Abstract:
A wireless communication system including first and second wireless devices, and first and second access points to synchronize the first and second wireless devices, wherein the first access point determines whether the second access point exists in a neighboring area, periodically checks communication states of the second access point, sends an access point replacement command to the second wireless device linked to the second access point in response to determining the second access point is communication-disabled, and forms a new communication channel with the second wireless device according to an association request signal received from the second wireless device in response to the access point replacement command.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 2003-50245, dated Jul. 22, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a wireless communication system and a method thereof, and, more particularly, to a wireless communication system and a method thereof in wireless infrastructure networking environments.  
         [0004]     2. Description of the Related Art  
         [0005]     Recently, wireless networking environments, together with wireless communication technology developments, have become widespread in everyday life. For example, as an alternative technology for a conventional wired LAN, Wireless Local Area Network (WLAN) technologies such as IEEE 802.11 are being used more and more. The IEEE stands for the Institute of Electrical and Electronics Engineers.  
         [0006]     The IEEE 802.11 wireless LAN features the use of a wireless Radio Frequency (RF) technology using the 2.4 GHz band called the “Industrial Scientific Medical(ISM) band,” instead of the use of cable, thereby enabling the networking capability to be equal to that of the wired LAN. There are two transmission modes of infrastructure networking and Ad-hoc networking for the IEEE 802.11 wireless LAN. Here, the Ad-hoc mode, in which a network is constructed with only devices mounting a wireless LAN therein, is not connected to external networks. That is, communications are performed among the wireless LAN devices in the Ad-hoc mode, so that the Ad-hoc mode is used for small-sized offices or small-scaled networks.  
         [0007]     The infrastructure mode can be used in offices with environments that are equal to that of the existing wired LAN, and wireless networks for the infrastructure mode are constructed with access points, which are wired/wireless interfacing devices, connected to wired networks (Ethernets). An access point serves as a bridge between a wireless LAN device and a wired LAN device, enabling mutual data transmissions and receptions.  
         [0008]     A wireless device has to exist in a wireless communication range of an access point to communicate with wired devices through the access point, and has the same ID as a basic service set identifier (BSSID) and a service set identifier (SSID) assigned to the access point. To do so, the wireless device receives a beacon frame that an access point periodically sends when a wireless LAN channel is changed. The wireless device, having received the beacon frame, sends a response message for an association request to the access point sending the beacon frame.  
         [0009]     The access point, having received the association request from the wireless device, sends an association response message to the corresponding wireless device, including a BSSID and an SSID assigned to the access point. The wireless device receives and registers the association response message for its own network information, so that a communication channel is linked between the access point and the wireless device.  
         [0010]     If a communication channel is linked between an access point and a wireless device, the wireless device can form one network with wired devices through the access point, and share the network resources. However, if the access point does not perform normal operations due to system defects such as a system failure, wireless devices connected to the access point cannot participate in the network any more. In this case, the wireless devices connected to the access point temporarily stop their data transmission/reception operations, and wait for an arbitrarily set period of time. Thereafter, the wireless devices attempt to associate with the access point, but cannot connect to the corresponding network until the access point performs its normal operations. Accordingly, there exists a problem in that the communication efficiency between the wireless devices and the access point is reduced.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention has been devised to solve the above and/or other problems, so it is an aspect of the present invention to provide a wireless communication system, and a method thereof, capable of, in a case in which a wireless device cannot connect to an associated access point in a wireless infrastructure networking environment, transferring the wireless devices associated with the failed access point to a different access point.  
         [0012]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
         [0013]     In order to achieve the above aspect, a wireless communication system, according to an embodiment of the present invention, comprises first and second wireless devices; and first and second access points to synchronize the first and second wireless devices, wherein the first access point determines whether the second access point exists in a neighboring area, periodically checks communication states of the second access point, sends an access point replacement command to the second wireless device linked to the second access point in response to determining the second access point is communication-disabled, and forms a new communication channel with the second wireless device according to an association request signal received from the second wireless device in response to the access point replacement command.  
         [0014]     The access point may include a wireless transmission/reception unit to communicate with the first wireless device and the second wireless device; a storage unit to store information regarding the second access point; and a control unit to determine whether the second access point exists in the neighboring area, store in the storage unit the information regarding the second access point, periodically check the communication states of the second access point with reference to the stored information, send the access point replacement command through the wireless transmission/reception unit, and form the communication channel with the second wireless device.  
         [0015]     The information on the second access point may include media access control (MAC) address information and network address information.  
         [0016]     The control unit may determine whether a beacon frame is received through the wireless transmission/reception unit, and then determine whether the second access point exists in the neighboring area.  
         [0017]     The wireless communication system may further comprise a signal level detection unit to detect a level of a signal received through the wireless transmission/reception unit, wherein the control unit determines the second access point exists in the neighboring area in response to the signal level of the beacon frame being more than a predetermined value.  
         [0018]     A communication method for a wireless communication system having first and second wireless devices and first and second access points to synchronize the first and second wireless devices, according to an embodiment of the present invention, may comprise determining whether the second access point exists in a neighboring area of the first access point, and storing information on the second access point; periodically checking communication states of the second access point, and sending an access point replacement command to the second wireless device linked to the second access point in response to determining the second access point to be in a communication-disabled state; and forming a communication channel with the second wireless device according to an association request signal received from the second wireless device in response to the access point replacement command.  
         [0019]     The information on the second access point may include MAC address information and network address information.  
         [0020]     The determining whether a second access point exists in the neighboring area of the first access point may comprise determining whether a beacon frame is received through a wireless communication channel.  
         [0021]     The forming the new communication channel with the second wireless device may include broadcasting the association request signal to the second access point; determining the communication states of the second access point according to whether an association response signal is received from the second access point; and sending the access point replacement command to the second wireless device in response to the second access point being determined to be in the communication-disenabled state. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0023]      FIG. 1  is a diagram illustrating a wireless communication system in wireless infrastructure networking environments according to an embodiment of the present invention;  
         [0024]      FIG. 2  is a block diagram illustrating an access point such as shown in  FIG. 1 ;  
         [0025]      FIG. 3  is a block diagram illustrating a wireless device such as shown in  FIG. 1 ; and  
         [0026]      FIG. 4  to  FIG. 6  are flow charts illustrating communication processes for the wireless communication system according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0028]      FIG. 1  is a diagram illustrating a wireless communication system in wireless infrastructure networking environments according to an embodiment of the present invention.  
         [0029]     Referring to  FIG. 1 , wireless devices  1 ,  2 ,  3 , and  4  construct one network with an access point AP 1 , and wireless devices  5 ,  6 , and  7  construct another network with an access point AP 2 . The AP 1  and AP 2  are connected through a wired LAN  100 , and act as a bridge connecting wired devices connected through the wired LAN  100  and the wireless devices  1  to  7 . Reference letters A and B denote a wireless communication range of the AP 1  and AP 2 , respectively, in  FIG. 1 .  
         [0030]     The wireless devices  1  to  4  connected to the AP 1  have the same IDs as the BSSID and SSID assigned to AP 1 , and can communicate with wired devices through the AP 1  only. The wireless devices  5  to  7  connected to the AP 2  have the same IDs as the BSSID and SSID assigned to the AP 2 , and can communicate with the wired devices through the AP 2  only.  
         [0031]      FIG. 2  is a block diagram illustrating an access point such as shown in  FIG. 1 .  
         [0032]     Referring to  FIG. 2 , an access point  200  has a control unit  210 , a wireless transmission/reception unit  220 , a wired transmission/reception unit  230 , a storage unit  240 , and a signal level detection unit  250 .  
         [0033]     The wireless transmission/reception unit  220  provides a communication interface between the control unit  210  and a wireless LAN device. That is, the wireless transmission/reception unit  220  receives data packets sent from a wireless LAN device through an antenna, or transmits data packets to the wireless LAN device through the antenna.  
         [0034]     The wired transmission/reception unit  230  provides a communication interface between the control unit  210  and a wired LAN device. That is, the wired transmission/reception unit  230  controls data packet transmissions and receptions between the control unit  210  and wired LAN devices.  
         [0035]     The storage unit  240  has a ROM to store control programs to control the overall operations of the AP  200 , and a RAM to temporarily store data packets sent from the wireless transmission/reception unit  220  and the wired transmission/reception unit  230 . The storage unit  240  according to this embodiment of the present invention stores registration list information on neighboring APs. Table 1 shows a registration list regarding neighboring APs stored in the storage unit  240 , for example.  
                                   TABLE 1                                   AP NAME   SSID   BSSID   Etc                           AP1   aaa   DDDDDDDD   . . .           AP2   bbb   EEEEEEEE   . . .           AP3   bcc   AAAAAAAA   . . .           AP4   ddd   FFFFFFFF   . . .                      
 
         [0036]     As shown in Table 1, information on neighboring APs includes neighboring AP names, AP network IDs (SSID, BSSID), and other information that is not shown, such as AP Media Access Control (MAC) addresses.  
         [0037]     The signal level detection unit  250  detects a level of a signal received through the wireless transmission/reception unit  220  and the wired transmission/reception unit  230 . A signal level value detected by the signal level detection unit  250  is applied to the control unit  210 .  
         [0038]     The control unit  210  controls the overall operations of the AP  200  according to the control programs stored in the storage unit  240 . The control unit  210  determines whether beacon frames are received from neighboring APs in order for optimum communications to be enabled, and determines whether neighboring APs exist according to signal levels of the received beacon frames. At this time, the control unit  210  compares a predetermined threshold value with the signal level value received from the signal level detection unit  250  corresponding to the received beacon frames, and determines whether a different AP exists in the wireless communication range of the AP  200  according to a result of the comparison. The control unit  210  determines a different AP exists at a neighboring location if the received signal level value is more than the predetermined threshold value.  
         [0039]     Further, the control unit  210  checks communication states of neighboring APs through communications with the neighboring APs, and, in the case that a neighboring AP does not perform communications, broadcasts an AP replacement command signal so that wireless devices associated with the neighboring AP can replace the neighboring AP.  
         [0040]      FIG. 3  is a block diagram illustrating a wireless device such as shown in  FIG. 1 .  
         [0041]     As shown in  FIG. 3 , a wireless device  300  has a control unit  310 , a wireless transmission/reception unit  320 , and a storage unit  330 .  
         [0042]     The wireless transmission/reception unit  320  controls a communication interface between the control unit  310  and a wireless device. The wireless transmission/reception unit  320  sends and receives data packets through an antenna.  
         [0043]     The storage unit  330  has a ROM to store control programs to control the overall operations of the wireless device  300 , and a RAM to temporarily store data packets to be sent or received through the wireless transmission/reception unit  320 .  
         [0044]     The control unit  310  controls the overall operations of the wireless device  300  according to the control programs stored in the storage unit  330 . If a signal requesting an AP replacement is received from a different AP while waiting for communications due to disassociation with a current AP, the control unit 310 requests an association with the neighboring AP having sent the AP replacement request signal. If a communication channel with the neighboring AP is formed, the wireless device  300  can perform communications through the neighboring AP.  
         [0045]      FIG. 4  to  FIG. 6  are flow charts illustrating a communication method for the wireless communication system according to an embodiment of the present invention.  
         [0046]      FIG. 4  is a flow chart illustrating an operation process for an access point. The present embodiment will be described with the AP 1  shown in  FIG. 1 .  
         [0047]     Referring to  FIG. 4 , the AP 1  determines whether a beacon frame is received to check if there is a neighboring AP (S 400 ). If a beacon frame is determined to be received, the AP 1  determines whether a signal level of the beacon frame being currently received is more than a predetermined threshold value (S 410 ). If the received signal level is determined to be more than the predetermined threshold value in operation S 410 , the AP 1  determines that a neighboring AP exists (S 420 ). On the contrary, if the received signal level is determined to be less than the predetermined threshold value, the AP 1  determines that a neighboring AP does not exist, and ends the operations. Hereinafter, descriptions will be made with the AP 2  of  FIG. 1  as a neighboring AP, for example.  
         [0048]     Next, the AP 1  sends an association request signal to AP 2 , requiring a communication establishment. At this time, the AP 2  sends to the AP 1  an association response signal including BSSID and SSID information necessary for the communication establishment.  
         [0049]     The AP 1  determines whether the AP 2  is a registered neighboring AP in use of the BSSID and SSID included in the association response signal received from the AP 2  (S 430 ).  
         [0050]     If the AP 2  is determined to be a non-registered neighboring AP in operation S 430 , the AP 1  stores registration information BSSID and SSID of the AP 2  onto a neighboring AP registration list (S 440 ). Further, the AP 1  periodically communicates with the AP 2  (S 450 ).  
         [0051]     The operation S 450  will be described in more detail with reference to  FIG. 5 . The AP 1  registers the AP 2  as a neighboring AP in operation S 440 , and the AP 1  then determines whether a predetermined period of time lapses (S 451 ). If it is determined that the predetermined period of time lapses in operation S 451 , the AP 1  sends a beacon frame to the AP 2  (S 452 ). Further, the AP 1  determines whether a response signal is received from the AP 2  in correspondence to the beacon frame in order to check the communication states of the AP 2  (S 453 ). In the meantime, since the AP 1  and AP 2  periodically broadcast beacon frames for synchronizations with wireless devices, the AP 1  checks whether a beacon frame is received from the AP 2 , to thereby identify the communication states of the AP 2 .  
         [0052]     If it is determined that a response signal to the sent beacon frame is not received from the AP 2 , or a beacon frame is not received for a predetermined period of time in operation S 453 , the AP 1  deletes the information on the AP 2  from the neighboring AP registration list (S 454 ). Further, the AP 1  sends a communication standby signal to the wireless devices  1  to  4  connected thereto (S 455 ). At this time, the wireless devices  1  to  4  connected to the AP 1  wait until a communication restart signal is received from the AP 1 .  
         [0053]     After operation S 455 , the AP 1  sends an AP replacement command to the wireless devices  5  to  7  connected to the AP 2  (S 456 ). After sending the AP replacement command signal to the wireless devices  5  to  7 , the AP 1  sends the communication restart signal to the wireless devices  1  to  4 , which are in the communication standby (S 457 ). Further, if the AP 1  receives an association request signal from any of the wireless devices  5  to  7  connected to the AP 2  in correspondence to the AP replacement command signal, the AP 1  establishes a new communication channel through the association with the wireless device having requested the association.  
         [0054]     In the operations described above, the communication standby signal and the communication restart signal are sent to the wireless devices  1  to  4  from the AP 1 , and the AP replacement command signal is sent from the AP 1  to the wireless devices  5  to  7 , the signals being included in a management frame of data frames used in the wireless communication system according to this embodiment of the present invention. The management frame is the same as defined in the IEEE 802.11 standard. That is, the management frame is structured with a body field, a duration field, a destination address field, a source address field, a BSSID field, a sequence control field, an information element field, and a frame check sequence (FCS) field. State codes corresponding to the communication standby signal, communication restart signal, and AP replacement command signal can be set for use in the information element field of the management frame.  
         [0055]      FIG. 6  is a flow chart illustrating operations of a wireless device according to this embodiment of the present invention. The present embodiment will be described with the operations of the wireless device  5  connected to the AP 2  of  FIG. 1 , for example.  
         [0056]     Referring to  FIG. 6 , the wireless device  5  sends an association request signal to the AP 2  (S 500 ), and determines whether an association response signal is received from the AP 2  in correspondence to the wireless association request signal (S 510 ). If it is determined that the association response signal is not received in operation S 510 , the wireless device  5  waits for a predetermined period of time (S 520 ), and re-sends the association request signal to the AP 2  (S 530 ). If it is determined in operation S 540  that the association response signal is received in response to the re-sending of operation S 530 , the wireless device  5  communicates data with a wired device through the AP 2  (S 550 ).  
         [0057]     In the meantime, if the association response signal is determined to not be received from the AP 2  in response to the association request signal of operation S 530 , the wireless device  5  determines whether an AP replacement command signal is received from a new AP such as the AP 1  (S 560 ). That is, the wireless device  5  determines whether a beacon frame is received. If the beacon frame is determined to be received, the wireless device  5  determines whether the information of BSSID and SSID included in the received signal matches the information of BSSID and SSID registered therein. If the two pieces of information on BSSID and SSID are determined to not be the same, the wireless device  5  determines a new AP exists at a neighboring location.  
         [0058]     Accordingly, the wireless device  5  sends the association request signal to the AP 1  for a connection attempt (S 570 ). In response to the attempt, if the wireless device  5  receives the association response signal from the AP 1  (S 580 ), the wireless device  5  changes its own information of BSSID and SSID to the information of BSSID and SSID assigned to the AP 1 . Thereafter, the wireless device  5  communicates data with wired devices through the AP 1  (S 590 ).  
         [0059]     In the meantime, the wireless device  5  connected to the AP 2  as described above exists in the wireless communication range of the AP 1 , so that it can participate in the network environment of the AP 1 . Accordingly, the wireless devices  6  and  7 , as shown in  FIG. 1 , cannot participate in the network environment of the AP 1  because they do not exist in the wireless access point range of the AP 1 . However, even though not shown in the drawings, in the case that a neighboring AP exists around the wireless devices  6  and  7 , the wireless devices  6  and  7  can communicate with wired devices through the neighboring AP.  
         [0060]     As described so far, in the wireless communication system and the optimum communication method therefor according to the present invention, if an access point associating with wireless devices fails to act as a mediator due to a sudden situation, the wireless devices sharing one network environment through the access point can associate with a neighboring access point, having sent an access point replacement command and continuing communications through the new access point, to thereby enhance the communication efficiency.  
         [0061]     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.