Patent Publication Number: US-2007097906-A1

Title: Wireless line control system, centralized control apparatus, wireless line control method used therein and program therefor

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a wireless line control system, a centralized control apparatus, a wireless line control method used therein and a program therefor. In particular, the present invention relates to controlling wireless lines in a wireless mesh network.  
      2. Description of the Prior Art  
      Conventionally, as a wireless mesh network, a network has been proposed which distributively arranges wireless terminals at certain intervals in a mesh pattern to configure a wireless mesh, and transfers packet data between mutually adjacent wireless terminals to relay the packet data to a destination terminal (for instance, refer to Japanese Patent Laid-Open No. 2000-115171).  
      In this wireless mesh network, congestion processing is performed by wireless terminals by changing transmission speed according to the volume of data in the network or changing transfer rates according to destination of transmission. Additionally, the wireless mesh network is equipped with functions such as attaching directional characteristics to data upon transmission, performing data transmission using two or more channels provided in anticipation of collision of the data on radio waves, or providing each wireless terminal with a function to select a nearest connection point from a plurality thereof.  
      In a conventional wireless mesh network such as described above, controlling its wireless lines through centralized control is considered unrealistic from the viewpoints of increased load on a control station or following capability to traffic volume which fluctuates instantaneously and the like (for instance, refer to Japanese Patent Laid-Open No. 2002-345016).  
     BRIEF SUMMARY OF THE INVENTION  
      In the conventional wireless mesh network described above, since destinations of relay radio between wireless nodes which configure the wireless mesh network are changed for load distribution in a state where the loads on the wireless nodes are high, loads due to control signals for switching relay radio in relation to wireless nodes with high loads are increased.  
      Additionally, in the conventional wireless mesh network, since switching of relay radio is performed within the network in a high-load state during which many user terminals are connected, instantaneous interruption or disconnection occurs at many of the connected user terminals.  
      Furthermore, in the conventional wireless mesh network, since switching of destinations is performed by searching wireless nodes to be alternative destinations after radio wave conditions of relay radio between wireless nodes have deteriorated, instantaneous interruption or a long period of disconnection occur at the connected user terminals in cases where no destinations could be found or where traffic at destinations are high.  
      In consideration of the above, an object of the present invention is to solve the above problems by providing a wireless line control system, centralized control apparatus, wireless line control method used therein and program therefor which are capable of reducing control signals to wireless nodes with high loads as well as reducing occurrences of instantaneous interruption or disconnection at user terminals connected to the wireless nodes.  
      A wireless line control system according to the present invention distributively arranges a plurality of wireless nodes at certain intervals in a mesh pattern to configure a wireless mesh, and transfers packet data between mutually adjacent wireless nodes, the wireless line control system comprising: 
          a centralized control apparatus which controls each of the plurality of wireless nodes; and     a gateway wireless node which transmits to and receives from other networks user data that is transmitted to and received from the plurality of wireless nodes; wherein        

      the centralized control apparatus comprises: means of analyzing radio wave propagation state based on traffic information and reception levels between the wireless nodes collected in advance from the gateway wireless node and each of the plurality of the wireless nodes; and means of establishing a wireless mesh, based on the analysis results, before the wireless nodes enter high-load states and before radio wave conditions of relay radio between the wireless nodes deteriorate.  
      The centralized control apparatus according to the present invention is a centralized control apparatus which controls each of a plurality of wireless nodes in a wireless line control system which distributively arranges a plurality of wireless nodes at certain intervals in a mesh pattern to configure a wireless mesh, and transfers packet data between mutually adjacent wireless nodes, the centralized control apparatus comprising:  
      means of analyzing radio wave propagation state based on traffic information and reception levels between the wireless nodes collected in advance from a gateway wireless node which transmits to and receives from other network user data being transmitted to and received from the plurality of wireless nodes and each of the plurality of the wireless nodes; and means of establishing a wireless mesh, based on the analysis results, before the wireless nodes enter high-load states and before radio wave conditions of relay radio between the wireless nodes deteriorate.  
      A wireless line control method according to the present invention is a wireless line control method used in a wireless line control system which distributively arranges a plurality of wireless nodes at certain intervals in a mesh pattern to configure a wireless mesh, and transfers packet data between mutually adjacent wireless nodes, the wireless line control method comprising:  
      a centralized control apparatus which controls each of the plurality of wireless nodes; and a gateway wireless node which transmits to and receives from other networks user data that is transmitted to and received from the plurality of wireless nodes; wherein  
      the centralized control apparatus executes: processing for analyzing radio wave propagation state based on traffic information and reception levels between the wireless nodes collected in advance from the gateway wireless node and each of the plurality of the wireless nodes; and processing for establishing a wireless mesh, based on the analysis results, before the wireless nodes enter high-load states and before radio wave conditions of relay radio between the wireless nodes deteriorate.  
      A program for a wireless line control method according to the present invention is a program for a wireless line control method used in a wireless line control system which distributively arranges a plurality of wireless nodes at certain intervals in a mesh pattern to configure a wireless mesh, and transfers packet data between mutually adjacent wireless nodes, the program for the wireless line control method comprising:  
      a centralized control apparatus which controls each of the plurality of wireless nodes; and a gateway wireless node which transmits to and receives from other networks user data that is transmitted to and received from the plurality of wireless nodes; wherein  
      the program for the wireless line control method causes a computer of the centralized control apparatus to execute: processing for analyzing radio wave propagation states based on traffic information and reception levels between the wireless nodes collected in advance from the gateway wireless node and each of the plurality of wireless nodes; and processing for establishing a wireless mesh, based on the analysis results, before the wireless nodes enter high-load states and before radio wave conditions of relay radio between the wireless nodes deteriorate.  
      In other words, the wireless line control system according to the present invention enables reduction of control over wireless nodes with high loads as well as reduction of occurrences of instantaneous interruption or disconnection at user terminals connected to the wireless nodes by having means of establishing an appropriate wireless network before the wireless nodes enter high-load states or before radio wave conditions of relay radio between the wireless nodes deteriorate by analyzing traffic information collected in advance or by analyzing radio wave propagation states.  
      A first characteristic of the present invention is that, when establishing a network with wireless nodes for establishing a wireless mesh network, the centralized control node collects traffic information in advance from each wireless node, and a traffic pattern from the present to the future is estimated by analyzing such historical traffic information to achieve establishment of a mesh network of the wireless nodes before traffic load rises so that the configured network distributes load over the entire mesh network to enable optimum throughput.  
      The above-described wireless nodes correspond to access points in a wireless LAN (local area network) or base stations in a mobile communication system, and the same definition of wireless nodes will be used in the description below.  
      A second characteristic of the present invention is that, when establishing a network with wireless nodes for establishing a wireless mesh network, the centralized control node collects in advance radio wave reception levels between wireless nodes from each wireless node, and radio wave propagation states from the present to the future is estimated by analyzing such historical radio wave reception levels to achieve establishment of a mesh network of the wireless nodes so that throughput attenuation due to radio waves in the configured network becomes minimal.  
      A third characteristic of the present invention is that, when establishing a network with wireless nodes for establishing a wireless mesh network, accurate estimation of traffic patterns or radio wave propagation states is made possible by having the centralized control node repeatedly acquire traffic information or information regarding radio wave reception levels from each wireless node.  
      In wireless mesh networks, there are wireless lines which relay data between wireless nodes, and wireless lines which transmit and receive data between wireless nodes and user terminals. In the following description, the former will be defined as relay radio while the latter will be defined as access radio.  
      To be more precise, in the wireless line control system according to the present invention, the centralized control node acquires in advance reception levels between individual wireless nodes from each wireless node so that two wireless nodes that are connectable are verified. The centralized control node then periodically acquires traffic information from each wireless node, and calculates and stores average values of the acquired traffic information. Relay radio loads, number of relay radio lines, access radio loads, number of access radio lines and the like may be considered as traffic information.  
      In relation to a load pattern (trend based on time slots such as weekdays and holidays) from the present to the future which is estimated from the average values of stored historical traffic information, the centralized control node distributes the load on the entire network and determines a configuration of the wireless mesh network so that optimum throughput is obtained, and issues instructions for mesh configuration including information necessary for establishing the mesh network to each wireless node. Messages for realizing the instructions on mesh configuration include wireless nodes which are destinations of relay radio, allowable relay radio load, allowable access radio load and the like.  
      As seen, in the wireless line control system according to the present invention, since traffic information of each wireless node and reception levels between wireless nodes are acquired in advance by the centralized control node, and a wireless mesh network is established based on estimated future traffic patterns or information on radio wave propagation states, an appropriate wireless mesh network may be established before traffic loads rise.  
      This means that, in the wireless line control system according to the present invention, by analyzing historical traffic information or historical radio propagation states collected in advance by the centralized control node, an appropriate wireless mesh network may be established before the wireless nodes enter high-load states or before radio wave conditions of relay radio between the wireless nodes deteriorate, thereby enabling reduction of control signals to wireless nodes with high loads as well as reduction of occurrences of instantaneous interruption or disconnection at user terminals connected to the wireless nodes.  
      As seen, in the wireless line control system according to the present invention, since average values of traffic information collected in advance are calculated per specific days of the week or time slots so that a wireless mesh network which realizes optimum throughput is configured before loads on wireless nodes rise according to traffic states estimated in advance, it is possible to reduce control, which accompany changing configurations of the network, over wireless nodes with high loads.  
      Additionally, in the wireless line control system according to the present invention, since average values of traffic information collected in advance are calculated per specific days of the week or time slots so that a wireless mesh network which realizes optimum throughput is configured before loads on wireless nodes rise according to traffic states estimated in advance, it is possible to reduce occurrences of instantaneous interruption or disconnection which accompany changes in network configuration at many of the user terminals connected to wireless nodes.  
      Furthermore, in the wireless line control system according to the present invention, since average values of radio propagation states collected in advance are calculated per specific days of the week or time slots so that a wireless mesh network which uses usable relay radio is configured before radio wave states of relay radio between wireless nodes estimated in advance deteriorate, it is possible to reduce occurrences of instantaneous interruption or disconnection at user terminals as compared to a case where alternate destinations are searched and switching is performed after radio wave states of relay radio deteriorate. While this effect is weak when using a licensed frequency band as relay radio since there is less influence due to interference from others, the effect increases when using a frequency band which may be used without a license as relay radio since there is greater influence due to interference from others.  
      By arranging the present invention to have the following configuration and to perform the following operations, the effects of reduction of control signals to wireless nodes with high loads as well as reduction of occurrences of instantaneous interruption or disconnection at user terminals connected to the wireless nodes may be achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram showing a configuration of a wireless line control system according to an embodiment of the present invention;  
       FIG. 2  is a block diagram showing a configuration of a centralized control node shown in  FIG. 1 ;  
       FIG. 3  is a sequence chart showing operations of the wireless line control system according to an embodiment of the present invention;  
       FIG. 4  is a flowchart showing processing operations for calculating an average value of traffic information using the centralized control node shown in  FIG. 1 ;  
       FIG. 5  is a diagram showing an example of acquisition of traffic information notified in the processing of a 5  shown in  FIG. 3 ;  
       FIG. 6  is a diagram showing an example of organizing average values of traffic information of wireless node (a)  3 - 1 , calculated in the processing of a 6  shown in  FIG. 3 , according to respective time slots;  
       FIG. 7  is a diagram showing an example of a configuration of a wireless mesh network which achieves optimum throughput over its entirety when average values shown in  FIG. 5  are calculated from historical traffic information;  
       FIG. 8  is a block diagram showing a configuration of a wireless line control system according to another embodiment of the present invention; and  
       FIG. 9  is a sequence chart showing operations of the wireless line control system according to the other embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the present invention will now be described with reference to the drawings.  FIG. 1  is a block diagram showing a configuration of a wireless line control system according to an embodiment of the present invention. In  FIG. 1 , the wireless line control system according to an embodiment of the present invention is comprised of a centralized control node  1 , a gateway wireless node  2 , wireless nodes (a to e)  3 - 1  to  3 - 5 , and user terminals A such as mobile units  41  to  47  and PCs (personal computers)  51  to  56 .  
      The centralized control node  1  is equipped with a function for collecting reception levels which indicate radio wave propagation states between the wireless nodes and information indicating traffic states at the wireless nodes from each wireless node (a to e)  3 - 1  to  3 - 5 , a function for analyzing and storing the collected information, a function for determining a configuration of a wireless mesh network that is appropriate for future load patterns based on the analyzed historical radio wave propagation states or traffic information, and a function for instructing each wireless node (a to e)  3 - 1  to  3 - 5  to establish the determined network configuration through notification of information for configuring the wireless mesh network.  
      In wireless mesh networks, there are wireless lines which relay data between wireless nodes, and wireless lines which transmit and receive data between wireless nodes and user terminals. In the following description, the former will be defined as relay radio while the latter will be defined as access radio. In addition, relay radio loads, number of relay radio lines, access radio loads, number of access radio lines and the like may be considered as traffic information described above. Furthermore, wireless nodes which are destinations of relay radio, allowable relay radio load, allowable access radio load and the like may be considered as information for configuring the wireless mesh network.  
      The gateway wireless node  2  is equipped with a function to measure reception levels of radio waves transmitted from other wireless nodes (a to e)  3 - 1  to  3 - 5  and notify the measured reception levels to the centralized control node  1 , a function to measure relay radio loads and the number of relay radios and notify the same to the centralized control node  1  when relay radios are established with the other wireless nodes (a to e)  3 - 1  to  3 - 5 , a function to measure access radio loads and the number of access radios and notify the same to the centralized control node  1  when a user terminal A (for instance, mobile unit  41 ) exists which is performing communication within its own service area, and a function to configure a wireless mesh network according to information provided by the centralized control node  1 , in response to requests from the centralized control node  1 .  
      In addition, the gateway wireless node  2  is wire-connected to a LAN (local area network) environment, and is equipped with a function to transmit to and receive from another network  100  user data that is transmitted to and received from other wireless nodes (a to e)  3 - 1  to  3 - 5 . Wireless nodes which are destinations of relay radio, allowable relay radio load, allowable access radio load and the like may be considered as information provided by the centralized control node  1 .  
      The wireless nodes (a to e)  3 - 1  to  3 - 5  correspond to access points in a wireless LAN, or base stations in a mobile communication system. In addition, the wireless nodes (a to e)  3 - 1  to  3 - 5  are equipped with functions to measure reception levels of radio waves transmitted from other wireless nodes and notify the measured reception levels to the centralized control node  1  in response to requests from the centralized control node  1 , functions to measure relay radio loads and the number of relay radios and notify the same to the centralized control node  1  when relay radios are established between the other wireless nodes, functions to measure access radio loads and the number of access radios and notify the same to the centralized control node  1  when a user terminal (for instance, mobile units  42  to  47  or PCs  51  to  56 ) exists which is performing communication within its own service area, and functions to configure a wireless mesh network according to information provided by the centralized control node  1 .  
      Wireless nodes which are destinations of relay radio, allowable relay radio load, allowable access radio load and the like may be considered as information provided by the centralized control node  1 .  
      The user terminal A, such as mobile units  41  to  47  or PCs  51  to  56 , is equipped with a transmitting/receiving function for transmitting and receiving continuous data such as audio or packet data such as Web browsing between the wireless nodes. However, since such user terminals are well known in the art and are not directly related to the present invention, a description on a detailed configuration thereof will be omitted. In addition, since the other network  100  is similarly not directly related to the present invention, a detailed description on a configuration thereof will be omitted. Incidentally, the configuration of the present embodiment may include more wireless nodes, or include a plurality of gateway wireless nodes.  
       FIG. 2  is a block diagram showing a configuration of the centralized control node  1  shown in  FIG. 1 . In  FIG. 2 , the centralized control node  1  is comprised of a CPU (central processing unit)  11  which controls the various sections within the node, a main memory  12  which stores a control program  12   a  executed by the CPU  11 , a storage unit  13  which the CPU  11  uses as a work area when executing the control program  12   a , and a communication control section  14  which controls communication with the gateway wireless node  2  or another network  100  and the like. In addition, in the centralized control node  1 , the CPU  11 , the main memory  12 , the storage unit  13  and the communication control section  14  are respectively connected to an internal bus  110 .  
      Furthermore, the storage  13  comprises an internodal reception level average value retaining area  131  which retains calculated average levels of internodal reception levels, a traffic information average value retaining area  132  which retains calculated average levels of traffic information, and a mesh configuration information retaining area  133  which retains mesh configuration information. Incidentally, at the centralized control node  1 , the above-described functions are realized through execution of the control program  12   a  by the CPU  11 .  
       FIG. 3  is a sequence chart showing operations of the wireless line control system according to an embodiment of the present invention. Operations of the wireless line control system according to an embodiment of the present invention will now be described with reference to FIGS.  1  to  3 . Incidentally, the operations of the centralized control node  1  shown in  FIG. 3  are realized through execution of the control program  12   a  by the CPU  11 .  
      When the centralized control node  1  requests each wireless node (a to e)  3 - 1  to  3 - 5  for reception levels indicating radio wave propagation states between the wireless nodes (refer to a 1  in  FIG. 3 ), each wireless node (a to e)  3 - 1  to  3 - 5  measures reception levels of relay radio transmitted from the other wireless nodes, and notifies the same to the centralized control node  1  (refer to a 2  in  FIG. 3 ). Depiction of the operations of the wireless nodes (c to e)  3 - 3  to  3 - 5  are omitted.  
      The centralized control node  1  calculates average values of the reception levels obtained from each wireless node (a to e)  3 - 1  to  3 - 5 , and respectively stores the average values for each wireless node (refer to a 3  in  FIG. 3 ). This allows the centralized control node  1  to identify usable relay radio between each wireless node.  
      In addition, when the centralized control node  1  requests each wireless node (a to e)  3 - 1  to  3 - 5  for traffic information (refer to a 4  in  FIG. 3 ), each wireless node (a to e)  3 - 1  to  3 - 5  measures traffic information and notifies the same to the centralized control node  1  (refer to a 5  in  FIG. 3 ). While traffic information indicated at this point includes relay radio loads, number of relay radio lines, access radio loads, number of access radio lines and the like, other information indicating traffic volume may alternatively be used.  
      The centralized control node  1  calculates average values of the traffic information obtained from each wireless node (a to e)  3 - 1  to  3 - 5 , and respectively stores the average values for each wireless node (refer to a 6  in  FIG. 3 ). The processing of a 1  to a 6  (calculating and storing average values of reception levels, calculating and storing average values of traffic information) is repeatedly performed.  
      Based on the averaged historical traffic information and reception levels between wireless nodes, the centralized control node  1  determines a configuration of a wireless mesh network which is appropriate for the present to the future (a 7  in  FIG. 3 ). In accordance with the determined wireless mesh network configuration, the centralized control node  1  transmits configuration instructions to each wireless node (a to e)  3 - 1  to  3 - 5  (refer to a 8  in  FIG. 3 ). While the information transmitted upon instructing configuration includes wireless nodes which are destinations of relay radio, allowable relay radio load, allowable access radio load and the like, the information may also include other elements for configuring the wireless mesh network.  
      After configuring the wireless mesh network according to configuration information instructed by the centralized control node  1 , each wireless node (a to e)  3 - 1  to  3 - 5  transmits a response (refer to a 9  in  FIG. 3 ).  
       FIG. 4  is a flowchart showing processing operations for calculating average values of traffic information performed by the centralized control node  1  shown in  FIG. 1 . Processing operations by the centralized control node  1  for calculating average values of traffic information will now be described with reference to FIGS.  1  to  4 . Incidentally, the processing shown in  FIG. 4  is realized through execution of the control program  12   a  by the CPU  11 .  
      In the centralized control node  1 , traffic information obtained from the wireless node (a)  3 - 1  is defined as a, the number of collections of traffic as N (initial value is 0), and average traffic information per collection time as A (initial value is 0) (step S 1  in  FIG. 4 ). After obtaining traffic information from the wireless node (a)  3 - 1  (step S 2  in  FIG. 4 ), the centralized control node  1  calculates and updates average traffic information per collection time A using the following equation (step S 3  in  FIG. 4 ):
 
 A= ( N×A+a )/( N+ 1)
 
      The centralized control node  1  next counts up (N=N+1) the number of collections of traffic (step S 4  in  FIG. 4 ).  
      Next, at the centralized control node  1 , average values with higher accuracy may be obtained by repeatedly performing the processing of steps S 1  to S 4  within the predetermined unit time. The above-described processing operations are respectively performed for each wireless node (a to e)  3 - 1  to  3 - 5 , and are individually stored.  
       FIG. 5  is a diagram showing an example of acquisition of traffic information notified in the processing of a 5  shown in  FIG. 3 .  FIG. 6  is a diagram showing an example of average values of traffic information of wireless node (a)  3 - 1 , calculated in the processing of a 6  shown in  FIG. 3 , organized according to respective time slots.  FIG. 7  is a diagram showing an example of a configuration of a wireless mesh network which achieves optimum throughput over its entirety when average values shown in  FIG. 5  are calculated from historical traffic information.  
      In  FIG. 5 , for the gateway wireless node  2  or wireless nodes (a to e)  3 - 1  to  3 - 5 , traffic information respectively includes relay radio loads, the number of relay radios, access radio loads, the number of access radios and the like. For instance, at the gateway wireless node  2 , the relay radio load is “54 Mbps (maximum)”, the number of relay radios is “2”, the access radio load is “2 Mbps (small)”, and the number of access radios is “1”.  
      At wireless node (a)  3 - 1 , the relay radio load is “2 Mbps (small)”, the number of relay radios is “1”, the access radio load is “2 Mbps (small)”, and the number of access radios is “1”. At wireless node (b)  3 - 2 , the relay radio load is “30 Mbps (large)”, the number of relay radios is “3”, the access radio load is “26 Mbps (large)”, and the number of access radios is “10”.  
      At wireless node (c)  3 - 3 , the relay radio load is “50 Mbps (maximum)”, the number of relay radios is “2”, the access radio load is “20 Mbps (large)”, and the number of access radios is “8”. At wireless node (d)  3 - 4 , the relay radio load is “2 Mbps (small)”, the number of relay radios is “1”, the access radio load is “2 Mbps (small)”, and the number of access radios is “1”. At wireless node (e)  3 - 5 , the relay radio load is “2 Mbps (small)”, the number of relay radios is “1”, the access radio load is “2 Mbps (small)”, and the number of access radios is “1”.  
      In  FIG. 6 , the average values of the traffic information of the wireless node (a)  3 - 1  are organized on a per-unit time basis, and for each unit time includes relay radio loads, the number of relay radios, access radio loads, the number of access radios and the like. For instance, for weekdays (0:00 to 7:00), the relay radio load is “4 Mbps”, the number of relay radios is “3”, the access radio load is “2 Mbps”, and the number of access radios is “1”.  
      For weekdays (7:00 to 21:00), the relay radio load is “30 Mbps”, the number of relay radios is “1”, the access radio load is “30 Mbps”, and the number of access radios is “10”. For weekdays (12:00 to 13:00), the relay radio load is “50 Mbps”, the number of relay radios is “2”, the access radio load is “4 Mbps”, and the number of access radios is “2”.  
      For weekdays (13:00 to 17:00), the relay radio load is “50 Mbps”, the number of relay radios is “1”, the access radio load is “50 Mbps”, and the number of access radios is “50”. For weekdays (17:00 to 19:00), the relay radio load is “30 Mbps”, the number of relay radios is “1”, the access radio load is “30 Mbps”, and the number of access radios is “20”.  
      For weekdays (19:00 to 21:00), the relay radio load is “10 Mbps”, the number of relay radios is “2”, the access radio load is “5 Mbps”, and the number of access radios is “5”. For weekdays (21:00 to 24:00), the relay radio load is “50 Mbps”, the number of relay radios is “4”, the access radio load is “2 Mbps”, and the number of access radios is “2”.  
      According to the example shown in  FIG. 6 , while averaging is performed by dividing a “weekdays” group into time slots such as early morning “0:00 to 7:00” and morning “7:00 to 12:00”, averaging may be performed using Sunday, Saturday or other holidays as groups, or using the days of the week from Monday to Friday as separate groups. In addition, time may be split on an hour basis or a minute basis.  
      Next, referring to  FIG. 5  which is historical traffic information, it is estimated at the wireless nodes (b)  3 - 2  and (c)  3 - 3  that at the same time in the future of  FIG. 5 , access radio loads and the number of access radios will be high, and throughput will be compressed when a plurality of relay radios are retained. Therefore, the centralized control node  1  instructs the wireless nodes (b)  3 - 2  and (c)  3 - 3  in advance to prioritize access radio processing by restricting the number of relay radios to “1” in order to prevent the wireless nodes from performing relay processing.  
      In addition, referring to  FIG. 5 , at the gateway wireless node  2 , it is assumed that relay radio load will be high at the same time in the future of  FIG. 5 . Therefore, the centralized control node  1  makes the gateway wireless node  2  secure a processable relay radio load by instructing the gateway wireless node  2  in advance to increase the number of relay radios to wireless nodes (a)  3 - 1  and (c)  3 - 3 , and instructs the gateway wireless node  2  in advance to prioritize relay radio processing by restricting the access radio loads and the number of access radios.  
      Furthermore, referring to  FIG. 5 , at the wireless node (a)  3 - 1 , it is assumed that load will not be high at the same time in the future of  FIG. 5 . However, as described above, it is estimated that the relay radio between wireless nodes (b)  3 - 2  and (d)  3 - 4  will be stored in order to configure the network so that the wireless node (b)  3 - 2  does not perform relay processing. Therefore, the centralized control node  1  instructs the wireless node (a)  3 - 1  in advance to prioritize relay radio processing to the wireless nodes (b)  3 - 2  and (d)  3 - 4  by restricting the access radio load and the number of access radios.  
      Moreover, referring to  FIG. 5 , at the wireless nodes (d)  3 - 4  and (e)  3 - 5 , it is assumed that loads will not be high at the same time in the future of  FIG. 5 . However, as described above, it is estimated that the relay radio load of wireless node (a)  3 - 1 , which is the radio relay destination, will increase. Therefore, the centralized control node  1  instructs the wireless nodes (d)  3 - 4  and (e)  3 - 5  in advance to suppress relay radio load of the wireless node (a)  3 - 1 , which is the radio relay destination, by restricting the access radio load and the number of access radios. A result of a wireless mesh network in which the above processing has been executed is shown in  FIG. 7 .  
      As seen, in the present invention, since an average value of traffic information collected in advance is calculated per specific days of the week or time slots so that a wireless mesh network which realizes optimum throughput is configured before loads on wireless nodes (a to e)  3 - 1  to  3 - 5  rise according to traffic states estimated in advance, it is possible to reduce control, which accompany changes in network configurations, over wireless nodes with high loads.  
      Additionally, in the present invention, since an average value of traffic information collected in advance is calculated per specific days of the week or time slots so that a wireless mesh network which realizes optimum throughput is configured before loads on wireless nodes (a to e)  3 - 1  to  3 - 5  rise according to traffic states estimated in advance, it is possible to reduce occurrences of instantaneous interruption or disconnection which accompany changes in network configurations at many user terminals A connected to wireless nodes (a to e)  3 - 1  to  3 - 5 .  
      Furthermore, in the present invention, since an average value of radio propagation states collected in advance is calculated per specific days of the week or time slots so that a wireless mesh network which uses usable relay radio is configured before relay radio wave states between wireless nodes estimated in advance deteriorate, it is possible to reduce occurrences of instantaneous interruption or disconnection at the user terminal A as compared to a case where alternate destinations are searched and switching is performed after relay radio wave states deteriorate. While this effect is weak when using a licensed frequency band as relay radio since there is less influence due to interference from others, the effect is significant when using a frequency band which may be used without a license as relay radio since there is greater influence due to interference from others.  
       FIG. 8  is a block diagram showing a configuration of a wireless line control system according to another embodiment of the present invention. In  FIG. 8 , the wireless line control system according to the other embodiment of the present invention is similar in configuration to the wireless line control system according to an embodiment of the present invention shown  FIG. 1 , with the exception of the gateway wireless node now being separated into a control signal processing node  2 - 2  and a user signal processing node  2 - 1 . As used herein, control signals indicate signals transmitted and received between the centralized control node  1  and each wireless node (a to e)  3 - 1  to  3 - 5 , while user signals indicate signals such as HTTP (hypertext transfer protocol), e-mail, audio, image, moving image and the like which are transmitted and received via the user terminal A and another network  100  which includes the Internet.  
      The centralized control node  1  is similar in configuration to the centralized control node  1  according to an embodiment of the present invention shown in  FIG. 2 , and achieves similar functions as the centralized control node  1  according to an embodiment of the present invention through execution of the control program  12   a  by the CPU  11 .  
      The gateway wireless node  2 - 2  for control signal is equipped with a function for relaying control signals transmitted and received between the centralized control node  1  and the wireless nodes (a to e)  3 - 1  to  3 - 5 , but does not possess a function for relaying user signals. In addition, since the gateway wireless node  2 - 2  for control signal prioritizes relay radio between the wireless nodes (a to e)  3 - 1  to  3 - 5 , the gateway wireless node  2 - 2  for control signal needs not to possess a function for processing access signals used for communication with the user terminal A.  
      The gateway wireless node  2 - 1  for user signal is equipped with nearly similar functions to the above-described gateway wireless node  2  according to an embodiment of the present invention, except that the user signal gateway wireless node  2 - 1  does not possess a function to relay control signals.  
      The wireless nodes (a to e)  3 - 1  to  3 - 5  possess similar functions to the wireless nodes (a to e)  3 - 1  to  3 - 5  according to an embodiment of the present invention described earlier, and additionally possess functions to differentiate transmitting and receiving destinations of control signals and user signals.  
      Relay radio for control signals, as well as relay radio and access radio for user signals may respectively use either the same or different frequency band, and may respectively use either the same or different radio system.  
      In the present embodiment, operations between the centralized control node  1  and the wireless nodes (a to e)  3 - 1  to  3 - 5  are nearly similar to those in the above-described embodiment of the present invention, with the exception of the reception levels and traffic information acquired by the centralized control node  1  from each wireless node (a to e)  3 - 1  to  3 - 5  now target relay radio for user signal instead of relay radio for control signal. In addition, instructions from the centralized control node  1  regarding configuration changes of the wireless mesh network are targeted at relay radios for user signal, and relay radios for control signal are not considered change targets.  
      As seen, in the present embodiment, relay radio between the wireless nodes are separated into those for control signals and those for user signals. Therefore, for instance, while it is necessary to extend propagation distance for relay radio for control signal, the frequency band to be used may be narrow, and a licensed band may be used. Meanwhile, for relay radio for user signal, since it is desirable to use a wide frequency band even if propagation distance is short, an unlicensed band may be used. By enhancing the degree of freedom in frequency use in this manner, frequencies limited to each carrier may now be used more effectively.  
       FIG. 9  is a sequence chart showing operations of the wireless line control system according to the other embodiment of the present invention. The wireless line control system according to the other embodiment of the present invention is similar in configuration to the wireless line control system according to the embodiment of the present invention shown in  FIG. 1 . Likewise, the centralized control node  1  is similar in configuration to the embodiment of the present invention shown in  FIG. 1 .  
      In the other embodiment of the present invention, reception levels or traffic information are respectively measured per specific periods in each wireless node (a to e)  3 - 1  to  3 - 5  and averaged, and are notified to the centralized control node  1  from each wireless node (a to e)  3 - 1  to  3 - 5 . Incidentally, in  FIG. 9 , depiction of the operations of the wireless nodes (b to e)  3 - 2  to  3 - 5  are omitted. A description will now be provided with reference to  FIGS. 1 and 9 .  
      Each wireless node (a to e)  3 - 1  to  3 - 5  measures reception levels of relay radio between wireless nodes for each specific period and calculates average values thereof (refer to b 1 , b 2  in  FIG. 9 ), and notifies the average values of the reception levels between each wireless node to the centralized control node  1  (refer to b 3  in  FIG. 9 ). The centralized control node  1  stores the notified average values of reception levels according to each wireless node (a to e)  3 - 1  to  3 - 5  (refer to b 4  in  FIG. 9 ).  
      In addition, each wireless node (a to e)  3 - 1  to  3 - 5  measures traffic information for each specific period and calculates average values thereof (refer to b 5 , b 6  in  FIG. 9 ), and notifies the average values of the traffic information to the centralized control node  1  (refer to b 7  in  FIG. 9 ). The centralized control node  1  stores the notified average values of traffic information according to each wireless node (a to e)  3 - 1  to  3 - 5  (refer to b 8  in  FIG. 9 ). The processing of b 1  to b 8  (calculating and storing average values of reception levels, calculating and storing average values of traffic information) is repeatedly performed.  
      Based on the averaged historical traffic information and reception levels between wireless nodes, the centralized control node  1  determines a configuration of a wireless mesh network which is appropriate for the present to the future (b 9  in  FIG. 9 ). In accordance with the determined wireless mesh network configuration, the centralized control node  1  transmits configuration instructions to each wireless node (a to e)  3 - 1  to  3 - 5  (refer to b 10  in  FIG. 9 ). After configuring the wireless mesh network according to configuration information instructed by the centralized control node  1 , each wireless node (a to e)  3 - 1  to  3 - 5  transmits a response (refer to b 11  in  FIG. 9 ).  
      As seen, with the present embodiment, since messages from the centralized control node  1  for requesting reception levels or traffic information from each wireless node (a to e)  3 - 1  to  3 - 5  are no longer necessary, an advantage is gained where the control signal volume is reduced.  
      In the above described embodiments of the present invention, while acquisition of reception levels between wireless nodes and acquisition of traffic information are performed with separate messages, it is also possible to perform requesting/notification collectively using a single message. This will reduce the amount of messages between the centralized control node  1  and each wireless node (a to e)  3 - 1  to  3 - 5 . Thus, an advantage will be gained where the overall control signal volume is reduced.  
      In addition, in the present invention, the means of analyzing reception levels between wireless nodes and traffic information need not be simply calculation of average values. Instead, analysis may be performed using various analysis means, such as performing averaging while exempting values significantly distant from the average value according to the variance pattern of the acquired data, or calculating mode values to be used as elements for configuring the wireless mesh network. This allows an advantage to be gained by the present invention in that appropriate analysis may be performed according to the variance pattern of the acquired data.  
      Furthermore, with the present invention, in the event that an increase in traffic due to an extraordinary movement of people is anticipated, such as with concerts or exhibitions and the like, it is possible to establish an appropriate wireless mesh network by manually inputting traffic information that is respectively anticipated for each wireless node (a to e)  3 - 1  to  3 - 5  to the centralized control node  1 . This allows an advantage to be gained by the present invention in that a wireless mesh network may be established which also preliminarily takes into consideration irregular and extraordinary increases in traffic.  
      Moreover, with the present invention, when transmission output of relay radio and access radio are arranged to be variable, it is now possible to have the centralized control node  1  instruct appropriate relay radio transmission output to each wireless node (a to e)  3 - 1  to  3 - 5  by having the centralized control node  1  acquire reception levels of relay radio from each wireless node (a to e)  3 - 1  to  3 - 5  while simultaneously acquiring transmission output of relay radio, and convert the relationship between the transmission output of the transmitting-side wireless node and the reception level of the receiving-side wireless node into wireless node data and storing the same. This will prevent the wireless nodes (a to e)  3 - 1  to  3 - 5  from transmitting extraneous radio waves in the present invention. Thus, an advantage is gained where interference by other radio may be suppressed.