Abstract:
A tag conflict avoidance method and system are provided. The tag conflict avoidance system includes a plurality of tags receiving a first signal, converting identification codes of the tags into predetermined codes according to the first signal, and outputting the converted codes as second signals; and a reader outputting the first signal, receiving the second signals, and identifying the tags using the codes included in the second signals.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 10-2004-0082814, filed on Oct. 15, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a tag conflict avoidance method and apparatus, and more particularly, to a method and apparatus of recognizing a plurality of tags using a K-nary tree search.  
         [0004]     2. Description of the Related Art  
         [0005]     Tag conflict avoidance refers to recognition of a plurality of tags without conflict when the tags are simultaneously activated by one reader. Recently, as radio frequency identification (RFID) technology is used in managing various materials or data, a plurality of tags must be simultaneously recognized when the tags are located in a field.  
         [0006]     The RFID is an automatic recognizer which transmits/receives data stored in a tag, a label, or a card in which a micro chip is mounted, to/from a reader using a radio frequency. The RFID system includes a tag and a reader. The tag converts a unique identification code into a RF signal and transmits the RF signal to the reader by a call of the reader, and the reader suitably processes the received RF signal to identify the tag. If the tag is identified, data regarding an object bearing the tag is properly processed in a data processing system connected to the reader.  
         [0007]     In the event of a conflict among tags in the RFID system, the output signals of the tags interfere with each other and cannot reach the reader. Accordingly, when a plurality of the tags simultaneously enter into a cover of the reader, the tags should be identified while avoiding such a conflict.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a method and apparatus of avoiding tag conflict by identifying a RFID using a K-nary tree search.  
         [0009]     According to an aspect of the present invention, there is provided a tag conflict avoidance system comprising a plurality of tags receiving a first signal, converting identification codes of the tags into predetermined codes according to the first signal, and outputting the converted codes as second signals; and a reader outputting the first signal, receiving the second signals, and identifying the tags using the codes included in the second signals.  
         [0010]     According to another aspect of the present invention, there is provided a tag conflict avoidance method comprising a plurality of tags receiving a first signal, reading and converting their own identification codes into predetermined codes according to the first signal, and outputting the converted codes as second signals; and receiving the converted codes and classifying the tags. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0012]      FIG. 1  is a block diagram of a tag and a reader to which a tag conflict avoidance method of an exemplary embodiment of the present invention is applied;  
         [0013]      FIG. 2  is a flowchart illustrating the tag conflict avoidance method according to an exemplary embodiment of the present invention;  
         [0014]      FIGS. 3A, 3B  and  3 C conceptually illustrate operations of the tag conflict avoidance method according to an exemplary embodiment of the present invention;  
         [0015]      FIG. 4A  illustrates a K-nary tree search method of an exemplary embodiment of the present invention;  
         [0016]      FIG. 4B  illustrates a conventional binary tree search method;  
         [0017]      FIG. 5  illustrates a process of identifying tags by the conventional binary tree search method when a plurality of tags enter into one reader field; and  
         [0018]      FIG. 6  illustrates a process of identifying tags by the K-nary tree search method of an exemplary embodiment of the present invention when a plurality of tags enter into one reader field. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     Hereinafter, the present invention will be described in detail with reference to the attached drawings.  
         [0020]      FIG. 1  is a block diagram of a tag  10  and a reader  11  to which a tag conflict avoidance method of the present invention is applied.  
         [0021]     The tag  10  includes a storage unit  101 , a control unit  102 , a code conversion unit  103 , and an antenna  104 . The storage unit  101  stores a unique identification code of the tag  10 , for example, a 64-bit electronic product code. The control unit  102  receives the identification code transmission command from the reader  11  and reads n bits of the identification code stored in the storage unit  101  starting from the MSB (Most Significant Bit). The code conversion unit  103  converts the read n-bit code into a k-bit code including one bit value “1”. Here, K is greater than n. The K-bit code is transmitted to the reader  11  through the antenna  104 .  
         [0022]     The RFID reader  11  includes an antenna  111  and a control unit  112 . The control unit  112  transmits the identification code transmission command to the tag  10  through the antenna  111 . Also, the control unit  112  identifies the identification code received through the antenna  111 .  
         [0023]     Operations of the tag  10  and the reader  11  will now be described with reference to  FIG. 2  which is a flowchart illustrating the tag conflict avoidance method according to the present invention.  
         [0024]     First, the control unit  112  of the reader  11  outputs the identification code transmission command (operation  21 ). The control unit  102  of the tag  10  reads the n-bit code starting from the MSB of the identification code stored in the storage unit  101  according to the identification code transmission command and outputs it to the code conversion unit  103  (operation  22 ). The code conversion unit  103  converts the n-bit data into the K-bit code including one bit value “1” and transmits the K-bit code to the reader  11  through the antenna  104  (operation  23 ). In the code conversion, 3-bit data can be converted into 8-bit data as expressed in Table 1.  
                           TABLE 1                                   3-bit code   Converted code                           000   0000 0001           001   0000 0010           010   0000 0100           011   0000 1000           100   0001 0000           101   0010 0000           110   0100 0000           111   1000 0000                      
 
         [0025]     The control unit  112  of the reader  11  judges the location of one bit value “1” in the bit code to identify the tag (operation  24 ). The tag conflict avoidance method will now be described with reference to  FIGS. 3A  and  3 B which illustrate the identification codes of a first tag and a second tag received by the reader  11 , respectively. These identification codes contain one bit value “1” at different locations.  FIG. 3C  illustrates another example of the identification code received by the reader  11 . Referring to  FIG. 3C , the reader  11  detects two bit values “1” at the identification locations of the first tag and the second tag, respectively. Thereby, the first and second tags can be identified in the same read field without conflict.  
         [0026]     If the identification of every bit of the identification code is completed (operation  25 ), the process is finished. If the identification is not completed, an additional identification code transmission command for the tags having one value in the code identified in operation  24  is transmitted (operation  26 ). For example, the tag having the code “0000 0001” is instructed to transmit the next n-bit code. The control unit  102  of the tag which receives the additional identification code transmission command reads the next n-bit code from the identification code (operation  27 ). The read n-bit data is converted into the code having one bit value “1” by the code conversion unit  103  again and then operations  24  through  27  are repeated.  
         [0027]      FIG. 4A  illustrates a K-nary tree search method of the present invention and  FIG. 4B  illustrates a conventional binary tree search method. Referring to  FIGS. 4A and 4B , if a plurality of identification codes are divided into 8 groups, the identification codes can all be classified with just one iteration in the K-nary tree search method of the present invention. However, in the conventional binary tree search method, classification of the identification codes requires seven iterations.  
         [0028]      FIG. 5  illustrates a process of identifying a plurality of tags by the conventional binary tree search method when the tags enter into one reader field. In the present embodiment, suppose that the tags are classified into four groups.  
         [0029]     Column (a) of  FIG. 5 ( a ) illustrates a process by which the reader instructs the tags having identification codes in which 8 bits of the MSB is smaller than 11111111 to transmit their identification codes. Column (b) of  FIG. 5  illustrates a process by which the tags transmit their identification codes in response to the transmission command. Here, X marks a bit location where different values in the identification codes of the tags conflict. Referring to column (b) of  FIG. 5 , the identification codes can be classified into two groups of 101X001X and 111X001X.  
         [0030]     Column (c) of  FIG. 5  illustrates a process of instructing the tags to transmit identification codes smaller than “10111111” to further classify the group of 101X001X from the read result of column (b) of  FIG. 5 . Column (d) of  FIG. 5  illustrates the process by which tag groups  1  and  2  transmit their identification codes in response to the transmission command of column (c) of  FIG. 5  and the read result thereof. Referring to column (d) of  FIG. 5 , it can be noted that the identification codes are classified into 1010001X, 1011001X, and 111X001X.  
         [0031]     Column (e) of  FIG. 5  illustrates a process of instructing the tags to transmit identification codes smaller than 11101111 to further classify the group of 111X001X from the read result of column (b) of  FIG. 5 . Column (f) of  FIG. 5  illustrates the process of tag groups  3  and  4  transmitting their identification codes in response to the transmission command of column (e) of  FIG. 5  and the read result thereof. Referring to column (f) of  FIG. 5 , it can be noted that the identification codes are classified into 1110001X and 11110011.  
         [0032]      FIG. 6  illustrates a process of identifying a plurality of tags by the K-nary tree search method of the present invention, when the tags enter into a reader field. Column (a) of  FIG. 6  illustrates a process by which the reader instructs the tags to transmit their identification codes. Column (b) of  FIG. 6  illustrates the result of reading the identification codes transmitted by the tags. Here, X marks the bit location where different values in the identification codes of the tags conflict. Referring to column (b) of  FIG. 6 , the read result is X0X000XX, and the identification codes are classified into 00000010, 00100000, 00000001, and 10000000.  
         [0033]     Comparing the cases shown in  FIGS. 5 and 6 , it can be noted that the classification is accomplished by one transmission command read operation in the K-nary tree search method, while the full classification requires 7 transmission command read operations in the conventional binary tree search method.  
         [0034]     The invention can also be embodied as computer codes stored on a computer-readable recording medium. The computer-readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer-readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission over the Internet). The computer-readable recording medium can also be distributed over a network of coupled computer systems so that the computer code is stored and executed in a decentralized fashion. Also, functional programs, codes, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains.  
         [0035]     According to the present invention, the identification code can be searched and identified rapidly compared with the conventional binary tree search method.  
         [0036]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.