阅读说明：本技术 无线通信系统中报告可接入性测量的方法和ue (Method and UE for reporting accessibility measurement in wireless communication system ) 是由 F·A·拉瑟夫 M·A·因加尔 于 2020-04-29 设计创作，主要内容包括：本公开涉及被提供用于支持超越第四代(4G)通信系统(诸如长期演进(LTE))的更高数据速率的预第五代(5G)或5G通信系统。本文的实施例公开了一种用于在无线通信系统中由用户设备(100)基于RRC连接建立失败来报告可接入性测量的方法。该方法包括检测RRC连接建立失败,并日志记录在尝试失败的RRC连接建立时选择的参数,其中,日志记录的参数被称为可接入性测量。此外,该方法包括向基站(200)指示连接建立失败报告的存在,并且响应于从基站(200)接收到请求,向基站(200)报告连接建立失败报告,其中,该失败报告包括可接入性测量,该可接入性测量包括在小区接入期间选择的并且随后在其上UE遇到RRC连接建立失败的SSB信息和在小区接入期间选择的并且随后在其上UE遇到建立失败的上行链路载波信息中的至少一个。(The present disclosure relates to pre-fifth generation (5G) or 5G communication systems provided for supporting 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 RRC connection setup failure in a wireless communication system. The method comprises detecting an RRC connection setup failure and logging parameters selected at the time of attempting the failed RRC connection setup, wherein the logged parameters are referred to as accessibility measurements. Further, the method includes indicating to the base station (200) the presence of a connection establishment failure report, 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 comprising at least one of SSB information selected during cell access and on which the UE subsequently experienced an RRC connection establishment failure, and uplink carrier information selected during cell access and on which the UE subsequently experienced an establishment failure.)

1. A method performed by a User Equipment (UE) for a Random Access Channel (RACH) procedure in a wireless communication system (1000), comprising:

detecting a Radio Resource Control (RRC) Connection Establishment Failure (CEF);

transmitting a report including at least one of beam information and uplink carrier information to a base station;

wherein the uplink carrier information includes at least one of a Supplemental Uplink (SUL) carrier and a Normal Uplink (NUL) carrier,

wherein the beam information includes a Synchronization Signal Block (SSB) index.

2. The method of claim 1, wherein the beam information is indicated as RACH information.

3. The method of claim 1, wherein the SSB index is indicated as RACH information.

4. The method of claim 1, wherein the carrier information is included in the report.

5. The method of claim 1, wherein the RRC connection setup failure (CEF) comprises at least one of an RRC connection setup failure and an RRC connection recovery failure.

6. The method of claim 1, wherein the report comprises at least one of a fifth generation new radio resource control (5G NR RRC) setup failure report and a 5G NR RRC recovery failure report.

7. The method of claim 1, further comprising:

storing the uplink carrier information and the beam information when the RRC connection setup failure (CEF) is encountered.

8. A method performed by a Base Station (BS) for a Random Access Channel (RACH) procedure in a wireless communication system (1000), comprising:

receiving a report including at least one of beam information and uplink carrier information from a user equipment;

wherein the uplink carrier information includes at least one of a Supplemental Uplink (SUL) carrier and a Normal Uplink (NUL) carrier,

wherein the beam information includes a Synchronization Signal Block (SSB) index.

9. The method of claim 8, wherein the beam information is indicated as RACH information.

10. The method of claim 8, wherein the SSB index is indicated as RACH information.

11. The method of claim 8, wherein the carrier information is included in the report.

12. The method of claim 8, wherein the report comprises at least one of a fifth generation new radio resource control (5G NR RRC) setup failure report and a 5G NR RRC recovery failure report.

13. The method of claim 8, further comprising:

storing the uplink carrier information upon encountering the RRC Connection Establishment Failure (CEF).

14. The method of claim 1, further comprising:

storing the beam information upon encountering the RRC Connection Establishment Failure (CEF).

15. An apparatus of a User Equipment (UE) or a base station, arranged to implement the method of one of claims 1 to 14.

Technical Field

The present disclosure relates to a wireless communication system, and more particularly, to a method and User Equipment (UE) for making accessibility measurements based on Radio Resource Control (RRC) connection failures in a wireless communication system. This application is based on indian application No. 201941017815 filed on 3/5/2019, the disclosure of which is incorporated herein by reference, and claims priority.

Background

In order to meet the increasing demand for wireless data traffic since the deployment of fourth generation (4G) communication systems, efforts have been made to develop improved fifth generation (5G) or pre-5G communication systems. Accordingly, the 5G or pre-5G communication system is also referred to as a "super 4G network" or a "post Long Term Evolution (LTE) system".

The 5G communication system is considered to be implemented in a frequency band of higher frequencies (millimeter waves), for example, a 60GHz band, in order to achieve a higher data rate. In order to reduce propagation loss of radio waves and increase transmission distance, beamforming, massive Multiple Input Multiple Output (MIMO), full-dimensional MIMO (FD-MIMO), array antenna, analog beamforming, massive antenna techniques are discussed in the 5G communication system.

Further, in the 5G communication system, development of system network improvement is being performed based on advanced small cells, cloud Radio Access Network (RAN), ultra dense network, device-to-device (D2D) communication, wireless backhaul, mobile network, cooperative communication, coordinated multipoint (CoMP), reception-side interference cancellation, and the like.

In 5G systems, hybrid Frequency Shift Keying (FSK) and quadrature amplitude modulation (FQAM) and Sliding Window Superposition Coding (SWSC) have been developed as Advanced Coding Modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and Sparse Code Multiple Access (SCMA) as advanced access techniques.

Fifth generation (5G) communication systems (new radios (NR)) are being developed to meet the increasing broadband demand through enhanced mobile broadband (eMBB) while also supporting new usage scenarios such as ultra-reliable low latency communication (URLLC) and large-scale machine type communication (mtc). NR is an Orthogonal Frequency Division Multiplexing (OFDM) based air interface designed to support a wide variation 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 (data-uplink or downlink, call, etc.) it needs. 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 case).

The base station (200) RAN node (i.e. the gbodeb)/eNB in LTE in the NR always maintains context on the UE with which it is in an active RRC connection. At any point in time, the gNB may handover 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) by means of measurement reports on neighbouring cells, optionally based on assistance received from the UE (i.e. the gNB configures the UE to measure signal conditions of the serving cell and neighbouring cells possibly belonging to different gnbs). There are specific measurement criteria and specific reporting criteria, both of which are configured by the serving gNB. For various reasons, such as weak signal conditions, heavy loading on the serving gbb, etc., the serving gbb may handover the device to a neighboring cell or target gbb, which may be done based on assistance in the form of measurement reports received from the UE.

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 transmissions from the base station and to successfully transmit to the base station. When the UE recognizes that the link quality becomes weak, a Radio Resource Management (RRM) function, which performs Radio Link Monitoring (RLM) at the PHY layer, transmits an out of sync (out of sync) indication to the higher layer, i.e., the RRC layer, thereby indicating radio link quality degradation to the higher layer. Once the link degradation condition reaches the allowed limit, i.e. the configured threshold condition, the UE enters an outage (outage) state, i.e. a poor radio condition where the UE experiences Qout (out of sync indication from the radio resource manager) due to a high block error rate. The current specification provides for the use of a configured T310 timer in this state. Upon expiration of this timer T310, the UE declares a Radio Link Failure (RLF) and initiates a cell selection procedure to attempt recovery.

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

It is therefore desirable to address the above disadvantages or at least to provide a useful alternative.

Disclosure of Invention

Technical problem

The invention provides a method and UE for controlling enhanced mobility in LTE and NR.

Further, the present invention provides a method and a UE for performing handover in a wireless communication system.

Solution to the problem

Accordingly, embodiments herein disclose a method for reporting accessibility measurements by a UE based on RRC connection setup failure in a wireless communication system. The method includes detecting, by the UE, an RRC connection setup failure. Further, the method includes logging (log) parameters selected by the UE upon attempting the failed RRC connection setup, wherein the logged parameters are referred to as accessibility measurements. Further, the method includes indicating, by the UE, the presence of a connection establishment failure report to the base station, and reporting, by the UE, the connection establishment failure report to the base station in response to receiving the request from the base station, wherein the failure report includes the accessibility measurement. The accessibility measurement includes at least one of Synchronization Signal Block (SSB) information selected during cell access and on which the UE subsequently encounters an RRC connection setup failure and uplink carrier information selected during cell access and on which the UE subsequently encounters an RRC connection setup failure. Furthermore, the accessibility measurements enable the base station to accurately assess the resources used by the UE during RRC connection setup failure.

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

In an embodiment, the RRC connection establishment failure (connection establishment failure) is one of an RRC connection setup failure (connection setup failure) and an RRC connection recovery failure (connection resume failure).

In an embodiment, the carrier information is one of a Supplemental Uplink (SUL) carrier and a Normal Uplink (NUL) carrier selected during cell access and subsequently logged by the UE upon encountering an RRC connection setup failure.

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

In an embodiment, the SSB information is an SSB index selected during cell access and subsequently logged by the UE upon encountering an RRC connection setup failure.

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

Accordingly, embodiments herein disclose a UE for accessibility measurement based on RRC connection setup failure in a wireless communication system. The UE includes a processor coupled with a memory. The processor is configured to detect an RRC connection failure and log parameters selected at the time of attempting the failed RRC connection establishment, wherein the logged parameters are referred to as accessibility measurements. Further, the processor is configured to indicate to the base station the presence of a connection establishment failure report, and receive a request from the base station corresponding to the connection establishment failure report. In response to receiving the request from the base station, the processor is configured to report a connection establishment failure report to the base station in the wireless communication system. The connection establishment failure report includes an 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 subsequently encounters an RRC connection establishment failure and uplink carrier information selected during cell access and on which the UE subsequently encounters an RRC connection establishment failure.

Accordingly, embodiments herein disclose a method for performing handover by a UE in a wireless communication system. The method includes receiving, by a UE, 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 the at least one candidate target cell from the plurality of candidate target cells. Further, the method includes evaluating, by the UE, an execution condition associated with the at least one candidate target cell. Further, the method includes determining, by the UE, that an execution condition is satisfied for a target cell from the plurality of candidate target cells. Further, the method includes performing, by the UE, a handover to the target cell based on the determination.

Accordingly, embodiments herein disclose a UE for performing handover in a wireless communication system. The UE includes a processor coupled with a memory. The processor 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. Further, the processor is configured to evaluate an execution condition associated with the at least one candidate target cell. Further, the processor is configured to determine that an execution condition is satisfied for the target unit. Further, the processor is configured to perform a handover to the target cell based on the determination.

These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

Advantageous effects of the invention

The invention has the beneficial effect of providing the method and the UE for carrying out accessibility measurement based on RRC connection establishment failure in the wireless communication system.

Drawings

The method and system are illustrated in the accompanying drawings in which like reference numerals refer to corresponding parts throughout the various views. The embodiments herein will be better understood from the following description with reference to the accompanying drawings, in which:

fig. 1 is a schematic diagram of a wireless communication system for accessibility measurements based on RRC connection failure, according to an embodiment disclosed herein;

fig. 2A is a flow diagram illustrating a method for reporting accessibility measurements based on RRC connection establishment failures in a wireless communication system, according to embodiments disclosed herein;

Fig. 2B is a flow chart illustrating a method for performing a handover in a wireless communication system according to embodiments disclosed herein;

FIG. 3A shows a sequence diagram of a simplified model in which version 15 switching is depicted, according to the current version 15 specification;

fig. 3B shows a sequence diagram of a transmission in which a source cell initiates SN status transfer and data forwarding to a target cell indicated in a measurement report triggering CHO execution at a UE, according to embodiments disclosed herein;

fig. 4A shows a sequence diagram in which a source cell ignores a handover ACK received for normal handover preparation if the source cell has received a measurement report from the UE indicating a CHO execution, according to embodiments disclosed herein;

fig. 4B shows a sequence diagram in which the UE cancels CHO execution and performs normal HO execution if a normal HO command is received from the source cell before receiving an L2 ACK or HARQ ACK for CHO measurement report transmission according to embodiments disclosed herein;

fig. 5 illustrates a base station configuring a UE with a plurality of CHO conditions to enable the UE to evaluate candidate target cells for performing CHO in accordance with embodiments disclosed herein; and is

Fig. 6 shows a sequence diagram according to embodiments disclosed herein, where the source cell continues to serve the UE even after providing a handover command until the expiration of a timer at the source cell (which corresponds to a T304 timer configured for the UE for handover), or in the event of receiving a UE CONTEXT RELEASE (UE CONTEXT RELEASE) message from the target cell upon successful completion of the path switch.

Detailed Description

The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Furthermore, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments may be combined with one or more other embodiments to form new embodiments. As used herein, the term "or" refers to a non-exclusive or unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, these examples should not be construed as limiting the scope of the embodiments herein.

Embodiments may be described and illustrated with respect to blocks performing one or more of the described functions, as is conventional in the art. These blocks, which may be referred to herein as managers, units, modules, hardware components, and the like, 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, hardwired circuits, and the like), and may optionally be driven by firmware and software. For example, the circuitry may be embodied in one or more semiconductor chips, or on a substrate support such as a printed circuit board or the like. The circuitry making up the blocks may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware for performing some of the functions of the blocks and a processor for performing other functions of the blocks. Each block of an embodiment may be physically separated into two or more interacting discrete blocks without departing from the scope of the disclosure. Also, the blocks of an embodiment may be physically combined into more complex blocks without departing from the scope of the present disclosure.

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

Accordingly, embodiments herein disclose a method for reporting accessibility measurements by a UE based on RRC connection setup failure in a wireless communication system. The method includes detecting, by the UE, an RRC connection setup failure. Further, the method comprises logging, by the UE, parameters selected at the time of attempting the failed RRC connection setup, wherein the logged parameters are referred to as accessibility measurements. Further, the method includes indicating, by the UE, the presence of a connection establishment failure report to the base station, and reporting, by the UE, the connection establishment failure report to the base station in response to receiving the request from the base station, wherein the failure report includes the accessibility measurement. The accessibility measurement includes at least one of Synchronization Signal Block (SSB) information selected during cell access and on which the UE subsequently encounters an RRC connection setup failure and uplink carrier information selected during cell access and on which the UE subsequently encounters an RRC connection setup failure. Furthermore, the accessibility measurements enable the base station to accurately assess the resources used by the UE during RRC connection setup failure.

Unlike conventional methods and systems, this method can 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 the UE. The method may be used to avoid repeated handover commands to the UE. The method may be used to configure CHO execution conditions to identify conditions to stop transmission on the source cell during the eMBB-based handover.

The method may be used to indicate a beam ID in accessibility measurements in logged MDTs. 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 the UE the type(s) for which a make before break (make before break) handover is supported. In the proposed method, the base station (200) specifies a make-before-break handover based on one of a plurality of handover types supported by the UE.

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

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 its choice to access the SSB of 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 its choice to access the SSB of the cell. The method may be used to correctly evaluate the resources used when the UE encounters a connection establishment failure and the UE needs to indicate its choice to access the UL carrier of the cell. The method may be used to correctly evaluate the resources used when the UE encounters a connection recovery failure and the UE needs to indicate its choice to access the UL carrier of the cell.

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

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

Referring now to the drawings, and more particularly to fig. 1-6, wherein like reference numerals represent corresponding features consistently throughout the several views, there is shown a preferred embodiment.

Fig. 1 is a schematic diagram of a wireless communication system (1000) for accessibility measurements based on RRC connection failure, according to embodiments disclosed herein. In an embodiment, a wireless communication system (1000) includes a UE (100) and a base station (200). The UE (100) may be, for example but not limited to, a cellular phone, a tablet, a smart phone, a laptop, 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, a Unmanned Aerial Vehicle (UAV), an airplane, and so forth. The UE (100) may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless communications device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, etc. The base station (200) may also be referred to as a base transceiver station, radio base station, radio transceiver, transceiver function, Basic Service Set (BSS), Extended Service Set (ESS), eNB, gNB, etc.

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

The memory (130) stores instructions to be executed by the processor 140. The memory (130) may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard disks, optical disks, floppy disks, flash memory, or various forms of electrically programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). Further, 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 wave or propagated signal. However, the term "non-transitory" should not be construed as an immobility of the memory (130). In some examples, the memory (130) may be configured to store a greater amount of information than memory. In some examples, a non-transitory storage medium may store data that may change over time (e.g., in Random Access Memory (RAM) or cache).

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

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

In response to receiving a request from a base station (200), an RRC connection setup failure determination engine (110a) based on accessibility measurements is configured to report a connection setup failure report to the base station in the wireless communication system. The connection establishment failure report includes an 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.

In an embodiment, the accessibility measurements enable the base station (200) to evaluate resources used by the UE (100) during an RRC connection setup failure.

In an embodiment, the uplink carrier information is one of a Supplemental 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) upon encountering an RRC connection setup failure.

In an embodiment, the SSB information comprises at least one of SSB indices selected during cell access and subsequently logged by the UE (100) upon encountering an RRC connection setup failure.

In an embodiment, in response to receiving a request from a base station (200), a log value of the SSB index is included in the connection setup report.

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

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

In an embodiment, the execution condition includes a measurement identification linking the measurement object and one of: a single reporting configuration or two reporting configurations.

In an embodiment, if two reporting configurations are included in the execution condition, the first reporting configuration indicates the measurement event as one of an A3 event or an a5 event and the trigger amount as one of a Reference Signal Received Power (RSRP) or a Reference Signal Received Quality (RSRQ) or a signal to interference and noise ratio (SINR), the second reporting configuration indicates the measurement event as one of an A3 event or an a5 event or an a4 event and the trigger amount as one of RSRP or RSRQ or SINR, and wherein the trigger amount in the first reporting configuration is different from the trigger amount in the second reporting configuration. Furthermore, the reference signal type in the first reporting configuration and the reference signal type in the second reporting configuration are the same.

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

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

Further, the CHO engine (110b) is configured to perform a handover to the candidate target cell based on the determination. In an embodiment, the handover to the candidate target cell is performed upon selecting the target cell from a plurality of candidate target cells for which a joint implementation of the event is determined and applying the target cell configuration associated with the selected target cell from the received handover configuration.

Although fig. 1 illustrates various hardware components of a wireless communication system (1000), it should be understood that other embodiments are not so limited. In other embodiments, the wireless communication system (1000) may include a fewer or greater number of 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 together to perform the same or substantially similar functions of processing accessibility measurements based on RRC connection failures.

According to various embodiments, the present invention provides a User Equipment (UE) (100) for reporting accessibility measurements in a wireless communication system (1000), comprising:

a memory (130); and

a processor (110), coupled with the memory (130), configured to:

detecting a Radio Resource Control (RRC) connection establishment failure;

Logging parameters selected at the time of attempting the failed RRC connection setup, wherein the logged parameters are referred to as accessibility measurements;

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

According to various embodiments, wherein reporting a connection establishment failure report to a base station (200) in a wireless communication system (1000) based on the log comprises:

indicating an RRC connection setup failure to the base station (200);

receiving a request corresponding to the indicated RRC connection setup failure report from the base station (200); and

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

According to various embodiments, wherein the connection establishment failure report comprises an accessibility measurement, wherein the accessibility measurement comprises at least one of Synchronization Signal Block (SSB) information and uplink carrier information.

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

According to various embodiments, wherein the RRC connection setup failure is one of an RRC connection setup failure and an RRC connection recovery failure.

According to various embodiments, wherein the uplink carrier information is one of a Supplemental 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) upon encountering an RRC connection setup failure.

According to various embodiments, wherein the SSB information comprises at least one of SSB indices selected during cell access and subsequently logged by the UE (100) upon encountering an RRC connection setup failure.

According to various embodiments, wherein in response to receiving a request from a base station (200), a log value of the SSB index is included in the connection setup report.

According to various embodiments, wherein the logged values of the uplink carrier information are included in a connection setup failure report in response to receiving a request from the base station (200).

Fig. 2A is a flowchart illustrating a method for reporting accessibility measurements based on RRC connection setup failure in a wireless communication system (1000) (S200a) according to embodiments disclosed herein. Operations (S202a to S210a) are performed by the processor (110).

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

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

At 210a, the method includes reporting a connection establishment failure report to a base station (200) in the wireless communication system (1000) in response to receiving a request from the base station (200). The connection establishment failure report includes an 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 (10) 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.

Fig. 2B is a flowchart illustrating a method for performing handover in a wireless communication system (1000) according to an embodiment disclosed herein (S200B). Operations (S202b to S208b) are performed by the processor (110).

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

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

detecting, by a User Equipment (UE) (100), a Radio Resource Control (RRC) connection establishment failure;

logging, by the UE (100), parameters selected at the time of attempting the failed RRC connection setup, wherein the logged parameters are referred to as accessibility measurements; and

reporting, by the UE (100), a connection establishment failure report to a base station (200) in the wireless communication system (1000) based on the log.

According to various embodiments, wherein reporting, by the UE (100), the connection establishment failure report to the base station (200) in the wireless communication system (1000) based on the log comprises:

indicating, by the UE (100), an RRC connection setup failure to the base station (200);

receiving, by the UE (100), a request from the base station (200) corresponding to the indicated RRC connection setup failure report; and

reporting, by the UE (100), a connection establishment failure report to a base station (200) in the wireless communication system (1000) based on the request.

According to various embodiments, wherein the connection establishment failure report comprises an accessibility measurement, wherein the accessibility measurement comprises at least one of Synchronization Signal Block (SSB) information and uplink carrier information.

According to various embodiments, wherein the RRC connection setup failure is one of an RRC connection setup failure and an RRC connection recovery failure.

According to various embodiments, wherein the uplink carrier information is one of a Supplemental 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) upon encountering an RRC connection setup failure.

According to various embodiments, wherein the SSB information comprises at least one of SSB indices selected during cell access and subsequently logged by the UE (100) upon encountering an RRC connection setup failure.

According to various embodiments, wherein in response to receiving a request from a base station (200), a log value of the SSB index is included in the connection setup report.

According to various embodiments, wherein the logged values of the uplink carrier information are included in a connection setup failure report in response to receiving a request from the base station (200).

Fig. 3A illustrates a sequence diagram of a simplified model in which version 15 switching is depicted, according to embodiments disclosed herein.

During the mobility procedures currently available in the normal LTE HO and NR Release 15 specifications, upon receiving a handover command (or synchronization reconfiguration) from the base station (200), the UE (100) suspends operation on the originating 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 operation on the source eNB/gNB and resuming operation on the target eNB/gNB. Furthermore, existing handover models rely on measurement reports sent by the UE (100) to the base station (200) so that the base station (200) is aware of the weak source cell and one or more better neighbor cells than the source cell. RF and coverage planning for a base station (200) is accomplished such that adjacent cells have minimal overlap at the cell edges. The overlap is sufficient to facilitate handover between these cells and does not create 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 that the neighboring cell becomes stronger than the current serving cell, is based on a trigger condition, referred to as a measurement event. When a 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. A handover confirmation is provided to the source cell upon completion of admission control to the UE (100) at the potential target node. The source cell decides the target cell and provides the handover command to the UE (100) along with the necessary configuration to access the target cell.

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 the 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 degraded signal conditions. This is especially common in high mobility scenarios or if the handover area suffers from high interference. As a result, in release 16, both LTE and NR introduced a new handover model in which the target cell was prepared in advance for handover, and the UE (100) can autonomously perform handover to the target cell based on the condition(s) provided by the base station (200). This switching model is called conditional switching. Since the traditional handover model under the control of the complete base station is separated, compared with the traditional handover, the conditional handover under the control of part of the base stations needs a certain change.

In an embodiment, the method may be used for initiating data forwarding in a conditional handover based on an indication from the UE (100). Once admission control is successful at the target node, the UE (100) sends a handover acknowledgement to the source node. During this time, the user plane connection to the core network (500) (i.e., path switch) is still at the source node and has not yet been switched to the target node. Path switching from a source cell to a target cell can only be done upon successful completion of the handover to the target cell. The source node now sends the target node an SN delivery status so that the target node knows the Sequence Numbers (SNs) it must apply to transmissions in its Downlink (DL) and Uplink (UL) and performs data forwarding. Data forwarding is the process of forwarding all pending packets from a source node to a destination node. This is done because the source cell stops communicating with the UE (100) as soon as the source cell receives a handover acknowledgement from the target cell and sends a handover command (synchronous reconfiguration) to the UE (100). Upon successful handover, i.e. upon successful completion of random access in the target cell, the forwarded packets are delivered to the UE (100) via the target cell.

In release 15 handover, the source typically decides the target cell from one or more target cells reported by the UE (100) based on measurement reports received from the UE (100). Only one target cell may be prepared for handover by the source cell. Thus, upon receiving a handover acknowledgement from the target cell, data forwarding and SN status transfer to the target may be performed. However, in conditional handover, there may be multiple cells ready for potential handover of the UE (100), 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. 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 introduces a heavy load on the X2 interface of the base station (200) and thus causes a huge waste of resources. It is therefore essential that the conventional timing and triggering of data forwarding from the source node to the target node once the target cell is ready for handover cannot be employed in conditional handovers.

A new trigger condition for data forwarding in Conditional Handover (CHO) then needs 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 condition is fulfilled, i.e. when a measurement event is triggered. Handover execution to the target cell is controlled by conditions configured to the UE (100) together with the CHO configuration.

In the method, the UE (100) sends an indication to the source cell when a condition for performing CHO is met. Theoretically, measurement objects (e.g., event A3, event a5) related to serving and target cell evaluations are used to assist the base station (200) in initiating handover of the UE (100) to a neighboring cell. It serves 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 a neighboring cell. To facilitate conditional handover, there is no need to send measurement reports to the source cell, since the target cell is already ready for handover. However, the source cell needs to be informed of the target cell to which the UE (100) is performing handover. This will allow the source cell to trigger SN delivery status and data forwarding only to the target cell, and the forwarded data is already available at the target cell when the UE (100) successfully completes random access to the target cell. Thus, in this mechanism, data forwarding is performed to only one target cell, avoiding waste of resources on the X2 interface and allowing less outage time during handover, since the target cell already has data to be forwarded to the UE (100) when the UE (100) successfully accesses the target cell. In an embodiment, a UE (100) reports to a source cell a measurement report triggering CHO to be performed on a target cell. In an embodiment, the UE (100) indicates a target cell identifier that triggers CHO execution. The target cell identifier is one of a Physical Cell Identifier (PCI) and a DL-ARFCN (i.e., DL frequency) of the target cell, or one of a global cell identifier and a DL-Absolute Radio Frequency Channel Number (ARFCN) of the target cell. This information about the target cell may be indicated together with the measurement results in a measurement report or in any other new RRC message.

In conventional base station (200) controlled HO, most handover failures occur because the UE (100) does not receive the handover command in time. The delay from sending measurement reports with neighbour cell details to the base station (200) and receiving a handover command with target cell configuration from the base station (200) is due to the time taken to prepare the target cell for handover. When the target cell is successfully prepared for handover, the source cell signal conditions may further degrade such that the UE (100) is less likely to successfully receive the downlink transmission. However, the probability of receiving a measurement report from the UE (100) indicating measurement results of one or more neighboring cells 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 similar configuration as measurement reports in conventional handover to indicate to the source cell that the UE (100) is moving towards a neighboring cell. Therefore, the probability of successful reception of the measurement report by the source node is high. The source node acts as a trigger for the reception of the measurement report to initiate data forwarding to the target cell indicated in the measurement report.

As shown in fig. 3A, at S302a, the UE (100) sends a measurement report to the SgNB (300). At S304a, based on the measurement report, SgNB (300) sends a handover request to TgNB (400). Based on the handover request, at S306a, the TgNB (400) performs an admission control procedure. Based on the admission control procedure, at S308a, the TgNB (400) sends a handover request confirm message to the SgNB (300). After receiving the handover request confirm message from the TgNB (400), the SgNB (300) transmits a HO command/synchronization reconfiguration message to the UE (100) at S310 a. 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, SgNB (300) sends an SN status transfer message to TgNB (400), and at S316a, SgNB (300) sends data forwarding to TgNB (400). At S318a, a RAN handover complete 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 confirm message to the TgNB (400). At S324a, the TgNB (400) sends a UE context release to the SgNB (300).

Fig. 3B shows a sequence diagram of a transmission in which a source cell initiates SN status transfer and data forwarding to a target cell indicated in a measurement report triggering CHO execution at the UE (100), according to embodiments disclosed herein. In another embodiment, the source cell initiates transmission of the SN status transfer and data forwarding to the target cell indicated in the measurement report triggering CHO execution at the UE (100).

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 an 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 the transmit/receive operation on the source cell depending on the type of handover-for handovers that do not support simultaneous connections with the source cell and the target cell. For handovers that allow the continuation of activity on the source cell even after handover execution is triggered (i.e. make-before-break type HO), when the UE (100) tunes to the target cell frequency, it does not suspend the transmission/reception operation on the source cell. 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. Thus, in another embodiment, the UE (100) waits for an L2 ACK (i.e., RLC ACK) for the sent measurement report before suspending operation on the source cell or initiating HO execution to the target cell.

It is possible that when the UE (100) receives the L2 ACK (i.e., RLC ACK), the signal conditions have degraded and the UE (100) is unable to successfully decode the Physical Downlink Shared Channel (PDSCH). To handle this, a timer (predefined or configurable) may be used. The timer is started when a measurement report triggering CHO execution is sent to the base station (200). The timer stops when an L2 ACK is received for the measurement report. When the timer expires, the UE (100) stops monitoring the L2 ACK of the source cell and attempts handover on the target cell, i.e. triggers HO execution on the target cell.

In the case where signal conditions may degrade at a very fast rate (e.g., deep fading in the higher frequency range), the measurement report sent to the source cell may not be successfully received. However, the UE (100) may still proceed to CHO of the target cell when the CHO condition is met and the timer to receive the RLC ACK expires. 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 is established/no SN status transfer is received from the source cell, the target cell may request the source cell for SN status transfer and data forwarding. In an embodiment, the target cell requests the source cell to perform SN status transfer and data forwarding 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.

At S302b, the UE (100) sends a measurement report to the SgNB (300). At S304b, based on the measurement report, SgNB (300) sends a handover request to TgNB1(400 a). Based on the handover request, at S306b, the TgNB1(400a) performs an admission control procedure. Based on the admission control procedure, at S308b, the TgNB1(400a) sends a handover request confirm message to the SgNB (300).

After receiving the handover request confirm message from TgNB1(400a), SgNB (300) sends a handover request to TgNB2(400b) at S310 b. Based on the handover request, at S312b, the TgNB2(400b) performs an admission control procedure. Based on the admission control procedure, at S314b, the TgNB2(400b) sends a handover request confirm message to the SgNB (300).

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

Fig. 4A shows a sequence diagram in which a source cell ignores a handover ACK received for normal handover preparation if the source cell has received a measurement report from the UE (100) indicating a CHO execution, according to embodiments disclosed herein.

In an embodiment, the method may 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 mobility of the UE is towards other neighboring cells that are not part of the CHO candidate. In this case, the base station (200) configures a conventional handover based on the measurement report from the UE (100). The handover command has a higher priority than the received CHO configuration and therefore takes precedence if the CHO condition is not triggered.

In another scenario, the UE (100) may send a measurement report for a neighbor cell that is not a CHO candidate (e.g., TgNB-2 in fig. 4A). The neighbor 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) fulfils the conditions for CHO execution for the candidate cell (TgNB-1 in fig. 4A) in the CHO configuration and sends a relevant measurement report to the source cell. At this time, the source cell has 2 target cells prepared for handover — one is a target cell (TgNB-2) prepared based on normal handover and the other is a target cell (TgNB-1) prepared based on CHO. However, when the source cell receives the measurement report for TgNB-1, it has not received the HO request ACK from TgNB-2. The UE (100) can only perform handover to one of them and the source cell has to perform SN status transfer and data forwarding to the same target cell (i.e. TgNB-1) to which the UE (100) is attempting to handover. In an embodiment, if the source cell has received a measurement report from the UE indicating CHO execution, the source cell ignores the handover ACK received for normal handover preparation, as shown in fig. 4A.

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

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

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

Fig. 4B shows a sequence diagram where the UE (100) cancels CHO execution and performs normal HO execution if a normal HO command is received from the source cell before receiving an L2 ACK or HARQ ACK for CHO measurement report transmission according to embodiments disclosed herein.

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 measurement report for a neighbor cell that is not a CHO candidate (e.g., TgNB-2 in fig. 4B). The neighbor cell (TgNB-2) is prepared for handover and a handover ACK is sent to the source cell. It is possible that after the HO preparation phase for TgNB-2 is completed, the UE (100) fulfils the conditions for CHO execution for the candidate cell in the CHO configuration (TgNB-1 in fig. 4B) 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 a target cell (TgNB-2) prepared based on normal handover and the other is a target cell (TgNB-1) prepared based on CHO. However, the source has received a HO request ACK from TgNB-2 before receiving the measurement report for TgNB-1. The UE (100) can only perform handover to one of them and the source cell has to perform SN status transfer and data forwarding to the same target cell (i.e. TgNB-2) to which the UE attempts handover.

In an embodiment, as shown in fig. 4B, if a normal HO command is received from the source cell before receiving an L2ACK (i.e., RLC ACK) or HARQ ACK for CHO measurement report transmission, the UE (100) cancels CHO execution and performs normal HO execution. As a corollary, once handover execution details (i.e. measurement report for CHO or 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 later. As a result, if the UE (100) receives the HO command after transmitting the CHO MR (before the L2ACK 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 triggered measurement report. Thus, data forwarding is initiated by the source cell to the target cell for which the handover indication was received earliest at the source cell.

In an embodiment, the method may be used to configure CHO execution conditions. The UE (100) reports event a1 only when serving cell signal conditions are good, i.e., a1 when serving cell signal conditions are better than a network configured threshold. The base station (200) (i.e., source gNB) may reconfigure/add/remove other measurement ids upon receiving event a1 from the UE (100), e.g., to configure a2 to identify when the signal condition of the UE begins to degrade below the configured value. Therefore, the a1 event is not suitable for triggering a handover to a neighboring cell.

The UE (100) reports event a2 only when the serving cell signal condition is poor and does not indicate to the base station (200) a potential neighbor cell in good signal condition, i.e., reports a2 when the serving cell signal condition is weaker than a network configured threshold. The source gNB may reconfigure/add/remove the measurement id upon receiving event a2, e.g., the source gNB configures a1 to identify when the UE signal conditions improve, or configures A3/a5 to identify whether the neighboring cell is in proper signal conditions to serve the UE (100). Alternatively, the source gNB may perform blind preparation of the target cell and provide handover commands to the UE. However, this does not guarantee a good handover success rate, since the source gbb does not know that the UE is adjacent to these neighboring cells. Blind handovers based on event a2 may only be useful in cases where: there are two collocated (collocated) cells, one of which belongs to low frequencies and the other to high frequencies, and the coverage of these cells is overlapping and superimposed. In these cases, a UE (100) connected to a higher frequency cell may be handed over to a cell operating on a lower frequency without knowing the signal conditions 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 applicable in a practical deployment. While event a2 may be used to trigger a handover, event a2 alone cannot be used to perform a reliable handover.

The UE (100) reports event a4 only when the neighbor cell signal conditions are good, i.e., a4 when the neighbor cell signal conditions are better than the network configured threshold. The source gNB may reconfigure/add/remove other measurement ids upon receiving event a4, e.g., the source gNB configures event A3/a5 to understand the neighbor cell signal conditions as compared to the serving cell signal conditions. Alternatively, the source gNB may provide the UE (100) with a handover command to the neighboring cell reported in event a 4. Although handover to the target cell may be successful due to good signal conditions of the target cell, it does not ensure that the target cell is better than the source cell. The target cell may provide poorer signal conditions and QoS than the source cell. While event a4 may be used to trigger a handover, event a4 alone cannot be used to perform a reliable handover.

In order to provide reliable handover to a neighbouring cell, the source gNB should be aware that the neighbouring cell may provide a better service to the UE (100) than the current serving cell. Events A3 and a5 provide both serving cell signal conditions and neighbor cell signal conditions to the base station (200). A3 is reported when the neighbor cell signal condition is better than the serving cell by at least one configured offset. Report a5 when serving cell signal condition is weaker than a configured threshold and neighbor cell signal condition is better than another network configured threshold. Thus, the source gNB can understand whether the neighboring cell can provide better service. However, in some cases, more than one event is required to reliably trigger a handover.

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

However, in case of conditional handover, a condition for performing handover is configured to the UE (100), and the UE (100) autonomously performs handover based on the condition. Thus, the CHO is under control of part of the base station (200). When the UE (100) performs CHO towards the target, there is no intelligence (intelligence) at the UE (100), unlike the intelligence of the base station (200) in conventional handover, where the base station (200) judiciously decides the handover of the UE (100) to a neighboring target cell based on such base station (200) intelligence (e.g., the load condition of the target). In conventional 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 switching, the conditions that trigger CHO execution are provided much earlier in time. It is possible that during this time the target cell load is low enough to allow more UEs (100) to access the cell. However, actual CHO execution occurs at a later time, by which time the load on the target unit may have changed. However, when the CHO triggers and the UE (100) performs handover to the target cell, the load in the target has increased. In this scenario, the service provided on the target cell may be worse/weaker than the service on the source cell.

To overcome this, it is necessary to infuse the UE (100) with some intelligence for making decisions on CHO execution. This may be achieved by introducing the requirement that a plurality of reporting configurations be fulfilled by the UE (100). For example, the UE (100) may be configured to trigger event a3 with the amount set to RSRP. When the UE (100) successfully satisfies a3, it knows that the signal strength of the neighbor cell is better than the serving cell/suitable for the serving UE (100). However, it does not know the load and quality of the neighboring cells. To enable the UE (100) to make an intelligent evaluation of the target cell, the base station (200) may configure event a4 with the trigger amount set to RSRQ. The RSRQ measurement provides an indication of the load on the target cell. Together, RSRP based A3 indicates that the target cell signal condition is good and RSRQ based a4 indicates that the load on the target cell is acceptable. Therefore, the handover is not more reliable than in the case of CHO execution based on a single condition/trigger.

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

a. A3/A5 based UE assisted handover where stronger neighbors are indicated in the MR, or

b. A4 based UE assisted handover, 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).

c. Blind HO based on a2, where no neighbors are indicated in the MR.

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

To manage and assist HO decisions, the source cell may configure multiple measurement report configurations for the same MO and ultimately make decisions based on the MR it receives from the UE (100). MR is not always A3/A5, but can also be A2/A4. In the above example, Beam Failure Recovery (BFR) is indicated as one of the possible consequences of sudden cell degradation (in FR 2). Typical values for time-to-trigger (TTT) configured in LTE deployments often vary between 256ms and 1024 ms. If BFR is triggered due to sudden drop of beam quality in a mobile scenario, a new RA preamble is transmitted every 10ms if RAR is not received, considering that PRACH resources are configured every 10ms (including time for monitoring RAR). Based on preambleTransMax, RA failure may occur before TTT is complete, and may result in RLF even in the case of CHO configuration.

The above examples are for illustrative purposes only, and the present application is not limited to this description. This combination of reporting configurations for CHO assessment may be done in any combination or the same/different reporting configurations with the same/different trigger quantities, the same/different RS types, etc. In an embodiment, the base station (200) may configure the UE with multiple CHO conditions.

As shown in fig. 4B, at S402B, the UE (100) sends a measurement report to the SgNB (300). At S404b, based on the measurement report, SgNB (300) sends a handover request for CHO to TgNB1(400 a). Based on the handover request, at S406b, the TgNB1(400a) performs an admission control procedure. Based on the admission control procedure, at S408b, the TgNB1(400a) sends a handover request confirm message to the SgNB (300). At S410b, the SgNB (300) sends the CHO configuration to the UE (100), and at S412b, the UE (100) performs CHO candidate evaluation. At S414b, the UE (100) sends an MR indicating a normal HO to the TgNB-2(400b) through the SgNB (300).

At S416b, SgNB (300) sends a handover request for normal HO to TgNB2(400 b). At S418b, the UE (100) sends an indication of the CHO-performed MR to TgNB-1(400a) through SgNB (300). Based on the handover request, at S420b, the TgNB2(400b) performs an admission control procedure. Based on the admission control procedure, at S422b, the TgNB2(400b) sends a handover request confirm message to the SgNB (300).

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

Fig. 5 shows that the base station (200) may configure the UE (100) with 1-bit indication (multiconditioniontrigger) and CHO condition configuration to provide the UE (100) with more decision freedom according to embodiments disclosed herein. To provide a more informed decision control to the UE (100), the base station (200) may configure the UE (100) with a 1-bit indication (multipleconomiontrigger in fig. 5) and a CHO condition configuration. If the indication is configured in the CHO configuration, it means that there are multiple reporting configurations, provided that CHO will be executed only if all reporting configurations are met. If this field is not present it means that only one reporting configuration is provided, or that multiple reporting conditions are provided, but if any configured reporting configuration is met, CHO may be performed. Fig. 5 also shows that the network is configuring multiple CHO conditions to the UE to enable the UE to evaluate candidate target cells for performing CHO.

Fig. 6 shows a sequence diagram according to embodiments disclosed herein, where the source cell continues to serve the UE (100) even after providing a handover command, until the expiration of a timer at the source cell (which corresponds to the T304 timer configured for the UE (100) to handover), or in the event of receiving a UE CONTEXT RELEASE message from the target cell upon successful completion of the path switch.

As shown in fig. 6, at S602, the UE (100) transmits a measurement report to the SgNB (300). At S604, based on the measurement report, SgNB (300) sends a handover request to TgNB (400). Based on the handover request, at S606, the TgNB (400) performs an admission control procedure. Based on the admission control procedure, at S608, the TgNB (400) sends a handover request confirm message to the SgNB (300). After receiving the handover request confirm message from the TgNB (400), the SgNB (300) transmits a HO command/synchronization reconfiguration message to the UE (100) at S610. 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 a timer T304.

At S616, SgNB (300) sends an SN status transfer message to TgNB (400), and at S618, SgNB (300) sends data forwarding to TgNB (400). At S620, 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 acknowledge message to the TgNB (400). At S626, the TgNB (400) sends a UE context release to the SgNB (300).

In an embodiment, the method may be used to identify a condition to stop transmission on a source cell during an eMBB-based handover. In release 14 make-before-break handover 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) is unaware of the time until which the UE (100) continues to monitor the DL channel from the source cell. This is because the UE (100) is assumed to have a single receive chain (single Rx) and cannot receive from both the source and target simultaneously. Therefore, it is not possible 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 with DL transmission are left to implementation.

In release 16, both LTE and NR are dedicated to the enhanced MBB procedure, where the UE (100) is expected to have 2 receive chains. Thus, the UE (100) may receive from both the source cell and the target cell simultaneously. As a result, the source may continue transmission on the source cell and the UE (100) may receive on the source cell until successful access to the target cell. Thus, it is possible to correctly identify when the source cell can stop transmission to the UE (100). One way is when the UE (100) releases the source cell connection and only performs actions on the target cell, the UE (100) indicates to the source cell via MAC CE or other uplink signaling method. However, this approach 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.

Another way to indicate the release of the source cell is that the target cell indicates to the source cell once the UE (100) successfully accesses the target cell (handover on target cell is complete). However, this approach may result in a delay in the indication to the source cell and introduce additional overhead from the target cell to the source cell requesting the source to suspend active new signaling from the source cell.

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, the source cell continues to serve the UE (100) even after the handover command is provided, until a timer at the source cell (which corresponds to a T304 timer configured for the UE (100) to handover) expires, or in the event of a UE CONTEXT RELEASE message being received from the target cell upon successful completion of the path switch. This is shown in fig. 6. In another embodiment, the source cell may continue to serve the UE (100) until a portion of the T304 timer.

In an embodiment, the method may be used to indicate the beam ID in accessibility measurements in logged Minimization of Driving Tests (MDT). In LTE, the accessibility measurements contain the number and location information of preambles transmitted during failed connection setup attempts, as well as other parameters. In beamforming systems like NR, a UE (100) may be within coverage of more than one beam. The UE (100) selects a beam for random access based on a threshold configured in the system information. Thus, different UEs receiving signals from the same beam set at the same location may 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 chooses to access the cell. In an embodiment, the SSB ID on which the UE (100) encounters a connection establishment failure is indicated to the base station (200) in the accessibility measurement as follows:

in LTE, accessibility measurements contain the number and location information of preambles transmitted during failed connection setup attempts and other parameters, and these can be reused for NR recovery failure reporting. In beamforming systems like NR, a UE (100) may be within coverage of more than one beam. The UE (100) selects a beam for random access based on a threshold configured in the system information. Thus, 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 chooses to access the cell. In another embodiment, the SSB id on which the UE (100) encounters a connection recovery failure is indicated to the base station (200) in the accessibility measurement as follows:

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

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

In another embodiment, the method may be used to indicate UE capabilities that support different enhanced mobility procedures for handover. There are a number of ways in which mobility interruption time can be reduced based on a make-before-break 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 capability and supported way to perform MBB based handover. This must be indicated as part of the UE capability. In an embodiment, a UE (100) has the capability to support one or both of a single stack-based enhanced MBB HO or a dual stack-based enhanced MBB HO.

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 operation on the source until a certain time. During this time, the target stack may be partially active or not active at all based on the UE capabilities. Upon successful access to the target cell, the UE (100) releases the protocol stack associated with the source cell and operates using only the protocol stack associated with the target.

In a dual-stack based 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. Both stacks are active simultaneously for only a short time to facilitate the transfer of resources/packets from the source cell to the target cell. The description indicating the capability of the UE supporting the mobility type is as follows:

in another embodiment, the method may be used to indicate the MBB type that the UE should apply for the configured handover. Since the UE (100) may support more than one type of MBB-based handover, i.e. single stack-based MBB HO and dual stack-based MBB HO, it is required to indicate to the UE (100) the type of handover that has to be performed when providing a synchronous reconfiguration. Thus, the base station (200) provides the type of MBB needed for the current handover based on several factors, which may include UE capabilities, outage requirements for ongoing service, deployment scenarios, etc. In an embodiment, the serving PCell indicates to the UE (100) the MBB type it must apply for the current handover.

This indication may be provided as part of the synchronization 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 follows:

In another embodiment, the method may optionally include an indication, wherein if the indication is included, the handover must be a dual stack based MBB HO, if the indication is not included (or vice versa), the handover must be a single stack based MBB HO, as follows:

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

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 elements.

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

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Thus, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments described herein.