Abstract:
A method is provided for propagating data among multiple locations in an area. The method includes using a plurality of transponders distributed throughout the area, each able to receive, store, and transmit data. The method further includes using scanners moving relative to the transponders, and able to transfer data to and from these transponders over a wide or limited range. When a scanner encounters a transponder (becomes close enough for data communication), it reads data from the transponder and writes data to the transponder, including data read from prior encounters with other transponders. Data written to a transponder by a scanner may include data associated with that scanner, including but not limited to one or more of identification, speed, direction, and time stamp. The method thus propagates data among transponders and makes this transponder data available to scanners as they encounter these transponders. The method propagates data throughout an area without a requirement for a wired or wireless connection between and among the transponders, at a speed dependent on the number of and speed of scanners moving within the area. The method further includes optionally connecting a subset of transponders with a wired or wireless network to more quickly propagate data over the area, while still not requiring every transponder be connected to this network. The method further includes using RFID tags, both adapted and non-adapted to the specific application, as the transponders, and RFID scanners to write to and read from these RFID tags.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to data storage and communication, and, more particularly, to a method and system for writing, storing, reading, and propagating data throughout a distributed wireless network utilizing wireless transponders and scanners which are moving relative to each other. 
         [0003]    2. Description of the Related Art 
         [0004]    Traditional data access and storage systems utilize data access points (for input and/or output of data) at a number of locations, often using a terminal with keyboard and display. Data thus entered or requested, along with data from other sources connected to the network, is typically then transported on a wired or wireless network to and from one or more data storage locations. The wired or wireless network, connecting the multiple access points with the data storage mechanism, enables data access at multiple locations across the network. The cost of each data access point is typically relatively high, given the complexity of electronics at each location. Additionally, the wired or wireless network and data storage hubs used in the typical system further complicate the system. In many such systems, manual input of data is typical, often using a keyboard or barcode reader. If knowledge of user location is desired, such location is typically manually input or is inferred from location of terminals used for data access. 
         [0005]    A distributed database minimizing or eliminating the need for a wired or wireless network, could significantly reduce the cost and complexity of such data systems. Position information for users of or items within the area served by the network could also be beneficial. 
       SUMMARY OF THE INVENTION 
       [0006]    In one embodiment of the present invention, a method is provided for writing, storing, and reading data to and from transponders at multiple locations in an area, and for propagating data from location to location, without requiring a wired or wireless data network connecting these multiple locations. The method includes storing data on one or more transponders at locations in the area, each transponder having data receiving, data storage, and data transmission capability. The method also includes reading data from a first of one or more transponders by one or more scanning devices (scanners), storing this data on the scanner, moving the one or more scanners into communication range of a second or subsequent of one or more transponders, and writing all or a portion of the data stored on the scanner to the second or subsequent transponder. In this manner, data from transponders is migrated from each transponder to others, by movement of scanners, relative to the transponders, through the area. If the data transfer between a scanner and transponder can occur only over a limited range, and if a scanner writes identifying data to transponders as they are encountered, a record of scanner encounters is left on those transponders. If transponders are in known, fixed positions within the area, a data record of scanner position is generated and stored on those transponders, which data may then be transferred to other scanners as they encounter those transponders. 
         [0007]    In another embodiment of the present invention, the method described above further comprises multiple radio frequency identification (RFID) tags adapted to function as transponders distributed throughout an area, and one or more RFID scanners moving through the area relative to those transponders and able to write data to and read data from these RFID tags. As described above, data from RFID tags is thus migrated from one to others, by relative physical movement of RFID scanners through the area, rather than by a wired or wireless network infrastructure. If the communication range of the RFID tags and RFID scanners is limited, data on approximate position of RFID scanners may be stored on RFID tags as the scanners encounter tags. This position data, which may also include a time stamp for each encounter, is then propagated through the area as described above. 
         [0008]    In another embodiment of the present invention, the method further includes connecting a subset of transponders or RFID tags by a wired or wireless network, thus facilitating communication of data between or among two or more locations in the area, more rapidly than would occur by relative physical movement of scanners through the area. 
         [0009]    In yet another embodiment of the present invention, a system comprises multiple transponders in an area, and one or more scanners moving through the area relative to those transponders, the scanners able to write data to and read data from the transponders. The transponders are adapted to receive and store data from scanners, and transmit data to scanners. The scanners are adapted to receive and store data from transponders, and write to transponders all or a portion of data received from prior encounters with other transponders. Data from transponders is thus migrated from one to others by relative physical movement of scanners through the area, rather than by a wired or wireless network infrastructure. 
         [0010]    Technical advantages of one or more embodiments of the present invention may include significant cost reduction of the overall data storage and access system, especially if the stationary transponders are low-cost passive RFID tags. Further significant cost and complexity reduction may be achieved by reducing or eliminating the need for a network infrastructure connecting multiple locations in the area. Writing and reading data to and from the RFID tags may also occur without user intervention, when a scanner encounters a tag. Positional awareness is a further technical advantage, if the communication range between scanner and transponder is limited, as is generally the case with RFID tags and RFID scanners. 
         [0011]    As further described below, the disclosed embodiments provide a combination of desirable properties not available in the known art. These properties include the technical and cost advantages described above. Further benefits and advantages will become apparent to those skilled in the art to which the invention relates. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Example embodiments of the invention are described below with reference to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a block diagram of a typical known passive RFID tag; 
           [0014]      FIG. 2  is a block diagram of a typical known RFID scanner; 
           [0015]      FIG. 3  is a flow diagram showing propagation of data among a plurality of fixed transponders by moving scanners; 
           [0016]      FIG. 4  is a block diagram of a system for tracking location of personnel or equipment within an area; 
           [0017]      FIG. 5  is a diagram of a system for propagating traffic speed data along a highway, without requiring physical or wireless connection among transponders along the highway; and 
           [0018]      FIG. 6  is a diagram showing the addition of a wired or wireless network linking a subset of transponders of  FIG. 5 . 
       
    
    
       [0019]    Throughout the drawings, like elements are referred to by like numerals. 
       DETAILED DESCRIPTION 
       [0020]    Embodiments of the present invention and its advantages are best understood by referring to  FIGS. 1 through 6  of the drawings, like numerals being used for like and corresponding parts of the various drawings. 
         [0021]      FIG. 1  is a block diagram of a typical transponder, which in some embodiments is a passive RFID tag. Antenna  102 , when excited by the radio-frequency (RF) field of a nearby transmitter (scanner), generates an alternating current or voltage which is rectified by RF rectification voltage generator  104 . This rectified RF signal produces the voltage and current required for operation of the RFID tag, thus eliminating the need for a battery in the RFID tag. Alternate tag embodiments, called active RFID tags, use a battery rather than rectified RF for power, typically to allow greater transmit power and range. RF energy from antenna  102  also is coupled to diplexer  106 . This diplexer acts to couple received energy from the antenna  102  to data receiver  108  (during reception), and transmitted energy from data transmitter  110  to antenna  102  (during transmission). 
         [0022]    Data receiver  108  receives and demodulates the RF signal, providing as an output digital data on data bus  116 . Data received is stored in non-volatile memory  112 . Control logic  114  controls timing of reception and transmission of data, and data selection and flow from receiver to memory and memory to transmitter. Data transmitter  110  modulates and transmits data from memory  112 , as controlled by control logic  114 . The output of data transmitter  110  is coupled through diplexer  106  to antenna  102 . The transponder thus can receive data from a nearby scanner, and transmit data back to the scanner. 
         [0023]      FIG. 2  is a block diagram of a typical scanner, which in some embodiments is an RFID scanner. Data stored in non-volatile memory  212  is modulated and transmitted by data transmitter  208 , which is coupled to antenna  202  through diplexer  204 . Received signals from antenna  102  are coupled through diplexer  204  to data receiver  206 . 
         [0024]    Data receiver  206  receives and demodulates the incoming RF signal, providing as an output digital data on data bus  210 . Data received is stored in non-volatile memory  212 . Control logic  214  controls timing of reception and transmission of data, and data selection and flow from receiver to memory and memory to transmitter. Data transmitter  208  modulates and transmits data from memory  212 , as controlled by control logic  214 . The output of data transmitter  208  is coupled through diplexer  204  to antenna  202 . 
         [0025]    Input and display  216  comprises typical data entry and display mechanisms such as a keypad, keyboard, bar-code scanner, liquid-crystal display (LCD) viewing screen, or other known input and display mechanisms. It enables input of data which is then stored in non-volatile memory  212 , as well as display of data received from transponders. Control logic  214  regulates the flow of data among the receiver  206 , memory  212 , transmitter  208 , and input/display  216 . 
         [0026]      FIG. 3  shows schematically an example of the flow of data over time as two scanners move through an area having 4 transponders (tags). In this example, movement of scanners from one tag to another occurs at the same time (synchronously) for simplicity and clarity. It will be apparent that asynchronous movement of transponders (the more likely scenario) has a similar effect of spreading data through the area. 
         [0027]    At time T 1 , scanner  1   302  and scanner  2   304  both encounter tag  1   306 —that is they are near enough to activate the tag, transmit data to the tag, and receive data from the tag. At time T 1 , tag  1   306  has data A in tag memory. This data A is transmitted to both scanner  1   302  and scanner  2   304 , which both store the data in scanner memory. In this example, prior to receiving data A from tag  1   306 , scanners  1   302  and  2   304  have no data in memory. After the encounter with tag  1   306 , scanners  1   302  and  2   304  thus have data A in scanner memory. 
         [0028]    At time T 2 , scanner  1   302  encounters tag  2   308 . Scanner  1   302  transmits data A (from its earlier encounter with tag  1   306 ) to tag  2   308 , which stores the data in tag memory. Tag  2   308  has previously-stored data B in tag memory, which is transmitted to scanner  1   302  and stored in scanner memory. At the completion of the encounter, scanner  1   302  has data AB in scanner memory, and tag  2   308  has data AB in tag memory. Also at time T 2 , scanner  2   304  encounters tag  4   312 . Scanner  2   304  transmits data A (from its earlier encounter with tag  1   306 ) to tag  4   312 , which stores the data in tag memory. Tag  4   312  has previously-stored data D in tag memory, which is transmitted to scanner  2   304  and stored in scanner memory. At the completion of the encounter, scanner  2   304  has data AD in scanner memory, and tag  4   312  has data AD in tag memory. 
         [0029]    At time T 3 , scanner  1   302  is too far from any tag for data communication, and retains data AB in tag memory. Also at time T 3 , scanner  2   304  encounters tag  3   310 . Scanner  2   304  transmits data AD (from its earlier encounters with tags  1   306  and  4   312 ) to tag  3   310 , which stores the data in tag memory. Tag  3   310  has previously-stored data C in tag memory, which is transmitted to scanner  2   304  and stored in scanner memory. At the completion of the encounter, scanner  2   304  has data ACD in scanner memory, and tag  3   310  has data ACD in tag memory. 
         [0030]    At time T 4 , scanner  1   302  encounters tag  3   310 . Scanner  1   302  transmits data AB (from its earlier encounters with tag  1   306  and tag  2   308 ) to tag  3   310 , which stores the data in tag memory. Tag  3   310  has previously-stored data ACD in tag memory, which is transmitted to scanner  1   302  and stored in scanner memory. At the completion of the encounter, scanner  1   302  has data ABCD in scanner memory, and tag  3   310  has data ABCD in tag memory. Also at time T 4 , scanner  2   304  again encounters tag  1   306 . Scanner  2   304  transmits data ACD (from its earlier encounters with tag  1   306 , tag  3   310 , and tag  4   312 ) to tag  1   306 , which stores the data in tag memory. Tag  1   306  has previously-stored data A in tag memory, which is transmitted to scanner  2   304  and stored in scanner memory. At the completion of the encounter, scanner  2   304  has data ACD in scanner memory, and tag  1   306  has data ACD in tag memory. 
         [0031]    After four time periods, tag  3   310  thus has the full set of data from all 4 tags. Data A and D was received from scanner  2   304  at time T 3 ; data B was received from scanner  1   302  at time T 4 ; data C was originally stored on tag  3   310 . By extension, it can be seen that further random movement of one or more scanners among multiple tags will eventually result in most or all tags having most or all of the data from the other tags. 
         [0032]      FIG. 4  shows an example application of such a method and system in a facility  402  where it is desired to know the whereabouts of persons and/or equipment. Tags are placed at locations throughout the facility where movement of persons and/or equipment is anticipated—for example, doorways to each area  408 ,  410 ,  412 ,  414 , area  404 , area  406 , and so forth. Each person and/or piece of equipment carries a scanner  436 ,  438 ,  440  able to encounter tags as described above. As scanners move through the facility and encounter tags, each transmits a time-stamped, unique identification to that tag. A database of scanner location and time at each location is thus generated on the plurality of transponders, and is available to other scanners as they encounter transponders. A querying scanner may determine the position of another scanner on other personnel or equipment with reasonable precision, by interrogating this database to determine which transponder corresponds to the most recent time stamp for the scanner identification whose position is being sought. Although not required for system operation, a subset of tags, for example tag  6   418  and tag  2   422  as shown, can be connected to data local area network (LAN)  434  via interfaces  430 ,  432 . Such a connection may be used to more rapidly transfer and synchronize data on tags so connected, and may further provide tag data to a centralized data query point such as terminal  428  in area  404 . Multiple tags may be used at each point of connection to a data network if required for additional storage capacity. 
         [0033]    The example application of  FIG. 4  shows 3 scanners. One user with scanner  1   436  is in area  406 , near enough tag  6   418  for data transfer; a piece of equipment has scanner  2   438  and is in area  412 , near enough tag  3   424  for data transfer; and a user with scanner  3   440  is outside area  408 , but near enough tag  1   420  for data transfer. As scanners move through the various areas, position versus time data for each scanner propagates to all or most of the tags and other scanners, and to terminal  428  via the LAN  434 . 
         [0034]      FIG. 5  shows an application of distributed transponders and mobile scanners used for propagating traffic information to vehicles traveling along a roadway.  FIG. 5  shows, schematically and not to scale, a portion of highway  502 , with six uniquely serialized RFID tags  1  through  6  ( 504 ,  506 ,  508 ,  510 ,  512 ,  514 ) placed typically in the center of the highway at 1-mile intervals (“mile markers”). Eastbound traffic is flowing at a steady 60 MPH; westbound traffic is also flowing 60 MPH except for a slowdown to 30 MPH between mile marker  4  and mile marker  2 . Some or all vehicles in each direction are equipped with scanners operable to read and write data from and to tags along the roadway. 
         [0035]    As a scanner-equipped vehicle passes a tag, the scanner writes the vehicle&#39;s current speed and direction data to the tag. Each tag has a storage register for both westbound and eastbound speed, that register typically storing data on tag number, speed, and direction (E or W in this example). Eastbound vehicles read from the tag the westbound tag number and speed values from the westbound registers, and westbound vehicles read from the tag the eastbound tag number and speed values from the eastbound registers. As an eastbound vehicle moves past multiple tags, it thus writes its current eastbound speed data to each tag, and reads westbound speed data at that tag for the most recent westbound vehicle. The result is a dataset on the eastbound scanner of n westbound speed values for the last n miles. These n values are stored in a first-in-first-out manner, resulting in the eastbound scanner having westbound speed data for the most recently passed n tags. This n-value westbound speed dataset is written to each tag as it is passed, overwriting prior datasets. Westbound scanners in a like manner store a dataset of eastbound speeds and write that eastbound speed dataset to tags as they are passed. 
         [0036]    After a suitable time period, each tag therefore has an eastbound and westbound speed dataset, each having n speed values and thus covering +/−n miles from the tag location. The dataset of eastbound speeds is propagated westward by westbound scanners and vice versa. The scanners are able to read this dataset as tags are passed, giving the driver recent information on traffic conditions ahead up to n miles. 
         [0037]    In the example of  FIG. 5 , a method for propagating traffic speed data over a 5-mile portion of highway is described. An eastbound vehicle equipped with a scanner  516  as described above, capable of reading from and writing to the memory of the RFID tags  504 - 514  along the roadway. Tags are labeled according to the mile marker; tag  1   504  is at mile marker  1 , for example. 
         [0038]    When scanner  516  passes tag  1   504 , the scanner  516  writes current speed data for its vehicle to tag  1   504  register V(e, 1 ) (current eastbound speed, at tag  1 ). It also reads speed data from tag  1   504  register V(w, 1 ) (current westbound speed, at tag  1 ), which was written by the last westbound vehicle passing tag  1   504 . This westbound speed data V(w, 1 ) is stored in the first of 5 registers on scanner  516 . As scanner  516  continues to pass tags  506 ,  508 ,  510 ,  512 , and  514  during the next 5 minutes, it writes its current speed data to each as described for tag  1 , and reads V(w,n) from each tag, storing each V(w,n) in registers  2  through  5  on scanner  516 . On passing tag  6   514 , scanner  516  has completed a dataset for westbound speeds at tags  1  through  5 , and writes this dataset to tag  6   514 . A westbound vehicle  518  passing tag  6   514  thus is able to read from tag  6   514  a dataset of westbound speeds for the 5 miles ahead, current within 5 minutes. The slowdown two miles ahead will be apparent, allowing appropriate deviation if desired. 
         [0039]    The system and method described uses moving scanners and fixed tags to generate a database of traffic conditions on each tag covering m miles in either direction. At normal traffic speeds and densities, especially in areas where monitoring traffic flow is desirable, the data for many miles of roadway is only minutes old and is constantly updated as scanner-equipped vehicles travel the roadway. 
         [0040]      FIG. 6  shows schematically and not to scale how a wired or wireless data network may be used to link one or more tags of the system described in  FIG. 5  to each other and to a central data monitoring location. As described above, tag  506  at mile marker  2  gathers speed data from westbound and eastbound vehicles; scanners in the vehicles then propagate that data to more distant tags. Data link  608  is a wired or wireless data connection using known methods and apparatus to move data between tag  506  and network node  610 . Data link  604  is a wired or wireless data connection using known methods and apparatus to move data between tag  602  at mile marker  22  and network node  606 . Node  610 , node  606 , and data gathering computer  618  at central location  614  are all linked by network connection  612 , which is a wired or wireless network using known technology. Eastbound speed data present on tag  602  is quickly sent to tag  506 , providing an additional 20 miles of traffic data. Thus, speed data for 40 miles ahead is made available at tag  506  and at central data monitoring location  614 , with data latency less than if data was propagated only by moving scanners. Data passed from tag  506  to tag  602  similarly provides increased traffic data for westbound vehicles. 
         [0041]    At normal traffic flows, tags  506  and  602  (spaced for example 20 miles apart) have speed data for 40 miles as described above, with data latency of typically 20 minutes at normal traffic speeds, and using only two network nodes spaced 20 miles apart. The density of network nodes is much less than would be required by a traditional system having a network node at every data gathering location (every mile in this example). Many traditional systems also would typically utilize a more expensive flow monitoring system at each mile of the roadway, each requiring a communication link back to the central data collection point. 
         [0042]    Those skilled in the art to which the invention relates will appreciate that yet other substitutions and modifications can be made to the described embodiments, without departing from the spirit and scope of the invention as described by the claims below.