KR20100043366A - A method for cell measurement for handover in a wireless communication network and a system thereof - Google Patents

Abstract

PURPOSE: A method for cell measurement for handover in a wireless communication network and a system thereof for preventing a ping pong phenomenon due to frequent movement are provided to optimize a measurement of around cell by setting source measurement interrupt time differently according to the speed of a user terminal. CONSTITUTION: A user terminal peripheral base stations measures periodically according to a wireless environment parameter(S201). A user terminal reports a result of measurement about around stations to source base station(S205). The source base station directs handover to target base station to the user terminal(S207). During the present time, measurement stops(S215).

Description

A method for cell measurement for handover in a wireless communication network and a system

The present invention relates to a handover of a wireless communication network, and more particularly, to a cell measuring method and a system for the handover of a wireless communication network to prevent the ping-pong phenomenon due to frequent movement.

Handover, or handoff, refers to a technology that automatically switches the communication channel when a mobile subscriber moves from one wireless communication zone to another, so that communication in service is not interrupted.

If a terminal of the LTE system finds a neighbor cell that is mobile and is better than a serving cell currently being served, handover occurs.

In order to perform such a handover, an evolved NodeB (eNodeB), which is a base station of an LTE system, transmits a measurement parameter to a user equipment (UE), and the user terminal measures neighbor base stations according to the parameter transmitted by the base station. . Peripheral base stations include a serving base station and base stations adjacent to the user terminal. In this case, the term measurement refers to measuring a wireless environment between the terminal and the base station. As a result of this measurement, the user terminal performs a handover to a base station having a better wireless environment.

An unintentional handover may occur in the border area of the cell due to the wireless environment in which the terminal is constantly changed by the surrounding environment. Not only does it put a heavy load on the system, but it also adversely affects the service of the user terminal.

That is, when a handover occurs, the wireless communication network (base station) and the user terminal perform a procedure for performing handover with each other, thereby putting a load on the system. In addition, tasks currently being serviced may be delayed or interrupted due to handover. In severe cases, packets may be lost during handover.

On the other hand, if the handover condition is enhanced by reducing the handover condition in order to reduce the unintended handover, proper handover may not be performed and the quality of service provided to the user terminal may be degraded.

One of the most hand-loading problems in the system is the ping-pong phenomenon. The ping pong phenomenon is a phenomenon in which a user terminal in a cell border region continuously moves between cells, and an unnecessary handover frequently occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring method and system for the handover of a wireless communication network for preventing the ping-pong phenomenon caused by frequent movement between cells in a cell border region. have.

Another object of the present invention is to provide a cell measuring method and system for the handover of a wireless communication network optimized by measuring a neighboring cell in consideration of the speed of the terminal.

In the measurement method for handover of a wireless communication network according to a preferred embodiment of the present invention for achieving the above object, the user terminal periodically measures the neighbor base station according to the radio environment parameters to measure the measurement result of the neighbor base station Reporting to the source base station, instructing the user terminal to handover to the target base station according to the measurement result by the source base station, and after the user terminal moves to the target base station according to the instruction, And stopping the measurement for a preset time.

The stopping process may vary the time for stopping the measurement according to the moving speed of the user terminal.

In a system for cell measurement according to a handover of a wireless communication network according to a preferred embodiment of the present invention for achieving the above object, a radio environment parameter and a measurement stop parameter for radio environment measurement for neighboring base stations A source base station for providing a user terminal with a user terminal and instructing a user terminal of a handover to a target base station according to the measurement result when receiving a measurement result of a neighbor base station of the user terminal according to the radio environment parameter; And a user terminal moving to the target base station according to the instruction and stopping the measurement of the source base station for a preset time according to the measurement stop parameter.

The user terminal may vary the time for stopping the measurement according to the moving speed of the user terminal based on the measurement stop parameter.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that those skilled in the art may better understand it from the following detailed description of the invention. In addition to these features and advantages, further features and advantages of the present invention which form the subject of the claims of the present invention will be better understood from the following detailed description of the invention.

According to the present invention as described above, the present invention can prevent the ping-pong phenomenon by stopping the measurement of the source cell for a predetermined time after moving to the target cell. In addition, by setting the source measurement stop time according to the speed of the user terminal, it is possible to optimize the measurement of the neighboring cells. As such, according to an exemplary embodiment of the present invention, it is possible to improve cell performance by optimizing cell measurement for handover.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. At this time, it should be noted that the same components in the accompanying drawings are represented by the same reference numerals as possible. In addition, detailed descriptions of well-known functions and configurations that may blur the gist of the present invention will be omitted.

First, a wireless communication network according to an embodiment of the present invention will be briefly described. 1 is a view showing a schematic structure of a wireless communication network according to an embodiment of the present invention.

Referring to FIG. 1, in a wireless communication network according to an embodiment of the present invention, an Evolved Radio Access Network (hereinafter referred to as an E-RAN) 110 and 112 may include an Evolved NodeB (ENB) 120, 122, 124, 126, and 128 and an Evolved Gateway GPRS Serving Node (EGGSN) 130 and 132. Here, GPRS is an abbreviation of General Packet Radio Service.

The UE (User Equipment) 101 connects to the Internet Protocol (IP) network 114 by the E-RANs 110 and 112. The ENBs 120, 122, 124, 126, and 128 are nodes corresponding to the existing NodeBs and are connected to the user terminal 100 through a wireless channel. Unlike the existing NodeB, ENB (120, 122, 124, 126, 128) plays a more complex role. Next-generation wireless communication systems provide all user traffic, including real-time services such as Voice over IP (VoIP), through a shared channel. For this reason, there is a need for an apparatus for scheduling by gathering situation information of UEs 101, and ENBs 120, 122, 124, 126, and 128 are responsible for the scheduling. One ENB (one of 120, 122, 124, 126, 128) controls multiple cells. In order to realize a transmission rate of up to 100 Mbps, a wireless communication system uses Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology in a 20 MHz bandwidth. In addition, an adaptive modulation & coding (AMC) scheme for determining a modulation scheme and a channel coding rate according to the channel state of the UE 101 may be applied.

Hereinafter, the E-RAN 110, 112 including the ENBs 120, 122, 124, 126, and 128 and the EGGSNs 130, 132, the base station 200, the UE 101, and the user terminal 100. It will be referred to as.

In an embodiment of the present invention, the base stations 200 actually provide radio resources allocated to the user terminal 100. Radio resources are configured for each cell, the radio resources provided by each base station 200 means a radio resource for a specific cell managed by the base station 200. The user terminal 100 sets a radio channel using radio resources for a specific cell managed by the base station 200, and transmits and receives data through the set radio channel. Since the user terminal 100 recognizes only the physical channel configured for each cell, the distinction between the base station 200 and the cell is meaningless. Therefore, in the present specification, the base station 200 and the cell are used interchangeably.

In an embodiment of the present invention, the base station 200 may include a serving base station currently providing a wireless communication service to a specific user terminal, and a neighbor base station located in the vicinity of the user terminal. In addition, during handover, the serving base station is referred to as a serving base station before the user terminal moves, and the base station to which the user terminal moves is called a target base station.

The source base station 200 provides a radio environment parameter and a measurement stop parameter for radio environment measurement for a neighbor base station to the user terminal. Then, the user terminal 100 measures the neighbor base station according to the radio environment parameters. In addition, when a specific event occurs, the user terminal 100 transmits a result of measuring a neighboring base station to the source base station.

The source base station makes a handover decision, and according to this decision, the user terminal 100 moves to the target base station. After this movement, the user terminal 100 stops measuring the source base station according to the measurement stop parameter. A method of measuring a neighbor base station (cell) for handover of the user terminal 100 in the wireless communication network as described above will be described.

First, according to an embodiment of the present invention, a measurement stop parameter is provided to support optimal handover. Table 1 below is for explaining a measurement stop parameter for stopping the measurement of the source cell according to an embodiment of the present invention.

parameter compare One High_Mobility_Block_Time Above the first speed. 2 Medium_Mobility_Block_Time Below first speed above second speed 3 Normal_Mobility_Block_Time Less than 2nd speed

Referring to Table 1, parameters for stopping the measurement of the source cell according to an embodiment of the present invention are classified according to the speed of the user terminal 100.

That is, the parameters provided by the base station 200 through the measurement request message are as follows.

First, High_Mobility_Block_Time is a measurement stop time for the source cell of the user terminal 100 when the speed of the user terminal 100 is greater than or equal to a preset first speed.

Second, Medium_Mobility_Block_Time is a measurement stop time for the source cell of the user terminal 100 when the speed of the user terminal 100 is less than the first predetermined speed or greater than the second speed.

Finally, Normal_Mobility_Block_Time is a measurement stop time for the source cell of the user terminal 100 when the speed of the user terminal 100 is less than the second preset speed.

Here, the first speed is faster than the second speed. This first speed and the second speed can be derived in the following manner. The first speed and the second speed may be set according to the number of times the user terminal 100 changes the serving cell.

For example, the user terminal 100 moving at a high speed will frequently change the serving cell, and the user terminal 100 moving at a slow speed or not moving will have a relatively small number of changing serving cells.

Therefore, the user terminal 100 may set the case of changing the serving cell more than a preset number of times for a preset time as the first speed, and the case of changing the serving cell less than the preset number of times as the second speed.

That is, High_Mobility_Block_Timer is a time when the user terminal 100 moving at a high speed does not measure the source cell after the handover but before the handover.

In addition, Medium_Mobility_Block_Timer is a time for not measuring the source cell of the terminal of medium speed, and Normal_Mobility_Block_Timer is a parameter indicating time for not measuring the source cell of the terminal that does not move very much.

A handover method using these parameters will be described. 2 is a view for explaining a handover method according to an embodiment of the present invention.

In Fig. 2, the source cell (base station) is the serving cell (base station) before performing the handover. That is, in the case of moving after handover, it means a serving cell (base station) before moving.

Referring to FIG. 2, in step S201, the source base station 201 transmits a measurement control message to the user terminal 100.

The measurement control message includes a parameter for measuring a neighboring base station radio environment and a measurement stop parameter according to an embodiment of the present invention.

Here, the measurement stop parameter includes High_Mobility_Block_Time, Medium_Mobility_Block_Time, and Normal_Mobility_Block_Time, as described in Table 1.

In addition, parameters for wireless environment measurement include signal strength and hold time.

The signal strength is a parameter related to the signal strengths of the source base station 201 and neighboring base stations measured by the user terminal 100. The user terminal 100 may transmit a measurement report message to the base station when a specific condition is satisfied using these parameters.

For example, the specific condition may be that the handover is triggered when the signal strength of the neighboring base station measured by the user terminal 100 is greater than or equal to a preset offset greater than the signal strength of the source base station 201.

In addition, the signal strength of the source base station 201 measured by the user terminal 100 is less than the first threshold threshold1, and the signal strength of at least one of the neighbor base stations is greater than or equal to the preset second threshold2. This can be the case.

In addition, the holding time is a parameter for the time for holding a certain condition for a certain time.

For example, it may be a case where the signal strength of the neighboring base station measured by the user terminal 100 is greater than a preset offset greater than the signal strength of the source base station 201 for a preset time.

In addition, the signal strength of the source base station 201 measured by the user terminal 100 is less than the first threshold threshold1, and the signal strength of at least one of the neighbor base stations is greater than or equal to the preset second threshold2. This may be the case when the state maintains a preset time.

The measurement control message may be transmitted during initial connection between the user terminal 100 and the base station, or periodically, or when a specific parameter is changed.

The user terminal 100 receiving the measurement control message including the parameter as described above stores the parameter values of the measurement control message.

In addition, the user terminal 100 measures the neighboring base station according to the parameter for measuring the radio environment included in the measurement control message in step S203. Measurements for neighbor base stations may be performed periodically. That is, the source base station 201 transmits the above-described parameters of the signal strength offset, the first threshold value, the second threshold value, and the holding time through the measurement request message, and the user terminal 100 transmits the neighboring base station according to these parameters. Measure periodically.

As a result of this measurement, the user terminal 100 determines whether the conditions according to the above-described parameters are satisfied. In this case, it is assumed that the above-described parameters such as the offset of the signal strength, the first threshold value, the second threshold value, and the holding time are satisfied.

Then, the user terminal 100 transmits to the source base station 201 a measurement report message including a result of measuring the neighboring base station in step S205. The measurement report message includes an identifier of the neighbor base station and the source base station 201 and the measurement result accordingly. In particular, the measurement report message may include measurement results of a plurality of neighboring base stations.

The source base station 201 receiving the measurement report message determines the handover according to parameters such as signal strength of the neighboring base station of the received measurement report message. Based on the parameter values described above, it is assumed that the source base station 201 has determined a handover. In this case, when there are a plurality of measurement results of the neighboring base stations included in the measurement report message, the source base station 201 may select any one of the plurality of neighboring base stations as the target base station 203.

As such, when the target base station 203 is determined, the source base station 201 exchanges handover related information with the target base station 203 in step S207. This exchange of handover related information is a process of preparing the handover to the target base station 203. To this end, the source base station 201 may transmit a query message to the target base station 203 whether the user terminal 100 can be handed over. In addition, the handover related information may be information (about connection and service with the base station) of the user terminal 100 corresponding to the identifier and identifier of the user terminal 100 owned by the source base station 201. In this case, when the target base station 203 allows handover of the corresponding terminal, a message indicating that the handover is allowed is transmitted to the source base station 201.

Then, the source base station 201 transmits a mobility control message (mobility control) requesting the user terminal 100 to move to the target base station 203 in step S209. The user terminal 100 receiving this exchanges information for connection with the target base station 203 in step S211, and moves to the target base station 203.

In this case, the user terminal 100 stops the measurement of the source base station 201 in step S213. In particular, the user terminal 100 varies the source base station 201 measurement stop time according to its moving speed based on the measurement stop parameter previously received in step S213. Then, after a preset time such as step S215, the user terminal 100 resumes the measurement of the source base station 201 in step S217.

Next, the operation of the user terminal 100 according to an embodiment of the present invention will be described. 3 is a diagram illustrating a method of measuring a neighbor cell for handover of a user terminal according to an exemplary embodiment of the present invention.

In FIG. 3, the user terminal 100 receives a measurement control message from the source base station 201, and measures a parameter for measuring a wireless environment of a neighboring base station of the measurement control message and a measurement stop parameter according to an embodiment of the present invention. Assume that we have stored in advance.

Referring to FIG. 3, the user terminal 100 measures neighboring base stations according to parameters for wireless environment measurement included in a measurement control message in step S301. Measurements for neighbor base stations may be performed periodically.

As a result of this measurement, the user terminal 100 determines whether the conditions according to the above-described parameters are satisfied in step S303. That is, as described above, it is determined whether the signal strength, the holding time, etc. of the neighboring base stations satisfy the parameter value.

In this case, when the condition is satisfied, the user terminal 100 transmits a measurement report message including a result of measuring the neighboring base station in step S305 to the source base station 201. The measurement report message includes an identifier of the neighbor base station and the source base station 201 and the measurement result accordingly. In particular, the measurement report message may include measurement results of a plurality of neighboring base stations.

On the other hand, if it is determined in step S303 that the condition is not satisfied, the user terminal waits for a preset time in step S317, and proceeds to step S301 to perform measurement of neighboring base stations.

The source base station 201 receiving the measurement report message determines the handover according to parameters such as signal strength of the neighboring base station of the received measurement report message. In this case, when there are a plurality of measurement results of the neighboring base stations included in the measurement report message, the source base station 201 may select any one of the plurality of neighboring base stations as the target base station 203. As such, when the target base station 203 is determined, the source base station 201 exchanges handover related information with the target base station 203 and whether the corresponding user terminal 100 is capable of handover to the target base station 203. Tag. In this case, when the target base station 203 allows handover of the corresponding terminal, a message indicating that the handover is allowed is transmitted to the source base station 201. Then, the source base station 201 transmits a mobility control message requesting the user terminal 100 to move to the target base station 203.

The user terminal 100 determines whether such a movement control message is received in step S307. In this case, when the movement control message is received in step S307, the user terminal 100 establishes a connection with the target base station 203 in step S309, and moves to the target base station 203.

On the other hand, if the determination result of step S307, if the movement control message is not received, the user terminal waits for a predetermined time in step S317, proceeds to step S301 to perform the measurement of the neighbor base stations.

Then, the user terminal 100 stops measuring the source base station 201 for a preset time according to the moving speed of the user terminal 100 in step S309. Here, the measurement stop parameter includes High_Mobility_Block_Time, Medium_Mobility_Block_Time, and Normal_Mobility_Block_Time, as described in Table 1.

In addition, the user terminal 100 determines whether the preset time has elapsed in step S311. As a result of this determination, when the preset time has elapsed, the user terminal 100 resumes the measurement of the source cell in step S313.

According to the embodiment of the present invention as described above, in the case of the border region of the cell, the user terminal 100 may move to the target cell, measure the source cell again, and may cause a ping-pong phenomenon to return to the source cell. At this time, the measurement of the source cell may be stopped to prevent the ping-pong phenomenon.

In addition, by varying the measurement stop time for each speed of the user terminal 100, it is possible to optimize the measurement for handover.

As described above, High_Mobility_Block_Timer is a time when the user terminal 100 moving at a high speed does not measure the source cell, and Medium_Mobility_Block_Timer is a measurement of the source cell of the user terminal 100 at medium speed. In this case, Normal_Mobility_Block_Timer is a parameter indicating a time for which no measurement is performed on the source cell of the UE that does little movement.

The user terminal 100 having a high speed at the time of handover has a high probability of moving at a high speed even after the handover, and the terminal having a low speed at the time of handover has a high probability of moving at a slow speed even after handover. Therefore, it is preferable to determine the measurement stop time of the source cell according to the speed of the user terminal 100 after the handover.

The neighbor base station measurement method according to the embodiment of the present invention as described above can be applied not only after handover but also during cell reselection. When a user terminal 100 having no dedicated channel moves from one cell to another cell, a cell reselection procedure is performed. During the cell reselection procedure, the terminal measures signals of neighboring cells (ie neighboring cells), reports measurement results, and finally performs cell selection / reselection. The purpose of cell reselection is to accurately find the best cell for the terminal to camp and to set the found best cell as a serving cell. That is, after cell reselection according to an embodiment of the present invention, measurement of a cell (source cell) may be stopped before moving for a predetermined time.

As described above, according to an embodiment of the present invention, after the handover is performed or after the cell reselection, the ping-pong phenomenon is removed in the border region of the cell by stopping the measurement of the source base station 201 for a predetermined time. It can prevent. This advantage of the present invention will be described.

4 is a diagram illustrating a cell measuring method in an adjacent area of three or more cells according to an exemplary embodiment of the present invention.

Cells A, B, and C (10, 20, 30) are shown in FIG. Some of the cell coverage of cells A, B, and C (10, 20, 30) overlap. In this case, it is assumed that the user terminal 100 sequentially moves to the cell A, the cell B, and the cell C as shown by reference numeral 4.

In this case, in the case of general handover, it is impossible to consider the directivity of the user terminal 100 at all. However, if the measurement of the source cell is stopped for a predetermined time according to an embodiment of the present invention, handover to cell B and cell C of the user terminal 100 occurs at an appropriate time.

5 is a view for explaining a cell measuring method in two or more adjacent areas according to an embodiment of the present invention.

In Fig. 5, cells D and E 40, 50 are shown. Some of the cell coverage of cells D and E 40, 50 overlap. In this case, it is assumed that the user terminal 100 sequentially moves to the cell D 40, the cell E 50, and the cell D 40 as shown by reference numeral 5.

In this case, the speed of the user terminal 100 may be divided into three stages based on the parameters shown in Table 1. In this case, when the same value is applied to the user terminals 100 having different speeds, a ping pong phenomenon may occur in the case of the user terminal 100 which is very slow or does not move.

On the contrary, assuming that the user terminal 100 moves at high speed, when the user terminal 100 moves from the cell D 40 to the cell E 50 and then returns to the cell D 40 again, the user terminal 100 Handovers happen slowly, so you can't get good quality service.

Therefore, in the embodiment of the present invention, when the speed of the user terminal 100 is slow, the measurement stop time of the source cell is long, and when the speed of the user terminal 100 is fast, the measurement stop time of the source cell is short. Do.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

1 illustrates a schematic structure of a wireless communication network according to an embodiment of the present invention.

2 is a view for explaining a handover method according to an embodiment of the present invention.

3 is a diagram illustrating a method of measuring a neighboring cell for handover of a user terminal according to an exemplary embodiment of the present invention.

4 is a view for explaining a cell measurement method in an adjacent area of three or more cells according to an embodiment of the present invention.

5 is a view for explaining a cell measurement method in two or more adjacent areas according to an embodiment of the present invention.

Claims (4)

In the measurement method for handover of a wireless communication network, Periodically measuring, by the user terminal, a neighbor base station according to a radio environment parameter, and reporting the measurement result of the neighbor base station to the source base station; Instructing, by the source base station, the user terminal to hand over to the target base station according to the measurement result; And after the user terminal moves to the target base station according to the indication, stopping the measurement for a preset time for the source base station. The method of claim 1, The process of stopping, And a time for stopping the measurement according to the moving speed of the user terminal. In a wireless communication network, When the radio environment parameter and the measurement stop parameter for radio environment measurement for the neighbor base station are provided to the user terminal, and the measurement result of the neighbor base station measurement of the user terminal according to the radio environment parameter is received, the hand to the target base station according to the measurement result. A source base station instructing the user terminal to over; And And a user terminal for stopping the measurement of the source base station for a preset time according to the measurement stop parameter after moving to the target base station according to the instruction. System. The method of claim 3, The user terminal And a time for stopping the measurement according to the moving speed of the user terminal based on the measurement stop parameter.

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