Method and apparatus for supporting network optimization in next generation mobile communication system

Abstract

The disclosure relates to a communication technology and a system thereof that combine IoT technology with a 5G communication system to support a higher data transmission rate than a 4G system. Based on 5G communication technology and IoT-related technology, the disclosure can be applied to intelligent services (e.g., smart homes, smart buildings, smart cities, smart cars or connected cars, health care, digital education, retail businesses, security and safety-related services, etc.). The present invention provides a method and apparatus for implementing a handover operation and composing wireless connection failure information accompanying the handover operation.

Description

Technical Field

[0001] This disclosure relates to methods and apparatus for constituting handover operations and subsequent wireless connection failure information. Background Technology

[0002] Since the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems to meet the growing demand for wireless data services. Therefore, 5G or pre-5G communication systems are also referred to as "beyond 4G networks" or "post-LTE systems." To achieve high data transmission rates, the implementation of 5G communication systems in ultra-high frequency (millimeter wave (mmWave)) bands (e.g., the 60GHz band) is being considered. To mitigate path loss of radio waves and increase transmission distance in ultra-high frequency bands, beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive MIMO technologies are being discussed for 5G communication systems. Furthermore, in 5G communication systems, development is underway to improve system networks based on evolved small cells, advanced small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, cooperative multipoint (CoMP), and receiver interference cancellation. In addition, hybrid FSK (Frequency Shift Keying) and QAM (Four-way Amplitude Modulation) modulation and sliding window superposition coding (SWSC) have been developed as advanced coding and modulation (ACM) systems, as well as filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] On the other hand, the Internet, as a human-centric network for generating and consuming information, is now evolving into the Internet of Things (IoT) network, where distributed entities exchange and process information. The Internet of Everything (IoE) technology, combining IoT technology with cloud server connectivity and big data processing technology, has emerged. IoT implementation requires technological elements such as sensing technology, wired / wireless communication and network infrastructure, service interface technology, and security technology; therefore, technologies for connecting things are currently under research, such as sensor networks, machine-to-machine (M2M) communication, and machine-type communication (MTC). Such an IoT environment can provide intelligent Internet of Things (IT) services, creating new value for human life by collecting and analyzing data generated between connected things. Through the convergence and integration of existing information technology (IT) and various industrial applications, IoT can be applied to a wide range of fields, including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, healthcare, smart appliances, and advanced medical services.

[0004] Correspondingly, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine-to-machine (M2M) communication, and machine-type communication (MTC) can be implemented using beamforming, MIMO, and array antenna technologies corresponding to 5G communication technologies. Cloud radio access networks (cloud RAN), as an application of the aforementioned big data processing technologies, can also be considered an example of the convergence between 5G and IoT technologies.

[0005] Furthermore, unlike general handover, condition-based handover is characterized by the fact that, upon receiving configuration information from the base station instructing the UE to perform handover, the UE does not immediately execute the handover operation. Instead, it executes the handover operation only when predetermined conditions are met. In this case, since the UE can grasp changes in channel quality status most quickly, determining the start time of the handover operation may help minimize the probability of handover failure. Summary of the Invention

[0006] Technical issues

[0007] In the event of continuous conditional handover and continuous radio link failures (RLFs), the RLF report stored when the first RLF occurs may be deleted based on subsequent RLF occurrences, which may result in mobile communication service providers not being able to accurately detect the first RLF situation.

[0008] One aspect of this disclosure is to provide a method for configuring multiple RLF reports in the event of consecutive RLFs occurring during a conditional handover process.

[0009] Technical solution

[0010] According to embodiments of this disclosure, in order to solve the above-mentioned problems, a method performed by a terminal in a wireless communication system may include: identifying that the terminal supports condition-based handover; receiving configuration information about condition-based handover from a base station; performing handover to a first cell if predetermined conditions are identified based on the configuration information as being met; performing a cell selection operation if handover to the first cell fails; performing handover to a second cell if a second cell is selected based on the cell selection operation; and sending a radio link failure (RLF) report to the base station based on the establishment of a radio resource control (RRC) connection with the base station if handover to the second cell fails, wherein the RLF report includes first RLF information associated with the handover failure to the first cell and second RLF information associated with the handover failure to the second cell.

[0011] Furthermore, according to embodiments of this disclosure, a method performed by a base station in a wireless communication system may include: receiving capability information from a terminal indicating support for conditional handover; determining, based on the capability information, to trigger conditional handover for the terminal; sending configuration information regarding conditional handover to the terminal; and, in the case of establishing a radio resource control (RRC) connection with the terminal, receiving a radio link failure (RLF) report from the terminal based on the configuration information, wherein the RLF report includes first RLF information associated with a handover failure to a first cell and second RLF information associated with a handover failure to a second cell.

[0012] Furthermore, according to embodiments of this disclosure, a terminal in a wireless communication system may include: a transceiver; and a controller configured to: identify that the terminal supports condition-based handover; control the transceiver to receive configuration information about condition-based handover from a base station; perform handover to a first cell if a predetermined condition is identified based on the configuration information; perform a cell selection operation if handover to the first cell fails; perform handover to a second cell if a second cell is selected based on the cell selection operation; and control the transceiver to send a radio link failure (RLF) report to the base station based on a radio resource control (RRC) connection established with the base station if handover to the second cell fails, wherein the RLF report includes first RLF information associated with the handover failure to the first cell and second RLF information associated with the handover failure to the second cell.

[0013] Furthermore, according to embodiments of this disclosure, a base station in a wireless communication system may include: a transceiver; and a controller configured to: control the transceiver to receive capability information indicating support for conditional handover from a terminal; determine, based on the capability information, to trigger conditional handover of the terminal; control the transceiver to send configuration information regarding conditional handover to the terminal; and, in the case of establishing a Radio Resource Control (RRC) connection with the terminal, control the transceiver to receive a Radio Link Failure (RLF) report based on the configuration information from the terminal, wherein the RLF report includes first RLF information associated with a handover failure to a first cell and second RLF information associated with a handover failure to a second cell.

[0014] Technical effect

[0015] According to embodiments of this disclosure, even if consecutive RLFs occur during a conditional handover process, the mobile communication service provider can accurately grasp information about all RLF situations. Attached Figure Description

[0016] Figure 1 This is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0017] Figure 2 This is a diagram illustrating the radio access state transition in a next-generation mobile communication system according to embodiments of the present disclosure.

[0018] Figure 3 This is a diagram illustrating the techniques for collecting and reporting cell measurement information according to embodiments of this disclosure.

[0019] Figure 4 This is a diagram illustrating a method for collecting and reporting cell measurement information according to an embodiment of the present disclosure.

[0020] Figure 5 This is a flowchart of the operation of collecting and reporting cell measurement information according to embodiments of the present disclosure.

[0021] Figure 6 This is a flowchart of a general handover operation according to an embodiment of the present disclosure.

[0022] Figure 7 This is a flowchart of a condition-based handover operation according to an embodiment of the present disclosure.

[0023] Figure 8 This is a flowchart of the operation of an indicator that records the execution status of a late CHO according to an embodiment of the present disclosure.

[0024] Figure 9 This is a flowchart of UE operation of an indicator that records the execution status of a delayed CHO according to an embodiment of the present disclosure.

[0025] Figure 10 This is a flowchart of a conventional operation for recording RLF information in the event of a handover failure based on continuous conditions, according to embodiments of the present disclosure.

[0026] Figure 11 This is a flowchart of the operation of recording RLF information in the event of a handover failure based on continuous conditions, according to an embodiment of the present disclosure.

[0027] Figure 12 This is a flowchart of a UE operation that records RLF information in the event of a handover failure based on continuous conditions, according to an embodiment of this disclosure.

[0028] Figure 13 This is a diagram illustrating the method by which a UE performs cell reselection according to this disclosure.

[0029] Figure 14 This is a flowchart illustrating the operation of an indicator that has been affected by measurement results recorded according to power-saving techniques, according to embodiments of the present disclosure.

[0030] Figure 15This is a flowchart illustrating the operation of an indicator that has been affected by the measurement results recorded according to the configuration of interFreqTargetList, according to an embodiment of this disclosure.

[0031] Figure 16 This is a flowchart illustrating the operation of an indicator that has been affected by measurement results recorded according to power-saving techniques, according to embodiments of the present disclosure.

[0032] Figure 17 This is a block diagram illustrating the internal structure of a UE that applies this disclosure.

[0033] Figure 18 This is a block diagram illustrating the configuration of a base station according to the present disclosure. Detailed Implementation

[0034] The operating principles of this disclosure will be described in detail below with reference to the accompanying drawings. In describing this disclosure, detailed descriptions of relevant known functions or constructions will be omitted if they unnecessarily obscure the essential points of this disclosure. Furthermore, the terms described below are defined in consideration of their function in this disclosure and may vary depending on the intent or habit of the user or operator. Therefore, they should be defined based on the entirety of this disclosure's description.

[0035] In describing this disclosure below, detailed explanations of any known functions or configurations that unnecessarily obscure the essential points of this disclosure will be omitted. Embodiments of this disclosure will be described below with reference to the accompanying drawings.

[0036] In describing this disclosure below, detailed explanations of any known functions or configurations that unnecessarily obscure the essential points of this disclosure will be omitted. Embodiments of this disclosure will be described below with reference to the accompanying drawings.

[0037] Figure 1 This is a diagram showing the structure of a next-generation mobile communication system.

[0038] refer to Figure 1 As shown in the figure, the radio access network of the next-generation mobile communication system (New Radio (NR)) consists of a new radio node B (hereinafter referred to as gNB) 1a-10 and a new radio core network (AMF) 1a-05. New radio user equipment (hereinafter referred to as NR UE or terminal) 1a-15 accesses the external network through gNB 1a-10 and AMF 1a-05.

[0039] exist Figure 1In this context, the gNB corresponds to the Evolved Node B (eNB) in the existing LTE system. The gNB connects to the NR UE on the radio channel, thus providing superior service compared to existing Node Bs (1a-20). Because all user services in next-generation mobile communication systems share a channel, a device is needed to perform scheduling by combining state information (such as the buffer state, available transmission power state, and channel state of each UE), and gNBs 1a-10 are responsible for this. A gNB typically controls multiple cells. To achieve ultra-high-speed data transmission compared to existing LTE, the gNB can have the maximum bandwidth available or even greater, and beamforming technology can be additionally adopted, taking into account Orthogonal Frequency Division Multiplexing (hereinafter referred to as "OFDM") as the radio access technology. Furthermore, an Adaptive Modulation and Coding (hereinafter referred to as "AMC") scheme that determines the modulation scheme and channel coding rate is applied to match the UE's channel state.

[0040] The AMF 1a-05 performs mobility support, bearer configuration, and QoS configuration functions. The AMF is responsible not only for UE mobility management but also for various control functions and connects to multiple base stations. Furthermore, next-generation mobile communication systems can be interlocked with existing LTE systems, and the AMF connects to the MME 1a-25 via a network interface. The MME connects to the eNB 1a-30, which acts as an existing base station. UEs supporting LTE-NR dual connectivity can send data to and receive data from both the gNB and eNB, while maintaining connectivity with the eNB (1a-35).

[0041] Figure 2 This is a diagram illustrating the transition of radio access states in next-generation mobile communication systems.

[0042] Next-generation mobile communication systems have three Radio Resource Control (RRC) states. Connected mode (RRC_CONNECTED) 1b-05 corresponds to a radio access state where the UE can perform data transmission / reception. Idle mode (RRC_IDLE) 1b-30 corresponds to a radio access state where the UE monitors whether it has sent a paging message to itself. These two modes correspond to radio access states even applied to existing LTE systems, and their detailed technology is the same as that of existing LTE systems. In next-generation mobile communication systems, a new inactive (RRC_INACTIVE) radio access state 1b-15 has been defined. In the RRC_INACTIVE radio access state, the UE context is maintained in both the base station and the UE, and paging based on the Radio Access Network (RAN) is supported. The characteristics of the new radio access state are arranged as follows.

[0043] -Cell reselection mobility;

[0044] - A CN-NR RAN connection (two C / U planes) has been established for the UE;

[0045] - The UE AS context is stored in at least one gNB and UE;

[0046] - Paging is initiated by NR RAN;

[0047] - RAN-based notification areas are managed by NR RAN;

[0048] -NR RAN knows the RAN-based notification area to which the UE belongs;

[0049] A new RRC_INACTIVE radio access state can be transitioned to either connected or idle mode using a specific procedure. The mode switches from RRC_INACTIVE to connected mode according to the recovery procedure, and from connected mode to RRC_INACTIVE mode again using a release procedure that includes pause configuration information (1b-10). During the above process, one or more RRC messages are sent and received between the UE and the base station, and the process consists of one or more operations. Furthermore, after the recovery procedure (1b-20), the mode can be switched from RRC_INACTIVE to idle mode via a release procedure. The switching between connected and idle modes follows existing LTE technology. That is, mode switching is performed through an establishment or release procedure (1b-25).

[0050] Figure 3 This is a diagram illustrating the techniques for collecting and reporting cell measurement information as described in this disclosure.

[0051] During network establishment or optimization, mobile communication service providers typically go through the process of measuring signal strength in the expected service area and, based on this, deploying or repositioning base stations within the service area. Service providers load signal measurement equipment into vehicles and collect cell measurement information within the service area, thus requiring significant time and money. Generally, this process is conducted using vehicles and is commonly referred to as drive testing.

[0052] The UE is equipped with the ability to measure base station signals to support cell reselection or handover operations, or to facilitate serving cell additions during inter-cell movement. Therefore, the UE within the serving area can be used instead of drive testing; this is known as Minimized Drive Testing (MDT). Service providers can configure MDT operations for specific UEs through several network configuration devices, and the UE collects and stores signal strength information from the serving cell and peripheral cells in connected mode (RRC_Connected), idle mode (RRC_Idle), or inactive mode (RRC_Inactive). In addition, the UE stores various information such as location, time, and signal quality information. When the UE is in connected mode, the stored information can be reported to the network and transmitted to a specific server.

[0053] MDT operations can be simply divided into Immediate MDT and Logged MDT.

[0054] The defining characteristic of real-time MDT is the immediate reporting of collected information to the network. Because the reporting must be performed instantly, only connected UEs can execute the reports. Typically, the RRM measurement procedures used to support handover and servicing cell addition operations are reused, and location and time information are reported separately.

[0055] The characteristic of recorded MDT is that it stores the collected information without immediately reporting it to the network, and then reports the stored information after the UE switches to connected mode. Typically, a UE in idle mode cannot immediately report to the network; it performs this operation. Recorded MDT is performed by UEs in inactive modes introduced in next-generation mobile communication systems. When a particular UE is in connected mode, the network provides the UE with configuration information for performing recorded MDT operations, and the UE collects and stores this configuration information after switching to idle or inactive mode.

[0056] RRC status Real-time MDT RRC_Connected Recorded MDT RRC_Idle, RRC_Inactive

[0057] Figure 4 This is a diagram illustrating the method used in this disclosure for collecting and reporting cell measurement information.

[0058] UE 1d-05 switches from idle mode or inactive mode 1d-10 to connected mode 1d-15. In connected mode, the UE collects MDT data through immediate MDT operations and reports the collected MDT data to the base station. The base station provides the UE, which has switched to connected mode, with recorded MDT configuration information (1d-20) executed in idle mode or inactive mode. The configuration information is included in a specific RRC message to be sent to the UE, and the UE that has received this message drives the first timer (1d-55). The UE executes the recorded MDT operations in the idle mode or inactive mode portion until the first timer expires.

[0059] The value of the first timer is included in the recorded MDT configuration information. If the UE is switched to idle mode or inactive mode, the UE executes the recorded MDT (1d-25) according to the received configuration information. The UE stores specific information collected for each configuration period and recording interval 1d-35 (1d-30 and 1d-45). Furthermore, if valid location information is collected 1d-40, the UE should also store the same information. If no specific time 1d-50 has elapsed after information collection, the location information is determined to be valid. The specific time is shorter than or equal to the recording interval.

[0060] Even if the first timer has not expired, when the UE switches to connected mode, the UE suspends the recorded MDT operations that have already been performed (1d-60). However, even during the connected mode portion, the first timer continues to run without pausing. That is, the first timer is continuously run regardless of changes in the RRC state. However, the first timer stops if the UE can no longer store MDT data due to insufficient memory for storing MDT data, or if the recorded MDT configuration information is released. The recorded MDT configuration information is released when another recorded MDT configuration information is provided from the serving RAT or another RAT, or when the UE is disconnected or its power is cut off. During RRC connection establishment or RRC connection recovery, the UE reports to the base station that the UE has collected information (MDT data) stored by the UE itself using an RRC establishment complete message or an RRC recovery complete message (1d-65).

[0061] The connection establishment process is the process by which the UE switches from idle mode to connected mode. Typically, this process consists of three operations and uses three types of RRC messages.

[0062] Step 1: The UE sends an RRC establishment request message to the base station.

[0063] Step 2: The base station sends an RRC establishment message to the UE.

[0064] Step 3: The UE sends an RRC establishment complete message to the base station.

[0065] The connection restoration process is the process by which a UE switches from inactive mode to connected mode. Typically, this process consists of three operations and uses three types of RRC messages.

[0066] Step 1: The UE sends an RRC recovery request message to the base station.

[0067] Step 2: The base station sends an RRC recovery message to the UE.

[0068] Step 3: The UE sends an RRC recovery complete message to the base station.

[0069] Even during RRC connection re-establishment and handover processes other than connection establishment or connection recovery procedures, the UE reports information to the target base station indicating that the UE has collected information. If a recorded MDT has been established but no information has been collected and stored, the UE omits this report. If needed, the base station that has received the report can request the UE to report the MDT data stored in the UE. The UE should continuously store MDT data that has not been reported within a specific time period.

[0070] If the UE switches back to idle or inactive mode and the first timer has not yet expired, the recorded MDT operation resumes (1d-70). If the first timer has expired, the recorded MDT operation stops (1d-75). The UE that has stopped the above operation drives the second timer (1d-80) and retains the stored MDT data until the timer expires. Whether to delete the stored MDT data after the timer expires is determined by the UE implementation. The value of the second timer is included in the recorded MDT configuration information, or it is not configured, but a predefined value is applied.

[0071] If the UE switches back to connected mode, the UE reports to the base station that it has collected information (MDT data) stored by itself (1d-85). In this case, the base station requests the UE to report the MDT data stored by the UE using a specific RRC message (1d-90). In response, the UE includes the stored MDT data in the specific RRC message and reports the message to the base station (1d-95).

[0072] Figure 5 This is a flowchart of the operations for collecting and reporting cell measurement information in this disclosure.

[0073] UE 1e-05 establishes a connection with base station 1e-10 (1e-15). The UE can provide the base station with UE capability information (1e-20) and can indicate whether the base station supports MDT operations and what frequencies the base station can measure. The base station includes the configuration information required to perform the recorded MDT operations in a specific RRC message and sends the RRC message to the UE (1e-25). For example, the configuration information includes at least one of the following.

[0074] - Tracking Reference Information

[0075] - Track and record session reference information

[0076] - Tracking Collection Entity (TCE) ID Information: The base station sends the MDT data information reported by the UE to the data server specified by the TCE ID.

[0077] - Absolute Time Information: Provides the absolute time in the current cell for recording MDT configuration information.

[0078] - Area Configuration: This refers to the area information that enables the collection and storage of measurement information through recorded MDT operations, and is indicated on a cell-by-cell basis. Furthermore, this can include RAT information used for collecting measurement information. The lists included in the RAT information can be blacklists or whitelists. In the case of a blacklist, cell measurement information is collected for RATs not included in the list. In the case of a whitelist, cell measurement information is not collected for RATs not included in the list.

[0079] - Recording duration: This is the value of the first timer. When the timer is driven, the recorded MDT operations are executed in idle or inactive mode.

[0080] - Recording interval: This is the interval at which the collected information is stored.

[0081] -MDT PLMN List (i.e., plmn-IdentityList): This is a list of PLMN information, including not only information for performing MDT operations on records but also information for reporting whether MDT data is stored and the PLMN information for MDT data.

[0082] - An indicator that specifies whether the recording MDT operation is performed in idle mode, inactive mode, or both. This indicator may specify the RRC state used to perform the recording MDT operation, or it may be defined as always performing the recording MDT operation in idle mode and inactive mode without an indicator. The UE performs the recording MDT operation only in the RRC state indicated by the indicator.

[0083] - An indicator indicating whether beamlevel measurement information is collected and stored. Beam antennas can be used in next-generation mobile communication systems. Regarding the frequency at which beam-based operations are performed without an indicator, it can be defined that beamlevel measurements are always collected and stored.

[0084] - Information about the maximum number of beams collected and stored, and information about the minimum signal strength of the stored beams. The UE may omit storing information about beams weaker than the minimum signal strength. If all beams are weaker than the configured minimum signal strength, the UE may store information about the beam with the strongest signal strength, or may include an indicator indicating that all beams are weaker than the configured minimum signal strength.

[0085] - An indicator that suggests whether the MDT retrieval operation can be triggered during the second step of the RRC recovery process.

[0086] The UE, having received the recorded MDT configuration information, activates the first timer (1e-30). The value of the first timer is configured to be the same as the recording duration. The base station switches the UE to idle mode or inactive mode using an RRC release message (1e-35). Depending on which RRC state the UE switches to, the RRC release message includes configuration information for the operation in that RRC state. If the first timer is being activated, the UE performs the recorded MDT in idle mode or inactive mode (1e-40). For example, the UE measures the signal strength of the serving cell and neighboring cells and obtains location information. Furthermore, if beam level measurement is configured, the UE collects and stores the signal strength values ​​of beams greater than the configured minimum values ​​in the serving cell and neighboring cells. Here, the maximum number of beams that can be stored is configured or predefined. Signal strength refers to Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), or Signal-to-Interference-Noise Ratio (SINR). The UE stores the information collected for each recording interval. Afterward, if the first timer expires (1e-45), the UE stops the recorded MDT operation (1e-50).

[0087] When the UE is in idle or inactive mode via RRC release message and receives RAN or CN paging from the base station, or MO data transmission is activated, the UE initiates a setup or recovery procedure to switch from idle or inactive mode to connected mode.

[0088] The setup or recovery process can consist of the following operations.

[0089] - Step 1: The UE sends an RRC establishment request message or an RRC recovery request message (1e-55) to the base station.

[0090] - Step 2: The base station sends an RRC establishment message or an RRC recovery message (1e-60) to the UE.

[0091] - Step 3: The UE sends an RRC establishment complete message or an RRC recovery complete message (1e-65) to the base station.

[0092] The UE includes an indicator indicating whether MDT data stored by the UE itself exists in the RRC establishment completion message or RRC recovery completion message. If needed, the base station that has received the RRC establishment completion message requests an MDT data report using a specific RRC message, such as UEInformationRequest (1e-70). The UE that has received the request reports the MDT data using a specific RRC message, such as UEInformationResponse (1e-75).

[0093] In this disclosure, a typical handover operation is characterized by the UE immediately performing the handover operation upon receiving configuration information from the base station instructing it to perform the handover. In contrast, a conditional handover operation is characterized by the UE not immediately performing the handover operation upon receiving configuration information from the base station instructing it to perform the handover, but rather performing the handover operation when predetermined conditions are met. Due to this characteristic, conditional handover is called conditional handover (CHO). Since the UE can most quickly grasp changes in channel quality status, determining the start time of the handover operation is advantageous in minimizing the probability of handover failure. Therefore, conditional handover is considered a more advanced technique compared to typical handover. Typical handover may consider only one target cell, while conditional handover may consider one or more target cells. The network determines the number of target cells to consider in conditional handover.

[0094] Figure 6 This is a flowchart of a general handover operation according to an embodiment of the present disclosure.

[0095] In connected mode, UE 1f-05 performs data transmission / reception operations with source cell 1f-10 (1f-20). The UE receives a specific RRC message (1f-25) from the source cell, which includes measurement configuration information.

[0096] The UE measures the signal quality of the serving cell and neighboring cells by applying measurement configuration information (1f-30), and periodically or when a configured event occurs, reports the collected cell measurement information to the source cell (1f-35).

[0097] The source cell determines whether to trigger a general handover operation based on the reported cell measurement information (1f-40). For example, if event A3 is met (a neighbor becomes better offset than SpCell) and cell measurement information is reported accordingly, the source cell can determine a general handover. If a general handover is determined to be triggered, the source cell requests a general handover from a target cell (1f-15) via a specific inter-node message (1f-45). The target cell, having received the request, accepts the request using specific admission control (1f-50) and sends the handover configuration information required for the general handover operation to the source cell (1f-55). The source cell includes the handover configuration information and additional configuration information received from the target cell in a specific RRC message and sends the RRC message to the UE (1f-60). The configuration information includes the target cell ID, frequency information, configuration information required for random access operations to the target cell (dedicated preamble information and dedicated radio resource information), transmission power information, and C-RNTI information used in the target cell.

[0098] Upon receiving the handover configuration information, the UE immediately executes the random access procedure to the target cell and starts timer T304 (1f-65). Furthermore, the UE stops data transmission / reception operations with the source cell (1f-70). The UE also sends the provided preamble (1f-75). If no dedicated preamble is provided, the UE sends one of the preambles currently in use based on contention. The target cell, having received the preamble, sends a Random Access Response (RAR) message to the UE (1f-85). The UE sends msg 3 to the target cell (1f-85) using the UL clearance information included in the RAR. msg 3 includes an RRCReconfigurationComplete message. If the random access procedure completes successfully, the UE considers the general handover to be successful and stops driving timer T304. The UE then performs data transmission / reception operations with the target cell (1f-90). If the general handover is not successfully completed before timer T304 expires (1f-95), the UE considers the handover to have failed. In this situation, the UE declares an RLF and performs a rebuild operation (1f-98). When declaring an RLF, the UE records the useful information that can be collected at that time, and when it later connects to a cell, it can report the same information as reported by the RLF.

[0099] Figure 7 This is a flowchart of a condition-based handover operation according to an embodiment of the present disclosure.

[0100] UE 1g-05 reports its own capability information to source cell 1g-10 (1g-16). The capability information indicates whether the UE supports condition-based handover. The UE receives a specific RRC message (1g-17) from the source cell, which includes measurement configuration information. The UE measures the signal quality of the serving cell and neighboring cells by applying the measurement configuration information (1g-18) and periodically or when a configured event occurs, reports the collected cell measurement information to the source cell (1g-19).

[0101] The source cell determines whether to trigger a condition-based handover operation based on the reported cell measurement information (1g-20). To configure condition-based handover, the UE is required to support condition-based handover.

[0102] If a condition-based handover is triggered, the source cell requests a condition-based handover from one or more target cells (1g-15) via a specific inter-node message (1g-25). Target cells that have received the request accept it through specific admission controls (1g-30) and send the handover configuration information required for the condition-based handover operation to the source cell (1g-35). Target cells that do not accept the request are excluded from the condition-based handover.

[0103] The source cell includes the handover configuration information and additional configuration information received from the target cell in a specific RRC message and sends the RRC message to the UE (1g-40). The configuration information includes the target cell ID, frequency information, configuration information required for random access operations to the target cell (dedicated preamble information and dedicated radio resource information for each target cell), transmission power information, C-RNTI information used in each target cell, and conditions for triggering random access operations to each target cell.

[0104] Here, the conditions can vary depending on the target cell, and multiple conditions can be configured for a single target cell. If the suitable cell found through the first cell selection operation after a handover failure is one of the candidate target cells for conditional handover, the attemptCondReconfig field included in the configuration information is an indicator of whether to perform conditional handover to the cell.

[0105] The UE, having received the handover configuration information, assesses whether the provided conditions are met (1g-45). Until the conditions are met, the UE maintains data transmission / reception operations with the source cell (1g-50). If the conditions associated with a specific target cell are met (1g-55), the UE performs a random access procedure to the target cell and drives timer T304 (1g-60). For example, if event A3 (a neighbor becomes better offset than SpCell) has been configured as a condition and has been met, the UE sends the provided preamble to the relevant target cell (1g-65). If no dedicated preamble is provided, the UE sends one of the preambles currently in use based on contention. The target cell, having received the preamble, sends a Random Access Response (RAR) message to the UE (1g-70). The UE sends msg 3 to the target cell using the UL clearance information included in the RAR (1g-75). msg 3 includes the RRCReconfigurationComplete message.

[0106] If the random access procedure completes successfully, the UE considers the conditional handover to have been successfully completed and stops driving timer T304. If the conditional handover has not successfully completed by the timer T304 expires (1g-80), the UE considers the handover to have failed. In this case, the UE declares an RLF and performs a reconstruction operation (1g-85). During the reconstruction operation, if a suitable cell found through the cell selection operation is one of the candidate target cells for conditional handover, the UE can perform handover to that cell again (1g-90).

[0107] If the handover is successful, the UE deletes its handover configuration information. In response to the successful handover report from the target cell, the source cell deletes the UE's context information. The success of the handover can even be determined by the UE context release message, an inter-node message sent from the target cell to the source cell. Furthermore, the source cell instructs other candidate target cells included in the handover configuration information to delete the handover configuration information (or UE context information) (or notifies the candidate target cells that the handover configuration information is no longer valid). Even without an instruction from the source cell, a candidate target cell itself can delete its handover configuration information after a specific period of time following the receipt of the handover request.

[0108] This disclosure proposes a method for logging and reporting specific information through an RLF report or a recorded MDT.

[0109] Figure 8 This is a flowchart illustrating the operation of an indicator that records the execution status of a delayed CHO according to an embodiment of this disclosure.

[0110] In this disclosure, the delayed CHO execution scenario is defined as follows.

[0111] - Delayed CHO Execution: This occurs when a UE, having already received conditional handover configuration information from the base station, evaluates whether the configuration conditions are met based on the configuration information, and an RLF (Regular Life Failure) occurs.

[0112] In other words, when an RLF occurs, preventing the UE from performing handover at the optimal time due to inappropriate base station configuration conditions, this is referred to as a delayed Choo execution. With the above definition, additional conditions can be added. For example, if a suitable cell found after the UE declares an RLF, while meeting the definition, is one of the candidate target cells indicated in the conditional handover configuration information, this can be considered a delayed Choo execution. When a delayed Choo execution occurs, the mobile communication service provider needs to be aware of this. A mobile communication service provider that has recognized the scenario can appropriately adjust the conditional parameters applied to conditional handover. A feature of this embodiment is that, in the case of a final Choo execution, an indicator indicating such a situation is included in the RLF report and reported to the base station.

[0113] UE 1h-05 receives configuration information regarding condition-based handover from source base station 1h-10 (1h-20). The UE that has received this information evaluates whether the configured conditions are met (1h-25). If a radio link failure occurs before the conditions are met, an RLF is declared (1h-30). The radio link failure is determined by the UE through Radio Link Monitoring (RLM) operations.

[0114] In this scenario, for an RLF, the UE determines whether condition-based handover has been configured and whether the corresponding handover has not yet been performed (1h-35). If so, the UE stores a 1-bit indicator indicating delayed CHO execution in the content to be included in the RLF report (1h-40). The stored RLF content at the time of RLF declaration is shown in Table 1 below.

[0115] [Table 1]

[0116]

[0117] Subsequently, the UE connects to a specific base station through the RRC establishment, RRC recovery, and RRC reconstruction processes (1h-45). When storing RLF content, the UE includes an availability indicator for the RLF content in the RRCSetupComplete, RRCResumeComplete, and RRCReestablishmentComplete messages (1h-50). The base station requests the stored RLF content from the UE using a UEInformationRequest message (1h-55). The UE, having received the request, reports the RLF content being stored using a UEInformationResponse message (1h-60). This reporting of RLF content is referred to as an RLF report.

[0118] Figure 9 This is a flowchart of UE operation of an indicator that records the execution status of a delayed CHO according to an embodiment of the present disclosure.

[0119] In step 1i-05, the UE identifies that a radio link failure has occurred.

[0120] In steps 1i-10, the UE determines whether a condition-based handover has been configured by evaluating whether the conditions are met, and whether the handover has not been performed because no conditions have been met (in other words, the UE determines whether a delayed CHO execution has occurred).

[0121] In steps 1i-15, if the delayed CHO execution does not occur, the UE stores the traditional RLF content.

[0122] In steps 1i-20, if a delayed CHO execution has already occurred, the UE will store the indicator indicating that a delayed CHO execution has occurred along with the traditional RLF content.

[0123] In steps 1i-25, the UE connects to a base station.

[0124] In steps 1i-30, the UE reports to the base station an availability indicator that instructs the UE to store the RLF report.

[0125] In steps 1i-35, the base station requests the UE to report an RLF report.

[0126] In steps 1i-40, the UE reports an RLF report to the base station.

[0127] Figure 10 This is a flowchart of a conventional operation for recording RLF information in the event of a handover failure based on continuous conditions, according to embodiments of the present disclosure.

[0128] UE 1j-05 receives configuration information regarding conditional handover from source base station 1j-10 (1j-20). This configuration information includes the target cell ID, frequency information, configuration information required for random access operations to the target cell (dedicated preamble information and dedicated radio resource information for each target cell), transmission power information, C-RNTI information used in each target cell, and conditions for triggering random access operations to each target cell. These conditions may vary depending on the target cell, and multiple conditions may be configured for a single target cell. If, after a handover failure, a suitable cell found through the first cell selection operation is one of the candidate target cells for conditional handover, the attemptCondReconfig field included in the configuration information is an indicator indicating whether conditional handover to the cell should be performed.

[0129] The UE, having received the handover configuration information, assesses whether the provided conditions (1j-25) are met. Until the conditions are met, the UE maintains data transmission / reception operations with the source cell. If the conditions associated with a specific target cell (1j-30) are met, the UE performs a random access procedure for the target cell and drives timer T304 (1j-35). For example, if event A3 (a neighbor becomes better offset than SpCell) has been configured as a condition and has been met, the UE sends the provided preamble to the relevant target cell. If no dedicated preamble is provided, the UE sends one of the preambles currently in use based on contention. The target cell, having received the preamble, sends a Random Access Response (RAR) message to the UE. The UE sends msg 3 (or PUSCH) to the target cell using the UL clearance information included in the RAR. msg 3 includes the RRCReconfigurationComplete message.

[0130] If the random access procedure is successfully completed, the UE considers the conditional handover to be successfully completed and stops driving timer T304. If the conditional handover has not been successfully completed by the timer T304 expires (1j-40), the UE considers the handover to have failed. In this case, the UE declares an RLF (1j-45) and stores the aforementioned RLF content (1j-50).

[0131] If the suitable cell found through the cell selection operation is one of the candidate target cells for conditional handover, the UE can perform handover to that cell again (1j-55). In this case, timer T304 is driven again (1j-65), and if the timer expires (1j-70), the RLF is declared again (1j-80). In this case, the existing stored RLF content is deleted, and the RLF content corresponding to the most recent RLF is stored (1j-80).

[0132] Subsequently, the UE connects to a specific base station through the RRC establishment, RRC recovery, and RRC reconstruction procedures (1j-85). When storing RLF content, the UE includes an availability indicator of the RLF content in the RRCSetupComplete, RRCResumeComplete, and RRCReestablishmentComplete messages (1j-90). The base station requests the stored RLF content from the UE using a UEInformationRequest message (1j-92). The UE, having received the request, reports the RLF content being stored using a UEInformationResponse message (1j-95).

[0133] As is the case in conventional operations, when a first RLF occurs, the stored RLF report is deleted based on subsequent RLF occurrences. Therefore, mobile communication service providers cannot accurately identify the first RLF situation. This disclosure proposes a method for configuring multiple RLF reports in the event of consecutive RLFs during a conditional handover process. Specifically, when a second RLF occurs, the RLF report corresponding to the first RLF remains unchanged, or is supplemented / corrected without being deleted, and predefined content is stored in the RLF report corresponding to the second RLF. In this disclosure, the RLF report corresponding to the first RLF is referred to as the first RLF report, and the RLF report corresponding to the second RLF is referred to as the second RLF report.

[0134] When multiple RLF reports are configured, several options are possible.

[0135] Option 1: All predefined content is stored in two RLF reports. However, in this case, duplicate information may be stored in both RLF reports. Furthermore, existing content may not fit into a particular RLF report.

[0136] Option 2: Duplicate information may be stored in only one RLF report, while the rest of the information may be stored in two RLF reports.

[0137] In both the first and second RLF reports, the information related to the source cell can be the same. This information corresponds to c-RNTI, failedPCellId-EUTRA, and previousPCellId.

[0138] Furthermore, information related only to radio link failures and not to handover failures need not be included in the two RLF reports. This information corresponds to connectionFailureType, csi-rsRLMConfigBitmap, rlf-Cause, and ssbRLMConfigBitmap.

[0139] The information listed above will only be included in one of the two RLF reports. For example, the information may be included in the first RLF report.

[0140] Specifically, it might be more appropriate to include only certain information in the second RLF report. This information corresponds to noSuitableCellFound and reconnectCellId.

[0141] Furthermore, depending on which RLF report the information is included in, the following information requires different definitions.

[0142] The timeConnFailure information is time information from the time the handover was executed until the connection failed. When included in the first RLF report, the information indicates the time from the time the first handover was executed until the first handover failed, and when included in the second RLF report, the information indicates the time from the time the second handover was executed until the second handover failed.

[0143] The `timeSinceFailure` information represents the time elapsed from the handover failure until the reporting of the RLF report. When included in the first RLF report, the information indicates the time elapsed from the execution of the first handover until the reporting of the RLF report; similarly, when included in the second RLF report, the information indicates the time elapsed from the execution of the second handover until the reporting of the RLF report. Furthermore, if a second handover failure occurs, the corresponding timer can be restarted.

[0144] The `timeUntilReconnection` information represents the time until the UE switches back to connected mode after a handover failure. When included in the first RLF report, the information indicates the time from the first handover execution until the UE switches back to connected mode; similarly, when included in the second RLF report, the information indicates the time from the second handover execution until the UE switches back to connected mode. Furthermore, in the event of a second handover failure, the corresponding timer can be restarted.

[0145] Option 3: Store only simple information in one RLF report, and store all predefined content in other RLF reports.

[0146] For example, an RLF report may include only specific information, such as a 1-bit indicator or failedPCellId, to identify whether an RLF has occurred, and all predefined information may be stored in other RLF reports.

[0147] The content corresponding to the first RLF report and the second RLF report can be stored together in the UE variable VarRLF-Report, or it can be stored separately in a separate UE variable (e.g., VarRLF-REportExt) for the second RLF report.

[0148] Figure 11 This is a flowchart of the operation of recording RLF information in the event of a handover failure based on continuous conditions, according to an embodiment of the present disclosure.

[0149] UE 1k-05 reports its own capability information to source cell 1k-10 (1k-25). The capability information indicates whether the UE supports conditional handover. In addition, the capability information can indicate whether the UE has the ability to configure multiple RLF reports in the event of consecutive RLFs during conditional handover.

[0150] The UE receives a specific RRC message (1k-30) from the source cell, which includes measurement configuration information. The UE measures the signal quality of the serving cell and neighboring cells using the measurement configuration information (1k-35), and periodically or when a configured event occurs, reports the collected cell measurement information to the source cell (1k-40). The base station can configure whether to perform multiple RLF reporting operations based on UE capability information. Furthermore, UEs supporting multiple RLF reporting operations can always perform multiple RLF reporting operations.

[0151] The source cell determines whether to trigger a condition-based handover operation based on reported cell measurement information (1k-45). To configure condition-based handover, the UE must support condition-based handover. If it is determined that a condition-based handover must be triggered, the source cell requests a condition-based handover (1k-50) from one or more target cells (1k-20) via a specific inter-node message. The target cells that have received the request accept it using specific admission controls and send the handover configuration information required for the condition-based handover operation to the source cell (1k-55).

[0152] The UE receives configuration information (1k-60) regarding conditional handover from the source base station. This configuration information includes the target cell ID, frequency information, configuration information required for random access operation to the target cell (dedicated preamble and dedicated radio resource information for each target cell), transmission power information, C-RNTI information used in each target cell, and conditions for triggering random access operation to the target cell. These conditions may vary depending on the target cell, and multiple conditions may be configured for a single target cell. If, after a handover failure, the suitable cell found through the first cell selection operation is one of the candidate target cells for conditional handover, the attemptCondReconfig field included in the configuration information is an indicator indicating whether to perform conditional handover to the cell.

[0153] The UE, having received the handover configuration information, assesses whether the provided conditions (1k-65) are met. Until the conditions are met, the UE maintains data transmission / reception operations with the source cell. If the conditions associated with a specific target cell (1k-70) are met, the UE performs a random access procedure for the target cell and drives timer T304 (1k-75). For example, if event A3 (a neighbor becomes better offset than SpCell) has been configured as a condition and has been met, the UE sends the provided preamble to the relevant target cell. If no dedicated preamble is provided, the UE sends one of the preambles currently in use based on contention. The target cell, having received the preamble, sends a Random Access Response (RAR) message to the UE. The UE sends msg 3 (or PUSCH) to the target cell using the UL clearance information included in the RAR. msg 3 includes the RRCReconfigurationComplete message.

[0154] If the random access procedure is successfully completed, the UE considers the conditional handover to be successfully completed and stops driving timer T304. If the conditional handover has not been successfully completed by the timer T304 expiration (1k-80), the UE considers the handover to have failed. In this case, the UE declares an RLF (1k-85) and stores the content corresponding to the first RLF report mentioned above (1k-90).

[0155] If the attemptCondReconfig field is configured and the suitable cell found through the cell selection operation is one of the candidate target cells for conditional handover (1k-95), the UE can perform handover to the cell again (1k-100). In this case, timer T304 is driven again (1k-105), and if the timer expires (1k-110), a second RLF is declared (1k-115). In this case, the existing stored RLF content remains as is, or is supplemented / corrected, and the RLF content corresponding to the second RLF is also stored (1k-120).

[0156] Subsequently, the UE connects to a specific base station through the RRC establishment, RRC recovery, and RRC reconstruction procedures (1k-125). When storing RLF content, the UE includes an availability indicator (1k-130) in the RRCSetupComplete, RRCResumeComplete, and RRCReestablishmentComplete messages. The base station requests the stored RLF content from the UE using a UEInformationRequest message (1k-135). The UE, having received the request, reports the RLF content being stored using a UEInformationResponse message (1k-140).

[0157] For both the first and second RLF reports, a common availability indicator, an indicator for the common retrieval request (in the UEInformationRequest), and a common RLF report IE (in the UEInformationResponse) are used. Furthermore, separate availability indicators, separate retrieval request indicators, and separate RLF report IEs can be defined for the second RLF report. With separate indicators and IEs, the base station has the advantage that only preferred information can be selectively reported to it.

[0158] Figure 12 This is a flowchart of a UE operation that records RLF information in the event of a handover failure based on continuous conditions, according to an embodiment of this disclosure.

[0159] In step 1l-05, the UE reports its own capability information to the source base station. The capability information indicates whether the UE supports conditional handover. Furthermore, the capability information can indicate whether the UE has the capability to configure multiple RLF reports in the event of consecutive RLFs during conditional handover.

[0160] In steps 11-10, the UE receives configuration information about condition-based handover from the source base station.

[0161] In steps 11-15, the UE determines whether the conditions indicated in the condition-based handover configuration information are met.

[0162] In steps 11-20, if at least one condition is met, the UE performs a handover to the target cell corresponding to the condition and drives timer T304.

[0163] In steps 11-25, if the handover is not successfully completed before the driven timer T304 expires, the UE considers the handover to have failed.

[0164] In steps 11-30, the UE stores the content corresponding to the first RLF report that corresponds to the failure.

[0165] In steps 11-35, the UE finds one of the candidate target cells for conditional handover as the appropriate cell.

[0166] In steps 11-40, the UE determines whether the attemptCondReconfig field has been configured. That is, the UE determines whether it is allowed to perform a handover to a suitable cell instead of a rebuild operation.

[0167] In steps 11-45, if the field has not yet been configured, the UE performs an RRC reconstruction operation on the appropriate cell.

[0168] In steps 11-50, if the field has been configured, the UE performs handover to the appropriate cell and drives timer T304.

[0169] In steps 11-55, if the handover is not successfully completed before the driven timer T304 expires, the UE considers the handover to have failed.

[0170] In steps 11-60, the UE determines whether it supports multiple RLF reporting operations.

[0171] In steps 11-65, if the UE does not support multiple RLF report operations, the UE deletes the contents of the existing stored RLF reports.

[0172] In steps 11-70, if the UE supports multiple RLF reporting operations, the UE retains or supplements / corrects the content of the existing stored RLF reports and stores the content of the RLF report corresponding to the second handover failure. To optimize the amount of information in the content of the first and second RLF reports, duplicate information can be included only on either side, and unnecessary information from a specific RLF can be excluded from the content of the corresponding RLF report. Furthermore, the definition of the included content may differ depending on the specific RLF.

[0173] If two consecutive handovers fail in a conditional handover, it means that the handover can no longer be carried out, and a reconstruction operation will be performed according to the relevant technology.

[0174] Figure 13 This is a diagram illustrating the method by which a UE performs cell reselection according to this disclosure.

[0175] Regardless of the serving cell's measured signal strength, the UE always performs frequency / RAT inter-measurement on a higher priority frequency or RAT. If the serving cell's measured signal strength is lower than SintraSearch(1m-25), the UE performs intra-frequency measurement. If the serving cell's measured signal strength is lower than SnonintraSearch(1m-30), the UE performs frequency / RAT inter-measurement on a frequency with a priority equal to or lower than the current serving cell's frequency. As mentioned above, the reason for the UE progressively triggering measurements is to reduce power consumption due to neighboring cell measurements. If the channel QoS of cell 1m-10 on a higher priority frequency becomes higher than a specific threshold ThreshX-high 1m-35, the UE reselects a cell on the higher priority frequency as the serving cell. If the channel QoS of cell 1m-00 on a lower priority frequency is higher than a specific threshold ThreshX-low 1m-15, and the serving cell's QoS becomes lower than ThreshServing-low 1m-20, the UE reselects a cell on the lower priority frequency as the serving cell.

[0176] During cell reselection, Received Signal Strength Ratio (RSRP) or Received Signal Quality Ratio (RSRQ) can be considered. RSRP is the average value of the received signal strength or received signal quality calculated using the S standard. This could be Srxlev or Squal.

[0177] Srxlev=Q rxlevmeas -(Q rxlevmin +Q rxlevminoffset )-P compensation -Qoffset temp

[0178] Squal = Qqualmeas -(Q qualmin +Q qualminoffset -Qoffset temp

[0179] in:

[0180]

[0181] Specifically, in the case of inter-RAT cell reselection to NR, Srxlev is used, and the Srxlev value is compared with a specific threshold ThreshX-high or ThreshX-low.

[0182] In this disclosure, the LTE base station provides a q-RxLevMinSUL value for a specific NR frequency via system information. If the UE supports SUL, when performing inter-ATA cell reselection for an NR cell belonging to the NR frequency, the LTE base station derives the Srxlev value by applying the q-RxLevMinSUL value as the Qrxlevmin value of Srxlev. A q-RxLevMinSUL value is provided for each NR frequency, and if an NR cell belonging to a specific NR frequency supports SUL, the q-RxLevMinSUL value for that specific NR frequency is provided. For NR frequencies that do not support SUL, no q-RxLevMinSUL value is provided. When using received signal quality (i.e., RSRQ), the base station provides Threshserving-lowQ, ThreshX-lowQ, and ThreshX-highQ individually to the UE via broadcast. When using received signal strength, Threshserving-lowP, ThreshX-lowP, and ThreshX-highP are used.

[0183] Figure 14 This is a flowchart illustrating the operation of an indicator that has been affected by measurement results recorded according to power-saving techniques, according to embodiments of the present disclosure.

[0184] Typically, UEs perform cell measurement operations for mobility support. For example, UEs in idle or inactive modes perform intra-frequency / inter-frequency / inter-RAT frequency measurement operations by periodically including the serving cell. Such measurement operations result in UE power consumption, and UE power consumption can be saved by relaxing the requirements for measurement operations unless mobility technology operations such as cell reselection occur in the near future. This is known as RRM measurement relaxation techniques in Next Generation Mobile Communications (NR) systems. These requirements mean that measurement operations are stopped for a specific period of time or that longer measurement periods are applied. Furthermore, to determine that mobility technology operations such as cell reselection will not occur in the near future, consider two conditions in the TS38.304 standard document, as shown in Table 2 below.

[0185] [Table 2]

[0186]

[0187] In Rel-16NR, serving cell measurements should always be performed, regardless of the conditions mentioned above. Furthermore, for frequencies with a higher priority than the currently camped frequency, measurement relaxation can even be applied to higher priority frequencies when the above conditions are met, depending on whether the base station has configured the `highPriorityMeasRelax` field. Simultaneously, measurement results with relaxation requirements are stored by the UE configured with MDT operations. Without an indication of the impact of measurement relaxation, the mobile communication service provider cannot ascertain whether the cell or frequency to be measured does not exist, or whether the measurement was not performed due to other characteristics. Therefore, this disclosure proposes a method to indicate, when storing cell measurement results via recorded MDT operations, whether there are cells or frequencies that were not measured due to other characteristics or configurations.

[0188] UE 1n-05 receives a LoggedMeasurementConfiguration message from base station 1n-10 (1n-15) that includes recorded MDT configuration information. The message may include configuration information indicating whether to store an indicator that indicates whether there are cells or frequencies that were not measured due to the influence of other features or configurations when storing the MDT measurement results of the cell.

[0189] The UE that has received the message drives timer T330 (1n-20). The UE in idle or inactive mode performs the recorded MDT operation until the timer expires. The UE receives an RRC Release message (1n-25) from the base station indicating it is leaving connected mode. Depending on whether the message includes suspendConfig information, the UE that has received the message is switched to idle or inactive mode (1n-30).

[0190] The UE begins recording MDT operations based on the recorded MDT configuration information (1n-35). The UE performs cell and frequency measurement operations based on the cell measurement configuration information included in the SIB 1n-40 broadcast by the base station. The SIB includes not only configuration parameters for reducing UE power consumption, such as S_IntraSearch and S_nonIntraSearch in related technologies, but also configuration information regarding measurement relaxation. For example, the SIB includes configuration parameters related to measurement relaxation conditions and highPriorityMeasRelax field information. The UE performs measurement operations based on the cell measurement configuration information and determines whether the measurement relaxation conditions are met (1n-45). If the highPriorityMeasRelax field is configured to true, the UE can even apply measurement relaxation to higher priority frequencies (1n-50) depending on whether the above conditions are met. The UE stores the valid measurement results for each recording interval and includes the following indicators for each record (LogMeasInfo IE) according to specific rules (1n-55).

[0191] - First indicator

[0192] The highPriorityMeasRelax field, which has been configured to true by the UE performing the recorded MDT operation, is used to indicate that no priority frequency is being measured in order to save UE power consumption, provided that the condition is met that no specific priority frequency is being measured.

[0193] In addition to the indicators described above, information regarding the types of relaxations that meet and apply the conditions described above (e.g., stopping measurements or applying long measurement periods) can be stored, as well as a list of (unmeasured) priority frequencies indicated in the SIB. Priority frequencies among those configured in the SIB can be selected and indicated.

[0194] -Second indicator

[0195] If the UE performing the recorded MDT operation meets the above conditions and there is no measurement frequency within the range of the conditions being met, this indicator is used to indicate that there is no measurement frequency to save UE power consumption.

[0196] In addition to the indicators mentioned above, information about the types of relaxations that meet and apply the conditions described above (e.g., stopping measurement or applying a long measurement period) and information within the (unmeasured) frequency range indicated in the SIB can be stored.

[0197] -Third indicator

[0198] If the UE performing the recorded MDT operation meets the above conditions and no frequency between / RAT is measured due to the satisfaction of the conditions, this indicator is used to indicate that no frequency is measured in order to save UE power consumption.

[0199] In addition to the indicators mentioned above, information on the types of relaxations that meet and apply the above conditions (e.g., stopping measurement or applying a long measurement period) can be stored, as well as a list of (unmeasured) frequency-to-frequency / RAT-to-frequency information indicated in the SIB.

[0200] In related technologies, even when the values ​​derived from the S standard are greater than S_IntraSearch and S_nonIntraSearch, the intra-frequency / inter-frequency / RAT frequencies are not measured to save power. Even in this case, a specific indicator can be used to indicate that the intra-frequency / inter-frequency / RAT frequencies were not measured according to the above conditions.

[0201] -Fourth indicator

[0202] If the value derived from the S standard is greater than S_IntraSearch, this indicator is used to indicate that no frequency is being measured to save UE power consumption. Therefore, the UE performing the recorded MDT operation is not measuring intra-frequency / inter-frequency / inter-RAT frequencies.

[0203] In addition to the indicators mentioned above, frequency information within / between / between RATs indicated in the SIB (unmeasured) can be stored.

[0204] -Fifth indicator

[0205] This indicator is used to indicate that if the value derived from the S standard is greater than S_nonIntraSearch, no frequency is measured to save UE power consumption. Therefore, the UE performing the recorded MDT operation does not measure the frequency between frequencies / RATs.

[0206] In addition to the indicators mentioned above, frequency information between (unmeasured) frequencies indicated in the SIB / between RATs can be stored.

[0207] In current standard technologies, a serving cell should always be specified, regardless of the conditions mentioned above. However, to save additional power consumption relative to MDT / IoT devices that do not move at all, serving cell measurements can be stopped, or measurements can be performed for extended periods. In this case, for each stored record, there may be no valid serving cell measurement results. Therefore, a specific indicator can be used to indicate that a serving cell has not yet been measured.

[0208] -Sixth indicator

[0209] When specific fields are configured and the above conditions are met, this indicator is used to indicate that no frequency is being measured to save UE power consumption, therefore the UE performing the recorded MDT operation is not measuring the serving cell frequency.

[0210] In addition to the indicators mentioned above, information about the types of relaxations that meet and apply the above conditions (e.g., stopping measurements or applying long measurement periods) and serving cell frequency information can be stored.

[0211] Subsequently, the UE connects to the base station via the RRC establishment, RRC recovery, and RRC reconstruction procedures (1n-60). If MDT measurement results exist, the UE includes an availability indicator in the RRCSetupComplete, RRCResumeComplete, and RRCReestablishmentComplete messages (1n-65) to indicate this. The base station requests the stored MDT measurement results from the UE using the UEInformationRequest message (1n-70). The requested UE reports the stored MDT measurement results using the UEInformationResponse message (1n-75).

[0212] Figure 15 This is a flowchart of an operation according to an embodiment of the present disclosure, showing that the operation has been affected by the measurement results recorded according to the configuration of interFreqTargetList (inter-frequency target list).

[0213] The `interFreqTargetList` field is information included in the `LoggedMeasurementConfiguration` message and is used by the UE to indicate information about neighboring cells that should be stored as MDT measurement results. If a frequency belonging to a neighboring cell is indicated in SIB4, the UE measures that frequency and stores the measurement result. However, frequencies not belonging to this field are not stored. This is because mobile service providers efficiently manage UE memory by measuring only frequencies of interest. This disclosure proposes a method for indicating, through recorded MDT operations, whether there are cells or frequencies not measured by the configuration of the `interFreqTargetList` field when storing cell measurement results.

[0214] UE1o-05 receives a LoggedMeasurementConfiguration message from base station 1o-10 (1o-15) that includes recorded MDT configuration information. This message may include configuration information indicating whether to store an indicator that indicates whether there are cells or frequencies that are not configured to be measured by the interFreqTargetList field when storing the MDT measurement results of a cell.

[0215] The UE that has received the message drives timer T330 (1o-20). The UE in idle or inactive mode performs recorded MDT operations until the timer expires. The UE receives an RRRCRelease message from the base station indicating it is leaving connected mode (1o-25). Depending on whether the message includes suspendConfig configuration information, the UE that has received the message is switched to idle or inactive mode (1o-30). Furthermore, the UE begins recorded MDT operations based on the recorded MDT configuration information (1o-35). The UE performs cell and frequency measurement operations based on the cell measurement configuration information included in SIB4 (1o-40). For example, the UE performs measurement operations based on the cell / frequency configuration information (1o-45). The UE stores valid measurement results at each recording interval and includes the following indicator (LogMeasInfo IE) for each record according to specific rules (1o-50).

[0216] -Seventh indicator

[0217] This is an indicator that shows whether the interFreqTargetList field is configured.

[0218] As an alternative approach, the configured interFreqTargetList field information is included in the LogMeasReport IE to be reported to the base station.

[0219] Subsequently, the UE connects to the specific base station through the RRC establishment, RRC recovery, and RRC reconstruction procedures (1o-55). When storing MDT measurement results, the UE includes an availability indicator of the MDT measurement results in the RRCSetupComplete, RRCResumeComplete, and RRCReestablishmentComplete messages (1o-60). The base station requests the stored MDT measurement results from the UE using a UEInformationRequest message (1o-65). The UE, having received the request, reports the MDT measurement results being stored using a UEInformationResponse message (1o-70).

[0220] Figure 16 This is a flowchart of an operation of an indicator that records, according to an embodiment of the present disclosure, that indicates that the operation has been affected by measurement results recorded according to power saving technology.

[0221] In step 1p-05, the UE receives the Logged Measurement Configuration message from the base station.

[0222] In steps 1p-10, the UE receives an RRC release (RRCRelease) message from the base station and is switched to idle mode or inactive mode.

[0223] In steps 1p-15, the UE performs the LoggedMDT operation based on the configuration information received in the LoggedMeasurementConfiguration message.

[0224] In steps 1p-20, the UE stores an indicator that indicates that the measurement results for a specific cell or frequency were not stored due to being affected by a specific feature or configuration being performed (i.e., interFreqTargetList).

[0225] In steps 1p-25, the UE switches to connected mode via an RRC (re-establishment) or RRC recovery procedure. During this procedure, the UE reports an indicator to the base station indicating the presence of stored DMT measurement results.

[0226] In step 1p-30, the base station requests the UE to report the MDT measurement results.

[0227] In steps 1p-35, the UE reports the stored MDT measurement results to the base station.

[0228] Figure 17 This is a block diagram illustrating the internal structure of a UE that applies this disclosure.

[0229] Referring to the attached figures, the UE includes a radio frequency (RF) processor 1q-10, a baseband processor 1q-20, a storage unit 1q-30, and a controller 1q-40.

[0230] RF processor 10 performs functions such as transmitting and receiving signals on a radio channel, including signal band conversion and amplification. Specifically, RF processor 1q-10 performs up-conversion from the baseband signal provided by baseband processor 1q-20 to an RF band signal for transmission via an antenna, and performs down-conversion from the RF band signal received via the antenna to a baseband signal. For example, RF processor 1q-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, digital-to-analog converters (DACs), and analog-to-digital converters (ADCs). Although only one antenna is shown in the figures, the UE may be equipped with multiple antennas. Furthermore, RF processor 1q-10 may include multiple RF chains. Additionally, RF processor 1q-10 can perform beamforming. For beamforming, RF processor 1q-10 can adjust the phase and magnitude of signals transmitted or received via multiple antennas or antenna elements. Furthermore, RF processor 1q-10 can perform MIMO and can receive several layers during MIMO operation.

[0231] The baseband processor 1q-20 performs conversion functions between baseband signals and bit strings according to the system's physical layer standard. For example, during data transmission, the baseband processor 1q-20 generates complex symbols by encoding and modulating the transmitted bit strings. Furthermore, during data reception, the baseband processor 1q-20 recovers the received bit strings by demodulating and decoding the baseband signals provided by the RF processor 1q-10. For example, in the case of conforming to the Orthogonal Frequency Division Multiplexing (OFDM) method, during data transmission, the baseband processor 1q-20 generates complex symbols by encoding and modulating the transmitted bit strings, performs mapping of complex symbols to subcarriers, and then configures the OFDM symbols through inverse Fast Fourier Transform (IFFT) operations and cyclic prefix (CP) insertion. Furthermore, during data reception, the baseband processor 1q-20 divides the baseband signals provided by the RF processor 1q-10 into units of OFDM symbols, recovers the signals mapped to the subcarriers through Fast Fourier Transform (FFT), and then recovers the received bit strings through demodulation and decoding.

[0232] The baseband processor 1q-20 and RF processor 1q-10 transmit and receive signals as described above. Therefore, the baseband processor 1q-20 and RF processor 1q-10 can be referred to as transmitters, receivers, transceivers, or communication units. Furthermore, to support different radio access technologies, at least one of the baseband processor 1q-20 and RF processor 1q-10 may include multiple communication modules. Additionally, to process signals in different frequency bands, at least one of the baseband processor 1q-20 and RF processor 1q-10 may include different communication modules. For example, different radio access technologies may include wireless LAN (e.g., IEEE 802.11) and cellular networks (e.g., LTE). Furthermore, different frequency bands may include ultra-high frequency (SHF) bands (e.g., 2.0 NR Hz or NR Hz) and millimeter (mm) wave (e.g., 60 GHz) bands.

[0233] Storage unit 1q-30 stores data related to basic programs, application programs, and configuration information for UE operation. Specifically, storage unit 1q-30 may store information related to a second access node performing wireless communication using a second radio access technology. Furthermore, storage unit 1q-30 provides the stored data upon request from controller 1q-40.

[0234] Controller 1q-40 controls the overall operation of the UE. For example, controller 1q-40 transmits and receives signals via baseband processor 1q-20 and RF processor 1q-10. Furthermore, controller 1q-40 records data in or reads data from storage unit 1q-30. For this purpose, controller 1q-40 may include at least one processor. For example, controller 1q-40 may include a communication processor (CP) that performs communication control and an application processor (AP) that controls upper layers (such as applications).

[0235] Figure 18 This is a block diagram illustrating the configuration of a base station according to the present disclosure.

[0236] As shown in the figure, the base station is configured to include an RF processor 1r-10, a baseband processor 1r-20, a backhaul communication unit 1r-30, a storage unit 1r-40, and a controller 1r-50.

[0237] RF processor 1r-10 performs functions such as transmitting and receiving signals on a radio channel, including signal band conversion and amplification. Specifically, RF processor 1r-10 performs up-conversion from the baseband signal provided by baseband processor 1r-20 to an RF band signal for transmission via an antenna, and down-conversion from the RF band signal received via the antenna to a baseband signal. For example, RF processor 1r-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, DACs, and ADCs. Although only one antenna is shown in the figures, the first access node may be equipped with multiple antennas. Furthermore, RF processor 1r-10 may include multiple RF chains. Additionally, RF processor 1r-10 can perform beamforming. For beamforming, RF processor 1r-10 can adjust the phase and magnitude of signals transmitted or received through multiple antennas or antenna elements. The RF processor can perform down-MIMO operation through one or more layers of transmission.

[0238] The baseband processor 1r-20 performs the conversion function between baseband signals and bit strings according to the physical layer standard of the first radio access technology. For example, during data transmission, the baseband processor 1r-20 generates complex symbols by encoding and modulating the transmitted bit strings. Furthermore, during data reception, the baseband processor 1r-20 recovers the received bit strings by demodulating and decoding the baseband signals provided from the RF processor 1r-10. For example, in the case of conforming to the OFDM method, during data transmission, the baseband processor 1r-20 generates complex symbols by encoding and modulating the transmitted bit strings, performs a mapping of complex symbols to subcarriers, and then configures the OFDM symbols through IFFT operations and CP insertion. Furthermore, during data reception, the baseband processor 1r-20 divides the baseband signals provided from the RF processor 1r-10 into units of OFDM symbols, recovers the signals mapped to subcarriers through FFT operations, and then recovers the received bit strings through demodulation and decoding. The baseband processor 1r-20 and the RF processor 1r-10 transmit and receive signals as described above. Therefore, the baseband processor 1r-20 and the RF processor 1r-10 can be referred to as transmitters, receivers, transceivers, communication units, or wireless communication units.

[0239] The backhaul communication unit 1r-30 provides an interface for performing communication with other nodes in the network. That is, the backhaul communication unit 1r-30 converts bit strings sent from the main base station to other nodes (e.g., auxiliary base stations and the core network) into physical signals, and converts physical signals received from other nodes into bit strings.

[0240] Storage unit 1r-40 stores data related to basic procedures, application programs, and configuration information for the operation of the main base station. Specifically, storage unit 1r-40 can store information about bearers assigned to connected UEs and measurement results reported from connected UEs. Furthermore, storage unit 1r-40 can store information that forms the basis for determining whether to provide or suspend multiple connections to a UE. Additionally, storage unit 1r-40 provides the stored data upon request from controller 1r-50.

[0241] The controller 1r-50 controls the overall operation of the main base station. For example, the controller 1r-50 transmits and receives signals via the baseband processor 1r-20 and the RF processor 1r-10, or via the backhaul communication unit 1r-30. Furthermore, the controller 1r-50 records data in or reads data from the storage unit 1r-40. For this purpose, the controller 1r-50 may include at least one processor.

[0242] In the detailed embodiments described above, depending on the proposed detailed embodiments, the elements included in this disclosure may be represented in singular or plural form. However, singular or plural expressions have been suitably selected for the purposes of description, and this disclosure is not limited to singular or plural elements. Although an element has been expressed in plural form, it may be constituted in singular form, and although an element has been expressed in singular form, it may be constituted in plural form.

[0243] Although detailed embodiments have been described in the detailed description of this disclosure, this disclosure can be modified in various ways without departing from its scope. Therefore, the scope of this disclosure should not be limited to the above embodiments, but should be defined not only by the claims, but by their equivalents.

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: Send information to the base station indicating the capability to support condition-based handover; Receive configuration information about condition-based handover from the base station based on capability information; If the predetermined conditions based on the configuration information are met, the first handover to the first cell is executed; If the first handover fails, perform a cell selection operation; Since the second cell was selected by the cell selection operation, the second handover to the second cell is executed. as well as If a Radio Resource Control (RRC) connection with the base station is established after a second handover failure, a Radio Link Failure (RLF) report is sent to the base station. The RLF report includes first RLF information associated with the first handover failure and second RLF information associated with the second handover failure. Specific information is included in one of the first RLF information and the second RLF information. This specific information includes at least one of the following: information about the source cell, information about the type of connection failure, information about the reason for the RLF, and information regarding the timing of the reconnection. Where time information is included in the first RLF information, the time information indicates the time from the first handover execution until the establishment of the RRC connection with the base station, and Where time information is included in the second RLF information, the time information indicates the time from the second handover execution until the establishment of the RRC connection with the base station.

2. The method according to claim 1, further comprising: Based on the failure of the first handover to the first cell, store the first RLF information; and Based on the second handover failure to the second cell, store the second RLF information.

3. The method according to claim 1, in, Information about the second cell included in the second RLF information was not included in the first RLF information.

4. The method according to claim 1, in, The second cell is included in the candidate cell list in the configuration information, and The configuration information also includes at least one of the following: information about the cell identifier (ID) of the target cell included in the candidate cell list, information about the frequency, information about the resources used to perform random access to the target cell, and information about the conditions for triggering random access.

5. A method performed by a base station in a wireless communication system, the method comprising: Receive capability information from the terminal indicating support for condition-based handover; Based on capability information, determine the condition-based handover of the triggering terminal; Send configuration information about conditional handover to the terminal; as well as After a Radio Resource Control (RRC) connection with the terminal is established, a Radio Link Failure (RLF) report based on configuration information is received from the terminal. The RLF report includes first RLF information associated with a first handover failure to the first cell and second RLF information associated with a second handover failure to the second cell. Specific information is included in one of the first RLF information and the second RLF information. This specific information includes at least one of the following: information about the source cell, information about the type of connection failure, information about the reason for the RLF, and information regarding the timing of the reconnection. Where time information is included in the first RLF information, the time information indicates the time from the first handover execution until the establishment of the RRC connection between the terminal and the base station, and Where time information is included in the second RLF information, the time information indicates the time from the second handover execution until the establishment of the RRC connection between the terminal and the base station.

6. The method according to claim 5, in, Information about the second cell included in the second RLF information was not included in the first RLF information. The second cell is included in the candidate cell list in the configuration information, and The configuration information also includes at least one of the following: information about the cell identifier (ID) of the target cell included in the candidate cell list, information about the frequency, information about the resources used to perform random access to the target cell, and information about the conditions for triggering random access.

7. A terminal in a wireless communication system, the terminal comprising: transceiver; and The controller is configured as follows: The control transceiver sends capability information to the base station indicating support for condition-based handover. The control transceiver receives configuration information about condition-based handover from the base station based on capability information. If the predetermined conditions based on the configuration information are met, the first handover to the first cell is executed. Based on the failure of the first handover, a cell selection operation is performed. Since the second cell was selected by the cell selection operation, the second handover to the second cell is executed, and If a Radio Resource Control (RRC) connection with the base station is established after a second handover failure, the control transceiver sends a Radio Link Failure (RLF) report to the base station. The RLF report includes first RLF information associated with the first handover failure and second RLF information associated with the second handover failure. Specific information is included in one of the first RLF information and the second RLF information. This specific information includes at least one of the following: information about the source cell, information about the type of connection failure, information about the reason for the RLF, and information regarding the timing of the reconnection. Where time information is included in the first RLF information, the time information indicates the time from the first handover execution until the establishment of the RRC connection with the base station, and Where time information is included in the second RLF information, the time information indicates the time from the second handover execution until the establishment of the RRC connection with the base station.

8. The terminal according to claim 7, in, The controller is also configured to store first RLF information based on a first handover failure to the first cell, and to store second RLF information based on a second handover failure to the second cell.

9. The terminal according to claim 7, in, Information about the second cell included in the second RLF information was not included in the first RLF information.

10. The terminal according to claim 7, in, The second cell is included in the candidate cell list in the configuration information, and The configuration information also includes at least one of the following: information about the cell identifier (ID) of the target cell included in the candidate cell list, information about the frequency, information about the resources used to perform random access to the target cell, and information about the conditions for triggering random access.

11. A base station in a wireless communication system, the base station comprising: transceiver; and The controller is configured as follows: The control transceiver receives information from the terminal indicating the capability to support condition-based handover. Based on capability information, determine the condition-based handover that triggers the terminal. The control transceiver sends configuration information about conditional handover to the terminal, and After a Radio Resource Control (RRC) connection with the terminal is established, the control transceiver receives a Radio Link Failure (RLF) report from the terminal based on configuration information. The RLF report includes first RLF information associated with a first handover failure to the first cell and second RLF information associated with a second handover failure to the second cell. Specific information is included in one of the first RLF information and the second RLF information. This specific information includes at least one of the following: information about the source cell, information about the type of connection failure, information about the reason for the RLF, and information regarding the timing of the reconnection. Where time information is included in the first RLF information, the time information indicates the time from the first handover execution until the establishment of the RRC connection between the terminal and the base station, and Where time information is included in the second RLF information, the time information indicates the time from the second handover execution until the establishment of the RRC connection between the terminal and the base station.

12. The base station according to claim 11, in, Information about the second cell included in the second RLF information was not included in the first RLF information. The second cell is included in the candidate cell list in the configuration information, and The configuration information also includes at least one of the following: information about the cell identifier (ID) of the target cell included in the candidate cell list, information about the frequency, information about the resources used to perform random access to the target cell, and information about the conditions for triggering random access.

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