Abstract:
System and method for tracking inventory of a multiplicity of products. First RFID tags are associated with respective products or groups of products. Second Active RFID tags are associated with respective first containers for the multiplicity products. A third Active RFID tag is associated with a second container for the first containers. First RFID tags broadcast their respective identifications. Second Active RFID tags hash the identities of the first RFID tags within their respective first containers and broad their hashed values. Third Active RFID tag hash the hashed values broadcast by the second Active RFID tags. An expected value is compared to a result of the third Active RFID tag hashing the hashed values broadcast by the second Active RFID tags.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This is a continuation of U.S. patent application Ser. No. 11/333,122 which was filed on Jan. 17, 2006, now U.S. Pat. No. 7,348,886 to Himberger et al. 

   FIELD OF THE INVENTION 
   The present invention relates generally to inventory tracking systems, and more particularly to an inventory tracking system using RFID tags. 
   BACKGROUND 
   Active RFID tags are well known today. For example, the Matrics Group manufactures “MicroSensys™” Active RFID tags, and KSW Microtec manufactures “Smart Active Label™” Active RFID tags. An Active RFID tag includes a small battery, and transmits RF signals via an integral antenna. The battery adds significant cost to the Active RFID tag. The Active RFID may be preprogrammed with an identity that represents the identity of the product which bears the RFID tag. The transmitted RF signals typically include the identity of the Active RFID tag. If the Active RFID tag includes data such as a recorded temperature, the Active RFID tag may transmit the data as well. An Active RFID tags can effectively transmit to a receiver up to 100 meters away. 
   Passive RFID tags are also well known today. A Passive RFID tag does not include a battery; instead, the Passive RFID tag has an integral antenna which receives RF signals from an Active RFID tag or remote transceiver. The transmitted RF signals power the Passive RFID tag, i.e. the Passive RFID tag captures the energy of the RF signals which it receives and uses the energy to drive transceiver and other circuitry on the Passive RFID tag. The transceiver circuitry on the Passive RFID tag transmits the identity coded into the Passive RFID to identify the product which bears the Passive RFID tag. The Passive RFID tag may also include a memory to store any type of information transmitted by the Active RFID tag or other remote transceiver. Typically, Passive RFID tags have a range of about three meters. 
   A known remote transceiver reads the identity information broadcast by the Passive RFIDs or Active RFIDs. The remote transceiver can read RFID tags on packages contained in a box to determine what packages the box contains or to confirm that the packages are all there. Also, the remote readers can read RFID tags on packages at a cash register to determine an amount to charge to the customer (as does a known bar code reader). Also, the remote readers can detect packages at a store exit which bear RFID tags which have not been “disabled” at a cash register, and thereby detect shoplifters. 
   An object of the present invention is to track inventory such as boxes and packages within the boxes. 
   Another object of the present invention is to track inventory of boxes and packages within shipping containers. 
   SUMMARY OF THE INVENTION 
   The present invention resides in a system and method for tracking inventory of a multiplicity of products. First RFID tags are associated with respective products or groups of products. Second Active RFID tags are associated with respective first containers for the multiplicity products. A third Active RFID tag is associated with a second container for the first containers. First RFID tags broadcast their respective identifications. Second Active RFID tags hash the identities of the first RFID tags within their respective first containers and broadcast their hashed values. Third Active RFID tag hash the hashed values broadcast by the second Active RFID tags. An expected value is compared to a result of the third Active RFID tag hashing the hashed values broadcast by the second Active RFID tags. 
   In accordance with features of the present invention, the first RFID tags are Passive RFID tags and the second Active RFID tags are attached to packages containing each product or group of products. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of an RFID inventory tracking system which incorporates the present invention. 
       FIG. 2  is a block diagram of an Active RFID tag; such a tag is included within or attached to each box, each pallet and each shipping container of the RFID inventory tracking system of  FIG. 1 . 
       FIG. 3  is a block diagram of a Passive RFID tag within each package within the RFID inventory tracking system of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described in detail with reference to the figures.  FIG. 1  illustrates an RFID inventory tracking system generally designated  10  according to the present invention. In the illustrated embodiment, system  10  is used in a shipping container  11  containing a multiplicity of pallets  13   a,b , and a plurality of boxes  15  and  17  on pallet  13   a , and a plurality of boxes  19  and  21  on pallet  13   b . In the illustrated example, there are just two boxes on each pallet; however, this is just to simplify the explanation of the present invention. Typically, there are many more boxes on each pallet. Within box  15  are a multiplicity of packages  115   a,b,c , within box  17  are a multiplicity of packages  117   a,b,c , within box  19  are a multiplicity of packages  119   a,b,c  and within box  21  are a multiplicity of packages  121   a,b,c . In the illustrated example, there are just three packages in each box; however this is just to simplify the explanation of the present invention. Typically, there are many more packages in each box. 
   Active RFID tags  33   a,b  are attached to pallets  13   a,b , respectively. In the illustrated embodiment, packages  115   a,b,c  (containing products, not shown) include respective Passive RFID tags  215   a,b,c , packages  117   a,b,c  (containing products, not shown) include respective Passive RFID tags  217   a,b,c , packages  119   a,b,c  (containing products not shown) include respective Passive RFID tags  219   a,b,c  and packages  121   a,b,c  (containing products not shown) include respective Passive RFID tags  221   a,b,c . The Passive RFID tags can be attached to the respective packages by sticky labels that contain flat RFID tags. Alternately, the products themselves within the packages can bear the Passive RFID tags. Alternately, the products themselves bear the Passive RFID tags, and there are not packages at all. Instead, the products are lumped into the boxes. Boxes  15 ,  17 ,  19  and  21  include respective Active RFID tags  315 ,  317 ,  319  and  321 . The Active RFID tags can be attached to the respective boxes by adhesives or embedded within the container walls. There is also an Active RFID tag  400  attached to container  11 . By way of example, container  11  is a shipping container such as that commonly found on an eighteen wheel truck or on a flat bed car of a train. By way of example, Active RFID tag  400  is attached to the underside of a ceiling of container  11 . 
   Active RFID tag  315  transmits RF signals to Passive RFID tags  215   a,b,c  (and incidentally to other Passive RFID tags in the vicinity). The RF signals provide power to operate the Passive RFID tags  215   a,b,c  and identify the Active RFID tag  315 . After authenticating the source of the RF information, each of the Passive RFID tags  215   a,b,c  broadcasts its identification in return. Active RFID tag  315  has a list of all Passive RFID tags within box  15 . Active RFID tag  315  receives the identity of each Passive RFID tag  215   a,b,c , confirms that they are in the list of all Passive RFID tags within box  15 , and then hashes these identities. By way of example, the hashing comprises an XOR (exclusive or), Shift or other bitwise algorithm. 
   Active RFID tag  317  transmits RF signals to Passive RFID tags  217   a,b,c  (and incidentally to other Passive RFID tags in the vicinity). The RF signals provide power to operate the Passive RFID tags  217   a,b,c  and identify the Active RFID tag  317 . After authenticating the source of the RF information, each of the Passive RFID tags  217   a,b,c  broadcasts its identification in return. Active RFID tag  317  has a list of all Passive RFID tags within box  17 . Active RFID tag  317  receives the identity of each Passive RFID tag  217   a,b,c , confirms that they are in the list of all Passive RFID tags within box  17 , and then hashes these identities. By way of example, the hashing comprises an XOR (exclusive Or), Shift or other bitwise algorithm. 
   Active RFID tag  319  transmits RF signals to Passive RFID tags  219   a,b,c  (and incidentally to other Passive RFID tags in the vicinity). The RF signals provide power to operate the Passive RFID tags  219   a,b,c  and identify the Active RFID tag  319 . After authenticating the source of the RF information, each of the Passive RFID tags  219   a,b,c  broadcasts its identification in return. Active RFID tag  319  has a list of all Passive RFID tags within box  19 . Active RFID tag  319  receives the identity of each Passive RFID tag  219   a,b,c , confirms that they are in the list of all Passive RFID tags within box  19 , and then hashes these identities. By way of example, the hashing comprises an XOR (exclusive Or), Shift or other bitwise algorithm. 
   Active RFID tag  321  transmits RF signals to Passive RFID tags  221   a,b,c  (and incidentally to other Passive RFID tags in the vicinity). The RF signals provide power to operate the Passive RFID tags  221   a,b,c  and identify the Active RFID tag  321 . After authenticating the source of the RF information, each of the Passive RFID tags  221   a,b,c  broadcasts its identification in return. Active RFID tag  321  has a list of all Passive RFID tags within box  21 . Active RFID tag  321  receives the identity of each Passive RFID tag  221   a,b,c , confirms that they are in the list of all Passive RFID tags within box  221 , and then hashes these identities. By way of example, the hashing comprises an XOR (exclusive Or), Shift or other bitwise algorithm. 
   In an alternative embodiment of the present invention, Active RFID tags  315 ,  317 ,  319 ,  321  could also be sent information from another reader as a measure of the products in the container. For example, a forklift equipped with a reader can scan the products and hash the results as the products are loaded into the container or other storage unit. Then, the forklift reader sends the hashed results to the Active RFID tags  315 ,  317 ,  319 ,  321 . 
   Active RFID tag  315  broadcasts its identity and hashed value (based on the hashing of the identities of Passive RFID tags  215   a,b,c ). Active RFID tag  317  broadcasts its identity and hashed value (based on the hashing of the identities of Passive RFID tags  217   a,b,c ). After authenticating Active RFID tag  315  and Active RFID tag  317 , Active RFID tag  33   a  hashes the hashed values broadcast from Active RFID tag  315  and Active RFID tag  317 , and broadcasts the result along with the identity of Active RFID tag  33   a.    
   Active RFID tag  319  broadcasts its identity and hashed value (based on the hashing of the identities of Passive RFID tags  219   a,b,c ). Active RFID tag  321  broadcasts its identity and hashed value (based on the hashing of the identities of Passive RFID tags  221   a,b,c ). After authenticating Active RFID tag  319  and Active RFID tag  321 , Active RFID tag  33   b  hashes the hashed values broadcast from Active RFID tag  319  and Active RFID tag  321 , and broadcast the result along with the identity of Active RFID  33   b.    
   After authenticating Active RFID tag  33   a  and Active RFID tag  33   b , Active RFID tag  400  hashes the hashed values broadcast from Active RFID tag  33   a  and Active RFID tag  33   b . Active RFID tag  400  stores and periodically broadcasts the hashed value that it computed from the hashed values broadcast from Active RFID tag  33   a  and Active RFID tag  33   b . (Known software allows the reader to “focus” its read attempts to certain tags, for example, tags that begin with a certain alphanumeric. So if a shipping container had reusable tags for the pallets and the overall reader, then those could be “focused.”) 
   When the shipping container  11  is initially loaded with pallets  13   a,b  and their boxes, the foregoing process is performed so that Active RFID tag  400  computes the initial hash value. Then, the shipping container is transported on a tractor-trailer truck, train, ship etc., and when it reaches each destination an external RFID Reader (not shown) reads the hashed value computed by Active RFID tag  400  and compares it to an expected hashed value. Preferably, the expected hash value is the original hash value determined by Active RFID tag  400  at the initial point of departure. Thus, if one of the Passive RFID tags is not working or missing at the initial point of departure, the expected hash value can still equal the actual hash value determined at the destination. Alternately, the expected hashed value is the hashed value that would result if all of the Passive RFID tags on all of the packages are present (their Passive RFID tags worked and the Active RFID tags properly performed their hashing functions). In either case, the external RFID Reader can obtain the expected hash value from a network. If the actual hashed value broadcast by Active RFID tag  400  at the destination matches the expected hash value, then the inventory in the shipping container is complete, i.e. nothing was lost during shipment. Because hashed values are broadcast by the Active RFID tags, the identities of the packages are hidden. The foregoing process is periodically repeated, so if some of the boxes are unloaded at a destination, new hashed values will be computed as described above for the remaining boxes (and the packages within the remaining boxes), and Active RFID tag  400  will broadcast a new hashed value to the external RFID Reader at the next destination. The external RFID Reader at the next destination will receive (securely via a network, such as PGP, SSH, SCP, or HTTPS) the expected hash value for the remaining contents of the shipping container, and compare the expected hash value to that broadcast from Active RFID tag  400 . If they match, then the inventory in the shipping container is complete, i.e. nothing was lost during shipment. 
     FIG. 2  illustrates each Active RFID tag  315 ,  317 ,  319 ,  321  and  400 , in more detail. Each Active RFID tag includes a battery  40  (such as a Lithium-Ion battery), electronic transceiver circuitry  42 , antenna  44 , integrated circuit CPU  48 , memory  49  (such as EEPROM or SRAM), and memory  56  (such as EEPROM or SRAM). Each Active RFID tag also includes a hashing program  51  in memory  49  for execution on CPU  48 . Transceiver  42  includes a transmitter and a receiver coupled to antenna  44  to transmit and receive RF signals. An RF encoding program  50  in memory  49  executes on CPU  48  to initiate broadcast of the identity of the Active RFID tag to the Passive RFID tags. Memory  56  also stores the identity of Active RFID tag. 
     FIG. 3  illustrates each Passive RFID tag  215   a,b,c ,  217   a,b,c ,  219   a,b,c  and  221   a,b,c  in more detail. Each Passive RFID tag comprises known types of CPU  68 , memory  69  (such as EEPROM or SRAM), transceiver  62 , antenna  64  for the transmitter and receiver, and memory  76  (such as EEPROM or SRAM). Memory  69  contains an RF authentication program  70  which executes on CPU  68  to authenticate a received RF signal and, if authentic, respond with the Passive RFID&#39;s identification. 
   Based on the foregoing, a system and method for tracking inventory of a container have been disclosed. However, numerous modifications and substitutions can be made without deviating the scope of the present invention. For example, in system  10 , the Active RFID tags  33   a  and  33   b  can be omitted, Active RFID tag  400  hashes the hashed values broadcast by Active RFID tags  315 ,  317 ,  319  and  321 , and the hashed valued computed by Active RFID tag  400  and transmitted to an external transceiver is compared to an expected value similarly computed at the initial point of departure. As another example, Active RFID tags could substitute for the Passive RFID tags for items  115   a - c ,  117   a - c ,  119   a - c , and  121   a - c  in  FIG. 1 . In another embodiment of the present invention, there is another layer in the RFID hierarchy such that Active RFID tag  400  reads multiple tags (akin to Active RFID tags  33   a,b ), but these would read sections of tags on the Active RFID tag  33  level. In other words, Active RFID tag  400  would read Active RFID tags  500 - 50 X which would read Active RFID tags  33   a - x  which would read Passive RFID tags  315 ,  317 ,  319 . Therefore, the present invention has been disclosed by way of illustration and not limitation, and reference should be made to the following claims to determine the scope of the present invention.