Abstract:
A system and method selectively reads radio frequency identification (“RFID”) tags within an RFID interrogation zone. A portion of the RFID tags have a first operating range and a portion of the RFID tags have a second operating range that is different from the first operating range. Each RFID tag is programmed with an identifier associated with the operating range of the RFID tag. A first interrogation signal is transmitted which has sufficient power to activate RFID tags that are located within the RFID interrogation zone and have the first operating range. A response signal is received from each RFID tag capable of receiving the first interrogation signal. Each response signal indicates the identifier of the associated RFID tag. Each RFID tag that has an identifier associated with the first operating range is selected.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
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     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     FIELD OF THE INVENTION 
     The present invention relates generally to radio frequency identification (“RFID”) systems and more specifically to a method and system for discriminating between short range RFID tags and long range RFID tags, and only identifying tags passing through an RFID portal. 
     BACKGROUND OF THE INVENTION 
     One of the key applications for RFID is inventory control. When an item is tagged with an RFID tag and moved through the supply chain, the ability to track the RFID tag facilitates the operation of the supply chain. However, RFID readers are not installed to cover the whole supply chain due to the cost and complication with such an approach. Instead, RFID readers are deployed at the check/transition points along the supply chain, e.g., at a loading dock door between the warehouse and truck, at a doorway between backroom and retail floor, etc. RFID readers in these locations are sometimes referred to as portal readers. The RFID tags on the items are supposed to be read only when the item passes through the portal. However, some “long range” RFID tags are generally designed to maximize the gain and efficiency of their antennas. This mixed tag environment results in long range RFID tags that are near the portal but beyond the doorway being unintentionally read, leading to errant tracking of the tagged item. This problem is generally referred to as over-range problem. 
     To limit the range of the RFID reader to the doorway, a reduction of the reader transmit power is sometimes used. This approach requires that all RFID tags have a similar read range. As other RFID applications have developed, some items now require the use of a small “short range” tag which has a lower read range. The small tag is not able to be read with the reduced transmitted power. Therefore, configuring the transmit power of the RFID reader to accommodate all tags in this mixed tag environment results in either over range or a failed read. 
     In addition to reducing the level of transmit power as described above, others have attempted to improve the performance of the small tag. Due to the physics behind the electromagnetic radiation and the interaction of antenna configuration of the RFID tag, such attempts inefficiently result in a physically larger tag than is actually required for the application. 
     RFID readers having more complex antenna systems have been designed to focus the RF field and restrict read range to a limited area or volume. However, the deployment of complex antenna naturally results in higher cost. 
     Therefore, what is needed is a system and method to discriminate between short range RFID tags and long range RFID tags and only read tags passing through an RFID interrogation zone, e.g., RFID portal. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously provides a method and system for selectively reading only radio frequency identification (“RFID”) tags located within an RFID interrogation zone. Generally, each RFID tag is programmed with an identifier associated with the operating range of the RFID tag. Depending upon the transmit power level of an RFID reader, only RFID tags programmed with a predetermined identifier are selected for reading. 
     In accordance with one embodiment of the present invention, a method is provided for selectively reading RFID tags within an RFID interrogation zone. A portion of the RFID tags have a first operating range and a portion of the RFID tags have a second operating range different from the first operating range. Each RFID tag is programmed with an identifier associated with the operating range of the RFID tag. A first interrogation signal is transmitted which has sufficient power to activate RFID tags located within the RFID interrogation zone which have the first operating range. A response signal is received from each RFID tag capable of receiving the first interrogation signal. Each response signal indicates the identifier of the associated RFID tag. Each RFID tag that has an identifier associated with the first operating range is selected. 
     In accordance with another aspect of the present invention, an RFID reader for selectively reading RFID tags within an RFID interrogation zone includes a transceiver and a processor. A portion of the RFID tags have a first operating range and a portion of the RFID tags have a second operating range different from the first operating range. Each RFID tag is programmed with an identifier associated with the operating range of the RFID tag. The transceiver is operable to transmit a first interrogation signal having sufficient power to activate RFID tags located within the RFID interrogation zone which have the first operating range and receive a response signal from each RFID tag capable of receiving the first interrogation signal. Each response signal indicates the identifier of the associated RFID tag. The processor is electrically connected to the transceiver. The processor is operable to select each RFID tag having an identifier associated with the first operating range. 
     In accordance with yet another aspect of the present invention, an RFID system includes a plurality of RFID tags and an RFID reader. A portion of the RFID tags have a first operating range and a portion of the RFID tags have a second operating range. The first operating range is smaller than the second operating range. Each RFID tag is programmed with an identifier associated with the operating range of the RFID tag. The RFID reader is operable to transmit a first interrogation signal having sufficient power to activate RFID tags located within an interrogation zone which have the first operating range and receive a response signal from each RFID tag capable of receiving the first interrogation signal. Each response signal indicates the identifier of the associated RFID tag. The RFID reader is further operable to select each RFID tag having an identifier associated with the first operating range and read each selected RFID tag. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a block diagram of an exemplary radio frequency identification (“RFID”) system constructed in accordance with the principles of the present invention; 
         FIG. 2  is a block diagram of an exemplary RFID reader constructed in accordance with the principles of the present invention; 
         FIG. 3  is a flow chart of an exemplary RFID tag discriminating process according to the principles of the present invention; 
         FIG. 4  is a diagram of an exemplary RFID system identifying short range tags according to the principles of the present invention; and 
         FIG. 5  is a diagram of an exemplary RFID system identifying long range tags according to the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before describing in detail exemplary embodiments that are in accordance with the present invention, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to implementing a system and method for discriminating between short range radio frequency identification (“RFID”) tags and long range RFID tags so that only RFID tags passing through an RFID portal are read. Accordingly, the system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
     As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. Additionally, as used herein, the terms “RFID tags” and “RFID labels” are used interchangeably. 
     One embodiment of the present invention advantageously provides a method and system for discriminating between short range RFID tags and long range RFID tags. Generally, one embodiment of the present invention provides an RFID reader with the ability to switch to different transmit levels and read the stored information on the read range of the tag to overcome the over range or inadequate read problem due to the different range of tags of different designs. RFID tags are identified as short range or long range tags by setting at least one identification bit in the RFID tag. When the reader is at high transmit level, reads associated with short range tags are all valid, while at low transmit level, both the short range and long range tag reads are valid. Therefore, to validate the read, the reader requires the knowledge about the read range of the tag which could be stored in and read from the memory of the RFID tag. 
     Referring now to the drawing figures in which like reference designators refer to like elements, there is shown in  FIG. 1  one configuration of an exemplary RFID system  10  constructed in accordance with the principles of the present invention and located, for example, at a facility entrance. RFID system  10  includes a pair of pedestals  12   a ,  12   b  (collectively referenced as pedestal  12 ) on opposite sides of an entrance. One or more antennas for the EAS detection system  10  may be included in pedestals  12   a ,  12   b . The antennas located in the pedestals  12  are electrically coupled to an RFID reader  14  which transmits a radio frequency signal forming an interrogation zone  16  between the pedestals  12   a ,  12   b . The RFID reader  14  is capable of distinguishing between long range RFID tags  18   a ,  18   b ,  18   c  (referenced collectively as “long range tag  18 ”) and short range RFID tags  20   a ,  20   b ,  20   c ,  20   d ,  20   e ,  20   f  (referenced collectively as “short range tag  20 ”). 
     In one embodiment, each RFID tag  18  and  20  includes an RFID chip having a memory (not shown) designated for information associated with the manufacturer of the RFID chip. For example, the TID memory location of the RFID chip may be used to discriminate two tag designs during inventory—one with a small inlay design (“short range”) and one with a large inlay design (“long range”). The Transponder ID (“TID”) memory location of the RFID chip may be programmed at the point of manufacture with specific 12 bit tag model numbers, e.g., bits  14   h  to  1 Fh are currently allocated for the tag model number. One model number may designate a short range tag, and another model number may designate a long range tag. The standard Electronic Product Code (“EPC”) air protocol may be used to conduct and inventory round customized for each tag design, for example, by using the EPC SELECT command. 
     Referring now to  FIG. 2 , an exemplary RFID reader  14  may include a controller  22  (e.g., a processor or microprocessor), a power source  24 , a transceiver  26 , a memory  28  (which may include non-volatile memory, volatile memory, or a combination thereof) and a communication interface  30 . The controller  22  controls radio communications, storage of data to memory  28 , and communication of stored data to other devices. The power source  24 , such as a battery or AC power, supplies electricity to the RFID reader  14 . 
     The transceiver  26  may include a transmitter  32  electrically coupled to one or more transmitting antennas  34  and a receiver  36  electrically coupled to one or more receiving antennas  38 . Alternately, a single antenna or pair of antennas may be used as both the transmitting antenna  34  and the receiving antenna  38 . The transmitter  32  transmits a radio frequency signal using the transmit antenna  34  to “energize” a passive RFID tag within the interrogation zone  16  of the RFID system  10  and/or communicate with an active RFID tag. The receiver  36  detects the response signal of the RFID tag using the receive antenna  38 . A gain controller  40  controls the output power level of the transmitter  32  and/or the receiver  36  sensitivity to switch the transceiver  26  between a short range tag detection mode and a long range detection mode. 
     The memory  28  may include an RFID tag discriminator  42  for determining the type of RFID tag responding within the interrogation zone. Operation of the RFID tag discriminator  42  is described in greater detail below. 
     Referring now to  FIG. 3 , a flow chart is provided that describes exemplary steps performed by the RFID reader  14  to identify only RFID tags that are located within the interrogation zone  16 . In this embodiment, the RFID system  10  makes use of the RFID tag&#39;s EPC TID memory during an inventory, specifically to prevent reading and reporting tag IDs, e.g., EPC numbers, beyond the intended range of the RFID portal. It should be noted that the RFID system  10  may include multiple RFID readers  14  and antennas  12  performing inventory functions for different portal zones. An RFID reader  14  prepares to inventory short range tags  20  (“short range tag inventory”) by setting the transmit power to a setting optimized for these short range tags  20  (step S 102 ).  FIG. 4  illustrates a scenario for short range tag inventory. The short range tag power setting may be determined in practice by determining the maximum transmit power required to read short range tags  20  within the intended portal range  16  with reasonable reliability. Short range tags  20  beyond the intended portal zone  16 , e.g., in zone  44  in  FIG. 4 , are not read due to insufficient power. The reader  14  issues a SELECT command specifying only the short range tag model number in the tag TID (step S 104 ). Because of this SELECT command, long range tags  18  will not respond to the inventory round that follows. In the absence of the present invention, long range tags  18  that are outside the intended portal range  16 , e.g., in zone  46  in  FIG. 4 , at this reader transmit power level, would normally respond during the inventory. The SELECT command advantageously prevents these long range tags  18  from responding. The RFID reader  14  then reads the short range tags  20  within the intended portal range  16  to complete the short range tag inventory (step S 106 ). 
     Once the “short range tag inventory” is completed, the RFID reader  14  prepares to inventory long range tags  18  (“long range tag inventory”) by setting the transmit power to a setting optimized for these long range tags  18  (step S 108 ).  FIG. 5  illustrates a scenario for long range tag inventory. The long range power setting may be determined in practice by determining the maximum transmit power required to read long range tags  18  within the intended portal range  16  with reasonable reliability. The long range power tends to be a lower transmit power than the setting used in the “short range tag inventory.” Thus, both the long range tags  18  and short range tags  20  that are outside the intended portal zone  16 , e.g., in zone  48  and zone  50  in  FIG. 5 , are out of range and do not respond. The RFID  14  reader issues a SELECT command specifying only the long range tag model number in the tag TID (step S 110 ). Because of this SELECT command, short range tags  20  within the intended portal zone  16  do not respond to the inventory round that follows and only the long range tags  18  within the intended portal zone  16  are read (step S 112 ). Optionally, at this lower power setting, the SELECT command could be omitted, reading all tag models in the inventory round that follows. It is noted that that process shown in  FIG. 3  can be periodically repeated by reader  14  at predetermined intervals to update the inventory within interrogation zone  16 . 
     An alternative embodiment of the present invention uses an EAS bit. The existence of an EAS bit is currently being proposed and reviewed by the EPCglobal Hardware Action Group; however, there is no defined use for the functionality of the EAS bit. This alternative approach is particularly appropriate for combination EAS and RFID item level intelligence applications where the over range/inadequate read problem was first observed. A hard tag with very small footprint is required in this item level intelligence application. The small footprint limits the read range of the tag. Using the EAS bit, which should always be active in an EAS hard tag, the reader can determine that it is a short read range tag. Another advantage of using the EAS bit in the RFID is the capability of direct access to the EAS bit before accessing the ID of the tag, thereby allowing for a quick determination of a short range tag without having to read the model number. 
     The present invention can be realized in hardware, software, or a combination of hardware and software. Any kind of computing system, or other apparatus adapted for carrying out the methods described herein, is suited to perform the functions described herein. 
     A typical combination of hardware and software could be a specialized or general purpose computer system having one or more processing elements and a computer program stored on a storage medium that, when loaded and executed, controls the computer system such that it carries out the methods described herein. The present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which, when loaded in a computing system is able to carry out these methods. Storage medium refers to any volatile or non-volatile storage device. 
     Computer program or application in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following a) conversion to another language, code or notation; b) reproduction in a different material form. 
     In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. Significantly, this invention can be embodied in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be had to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.