JP2008131151A - Mobile communication system, control station apparatus, and frequency channel control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress increase in a controlling time duration of a frequency channel, along with increase in the number of cells, when a frequency channel assigned to cells such as pico cells is controlled dynamically. <P>SOLUTION: A station in charge 10 acquires cell overlap information indicative of an overlap relation of cells formed by a wireless base station 2 under and a wireless base station 2 not under a central control station 1 respectively, and selects a target wireless base station 2 for fixing a frequency channel from a combination of wireless base stations 2 under different central control station 1 where cells thereof overlap based on the cell overlap information. Then, it assigns a frequency channel to be used to the selected wireless base station 2. The central control station 1 assigns a frequency channel to each of subordinate wireless base stations 2 so as to avoid or alleviate interference by frequency channels which may be produced among cells of each wireless base station 2, while observing the frequency channel of a specific wireless base station 2 determined by the station in charge 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mobile communication system, a control station apparatus, and a frequency channel control method.

  In a future mobile communication system, it is conceivable to communicate a wideband signal using a high frequency band. Therefore, the cell size that can be covered by one base station is expected to be reduced. For this reason, there is a concern that in the conventional base station arrangement, an insensitive zone of radio waves is generated and an area where communication is not possible occurs, or traffic is biased in a large area in order to provide high-speed communication. In order to flexibly cope with such a radio wave insensitive zone and high traffic, a system in which a pico cell having a small cell size is locally arranged using a simple base station has been studied.

As a conventional frequency channel allocation method, for example, a method described in Patent Document 1 is known. In the method described in Patent Document 1, in an environment in which cells assuming a polygonal shape are arranged without interruption, interference between cells is estimated from the traffic amount and the like, and when the interference between a plurality of cells is large, the same frequency band If the interference is small, the distance between cells to which the same frequency band is assigned is reduced.
JP 2005-27189 A

  However, in a picocell system, since picocells are usually arranged irregularly, it is difficult to apply a conventional placement design assuming a zone configuration in which regular polygonal cells are regularly arranged. If not, communication quality may be degraded due to interference between overlapping cells. For this reason, in frequency channel allocation in a pico cell system, it is desired to dynamically control the frequency channel allocated to the pico cell. However, when the number of pico cells increases, it is necessary to suppress an increase in the control time of the frequency channel. It becomes.

  The present invention has been made in consideration of such circumstances, and its object is to dynamically control the frequency channel allocated to a cell such as a pico cell, and the control time of the frequency channel increases with the increase in the number of cells. An object of the present invention is to provide a mobile communication system, a control station apparatus, and a frequency channel control method that can suppress this.

  In order to solve the above problems, a mobile communication system according to the present invention includes a centralized control station that allocates a frequency channel to be used for communication with a mobile station to a radio base station under its control, and a plurality of the centralized stations. A control station having a control station under the control station, and the control station acquires cell overlap information indicating a cell overlap relationship formed by a radio base station under the central control station and a radio base station under the subordinate Based on the cell duplication information acquisition means and the cell duplication information, each cell overlaps and a radio base station to fix a frequency channel from a combination of radio base stations under the control of the centralized control station And a frequency channel determining means for allocating a frequency channel to be used for the selected radio base station, wherein the central control station has a specific radio base determined by the supervising station. Frequency channel allocation control means for allocating frequency channels to subordinate radio base stations so as to avoid or reduce frequency channel interference that may occur between cells of each radio base station while complying with the frequency channels used by the stations It is characterized by that.

  In the mobile communication system according to the present invention, the supervising station has overlapping number information acquisition means for acquiring overlapping number information indicating the overlapping number of overlapping cells indicated by the cell overlapping information, and the frequency channel The determining means selects a target radio base station to fix a frequency channel from the radio base stations having the largest number of overlapping cells based on the duplication number information.

  A control station apparatus according to the present invention is a control station apparatus that supervises a centralized control station that allocates a frequency channel used for communication with a mobile station to a radio base station under its control, wherein the centralized control station Cell duplication information acquisition means for acquiring cell duplication information indicating the duplication relationship of cells formed by subordinate radio base stations and non-subordinate radio base stations, respectively, based on the cell duplication information, each cell is duplicated, In addition, a frequency channel for selecting a target radio base station to fix a frequency channel from a combination of radio base stations under different centralized control stations and assigning a frequency channel to be used to the selected radio base station And determining means.

  In the control station apparatus according to the present invention, the control station apparatus further comprises duplication number information acquisition means for acquiring duplication number information indicating the duplication number of overlapping cells indicated by the cell duplication information, the frequency channel determination means, Based on the duplication number information, a radio base station to be fixed to the frequency channel is selected from the radio base stations having the largest number of duplications in the cell.

  A control station apparatus according to the present invention is a control station apparatus that assigns a frequency channel used for communication with a mobile station to a radio base station under its control, and has a plurality of the control station apparatuses under its control In order to avoid or reduce interference of frequency channels that may occur between cells of each radio base station, while complying with the frequency channels used by the specific radio base station determined by the station, the frequency channel to each subordinate radio base station The frequency channel assignment control means for assigning is provided.

  A frequency channel control method according to the present invention is a frequency channel control method in a mobile communication system having a centralized control station that allocates a frequency channel used for communication with a mobile station to a radio base station under its control, Based on the cell duplication information, a cell duplication information obtaining process for obtaining cell duplication information indicating a duplication relationship between cells formed by radio base stations under control of the centralized control station and non-subordinate radio base stations, respectively, A frequency to be used for the selected radio base station by selecting a target radio base station for fixing a frequency channel from a combination of radio base stations under the control of the centralized control station, each having overlapping cells. The frequency channel determination process for assigning the channel and the frequency channel used by the specific radio base station determined in the frequency channel determination process must not be observed. And a frequency channel assignment control process for assigning a frequency channel to each radio base station under the centralized control station so as to avoid or reduce frequency channel interference that may occur between cells of each radio base station. Features.

  In the frequency channel control method according to the present invention, the frequency channel control method further includes a duplication information acquisition process for obtaining duplication information indicating the duplication number of the overlapping cells indicated by the cell duplication information, and in the frequency channel determination process, Based on the duplication number information, a radio base station to which a frequency channel is to be fixed is selected from radio base stations having the largest number of cell duplications.

  According to the present invention, when dynamically controlling the frequency channel allocated to a cell such as a pico cell, even if the number of cells increases, it is possible to cope with load distribution by a plurality of centralized control stations, and radio under the control of different centralized control stations. It is possible to appropriately allocate frequency channels for cell duplication between base stations. As a result, for example, even if the number of picocells increases due to an increase in the number of picocell base stations, it becomes possible to cope with load distribution by a plurality of centralized control stations, thereby suppressing an increase in frequency channel control time. Can do.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a mobile communication system according to an embodiment of the present invention. The mobile communication system shown in FIG. 1 includes a central control station 1, a radio base station 2, a mobile station 3, and a supervising station 10.

  In FIG. 1, the management station 10 controls a plurality of central control stations 1. The supervising station 10 is connected to each central control station 1 via a communication line. A plurality of radio base stations 2 are provided under the centralized control station 1. The central control station 1 is connected to each radio base station 2 via a communication line. Each radio base station 2 forms a cell 100 which is a radio connection service area. The mobile station 3 can wirelessly connect to the radio base station 2 of the cell 100 in which the mobile station 3 is located.

  In the example of FIG. 1, the three cells 100 are arranged overlapping each other. For this reason, there is a possibility that frequency channel interference may occur between cells of each radio base station 2, and it is desirable to take measures against interference. Therefore, in the present embodiment, the controlling station 10 and the centralized control station 1 adjust the frequency channel assignment to avoid or reduce frequency channel interference that may occur between cells of each radio base station 2.

  Hereinafter, the configuration of frequency channel assignment control according to the present embodiment will be described in detail.

  When base stations are arbitrarily installed and abolished as in a pico-cell mobile communication system, it is impossible to accurately grasp the positional relationship between all base stations, so that cells are overlapped. Even so, it is difficult to know the positional relationship between the overlapping cells from the positional relationship between the base stations. Therefore, in the present embodiment, the radio base stations 2 accessible by the mobile station 3 are listed as an accessible station list, and the controlling station 10 and the centralized control station 1 determine each radio base station based on the accessible station list. The overlapping relationship of the areas between the two cells is estimated, it is determined whether frequency channel interference can occur when the same frequency channel is used, and the frequency channel assigned to each cell is determined from the determination result.

FIG. 2 is a block diagram showing the configuration of the mobile station 3 shown in FIG.
In FIG. 2, the mobile station 3 includes a received radio wave measurement unit 21, an accessible station list creation unit 22, and an accessible station list transmission unit 23.
The received radio wave measurement unit 21 measures the signal intensity of the radio wave received by the mobile station 3. With this measurement, the signal strength of the received radio wave is measured for each radio base station 2.

  The accessible station list creation unit 22 determines the radio base station 2 accessible from the mobile station 3 based on the measured received signal strength for each base station, and the radio base station accessible from the mobile station 3 An accessible station list describing the station 2 is created. Here, “accessible” means that the control signal from the radio base station can be demodulated and analyzed to read base station information. That is, even if there is a radio base station that may cause interference, the radio base station is not detected as an interference station if the received signal strength from the radio base station is low.

  The accessible station list transmission unit 23 transmits the created accessible station list to the radio base station 2 to which the mobile station 3 is connected. The radio base station 2 transmits the accessible station list received from the mobile station 3 to the central control station 1.

  FIG. 3 shows an example of the accessible station list. In the example of the mobile communication system shown in FIG. 3 (the centralized control station 1 is not shown in FIG. 3), there are four radio base stations 2A, 2B, 2C, and 2D, and corresponding cells 100A and 100B, respectively. , 100C, 100D are formed. The cells 100A, 100B, 100C, and 100D are arranged in an overlapping manner. Specifically, the cells 100A, 100B, and 100C are arranged overlapping each other. Further, the cells 100B, 100C, and 100D are arranged overlapping each other. Cells 100A and 100D do not overlap. In the example of FIG. 3, there are three mobile stations 3a, 3b, and 3c. The mobile station 3a is located in an overlapping area between the cells 100A and 100B. The mobile station 3b is located in the overlapping area of the cells 100A, 100B, and 100C. The mobile station 3c is located in an overlapping area between the cells 100C and 100D.

  In FIG. 3, since the mobile station 3a can access the radio base stations 2A and 2B, an accessible station list 200a describing the radio base stations 2A and 2B is created. Since the mobile station 3b can access the radio base stations 2A, 2B, and 2C, an accessible station list 200b that describes the radio base stations 2A, 2B, and 2C is created. Since the mobile station 3c can access the radio base stations 2C and 2D, an accessible station list 200c describing the radio base stations 2C and 2D is created. Each accessible station list 200a, 200b, 200c is sent to the centralized control station 1 via the radio base station to which each mobile station is connected.

FIG. 4 is a block diagram showing the configuration of the centralized control station 1 shown in FIG.
In FIG. 4, the central control station 1 includes a control start notification unit 31, an accessible station list reception unit 32, an accessible station list determination unit 33, an accessible station list determination result notification unit 34, a frequency channel notification reception unit 35, and a frequency. A channel assignment control unit 36 and a use frequency channel notification unit 37 are provided.

  The control start notifying unit 31 notifies the start of the frequency channel assignment operation to the radio base station 2 subordinate to the own centralized control station 1. By this notification, the radio base station 2 requests an accessible station list from the connected mobile station 3. In response to this request, the mobile station 3 creates an accessible station list.

The accessible station list receiving unit 32 receives the accessible station list created by each mobile station 3 via each radio base station 2 under the control of the central control station 1.
The accessible station list determination unit 33 determines whether the received accessible station list includes a radio base station 2 that is not under the control of the central control station 1.

  From the determination result, the accessible station list determination result notifying unit 34 reports to the controlling station 10 the radio base station 2 that is not under the control of the own centralized control station 1 included in the accessible station list. This report content includes a set of a non-subordinate radio base station 2 included in the accessible station list and a subordinate radio base station 2 that created the accessible station list. Further, the report content includes a plurality of subordinate radio base stations 2 included in the report group. This duplication number is the number of cells of other radio base stations 2 (including both subordinate and non-subordinates of the own centralized control station 1) in which the cells of the subordinate radio base stations 2 included in the reporting group overlap. is there.

  For example, in the example of FIG. 3, the radio base station 2A is described together with the other two radio base stations 2B and 2C in the accessible station list 200b of the mobile station 3b. The wireless base station 2A is described in the accessible station list 200a of the mobile station 3a, but there is only one other wireless base station, and the wireless base station is in the accessible station list 200b of the mobile station 3c. 2A is not described. Thereby, the duplication number of the radio base station 2A becomes 2 from the accessible station list 200b in which the most other radio base stations are described together with the radio base station 2A.

The frequency channel notification receiving unit 35 receives a frequency channel notification from the governing station 10. This notification notifies the frequency channel assigned to the specific radio base station 2 determined by the governing station 10.
The frequency channel allocation control unit 36 assigns to each radio base station 2 based on the accessible station list received by the accessible station list receiving unit 32 and the frequency channel notification received by the frequency channel notification receiving unit 35. Assign frequency channels.
The used frequency channel notification unit 14 notifies each radio base station 2 of the frequency channel information of the allocation result.

FIG. 5 is a block diagram showing a configuration of the administration station 10 shown in FIG.
In FIG. 5, the governing station 10 includes a control start notification unit 41, an accessible station list determination result reception unit 42, a frequency channel determination unit 43, and a frequency channel notification unit 44.

  The control start notifying unit 41 notifies the start of the frequency channel assignment operation to the centralized control station 1 subordinate to the self-managed station 10. By this notification, the central control station 1 notifies the subordinate radio base station 2 of the start of the frequency channel assignment operation.

The accessible station list determination result receiving unit 42 receives a report of the non-subordinate radio base station 2 included in the accessible station list from the central control station 1 subordinate to the self-managed station 10.
The frequency channel determination unit 43 determines a frequency channel to be assigned to the specific radio base station 2 based on the report. The specific radio base station 2 is selected from a combination of radio base stations 2 under the control of the centralized control station 1, each cell overlapping.
The frequency channel notification unit 44 notifies the central control station 1 of the frequency channel assigned to the specific radio base station 2 determined by the frequency channel determination unit 43.

Next, with reference to FIG. 6, the overall processing flow of the frequency channel assignment control according to the present embodiment will be described. FIG. 6 is a sequence chart showing the overall processing flow of frequency channel allocation control according to the present embodiment.
In FIG. 6, first, the governing station (GM) 10 and the central control station (CM) 1 notify the start of the frequency channel assignment operation (step S1). The start of this frequency channel assignment operation may be instructed periodically by the controlling station 10, or each central control station 1 instructs in an event-driven manner, and this is sent to other central control stations 1 via the controlling station 10. You may make it instruct | indicate.

  Next, when receiving the notification of the start of the frequency channel assignment operation, the radio base station (BS) 2 requests an accessible station list from the connected mobile station (SS) 3 (step S2). In response to the request, the mobile station 3 creates an accessible station list (step S3), and transmits the created accessible station list (step S4). The accessible station list is transferred to the central control station 1 via the radio base station 2.

  Next, when the centralized control station 1 receives the accessible station list from each mobile station 3, the centralized control station 1 checks the accessible station list and determines whether the wireless base station 2 that is not under its control is included. From the determination result, the centralized control station 1 reports the radio base station 2 that is included in the accessible station list and is not under its control to the governing station 10 (step S5). This report includes non-subordinate base station information that identifies a set of a non-subordinate radio base station 2 included in the accessible station list and a subordinate radio base station 2 that created the accessible station list. Including. Further, the report content includes overlap information indicating the overlap of the subordinate radio base stations 2 included in the reporting group. This duplication number is the number of cells of other radio base stations 2 (including both subordinate and non-subordinates of the own centralized control station 1) in which the cells of the subordinate radio base stations 2 included in the reporting group overlap. is there. The non-subordinate base station information is cell duplication information indicating the overlapping relationship between the cells formed by the radio base station 2 under the control of the central control station 1 and the radio base station 2 under the subordinate. The overlap information indicates the overlap of overlapping cells indicated by the cell overlap information.

  Next, when the supervising station 10 receives the non-subordinate base station information and the overlapping plural information from each centralized control station 1, the frequency channel assigned to the specific radio base station 2 based on the non-subordinate base station information and the overlapping plural information Is determined to be fixed (step S6). In this frequency channel fixing process, the radio base station 2 to which the frequency channel is to be fixed is selected from combinations of radio base stations 2 under the control of the central control station 1 that overlap each other. Furthermore, the radio base station 2 having the largest number of overlapping cells is selected. The selected radio base station 2 assigns the frequency channel by the controlling station 10 so as to fix the frequency channel. Details of the frequency channel fixing process in step S6 will be described later. Next, the supervising station 10 notifies the centralized control station 1 of the frequency channel assigned to the determined specific radio base station 2 (step S7).

  Next, the centralized control station 1 sends to each radio base station 2 based on the notification of the frequency channel assigned to the specific radio base station 2 received from the supervising station 10 and the accessible station list received from each mobile station 3. A frequency channel is assigned (step S8). Details of the frequency channel assignment processing in step S8 will be described later. Next, the central control station 1 notifies the frequency channel assigned to each radio base station 2 (step S9).

  Next, the radio base station 2 and the mobile station 3 change to the frequency channel assigned by the central control station 1 (step S10).

  Next, the frequency channel fixing process (step S6 in FIG. 6) according to the present embodiment will be described.

  First, an outline of the frequency channel fixing process according to the present embodiment will be described with reference to FIG. FIG. 7 is an explanatory diagram for explaining the outline of the frequency channel fixing process according to the present embodiment. In FIG. 7, three central control stations 1-1, 1-2, and 1-3 are provided under the control station 10. Three radio base stations 2 are provided under the control of the central control stations 1-1, 1-2, and 1-3, respectively. The cell 100A formed by the radio base station 2A under the central control station 1-1 and the cell 100B formed by the radio base station 2B under the central control station 1-2 overlap. The cell 100C formed by the radio base station 2C under the centralized control station 1-2 and the cell 100D formed by the radio base station 2D under the centralized control station 1-3 overlap.

  In the example of FIG. 7, the centralized control station 1-1 finds a radio base station 2 B that is not under control from the accessible station list of the radio base station 2 A, and sets a group of “radio base station 2 A, radio base station 2 B” to It is transmitted to the governing station 10 as subordinate base station information. The centralized control station 1-2 discovers the non-subordinate radio base station 2A from the accessible base station list of the radio base station 2B, and discovers the non-subordinate radio base station 2D from the accessible base station list of the radio base station 2C. Then, the set of “wireless base station 2B and wireless base station 2A” and the set of “wireless base station 2C and wireless base station 2D” are transmitted to the controlling station 10 as non-subordinate base station information. The central control station 1-3 discovers the non-subordinate radio base station 2C from the accessible base station list of the radio base station 2D, and manages the set of “radio base station 2D, radio base station 2C” as non-subordinate base station information. Transmit to station 10.

  Based on the non-subordinate base station information received from each of the central control stations 1-1, 1-2, 1-3, the supervising station 10 overlaps each of the cells, and the radio under the control of the different central control station 1 As a combination of the base stations 2, two sets of “wireless base station 2A, wireless base station 2B” and “wireless base station 2C, wireless base station 2D” are found. Next, the supervising station 10 assigns a fixed frequency channel to any one of the radio base stations 2 included in the discovered set. In the example of FIG. 7, for the set of “radio base station 2A, radio base station 2B”, the supervising station 10 assigns a frequency channel to the radio base station 2B and assigns the frequency channel assigned to the radio base station 2B to each Notify the central control station 1-1, 1-2, 1-3. Further, for the set of “radio base station 2C, radio base station 2D”, the supervising station 10 assigns a frequency channel to the radio base station 2D, and assigns the frequency channel assigned to the radio base station 2D to each central control station 1 -1, 1-2, 1-3 are notified.

  Each of the central control stations 1-1, 1-2, and 1-3 observes the use frequency channel of the radio base station 2B and the use frequency channel of the radio base station 2D notified from the supervising station 10, and controls the other subordinate control stations 1-1, 1-2, and 1-3. The frequency channel is assigned to the radio base station 2.

Next, details of the frequency channel fixing process according to the present embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing an operation flow of the controlling station 10 shown in FIG.
In FIG. 8, in step S <b> 21, the supervising station 10, based on the non-subordinate base station information received from each centralized control station 1, each cell overlaps and the radio base station under the different centralized control station 1 List the two combinations. This list is referred to as a fixed target list. In step S22, the supervising station 10 selects the radio base station 2 having the largest number of duplicates in the fixed target list based on the duplicate information received from each central control station 1 as a fixed target of the frequency channel. A frequency channel is assigned to the base station 2. Then, the combination including the assigned radio base station 2 is deleted from the fixed target list.

  In step S23, the radio base station 2 having the largest number of duplicates is selected as a frequency channel fixing target from the subordinate central control station 1 that does not control the radio base station 2 that has been assigned previously. Assign frequency channels. Then, the combination including the assigned radio base station 2 is deleted from the fixed target list.

  In step S24, it is determined whether the frequency channel of one radio base station 2 has been assigned to all combinations. When the frequency channel of one radio base station 2 has been assigned to all combinations, the list is empty.

  If the result of determination in step S24 is that the list is not empty and there is still a combination to which no frequency channel is assigned to both radio base stations 2, the process returns to step S22. On the other hand, if the list is empty and the frequency channel of one radio base station 2 has already been assigned to all combinations, in step S25, the frequency channels assigned to the assigned radio base station 2 are assigned to all central control stations. 1 is notified.

  The supervising station 10 assigns different frequency channels to the radio base station 2 that fixes the used frequency channel.

  Next, the frequency channel fixing process according to the present embodiment will be specifically described with reference to FIGS. 9 to 12 are specific explanatory diagrams for explaining the frequency channel fixing process according to the present embodiment. 9 to 12, the radio base station 2 is referred to as a “node”.

  In FIG. 9, five nodes a to e are provided under the same centralized control station 1. Further, the five nodes A to E are the central control station 1 different from the nodes a to e, and are provided under the same central control station 1. Nodes a to e and nodes A to E have the cell overlap relationship shown in FIG. In FIG. 10, cells overlap between nodes connected by branches. For example, the cell of node a overlaps with the cells of nodes b and c. Further, cells overlap between nodes d and A, nodes e and A, and nodes e and B under different central control stations 1.

  From FIG. 10, each cell overlaps and the combination of nodes under different central control stations 1 is “node d, node A”, “node e, node A”, “node e, node B”. Three sets. Among these, the node with the most overlapping number is node A, and the overlapping number is 5. In node A, cells overlap among five nodes d, e, B, C, and D. For this reason, a frequency channel is first assigned to the node A and fixed. Then, the combinations “node d, node A” and “node e, node A” including node A are deleted.

  Next, in the remaining set “node e, node B”, the node e that has the largest number of duplicates is selected as a frequency channel fixed target from the subordinate of the central control station 1 that does not control the node A, and a frequency is assigned to the node e. Assign and fix the channel. The frequency channels assigned to node e and node A are made different. The result is shown in FIG.

  Next, each central control station 1 observes the frequency channel fixing result and performs frequency channel assignment to subordinate nodes. In the frequency channel assignment to the nodes a to e, as shown in FIG. 12A, the fixed frequency channels of the node e and the node A are considered. That is, a frequency channel different from the fixed use frequency channel of the node e is assigned to the node c. Further, a frequency channel different from the fixed frequency channels of both the node e and the node A is assigned to the node d.

  Similarly, in the frequency channel assignment to the nodes A to E, as shown in FIG. 12 (2), the fixed use frequency channels of the node e and the node A are considered. That is, a frequency channel different from the fixed frequency channels used by both the node e and the node A is allocated to the node B. Further, a frequency channel different from the fixed used frequency channel of the node A is assigned to the node C. In addition, a frequency channel different from the fixed frequency channel of node A is assigned to the node D.

  In the above-described embodiment, the central control station 1 creates non-subordinate base station information and duplication information and transmits the information to the governing station 10. However, the central control station 1 lists all accessible stations from the central control station 1 to the governing station 10. And the controlling station 10 may create non-subordinate base station information and duplication information from the received accessible station list.

  As described above, according to this embodiment, when cell duplication occurs between radio base stations under different centralized control stations, the governing station determines the frequency channel of the radio base station related to the cell duplication. . Then, the centralized control station assigns frequency channels to the subordinate radio base stations in compliance with the determined frequency channel of use of the radio base station, so that the subordinate radio base stations and the non-subordinate radio base stations Interference between frequency channels that may occur between cells in between can be avoided or reduced.

  As a result, when dealing with an increase in the number of radio base stations by load sharing by multiple central control stations, even if cell duplication between radio base stations under different central control stations occurs, the frequency channel Assignments can be made. Therefore, for example, even if the number of picocells increases due to an increase in the number of picocell base stations, it becomes possible to cope with load distribution by a plurality of centralized control stations, so it is possible to suppress an increase in the control time of the frequency channel. it can.

Next, the frequency channel assignment process (step S8 in FIG. 6) according to the present embodiment will be described.
The centralized control station 1 includes a list of accessible stations created by each mobile station 3 connected to the subordinate radio base station 2 and a notification of frequency channels assigned to the specific radio base station 2 determined by the controlling station 10. The frequency channel to be assigned to each subordinate radio base station 2 is determined based on the above. At this time, the central control station 1 avoids or reduces the interference of the frequency channel that may occur between the cells of each radio base station 2 while observing the use frequency channel of the specific radio base station 2 determined by the supervising station 10. Thus, a frequency channel is allocated to each subordinate radio base station 2.

  Various methods can be used as the frequency channel allocation method. In this embodiment, a method using a chromatic polynomial is adopted. Hereinafter, the frequency channel allocation method using the chromatic polynomial according to the present embodiment will be described with reference to FIG. FIG. 13 is a flowchart showing a procedure of frequency channel assignment processing according to the present embodiment.

  In FIG. 13, first, in step 31, the central control station 1 checks the overlapping relationship between the cells of each radio base station 2 based on the accessible station list created by each mobile station 3. In step S32, a radio base station graph is created from the investigation result. The radio base station graph represents whether or not interference may occur between cells of each radio base station 2.

  FIG. 14 shows a radio base station graph 300 created based on the three accessible station lists 200a, 200b, and 200c illustrated in FIG. In the radio base station graph 300 of FIG. 14, nodes A, B, C, and D represent radio base stations 2A, 2B, 2C, and 2D, respectively. The branch connecting the nodes indicates that there is an overlap of cells between the radio base stations 2 corresponding to the two connected nodes, that is, interference occurs between the cells of the two radio base stations 2 It represents what can be done.

  As a method of creating a radio base station graph, the nodes are connected by branches on the assumption that interference may occur between cells of each radio base station 2 described in the same accessible station list. Thereby, in the radio base station graph 300 of FIG. 14, between the radio base stations 2A and 2B described in the accessible station list 200a and between the radio base stations 2A, 2B and 2C described in the accessible station list 200b. Between the nodes, the corresponding nodes between the radio base stations 2C and 2D described in the accessible station list 200c are connected by branches.

  Note that the radio base station graph may be composed of nodes and branches substantially as illustrated in FIG. 14, and is not limited to the expression method. For example, as illustrated in FIG. 15, the radio base station graph may be configured in a matrix format. In FIG. 15, the radio base station graph 300 shown in FIG. 14 is configured in a matrix format. In FIG. 15, each row and each column corresponds to nodes A, B, C, and D. A matrix element corresponding to a combination of nodes represents the presence or absence of a branch between the nodes, a matrix element “1” represents presence of a branch, and a matrix element “0” represents absence of a branch. For example, the 1-by-2 matrix element corresponding to the combination of node A and node B is “1”, indicating that there is a branch between the nodes A and B. On the other hand, the 1 × 4 matrix element corresponding to the combination of node A and node D is “0”, indicating that there is no branch between the nodes A and D.

  In the radio base station graph, there is a possibility that interference may occur between cells of each radio base station 2 corresponding to each node at both ends of the branch, and there is a mobile station 3 that adversely affects communication due to the interference. It has been shown. Therefore, in order to avoid or reduce the interference, different frequency channels may be assigned to the radio base stations 2 corresponding to the two nodes connected by the branches in the radio base station graph. However, the use frequency channel of the specific radio base station 2 determined by the supervising station 10 is observed.

  Returning to FIG. In steps S33 to S36, frequency channels are assigned to the radio base station 2 based on the radio base station graph. Here, it is determined whether it is possible to assign a frequency channel that can avoid inter-cell interference to each radio base station 2 with a predetermined number of frequency channels that can be used under the control of the centralized control station 2. In this embodiment, this problem is treated as a coloring problem in graph theory. That is, each node at both ends of the branch in the radio base station graph is treated as a problem of coloring with different colors. The number of colors available for coloring is the number of available frequency channels. The number of available frequency channels is predetermined.

  First, in step S33, a chromatic polynomial P (k) corresponding to the radio base station graph is generated. k is the number of colors available for coloring. The chromatic polynomial P (k) is a function (coloring function) that gives the number of painting methods when an arbitrary graph is colored with k colors. If the given graph is a simple graph (a graph in which there is always only one branch connecting each node), the coloring function is always a polynomial of k. If it is guaranteed that the value of the chromatic polynomial P (k) is always 1 or more under the condition of “k = R”, the given graph can be colored with the R color.

  Since the radio base station graph of the present embodiment is a simple graph, a chromatic polynomial P (k) can always be generated. Therefore, when the number of available frequency channels is R, if the value of the chromatic polynomial P (k) is 1 or more under the condition of “k = R”, there is at least one painting method. The station graph can be colored in R color. If the radio base station graph can be colored with R color, it can be determined that the frequency channel can be successfully assigned to each radio base station 2 with a predetermined number R of frequency channels.

  In step S34, it is determined whether the value P (R) of the chromatic polynomial P (k) under the condition “k = R” is 1 or more. As a result, if the value P (R) is less than 1, the branch of the radio base station graph is cut (step S35). At this time, the branch to be cut is a branch between nodes that is less affected by interference between cells. After the branch cut, the process returns to step S33 to regenerate the chromatic polynomial P (k).

  If the value P (R) is equal to or greater than 1 as a result of the determination in step S34, the radio base station graph can be colored in R color. Therefore, based on the radio base station graph, the frequency channel to each radio base station 2 is determined. Allocation is performed (step S36). At this time, first, the determined frequency channel is assigned to the specific radio base station 2 for which the use frequency channel is determined by the governing station 10. Next, regarding the remaining radio base stations 2, different frequency channels are allocated to the radio base stations 2 corresponding to the two nodes connected by the branches in the radio base station graph.

  In step S37, the assigned frequency channel is notified to each radio base station 2.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.
For example, the present invention is applicable to radio communication systems of various cell systems such as a pico cell system.

  In the above-described embodiment, the central control station is provided as a single device, but the wireless base station may be provided with the function of the central control station. One example of this will be described below with reference to FIGS.

  FIGS. 16 and 17 show configuration examples of mobile communication systems in which macro cells and pico cells are mixed in the same mobile communication system. The macro cell provides a wider wireless communication service area than the pico cell. Although the macro cell base station forming the macro cell and the pico cell base station forming the pico cell have different transmission outputs and antennas, the communication system is the same.

  In FIG. 16, macro cell base stations 2a and 2A that form a macro cell and pico cell base stations 2b, 2c, 2d, 2e, 2B, 2C, and 2D that form a pico cell are provided. The macro cell base stations 2a and 2A have a function of a central control station. FIG. 17 shows a control system of the mobile communication system of FIG. Under the control station 10, macro cell base stations 2a and 2A are provided. Under the macro cell base station 2a, pico cell base stations 2b, 2c, 2d, and 2e are provided. Picocell base stations 2B, 2C, and 2D are provided under the macrocell base station 2A.

  The macro cell base stations 2a and 2A function as centralized control stations, and assign frequency channels to subordinate pico cell base stations. At this time, as in the above-described embodiment, the use frequency channel of a specific radio base station determined by the governing station 10 is observed. In the example of FIG. 16, pico cells overlap between the pico cell base stations 2d and 2e under the macro cell base station 2a and the pico cell base station 2D under the macro cell base station 2A. Therefore, the governing station 10 determines the frequency channel of the picocell base station related to the overlapping picocell and notifies the macrocell base stations 2a and 2A.

  The macro cell base stations 2a and 2A allocate frequency channels to subordinate pico cell base stations in compliance with the frequency channels used by the pico cell base stations notified from the governing station 10. At this time, the macrocell base stations 2a and 2A consider their own frequency channels. In other words, the macrocell base stations 2a and 2A naturally have frequency channels used by themselves. For example, in the case of a macro cell that provides a mobile phone service, the use frequency channel is usually fixed. Accordingly, the macro cell base stations 2a and 2A can observe both the own use frequency channel and the use frequency channel of the pico cell base station notified from the supervising station 10 while inter-cell of each radio base station including itself. The frequency channel is allocated to the subordinate picocell base station so as to avoid or reduce the interference of the frequency channel that may occur in (1).

  As described above, even in the case where a macro cell to which frequency channels are fixedly assigned to the same frequency band and a pico cell to be dynamically assigned are mixed, the above-described embodiment can be similarly applied.

It is a block diagram which shows the structure of the mobile communication system which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the mobile station 3 shown in FIG. It is a figure which shows the example of the accessible station list which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the centralized control station 1 shown in FIG. It is a block diagram which shows the structure of the management station 10 shown in FIG. It is a sequence chart which shows the flow of the whole process of the frequency channel allocation control which concerns on one Embodiment of this invention. It is explanatory drawing for demonstrating the outline of the frequency channel fixing process which concerns on one Embodiment of this invention. It is a flowchart which shows the operation | movement flow of the management station 10 shown in FIG. It is a specific explanatory view for explaining a frequency channel fixing process according to an embodiment of the present invention. It is a specific explanatory view for explaining a frequency channel fixing process according to an embodiment of the present invention. It is a specific explanatory view for explaining a frequency channel fixing process according to an embodiment of the present invention. It is a specific explanatory view for explaining a frequency channel fixing process according to an embodiment of the present invention. It is a flowchart which shows the procedure of the frequency channel allocation process which concerns on one Embodiment of this invention. It is a figure which shows the example of the radio base station graph which concerns on one Embodiment of this invention. It is a figure which shows the other example of the wireless base station graph which concerns on one Embodiment of this invention. It is a block diagram of the mobile communication system which concerns on other embodiment of this invention. It is a figure which shows the control system of the mobile communication system shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Central control station, 2 ... Wireless base station, 3 ... Mobile station, 10 ... Administration station, 21 ... Received radio wave measuring part, 22 ... Accessible station list creation part, 23 ... Accessible station list transmission part, 31 ... Control Start notification unit, 32 ... accessible station list reception unit, 33 ... accessible station list determination unit, 34 ... accessible station list determination result notification unit, 35 ... frequency channel notification reception unit, 36 ... frequency channel allocation control unit, 37 Use frequency channel notification unit, 41 ... Control start notification unit, 42 ... Accessible station list determination result reception unit, 43 ... Frequency channel determination unit, 44 ... Frequency channel notification unit, 100 ... Cell, 300 ... Radio base station graph

Claims (7)

A centralized control station that allocates a frequency channel to be used for communication with a mobile station to a radio base station under its control;
A control station having a plurality of the central control stations under its control,
The governing authority
Cell duplication information obtaining means for obtaining cell duplication information indicating a duplication relation between cells formed by radio base stations under the control of the centralized control station and non-subordinate radio base stations, respectively;
Based on the cell duplication information, each cell is duplicated, and a radio base station to be fixed to a frequency channel is selected from a combination of radio base stations under the control of the central control station, which are different from each other. Frequency channel determining means for allocating a frequency channel to be used for the radio base station,
The central control station is
In order to avoid or reduce interference of frequency channels that may occur between cells of each radio base station, while complying with the frequency channels used by the specific radio base station determined by the supervising station, each subordinate radio base station Having frequency channel assignment control means for assigning frequency channels;
A mobile communication system. The governing authority
A duplication number information acquisition means for acquiring duplication number information indicating the duplication number of overlapping cells indicated by the cell duplication information;
The frequency channel determining means selects a radio base station to fix a frequency channel from among the radio base stations having the largest number of cell duplications based on the duplication number information.
The mobile communication system according to claim 1. A control station device that supervises a centralized control station that allocates a frequency channel used for communication with a mobile station to a radio base station under its control,
Cell duplication information obtaining means for obtaining cell duplication information indicating a duplication relation between cells formed by radio base stations under the control of the centralized control station and non-subordinate radio base stations, respectively;
Based on the cell duplication information, each cell is duplicated, and a radio base station to which a frequency channel is fixed is selected from a combination of radio base stations under the control of the central control station, and the selected radio base station is selected. A frequency channel determining means for allocating a frequency channel to be used for the radio base station;
A control station apparatus comprising: A duplication number information acquisition means for acquiring duplication number information indicating the duplication number of overlapping cells indicated by the cell duplication information;
The frequency channel determining means selects a radio base station to fix a frequency channel from among the radio base stations having the largest number of cell duplications based on the duplication number information.
The control station apparatus according to claim 3. A control station apparatus that assigns a frequency channel to be used for communication with a mobile station to a radio base station under its control,
To avoid or reduce interference of frequency channels that may occur between cells of each radio base station, while complying with the frequency channels used by specific radio base stations determined by a controlling station having a plurality of control station devices under control And a frequency channel allocation control means for allocating a frequency channel to each of the subordinate radio base stations. A frequency channel control method in a mobile communication system having a centralized control station that assigns a frequency channel to be used for communication with a mobile station to a radio base station under its control,
A cell duplication information acquisition process for acquiring cell duplication information indicating a duplication relationship between cells formed by radio base stations under the centralized control station and non-subordinate radio base stations, respectively;
Based on the cell duplication information, each cell is duplicated, and a radio base station to which a frequency channel is fixed is selected from a combination of radio base stations under the control of the central control station, and the selected radio base station is selected. A frequency channel determination process for allocating a frequency channel to be used for a radio base station;
In order to avoid or reduce interference of frequency channels that may occur between cells of each radio base station while observing the frequency channels used by the specific radio base stations determined in the frequency channel determination process, A frequency channel assignment control process for assigning a frequency channel to each subordinate radio base station;
A frequency channel control method comprising: A duplication number information acquisition step of obtaining duplication number information indicating the duplication number of overlapping cells indicated by the cell duplication information,
In the frequency channel determination process, based on the duplication number information, a radio base station to which a frequency channel is to be fixed is selected from the radio base stations having the largest number of cell duplications.
The frequency channel control method according to claim 6.

Images