Patent Publication Number: US-2009224892-A1

Title: Mobile rfid tag tracking system using cellular systems

Description:
This application claims the benefit of U.S. provisional patent application Ser. No. 60/606,051, filed Aug. 31, 2004, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to tracking the location of a Radio Frequency Identification (RFID) tag attached to an object using a cellular network and more particularly relates to tracking the RFID while within and outside of the cellular network. 
     BACKGROUND OF THE INVENTION 
     In today&#39;s society, there is an ever increasing number of kidnappings and burglaries, and the focus on Homeland Security has become of utmost importance. Accordingly, it is desirable to monitor the movement of entities such as children, automobiles, weapons, and the like. However, to date, no system exists for tracking the movement of entities across a large geographic area such as a city, state, or country. Thus, there is a need for a system for tracking the movement of valuable entities over a large geographic area. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system for tracking a Radio Frequency Identification (RFID) tag within or outside of a cellular network using mobile hosts associated with the cellular network. In general, a person or entity sends a request for the location of the RFID tag to a processing node of the cellular network. The processing node of the cellular network then instructs each mobile host within the cellular network to track the RFID tag. When any RFID tag enters a coverage area of one of the mobile hosts, the identification indicia (ID) of the RFID tag is communicated to the mobile host. The mobile host determines if the RFID tag is the one to be tracked. If so, the mobile host obtains its location and stores the location and a time stamp for the RFID tag. The mobile host provides the location and time stamp of the RFID tag to other mobile hosts using a broadcast transceiver or other wireless communication device directly without using the cellular network. More specifically, when other mobile hosts enter a coverage area of the mobile host, the location and time stamp for the RFID tag are provided to the other mobile hosts. Thereafter, each of the mobile hosts having the location and time stamp for the RFID tag continues to communicate the location and time stamp to other mobile hosts. In the event that two mobile hosts communicate location information to each other regarding the same RFID tag, then the location associated with the most recent time stamp takes precedence. Consequently, if the mobile host receiving the broadcast transmission from another mobile host has location information that has a more recent time stamp than the location information being broadcast, the location information of the receiving mobile host will not change. Conversely, if the receiving mobile host location information is less recent than the location information being broadcast, then the location information at the receiving mobile host will be updated. In this manner, each of the mobile hosts obtains the most recent location information for the RFID tag. When one of the mobile hosts having the location and time stamp for the RFID tag enters the cellular network, the mobile host provides the location and time stamp of the RFID tag to the processing node via the cellular network. The processing node stores the location and time stamp of the RFID tag and communicates the location, and optionally the time stamp, to the requesting person or entity. 
     Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  illustrates an exemplary system for tracking a Radio Frequency Identification (RFID) within and external to a cellular network according to one embodiment of the present invention; 
         FIG. 2  is a data management diagram of the system of  FIG. 1 ; 
         FIG. 3A  illustrates an exemplary active RFID according to one embodiment of the present invention; 
         FIG. 3B  illustrates an exemplary passive RFID according to one embodiment of the present invention; 
         FIG. 4  is an exemplary embodiment of a mobile host including a transceiver enabling communication with the cellular network, a broadcast transceiver enabling communication with an RFID and other mobile hosts, and a Global Positioning System (GPS) receiver; 
         FIG. 5  is a second exemplary embodiment of a mobile host including a transceiver enabling communication with the cellular network, a broadcast transceiver enabling communication with an RFID and other mobile hosts, and a Global Positioning System (GPS) receiver; and 
         FIG. 6  is a more detailed block diagram illustrating the processing node of the cellular network illustrated in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     As illustrated in  FIG. 1 , the present invention provides a system  10  for tracking an Radio Frequency Identification (RFID) tag  12  or similar device within or external to a cellular network  14  using mobile hosts  16  ( 16 A- 16 D) associated with the cellular network  14 . There may be any number of RFID tags  12  in the system  10 . However, for clarity, only one RFID tag  12  is illustrated. In one embodiment, RFID tag  12  operates in one of the Industrial, Scientific, or Medical (ISM) bands, which are 900 MHz, 2.4 GHz, and 5.8 GHz. Further, exemplary embodiments of the RFID tag  12  may have a transmission range in the range of and including 1 m to 100 m. Longer or shorter transmission ranges may be used as needed or desired. The RFID tag  12  may be attached to various types of objects, persons, or animals that are desired to be tracked, which are generally referred to herein as tagged objects. For example, the RFID tag  12  may be attached to a passport, inventory, children, prisoners, automobiles, and the like. In one embodiment, when it is desirable to track a person or animal, the RFID tag  12  may be implanted into the person or animal. Also, the any of the mobile hosts  16  may operate as an RFID tag through the association of a unique identification code that the mobile host  16  broadcasts in an identical fashion to an active RFID tag. 
     In its simplest form, the RFID tag  12  stores and communicates an identification indicia (ID) associated with the person, animal, or object to be tracked. The RFID tag  12  may also obtain dynamic information relating to the tagged object such as health status of a person or animal in terms of heart rate, temperature, or blood pressure. Other types of dynamic information may include information indicating whether the RFID tag  12  has been removed from the tagged object and information indicating whether the tagged object, such as a child, has actively placed the RFID tag  12  into a panic state by, for example, pressing a panic button. 
     The mobile hosts  16  are mobile devices having transceivers for communicating with the cellular network  14 . For example, the mobile hosts  16  may be mobile telephones  16 A,  16 B or a device  16 C,  16 D installed in a mobile vehicle such as an automobile. In addition, each of the mobile hosts  16  includes a broadcast transceiver, or other wireless communication circuitry, and location system such as a Global Positioning System (GPS) receiver (see  FIGS. 4 and 5 ). The broadcast transceiver enables direct communication with the RFID tag  12  and other mobile hosts  16 , and the location system provides the location of the mobile host  16  when desired. Like the RFID tag  12 , in one embodiment, the broadcast transceiver operates in one of the Industrial, Scientific, or Medical (ISM) bands, which are 900 MHz, 2.4 GHz, and 5.8 GHz. Further, exemplary embodiments of the broadcast transceiver have a transmission range in the range of and including 1 m to 100 m. Longer or shorter transmission ranges may be used as needed or desired. Using the broadcast transceiver, the mobile host  16  may obtain the ID, and optionally additional dynamic information, from the RFID tag  12  when the RFID tag  12  is within its coverage area. In addition, the mobile host  16  may use the broadcast transceiver to communicate information indicating the IDs of the RFID tags  12  to track, the location information of the RFID tags  12  to track, and optionally dynamic information from the RFID tags  12  to track to other mobile hosts  16 . 
     In operation, a person or entity desiring to know the location of the tagged object requests the location of the RFID tag  12  from the cellular network  14 . The location of the tagged object may be requested via one of the mobile hosts  16 . However, the location of the tagged object may also be requested via a land-line phone or over the internet. Many other methods of requesting the location of the tagged object will be apparent to one of ordinary skill in the art upon reading this disclosure. Various security features may be implemented to ensure that only authorized persons or entities may request the location of the RFID tag  12 . For example, in one embodiment, only the parents or guardians of a child tagged with the RFID tag  12  may request the location of the RFID tag  12 . 
     In response to receiving the request, the cellular network  14  notifies each of the mobile hosts  16  within the cellular network  14  to track the RFID tag  12 . As discussed below, this may be done by updating an RFID tag register storing a list of RFID tags to track in each of the mobile hosts  16  to include the RFID tag  12 . Thereafter, the mobile host  16  provides the list of RFID tags  12  to track to other mobile hosts  16  within its coverage area. In one embodiment, the mobile host  16  broadcasts the lists of RFID tags  12  to track to other mobile hosts  16  regardless of whether the mobile host  16  is within or outside of the cellular network  14 . In another embodiment, the mobile host  16  broadcasts the list of RFID tags  12  to track only when outside of the cellular network  14 . 
     When the RFID tag  12  enters the coverage area of the broadcast transceiver of one of the mobile hosts  16 , the ID stored by the RFID tag  12 , and optionally dynamic information, is communicated to the mobile host  16 . Upon receiving the ID from the RFID tag  12 , the mobile host  16  determines if the RFID tag  12  is one of the RFID tags to be tracked by comparing the ID from the RFID tag  12  to the IDs in the list of RFID tags  12  to track. If the RFID tag  12  is one of the RFID tags  12  to track, the mobile host  16  determines its location and stores the location and a time stamp for the RFID tag  12  in an RFID tag location register of the mobile host  16 . 
     Thereafter, if the mobile host  16  is within the cellular network  14 , the mobile host  16  communicates the location, time stamp, and optionally dynamic information for the RFID tag  12  to the cellular network  14 . In one embodiment, the cellular network  14  periodically polls the mobile hosts  16  within the cellular network  14  for the location of the RFID tag  12 , thereby initiating communication of the location, time stamp, and optionally dynamic information for the RFID tag  12  from the mobile host  16  to the cellular network  14 . The cellular network  14  stores the location, time stamp, and optionally dynamic information, and communicates this information to the requesting person or entity. The location, time stamp, and optionally dynamic information for the RFID tag  12  may be cleared from the memory of the mobile host  16  after it is communicated to the cellular network  14 . It should be noted that in one embodiment, the cellular network  14  may store only a predetermined number of most recent locations of the RFID tag  12 . For example, the cellular network  14  may store the 100 most recent locations of the RFID tag  12  when tracking the RFID tag  12 . 
     If the mobile host  16  is outside of the cellular network  14  when the location of the RFID tag  12  is determined, the mobile host  16  periodically transmits the IDs of the RFID tags to be tracked to other mobile hosts  16  within its coverage area using its broadcast transceiver. In addition, since the mobile host  16  has obtained the location of the RFID tag  12 , the mobile host  16  periodically transmits the location, time stamp, and optionally dynamic information for the RFID tag  12  in addition to the list of RFID tags to track to other mobile hosts  16  within its coverage area using the broadcast transceiver. Thereafter, each mobile host  16  having the location, time stamp, and optionally dynamic information for the RFID tag  12  continues to broadcast this information to other mobile hosts  16 . When one of the mobile hosts  16  having the location, time stamp, and optionally dynamic information for the RFID tag  12  enters the cellular network  14 , that mobile host  16  communicates the location, time stamp, and optionally dynamic information for the RFID tag  12  to the cellular network  14 . As discussed above, the cellular network  14  stores this information and provides the location of the RFID tag  12  to the requesting party. It should be noted that the location and time stamp of the RFID tag  12  may be communicated between any number of mobile hosts  16  outside the cellular network  14 . In the event that two mobile hosts  16  transmit RFID tag location information to each other, the location with the most recent time stamp takes precedence and is used to update the location registers of the mobile hosts  16 . In the event that the location and time exchange between two mobile hosts  16  with respect to the same RFID tag are identical then no update of the location registers is made. 
     In another embodiment, the tracking of the RFID tag  12  may be initiated by the RFID tag  12  when the RFID enters a panic state by, for example, activation of a panic button. Alternatively, the panic state may be entered automatically by the RFID tag  12  based upon dynamic information such as the blood pressure, pulse, or the like of the person to whom the RFID tag  12  is attached. If the RFID tag  12  is not already one of the RFID tags to track, the entering the panic state may add the RFID tag  12  to the list of RFID tags to track. More specifically, another mobile host  16  coming into the coverage area of the RFID tag  12  may not be tracking the RFID tag  12 . However, in response to the entering the panic state, the RFID tag  12  may provide information to the mobile host  16  indicating that it is to be added to the location register as an RFID tag  12  to be tracked. The mobile host  16  may then broadcast the updated list of RFID tags  12  to track along with the location and time stamp for the RFID tag  12 . Once the location and time stamp for the RFID tag  12  is communicated to the cellular network  14 , the cellular network  14  may then determine that the RFID tag  12  has come online to be tracked the cellular network  14 . The cellular network  14  may then alert the mobile hosts  16  within the cellular network  14  that the RFID tag  12  is to be tracked and contact emergency authorities and those paying for monitoring of the RFID tag  12 . This sequence of events is different from the search being initiated by a user contacting the cellular network  14  and requesting a search in that the search is initiated by the RFID tag  12  rather than a requesting party. 
     Now turning to the specific example illustrated in  FIG. 1 , the user of the mobile host  16 A requests the location of the RFID tag  12  from the cellular network  14  via the mobile host  16 A. The cellular network  14  then notifies each of the mobile hosts  16 A,  16 B, and  16 C within the cellular network  14  to track the RFID tag  12 . Thereafter, the mobile host  16 B moves outside of the cellular network  14 , and the RFID tag  12  enters the coverage area of the broadcast transceiver of the mobile host  16 B. While the RFID tag  12  is within the coverage area of the broadcast transceiver of the mobile host  16 B, the ID of the RFID tag  12  and optionally dynamic information from the RFID tag  12  is communicated to the mobile host  16 B. The mobile host  16 B compares the ID of the RFID tag  12  to the list of RFID tags to track previously provided by the cellular network  14 . Since the RFID tag  12  is to be tracked, the mobile host  16 B determines its location using a GPS receiver or the like, and stores the location, a time stamp, and optionally the dynamic information for the RFID tag  12 . While RFID tag  12  remains within the coverage area of the mobile host  16 B, the time and location information associated with RFID tag  12  will be periodically updated. In an alternative embodiment, the RFID tag  12  may include a GPS receiver or a similar location system such that the location of the RFID tag  12  is determined by the RFID tag  12  rather than the mobile host  16 B, as would be the case if a mobile host  16 B were the RFID tag to be located 
     At some point, the mobile host  16 B moves away from the RFID tag  12 . Similarly, the mobile host  16 C moves out of the cellular network  14 . Thereafter, the mobile hosts  16 B and  16 C come in contact with one another at a point  18 , wherein the mobile host  16 C is within the coverage area of the broadcast transceiver of the mobile host  16 B and vise versa. Using its broadcast transceiver, the mobile host  16 B communicates the location, time stamp, and optionally dynamic information for the RFID tag  12  to the mobile host  16 C. The mobile host  16 C then comes into contact with the mobile host  16 D at point  20 , wherein the mobile host  16 D is within the coverage area of the broadcast transceiver of the mobile host  16 C and vise versa. Using its broadcast transceiver, the mobile host  16 C communicates the IDs of the RFID tags to track, which include the ID of the RFID tag  12 , to the mobile host  16 D. In addition, the mobile host  16 C communicates the location, time stamp, and optionally dynamic information for the RFID tag  12  to the mobile host  16 D. In the event that mobile host  16 D already has a time and location associated with the RFID tag  12 , then the location and optionally dynamic information with the most recent time stamp takes precedence and is used to update the location register of mobile hosts  16 C and  16 D. Thereafter, the mobile host  16 D enters the cellular network  14 , and the location, time stamp and optionally dynamic information for the RFID tag  12  is communicated to the cellular network  14  from the mobile host  16 D. As stated above, in one embodiment, the cellular network  14  periodically polls the mobile hosts  16  within the cellular network  14  for the location of the RFID tag  12 , thereby initiating communication of the location and time stamp for the RFID tag  12  from the mobile host  16 D to the cellular network  14 . The cellular network  14  stores the location and time stamp for the RFID tag  12  and communicates this information to the requesting person or entity. It should be noted that in one embodiment, the cellular network  14  may store only a predetermined number of most recent locations of the RFID tag  12 . For example, the cellular network  14  may store the 100 most recent locations of the RFID tag  12  when tracking the RFID tag  12 . 
       FIG. 2  is a data management diagram of the system  10  for tracking the RFID tag  12  according to one embodiment of the present invention. In general, to initiate tracking of the RFID tag  12 , a person or entity  22  sends a request for the location of the RFID tag  12  to the cellular network  14 . More specifically, the request is sent to a processing node  24  of the cellular network  14 . In this embodiment, the processing node  24  is part of the cellular network  14 . However, the processing node  24  may alternatively not be part of the cellular network  14 . As used herein, dashed lines represent wireless connections and solid lines represent wired connections. Thus, as indicated by the dashed line  26 , the person or entity  22  may send the request wirelessly through the cellular network  14 . Alternatively, the person or entity  22  may send the request to the cellular network  14  through a wired connection (line  28 ). The processing node  24  of the cellular network  14  then adds the ID of the RFID tag  12  to the RFID tag register  30 . In this embodiment, the connection between the processing node  24  and the RFID tag register  30  is a wired connection (line  32 ). The RFID tag register  30  of the cellular network  14  contains a list of every RFID tag to be tracked by the cellular network  14 . The processing node  24  of the cellular network  14  then updates the RFID tag registers  34  of the mobile hosts  16  within the cellular network  14  with the ID of the RFID tag  12  to be tracked (dashed line  36 ). 
     When the RFID tag  12  enters the coverage area of the broadcast transceiver of one of the mobile hosts  16 , the ID of the RFID tag  12 , and optionally dynamic information, is communicated wirelessly from the RFID tag  12  to the mobile host  16 , as indicated by dashed line  38 . When the mobile host  16  receives the ID information from the RFID tag  12 , the mobile host  16  compares the ID to the list of RFID tags to track stored in the RFID tag register  34 . If the ID matches that of an RFID in the list of RFID tags to track or if the transmission from the RFID tag  12  carries a request to be tracked, such as when the panic button on the RFID tag has been pressed, the mobile host  16  then acquires the location of the mobile host  16  via a satellite navigation system  40 , such as the GPS. Note if a new RFID tag  12  is added to the location register of a mobile host  16  by the RFID tag  12  being placed in panic mode, then the mobile host  16  will transfer the new ID of the new RFID tag to track to other mobile hosts  16  in its broadcast area and also to the cellular network  14 . For the GPS, signals (dashed line  42 ) are transmitted by a constellation of satellites. Based on these signals, a GPS receiver within the mobile host  16  determines its location. 
     Once the mobile host  16  has determined its location, the location, time stamp, and optionally dynamic information for the RFID tag  12  are stored in a RFID tag location register  44 . When the mobile hosts  16  are outside of the cellular network  14  and within the coverage area the broadcast transceiver of another mobile host  16 , information indicating the RFID tags to track and the location, time stamp, and optionally dynamic information for the RFID tag  12  are exchanged (dashed line  46 ) such that each of the mobile hosts  16  has the most up-to-date list of RFID tags to track in their RFID tag register  32  and the location, time stamp, and optionally dynamic information for the RFID tag  12  stored in their respective RFID tag location register  44 . Once either of the mobile hosts  16  re-enters the cellular network  14 , the location, time stamp, and optionally dynamic information for the RFID tag  12  is communicated to the processing node  24  of the cellular network  14  (dashed line  36 ), and the processing node  24  stores the location, time stamp, and optionally dynamic information for the RFID tag  12  in an RFID tag location register  48 . The RFID tag location register  48  stores one or more locations and corresponding time stamps for each of the RFID tags stored in the RFID tag register  30 . For example, the RFID tag location register  48  may store 100 most recent locations for each RFID tag to be tracked by the cellular network  14 . The processing node  24  may then communication the most recent location or all stored locations for the RFID tag  12  to the requesting person or entity  22  via wireless connection  26  or wired connection  28 . 
       FIGS. 3A and 3B  illustrate exemplary embodiments of the RFID tag  12 . More specifically,  FIG. 3A  illustrates an exemplary embodiment of the RFID tag  12  wherein the RFID tag  12  is an active RFID tag. In this embodiment, the active RFID tag  12  includes a battery  50 , a microcontroller  52 , a transmitter  54 , and an antenna  56 . The battery  50  powers both the microcontroller  52  and the transmitter  54 . The microcontroller  52  contains the ID of the RFID tag  12 . In one embodiment, the microcontroller  52  periodically provides the ID of the RFID tag  12  to the transmitter  54  for transmission. In another embodiment, the transmitter  54  also includes receiver circuitry, thus making the transmitter  54  a transceiver, and the RFID tag  12  operates in a sleep mode until an interrogation signal is received from one of the mobile hosts  16 . More specifically, when in the sleep mode, the RFID tag  12  does not transmit the ID of the RFID tag  12 . When the RFID tag  12  receives an interrogation signal from one of the mobile hosts  16 , the RFID tag  12  enters a normal mode of operation and periodically transmits the ID of the RFID tag  12 , as discussed above. By operating in sleep mode until the RFID tag  12  is within the coverage area of the broadcast transceiver of one of the mobile hosts  16 , the RFID tag  12  conserves the power stored by the battery  50 . 
     The RFID tag  12  of  FIG. 3A  may optionally include a dynamic information gathering device  58 , such as a device for monitoring the heart rate, temperature, blood pressure, or the like of a child or other person to whom the RFID tag  12  is attached. The dynamic information gathering device  58  may also obtain information indicating whether the RFID tag  12  has been removed from the tagged object or whether the tagged object such as a child has actively placed the RFID tag  12  in a panic condition. Dynamic information from the device  58  is communicated to the microcontroller  52  and transmitted to the mobile host  16  along with the ID of the RFID tag  12 . If the dynamic information indicates an emergency situation, the cellular network  14  may dispatch emergency personnel upon receiving the location of the RFID tag  12  and the dynamic information. Again, it should be noted that the dynamic information gathering device  58  is optional and not necessary for the present invention. 
       FIG. 3B  illustrates an exemplary embodiment of the RFID tag  12  wherein the RFID tag  12  is a passive RFID tag. Similarly to the active RFID tag of  FIG. 3A , the passive RFID tag  12  of  FIG. 3B  includes the microcontroller  52 , the transmitter  54 , and the antenna  56 . The passive RFID tag  12  also includes circuitry  60  for providing power to the microcontroller  52  and the transmitter  54  by obtaining power by rectifying received RF energy. More particularly, as known to one of ordinary skill in the art and discussed below in more detail, the mobile hosts  16  provide an RFID tag excitation signal to the RFID tag  12 . The circuitry  60  receives the RFID tag excitation signal and powers the microcontroller  52  and the transmitter  54  using the power from the RFID excitation signal. When powered, the microcontroller  52  provides the ID of the RFID tag  12  to the transmitter  54  for transmission. 
     Similarly to the active RFID tag  12  of  FIG. 3A , the passive RFID tag  12  of  FIG. 3B  may optionally include the dynamic information gathering device  58 . In the illustrated embodiment, the device  58  is powered by a battery  62 . Dynamic information from the device  58  is communicated to the microcontroller  52  and transmitted to the mobile host  16  along with the ID of the RFID tag  12 . Again, it should be noted that the dynamic information gathering device  58  and the battery  62  are optional and not necessary for the present invention. 
       FIG. 4  is an exemplary embodiment of one of the mobile hosts  16 . The mobile host  16  may be a single circuit containing the component parts illustrated in  FIG. 4 . The component parts of the mobile host  16  enable it to communicate via a broadcast transceiver with other mobile hosts  16 , communicate with the cellular network  14  via a cellular transceiver, and receive position and time information from the GPS satellite system via a GPS receiver. Note that GPS is not the only available satellite system capable of provisioning time and location. Other positioning systems include: Glonass (Global Navigation Satellite System) and Galileio, which are a Russian version and a European version of the GPS. Hence reference to satellite navigation system is broader, with GPS being a specific embodiment. 
     The basic architecture of the mobile host  16  includes a receiver front end  63 , a radio frequency transmitter section  64 , an antenna  66 , a multiplexer  68 , a baseband processor  70 , a control system  72 , a frequency synthesizer  74 , and an interface  76 . The receiver front end  63  receives information bearing radio frequency signals from one or more remote transmitters provided by a base station in the cellular network  14  ( FIG. 1 ). A low noise amplifier  78  amplifies the signal. A filter circuit  80  minimizes broadband interference in the received signal, while a downconverter  82  downconverts the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. The receiver front end  63  typically uses one or more mixing frequencies generated by the frequency synthesizer  74 . 
     The baseband processor  70  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  70  is generally implemented in one or more digital signal processors (DSPs). 
     On the transmit side, the baseband processor  70  receives digitized data from the control system  72 , which it encodes for transmission. The encoded data is output to the transmitter  64 , where it is used by a modulator  84  to modulate a carrier signal that is at a desired transmit frequency. Power amplifier circuitry  86  amplifies the modulated carrier signal to a level appropriate for transmission from the antenna  66 . 
     A user may interact with the mobile host  16  via the interface  76 , which may include interface circuitry  88  associated with a microphone  90 , a speaker  92 , a keypad  94 , and a display  96 . The interface circuitry  88  typically includes analog-to-digital converters, digital-to-analog converters, amplifiers, and the like. Additionally, it may include a voice encoder/decoder, in which case it may communicate directly with the baseband processor  70 . 
     The microphone  90  will typically convert audio input, such as the user&#39;s voice, into an electrical signal, which is then digitized and passed directly or indirectly to the baseband processor  70 . Audio information encoded in the received signal is recovered by the baseband processor  70 , and converted into an analog signal suitable for driving speaker  92  by the I/O and interface circuitry  88 . The keypad  94  and display  96  enable the user to interact with the mobile host  16 . For example, if the mobile host  16  is a mobile telephone, the keypad  94  and display  96  enable the user to input numbers to be dialed, address book information, or the like, as well as monitor call progress information. 
     According to the present invention, the mobile host  16  also includes a broadcast transceiver  98  and a GPS receiver  100 . The GPS receiver  100  may generally be referred to as a location system. In this embodiment, the broadcast transceiver  98  includes a low noise amplifier (LNA)  102 , filtering circuitry  103 , a down-converter  104 , and an analog-to-digital converter  106  forming a receiver. The broadcast transceiver  98  also includes a digital-to-analog converter  108 , an up-converter  110 , and power amplifier circuitry  112  forming a transmitter and a frequency synthesizer  113 . The input of the LNA  102  and the output of the power amplifier circuitry  112  are coupled to the antenna  66  via the multiplexer  68 . 
     In operation, when the mobile host  16  is within the cellular network  14  ( FIG. 1 ), the cellular network  14  updates the RFID tag register  34  of the mobile host  16  by communicating the list of RFID tags to track to the baseband processor  70  through the receiver front end  63 . The baseband processor  70  stores the list of RFID tags to track in the RFID tag register  34 . The mobile host  16  also communicates with the cellular network  14  via the receiver front end  63  and the transmitter  64  such that the mobile host  16  provides any location and time stamp information stored in the RFID tag location register  44  to the cellular network  14 . 
     The mobile host  16  uses the broadcast transceiver  98  to communicate with the RFID tag  12  ( FIG. 1 ) and other mobile hosts  16 . In this embodiment, the broadcast transceiver  98  enables communication with the active RFID tag  12  of  FIG. 3A  or the like. As discussed above, the active RFID tag  12  may periodically transmit its ID number. When the active RFID tag  12  is within the coverage area of the broadcast transceiver  98 , a signal from the RFID tag  12  containing the ID number of the active RFID tag  12  is received by the antenna  66  and provided to the LNA  102  via the multiplexer  68 . The LNA  102  amplifies the received signal. The received signal may then be filtered and down-converted to a baseband signal by the down-converter  104 . The down-converted signal is then digitized by the A/D converter  106  and provided to the baseband processor  70  which processes the digital signal to obtain the ID of the active RFID tag  12 . The baseband processor  70  compares the ID number of the RFID tag  12  to the list of RFID tags to track stored in the RFID tag register  34 . If the RFID tag  12  is one of the RFID tags to track, the baseband processor  70  obtains the location of the mobile host  16  from the GPS receiver  100 . It should be noted that the GPS receiver  100  may be coupled to its own antenna  114  or alternatively to the antenna  66  for receiving signals from the constellation of satellites forming the GPS. The baseband processor  70  then stores the location and a time stamp for the active RFID tag  12  in the RFID tag location register  44 . 
     The broadcast transceiver  98  may also be used to communicate with the active RFID tag  12  of  FIG. 3A  that operates in sleep mode when it is not within the coverage area of the broadcast transceiver  98  of one of the mobile hosts  16 . In this embodiment, the mobile host  16  periodically transmits an interrogation signal. For example, the baseband processor  70  may provide a digital representation of the interrogation signal to the D/A converter  108 . The output of the D/A converter  108  is up-converted by the up-converter  110  and amplified by the power amplifier circuitry  112 . The interrogation signal is then provided to the antenna  66  via the multiplexer  68  for transmission. In response to receiving the interrogation signal, the active RFID tag  12  transitions from sleep mode to a normal mode wherein the active RFID tag  12  periodically transmits its ID. Then, as discussed above, the ID is received by the mobile host  16  and compared to the list of RFID tags to track stored in the RFID tag register  34 . If the ID corresponds to one of the RFID tags to track, then the location of the mobile host  16  is obtained via the GPS receiver  100 , and the location and time stamp are stored in the RFID tag location register  44 . 
     The broadcast transceiver  98  also enables communication between the mobile host  16  and another mobile host  16  within the coverage area of the broadcast transceiver  98 . In general, the baseband processor  70  periodically transmits the IDs of the RFID tags to be tracked via the broadcast transceiver  98 . In addition, once the mobile host  16  has obtained the location and time stamp for a particular RFID tag, the baseband processor  70  transmits the location and time stamp along with the ID of the RFID tag via the broadcast transceiver  98 . In doing so, any mobile host  16  within the coverage area of the broadcast transceiver  98  can update the information in its RFID tag register  34  and RFID tag location register  44 . 
     When the mobile host  16  is in the cellular network  14 , the mobile host  16  communicates the location and time stamp of any of the RFID tags to track from the RFID tag location register  44  to the cellular network via the transmitter  64 . This communication may be initiated by a polling signal from the cellular network  14 . It should be noted that in the embodiment where the mobile host  16  is a mobile telephone, communication between the mobile host  16  and the cellular network  14  for purposes of tracking the RFID tag  12  may only occur during idle time such as when the mobile host  16  is not being used for a phone call. 
       FIG. 5  illustrates an embodiment of the mobile host  16  substantially the same as the embodiment illustrated in  FIG. 4 . However, in this embodiment, the broadcast transceiver  98  also enables communication with the passive RFID tag  12  of  FIG. 3B  and the like. In addition to the discussion of the mobile host  16  with respect to  FIG. 4 , the mobile host  16  of  FIG. 5  includes an RFID excitation signal generator  116 . Thus, when the mobile host  16  desires to initiate communication with the passive RFID tag  12 , the RFID tag excitation signal generator  116  provides an RFID tag excitation signal to the antenna  66  via the multiplexer  68 . As discussed above, the RFID tag excitation signal is rectified by the passive RFID tag  12  to obtain power for transmitting the ID of the passive RFID tag  12  back to the mobile host  16  via the broadcast transceiver  98 . It should be noted that the embodiment of the mobile host  12  shown in  FIG. 5  enables communication with both the active and passive RFID tag  12 . 
     It may be beneficial to note that the operation of the broadcast transceiver  98  and tracking of the RFID tag  12  may be entirely invisible to the owner or operator of the mobile host  16 . More specifically, the ID of the RFID tag  12  and location of the RFID tag  12  are only visible to the cellular network  14 , which then provides the location information to the requesting person or entity. 
       FIG. 6  illustrates an exemplary embodiment of the processing node  24  of  FIG. 2 . In general, the processing node  24  includes a control system  118  associated with memory  120  containing software  122 . The processing node  24  also includes one or more communications interfaces  124  enabling communication with the cellular network  14 , the RFID tag register  30 , and the RFID tag location register  48 . In operation, the control system  118  operates to run the software  122 , wherein the software  122  provides the functionality of the processing node  24  described above. 
     The present invention provides substantial opportunity for variation without departing from the spirit or scope of the invention. For example, although the broadcast transceiver  98  is disclosed for direct communication between the mobile hosts  16 , peer-to-peer communication may alternatively be used. Any type of direct wireless communication or wireless networking scheme may be used for communication between the mobile hosts  16 . As another example, the types of objects that may be tracked by the system  10  of the present invention are too numerous to list, and any object such as passports, children, prisoners, parolees, inventory, automobiles, or the like may be tracked by the present invention. 
     Additionally, as discussed above, one or more of the mobile hosts  16  may include unique identifiers and operate as RFID tags  12 . Extension of the functionality of the mobile host  16  to that of an RFID tag enables several additional applications with respect to the tracking system. Firstly, as the mobile hosts  16  also broadcast a unique identifier, short range low bandwidth text messaging over the broadcast channel would be possible. It would also be possible for authorities such as police to scan the broadcast band associated with the mobile hosts  16  and determine the people located within a desired area, such as a room. It would also be possible to establish a self tracking system wherein the mobile hosts  16  also log location and time a vehicle, such as a truck, over long distances. While the truck is out of the cellular network  14 , the location register of the mobile host  16  is periodically appended with the location and time of the truck as it moves along its route. Once the truck re-enters the cellular network  14 , the location and time information can then be downloaded to the cellular network  14  where a complete log of the position and time of the truck during its journey can be generated. 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.