Abstract:
A radio frequency identification (RFID) communication system and the search method thereof are disclosed, which apply search instructions and reads instructions to communicate between a read and a plurality of transponders. Each transponder generates a random number for comparison with received search instructions. When the random number meets with the number of received search instructions, a response request is sent by a corresponding transponder such that the reader can read the content of the corresponding transponder.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a radio frequency identification (RFID) communication system and, more particularly, to a radio frequency identification (RFID) communication system and the search method thereof.  
           [0003]    2. Description of Related Art  
           [0004]    [0004]FIG. 1 is a schematic diagram of essential devices of a typical RFID communication system. In FIG. 1, the system includes a reader  11  and a transponder  12 . As shown in FIG. 1, the operation principle for the system is that the reader  11  sends a carrier with instructions to the transponder  12  and the transponder  12  obtains DC power via rectifying the carrier. Further, a demodulator inside the transponder demodulates instructions on the carrier, thereby responding the reader or sending required data according to the instructions demodulated.  
           [0005]    RFID communication system is increasing quickly and its applications become more diversified, thus typical one-to-one communication cannot meet existing applications. For example, a reader may communicate with a plurality of transponder. FIG. 2 is a schematic diagram of one reader  21  to multiple transponders  22 - 25 . When the transponders  22 - 25  concurrently send responds to the reader  21 , signal interfere among the transponders can cause collision.  
           [0006]    Currently, three solutions are applied to prevent collisions, which, as shown in FIG. 2, are spatial domain, frequency domain and time domain. For spatial domain, it is assumed that the transponders  22 - 25  are separated by a space from each other. Such a solution is applied mostly to microwave systems and can discriminate each object by means of directional antenna. However, such a solution is hard in design for a non-microwave system. For frequency domain, the reader  21  sends a carrier and instructions to the transponder  22 - 25  at fixed frequency points (band) and the transponders  22 - 25  respectively selects, according to instructions decoded, one from corresponding multiple back-transmittable frequencies in order to send corresponding ID codes to the reader  21 . Since the transponders  22 - 25  send the ID codes back to the reader  21  in different frequencies, the collision is avoided. However, such a solution costs very high and is limited in specific applications. For time domain, the transponders  22 - 25  are scheduled such that each of the transponders  22 - 25  can send its own data in the scheduled time.  
           [0007]    One more typical collision solution mostly seen is using polling for searching. Namely, one-to-one roll call is applied for searching. However, such a solution has a poor performance when the number of transponders is large. Accordingly, current collision solution generally adopts binary search algorithm in time domain to thus quickly obtain ID codes of all transponders, or random number method, i.e., using the transponders to generate random numbers to accordingly determine each transponder&#39;s transmission time. Since each of the transponders generates different random numbers and thus has different response time, signal interfere probability among the transponders is relatively reduced when random space is much greater than transponder number, such that ID codes of the transponders in read range can be read. Generally, upon read efficiency increase in the random number method, a number of read instructions are increased. For example, a mute instruction is applied to make transponders accurately read corresponding ID codes enter in a mute mode, thereby reducing transponder number facing a reader.  
           [0008]    Operation principles respectively for the cited binary search algorithm and the random number method are described as follows. The binary search algorithm is shown in FIGS. 3 and 4. FIG. 3 is a schematic diagram of the binary search algorithm. FIG. 4 is a flowchart of communication between a read  41  and a transponder  42 . As shown in FIGS. 3 and 4, for searching ID codes of 0000 and 0011 in a given example of four bits, a search is performed sequentially from MSB to LSB and a collision occurs at third bits of 0000 and 0011. When the reader  41  sees the collision, the reader  41  sets searching 000 firstly until 0000 ID code is found, and then 001 until 0011 ID code is found. As such, applying the binary search algorithm is simple and quick but heavy communication between the reader  41  and the transponder  42  is required, which needs guard time for switch between the reader  41  and the transponder  42  in order to avoid error caused by the switch. However, it wastes time and reduces entire performance.  
           [0009]    [0009]FIG. 5 is a timing of every transponder using the random number method. As shown in FIG. 5, every transponder generates a random number and a reader sets a response cycle. Next, the random numbers determine corresponding periods for transponders respectively. For example, the response cycle is 4, i.e., transmission every 4 periods, and every transponder has different duration for one period, determined by the random number. Accordingly, transmission time for every transponder is different such that every ID code in response can be read accurately. As shown in FIG. 5, ID code of a transponder C is read first, then ID code of a transponder A is read and final ID code of a transponder B is read. In some random number methods, a random number is compared with a value preset by a reader, and an ID code corresponding to the random number can be transmitted when the random number has the same value as the reader or conversely the ID code cannot be transmitted. However, applying the random number method may cause no response signal during a certain time, and both occurrence point and duration regarding the certain time are unpredictable, thus leading to poor time efficiency. For example, time is wasted at Tc 1 -Tc 4  and Ta 2 -Ta 4  of FIG. 5.  
           [0010]    Therefore, it is desirable to provide an improved system and method to mitigate and/or obviate the aforementioned problems.  
         SUMMARY OF THE INVENTION  
         [0011]    An object of the present invention is to provide a radio frequency identification (RFID) communication system and the search method thereof, which can increase time efficiency.  
           [0012]    Another object of the present invention is to provide a radio frequency identification (RFID) communication system and the search method thereof, which can reduce unnecessary communication and switch between a read and a plurality of transponders, reduce unnecessary guard time and shorten blank time of transmission.  
           [0013]    According to a feature of the present invention, a radio frequency identification (RFID) communication system is provided. The system essentially includes a reader to produce at least one search instruction and to send the search instruction to a communication region; and a plurality of transponders, each, with built-in data, having a first receiver, a first transmitter, a counter, a random number generator and a first controller. When the transponders enter the communication region, in each transponder, the random number generator generates a random number and the counter starts to count the search instruction received by the first receiver to thus obtain a counting value. When in one of the transponders, the counting value meets with the random number, the first controller sends a response request to the reader through the first transmitter, such that the reader after received the response request does not send the search instruction but sends at least one read instruction to read the built-in data.  
           [0014]    According to another feature of the present invention, a search method for radio frequency identification (RFID) communication system is provided. The method includes: a search step, which uses a reader to search at least one transponder in a communication region by means of a plurality of search instructions; a transponder start step, which starts the at least one transponder in the communication region in order to generate a random number and receive the search instructions for counting and further obtaining a counting value; a comparison step, which compares the random number and the counting value such that a response request is sent to the reader as the random number meets with the counting value; and a read step, which uses the reader to send at least one read instruction to the communication region such that one transponder corresponding to the response request sends its built-in data to the reader. At this point, remaining transponders do not count until the built-in data of the transponder is sent completely. Next, the remaining transponders repeat the transponder start step, the comparison step and the read step until all built-in data is read by the reader.  
           [0015]    Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a schematic diagram of essential devices of a typical RFID communication system;  
         [0017]    [0017]FIG. 2 is a schematic diagram of communication between one reader and a plurality of transponders;  
         [0018]    [0018]FIG. 3 is a schematic diagram of the binary search algorithm;  
         [0019]    [0019]FIG. 4 is a flowchart of communication between a read  41  and a transponder  42 ;  
         [0020]    [0020]FIG. 5 is a timing of every transponder using the random number method;  
         [0021]    [0021]FIG. 6 is a schematic diagram of a system configuration according to an embodiment of the invention;  
         [0022]    [0022]FIG. 7 is a flowchart of FIG. 5 according to an embodiment of the invention; and  
         [0023]    [0023]FIG. 8 is a timing of FIG. 5 according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]    [0024]FIG. 6 is a schematic diagram of a system configuration in accordance with a preferred embodiment of the invention, where an example of personnel access control is given. In FIG. 6, the system consists of a reader  61  and three transponders  62 - 64 . As shown in FIG. 6, the reader  61  has a transmitter  611 , a controller  612  and a receiver  613 . Each of the transponders  62 - 64  has a receiver  621 , a transmitter  622 , a counter  623 , a random number generator  624 , a comparator  625  and a controller  626 .  
         [0025]    In this embodiment, the reader  61  is implemented on important entrances and each of the transponders  62 - 64  represents a personal smart card with built-in data (e.g., employee number and certificate number) in an internal memory or represented by received voltage on an external pin. Therefore, personnel access control is achieved by applying the reader  61  to read built-in data of the transponders  62 - 64 .  
         [0026]    The reader  61  can detect a communication region so as to find the transponders  62  in the communication region and read its response data, i.e., the reader  61  transmits a magnetic field such that when the transponder  62  enters the magnetic field, its coil can be induced to produce current to start itself operation. How the reader  61  searches the transponders  62 - 64  and associated built-in data is described hereinafter.  
         [0027]    Next, with reference to FIGS. 6 and 7, there are shown an operation flow of the invention. The controller  612  of the reader  61  continuously sends a plurality of search instructions to the communication region through the transmitter  611 . Each of the search instructions represents a time slot, so that time for continuously sending the search instructions by the reader  61  is divided into many time slots (step S 701 ).  
         [0028]    When three transponders  62 - 64  enter the communication region at the same time (e.g., the time to go to work and off duty), each can produce enough current for work via the magnetic field. After starting the current, each internal random number generator  624  generates a random number. For example, the transponder  62  generates a random number 3, the transponder  63  generates a random number 5 and the transponder  64  generates a random number 5, wherein each random number is regarded as respectively sequential number for read (step S 702 ).  
         [0029]    Each of the transponders  62 - 64  starts to receive search instructions through its receiver  622  and to count search instructions received through its counter  623 , thereby obtaining a counting value. Next, the comparator  625  determines if the counting value meets with the random number (sequential number for read). When the counting value meets with the random number, the controller  626  generates a response request to the reader  61  through the transmitter  622 . For example, when the counter  623  counts to 3, the counting value is found as equal to the random number (sequential number for read) and thus the transponder  62  signals a response request (step  703 ).  
         [0030]    At this point, the receiver  613  receives the response request and accordingly knows having the transponder  62  in the communication region. The controller of the reader  61  issues read instructions of at least one time slot to the communication region (step S 704 ). The transponders  62 - 64  see (receive) the read instructions issued by the reader  61 , whereas only the transponder  62  which issues the response request can respond to the read instructions. Therefore, the controller  626  sends its built-in data to the reader through the transmitter  622 . Because the transponders  63  and  64  do not issue any response request, the read instructions are not available to the transponders  63  and  64 . Thus, the transponders  63  and  64  do not send their built-in data to the reader  61 . At this point, since no search instruction is received, the counting for the search instruction is paused to stop the counting value at 3 (step S 705 ).  
         [0031]    Duration of sending the built-in data by the transponder  62  is based on time slots used in the read instructions issued by the reader  61 . For example, the reader  61  issues the read instructions with 4 time slots and accordingly the transponder  62  sends its built-in data with 4 time slots. When the reader  61  sends the read instructions and starts to receive the built-in data from the transponder  62 , it also detects if collision occurs. If no collision occurs, the reader  61  performs data error detection after the built-in data is received completely. In this embodiment, the data error detection adopts CRC detection. Namely, the reader  61  sends a certain preset number of read instructions to the transponder  62 . The transponder  62  counts read instructions received. When the number of read instructions counted meets with the certain preset number of read instructions, it represents CRC operation is accurate, i.e., transfer success. Next, the transponder  62  enters a mute mode (step S 706 ) such that the reader  61  can focus on reading unsuccessful built-in data from the transponders  63  and  64 .  
         [0032]    Accordingly, the reader  61  sends at least one search instruction again to the communication region (step S 707 ) to start counting action at the transponders  63  and  64 . The counting action starts with the previous value paused, i.e., the value of 3. When the transponders  63  and  64  reach to a counting value of 5, the transponders  63  and  64  concurrently send a response request to the reader  61  because the counting value of 5 meets with their random numbers, such that the reader  61  sends read instructions for sending built-in data to the reader  61  from the transponders  63  and  64 , which causes a collision. When the reader  61  detects data transfer error (CRC operation error) or a collision occurs, the reader  61  does not send read instructions and its controller  612  sends search instruction again to interrupt data transmission. At this point, the transponders  63  and  64  see the collision or the data transfer error because they do not completely send the built-in data but receive the search instruction again. Therefore, the transponders  63  and  64  stop the data transfer and generate a new random number each. For example, the transponder  63  generates a new random number 0 while the transponder  64  generates a new random number 2. After counters in the transponders  63  and  64  is reset to zero for counting. Following steps for sending built-in data of the transponders  63  and  64  are operated as same as steps S 703 -S 706 . Thus, built-in data is read completely from the transponders  62 - 64  to the reader  61 , as shown in FIG. 8, which shows communication between the reader  61  and the transponders  62 - 64 .  
         [0033]    When the reader  61  finds serious collision, the controller  612  generates random length instructions to the communication region, thereby increasing random number range generated by the transponders  62 - 64  and reducing collision probability. If the transponders  62 - 64  have no response (blank time) for a long time, the reader  61  sends random length instruction again, thereby reducing random number range generated by the transponders  62 - 64  and thus shortening the blank time.  
         [0034]    In view of the foregoing, it is known that the invention essentially uses two types of instructions between a reader and multiple transponders. Namely, search instruction and read instruction are used to complete entire read process such that a transponder does not require sending additional information except response request and built-in data. Accordingly, entire communication process is simple and has no guard time. The reader can adjust random number length generated by internal random number generator of each transponder and reduce blank time based on collision situation, thereby increasing read time efficiency.  
         [0035]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.