Patent Publication Number: US-2005122944-A1

Title: Frame structure for selecting bridge device in high-speed wireless personal area network and method of selecting bridge device therein

Description:
CLAIM OF PRIORITY  
      This application claims, pursuant to 35 USC 119, priority to that patent application entitled “Frame Structure For Selecting Bridge Device In High-Speed Wireless Personal Area Network And Method Of Selecting Bridge Device Therein” filed in the Korean Intellectual Property Office on Dec. 5, 2003 and assigned Serial No. 2003-88049, the contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an IEEE 802.15.3 high-speed wireless personal area network (WPAN) using an ultra-wide band (UWB), and more particularly to a high-speed WPAN which can support communications among devices included in different piconets in the high-speed WPAN.  
      2. Description of the Related Art  
      A wireless communication technique using UWB is a technique that guarantees a transmission distance in the range of 10 m to 1 km. The UWB wireless communication technique had been used as a military wireless communication technique by the US Department of Defense for the past 40 years, and has been open to the nonmilitary sector by the Federal Communications Commission (FCC), which is the US authority on communication frequencies.  
      The UWB wireless communication technique is a ultrahigh-speed wireless data transmitting technique using a UWB of several GHz, and has the characteristics of a high transmitting speed (of 500 Mbps to 1 Gbps) and a low power consumption ({fraction (1/100)} of the power consumption of a mobile phone or a wireless LAN) in comparison to the existing IEEE 802.11, Bluetooth, etc. The UWB wireless communication technique can be used in diverse fields such as a short-distance personal communication network that connects a computer, peripheral devices and home appliances to an ultrahigh-speed wireless interface in a short distance, e.g. up to 100 m , a radar for examining, by fluoroscopy, the interior of a building, a high-precision position measurement, a device for preventing a car collision, an underground mine detector, a system for preventing the loss of an article, a detection of an object inside a body, etc.  
      A standard for the UWB wireless communication technique that has been proposed as a high-speed wireless personal area network (WPAN) is referred to as IEEE 802.15.3. In the standards of IEEE 802 groups, IEEE 802.15.1 is a group that establishes the Bluetooth standards, and IEEE 802.11 is a group that establishes the wireless LAN standards.  
      Bluetooth has been commercialized as a widely known personal area network (PAN), and has recently been applied to many network-related products. Bluetooth generally uses a frequency band of 2.4 GHz (i.e., ISM band), and provides a personal area network (PAN) solution with its communication distance limited to less than 10 m. The wireless LAN using IEEE 802.11 group protocol has already been standardized and uses the 2.4 GHz and the 5.0 GHz frequency bands.  
      IEEE 802.15.3 is further divided into TG1 (Task Group 1), TG2 and TG3. Here, TG1 is a group that establishes the Bluetooth standards, and TG2 is a group that makes a technical analysis of methods for enabling the Bluetooth products and the existing wireless LAN business to coexist. TG3 is a group that researches the standard of a high data rate PAN solution, and is now conducting research in a transmission system having a transmission speed of more than 55 Mbps. The present invention concerns the high data rate PAN solution according to TG3.  
       FIG. 1  is a view illustrating an example of a piconet designated among communication devices in an IEEE 802.15.3 high-speed wireless PAN. As shown, the piconet that designates the high-speed wireless PAN is composed of a plurality of communication devices  10 ,  12 ,  14 ,  16  and  18 . One device  10  among them operates as a piconet coordinator (PNC). Here, the PNC serves as a master of the corresponding piconet and performs synchronization with the respective devices, manages time slots for data communication, and performs other control operations.  
      Specifically, the PNC device  10  manages the time slots required for the communications among the devices located in the piconet by using a message called a beacon in order to perform synchronization with the other connected devices  12 ,  14 ,  16  and  18 . PNC  10  additionally serves to control a QoS (Quality of Signal), a power save mode, and piconet access.  
      As described above, the IEEE 802.15.3 device  10 , which serves as the piconet coordinator, can designate a piconet as follows: 
          1. PNC device  10  searches channels in order to start the piconet, selects one of the channels which are not in use;     2 broadcasts a beacon frame through the selected channel; and     3. provides and allocates identifications for the respective devices, in this case, devices  12 ,  14 ,  16  and  18 , which have received the broadcast beacon frame and set the channel for their communications in response to the received beacon frame.        

      In another aspect, a device, which has moved from the outside to the already designated piconet A, may request connection with another device in the piconet A designated by the PNC device  10 . Accordingly, the PNC device  10 , as controller, provides a single device ID, which can be used in the piconet A, to the device that has requested the connection.  
      Through the above-described process, the piconet as shown in  FIG. 1  is designated. In this case, devices  12 ,  14 ,  16  and  18  make requests of PNC device  10  for data transmission. The PNC device  10  allocates communicable time slots to the respective devices  12 ,  14 ,  16  and  18  in response to the data transmission request from the respective devices  12 ,  14 ,  16  and  18 . When the PNC device  10  allocates the time slots to the respective devices  12 ,  14 ,  16  and  18 , it uses the beacon frame. The respective devices  12 ,  14 ,  16  and  18  perform the data transmission for a time corresponding to the time slot allocated by the PNC device  10 .  
      Meanwhile, if a device desires to terminate the communication in the piconet or to perform a disconnection from the device, a piconet disassociation procedure is performed between the PNC device  10  and the corresponding device. Accordingly, the PNC device  10  deletes information about the recorded device through the piconet disassociation procedure.  
      The piconet designated between the PNC device  10  and the respective devices  12 ,  14 ,  16  and  18  may be divided into an independent piconet which can independently allocate the time slots to the devices existing in the piconet, and a dependent piconet which distributes and allocates the time slots provided from a PNC device located outside the piconet to the devices existing in the piconet. If a dependent piconet is newly produced in an independent piconet, the independent piconet is referred to as a parent piconet, and the newly produced dependent piconet is referred to as a child piconet or a neighbor piconet. That is, the independent piconet becomes the parent piconet, and the dependent piconet becomes the child piconet. In this case, the child piconet (i.e., dependent piconet) shares and uses the channel provided from the PNC device of the parent piconet.  
       FIG. 2  is a view illustrating an example of a dependent piconet designated in the IEEE 802.15.3 high-speed wireless PAN network. In this illustrative example, the existing piconet becomes a parent piconet  30 , and a PNC device, for example device  32 , of the parent piconet  30  is called a P-PNC device. Another device having the capability of being a PNC device, other than the already designated P-PNC device  32  among the devices  22 ,  32  and  42 , which constitute the parent piconet  30 , can be designated a child piconet  20 . In this case, device  22  is selected to be the child PCN (C-PCN)  
      In this case, the P-PNC device  32 , which is located in the parent piconet  30 , allocates time slots to the C-PCN device  22  and another device  34 , that is shown herein representative of the child piconet, and transmits the beacon frame. Here, the C-PNC device  22  is a device that performs a PNC function in the child piconet  20 .  
      C-PNC device  22  may also designate the child piconet  20 , and separately manage and control the device  24  that designates the child piconet  20 . The communication in the child piconet  20  can be performed only between the devices  22  and  24  that designate the child piconet  20 .  
      Accordingly, the C-PNC device  22  is a member of parent piconet  30 , while also managing and controlling the child piconet  20 . Thus, the C-PNC device  22  can perform a communication with the devices  32  and  34  in the parent piconet  30 .  
       FIG. 3  is a view illustrating a conventional WPAN composed of a parent piconet and a child piconet. In this illustrative example, a P-PNC device  62  manages a C-PNC device  42  and a device G  64  which are members of a parent piconet  60 . Also, the C-PNC device  42  manages a device A  47  and a device B  49  as members of a child piconet  40 .  
      The P-PNC device  62  generates mapping information composed of MAC (Media Access Control) addresses of 64 bits and device IDs of 8 bits using information transmitted from the devices  42  and  64 , and stores and manages the mapping information in a P-MIB (Parent Piconet Management Information Base)  63 . Also, the P-PNC device  62  broadcasts information about the devices  42  and  64  registered in the parent piconet  60  using a beacon frame. Only the devices  42 ,  62  and  64  registered in the parent piconet  60  can receive the beacon frame broadcast by the P-PNC device  501 . The respective devices  42  and  64  in the parent piconet  60  generate mapping information about the devices  42  and  64  using information of the beacon frame transmitted from the P-PNC device  62 , store and manage the mapping information in P-MIBs  44  and  65  of the respective devices.  
      In the case of transmitting data to the P-PNC device  62 , the device G  64  searches for the mapping information from the P-MIB  65 , and transmits the data with reference to the device ID of the P-PNC device  62 .  
      Meanwhile, the C-PNC device  42  that manages and controls the child piconet  40  broadcasts information about the device A  47  and the device B  49  that exist in the child piconet  40 , which are not registered as mapping information of a C-MIB (Child Piconet Management Information Base)  43 , using the beacon frame. Here, only the devices  46  and  48 , which are registered as the child piconet  40  in the C-PNC device  42 , can receive the beacon frame.  
      Device A  46  and device B  48  also store and manage the mapping information about the devices registered in the C-MIB  43  of the C-PNC device  42  in the C-MIBs  47  and  49  using the beacon frame information broadcast from the C-PNC device  42 . Accordingly, in the case of transmitting data to the device B  48 , the device A  46  searches for the mapping information stored in the C-MIB  47 , and transmits the data with reference to the device ID information of the device B  48 .  
      As described above, the current IEEE 802.15.3 standard does not consider such communications between devices located in different piconets, but defines only a PNC device and a general device. Hence, there is a need in the industry to enable communications between piconets that will extend the range of UWB devices.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a bridge device, and bridge device selecting method that is required for communications between different piconets, a new frame structure for selecting a bridge device, and new information elements thereof in a IEEE 802.15.3 high-speed wireless personal area network (WPAN) using a UWB (Ultra-Wide Band).  
      In order to accomplish this object, there is provided a frame structure for selecting a bridge device in a high-speed wireless personal area network (WPAN) which includes a parent piconet designated in advance and having a plurality of devices, a newly designated child piconet using time slots allocated from the devices located in the parent piconet, and a bridge device which is located in the child piconet, that broadcasts information about the devices of the parent piconet and information about the devices of the child piconet to the devices included in the high-speed WPAN, and operates to perform a data transfer between a first specific device included in the child piconet and a second specific device included in the parent piconet, the frame structure providing a media access control (MAC) frame which includes an overall capability field, composed of 9 bytes, for indicating an overall capability of a specific device, a length field, composed of one byte, for indicating a length of a frame, and an element identifier (ID) field for identifying respective elements, wherein the overall capability field includes a device capability field for indicating a capability of the specific device, a piconet coordinator capability field for indicating a capability for determining whether the specific device can be a piconet coordinator (PNC), and a bridge capability field for indicating a capability for determining whether the specific device can be the bridge device.  
      In another aspect of the present invention, there is provided a method of selecting a bridge device in a high-speed wireless personal area network (WPAN) which includes a parent piconet designated in advance and having a plurality of devices, a newly designated child piconet using time slots allocated from the devices located in the parent piconet, and a bridge device which is located in the child piconet, that broadcasts information about the devices of the parent piconet and information about the devices of the child piconet to the devices included in the high-speed WPAN, and operates to perform a data transfer between a first specific device included in the child piconet and a second specific device included in the parent piconet, the method comprising a first step of detecting devices which can operate as the bridge device, a second step of selecting the corresponding device as the bridge device if one device which can operate as the bridge device is detected, while comparing sizes of buffers of the detected devices, which have physically been determined, if plural devices which can operate as the bridge device are detected, a third step of selecting the device having the largest buffer size as a result of comparison at the second step as the bridge device, and if there are plural devices having the same largest buffer size, selecting a piconet coordinator among the devices having the same largest buffer size as the bridge device, a fourth step of selecting the device whose security bit is activated as the bridge device if there is no piconet coordinator among the devices having the same largest buffer size, a fifth step of selecting the device having a power source as the bridge device if there are plural devices whose security bits are activated, or if there is no device whose security bit is activated at the fourth step, a sixth step of selecting the device having a large number of associated devices as the bridge device if there are plural devices having the power source, or if there is no devices having the power source at the fifth step, a seventh step of selecting the device having a large output power if there are plural devices having a large number of associated devices at the sixth step, and an eighth step of selecting the device having a high transmission speed as the bridge device if there are plural devices having the large output power, or if there is no device having the large output power at the seventh step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a view illustrating an example of a piconet designated among devices in an IEEE 802.15.3 high-speed wireless personal area network;  
       FIG. 2  is a view illustrating an example of a dependent piconet designated in an IEEE 802.15.3 high-speed wireless personal area network;  
       FIG. 3  is a view illustrating a conventional WPAN composed of a parent piconet and a child piconet;  
       FIG. 4  is a view illustrating a high-speed WPAN system having a bridge device according to an embodiment of the present invention;  
       FIG. 5  is a view illustrating a conventional capability field structure of a device of a MAC frame according to the IEEE 802.15.3;  
       FIG. 6  is a view illustrating a capability field structure of a device of a MAC frame according to the present invention;  
       FIG. 7  is a view illustrating an example of a bridge group information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention;  
       FIG. 8  is a view illustrating another example of a bridge group information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention;  
       FIG. 9  is a view illustrating an example of a bridge shutdown information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention; and  
       FIG. 10  is a view illustrating an example of a bridge device change information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, a frame structure for selecting bridge device in high-speed wireless personal area network (WPAN) and a method of selecting bridge device therein according to embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, same drawing reference numerals are used for the same elements even in different drawings. For purposes of clarity, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unclear.  
       FIG. 4  is a view illustrating a high-speed WPAN system having a bridge device according to an embodiment of the present invention. As shown, the high-speed WPAN system according to the present invention is composed of a device having a bridging function and other devices.  
      The device having the bridging function broadcasts information about the devices which are located in different piconets to the devices which exist in the different piconets. Here, the information about the devices which exist in the different piconets is called bridging information. If the respective devices receive the information about the devices which exist in the different piconets, they generate B-MIBs (Bridging Management Information Bases) of the devices through the received information about the devices. Meanwhile, the device having the bridging function switches the data transmitted from the devices located in the different piconets.  
      In the present invention, the device having the bridging function is set as a C-PNC device  120 . Accordingly, the C-PNC device  120  has a bridge  122  for switching data transmitted from the different piconets.  
      The high-speed WPAN as illustrated in  FIG. 4  forms different piconets which are a parent piconet  200  and a child piconet  100 . Here, the piconet ID of the parent piconet  200  is designated with the letter ‘P’, and the piconet ID of the child piconet  100  is designated with the letter ‘C’. In this case, it is assumed that information about addresses and IDs of the devices which are located in the parent piconet  200  and the child piconet  100  is the same as the information as illustrated in  FIG. 3 .  
      A P-PNC device  220  manages a C-PNC device  120  having a bridging function and a device G  240 , which are members of the parent piconet  200 . Also, the C-PNC device  120  manages ad evice A  140  and a device B  160  as members of the child piconet  100 .  
      The P-PNC device  220  generates and manages P-MIB (Parent Piconet Management Information Base) mapping information which includes MAC (Media Access Control) addresses of 64 bits and device IDs of 8 bits using information transmitted from the devices  120  and  240  located in the parent piconet  200 . Also, the P-PNC device  220  broadcasts information about the devices  120  and  240  registered as the parent piconet  200  in a P-MIB  222 . The C-PNC device  120  and the device G  240  generate mapping information using information of the beacon frame broadcast from the P-PNC device  220 , and store the mapping information in the P-MIBs  126  and  242 .  
      Accordingly, the devices  220 ,  120  and  240  located in the parent piconet  200  communicate with one another using the mapping information stored in the shared P-MIBs  222 ,  126  and  242 .  
      The C -PNC device  120  broadcasts information about the device A  140  and the device B  160  which exist in the child piconet  100 , which are registered in a C-MIB (Child Piconet Management Information Base)  124 , using the beacon frame. The device A  140  and the device B  160  construct and manage C-MIBs  142  and  162  of the devices which are located in the child piconet  100  using the beacon frame information broadcast from the C-PNC device  120 .  
      Accordingly, the devices  120 ,  140  and  160  located in the child piconet  100  communicate with one another using the shared C-MIBs  124 ,  142  and  162 .  
      Meanwhile, the C-PNC device  120  that is the device having the bridging function has access to both the C-MIB  124  in which the mapping information about the devices located in the child piconet  100  and the P-MIB  126  in which the mapping information about the devices located in the parent piconet  200 .  
      The C-PNC device  120  broadcasts the mapping information stored in the P-MIB  126  to the devices  140  and  160  located in the child piconet  100 , and broadcasts the mapping information stored in the C-MIB  124  to the devices located in the parent piconet  200 .  
      The device A  140  and the device B  160  which are located in the child piconet  100  generate mapping information for bridging the devices  220  and  240  located in the parent piconet  200  through the mapping information broadcast from the C-PNC device  120 , and store and manage the generated mapping information in B-MIBs (Bridging Management Information Bases)  144  and  164 .  
      The P-PNC device  220  and the device G  240  which are located in the parent piconet  200  generate mapping information for bridging the devices  140  and  160  located in the child piconet  100  through the mapping information broadcast from the C-PNC device  120 , and store and manage the generated mapping information in B-MIBs  224  and  244 . Accordingly, the respective devices  140 ,  160 ,  220  and  240  can transmit data to destinations devices located in different piconets with reference to the B-MIBs.  
      For example, in the case of transmitting data to the device G  240 , the device A detects a MAC address of the device G  240 , a device ID and a piconet with reference to the mapping information stored in the B-MIB  144 , and inserts the detected information in a header of data. The data is transmitted to the C-PNC device  120  for an allocated time slot.  
      The C-PNC device  120  confirms the destination to which the data is to be transmitted by analyzing the header of the data transmitted from the device A  140 . The C-PNC device  120  performs a bridging operation for transmitting the data transmitted from the device A  140  to the device G  240  by controlling the bridge  122 . Accordingly, it can transmit the data transmitted from the device located in the child piconet  100  to the device located in the parent piconet  200  using the bridging function.  
      Accordingly, by making communications possible by applying a bridging protocol that supports communications among the devices located in the different piconets in the high-speed WPAN, the possible communication distance can be extended in the high-speed WPAN.  
       FIG. 5  is a view illustrating a conventional capability field structure of a device of a MAC frame according to the IEEE 802.15.  
      As shown in  FIG. 5 , the conventional capability field according to the IEEE 802.15.3 includes an overall capability field  51  composed of 7 bytes, a length field  52  composed of one byte, and an element ID field  53 , composed of one byte, for discrimination among respective elements. Here, the detailed contents of the element ID field  53  are shown in Table 1 below.  
                                   Element ID           Hex value   Element                  0x00   Channel time allocation       0x01   BSID       0x02   Parent piconet       0x03   DEV association       0x04   PNC shutdown       0x05   Piconet parameter change       0x06   Application specific       0x07   Pending channel time map       0x08   PNC handover       0x09   CTA status       0x0A   Capability       0x0B   Transmit power parameter       0x0C   PS status       0x0D   Continued wake beacon (CWB)       0x0E   Overlapping PNID       0x0F   Piconet services       0x10-0x7F   Reserved       0x80-0xFF   Vendor specific                  
 
      In Table 1, an element ID having a value of 0×00 includes channel time allocation information. An element ID having a value of 0×01 includes BSID (Beacon Source Identifier) information for identifying a source of a beacon. An element ID having a value of 0×02 includes parent piconet information for indicating a parent piconet. An element ID having a value of 0×03 indicates a device (DEV) association for indicating information of devices included in a piconet. An element ID having a value of 0×04 indicates a PNC shutdown for indicating a shutdown of a piconet coordinator (PNC). An element ID having a value of 0×05 indicates a piconet parameter change for indicating that the parameter of a piconet is changed. An element ID having a value of 0×06 indicates a specific application for permitting typical information for an extended operation in the standard. An element ID having a value of 0×07 indicates a PCTM (Pending Channel Time Map) for requesting a switchover to an active mode. An element ID having a value of 0×08 indicates a PNC handover in which a previous piconet coordinator (PNC) reports abandonment of the piconet control. An element ID having a value of 0×09 indicates a CTA (Channel Time Allocation) status whereby the PNC transfers a certain status of CTA to a specific device.  
      Also, an element ID having a value of 0×0A indicates a capability of the corresponding device. An element ID having a value of 0×0B indicates a transmission power parameter for transmitting a transmission power control capability of the corresponding device. An element ID having a value of 0×0C indicates a PS (Power Save) status of the corresponding device. An element ID having a value of 0×0D indicates a CWB (Continued Wake Beacon) for the corresponding device. An element ID having a value of 0×0E indicates an overlapping PNID for communications with another PNID sensed through the channel of the corresponding device or another channel. An element ID having a value of 0×0F indicates an overlapping PNID for providing information about application layer capabilities of the respective devices. An element ID having a value of 0×10 to 0×7F indicates a reserved area, and an element ID having a value of 0×80 to 0×FF indicates a specific vendor.  
      The overall capability field  51  includes a device (DEV) capability field  54 , composed of three bytes, for indicating a device capability, and a PNC capability field  55 , composed of four bytes, for indicating a capability for determining whether the specific device can be the PNC.  
       FIG. 6  is a view illustrating a capability field structure of a device of a MAC frame according to the present invention. As shown in  FIG. 6 , the capability field of a device of a MAC frame according to the present invention includes an overall capability field  61  composed of 9 bytes, a length field  62  composed of one byte, and an element identifier (ID) field  63 , composed of one byte, for discrimination among respective elements.  
      The overall capability field  61  includes a device capability field  64 , composed of three bytes, for indicating a device capability, a piconet coordinator (PNC) capability field  65 , composed of four bytes, for indicating a capability for determining whether the specific device can be a PNC, and a bridge capability field  66 , composed of two bytes, for indicating a capability for determining whether the specific device can operate as the bridge device. Here, the bridge capability field  66  includes a bridge order field  67 , composed of one byte, for determining the order in which a device can be a bridge device, and a buffer size field  68 , composed of one byte, for indicating a buffer size of the corresponding device. The bridge order field  67  includes a PNC possibility field  610  for indicating whether a device can be a PNC, a bridge Des-mode field  611  for indicating whether a device can be a bridge device, and a reserved field  612 . The standard for selecting a bridge device is shown in Table 2 below.  
                                       Order   Information   Note                  1   BRG Des-mode bit in BRG   BRG Des-mode = 1 is preferred           capabilities field       2   Buffer Size (PHY dependent)   Higher value is preferred       3   PNC Des-mode bit in PNC   PNC Des-mode = 1 is preferred           capabilities field       4   SEC bit in PNC capabilities field   SEC = 1 is preferred       5   PSRC bit in PNC capabilities   PSRC = 1 is preferred           field       6   Max associated DEVs   Higher value is preferred       7   Transmitter power level   Higher value is preferred           (PHY dependent)       8   MAX PHY rate   Higher value is preferred           (PHY dependent)                  
 
      In selecting a bridge device, in the first order, a device whose bridge (BRG) Des-mode is “1” is selected as the bridge (BRG), and in the second order, a device having a large buffer size already physically determined is selected. In the third order, a device whose PNC Des-mode is “1” is selected, and in the fourth order, a device whose security bit is “1” is selected. In the fifth order, a device having a power source (PSRC) is selected, and in the sixth order, a device having a large number of associated devices is selected. In the seventh order, a device having a large output power is selected, and in the eighth order, a device having a high transmission speed is selected.  
      Following the above-described priority order, the probability that the C-PNC serves as the bridge device is heightened.  
      Here, even though it is proper for the C-PNC to serve as the bridge device, the reason why the first and second orders are determined, as described above, is to avoid the limitation that only the C-PNC may serve as the bridge device. That is, not even the C-PNC serves as the bridge device if it does not have the bridging function.  
      Also, in the present invention, by adding the bridge (BRG) capability field to the capability field of the device of the existing IEEE 802.15.3 MAC frame, a device which will perform the bridging function between the different piconets is selected in the order as defined in Table 2.  
      In the embodiment of the present invention, the priority order in Table 2 is determined so as to first consider the priority order that defines the piconet coordinator of the child piconet, and thus the piconet coordinator of the child piconet properly serves as the bridge device.  
      Meanwhile, if one device performs the bridging function in the high-speed WPAN according to the present invention, an information element should be added accordingly.  
      The newly added information element as above may be included in the “Reserved field (0×10−0×7F)” shown in Table 1, which includes a bridge group information element, a bridge shutdown information element and a bridge change information element.  
       FIG. 7  is a view illustrating an example of a bridge group information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention. The bridge group information element includes a bridge ID (BRGID) field  71 , composed of one byte, for identifying the bridge device, device ID 1  (DEVID 1 ) field  72 - 1  to device IDn (DEVIDn) field  72 - n,  each composed of one byte, for indicating respective device IDs which are managed by the corresponding bridge device, a length field  73  composed of one byte, and an element ID field  74  composed of one byte. Here, the element ID included in the element ID field  74  includes a hex value of an information element in Table 1. The element ID newly added according to the present invention is allocated with a specified value of the reserved region of 0×10 to 0×7F.  
       FIG. 8  is a view illustrating another example of a bridge group information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention.  
      In this aspect of the invention, the bridge group information element includes a bridge ID (BRGID) field  81 , composed of one byte, for identifying the bridge device, PNID 1  field  82 - 1  to PNID 2  field  82 - 2 , each composed of one byte, for indicating respective piconet IDs which are managed by the corresponding bridge device, a length field  83  composed of one byte, and an element ID field  84  composed of one byte. Here, the element ID included in the element ID field  84  includes a hex value (base  16 ) of an information element in Table 1. The element ID newly added according to the present invention is allocated with a specified value of the reserved region of 0×10 to 0×7F (base  16 ).  
       FIG. 9  is a view illustrating an example of a bridge shutdown information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention. In this aspect of the invention, the bridge shutdown information element includes a device ID (DEVID) field  91 , composed of one byte, for identifying the ID of the remaining device in order to select the bridge device, a length field  93  composed of one byte, and an element ID field  94  composed of one byte. Here, the element ID included in the element ID field  94  includes a hex (base  16 ) value of an information element in Table 1. The element ID newly added according to the present invention is allocated with a specified value of the reserved region of 0×10 to 0×7F.  
      The operation of each device according to the shutdown information element is shown in Table 3.  
                                                   TABLE 3                       Element           DEV   PNC   DEV   DEV   PNC   PNC   BRG       ID Hex       Present in   allowed to   allowed to   receives   receives   receives   allowed to   allowed to       value   Element   beacon   request?   request?   from BRG   from PNC   from BGR   send?   send?                  0x14   BRG   Non-   Shall not   Shall not   Shall ignore   Shall ignore   Shall not   May not   May           shutdown   beacon   request   request           ignore   allowed   allowed               IE                  
 
      Table 3 illustrates an authority to request a bridge (BRG) shutdown and an order of processing the given authority. In Table 3, an element ID HEX value is identified as 0×14 of the reserved region in Table 1. However, other values may also be used as the element ID HEX value.  
      The element indicates a bridge (BRG) shutdown operation, and the bridge shutdown information is not presented in the beacon (Non-Beacon IE). The device or the PNC is not allowed to request, i.e., shall not request, the bridge shutdown. If the device receives the bridge shutdown information from the bridge or the PNC, it shall ignore this, but if the PNC receives the bridge shutdown information from the bridge, it shall not ignore this. The PNC may not be allowed to send the bridge shutdown information, and the bridge may be allowed to send the bridge shutdown information.  
      Specifically, devices which exist in the piconet may be a PNC (e.g., a piconet manager), a bridge (e.g., device having a bridging function) and a DEV (e.g., general device). If a device having a bridging function intends to discontinue the bridging function, only the present bridge may be allowed to send this information, but the general device or PNC may not be allowed to send the information. On the contrary, only the PNC (or CPNC) can receive, i.e., may not ignore, the bridge shutdown information in principle. Accordingly, the present bridge does not directly cause the next bridge candidate to operate, but informs the PNC that controls the piconet of the bridge shutdown information, so that the PNC recognizes that the next bridge candidate will be a new bridge device, and then informs other devices of this information. The existing bridge device informs other devices of which device is the next bridge candidate as shown as the information element of  FIG. 9 . This information element is not presented in the beacon.  
      That is, the information element of  FIG. 9  is used for the present bridge device to one-sidedly inform the next bridge candidate of the bridge shutdown information when the present bridge device stops its bridging function. As shown in Table 3, the present bridge device sends other devices the corresponding information before it stops its bridging function, and only the PNC can refer to this information.  
       FIG. 10  is a view illustrating an example of a bridge device change information element that is added to a MAC frame in which a bridge (BRG) capability field is included according to the present invention. In this aspect of the invention, the bridge device change information element includes a change beacon number field  1001 , composed of one byte, for indicating information about the changed beacon number, a new bridge device (BRG DEV) field  1002  for indicating the ID of the device which will be a new bridge device, a new bridge (BRG) address field  1003  for indicating the address of the device which will be a new bridge device, a length field  1004  composed of one byte, and an element ID field  1005  composed of one byte.  
      The bridge device change information element as illustrated in  FIG. 10  is used for the PNC device that controls the beacon of the piconet to provide all the devices in the piconet with the information about the change of the bridge device. Here, the element ID included in the element ID field  1005  includes a hex value of the information element in Table 1. The element ID newly added according to the present invention is allocated with a specified value of the reserved region of 0×10 to 0×7F.  
      As described above, the present invention has the advantages in that it can select a device that can take charge of the bridging function among plural devices in the piconet by determining priority orders by defining a bridge capability value field for selecting the bridging function in the existing MAC frame structure.  
      Also, the present invention has the effect of providing an expected information element by defining a newly added bridge capability value field.  
      The method according to the present invention as described above may be implemented by a program, and stored in a recording medium (e.g., CD ROM, floppy disc, hard disc, optomagnetic disc, etc.) in the form readable through a computer.  
      While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.