Abstract:
An apparatus and method for sharing a frequency are provided. A cognitive wireless communication device having a minimum ROI may be selected from among a plurality of cognitive wireless communication devices, and an idle frequency of a primary system may be allocated to the selected cognitive wireless communication device, thereby increasing an opportunistic utilization efficiency of the idle frequency.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2009-0125366 and of Korean Patent Application No. 10-2010-0014128, respectively filed on Dec. 16, 2009 and Feb. 17, 2010, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an apparatus and method for sharing a frequency, and more particularly, to an apparatus and method for sharing a frequency that may increase an opportunistic utilization efficiency of an idle frequency of a primary system of a cognitive wireless communication device. 
     2. Description of the Related Art 
     To increase a frequency utilization efficiency in a frequency band in use, a cognitive wireless technology includes a spectrum overlay sharing technology where a secondary system uses an idle frequency that is not used temporally and/or spatially in a frequency band of a primary system, without interfering with the primary system. 
     Since the cognitive wireless technology enables opportunistic use of a frequency band, it is possible to solve a frequency resource depletion problem where frequency resources are increasingly limited due to an advent of new wireless communication services and developments in radio communication technology. 
     In other words, it is important to develop a technology of increasing an opportunistic utilization efficiency of an idle frequency in the cognitive wireless technology. 
     Accordingly, there is a desire for a method to increase an opportunistic utilization efficiency of an idle frequency of a cognitive wireless communication device. 
     SUMMARY 
     An aspect of the present invention provides a method of selecting a cognitive wireless communication device having a minimum Range of Interference (ROI) from among a plurality of cognitive wireless communication devices, and allocating an idle frequency of a primary system to the selected cognitive wireless communication device, thereby increasing an opportunistic utilization efficiency of the idle frequency. 
     According to an aspect of the present invention, there is provided an apparatus for sharing a frequency, the apparatus including a receiver to receive information regarding a Range of Interference (ROI) from a plurality of cognitive wireless communication devices, when the plurality of cognitive wireless communication devices desire to use an idle frequency of a primary system; and a frequency allocator to select a cognitive wireless communication device having a minimum ROI from among the plurality of cognitive wireless communication devices based on the received information regarding the ROI, and to allocate the idle frequency to the selected cognitive wireless communication device. 
     According to another aspect of the present invention, there is provided a method of sharing a frequency, the method including receiving information regarding an ROI from a plurality of cognitive wireless communication devices, when the plurality of cognitive wireless communication devices desire to use an idle frequency of a primary system; selecting a cognitive wireless communication device having a minimum ROI from among the plurality of cognitive wireless communication devices based on the received information regarding the ROI; and allocating the idle frequency to the selected cognitive wireless communication device. 
     EFFECT 
     According to embodiments of the present invention, it is possible to select a cognitive wireless communication device having a minimum Range of Interference (ROI) from among a plurality of cognitive wireless communication devices, and to allocate an idle frequency of a primary system to the selected cognitive wireless communication device, thereby increasing an opportunistic utilization efficiency of the idle frequency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects, features, and advantages of the invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a diagram illustrating a primary system and a secondary system according to an embodiment of the present invention; 
         FIG. 2  is a diagram illustrating a secondary system according to an embodiment of the present invention; 
         FIG. 3  is a block diagram illustrating a configuration of a frequency sharing apparatus according to an embodiment of the present invention; and 
         FIG. 4  is a flowchart illustrating a method of sharing a frequency according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Exemplary embodiments are described below to explain the present invention by referring to the figures. 
       FIG. 1  is a diagram illustrating a primary system  120  and a secondary system  110  according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the secondary system  110  includes a secondary base station  111 , and a secondary terminal  112 . The primary system  120  includes a primary base station  121 , and a primary terminal  122 . 
     The secondary system  110  may determine a part of or all of frequency resources allocated to the primary system  120  to be available, using a cognitive wireless technology. The secondary base station  111  and the secondary terminal  112  in the secondary system  110  may transmit/receive data using the frequency resources determined to be available. Hereinafter, all communication devices contained in the secondary system  110 , for example the secondary base station  111  and the secondary terminal  112 , may be referred to as “cognitive wireless communication devices”. 
     Information may need to be exchanged between the primary base station  121  and the primary terminal  122 , so that the cognitive wireless communication devices may use an idle frequency of the primary system  110 . 
     When an identical frequency resource is used by the primary system  120  and the secondary system  110 , the primary system  120  and the secondary system  110  may collide with each other. However, the primary system  120  may have a higher priority for the allocated frequency resources than the secondary system  110 . 
     Specifically, the secondary system  110  may use a part of or all of the frequency resources allocated to the primary system  120 , without interrupting a communication operation of the primary system  120 . The secondary base station  111  and the secondary terminal  112  may sense a signal of the primary system  120 , and may perform data communication based on the sensed signal. For example, when the signal of the primary system  120  does not exist, or when a level of an interference in the primary system  120  by the data communication of the secondary base station  111  and the secondary terminal  112  is equal to or less than a predetermined level, the secondary base station  111  and the secondary terminal  112  may use a part of or all of the frequency resources allocated to the primary system  120 . 
       FIG. 2  is a diagram illustrating a secondary system  200  according to an embodiment of the present invention. 
     Referring to  FIG. 2 , the secondary system  200  includes a secondary transmitter  210 , and a secondary receiver  220 . Depending on embodiments, the secondary transmitter  210  may function as a secondary base station of the secondary system  200 , and the secondary receiver  220  may function as a secondary terminal of the secondary system  200 . Cognitive wireless communication devices may be all communication devices, such as the secondary transmitter  210  and the secondary receiver  220  in the secondary system  200 . 
     The secondary transmitter  210  may have a Transmission Range (TR)  211 , and a Carrier Sensing Range (CSR)  213 . 
     The TR  211  may be a range that enables the secondary transmitter  210  to transmit data to the secondary receiver  220  in the secondary system  200 . Depending on embodiments, the TR  211  may have a circular shape, and the secondary transmitter  210  may be located at a center of the TR  211 . Here, a maximum distance of the TR  211  may be represented as a Transmission Range of Secondary Transmitter (TR 5 )  212  as illustrated in  FIG. 2 . 
     The CSR  213  may be a range that enables the secondary transmitter  210  to sense a signal of a primary system. Depending on embodiments, the secondary transmitter  210  may sense whether another transmitter exists in the CSR  213 . Depending on embodiments, the CSR  213  may have a circular shape, and the secondary transmitter  210  may be located at a center of the CSR  213 . Here, a maximum distance of the CSR  213  may be represented as a Carrier Sensing Range of Secondary Transmitter (CSR 5 )  214  in  FIG. 2 . 
     The secondary receiver  220  may have an Interference Range (IR)  221 . 
     The IR  221  may be a range that enables the secondary receiver  220  to communicate data with the secondary transmitter  210  without any interference by transmitters other than the secondary transmitter  210 . For example, to perform data communication between the secondary receiver  220  and the secondary transmitter  210  without interference, another transmitter should not exist in the IR  221 . Depending on embodiments, the IR  221  may have a circular shape, and the secondary receiver  220  may be located at a center of the IR  221 . Here, a maximum distance of the IR  221  may be represented as an Interference Range of Secondary Transmitter (IR 5 )  222  in  FIG. 2 . 
     A Range of Interference (ROI)  230  may be within the IR  221  of the secondary receiver  220 , and may be outside the CSR  213  of the secondary transmitter  210 . 
     Since the ROI  230  is out of the CSR  213  of the secondary transmitter  210 , another transmitter other than the secondary transmitter  210  may exist in the ROI  230 . Additionally, since the ROI  230  is contained in the IR  221  of the secondary receiver  220 , when another transmitter other than the secondary transmitter  210  exists in the IR  221 , data communication between the secondary transmitter  210  and the secondary receiver  220  may fail due to an interference by the other transmitter. Thus, as the ROI  230  is reduced in size, a probability that the other transmitter may interfere with the data communication between the secondary transmitter  210  and the secondary receiver  220  may be reduced. 
       FIG. 3  is a block diagram illustrating a configuration of a frequency sharing apparatus  300  according to an embodiment of the present invention. 
     Referring to  FIG. 3 , the frequency sharing apparatus  300  includes a receiver  310 , and a frequency allocator  320 . 
     The frequency sharing apparatus  300  may be inserted as a single module into cognitive wireless communication devices of a secondary system that desire to use an idle frequency of a primary system. 
     The receiver  310  may receive information regarding an ROI from a plurality of cognitive wireless communication devices, when the plurality of cognitive wireless communication devices desire to use an idle frequency of a primary system. Specifically, information regarding an ROI of each of the plurality of cognitive wireless communication devices may be received from each of the plurality of cognitive wireless communication devices. 
     Depending on embodiments, the information regarding the ROI may include information regarding a size and a location of the ROI, and the like. 
     The frequency allocator  320  may select at least one cognitive wireless communication device having a minimum ROI from among the plurality of cognitive wireless communication devices based on the information regarding the ROI received by the receiver  310 . Additionally, the frequency allocator  320  may allocate the idle frequency of the primary system to the selected cognitive wireless communication device. 
     Depending on embodiments, a plurality of cognitive wireless communication devices may have a minimum ROI. Here, the frequency allocator  320  may select one cognitive wireless communication device from among the plurality of cognitive wireless communication devices having the minimum ROI, and may allocate the idle frequency to the selected cognitive wireless communication device. 
     According to an aspect of the present invention, the frequency sharing apparatus  300  may further include a calculating unit  330 . 
     The calculating unit  330  may calculate a size of an ROI of each of the cognitive wireless communication devices. 
     Depending on embodiments, the receiver  310  may receive information regarding a CSR, information regarding a TR, and information regarding an IR from the plurality of cognitive wireless communication devices. Additionally, the calculating unit  330  may calculate the size of the ROI based on the information regarding the CSR, the information regarding the TR, and the information regarding the IR that are received by the receiver  310 . 
     According to an aspect of the present invention, a portion of the plurality of cognitive wireless communication devices that desire to use the idle frequency of the primary system may transmit the information regarding the ROI to the frequency sharing apparatus  300 , and the remaining portion may transmit the information regarding the CSR, the information regarding the TR, and the information regarding the IR to the frequency sharing apparatus  300 . 
     When the information regarding the ROI is received from the cognitive wireless communication devices, the receiver  310  of the frequency sharing apparatus  300  may transmit the received information to the frequency allocator  320 . When the information regarding the CSR, the information regarding the TR, and the information regarding the IR is received from the cognitive wireless communication devices, the receiver  310  may transmit the received information to the calculating unit  330 . Depending on embodiments, the calculating unit  330  may calculate the size of the ROI of each of the cognitive wireless communication devices based on the received information regarding the CSR, the received information regarding the TR, and the received information regarding the IR, and may transmit the calculated value to the frequency allocator  320 . 
     When a maximum distance of a CSR of a cognitive wireless communication device is identical to a maximum distance of an IR, the calculation unit  330  may calculate the size of the ROI using the following Equation 1: 
     
       
         
           
             
               
                 
                   ROI 
                   = 
                   
                     
                       π 
                       · 
                       
                         IR 
                         5 
                         2 
                       
                     
                     - 
                     
                       2 
                       ⁢ 
                       
                         a 
                         2 
                       
                       ⁢ 
                       
                         
                           cos 
                           
                             - 
                             1 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               TR 
                               5 
                             
                             
                               2 
                               ⁢ 
                               a 
                             
                           
                           ) 
                         
                       
                     
                     - 
                     
                       
                         TR 
                         5 
                       
                       ⁢ 
                       
                         
                           
                             
                               a 
                               2 
                             
                             - 
                             
                               
                                 ( 
                                 
                                   
                                     TR 
                                     5 
                                   
                                   2 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 1, ROI denotes a size of an ROI of a cognitive wireless communication device, TR 5  denotes a maximum distance of a TR of a cognitive wireless communication device, IR 5  denotes a maximum distance of an IR of a cognitive wireless communication device, and a=CSR 5 =IR 5  where CSR 5  denotes a maximum distance of a CSR of a cognitive wireless communication device. 
     When the maximum distance of the CSR is greater than the maximum distance of the IR, the calculating unit  330  may calculate different sizes of the ROI based on a maximum distance of a TR of a cognitive wireless communication device. 
     Depending on embodiments, the calculating unit  330  may classify a maximum distance of a TR of a cognitive wireless communication device into four cases below, and may calculate different sizes of the ROI for each case. Here, the maximum distance of the TR may be represented as “TR 5 .” 
     When the first case is for 0≦TR 5 &lt;(IR 5 −CSR 5 ), the calculating unit  330  may calculate the size of the ROI to be a value of “0”. 
     When the second case is for 
                 (       IR   5     -     CSR   5       )     &lt;     TR   5     &lt;       IR   5     ·     cos   ⁡     (       sin     -   1       ⁢       CSR   5       IR   5         )           ,         
the calculating unit  330  may calculate the size of the ROI using the following Equation 2:
 
     
       
         
           
             
               
                 
                   ROI 
                   = 
                   
                     
                       π 
                       · 
                       
                         IR 
                         5 
                         2 
                       
                     
                     - 
                     
                       
                         CSR 
                         5 
                         2 
                       
                       · 
                       β 
                     
                     + 
                     
                       
                         IR 
                         5 
                         2 
                       
                       · 
                       α 
                     
                     - 
                     
                       
                         1 
                         2 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               
                                 IR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               α 
                             
                             - 
                             
                               
                                 CSR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               
                                 ( 
                                 
                                   π 
                                   - 
                                   β 
                                 
                                 ) 
                               
                             
                           
                           ) 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 2, ROI denotes a size of an ROI of a cognitive wireless communication device, 
     
       
         
           
             
               α 
               = 
               
                 
                   sin 
                   
                     - 
                     1 
                   
                 
                 ( 
                 
                   
                     2 
                     ⁢ 
                     
                       
                         
                           s 
                           ⁡ 
                           
                             ( 
                             
                               ɛ 
                               - 
                               
                                 CSR 
                                 5 
                               
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             ɛ 
                             - 
                             
                               IR 
                               5 
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             ɛ 
                             - 
                             
                               TR 
                               5 
                             
                           
                           ) 
                         
                       
                     
                   
                   
                     
                       CSR 
                       5 
                     
                     ⁢ 
                     
                       TR 
                       5 
                     
                   
                 
                 ) 
               
             
             , 
             
               
 
             
             ⁢ 
             
               β 
               = 
               
                 
                   sin 
                   
                     - 
                     1 
                   
                 
                 ( 
                 
                   
                     2 
                     ⁢ 
                     
                       
                         
                           s 
                           ⁡ 
                           
                             ( 
                             
                               s 
                               - 
                               
                                 CSR 
                                 5 
                               
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             s 
                             - 
                             
                               IR 
                               5 
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             s 
                             - 
                             
                               TR 
                               5 
                             
                           
                           ) 
                         
                       
                     
                   
                   
                     
                       IR 
                       5 
                     
                     ⁢ 
                     
                       TR 
                       5 
                     
                   
                 
                 ) 
               
             
             , 
             
               
 
             
             ⁢ 
             and 
           
         
       
       
         
           
             s 
             = 
             
               
                 
                   
                     CSR 
                     5 
                   
                   + 
                   
                     IR 
                     5 
                   
                   + 
                   
                     TR 
                     5 
                   
                 
                 2 
               
               . 
             
           
         
       
     
     When the third case is for 
                   IR   5     ·     cos   ⁡     (       sin     -   1       ⁢       CSR   5       IR   5         )         ≤     TR   5     &lt;     (       CSR   5     +     IR   5       )       ,         
the calculating unit  330  may calculate the size of the ROI using the following Equation 3:
 
     
       
         
           
             
               
                 
                   
                     R 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     O 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     I 
                   
                   = 
                   
                     
                       π 
                       · 
                       
                         IR 
                         5 
                         2 
                       
                     
                     - 
                     
                       
                         CSR 
                         5 
                         2 
                       
                       · 
                       β 
                     
                     + 
                     
                       
                         IR 
                         5 
                         2 
                       
                       · 
                       α 
                     
                     - 
                     
                       
                         1 
                         2 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               
                                 IR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               a 
                             
                             + 
                             
                               
                                 CSR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               β 
                             
                           
                           ) 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     When the fourth case is for (CSR 5 +IR 5 )≦TR 5 , the calculating unit  330  may calculate the size of the ROI using the following Equation 4:
 
ROI=π·IR 5   2 .  [Equation 4]
 
       FIG. 4  is a flowchart illustrating a method of sharing a frequency according to an embodiment of the present invention. 
     Referring to  FIG. 4 , in operation S 410 , whether there are a plurality of cognitive wireless communication devices desiring to use an idle frequency of a primary system may be determined. 
     When a single cognitive wireless communication device desires to use the idle frequency of the primary system, the idle frequency may be allocated to the cognitive wireless communication device. 
     In operation S 420 , when the plurality of cognitive wireless communication devices desire to use the idle frequency of the primary system, information regarding an ROI may be received from the plurality of cognitive wireless communication devices. 
     In operation S 421 , information regarding a CSR, information regarding a TR, and information regarding an IR may be received from the plurality of cognitive wireless communication devices. 
     In operation  422 , a size of the ROI of each of the cognitive wireless communication devices may be calculated based on the received information regarding the CSR, the received information regarding the TR, and the received information regarding the IR. 
     When a maximum distance of a CSR of a cognitive wireless communication device is identical to a maximum distance of an IR, the size of the ROI may be calculated using the following Equation 5: 
     
       
         
           
             
               
                 
                   
                     R 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     O 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     I 
                   
                   = 
                   
                     
                       π 
                       · 
                       
                         IR 
                         5 
                         2 
                       
                     
                     - 
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         a 
                         2 
                       
                       ⁢ 
                       
                         
                           cos 
                           
                             - 
                             1 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               TR 
                               5 
                             
                             
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               a 
                             
                           
                           ) 
                         
                       
                     
                     - 
                     
                       
                         TR 
                         5 
                       
                       ⁢ 
                       
                         
                           
                             
                               a 
                               2 
                             
                             - 
                             
                               
                                 ( 
                                 
                                   
                                     TR 
                                     5 
                                   
                                   2 
                                 
                                 ) 
                               
                               2 
                             
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 5, ROI denotes a size of an ROI of a cognitive wireless communication device, TR 5  denotes a maximum distance of a TR of a cognitive wireless communication device, IR 5  denotes a maximum distance of an IR of a cognitive wireless communication device, and a=CSR 5 =IR 5  where CSR 5  denotes a maximum distance of a CSR of a cognitive wireless communication device. 
     When the maximum distance of the CSR is greater than the maximum distance of the IR, different sizes of the ROI may be calculated based on a maximum distance of a TR of a cognitive wireless communication device. 
     Depending on embodiments, a maximum distance of a TR of a cognitive wireless communication device may be classified into four cases as below, and different sizes of the ROI may be calculated for each case. Here, the maximum distance of the TR may be represented as “TR 5 .” 
     When the first case is for 0≦TR 5 &lt;(IR 5 −CSR 5 ), the size of the ROI may be calculated to be a value of “0”. 
     When the second case is for 
                 (       IR   5     -     CSR   5       )     &lt;     TR   5     &lt;       IR   5     ·     cos   ⁡     (       sin     -   1       ⁢       CSR   5       IR   5         )           ,         
the size of the ROI may be calculated using the following Equation 6:
 
     
       
         
           
             
               
                 
                   ROI 
                   = 
                   
                     
                       π 
                       · 
                       
                         IR 
                         5 
                         2 
                       
                     
                     - 
                     
                       
                         CSR 
                         5 
                         2 
                       
                       · 
                       β 
                     
                     + 
                     
                       
                         IR 
                         5 
                         2 
                       
                       · 
                       α 
                     
                     - 
                     
                       
                         1 
                         2 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               
                                 IR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               a 
                             
                             + 
                             
                               
                                 CSR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               
                                 ( 
                                 
                                   π 
                                   - 
                                   β 
                                 
                                 ) 
                               
                             
                           
                           ) 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 6, ROI denotes a size of an ROI of a cognitive wireless communication device, 
     
       
         
           
             
               α 
               = 
               
                 
                   sin 
                   
                     - 
                     1 
                   
                 
                 ( 
                 
                   
                     2 
                     ⁢ 
                     
                       
                         
                           
                               
                             3 
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                   
                                 3 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 CSR 
                                 5 
                               
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             
                                 
                               3 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               IR 
                               5 
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             
                                 
                               3 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               TR 
                               5 
                             
                           
                           ) 
                         
                       
                     
                   
                   
                     
                       CSR 
                       5 
                     
                     ⁢ 
                     
                       TR 
                       5 
                     
                   
                 
                 ) 
               
             
             , 
             
               
 
             
             ⁢ 
             
               β 
               = 
               
                 
                   sin 
                   
                     - 
                     1 
                   
                 
                 ( 
                 
                   
                     2 
                     ⁢ 
                     
                       
                         
                           s 
                           ⁡ 
                           
                             ( 
                             
                               s 
                               - 
                               
                                   
                               
                               ⁢ 
                               
                                 CSR 
                                 5 
                               
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           ( 
                           
                             s 
                             - 
                             
                                 
                             
                             ⁢ 
                             
                               IR 
                               5 
                             
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           
                             s 
                             - 
                             
                                 
                             
                             ⁢ 
                             
                               TR 
                               5 
                             
                           
                           ) 
                         
                       
                     
                   
                   
                     
                       IR 
                       5 
                     
                     ⁢ 
                     
                       TR 
                       5 
                     
                   
                 
                 ) 
               
             
             , 
             
               
 
             
             ⁢ 
             and 
           
         
       
       
         
           
             s 
             = 
             
               
                 
                   
                     CSR 
                     5 
                   
                   + 
                   
                     IR 
                     5 
                   
                   + 
                   
                     TR 
                     5 
                   
                 
                 2 
               
               . 
             
           
         
       
     
     When the third case is for 
                   IR   5     ·     cos   ⁡     (       sin     -   1       ⁢       CSR   5       IR   5         )         ≤     TR   5     &lt;     (       CSR   5     +     IR   5       )       ,         
the size of the ROI may be calculated using the following Equation 7:
 
     
       
         
           
             
               
                 
                   
                     R 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     O 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     I 
                   
                   = 
                   
                     
                       π 
                       · 
                       
                         IR 
                         5 
                         2 
                       
                     
                     - 
                     
                       
                         CSR 
                         5 
                         2 
                       
                       · 
                       β 
                     
                     + 
                     
                       
                         IR 
                         5 
                         2 
                       
                       · 
                       α 
                     
                     - 
                     
                       
                         1 
                         2 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             
                               
                                 IR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               a 
                             
                             + 
                             
                               
                                 CSR 
                                 5 
                                 2 
                               
                               ⁢ 
                               sin 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               β 
                             
                           
                           ) 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
             
           
         
       
     
     When the fourth case is for (CSR 5 +IR 5 )≦TR 5 , the size of the ROI may be calculated using the following Equation 8:
 
ROI=π·IR 5   2 .  [Equation 8]
 
     In operation S 430 , a cognitive wireless communication device having a minimum ROI may be selected from among the plurality of cognitive wireless communication devices. Here, the minimum ROI may be received or calculated. When a plurality of cognitive wireless communication devices have the minimum ROI, one cognitive wireless communication device may be selected from among the plurality of cognitive wireless communication devices having the minimum ROI. 
     In operation S 440 , the idle frequency may be allocated to the selected cognitive wireless communication device. 
     The above-described embodiments of the present invention may be recorded in non-transitory computer-readable media including program instructions to implement various operations embodied by a computer. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of non-transitory computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM disks and DVDs; magneto-optical media such as optical disks; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like. Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. The described hardware devices may be configured to act as one or more software modules in order to perform the operations of the above-described embodiments of the present invention, or vice versa. 
     Although a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.