Wireless communication system, centralized control device, wireless communication method, and centralized control program

Abstract

A wireless communication system according to one embodiment of the present invention determines whether or not a state change exceeding a prescribed condition has occurred in mutual interference among a plurality of base stations, on the basis of each set of received power information transmitted by maintenance devices and RSSI information transmitted from each base station, calculates a utility function for each base station determined to have undergone a state change exceeding the prescribed condition in the mutual interference, and performs control to change the channel and the bandwidth of each of the base stations having undergone a state change exceeding the prescribed condition in the mutual interference, so as to increase the total value of the calculated utility functions.

Description

Wireless communication system, centralized control device, wireless communication method, and centralized control program

[0001] The present invention relates to a wireless communication system, a central control device, a wireless communication method, and a central control program.

[0002] For example, RATOP (Resource allocation based on Area Throughput Optimization Policy) is known as a method for maximizing the effective capacity of the entire system by centrally controlling wireless resources such as frequency bandwidths and channels used by wireless LAN base stations (APs) (see, for example, Non-Patent Document 1).

[0003] In RATOP, a centralized control device grasps the status of each AP and allocates wireless resources such as frequency channels and bandwidths to be used by each AP.

[0004] For example, in RATOP, the evaluation index for wireless resource allocation is defined as the ratio (utility function) of the estimated amount of traffic that can be transmitted (transmittable traffic volume) based on the allocated wireless resources (channels and bandwidth) to the estimated value of the maximum traffic volume (accommodated traffic volume) of each AP.The centralized control device then performs control so as to maximize the total value of the utility function.

[0005] BAHirantha Sithira Abeysekera et al., "Network Controlled Frequency Channel and Bandwidth Allocation Scheme for IEEE 802.11a / n / ac Wireless LANs: RATOP", 2014 IEEE 25th International Symposium on Personal, Indoor and Mobile Radio Communications, pp.1041-1045

[0006] In a centralized control method for wireless resources such as RATOP, it is assumed that parameters of base stations (APs) in the entire system are updated. Therefore, if parameters of all base stations are updated when a change in radio wave conditions occurs in only some base stations in the system, it is possible that unnecessary processing or communication interruptions will occur.

[0007] The present invention aims to provide a wireless communication system, a centralized control device, a wireless communication method, and a centralized control program that can efficiently increase the effective capacity of the entire system when a state change occurs in only some of the base stations in the system.

[0008] A wireless communication system according to one embodiment of the present invention includes a plurality of base stations each accommodating a wireless terminal, a centralized control device for centrally controlling each of the base stations, and a maintenance device for monitoring radio waves transmitted by each of the base stations, wherein the maintenance device receives radio waves transmitted by each of the base stations and transmits reception power information indicating reception power to the centralized control device, and the base stations transmit RSSI information indicating RSSI of radio waves transmitted by each of the other base stations to the centralized control device, and the centralized control device monitors the reception power of each of the plurality of base stations based on the reception power information transmitted by the maintenance device and the RSSI information transmitted by each of the base stations. a determination unit that determines whether the mutual interference of each base station has changed in state beyond a predetermined condition; a utility function calculation unit that, when the determination unit determines that the mutual interference has changed in state beyond the predetermined condition, calculates, as a utility function, the ratio of an estimated value of the transmittable traffic volume based on the channel and bandwidth assigned to the base station to an estimated value of the maximum traffic volume of the base station determined by the determination unit that the mutual interference has changed in state beyond the predetermined condition; and a change control unit that controls to change the channel and bandwidth of each of the base stations that have changed in state beyond the predetermined condition so as to increase the total value of each utility function calculated by the utility function calculation unit.

[0009] Furthermore, a centralized control device according to one embodiment of the present invention is characterized in that the centralized control device, which centrally controls each of a plurality of base stations that accommodate wireless terminals, comprises: a determination unit that determines whether or not mutual interference between each of the plurality of base stations has changed in state beyond a predetermined condition, based on received power information indicating the received power of radio waves received by a maintenance device from each of the base stations and RSSI information indicating the RSSI of radio waves transmitted to each other by the base stations; a utility function calculation unit that, when the determination unit determines that the mutual interference has changed in state beyond the predetermined condition, calculates, as a utility function, the ratio of an estimated value of transmittable traffic volume based on the channel and bandwidth assigned to the base station to an estimated value of maximum traffic volume of the base station determined by the determination unit to have changed in state beyond the predetermined condition; and a change control unit that controls to change the channel and bandwidth of each of the base stations that has changed in state beyond the predetermined condition due to mutual interference, so as to increase the total value of the utility functions calculated by the utility function calculation unit.

[0010] Furthermore, a wireless communication method according to one embodiment of the present invention is a wireless communication method performed by a wireless communication system including a plurality of base stations accommodating wireless terminals, a centralized control device that centrally controls each of the base stations, and a maintenance device that monitors radio waves transmitted by each of the base stations, the maintenance device receiving radio waves transmitted by each of the base stations and transmitting reception power information indicating reception power to the centralized control device, the base stations transmitting RSSI information indicating RSSI of radio waves transmitted by each of the other base stations to the centralized control device, and the centralized control device monitoring radio waves transmitted by each of the plurality of base stations based on the reception power information transmitted by the maintenance device and the RSSI information transmitted by each of the base stations. The system includes a determination step of determining whether or not the mutual interference of each station has changed to a state exceeding a predetermined condition; a utility function calculation step of, when it is determined in the determination step that the mutual interference has changed to a state exceeding the predetermined condition, calculating, as a utility function, the ratio of an estimated value of the transmittable traffic volume based on the channel and bandwidth assigned to the base station to an estimated value of the maximum traffic volume of the base station determined to have changed to a state exceeding the predetermined condition; and a change control step of controlling the channel and bandwidth of each of the base stations whose mutual interference has changed to a state exceeding the predetermined condition so as to increase the total value of each utility function calculated in the utility function calculation step.

[0011] According to the present invention, when a state change occurs in only some base stations in the system, it is possible to efficiently increase the effective capacity of the entire system.

[0012] 6 is a diagram illustrating an overview of a wireless communication system. FIG. 7 is a diagram illustrating a specific example of a RATOP algorithm executed by a centralized control device. FIG. 8 is a diagram illustrating a configuration example of a wireless communication system according to an embodiment. FIG. 9 is a functional block diagram illustrating functions possessed by a centralized control device according to an embodiment. FIG. 10 is a diagram illustrating a first example of a specific operation of a wireless communication system according to an embodiment. FIG. 11 is a diagram illustrating the influence of radio waves transmitted by a base station on a maintenance device and the base station. FIG. 12 is a graph illustrating an example of a state change in the state shown in FIG. 6. FIG. 13 is a diagram illustrating a second example of a specific operation of a wireless communication system according to an embodiment. FIG. 14 is a diagram illustrating the influence of interference of radio waves transmitted by a base station on a base station and a maintenance device. FIG. 15 is a graph illustrating an example of a state change in the state shown in FIG. 10.

[0013] An overview of a wireless communication system will be described below with reference to the drawings. Fig. 1 is a diagram showing an overview of a wireless communication system 1. As shown in Fig. 1, the wireless communication system 1 has, for example, a plurality of base stations (APs) 2, a centralized control device 3, and a plurality of wireless terminals 10 connected to a network 100. Each of the base stations 2 is centrally controlled by the centralized control device 3, and thereby accommodates a plurality of wireless terminals 10. Hereinafter, the base stations may be referred to as APs.

[0014] The centralized control device 3 controls RATOP for a plurality of base stations 2. At this time, the control index is assumed to be a utility function U (corresponding to satisfaction level) shown in the following equation (1).

[0015] a: AP identifier b: Bandwidth c: Channel (primary channel) R: Data rate (MCS)

[0016] The traffic volume that AP(a) can transmit depends on the channel usage status of other APs, etc. The accommodating traffic volume (which depends on the amount of generated data) is set to the maximum traffic estimate value of AP(a) shown in the following formula (2), for example.

[0017]

[0018] In this case, the maximum traffic estimated value may be assumed to be the accommodated traffic volume per wireless terminal multiplied by the expected number of wireless terminals.The centralized control device 3 then performs processing to maximize the sum ΣU of the utility functions U according to the following algorithm.

[0019] RATOP algorithm: (A): The centralized control device 3 "provisionally allocates" the channels and bandwidths used by each AP according to predetermined rules. (B): The centralized control device 3 calculates the sum ΣU of the utility functions U of each AP in the case of (A) above. (C): The centralized control device 3 reallocates channels and bandwidths to APs with low utility functions U, and controls so that ΣU does not decrease. The centralized control device 3 then repeats (C) within the range of predetermined conditions.

[0020] Fig. 2 is a diagram showing a specific example of the RATOP algorithm executed by the centralized control device 3. As shown in Fig. 2, the centralized control device 3 performs processing in Phase I (initial calculation) and Phase II (optimization).

[0021] In Phase I, the centralized control device 3 selects one AP as AP-a (S100), selects a bandwidth b that can be allocated to AP-a (S102), selects a channel (primary channel) c that can be allocated to AP-a (S104), and calculates the utility function U of AP-a (S106).

[0022] Then, the central control device 3 executes the process of S104 and the process of S106 for all channels c, and further repeats the process for all bandwidths b.

[0023] Next, the central control device 3 selects the combination (b, c) that maximizes the utility function U (S108), and repeats the process for all APs.

[0024] In Phase II, the centralized control device 3 selects, for example, an AP with a small utility function U, and then repeats the process of selecting a combination (parameters) of (b, c) that maximizes the utility function U and does not degrade the sum ΣU of the utility functions U (S110).

[0025] Then, the central control device 3 sets the combination of (b, c) selected by each AP as the allocated bandwidth and channel after control (S112).

[0026] 3 is a diagram showing an example of the configuration of a wireless communication system 1a according to an embodiment that utilizes the above-described algorithm more efficiently. As shown in FIG. 3, the wireless communication system 1a according to the embodiment includes, for example, base stations 2-1 to 2-6, a central control device 3, and maintenance devices 4-1 to 4-4, which are connected to each other via a network 100.

[0027] Each of the base stations 2-1 to 2-6 accommodates a wireless terminal (not shown). Furthermore, the base stations 2-1 to 2-6 transmit RSSI information indicating the received signal strength indicator (RSSI) of radio waves transmitted by the other base stations to the central control device 3, for example, at a low frequency.

[0028] The centralized control device 3 centrally controls each of the base stations 2-1 to 2-6. The maintenance devices 4-1 to 4-4 monitor the radio waves transmitted by each of the base stations 2 and transmit the monitoring results to the centralized control device 3. For example, the maintenance devices 4 receive the radio waves transmitted by each of the base stations 2 and transmit reception power information indicating the reception power to the centralized control device 3.

[0029] Also, suppose that, for example, interfering base stations 2-X and 2-Y having the same functions as the base stations 2-1 to 2-6 are located around the wireless communication system 1a. Here, the interfering base stations 2-X and 2-Y are not subject to centralized control by the centralized control device 3, and can be sources of radio wave interference for the base stations 2-1 to 2-6. In other words, the centralized control device 3 treats the base stations 2-1 to 2-6 as base stations to be managed, and treats the interfering base stations 2-X and 2-Y as base stations not to be managed.

[0030] The maintenance device 4 then receives radio waves transmitted by non-target base stations (interfering base stations 2-X, 2-Y) that are not subject to centralized control by the centralized control device 3, and further transmits received power information indicating the received power to the centralized control device 3.

[0031] Furthermore, the maintenance device 4 may further transmit to the central control device 3 each piece of throughput information indicating the throughput of the radio waves transmitted by each base station 2 .

[0032] Next, the centralized control device 3 according to one embodiment will be described in detail. When there is no need to specify one of the multiple configurations, such as base stations 2-1 to 2-6, it will be simply abbreviated as base station 2. Furthermore, in the wireless communication system 1a, the number of base stations 2 and maintenance devices 4 is not limited and can be any number.

[0033] 4 is a functional block diagram illustrating functions of the centralized control device 3 according to one embodiment. As shown in FIG. 4, the centralized control device 3 includes, for example, a NW interface unit 30, a collection unit 31, a determination unit 32, a utility function calculation unit 33, a change control unit 34, and a main control unit 35.

[0034] The NW interface unit 30 transmits and receives control information to and from each base station 2 .

[0035] The collection unit 31 collects information about each base station 2 via the NW interface unit 30 and outputs the information to the determination unit 32. For example, the collection unit 31 collects information such as the RSSI of radio waves received by a base station 2 from other base stations 2, the location of the base station 2, the number of wireless terminals connected to each base station 2, and traffic information (such as the ratio of uplink to downlink).

[0036] The judgment unit 32 judges whether the mutual interference between each of the multiple base stations 2 has changed in state beyond a predetermined condition based on each of the received power information transmitted by the maintenance device 4 and the RSSI information transmitted by each of the base stations 2, and outputs the judgment result to the utility function calculation unit 33.

[0037] The determination unit 32 may further determine whether the estimated value of the transmittable traffic volume calculated by the utility function calculation unit 33 has changed to exceed a predetermined value, based on the throughput information transmitted by the maintenance device 4. In this case, when determining that the estimated value of the transmittable traffic volume has changed to exceed the predetermined value, the determination unit 32 may determine that the mutual interference has changed to exceed a predetermined condition.

[0038] When the determination unit 32 determines that the mutual interference has changed in state beyond a predetermined condition, the utility function calculation unit 33 calculates the ratio of the estimated value of the transmittable traffic volume based on the channel and bandwidth assigned to the base station 2 to the estimated value of the maximum traffic volume of the base station 2 for which the determination unit 32 has determined that the mutual interference has changed in state beyond the predetermined condition, as a utility function, and outputs the calculated utility function to the change control unit 34.

[0039] The change control unit 34 controls the change of the channel and bandwidth of each base station 2 whose state has changed so that mutual interference exceeds a predetermined condition, so as to increase the total value of each utility function calculated by the utility function calculation unit 33.

[0040] The main control unit 35 controls each unit constituting the central control device 3 .

[0041] Next, a specific example of the operation of the wireless communication system 1a will be described.

[0042] 5 is a diagram illustrating a first example of a specific operation of the wireless communication system 1a according to an embodiment. As indicated by the dashed double-headed arrows, a base station 2 may cause radio wave interference with other base stations 2. Furthermore, as indicated by the dashed arrows, the interfering base stations 2-X, 2-Y, and 2-Z may cause radio wave interference with the base station 2 and the maintenance device 4.

[0043] The maintenance device 4 constantly monitors the reception level of radio waves from each of the base stations 2-1 to 2-4 connected via the network 100. If any abnormality or change in status occurs in any of the base stations 2, the maintenance device 4 immediately notifies the centralized control device 3.

[0044] The centralized control device 3 refers to the reception levels from each base station 2 received by the maintenance device 4 and the past RSSI of other base stations 2, and if it determines that there is a change in the RSSI value between base stations, it performs control (parameter updates) by applying the RATOP algorithm to the base station 2 where the change in status has occurred.

[0045] For example, the centralized control device 3 refers to the reception level transmitted from the maintenance device 4 and the history of RSSI information for each base station 2, and determines whether there has been a change in status based on the range of fluctuation in the RSSI, the magnitude of deviation from the normal value of the RSSI, the duration of the change in the RSSI, etc.

[0046] In the example shown in FIG. 5, the maintenance device 4-2 located around the base station 2-2 transmits to the central control device 3 the reception level of the radio wave received from the base station 2-2.

[0047] Here, when the central control device 3 determines that there is a change in the reception state of the radio waves from the base station 2-2 at the base stations 2-1 and 2-4, it performs control (updates parameters) using the RATOP algorithm.

[0048] 6 is a diagram showing the effect of radio waves transmitted from the base station 2-2 on the maintenance device 4-2 and the base station 2-1. FIG. 7 is a graph showing an example of the state change in the state shown in FIG.

[0049] For example, the central control device 3 estimates that when the reception level from the base station 2-2 at the maintenance device 4 drops from the range of steady state A, the RSSI from the base station 2-2 at the base station 2-1 also drops.

[0050] Then, if the RSSI from base station 2-2 at base station 2-1 continues to be lower than, for example, the carrier sense threshold, the centralized control device 3 assumes that base station 2-1 and base station 2-2 are not in a state of mutual interference, and performs control (parameter updates) using the RATOP algorithm.

[0051] Furthermore, the central control device 3 may determine whether or not there is a change in state based on the physical state of each base station 2 (whether or not there is line of sight, etc.).

[0052] In the wireless communication system 1a, the central control device 3 does not frequently perform control using the RATOP algorithm during normal operation.

[0053] 8 is a diagram illustrating a second example of the specific operation of the wireless communication system 1a according to an embodiment. As indicated by the dashed double-headed arrows, a base station 2 may cause radio wave interference with other base stations 2. Furthermore, as indicated by the dashed arrows, the interfering base stations 2-X, 2-Y, and 2-Z may cause radio wave interference with the base station 2 and the maintenance device 4.

[0054] The maintenance device 4 constantly monitors the reception level of radio waves from each of the base stations 2-1, 2-2, and 2-4 connected via the network 100, as well as the reception level of radio waves from each of the interfering base stations 2-X and 2-Y. If any abnormality or change in status occurs in any of the base stations 2, the maintenance device 4 immediately notifies the centralized control device 3.

[0055] In the example shown in FIG. 8, the maintenance device 4-2 transmits to the central control device 3 the reception levels of radio waves received from the base stations 2-1, 2-2, and 2-4 and the interfering base stations 2-X and 2-Y.

[0056] Here, if the central control device 3 determines that there has been a change in the reception status of radio waves from base stations 2-1, 2-4 and interfering base stations 2-X, 2-Y at base station 2-2, it performs control (parameter updates) using the RATOP algorithm.

[0057] 9 is a diagram showing the influence of interference of radio waves transmitted from the base station 2-2 on the base station 2-2 and the maintenance device 4-2. FIG. 10 is a graph showing an example of a change in state in the state shown in FIG.

[0058] For example, the central control device 3 estimates that when the reception level from the base station 2-1 at the maintenance device 4 drops from the range of steady state A, the RSSI from the base station 2-1 at the base station 2-2 will also drop.

[0059] Then, if the RSSI from base station 2-1 at base station 2-2 continues to be lower than, for example, the carrier sense threshold, the centralized control device 3 assumes that base station 2-1 and base station 2-2 are not in a state of mutual interference, and performs control (parameter updates) using the RATOP algorithm.

[0060] 11 is a diagram illustrating a third example of the specific operation of the wireless communication system 1a according to an embodiment. For example, as indicated by the dashed double-headed arrows, a base station 2 may experience radio wave interference with another base station 2. Furthermore, for example, as indicated by the dashed arrows, an interfering base station 2-X or 2-Y may cause radio wave interference with the base station 2.

[0061] The maintenance device 4 receives data from the base station 2 to monitor the throughput, and notifies the central control device 3 of the throughput of the base station 2 .

[0062] The centralized control device 3 then refers to the throughput of the base station 2 estimated from the throughput notified by the maintenance device 4 and the most recent transmittable traffic volume, and if the utility function differs from the expected value, it applies the RATOP algorithm to the base station 2 whose status has changed (updates the parameters).

[0063] For example, the maintenance device 4 periodically receives data from the base station 2-3, observes the throughput, and transmits the observed throughput to the centralized control device 3. The centralized control device 3 derives an estimate of the throughput of the base station 2, compares it with the most recent transmittable traffic volume, and calculates a utility function.

[0064] If the utility function differs from the expected value, the centralized control device 3 applies the RATOP algorithm to the base station 2 in which the state change has occurred (updates the parameters).

[0065] 12 is a flowchart illustrating an example of operation of a wireless communication system 1a according to an embodiment. As illustrated in FIG. 12, in the wireless communication system 1a, the centralized control device 3 determines whether or not a notification indicating that an abnormality or a state change has occurred in a base station 2 has been received from the maintenance device 4 (S200). If a notification has been received from the maintenance device 4 (S200: Yes), the centralized control device 3 proceeds to processing of S202. If no notification has been received from the maintenance device 4 (S200: No), the centralized control device 3 continues processing of S200.

[0066] The central control device 3 periodically receives and collects RSSI information from each of the base stations 2 .

[0067] In the process of S202, the centralized control device 3 determines (estimates) whether or not a state change has occurred between the base station 2 and another base station 2. For example, the centralized control device 3 estimates the current RSSI of the base station 2 based on the RSSI history of each base station 2 and the reception level of the radio waves received from the maintenance device 4, and compares it with the carrier sense level to determine whether or not a state change has occurred.

[0068] If the central control device 3 determines that a state change has occurred (S202: Yes), it proceeds to processing S204, and if it determines that no state change has occurred (S202: No), it returns to processing S200.

[0069] In the process of S204, the central control device 3 controls the base station 2 that is the target of control (parameter update) to which the RATOP algorithm is applied.

[0070] In this way, the wireless communication system 1a in one embodiment determines whether the mutual interference of each of multiple base stations 2 has changed in state beyond a predetermined condition based on each piece of received power information transmitted by the maintenance device 4 and the RSSI information transmitted by each base station 2, calculates the utility function of each base station 2 determined to have changed in state beyond the predetermined condition, and performs control to change the channel and bandwidth of each base station 2 whose mutual interference has changed in state beyond the predetermined condition so as to increase the total value of each utility function.Therefore, when a change in state occurs in only some of the base stations in the system, the effective capacity of the entire system can be efficiently increased.

[0071] In addition, each function of the centralized control device 3 may be configured in part or in whole by hardware such as a PLD (Programmable Logic Device) or an FPGA (Field Programmable Gate Array), or may be configured as a program executed by a processor such as a CPU.

[0072] For example, the central control device 3 can be realized using a computer and a program, and the program can be recorded on a storage medium or provided via a network.

[0073] 13 is a diagram illustrating a hardware configuration of a centralized control device 3 according to one embodiment. As shown in FIG. 13, the centralized control device 3 has an input unit 50, an output unit 51, a communication unit 52, a CPU 53, a memory 54, and an HDD 55 connected via a bus 56, and functions as a computer. The centralized control device 3 is also capable of inputting and outputting data to and from a computer-readable storage medium 57.

[0074] The input unit 50 is, for example, a keyboard and a mouse, etc. The output unit 51 is, for example, a display device such as a display.

[0075] The communication unit 52 is a communication interface that communicates with, for example, the base station 2 to be controlled and the maintenance device 4 .

[0076] The CPU 53 controls each component of the central control device 3 and performs predetermined processing, etc. The memory 54 and HDD 55 store data, etc.

[0077] The storage medium 57 is capable of storing programs and the like that cause the central control device 3 to execute the functions of the central control device 3. Note that the architecture that constitutes the central control device 3 is not limited to the example shown in FIG.

[0078] 1, 1a... wireless communication system, 2, 2-1 to 2-6... base stations, 2-X, 2-Y, 2-Z... interfering base stations, 3... centralized control device, maintenance devices 4-1 to 4-4, 10... wireless terminal, 30... NW interface unit, 31... collection unit, 32... determination unit, 33... utility function calculation unit, 34... change control unit, 35... main control unit, 50... input unit, 51... output unit, 52... communication unit, 53... CPU, 54... memory, 55... HDD, 56... bus, 57... storage medium, 100... network

Claims

1. A wireless communication system comprising a plurality of base stations accommodating wireless terminals, a centralized control device for centrally controlling each of the base stations, and a maintenance device for monitoring radio waves transmitted by each of the base stations, wherein the maintenance device receives radio waves transmitted by each of the base stations and transmits received power information indicating received power to the centralized control device, and each of the base stations transmits RSSI information indicating the RSSI of radio waves transmitted by the other base stations to the centralized control device, and the centralized control device comprises: a determination unit for determining whether or not mutual interference between each of the plurality of base stations has changed in state beyond a predetermined condition based on the received power information transmitted by the maintenance device and the RSSI information transmitted by each of the base stations; and a utility function calculation unit for calculating, when the determination unit determines that the mutual interference has changed in state beyond the predetermined condition, a ratio of an estimated value of transmittable traffic volume based on a channel and bandwidth assigned to the base station to an estimated value of maximum traffic volume of the base station determined by the determination unit that the mutual interference has changed in state beyond the predetermined condition as a utility function; and a change control unit that controls changing the channel and bandwidth of each of the base stations in which a state change in mutual interference exceeds a predetermined condition so as to increase the total value of each utility function calculated by the utility function calculation unit.

2. A wireless communication system according to claim 1, characterized in that the maintenance device receives radio waves transmitted from base stations not subject to centralized control by the centralized control device, and further transmits reception power information indicating the reception power to the centralized control device.

3. The wireless communication system of claim 1, wherein the maintenance device further transmits to the centralized control device each piece of throughput information indicating the throughput of radio waves transmitted by each of the base stations, and the determination unit further determines whether or not the estimated value of the transmittable traffic volume calculated by the utility function calculation unit has changed beyond a predetermined value based on the throughput information transmitted by the maintenance device, and when it determines that the estimated value of the transmittable traffic volume has changed beyond the predetermined value, determines that the mutual interference has changed in state beyond a predetermined condition.

4. A centralized control device that centrally controls each of a plurality of base stations that accommodate wireless terminals, comprising: a determination unit that determines whether or not mutual interference between each of a plurality of base stations has changed in state beyond a predetermined condition, based on each piece of reception power information indicating the reception power of radio waves received by a maintenance device from each of the base stations, and each piece of RSSI information indicating the RSSI of radio waves transmitted to each other by the base stations; a utility function calculation unit that, when the determination unit determines that the mutual interference has changed in state beyond the predetermined condition, calculates, as a utility function, the ratio of an estimated value of transmittable traffic volume based on the channel and bandwidth assigned to the base station to an estimated value of maximum traffic volume of the base station that the determination unit has determined to have changed in state beyond the predetermined condition; and a change control unit that performs control to change the channel and bandwidth of each of the base stations that have changed in state beyond the predetermined condition in order to increase the total value of each utility function calculated by the utility function calculation unit.

5. The centralized control device according to claim 4, characterized in that the judgment unit further judges whether or not the estimated value of the transmittable traffic volume calculated by the utility function calculation unit has changed beyond a predetermined value based on each piece of throughput information indicating the throughput of the radio waves transmitted by each of the base stations, and when it is determined that the estimated value of the transmittable traffic volume has changed beyond the predetermined value, judges that the mutual interference has changed in state beyond a predetermined condition.

6. A wireless communication method performed by a wireless communication system including a plurality of base stations accommodating wireless terminals, a centralized control device for centrally controlling each of the base stations, and a maintenance device for monitoring radio waves transmitted by each of the base stations, wherein the maintenance device receives radio waves transmitted by each of the base stations and transmits reception power information indicating reception power to the centralized control device, and each of the base stations transmits RSSI information indicating the RSSI of radio waves transmitted by the other base stations to the centralized control device, and the centralized control device performs a determination step of determining whether or not mutual interference between each of the plurality of base stations has changed in state exceeding a predetermined condition based on the reception power information transmitted by the maintenance device and the RSSI information transmitted by each of the base stations, and a utility function calculation step of calculating, when it is determined in the determination step that the mutual interference has changed in state exceeding the predetermined condition, a ratio of an estimated value of transmittable traffic volume based on a channel and bandwidth assigned to the base station to an estimated value of maximum traffic volume of the base station determined to have changed in state exceeding the predetermined condition as a utility function, and a change control step of controlling the change of the channel and bandwidth of each of the base stations in which the state change of the mutual interference exceeds a predetermined condition so as to increase the total value of each of the utility functions calculated in the utility function calculation step.

7. The wireless communication method according to claim 6, wherein the maintenance device receives radio waves transmitted from a non-target base station that is not subject to centralized control by the centralized control device, and further transmits reception power information indicating the reception power to the centralized control device.

8. A centralized control program for causing a computer to function as each part of the centralized control device according to claim 4 or 5.