KR20230141240A - Method and apparatus for handover for mobility robustness enhancement in mobile communication system - Google Patents

Abstract

A handover method and device for improving mobility robustness in a mobile communication system are provided. When the terminal connects, the source base station immediately transmits a CHO (Conditional Handover) request message to at least one candidate target base station, and includes the configuration of a CHO candidate cell related to the candidate target base station that transmitted a response message to the CHO request message. A message is sent to the terminal. Thereafter, when the source base station receives a message indicating that the handover of the terminal has been completed from one candidate target base station among at least one candidate target base station, it transmits a CHO cancellation message to the remaining candidate target base stations except for the one candidate target base station. do.

Description

{Method and apparatus for handover for mobility robustness enhancement in mobile communication system}

The present invention relates to handover, and more specifically, to a handover method and device for improving mobility robustness in a mobile communication system.

Several mobility robustness features have been introduced in mobile communication networks. However, in some network areas, there is still a problem that a large number of handover (HO) failures leads to a higher attrition rate and a large number of radio resource control (RRC) re-establishments. These problems often occur when the wireless state changes quickly during the handover preparation phase or after attempting to execute a handover.

Self-organizing network (SON) algorithms cannot cope with such dynamic changes in the environment, but the user equipment (UE) itself continuously monitors the radio quality during the handover procedure and finally selects possible cells from the list of candidate neighbors cells. Improvements are possible if the best target cell can be selected.

This new feature is also called Conditional Handover (CHO) and is defined in 3GPP for both NG RAN (5G SA NR) and E-UTRAN (LTE).

However, even in this CHO method, when the terminal needs to transmit a measurement report, if wireless link (uplink) performance deteriorates, a problem may occur in which the measurement report is not connected to the network.

In addition, even if a measurement report is transmitted, if the HO command must be transmitted in the network, if wireless link (downlink) performance deteriorates, a problem may occur in which the HO command is not connected to the terminal. In this case, even if the CHO method is used for mobility robustness, it is bound to have the same problems as the existing method. Additionally, if it takes a long time to prepare the CHO, the probability that the handover may fail increases if the terminal moves at high speed.

The problem to be solved by the present invention is to provide a handover method and device that can further improve mobility robustness in a mobile communication system.

According to one embodiment, a handover method is provided. The handover method includes the steps of a source base station transmitting a CHO (Conditional Handover) request message to at least one candidate target base station immediately when a terminal connects; transmitting, by the source base station, a message including the configuration of a CHO candidate cell related to a candidate target base station that transmitted a response message to the CHO request message to the terminal; And when the source base station receives a message indicating that the handover of the terminal has been completed from one candidate target base station among the at least one candidate target base station, a CHO cancellation message is sent to the remaining candidate target base stations except for the one candidate target base station. It includes the step of transmitting.

According to an embodiment of the present invention, in a mobile communication system, handover failure may occur when a terminal moves at high speed or the wireless state changes quickly after a handover preparation phase or a handover execution attempt, thereby degrading wireless link performance. The number (probability) can be reduced.

In addition, as soon as the terminal connects to the base station, the source base station requests CHO from nearby candidate target base stations, so it prepares for handover at a high speed, so the number of handover failures (probability) that can occur when the terminal moves at high speed ) can be reduced.

Accordingly, mobility robustness during handover can be improved.

Figure 1 is a diagram showing a network environment according to an embodiment of the present invention.
Figure 2 is a flowchart of a handover method according to an embodiment of the present invention.
Figure 3 is a diagram showing a network environment after handover according to an embodiment of the present invention.
Figure 4 is a diagram showing the structure of a handover device 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, when a part “includes” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

In this specification, expressions described as singular may be interpreted as singular or plural, unless explicit expressions such as “one” or “single” are used.

Additionally, terms including ordinal numbers, such as first, second, etc., used in embodiments of the present invention may be used to describe components, but the components should not be limited by the terms. Terms are used only to distinguish one component from another. For example, a first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component without departing from the scope of the present invention.

Throughout the specification, terminal refers to user equipment (UE), mobile station (MS), mobile terminal (MT), advanced mobile station (AMS), high reliability mobile station. (high reliability mobile station, HR-MS), subscriber station (SS), portable subscriber station (PSS), access terminal (AT), machine type communication device, MTC device), etc., and may include all or part of the functions of terminal, MS, MT, AMS, HR-MS, SS, PSS, AT, etc.

In addition, the base station (BS) is Node B, evolved Node B (eNB), next generation Node B (gNB), advanced base station (ABS), and high reliability base station. (high reliability base station, HR-BS), access point (AP), radio access station (RAS), base transceiver station (BTS), mobile multihop relay (MMR)-BS, Relay station (RS) performing the role of a base station, Relay Node (RN) performing the role of a base station, Advanced relay station (ARS) performing the role of a base station, High reliability performing the role of a base station Repeater (high reliability relay station, HR-RS), small base station (femto BS), home Node B (HNB), home eNodeB (HeNB), pico base station (pico BS), macro base station ( It may refer to a macro BS, a micro BS, or a base station that supports RAT (Radio Access Technology), and may also refer to NB, eNB, gNB, ABS, AP, RAS, BTS, MMR-BS, RS, RN, It may include all or part of the functions of ARS, HR-RS, small base station, etc.

Hereinafter, a handover method and device for improving mobility robustness in a mobile communication system according to an embodiment of the present invention will be described.

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

As an example of an implementation, in a 5G-based mobile communication system, as shown in FIG. 1, within a cell where a plurality of base stations (e.g., gNB) exist, the terminal 1 is connected to the source base station 2 to provide a service. You can receive it. For example, it may be a heterogeneous network (HetNet) environment in which macro cells and small cells are mixed.

In this state, since the source base station 2 already knows the information about the base stations located around it, it sets its surrounding base stations as candidate target base stations 31 to 33 and automatically performs a CHO (Conditional Handover) operation. can be performed.

In an embodiment of the present invention, in order to improve mobility robustness when performing handover in such a network environment, uplink messages or downlink messages exchanged between the source base station and the terminal are omitted.

Figure 2 is a flowchart of a handover method according to an embodiment of the present invention.

In a network environment as shown in FIG. 1, the terminal 1 connects to the source base station 2 as shown in the attached FIG. 2 (S100).

The source base station 2 decides to use CHO (S110). Thereafter, the source base station 2 sets one or more base stations located within a set radius as candidate target base stations based on already known information about base stations located nearby (S120).

Then, a CHO request message is sent to the set candidate target base stations (e.g., Candidate Target1, 31, Candidate Target2, 32, and Candidate Target3, 33 in FIG. 1). CHO request) is transmitted (S130, S140).

As such, in an embodiment of the present invention, the source base station 2 determines the CHO and sets candidate target base stations without an uplink message (eg, measurement report message) from the terminal. In particular, since the terminal 1 connects to the source base station 2 and at the same time the source base station 2 requests CHO from nearby candidate target base stations, handover can be prepared at a high speed.

According to this CHO request message, the candidate target base station (eg, 31 to 33) transmits a CHO response message to the source base station 2 (S150, S160). The candidate target base station (e.g., 31 to 33) transmits a CHO response (HO REQUEST ACKNOWLEDGE) including the configuration of the CHO candidate cell to the source base station (2).

The source base station 2 transmits an RRC reconfiguration message including a CHO candidate cell and CHO execution conditions to the terminal 1 (S170), and the terminal 1 sends an RRC reconfiguration complete message (RRCReconfigurationComplete) to the source base station. Send to (2) (S180).

Afterwards, the terminal 1 connects to one candidate target base station (eg, Candidate Target2, 32) among the candidate target base stations 31 to 33 and completes the handover procedure (S190). After receiving the CHO configuration, the UE 1 maintains a connection with the source base station 2 and begins evaluating CHO execution conditions for the candidate target base station. And if one or more CHO candidate cells (e.g., candidate target base station 32) satisfy the corresponding CHO execution conditions, the terminal 1 is separated from the source base station 2 and operates on the selected candidate target base station 32. The stored configuration is applied, synchronized to the candidate target base station 32, and an RRC reconfiguration complete message (RRCReconfigurationComplete) is transmitted to the candidate target base station 32 to complete the RRC handover procedure. The terminal 1 releases the stored CHO configuration after successfully completing the RRC handover procedure.

As such, in an embodiment of the present invention, the terminal 1 performs a handover to a candidate target base station that satisfies the corresponding CHO execution conditions based on the configuration of the CHO candidate cell without an HO command message from the source base station 2. Perform.

Thereafter, the candidate target base station 32 notifies the source base station 2 that the terminal 1 has been successfully accessed (S200). At this time, a handover success notification message is transmitted to indicate that the terminal has successfully accessed itself.

In response, the source base station 2, in return, transmits a status transfer message (STATUS TRANSFER) to inform which uplink/downlink packets should be transmitted and received from the terminal (S210).

The source base station 2 cancels CHO for the terminal to the remaining candidate target base stations 31 and 33, excluding the candidate target base station 32 (Candidate Target2) (S220). The source base station 2 cancels the CHO for the terminal by transmitting a CHO cancellation message (HANDOVER CANCEL) through other signaling connections or directly to other candidate target base stations 31 and 33.

Afterwards, the new source base station (formerly candidate target base station 32, Candidate Target2) automatically performs the operation from step S110.

Figure 3 is a diagram showing a network environment after handover according to an embodiment of the present invention.

As the handover of the terminal 1 is performed in the network environment shown in FIG. 1, in FIG. 3, the candidate target base station (Candidate Target2) becomes a new source base station, and the base station that was the source base station becomes the candidate target base station (Candidate Target2) after the handover operation. 34, Candidate Target4). When a base station that was previously a candidate target base station becomes a source base station, it automatically requests CHO from neighboring candidate target base stations to prepare the terminal for handover.

In this way, when a base station that was a candidate target base station before the handover operation is converted to a new source base station, handover can be prepared at a high speed by requesting a CHO from a nearby candidate target base station.

According to this embodiment of the present invention, even if the wireless link performance deteriorates due to a rapid change in the wireless state after the handover preparation step or the handover execution attempt, the uplink message (Measurement Report message) or Because the downlink message (HO Command) is omitted, problems that may occur in existing handover can be resolved.

Therefore, compared to the existing handover method, it is possible to improve mobility robustness.

Figure 4 is a diagram showing the structure of a handover device according to an embodiment of the present invention.

As shown in the attached FIG. 4, the handover device 200 according to an embodiment of the present invention includes at least one processor 210, a memory 220, and a transmitting and receiving device 230 that is connected to a network and performs communication. It can be included. Additionally, the handover device 200 may further include an input interface device 240, an output interface device 250, a storage device 260, etc. Each component included in the handover device 200 is connected by a bus 270 and can communicate with each other.

However, each component included in the handover device 200 may be connected through an individual interface or individual bus centered on the processor 210, rather than 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) or a dedicated processor for performing a method according to an embodiment of the present invention. This processor 210 may be configured to implement corresponding functions in the method described based on FIGS. 1 to 3 above.

Each of the memory 220 and the storage device 260 may be comprised of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may be comprised of at least one of read only memory (ROM) and random access memory (RAM). The memory 220/storage device 260 may be located inside or outside the processor 210 and may be connected to the processor 210 through various known means.

The handover device 200 having this structure can be implemented in a form included in a terminal or a base station and implement the corresponding function in the above method according to an embodiment of the present invention.

Additionally, at least some of the methods according to an embodiment of the present disclosure may be implemented as a program or software executed in the handover device 200, and the program or software may be stored in a computer-readable medium.

Additionally, at least some of the methods according to an embodiment of the present disclosure may be implemented as hardware that can be electrically connected to the handover device 200.

The embodiments of the present disclosure 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 disclosure, recording media on which the programs are recorded, etc. This implementation can be easily implemented by an expert in the technical field to which this disclosure belongs based on the description of the embodiments described above.

Although the embodiments of the present disclosure have been described in detail above, the scope of the rights of the present disclosure is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present disclosure defined in the following claims are also possible. It falls within the scope of rights.

Claims (1)

A method of performing handover in a mobile communication system, comprising:
A source base station transmitting a CHO (Conditional Handover) request message to at least one candidate target base station immediately when the terminal connects;
transmitting, by the source base station, a message including the configuration of a CHO candidate cell related to a candidate target base station that transmitted a response message to the CHO request message to the terminal; and
When the source base station receives a message indicating that the handover of the terminal has been completed from one candidate target base station among the at least one candidate target base station, it sends a CHO cancellation message to the remaining candidate target base stations except for the one candidate target base station. Steps to transfer
A handover method including.

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