Abstract:
Described is an RFID tracking system, an RFID tag and method, The tag includes a memory storing identification data and a radio frequency transceiver receiving a signal from a first wireless transceiver. The first wireless transceiver is part of a wireless wide area network (WWAN). The radio frequency transceiver transmits a response signal including the identification data to at least one second wireless transceiver. The at least one second wireless transceiver being part of a wireless local area network (WLAN). A location of the RFID tag is determined as a function of the response signal.

Description:
PRIORITY CLAIM 
     The present application is a Continuation application of U.S. patent application Ser. No. 10/215,998 filed Aug. 8, 2002 now U.S. Pat. No. 7,019,663 “RF Tracking System and Method”, the entire disclosure of which is expressly incorporated herein by reference. 
    
    
     BACKGROUND INFORMATION 
     A conventional tracking system often utilizes Radio Frequency (“RF”) tags attached to assets (e.g., a computer, a mechanical device, machinery, equipment, etc.) to identify, locate or track such assets. One of the major benefits of such an RF tracking system is that a line of sight (“LOS”) between an RF reader or interrogator and the RF tag is not required for communication. This allows a large group of assets to be entered into the RF tracking system without any significant handling. In contrast to the RF tracking system, a bar code tracking system requires the LOS between a bar code reader and a bar code. Thus, either personnel or a mechanical asset is required to register enter the asset with the bar code tracking system. The registration may be done by, e.g., placing the bar code in front of the bar code reader. 
     Another advantage of the RF tracking system is that the RF tags are capable of surviving harsh and hostile environments, while the bar code may be easily damaged. These features make the RF tracking system more robust and easier to manage than the bar code tracking system. 
     However, even the RF tracking systems have disadvantages. For example, one of the disadvantages of the conventional RF tracking system is a trade-off between the accuracy in locating the RF tags and their operating range. The ability to locate remote or far away RF tags comes at the expense of accuracy in determining their location. A main contributor to this trade-off is a multipath spreading which is relatively significant in Wide Wireless Area Networks (“WWANs”). On the other hand, in Local Wireless Area Networks (“WLANs”), multipath signals are spread over a much smaller time range, and thus, the achieved accuracy is much greater. The problem with the WLANs is that it is inefficient to send requests to a large number of WLANs to determine a location of a particular asset with the RF tag. Therefore, there is a great need for a high-accuracy RF tracking system for locating remote or far-away assets having the RF tag. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an RFID tracking system, an RFID tag and method, The tag includes a memory storing identification data and a radio frequency transceiver receiving a signal from a first wireless transceiver. The first wireless transceiver is part of a wireless wide area network (WWAN). The radio frequency transceiver transmits a response signal including the identification data to at least one second wireless transceiver. The at least one second wireless transceiver being part of a wireless local area network (WLAN). A location of the RFID tag is determined as a function of the response signal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows an exemplary embodiment of an RF tracking system according to the present invention; 
         FIG. 2   a  shows an exemplary embodiment of a method according to the present invention; 
         FIG. 2   b  shows another exemplary embodiment of a method according to the present invention; and 
         FIG. 3  shows an exemplary graph which is indicative of characteristic differences of a Wireless Wide Area Network and a Wireless Local Area Network. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exemplary embodiment according to the present invention of an RF tracking system  1  for tracking the location of an asset  20  having an RF tag  30 . The RF tracking system  1  may operate within a Wireless Wide Area Network (“WWAN”)  100  which may include a plurality of Wireless Local Area. Networks (“WLAN”) (e.g. WLAN  200 ). The RF tag  30  may a dual mode tag which can communicate with both the WWAN  100  and the WLAN  200 . 
     The WWAN  100  may include a plurality of transceivers  110  and a first computer  40  or other computing processing devices. The transceiver  110  transmits and/or receives signals to and from the RF tags  30  within the coverage area of the WWAN  100 . The first computer  40  may perform a plurality of functions, such as generate signals to be transmitted to the RF tag  30 , analyze signals received from the RF tag  30 , determine a location of the RF tag  30 , etc. In particular, the transceiver  110  is capable of transmitting to the RF tag  30  a High Powered Message (“HPM”) signal. The HPM signal is a signal transmitted at a high power low bit-rate. 
     The WLAN  200  may be, e.g., a wireless system as described by IEEE 802.11b specifications. The WLAN  200  may include a plurality of transceivers  210 ,  211 ,  212  which communicate with a second computer  41 . The second computer  41  communicates with the first computer  40 . In particular, the transceiver  210  is capable of transmitting to the RF tag  20  a Low Powered Message (“LPM”) signal. The LPM signal is a signal transmitted at a low power high bit-rate. Those skilled in the art will understand that the first computer  40  and the second computer  41  may be combined into a single computing arrangement. 
       FIG. 2   a  shows a flow chart describing a method according to the exemplary embodiment of the present invention utilized to locate the asset  20  having the RF tag  30 . The method will be described with reference to  FIG. 1 . Those skilled in the art will understand that other systems having varying configurations, for example, different numbers of WWANs, WLANs, RF tags and assets may also be used to implement the exemplary method. 
     In step  300 , the first computer  40  may initiate a tracking process of the asset  20  by generating the HPM signal. The HPM signal may include a plurality of data, e.g., an RF tag identification, an identifier of the asset  20 , instructions to activate a response mode, etc. The HPM signal is transmitted to the transceiver  110  for broadcasting to the RF tag  30 . In step  303 , the transceiver  110  broadcasts the HPM signal (i.e., a high power low bit-rate signal/waveform) within the WWAN  100  coverage area. Typical specifications for the HPM are 1 Watt (“W”) of power at a low bit rate of 10 kilobits per second (“Kbps”). The received Signal-to-Noise Ratio for the HPM is relatively low, thus allowing for the HPM signal to be received at large distances. As illustrated in  FIG. 3 , the HPM signal may allow to locate the asset  20  with an accuracy of 100 to 1,000 meters. 
     In step  305 , the RF tag  30  receives the HPM signal and generates a response signal. The response signal may include identification of the RF tag  30 , time of reception of the LPM signal, etc. The response signal is transmitted back to the WWAN  100  (step  307 ). In particular, the transceiver  110  of the WWAN  100  receives the response signal and forwards it to the first computer  40 . 
     In step  310 , the first computer  40  processes the response signal to determine the WLAN  200  within which coverage area the RF tag  30  is located. Such determination, may be made as a function of data included in the HPM and response signals, time difference of arrival the response signals, a power measurement of the response signal, etc. 
     Subsequently, the first computer  40  generates the LPM signal to determine a precise location of the asset  20 . The LPM signal may include the RF tag identification, etc. The LPM signal is lower power high bit-rate and may be broadcasted to the asset  20  within the coverage area of the WLAN  200  using the transceivers  210 - 212  (step  313 ). Typical specifications for the LPM signal may be 100 milliwatts (“mW”) of power at a high bit rate of upto 100 megabits per second (“Mbps”). As illustrated in  FIG. 3 , the LPM signal may allow to locate the asset  20  with an accuracy of 1 to 10 meters. 
     In step  315 , the RF tag  30  receives the LPM signal and generates a response. The response is transmitted to the WLAN  200 . The transceivers  210 - 212  receives the response signal to LPM signal and transmits the response signal along other data (e.g., such as time of receipt of the signal, power strength of the signal, etc) to the second computer  41 . The second computer  41  processes the received data to determine a location of the RF tag  30  (e.g., X Y coordinates of the RF tag  30 ) and transmits it to the first computer  40  (step  320 ). 
     There are a number of ways of determining the location of the RF tag  30 . For example, the location of the RF tag  30  may be determined by measuring a time difference of arrival (“TDOA”) of the response signal. In particular, the transceivers  210 - 212  record the time when the response signal arrived at the corresponding transceiver. The arrival time, the response signal and location of each of the transceivers  210 - 212  are utilized by the second computer  41  to calculate the X Y coordinates of the RF tag  30 . 
     In the alternative exemplary embodiment, the X Y coordinates may be determined using a power measurement reading of the response signal (i.e., a Received Signal Strength Indication (“RSSI”) method). The RSSI method utilizes the intensity of the response signal and compares it with predetermined geographically marked points. For example, the WLAN  200  has a certain number of marked points; each point has a measured power reading. Then, the second computer  41  compares the powered reading of the response signal received by each of the transceivers  210 - 212  to the marked power reading. Based on this comparison, the X Y coordinates of the RF tag are determined. 
     Another method of determining the X Y coordinates of the RF tag  30  is similar to the first method described above, except that the RF tag  30  receives beacons from the transceivers  210 - 212  and records the time of reception of these beacons. The reception time is included into the response signal and transmitted to the WLAN  200 . The second computer  41  utilizes the data included in the response along with data received from the transceivers  210 - 212  (e.g., exact location of transceivers  210 - 212  and time when the beacons were transmitted to the RF tag  30 ) to calculate to the X Y coordinates. 
       FIG. 2   b  shows another exemplary embodiment of the method according to the present invention. According to this method, the steps  300 - 305  are substantially similar to steps shown in  FIG. 2   a  and described above. 
     In step  306 , the RF tag  30  generates a response signal which is LPM signal. The LPM response signal may include RF tag identification, time of reception of the HPM signal, etc. The LPM response signal is transmitted to the WLAN  200 . 
     The transceivers  210 - 212  of the WLAN  200  receive the LPM response and record exact time of the reception (step  308 ). Then, the transceivers  210 - 212  forward the LPM response signal along with its geographical location and time of the reception to the second computer  41  (step  311 ). Based on the information provided, the second computer  41  calculates the X Y coordinates of the RF tag  20  utilizing one of the method described above. The X Y coordinates then may be forwarded to the first computer  40 . Those skilled in the art would understand that other data may collected that would allow to determine a location of the asset  20 , e.g., using one of the three above-described methods. 
     The present invention may be utilized in a plurality of industries. For example, it may be utilized for tracking the assets  20  in airports. First, the HPM signal is transmitted within the WWAN  200  which covers, e.g., the New York Metropolitan Area. The asset  20  having the RF tag  30  is located within the area which is covered by the WLAN  200 , e.g., JFK International Airport. Then, the LPM signal is broadcasted to the RF tag  30  using the transceiver  210  of the WLAN  200 . Based on the response signal to the LPM signal generated by the RF tag  30 , the second computer  41  would be able to determine that the asset  20  is located at a specific location, e.g., Gate  11  in Terminal B. 
     Alternatively, the RF tag  30  may generated a LPM response signal to the HPM signal. The LPM response signal is transmitted to the WLAN  200 . The second computer  41  of the WLAN  200  determined exact position of the RF tag  30 . 
     The present invention has been described with reference to an embodiment having a single RF tag  30 , the WWAN  100 , the WLANs  200  and transceivers  110 ,  210 - 212  for each corresponding network. One skilled in the art would understand that the present invention may also be successfully implemented, for example, for a plurality of RF tags  30  and a plurality of the WLANs  200 . Accordingly, various modifications and changes may be made to the embodiments without departing from the broadest spirit and scope of the present invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.