KR20180093194A - Method for handover in mobile communication system - Google Patents

Abstract

The present invention provides a method for performing handover. The method includes a step of receiving the cell visit history information of a terminal from a terminal to be handed over, a step of determining whether an overload ping-pong phenomenon occurs in a terminal based on the cell visit history information, the load information of a serving cell and the neighboring cell of the serving cell managed by a base station, and a step of adjusting CIO if it is determined that the overload ping-pong phenomenon occurs. It is possible to prevent a waste of handover resources.

Description

[0001] METHOD FOR HANDOVER IN MOBILE COMMUNICATION SYSTEM [0002]

The present invention relates to a handover method capable of appropriately responding to a ping-pong phenomenon of a mobile communication system.

Generally, in a mobile communication network, a ping-pong phenomenon refers to a phenomenon that a mobile station frequently moves between cell boundaries. When a ping-pong phenomenon occurs in a mobile communication network, the configuration parameters of the wireless network, such as the handover configuration parameters, are also changed frequently. In addition, the UE must change an evolved packet system (EPS) bearer of a previous cell to an EPS bearer of a new cell during a handover to move the cell. Thus, the ping-pong phenomenon in a mobile communication network causes network-wide signaling overhead.

One embodiment provides a handover method that is performed in response to a ping-pong phenomenon of a mobile communication network based on cell visit history information and cell load information of a mobile station.

According to one embodiment, a method of performing a handover is provided. The handover performing method includes: receiving cell visit history information of a terminal from a terminal to be handed over, performing a handover based on cell visit history information and load information of a neighboring cell of a serving cell and a serving cell managed by the base station, Determining if an overload ping-pong phenomenon has occurred, and adjusting a cell individual offset (CIO) if it is determined that an overload ping-pong has occurred.

It is possible to accurately distinguish the type of the ping-pong phenomenon occurring in the mobile communication network based on the cell visit history information of the terminal and the load information of the cell, and to prevent the waste of the hand-over resource by performing an appropriate solution for each type of ping-

1 is a conceptual diagram illustrating a ping-pong phenomenon and an overload ping-pong phenomenon in a mobile communication network.
2 is a flowchart illustrating a handover method according to an embodiment of the present invention.
3 is a diagram illustrating a pseudo code illustrating a ping-pong phenomenon determination method according to an embodiment of the present invention.
4 is a block diagram illustrating a wireless communication system according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, the present disclosure can be embodied in various different forms and is not limited to the embodiments described herein. In order to clearly illustrate the present invention in the drawings, parts not related to the description are omitted, and like reference numerals are given to similar parts throughout the specification.

Throughout the specification, a terminal is referred to as a mobile station (MS), a mobile terminal (MT), an advanced mobile station (AMS), a high reliability mobile station A subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), a user equipment (UE), a machine type communication device MTC device and the like and may include all or some functions of MT, MS, AMS, HR-MS, SS, PSS, AT, UE,

Also, a base station (BS) is an advanced base station (ABS), a high reliability base station (HR-BS), a node B, an evolved node B, eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR) (RS), a relay node (RN) serving as a base station, an advanced relay station (ARS) serving as a base station, a high reliability relay station (HR) (BS), a home Node B (HNB), a home eNodeB (HeNB), a pico BS, a macro BS, a micro BS ), Etc., and all or all of ABS, Node B, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR- And may include negative functionality.

1 is a conceptual diagram illustrating a ping-pong phenomenon and an overload ping-pong phenomenon in a mobile communication network.

1 (a) shows a general ping-pong phenomenon of a mobile communication network, and Fig. 1 (b) shows an overload ping-pong phenomenon of a mobile communication network. A typical ping pong phenomenon can be mitigated by adjusting the time-to-trigger (TTT) value, the hysteresis value, or the a3-offset value.

In a mobile communication system, an overload ping-pong phenomenon may occur when mobility load balancing (MLB) among self-organizing networks (SON) functions is performed. The MLB is a function that hand over a terminal connected to an overloaded cell to a neighbor cell that is not overloaded. An overloaded cell can reduce the load through the MLB function. The MLB function can adjust the O _cn and O _cp values of the cell individual offsets (CIOs). O _cn is the cell specific offset of the neighboring cell and O _cp is the cell specific offset of the serving cell. For example, if the O _cp of the terminal is reduced and O _cn is increased, an early handover occurs.

Referring to FIG. 1B, the first and third base stations 110 and 130 are almost overloaded at the same time, and the first and third base stations 110 and 130 are connected to a cell To the cell of the second base station (120).

First, when the first base station 110 is overloaded, the first base station 110 forcibly hands over the first terminal 210 located at the cell boundary to the second base station 120. At the same time, the third base station 130, which has become overloaded, forcibly hands over the second terminal 220 located at the cell boundary to the second base station 120. The second base station 120 is overloaded by the handover terminals (the first terminal and the second terminal) from the first base station 110 and the third base station 130, The first terminal 210 and the second terminal 220 are forcibly handed over to the first base station 110 and the third base station 130 again. That is, a terminal located at a cell boundary due to an overload in a cell is repeatedly handed over between two cells, which is called an overload ping-pong phenomenon.

According to one embodiment, a base station performs a handover through the following method in order to prevent an overloaded ping-pong phenomenon.

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

Referring to FIG. 2, the base station receives visited cell history information of a terminal from the terminal to be handed over in order to handover the terminal receiving the service in the cell to another cell (S110). At this time, the base station can obtain cell visit history information of the UE through radio resource control (RRC) signaling, an application protocol (AP), or X2AP. The cell visit history information of the terminal may be history information of the terminal of the conventional standard. The cell visit history information of the terminal of the conventional standard is defined as mobility history information of the terminal of 3GPP TS 36.331, UE information element of the history information of 3GPP TS 36.413 and UE of 3GPP TS9 36.423 And a history information IE. The base station transmits the UEInformationRequest message of the RRC signal procedure of 3GPP TS 36.331 to the UE and receives the UEInformationResponse message from the UE to know the cell visit history information of the UE. When the S1 application protocol of 3GPP TS 36.413 is used, the BS receives the UE History Information IE in the Source eNB to Target eNB Transparent Container IE, which is transmitted to the target base station at the time of handover, to know the cell visit history information of the UE. When the X2AP of 3GPP TS9 36.423 is used, the base station can know the cell visit history information of the UE by receiving the UE History Information IE in the handover request (HANDOVER REQUEST). That is, the base station requests cell visit history information to the UE through RRC signaling, receives the cell visit history information from the UE, or receives the cell visit history information included in the handover start time message received through the S1AP or X2AP .

At this time, the cell visit history information of the terminal includes the ID of the cell to which the terminal is connected and the time when the terminal stays in the cell. The cell visit history information of the terminal may further include a time when the terminal proceeds from the cell and a time when the terminal enters the cell.

The base station examines the cell visit history information and confirms the handover history of the terminal (S120). The BS can confirm that the previous two handover of the MS has been performed between the serving cell managed by the BS and the neighboring cell of the serving cell.

Thereafter, if the previous handover of the mobile station has been performed twice before and after the handover from the serving cell to the neighboring cell and from the neighboring cell to the serving cell (i.e., the mobile station returns to the serving cell through two hand- ), The base station determines whether the handover history of the terminal corresponds to the ping-pong phenomenon based on the _ping- pong timer (S130). 3 is a diagram illustrating a pseudo code illustrating a ping-pong phenomenon determination method according to an embodiment of the present invention. Referring to FIG. 3, if the time interval between the time when the UE proceeds from the serving cell and the time when the UE returns to the serving cell is shorter than the ping-pong timer, the BS determines that a ping-pong phenomenon has occurred in the UE. That is, if the UE moves from the serving cell to the neighboring cell and then moves from the neighboring cell to the serving cell in the T _ping pong, the BS determines that the ping-pong phenomenon has occurred.

Next, the base station determines whether the ping-pong phenomenon is a normal ping-pong phenomenon or an overload ping-pong phenomenon using the load information of the serving cell and the neighboring cell (S140). At this time, the load information of the serving cell and the neighboring cell indicates whether the load status of the cell is normal or overloaded and is acquired through S1AP or X2AP according to a predetermined time interval, and is stored in the database of the base station .

According to one embodiment, the BS determines the ping-pong phenomenon to be a normal ping-pong phenomenon if the load state of the serving cell and the neighbor cell are both normal during the previous consecutive 2 consecutive handovers. Table 1 below is a terminal cell (1 ^st visited cell) connected to the first, the first hand-over after the second cell (2 ^nd visited cell), the second hand-over third cells in later connected to (3 ^rd visited cell ) At the time of handover. The first connected cell and the third connected cell are the serving cell (cell ID = 1), and the second connected cell is the neighboring cell (cell ID = 2). The previous load status indicates the load status before each handover, and the current load status indicates the load status at each handover time. According to one embodiment, the base station increases the TTT value, the hysteresis value, or the a3-offset in order to alleviate the ping-pong phenomenon in the case of the normal ping-pong phenomenon.

One ^st  visited cell 2 ^nd  visited cell 3 ^rd  visited cell Cell ID One 2 One Previous Load State normal normal normal Current load status normal normal normal

However, if the state of the serving cell is overloaded and the state of the neighboring cell is normal in the first handover of the UE and the state of the neighboring cell is overloaded and the state of the serving cell is normal in the second handover that follows the first handover , The base station determines that the ping pong phenomenon is an overload ping pong phenomenon. That is, if the handover of the terminal consecutively two consecutive times is a forced handover due to overload, the base station can determine that the ping-pong phenomenon is an overload ping-pong phenomenon. Table 2 below is a terminal cell (1 ^st visited cell) connected to the first, the first hand-over after the second cell (2 ^nd visited cell), the second hand-over third cells in later connected to (3 ^rd visited cell ) At the time of handover. The first connected cell and the third connected cell are the serving cell (cell ID = 1), and the second connected cell is the neighboring cell (cell ID = 2). The previous load status indicates the load status before each handover, and the current load status indicates the load status at each handover time. Referring to Table 2, the first handover is a forced handover from a serving cell to a neighboring cell due to an overload because the load state of the serving cell is overloaded and the load state of the neighboring cell is normal at the first handover. In the second handover, the load state of the neighboring cell is overloaded and the load state of the serving cell is normal. Therefore, the second handover is a forced handover from the neighboring cell to the serving cell due to overload. According to one embodiment, the base station adjusts the CIO to mitigate the ping-pong phenomenon in the case of an overload ping-pong phenomenon. For example, the base station increases the O _cp of the serving cell for the terminal and decreases the O _cn of the neighboring cell.

One ^st  visited cell 2 ^nd  visited cell 3 ^rd  visited cell Cell ID One 2 One Previous Load State do not care normal normal Current load status overload overload do not care

As described above, the BS accurately classifies the types of ping-pong phenomena occurring in the mobile communication network based on the cell visit history information of the mobile station and the load information of the cell, and determines a proper solution for each type of ping-pong phenomenon (general ping pong phenomenon or overload ping pong phenomenon) It is possible to prevent the waste of the handover resources.

4 is a block diagram illustrating a wireless communication system according to an embodiment.

Referring to FIG. 4, a wireless communication system according to an embodiment includes a base station 410 and a terminal 420.

The base station 410 includes a processor 411, a memory 412, and a radio frequency unit (RF unit) 413. The memory 412 may be coupled to the processor 411 to store various information for driving the processor 411 or at least one program executed by the processor 411. [ The wireless communication unit 413 is connected to the processor 411 to transmit and receive a wireless signal. The processor 411 may implement the functions, processes, or methods proposed in the embodiments of the present disclosure. At this time, in the wireless communication system according to the embodiment of the present invention, the wireless interface protocol layer can be implemented by the processor 411. The operation of base station 410 in accordance with one embodiment may be implemented by processor 411. [

The terminal 420 includes a processor 421, a memory 422, and a wireless communication unit 423. The memory 422 may be coupled to the processor 421 to store various information for driving the processor 421 or at least one program to be executed by the processor 421. [ The wireless communication unit 423 is connected to the processor 421 to transmit and receive a wireless signal. The processor 421 may implement the functions, steps, or methods suggested in the embodiments of the present disclosure. At this time, in the wireless communication system according to the embodiment of the present invention, the wireless interface protocol layer can be implemented by the processor 421. [ The operation of the terminal 420 according to one embodiment may be implemented by the processor 421. [

In an embodiment of the present disclosure, the memory may be located inside or outside the processor, and the memory may be connected to the processor through various means already known. The memory may be any type of volatile or nonvolatile storage medium, e.g., the memory may include read-only memory (ROM) or random access memory (RAM).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (1)

A method for performing handover,
Receiving cell visit history information of the terminal from a terminal to be handed over;
Determining whether an overload ping-pong phenomenon has occurred in the terminal based on the cell visit history information, the serving cell managed by the base station, and the load information of a neighboring cell of the serving cell, and
If it is determined that the overload ping phenomenon has occurred, adjusting the cell individual offset (CIO)
And performing a handover.

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