KR102492305B1 - Communication node for operating handover and therefor method in wireless communication system - Google Patents

Abstract

A method of operating a terminal in a wireless communication system is disclosed. The operating method of the terminal may include receiving configuration information of a handover event from a serving base station; Measuring channel conditions of the serving base station and the target base station; Determining that a handover preparation event has occurred when the difference between the received signal strength of the serving base station and the received signal strength of the target base station based on the channel state of the serving base station is greater than or equal to the handover preparation offset indicated by the setting information step; and transmitting a measurement report message to the serving base station according to the occurrence of the handover preparation event. When the difference between the received signal strength of the serving base station and the received signal strength of the target base station based on the channel state of the serving base station is equal to or greater than the handover execution offset indicated by the setting information, a handover execution event indicating a handover execution step determining that has occurred; and transmitting, to the serving base station, a handover notification message notifying the execution of handover to the target base station in advance according to the occurrence of the handover execution event.

Description

Communication node for performing handover in a wireless communication system and its operating method

The present invention relates to a communication node for performing handover in a wireless communication system and an operating method thereof.

In a Long Term Evolution (LTE) system, when a terminal moves from a cell of a serving base station to a cell of another base station, the terminal may perform handover from the serving base station to another base station. For example, the terminal may measure the signal strength of neighboring base stations and report it to the serving base station. The serving base station may prepare a target base station for handover of the terminal based on the report on the signal strength of neighboring base stations received from the terminal. After completing preparations for the target base station, the serving base station may transmit a handover command instructing the terminal to perform handover. The terminal may access the target base station by performing handover to the target base station based on the handover command received from the serving base station.

However, the radio link state with the serving base station may not be good in a temporal or spatial domain in which the terminal can perform handover. At this time, the serving base station may not be able to receive a measurement report on the signal strength of neighboring base stations received from the terminal in real time. Also, the terminal may not be able to receive a handover command from the serving base station in real time. Therefore, during the time when the terminal performs handover, the time during which data transmitted/received with the serving base station is disconnected may increase, and thus communication quality may deteriorate.

The terminal may trigger a handover when the received signal strength of the target base station is greater than the received signal strength of the serving base station by a predetermined threshold. At this time, the terminal may not trigger a handover when the received signal strength of the target base station is less than a predetermined threshold value than the received signal strength of the serving base station even though the receiving signal strength of the serving base station is low.

Therefore, a radio link failure (RLF) may occur between the terminal and the serving base station. After RLF occurs, the terminal may perform an operation of selecting a target base station to recover RLF. During the time when the terminal performs an operation of selecting a target base station, transmission and reception of data is disconnected, and communication quality may deteriorate.

A time during which data transmission/reception is disconnected according to handover may be 50 ms. In addition, the time during which data transmission and reception is disconnected according to access stratum (AS) RLF recovery through re-establishment of the connection between the terminal and the base station may be hundreds of ms. In addition, after an access stratum (AS) RLF recovery failure, data transmission and reception according to non-access stratum (NAS) RLF recovery through initial access may be disconnected for several seconds. Therefore, when RLF occurs due to handover failure and AS RLF recovery is performed, or when AS RLF recovery fails and NAS RLF recovery is performed, communication quality degradation may occur due to data disconnection for a long time. .

An object of the present invention to solve the above problems is to provide a communication node and an operating method thereof for performing an improved handover to prevent a radio link error in a wireless communication system.

One embodiment of the present invention for achieving the above object is disclosed a method of operating a terminal in a wireless communication system. The operating method of the terminal may include receiving configuration information of a handover event from a serving base station; Measuring channel conditions of the serving base station and the target base station; Determining that a handover preparation event has occurred when the difference between the received signal strength of the serving base station and the received signal strength of the target base station based on the channel state of the serving base station is greater than or equal to the handover preparation offset indicated by the setting information step; Transmitting a measurement report message to the serving base station according to the occurrence of the handover preparation event; Determining that a handover execution event has occurred when the difference between the received signal strength of the serving base station and the received signal strength of the target base station based on the channel state of the serving base station is greater than or equal to the handover execution offset indicated by the setting information step; and transmitting a handover notification message notifying the execution of handover to the target base station in advance according to the occurrence of the handover execution event. The channel state indicates a normal state, an abnormal state, and a radio link failure state. The setting information indicates different handover triggering values according to the channel state.

The handover triggering value includes a first handover preparation offset and a first handover execution offset for a handover event triggered in the normal state, such as when the received signal strength of the serving base station is equal to or greater than a first predetermined threshold, A second handover preparation offset and a second handover execution offset for a handover event triggered in the abnormal state, such as when the received signal strength of the serving base station is less than the first threshold, and a radio link failure with the serving base station may include a third handover execution offset for a handover event that is triggered when . The first handover preparation offset may have a greater value than the second handover preparation offset. The first handover execution offset may have a greater value than the second handover execution offset. The second handover execution offset may have a greater value than the third handover execution offset. The first threshold value may have a value greater than the second threshold value.

The operating method of the terminal may further include, after the step of measuring the channel state, receiving a handover command message for the target base station from the serving base station.

The handover preparation event occurs when the channel state of the serving base station is the normal state and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the first handover preparation offset indicated by the setting information. can be determined to have occurred. The handover execution event may be determined to have occurred when a difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the first handover execution offset.

The handover preparation event occurs when the channel state of the serving base station is in the abnormal state, and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the second handover preparation offset indicated by the configuration information. can be determined to have occurred. The handover execution event may be determined to have occurred when a difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the second handover execution offset.

The operating method of the terminal may further include performing handover to the target base station based on the handover command message.

Also, according to another embodiment of the present invention, the handover may be performed regardless of whether or not the handover notification message is received.

The operating method of the terminal may further include performing a cell selection operation when the channel state of the serving base station is the RLF state. A handover execution event may be determined to have occurred when a difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the third handover execution offset according to a result of performing the cell selection operation. The handover may be performed when a handover command message for the target base station is stored in advance.

In addition, a method of operating a serving base station in a wireless communication system according to an embodiment of the present invention is disclosed. The operating method of the serving base station may include transmitting configuration information of a handover event to a terminal; Receiving a measurement report message for a target base station from the terminal; preparing for handover of the terminal based on the measurement report message and transmitting a handover command message to the terminal; Receiving a handover notification message notifying in advance of execution of handover from the terminal to the target base station; and transmitting a response message to the handover notification message to the terminal. The measurement report message is transmitted from the terminal when a handover preparation event indicated by the configuration information occurs. The handover notification message is transmitted from the terminal when a handover execution event indicated by the setting information occurs.

The measurement report message is transmitted from the terminal when the difference between the received signal strength of the serving base station and the received signal strength of the target base station is equal to or greater than the handover preparation offset value indicated by the configuration information.

The handover notification message is transmitted from the terminal when the difference between the received signal strength of the serving base station and the received signal strength of the target base station is equal to or greater than the handover execution offset value indicated by the configuration information.

The setting information includes a first handover preparation offset and a first handover execution offset for a handover event triggered in the normal state, such as when the received signal strength of the serving base station is equal to or greater than a predetermined threshold value, and a first handover execution offset of the serving base station. A second handover preparation offset and a second handover execution offset for a handover event triggered in the abnormal state, such as when the received signal strength is less than the predetermined threshold, and when a radio link failure with the serving base station occurs A third handover execution offset for a triggered handover event may be included. The first handover preparation offset may have a greater value than the second handover preparation offset. The first handover execution offset may have a greater value than the second handover execution offset. The second handover execution offset may have a greater value than the third handover execution offset.

In addition, a terminal is disclosed in a wireless communication system according to an embodiment of the present invention. The terminal, a processor (processor); and a memory in which at least one command executed by the processor is stored. The at least one command may include receiving configuration information of a handover event from a serving base station; Measure channel conditions of the serving base station and the target base station; When the difference between the received signal strength of the serving base station and the received signal strength of the target base station based on the channel state of the serving base station is greater than or equal to the handover preparation offset indicated by the setting information, it is determined that a handover preparation event has occurred ; Transmitting a measurement report message to the serving base station according to the occurrence of the handover preparation event; When the difference between the received signal strength of the serving base station and the received signal strength of the target base station based on the channel state of the serving base station is greater than or equal to the handover execution offset indicated by the setting information, it is determined that a handover execution event has occurred ; In response to the occurrence of the handover execution event, a handover notification message notifying the execution of handover to the target base station in advance is transmitted. The channel state indicates a normal state, an abnormal state, and a radio link failure state. The setting information indicates different handover triggering values according to the channel state.

The handover triggering value includes a first handover preparation offset and a first handover execution for a first handover event triggered in the normal state, such as when the received signal strength of the serving base station is equal to or greater than a first predetermined threshold. Offset, a second handover preparation offset and a second handover execution offset for a second handover event triggered in the abnormal state, such as when the received signal strength of the serving base station is less than the first threshold, and the serving base station and a third handover execution offset for a third handover event triggered when a radio link failure occurs. The first handover preparation offset may have a greater value than the second handover preparation offset. The first handover execution offset may have a greater value than the second handover execution offset. The second handover execution offset may have a greater value than the third handover execution offset. The first threshold value may have a value greater than the second threshold value.

The at least one command may be further executed to receive a handover command message for the target base station from the serving base station.

The handover preparation event occurs when the channel state of the serving base station is the normal state and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the first handover preparation offset indicated by the setting information. can be determined to have occurred. The handover execution event may be determined to have occurred when a difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the first handover execution offset.

The handover preparation event occurs when the channel state of the serving base station is in the abnormal state, and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the second handover preparation offset indicated by the configuration information. can be determined to have occurred. The handover execution event may be determined to have occurred when a difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the second handover execution offset.

The at least one command may be further executed to perform handover to the target base station based on the handover command message.

Also, according to another embodiment of the present invention, the handover may be performed regardless of whether the response message is received or not.

The at least one command may be further executed to perform a cell selection operation when the channel state of the serving base station is the RLF state. The handover execution event may be determined to have occurred when a difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the third handover execution offset according to a result of performing the cell selection operation. The handover may be performed when a handover command message for the target base station is stored in advance.

According to an embodiment of the present invention, the terminal sets different handover execution values depending on whether the received signal strength of the serving base station is greater than or equal to a predetermined received signal strength, and thus, depending on the radio link state with the serving base station, the terminal is more than the conventional method. By performing handover quickly, occurrence of radio link errors can be reduced.

In addition, according to an embodiment of the present invention, when an RLF occurs, when there is a target base station for which the received signal strength exceeding the received signal strength of the serving base station is measured, the terminal does not execute the AS RLF recovery procedure for the target base station. By executing the handover without performing the handover, it is possible to prevent the occurrence of a radio link error and reduce the data disconnection time.

1 is a conceptual diagram illustrating a wireless communication system according to a first embodiment of the present invention.
2 is a block diagram showing a communication node in a wireless communication system according to a first embodiment of the present invention.
3 is a conceptual diagram illustrating a time point at which a terminal performs handover based on received signal strength of a serving base station and received signal strength of a target base station in a wireless communication system according to the first embodiment of the present invention.
4 is a flowchart illustrating signal flow between a terminal, a serving base station, and a plurality of target base stations for performing handover in a wireless communication system according to the first embodiment of the present invention.
5A to 5C are flowcharts illustrating an operation sequence of a terminal performing handover in a wireless communication system according to a second embodiment of the present invention.

Since the present invention can make various changes and have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. The terms and/or include any combination of a plurality of related recited items or any of a plurality of related recited items.

It is understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may exist in the middle. It should be. On the other hand, when an element is referred to as “directly connected” or “directly connected” to another element, it should be understood that no other element exists in the middle.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in this application, they should not be interpreted in an ideal or excessively formal meaning. don't

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail. In order to facilitate overall understanding in the description of the present invention, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

Throughout the specification, a terminal includes a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), and a high reliability mobile station (HR-MS). MS), subscriber station (SS), portable subscriber station (PSS), access terminal (AT), user equipment (UE), etc. , MS, AMS, HR-MS, SS, PSS, AT, UE, etc. may include all or some functions.

In addition, the base station (BS) includes an advanced base station (ABS), a high reliability base station (HR-BS), a node B, and an evolved node B , eNodeB), access point (AP), radio access station (RAS), base transceiver station (BTS), mobile multihop relay (MMR)-BS, repeater that serves as a base station ( relay station (RS), a high reliability relay station (HR-RS) serving as a base station, and a small base station. , BTS, MMR-BS, RS, HR-RS, small base stations, etc. may include all or some of the functions.

1 is a conceptual diagram illustrating a communication system according to a first embodiment of the present invention.

Referring to FIG. 1, a communication system 100 includes a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of the plurality of communication nodes may support at least one communication protocol. For example, each of the plurality of communication nodes is a communication protocol based on code division multiple access (CDMA), a communication protocol based on wideband CDMA (WCDMA), a communication protocol based on time division multiple access (TDMA), and a frequency division multiple (FDMA) access) based communication protocol, OFDM (orthogonal frequency division multiplexing) based communication protocol, OFDMA (orthogonal frequency division multiple access) based communication protocol, SC (single carrier)-FDMA based communication protocol, NOMA (non-orthogonal multiple access) access)-based communication protocol, space division multiple access (SDMA)-based communication protocol, and the like may be supported. The structure of each of the plurality of communication nodes will be described with reference to FIG. 2 below.

2 is a block diagram showing a communication node in a communication system according to a first embodiment of the present invention.

Referring to FIG. 2 , a communication node 200 may include at least one processor 210, a memory 220, and a transceiver 230 connected to a network to perform communication. In addition, the communication node 200 may further include an input interface device 240, an output interface device 250, a storage device 260, and the like. Each component included in the communication node 200 may be connected by a bus 270 to communicate with each other.

However, each component included in the communication node 200 may be connected through an individual interface or an individual bus centered on the processor 210 instead of the common bus 270 . For example, the processor 210 may be connected to at least one of the memory 220, the transmission/reception device 230, the input interface device 240, the output interface device 250, and the storage device 260 through a dedicated interface. .

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260 . The processor 210 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may include at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may include at least one of a read only memory (ROM) and a random access memory (RAM).

3 is a conceptual diagram illustrating a time point at which a terminal performs handover based on received signal strength of a serving base station and received signal strength of a target base station in a wireless communication system according to the first embodiment of the present invention.

Referring to FIG. 3 , in a wireless communication system, a terminal may measure received signal strengths of neighboring base stations including a serving base station covering a serving cell and a target base station covering a target cell. For example, the terminal may measure the reference signal received power (RSRP) of each of the neighboring base stations.

Here, the wireless communication system may be the same as or similar to the wireless communication system 100 of FIG. 1 . In addition, each structure of the terminal, the serving base station, and the target base station may be the same as or similar to the structure of the communication node 200 of FIG. 2 .

The terminal may determine whether a state in which a difference between the received signal strength of the target base station and the received signal strength of the serving base station is equal to or greater than a handover margin (HOM) continues for a predetermined time. For example, when the difference between the signal strength of the target base station and the signal strength of the serving base station is greater than or equal to a handover margin during a predetermined trigger time (TTT), the terminal sends a measurement report message to the serving base station. can transmit Here, the measurement report message may include channel state information including information about received signal strengths of each of the serving base station and the neighboring base station. The handover margin may be the first offset of the A3 event. The A3 event may mean a case in which the signal strength of the neighboring base station is greater than the signal strength of the serving base station by a first offset or more.

The serving base station may receive a measurement report message from the terminal. The serving base station may determine the handover of the terminal based on the received signal strengths of the serving base station and neighboring base stations included in the measurement report message. At this time, the serving base station may transmit a handover preparation message to the target base station for the handover of the terminal. The target base station may receive a handover preparation message from the serving base station. The target base station may determine whether to accept the handover of the terminal based on the handover preparation message. The target base station may transmit a handover preparation response message including information indicating whether to accept the handover of the terminal to the serving base station.

The serving base station may receive a handover preparation response message from the target base station. The serving base station may transmit a handover command message for instructing handover to the terminal when the handover preparation response message includes information indicating that the handover for the terminal is accepted. Here, the handover command message may be a radio resource control (RRC) connection reconfiguration message.

After determining handover for the terminal, the serving base station may transmit a handover command message to the terminal. At this time, a radio link state between the serving base station and the terminal may not be good in the handover area where the terminal is located. Therefore, the serving base station may not be able to receive the measurement report message transmitted from the terminal in real time. Also, the terminal may not be able to receive a handover command message transmitted from the base station in real time. Therefore, handover may fail depending on the state of the radio link between the terminal and the serving base station. Accordingly, if a handover failure occurs while the terminal is performing a handover operation, the time during which data transmitted/received by the terminal is disconnected may increase and communication quality may deteriorate.

Meanwhile, the terminal may drive the T310 timer when the received signal strength of the serving base station is less than Qout. Here, Qout is defined as a case in which a control channel decoding error is greater than 10%, and in the LTE standard, it is defined and used as a case in which a signal to interference noise ratio (SINR) is -8dB. The T310 timer is a timer for determining RLF. The terminal may stop the T310 timer when the received signal strength of the serving base station is equal to or greater than Qin after the T310 timer is driven. At this time, Qin may be SINR of -6dB. When the received signal strength of the serving base station is less than Qin, the T310 timer may expire. When the T310 timer expires, the UE may determine that RLF has occurred. When an RLF occurs, the UE may perform an RLF recovery procedure.

For example, when an RLF occurs, the terminal can select a base station having the best channel condition among base stations to which the terminal can connect through cell selection. At this time, the terminal may perform a procedure for re-establishing a connection to the selected base station (re-establishment procedure).

At this time, the terminal may be able to resume communication through a connection resetting and recovery procedure only when the selected cell is a cell of a serving base station or a cell of a target base station for which handover is prepared. When the terminal selects a cell other than the cell of the serving base station or the cell of the target base station for which handover is prepared, connection re-establishment may fail. At this time, the terminal may perform the network access procedure again from the beginning. In this case, the data disconnection time may last 1 second or more. Therefore, communication quality of the terminal may be deteriorated.

4 is a flowchart illustrating signal flow between a terminal, a serving base station, and a plurality of target base stations for performing handover in a wireless communication system according to the first embodiment of the present invention.

Referring to FIG. 4 , a wireless communication system may include a terminal 401, a serving base station 402, a first target base station 403, and a second target base station 404. Here, the wireless communication system may be the same as or similar to the wireless communication system of FIG. 3 . Also, the terminal 401 may operate the same as or similar to the terminal of FIG. 3 . In addition, the serving base station 402 may operate the same as or similar to the serving base station of FIG. 3 . In addition, each of the first target base station 403 and the second target base station 404 may operate the same as or similar to the target base station of FIG. 3 .

The serving base station 402 may transmit configuration information to the terminal 401 (S400). The terminal 401 may receive configuration information from the serving base station 402 . Here, the configuration information may be configuration information of a handover event.

The configuration information may include information indicating a first handover preparation offset and a first handover execution offset for a first handover event triggered when the received signal strength of the serving base station is equal to or greater than a predetermined threshold. In addition, the setting information may include information indicating a second handover preparation offset and a second handover execution offset for a second handover event triggered when the received signal strength of the serving base station is less than the predetermined threshold. there is. In addition, the configuration information may include information indicating a third handover execution offset for a third handover event triggered when a radio link failure with the serving base station occurs. The first handover execution offset may have a greater value than the second handover execution offset. The second handover execution offset may have a greater value than the third handover execution offset.

The terminal 401 may determine whether a handover preparation event for the first target base station 403 occurs (S410). For example, when the difference between the received signal strength of the serving base station 402 and the received signal strength of the first target base station 403 is greater than or equal to the first offset, the terminal 401 performs handover to the first target base station 403. It may be determined that a preparation event has occurred.

The terminal 401 may transmit a measurement report message including information about the received signal strength of the first target base station 403 to the serving base station 402 (S421). The serving base station 402 may receive a measurement report message from the terminal 401 .

The serving base station 402 may transmit a handover preparation message to the first target base station 403 based on the measurement report message received from the terminal 401 (S422). The first target base station 403 may receive a handover preparation message from the serving base station 402 .

The first target base station 403 may reserve resources for the terminal 401 based on the handover preparation message received from the serving base station 402 (S423).

The first target base station 403 may transmit a handover preparation response message to the serving base station 402 (S424). The handover preparation response message may be a response message to the handover preparation message. The handover preparation message may include a message notifying that resources for the terminal 401 are reserved. The serving base station 402 may receive a handover command message from the first target base station 403 .

The serving base station 402 may transmit a handover command message to the terminal 401 based on the handover preparation response message received from the first target base station 403 (S425). The terminal 401 may receive a handover command message from the serving base station 402 .

Similarly, the terminal 401 may determine whether a handover preparation event for the second target base station 404 occurs (S430). For example, when the difference between the received signal strength of the serving base station 402 and the received signal strength of the second target base station 404 is equal to or greater than the first offset, the terminal 401 performs handover to the second target base station 404. It may be determined that a preparation event has occurred.

The terminal 401 may transmit a measurement report message including information about the received signal strength of the second target base station 404 to the serving base station 402 (S441). The serving base station 402 may receive a measurement report message from the terminal 401 .

The serving base station 402 may transmit a handover preparation message to the second target base station 404 based on the measurement report message received from the terminal 401 (S442). The second target base station 404 may receive a handover preparation message from the serving base station 402 .

The second target base station 404 may reserve resources for the terminal 401 based on the handover preparation message received from the serving base station 402 (S443).

The second target base station 404 may transmit a handover preparation response message to the serving base station 402 (S444). The handover preparation response message may be a response message to the handover preparation message. The handover preparation message may include a message notifying that resources for the terminal 401 are reserved. The serving base station 402 may receive a handover preparation response message from the second target base station 404 .

The serving base station 402 may transmit a handover command message to the terminal 401 based on the handover preparation response message received from the second target base station 404 (S445). The terminal 401 may receive a handover command message from the serving base station 402 .

The terminal 401 may monitor the received signal strength of each of the serving base station 402 and the plurality of target base stations 403 and 404 (S450). That is, after receiving the handover command message from the serving base station 402, the terminal 401 may not immediately perform handover. For example, when the terminal 401 receives a plurality of handover command messages from the serving base station 402 (S425 and S445), the received signal strength of each of the plurality of target base stations 403 and 404 and the serving base station ( Based on the result of comparing received signal strengths in step 402, a handover execution time point and a target base station to be handed over may be determined.

For example, the terminal 401 may determine whether a base station having a difference in received signal strength from the serving base station 402 among the plurality of target base stations 403 and 404 is equal to or greater than the handover execution offset.

For example, when the difference between the received signal strength of the first target base station 403 and the received signal strength of the serving base station 402 is equal to or greater than the handover execution offset, the terminal 401 receives a handover for the first target base station 403. It may be determined that an over event has occurred (S451). The terminal 401 may determine a time when a handover event for the first target base station 403 occurs as a time point for performing handover for the first target base station 403 . In addition, when a handover event occurs for the first target base station 403, the terminal 401 selects the first target base station 403 among a plurality of target base stations 403 and 404 as a target base station for handover. can decide

When a handover execution event for the first target base station 403 occurs, the terminal 401 notifies the serving base station 402 of handover to the first target base station 403 in advance (handover notification). ) message can be transmitted (S461). The serving base station 402 may receive a handover notification message from the terminal 401 .

The serving base station 402 may transmit a handover notification response message to the terminal 401 based on the handover notification message received from the terminal 401 (S462). The terminal 401 may receive a handover notification response message from the serving base station 402 .

The serving base station 402 may forward the handover notification message received from the terminal 401 to the first target base station 403 (S463). At this time, the serving base station 402 may transmit data to be transmitted to the terminal 401 to the first target base station 403 together with a handover notification message.

The terminal 401 may perform handover to the first target base station 403 (S470). The first target base station 403 may be connected to the terminal 401 according to handover of the terminal 401 .

After the serving base station 402 transmits the handover notification message to the first target base station 403, the resource release requests the second target base station 404 to release resources reserved for the terminal 401. A message can be transmitted (S480). The second target base station 404 may receive a resource release message from the serving base station 402 . The second target base station 404 may release resources reserved for the terminal 401 based on the resource release message received from the serving base station 402 .

5A to 5C are flowcharts illustrating an operation sequence of a terminal performing handover in a wireless communication system according to a second embodiment of the present invention.

Referring to FIG. 5A , in a wireless communication system, a terminal may perform an operation for setting an initial handover event and transmitting a measurement report (S501). For example, the terminal can access the serving base station. At this time, the serving base station may transmit configuration information of the handover event to the terminal. That is, the terminal can receive configuration information from the serving base station. The terminal may configure a handover event based on configuration information received from the serving base station. The handover event may include a handover preparation event and a handover execution event. For example, the UE may set an initial handover preparation offset value and a handover execution offset value based on configuration information.

Here, the wireless communication system may be the same as or similar to the wireless communication system of FIG. 4 . Also, the terminal may operate the same as or similar to the terminal 401 of FIG. 4 . In addition, each of the first target base station and neighboring base stations below may operate the same as or similar to the first target base station 403 or the second target base station 404 of FIG. 4 .

The terminal may transmit a measurement report message to the serving base station when a handover preparation event occurs based on the handover event. For example, the terminal may determine that a handover preparation event has occurred when the difference between the received signal strength of the serving base station and the received signal strength of the target base station is equal to or greater than the handover preparation offset value. At this time, the terminal may transmit a measurement report message including channel state information about the received signal strength of the target base station to the serving base station.

The configuration information includes a first handover preparation offset value and a first handover preparation offset value capable of determining a handover preparation event and a handover execution event, which are triggered when the terminal has a radio link state with the serving base station in a normal state. 1 may further include a handover execution offset value. When the received signal strength of the serving base station is greater than or equal to a predetermined threshold value, the terminal may determine that the radio link state with the serving base station is normal.

In addition, the setting information includes a second handover preparation offset value and a second handover preparation event capable of determining each of a handover preparation event and a handover execution event triggered when the radio link state between the terminal and the serving base station is abnormal. It may further include an execution offset value. When the received signal strength of the serving base station is less than a predetermined threshold value, the terminal may determine that the radio link state with the serving base station is abnormal.

In addition, the configuration information may further include a third handover execution offset value capable of determining a handover execution event triggered when a radio link failure with respect to the serving base station occurs.

In this case, the first preparation offset value may exceed the second preparation offset value. The first running offset value may exceed the second running offset value. The second running offset value may exceed the third running offset value.

For example, first and second handover preparation offset values and first to third handover execution offset values may be set as shown in Table 1 below.

Handover preparation offset value Handover Execution Offset Value Radio link status normal A3 offset 2db A3 offset 5db Wireless link status abnormal A3 offset 1db A3 offset 3db RLF occurs - A3 offset 0db

The terminal may determine that a handover preparation event or a handover execution event has occurred when the received signal strength of the target base station is greater than the received signal strength of the serving base station by a specific offset. For example, a wireless communication system according to an embodiment of the present invention may include an LTE system. At this time, the terminal may use the measurement A3 (measurement A3) event of the LTE system as a handover execution event and a handover preparation event. In addition, the terminal may use other measurement events other than the measurement A3 event. In general, an offset value for a handover execution event may have a larger value than an offset value for a handover preparation event.

Based on the handover event set based on the handover configuration information received from the serving base station, the terminal can determine the occurrence of a handover preparation event and a handover execution event according to the state of a radio link with the serving base station and whether RLF has occurred. .

For example, the terminal may determine that a handover preparation event has occurred when the difference between the received signal strength of the first target base station and the received signal strength of the serving base station is greater than or equal to a preset handover preparation offset value. When a handover preparation event occurs, the terminal may transmit a measurement report message to the serving base station. The measurement report message may include channel state information including information about the received signal strength of the first target base station measured by the terminal. The serving base station may receive a measurement report message from the terminal.

The serving base station may transmit a handover preparation message to the first target base station based on the measurement report message received from the terminal. The first target base station may receive a handover preparation message from the serving base station.

The first target base station may transmit a handover preparation response message to the serving base station based on the handover preparation message received from the serving base station. The serving base station may receive a handover preparation response message from the first target base station. The serving base station may transmit a handover command message to the terminal based on the handover preparation response message from the first target base station.

The terminal may receive a handover command message from the serving base station (S502).

The terminal may determine whether a handover execution event occurs for the first target base station (S503). For example, the terminal may determine whether a difference between the received signal strength of the first target base station and the received signal strength of the serving base station is greater than or equal to a preset handover execution offset value for a preset time. The terminal may determine that a handover execution event for the first target base station has occurred when the difference between the received signal strength of the first target base station and the received signal strength of the serving base station is greater than or equal to a preset handover execution offset value for a preset time. there is. At this time, the terminal may proceed to step S512 and perform handover to the first target base station based on the handover command message received from the serving base station.

On the other hand, if the difference between the received signal strength of the first target base station and the received signal strength of the serving base station is less than a preset handover execution offset value for a preset time period, the terminal does not generate a handover execution event for the first target base station. sound can be determined. At this time, the terminal may store the handover command message received from the serving base station (S504). Thereafter, the terminal may perform measurement of a radio link state with the serving base station (S505).

Referring to Figure 5b, the terminal can determine whether the radio link state with the serving base station is a normal state (S506). For example, when the received signal strength of the serving base station is greater than or equal to a predetermined threshold strength, the terminal may determine that the radio link state with the serving base station is a normal state.

The terminal may apply the handover preparation and execution event values in the normal state (S507). For example, the terminal may set the first handover preparation offset value as a handover preparation event triggering value when the radio link is in a normal state based on the handover configuration information received from the serving base station. Accordingly, when the radio link is in a normal state and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the first handover preparation offset value for a preset time, the terminal handover to the first target base station It is possible to detect that an over preparation event has occurred.

In addition, the terminal may set the first handover execution offset value as a handover execution event triggering value when the radio link is in a normal state based on the handover configuration information received from the serving base station. Accordingly, when the radio link is in a normal state and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the first handover execution offset value for a preset time, the terminal performs a handover for the first target base station. It is possible to detect that an overrun event has occurred.

On the other hand, in step S506, when the radio link state with the serving base station is in an abnormal state, the terminal may proceed to step S508. For example, when the received signal strength of the serving base station is less than a predetermined threshold strength, the terminal may determine that the radio link state with the serving base station is an abnormal state. Here, the received signal strength of the serving base station may mean reference signal received quality (RSRQ) or reference signal received power (RSRP).

In addition, when a radio problem occurs and the RLF timer operates, the terminal may determine that the radio link state with the serving base station is in an abnormal state. Here, the RLF timer may be a T310 timer of the LTE system.

At this time, the terminal may determine whether an RLF with the serving base station has occurred (S508). When the RLF with the serving base station occurs, the terminal may proceed to step S515.

When the RLF with the serving base station does not occur, the terminal may apply handover preparation and execution event values in an abnormal state (S509). For example, the terminal may set the second handover preparation offset value as a handover preparation event triggering value when the radio link is in an abnormal state based on the handover configuration information received from the serving base station. Accordingly, when the radio link is in an abnormal state, and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the second handover preparation offset value for a preset time, the terminal handover to the first target base station It is possible to detect that an over preparation event has occurred.

In addition, the terminal may set the second handover execution offset value as a handover execution event triggering value when the radio link is in an abnormal state based on the handover configuration information received from the serving base station. Accordingly, when the radio link is in an abnormal state, and the difference between the received signal strength of the serving base station and the received signal strength of the target base station is greater than or equal to the second handover execution offset value for a preset time, the terminal performs handover for the first target base station. It is possible to detect that an overrun event has occurred.

The terminal may determine whether a condition for generating a handover execution event is satisfied (S510). For example, when the radio link state with the serving base station is in a normal state, the terminal may determine whether a difference between the received signal strength of the serving base station and the received signal strength of the first target base station is greater than or equal to a first handover execution offset value. there is. Alternatively, when the non-state of the radio link with the serving base station is in a normal state, the terminal may determine whether a difference between the received signal strength of the serving base station and the received signal strength of the first target base station is greater than or equal to the second handover execution offset value. .

When a condition for generating a handover execution event is satisfied, the terminal may determine whether a handover command for the first target base station is stored (S511). For example, when the difference between the received signal strength of the serving base station and the received signal strength of the first target base station is greater than or equal to a first handover execution offset value when the radio link with the serving base station is in a normal state, the user equipment for the first target base station It may be determined whether a handover command is stored in advance. In addition, when the difference between the received signal strength of the serving base station and the received signal strength of the first target base station is greater than or equal to the second handover execution offset value when the radio link is in an abnormal state, the terminal stores a handover command for the first target base station in advance. You can decide whether it is or not.

When the handover command for the first target base station is stored, the terminal may perform handover to the first target base station (S512). On the other hand, if the handover command for the first target base station is not stored, the terminal may transmit a measurement report message including channel state information about the received signal strength of the first target base station to the serving base station (S514).

If the conditions for generating a handover execution event are not satisfied in step S510, the terminal may determine whether the conditions for generating a handover preparation event are satisfied (S513). For example, when the difference between the received signal strength of the serving base station and the received signal strength of the first target base station is greater than or equal to the first handover preparation offset value when the radio link with the serving base station is in a normal state, the terminal determines the first target base station. It may be determined that a condition for generating a handover preparation event is satisfied. In addition, when the difference between the received signal strength of the serving base station and the received signal strength of the first target base station is greater than or equal to the second handover preparation offset value, the terminal generates a handover preparation event for the first target base station when the radio link is in an abnormal state. It can be judged that the conditions for doing so are met.

When a condition for generating a handover preparation event is satisfied, the terminal may transmit a measurement report message to the serving base station (S514). For example, when a condition for generating a handover preparation event for a first target base station is satisfied, the terminal transmits a measurement report message including channel state information about the received signal strength of the first target base station to the serving base station. can At this time, when the radio link state with the serving base station is abnormal, the terminal may set a short period for transmitting the measurement report message to the serving base station to the serving base station for quicker response. That is, when the radio link state with the serving base station is abnormal, the terminal may transmit a measurement report message to the serving base station at a rapid cycle.

The serving base station may receive a measurement report message from the terminal. After transmitting the measurement report message to the serving base station, the terminal may return to step S502.

Referring to FIG. 5C , when the terminal detects RLF for the serving base station in step S508, the terminal may apply handover preparation and execution event values in the RLF state (S515). For example, the terminal may set the third handover execution offset value indicated by the handover configuration information received from the serving base station to a value triggering a handover execution event in the RLF state.

Thereafter, the terminal may perform measurement for cell selection (S516). For example, the terminal may measure the received signal strength of each of the measurable neighboring base stations.

The terminal may determine whether a condition for generating a handover execution event is satisfied based on the received signal strength of each neighboring base station (S517). For example, the terminal compares the difference between the received signal strength of the serving base station and the received signal strength of each neighboring base station, and the received signal strength is greater than or equal to the third handover execution offset value than the received signal strength of the serving base station for a preset time. A target base station can be determined.

At this time, the terminal may determine whether a handover command for the determined target base station is stored (S518). When the handover command for the determined target base station is stored, the terminal may perform handover to the determined target base station (S519).

The terminal may use a specific offset value set by the terminal without setting a separate handover event when RLF is detected. For example, when RLF is detected, the terminal may apply a low handover execution offset value so that handover is executed instead of performing an AS RLF recovery procedure in order to reduce data disconnection time. For example, when RLF is detected, the terminal may perform handover even if the received signal strength of the target base station corresponding to the stored handover command has a difference of less than 0 db from the received signal strength of the serving base station.

On the other hand, if the condition for generating a handover execution event is not met in step S517, the terminal may perform an RLF recovery procedure (S520). In addition, when the handover command for the target base station determined in step S518 is not stored, the terminal may perform an RLF recovery procedure.

The methods according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer readable medium. Computer readable media may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on a computer readable medium may be specially designed and configured for the present invention or may be known and usable to those skilled in computer software.

Examples of computer readable media include hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include high-level language codes that can be executed by a computer using an interpreter or the like as well as machine language codes generated by a compiler. The hardware device described above may be configured to operate with at least one software module to perform the operations of the present invention, and vice versa.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims are also included in the scope of the present invention. that fall within the scope of the right.

Claims (20)

As a method of operating a terminal in a communication system,
Receiving first setting information for a handover preparation event and second setting information for a handover execution event from a serving base station;
performing a measurement operation based on the first setting information;
determining that the handover preparation event has occurred based on a result of the measurement operation;
Transmitting a measurement report message including a result of the measurement operation for one or more cells to the serving base station;
Receiving a handover command message for at least one candidate cell among the one or more cells from the serving base station;
declaring a radio link failure (RLF) in a handover procedure;
selecting a first cell by performing a cell selection operation when the RLF is declared;
determining whether the first cell is one of the at least one candidate cell; and
and performing the handover procedure to the first cell when the first cell is one of the at least one candidate cell. The method of claim 1,
The operation method of the terminal,
If the first cell is not one of the at least one candidate cell, performing a radio resource control (RRC) connection re-establishment procedure to the first cell, of the terminal how it works. The method of claim 1,
The one or more cells include a cell of the serving base station and a cell of a neighboring base station. The method of claim 1,
The first setting information includes a first parameter set used to determine whether a handover preparation event has occurred, and the second setting information includes a second parameter set used to determine whether a handover execution event has occurred. A method of operating a terminal, including a parameter set. The method of claim 4,
The first parameter set includes a handover margin and a time to trigger (TTT). The method of claim 1,
When the measurement report message is received at the serving base station, a handover preparation message is transmitted from the serving base station to one or more neighboring base stations. As a terminal in a communication system,
processor;
a memory that communicates electronically with the processor; and
Includes instructions stored in the memory;
When the instructions are executed by the processor, the instructions cause the terminal to:
receiving first setting information for a handover preparation event and second setting information for a handover execution event from a serving base station;
performing a measurement operation based on the first setting information;
determining that the handover preparation event has occurred based on a result of the measurement operation;
Transmitting a measurement report message including a result of the measurement operation for one or more cells to the serving base station;
Receiving a handover command message for at least one candidate cell among the one or more cells from the serving base station;
Declare a radio link failure (RLF) in the handover procedure;
if the RLF is declared, selecting a first cell by performing a cell selection operation;
determining whether the first cell is one of the at least one candidate cell;
If the first cell is not one of the at least one candidate cell, performing a radio resource control (RRC) connection re-establishment procedure to the first cell; And
If the first cell is one of the at least one candidate cell, cause the handover procedure to be performed to the first cell. delete The method of claim 7,
The first setting information includes a first parameter set used to determine whether a handover preparation event has occurred, and the second setting information includes a second parameter set used to determine whether a handover execution event has occurred. A terminal, including a set of parameters. The method of claim 9,
The first parameter set includes a handover margin and a time to trigger (TTT). delete delete delete delete delete delete delete delete delete delete

Images