Abstract:
A system and method are disclosed for transporting deterministic traffic in a gigabit passive optical network. A system that incorporates teachings of the present disclosure may include, for example, an Optical Line Termination (OLT) for exchanging data traffic in a Gigabit Passive Optical Network (GPON) having a controller programmed to generate a timeslot schedule for transport of a desired bandwidth of constant bit rate (CBR) data traffic by selecting one or more timeslots from periodic frame clusters operating according to a GPON Transmission Convergence (GTC) protocol. Additional embodiments are disclosed.

Description:
[0001]    This application is a continuation of U.S. patent application Ser. No. 13/042,402, filed Mar. 7, 2011, which is currently allowed and is a continuation of U.S. Ser. No. 11/999,398, filed Dec. 5, 2007, now U.S. Pat. No. 7,902,985, both of which herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a radio frequency identification (RFID) systems that use RFID tags to track product inventory, or other mobile items. 
       BACKGROUND OF THE INVENTION 
       [0003]    Information management systems are being developed to track the location and/or status of a large variety of mobile entities such as products, vehicles, people, animals, etc. A widely used tracking technology uses so-called RFID tags that are placed physically on the items being tracked. Reference herein to “items” being tracked is intended to include the variety of entities just mentioned as well as, more commonly, product inventories. 
         [0004]    RFID tags may be active or passive. Active tags typically have associated power systems and can transmit data over modest distances. Passive systems lack internal power but derive transmitting signal power from an incoming RF signal. However, transmitting distances with passive RFID tags are very limited. To read a large number of RFID tags, spread over a wide physical area, requires either a large number of RFID readers, or a reliable system of moving RFID readers. One proposed solution to this problem is to use active RFID tags on the products. However, active tags are relatively costly. Although they lend more function to a tracking system, and transmit more effectively, passive tags are typically more cost effective where inventories being tracked are large. 
         [0005]    What is needed is an improved system for RFID tracking where the scale of the application exceeds the performance capability of conventional RFID approaches. 
       STATEMENT OF THE INVENTION 
       [0006]    We have developed a new architecture for RFID systems that is adapted to process large numbers of RFID tags and provide information about a large number of items. The system provides for multiple tag readers. The tag readers are active and have both transmit and receive capability. The system includes a new element called a gateway tag that receives information about individual items from the multiple readers and thus contains data on the entire inventory of items. This allows each of the multiple readers to access data for the entire inventory of items. The gateway tag may interface with an information storage center that also contains data for the entire inventory of items. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The invention may be better understood when considered in conjunction with the drawing in which: 
           [0008]      FIG. 1  is a schematic view of a typical RFID tag system; 
           [0009]      FIG. 2  is a representation of a passive RFID tag; 
           [0010]      FIG. 3  is a representation of an active RFID reader; 
           [0011]      FIG. 4  is a schematic view of the RFID tag system of the invention; and 
           [0012]      FIG. 5  is a representation of a gateway RFID tag according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  is a schematic representation of a typical RFID system wherein the RFID tag is shown at  11 , the RFID reader at  12  and a central information store at  13 . A wide variety of implementations are used for the function of tracking large numbers of items, many of which use the basic elements shown in  FIG. 1 . Typically, the RFID tag  11  is a passive device attached to the item being tracked. The reader  12  is an active RFID device that communicates with large numbers of passive RFID tags, and typically either stores data in the reader, and/or relays data to a central database  13 . The central database keeps data for all items in the system. In many applications, for example, large retail outlets, the RFID readers are mobile devices that are moved around the vicinity of the RFID tags to record the RFID tag data. Mobility in this application is necessary since the transmission distance between the RFID tags and the RFID readers is very limited, for example, tens of meters maximum, and typically less than 10 meters. The RFID readers are typically powered, which extends the range of transmission between the RFID readers and a remotely located receiver. That allows the option of using a RFID reader to simply relay RFID tags to a central database. More typically, the reader reads the passive RFID and stores the information locally. This data may be downloaded to the central store periodically, by placing the reader in a docking device that is connected by wireless or hardwired link to the central database. In the latter case, a wireless link between the RFID reader and a remote receiver may or may not be used. 
         [0014]    A passive RFID tag is shown at  21  in  FIG. 2 . RFID tags are miniaturized as much as practical to allow for the essential elements of a semiconductor IC chip  22 , typically a CMOS chip, and an antenna  23 . The IC chip contains a memory, usually a read-only memory encoded with item data. The antenna is a serpentine metal conductor that receives small amounts of power from the RFID reader by inductive coupling. When the IC chip is powered, it transmits item data back to the RFID reader via antenna  23 . 
         [0015]    Passive RFID tag designs are available in many sizes and designs. Common characteristics are a platform, an IC chip, and an antenna. Depending on the application the platform may be glass, ceramic, epoxy, paper, cardboard, or any suitable plastic. An onboard power source is not included in a passive RFID tag. All power for the tag is derived from RF signals in the vicinity of the tag. The tag responds to the reader using RF backscatter, which basically reflects the carrier wave from the reader after encoding data on the carrier wave. Variables in the communication specification include the frequency of the carrier, the bit data rate, the method of encoding and any other parameters that may be needed. ISO 18000 and EPCGlobal are the standards for this interface. The interface may also include an anti-collision protocol that allows more than one tag in the range of the reader to signal concurrently. There are many specific implementations of this, and these form no part of the invention. 
         [0016]    A typical schematic for an RFID reader is shown in  FIG. 3 . The reader  31  includes RF transceiver chip  32 , microprocessor chip  33 , and battery  34 . The transceiver chip communicates through an attached antenna as indicated. These components allow the reader to not only receive data from the passive RFID tags, but to store and process the data and transmit the data to another device or station. Since the reader is powered, it can transmit data over significant distances, for example, 100 to 3000 thousand feet. 
         [0017]    A schematic of an RFID tag system according to the invention is shown in  FIG. 4 . The RFID tags are shown organized in groups A, B, and C. These groups may represent different departments in a retail outlet, separate floors or buildings in a warehouse complex, separate railroad cars or shipping containers, etc. In the arrangement shown, each group communicates with an associated RFID reader  41 ,  42 , and  43 . It should be understood that this arrangement is shown by way of example only. There are many alternative configurations using RFID tags and readers. The RFID readers communicate with gateway RFID tag  45 . The link between the RFID readers and the gateway RFID tag may operate at a frequency different than the frequency used in the link between the RFID readers and the passive RFID tags. The readers collectively provide data to the gateway RFID tag for all of the items in the system. This arrangement allows any reader in the system to access data on any item in the system via the gateway RFID tag. Since the transmission to and from the gateway RFID tag to the RFID readers is powered, that link may be essentially any distance within the facility served by the RFID system. The gateway RFID tag may be a standalone unit, or, as indicated in  FIG. 4 , interfaced via network  46  to a central database and memory store  47 . The network may be a wireless network, or a wired network (land line). 
         [0018]    A schematic of the gateway RFID tag  45  in  FIG. 4  is shown in  FIG. 5 . The gateway RFID tag is an active tag, with battery  54 . It also has a processor  53 , a large memory  56 , and an RF transceiver  52 . The gateway RFID tag interfaces with each of the RFID readers as shown in  FIG. 4 , and may interface with a central database via a wireless or wired network. The latter is an optional feature. The system may be designed with a direct interface between the RFID readers and the central database, as described in conjunction with  FIG. 1 , and with a parallel link between the RFID readers and the gateway RFID tag. Adding a link between the gateway RFID tag and the central database allows data consistency between the two to be verified. Both of these subsystems typically contain data on all of the items being tracked by the system, i.e. universal system data. However, using an arrangement like that shown in  FIG. 4  allows the universal system data stored at the gateway RFID tag to be different (typically less detailed) than the data stored at the central database. 
         [0019]    For the purpose of defining terms used herein, a passive RFID tag means a device containing at least an integrated circuit chip operating at a given frequency and an antenna, but no onboard power source. The antenna operates as a low power RF transceiver. The integrated circuit chip contains a memory. An RFID reader means a device containing at least an integrated circuit chip, an antenna, an RF transmitter, an RF receiver, and a power source. The integrated circuit chip in the RFID reader contains a memory. The RFID reader has an RF transmitter that operates at the same frequency as the RFID tags, and an RF transmitter that may operate at a frequency different from that of the RFID tags. A gateway RFID tag means a device containing at least an integrated circuit chip, an antenna, an RF transmitter, an RF receiver, and a power source. The integrated circuit chip in the gateway RFID reader contains a memory. The gateway RFID reader has an RF transmitter that operates at the same frequency as the RFID readers, and may have a communications link to a remote central database. A remote central database has a microprocessor and a memory store. It may or may not be located on the same physical premises as the gateway RFID tag. 
         [0020]    Transmitting range means the range over which signals transmitted from a transmitting device can be received by a receiving device. 
         [0021]    In summary, an aspect of the invention is that data from an item that is not in the vicinity of an RFID reader, and thus not accessible directly from that reader, can nevertheless be accessed by that reader through the gateway RFID tag. The sequence of operations for accomplishing this involves transmitting an RFID signal between a first RFID reader and a first group of passive RFID tags, receiving at the first RFID reader first data from the first group of passive RFID tags, transmitting said first data from the RFID reader to a gateway RFID tag, receiving and storing the first data at the gateway RFID tag, transmitting an RFID signal between a second RFID reader and a second group of passive RFID tags, receiving at the second RFID reader second data from the second group of passive RFID tags, transmitting said second data from the RFID reader to the gateway RFID tag, receiving and storing the second data at the gateway RFID tag, transmitting to the gateway RFID tag a query from the first RFID reader, receiving the query at the gateway RFID tag, and transmitting second data from the gateway RFID tag to the first RFID reader. 
         [0022]    Various additional modifications of this invention will occur to those skilled in the art. All deviations from the specific teachings of this specification that basically rely on the principles and their equivalents through which the art has been advanced are properly considered within the scope of the invention as described and claimed.