Abstract:
Provided are a method and apparatus for data communication in a wireless personal area network (WPAN) using directional beams, the method including: setting priorities to a plurality of beam paths capable of establishing a link between a first device and a second device; generating a list of the beam paths to which the priorities are set; and establishing a link between the first device and the second device with reference to the generated list. Accordingly, time and wireless resources for restoring the link can be minimized.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application is a National Stage application under 35 U.S.C. §371 of PCT/KR2008/007051 filed on Dec. 1, 2008, which claims priority from Korean Patent Application No. 10-2008-0034660, filed on Apr. 15, 2008 in the Korean Intellectual Property Office, all the disclosures of which are incorporated herein in their entireties by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Apparatuses and methods consistent with exemplary embodiments relate to a wireless personal area network (WPAN), and more particularly, to transceiving data between devices in the WPAN using directional beams. 
         [0004]    2. Description of the Related Art 
         [0005]    A wireless personal area network (WPAN) is a wireless network in which devices arranged at short distances from one another transceive data at low power. In a WPAN, data communication is performed using a time division multiple access (TDMA) method. Accordingly, devices desiring to perform data communication occupy a channel exclusively for a channel time allocation period (CTAP), which is allocated by a device referred to as a Piconet coordinator (PNC), to perform data communication. Further description on WPAN is disclosed in IEEE 802.15 family standard documents, and will therefore be omitted here. 
         [0006]    Recently, studies on a high speed data transmission technology using a millimeter (mm)-wave, which is a high frequency wave having a short wavelength of 1-10 mm and high directivity, are ongoing. For example, an IEEE 802.15.3c Task Group is working on standardization of a physical layer (PHY) for data communication using an mm-wave in a WPAN. As described above, mm-wave is a high frequency wave having a short wavelength of 1-10 mm and high directivity, and can be used for transmission of large capacities of data (such as high definition (HD) quality moving images) in a home network. 
         [0007]      FIG. 1  is a schematic view for comparing frequency bands used in data communication according to IEEE 802.11 family standards and in communication using an mm-wave. 
         [0008]    As illustrated in  FIG. 1 , the carrier frequency of IEEE 802.11b standard or IEEE 802.11 g standard is 2.4 GHz and the channel bandwidth thereof is about 20 MHz. Also, the carrier frequency of IEEE 802.11a standard or IEEE 802.11n standard is 5 GHz and the channel bandwidth thereof is also about 20 MHz. In contrast, an mm-wave uses a carrier frequency of 60 GHz and has a channel bandwidth of about 0.5 to 2.5 GHz. As described above, an mm-wave has significantly larger carrier frequency and channel bandwidth in comparison to the IEEE 802.11 family standards. Thus, by using an mm-wave, a high transmission rate of several Gbps can be obtained, the size of an antenna can be kept to 1.5 mm or less, and a single chip including an antenna can be realized. Also, since attenuation in air is high, interference between devices can also be reduced. 
         [0009]      FIG. 2  is a flowchart illustrating a related art process of performing data communication between devices using an mm-wave in a WPAN. 
         [0010]    Referring to  FIG. 2 , in operation  201 , a transmitter device and a receiver device perform beam searching. Since directional beams are used in data communication using an mm-wave, various beam paths may be present, wherein these beam paths can establish a link between the transmitter device and the receiver device. Beam searching is a process of searching for various beam paths. 
         [0011]    In operation  202 , an optimum beam path to be used for establishing a link is selected among the discovered beam paths. For example, a beam path having a largest receiving signal strength in the receiver device may be selected. 
         [0012]    In operation  203 , the transmitter device and the receiver device establish a link using the selected beam path. 
         [0013]    In operation  204 , the transmitter device and the receiver device perform data communication using the link. As described above, directional beams are used to perform data communication. 
         [0014]    In operation  205 , the transmitter and receiver devices judge whether the link for data communication is down. If the link is down, beam searching is performed again to restore the link between the devices using a new beam path. 
         [0015]      FIG. 3  is a schematic view for explaining a related art data communication method performed by a WPAN device using an mm-wave. 
         [0016]    As illustrated in  FIG. 3 , a Piconet coordinator (PNC)  310 , a device  1   301 , a device  2   302 , a device  3   303 , and a device  4   304  are included in a WPAN. 
         [0017]    The device  1   301  desires to transmit data to the device  2   302 , and the device  3   303  desires to transmit data to the device  4   304 . Accordingly, the device  1   301  and the device  3   303  request the PNC  310  for a wireless resource allocation, and the PNC  310  allocates a channel time allocation period (CTAP) to the device  1   301  and the device  3   303 . 
         [0018]    The device  1   301  and the device  2   302  perform data communication during a CTAP that is allocated to them. First, the devices  301  and  302  perform beam searching to find a beam path in which to establish a link. The device  1   301  selects a path  1 , among the paths found by the beam searching, to perform data communication. 
         [0019]    If an obstacle blocks a beam path during data communication using a directional beam such as an mm-wave, it is likely that data communication will be interrupted at the same time as a link goes down. Thus, when an obstacle blocks a path  1 , the device  1   301  and the device  2   302  search for beam paths again and find a path  2  and a path  3 . Accordingly, the devices  301  and  302  restore the link using an optimum beam path among the found beam paths according to receiving signal strengths. 
         [0020]    According to a related art, when the link has gone down because of, for example, an obstacle blocking beam paths in a WPAN in which data communication is performed using directional beams, the devices search for beam paths again, and compare the reception signal intensities of the found beam paths to find an optimum beam path. Thus, a large amount of time and resources are consumed to restore the link. Moreover, when selecting an optimum path among the various beam paths, if another factor besides the receiving signal strength is to be taken into consideration, the above problem becomes more serious and complex. 
       SUMMARY 
       [0021]    One or more exemplary embodiments provide a method and apparatus for restoring a link when a link between devices in a wireless personal area network (WPAN) goes down, using reduced time and resources. 
         [0022]    According to an aspect of an exemplary embodiment, there is provided a data communication method for a first device in a wireless personal area network (WPAN) using directional beams, the method including: setting priorities to a plurality of beam paths capable of establishing a link between the first device and a second device; generating a list of the beam paths to which the priorities are set; and establishing a link between the first device and the second device with reference to the generated list. 
         [0023]    The establishing the link may include establishing the link using a beam path of a next highest priority in the list when a link currently being used for data communication is down. 
         [0024]    In the setting the priorities, the priorities may be set with reference to whether interference is generated by the beam paths in data communication between a third device and a fourth device, and the data communication between the third device and the fourth device may be performed by sharing a channel time allocation period (CTAP) with the first device and the second device. 
         [0025]    The data communication may be performed using a millimeter wave. 
         [0026]    According to an aspect of another exemplary embodiment, there is provided a computer readable recording medium having embodied thereon a computer program for executing the above-described method. 
         [0027]    According to an aspect of another exemplary embodiment, there is provided an apparatus for data communication performed by a first device in a wireless personal area network (WPAN) using directional beams, the apparatus including: a priority setting unit which sets priorities to a plurality of beam paths capable of establishing a link between the first device and a second device; a list generating unit which generates a list of the beam paths to which the priorities are set; and a link establishing unit which establishes a link between the first device and the second device with reference to the generated list. 
         [0028]    According to an aspect of another exemplary embodiment, there is provided a data communication method for a first device in a wireless personal area network (WPAN) using directional beams, the method including: when an established link using a first beam path between the first device and a second device is down, establishing another link between the first device and the second device using a second beam path having a next highest set priority, as compared to the first beam path, with reference to a generated list of beam paths to which priorities are set. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a schematic view for comparing frequency bands used in communication according to IEEE 802.11 family standard and in communication using an mm-wave; 
           [0030]      FIG. 2  is a flowchart illustrating a related art process of performing data communication between devices using an mm-wave in a WPAN; 
           [0031]      FIG. 3  is a schematic view for explaining a related art data communication method performed by a WPAN device using an mm-wave; 
           [0032]      FIG. 4  is a flowchart illustrating a data communication method of a WPAN device according to an exemplary embodiment; 
           [0033]      FIG. 5  is a flowchart illustrating a data communication method by spatial reuse according to an exemplary embodiment; 
           [0034]      FIG. 6  is a list of beam paths generated by a WPAN device according to an exemplary embodiment; and 
           [0035]      FIG. 7  is a schematic view of a device performing data communication in a WPAN according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0036]    Exemplary embodiments will now be described more fully with reference to the accompanying drawings, in which like reference numerals refer to like elements throughout. Furthermore, expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
         [0037]      FIG. 4  is a flowchart illustrating a data communication method of a wireless personal area network (WPAN) device according to an exemplary embodiment. 
         [0038]    Referring to  FIG. 4 , in operation  401 , devices, i.e., transmitter and receiver devices, perform beam searching to search for beam paths to establish a link. 
         [0039]    In operation  402 , the devices set priorities to found beam paths. For example, at least one of receiving signal strengths, whether interference with other devices occurs (e.g., when spatial reuse is applied), and the like may be referred to when setting the priorities. The case where spatial reuse is applied will be described in detail later with reference to  FIG. 5 . 
         [0040]    In operation  403 , the devices generate a list of beam paths to which the priorities are set. 
         [0041]    In operation  404 , the devices select a beam path having a highest priority with reference to the list of the beam paths. 
         [0042]    In operation  405 , the devices establish a link for data communication using the beam path selected in operation  404 . 
         [0043]    In operation  406 , the devices perform data communication using directional beams using the link established in operation  405 . 
         [0044]    In operation  407 , the devices judge whether the link is down. A link that is down refers to a link via which data communication is not possible anymore. 
         [0045]    In operation  408 , the devices select a beam path of a next highest priority with reference to the list generated in operation  403 , and restore the link using the selected beam path of the next highest priority. 
         [0046]    Thus, unlike the related art, a list is generated using information on the beam paths obtained in a prior beam path search. Moreover, when the link goes down during data communication, the link is restored using a beam path of a next priority instead of searching for beam paths again. Accordingly, time and resources for performing subsequent beam path searches are not required. 
         [0047]      FIG. 5  is a flowchart illustrating a data communication method by spatial reuse according to an exemplary embodiment. 
         [0048]    As in the WPAN using an mm-wave, in a wireless network using a time division multiple access (TDMA) method of data communication using directional beams, even when data communication is performed at the same time using two or more links according to the spatial position of the devices, interference may not occur. Thus, if no interference occurs, four or more devices can transceive data by sharing a channel time allocation period (CTAP). Such a data communication method is referred to as spatial reuse. 
         [0049]    However, according to the spatial reuse communication method, beam paths are to be selected such that no interference occurs between links, as described above.  FIG. 5  illustrates a process of examining whether interference is generated according to an exemplary embodiment. 
         [0050]    Referring to  FIG. 5 , in operation  501 , a device  1  requests a network coordinator, such as a Piconet coordinator (PNC), for spatial reuse to transmit data to a device  2 . When spatial reuse is requested, a control channel may be used. A control channel is a channel for transmitting and receiving various control signals, different from a channel used for data communication, and uses an omni-directional signal instead of a directional beam. 
         [0051]    In operation  502 , the PNC allocates to a portion of a super frame a channel time for an interference test in order to judge whether interference occurs when the device  1  transmits data to the device  2  while a device  3  transmits data to a device  4 , that is, whether the device  1  and the device  3  may share a CTAP. This allocation of the interference test channel time can be made known to all devices in the WPAN via a beacon frame. 
         [0052]    In operation  503 , the device  3  transmits a test frame to the device  4  using a directional beam. 
         [0053]    In operation  504 , the device  1  performs beam searching, and transmits a test frame to the device  2  using found beam paths. Here, index information or an identifier for each of the beam paths may be included in the test frame. 
         [0054]    In operation  505 , a PNC receives a report from the device  1  and the device  3  on whether a test frame has been detected or not. That is, the device  1  reports to the PNC whether the device  1  has detected the test frame transmitted by the device  3  to the device  4 . Also, the device  3  reports to the PNC whether the device  3  has detected the test frame transmitted by the device  1  to the device  2 . In detail, index information or an identifier of a beam path may be provided to the PNC to report that the test frame has been detected when the test frame is transmitted through a certain beam path and to indicate a quality of the beam path. 
         [0055]    In operation  506 , the PNC judges whether interference occurs between the two links. If a test frame transceived in one link is sensed by the other link, the PNC determines that interference has occurred. 
         [0056]    In operation  507 , the PNC informs the device  1  of the result of the interference test based on the judgment in operation  506 , that is, whether spatial reuse is allowed. Index information or an identifier of a beam path to which no interference is generated can be provided. Although not illustrated in the drawing, the device  1  may determine priorities of beam paths with reference to the interference test result and may generate a list of the beam paths. 
         [0057]    As such, when spatial reuse is applied, the devices consider the receiving signal strength and the interference. According to the present exemplary embodiment, even when the link goes down, the link can be restored using a beam path of a next highest priority from the list of the beam paths, without having to perform operations  501  through  507  again. Thus, time and resources used for restoring the link are minimal. 
         [0058]      FIG. 6  is a list of beam paths generated by a WPAN device according to an exemplary embodiment. 
         [0059]    As shown in  FIG. 6 , four beam paths are found, and receiving signal strength indicators (RSSI) of the beam paths are in the order of No. 1, 2, 3, and 4. 
         [0060]    However, the beam path No. 1 has the lowest priority despite having the highest RSSI because interference has occurred in its interference test. For example, in the present exemplary embodiment, the result of the interference test is given more deference than the RSSI when spatial reuse is applied. 
         [0061]    Here, Tx ANT and Rx ANT are information on beam forming, and beam forming refers to adjustment of a direction of an antenna such that the transmitter device and the receiver device can precisely transmit and receive directional beams. 
         [0062]      FIG. 7  is a schematic view of a device  700  performing data communication in a WPAN according to an exemplary embodiment. 
         [0063]    As illustrated in  FIG. 7 , a WPAN device  700  includes a beam searching unit  710 , a priority setting unit  720 , a list generating unit  730 , a link establishing unit  740 , an antenna controlling unit  750 , and an antenna  760 . 
         [0064]    The beam searching unit  710  searches for beam paths that may be used for data communication. Since directional beams are used, various beam paths may be found. 
         [0065]    The priority setting unit  720  sets priorities to the beam paths searched by the beam searching unit  710 . As described above, various factors such as an RRSI, a result of an interference test, etc., can be taken into consideration. 
         [0066]    The list generating unit  730  generates a list of beam paths to which priorities are set. An example of the list is shown in  FIG. 6 . 
         [0067]    The link establishing unit  740  forms a link using a beam of a highest priority with reference to the list of the beam paths generated by the list generating unit  730 . When a link is down during data communication, the link establishing unit  740  restores the link using a beam path of a next highest priority from the list. 
         [0068]    The antenna controlling unit  750  controls the antenna  760  according to a command of the beam searching unit  710  or the link establishing unit  740 . The antenna  760  may be able to transmit and receive directional beams in various directions. The antenna  760  may be a sectorized antenna or an array antenna. 
         [0069]    While not restricted thereto, one or more exemplary embodiments can be written as computer programs and can be implemented in general-use digital computers that execute the programs using a computer readable recording medium. 
         [0070]    Examples of the computer readable recording medium include magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.) and optical recording media (e.g., CD-ROMs, or DVDs). Furthermore, exemplary embodiments may be written as computer programs transmitted over a computer-readable transmission medium, such as carrier waves (e.g., transmission through the Internet), and received and implemented in general-use or special-purpose digital computers that execute the programs. 
         [0071]    According to exemplary embodiments, time and wireless resources used for restoring a link can be minimized even when a link goes down during data communication in a WPAN using directional beams. For example, when spatial reuse is applied, there is no need to conduct interference test procedures every time a link goes down. 
         [0072]    While exemplary embodiments have been particularly shown and described with reference to the drawings, 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 inventive concept as defined by the appended claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the inventive concept is defined not by the detailed description of the exemplary embodiments but by the appended claims, and all differences within the scope will be construed as being included in the present inventive concept.