Abstract:
A situation is circumvented where wireless communication becomes impossible in a wireless LAN system under the influence of a blocking object, noise caused by an electromagnetic wave, or the like. A wireless LAN system comprises: a relay which can communicate with an external system; a master which can communicate with the relay; and a plurality of slaves which can wirelessly communicate with the master, the plurality of slaves including a first group and a second group, the first group comprising an alternative slave having a function of transmitting, when a portion of the slaves cannot receive a synchronization signal from the master, an information signal received from the master to the portion of slaves, and the second group comprising non-alternative slaves and not having the function of transmitting the information signal to the portion of slaves.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation application of copending U.S. patent application Ser. No. 12/599,104, filed Nov. 25, 2009, entitled “Wireless Local Area Network (LAN) System”, which is herein incorporated by reference, which is a National Stage application of International Application PCT/JP2008/057532, filed Apr. 17, 2008. This application claims priority under 35 U.S.C. §120 of U.S. patent application Ser. No. 12/599,104, filed Nov. 25, 2009 and of International Application PCT/JP2008/057532, filed Apr. 17, 2008. This application further claims priority under 35 U.S.C. §119 of Japanese Application 2007-123906, filed May 8, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to a wireless local area network (LAN) system. More specifically, the present invention relates to a LAN system in a relatively small space such as a home or office. 
       BACKGROUND ART 
       [0003]    In recent years, IEEE 802.11a/g/b-based wireless LANs have become common for home use. Higher speed wireless standards are also under development. In the industry, there are trends to place wireless LANs as home network infrastructure by the distribution of AV streams using a high-speed wireless LAN, a home security sensor (glass breakage detection) using the easiness of wireless installation, and the like. 
         [0004]    Meanwhile, due to characteristics of radio waves, wireless LANs are susceptible to blocking objects, noise caused by electromagnetic waves, and the like. Particularly, millimeter waves, UWB, etc., for high-speed wireless LANs are susceptible to obstacles and the like. In order to spread high-speed wireless LANs as home network infrastructure, there is a need to take measures against such interference. 
         [0005]    However, wireless LANs are premised on an ad-hoc connection (which is not continuous communication but a dynamic network connection). Thus, wireless disconnection is not recognized as an abnormal condition. The IEEE 802.15.3 standard and the like do not even consider a mechanism for treating wireless disconnection as an abnormal condition. Also, there is no mechanism for notifying communication disconnection in a wireless network layer. Particularly, in the case of a network where a wired portion is tunneled (an IP packet or Ethernet frame is encapsulated), a device on the Ethernet side considers wireless disconnection as an unexplained communication failure. 
         [0006]    The development of the high-speed wireless LAN is still at an experimental stage towards the practical use. In current measures, circumventing measures from the viewpoint of devising strategies for prevention of radio interference, such as “sending radio waves from a location with a clear view using a waveguide” or “appropriately adjusting an output” is mainstream. 
         [0007]    As a conventional technique, Japanese Unexamined Patent Publication (Kokai) No. 2004-282758 discloses a method in which, in a wireless network which is controlled by a single controller, when the controller breaks down (or stops) the controller is switched to an alternative controller and network control is performed using the alternative controller, whereby the wireless network is maintained. However, this method is not to circumvent a situation where wireless communication becomes difficult under the influence of a blocking object, noise caused by an electromagnetic wave, or the like. 
       SUMMARY 
       [0008]    It is an object of the present invention to automatically maintain a communication service when radio interference occurs in a wireless LAN system. 
         [0009]    It is another object of the present invention to circumvent a situation where wireless communication becomes impossible in a wireless LAN system under the influence of a blocking object, noise caused by an electromagnetic wave, or the like. Note that the expression “wireless communication becomes impossible” as used herein involves not only the case where communication cannot be performed at all but also the case in which communication cannot be performed stably (e.g., the case in which communication frequently or intermittently is lost). 
         [0010]    According to one embodiment of the present invention, there is provided a wireless LAN system comprising: a relay which can communicate with an external system; a master which can communicate with the relay; and a plurality of slaves which can wirelessly communicate with the master, the plurality of slaves including a first group and a second group, the first group comprising an alternative slave having a function of transmitting, when a portion of the slaves cannot receive a synchronization signal from the master, an information signal received from the master to the portion of slaves, and the second group including non-alternative slaves not having the function of transmitting the information signal to the portion of slaves. 
         [0011]    According to another embodiment of the present invention, there is provided a wireless communication method between a master and a plurality of slaves which are included in a wireless LAN system, comprising the steps of: transmitting a first synchronization signal to the plurality of slaves from the master; transmitting a first received signal to the master from a slave having received the first synchronization signal; sending a second synchronization signal from a specific slave among the plurality of slaves to other slaves; transmitting a second received signal to the specific slave from slaves having received the second synchronization signals; transmitting an information signal to the specific slave from the master; and transmitting the information signal from the specific slave to a slave not having sent a first received signal among the slaves having received the second synchronization signals. 
         [0012]    According to an embodiment of the present invention, even when communication becomes impossible between a master and a portion of slaves in a wireless LAN system due to wireless communication failure caused by an obstacle, noise, or the like, an alternative communication route between the master and the portion of slaves can be automatically secured. 
         [0013]    According to an embodiment of the present invention, when communication becomes impossible between a master and a portion of slaves in a wireless LAN system due to wireless communication failure caused by an obstacle, noise, or the like, a specific slave among slaves automatically substitutes for (relays) the master, whereby the communication between the master and the portion of slaves can be maintained. 
         [0014]    According to an embodiment of the present invention, when wireless communication failure caused by an obstacle, noise, or the like in a wireless LAN system is removed, the communication route can automatically revert to the one used before occurrence of the failure. 
         [0015]    According to and embodiment of the present invention, regardless of occurrence of wireless communication failure caused by an obstacle, noise, or the like in a wireless LAN system, a communication (service) between a master and slaves can be maintained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a diagram showing a basic configuration of a LAN packet communication system using a normal PICONET, according to the present invention; 
           [0017]      FIG. 2  is a diagram showing a system configuration in the present invention; 
           [0018]      FIG. 3  is a diagram showing a system configuration (before occurrence of failure) in the present invention; 
           [0019]      FIG. 4  is a diagram showing a system configuration (immediately after occurrence of failure) in the present invention; 
           [0020]      FIG. 5  is a diagram showing a system configuration (a state showing securing of an alternative route after occurrence of failure) in the present invention; 
           [0021]      FIG. 6  is a diagram showing a switching table and a connection table which are included in a PNC; 
           [0022]      FIG. 7  is a diagram showing a table for the case in which a DEV-B (# 5 ) in  FIG. 2  is registered as IP# 5 ; 
           [0023]      FIG. 8  is a diagram showing a table for the case in which a DEV-B (# 4 ) in  FIG. 2  is registered as IP# 4 ; 
           [0024]      FIG. 9  is a diagram showing a state in which, after # 4  in  FIG. 8  is recognized, DEVs-B with # 3  and # 6  are further connected; 
           [0025]      FIG. 10  is a diagram showing a state in which connections between the DEVs-B (# 3  and # 4 ) and the PNC are disconnected; 
           [0026]      FIG. 11  is a diagram showing a state in which a connection between the DEV-B (# 3 ) and the PNC is secured by an alternative route via a DEV-A (# 1 ); and 
           [0027]      FIG. 12  is a diagram showing a state in which the interference is removed and the original connection between the DEV-B (# 3 ) and the PNC is recovered. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The present invention will be described below with reference to the drawings. The following description is premised on the use of PICONET based on the IEEE 802.15.3 standard. However, the present invention is not limited to this premise and other standards, methods, or the like, can of course be used. 
         [0029]    In one embodiment of the present invention, a system for transmitting and receiving LAN packets in an IEEE 802.15.3 PICONET is assumed. PICONET refers to a wireless communication subnet defined by IEEE 802.15.3. In the present embodiment, the following contents (A and B) are disclosed. Note that a ChildPICONET which appears below refers to the minimum unit of a network defined by IEEE 802.15.3. 
         [0030]    A. System for dynamically securing another route using a ChildPICONET, when a failure (wireless disconnection) occurs
       (a-1) System configuration for securing another route during failure (wireless disconnection)   (a-2) Method for detecting occurrence of failure (wireless disconnection), by each device in the system   (a-3) Method for selecting another route   (a-4) Method for detecting recovery from failure and reverting to the original route       
 
         [0035]    B. Method for recognizing, in a wireless layer, occurrence of failure in a wireless portion between specific devices and alerting notified failure 
         [0036]      FIG. 1  shows a basic configuration of a LAN packet communication system using a PICONET, according to the present invention. In this configuration, a PNC (PICONET coordinator)  10  for controlling a PICONET is wirelessly connected to a plurality of DEVs (DEVices)  20  and a LAN packet is tunneled (or protocol-converted). The PNC  10  is connected to an external system via a relay (not shown). In optical communication (FTTH), a relay includes a converter for converting light into an electrical signal (millimeter wave or the like). A line  30  between the PNC  10  and each DEV  20  means the presence of a wireless communication route. The meaning of the lines  30  is also the same in other drawings. IP# 1  to IP# 4  represent LAN devices (PCs, various household electrical appliances, or the like) assigned to the respective DEVs. At the same time, IP#n also represents an Ethernet MAC address or an IP address of an IP packet, which corresponds to each device. The meaning of IP#n is also the same in other drawings. 
         [0037]    IEEE 802.15.3 defines that devices in a PICONET can mutually communicate. In communication that provides an Internet connection to a home, communication between DEVs also uses a route of DEV→PNC→DEV for the following reasons:
       (a) a PNC is only one gateway to the Internet; and   (b) the DEVs are not always installed in communicable areas.   Although the connection to the PICONET is ad hoc, a route of a LAN packet is configured by a combination of DEVs and the PNC. In order to expand a wireless coverage, IEEE 802.15.3 also defines that a child PICONET can be used.       
 
         [0041]    A. System for dynamically securing another route when a failure (wireless disconnection) occurs
       (a-1) System configuration for securing another route during failure (wireless disconnection)     FIG. 2  shows a system configuration in the present invention for securing another route during failure (wireless disconnection). There is one PNC  100 . DEVs are of two types: DEV-A and DEV-B. DEV-As  110  have the function of becoming a PNC of a child PICONET. DEVs-B  120  do not have the function of becoming a PNC.       
 
         [0044]    Referring to  FIGS. 3 to 5 , a process flow performed during failure (wireless disconnection) is shown below.
       (1) In  FIG. 3 , in one PICONET which is normally managed by a PNC  100 , the PNC  100 , DEVs-A, and DEVs-B perform wireless communication. Specifically, LAN packet communication is performed with LAN devices (IP#n). In  FIG. 3 , for example, the PNC  100  communicates with IP# 3  of a DEV-B  122 .   (2) In  FIG. 4 , when an obstacle  200  or the like is placed, some DEVs-B become unable to communicate with the PNC  100 . In  FIG. 4 , two DEVs-B, i.e., a DEV-B  122  (IP# 3 ) and a DEV-B  124  (IP# 4 ), cannot communicate with the PNC  100 .   (3) In  FIG. 5 , a DEV-A  112  which has detected a failure (wireless disconnection) operates as an alternative PNC and creates a child PICONET. In  FIG. 5 , the DEV-B  122  (IP# 3 ) and the DEV-B  124  (IP# 4 ) which have become unable to communicate with the PNC  100  switch their connections to the DEV-A  112  (PNC). LAN packets are transmitted through an alternative route of PNC  100 -DEV-A  112 -DEV-B  122 / 124 .   (4) When the failure is removed, the route reverts to the original one shown in  FIG. 3 .       
 
         [0049]    The operation of the system in the present invention exemplified in  FIGS. 2 to 5  has the following two features.
       (1) In a conventional method for selecting an alternative route for a network failure, complex routing information exchange based on a routing protocol is performed. In the present invention, however, only by multicasting by a device a packet for notifying other devices of its presence, switching to an alternative route is performed. The method of the present invention is different from a conventional one in which the load of routing information exchange is heavy and a route request is made during failure, and thus, fast switching to an alternative route is performed.   (2) In the present invention, handling devices that require a static connection in distinction from devices (ad hoc) that do not require a static connection can prevent an increase in system load caused by activation of an unnecessary alternative route.       
 
         [0052]    (a-2) Method for detecting occurrence of failure (wireless disconnection), by each device in the system
       The PNC periodically sends a beacon (synchronization signal) to inform each DEV of its presence. Sending of a beacon is performed based on IEEE 802.15.3. DEVs-A periodically transmit a “static connection info” packet. The PNC has (a) switching table and (b) connection table shown in  FIG. 6 , in order to manage a connection relationship with each DEV. In (b) connection table in  FIGS. 6 , # 1  and # 2  are entered as DEVs (DEVs-A) of type A. The term “static” in (b) connection table refers to a static connection. (# 2 ) and (# 1 ) shown next to the terms “static” respectively indicate that the DEV-A (# 1 ) can see (communicate with) the DEV-A (# 2 ) and vice versa. If the PNC does not receive a “static connection info” packet for a certain period of time, the PNC determines that the DEVs-A cannot be seen.       
 
         [0054]    Among DEVs of type B, a DEV-B that requires a static connection periodically multicasts a “static connection info” packet. The “static connection info” packet is the same as the one used to verify the presence of a DEV-A.  FIG. 7  shows a table for the case in which a DEV-B (# 5 ) in  FIG. 2  is registered as IP# 5 . (b) connection table in  FIG. 7  shows that the DEV-B with # 5  is static and can be connected to the DEVs-A with # 1  and # 2 . 
         [0055]    A DEV-B that does not require a static connection, i.e., a DEV-B using an ad-hoc connection, does not multicast a “static connection info” packet. This DEV-B operates as defined in IEEE 802.15.3.  FIG. 8  shows a table for the case in which a DEV-B (# 4 ) in  FIG. 2  is registered as IP# 4 . In (b) connection table in  FIG. 8 , information that the DEV-B with # 4  is ad hoc is entered. As such, by using a connection table, even when both static and ad-hoc devices are present, the devices can be appropriately managed. 
         [0056]    (a- 3 ) Method for selecting another route
       A selection of another route is performed in the manner shown below using switching tables managed by PMC/DEV-A.   (1) In  FIG. 9 , in a normal state, based on (b) switching table of the PNC  100 , a LAN packet is encapsulated by a protocol of a wireless portion to perform tunneling.  FIG. 9  shows a state in which, after # 4  in  FIG. 8  is recognized, DEVs-B with # 3  and # 6  are further connected.   (2) In  FIGS. 10 and 11 , it is assumed that connections between the DEVs-B (# 3  and # 4 ) and the PNC  100  are disconnected, for example.   2-1) The DEV-B  124  with # 4  that does not require a static connection closes its connection as defined in IEEE 802.15.3.   2-2) The DEV-B  122  with # 3  that requires a static connection is connected to the DEV-A  112  which is an alternative PICONET (child PICONET managed by # 1 ).   2-3) The DEV-A (# 1 )  112  registers IP# 3  in (a) switching table included in # 1 .   2-4) The DEV-A (# 1 )  112  notifies the PNC (# 0 )  100  that # 3  is connected to the DEV-A (# 1 )  112  as an alterative path (a process of this notification by # 0  is asynchronous).   2-5) The PNC  100  having detected the disconnection from # 3  and # 4  deletes information on # 3  and # 4  from (b) switching table ( FIG. 10 ).   2-6) When a LAN packet destined for # 3  arrives, the PNC  100  broadcasts the LAN packet throughout the PICONET.   2-7) The DEV-A (# 1 ) receives the LAN packet and transmits the LAN packet to # 3  registered in the switching table of # 1 .   2-8) The DEV-B (# 3 ) send/receives the LAN packet through an alternative route of # 0 &lt;-&gt;# 1 &lt;-&gt;# 3 .   (3) When a process by # 1  in the above 2-4) ends, information indicating that data to # 3  is transmitted via # 1  (DEV# 1 ) is registered in (b) switching table ( FIG. 11 ) of the PNC (# 0 )  100 . After this, when a LAN packet destined for # 3  arrives, the PNC  100  unicasts the LAN packet to the DEV-A (# 1 ).       
 
         [0069]    (a-4) Method for detecting recovery from failure and reverting to the original route
       In  FIG. 12 , the DEV-B (# 3 )  122  using the alternative route monitors resumption of a beacon from the PNC  100 . When a beacon is resumed by removal of the obstacle, for example, the connection of the DEV-B (# 3 )  122  to the PNC  100  reverts. The contents of the switching tables of the PNC  100  and the DEV-A (# 1 )  112  are reset to normal and transmission and reception of a LAN packet using the original route are performed.       
 
         [0071]    For a method for recognizing, in a wireless layer, occurrence of failure in a wireless portion and alerting notified failure, first, whether a connection request by each DEV is static or ad hoc is managed using a connection table. When a situation different from a normal one occurs, the PNC or a DEV provides a notification. The notification is performed by an email, sound, phone call, or the like. Information that a notification is being provided is entered in and managed by the connection table. 
         [0072]    A PNC of the present invention operates as a PC based dedicated device, for example, by SW which operates thereon. A DEV-A of the present invention is installed in a room, for example, so as to be seen from a plurality of DEVs-B and the PNC (in a wirelessly communicable manner). A DEV-A is provided as a box-type device having an Eth/millimeter-wave interface, for example. Such a device can incorporate embedded software (SW) for implementing a method of the present invention. The device is operated based on some kind of embedded OS and functions as a driver for operating hardware (HW) of the Eth/millimeter-wave interface included in the device. 
         [0073]    When a DEV-B of the present invention is a terminal personal computer (PC), for example, the DEV-B is operated by software which is supplied with a millimeter-wave wireless LAN card. Alternatively, when the DEV-B is an external device (when the DEV-B is a LAN-compatible security device or household electrical appliance which cannot expand a card as in a PC), the DEV-B is operated by embedded SW which operates in a box-type device, as with the DEV-A. 
         [0074]    The present invention has been described with reference to the drawings. However, the present invention is not limited to the above-described embodiment. It will be obvious to those skilled in the art that modifications may be made to the embodiment without departing from the spirit and scope of the present invention.