Abstract:
A communication relay apparatus that relays a wireless communication for a communication device includes a wireless transmitting unit and a wireless receiving unit. the wireless transmitting unit transmits data to the communication device via a transmission antenna. The wireless receiving unit receives data from the communication device via a reception antenna of which a reception area overlaps partially with a transmission area of the transmission antenna.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a technology for limiting a wireless communication area of a communication device to a predetermined area in wireless communication.  
         [0003]     2. Description of the Related Art  
         [0004]     A wireless local area network (LAN) allows for cable-free data communication between a terminal device and a network by rendering wireless data communication between the terminal device and the network via radio waves.  
         [0005]     In the data communication using the radio waves, an antenna is employed on an access point that takes a role of a communication relay between the terminal device and the network.  
         [0006]     The antenna used in the wireless LAN includes a nondirectional antenna and a directional antenna. The nondirectional antenna has a circular data communication area, as disclosed in Melco Inc., “Nondirectional antenna WLE-NDR”, [online], [searched on Sep. 12, 2003], internet &lt;URL: http://buffalo.melcoinc.co.jp/products/catalog/item/w/wlendr/index.html&gt;. Consequently, the nondirectional antenna allows for the data communication with any terminal device in a 360-degree field in a lateral direction.  
         [0007]     On the other hand, the directional antenna has a data communication area that extends in a specific direction, as disclosed in Melco Inc., “Directional antenna WLE-DA”, [online], [searched on Sep. 12, 2003], internet &lt;URL: http://buffalo.melcoinc.co.jp/products/catalog/item/w/wleda/index.html&gt;. Thus, unlike the nondirectional antenna, the directional antenna allows for a long-distance data communication by extending the data communication area only in a specific direction.  
         [0008]     However, in the nondirectional antenna disclosed in the former literature, the data communication area cannot be restricted to a desired area. In particular, the nondirectional antenna, which has a data communication area that expands 360 degrees in the lateral direction, has a data communication distance of about 60 meters radius around the antenna.  
         [0009]     As a result, when performing a data communication using the nondirectional antenna, the data communication area extends beyond a desired range, which may allow a third party to wiretap or have an unauthorized access.  
         [0010]     The directional antenna disclosed in the latter literature can extend its data communication area only in a specific direction, with a data communication distance of about 100 meters.  
         [0011]     Thus, even with the directional antenna that expands the data communication area only in a specific direction, the coverage of the data communication area reaches outside the desired range.  
         [0012]     In other words, because the coverage of the data communication area by way of the conventional wireless LAN is far larger than the desired area, there has been a security problem. It has therefore been an essential issue to limit the data communication area to a specific area that a user wishes.  
       SUMMARY OF THE INVENTION  
       [0013]     It is an object of the present invention to at least solve the problems in the conventional technology.  
         [0014]     A communication relay apparatus according to one aspect of the present invention relays a wireless communication for a communication device. The communication relay apparatus includes a wireless transmitting unit that transmits data to the communication device via a transmission antenna; and a wireless receiving unit that receives data from the communication device via a reception antenna of which a reception area overlaps partially with a transmission area of the transmission antenna.  
         [0015]     A method of relaying a wireless communication for a communication device, according to another aspect of the present invention, includes transmitting data to the communication device via a transmission antenna; and receiving data from the communication device via a reception antenna of which a reception area overlaps partially with a transmission area of the transmission antenna.  
         [0016]     A computer-readable recording medium according to still another aspect of the present invention stores a computer program for relaying a wireless communication for a communication device. The computer program causes a computer to execute the above method according to the present invention.  
         [0017]     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a schematic diagram for explaining a concept of an access point according to a first embodiment of the present invention;  
         [0019]      FIG. 2  is a functional block diagram of the access point according to the first embodiment;  
         [0020]      FIG. 3  is a flowchart of a processing procedure for a process of the access point according to the first embodiment receiving a packet from a router;  
         [0021]      FIG. 4  is a flowchart of a processing procedure for a process of the access point according to the first embodiment receiving a packet from a terminal device;  
         [0022]      FIG. 5  is a schematic diagram for explaining a concept of an access point according to a second embodiment of the present invention;  
         [0023]      FIG. 6  is a functional block diagram of the access point according to the second embodiment;  
         [0024]      FIG. 7  is a flowchart of a processing procedure for a process of the access point according to the second embodiment receiving a packet from a router;  
         [0025]      FIG. 8  is a schematic diagram for explaining a concept of an access point according to a third embodiment of the present invention;  
         [0026]      FIG. 9  is a functional block diagram of the access point according to the third embodiment;  
         [0027]      FIG. 10  is a flowchart of a processing procedure for a process of the access point according to the third embodiment receiving a packet from a router;  
         [0028]      FIG. 11  is a flowchart of a processing procedure for a process of the access point according to the third embodiment receiving a packet from a terminal device;  
         [0029]      FIG. 12  is a schematic diagram for explaining a concept of an access point according to a fourth embodiment of the present invention;  
         [0030]      FIG. 13  is a functional block diagram of the access point according to the fourth embodiment;  
         [0031]      FIG. 14  is an example of a registered-MAC-address table;  
         [0032]      FIG. 15  is a flowchart of a processing procedure for the access point according to the fourth embodiment registering a MAC address of a terminal device;  
         [0033]      FIG. 16  is a flowchart of a processing procedure for the access point according to the fourth embodiment sending a packet from a terminal device to a router;  
         [0034]      FIG. 17  is a flowchart of a processing procedure for the access point according to the fourth embodiment sending a packet from a router to a terminal device;  
         [0035]      FIG. 18  is a flowchart of a processing procedure for a MAC-address registering unit updating the registered-MAC-address table according to the fourth embodiment;  
         [0036]      FIG. 19  is a schematic diagram for explaining a concept of an access point according to a fifth embodiment of the present invention; and  
         [0037]      FIG. 20  is a functional block diagram of the access point according to the fifth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]     Exemplary embodiments of the present invention will be explained in detail below with reference to the accompanying drawings.  
         [0039]      FIG. 1  is a schematic diagram for explaining a concept of an access point  1  according to a first embodiment of the present invention. The access point  1  is connected to a directional antenna  2  and a directional antenna  3 . The access point  1  is also connected to a network by way of a router (not shown).  
         [0040]     The directional antenna is utilized when data is sent to and received from a wireless communication terminal device that is located within a predetermined distance in a predetermined direction.  
         [0041]     When receiving a packet from the network, the access point  1  sends the received packet only to the directional antenna  2 , but not to the directional antenna  3 . This means that the terminal device that is to receive the packet from the network has to be present in the coverage of a packet reception area  5 .  
         [0042]     When the access point  1  receives the packet from a terminal device, only the directional antenna  3  is used. This means that the terminal device that is to send the packet to the network has to be present in the coverage of a packet transmission area  4 .  
         [0043]     In other words, a terminal device that is to perform a data communication with the network has to be present in the packet communication area  6 .  
         [0044]     Hence, the access point  1  according to the first embodiment limits the data communication area to a specific area, by using the directional antenna  2  specially to send the packet to a terminal device, while using the directional antenna  3  specially to receive the packet.  
         [0045]      FIG. 2  is a functional block diagram of the access point  1  according to the first embodiment. The access point  1  is connected to the directional antenna  2 , the directional antenna  3  and a router  10 .  
         [0046]     The access point  1  includes an input/output unit  7 , a control unit  8  and a wired-LAN interface  9 .  
         [0047]     The control unit  8  includes a wireless transmitting unit  8   a  and a wireless receiving unit  8   b . The wireless transmitting unit  8   a  receives the packet from the wired-LAN interface  9 , and sends the received packet to the directional antenna  2  via the input/output unit  7 .  
         [0048]     The wireless receiving unit  8   b  receives the packet from the directional antenna  3  via the input/output unit  7 , and sends the received packet to the router  10  via the wired-LAN interface  9 .  
         [0049]     The wired-LAN interface  9  sends the packet received from the router  10  to the control unit  8 . The wired-LAN interface  9  sends the packet received from the control unit  8  to the router  10 .  
         [0050]      FIG. 3  is a flowchart of a processing procedure for a process of the access point  1  according to the first embodiment receiving the packet from the router  10 . The wired-LAN interface  9  receives the packet from the router  10  (step S 101 ), and sends the received packet to the wireless transmitting unit  8   a  (step S 102 ).  
         [0051]     The wireless transmitting unit  8   a  sends the received packet to the input/output unit  7  (step S 103 ), and the input/output unit  7  sends the received packet to the directional antenna  2  (step S 104 ).  
         [0052]     In such a manner, the access point  1  sends the packet to the terminal device by using the directional antenna  2  only, when receiving the packet from the router  10 .  
         [0053]      FIG. 4  is a flowchart of a processing procedure for a process of the access point  1  according to the first embodiment receiving the packet from the terminal device. The input/output unit  7  receives the packet from the terminal device via the directional antenna  3  (step S 201 ), and sends the received packet to the wireless receiving unit  8   b  (step S 202 ).  
         [0054]     The wireless receiving unit  8   b  sends the received packet to the wired-LAN interface  9  (step S 203 ), and the wired-LAN interface  9  sends the received packet to the router  10  (step S 204 ).  
         [0055]     The access point  1  receives the packet from the terminal device by way of the directional antenna  3  only, and sends the received packet to the router  10 .  
         [0056]     As described above, the access point  1  according to the first embodiment utilizes only the directional antenna  2  when the wireless transmitting unit  8   a  sends the packet received from the router  10  to the terminal device. In addition, the wireless receiving unit  8   b  receives the packet from the terminal device by way of the directional antenna  3  only. It is therefore necessary for the terminal device to be positioned within the packet communication area  6  to perform the wireless data communication with the network.  
         [0057]     Hence, the packet communication area can be limited to an area that the user desires by adopting the directional antenna  2  and the directional antenna  3 . This can prevent a third party from wiretapping and having an unauthorized access, and improve security in the wireless communication.  
         [0058]      FIG. 5  is a schematic diagram for explaining a concept of an access point  11  according to a second embodiment of the present invention.  
         [0059]     The access point  11  is connected to a directional antenna  12  and a directional antenna  13 . The access point  11  is also connected to a network via a router (not shown).  
         [0060]     The access point  11  uses the directional antenna  12  and the directional antenna  13  alternately, when sending a packet received from the router to a terminal device.  
         [0061]     Thus, the terminal device cannot receive all the packets unless it is positioned within an entire packet reception area  16  that includes the overlapping area of a packet reception area  15  for the packet from the directional antenna  12  and a packet reception area  14  for the packet from the directional antenna  13 .  
         [0062]     In other words, the data communication area can be limited to a specific area that the user desires by using the directional antenna  12  and the directional antenna  13  alternately when sending data to a predetermined terminal device.  
         [0063]      FIG. 6  is a functional block diagram of the access point  11  according to the second embodiment. The access point  11  is connected to the directional antenna  12 , the directional antenna  13 , and a router  10 .  
         [0064]     The access point  11  includes a control unit  17 . Since the rest of the structure and operation of the access point  11  is the same as the access point  1  described in the first embodiment, the same reference numerals are adopted for the same structural elements, and the explanation is omitted.  
         [0065]     The control unit  17  includes a transmission determining unit  17   a , a wireless transmitting unit  17   b , and a wireless receiving unit  17   c . The transmission determining unit  17   a  determines a directional antenna to be used so that the packet received from the router  10  is sent alternately to the directional antenna  12  and the directional antenna  13 , and sends a result of the determination to the wireless transmitting unit  17   b.    
         [0066]     The wireless transmitting unit  17   b  sends the packet sent from the router  10  to the directional antenna  12  or the directional antenna  13  via the input/output unit  7 , based on the result of the determination by the transmission determining unit  17   a.    
         [0067]     The wireless receiving unit  17   c  receives the packet sent from the terminal device by way of the directional antenna  12  or the directional antenna  13 , and sends the received packet to the router  10  via the wired-LAN interface  9 .  
         [0068]      FIG. 7  is a flowchart of a processing procedure for a process of the access point  11  according to the second embodiment receiving the packet from the router  10 .  
         [0069]     The wired-LAN interface  9  receives the packet from the router  10  (step S 301 ), and sends the received packet to the control unit  17  (step S 302 ). The transmission determining unit  17   a  determines a directional antenna to be used so that packet is sent alternately to the directional antenna  12  and the directional antenna  13  (step S 303 ). The wireless transmitting unit  17   b  sends the packet to the directional antenna determined by the transmission determining unit  17   a  (step S 304 ). The process indicated in  FIG. 7  is repeated every time the access point  11  receives the packet.  
         [0070]     By determining a directional antenna to be used so that the packet is sent alternately to the directional antenna  12  and the directional antenna  13  at step S 303 , if the directional antenna  12  is used at a previous time when the packet is sent, the directional antenna  13  is to be used next, and if the directional antenna  13  is used at the previous time when the packet is sent, the directional antenna  12  is to be used next.  
         [0071]     As described above, the access point  11  according to the second embodiment receives the packet from the router  10 , and the transmission determining unit  17   a  determines a directional antenna to be used so that the received packet will be sent alternately to the directional antenna  12  and the directional antenna  13 . The wireless transmitting unit  17   b  sends the packet to the directional antenna  12  or the directional antenna  13 , based on the determination made by the transmission determining unit  17   a . In other words, the terminal device cannot perform the data communication with the network unless it is located within the entire packet reception area  16 .  
         [0072]     As a result, the data communication area can be limited to a specific area by utilizing the directional antenna  12  and the directional antenna  13  alternately, and security can be improved in the wireless communication.  
         [0073]     The packet is used as an example in the second embodiment. However, the present invention is not limited to this scheme. The structure may be such that a piece of data having a predetermined size is received, the received data is divided, and the divided data is sent alternately to the directional antenna  12  and the directional antenna  13 .  
         [0074]      FIG. 8  is a schematic diagram for explaining a concept of an access point  20  according to a third embodiment of the present invention.  
         [0075]     The access point  20  is connected to a directional antenna  21  and a directional antenna  22 . The access point  20  is also connected to a network via a router (not shown).  
         [0076]     The access point  20  uses the directional antenna  21  but not the directional antenna  22  when performing a data communication relay between the router and a predetermined terminal device. Only when the packet passing the access point  20  reaches a predetermined size, the antenna is switched to the directional antenna  22 , and the directional antenna  21  is deactivated.  
         [0077]     In addition, when the packet passing the access point  20  reaches the predetermined size after the antenna in use is switched to the directional antenna  22 , the antenna is switched back to the directional antenna  21 , and the directional antenna  22  is inactivated.  
         [0078]     In other words, the directional antennas are switched every time the packet that passes the access point  20  reaches the predetermined size. Therefore, the terminal device can perform the data communication with the network only when it is positioned within a packet communication area  25  where a packet communication area  24  of the directional antenna  21  and a packet communication area  23  of the directional antenna  22  overlap each other.  
         [0079]      FIG. 9  is a functional block diagram of the access point  20  according to the third embodiment. The access point  20  is connected to the directional antenna  21 , the directional antenna  22 , and a router  10 .  
         [0080]     The access point  20  includes a control unit  26 . Since the rest of the structure and operation of the access point  20  is the same as the access point  1  described in the first embodiment, the same reference numerals is adopted for the same structural elements, and the explanation is omitted.  
         [0081]     The control unit  26  includes a data-size measuring unit  26   a , a wireless transmitting unit  26   b , and a wireless receiving unit  26   c . The data-size measuring unit  26   a  measures a size of the packet that is sent from the router  10  to the directional antenna  21  or the directional antenna  22  and a size of packet that is sent from the terminal device to the router  10 .  
         [0082]     The data-size measuring unit  26   a  sends a command to switch the directional antenna currently used each time the measured size of the packet reaches a predetermined level to the wireless transmitting unit  26   b  and the wireless receiving unit  26   c.    
         [0083]     The wireless transmitting unit  26   b  and the wireless receiving unit  26   c  use the directional antenna  21  at the beginning when carrying out the data transmission and reception between the terminal device and the router  10 . When receiving the command from the data-size measuring unit  26   a  to switch the directional antenna currently used, the wireless transmitting unit  26   b  and the wireless receiving unit  26   c  switch the antenna to the directional antenna  22 .  
         [0084]     In other words, the wireless transmitting unit  26   b  and the wireless receiving unit  26   c  use the directional antenna  22  when carrying out the data communication between the terminal device and the router  10 .  
         [0085]      FIG. 10  is a flowchart of a processing procedure for a process of the access point  20  according to the third embodiment receiving a packet from the router  10 . The process described in  FIG. 10  is repeated while the access point  20  is in operation.  
         [0086]     For the explanation of the process described in  FIG. 10 , a case where the access point  20  currently utilizes the directional antenna  21  will be used as an example.  
         [0087]     The wired-LAN interface  9  receives the packet from the router  10  (step S 401 ), and sends the received packet to the control unit  26  (step S 402 ).  
         [0088]     The wireless transmitting unit  26   b  sends the received packet to the directional antenna  21  via the input/output unit  7  (step S 403 ). The data-size measuring unit  26   a  determines whether a total size of the received packet received from the router  10  is equal to or larger than a predetermined level (step S 404 ).  
         [0089]     When the total size of the received packet is equal to or larger than the predetermined level (step S 404 , Yes), the data-size measuring unit  26   a  sends a command to switch the directional antenna to the wireless transmitting unit  26   b  and the wireless receiving unit  26   c , and the wireless transmitting unit  26   b  and the wireless receiving unit  26   c  switch the directional antenna to be used for packet transmission and reception (step S 405 ).  
         [0090]     On the other hand, when the total size of the received packet is smaller than the predetermined level (step S 404 , No), the process is terminated.  
         [0091]     This means that the access point  20  is configured to receive the packet from the router  10 , measure the size of the received packet, and switch the directional antenna in use whenever the measured size of the received packet is equal to or larger than the predetermined level.  
         [0092]      FIG. 11  is a flowchart of a processing procedure for a process of the access point  20  according to the third embodiment receiving a packet from the terminal device. The process described in  FIG. 11  is repeated during the operation of the access point  20 .  
         [0093]     To explain the process indicated in  FIG. 11 , the case where the access point  20  currently uses the directional antenna  21  is taken as an example.  
         [0094]     The wireless receiving unit  26   c  receives the packet sent from the terminal device via the input/output unit  7  by way of the directional antenna  21  (step S 501 ). The wireless receiving unit  26   c  sends the received packet to the router  10  via the wired-LAN interface  9  (step S 502 ), and the data-size measuring unit  26   a  determines whether the total size of the packet received from the terminal device is equal to or larger than the predetermined level (step S 503 ).  
         [0095]     When the total size of packet received from the terminal device is equal to or larger than the predetermined level (step S 503 , Yes), the data-size measuring unit  26   a  sends a command to switch the directional antenna the wireless transmitting unit  26   b  and the wireless receiving unit  26   c , and the wireless transmitting unit  26   b  and the wireless receiving unit  26   c  switch the directional antenna to be used for packet reception (step S 504 ).  
         [0096]     On the other hand, when the total size of the received packet is smaller than the predetermined level (step S 503 , No), the process is terminated.  
         [0097]     The access point  20  is configured to receive the packet from a specific terminal device, measure the size of the received packet, and switch the directional antenna currently used whenever the measured size of the packet is equal to or larger than the predetermined level.  
         [0098]     In the access point  20  according to the third embodiment, the data-size measuring unit  26   a  measures the size of the packet sent from the router  10  or the terminal device, and sends the command to switch the directional antenna for transmission and reception to the wireless transmitting unit  26   b  and the wireless receiving unit  26   c  whenever the measured total size of the packet is equal to or larger than the predetermined level.  
         [0099]     For this reason, it is essential that the terminal device be located within the packet communication area  25  to perform the data communication with the network. Hence, the data communication area can be limited to a predetermined area by alternating the directional antenna  21  and the directional antenna  22 , thereby improving security in the wireless communication.  
         [0100]     However, the present invention is not limited to this scheme, and the structure may be such that, for example, the data-size measuring unit  26   a  sends the command to switch the directional antenna for transmission and reception at predetermined time intervals.  
         [0101]      FIG. 12  is a schematic diagram for explaining a concept of an access point  30  according to a fourth embodiment of the present invention.  
         [0102]     The access point  30  is connected to a directional antenna  31  and a directional antenna  32 . The access point  30  is also connected to a network via a router (not shown).  
         [0103]     The access point  30  first utilizes the directional antenna  31  to register a media-access-control (MAC) address that identifies a terminal device included in a MAC-address-information collecting area  34 . The access point  30  detects the MAC address that identifies a terminal device to which or from which a packet is to be sent, when performing data communication between the router and the terminal device by way of the directional antenna  32 .  
         [0104]     Then, the access point  30  determines whether the same MAC address as the detected MAC address is registered. The access point  30  enables packet transmission and reception only when the same MAC address is registered.  
         [0105]     Thus, the terminal device cannot perform the data communication with the network unless it is located within a packet communication area  35  that covers the overlapping area of the MAC-address-information collecting area  34  and a packet communication area  33 .  
         [0106]      FIG. 13  is a functional block diagram of the access point  30  according to the fourth embodiment. The access point  30  is connected to the directional antenna  31 , the directional antenna  32 , and a router  10 .  
         [0107]     The access point  30  includes a control unit  36  and a storing unit  39 . Since the rest of the structure and operations of the access point  30  are the same as the access point  1  described in the first embodiment, the same reference numerals are adopted for the same structural elements, and the explanation is omitted.  
         [0108]     The control unit  36  includes a MAC-address processing unit  37  and a packet communicating unit  38 . The MAC-address processing unit  37  includes a MAC-address registering unit  37   a  and a MAC-address determining unit  37   b.    
         [0109]     The MAC-address registering unit  37   a  uses the directional antenna  31  to receive radio waves from the terminal device located in the MAC-address-information collecting area  34  and to detect the MAC address that identifies the terminal device. Then, the MAC-address registering unit  37   a  registers the detected MAC address and the time at which the MAC address is detected on a registered-MAC-address table  39   a  of the storing unit  39 .  
         [0110]     The registered-MAC-address table  39   a  stores a serial number, the MAC address, and the time at which the MAC address is detected, as shown in  FIG. 14 . The MAC-address registering unit  37   a  deletes a registered MAC address from the registered-MAC-address table  39   a  when a predetermined time has passed since the time at which the MAC address is detected.  
         [0111]     The MAC-address determining unit  37   b  detects the MAC address that identifies the terminal device to which or from which the packet is sent, based on the packet information sent from the router  10  or the terminal device. Then, the MAC-address determining unit  37   b  determines whether the detected MAC address is registered on the registered-MAC-address table  39   a . The packet transmission is permitted only when the detected MAC address is registered on the registered-MAC-address table  39   a.    
         [0112]     The packet communicating unit  38  sends the received packet information to the MAC-address determining unit  37   b  when receiving the packet from the router  10  or the terminal device. When the MAC-address determining unit  37   b  permits the packet transmission, the packet communicating unit  38  sends the packet to the directional antenna  32  or the router  10 .  
         [0113]     An explanation will be given for a process where the access point  30  registers the MAC address that identifies the terminal device included in the MAC-address-information collecting area  34 .  FIG. 15  is a flowchart of a processing procedure for the access point  30  according to the fourth embodiment registering the MAC address of the terminal device.  
         [0114]     The directional antenna  31  receives radio waves from the terminal device (step S 601 ). The MAC-address registering unit  37   a  receives the radio waves via the input/output unit  7  and the packet communicating unit  38 , and detects the MAC address from the received radio waves (step S 602 ).  
         [0115]     The MAC-address registering unit  37   a  determines whether the detected MAC address is registered on the registered-MAC-address table  39   a  (step S 603 ). If the detected MAC address is registered on the registered-MAC-address table  39   a  (step S 603 , Yes), the time corresponding to the detected MAC address is updated to the latest time at which MAC address is detected (step S 604 ).  
         [0116]     On the other hand, if the detected MAC address is not registered on the registered-MAC-address table  39   a  (step S 603 , No), the detected MAC address and the time at which the MAC address is detected are registered onto the registered-MAC-address table  39   a  (step S 606 ).  
         [0117]      FIG. 16  is a flowchart of a processing procedure for the access point  30  according to the fourth embodiment sending a packet from the terminal device to the router  10 .  
         [0118]     The packet communicating unit  38  receives the packet by way of the directional antenna  32  (step S 701 ), and sends packet information to the MAC-address determining unit  37   b . Then, the MAC-address determining unit  37   b  detects the MAC address from the received packet information (step S 702 ).  
         [0119]     The MAC-address determining unit  37   b  determines whether the detected MAC address is registered on the registered-MAC-address table  39   a  (step S 703 ). If the detected MAC address is not registered on the registered-MAC-address table  39   a  (step S 703 , No), the MAC-address determining unit  37   b  sends a command to abandon the packet to the packet communicating unit  38  (step S 704 ).  
         [0120]     On the other hand, if the detected MAC address is registered (step S 703 , Yes), the MAC-address determining unit  37   b  updates the time on the registered-MAC-address table  39   a  to the latest time at which the MAC address is detected (step S 705 ).  
         [0121]     The MAC-address determining unit  37   b  allows the packet communicating unit  38  to send the packet (step S 706 ), and the packet communicating unit  38  sends the packet via the wired-LAN interface  9  to the router  10  (step S 707 ).  
         [0122]     When receiving the packet from the terminal device by way of the directional antenna  32 , the access point  30  determines whether the packet should be sent to the router  10 , based on the registered-MAC-address table  39   a  and the MAC address that identifies the terminal device from which the packet is sent. In other words, the MAC-address determining unit  37   b  permits the packet transmission only when the MAC address that identifies the sender terminal device is registered on the registered-MAC-address table  39   a.    
         [0123]      FIG. 17  is a flowchart of a processing procedure for the access point  30  according to the fourth embodiment sending a packet from the router  10  to the terminal device.  
         [0124]     The packet communicating unit  38  receives the packet from the router  10  via the wired-LAN interface  9  (step S 801 ). The packet communicating unit  38  sends the packet information to the MAC-address determining unit  37   b . The MAC-address determining unit  37   b  detects the MAC address of the sender from the packet information (step S 802 ), and determines whether the detected MAC address is registered on the registered-MAC-address table  39   a  (step S 803 ).  
         [0125]     If the detected MAC address is not registered on the registered-MAC-address table  39   a  (step S 803 , No), the MAC-address determining unit  37   b  sends a command to abandon the packet to the packet communicating unit  38  (step S 804 ).  
         [0126]     On the other hand, if the detected MAC address is registered on the registered-MAC-address table  39   a  (step S 803 , Yes), the MAC-address determining unit  37   b  updates the time on the registered-MAC-address table  39   a  to the latest time at which the MAC address is detected (step S 805 ).  
         [0127]     Then, the MAC-address determining unit  37   b  allows the packet communicating unit  38  to send the packet (step S 806 ), and the packet communicating unit  38  sends the packet via the input/output unit  7  to the directional antenna  32  (step S 807 ).  
         [0128]     When receiving the packet from the router  10 , the access point  30  determines whether the packet should be sent to the directional antenna  32 , based on the registered-MAC-address table  39   a  and the MAC address that identifies the terminal device to which the packet is sent. In other words, the MAC-address determining unit  37   b  permits the packet transmission only when the MAC address that identifies the destination terminal device is registered on the registered-MAC-address table  39   a.    
         [0129]      FIG. 18  is a flowchart of a processing procedure for a MAC-address registering unit  37   a  updating the registered-MAC-address table  39   a.    
         [0130]     The MAC-address registering unit  37   a  detects the MAC address and the time at which the MAC address is detected from the registered-MAC-address table  39   a  (step S 901 ), and determines whether a predetermined time has passed since the time at which the MAC address is detected (step S 902 ). If the predetermined time has passed since the time (step S 902 , Yes), the MAC-address registering unit  37   a deletes the detected MAC address (step S 903 ), and checks whether all the times and MAC addresses have been detected (step S 904 ).  
         [0131]     On the other hand, if the predetermined time has not passed since the time (step S 902 , No), the MAC-address registering unit  37   a  equally checks whether all the times and MAC addresses have been detected (step S 904 ).  
         [0132]     If all the MAC addresses and times have not yet been detected (step S 904 , No), the process proceeds to step S 901 , otherwise (step S 904 , Yes), the process is terminated.  
         [0133]     As described above, in the access point  30  according to the fourth embodiment, the MAC-address registering unit  37   a  registers in advance the MAC address that identifies the terminal device located in the MAC-address-information collecting area  34 , by way of the directional antenna  31 .  
         [0134]     The MAC-address determining unit  37   b  determines whether the MAC address that identifies the destination terminal device to which the packet that are sent from the router  10  or the sender terminal device from which the packet is sent is registered on the registered-MAC-address table  39   a , and allows the packet communicating unit  38  to send or receive the packet only when the registration is completed.  
         [0135]     In other words, the terminal device needs to be located in the packet communication area  35  where the MAC-address-information collecting area  34  and the packet communication area  33  overlap each other, to have the data communication with the network. The user can limit the data communication area of the terminal device by adopting the directional antenna  31  and the directional antenna  32 , thereby improve security in the wireless communication.  
         [0136]     Although the directional antenna  31  is utilized to receive the MAC address that identifies the terminal device while the directional antenna  32  is utilized to send the packet to and receive the packet from the terminal device according to the fourth embodiment, the structure may be designed such that the directional antenna  31  is utilized for the packet transmission and reception with the terminal device while the directional antenna  32  is utilized for reception of the MAC address that identifies the terminal device.  
         [0137]      FIG. 19  is a schematic diagram for explaining a concept of an access point  40  according to a fifth embodiment of the present invention.  
         [0138]     The access point  40  is connected to a directional antenna  41 , a directional antenna  42 , and a nondirectional antenna  43 . The packet transmission and reception is enabled in a predetermined area and in a 360-degree field in a lateral direction by incorporating the nondirectional antenna  43  to the structure. The access point  40  is also connected to a network via a router (not shown).  
         [0139]     The access point  40  receives radio waves in advance from a terminal device located in a MAC-address-information collecting area  44  by way of the directional antenna  41  and the directional antenna  42 , detects the MAC address that identifies the terminal device from the received radio waves, and registers the detected MAC address.  
         [0140]     When receiving the packet sent from the router or the terminal device, the access point  40  detects the MAC address of the terminal device from which or to which the packet is sent, and permits the packet transmission and reception with the terminal device by way of the nondirectional antenna  43  only when the detected MAC address is not registered.  
         [0141]     Thus, the terminal device can achieve the data communication with the network only when the terminal device is located within a packet communication area  45  that does not overlap with the MAC-address-information collecting area  44 .  
         [0142]      FIG. 20  is a functional block diagram of the access point  40  according to the fifth embodiment. The access point  40  is connected to the directional antenna  41 , the directional antenna  42 , the nondirectional antenna  43 , and a router  10 .  
         [0143]     The access point  40  includes a control unit  46 . Since the rest of the structure and operations of the access point  40  is the same as the access point  30  described according to the fourth embodiment, the same reference numerals are assigned to the same structural elements, and the explanation is omitted.  
         [0144]     The control unit  46  includes a MAC-address processing unit  47  and a packet communicating unit  48 . The MAC-address processing unit  47  includes a MAC-address registering unit  47   a  and a MAC-address determining unit  47   b.    
         [0145]     The MAC-address registering unit  47   a  receives radio waves from the terminal device included in the MAC-address-information collecting area  44  by way of the directional antenna  41  and the directional antenna  42 , and detects the MAC address that identifies the terminal device. Then, the MAC-address registering unit  47   a  registers the detected MAC address and the time at which the MAC address is detected on the registered-MAC-address table  39   a  of the storing unit  39 . The MAC-address determining unit  47   b  detects the MAC address that identifies the terminal device from which or to which the packet is sent, from the packet information sent from the router  10  or the terminal device. Then, the MAC-address determining unit  47   b  determines whether the detected MAC address is registered on the registered-MAC-address table  39   a , and permits the packet transmission and reception by way of the nondirectional antenna  43  only when the detected MAC address is not registered on the registered-MAC-address table  39   a.    
         [0146]     When receiving the packet from the router  10  or the terminal device, the packet communicating unit  48  sends the received packet information to the MAC-address determining unit  47   b . The packet communicating unit  48  then sends the packet to the nondirectional antenna  43  or the router  10  when the MAC-address determining unit  47   b  permits the packet transmission and reception.  
         [0147]     As described above, in the access point  40  according to the fifth embodiment, the MAC-address registering unit  47   a  registers in advance the MAC address that identifies the terminal device located in the MAC-address-information collecting area  44  by way of the directional antenna  41  and the directional antenna  42 . The MAC-address determining unit  47   b  determines whether the same MAC address as the MAC address of the destination terminal device to which the packet is sent or the sender terminal device from which the packet is sent is registered on the Registered-MAC-address table  39   a.    
         [0148]     The MAC-address determining unit  47   b  permits the packet transmission and reception only when the detected MAC address is not registered on the Registered-MAC-address table  39   a , and the packet communicating unit  48  sends and receives the packet by way of the nondirectional antenna  43 .  
         [0149]     In other words, the terminal device needs to be included in the packet communication area  45  that does not overlap with the MAC-address-information collecting area  44 . Thus, the user can limit the data communication area of the terminal device by adopting the directional antenna  41 , the directional antenna  42 , and the nondirectional antenna  43 , and improve security in the wireless communication.  
         [0150]     As explained above, according to the present invention, the terminal device can perform the wireless communication with the wired-network only in the overlapping area of the transmission enabled area and reception enabled area, while the wireless communication with the wired-network is not permitted in an area other than the overlapping area. Therefore, the present invention has an advantage that the wirelessly communication area can be limited to a predetermined area, and that security can be improved in the wireless communication.  
         [0151]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.