Patent Publication Number: US-2023137745-A1

Title: Wireless communication system, and wireless communication control apparatus, and method

Description:
TECHNICAL FIELD 
     An embodiment of the present invention relates to a wireless communication system, a wireless communication control device, and a method. 
     BACKGROUND ART 
     A communication system (hereinafter may be referred to as a “system”) to which a wireless LAN (Local Area Network) is applied is a wireless communication system that can be used at a low cost in a frequency band for which license is unnecessary, and accordingly, such systems have rapidly become popular, and a situation where a large number of wireless LAN terminals are present in the same area and interfere with each other is thought to be an issue (see NPL 1, for example). 
     Therefore, a large number of technologies are proposed to minimize influence of interference between wireless LAN terminals and increase the communication capacity of individual terminals or the entire system. 
     In a wireless communication system, for example, wireless LAN access points (base stations, APs: Access Points) interfering with each other acquire interference information of a surrounding region, and transmit the acquired information as wireless environment information to a control server, which serves as a wireless communication control device. 
     The control server performs calculation in order to allocate frequency channels to the APs such that the throughput of the group of APs is maximized, and sends back the result of calculation as control information to each AP. 
     On the other hand, types of wireless LAN terminals (STAs (stations)) that are connected to the APs, uses of the wireless LAN terminals, and types of introduced devices are increasing in the wireless communication system. Accordingly, the control server needs to calculate optimized parameters, taking information of the terminals connected to the APs into consideration. 
     Also, communication speed, delay time, the number of terminals that can be connected, the range of a communication area, and requirements of communication vary in a wide range according to an application program (hereinafter referred to as an “application”) used in the system. 
     In addition, a requirement that is to be prioritized varies according to usage scenes such as an application and a device that use the wireless LAN. 
     For example, the 920 MHz band can be used in Japan by two types of stations, i.e., a specified low power radio station of which the maximum transmission power is 20 mW and a land mobile station of which the maximum transmission power is 250 mW. 
     Therefore, in a predetermined frequency bandwidth, the maximum transmission power, i.e., the radius of an area that can be covered varies according to a corresponding license. 
     It is necessary to consider such a difference in communication capability in implementation, when a parameter is optimized. 
     Also, content of frequency rules that are applied varies depending on whether the system is used in Japan or abroad, and the range of frequency channels that are supported differs between devices. These factors need to be considered as well when a parameter is optimized. 
     For example, bandwidths of frequency channels that are specified in the communication standard IEEE802.11ah are the following five bandwidths: 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz. Out of these bandwidths, only 1 MHz is the frequency bandwidth that is allowed in Japan, whereas a plurality of frequency bandwidths up to 16 MHz are allowed in some countries abroad. As described above, usage constraints on a wireless communication system vary according to the country in which wireless communication devices are used. 
     Furthermore, the frequency bandwidths described above include essential frequency bandwidths and optional frequency bandwidths, and accordingly, it is thought that frequency bandwidths used in the system vary according to the cost and uses of the devices. 
     Moreover, requirements relating to wireless communication vary according to a scenario in which the system is used and the type of an application used in the system. 
     For example, when a large number of sensor devices are used through wireless communication, maximization of the number of connected terminals and power saving of the sensor devices are requirements that are to be most prioritized. 
     When a moving image shot by a security camera is relayed through wireless communication, the communication speed of wireless communication is the requirement that is to be most prioritized. 
     When data communication is performed in a farm, a factory, or the like, the communication range of wireless communication is the requirement that is to be most prioritized. 
     As described above, the requirement that is to be most prioritized varies according to a scenario in which the system is used and the type of an application that is used, and accordingly, optimizing the throughput and the communication capacity uniformly may be insufficient for a user. 
     CITATION LIST 
     Non Patent Literature 
     [NPL 1] IEEE Std 802.11ahTM-2016 (IEEE Standard for Information technology-Telecommunications and information exchange between systems Local and metropolitan area networks-Specific equirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, Amendment 2: Sub 1 GHz License Exempt Operation, IEEE Computer Society) 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     As described above, in order to optimize wireless communication resources that are applied to various communication devices, or various services and applications in which wireless communication is used, it is insufficient to perform optimization uniformly as described above. 
     Accordingly, it is necessary to realize optimization that reflects usage constraints and requirements corresponding to each device and each usage scene. 
     The present invention was made focusing on the above circumstances, and has an object of providing a wireless communication system, a wireless communication control device, and a method with which setting information relating to wireless communication can be optimized. 
     Means for Solving the Problem 
     A wireless communication system according to an aspect of the present invention is a wireless communication system including: a wireless base station configured to perform wireless communication with a wireless terminal that belongs to the wireless base station; and a wireless communication control station that is communicably connected to the wireless base station and is configured to notify the wireless base station of information that indicates a parameter to be used for communication control by the wireless base station and the wireless terminal, based on wireless environment information regarding the wireless base station, wherein the wireless communication control station includes: a determination unit that determines a requirement that is prioritized among multiple types of requirements in wireless communication, according to a current use case of wireless communication; a setting unit that sets the information indicating the parameter to be used for communication control by the wireless base station and the wireless terminal, based on the requirement determined by the determination unit and the wireless environment information regarding the wireless base station; and a transmission unit that transmits the information set by the setting unit to the wireless base station. 
     A wireless communication control device according to an aspect of the present invention is a wireless communication control device that is communicably connected to a wireless base station that performs wireless communication with a wireless terminal that belongs to the wireless base station, the wireless communication control device including: a determination unit configured to determine a requirement that is prioritized among multiple types of requirements in wireless communication, according to a current use case of wireless communication; a setting unit configured to set information that indicates a parameter to be used for communication control by the wireless base station and the wireless terminal, based on the requirement determined by the determination unit and wireless environment information regarding the wireless base station; and a transmission unit configured to transmit the information set by the setting unit to the wireless base station. 
     A wireless communication method according to an aspect of the present invention is a method performed by a wireless communication control device that is communicably connected to a wireless base station that performs wireless communication with a wireless terminal that belongs to the wireless base station, the method including: determining a requirement that is prioritized among multiple types of requirements in wireless communication, according to a current use case of wireless communication; setting information that indicates a parameter to be used for communication control by the wireless base station and the wireless terminal, based on the determined requirement and wireless environment information regarding the wireless base station; and transmitting the set information to the wireless base station. 
     Effects of the Invention 
     According to the present invention, it is possible to optimize setting information relating to wireless communication. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram showing an application example of a typical wireless communication system. 
         FIG.  2    is a flowchart showing an example of control performed in the typical wireless communication system. 
         FIG.  3    is a diagram showing an application example of a wireless communication system according to an embodiment of the present invention. 
         FIG.  4    is a block diagram showing a functional configuration example of a control server. 
         FIG.  5    is a flowchart showing an example of control performed in the wireless communication system according to an embodiment of the present invention. 
         FIG.  6    is a diagram showing an example of parameters of constitutional elements of use cases, in the form of a table. 
         FIG.  7    is a diagram showing an example of parameters of constitutional elements of use cases, in the form of a table. 
         FIG.  8    is a diagram showing an example of scores set for respective requirements, with respect to a parameter of a constitutional element of use cases, in the form of a table. 
         FIG.  9    is a diagram showing an example of scores set for respective requirements, with respect to a parameter of a constitutional element of use cases, in the form of a table. 
         FIG.  10    is a diagram showing an example of scores set for respective requirements, with respect to a parameter of a constitutional element of use cases, in the form of a table. 
         FIG.  11    is a diagram showing an example of scores set for respective requirements, with respect to a parameter of a constitutional element of use cases, in the form of a table. 
         FIG.  12    is a diagram showing an example of scores set for respective requirements, with respect to a parameter of a constitutional element of use cases, in the form of a table. 
         FIG.  13    is a diagram showing an example of scores set for respective requirements, with respect to a parameter of a constitutional element of use cases, in the form of a table. 
         FIG.  14    is a diagram showing an example of calculation of scores relating to determination of a requirement that is to be most prioritized, in the form of a table. 
         FIG.  15    is a diagram showing an example of calculation of scores relating to determination of a requirement that is to be most prioritized, in the form of a table. 
         FIG.  16    is a diagram showing an example of calculation of scores relating to determination of a requirement that is to be most prioritized, in the form of a table. 
         FIG.  17    is a diagram showing an example of calculation of scores relating to determination of a requirement that is to be most prioritized, in the form of a table. 
         FIG.  18    is a diagram showing an example of calculation of scores relating to determination of a requirement that is to be most prioritized, in the form of a table. 
         FIG.  19    is a diagram showing an example of calculation of scores relating to determination of a requirement that is to be most prioritized, in the form of a table. 
         FIG.  20    is a flowchart showing a first example of control performed in the wireless communication system according to an embodiment of the present invention, with respect to setting of a parameter based on a requirement that is to be prioritized. 
         FIG.  21    is a flowchart showing a second example of control performed in the wireless communication system according to an embodiment of the present invention, with respect to setting of a parameter based on a requirement that is to be prioritized. 
         FIG.  22    is a block diagram showing an example of a hardware configuration of the control server in the wireless communication system according to an embodiment of the present invention. 
     
    
    
     [DESCRIPTION OF EMBODIMENTS 
     The following describes an embodiment of the present invention with reference to the drawings. 
     First, a typical wireless communication system will be described to facilitate understanding of the embodiment. 
       FIG.  1    is a diagram showing an application example of the typical wireless communication system. 
     In the example shown in  FIG.  1   , the wireless communication system includes a control server  10  and a plurality of wireless LAN access points (APs)  20 . The control server  10  may also be referred to as a “wireless communication control station” or a “wireless communication control device”. The APs  20  may also be referred to as “wireless base stations”. 
     In  FIG.  2   , N APs  20  are denoted as AP “1”, AP “2”, ..., and AP “N”. In this system, the control server  10  is communicably connected to each AP  20  in an environment in which the plurality of APs  20  interfere with each other. 
     Each AP  20  can perform data communication with wireless LAN terminals (STAs) (not shown) that belong to the AP  20 , using wireless frames. The wireless LAN terminals may also be referred to as “communication terminals”. The APs  20  and STAs may also be referred to as “wireless communication terminals” in a broad sense. 
     In this system configuration, each AP  20  connected to the control server  10  can transmit wireless environment information to the control server  10 . “a” shown in  FIG.  1    corresponds to the wireless environment information. 
     Examples of the wireless environment information include: (1) usage information of a frequency channel such as APs for which SSIDs (Service Set Identifiers) acquired through carrier sense in a surrounding region can be identified, and a usage rate of the channel; and (2) parameters currently set for wireless devices in each AP, such as a frequency channel to be used, a channel bandwidth, a transmission power value, and a transmission time interval. 
     The control server  10  collects wireless environment information from each AP  20 . The control server  10  calculates optimized parameters for the APs  20  using the wireless environment information under conditions where it is assumed that all of the APs  20  have the same specification and similar communication capacities are necessary. 
     Examples of the calculated parameters include the position of a frequency channel, a channel bandwidth, a transmission power value, and a transmission time interval. 
     Calculation results are transmitted as control information to the APs  20 . “b” shown in  FIG.  1    corresponds to the control information. 
     Upon receiving the control information, each AP  20  changes relevant setting values in the AP  20  in accordance with the control information. 
     When control is executed periodically or upon occurrence of some control trigger, optimized parameters are calculated again based on updated wireless environment information, and control information is transmitted to each AP  20 . 
       FIG.  2    is a flowchart showing an example of control performed in the typical wireless communication system. 
     First, the control server  10  collects wireless environment information from each AP  20  (step S 10 ), and calculates optimized parameters based on the collected information (step S 11 ). 
     Here, the control server  10  transmits information that indicates the parameters calculated in step S 11  as control information to the APs  20  (step S 12 ). 
     Thereafter, when a predetermined period of time has elapsed, control is executed based on the parameters. Here, if occurrence of a control trigger has not been detected (No in step S 13 ) and the control does not end (No in step S 14 ), the control server  10  enters a standby state (step S 15 ), and if occurrence of a control trigger has been detected (Yes in step S 13 ), the control server  10  returns to step S 10  and collection of wireless environment information and the following processing are executed again. 
     In an embodiment of the present invention, when different requirements are required for different wireless communication terminals in an environment in which the wireless communication terminals are present and interfere with each other, optimization of control information is executed for one or more wireless communication terminals, with consideration given to the respective requirements. 
     In an embodiment of the present invention, optimum control information, e.g., an optimum parameter and optimum usage conditions are calculated in an environment in which wireless communication terminals that have constraint conditions of different devices or usage environments, and different requirements are present in the same environment, interfering with each other. The usage conditions are, for example, specifications of devices relating to wireless communication, such as the maximum transmission power of a wireless communication terminal and the gain of an antenna. 
     In an embodiment of the present invention, usage conditions, usage constraints, and requirements corresponding to usage scenes are considered with respect to each of a plurality of wireless communication terminals that are to be controlled, and an optimum value of a frequency resource for each wireless communication terminal and an optimum value of a parameter set for the wireless communication terminal are calculated based on collected wireless environment information and individual requirements, rather than a single condition. Examples of the usage constraints include a constraint regarding the maximum transmission power that is specified in frequency rules for a frequency band in which the wireless communication terminal is used. 
     In a wireless communication system according to an embodiment of the present invention, an initial setting value and a range of control values at the time of optimization control are set for each of the wireless communication terminals, based on usage conditions and usage constraints peculiar to the respective wireless communication terminals, and requirements corresponding to usage scenes. 
     In the wireless communication system according to an embodiment of the present invention, a requirement that is to be most prioritized in a use case of a communication standard is determined as a result of comprehensive addition of scores that are set for respective requirements, with respect to parameters of constitutional elements of the use case. In this system, an optimum value of a parameter is calculated using a method for calculating the optimum value corresponding to the determined requirement. 
     In an embodiment of the present invention, when an optimum value is calculated, a method for calculating the optimum value is selected based on a requirement corresponding to an envisaged use case, with consideration given to usage conditions and usage constraints peculiar to each wireless communication terminal, under the circumstances where various wireless communication terminals and various usage scenes are envisaged. Therefore, optimization control that corresponds to individual requirements can be executed, as compared to optimization control in which only a particular wireless communication terminal and a particular requirement are envisaged. 
     In the wireless communication system according to an embodiment of the present invention, a requirement that needs to be considered in an envisaged use case is determined based on a numerical value that represents the requirement, and thus, it is possible to eliminate ambiguity of the degree of priority of the requirement, and uniquely determine the requirement to be considered in setting. 
       FIG.  3    is a diagram showing an application example of the wireless communication system according to an embodiment of the present invention. 
     In the example shown in  FIG.  3   , the wireless communication system includes a control server  10  and a plurality of wireless LAN access points (APs)  20 . In  FIG.  3   , N APs  20  are denoted as AP “1”, AP “2”, ..., and AP “N”. In this system, the control server  10  is communicably connected to each AP  20  in an environment in which the plurality of APs  20  interfere with each other. 
     Each AP  20  can perform data communication with wireless LAN terminals (STAs)  30  that belong to the AP  20 , using wireless frames. In  FIG.  3   , three STAs  30  that belong to the AP “1” are denoted as STA “1”, STA “2”, and STA “3”. Also, the other APs can perform data communication with STAs (not shown) that belong to the APs, using wireless frames. 
     In this system configuration, each AP  20  connected to the control server  10  can transmit wireless environment information to the control server  10 . 
     Examples of the wireless environment information include: (1) usage information of a frequency channel such as APs for which SSIDs can be identified through carrier sense in a surrounding region, and a usage rate of the channel; (2) parameters currently set for wireless devices in each AP, such as a frequency channel to be used, a channel bandwidth, and a transmission power value; (3) usable ranges of parameters such as a frequency range and a range of transmission power values that are set for a region such as a country or set as specifications of a device, for example; (4) current connection information such as the number and types of wireless LAN terminals that are connected to the AP, information of channels that can be used by the wireless LAN terminals, and transmission power information; and (5) traffic information and information of an application program that are set or observed in an upper unit in the wireless communication system. 
     The control server  10  collects information acquired from the APs  20  and sets ranges of parameter values that can be set in the APs, as ranges of controllable values. 
     The control server  10  determines requirements relating to the wireless communication system according to observed traffic information, application information, or use cases that are envisaged for the respective APs  20  and set in the control server  10 . Furthermore, the control server  10  sets initial values of optimum parameters relating to the use cases based on current usage conditions of frequency channels in a surrounding region. 
     The set initial values are transmitted as control information from the control server  10  to the APs  20 . 
     Upon receiving the control information, each AP  20  changes setting values relating to STAs  30  that belong to the AP  20 , in accordance with the control information. 
     When control is executed by the control server  10  periodically or upon occurrence of some trigger, optimum values of the parameters are set again based on updated information such as current connection information and usage information of frequency channels in a surrounding region, and the set values are transmitted as control information to the APs  20 . 
       FIG.  4    is a block diagram showing a functional configuration example of the control server. 
     As shown in  FIG.  4   , the control server  10  includes an initial value setting unit  11 , a collecting unit  12 , a parameter calculation unit  13 , a transmission unit  14 , a control processing unit  15 , and a storage unit  16 . The parameter calculation unit  13  corresponds to a determination unit and a setting unit. Operations of the respective units will be described later. The control processing unit  15  controls operations of the initial value setting unit  11 , the collecting unit  12 , the parameter calculation unit  13 , and the transmission unit  14 . 
       FIG.  5    is a flowchart showing an example of control performed in the wireless communication system according to an embodiment of the present invention. 
     In the present embodiment, values of parameters of constitutional elements of use cases according to IEEE802.11ah are set by the initial value setting unit  11  of the control server  10  and are stored in the storage unit  16  (step S 20 ). 
     In the present embodiment, ranges of setting values relating to the APs  20  are individually set based on ranges of values of parameters that can be used in the wireless communication system. Also, in the present embodiment, a requirement that is to be prioritized is determined according to observed traffic information, application information, or a use case that is envisaged for each of the APs  20  and set in the control server  10 . 
     In the present embodiment, scores are set for respective requirements that are considered, with respect to values of parameters of constitutional elements of the use cases, for example. 
     In the present embodiment, the sum or an integrated value of scores relating to the respective constitutional elements is taken to be an overall score of a requirement, and a requirement that has the highest score among the requirements is taken to be the requirement that is to be most prioritized in the use case of the AP. 
     Next, an example of parameters of constitutional elements of the use cases according to IEEE802.11ah will be described.  FIG.  6    is a diagram showing an example of the parameters of the constitutional elements of the use cases, in the form of a table. 
     As shown in  FIG.  6   , in IEEE802.11ah, requirements of resource setting vary depending on use cases to be used. 
     In the example shown in  FIG.  6   , the constitutional elements of the use cases are “the number of terminals (standard number)”, “traffic load”, “traffic direction”, “access frequency”, “propagation environment”, and “area range”. 
     Types of the parameter of the constitutional element “the number of terminals” are “large (101 or more)”, “medium (10 to 100)”, and “small (9 or less)”. 
     Types of the parameter of the constitutional element “traffic load” are “high (video and the like)”, “medium (data and the like)”, and “low (sensor and the like)”. 
     Types of the parameter of the constitutional element “traffic direction” are “uplink direction is frequent” (which may be described as “uplink is frequent”), “downlink direction is frequent” (which may be described as “downlink is frequent”), and “uplink direction and downlink direction are equivalent” (which may be described as “uplink and downlink are equivalent”). 
     Types of the parameter of the constitutional element “access frequency” are “high (video and the like)”, “medium”, and “low (sensor and the like)”. 
     Types of the parameter of the constitutional element “propagation environment” are “indoor [concrete]”, “indoor [wooden construction]”, “outdoor [urban area, city]”, and “outdoor [suburb]”. 
     Types of the parameter of the constitutional element “area range” is “wide (300[m] or more)”, “medium (100[m] or more and less than 300[m])”, and “narrow (less than 100[m])”. 
       FIG.  7    is a diagram showing an example of parameters of constitutional elements of use cases, in the form of a table. 
       FIG.  7    shows an example of constitutional elements of use cases envisaged in IEEE802.11ah, and values of parameters of the constitutional elements in the respective use cases. 
     In the example shown in  FIG.  7   , the use cases are categorized as default, camera moving image transmission, monitoring, sensor, data distribution, data transfer, and so on. Values of parameters of the constitutional elements are shown with respect to each of the use cases, and are stored in the storage unit  16  of the control server  10 . For example, in the use case “camera moving image transmission”, the value of the parameter relating to the constitutional element “traffic load” is “high”. “Default” is a standard use case. 
     The values of parameters shown in  FIG.  7    may be changed through an input operation performed by an administrator of the system. It should be noted that the values of parameters of the constitutional elements in the use case “default” may be changed and a new use case relating to the changed values may be added. 
       FIGS.  8  to  13    are diagrams showing examples of scores set for respective requirements, with respect to parameters of constitutional elements of use cases, in the form of tables. 
     As shown in  FIGS.  8  to  13   , scores are set for respective requirements, with respect to values of parameters of constitutional elements of use cases, and are stored in the storage unit  16  of the control server  10 . In the examples shown in  FIGS.  8  to  13   , the requirements are “prioritize throughput per terminal (prioritize throughput/terminal)”, “prioritize high access efficiency”, “prioritize low power consumption”, and “prioritize wide area”. 
     In the example shown in  FIG.  8   , scores are set for the requirements “prioritize throughput per terminal”, “prioritize high access efficiency”, “prioritize low power consumption”, and “prioritize wide area”, with respect to each of the values “large (101 or more)”, “medium (10 to 100)”, and “small (9 or less)” of the parameter of the constitutional element “the number of terminals” of use cases. These scores indicate whether the degree of priority of a requirement to be set is high or low, with respect to the values of the parameter of the constitutional element of use cases. 
     In  FIG.  8   , the score of the requirement “prioritize throughput per terminal” set with respect to the value “large” of the parameter of the constitutional element “the number of terminals” is “0.3”. The score of the requirement “prioritize throughput per terminal” set with respect to the value “medium” of the parameter of the constitutional element “the number of terminals” is “0.5”. The score of the requirement “prioritize throughput per terminal” set with respect to the value “small” of the parameter of the constitutional element “the number of terminals” is “1.0”. 
     In the example shown in  FIG.  8   , the value “large” of the parameter of the constitutional element “the number of terminals” indicates that the degree of priority of the requirement “prioritize throughput per terminal” is relatively low, and the value “small” of the parameter of the constitutional element “the number of terminals” indicates that the degree of priority of the requirement “prioritize throughput per terminal” is relatively high. 
     In the example shown in  FIG.  9   , scores are set for the respective requirements, with respect to each of the values “high (video and the like)”, “medium (data and the like)”, and “low (sensor and the like)” of the parameter of the constitutional element “traffic load” of use cases. 
     In the example shown in  FIG.  10   , scores are set for the respective requirements, with respect to each of the values “uplink direction is frequent”, “downlink direction is frequent”, and “uplink direction and downlink direction are equivalent” of the parameter of the constitutional element “traffic direction” of use cases. 
     In the example shown in  FIG.  11   , scores are set for the respective requirements, with respect to each of the values “high (video and the like)”, “medium”, and “low (sensor and the like)” of the parameter of the constitutional element “access frequency” of use cases. 
     In the example shown in  FIG.  12   , scores are set for the respective requirements, with respect to each of the values “indoor [concrete]”, “indoor [wooden construction]”, “outdoor [urban area, city]”, and “outdoor [suburb]” of the parameter of the constitutional element “propagation environment” of use cases. 
     In the example shown in  FIG.  13   , scores are set for the respective requirements, with respect to each of the values “wide (300[m] or more)”, “medium (100[m] or more and less than 300[m])”, and “narrow (less than 100[m])” of the parameter of the constitutional element “area range” of use cases. 
     In the present embodiment, the initial value setting unit  11  of the control server  10  calculates, for example, the sum of scores set for a requirement with respect to constitutional elements of a target use case, and performs this calculation with respect to each requirement. 
     The initial value setting unit  11  determines at least one requirement that has the highest score among the requirements as a result of the calculation to be the requirement that is to be most prioritized. 
     As an example of the calculation described above, the initial value setting unit  11  selects one from options of each item M i  of the constitutional elements “the number of terminals”, “traffic load”, “traffic direction”, “access frequency”, “propagation environment”, and “area range”, with respect to each use case. 
     The selected item is represented by k, and a requirement for which calculation is to be performed is represented by 1. At this time, a numerical value relating to the requirement 1 with respect to the option k of the item M i  is represented by M i (k, 1). 
     An evaluation formula P i  of the prioritized item 1 to be calculated is the following formula (1), for example. 
     [Math. 1] 
     
       
         
           
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     Other than the above, the following formula (2) may be used as the evaluation formula. P i ═ΣM i (k,l) ... formula (2) 
     The following describes a specific example of calculation of the sum of scores and determination of a requirement that is to be most prioritized. 
       FIGS.  14  to  19    are diagrams showing examples of calculation of scores relating to determination of a requirement to be most prioritized, in the form of tables. The scores shown in  FIGS.  14  to  19    correspond to the scores shown in  FIGS.  8  to  13   . In  FIGS.  15  to  19   , scores that differ from those shown in  FIG.  14    and constitutional elements relating to the scores are shown in boldface. 
     The example shown in  FIG.  14    shows scores that are set for the respective requirements with respect to the constitutional elements “the number of terminals”, “traffic load”, “traffic direction”, “access frequency”, “propagation environment”, and “area range” of the use case “default”, according to the values of parameters of the constitutional elements of the use case “default” shown in  FIG.  7   . The sum of scores set for the requirement “prioritize throughput per terminal” with respect to the constitutional elements described above is “4.1”. The sum of scores set for the requirement “prioritize high access efficiency” with respect to the constitutional elements is “4.7”, and the sum of scores set for the requirement “prioritize low power consumption” with respect to the constitutional elements is “3.7”. The sum of scores set for the requirement “prioritize wide area” with respect to the constitutional elements is “4.6”. 
     In the example shown in  FIG.  14   , the sum “4.7” of scores set for the requirement “prioritize high access efficiency” with respect to the constitutional elements of the use case “default” is the highest among the sums of scores set for the respective requirements. Therefore, the requirement “prioritize high access efficiency” is the requirement that is to be most prioritized in the use case “default”. 
     In the example shown in  FIG.  15   , the sum “5.0” of scores set for the requirement “prioritize high access efficiency” with respect to the constitutional elements of the use case “camera moving image transmission” is the highest among the sums of scores set for the respective requirements. Therefore, the requirement “prioritize high access efficiency” is the requirement that is to be most prioritized in the use case “camera moving image transmission”. 
     In the example shown in  FIG.  16   , the sum “4.9” of scores set for the requirement “prioritize wide area” with respect to the constitutional elements of the use case “monitoring” is the highest among the sums of scores set for the respective requirements. Therefore, the requirement “prioritize wide area” is the requirement that is to be most prioritized in the use case “monitoring”. 
     In the example shown in  FIG.  17   , the sum “6.0” of scores set for the requirement “prioritize low power consumption” and the sum “6.0” of scores set for the requirement “prioritize wide area” with respect to the constitutional elements of the use case “sensor” are the highest among the sums of scores set for the respective requirements. Therefore, the requirements “prioritize low power consumption” and “prioritize wide area” are the requirements that are to be most prioritized in the use case “sensor”. 
     In the example shown in  FIG.  18   , the sum “4.7” of scores set for the requirement “prioritize throughput per terminal” with respect to the constitutional elements of the use case “data distribution” is the highest among the sums of scores set for the respective requirements. Therefore, the requirement “prioritize throughput per terminal” is the requirement that is to be most prioritized in the use case “data distribution”. 
     In the example shown in  FIG.  19   , the sum “4.7” of scores set for the requirement “prioritize high access efficiency” with respect to the constitutional elements of the use case “data transfer” is the highest among the sums of scores set for the respective requirements. Therefore, the requirement “prioritize high access efficiency” is the requirement that is to be most prioritized in the use case “data transfer”. 
     The description will be given referring again to  FIG.  5   . The collecting unit  12  of the control server  10  collects wireless environment information from each wireless communication terminal (step S 21 ). 
     The parameter calculation unit  13  of the control server  10  calculates optimum values of parameters relating to wireless communication terminals based on the wireless environment information collected in step S 21  (step S 22 ). 
     When the optimum values of the parameters are calculated, usage conditions of each wireless communication terminal, such as the maximum transmission power and the gain of an antenna can be considered in terms of control ranges. Also, a requirement that has been determined as described above can be considered when the optimum values of the parameters are calculated. 
     For example, in a case where the determined requirement is “prioritize wide area”, calculation of an optimum transmission power value is not executed, and control is performed such that the maximum transmission power value is used, for example. 
     As described above, calculation results of optimum values of parameters vary depending on the requirement to be prioritized, which is determined as described above. 
     The following describes examples of control relating to setting of a parameter based on a requirement to be most prioritized, which is performed in step S 22  described above.  FIG.  20    is a flowchart showing a first example of control relating to setting of a parameter based on a requirement to be prioritized, which is performed in the wireless communication system according to an embodiment of the present invention. 
     In the first example, the parameter calculation unit  13  of the control server  10  initially sets a frequency band (channel group) to be used in order to set an upper limit of the transmission power value, when setting transmission power values for APs and STAs that belong to the control server  10  and are to be controlled. 
     For example, as frequency bands that can be used in Japan for RFID (Radio Frequency Identifier) (received signal strength indicator), there are a frequency band in which the upper limit of transmission power is 250 mW and a frequency band in which the upper limit of transmission power is 20 mW. 
     When channels that can be used vary according to output as described above according to information of a country in which the system is operated (Yes in Step S 31 ), it is necessary to determine a channel group in which the APs and STAs to be controlled are to be operated, after transmission power values necessary for the APs and STAs are set. When No in step S 31 , processing in the first example of control ends. 
     When the requirement that is to be most prioritized, which has been determined as described above and corresponds to the highest score (including the case of a tie score), is “prioritize wide area” (written as “wide area” in  FIG.  20   ) (Yes in step S 32 ), the APs and STAs to be controlled need to transmit wireless signals as far as possible. In this case, if all of the APs and STAs to be controlled can output high power, which is 250 mW in this example (Yes in step S 33 ), the parameter calculation unit  13  sets the APs and STAs to be controlled to a high-output channel group in which 250 mW is the maximum transmission power (step S 34 ). 
     On the other hand, when the requirement to be most prioritized is not “prioritize wide area” (No in step S 32 ), the parameter calculation unit  13  sets the APs and STAs to be controlled to a regular channel group in which 20 mW is the maximum transmission power so that consideration will be given to the influence of interference on the surrounding region (step S 35 ). The same also applies to a case where No in step S 32 . 
     Next, the following describes an example of control relating to setting of the value of a parameter when only set items are referred to, other than the requirement to be most prioritized.  FIG.  21    is a flowchart showing a second example of control relating to setting of a parameter based on a requirement to be prioritized, which is performed in the wireless communication system according to an embodiment of the present invention. 
     In the second example, the parameter calculation unit  13  of the control server  10  sets a channel bandwidth for an AP that is to be controlled. 
     Here, if the requirement “prioritize throughput” is not the single requirement to be most prioritized (No in step S 41 ), as control that is performed on an AP of default setting, which is included in a list of control targets, the parameter calculation unit  13  allocates 1 MHz, which is the narrowest bandwidth, as the channel bandwidth for the AP to be controlled (step S 51 ), in order to avoid interference with wireless communication systems in a surrounding region. 
     On the other hand, if the requirement “prioritize throughput” is the single requirement to be most prioritized (Yes in step S 41 ), control for setting the value of a parameter from usable bandwidths according to values of items that are set when use conditions and requirements are calculated is performed as described below. 
     In the control, the parameter calculation unit  13  sets a maximum value BW of the channel bandwidth based on a channel group, a country code, and model performance, for example (step S 42 ). The parameter calculation unit  13  determines bw_1 using the following formula (3) (step S 43 ). 
     bw_1 = BW — (the number of controllable APs with which AP to be controlled interferes) ... formula (3) 
     Then, the parameter calculation unit  13  determines which of “low”, “medium”, and “high” the current traffic load corresponds to (step S 44 ). When the current traffic load is “low”, the parameter calculation unit  13  sets bw_2 to “1” (step S 45 ). When the current traffic load is “medium”, the parameter calculation unit  13  sets bw_2 to “2” (step S 46 ). When the current traffic load is “high”, the parameter calculation unit  13  sets bw_2 to the maximum value BW (step S 47 ) . 
     bw_1 and bw_2 are selected from a set {1, 2, 4, 8, 16}, rather than integers. When bw_1 is 0 or less, bw_1 is set to 1. 
     After step S 45 , S 46 , or S 47 , if bw_1 is no greater than bw_2 (No in step S 48 ), the parameter calculation unit  13  sets the channel bandwidth to bw_1 (step S 49 ). If bw_1 is greater than bw_2 (Yes in step S 48 ), the parameter calculation unit  13  sets the channel bandwidth to bw_2 (step S 49 ). As described above, an optimum value of a parameter is calculated in step S 22  based on the requirement determined as described above and the range of values of the parameter. 
     The description will be given referring again to  FIG.  5   . The transmission unit  14  of the control server  10  transmits information of calculated values of parameters as control information to the wireless communication terminals (step S 23 ). 
     Thereafter, in a case where control is performed based on the parameters after a predetermined period of time has elapsed, if occurrence of a control trigger has not been detected (No in step S 24 ) and the control does not end (No in step S 25 ), the control server  10  enters a standby state (step S 26 ), and if a control trigger has occurred (Yes in step S 24 ), the control server  10  returns to step S 21  and collection of wireless environment information is executed again. When the control has ended (Yes in step S 25 ), the series of processing steps shown in  FIG.  5    ends. 
     Next, the following describes a third example of control relating to setting of a parameter based on a requirement to be prioritized. 
     In the third example, the parameter calculation unit  13  of the control server  10  sets transmission time intervals for the APs and STAs that belong to the control server  10  and are to be controlled. Here, when the requirement to be prioritized is “prioritize high access efficiency” or the value of the parameter of the constitutional element “the number of terminals” is “large (101 or more)”, transmission time intervals of data frames at which the APs and STAs start transmission are controlled. 
     For example, in a wireless LAN that uses a frequency band for which license is unnecessary, a period of time for executing carrier sense (hereinafter referred to as a “carrier sense time”) in order to avoid collision of wireless signals is used as a period of time that is at least a predetermined period of time and is calculated using random numbers. Consequently, intervals between times at which wireless signals are transmitted are spaced apart from each other. 
     If the parameter calculation unit  13  makes the intervals between times at which wireless signals are transmitted long through setting, for example, the probability of wireless signals colliding with each other can be reduced even when the number of terminals present in the same area is large. 
     Also, if the parameter calculation unit  13  sets a period of time until the next wireless signal is transmitted after a terminal has completed transmission of a wireless signal, i.e., a pause period, to be longer than the usual carrier sense time, rather than making the carrier sense time long through setting, another terminal that has not completed transmission yet can be prioritized to start transmission. 
     Further, RAW (Restricted Access Window) and TWT (Target Wake Time) specified in IEEE802.11ah have functions of restricting time at which transmission is performed by STAs. In the third example of control, whether or not to use these functions and a setting value relating to the functions, e.g., the way to separate groups or time at which transmission can be performed, can be determined through setting of the requirement or the number of terminals performed by the parameter calculation unit  13 . 
     Control relating to transmission time intervals, which is performed to avoid collision of wireless signals when a large number of terminals are present in the same area as described above, reduces a usage rate of frequency resources per time when the number of terminals present in the same area is small, because overhead occurs in communication. Therefore, it is desirable that the control is adaptively performed according to the environment or the use case in which wireless communication is used, as in the embodiment of the present invention. 
       FIG.  22    is a block diagram showing an example of a hardware configuration of the control server of the wireless communication system according to an embodiment of the present invention. 
     In the example shown in  FIG.  22   , the control server  10  according to the above embodiment is constituted by a server computer or a personal computer, for example, and includes a hardware processor  111 A such as a CPU. A program memory  111 B, a data memory  112 , an input/output interface  113 , and a communication interface  114  are connected to the hardware processor  111 A via a bus  120 . The same configuration can also be employed for the APs  20  and the STAs  30 . 
     The communication interface  114  includes at least one wireless communication interface unit, for example, and enables transmission and reception of information to and from a communication network NW. As a wireless interface, for example, an interface for which a low-power wireless data communication standard of wireless LANs or the like is employed is used. 
     An input device  50  and an output device  60  for the administrator may be connected to the input/output interface  113 . 
     A non-volatile memory that enables writing and reading at any time, such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive), and a non-volatile memory such as a ROM (Read Only Memory), which are tangible non-temporary storage mediums, are used in combination as the program memory  111 B, for example, and a program that is necessary to execute various types of control processing according to an embodiment is stored in the program memory  111 B. 
     The non-volatile memory described above and a volatile memory such as a RAM (Random Access Memory), which are tangible storage mediums, are used in combination as the data memory  112 , for example, to store various types of data that are acquired or created when various types of processing are performed. 
     The control server  10  according to an embodiment of the present invention can be configured as a data processing device that includes, as processing functional units that are realized by software, the initial value setting unit  11 , the collecting unit  12 , the parameter calculation unit  13 , the transmission unit  14 , and the control processing unit  15 , which are shown in  FIG.  4   . 
     The storage unit  16  can be realized using the data memory  112  shown in  FIG.  22   . However, a storage region in the data memory  112  is not an essential constituent of the control server  10 , and may be a region in an external storage medium such as a USB (Universal Serial Bus) memory or a region in a storage device such as a database server provided in a cloud, for example. 
     All of the processing functional units of the control server  10  described above can be realized by causing the hardware processor  111 A to read and execute the program stored in the program memory  111 B. It should be noted that some or all of the processing functional units may be realized in various other forms including integrated circuits such as an ASIC (Application Specific Integrated Circuit) and an FPGA (Field-Programmable Gate Array). 
     The method described in the embodiment can be stored, as a program (software means) that can be executed by a computer, on a recording medium such as a magnetic disk (Floppy (registered trademark) disk, hard disk, etc.), an optical disc (CD-ROM, DVD, MO, etc.), or a semiconductor memory (ROM, RAM, Flash memory, etc.), or can be transmitted and distributed via a communication medium. The program stored on the medium also includes a setting program for configuring software means (including not only an execution program, but also a table and a data structure) to be executed by a computer, in the computer. A computer that realizes the device builds the software means by reading the program recorded on the recording medium, and using the setting program depending on cases, and executes the processing described above as a result of operations of the computer being controlled by the software means. The recording medium referred to in the present specification is not limited to a recording medium used for distribution, and encompasses storage mediums such as a magnetic disk and a semiconductor memory that are provided in the computer or a device connected via a network. 
     The present invention is not limited to the embodiment described above, and various changes can be made without departing from the gist of the present invention, when the present invention is implemented. Embodiments may be combined as appropriate, and in such a case, combined effects can be achieved. The above embodiment includes various inventions, and the various inventions can be extracted by combining constitutional elements selected from the disclosed constitutional elements. For example, if the problem can be solved and the effects can be achieved even when some constitutional elements of all the constitutional elements described in the embodiment are omitted, a configuration in which these constitutional elements are eliminated can be extracted as an invention. 
     REFERENCE SIGNS LIST 
     
         
           10  Control server 
           20  Wireless LAN access point (AP) 
           30  Wireless LAN terminal (STA)