Abstract:
A radio frequency identification (RFID) system employs multiple band transmission to prevent signal collision. The system includes a plurality of RFID tag groups and at least one RFID reader. Each RFID tag group includes at least one RFID tag. The RFID tags of the same RFID tag group are operated for radio frequency transmission in the same transmission frequency band, and those of different RFID tag groups are operated for radio frequency transmission in different transmission frequency bands. When the RFID reader simultaneously receives radio frequency signals issued from RFID tags of different RFID tag groups, since they are transmitted in different transmission frequency bands, signal collision among the RFID tags of the RFID tag groups can be avoided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a radio frequency identification system that is capable of preventing signal collision, in particular, to a radio frequency identification system with multi-band transmission for preventing signal collision. 
         [0003]    2. Related Art 
         [0004]    A radio frequency identification (RFID) system is an advanced technology that identifies an object by transmitting data through radio frequency and generally consists of an RFID tag and an RFID reader. 
         [0005]    In certain applications, the RFID reader may need to read multiple RFID tags at the same time and such a situation often leads to collision of tag signals. The readability of tag signals can be enhanced if the RFID tags are read one by one. However, it is often that a number of RFID pass by an RFID reader at the same time, and in such a situation, it becomes vitally important to properly handle collision of tag signals. 
         [0006]    Signal collision occurring in an RFID system can be classified as two categories, namely tag signal collision and reader signal collision. The former represents the situation where a RFID reader simultaneously receives signals returned from a number of RFID tags, leading to imprecise receiving of signals or incorrect result of reading, while the later indicates the situation where interference is caused by a tag receiving instructions from a number of readers at the same time. Signal collision simply results in failure and/or missing of signal transmission, or even leads to incorrect data due to incorrect reading of signals, both being hindering the operation of correct identification. 
         [0007]    The state-of-art solution for handling signal collision occurring in RFID tag transmission is the so-called time division multiple access (TDMA), wherein RFID readers are controlled to carry out signal transmission at different time points. However, such a solution is only good for RFID systems that are comprised of RFID readers of small numbers and once the number of the RFID readers installed reaches an upper limit, the reliability and performance of the system get lowered due to over division of time within a given time period. 
       SUMMARY OF THE INVENTION 
       [0008]    In view of the discussion given above, the present invention aims to provide an RFID system that uses multiple band transmission to prevent signal collision, wherein a method that carries out frequency shift for RFID tags returning tag signals to avoid signal collision is employed to ensure no signal collision occurring when RFID tags transmit tag information back to an RFID reader. 
         [0009]    In accordance with the present invention, an RFID system that uses multiple band transmission to prevent signal collision is provided, comprising a plurality of groups of RFID tags and at least one RFID reader. The RFID tag group comprises at least one RFID tag. The RFID tags belonging to the same RFID tag group are operated with radio frequency transmission within the same transmission frequency band, while the RFID tags of different RFID tag groups use different transmission frequency bands to carry out radio frequency transmission. Each RFID tag comprises a microprocessor connected to a memory unit and a radio frequency transmission/reception module for transmitting and receiving a radio frequency signal in a predetermined transmission frequency band. The RFID reader comprises a microprocessor connected to a memory unit and a multiple-band radio frequency transmission/reception module. The multiple-band radio frequency transmission/reception module can alternatively comprise a plurality of radio frequency transmission/reception modules for transmitting/receiving radio frequency signals respectively corresponding to the transmission frequency bands of the RFID tag groups. Since the RFID tags of the RFID tag groups are operated with different working frequencies, no signal collision between the RFID tags of different RFID tag groups may occur when the RFID tags of the different RFID tag groups are transmitting/receiving radio frequency with respect to the RFID reader at the same time. 
         [0010]    Through simple measure of hardware design, the solution provided by the present invention effectively eliminates occurrence of signal collision in applications where the number of RFID tags of an RFID system is increased and thus ensures system reliability and integrity of data transmission and reduces the chance of incorrect reading and data missing. Further, the cost for installing additional RFID readers in an RFID system can be substantially reduced, effectively lowering down the overall hardware installation cost of the RFID system. 
         [0011]    These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. It is to be understood that both the foregoing general description and the following detailed description are examples, and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus is not limitative of the present invention, and wherein: 
           [0013]      FIG. 1  shows a schematic view of a first embodiment in accordance with the present invention; 
           [0014]      FIG. 2  shows a system block diagram of the first embodiment of the present invention; 
           [0015]      FIG. 3  is a schematic view illustrating transmission of radio frequency signals of RFID tags of the first embodiment of the present invention; and 
           [0016]      FIG. 4  shows a system block diagram of a second embodiment in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description refers to the same or the like parts. 
         [0018]      FIG. 1  shows a schematic view of a first embodiment in accordance with the present invention. As shown, an RFID (Radio Frequency Identification) system  100  comprises a plurality of groups of RFID tags, respectively labeled G 1 , G 2 , G 3 . The RFID tag group G 1  is comprised of RFID tags  1   a,    1   b,    1   c;  the RFID tag group G 2  is comprised of RFID tags  2   a,    2   b,    2   c;  and the RFID tag group G 3  is comprised of RFID tags  3   a,    3   b,    3   c.  The RFID tags of the same RFID tag group are operated with radio frequency transmission within a given transmission frequency band, but RFID tags belonging to different RFID tag groups carry out operation of radio frequency transmission with different transmission frequency bands. Due to the fact that radio frequency transmission may be subjected to frequency drift caused by components aging or external interference, the transmission frequency band is set to cover a given reference frequency and a positive frequency interval and a negative frequency interval added on opposite sides of the reference frequency, so that undesired miss of signal transmission can be avoided. Thus, each RFID tag group G 1 , G 2 , G 3  are capable to communicate with an RFID reader  4  through radio frequency signals S 1 , S 2 , S 3  at different frequency bands respectively for transmitting data to a controller host  5  through the RFID reader  4 . Three RFID tag groups are taken as an example in the embodiment illustrated, yet it is apparent to those skilled in the art that the number of the RFID tag groups is not limited to such an example. 
         [0019]    Referring to  FIG. 2 , which illustrates a system block diagram of the first embodiment of the present invention, the illustration given by  FIG. 2  is based on one of the RFID tags constituting the RFID tag groups G 1 , G 2 , G 3  shown in  FIG. 1  and the RFID tag  1   a  of the RFID tag group G 1  will be taken as an example for description here. The RFID tag la comprises a microprocessor  11   a  connected to a radio frequency transmission/reception module  12   a,  a memory unit  13   a,  and a power supply unit  14   a.  The memory unit  13   a  stores tag information  131   a,  which includes a tag identification code  132   a  and tag identification data  133   a.    
         [0020]    Similarly, an RFID tag  2   a  of the RFID tag group G 2  comprises a microprocessor  21   a  connected to a radio frequency transmission/reception module  22   a,  a memory unit  23   a,  and a power supply unit  24   a.  The memory unit  23   a  stores tag information  231   a,  which includes a tag identification code  232   a  and tag identification data  233   a.    
         [0021]    Also, similar to the RFID tag  1   a  of the RFID tag group G 1  and the RFID tag  2   a  of the RFID tag group G 2 , an RFID tag  3   a  of the RFID tag group G 3  comprises a microprocessor  31   a  connected to a radio frequency transmission/reception module  32   a,  a memory unit  33   a,  and a power supply unit  34   a.  The memory unit  33   a  stores tag information  331   a,  which includes a tag identification code  332   a  and tag identification data  333   a.    
         [0022]    The radio frequency transmission/reception module  12   a,    22   a,    32   a  of the respective RFID tag  1   a,    2   a,    3   a  is operated within a respective predetermined transmission frequency band for transmitting and receiving the radio frequency signal S 1 , S 2 , S 3  at different transmission frequency bands and to transmit the tag identification code  132   a,    232   a,    323   a  and the tag identification data  133   a,    233   a,    333   a  of the RFID tag  1   a,    2   a,    3   a  through the radio frequency signal S 1 , S 2 , S 3 . 
         [0023]    The tag identification data  133   a,    233   a,    333   a  contains various information, including for example available tag power (which can be used to evaluate residual of power), tag mode (which can be used to determine if the tag is in a sleeping mode or an operation mode), data of firmware version (which can be used to update version of firmware), data of software version (which can be used to update version of software), transmission bandwidth (which can be used to determine the frequency to be used), transmission power (which can be used to determine transmission power), data of authenticity (which can be used to filter out counterfeit tags), tag owner (which indicates the owner of the tag), and tag group (which indicates the department to which the tag belongs). 
         [0024]    The RFID reader  4  comprises a microprocessor  41  connected to a multiple-band radio frequency transmission/reception module  42 , a memory unit  43 , and a connection interface  44 . The multiple-band radio frequency transmission/reception module  42  functions to transmit and/or receive a radio frequency signal S 1 , S 2 , S 3  in the predetermined transmission frequency band corresponding to each RFID tag group G 1 , G 2 , G 3 . The connection interface  44  connects to the controller host  5  to transmit received data to the controller host  5  for storage or subsequent processing. 
         [0025]    Referring to  FIG. 3 , which is a schematic view illustrating transmission of radio frequency signals of the RFID tags of the first embodiment of the present invention, as shown, since each RFID tag group G 1 , G 2 , G 3  carries out radio frequency transmission within different transmission frequency band, such transmission frequency bands are indicated as frequency points f 1 , f 2 , f 3  in a frequency axis F. In the embodiment illustrated, the RFID tags  1   a,    1   b,    1   c,    2   a,    2   b,    2   c,    3   a,    3   b,    3   c  of each RFID tag group G 1 , G 2 , G 3  are active RFID tags, which obtain the desired electrical power for operation from the power supply units thereof to actively transmit the radio frequency signals S 1 , S 2 , S 3 . When the RFID reader  4  attempts to receive the radio frequency signals S 1 , S 2 , S 3  from the RFID tag groups G 1 , G 2 , G 3 , since these radio frequency signals use different transmission frequency bands and, additionally, since a safety frequency margin is preset between the transmission frequency bands, signal collision occurring due to the RFID tag groups G 1 , G 2 , G 3  being operated at the same frequency can be effectively eliminated. It is apparent to those skilled in the art that although the embodiment discussed takes the active RFID tag as an example, the present invention is equally applicable to passive RFID tag. 
         [0026]    Referring to  FIG. 4 , which shows a system block diagram of a second embodiment in accordance with the present invention, as shown, the system provided by the second embodiment of the present invention is substantially identical to that of the first embodiment, so that identical components will bear the same reference numerals and the description thereof will be omitted. Once again, an RFID system in accordance with the second embodiment, which is broadly designated at  100 ′, comprises an RFID reader  4   a  that comprises a microprocessor  41  connected to a plurality of radio frequency transmission/reception modules  42   a,    42   b,    42   c,  a memory unit  43 , and a connection interface  44 . 
         [0027]    The constituent components of the second embodiment are of substantially identical functions of the counterparts thereof in the first embodiment and a difference resides in that the RFID reader  4   a  of the second embodiment uses the plurality of radio frequency transmission/reception modules  42   a,    42   b,    42   c  to respectively mate the transmission frequency bands of the RFID tag groups G 1 , G 2 , G 3  for transmitting/receiving tag information  131   a,    231   a,    331   a  of the RFID tags  1   a,    2   a,    3   a  of the respective RFID tag groups G 1 , G 2 , G 3 . The measure that is taken by the second embodiment to avoid signal collision between the RFID tag groups G 1 , G 2 , G 3  is similar to that of the first embodiment, and repeated description will be omitted herein. 
         [0028]    Additional advantages and modifications will readily occur to those proficient in the relevant fields. The invention in its broader aspects is therefore not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.