JP5465690B2 - Base station, radio communication system, and handover control method - Google Patents

Description

  The present invention relates to a base station, a radio communication system, and a handover control method, and more particularly to a base station, a radio communication system, and a handover control method that enable handover to an appropriate radio base station in the radio communication system.

In a wireless communication system, if the received power from a wireless base station that is currently communicating is weakened due to movement of a wireless communication terminal, a wireless base station with high received power is By selecting, resetting communication with the radio base station, and switching the radio base station, continuous communication is enabled. This switching technique is called handover.
In recent years, the speed of wireless communication has been increased, and the cell radius of the wireless base station has been reduced in order to secure communication capacity, and the cell radius is about 100 m in areas where users are crowded such as in the city center. As the cell radius decreases, the number of handovers increases and the number of handover destination candidate base stations also increases. Therefore, there is a need for an appropriate cell selection method and a reduction in time required for handover processing. Note that a cell means a range in which a radio base station and a radio communication terminal can communicate. In order to solve the above problem, Patent Document 1 acquires position information of a radio communication terminal and compares it with map information. A method of predicting a movement path of a communication terminal and selecting an optimum cell as a handover destination is used.
In Patent Document 2, an appropriate cell is defined as a cell having a high communication rate, and a method of selecting a cell that can obtain a high communication rate as a handover destination is employed.

JP 2004-228881 A JP 2008-288627 A

The problems to be solved by the present invention are shown below.
Particularly in urban areas, there are many branches on the moving route, and the moving direction is rarely determined uniquely. Therefore, with the conventional method in Patent Document 1 that detects the position of a wireless communication terminal from position information such as GPS, it is difficult to specify a route when there are many roads or track branches, and position detection and route search are performed. There is a problem that the number of times increases and as a result, the delay time increases.
In view of the above points, the present invention can be an appropriate handover destination for a handover to a cell in which many terminals are handed over to other cells in a short time using, for example, the movement history of the terminal. It is an object of the present invention to provide a base station, a radio communication system, and a handover control method capable of selecting a cell. Another object of the present invention is to reduce the number of handovers to an inappropriate cell and to reduce the delay time due to the handover process.

In the radio base station according to the present invention, a handover threshold for determining whether or not handover from a cell of the own base station to an adjacent cell adjacent to the cell is set for each adjacent cell. The radio base station is characterized in that the corresponding handover threshold value is different for at least two neighboring cells among the plurality of neighboring cells. Further, for the first cell and the second cell, a first handover threshold for determining whether or not handover from the first cell to the second cell is possible, and a first handover threshold for determining whether or not handover from the second cell to the first cell is possible. 2 The handover threshold is different.
The radio base station management apparatus according to the present invention is a statistical information management for collecting communication histories collected in a radio base station in a radio communication system having a plurality of radio base stations and a plurality of radio base station management apparatuses for managing them. Information and a statistical information database that stores the collected information, and a neighbor cell list management unit that calculates a handover feasibility determination threshold correction value using the information stored in the statistical information database and registers it in the neighboring cell list A device management unit that updates the above-described neighboring cell list in each radio base station is provided.
Further, the adjacent cell list management unit described above calculates a threshold correction value at the time of determining whether or not handover is possible from the handover history to each radio base station and the communication time within the cell in the stored communication history of the radio communication terminal. It is characterized by determining.
Further, the present invention provides a wireless communication system having a plurality of wireless base stations and a plurality of wireless base station management devices that manage them, and uses a neighbor cell list updated by the device management unit to perform wireless communication. The base station includes a handover control unit, and a handover process is executed by the above-described handover control unit.
Further, the present invention provides a wireless communication system having a plurality of wireless base stations and a plurality of wireless base station management devices that manage them, and uses a neighbor cell list updated by the device management unit to perform wireless communication. The base station and the radio communication terminal include a handover control unit, and the handover process is executed by the above-described handover control unit in the radio communication terminal.
In addition, the handover control method described above is characterized in that, when determining whether or not handover is possible, the correction value registered in the neighbor cell list is used and the threshold value for determining whether or not handover is possible in each radio base station.

According to the first solution of the present invention,
The base station in a radio communication system in which a cell with which a radio communication terminal communicates is switched by handover,
A handover threshold for determining whether or not handover from the cell of the own base station to a neighboring cell adjacent to the cell is set for each neighboring cell, and the handover threshold is stored for each identifier of the neighboring cell. Memory and
Receiving the received power from the neighboring cell and the identifier of the neighboring cell in the wireless communication terminal from the wireless communication terminal, and identifying the corresponding handover threshold by referring to the memory based on the received neighboring cell identifier; A handover controller that compares the received power with the handover threshold to determine whether or not handover to the neighboring cell is possible,
A base station is provided in which at least two neighboring cells of the plurality of neighboring cells have different values of corresponding handover threshold values.

According to the second solution of the present invention,
A wireless communication system comprising a plurality of base stations, in which a cell with which a wireless communication terminal communicates is switched by handover,
Each of the base stations is
A handover threshold for determining whether or not handover from the cell of the own base station to a neighboring cell adjacent to the cell is set for each neighboring cell, and the handover threshold is stored for each identifier of the neighboring cell. Memory and
Receiving the received power from the neighboring cell and the identifier of the neighboring cell in the wireless communication terminal from the wireless communication terminal, and identifying the corresponding handover threshold by referring to the memory based on the received neighboring cell identifier; A handover controller that compares the received power with the handover threshold to determine whether or not handover to the neighboring cell is possible,
Provided is a wireless communication system in which at least two neighboring cells among a plurality of neighboring cells have different values of corresponding handover threshold values.

According to the third solution of the present invention,
A handover control method in a radio communication system comprising a plurality of base stations and in which a cell with which a radio communication terminal communicates is switched by handover,
The handover threshold for determining whether or not handover from the cell of the first base station to the neighboring cell adjacent to the cell is determined for the wireless communication terminal, so that the corresponding handover threshold for at least two neighboring cells is different. Storing the handover threshold value in a memory for each neighbor cell identifier;
Receiving, from the wireless communication terminal, received power from an adjacent cell and an identifier of the adjacent cell in a wireless communication terminal communicating in a cell of the first base station;
Identifying a corresponding handover threshold with reference to the memory based on the received neighbor cell identifier;
A handover control method is provided that includes comparing the received power with the handover threshold to determine whether or not handover from the cell of the first base station to the neighboring cell is possible.

According to the present invention, for example, using a movement history of a terminal, it is possible to select a cell so as to be an appropriate handover destination for a handover to a cell in which many terminals are handed over to another cell in a short time. The base station, the wireless communication system, and the handover control method can be provided.
In addition, by reducing the number of terminals having a short communication time in a cell using the handover control method of the present invention, it is possible to expect a decrease in the number of handovers to an inappropriate cell and a delay time due to a handover process.

It is a block diagram of the management system in the 1st Example of this invention. It is a block diagram of the radio | wireless communications system in this invention. It is a block diagram of the radio base station in this invention. It is a block diagram of the radio base station management apparatus in this invention. It is a creation or update flowchart of the statistical information database in this invention. It is an example of the statistical information database in this invention. It is a correction value calculation flowchart of the handover possibility determination threshold in the present invention. It is an example (1) of the cell arrangement | positioning in the Example of this invention. It is an example (2) of the cell arrangement | positioning in the Example of this invention. It is an example of the adjacent cell list | wrist in this invention. It is a flowchart of the handover feasibility determination in the first embodiment of the present invention. It is a block diagram of the management system in 2nd Example of this invention. It is a flowchart of the handover feasibility determination in the second embodiment of the present invention. It is a table of the signal reception power from the adjacent cell in 2nd Example of this invention.

Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
1. First Embodiment FIG. 2 is a configuration diagram of a radio communication system according to a first embodiment. In the figure, there are three radio base stations 10A to 10C as an example, and the radio communication terminal 1 is communicating with the radio base station 10A. A radio base station management apparatus 20 that manages the radio base stations 10A to 10C is connected to the radio base stations 10A to 10C via a wired network 30. The wireless base stations 10 </ b> A to 10 </ b> C are also connected to the gateway 50 through the wired network 30, and communication is performed from the gateway 50 through the core network 60.
FIG. 1 is an explanatory diagram of a management system according to the first embodiment.
The radio base station 10 collects a communication history from the radio communication terminal 1 through the radio network 40 and stores it in the statistical information management unit 13. The communication history includes, for example, a wireless communication terminal ID for identifying the wireless communication terminal 1, communication cell information indicating a cell with which the wireless communication terminal 1 has communicated, and a communication time in that cell. There may be a case where a plurality of combinations of communication cell information and communication time are included due to movement of the wireless communication terminal 1 or the like. When the communication time is included, the communication disclosure time and the communication end time in each cell may be included. The communication history is transmitted from the wireless communication terminal 1 to the wireless base station 10 periodically or at an appropriate timing. The radio base station 10 may have one cell, and one radio base station 10 may have a plurality of cells.
The collected communication history is stored in the statistical information management unit 22 in the radio base station management device 20 through the wired network 30. The statistical information management unit 22 that has received the communication history updates the statistical information database 21. In response to the update of the statistical information database 21, the adjacent cell list management unit 24 updates the adjacent cell list database 23. In response to the update of the neighboring cell list database 23, the device management unit 25 updates the neighboring cell list of the handover control unit 14 of the radio base station 10. The radio base station management apparatus 20 also includes a timer 26 for performing the update timing of the adjacent cell list and the statistical information database 21 at a constant period.
Note that the update timing of the neighbor cell list from the statistical information database 21, the neighbor cell list database 23, and the device management unit 25 to the handover control unit 14 in the radio base station 10 is immediately after the update of each database and communication history for illustration. However, the present invention is not limited to this, and it is also possible to update at regular intervals using a timer or the like.
FIG. 3 is a configuration diagram of the radio base station 10 in the present embodiment. The radio base station 10 includes, for example, an antenna 11 for performing radio communication with the radio communication terminal 1, a radio communication unit 12 that processes a signal received from the antenna 11 or a transmission signal to the radio communication terminal 1, and a radio communication terminal 1 includes a statistical information management unit 13 that handles a communication history from 1, a handover control unit 14 that performs handover availability determination and management of a neighboring cell list, and a memory 15 that stores a neighboring cell list.

FIG. 4 is a configuration diagram of the radio base station management device 20 in the present embodiment. The radio base station management device 20 receives a communication history from the radio base station 10 through the wired network 30 and creates and updates a statistical information management unit 22 that updates the statistical information database 21 and an adjacent cell list database 23 from the communication history. A neighbor cell list management unit 24, a device management unit 25 that distributes the created neighbor cell list to the radio base station 10, and a timer 26 for performing update timing of the neighbor cell list and the statistical information database 21 at a constant cycle . In addition, the radio base station management device 20 includes a statistical information database 21 and an adjacent cell list database 23.
Hereinafter, the operation of each management unit in the radio base station management apparatus 20 will be described in detail.
FIG. 5 is a flowchart when the statistical information management unit 22 creates or updates statistical information stored in the statistical information database 21.
First, in S101, the statistical information management unit 22 starts a timer 26 for performing creation and update of statistical information in the statistical information database 21 at a constant period. The statistical information management unit 22 sorts the received data from the radio base station 10 in S102, and if it is a communication history, moves to the data storage flow in S103, otherwise discards it (or responds to the received data) Appropriate processing is performed), and the flow proceeds to S104. In S103, the statistical information management unit 22 stores the communication cell information and the communication time in the cell in the received communication history. Here, the communication time in the cell is defined by “communication end time in the cell−communication start time in the cell”.
In S104, the statistical information management unit 22 confirms the timer 26, and when a predetermined update cycle has elapsed, the statistical information management unit 22 stops the timer and ends the update process in S105. On the other hand, if the update period has not elapsed in S104, the statistical information management unit 22 returns to S102 and performs processing on the next received data.
Subsequently, in S106 to S109, when the statistical information in the statistical information database 21 is created and updated, when the data amount of the communication history is large, the communication time in the cell of the wireless communication terminal 1 is a certain value or less. Only the communication history of the wireless communication terminal 1 is stored in the database. For example, ON / OFF of such a filter function is set in advance, and the statistical information management unit 22 determines ON / OFF of the filter function in S106. If the statistical information management unit 22 is OFF, the process ends. If it is ON, the statistical information management unit 22 refers to the statistical information database 21 in S107, and for each wireless communication terminal ID, in the communication history, “cell in which the communication time within the cell ≦ predetermined threshold” is satisfied. It is determined whether or not an ID exists. If it does not exist, the statistical information management unit 22 deletes the communication history in the above-described wireless communication terminal ID in S109. On the other hand, if it exists, the communication history of the above-described wireless communication terminal ID is not deleted but is accumulated in the statistical information database 21. If there is a communication history of an unsearched wireless communication terminal ID in S108, the processing from S107 onward is executed on the communication history of the next wireless communication terminal ID in S110. When the search of the communication histories of all the wireless communication terminal IDs is completed, the creation and update processing of the statistical information database 21 ends. By adopting such a method, the amount of information stored in the statistical information database 21 can be reduced, and the amount of calculation when determining a correction value to be described later can also be reduced. In this flowchart, the saved communication history is deleted at regular time intervals, but when the communication history is received, the processing of S106 and S107 is performed to determine whether or not to save in the statistical information database 21. Also good.
FIG. 6 is an example of the statistical information database 21. For each wireless communication terminal ID, a set corresponding to the ID of the cell communicated by the wireless communication terminal 1 and the communication time is recorded in the communication order. Taking a wireless communication terminal with the wireless communication terminal ID a in the figure as an example, communication is started with cell ID: D, and communication is performed in the order of B, C, A after 2:30 (2:30 minutes) communication. Indicates that the cell has been moved. In addition, 0:05 communication is performed in the cell B, 1:50 communication is performed in the cell B, and 3:14 communication is performed in the cell A, and the communication is finished.

FIG. 7 is a flowchart for determining a threshold correction value for determining whether or not handover is possible. This flowchart is roughly divided into two parts. One is a process for determining a correction value (S201 to S204), and the other is the effect obtained when a handover is performed using the correction value. It is a process (S205-S209) which verifies whether it exists. Hereinafter, the flow will be described in detail with reference to FIGS. 7, 8, and 9.
First, processing for determining a correction value will be described. Here, for convenience of explanation, it is assumed that there are four cells as shown in FIG. In S201, the adjacent cell list management unit 24 determines that the cell with the shortest communication time among the cells indicated by each cell ID (for example, corresponding to the cell shown in FIG. 8) stored in the statistical information database 21 is the cell. Are extracted from the statistical information database. More specifically, the adjacent cell list management unit 24 refers to each communication time stored in the statistical information database 21, identifies a cell whose communication time is smaller than a predetermined threshold (first threshold), and Count the number of hits every time. The cell having the largest count number is set as a movement destination target cell (first cell). When there are a plurality of cells having the same maximum count number, all of them are set as destination cells. Here, it is assumed that the communication history is the example of FIG. 6, and the cell B corresponds to the movement destination target cell.

Next, in S <b> 202, the neighboring cell list management unit 24 extracts neighboring cells of the cell B. More specifically, the neighboring cell list management unit 24 refers to the neighboring cell list stored in the neighboring cell information database 23 based on the cell ID of the movement destination target cell, and extracts a plurality of corresponding cell IDs.
In S203, the neighboring cell list management unit 24 performs handover to the cell B from the extracted cells, and selects a cell having the largest number of terminals having a short communication time in the cell B as a movement source target cell. Here, for the cell selected in S201, it is specified from which cell the communication time is short. More specifically, the neighboring cell list management unit 24 refers to the statistical information database, and selects the destination target cell selected in S201 from the cell having the cell ID extracted in S202 (hereinafter referred to as a handover source cell). For the handover to, a handover whose communication time corresponding to the destination cell is smaller than a predetermined threshold (second threshold) is specified, and the number of hits is counted for each handover source cell. The handover source cell having the largest counted value is set as the movement source target cell (second cell). Here, it is assumed that the communication history is the example of FIG.
In this case, it is considered that the handover from the cell D to the cell B generates a large number of terminals with a short communication time in the cell B. Therefore, in S204, the neighboring cell list management unit 24 increases the threshold correction value for determining whether or not the handover from the cell D to the cell B is possible by a predetermined value (for example, 0.5 dB). For example, the correction value is stored in the neighboring cell list in correspondence with the cell ID of the handover source and the cell ID of the handover destination, and the neighboring cell list management unit 24 corrects the correction value ( Setting information) is increased by a predetermined value. The fluctuation value of the correction value shown here is controlled in units of 0.5 dB in consideration of the fact that it affects wireless communication terminals existing near the cell boundary. Note that other fluctuation ranges may be used. Thereafter, the device management unit 25 updates the neighboring cell list of the handover control unit 14 of the radio base station 10 according to the neighboring list including the changed correction value. For example, the device management unit 25 notifies the radio base station 10 that covers the handover source cell of FIG. 10 of the neighbor cell list corresponding to the handover source cell.
In the above example, the correction value is transmitted as setting information. However, identification information corresponding to the correction value, a handover threshold, and other appropriate information for determining a handover may be transmitted as setting information.

ここで、数式１に示したパラメータは以下の通りである。
ＳＮＣｏｎｔ＿ｏｌｄ：移動元対象セルからハンドオーバした端末のうち、制御前の移動先対象セルにおける通信時間が閾値より短い端末数
ＳＮＣｏｎｔ＿ｎｅｗ：移動元対象セルからハンドオーバした端末のうち、制御後の移動先対象セルにおける通信時間が閾値より短い端末数
ＳＮｉ＿ｏｌｄ：移動元対象セルからハンドオーバした端末のうち、制御前のセルＩＤ”ｉ”における通信時間が閾値より短い端末数
ＳＮｉ＿ｎｅｗ：移動元対象セルからハンドオーバした端末のうち、制御後のセルＩＤ”ｉ”における通信時間が閾値より短い端末数
なお、この式の概念については、具体例をあげて後に詳述する。 Next, the effect verification process by this control (correction value change) will be described.
For example, the adjacent cell list management unit 24 activates the timer 26 of the base station management apparatus 20 in S205 after the change of the threshold correction value is completed. After the timer is started, the adjacent cell list management unit 24 determines whether or not a certain period (predetermined time) has elapsed in S206, and enters the determination process if it has elapsed. The fixed period shown here is preferably controlled at intervals of, for example, about 24 hours in consideration of the time when the movement distribution variation of the wireless communication terminal becomes uniform to some extent. However, setting the above-described period to 24 hours is merely an example, and it is possible to change the determination cycle in consideration of the situation of the surrounding area and the fluctuation period. In the determination process of S207, whether or not there is an effect is determined depending on whether or not Expression 1 below is satisfied.

Here, the parameters shown in Formula 1 are as follows.
SNCont_old: Number of terminals in which the communication time in the destination target cell before control is shorter than the threshold among the terminals handed over from the source target cell SNCont_new: Of the terminals handed over from the source target cell, in the destination target cell after control Number of terminals having communication time shorter than threshold SNi_old: Number of terminals having communication time shorter than threshold in cell ID “i” before control among terminals handed over from movement source target cell SNi_new: Of terminals handed over from movement source target cell The number of terminals in which the communication time in the cell ID “i” after control is shorter than the threshold. The concept of this formula will be described in detail later with a specific example.

If the neighboring cell list management unit 24 determines that Formula 1 is not satisfied, that is, if there is no effect, in S208, the threshold value in the handover determination from the movement source target cell (cell D) to the movement destination target cell (cell B) Is reduced by 0.5 dB. If Formula 1 is satisfied, that is, it is determined that there is an effect, the threshold value is left as it is (or further increased). Finally, in S209, the timer is stopped, and a series of processing ends.
Hereinafter, the flow chart of FIG. 7 will be described by taking the cell arrangement shown in FIGS. 8 and 9 as an example. Here, description will be made assuming an area where cells A to D exist as shown in FIG. For cells A to D, a cell in which many terminals with a short communication time in the cell are present is extracted. In this example, it is assumed that cell B corresponds. Next, a neighbor cell of B is identified with reference to the neighbor cell list, a handover to cell B is performed from among the neighbor cells, and a terminal having a short communication time in the cell after the handover is counted. Is selected as a handover source cell. In addition, when there are a plurality of cells in which there are the most terminals with a short communication time in the cell, all the cells are set as the movement source target cells. In this example, D is the target cell. In this case, the threshold correction value for determining whether or not handover is possible from cell D to cell B is increased by 0.5 dB. Thereafter, the process proceeds to determination processing.
In the determination process, it is considered that handover to neighboring cells increases by increasing the threshold correction value for determining whether or not handover from cell D to cell B is 0.5 dB. In particular, it is considered that the movement to the adjacent cell where the cell B and the cell D are adjacent in common increases. For example, it is considered that the number of wireless communication terminals whose communication time in the cell is shorter than the threshold among the wireless communication terminals handed over from the cell D to the cell B after changing the correction value is reduced. If there is a large increase in the number of wireless communication terminals whose communication time in cells C and E is shorter than the threshold among the wireless communication terminals handed over to E, the communication time in the cell is shorter than the threshold as a whole area. The number of increases. Therefore, it is confirmed whether such a situation has occurred and the effect of this control is obtained.

First, in adjacent cells (cell C and cell E in FIG. 9 in this example) in which cell B and cell D are adjacent to each other, cells C and E are among the radio communication terminals handed over from cell D after changing the correction value. The number of wireless communication terminals whose communication time is shorter than the threshold is counted. These numbers are defined as SNC_new and SNE_new, respectively (SNi_new in equation 1 above, i = cell C, corresponding to cell E). Further, handover is performed from the cell D before the correction value change to the cells C and E, and the number of wireless communication terminals whose communication time in the cell is shorter than the threshold is read from the communication history in the statistical information database 21, and this number is read as SNC_old. And SNE_old (SNi_old in Equation 1 above, i = cell C, equivalent to cell E). Next, the number of wireless communication terminals whose communication time in cell B is shorter than the threshold among the wireless communication terminals handed over from cell D to cell B after the correction value change is counted. This number is defined as SNB_new (corresponding to SNCont_new in Equation 1 above). Further, the number of wireless communication terminals whose communication time in the cell B is shorter than the threshold among the wireless communication terminals handed over from the cell D to the cell B before the correction value change is read from the communication history in the statistical information database 21, and this number Is defined as SNB_old (corresponding to SNCont_old in Equation 1 above).
Here, the change in the number of wireless communication terminals whose communication time in cell B is shorter than the threshold among the wireless communication terminals handed over from cell D to cell B with the correction value change (first change): SND_old− SND_new and change in the number of wireless communication terminals whose communication time in cells C and E is shorter than the threshold among the wireless communication terminals handed over from cell D to cell C and cell E (second fluctuation): (SNC_old-SNC_new) ) + (SNE_old−SNE_new). (SND_old−SND_new) ≧ {(SNC_old−SNC_new) + (SNE_old−SNE_new)}, that is, the communication time in the cell B among the radio communication terminals handed over from the cell D to the cell B after changing the correction value The amount of decrease in the number of short wireless communication terminals is greater than the increase in the number of wireless communication terminals whose communication time in cells C and E is shorter than the threshold among the wireless communication terminals handed over from cell D to cell C and cell E. If so, the number of terminals having a short communication time within the cell is reduced as a whole area, and the correction value is maintained because the effect of this control is obtained. On the other hand, among the radio communication terminals handed over from the cell D to the cell B after the correction value change, the amount of decrease in the number of radio communication terminals whose communication time in the cell B is shorter than the threshold is changed from the cell D to the cells C and E. If the communication time in cells C and E is less than the increase in the number of wireless communication terminals shorter than the threshold among the wireless communication terminals handed over to the terminal, the communication time in the cell is shorter than the threshold as a whole area Therefore, it is determined that there is no effect of this control in the entire area, and the correction value is restored (lowered by 0.5 dB). The fluctuation value of the correction value shown here is controlled in units of 0.5 dB in consideration of the fact that it affects wireless communication terminals existing near the cell boundary. However, setting the above-described fluctuation value to 0.5 dB is merely an example, and the fluctuation value can be changed in consideration of the situation in the surrounding area and the influence on the wireless communication terminal.

FIG. 10 is an example of a neighbor cell list in the present embodiment. The handover source cell ID and the handover destination cell ID give a correction value in one-to-one correspondence. Therefore, when the handover source cell and the handover destination cell are reversed, the correction values are not necessarily the same.
Finally, a handover feasibility determination method in the first embodiment will be described.
FIG. 11 is a flowchart for determining whether or not handover is possible in the first embodiment. FIG. 11 shows a flowchart of the radio communication terminal 1 and a flowchart of the radio base station 10 together. The processing of the radio base station 10 is executed by, for example, the handover control unit 14.
The radio base station 10 communicating with the radio communication terminal 1 transmits an adjacent cell signal power measurement request to the radio communication terminal 1 in S301 when the reception state is deteriorated due to the notification information from the radio communication terminal 1. . The wireless communication terminal 1 that has received the adjacent cell signal power measurement request from the wireless base station 10 in S302 measures the received power of the reference signal (pilot signal) in the adjacent cell in S303. Thereafter, the wireless communication terminal 1 transmits the cell ID of the cell measured in S304 and the measured received power report value to the wireless base station 10.
The radio base station 10 that has received the report value or the like in S305 refers to the neighbor cell list stored in the memory 15 in S306, and refers to the correction value corresponding to the reported cell ID. The radio base station 10 compares the reference signal received power of the cell reported in S307 with the threshold, and the reference signal received power of the reported cell is: received power ≧ reference threshold for predetermined handover + reference If the correction value condition of the cell to be satisfied is satisfied, the handover process is executed. If the condition of the above equation is not satisfied, the handover process is not started and the communication with the radio base station 10 currently performing communication is continued. When there are a plurality of cells that satisfy the above conditions, one of them is selected and the handover process is performed. For example, a cell having the largest value of “signal received power− (reference threshold + correction value)” may be selected.

2. Second Example Next, a second example in which a wireless communication terminal performs handover availability determination processing will be described in detail with reference to the drawings.
FIG. 12 is a configuration diagram of the management system in the second embodiment. The radio base station 10 and the radio base station management device 20 are the same as those in FIG. 1. In this embodiment, the radio communication terminal 1 receives an antenna 2 that performs radio communication with the radio base station 10, and receives from the antenna 2. A radio communication unit 3 that processes a signal or a transmission signal to the radio base station 10 and a handover control unit 4 are provided.
Also in the present embodiment, the method for creating the statistical information database 21 and the adjacent cell list database 23 is the same as in the first embodiment. The neighbor cell list is updated by the wireless base station 10 transmitting to the wireless communication terminal 1 via the wireless network 40. In the wireless communication terminal 1, for example, the neighbor control list is stored in the handover control unit 4. Note that the update timing is sent to the wireless communication terminal 1 for a certain period, for example. The period in this case can also be controlled at intervals of, for example, about 24 hours, considering that the movement distribution variation of the wireless communication terminal is uniform to some extent, as in the first embodiment. desirable. However, setting the above-described period to 24 hours is merely an example, and it is possible to change the determination cycle in consideration of the situation of the surrounding area and the fluctuation period. For example, when the latest neighbor cell list is transmitted from the radio base station management device 20 to the radio base station 10, it may be transmitted to the radio communication terminal 1.

Next, a handover feasibility determination method in the second embodiment will be described.
FIG. 13 is a flowchart for determining whether or not handover is possible in this embodiment. In S401, the signal reception power from the radio base station 10 currently communicating in the radio communication terminal 1 satisfies the condition “reception power from the radio base station in communication ≦ predetermined threshold value a” In step S <b> 402, the wireless communication terminal 1 transmits a handover start request to the wireless base station 10. Note that the processing of the wireless communication terminal 1 in this flowchart is executed by, for example, the handover control unit 4. On the other hand, if the above condition is not satisfied, the wireless communication terminal 1 does not perform the handover process and ends this flow. In S403, the radio base station 10 (for example, the handover control unit 14) that has received the handover start request returns a response to the radio communication terminal 1 in S404. The wireless communication terminal 1 that has received the response from the wireless base station 10 in S405 refers to the neighboring cell list managed by the handover control unit 4 and determines the neighboring cell to be measured in S406. In S407, the wireless communication terminal 1 measures the received signal power from the above-described neighboring cell to be measured, and in S408, compares the measured received signal power with a threshold value. At this time, a comparison is made by referring to the corresponding correction value stored in the adjacent cell list, and cells satisfying “signal received power ≧ predetermined reference threshold value b + correction value” are extracted. In step S409, a cell having the best communication state is selected from the extracted cells, and a handover process (communication reconfiguration) is started. The cell with the best communication state in this example refers to a cell having the largest value of “signal reception power− (threshold b + correction value)”, for example.
Next, an example of the operation in the second embodiment will be described with reference to the drawings. Assuming the cell arrangement as shown in FIG. 8, description will be made assuming that the terminal is currently communicating in the cell B. At this time, the neighbor cell list is as shown in FIG. 10, and the correction values from cell B to each neighbor cell are A: 0.5 dB, C: 0 dB, D: 1 dB, E: -0.5 dB, F: -1.5 dB. , G: −1 dB. At this time, it is assumed that the reference threshold value b for determining whether or not handover is possible in FIG. 13 is −40 dBm. If the signal reception power of the adjacent cell in the wireless communication terminal 1 is as shown in FIG. 14, the cell (the cell extracted in S408 described above) that the wireless communication terminal 1 determines to be able to perform handover is the cell A. Cell G. At this time, although the reception power is higher in the cell G than in the cell A, the value of “signal reception power− (threshold b + correction value)” is larger in the cell A than in the cell G by using the correction value. , Cell A is selected as the handover destination cell.

3. Configuration Example of Base Station In the above-described embodiments, the entire system has been mainly described. However, from the viewpoint of the radio base station 10, for example, the following configuration can be used.
For example, the radio base station 10 is a base station in a radio communication system in which a cell with which the radio communication terminal 1 communicates is switched by handover,
A handover threshold for determining whether or not handover from the cell of the own base station to an adjacent cell adjacent to the cell is set for each adjacent cell for the wireless communication terminal 1, and the handover threshold is stored for each identifier of the adjacent cell. Memory 15 and
Receiving the received power from the neighboring cell and the identifier of the neighboring cell in the wireless communication terminal 1 from the wireless communication terminal, identifying the corresponding handover threshold by referring to the memory based on the received neighboring cell identifier, A handover control unit that compares the received power with the handover threshold to determine whether or not handover to the neighboring cell is possible;
Corresponding handover thresholds are different values for at least two neighboring cells of the plurality of neighboring cells.
The handover threshold can be set by the radio base station management apparatus 20 using the communication history as in the above-described embodiment.
For example, the above-described radio base station 10 receives from the radio communication terminal 1 a communication history including an identifier of a cell with which the radio communication terminal 1 communicated in the past and a communication time in the cell, and the radio base station management apparatus 20 Further includes a statistical information management unit 13 for transmitting to the handover control unit 14, obtains handover threshold setting information determined based on the communication history from the radio base station management device 20, and sets the handover threshold. To do.
In addition, at least two of the neighboring cells, when the handover is performed from the cell of the own base station to each neighboring cell in the communication history, the statistical value of the number of terminals having a short communication time between the wireless communication terminal 1 and each neighboring cell is large or small. The relationship and the magnitude relationship of the handover threshold for each neighboring cell are reversed. For example, for two of the neighboring cells, one cell having a larger number of terminals whose communication time in the cell is shorter than a predetermined threshold has a handover threshold smaller than the other cell. Other than this, an appropriate statistical value may be used.
In addition, when at least two of the adjacent cells are handed over from the cell of the own base station to the adjacent cell in the communication history, the number of terminals whose communication time in the adjacent cell is shorter than a predetermined threshold increases. The handover threshold for the neighboring cell increases.

4). System configuration example For example, the radio base station management device manages radio communication terminals that communicate by switching radio base stations by handover, a plurality of radio base stations with which the radio communication terminals communicate, and the radio base stations described above In a wireless communication system in which a wireless base station management device exists, a statistical information management unit including means for collecting the communication time of the wireless communication terminal and the connection history of the wireless base station, from the communication time and the connection history, Means for determining a threshold correction value for determining whether or not handover is possible for each cell, neighboring cell list management unit for registering in neighboring cell list in each radio base station, and device management for distributing neighboring cell list to each radio base station A part.
The update of the adjacent cell list in the above-described radio base station may be updated by the above-described device control unit every certain period or every time the adjacent cell list is updated.
Further, for example, the above-described radio base station is provided with a handover control unit, and handover can be performed by the radio base station using the neighbor cell list updated by the above-described device management unit.
Alternatively, the above-described radio base station and radio communication terminal are provided with a handover control unit, and the handover is initiated by the mobile communication terminal using the adjacent cell list updated from the above-described device management unit through the handover control unit of the radio base station. You can also
In the wireless communication system described above, whether or not handover can be performed is determined using a correction value that changes the threshold value for determining whether or not handover can be registered for each cell.
The above correction value uses the movement history of the wireless communication terminal as a control target for a cell in which a lot of terminals having a short communication time exist in the cell, and for the adjacent cell that has performed a handover to the control target cell. Among these, after extracting the adjacent cell that has been handed over by the terminal with the shortest communication time, the threshold value for determining whether or not to allow handover from the adjacent cell to the control target radio base station is changed.
In addition, the neighbor cell list can have a correction value for changing the above-described threshold value for determining whether handover is possible.
A handover control unit is provided in the radio base station, and whether or not handover is possible can be determined using the correction value of the handover availability determination threshold registered in the neighbor cell list in the handover control unit.

5. Modifications The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  The present invention is applicable to, for example, a wireless communication system.

DESCRIPTION OF SYMBOLS 1 Wireless communication terminal 2 Antenna 3 Wireless communication part 4 Handover processing part 10 Wireless base station 11 Antenna 12 Wireless communication part 13 Statistical information management part 14 Handover processing part 15 Memory 20 Wireless base station management apparatus 21 Statistical information database 22 Statistical information management part 23 Adjacent cell list database 24 Adjacent cell list management unit 25 Device management unit 26 Timer unit 30 Wired network 40 Wireless network 50 Gateway 60 Core network

Claims (9)

Cell wireless communication terminal is to communicate is a group destination station that put the radio communication system is switched by handover,
A handover threshold for determining whether or not handover from the cell of the own base station to a neighboring cell adjacent to the cell is set for each neighboring cell, and the handover threshold is stored for each identifier of the neighboring cell. and a memory that will be,
Receiving the received power from the neighboring cell and the identifier of the neighboring cell in the wireless communication terminal from the wireless communication terminal, and identifying the corresponding handover threshold by referring to the memory based on the received neighboring cell identifier; A handover controller that compares the received power with the handover threshold to determine whether or not handover to the neighboring cell is possible ;
A statistical information management unit that receives a communication history including an identifier of a cell with which the wireless communication terminal has communicated in the past and a communication time in the cell from the wireless communication terminal, and transmits the received communication history to the base station management apparatus; With
For at least two adjacent cells of the plurality of adjacent cells, Ri corresponding handover threshold different values der,
The handover control unit is a base station that acquires handover threshold setting information determined based on a communication history from the base station management apparatus and sets the handover threshold . For at least two of the neighboring cells, when handing over from the cell of the own base station to each neighboring cell in the communication history, the magnitude relation of the statistical value of the number of terminals with a short communication time between the wireless communication terminal and each neighboring cell; The base station according to claim 1 , wherein the magnitude relationship of the handover threshold value for each neighboring cell is reversed. As the number of terminals whose communication time in the adjacent cell is shorter than a predetermined threshold when handover is performed from the cell of the own base station to the adjacent cell in the communication history for at least two of the adjacent cells, The base station according to claim 1 , wherein a handover threshold for an adjacent cell increases. A cell having a plurality of base stations and a base station management device for determining a handover threshold based on a communication history including an identifier of a cell with which the wireless communication terminal has communicated in the past and a communication time in the cell, A wireless communication system that is switched by a handover,
Each of the base stations is
Wherein said handover threshold for determining a handover whether the wireless communication terminal from a cell of the base station to a neighboring cell adjacent to the cell, is set for each neighboring cell, the handover threshold for each identifier of the neighboring cell and a memory that will be stored,
Receiving the received power from the neighboring cell and the identifier of the neighboring cell in the wireless communication terminal from the wireless communication terminal, and identifying the corresponding handover threshold by referring to the memory based on the received neighboring cell identifier; A handover controller that compares the received power with the handover threshold to determine whether or not handover to the neighboring cell is possible ;
A statistical information management unit that receives a communication history from the wireless communication terminal and transmits the communication history to the base station management device ;
For at least two adjacent cells of the plurality of adjacent cells, Ri corresponding handover threshold different values der,
The wireless communication system , wherein the handover control unit obtains handover threshold setting information determined based on a communication history from the base station management apparatus and sets the handover threshold . For the first cell and the second cell,
A first handover threshold for determining a handover possibility from the first cell to the second cell, according to the second claim 4 in which the handover threshold is different for determining a handover possibility from the second cell to the first cell Wireless communication system. In a predetermined base station, at least two of the neighboring cells, the magnitude of the statistical value of the communication time between the wireless communication terminal and each neighboring cell when handover is performed from the cell of the base station to each neighboring cell in the communication history The wireless communication system according to claim 4 , wherein the relationship and the magnitude relationship of the handover threshold for each neighboring cell are reversed. Number of terminals whose communication time in the adjacent cell is shorter than a predetermined threshold when handover is performed from the cell of the base station to the adjacent cell in the communication history for at least two of the adjacent cells in a given base station The wireless communication system according to claim 4 , wherein a handover threshold for the neighboring cell increases as the value increases. The base station management device
Using the communication history of the wireless communication terminal, for each cell, the number of terminals whose communication time in the cell is shorter than a predetermined first threshold is obtained, and the cell having the largest number of terminals or the predetermined number is determined. The number of cells that are larger than the second threshold
For the handover to the destination cell, the number of terminals whose communication time in the destination cell is shorter than the first threshold is counted for each handover source cell, or the cell with the largest number of terminals is determined in advance. The number of cells that are larger than the second threshold
And it generates the setting information for changing the handover threshold to the destination target cell from the specified migration source target cell corresponding to the cell of the source object according to claim 4 to be transmitted to the base station Wireless communication system. A reference value for setting the handover threshold is preset,
5. The wireless communication according to claim 4 , wherein the base station management device changes a handover threshold obtained from the reference value and the correction amount by increasing or decreasing a correction amount and transmitting the setting information as the setting information to the base station. system.

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