KR102612279B1 - Method and apparatus for synchronized handover in mobile communication system - Google Patents

Abstract

A synchronized handover method and apparatus in a mobile communication system are provided. The source base station that provides data to the terminal transmits a handover command message for handover to the target base station to the terminal, and later stops transmitting data to the terminal when it receives a message indicating the time to execute handover from the terminal. do. Then, data about the terminal is forwarded to the target base station.

Description

Synchronized handover method and apparatus in mobile communication system {Method and apparatus for synchronized handover in mobile communication system}

The present invention relates to handover, and more specifically, to a method and apparatus for performing synchronized handover.

Generally, in a mobile communication system, a handover is performed when a terminal moves and changes the base station to which it connects. When a handover occurs because the terminal moves, a disconnection time occurs during which data is not received while disconnecting from the source base station and connecting to the target base station. In order to reduce disconnection time, a handover method is being discussed that maintains the connection with the source base station during handover and disconnects the connection with the source base station after the connection with the target base station is completed.

However, the source base station transmits data to the terminal while forwarding the data to the target base station without knowing the handover operation status of the terminal. In this situation, since the source base station cannot know when the terminal will handover to the target base station, a problem of wasting resources between base stations by forwarding unnecessary data to the target base station may occur. Additionally, even though the terminal has already performed a handover to the target base station, a problem may occur in which the source base station transmits data to the terminal, thereby wasting radio resources.

The technical problem to be solved by the present invention is to provide a handover method and device that allows the terminal, the source base station, and the target base station to know when the terminal performs a handover from the source base station to the target base station.

A handover method according to a feature of the present invention includes the steps of a source base station providing data to a terminal transmitting a handover command message for handover to a target base station to the terminal; and the step of continuing to exchange data with the terminal after the source base station transmits the handover command message.

The handover method includes the steps of stopping data transmission to the terminal when the source base station receives a message indicating a handover execution time from the terminal after transmitting the handover command message; And it may further include, by the source base station, forwarding data for the terminal to the target base station.

The handover method may further include, before stopping data transmission, the terminal that has received the handover command message transmitting a message indicating a handover execution time to the source base station.

Meanwhile, the handover method includes the steps of stopping data transmission to the terminal when the source base station receives a message from the target base station indicating that the terminal has handed over; And it may further include, by the source base station, forwarding data for the terminal to the target base station.

In this case, the handover method includes, before stopping data transmission, the terminal directly performing a handover to the target base station at the time of handover execution; When the target base station recognizes that the terminal has handed over and fails to receive data forwarding related information from the source base station, notifying the source base station that the terminal has handed over; And it may further include, by the source base station, forwarding data for the terminal to the target base station.

Meanwhile, the handover method may further include the step of transmitting, by the source base station, a message indicating the handover execution time to the target base station so that the target base station can know the handover execution time of the terminal. You can.

The message indicating the handover execution time may be a handover notification message that notifies the determined handover time after the terminal determines the handover time, and the handover notification message includes a radio resource control (RRC) control message, It may be one of a MAC (media access control) control message or a PHY (physical) control signal.

The source base station and the terminal determine when the source base station receives a message indicating the handover execution time or when the source base station transmits an ACK for the handover notification message to the terminal. It can be judged by the point in time when an over is performed.

Meanwhile, in the handover method, before the terminal receives the handover command message and transmits a message indicating the time to execute the handover, radio resource configuration information for at least one target base station is provided and set in advance. Additional steps may be included.

If the terminal is capable of performing the Pre-RACH (Random Access CHannel) procedure, the handover method includes the steps of the terminal performing the Pre-RACH procedure and transmitting a preamble for random access to the target base station; And the terminal may further include receiving a random access response from the target base station, where the response includes radio resource configuration information.

In this case, the handover method may further include the step of the terminal directly handing over to the target base station without a separate random access procedure based on the radio resource configuration information at the time of handover execution.

Additionally, the handover method may determine the point in time at which the random access response is successfully received as the handover execution point based on the success of the Pre-RACH procedure.

Meanwhile, the handover method may further include determining the time when the target base station receives a message indicating the handover execution time as the handover execution time of the terminal.

Meanwhile, the handover method includes, when the terminal does not perform a random access procedure to the target base station, the target base station transmitting data or uplink scheduling information to the terminal at the time of handover of the terminal. may further include.

A handover method according to another feature of the present invention includes the steps of a terminal receiving a handover command message for handover from a source base station to a target base station; After receiving the handover command message, the terminal receives and sets radio resource configuration information for at least one target base station in advance; transmitting, by the terminal, a message indicating a handover execution point to the source base station; and the step of the terminal disconnecting from the source base station at the time of executing the handover and performing handover to the corresponding target base station based on the radio resource configuration information.

A base station according to another feature of the present invention is a base station that performs handover, and includes a transceiver unit that transmits and receives signals through an antenna; and a processor connected to the transceiver and performing handover processing, wherein the processor receives a message indicating a handover execution time from the terminal after transmitting a handover command message to the terminal through the transceiver. Upon reception, it is configured to stop transmitting data to the terminal and forward the data for the terminal to the target base station.

The processor may be configured to transmit a message indicating the handover execution time to the target base station through the transceiver so that the target base station can know the handover execution time of the terminal.

A terminal according to another feature of the present invention is a terminal that performs handover, and includes a transmitter and receiver that transmits and receives signals through an antenna; and a processor connected to the transceiver and performing handover processing, wherein the processor receives a handover command message from the source base station through the transceiver and then provides radio resources for at least one target base station. Receive and set setting information in advance; transmitting a message indicating a handover execution time to the source base station through the transceiver; And, at the time of executing the handover, it is configured to disconnect from the source base station and perform handover to the corresponding target base station based on the radio resource configuration information.

The processor performs a Pre-RACH procedure, transmits a preamble for random access to the target base station through the transceiver, and receives a random access response - the response includes radio resource configuration information - from the target base station. It can be configured.

Depending on the success of the Pre-RACH procedure, the time when the random access response is successfully received may be determined as the handover execution time.

According to an embodiment of the present invention, during handover, the terminal, source base station, and target base station can all know when the terminal performs handover from the source base station to the target base station, so the time for the terminal and the base station to disconnect data is reduced. become the same

Accordingly, while the terminal is executing handover, the interruption time in which data is disconnected during handover can be reduced without wasting radio resources, and as a result, communication quality can be improved.

Figure 1 is a diagram showing a network environment in which handover is performed according to an embodiment of the present invention.
Figure 2 is a flowchart showing a general handover process.
Figure 3 is a diagram showing data interruption time.
Figure 4 is a flowchart of a handover method according to the first embodiment of the present invention.
Figure 5 is a flowchart of a handover method according to a second embodiment of the present invention.
Figure 6 is a diagram showing the structure of a terminal according to an embodiment of the present invention.
Figure 7 is a diagram showing the structure of a base station according to an embodiment of the present invention.

Below, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

Throughout the specification and claims, when a part is said to 'include' a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

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

In addition, the base station (BS) is an advanced base station (ABS), a high reliability base station (HR-BS), a node B, an evolved node B, eNodeB or eNB), access point (AP), radio access station (RAS), base transceiver station (BTS), mobile multihop relay (MMR)-BS, repeater that acts as a base station (relay station, RS), relay node (RN) that acts as a base station, advanced relay station (ARS) that acts as a base station, high reliability relay station (high reliability relay station) that acts as a base station , HR-RS), small base station [femto base station (femoto BS), home node B (HNB), home eNodeB (HeNB), pico base station (pico BS), metro base station (metro BS), micro base station ( micro BS), etc.] may refer to all or part of eNode, ABS, Node B, eNodeB, eNB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc. It may also include the functions of

Hereinafter, a handover method and device according to an embodiment of the present invention will be described.

Figure 1 is a diagram showing a network environment in which handover is performed according to an embodiment of the present invention.

As shown in Figure 1, in a network environment where a plurality of small cells are mixed, a user equipment (UE) 1 connects to the corresponding cell through a base station that manages each cell. While moving, the terminal 1 is connected to the target base station 3 (target station or S(source)-eNB) of the currently connected cell. Handover to T-eNB) can be performed.

In this wireless channel environment, handover as shown in FIG. 2 can be performed.

Figure 2 is a flowchart showing the existing handover process.

The terminal (1) measures the strength of the signal received from the source base station (2) and neighboring base stations and sends the channel status information of the serving cell and neighboring cells to the source base station (2) through a Measurement Report message. When transmitted, the source base station 2 determines whether to handover the terminal and transmits a message commanding handover to the terminal (S100). In this case, the source base station 2 stops transmitting data to the terminal 1 while transmitting a handover command message (HO command) (S110) and forwards the data to the target base station 3 (S120). The target base station 3 receives the forwarded data and stores it in a buffer (S130).

The terminal 1 receives and processes the handover command message (S140), disconnects the wireless connection with the source base station 2 according to the received handover command message, and attempts to connect to the target base station 3 (S140). . The terminal 1 transmits a preamble (RA preamble) for random access (RA) to the target base station (S160), and receives a random access response (uplink resource allocation (UL allocation) and When timing realignment (Timing Alignment (TA) information, etc.) is received (S170), a handover completion message (HO complete) is transmitted to the target base station 3 (S180). The target base station 3 receives the handover completion message and then transmits data to the terminal 1 (S170).

During this handover, data interruption occurs from the time the terminal disconnects the wireless connection with the source base station and attempts to connect to the target base station until it first receives data from the target base station. The data interruption time may be the time from when the source base station stops transmitting data to the terminal while transmitting a handover command message to the time when the target base station transmits data to the terminal after receiving a handover completion message.

Figure 3 is a diagram showing data interruption time.

The data interruption time can be expressed as follows.

Here, T _{break _source} indicates the time it takes for data transmission to the terminal to stop when the source base station transmits a handover command message to the terminal and for the terminal to receive the handover command message. T _proc represents the time required to process the handover command message received by the terminal. T _interrupt is a preprocessing task (e.g., RF/baseband tuning, downlink (DL) synchronization, waiting for RACH (random access channel) access opportunity) for the terminal to access the target base station. It represents the time required to perform RACH opportunity (RACH opportunity), etc. T _rach represents the time it takes for the terminal to transmit a preamble (RA preamble) for random access to the target base station and receive a random access response (RA response) in response. T _CR represents the time it takes for the target base station to receive a handover completion message from the terminal for contention resolution and to first transmit data to the terminal until the terminal receives the data.

In an embodiment of the present invention, in order to reduce this data disconnection time, the data disconnection time between the terminal and the base station is made the same.

Figure 4 is a flowchart of a handover method according to the first embodiment of the present invention.

In the first embodiment of the present invention, the source base station does not immediately stop data transmission to the terminal while transmitting the handover command message, but when it receives a message indicating the time to execute the handover from the terminal after transmitting the handover command message, the terminal Stop data transmission to. The message indicating the handover execution time can be used as a message indicating the handover execution time after the terminal determines the handover execution time, that is, a handover notification message (HO Indication). Hereinafter, the handover method according to the first embodiment of the present invention will be described, taking as an example the use of a handover notification message (HO Indication) as a message indicating the time of handover execution.

As shown in the attached FIG. 4, the source base station 2 determines whether to handover the terminal (S300) and transmits a message commanding handover to the terminal (S310). In this case, the source base station 2 maintains data transmission to the terminal 1 without stopping while transmitting a handover command message (HO command).

The terminal 1 receives and processes the handover command message (S320). Even at this time, the terminal 1 receives data from the source base station 2 while the data transmission of the source base station 2 continues (S330).

After determining the handover execution time, the terminal 1 transmits a handover notification message (HO Indication) indicating the handover execution time to the source base station 2 (S340, S350). For example, the terminal 1 may determine a specific point in time after receiving a handover command message as the handover execution time, and may determine the case when a handover execution event occurs as the handover execution time. . For example, the terminal 1 executes a preset handover execution event (e.g., when the signal strength of the target base station is greater than the signal strength of the source base station for a certain period of time, the terminal completes downlink synchronization with the target base station). When a handover occurs, the handover execution point is determined. The handover notification message may include information about the target base station determined by the terminal. Until this time, the terminal 1 can continue to receive data from the source base station 2, so no data interruption occurs.

When the source base station 2 receives the handover notification message (HO Indication), it forwards data to the target base station 3 (S360) and stops transmitting data to the terminal 1. The source base station 2 determines that the time of receiving the handover notification message (HO Indication) is the handover execution time of the terminal at which the terminal is performing handover, and stops transmitting data to the terminal. At this time, the source base station 2 transmits an information transfer message (eg, SN Status Transfer) to the target base station 3, and the information transfer message includes data sequence number information and data. The target base station 3 stores the forwarded data in a buffer (S370).

The terminal 1 transmits a handover notification message (HO Indication) and then performs handover to the target base station. That is, the terminal 1 disconnects the wireless connection from the source base station 2 and attempts to connect to the target base station 3 (S380). The terminal 1 transmits a preamble for RA to the target base station (S390), and upon receiving a random access response from the target base station 3 (S400), sends a handover completion message (HO complete) to the target base station. Send to (3) (S410).

During handover according to this embodiment of the present invention, the data disconnection time can be expressed as follows.

Here, T _rach represents the time it takes for the terminal to transmit a preamble for random access to the target base station and receive a random access response in response. T _CR represents the time it takes for the target base station to receive a handover completion message from the terminal to resolve contention and first transmit data to the terminal until the terminal receives the data.

Compared to before, T _{break _source} and T _proc can be set to "0". In particular, when the terminal transmits a message through MAC layer signaling, T _{break _source} can be set to exactly 0 ms.

In this way, compared to the existing case where the source base station stops transmitting data to the terminal while transmitting a handover command message, in the embodiment of the present invention, data transmission to the terminal is stopped even when the source base station transmits a handover command message. If a handover notification message is received from the terminal later, data transmission to the terminal is stopped, thereby significantly reducing the data disconnection time.

Figure 5 is a flowchart of a handover method according to a second embodiment of the present invention.

In the second embodiment of the present invention, the source base station does not immediately stop data transmission to the terminal while transmitting the handover command message, but when it receives a message indicating the time to execute the handover from the terminal after transmitting the handover command message, the terminal Stop data transmission to. The message indicating the time to execute handover may be the same message as exemplified in the first embodiment described above. In particular, in the second embodiment of the present invention, in order to further reduce data disconnection time, radio resources for the target cell are provided so that the terminal can perform handover immediately after transmitting a message indicating the handover execution time to the source base station. Setting information can be set in advance. Accordingly, RACH-less or Pre-RACH is applied to handover to reduce data disconnection time. RACH-less refers to a case where an RA procedure is not required when the terminal performs a handover to the target base station, and Pre-RACH refers to the case where the terminal secures and sets the radio resource configuration information of the target base station in advance before executing the handover. , This indicates a case in which the terminal performs an RA procedure in advance with the target base station before handover to the target base station, so that the RA procedure is not necessary at the time of actual handover to the target base station. When RACH-less is applied, the RACH preamble procedure, in which the UE transmits a preamble, and the uplink resource allocation and timing realignment procedures (UL allocation and TA for UE procedures) according to the RA response transmitted by the target base station to the UE can be omitted. there is.

Specifically, as shown in FIG. 5, the source base station 2 determines whether to handover the terminal (S500) and transmits a message commanding handover to the terminal (S510). In this case, the source base station 2 maintains data transmission to the terminal 1 without stopping while transmitting a handover command message (HO command).

The terminal 1 receives and processes the handover command message (S520). Even at this time, the terminal 1 still receives data from the source base station 2 (S530). The terminal 1 performs a Pre-RACH procedure to the target base station 3. That is, the terminal 1 transmits an RA preamble to the target base station (S540) and receives a random access response from the target base station 3 (S550). Even at this time, the source base station 2 maintains data transmission to the terminal 1 without stopping.

After performing the Pre-RACH procedure, the terminal 1 transmits a handover notification message (HO Indication) indicating when to execute the handover to the source base station 2 (S560, S570). As illustrated in the first embodiment, the terminal 1 may determine a specific point in time after receiving a handover command message as the handover execution time, or may determine a case in which a handover execution event occurs as the handover execution time. The handover notification message may include information about the target base station determined by the terminal. Additionally, the terminal 1 can determine the time when the Pre-RACH procedure is successfully completed as the handover execution time.

When the source base station 2 receives the handover notification message (HO Indication), it forwards data to the target base station 3 (S580) and stops transmitting data to the terminal 1. The source base station 2 determines that the time of receiving the handover notification message (HO Indication) is the handover execution time of the terminal at which the terminal is performing handover, and stops transmitting data to the terminal. At this time, the source base station 2 transmits an information transfer message (eg, SN Status Transfer) to the target base station 3, and the information transfer message includes data sequence number information and data. The target base station 3 stores the forwarded data in a buffer (S590).

The terminal 1 transmits a handover notification message (HO Indication) and then performs handover to the target base station. That is, the terminal 1 disconnects the wireless connection from the source base station 2 and connects to the target base station 3 (S600). Since the Pre-RACH procedure has already been performed in the previous steps (S540, S550), the terminal does not perform a separate RA procedure. Meanwhile, when the terminal's data is forwarded from the source base station (2), the target base station (3) transmits the data to the terminal (1) (S610).

The terminal 1 may preset radio resource configuration information for at least one target cell, and thus may perform handover immediately after transmitting a message notifying the source base station of the handover execution time. That is, the terminal immediately performs handover to the target cell by simply activating the radio resource setting information of the target cell that was set in advance at the time of handover execution.

Meanwhile, if the terminal does not need to perform the RA procedure as described above, the target base station 3 transmits data to the terminal immediately from the time of handover execution of the terminal or transmits a handover completion message through uplink scheduling. Information can be transmitted to the terminal.

During handover according to the embodiment of the present invention as described above, the data disconnection time can be expressed as follows.

Here, T _CR represents the time it takes for the target base station to receive a handover completion message from the terminal to resolve contention and first transmit data to the terminal until the terminal receives the data. Additionally, if the target base station transmits downlink data immediately at the time of handover of the terminal, T _CR can be set to 0, and data interruption time during handover can be completely eliminated.

In this way, compared to the existing case where the source base station stops transmitting data to the terminal while transmitting a handover command message, in the embodiment of the present invention, data transmission to the terminal is stopped even when the source base station transmits a handover command message. If a handover notification message is received from the terminal later, data transmission to the terminal is stopped, and in addition, while the source base station has stopped data transmission to the terminal, the terminal performs pre-processing before data transmission is stopped. Based on the RACH procedure, data disconnection time can be significantly reduced by directly connecting to the target base station without the RA procedure and receiving data.

In the embodiments of the present invention described above, the source base station 2 can forward the handover notification message (HO Indication) received from the terminal 1 to the target base station 3 as necessary. In this case, the target base station 3 may determine the time of receiving the handover notification message (HO Indication), which is a message indicating the handover execution time of the terminal, as the handover execution time of the terminal at which the terminal performs the handover. there is.

Additionally, in the first embodiment, the handover execution time point is determined according to the PRACH occasion at the target base station, and the waiting time for the PRACH occasion at the target base station can be set to close to 0 and less than 1 subframe. For example, during the data interruption time T _interrupt during handover, T _IU can be set to 0 ms. For example, if the PRACH occasion is set in the first subframe (even subframe subframe 1) of every even subframe (even subframe), the terminal can directly transmit the RA preamble to the target base station in even subframe subframe 1.

Additionally, in order to reduce data duplication, the terminal 1 may also transmit data information received from the source base station 2 when transmitting a handover notification message (HO Indication) to the source base station 2. At this time, the terminal 1 may transmit data information by including it in a predetermined message (Radio Link Control (RLC) Status Packet Data Unit (PDU) or Packet Data Convergence Protocol (PDCP) Status Report). Additionally, the source base station 2 may transmit a handover notification response message (HO Indication ACK) to the terminal 1 as a response message to the handover notification message (HO Indication). At this time, the source base station 2 may transmit the data information received from the terminal along with a handover notification response message (HO Indication ACK) by including it in a predetermined message (RLC Status PDU or PDCP Status Report).

Meanwhile, in the embodiment of the present invention described above, the handover notification message is a method of notifying handover performance using a media access control (MAC) control element, and a radio resource control (RRC) message. It can be transmitted through a method of notifying handover performance, a method of notifying handover performance using a PHY (physical) channel, etc. That is, the handover notification message may be a MAC control message, an RRC control message, or a PHY control signal. In addition, the terminal and the source base station consider the time when the handover notification message is received from the source base station or when the source base station transmits an ACK for the handover notification message to the terminal as the handover execution time of the terminal at which the terminal performs the handover. You can judge.

At the time of handover as described above, the terminal informs the source base station of the point in time when handover is performed from the source base station to the target base station. Accordingly, the source base station performs data forwarding to the target base station or the source base station sends a handover notification message. By transmitting the information to the target base station, the terminal, source base station, and target base station can all know the terminal's handover execution time. In addition, the terminal disconnects from the source base station after transmitting the handover notification message, and the source base station receives the handover notification message and stops transmitting data to the terminal, so that the time for the terminal and the base station to disconnect data is the same.

If the terminal fails to transmit the handover notification message, the handover may be performed immediately or the handover may be performed immediately without transmitting the handover notification message. At this time, the target base station may not receive data forwarding-related information from the source base station. In this case, as the terminal hands over to the target base station, the target base station notifies the source base station that the terminal has handed over, the source base station stops transmitting data to the terminal, forwards the data to the target base station, and sends an SN Status Transfer message. It can be delivered.

Figure 6 is a structural diagram of a terminal according to an embodiment of the present invention.

As shown in the attached FIG. 6, the terminal 1 according to an embodiment of the present invention includes a processor 110, a memory 120, and a transceiver 130. The processor 110 may be configured to implement the methods described based on FIG. 4 or FIG. 5 above.

The memory 120 is connected to the processor 110 and stores various information related to the operation of the processor 110. The memory 120 may store instructions to be executed by the processor 110 or may load instructions from a storage device (not shown) and temporarily store them. The processor 110 may execute instructions stored or loaded in the memory 120. The processor 110 and the memory 120 are connected to each other through a bus (not shown), and an input/output interface (not shown) may also be connected to the bus.

Figure 7 is a structural diagram of a base station according to an embodiment of the present invention.

As shown in the attached FIG. 7, the base station 2 according to an embodiment of the present invention includes a processor 210, a memory 220, and a transceiver 230.

The processor 210 may be configured to implement the methods described based on FIG. 4 or FIG. 5 above.

The memory 220 is connected to the processor 210 and stores various information related to the operation of the processor 210. The memory 220 stores instructions to be executed by the processor 210, or can load instructions from a storage device (not shown) and temporarily store them.

The processor 210 may execute instructions stored or loaded in the memory 220. The processor 210 and the memory 220 are connected to each other through a bus (not shown), and an input/output interface (not shown) may also be connected to the bus.

The embodiments of the present invention are not implemented only through the devices and/or methods described above, but can be implemented through programs for realizing functions corresponding to the configuration of the embodiments of the present invention, recording media on which the programs are recorded, etc. This implementation can be easily implemented by an expert in the technical field to which the present invention belongs based on the description of the embodiments described above.

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 of the present invention by operators using the basic concept of the present invention defined in the following claims are also possible. It falls within the scope of rights.

Claims (20)

In the operation method for handover,
A process of receiving, by a terminal, a handover command message for handover from a source base station to a target base station,
A process of determining, by the terminal, a handover execution time after receiving the handover command message;
In order for the target base station to recognize the handover execution time via the source base station, the terminal transmits a message informing the source base station of the handover execution time;
A process of transmitting and receiving data from a serving base station by the terminal while maintaining a connection with the serving base station until the handover execution time;
A process of executing, by the terminal, the handover to the target base station at the handover execution time;
The handover execution time is determined based on the timing of the first available uplink transmission to the target base station,
The first available time of uplink transmission is a time when random access preamble transmission to the target base station is possible or a time when uplink data can be transmitted to the target base station. In claim 1,
The process of receiving the handover command message is,
It includes a process of acquiring a PRACH (physical random access channel) occurrence indicating subframe information for random access preamble transmission,
The process of determining the handover execution time is,
A method including a process of determining a time when preamble transmission is possible based on PRACH permissions using the handover execution time. In claim 1,
After receiving the handover command message,
A process of performing, by the terminal, a Pre-RACH (pre-random access channel) procedure for transmitting a random access preamble to the target base station;
A process of receiving, by the terminal, a random access response from the target base station, wherein the random access response includes radio resource configuration information for uplink data transmission,
The process of determining the handover execution time is a method of determining a time when uplink data can be transmitted to the target base station as the handover execution time based on the radio resource configuration information. The method of claim 1, wherein the process of receiving the handover command message includes radio resource configuration information for uplink data transmission to the target base station and uplink synchronization information for the target base station without a random access procedure for the target base station. Including the process of acquiring,
The process of determining the handover execution time is such that when the random access procedure for the target base station is not needed, uplink data can be transmitted to the target base station based on the uplink synchronization information and the radio resource configuration information. A method including the process of determining a point in time as the handover execution time. The method of claim 1, wherein the source base station stops sending data to the terminal and forwards the data of the terminal to the target base station when receiving a message indicating the handover execution time. delete In claim 1,
The message indicating the handover execution time is,
This is a handover notification message that notifies the determined handover time after the terminal determines the handover time,
The handover notification message is one of a radio resource control (RRC) control message, a media access control (MAC) control message, and a physical (PHY) control signal. In the method for handover,
A process of acquiring radio resource control (RRC) context information of the terminal by the target base station through a handover preliminary procedure for the source base station,
A process of receiving a preamble for random access from the terminal by the target base station,
A process of receiving a preamble for random access from the terminal by the target base station,
A process of transmitting, by the target base station, a random access response containing radio resource configuration information for uplink data transmission to the terminal;
A process of receiving, by the target base station, a message from the source base station informing of the handover execution time determined by the terminal;
A method comprising transmitting a handover completion message or uplink scheduling information for data at the handover execution time of the terminal by the target base station. The method of claim 8, wherein the target base station determines the point in time at which the target base station receives the message indicating the handover execution time as the handover execution time of the terminal. The method of claim 8, wherein by the target base station,
When the terminal recognizes that it has been handed over to the target base station and does not receive data forwarding-related information, the method further includes the step of transmitting a message to notify that the terminal has been handed over from the source base station to the target base station. In claim 8,
The terminal and the source base station perform handover at the point when the source base station receives the message for informing the handover execution time or when the terminal receives the ACK for the handover indication message from the source base station. How to decide when to run . In a terminal for performing handover,
A transmitter and receiver for transmitting and receiving signals through an antenna, and
It includes a processor connected to the transceiver and executing a handover procedure,
The processor,
By the terminal, a handover command message for handover is received from the source base station to the target base station,
The terminal determines a handover execution time after receiving the handover command message,
In order for the target base station to recognize the handover execution time via the source base station, the terminal transmits a message informing the source base station of the handover execution time,
While maintaining the connection with the serving base station until the handover execution time, data is transmitted and received from the serving base station by the terminal,
By the terminal, the handover is performed to the target base station at the handover execution time,
The handover execution time is determined based on the timing of the first available uplink transmission to the target base station,
The first available time of uplink transmission is a time when random access preamble transmission to the target base station is possible or a time when uplink data can be transmitted to the target base station. The method of claim 12, wherein the processor:
Obtain a PRACH (physical random access channel) occurrence indicating subframe information for random access preamble transmission,
A device that determines when preamble transmission is possible based on PRACH permissions using the handover execution time. The method of claim 12, wherein the processor:
After receiving the handover command message,
The terminal performs a Pre-RACH (pre-random access channel) procedure to transmit a random access preamble to the target base station,
By the terminal, a random access response is received from the target base station, and the random access response includes radio resource configuration information for uplink data transmission,
A device that determines when uplink data can be transmitted to the target base station as the handover execution time based on the radio resource configuration information. The method of claim 14, wherein the processor:
A device that determines when uplink data can be transmitted to the target base station according to the success of the Pre-RACH as the handover execution time. The method of claim 12, wherein the processor is a base station that performs handover,
When a random access procedure is not required for the target base station, the time at which uplink data can be transmitted to the target base station is determined as the handover execution time based on pre-acquired uplink synchronization information and pre-acquired radio resource configuration information. A device that does.
delete delete delete delete

Images