JP2006101442A - Mobile communications system, base station controller and radio base station device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communications system, in which the influence caused by a change in cell size can be curbed and besides service outage time attributable to a cell operation cessation or the like can be kept to the minimum. <P>SOLUTION: The mobile communications system is equipped with a means of measuring a traffic amount in each cell and a means of holding memories of a first threshold at which a cell size is changed to a one step narrower size, depending on whether the traffic amount exceeds that value or not and of a second threshold at which the cell size changed to one step narrower one is restored to the initial cell size depending on whether the traffic amount is less than that value. Then, the mobile communication system changes automatically the sizes of each cell, depending on the traffic amount sequentially measured. These first and second threshold are determined individually between each of the cell sizes, and hence even if the traffic amount fluctuates near the vicinity of the first threshold, frequent changes in cell size will not be performed. Further, in a cell operation cessation, adjacent cells covering the area of the ceased cells, thus enabling service in the area to continue. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mobile communication system, a base station control device, and a radio base station device, and more particularly, to a cellular mobile communication system, a base station control device, and a radio base station device.

  In a conventional mobile communication system, cell arrangement design is performed in consideration of radio wave propagation conditions such as the presence or absence of obstacles in a service area, predicted traffic volume, user movement speed, and the like. In general, from the viewpoint of effective use of resources such as hardware and transmission path bandwidth of a radio base station, a cell with a large radius (referred to as a macro cell) is used for a low traffic area, and a cell with a small radius (a micro cell) is used for a high traffic area. Cell)). In addition to the above, it is said that frequent inter-cell handovers for users moving at high speed can be suppressed by arranging macro cells. Based on these, there is a configuration in which microcells and macrocells are arranged hierarchically for the purpose of complementing each other, but it is generally not considered to change these cell sizes during operation.

  On the other hand, from the viewpoint of using limited resources, we also propose a cellular mobile communication system that can change the cell size according to the fluctuation of traffic volume and cover a wide service area with fewer radio base stations. Has been done. For example, there is one described in Japanese Patent Application Laid-Open No. 2001-160984, and a cellular mobile communication system is disclosed in which the transmission power of a radio base station is relatively changed according to the traffic situation.

JP 2001-160984 A

  As described in the above publication, if the cell size can be dynamically changed, a wide service area can be covered with fewer resources. On the other hand, when the cell size is frequently changed, there is a problem in that handovers for mobile devices located in the cell to be changed are frequently performed.

  In addition, there are cases where the service in the corresponding area is forced to stop when the operation is stopped due to a failure of the radio base station apparatus or maintenance work. In preparation for such a case, it is desirable to provide an inexpensive and reliable backup resource. It is rare.

  The present invention has been made in view of the above-described circumstances, and is capable of avoiding a situation in which cell size changes are frequently performed, a cell variable mobile communication system, a base station control device, and a radio base An object is to provide a station apparatus. Another object of the present invention is to provide a cell variable type mobile communication system, a base station control device, and a radio base station device that can cope with the operation stop of the radio base station device.

  According to the first aspect of the present invention that provides means for solving the above-described problem, the cell size is reduced to a smaller cell size depending on the means for measuring the traffic volume in each cell and whether or not the traffic volume exceeds. Means for storing and holding a first threshold value to be changed and a second threshold value smaller than the first threshold value for returning from the one-step narrower cell size to the original cell size depending on whether or not the traffic volume is lower. A mobile communication system is provided that automatically changes the cell size of each cell in accordance with the traffic volume that is sequentially measured. In other words, in this mobile communication system, a traffic amount section is defined for each cell size, and an end of one section overlaps with a section of the latest higher and lower cell sizes by a predetermined width.

  Further, according to the second aspect of the present invention, in the above-described mobile communication system, adjacent cells are arranged so as to be able to cover each other, and a radio base station constituting one cell stops functioning. A mobile communication system is provided that treats a traffic volume with a maximum value in the cell as measured and expands the cell size of an adjacent cell.

  According to the third aspect of the present invention, when a cell size change command is received, the radio base station apparatus changes the cell size by changing any of transmission power, reception timing, antenna direction, and antenna directivity. And a means for measuring the traffic volume in each cell, a first threshold value for changing the cell size to a narrower cell size depending on whether or not the traffic volume exceeds, and whether or not the traffic volume is smaller than the first narrower cell size. Means for storing and holding a second threshold value smaller than the first threshold value for returning to the original cell size, and a cell size change command corresponding to the traffic volume to be sequentially measured to the radio base station A base station controller for transmission is provided.

  According to the present invention, the cell size is changed with reference to two threshold values with respect to the traffic volume, so that the mobile communication system can be operated stably without being unstable near a specific (threshold) value. Thus, it is possible to avoid a situation in which handovers occur frequently. In addition, even when operation is stopped due to a failure or maintenance work, the adjacent cell can be used as a backup resource and the service in the corresponding area can be continued.

  Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a cellular mobile communication system to which the present invention is applicable. Referring to FIG. 1, radio base stations 1a, 1b,..., 1n, a base station control device 2, a maintenance terminal 3, and cells 4a, 4b,.

  The radio base stations 1a, 1b,... 1n are arranged in a mobile communication system, have cells 4a, 4b,... 4n that each cover, and mobile devices such as mobile phone terminals located in each cell. Transmit and receive wireless data. The sizes of the cells 4a, 4b,..., 4n can be dynamically changed by adjusting the transmission power and the reception timing by the control command transmitted from the base station control device 2 or the maintenance terminal 3. Yes.

  The base station control device 2 sends a cell size change command for controlling the size of the cells 4a to 4n to each radio base station either spontaneously based on the traffic volume or based on the maintenance command from the maintenance terminal 3. Send. As will be described in detail later, the cell size is changed in consideration of the size of adjacent cells so that a dead zone is not formed.

  The maintenance terminal 3 is an information processing device capable of transmitting a maintenance command for controlling the base station control device 2. Further, when the maintenance terminal 3 receives the operation status of the cells 4a to 4n from the base station control device 2 and a failure notification is reported for a specific cell, the maintenance terminal 3 automatically increases the size of the cell adjacent to the cell. A program that sends maintenance commands is implemented.

  FIG. 2 is a diagram for explaining the cell size changing operation (cell size variable range) in the present embodiment. In the drawing, the solid line indicates the minimum size of the cells 4a, 4b, 4c, 4d, and 4e, and the dotted line indicates the maximum size. As shown in FIG. 2, each cell is not only arranged to share a part of the area, but also by maximizing the adjacent cells 4b, 4c, 4d, and 4e, It is laid out so that most of the area can be covered.

FIG. 3 is a diagram for explaining the relationship between the cell size and the traffic volume held in the base station control apparatus 2 in the present embodiment. As shown in FIG. 3, map data is prepared so that a smaller cell size is applied as the traffic volume increases. In addition, the sections (LL to UL) corresponding to the respective cell sizes are determined so as to overlap with the cell size sections of the preceding and following stages by a predetermined width. In the example of FIG. 3, the (first) threshold value when shifting from the maximum cell size CS ₁ to the cell size CS ₂ one level below is UL ₁ , but when shifting from the cell size CS ₂ to the maximum cell size CS ₁ LL ₂ smaller than UL ₁ is set as the (second) threshold. Therefore, if the traffic amount exceeds the (first) threshold UL ₁ when the current maximum cell size is CS ₁ , the cell size is changed to a narrower cell size, but the traffic amount then settles down to the (first) threshold UL ₁ . even below, not immediately return to the maximum cell size CS _1, if it falls below the (second) threshold value LL _2, enlargement control of cell size is performed.

  Subsequently, the operation of the present embodiment will be described. The base station controller 2 measures the usage rate of the call control resource of each radio base station at predetermined time intervals as the traffic volume. The usage rate of the call control resource is measured by sequentially reflecting the result of the call control resource allocation management performed by the base station control device 2.

The base station controller 2 considers whether the measured traffic volume belongs to the traffic volume section corresponding to the current cell size of the map illustrated in FIG. 3 and the traffic volume of the adjacent cell. Determine the size. For example, the call control resource usage rate in the cell 4a of FIG. 2 exceeds the (first) threshold UL _{n of} the current cell size, and the traffic volume of the adjacent cells 4b to 4e is sufficiently small (for example, the current cell size (( 2) is less than the threshold LL _n ), the base station controller 2 reduces the cell 4a and expands the adjacent cells 4b, 4c, 4d, and 4e to the radio base stations 1a to 1e. Send a cell size change command. As a result, the traffic concentrated on the cell 4a can be distributed to the adjacent cells 4b to 4e, so that a shortage of resources in the radio base station 1a supporting the cell 4a can be prevented. Then, when the cell 4a is reduced, a handover to the adjacent cells 4b, 4c, 4d, and 4e is urged for a mobile device that is located in the area of the original cell 4a.

Further, for example, even when the call control resource usage rate in the cell 4a in FIG. 2 exceeds the (first) threshold value UL _{n of} the current cell size, the traffic volume of the adjacent cells 4b to 4e is high and a dead zone appears. In such a case, the base station control device 2 does not transmit the cell size change command, and maintains the sizes of the cells 4a, 4b, 4c, 4d, and 4e.

On the contrary, the traffic volume in the cell 4a is lower than the (second) threshold value LL _n of the current cell size, and the traffic volume of any of the adjacent cells 4b to 4e is sufficiently high (for example, the (first) threshold value UL of the current cell size). _If it is greater than or _{equal to n} ), the base station control device 2 expands the cell 4a, and contracts a cell having a sufficiently high traffic volume among adjacent cells (of course, traffic of a cell adjacent to the cell to be reduced) Only if the amount is low). Then, when the cell 4a is enlarged, handover to the cell 4a is prompted for the mobile devices located in the areas of the cells 4b, 4c, 4d, and 4e.

  The frequency with which the above cell size is automatically changed can be adjusted by the overlapping width of the traffic amount sections determined for each stage of the cell size. For example, if the overlap width of the traffic volume is wide, the response to the restoration of the traffic volume will become dull, but it will also be difficult to return to the original cell size from the changed cell size, and the traffic volume will be near the threshold. Frequent changes in cell size due to back and forth can be suppressed. Therefore, the frequency of handover due to the dynamic change of the cell size can be reduced by adjusting the overlapping width of the cell size and traffic volume sections.

  Next, an operation when the radio base station is suspended due to a device failure will be described. The base station controller 2 also monitors the states of the cells 4a to 4e, which are logical resources of the radio base stations 1a to 1e, for the above-described call control resource allocation management. When the occurrence or restoration of a failure is detected, the base station control device 2 reports a failure notification specifying the cell where the occurrence or restoration of the failure is made to the maintenance terminal 3.

  When the maintenance terminal 3 receives the failure notification, the maintenance terminal 3 designates the cell and transmits a maintenance command predetermined for the failure to the base station control device 2. For example, when the occurrence of a failure is detected in the cell 4a of FIG. 2, the maintenance terminal 3 specifies the failure cell 4a or the adjacent cells 4b, 4c, 4d, and 4e for the base station control device 2 Send maintenance commands. The base station controller 2 that has received this maintenance command sets the traffic volume of the cell 4a so that the size of the adjacent cells 4b, 4c, 4d, and 4e can cover the area of the cell 4a where the failure has occurred. A cell size change command that is the maximum value and is the same as that when the traffic volume of the cells 4b, 4c, 4d, and 4e is the minimum value is generated and transmitted to each of the radio base stations 1b, 1c, 1d, and 1e. As a result, the mobile station located in the area of the cell 4a where the operation is stopped is prompted to be handed over to the adjacent cells 4b, 4c, 4d, and 4e.

  On the other hand, when the radio base station recovers from a failure, the operation is resumed with the minimum cell size. For example, in the above example, the base station control device 2 that has detected the failure recovery of the cell 4 a reports a failure recovery notification to the maintenance terminal 3.

  When the maintenance terminal 3 receives the failure recovery notification, the maintenance terminal 3 transmits a failure recovery maintenance command designating the failed cell 4a or the adjacent cells 4b, 4c, 4d, and 4e to the base station controller 2. Thereby, in the base station control device 2 that has received the maintenance command, the expansion operation of the cell 4a and the reduction operation of the cells 4b, 4c, 4d, and 4e according to the traffic volume are performed in stages. Then, as the cell 4a expands, a handover from the adjacent cells 4b, 4c, 4d, 4e to the cell 4a is prompted for the mobile station located in the area of the original cell 4a.

  Next, the operation when the operation of the base station is stopped due to maintenance work will be described. For example, when it is necessary to stop the service of the cell 4a in accordance with the maintenance work of the radio base station 1a in FIG. 2, the maintenance worker performs an operation from the maintenance terminal 3 to the base station control device 2 as a maintenance target. A maintenance command for maintenance work specifying the cell 4a or the adjacent cells 4b, 4c, 4d, 4e is transmitted. Receiving this maintenance command, the base station controller 2 expands the adjacent cells 4b, 4c, 4d, and 4e in a stepwise manner until it can cover the area of the cell 4a. The cell size change command is generated so as to be reduced in size, and transmitted to each of the radio base stations 1b, 1c, 1d, and 1e. Then, as the cell 4a shrinks, a handover to the adjacent cells 4b, 4c, 4d, and 4e is urged for the mobile device located in the area of the cell 4a. Then, after the size of the cell 4a is minimized, the radio base station 1a is stopped and maintenance work is performed.

  When the maintenance work is completed and the operation of the cell 4a is resumed, the maintenance worker operates the maintenance terminal 3 to increase the size of the cell 4a to the base station controller 2 as in the above-described failure recovery. And a maintenance command for stepwise reducing the size of the adjacent cells 4b, 4c, 4d, and 4e. Then, as the cell 4a expands, a handover from the adjacent cells 4b, 4c, 4d, 4e to the cell 4a is prompted for the mobile station located in the area of the original cell 4a.

  With the above operation, the cell size is appropriately changed, the service stop time when a failure occurs can be minimized, and the service can be continued even during maintenance work.

  In the above-described embodiment, the relationship between the radio base station and the cell is described as one-to-one for simplification of description, but the present invention can also be applied to a configuration in which a single radio base station supports a plurality of cells. . FIG. 4 is a diagram for explaining the cell size changing operation (cell size variable range) when the present invention is applied to this type of configuration. As shown in FIG. 4, the area supported by the radio base station is divided into sectoral areas 5a, 5b, and 5c called sectors, and each sector is treated as one cell. Also in this case, as in the above-described embodiment, the base station control device 2 causes the sector division angle to be dynamically changed based on the traffic volume, and causes the operation at the time of failure or maintenance work to be performed. It is possible. Note that the cell size change depending on the sector angle in this type of radio base station is performed by providing a mechanism for controlling the direction and directivity of the antenna in each radio base station.

  As described above, since the cell size supported by the radio base station is dynamically changed according to the traffic volume, a plurality of radio base stations can cover each other with respect to the physical area. It is possible to effectively use limited resources while suppressing the impact of changes. Further, even when a cell operation is stopped due to a failure or maintenance work, an adjacent cell can be used as a backup resource, and the service in the corresponding area can be continued.

  In the above-described embodiment, the maintenance terminal 3 has been described as automatically controlling the size of the cell adjacent to the operation stop cell in the event of a device failure. Of course. Similarly, in the above-described embodiment, the maintenance worker has been described as transmitting a maintenance command for maintenance work at the time of maintenance work, but when receiving a report that the maintenance work has started in a specific cell, Of course, the maintenance terminal 3 may automatically transmit a maintenance command.

1 is a schematic diagram of a mobile communication system according to the present invention. It is a figure for demonstrating the change operation (cell size variable range) of cell size in one embodiment of this invention. It is a figure for demonstrating the relationship between a cell size and the traffic amount. It is a figure for demonstrating the change operation (cell size variable range) of the cell size in another embodiment of this invention.

Explanation of symbols

1a, 1b, 1c, 1d, 1e Radio base station 2 Base station controller 3 Maintenance terminals 4a, 4b, 4c, 4d, 4e Cell 5a, 5b, 5c Cell (sector)

Claims (11)

A mobile communication system that provides a wireless communication service using a plurality of cells that can change the cell size in multiple stages,
Means for measuring the amount of traffic in each cell;
A first threshold value for changing the cell size to a smaller cell size depending on whether or not the traffic amount exceeds, and a first threshold value for returning from the smaller cell size to the original cell size depending on whether or not the traffic amount falls. Means for storing and holding a small second threshold,
Automatically changing the cell size of each cell according to the traffic volume measured sequentially,
A mobile communication system. The cell size change process is performed after determining whether or not the cell size of an adjacent cell can be changed. When a non-serviceable zone occurs between adjacent cells, the cell size change of the cell is suppressed. To do,
The mobile communication system according to claim 1. When the base station that constitutes one cell stops functioning, the cells are arranged so as to cover the cell by maximizing the cell size of the adjacent cell,
The mobile communication system according to claim 1 or 2. The maintenance shift operation that can gradually reduce the cell size of the maintenance target cell and gradually increase the cell size of the cell adjacent to the cell can be executed,
The mobile communication system according to any one of claims 1 to 3. Using a call control resource usage rate as the traffic volume;
The mobile communication system according to any one of claims 1 to 4. A base station controller for a mobile communication system that provides a wireless communication service using a plurality of cells whose sizes can be changed in multiple stages,
Means for measuring the amount of traffic in each cell;
A first threshold value for changing the cell size to a smaller cell size depending on whether or not the traffic amount exceeds, and a first threshold value for returning from the smaller cell size to the original cell size depending on whether or not the traffic amount falls. Means for storing and holding a small second threshold,
Sending a cell size change command according to the traffic volume to be sequentially measured to the radio base station corresponding to each cell;
A base station control device. The cell size change command transmission processing is performed after determining whether or not the cell size of an adjacent cell can be changed. If a service-disabled zone occurs between adjacent cells, the cell size change command is transmitted. Deterring,
The base station control device according to claim 6. When a maintenance command designating a cell is received from a predetermined maintenance terminal, a cell size change command is transmitted to a radio base station in charge of an adjacent cell so as to maximize the cell size of the cell;
The base station control device according to claim 6 or 7. The operation for maintenance transition that can gradually reduce the size of a specific cell and gradually increase the cell size of a cell adjacent to the cell can be executed.
The base station control device according to any one of claims 6 to 8. Using a call control resource usage rate as the traffic volume;
The base station control apparatus according to claim 6, wherein A cell size change command is received from the base station controller according to any one of claims 6 to 10,
Changing the cell size of the cell by changing any of transmit power, reception timing, antenna direction, antenna directivity,
A radio base station apparatus characterized by the above.

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