Patent Publication Number: US-2018049205-A1

Title: Communications system, communications control apparatus, radio communications apparatus, and communications method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/741,887, filed on Jun. 17, 2015, which is a continuation application of International Application PCT/JP2012/083394, filed on Dec. 25, 2012 and designating the U.S., the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The embodiments discussed herein are related to a communications system, a communications control apparatus, a radio communications apparatus, and a communications method. 
     BACKGROUND 
     Radio traffic continues to increase rapidly and demand for limited frequency resources continues to increase. As one means of achieving effective use of frequency, cognitive radio technology, which is cognizant of the local radio wave environment and optimizes communication, is being studied. For example, whitespace type (or frequency shared type) cognitive radio has a function that finds frequency whitespace (WS), which is dependent on time and location, to perform communication so as not to interfere with systems allowed preferential use of frequency. Use of TV whitespace (TVWS) for communications is under investigation in US, for example. 
     With whitespace type cognitive radio, for example, a system having priority to use a frequency is called a primary system, while a system finding a whitespace for communication is called a secondary system. In the case of TVWS, systems for TV broadcasting are primary systems. 
     Wide frequency bandwidths in the ultra-high frequency (UHF) spectrum, etc. are assigned for the TV broadcasting. The frequencies (physical TV channels) used differ from place to place and have little temporal variation. Methods of finding such quasi-static TVWS include, for example, a sensing scheme and a database accessing scheme. For example, rules announced by the federal communications commission (FCC) prescribe a sensing scheme and a database accessing scheme. 
     In the database accessing scheme, a secondary system, for example, accesses a database on the network to obtain WS information indicative of whitespace. The database stores WS information correlated with position information, the WS information being calculated from information such as the location of TV transmitting stations, transmission power, and transmission frequency. FCC rules prescribe that when using TVWS, a secondary system employing a database accessing scheme should access the database at least once a day. 
     According to a known technique (see, for example, Japanese Laid-Open Patent Publication No. 2012-54799), a detection frequency channel is detected based on radio waves transmitted from a first existing system, a reception frequency channel is received from a nearby device, and based on the detection frequency channel, the reception frequency channel, and list frequency channels indicated by a frequency list, a new frequency list indicating the frequency channels is created and stored. 
     Nonetheless, with the conventional technique above, frequency switching may increase since the available frequency changes with the movement of the radio communications device. 
     SUMMARY 
     According to an aspect of an embodiment, a communications system includes a radio communications apparatus and a communications control apparatus. The radio communications apparatus includes a radio communications interface configured to transmit to the communications control apparatus, route information indicating a position of the radio communications apparatus and a predicted route of the radio communications apparatus. The communications control apparatus includes a processor configured to calculate for each frequency available to the radio communications apparatus at the position of the radio communications apparatus, any one among a predicted time and a predicted movement distance for the frequency to become unavailable to the radio communications apparatus, based on the route information transmitted from the radio communications apparatus and, correspondence information of positions of the radio communications apparatus and frequencies available to the radio communications apparatus. The processor is further configured to select a frequency to be used by the radio communications apparatus among the frequencies available to the radio communications apparatus at the position of the radio communications apparatus, based on any one among the predicted time and the predicted movement distance calculated by the processor. The communications control apparatus further includes a radio communications interface configured to transmit to the radio communications apparatus, frequency information indicating the frequency selected by the processor. The radio communications interface of the radio communications apparatus is further configured to perform radio communication using the frequency indicated by the frequency information transmitted from the communications control apparatus. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a diagram of an example of a communications system according to a first embodiment; 
         FIG. 1B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 1A ; 
         FIG. 2  is a diagram of a first application example of the communications system according to the first embodiment; 
         FIG. 3A  is a diagram of an example of configuration of the communications system depicted in  FIG. 2 ; 
         FIG. 3B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 3A ; 
         FIG. 3C  is a diagram of an example of hardware configuration of an access point; 
         FIG. 3D  is a diagram of an example of hardware configuration of a WS database server; 
         FIG. 4  is a sequence diagram of an operation example of the communications system depicted in  FIG. 2 ; 
         FIG. 5  is a diagram of an example of predicted route information transmitted by the access point; 
         FIG. 6  is a diagram of an example of correspondence information stored in a WS database; 
         FIG. 7  is a diagram of an example of frequencies available at positions on the predicted route depicted in  FIG. 2 ; 
         FIG. 8  is a diagram of a second application example of the communications system according to the first embodiment; 
         FIG. 9A  is a diagram of an example of configuration of the communications system depicted in  FIG. 8 ; 
         FIG. 9B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 9A ; 
         FIG. 10  is a diagram of a third application example of the communications system according to the first embodiment; 
         FIG. 11  is a diagram of an example of frequencies available at positions on a predicted route depicted in  FIG. 10 ; 
         FIG. 12A  is a diagram of an example of the communications system according to a second embodiment; 
         FIG. 12B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 12A ; 
         FIG. 13  is a diagram of an application example of the communications system according to the second embodiment; 
         FIG. 14A  is a diagram of an example of configuration of the communications system depicted in  FIG. 13 ; 
         FIG. 14B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 14A ; 
         FIG. 15  is a sequence diagram of an operation example of the communications system depicted in  FIG. 13 ; 
         FIG. 16  is a diagram of an example of available frequency information; 
         FIG. 17  is a diagram of an example of switching history information; 
         FIG. 18  is a diagram of an example of frequency switching history on the predicted route depicted in  FIG. 13 ; 
         FIG. 19  is a diagram of another example of the switching history information; 
         FIG. 20  is a diagram of an application example of the communications system according to a third embodiment; 
         FIG. 21  is a sequence diagram of an operation example of the communications system depicted in  FIG. 20 ; 
         FIG. 22  is a diagram of an example of frequencies available at positions on a predicted route depicted in  FIG. 20 ; 
         FIG. 23  is a diagram of an application example of the communications system according to a fourth embodiment; 
         FIG. 24A  is a diagram of an example of configuration of the communications system depicted in  FIG. 13 ; 
         FIG. 24B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 24A ; 
         FIG. 25  is a sequence diagram of an operation example of the communications system depicted in  FIG. 23 ; 
         FIG. 26  is a diagram of an example of the distance between a history position and a current position; 
         FIG. 27  is a diagram of another example of a predetermined range; 
         FIG. 28A  is a diagram of an example of the communications system according to a fifth embodiment; 
         FIG. 28B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 28A ; 
         FIG. 28C  is a diagram of another example of signal flow in the communications system depicted in  FIG. 28A ; 
         FIG. 29  is a diagram of an application example of the communications system according to the fifth embodiment; 
         FIG. 30A  is a diagram of an example of configuration of the communications system depicted in  FIG. 29 ; 
         FIG. 30B  is a diagram of an example of signal flow in the configuration of the communications system depicted in  FIG. 30A ; 
         FIG. 31  is a sequence diagram of an operation example of the communications system depicted in  FIG. 29 ; 
         FIG. 32  is a diagram of an example of switching information; 
         FIG. 33  is a diagram of an application example of the communications system according to a sixth embodiment; 
         FIG. 34  is a diagram of an example of frequencies available at positions on a predicted route depicted in  FIG. 33 ; 
         FIG. 35  is a diagram of an example of an updated table indicating available frequencies; and 
         FIG. 36  is a diagram of another example of the updated table indicating available frequencies. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of a communications system, a communications control apparatus, a radio communications apparatus, and a communications method will be described in detail with reference to the accompanying drawings. 
       FIG. 1A  is a diagram of an example of a communications system according to a first embodiment.  FIG. 1B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 1A . As depicted in  FIGS. 1A and 1B , a communications system  100  according to the first embodiment includes a radio communications apparatus  110  and a communications control apparatus  120 . The radio communications apparatus  110  and the communications control apparatus  120  can communicate with each other. Various schemes of communication can be applied for the communication between the radio communications apparatus  110  and the communications control apparatus  120 . 
     The radio communications apparatus  110  includes an obtaining unit  111 , a transmitting unit  112 , a receiving unit  113 , and a communications unit  114 . The obtaining unit  111  obtains route information indicating a position of the radio communications apparatus  110  (the apparatus itself) and a predicted route of the radio communications apparatus  110  in the future. The position of the radio communications apparatus  110  is, for example, an approximate position of the radio communications apparatus  110  at present. The obtaining unit  111  outputs the obtained route information to the transmitting unit  112 . The transmitting unit  112  transmits to the communications control apparatus  120  (a radio communications apparatus), the route information output from the obtaining unit  111 . 
     The receiving unit  113  receives frequency information transmitted from the communications control apparatus  120 . The receiving unit  113  outputs the received frequency information to the communications unit  114 . The communications unit  114  performs radio communication using a frequency indicated by the frequency information output from the receiving unit  113 . For example, the communications unit  114  performs communication with a base station connected to a mobile communication network. 
     The communications control apparatus  120  includes a receiving unit  121 , an obtaining unit  122 , a calculating unit  123 , a selecting unit  124 , and a transmitting unit  125 . The receiving unit  121  receives route information transmitted from the radio communications apparatus  110 . The receiving unit  121  outputs the received route information to the calculating unit  123 . 
     The obtaining unit  122  obtains correspondence information for the position of the radio communications apparatus  110  and the frequencies available to the radio communications apparatus  110 . For example, the correspondence information is stored in the memory of the communications control apparatus  120 , and the obtaining unit  122  obtains the correspondence information from the memory of the communications control apparatus  120 . The obtaining unit  122  may receive the correspondence information from a communication apparatus external to the communications control apparatus  120 . The obtaining unit  122  outputs the obtained correspondence information to the calculating unit  123  and the selecting unit  124 . 
     The calculating unit  123  first specifies frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 , based on the position of the radio communications apparatus  110  indicated by the route information output from the receiving unit  121  and based on the correspondence information output from the obtaining unit  122 . For example, the calculating unit  123  searches the correspondence information for frequencies corresponding to the position of the radio communications apparatus  110  indicated by the route information, to thereby specify frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 . 
     For each of the specified frequencies, the calculating unit  123  calculates a predicted time taken for each frequency to become unavailable to the radio communications apparatus  110 , based on the predicted route of the radio communications apparatus  110  indicated by the route information and based on the correspondence information. The calculating unit  123  notifies the selecting unit  124  of the specified frequencies and predicted time calculated for each of the specified frequencies. 
     Based on the predicted time notified by the calculating unit  123 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  from among the frequencies notified by the calculating unit  123 . For example, the selecting unit  124  preferentially selects from among the frequencies notified by the calculating unit  123 , a frequency for which the predicted time notified by the calculating unit  123  is relatively longer. The selecting unit  124  outputs frequency information indicating the selected frequency to the transmitting unit  125 . The transmitting unit  125  transmits to the radio communications apparatus  110 , the frequency information output from the selecting unit  124 . 
     According to the communications system  100  depicted in  FIGS. 1A and 1B , the communications control apparatus  120  enables the radio communications apparatus  110  to set a frequency for which the predicted time taken to become unavailable is relatively long among frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 . This results in reduced frequency switching by the radio communications apparatus  110 . 
     The selecting unit  124  of the communications control apparatus  120  notify the calculating unit  123  of frequencies selected as frequencies to be used by the radio communications apparatus  110  at the position of the radio communications apparatus  110 . The calculating  123  specifies frequencies available to the radio communications apparatus  110  at a position where the frequencies notified by the selecting unit  124  become unavailable to the radio communications apparatus  110 . 
     For each of the specified frequencies, the calculating unit  123  calculates a predicted time taken for the frequency to become unavailable to the radio communications apparatus  110  before the position is reached where the frequencies notified by the selecting unit  124  become unavailable to the radio communications apparatus  110 . The calculating unit  123  notifies the selecting unit  124  of the specified frequencies and the predicted time calculated for each of the specified frequencies. 
     Based on the predicted times notified by the calculating unit  123 , the selecting unit  124  selects from among the frequencies notified by the calculating unit  123 , a frequency to be used by the radio communications apparatus  110  from the position where the already selected frequency becomes unavailable to the radio communications apparatus  110 . The selecting unit  124  outputs to the transmitting unit  125 , frequency information indicating a first frequency selected for the position of the radio communications apparatus  110  and a second frequency selected for a position where the first frequency becomes unavailable. 
     In this case, the frequency information has only to be information indicating the first frequency and the second frequency and indicating that the second frequency should be used after the first frequency. For example, assuming the first frequency and the second frequency to be F 1  and F 2 , respectively, the frequency information can be list information such as {F 1 , F 2 }. 
     The communications unit  114  of the radio communications apparatus  110  performs radio communication using the first frequency indicated by the frequency information. When the first frequency becomes unavailable as a result of movement of the radio communications apparatus  110 , the communications unit  114  performs radio communication using the second frequency indicated by the frequency information. This enables the radio communications apparatus  110  to set an available frequency and reduce frequency switching without again making an inquiry to the communications control apparatus  120  for available frequency when the frequency notified by the communications control apparatus  120  has become unavailable. 
     Although the case has been described where the communications control apparatus  120  issues a single frequency to be used when the frequency used at the position of the radio communications apparatus  110  has become unavailable, the communications control apparatus  120  may issue plural frequencies to be used when the frequency has become available. 
     Although a case has been described where the frequency is selected based on the predicted time for the frequency to become unavailable to the radio communications apparatus  110 , configuration may be such that the frequency is selected based on a predicted movement distance of the radio communications apparatus  110  for the frequency to become unavailable to the radio communications apparatus  110 . 
     For example, for each of the specified frequencies, the calculating unit  123  of the communications control apparatus  120  calculates a predicted movement distance of the radio communications apparatus  110  for the frequency to become unavailable to the radio communications apparatus  110 . The calculating unit  123  notifies the selecting unit  124  of the specified frequencies and predicted movement distances respectively calculated for the specified frequencies. 
     Based on the predicted movement distances notified by the calculating unit  123 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  from among the frequencies notified by the calculating unit  123 . For example, the selecting unit  124  preferentially selects a frequency for which the predicted movement distance notified by the calculating unit  123  is relatively long among the frequencies notified by the calculating unit  123 . 
     Thus, the communications control apparatus  120  enables the radio communications apparatus  110  to set a frequency for which the predicted movement distance of the radio communications apparatus  110  to become unavailable is relatively long among the frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 . This results in reduced frequency switching. 
       FIG. 2  is a diagram of a first application example of the communications system according to the first embodiment. The communications system  100  depicted in  FIGS. 1A and 1B  is applicable to a communications system  200  depicted in  FIG. 2 , for example. A bus vehicle  230  depicted in  FIG. 2  is equipped with an access point  231 . The radio communications apparatus  110  depicted in  FIGS. 1A and 1B  is applicable to the access point  231 , for example. The communications control apparatus  120  depicted in  FIGS. 1A and 1B  is applicable to a WS database server  240 , for example. 
     The access point  231  performs radio communication, for example, with communications terminals of passengers, etc., on the bus vehicle  230 . The access point  231  has, as a backbone network, a wide area cellular network of 3rd generation (3G), long term evolution (LTE), etc., and performs radio communication with base stations of the backbone network using WS (frequencies). This enables the communications terminals of the passengers, etc., on the bus vehicle  230  to connect to the wide area cellular network by way of the access point  231 . 
     The access point  231  can communicate with the WS database server  240 . Various communication schemes such as LTE or 3G wide area cellular schemes, for example, are applicable to the communication between the access point  231  and the WS database server  240 . The access point  231  transmits to the WS database server  240 , predicted route information indicating a predicted route L 1  of the bus vehicle  230 . Since the access point  231  is equipped on the bus vehicle  230 , the predicted route L 1  is a predicted route of the access point  231 . 
     The access point  231  receives from the WS database server  240 , available frequency information indicating frequencies (WS) used by the access point  231 . The access point  231  performs communications with the backbone network base stations using the frequencies indicated by the available frequency information received from the WS database server  240 . 
     Frequencies available for radio communication by the access point  231  are assumed to be the frequencies f 1  and f 2  in the example depicted in  FIG. 2 . The frequencies f 1  and f 2  differ from each other. The frequency (WS) actually available to the access point  231  among the frequencies f 1  and f 2  differs depending on the position of the access point  231 . 
     For example, a television station  210  communicates using the frequency f 1  in an area  211 . Therefore, the frequency f 1  is not available to the access point  231  in the area  211 . A television station  220  communicates using the frequency f 2  in an area  221 . Hence, the frequency f 2  is not available to the access point  231  in the area  221 . 
     Passage points p 1  to p 8  designate positions on the predicted route L 1  of the access point  231 . The passage point p 1  is in neither the area  211  nor the area  221 . Thus, the access point  231  can use the frequencies f 1  and f 2  at the passage point p 1 . The access points p 2  to p 7  are not in the area  211  but are in the area  221 . Therefore, at the passage points p 2  to p 7 , the access point  231  can use the frequency f 1  but cannot use the frequency f 2 . The passage point p 8  is in both the area  211  and the area  221 . Hence, at the passage point p 8 , the access point  231  cannot use the frequencies f 1  and f 2 . 
     A boundary point pA is a position on the predicted route L 1  where the access point  231  enters the area  221 . A boundary point pB is a position on the predicted route L 1  where the access point  231  enters the area  211 . 
     For example, when the access point  231  is located at the passage point p 1 , the frequencies f 1  and f 2  are available to the access point  231 . If the access point  231  sets the frequency f 2  at the passage point p 1 , the frequency f 2  becomes unavailable at the boundary point pA and consequently, the access point  231  has to perform frequency switching. On the other hand, if the access point  231  sets the frequency f 1  at the passage point p 1 , the frequency f 1  is available until the boundary point pB and consequently, the access point  231  need not perform frequency switching until the boundary point pB. 
     Accordingly, the WS database server  240  causes the access point  231  to set the frequency f 1  for which the predicted time for the frequency to become unavailable is longer among the frequencies f 1  and f 2  available to the access point  231  at the passage point p 1 . This enables a reduction of the frequency switching by the access point  231 . 
       FIG. 3A  is a diagram of an example of configuration of the communications system depicted in  FIG. 2 .  FIG. 3B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 3A . In  FIGS. 3A and 3B , parts identical to those depicted in  FIG. 2  are designated by the same reference letters or numerals used in  FIG. 2  and will not again be described. 
     As depicted in  FIGS. 3A and 3B , the access point  231  includes, for example, a route obtaining unit  311 , a communications unit  312 , a frequency setting unit  313 , and a communications unit  314 . The route obtaining unit  311  obtains predicted route information (see, e.g.,  FIG. 5 ) indicating the position of the access point  231 , and the predicted route L 1  (see, e.g.,  FIG. 2 ) of the access point  231 . 
     The memory of the access point  231  stores information indicating the predicted route, and the route obtaining unit  311  obtains from the memory of the access point  231 , the information indicating the predicted route. The route obtaining unit  311  may obtain from a car navigation system, etc., of the bus vehicle  230 , the information indicating the predicted route. The route obtaining unit  311  may use a global positioning system (GPS), for example, to obtain information indicating the position of the access point  231 . The route obtaining unit  311  outputs the obtained predicted route information to the communications unit  312 . 
     The communications unit  312  performs radio communication with the WS database server  240 . For example, the communications unit  312  transmits to the WS database server  240 , the predicted route information output from the route obtaining unit  311 . The communications unit  312  receives available frequency information transmitted from the WS database server  240 . The communications unit  312  outputs the received available frequency information to the frequency setting unit  313 . 
     The frequency setting unit  313  sets the frequency used for radio communication by the communications unit  314  to a frequency indicated by the available frequency information output from the route obtaining unit  311 . The communications unit  314  performs radio communication using the frequency set by the frequency setting unit  313 . For example, the communications unit  314  relays, via radio communication, communication between communications terminals on the bus vehicle  230  and base stations. The communications units  312  and  314  may be realized by a single communications unit. 
     The obtaining unit  111  depicted in  FIGS. 1A and 1B  can be realized, for example, by the route obtaining unit  311 . The transmitting unit  112  and the receiving unit  113  depicted in  FIGS. 1A and 1B  can be realized, for example, by the communications unit  312 . The communications unit  114  depicted in  FIGS. 1A and 1B  can be realized, for example, by the frequency setting unit  313  and the communications unit  314 . 
     As depicted in  FIGS. 3A and 3B , the WS database server  240  includes a WS database  321 , a communications unit  322 , and a frequency selecting unit  323 . The WS database  321  stores correspondence information associating the positions of the access point  231  with the frequencies available to the access point  231 . 
     The communications unit  322  performs radio communication with the access point  231 . For example, the communications unit  322  receives predicted route information transmitted from the access point  231 . The communications unit  322  outputs the received predicted route information to the frequency selecting unit  323 . The communications unit  322  transmits to the access point  231 , available frequency information output from the frequency selecting unit  323 . 
     The frequency selecting unit  323  specifies, as available frequencies of the access point  231 , frequencies available to the access point  231  at the current position of the access point  231 . For example, the frequency selecting unit  323  specifies the available frequencies of the access point  231 , based on the current position of the access point  231  indicated by the predicted route information output from the communications unit  322  and based on the correspondence information stored in the WS database  321 . 
     For each of the specified available frequencies, the frequency selecting unit  323  calculates a predicted time for the next frequency switching by the access point  231  if the access point  231  were to set the frequency. The frequency selecting unit  323  then selects, as the frequency to be used by the access point  231 , an available frequency for which the calculated predicted time is greatest among the specified available frequencies. The frequency selecting unit  323  outputs to the communications unit  322 , the available frequency information indicating the selected frequency to be used. 
     The receiving unit  121  and the transmitting unit  125  depicted in  FIGS. 1A and 1B  can be realized for example by the communications unit  322 . The obtaining unit  122  depicted in  FIGS. 1A and 1B  can be realized for example by the WS database  321 . The calculating unit  123  and the selecting unit  124  depicted in  FIGS. 1A and 1B  can be realized for example by the frequency selecting unit  323 . 
       FIG. 3C  is a diagram of an example of hardware configuration of the access point. The access point  231  depicted in  FIGS. 3A and 3B , for example, can be realized by an information processing apparatus  330  depicted in  FIG. 3C . The information processing apparatus  330  includes a CPU  331 , memory  332 , a user interface  333 , a radio communications interface  334 , and a GPS module  335 . The CPU  331 , the memory  332 , the user interface  333 , the radio communications interface  334 , and the GPS module  335  are connected by a bus  339 . 
     The CPU  331  (central processing unit) governs overall control of the information processing apparatus  330 . Further, the information processing apparatus  330  may include the CPU  331  in plural. The memory  332 , for example, includes main memory and auxiliary memory. The main memory, for example, is RAM (random access memory) and is used as a work area of the CPU  331 . The auxiliary memory, for example, is non-volatile memory such as a magnetic disk and flash memory. The auxiliary memory stores various types of programs that cause the information processing apparatus  330  to operate. Programs stored by the auxiliary memory are loaded to the main memory and are executed by the CPU  331 . 
     The user interface  333 , for example, includes an input device that receives operational input from the user and an output device that outputs information to the user. The input device, for example, can be realized by a key (e.g., a keyboard) or a remote controller. The output device, for example, can be realized by a display or a speaker. Further, the input device and the output device may be realized by a touch panel and the like. The user interface  333  is controlled by the CPU  331 . 
     The radio communications interface  334 , for example, is a communications interface that performs radio communication with external apparatuses of the information processing apparatus  330 . The radio communications interface  334  is controlled by the CPU  331 . 
     The GPS module  335  is a module that obtains information indicating the current position of the information processing apparatus  330 . The GPS module  335  is controlled by the CPU  331 . 
     The route obtaining unit  311  depicted in  FIGS. 3A and 3B , for example, can be realized by the CPU  331 , the memory  332 , and the GPS module  335 . The communications units  312  and  314  depicted in  FIGS. 3A and 3B , for example, can be realized by the CPU  331  and the radio communications interface  334 . The frequency setting unit  313  depicted in  FIGS. 3A and 3B , for example, can be realized by the CPU  331 . 
       FIG. 3D  is a diagram of an example of hardware configuration of the WS database server. The WS database server  240  depicted in  FIGS. 3A and 3B , for example, can be realized by the information processing apparatus  340  depicted in  FIG. 3D . The information processing apparatus  340  includes a CPU  341 , memory  342 , user interface  343 , a wire-based communications interface  344 , and a radio communications interface  345 . The CPU  341 , the memory  342 , the user interface  343 , the wire-based communications interface  344 , and the radio communications interface  345  are connected by a bus  349 . 
     The CPU  341  governs overall control of the information processing apparatus  340 . Further, the information processing apparatus  340  may include the CPU  341  in plural. The memory  342 , for example, includes main memory and auxiliary memory. The main memory, for example, is RAM and is used as a work area of the CPU  341 . The auxiliary memory, for example, is non-volatile memory such as a magnetic disk, an optical disk, and flash memory. The auxiliary memory stores various types of programs that cause the information processing apparatus  340  to operate. Programs stored by the auxiliary memory are loaded to the main memory and executed by the CPU  341 . 
     The user interface  343 , for example, includes an input device that receives operational input from the user and an output device that outputs information to the user. The input device, for example, can be realized by a key (e.g., a keyboard) or a remote controller. The output device, for example, can be realized by a display or a speaker. Further, the input device and the output device may be realized by a touch panel and the like. The user interface  343  is controlled by the CPU  341 . 
     The wire-based communications interface  344 , for example, is a communications interface that communicates with external apparatuses (e.g., higher order system) of the information processing apparatus  340  by cable. The wire-based communications interface  344  is controlled by the CPU  341 . 
     The radio communications interface  345 , for example, is a communications interface that performs radio communication with external apparatuses of the information processing apparatus  340 . The radio communications interface  345  is controlled by the CPU  341 . 
     The communications unit  322  depicted in  FIGS. 3A and 3B , for example, can be realized by the CPU  341  and the radio communications interface  345 . The WS database  321  depicted in  FIGS. 3A and 3B , for example, can be realized by the memory  342 . The frequency selecting unit  323  depicted in  FIGS. 3A and 3B , for example, can be realized by the CPU  341 . 
       FIG. 4  is a sequence diagram of an operation example of the communications system depicted in  FIG. 2 . The communications system  200  depicted in  FIG. 2  operates, for example, as indicated by the steps depicted in  FIG. 4 . First, the access point  231  transmits predicted route information of the access point  231  to the WS database server  240  (step S 401 ). 
     The WS database server  240  then specifies available frequencies corresponding to the current position of the access point  231 , based on the predicted route information transmitted at step S 401  and based on the correspondence information (step S 402 ). For each of the available frequencies specified at step S 402 , the WS database server  240  then calculates a predicted time for the next frequency switching by the access point  230  to occur if the WS database server  240  causes the access point  231  to set the available frequency (step S 403 ). 
     The WS database server  240  selects from among the available frequencies specified at step S 402 , the frequency for which the predicted time calculated at step S 403  is greatest (step S 404 ). The WS database server  240  transmits available frequency information indicating the frequency selected at step S 404  to the access point  231  (step S 405 ). 
     The access point  231  sets the frequency indicated by the available frequency information transmitted at step S 405 , as a frequency to be used for radio communication by the access point  231  (step S 406 ), and terminates a series of the operations. 
     The above operations enable the access point  231  to set a frequency for which the predicted time of becoming unavailable is longer among frequencies available to the access point  231  at the current position of the access point  231 . As a result, frequency switching by the access point  231  can be reduced. 
     The operations depicted in  FIG. 4  are executed, for example, at the time of powering on of the access point  231 . The timing at which the operations depicted in  FIG. 4  are executed is not limited hereto. For example, the operations depicted in  FIG. 4  may be executed every time the frequency being used by the access point  231  becomes unavailable as a result of movement of the access point  231 . This can reduce frequency switching, not only at the time of powering on. 
     The operations depicted in  FIG. 4  may be executed every time the predicted route L 1  of the access point  231  changes. The operations depicted in  FIG. 4  may be executed periodically. This enables the frequency switching by the access point  231  to be reduced, irrespective of a change in the predicted route L 1  of the access point  231  due to rerouting, etc. 
       FIG. 5  is a diagram of an example of predicted route information transmitted by an access point. The access point  231  transmits to the WS database server  240 , for example, predicted route information  500  depicted in  FIG. 5  as the predicted route information. In the predicted route information  500 , date (yy/mm/dd), time (hh:mm:ss), latitude, and longitude are correlated with one another for each passage point (passage points p 1  to p 8 , . . . ) on the predicted route L 1 . 
     For example, the predicted route information  500  indicates that the access point  231  is scheduled to pass through the passage point p 1  at 10:00:00 on Dec. 11, 2011, latitude (36 [degrees], 43′00″), and longitude (140 [degrees], 22′00″). In this manner, the predicted route information  500  can be position information arranged in time series. 
     The predicted route information  500  is, for example, information indicating positions on the predicted route L 1  and predicted times of passing through the positions on the predicted route L 1 . This enables the WS database server  240  to calculate a predicted time and a predicted movement distance for a given frequency to become unavailable to the access point  231 . When the WS database server  240  calculates the predicted movement distance for the given frequency to become unavailable to the access point  231 , the predicted route information  500  may omit the hour (date and time). 
       FIG. 6  is a diagram of an example of correspondence information stored in a WS database. The WS database server  240  stores, for example, correspondence information  600  depicted in  FIG. 6 . In the correspondence information  600 , frequencies available to the access point  231  are correlated with combinations of the latitude and the longitude. 
     For example, the correspondence information  600  indicates that the frequency f 1  is a frequency available to the access point  231  at the position of latitude (36 [degrees], 43′) and longitude (140 [degrees], 22′). 
       FIG. 7  is a diagram of an example of frequencies available at positions on the predicted route depicted in  FIG. 2 . The frequency selecting unit  323  of the WS database server  240  creates a table  700  depicted in  FIG. 7  through calculations based on predicted route information (see, e.g.,  FIG. 5 ) output from the communications unit  322  and based on correspondence information (see, e.g.,  FIG. 6 ) stored in the WS database  321 . 
     In the table  700 , frequencies available to the access point  231  are correlated with each passage point of the access point  231  based on the predicted route indicated by the predicted route information. The passage points of the table  700  include, in addition to the passage points p 1  to p 8 , . . . , indicated by the predicted route information, passage points supplemented based on the passage points p 1  to p 8 , . . . . 
     The table  700  includes distances between the passage points of the access point  231 , correlated with the passage points. The distances between the passage points can be calculated based on the latitudes and longitudes of the passage points. 
     The approximate current time is assumed to be 10:00:00 on Dec. 11, 2011. In this case, the current position of the access point  231  is latitude (36 [degrees], 43′00″) and longitude (140 [degrees], 22′00″). The frequency selecting unit  323  specifies the available frequencies f 1  and f 2  corresponding to the current position of the access point  23 , based on the created table  700 . 
     For each of the specified frequencies f 1  and f 2 , the frequency selecting unit  323  calculates based on the table  700 , a predicted time for the next frequency switching to occur by the access point  231  if the access point  231  sets the frequency. 
     In the example depicted in  FIG. 7 , if the frequency f 1  is set in the access point  231 , the frequency f 1  remains available until 10:34:00 of the same date and consequently, the predicted time for the frequency switching to occur by the access point  231  is 34 minutes. If the frequency f 2  is set in the access point  231 , the frequency f 2  is available until 10:07:00 of the same date and consequently, the predicted time for the frequency switching to occur by the access point  231  is 7 minutes. 
     The frequency selecting unit  323  thus selects, as the frequency to be used by the access point  231 , the frequency f 1  for which the predicted time for the frequency switching to occur by the access point  231  is longest among the specified frequencies f 1  and f 2 . 
     Although the example depicted in  FIG. 2  has been described in a case where the frequency to be used is selected based on the predicted time for the frequency switching to occur, configuration may be such that the frequency to be used is selected based on the predicted movement distance of the access point  231  for the frequency switching to occur. 
     For example, for each specified available frequency, the frequency selecting unit  323  calculates a predicted movement distance of the access point  231  for the next frequency switching to occur by the access point  231  if the access point  231  sets the available frequency. The frequency selecting unit  323  then selects, as the frequency to be used by the access point  231 , the available frequency for which the calculated predicted movement distance is greatest among the specified available frequencies. 
     In this case, if the frequency f 1  is set in the access point  231  in the example depicted in  FIG. 7 , the frequency f 1  remains available until the position of latitude (36 [degrees], 41′00″) and longitude (140 [degrees], 16′00″). Accordingly, the predicted movement distance of the access point  231  for the frequency switching to by in the access point  231  is 3+1.5+1.5+1.5+1.5+1.5+3+3=16.5 [km]. 
     If the frequency f 2  is set in the access point  231 , the frequency f 2  is available until the position of latitude (36 [degrees], 43′00″) and longitude (140 [degrees], 20′00″). Accordingly, the predicted movement distance of the access point  231  for the frequency switching to occur in the access point  231  is 3 [km]. 
     The frequency selecting unit  323  thus selects, as the frequency used by the access point  231 , the frequency f 1  for which the predicted movement distance for the frequency switching to occur by the access point  231  is longest among the specified frequencies f 1  and f 2 . 
       FIG. 8  is a diagram of a second application example of the communications system according to the first embodiment. In  FIG. 8 , parts identical to those depicted in  FIG. 2  are designated by the same reference letters or numerals used in  FIG. 2  and will not again be described. As depicted in  FIG. 8 , the communications system  200  includes a frequency management apparatus  810 , in addition to the configuration depicted in  FIG. 2 . In this case, the communications control apparatus  120  depicted in  FIGS. 1A and 1B  are applicable to the frequency management apparatus  810 , for example. 
     The frequency management apparatus  810  can communicate with the access point  231  and with the WS database server  240 . Radio communication, for example, can be used for communication between the frequency management apparatus  810  and the access point  231 . Wire-based communication, for example, can be used for communication between the frequency management apparatus  810  and the access point  240 . In this case, direct communication is not necessarily required between the WS database server  240  and the access point  231 . 
     The access point  231  transmits to the frequency management apparatus  810 , predicted route information indicating the predicted route L 1 . The access point  231  receives from the frequency management apparatus  810 , available frequency information indicating frequencies (WS) to be used by the access point  231 . The access point  231  performs radio communication with base stations of the backbone network using frequencies indicated by the available frequency information received from the frequency management apparatus  810 . 
     The frequency management apparatus  810  receives from the WS database server  240 , information indicating the WS available to the access point  231 . The frequency management apparatus  810  transmits to the WS database server  240 , position information indicating the position of the access point  231  indicated by the correspondence information  600  received from the access point  231 . 
     Such a function of selecting the frequencies to be used by the access point  231  notifying the access point  231  of them may be realized by a communications control apparatus (e.g., frequency management apparatus  810 ) different from the WS database server  240 . The WS database server  240  and the frequency management apparatus  810  may be managed by respectively different business operators. 
       FIG. 9A  is a diagram of an example of configuration of the communications system depicted in  FIG. 8 .  FIG. 9B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 9A . In  FIGS. 9A and 9B , parts identical to those depicted in  FIGS. 3A and 3B  are designated by the same reference letters or numerals used in  FIGS. 3A and 3B  and will not again be described. 
     As depicted in  FIGS. 9A and 9B , the WS database server  240  depicted in  FIG. 8  includes a communications unit  911  and the WS database  321 . The communications unit  911  transmits correspondence information stored in the WS database  321  to the frequency management apparatus  810 . Wire-based communication, for example, can be used for communication between the communications unit  911  and the frequency management apparatus  810 . 
     The frequency management apparatus  810  includes a communications unit  921 , the frequency selecting unit  323 , and the communications unit  322 . The communications unit  921  receives the correspondence information transmitted from the WS database server  240 . The communications unit  921  outputs the received correspondence information to the frequency selecting unit  323 . 
     The frequency selecting unit  323  specifies available frequencies of the access point  231 , based on the predicted route information output from the communications unit  322  and based on the correspondence information output from the communications unit  921 . For each of the specified available frequencies, the frequency selecting unit  323  calculates based on the correspondence information output from the communications unit  921 , a predicted time (or a predicted movement distance) for the next frequency switching to occur by the access point  231  if the access point  231  sets the frequency. 
     The frequency management apparatus  810  depicted in  FIGS. 9A and 9B  can be realized, for example, by the information processing apparatus  340  depicted in  FIG. 3D . In this case, the communications unit  322  depicted in  FIGS. 9A and 9B  can be realized for example by the CPU  341  and the radio communications interface  345 . 
     The frequency selecting unit  323  depicted in  FIGS. 9A and 9B  can be realized, for example, by the CPU  341 . The communications unit  921  depicted in  FIGS. 9A and 9B  can be realized, for example, by the CPU  341  and the wire-based communications interface  344 . 
     The WS database server  240  depicted in  FIGS. 9A and 9B  can be realized, for example, by the information processing apparatus  340  depicted in  FIG. 3D . In this case, however, the radio communications interface  345  depicted in  FIG. 3D  may be omitted. 
     The communications unit  911  depicted in  FIGS. 9A and 9B  can be realized, for example, by the CPU  341  and the wire-based communications interface  344 . The WS database  321  depicted in  FIGS. 9A and 9B  can be realized, for example, by the memory  342 . 
       FIG. 10  is a diagram of a third application example of the communications system according to the first embodiment. In  FIG. 10 , parts identical to those depicted in  FIG. 2  are designated by the same reference letters or numerals used in  FIG. 2  and will not again be described. The example depicted in  FIG. 10  assumes that the frequencies available for radio communication by the access point  231  are frequencies f 1  to f 4 . The frequencies f 1  to f 4  are frequencies differing from one another. 
     The access point  231  can perform radio communication using plural frequencies. Carrier aggregation in LTE or channel bonding in WiFi can be used for radio communication using plural frequencies, for example. 
     A television station  1010  communicates using the frequency f 3  in an area  1021 . Therefore, the frequency f 3  is unavailable to the access point  231  in the area  1011 . A television station  1020  communicates using the frequency f 4  in an area  1021 . Therefore, the frequency f 4  is unavailable to the access point  231  in the area  1021 . 
     In the example depicted in  FIG. 10 , the passage point p 1  is not in the areas  221  and  1021  but is in the area  1011 . Thus, the frequencies f 1  and f 2 , and f 4  are available to the access point  231  at the passage point p 1 . The passage points p 2  to p 7  are in the areas  221 ,  1011 , and  1021 . Thus, the frequency f 1  is available to the access point  231  at the passage points p 2  to p 7 . The passage point p 8  is not in the area  1011  but is in the areas  221  and  1021 . Therefore, the frequencies f 1  and f 3  are available to the access point  231  at the passage point p 8 . 
     The boundary point pA is a position on the predicted route L 1  where the access point  231  enters the area  221 . The boundary point pB is a position on the predicted route L 1  where the access point  231  enters the area  1021 . A boundary point pC is a position on the predicted route L 1  where the access point  231  leaves the  1011 . 
     For example, if the access point  231  is located at the passage point p 1 , frequencies available to the access point  231  are the frequencies f 1  and f 2 , and f 4 . If the access point  231  sets the frequency f 1  at the passage point p 1 , no frequency switching by the access point  231  occurs. If the access point  231  sets the frequency f 2  at the passage point p 1 , the frequency f 2  becomes unavailable at the boundary point pA resulting in frequency switching by the access point  231 . If the access point  231  sets the frequency f 4  at the passage point p 1 , the frequency f 4  becomes unavailable at the boundary point pB resulting in frequency switching by the access point  231 . 
     The WS database server  240  thus causes the access point  231  to set the frequency for which the predicted time for the frequency to become unavailable is longest among the frequencies f 1  and f 2 , and f 4  available to the access point  231  at the passage point p 1 . For example, if the access point  231  performs radio communication using two frequencies at the same time, the WS database server  240  causes the access point  231  to set the two frequencies for which the predicted times to become unavailable are longest. As a result, frequency switching by the access point  231  can be reduced. 
       FIG. 11  is a diagram of an example of frequencies available at positions on the predicted route depicted in  FIG. 10 . The frequency selecting unit  323  of the WS database server  240  depicted in  FIG. 10  creates, for example, a table  1100  depicted in  FIG. 11  through calculations based on the predicted route information output from the communications unit  322  and based on the correspondence information stored in the WS database  321 . 
     In the table  1100 , similar to the table  700  depicted in  FIG. 7 , frequencies available to the access point  231  are correlated with each passage point of the access point  231  based on the predicted route indicated by the predicted route information. 
     In the example depicted in  FIG. 11 , if the frequency f 1  is set in the access point  231 , the frequency f 1  remains available until the passage point p 8  at the terminal end of the predicted route L 1 , resulting in the longest predicted time for frequency switching to occur by the access point  231 . If the frequency f 2  is set in the access point  231 , the frequency f 2  is available until 10:04:00 of the same date, and the predicted time for frequency switching to occur by the access point  231  is 4 min. If the frequency f 4  is set in the access point  231 , the frequency f 4  is available until 10:07:00 of the same date, and the predicted time for frequency switching to occur by the access point  231  is 7 min. 
     The frequency selecting unit  323 , therefore, selects, as the frequencies to be used by the access point  231 , the two frequencies f 1  and f 4  for which the longest predicted times for frequency switching to occur by the access point  231  are longest among the specified frequencies f 1  and f 2 , and f 4 . 
     In this manner, according to the first embodiment, the radio communications apparatus can set a frequency for which the predicted time for the frequency to become unavailable is relatively long among the frequencies available to the radio communications apparatus at the position of the radio communications apparatus. Alternatively, the radio communications apparatus can set a frequency for which the predicted movement distance to become unavailable, among frequencies available to the radio communications apparatus at the position of the radio communications apparatus. As a result, the number of times of frequency switching can be reduced in the radio communications apparatus. 
     Parts of a second embodiment differing from the first embodiment will be described. 
       FIG. 12A  is a diagram of an example of the communications system according to a second embodiment.  FIG. 12B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 12A . In  FIGS. 12A and 12B , parts identical to those depicted in  FIGS. 1A and 1B  are designated by the same reference letters or numerals used in  FIGS. 1A and 1B  and will not again be described. 
     The radio communications apparatus  110  according to the second embodiment includes the obtaining unit  111 , the transmitting unit  112 , the receiving unit  113 , a calculating unit  1211 , the selecting unit  124 , and the communications unit  114 . The obtaining unit  111  obtains position information indicating the position of the radio communications apparatus  110 . The obtaining unit  111  then outputs the obtained position information to the transmitting unit  112 . 
     The obtaining unit  111  obtains route information indicating a predicted route of the radio communications apparatus  110  in the future. Based on the obtained route information, the obtaining unit  111  then obtains history information indicating a history of switching frequencies used for radio communication by the radio communications apparatus  110 , at positions on the predicted route of the radio communications apparatus  110 . The obtaining unit  111  outputs the obtained history information to the calculating unit  1211 . 
     The transmitting unit  112  transmits to the communications control apparatus  120  (radio communications apparatus), the position information output from the obtaining unit  111 . The receiving unit  113  receives frequency information transmitted from the communications control apparatus  120 . The receiving unit  113  then outputs the received frequency information to the calculating unit  1211 . 
     For each of the frequencies indicated by the frequency information output from the receiving unit  113 , the calculating unit  1211  calculates a predicted time for the frequency to become unavailable to the radio communications apparatus  110 , based on the history information output from the obtaining unit  111 . The calculating unit  1211  then notifies the selecting unit  124  of the frequencies indicated by the frequency information and the predicted time calculated for each frequency indicated by the frequency information. 
     Based on the predicted time notified by the calculating unit  1211 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  among the frequencies notified by the calculating unit  1211 . The selecting unit  124  then notifies the communications unit  114  of the selected frequency. The communications unit  114  performs radio communication using the frequency notified by the selecting unit  124 . 
     The communications control apparatus  120  includes the receiving unit  121 , a specifying unit  1221 , the obtaining unit  122 , and the transmitting unit  125 . The receiving unit  121  receives position information transmitted from the radio communications apparatus  110 . The receiving unit  121  then outputs the received position information to the specifying unit  1221 . The obtaining unit  122  outputs obtained correspondence information to the specifying unit  1221 . 
     The specifying unit  1221  specifies frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 , based on the position indicated by the position information output from the receiving unit  121  and based on the correspondence information output from the obtaining unit  122 . For example, the specifying unit  1221  searches the correspondence information for frequencies corresponding to the position of the radio communications apparatus  110  indicated by the position information, to thereby specify the frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 . 
     The specifying unit  1221  then outputs to the transmitting unit  125 , frequency information indicating the specified frequencies. The transmitting unit  125  transmits to the radio communications apparatus  110 , the frequency information output from the specifying unit  1221 . 
     The communications system  100  depicted in  FIGS. 12A and 12B  enables the radio communications apparatus  110  to set a frequency for which the predicted time for the frequency to become unavailable is relatively long among the frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 . As a result, frequency switching by the radio communications apparatus  110  can be reduced. 
     Although a case has been described where the frequency is selected based on the predicted time for the frequency to become unavailable to the radio communications apparatus  110 , configuration may be such that the frequency is selected based on a predicted movement distance of the radio communications apparatus  110  for the frequency to become unavailable to the radio communications apparatus  110 . 
     For example, for each of the specified frequencies, the calculating unit  1211  of the communications apparatus  110  calculates a predicted movement distance of the radio communications apparatus  110  for the frequency to become unavailable to the radio communications apparatus  110 . The calculating unit  1211  notifies the selecting unit  124  of the frequencies indicated by the frequency information and predicted movement distances respectively calculated for the frequencies indicated by the frequency information. 
     Based on the predicted movement distances notified by the calculating unit  1211 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  from among the frequencies notified by the calculating unit  1211 . For example, the selecting unit  124  preferentially selects a frequency for which the predicted movement distance notified by the calculating unit  1211  is relatively long among the frequencies notified by the calculating unit  1211 . 
     Thus, the communications apparatus  110  enables the radio communications apparatus  110  to set a frequency for which the predicted movement distance of the radio communications apparatus  110  to become unavailable is relatively long among the frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 . This results in reduced frequency switching at the communications apparatus  110 . 
       FIG. 13  is a diagram of an application example of the communications system according to the second embodiment. In  FIG. 13 , parts identical to those depicted in  FIG. 2  are designated by the same reference letters or numerals used in  FIG. 2  and will not again be described. Switching histories  1301  to  1304  depicted in  FIG. 13  are histories that respectively indicate a position where frequency switching occurred by the access point  231  in the past and the frequencies before and after the switching. For example, the switching history  1301  indicates that switching from frequency f 2  to frequency f 3  occurred at the boundary point pA in the past. The access point  231  obtains the switching histories  1301  and  1302  corresponding to positions on the predicted route L 1  of the access point  231 , among the switching histories  1301  to  1304 . 
     For example, when the access point  231  is located at the passage point p 1 , the frequencies f 1  and f 2  are assumed to be available to the access point  231 . If the access point  231  sets the frequency f 2  at the passage point p 1 , the frequency f 2  becomes unavailable at the boundary point pA and consequently, the access point  231  has to perform frequency switching. On the other hand, if the access point  231  sets the frequency f 1  at the passage point p 1 , the frequency f 1  is available until the boundary point pB and consequently, the access point  231  need not perform frequency switching until the boundary point pB. 
     Accordingly, the WS database server  240  causes the access point  231  to set the frequency f 1  for which the predicted time for the frequency to become unavailable is longer among the frequencies f 1  and f 2  available to the access point  231  at the passage point p 1 . This enables a reduction of the frequency switching by the access point  231 . 
       FIG. 14A  is a diagram of an example of configuration of the communications system depicted in  FIG. 13 .  FIG. 14B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 14A . In  FIGS. 14A and 14B , parts identical to those depicted in  FIGS. 3A and 3B  are designated by the same reference letters or numerals used in  FIGS. 3A and 3B  and will not again be described. 
     As depicted in  FIGS. 14A and 14B , the access point  231  includes for example the route obtaining unit  311 , the communications unit  312 , a switching history storage unit  1411 , a frequency selecting unit  1412 , and the communications unit  314 . The route obtaining unit  311  obtains current position information indicating the current position of the access point  231 . The route obtaining unit  311  outputs the obtained current position information to the communications unit  312 . The route obtaining unit  311  obtains predicted route information (see, for example,  FIG. 5 ) of the access point  231 . The route obtaining unit  311  then outputs the obtained predicted route information to the frequency selecting unit  1412 . 
     The communications unit  312  transmits to the WS database server  240 , the current position information output from the route obtaining unit  311 . The communications unit  312  receives available frequency information transmitted from the WS database server  240 . The communications unit then outputs the received available frequency information to the frequency selecting unit  1412 . 
     The switching history storage unit  1411  stores history information of the switching of frequencies used for radio communication by the access point  231 . The frequency selecting unit  1412  selects a frequency to be used by the access point  231 , based on the predicted route information output from the route obtaining unit  311 , the history information stored in the switching history storage unit  1411 , and the available frequency information output from the communications unit  312 . The frequency selecting unit  1412  then sets the selected frequency as a frequency to be used for radio communication by the communications unit  314 . The communications unit  314  performs radio communication using the frequencies set by the frequency selecting unit  1412 . 
     The obtaining unit  111  depicted in  FIGS. 12A and 12B  can be realized, for example, by the route obtaining unit  311 . The transmitting unit  112  and the receiving unit  113  depicted in  FIGS. 12A and 12B  can be realized, for example, by the communications unit  312 . The calculating unit  1211  depicted in  FIGS. 12A and 12B  can be realized, for example, by the frequency selecting unit  1412 . The communications unit  114  depicted in  FIGS. 12A and 12B  can be realized, for example, by the communications unit  314 . 
     As depicted in  FIGS. 14A and 14B , the WS database server  240  includes the communications unit  322  and the WS database  321 . The communications unit  322  receives current position information transmitted from the access point  231 . The communications unit  322  then outputs the received current position information to the WS database  321 . The communications unit  322  transmits to the access point  231 , available frequency information output from the WS database  321 . 
     The WS database  321  specifies in the stored correspondence information, frequencies corresponding to a position indicated by the current position information output from the access point  231 , to output to the communications unit  322 , available frequency information indicating the specified frequencies. 
     The receiving unit  121  and the transmitting unit  125  depicted in  FIGS. 12A and 12B  can be realized for example by the communications unit  322 . The specifying unit  1221  and the obtaining unit  122  depicted in  FIGS. 12A and 12B  can be realized for example by the WS database  321 . 
       FIG. 15  is a sequence diagram of an operation example of the communications system depicted in  FIG. 13 . The communications system  200  depicted in  FIG. 13  operates, for example, as indicated by the steps depicted in  FIG. 15 . First, the access point  231  transmits current position information indicating the current position of the access point  231  to the WS database server  240  (step S 1501 ). 
     The WS database server  240  then transmits to the access point  231 , available frequency information indicating frequencies available to the access point  231  at the position indicated by the current position information transmitted at step S 1501  (step S 1502 ). 
     The access point  231  obtains predicted route information and switching history information of the access point  231  (step S 1503 ). The access point  231  calculates for each available frequency indicated by the available frequency information transmitted at step S 1502 , a predicted time for frequency switching to occur by the access point  231  (step S 1504 ). 
     The access point  231  then selects from among the available frequencies indicated by the available frequency information transmitted at step S 1502 , a frequency for which the predicted time calculated at step S 1504  is longest (step S 1505 ). The access point  231  sets the frequency selected at step S 1505  as the frequency for use in radio communication (step S 1506 ), and terminates a series of operations. 
     The above operations enable the access point  231  to set a frequency for which the predicted time of becoming unavailable is longer among frequencies available to the access point  231  at the current position of the access point  231 . As a result, frequency switching by the access point  231  can be reduced. 
     The operations depicted in  FIG. 15  are executed, for example, at the time of powering on of the access point  231 . The timing at which the operations depicted in  FIG. 15  are executed is not limited hereto. For example, the operations depicted in  FIG. 15  may be executed every time the frequency being used by the access point  231  becomes unavailable as a result of movement of the access point  231 . This can reduce frequency switching, not only at the time of powering on. 
     The operations depicted in  FIG. 15  may be executed every time the predicted route L 1  of the access point  231  changes. The operations depicted in  FIG. 15  may be executed periodically. This enables the frequency switching by the access point  231  to be reduced, irrespective of a change in the predicted route L 1  of the access point  231  due to rerouting, etc. 
       FIG. 16  is a diagram of an example of available frequency information. The WS database server  240  transmits, for example, available frequency information  1600  depicted in  FIG. 16  to the access point  231 . In the available frequency information  1600  are arranged frequencies (f 1 , f 2 , . . . ) available to the access point  231  at the current position of the access point  231 . The access point  231  selects from among frequencies arranged in the available frequency information  1600 , a frequency for use in radio communications. 
       FIG. 17  is a diagram of an example of switching history information. The switching history storage unit  1411  of the access point  231  stores, for example, switching history information  1700  depicted in  FIG. 17 . In the switching history information  1700 , date (yy/mm/dd), time (hh:mm:ss), latitude, longitude, and frequencies before and after switching are correlated with each position where frequency switching occurred by the access point  231  in the past. “none” indicated for the frequencies before and after switching means that no frequencies were available to the access point  231 . 
     For example, a first record of the switching history information  1700  indicates that the access point  231  passed the passage point p 1  at 10:07:00 on Dec. 11, 2011, latitude (36 [degrees], 43′00″), and longitude (140 [degrees], 22′00″). The first record of the switching history information  1700  indicates that switching from frequency f 2  to frequency f 1  occurred when the access point  231  passed the passage point p 1 . 
       FIG. 18  is a diagram of an example of frequency switching history on the predicted route depicted in  FIG. 13 . The frequency selecting unit  1412  of the access point  231  creates a table  1800  depicted in  FIG. 18  through operations based on the predicted route information (see, for example,  FIG. 5 ) output from the route obtaining unit  311  and based on the switching history information (see, for example,  FIG. 17 ) stored in the switching history storage unit  1411 . 
     In the table  1800 , switching information is correlated with passage points where frequency switching occurred by the access point  231  in the past, among passage points of the access point  231  based on the predicted route indicated by the predicted route information. The switching information indicates frequencies before and after switching at a corresponding passage point. 
     For each of the specified frequencies f 1  and f 2 , the frequency selecting unit  1412  calculates based on the table  1800 , a predicted time for the next frequency switching to occur by the access point  231  if the specified frequency is set in the access point  231 . 
     In the example depicted in  FIG. 18 , if the frequency f 1  is set in the access point  231 , the frequency f 1  remains available until 10:34:00 of the same date and consequently, the predicted time for frequency switching to occur by the access point  231  is 34 min. If the frequency f 2  is set in the access point  231 , the frequency f 2  is available until 10:07:00 of the same date and consequently, the predicted time for frequency switching to occur by the access point  231  is 7 min. 
     Accordingly, the frequency selecting unit  1412  selects as the frequency to be used by the access point  231 , the frequency f 1  having for which the predicted time for frequency switching to occur by the access point  231  is longest among the specified frequencies f 1  and f 2 . 
     Although the example depicted in  FIG. 13  has been described in a case where the frequency to be used is selected based on the predicted time for frequency switching to occur, configuration may be such that the frequency to be used is selected based on the predicted movement distance of the access point  231  for frequency switching to occur. 
     For example, for each of the specified available frequencies, the frequency selecting unit  1412  calculates a predicted movement distance of the access point  231  for the next frequency switching to occur if the specified available frequency is set in the communications unit  314 . The frequency selecting unit  1412  then selects the available frequency for which the calculated predicted movement distance is greatest among the specified available frequencies, as the frequency to be used by the access point  231 . 
       FIG. 19  is a diagram of another example of the switching history information. In  FIG. 19 , parts identical to those depicted in  FIG. 17  are designated by the same reference letters or numerals used in  FIG. 17  and description thereof will be omitted. The switching history storage unit  1411  of the access point  231  may store, for example, the switching history information  1700  depicted in  FIG. 19 . In the switching history information  1700  depicted in  FIG. 19 , passage direction in addition to the items depicted in  FIG. 17  is correlated with each position where frequency switching occurred by the access point  231  in the past. 
     The passage direction of the switching history information  1700  depicted in  FIG. 19  is indicated, for example, by an angle relative to a predetermined direction (e.g., right direction in  FIG. 13 ). 
     For example, a first record of the switching history information  1700  indicates that at 10:07:00 on Dec. 11, 2011, the access point  231  passed a passage point p 1  in the direction of 180 degrees (e.g., left direction of  FIG. 13 ) relative to the predetermined direction. 
     In this manner, the switching history information  1700  may include a history of frequency switching by the access point  231 , corresponding to combinations of positions on the predicted route L 1  and directions in which the access point  231  passed through the positions on the predicted route L 1 . This enables the switching history (see, e.g.,  FIG. 18 ) of frequencies on the predicted route L 1  of the access point  231  to be more accurately determined. 
     In this manner, according to the second embodiment, the radio communications apparatus can set a frequency for which the predicted time for the frequency to become unavailable is relatively long among the frequencies available to the radio communications apparatus at the position of the radio communications apparatus. Alternatively, the radio communications apparatus can set a frequency for which the predicted movement distance for the frequency to become unavailable is longer among frequencies available to the radio communications apparatus at the position of the radio communications apparatus. As a result, frequency switching by the radio communications apparatus can be reduced. 
     Parts of a third embodiment differing from the first embodiment will be described. 
     The communications system  100  according to the third embodiment is similar to the communications system  100  depicted in  FIGS. 1A and 1B , for example. It is to be noted, however, that for each of the specified frequencies, the calculating unit  123  of the communications control apparatus  120  calculates for the radio communications apparatus  110 , a predicted frequency switching count of frequency switching that occurs on the predicted route of the radio communications apparatus  110  if the specified frequency is set in the radio communications apparatus  110 . The calculating unit  123  notifies the selecting unit  124  of the specified frequencies and the predicted count calculated for each specified frequency. 
     Based on the predicted count notified by the calculating unit  123 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  from among frequencies notified by the calculating unit  123 . For example, the selecting unit  124  preferentially selects a frequency for which the predicted count notified by the calculating unit  123  is lower among the frequencies notified by the calculating unit  123 . 
     The communications system  100  according to the third embodiment enables the radio communications apparatus  110  to set a frequency for which less frequency switching occurs on the predicted route, among the frequencies available at the position of the radio communications apparatus  110 . As a result, frequency switching by the radio communications apparatus  110  can be reduced. 
     Although description has been given of a configuration where the frequency of the radio communications apparatus  110  is selected at the communications control apparatus  120 , configuration may be such that as in the second embodiment, the frequency of the radio communications apparatus  110  is selected at the radio communications apparatus  110 . For example, for each of the specified frequencies, the calculating unit  1211  depicted in  FIGS. 12A and 12B  calculates a predicted frequency switching count for the predicted route of the radio communications apparatus  110  if the specified frequency is set in the radio communications apparatus  110 . The calculating unit  1211  then notifies the selecting unit  124  of the specified frequencies and the predicted count calculated for each of the specified frequencies. Based on the predicted count notified by the calculating unit  1211 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  from among the frequencies notified by the calculating unit  1211 . 
       FIG. 20  is a diagram of an application example of the communications system according to the third embodiment. In  FIG. 20 , parts identical to those depicted in  FIGS. 2 and 10  are designated by the same reference letters or numerals used in  FIGS. 2 and 10  and will not again be described. The example depicted in  FIG. 20  assumes that the frequencies available for radio communication by the access point  231  are frequencies f 1  to f 3 . The frequencies f 1  to f 3  are frequencies differing from one another. 
     In the example depicted in  FIG. 20 , the passage point p 1  is not in the area  221  but is in the area  1011 . Thus, the frequencies f 1  and f 2  are available to the access point  231  at the passage point p 1 . The passage points p 2  to p 7  are in the areas  221  and  1011 . Thus, the frequency f 1  is available to the access point  231  at the passage points p 2  to p 7 . The passage point p 8  is not in the area  1011  but is in the area  221 . Therefore, the frequencies f 1  and f 3  are available to the access point  231  at the passage point p 8 . 
     The boundary point pA is a position on the predicted route L 1  where the access point  231  enters the area  221 . The boundary point pB is a position on the predicted route L 1  where the access point  231  leaves the  1011 . 
     For example, if the access point  231  is located at the passage point p 1 , frequencies available to the access point  231  are the frequencies f 1  and f 2 . If the access point  231  sets the frequency f 1  at the passage point p 1 , the predicted frequency switching count for the access point  231  on the predicted route L 1  is 0. If the access point  231  sets the frequency f 2  at the passage point p 1 , the predicted frequency switching count is 1 for the frequency switch at the boundary point pA. 
     The WS database server  240  thus causes the access point  231  to set the frequency f 1  for which the predicted frequency switching count is smallest among the frequencies f 1  to f 3  available to the access point  231  at the passage point p 1 . As a result, frequency switching by the access point  231  can be reduced. 
     The access point  231  and the WS database server  240  depicted in  FIG. 20  are similar to those depicted in  FIGS. 3A and 3B , for example. However, for each of the specified available frequencies, the frequency selecting  323  of the WS database server  240  calculates a predicted frequency switching count for the access point  231  on the predicted route L in a case of the specified available frequency being set in the access point  231 . The frequency selecting unit  323  then selects, as the frequency to be used by the access point  231 , a frequency for which the calculated predicted count is smallest among the available frequencies of the access point  231 . 
       FIG. 21  is a sequence diagram of an operation example of the communications system depicted in  FIG. 20 . The communications system  200  depicted in  FIG. 20  operates, for example, as indicated by the steps depicted in  FIG. 21 . First, the access point  231  transmits predicted route information of the access point  231  to the WS database server  240  (step S 2101 ). 
     The WS database server  240  then specifies available frequencies corresponding to the current position of the access point  231 , based on the predicted route information transmitted at step S 2101  and based on the correspondence information (step S 2102 ). For each of the available frequencies specified at step S 2102 , the WS database server  240  then calculates a predicted count of frequency switching by the access point  230  if the WS database server  240  causes the access point  231  to set the available frequency (step S 2103 ). 
     The WS database server  240  selects from among the available frequencies specified at step S 2102 , the frequency for which the predicted count calculated at step S 2103  is smallest (step S 2104 ). The WS database server  240  transmits available frequency information indicating the frequency selected at step S 2104  to the access point  231  (step S 2105 ). 
     The access point  231  sets the frequency indicated by the available frequency information transmitted at step S 2105 , as a frequency to be used for radio communication by the access point  231  (step S 2106 ), and terminates a series of the operations. 
     The above operations enable the access point  231  to set a frequency for which the predicted count of frequency switching on the predicted route L 1  is smallest among frequencies available to the access point  231  at the current position of the access point  231 . As a result, frequency switching by the access point  231  can be reduced. 
     The operations depicted in  FIG. 21  are executed, for example, at the time of powering on of the access point  231 . Nonetheless, the timing at which the operations depicted in  FIG. 21  are executed are not limited hereto. 
       FIG. 22  is a diagram of an example of frequencies available at positions on the predicted route depicted in  FIG. 20 . The frequency selecting unit  323  of the WS database server  240  depicted in  FIG. 20  creates a table  2200  depicted in  FIG. 22  through calculations based on predicted route information output from the communications unit  322  and based on correspondence information stored in the WS database  321 . 
     In the table  2200 , similar to the table  700  depicted in  FIG. 7 , frequencies available to the access point  231  are correlated with each passage point of the access point  231  based on the predicted route indicated by the predicted route information. 
     In the example depicted in  FIG. 22 , if the frequency f 1  is set in the access point  231 , the predicted route L 1  has no history that the frequency f 1  became unavailable and consequently, the predicted frequency switching count on the predicted route L 1  is 0. If the frequency f 2  is set in the access point  231 , the predicted route L 1  has a history that the frequency f 2  became unavailable at the passage point p 2  and consequently, the predicted frequency switching count on the predicted route L 1  is 1. 
     The frequency selecting unit  323 , therefore, selects, as the frequency used by the access point  231 , the frequency f 1  for which the predicted frequency switching count on the predicted route L 1  is smallest among the specified frequencies f 1  and f 2 . 
     In this manner, according to the third embodiment, the radio communications apparatus can set a frequency for which the predicted frequency switching count for the predicted route is smallest among frequencies available to the radio communications apparatus at the position of the radio communications apparatus. As a result, frequency switching by the radio communications apparatus can be reduced. 
     Parts of a fourth embodiment differing from the second embodiment will be described. 
     The communications system  100  according to the fourth embodiment is similar to the communications system  100  depicted in  FIGS. 12A and 12B  for example. However, the obtaining unit  111  of the radio communications apparatus  110  obtains history information indicating history of switching of the frequencies used for radio communication by the radio communications apparatus  110  in a predetermined range that includes the position of the radio communications apparatus  110 . The obtaining unit  111  outputs the obtained history information to the calculating unit  1211 . 
     For each of the frequencies indicated by the frequency information output from the receiving unit  113 , the calculating unit  1211  calculates a count of switching from the frequency to another frequency occurring in the predetermined range, based on the history information output from the obtaining unit  111 . The calculating unit  1211  then notifies the selecting unit  124  of the frequencies indicated by the frequency information and the count calculated for each frequency indicated by the frequency information. 
     Based on the counts notified by the calculating unit  1211 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  among the frequencies notified by the calculating unit  1211 . The selecting unit  124  then notifies the communications unit  114  of the selected frequency. 
       FIG. 23  is a diagram of an application example of the communications system according to the fourth embodiment. In  FIG. 23 , parts identical to those depicted in  FIG. 2  are designated by the same reference letters or numerals used in  FIG. 2  and will not again be described. The communications system  100  according to the fourth embodiment is applicable to the communications system  200  depicted in  FIG. 23 , for example. A vehicle  2310  depicted in  FIG. 23  is equipped with the access point  231 . The radio communications apparatus  110  according to the fourth embodiment is applicable to the access point  231 , for example. The communications control apparatus  120  according to the fourth embodiment is applicable to the WS database server  240 , for example. 
     A predetermined range  2311  is a predetermined range that includes the position of the access point  231 . For example, the predetermined range  2311  is a range encompassed by a circle of a predetermined radius around the access point  231 . The predetermined radius is determined, for example, by the travelling speed of the access point  231 . For example, if the travelling speed (e.g., average travelling speed) of the access point  231  is v [km/h], the predetermined range  2311  is a range encompassed by a circle with a radius a·v (a is a constant) around the access point  231 . 
     An example is assumed in which the travelling speed of the access point  231  is 30 [km/h] with the constant a=1. In this case, the predetermined range  2311  is a circle with a radius of 30 [km] around the current position of the access point  231 . 
     Switching histories  2321  to  2327  depicted in  FIG. 23  are switching histories corresponding to positions in the predetermined range  2311 , among histories each indicating a position where frequency switching occurred by the access point  231  in the past and frequencies before and after the frequency switching. The access point  231  obtains the switching histories  2321  to  2327 . For example, the access point  231  extracts from stored histories, histories in which the distances between the positions corresponding to the histories and current position of the access point  231  are not more than the predetermined radius, to thereby obtain the switching histories  2321  to  2327 . 
     An example is assumed in which the frequencies available to the access point  231  at the current position of the access point  231  are the frequencies f 1  to f 3 . For each of the frequencies f 1  to f 3 , the access point  231  calculates the number of histories indicating a history of switching from a given frequency to another frequency, among the switching histories  2321  to  2327 . 
     In the example depicted in  FIG. 23 , the number of histories indicating a history of switching from the frequency f 1  to another frequency, among the switching histories  2321  to  2327  is the minimum (0). Thus, the access point  231  sets the frequency f 1  among the frequencies f 1  to f 3  available to the access point  231  at the current position of the access point  231 . As a result, frequency switching by the access point  231  can be reduced. 
       FIG. 24A  is a diagram of an example of configuration of the communications system depicted in  FIG. 13 .  FIG. 24B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 24A . In  FIGS. 24A and 24B , parts identical to those depicted in  FIGS. 14A and 14B  are designated by the same reference letters or numerals used in  FIGS. 14A  and  14 B and will not again be described. 
     As depicted in  FIGS. 24A and 24B , the access point  231  includes for example a range obtaining unit  2411  in place of the route obtaining unit  311 . The range obtaining unit  2411  obtains current position information indicating the current position of the access point  231 . The range obtaining unit  2411  outputs the obtained current position information to the communications unit  312 . The range obtaining unit  2411  obtains predicted range information for the access point  231 . The predicted range information is, for example, information indicating the range  2311  depicted in  FIG. 23 , for example. The range obtaining unit  2411  then outputs the obtained predicted route information to the frequency selecting unit  1412 . 
     The frequency selecting unit  1412  selects a frequency to be used by the access point  231 , based on the predicted range information output from a range obtaining unit  2411 , the available frequency information output from the communications unit  312 , and the switching history information output from the switching history storage unit  1411 . 
     The obtaining unit  111  according to the fourth embodiment can be realized, for example, by the range obtaining unit  2411 . 
       FIG. 25  is a sequence diagram of an operation example of the communications system depicted in  FIG. 23 . The communications system  200  depicted in  FIG. 23  operates, for example, as indicated by the steps depicted in  FIG. 25 . First, the access point  231  transmits current position information indicating the current position of the access point  231  to the WS database server  240  (step S 2501 ). 
     The WS database server  240  then transmits to the access point  231 , available frequency information indicating frequencies available to the access point  231  at the position indicated by the current position information transmitted at step S 2501  (step S 2502 ). 
     The access point  231  obtains predicted range information and switching history information of the access point  231  (step S 2503 ). The access point  231  calculates for each available frequency indicated by the available frequency information transmitted at step S 2502  and based on switching history information, a count of switching histories included in the predicted range indicated by the predicted range information (step S 2504 ). 
     The access point  231  then selects from among the available frequencies indicated by the available frequency information transmitted at step S 2502 , a frequency for which the calculated count is smallest (step S 2505 ). The access point  231  sets the frequency selected at step S 2505  as the frequency for use in radio communication (step S 2506 ), and terminates a series of operations. 
     The above operations enable the access point  231  to set a frequency for which the count of switching histories included in a predetermined range are few among the frequencies available to the access point  231  at the current position of the access point  231 . As a result, frequency switching by the access point  231  can be reduced. 
     The operations depicted in  FIG. 25  are executed, for example, at the time of powering on of the access point  231 . The timing at which the operations depicted in  FIG. 25  are executed is not limited hereto. 
       FIG. 26  is a diagram of an example of the distance between the history position and the current position. The frequency selecting unit  1412  of the access point  231  creates a table  2600  depicted in  FIG. 26 , for example, based on the predicted range information output from the range obtaining unit  2411  and based on the switching history information stored in the switching history storage unit  1411 . In the table  2600 , the distance between the history position (latitude and longitude) and the current position of the access point  231  is correlated with each record of the switching history information  1700  depicted in  FIG. 17 , for example. 
     An example is assumed in which the predetermined range  2311  depicted in  FIG. 23  is a circle with a radius of 30 [km] around the current position of the access point  231 . In this case, a record  2602  of the table  2600  has a distance of 35 [km] and therefore, is out of the predetermined range  2311 . On the contrary, the access point  231  selects a frequency based on a record  2601  of the table  2600 , corresponding to positions in the predetermined range  2311 . 
     In the example depicted in  FIG. 26 , the record  2601  has no history of switching from frequency f 1  to another frequency. The record  2601  has four histories of switching from frequency f 2  to another frequency. The record  2601  has three histories of switching from frequency f 3  to another frequency. 
     The frequency selecting unit  1412  thus selects, as the frequency to be used by the access point  231 , the frequency f 1  having the least number of histories in the predetermined range  2311  among the frequencies f 1  to f 3 . 
     Although a case has been described where the predetermined range  2311  is a range encompassed by a circle of a predetermined radius around the access point  231 , the predetermined range  2311  is not limited hereto. For example, the range may be determined based on the direction of travel of the access point  231 . 
       FIG. 27  is a diagram of another example of the predetermined range. In  FIG. 27 , Vx represents the average travelling speed of the access point  231  in an X-axis direction, while Vy represents the average travelling speed of the access point  231  in a Y-axis direction. (Px, Py) represents the current position of the access point  231 . In this case, the predetermined range  2311  can be a range expressed by equation (1). In equation (1), a is a real number value ranging in the range of 0≦a&lt;1. 
       ( X−Px−a·Vx ) 2 +( Y−Py−a·Vy ) 2   =Vx   2   +Vy   2   (1)
 
     As a result, the predetermined range  2311  can be a circle around a position offset in the direction of travel of the access point  231 , from the current position of the access point  231 . This enables the frequency to be selected based on the history information for a position having a high possibility of being a destination of the access point  231 . Thus, a frequency tending to reduce frequency switching by the radio communications apparatus can be selected. 
     In this manner, according to the fourth embodiment, the radio communications apparatus can set a frequency having a fewer number of histories of switching from a given frequency to another frequency in a predetermined range that includes the position of the radio communications apparatus, among frequencies available to the radio communications apparatus. As a result, frequency switching by the radio communications apparatus can be reduced. 
     For example, the frequency can be selected by calculating a predicted movement range of the access point  231  from the travelling speed, etc., of the access point  231  and counting the number of histories of frequency switching that occurred in the calculated predicted movement range. Thus, a frequency having a high possibility of reducing frequency switching by the radio communications apparatus can be selected. 
     The access point  231  may select a frequency based on the count of switching from a given frequency to another frequency, weighted according to the distance from the access point  231  to the position where the corresponding switching occurred. For example, a history weight increases as the distance decreases from the access point  231  to the position where the corresponding switching occurred. This enables a frequency to be selected increasing the history weight for a position having a high possibility of being a destination of the access point  231 . Thus, a frequency can be selected that tends to reduce frequency switching by the radio communications apparatus. 
     A history weight w(r) can be calculated using a monotonically decreasing function expressed in equation (2) below. In equation (2), R designates the radius of the predetermined range  2311 . r designates the distance from the access point  231  of the position where a switching corresponding to a history occurred. 
         w ( r )=1− r/R   (2)
 
     As a result, the history weight can be increased as the distance of the position where a corresponding switching occurred from the access point  231  becomes smaller. The history weight can be 0 at the boundary of the predetermined range  2311 . 
     If rf(i) denotes a distance from the access point  231  to an i-th position where a switching from a frequency f to another frequency occurred, the count of switching from a frequency f to another frequency can be calculated using, for example, equation (3) below. 
         Nf=Σ   i=0   nf   w{rf ( i )}  (3)
 
     In equation (3) above, of denotes the number of positions where a switching of a frequency f occurred in the predetermined range  2311 . In the example depicted in  FIG. 26 , for example, a count Nf (Nf 1 ) of switching of frequency f 1  is 0. A count Nf (Nf 2 ) of switching of frequency f 2  is as expressed by equation (4) below. A count Nf (Nf 3 ) of switching of frequency f 3  is as expressed by equation (5) below. 
     
       
         
           
             
               
                 
                   
                     Nf 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           1 
                           - 
                           
                             12 
                             30 
                           
                         
                         ) 
                       
                       + 
                       
                         ( 
                         
                           1 
                           - 
                           
                             26 
                             30 
                           
                         
                         ) 
                       
                       + 
                       
                         ( 
                         
                           1 
                           - 
                           
                             26 
                             30 
                           
                         
                         ) 
                       
                       + 
                       
                         ( 
                         
                           1 
                           - 
                           
                             21 
                             30 
                           
                         
                         ) 
                       
                     
                     = 
                     1.1666 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                     Nf 
                      
                     
                         
                     
                      
                     3 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           1 
                           - 
                           
                             23 
                             30 
                           
                         
                         ) 
                       
                       + 
                       
                         ( 
                         
                           1 
                           - 
                           
                             21 
                             30 
                           
                         
                         ) 
                       
                       + 
                       
                         ( 
                         
                           1 
                           - 
                           
                             24 
                             30 
                           
                         
                         ) 
                       
                     
                     = 
                     0.7333 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Parts of a fifth embodiment differing from the first embodiment will be described. 
       FIG. 28A  is a diagram of an example of the communications system according to a fifth embodiment.  FIG. 28B  is a diagram of an example of signal flow in the communications system depicted in  FIG. 28A . In  FIGS. 28A and 28B , parts identical to those depicted in  FIGS. 1A and 1B  are designated by the same reference letters or numerals used in  FIGS. 1A and 1B  and will not again be described. 
     Similar to the radio communications apparatus  110 , a radio communications apparatus  2830  selects a frequency available to the radio communications apparatus  2830  at the position of the radio communications apparatus  2830 , to perform radio communications. Information indicating correspondence between positions and available frequencies is common to the radio communications apparatus  110  and the radio communications apparatus  2830 . When frequency switching occurs, the radio communications apparatus  2830  transmits switching information to the communications control apparatus  120 . The switching information includes, for example, information indicating the time when and the position where the frequency switching occurred and the frequencies before and after switching. Plural radio communications apparatuses  2830  may be present. 
     The communications control apparatus  120  according to the fifth embodiment includes a receiving unit  2821  and a storage unit  2822 , in addition to the configuration depicted in  FIGS. 1A and 1B . The receiving unit  2821  receives switching information transmitted from the radio communications apparatus  2830 . The receiving unit  2821  then causes the storage unit  2822  to store the received switching information. 
     For each of the specified frequencies, the calculating unit  123  calculates a count of switching from a given frequency to another frequency on a predicted route indicated by the route information output from the receiving unit  121 , based on the switching information stored in the storage unit  2822 . The calculating unit  123  notifies the selecting unit  124  of the specified frequencies and the count calculated for each of the specified frequencies. 
     Alternatively, for each of the specified frequencies, the calculating unit  123  calculates the time or distance for switching to occur from a given frequency to another frequency on a predicted route indicated by the route information output from the receiving unit  121 , based on the switching information stored in the storage unit  2822 . The calculating unit  123  notifies the selecting unit  124  of the specified frequencies and the time or distance calculated for each of the specified frequencies. 
     Based on the count or the time or distance required for switching notified by the calculating unit  123 , the selecting unit  124  selects a frequency to be used by the radio communications apparatus  110  from among the frequencies notified by the calculating unit  123 . For example, the selecting unit  124  preferentially selects a frequency for which the count notified by the calculating unit  123  is fewer among the frequencies notified by the calculating unit  123 . If the notified information is the time or the distance required for switching, selection is made of a frequency having a longer time or a farthest distance. 
     The communications system  100  according to the fifth embodiment enables the radio communications apparatus  110  to set a frequency for which the number of times switching to another frequency on the predicted route occurs is fewer or for which the time or distance required for switching is greatest, among the frequencies available to the radio communications apparatus  110  in the position of the radio communications apparatus  110 . 
       FIG. 28C  is a diagram of another example of signal flow in the communications system depicted in  FIG. 28A . In  FIG. 28C , parts identical to those depicted in  FIG. 28B  are designated by the same reference letters or numerals used in  FIG. 28B  and description thereof will be omitted. As depicted in  FIG. 28C , the obtaining unit  111  of the radio communications apparatus  110  obtains range information indicating a predetermined range including the position of the radio communications apparatus  110 . The predetermined range is similar to the predetermined range (predicted movement range) described in the fourth embodiment, for example. The obtaining unit  111  outputs the obtained range information to the transmitting unit  112 . The transmitting unit  112  transmits to the communications control apparatus  120 , the range information output from the obtaining unit  111 . 
     The receiving unit  121  of the communications control apparatus  120  receives the range information transmitted from the radio communications apparatus  110 . The receiving unit  121  outputs the received range information to the calculating unit  123 . For each of the specified frequencies, the calculating unit  123  calculates based on the switching information stored in the storage unit  2822 , a count of switching from a given frequency to another frequency in the predetermined range indicated by the range information output from the receiving unit  121 . 
     The communications system  100  depicted in  FIG. 28C  enables the radio communications apparatus  110  to set a frequency having a fewer occurrences of switching to another frequency in the predetermined range, among the frequencies available to the radio communications apparatus  110  at the position of the radio communications apparatus  110 . As a result, frequency switching by the radio communications apparatus  110  can be reduced. 
     Similar to the radio communications apparatus  2830 , the radio communications apparatus  110  may also transmit switching information to the communications control apparatus  120  when frequency switching has occurred. The receiving unit  2821  receives switching information transmitted from the radio communications apparatus  2830  and causes the storage unit  2822  to store the received switching information. This enables the radio communications apparatus  110  to set a frequency having fewer occurrences of switching to another frequency by the radio communications apparatus  110  and by the radio communications apparatus  2830 . 
       FIG. 29  is a diagram of an application example of the communications system according to the fifth embodiment. In  FIG. 29 , parts identical to those depicted in  FIG. 2  are designated by the same reference letters or numerals used in  FIG. 2  and will not again be described. The communications system  100  depicted in  FIGS. 1A and 1B  is applicable to the communications system  200  depicted in  FIG. 29 , for example. A bus vehicle  2920  is equipped with an access point  2921 . A bus vehicle  2930  is equipped with an access point  2931 . The radio communications apparatus  2830  depicted in  FIGS. 28A and 28B  is applicable to the access points  2921  and  2931 , respectively, for example. 
     When frequency switching occurs, the access points  231 ,  2921 , and  2931  transmit to a switching history database server  2910 , switching information indicating the position where the frequency switching has occurred and frequencies before and after the switching. The switching history database server  2910  stores the switching information transmitted from the access points  231 ,  2921 , and  2931 . 
     In this manner, frequency switching information from plural WS devices is aggregated into the switching history database server  2910  so that a frequency to be used by the access point  231  can be selected based on the aggregated switching information. Frequencies used by the access points  2921  and  2931  may also be selected based on the switching information aggregated in the switching history database server  2910 . 
       FIG. 30A  is a diagram of an example of configuration of the communications system depicted in  FIG. 29 .  FIG. 30B  is a diagram of an example of signal flow in the configuration of the communications system depicted in  FIG. 30A . In  FIGS. 30A and 30B , parts identical to those depicted in  FIGS. 3A and 3B  are designated by the same reference letters or numerals used in  FIGS. 3A and 3B  and will not again be described. 
     As depicted in  FIGS. 30A and 30B , the switching history database server  2910  includes a communications unit  3011 , a switching history database  3012 , and a frequency selecting unit  3013 . The communications unit  3011  performs radio communication with access points  231 ,  2921 , and  2931 . For example, the communications unit  3011  receives switching information transmitted from the access points  2921  and  2931 . The receiving unit  3011  then causes the switching history database  3012  to store the received switching information. 
     The communications unit  3011  receives predicted route information transmitted from the access point  231 . The communications unit  3011  outputs the received predicted route information to the frequency selecting unit  3013 . The communications unit  3011  transmits to the WS database server  240 , current position information indicating the current position of the access point  231  indicated by the received predicted route information. 
     The communications unit  3011  receives available frequency information transmitted from the WS database server  240 . The communications unit  3011  outputs the received available frequency information to the frequency selecting unit  3013 . The communications unit  301  transmits to the access point  231 , available frequency information output from the frequency selecting unit  3013 . 
     The frequency selecting unit  3013  selects a frequency to be used by the access point  231 , based on the predicted route information and the available frequency information output from the communications unit  3011  and based on the switching information stored in the switching history database  3012 . The frequency selecting unit  3013  outputs available frequency information indicating the selected frequency to the communications unit  3011 . 
     As depicted in  FIGS. 30A and 30B , the WS database server  240  includes the WS database  321  and the communications unit  322 . The communications unit  322  performs wire-based communication with the switching history database server  2910 . For example, the communications unit  322  receives current position information transmitted from the switching history database server  2910 . The receiving unit  322  specifies available frequencies of the access point  231 , based on the current position of the access point  231  indicated by the received current position information and based on correspondence information stored in the WS database  321 . The communications unit  322  transmits available frequency information indicating the specified available frequencies to the switching history database server  2910 . 
     The receiving units  121  and  2821  and the transmitting unit  125  depicted in  FIGS. 28A and 28B  can be realized by the communications unit  3011 , for example. The obtaining unit  122  depicted in  FIGS. 28A and 28B  can be realized by the WS database server  240 , for example. The calculating unit  123  and the selecting unit  124  depicted in  FIGS. 28A and 28B  can be realized by the frequency selecting unit  3013 , for example. The storage unit  2822  depicted in  FIGS. 28A and 28B  can be realized by the switching history database  3012 . 
     The switching history database server  2910  can be realized by the information processing apparatus  340  depicted in  FIG. 3D , for example. The communications unit  3011  can be realized by the wire-based communications interface  344  and the radio communications interface  345  depicted in  FIG. 3D , for example. The switching history database  3012  can be realized by the memory  342  depicted in  FIG. 3D , for example. The frequency selecting unit  3013  can be realized by the CPU  341  depicted in  FIG. 3D , for example. 
       FIG. 31  is a sequence diagram of an operation example of the communications system depicted in  FIG. 29 . The communications system  200  depicted in  FIG. 29  operates, for example, as indicated by the steps depicted in  FIG. 31 . First, the access point  231  transmits predicted route information indicating the current position and predicted route of the access point  231  to the switching history database server  2910  (step S 2901 ). The switching history database server  2910  transmits to the WS database server  240 , current position information indicating the current position of the access point  231  indicated in the predicted route information transmitted at step S 3101  (step S 3102 ). 
     The WS database server  240  transmits to the switching history database server  2910 , available frequency information indicating available frequencies at the position indicated by the current position information transmitted at step S 3102  (step S 3103 ). 
     The switching history database server  2910  then calculates the number of switching histories on the predicted route indicated by the predicted route information, for each of the available frequencies indicated by the available frequency information transmitted at step S 3103  (step S 3104 ). The switching history database server  2910  then selects a frequency having a minimum number calculated at step S 3104 , among the available frequencies indicated by the available frequency information (step S 3105 ). 
     The switching history database server  2910  transmits to the access point  231 , available frequency information indicating the frequency selected at step S 3105  (step S 3106 ). The access point  231  sets the frequency indicated by the available frequency information transmitted at step S 3106 , as a frequency to be used for radio communication by the access point  231  (step S 3107 ), and terminates a series of the operations. 
     The above operations enable the access point  231  to set a frequency for which the switching history count on the predicted route is fewer among frequencies available to the access point  231  at the current position of the access point  231 . As a result, frequency switching by the access point  231  can be reduced. 
     The operations depicted in  FIG. 31  are executed, for example, at the time of powering on of the access point  231 . The timing at which the operations depicted in  FIG. 31  are executed are not limited hereto. For example, the operations depicted in  FIG. 31  may be executed every time the frequency being used by the access point  231  becomes unavailable as a result of movement of the access point  231 . This can reduce frequency switching, not only at the time of powering on. 
     The operations depicted in  FIG. 31  may be executed every time the predicted route L 1  of the access point  231  changes. The operations depicted in  FIG. 31  may be executed periodically. This enables the frequency switching by the access point  231  to be reduced, irrespective of a change in the predicted route L 1  of the access point  231  due to rerouting, etc. 
       FIG. 32  is a diagram of an example of switching information. When frequency switching occurs, the access points  231 ,  2921 , and  2931  transmit switching information  3200  depicted in  FIG. 32 , for example, to the switching history database server  2910 . In the switching information  3200 , switching information is correlated with the position where frequency switching has occurred. The switching information indicates the frequencies before and after the switching. 
     For example, a first record of the switching information  3200  indicates that the frequency has switched from frequency f 2  to frequency f 3  at latitude (36 [degrees], 38′55″) and longitude (140 [degrees], 33′20″). 
     In this manner, according to the fifth embodiment, the radio communications apparatus can set a frequency for which the occurrence of switching to another frequency on the predicted route is fewer among the frequencies available to the radio communications apparatus at the position of the radio communications apparatus. As a result, frequency switching by the radio communications apparatus can be reduced. 
     A sixth embodiment will be described about parts different from the above embodiments. In the above embodiments, although description has been given of a case where only a single network configured by WS devices such as the access point  231  is present, configuration may be such that mutual interference is taken into consideration, if plural networks are present. 
     For example, mutual interference can be prevented by managing the frequencies used by the WS devices belonging to respective networks in the WS database server  240  such that different frequencies are used between adjacent networks. 
     When receiving a predicted route from the access point  231  in motion, the WS database server  240  manages the frequencies used so as to suppress interference with the other WS devices on the route through which the access point  231  travels. 
     For example, frequency assignment to the access point  231  is performed in order of arrival. At the time of selecting the frequency to be used by the access point  231 , the frequency usage status is also considered of WS devices located near the predicted route of the access point  231 . 
     If the frequency selected by the methods described in the above embodiments has already been used by another WS apparatus located near the predicted route of the access point  231 , the other WS apparatus may be caused to change its frequency. 
       FIG. 33  is a diagram of an application example of the communications system according to the sixth embodiment. In  FIG. 33 , parts identical to those depicted in  FIG. 10  are designated by the same reference letters or numerals used in  FIG. 10  and will not again be described. 
     In the example depicted in  FIG. 33 , the passage point p 2  is not in the area  1021  but is in the areas  221  and  1011 . Thus, the frequencies f 1  and f 4 , are available to the access point  231  at the passage point p 2 . The passage points p 3  to p 6  are in the areas  221 ,  1011 , and  1021 . Thus, the frequency f 1  is available to the access point  231  at the passage points p 3  to p 6 . The passage point p 7  is not in the area  1011  but is in the areas  221  and  1021 . Therefore, the frequencies f 1  and f 3  are available to the access point  231  at the passage point p. 
     Assume however that a WS device  3310  is located near the predicted route L 1  of the access point  231  and that the WS device  3310  is performing radio communication using the frequency f 1 . An Area  3311  is an area in which interference occurs with radio communication performed by the WS device  3310  using the frequency f 1 . In this case, if the access point  231  uses the frequency f 1  from the boundary point pA to the passage point p 2 , for example, interference occurs with the WS device  3310 . 
     Since the access point  231  and the WS device  3310  are WS devices using frequencies secondarily and have no priority for assignment, unlike licensed systems such as television stations  220 ,  1010 , and  1020 . It is desirable, however, that the access point  231  and the WS device  3310  do not use the same frequency. 
     For instance, a table indicating available frequencies is updated also using frequencies selected by the access point  231  and the WS device  3310  so that frequencies of the access point  231  and the WS device  3310  can be selected using the updated table. 
       FIG. 34  is a diagram of an example of frequencies available at positions on the predicted route depicted in  FIG. 33 . The frequency selecting unit  323  of the WS database server  240  depicted in  FIG. 33  creates, for example, a table  3400  depicted in  FIG. 34  through calculations based on the predicted route information output from the communications unit  322  and based on the correspondence information stored in the WS database  321 . 
     In the table  3400 , similar to the table  700  depicted in  FIG. 7 , frequencies available to the access point  231  are correlated with each passage point of the access point  231  based on the predicted route indicated by the predicted route information. 
       FIG. 35  is a diagram of an example of an updated table indicating available frequencies. If the WS device  3310  is using the frequency f 1 , the access point  231  cannot use the frequency f 1  from the boundary point pA to the passage point p 2 . For this reason, the frequency f 1  is excluded from frequencies corresponding to the boundary point pA and the passage point p 2 . Thus, in this case, the frequency selected from among the frequencies f 1 , f 2 , and f 4  as a frequency to be used by the access point  231  is, for example, the frequency f 4  for which switching does not occur until the boundary point pB. 
       FIG. 36  is a diagram of another example of the updated table indicating available frequencies. For example, if the WS device  3310  switches the frequency from frequency f 1  to frequency f 4 , the access point  231  cannot use the frequency f 4  from the boundary point pA to the passage point p 2 . The access point  231  is allowed to use the frequency f 1  from the boundary point pA to the passage point p 2 . 
     For this reason, in the table  3400 , the frequency f 4  is excluded from frequencies corresponding to the boundary point pA and the passage point p 2 . Thus, in this case, for example, the frequency f 1  for which switching does not occur is selected as the frequency to be used by the access point  231  among the frequencies f 1 , f 2 , and f 4 . 
     As set forth hereinabove, according to the communications system, the communications control apparatus, the radio communications apparatus, and the communications method, frequency switching can be reduced. As a result, the volume of communication accompanying frequency switching, for example, can be reduced. 
     According to one aspect of the present invention, reduced frequency switching can be achieved. 
     All examples and conditional language provided herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.