish a radio resource control (RRC) connection for a dual stack based handover; generating first information including a synchronization signal block (SSB) index associated with a random access performed for the 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; as well as A second message for reporting the failure of establishing the RRC connection is sent to the base station, where the second message includes the first information, the second information and the third information.

2. The method according to claim 1, in, The uplink carrier includes a normal uplink (NUL) carrier or a supplemental uplink (SUL) carrier.

3. The method according to claim 1, wherein: The failure includes RRC connection establishment failure.

4. The method according to claim 1, further comprising: receiving a third message from the base station, the third message being used to request failure of establishment of the RRC connection, and The second message for reporting the failure is sent as a response to the third message for requesting the failure.

5. A method performed by a base station in a wireless communication system, the method comprising: Sending a first message for configuration synchronization reconfiguration to the terminal, the first message including information related to dual-stack-based switching; receiving a second message from the terminal, the second message being used to report a failure in establishing a radio resource control RRC connection for the dual stack based handover; as well as identifying a failure in establishing the RRC connection based on the first information, the second information, and the third information included in the second message, The first information includes a synchronization signal block SSB index associated with a random access performed for the RRC connection, The second information is associated with an uplink carrier for random access performed for the RRC connection, and The third information indicates whether contention is detected in the random access.

6. The method according to claim 5, wherein: The uplink carrier includes a normal uplink (NUL) carrier or a supplementary uplink (SUL) carrier, and The failure includes a failure to establish an RRC connection.

7. The method according to claim 5, further comprising: sending a third message to the terminal, the third message being used to request the failure of establishing the RRC connection, and The second message for reporting the failure is received as a response to the third message for requesting the failure.

8. A terminal in a wireless communication system, the terminal comprising: a transceiver configured to transmit or receive a signal; as well as A controller coupled to the transceiver and configured to: receiving a first message for configuring synchronization reconfiguration from a base station, the first message including information related to dual stack based handover, identifying a failure in establishment of a radio resource control, RRC, connection for dual stack based handover, generating first information including a synchronization signal block (SSB) index associated with a random access performed for the 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, and A second message for reporting the failure of establishing the RRC connection is sent to the base station, where the second message includes the first information, the second information and the third information.

9. The terminal according to claim 8, wherein: The uplink carrier includes a normal uplink (NUL) carrier or a supplemental uplink (SUL) carrier.

10. The terminal according to claim 8, wherein: The failure includes RRC connection establishment failure.

11. The terminal according to claim 8, wherein: The controller is also configured to: receiving a third message from the base station, the third message being used to request failure of establishment of the RRC connection, and The second message for reporting the failure is sent as a response to the third message for requesting the failure.

12. A base station in a wireless communication system, the base station comprising: a transceiver configured to transmit or receive a signal; as well as A controller coupled to the transceiver and configured to: Sending a first message for configuration synchronization reconfiguration to the terminal, the first message including information related to the dual-stack-based switching, receiving a second message from the terminal, the second message being used to report failure in establishing a radio resource control RRC connection for the dual stack based handover, and identifying a failure in establishing the RRC connection based on the first information, the second information, and the third information included in the second message, The first information includes a synchronization signal block SSB index associated with a random access performed for the RRC connection, The second information is associated with an uplink carrier for random access performed for the RRC connection, and The third information indicates whether contention is detected in the random access.

13. The base station according to claim 12, wherein: The uplink carrier includes a normal uplink (NUL) carrier or a supplemental uplink (SUL) carrier.

14. The base station according to claim 12, wherein: The failure includes RRC connection establishment failure.

15. The base station according to claim 12, wherein: The controller is also configured to: receiving a third message from the terminal, the third message being used to request failure of establishing the RRC connection, and The second message for reporting the failure is received as a response to the third message for requesting the failure.

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