KR20190111206A - Method for controlling handover and apparatus therefor in wireless communication system - Google Patents

Abstract

The present invention relates to a method and apparatus for controlling handover congestion in a wireless communication system. More particularly, the present invention relates to a handover congestion control method capable of significantly reducing handover congestion that may occur in a small cell base station by selectively handing over only those who stay at a bus stop for a predetermined time through a measurement report including an event receive count according to signal strengths of a macro base station and the small cell base station.

Description

METHOD FOR CONTROLLING HANDOVER AND APPARATUS THEREFOR IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a method and apparatus for controlling handover in a wireless communication network, and more particularly, to a method and apparatus for controlling handover congestion by selectively controlling a user in a wireless communication system.

The mobile small cell base station (Heaven Small Cell Base Station) on the market is currently inferior in capacity and performance compared to the macro base station (macro eNB), but at a low cost-effective high cost ratio to cover the macro base station is less cost-effective It is installed and operated. The bus station is one of them, and a small cell base station is installed in such a place and coexists with the macro base station.

FIG. 1 illustrates an operation of a small cell base station installed in a bus station as an example of operating a small cell base station.

In general, at bus stops, several buses arrive and depart at the bus stop periodically. Also, in certain time zones such as rush hours, suddenly a large number of buses travel to and from bus stops, which increases the chances of a handover in terms of handover.

Therefore, when handover is congested from the macro base station to the small cell base station with low capacity and performance, the probability of handover failure increases.

If the handover congestion is serious, there is a problem that the small cell base station may be a system down (system down).

Such a handover failure may adversely affect network performance by fostering unnecessary handover signaling messages, and system downtime of the small cell base station may lead to enormous expenses and user dissatisfaction for the network operator.

As a background art for solving the above problems, Korean Patent Application Publication No. 10-2017-0108320 (2017.09.27.) Discloses a method for operating a small cell, a small cell base station and a macro cell base station, and a terminal.

The background art is to select an optimal small cell in an unlicensed band dense environment, determine a transmission amount of serving small cells, and control the collision frequency in a congested environment.

However, the background art is different from the technology for selectively handing over a user while reflecting characteristics of a specific area such as a bus stop provided by the present invention.

An object of the present invention for solving the above problems is to provide a method and apparatus that can avoid the congestion situation by selectively handover control the user reflecting the characteristics of the bus station.

In accordance with another aspect of the present invention, there is provided an operating method of a macro base station for controlling handover congestion of a terminal, and includes an event receive count and an event threshold value according to a signal measurement of a small cell base station. Receiving measurement report information including a measurement report from the terminal, determining an event type using the event reception number and the event threshold value received from the terminal, and a use case according to the event type ( determining the type of use case, determining the handover type of the terminal according to the type of the use case, and selectively selecting the small size only for a terminal that stays in the small cell base station for a predetermined time or more in the handover type. Controlling handover to a cell base station. All.

The small cell base station selectively selects only those who stay at the bus station for a predetermined time through an event receive count and an event threshold value, which are measurement report information of event properties according to the configuration of the present invention. Can be handed over. Therefore, the present invention has an effect of significantly reducing the handover congestion that may occur in the small cell base station.

1 is an exemplary view showing an operation of a small cell base station installed in a bus station,
2 is a flowchart illustrating a flow of a handover congestion control method according to an embodiment of the present invention;
3 is an exemplary view showing an embodiment showing the use case 1 of the signal strength of the macro base station and the small cell base station in a bus station environment according to the present invention;
4 is an exemplary view illustrating an embodiment showing Use case 2 of signal strengths of a macro base station and a small cell base station in a bus station environment according to the present invention;
5 is an exemplary diagram illustrating a concept of N_A4, TH_A4_LOW, and TH_A4_HIGH according to an embodiment of an A4 event of the present invention.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

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

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

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. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

According to the conventional handover procedure, when the UE establishes a Radio Resource Control (RRC) connection with an eNB, the eNB determines whether to report received signal strength when there is an event to the UE (RRC Connection Reconfiguration). Message), and the terminal measures received signal strengths of the serving base station and neighboring base stations and reports these signal strengths through a measurement report message to the eNB when a corresponding event occurs. The eNB may proceed with a procedure of determining a handover and performing a handover to a target base station by referring to the signal strength information reported by the terminal and the overloaded state information of neighboring base stations.

Accordingly, the present invention is characterized in that the congestion control method of the handover.

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

The present invention is configured to include a macro base station (macro eNB) 100, a small cell base station (small HeNB) 200 and the terminal 300.

In this case, the small cell base station 200 refers to a base station installed and operated in a specific region and coexisting with the macro base station 100.

In this case, the specific area may be, for example, an area such as a bus stop. This is because the small cell base station 200 refers to a base station installed and operated in an area having low cost-effectiveness to cover the macro base station 100 with a high cost ratio.

The small cell base station 200 is a term used in terms of handover and may include the meaning of a target base station or a target cell.

The macro base station 100 is a base station for handover coexistence with the small cell base station 200 and receiving measurement report information transmitted by the terminal 300.

In this case, the macro base station 100 is a term used in terms of handover and may include a meaning of a serving base station or a serving cell.

In the present invention, the terminal 300 includes a measurement including an event receive count and an event threshold value according to signal strengths of the macro base station 100 and the small cell base station 200. Means a terminal for transmitting the report (measurement report).

In addition, throughout the present specification, the terminal 300 includes a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, and an access terminal. (access terminal) and the like, and may include all or part of the functions of a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user device, an access terminal, and the like.

The present invention is a small cell base station installed and operated in a specific area and handover coexists with the macro base station, a macro base station for handover coexisting with the small cell base station and receiving measurement report information transmitted by the terminal, and the macro base station and the small base station. Handover congestion for a terminal on a system configured with a terminal for transmitting measurement report information including an event receive count and an event threshold value according to a signal strength of a cell base station As an operation method of a macro base station 100 to control the macro base station 100, the macro base station 100 receives the measurement report information from the terminal (S100), the number of event reception received from the terminal and the event Determining an event type using a threshold value (S200), Use cas according to the event type Determining the type of e (S300), Determining the handover type of the terminal according to the use case type (S400) and Selective only for the terminal staying for more than a predetermined time in the small cell base station in the handover type This may include the step of controlling the handover to the small cell base station (S500).

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 3 shows an embodiment of Use Case 1 showing the signal strength of the macro base station and the small cell base station in the bus station environment according to the present invention.

As shown in FIG. 3, the case where the signal of the macro base station 100 is lowered and the signal of the small cell base station 200 is relatively large around the bus station is defined as use case 1 in the present invention.

In terms of handover, in the case of intra-RAT (Radio Access Technology), which is part of the same LTE network in 3GPP 36.331, both A3 event or A4 event or A5 event may occur.

The 3GPP 36.331 is a document that presents a protocol specification of Radio Resource Control (RRC) in Evolved Universal Terrestrial Radio Access (E-UTRA).

The A3 event, A4 event and A5 event discussed in the above document will be described in connection with the present invention.

The A3 event means that the received signal strength of the neighboring base station is greater than the received signal strength of the serving base station by an A3 offset value (offset parameter of event A3), an A3 event occurs and the terminal 300 transmits the measured value to the base station eNB. Means to report.

Accordingly, in the present invention, the neighbor base station may mean the small cell base station 200 or the macro base station 100, and the serving base station may also mean the macro base station 100 of the present invention.

The A4 event means that the received signal strength of the neighboring base station is better than a specific threshold. In this case, the neighbor base station may be the small cell base station 200.

In addition, the A5 event means that the signal strength of the serving base station is worse than the specific threshold value 1 and the signal strength of the neighboring base station is better than the specific threshold value 2.

In this case, the serving base station may be a macro base station 100, and the neighbor base station may be a small cell base station 200.

In addition, in the embodiment of the use case 1, when the macro base station 100 and the small cell base station 200 are different RATs such as LTE and WCDMA, that is, inter-RAT (Radio Access Technology), both B1 and B2 events may occur. have.

In this case, the B1 event means that the signal strength of the neighboring base station in inter-RAT is superior to a specific threshold value. In this case, the neighbor base station may be the small cell base station 200.

The B2 event means that the signal strength of the serving base station becomes worse than the specific threshold value 1 in the inter-RAT and the signal strength of the neighboring base station becomes better than the specific threshold value 2 in the inter-RAT.

The serving base station may be a macro base station 100 and the neighbor base station may be a small cell base station 200.

4 illustrates an embodiment of Use Case 2 showing signal strengths of a macro base station and a small cell base station in a bus station environment according to the present invention.

Thus, as shown in FIG. 4, the case where the signal strength of the macro base station 100 is very large and the signal strength of the small cell base station 200 is relatively small will be defined as use case 2 in the present invention.

In this case, the small cell base station 200 signal may be buried in the macro base station 100 signal in the same situation as the use case 2.

In terms of handover, the A4 event in 3GPP 36.331 can occur. This is because the signal strength of the serving cell is improved, so the A3 event and the A5 event are not likely to occur.

Accordingly, the A4 event means that the received signal strength of the neighboring base station is better than a specific threshold, where the neighboring base station may be the macro base station 100.

In addition, according to the embodiment of the use case 2, when the macro base station 100 and the small cell base station 200 are different inter-RAT (radio access technology), such as LTE and WCDMA, respectively, the signal strength of the neighboring base station is a specific threshold value. Being better can result in a B1 event.

And since the signal strength of the serving base station, that is, the macro support station, is improved, there is a high probability that a B2 event will not occur.

Based on the above description, in the present invention, when a signal condition preset by the base station to the terminal 300 is satisfied, the measurement report information of the event property transmitted by each terminal 300 and received by the serving base station is measured. The event receive count and the event threshold value are proposed to avoid handover congestion in both situations of Use case 1 and Use case 2 shown in FIGS. 3 and 4.

The event receive count value received by the serving base station includes N_A3, N_A4, N_A5, N_B1, and N_B2 for each type.

N_A3: count value of the A3 event received by the serving base station

N_A4: count value of the A4 event received by the serving base station

N_A5: count value of the A5 event received by the serving base station

N_B1: count value of the B1 event received by the serving base station

N_B2: Count value of B2 event received by serving base station

The event receive count value types are summarized in Table 1 below.

Event type Event count threshold Explanation A3 N_A3 count value of the A3 event received by the serving base station A4 N_A4 count value of the A4 event received by the serving base station A5 N_A5 count value of the A5 event received by the serving base station B1 N_B1 count value of B1 event received by the serving base station B2 N_B2 count value of B2 event received by the serving base station

The event threshold values received by the serving base station are TH_A3_HIGH, TH_A3_LOW, TH_A4_HIGH, TH_A4_LOW, TH_A5_HIGH, TH_A5_LOW, TH_B1_HIGH, TH_B1_LOW, TH_B2_HIGH, and TH_B2_LOW.

TH_A3_HIGH: Threshold HIGH value for N_A3

TH_A3_LOW: Threshold LOW value for N_A3

TH_A4_HIGH: Threshold HIGH value for N_A4

TH_A4_LOW: Threshold LOW value for N_A4

TH_A5_HIGH: Threshold HIGH value for N_A5

TH_A5_LOW: Threshold LOW value for N_A5

TH_B1_HIGH: Threshold HIGH value for N_B1

TH_B1_LOW: Threshold LOW value for N_B1

TH_B2_HIGH: Threshold HIGH value for N_B2

TH_B2_LOW: Threshold LOW value for N_B2

The event threshold value is summarized in a table as shown in Table 2 below.

Event type Event count threshold Explanation A3 TH_A3_HIGH Threshold HIGH value for N_A3 TH_A3_LOW Threshold LOW Value for N_A3 A4 TH_A4_HIGH Threshold HIGH value for N_A4 TH_A4_LOW Threshold LOW Value for N_A4 A5 TH_A5_HIGH Threshold HIGH value for N_A5 TH_A5_LOW Threshold LOW Value for N_A5 B1 TH_B1_HIGH Threshold HIGH value for N_B1 TH_B1_LOW Threshold LOW Value for N_B1 B2 TH_B2_HIGH Threshold HIGH value for N_B2 TH_B2_LOW Threshold LOW Value for N_B2

5 is an exemplary diagram illustrating a concept of N_A4, TH_A4_LOW, and TH_A4_HIGH according to an embodiment of an A4 event of the present invention. The definition of terms used in FIG. 5 will be described below.

TTT (Time to Trigger) means delay time of starting A4 event report.

Report Period Time (RPT) means report period time after A4 event report starts.

TH_A4_LOW is a preset A4 event count threshold value, which means a lower limit value.

TH_A4_HIGH is a preset A4 event count threshold value, which means an upper limit value.

In general, the TH_A4_HIGH value is set to a value larger than the TH_A4_LOW value.

N_A4 refers to the number of A4 events received by the serving base station.

When the signal strength of the small cell base station 200, which is a target base station, satisfies a preset event report start signal strength, the terminal 300 reports an A4 event to the serving base station of the corresponding terminal 300 in the RPT cycle after the TTT time. To start.

In addition, the terminal 300 immediately ends the A4 event report when the event event termination signal strength set in advance is satisfied.

Table 3 below is a case of the small cell base station 200 using the same intra-RAT (RAT) and the macro base station 100, handover for each situation of the received event proposed in the present invention ( handover) shows performance criteria.

Event type received Use case type judgment Determine the handover type you need Result A3 A4 A5 ○ ○ ○ Use case 1 Fast handover N_A3> TH_A3_LOW or
N_A4> TH_A4_LOW or
Handover performed only if N_A5> TH_A5_LOW ○ ○ × Use case 1 Fast handover N_A3> TH_A3_LOW or
Handover performed only if N_A4> TH_A4_LOW ○ × ○ Use case 1 Fast handover N_A3> TH_A3_LOW or
Handover performed only if N_A5> TH_A5_LOW ○ × × Use case 1 Fast handover Handover only if N_A3> TH_A3_LOW × ○ ○ Use case 1 Fast handover N_A4> TH_A4_LOW or
Handover performed only if N_A5> TH_A5_LOW × ○ × Use case 2 Delayed handover Handover only if N_A4> TH_A4_HIGH × × ○ Use case 1 Fast handover Handover performed only if N_A5> TH_A5_LOW × × × Unknown No handover Do not perform handover

In terms of handover, in a bus stop environment, some people may stay on the bus and some may get off the bus.

Therefore, the person who is riding on the bus is not required to hand over to the small cell base station 200 because the person who will move to another base station as soon as the bus moves. On the other hand, the person who gets off the bus stop may be waiting for a transfer, and there may be someone who will move to another place.

In the present invention, a handover is performed only when N_A4> TH_A4_HIGH in Use case 2 in which an A4 event occurs using the parameters proposed and described above. In other words, this may mean a method of handing over to the small cell base station 200 only for a person who stays in the small cell base station 200 for a predetermined time or more.

In the case where it is determined that Delayed handover is necessary in Table 3, the A3 event and the A5 event are not received (X), and only the A4 event is received (O), which is determined as Use case 2 of FIG. 4. it means.

Therefore, the person can be handed over only by distinguishing the person who stays in the small cell base station 200 for a predetermined time by getting off at the bus stop without making a handover. This is to wait until N_A4 is larger than TH_A4_HIGH according to the present invention to handover.

Table 4 below is a case of the small cell base station 200 using a different inter-RAT (RAT) different from the macro base station 100, handover for each situation of the received event proposed in the present invention ( handover) shows performance criteria.

Event type received Use case type judgment Determine the handover type you need Result B1 B2 ○ ○ Use case 1 Fast handover N_B1> TH_B1_LOW or
Handover performed only if N_B2> TH_B2_LOW ○ × Use case 1 Fast handover Handover performed only if N_B1> TH_B1_HIGH × ○ Use case 1 Fast handover Handover performed only if N_B2> TH_B2_LOW × × Use case 1 Fast handover Do not perform handover

In the case where it is determined that Delayed handover is necessary in Table 4, the B2 event is not received (X) and only the B1 event is received (O), which can be determined as Use case 2 of FIG. 3.

Therefore, it is possible to separate only those who stay in the small cell base station 200 for a predetermined time by getting off at the bus stop without making a handover and handing over only this person. Therefore, according to the present invention, until N_A4 is larger than TH_A4_HIGH, the handover is performed.

As described above, the handover process performed by the macro base station 100 according to the present invention will be described again. The macro base station 100 receives an event reception count that is measurement report information of an event property from the terminal 300. And receiving an event threshold value (S100), and determining an event type of any one of A3 event, A4 event, A5 event or B1 event, and B event (S200).

Thereafter, a step (S300) of determining one type of Use Case 1 or Use Case 2 of the terminal 300 according to the event type is performed.

Thereafter, the method 300 determines a required handover type such as a delayed handover according to the use case type of the terminal 300 (S400).

Thereafter, only the terminal 300 that stays in the small cell base station 200 for a predetermined time or more according to the handover type is selectively made through the step of controlling handover to the small cell base station 200 (S500).

Therefore, according to the above-described method and embodiment, there is an advantage that the handover congestion that may occur in the small cell base station 200 is significantly reduced.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

100: macro base station
200: small cell base station
300: terminal

Claims (1)

An operating method of a macro base station for controlling handover to a terminal,
Receiving measurement report information including an event receive count and an event threshold value according to a signal measurement of the small cell base station from the terminal;
Determining an event type by using the event reception count received from the terminal and the event threshold value;
Determining a type of use case according to the event type;
Determining a handover type of the terminal according to the type of the use case; And
And selectively performing handover to the small cell base station only for a terminal staying at the small cell base station for a predetermined time or more in the handover type.

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