Abstract:
An in-building location system for detecting the location of individuals or items within a building utilizes a scanner carried by an individual or an item and RFID tags to provide fiducial points for assisting in the location process, with the tags being scanned by the scanner and in which tag proximity to a scanner provides for accurate in-building location. Accurate location of the scanner relative to multiple tags may be ascertained utilizing triangulation.

Description:
RELATED APPLICATIONS 
     This Application claims rights under 35 USC §119(e) from U.S. Application Ser. No. 61/342,106 filed Apr. 9, 2010, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to in-building location systems and more particularly to the utilization of RFID tags to provide fiducial points to assist in locating an individual or item within a building. 
     BACKGROUND OF THE INVENTION 
     One of the largest problems in locating people or devices within a building is the precise location in a building where GPS coverage is not available. GPS essentially stops working at the door of a building such that inside the building one does not have the ability to access satellites. This is true even for assisted GPS systems depending on how far into a building one goes. It is understood that at least at some points in a building GPS signals are too attenuated to be usable. Therefore one can not get a precise in-building location utilizing the GPS system. 
     While triangulation be utilized from the cell towers, one can arguably get within 100 feet, however 100 feet is clearly insufficient and what is required is plus or minus two feet to properly locate devices or human beings within a building. 
     SUMMARY OF INVENTION 
     It is part of the subject invention to provide in-building location of people or devices utilizing RFID tags that have been stationed within the building at points where the location of each of the tags is known. If an individual or device is carrying a module that communicates with the RFID tags, when the hand-carried module is within proper proximity, the RFID tag will transmit to the module the fact of the proximity and the ID of the tag. Since the tag is pre-located one at least knows within a certain proximity the module is within the proximity range of the RFID tag that is serving as a fiducial point. 
     However, proximity alone may not yield the required location accuracy. If the RFID tags are arranged to transmit to each other in a network then if the hand-carried module is within the proximity of more than one tag then triangulation between the tags is possible based on the location of the tags, and for instance either the strength of the signal received by the tag which is range dependent, or an algorithm is utilized to calculate the position of the hand-carried module between a number of tags. 
     In one embodiment while the RFID tags may be pre-located and therefore have a known latitude and longitude, it may be possible to lay down a bread crumb of RFID tags as an individual moves into a building and then drops the RFID tags along the track that he takes through the building. Since the location of the individual can be determined by the GPS system as the person enters the portal of the building, the tags can be provided with inertial navigation systems including for instance accelerometers, magnetometers and for instance pedometers, along with either a compass or other means of detecting the direction of the acceleration so as to update the tags latitude and longitude based on dead reckoning from the initial latitude and longitude provided by GPS, coordinates at the entrance to the building. 
     In another embodiment, one could provide the module carried by the individual or device with the aforementioned inertial guidance and then correct the location provided by the inertial guidance information from fiducial RFID tags that have been pre-located within the building. 
     In summary, in in-building location system for detecting the location of individuals or items within a building utilizes a scanner carried by an individual or an item and RFID tags to provide fiducial points for assisting in the location process, with the tags being scanned by the scanner and in which tag proximity to a scanner provides for accurate in-building location. Accurate location of the scanner relative to multiple tags may be ascertained utilizing triangulation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the subject invention will be better understood in connection with the Detailed Description, in conjunction with the Drawings, of which: 
         FIG. 1  is a diagrammatic illustration of the utilization of pre-positioned RFID tags used to locate an individual or device therebetween, also showing providing inertial navigation units to each of the pre-positioned tags to provide exact location of the tags within the building; 
         FIG. 2  is a diagrammatic illustration illustrating a bread crumb embodiment of the subject invention in which tags are dropped along a path that an individual takes from outside a building to locations within the building; 
     
    
    
     DETAILED DESCRIPTION 
     As can be seen from  FIG. 1 , in one embodiment of the subject invention tags  10 , each having the ability to identify itself and its location are pre-positioned within a building  12 . 
     An individual  14  having a module  16  that can interrogate the tags and derive information therefrom is shown at various distances from tags  10 , here labeled T 1 , T 2  and T 3 . Note the module may be a small hand carried fob or like device. The range of each of the tags is respectively illustrated by circles  18 ,  20  and  22 . 
     If the tags are to be proximity sensors only, then this range can be indeed quite short, i.e. two feet such that the proximity of handheld module  16  to any one of the tags indicates the location of the handheld module to within two feet. 
     It is important in this embodiment that the tags be pre-located and have the latitude and longitude of the tags embedded in the tags so that they can report their location to module  16  which interrogates it. However, short range tags may not cover enough area and widening the range results in range overlap. One can then use range measurements or triangulation between tags to ascertain location. 
     Note that for triangulation purposes, when utilizing multiple RFID tags that it is convenient that the RFID tag transceivers operate on the same frequency so that simultaneous range measurements can be made. 
     Another way to communicate is to transmit to as many RFID tags that can hear the transmission from module  16  and then triangulate on the basis of the strength of the signal and time domain reflectometry from the individual RFID tags to the module. 
     A further way to establish the location of an individual or device within a building is to detect the GPS location of an individual  14  who carries module  16  which includes a GPS receiver when the individual enters portal  26  of building  12 . The location of the individual in the building can be established by connecting an inertial navigation unit  30  to module  16  such that as the person moves through the building inertial navigation techniques can be used to establish the latitude and longitude of the individual or module within the building. It is noted that this inertial navigation position can be corrected for proximity to the fiducial points established by the placement of the RFID tags throughout the building. 
     Note that the calculation of position is in module  16  or more specifically in a fob in which a GPS receiver and communications are located. The module also has an RFID reader and may include an ANT transceiver as well as a microprocessor. Once location has been calculated, the location may be transmitted by for instance antenna  32  to the outside world to establish the location of the device or individual within the building. 
     It is noted that proximity sensing utilizing three tags may give a better resolution than dead reckoning or any of the inertial navigation techniques that might be employed, thus to increase the accuracy of the in-building position. 
     Referring now to  FIG. 2 , rather than pre-positioning RFID tags in a building with known latitude and longitude positions, tags  40  may be deposited or dropped along a bread crumb path  42  traversed by an individual  44  as the individual enters building  46  and walks through it. 
     Each of the tags is provided with a magnetometer, accelerometer and/or pedometer  46  so as to establish the position of the bread crumbs, namely RFID tags  40 . 
     From the outputs of the magnetometer, accelerometer and pedometer one can establish the location of the tags within building  46  so that when these tags are read out by a module  50  held by the individual which has the aforementioned communications capability, the position of the individual can be accurately ascertained due to the information transmitted from the tags to the module. 
     Thus, in order to establish the position of the bread crumbs one requires in each of the RFID tags a distance sensor which could for instance be the number of steps taken by an individual once he passes portal  52  of building  46 . Alternatively, the distance may be computed by accelerometer outputs and differentiation techniques. 
     Secondly, the direction of the tag or sensor can be established by a magnetometer that is on board. Finally, when the tag is appropriately positioned the calculated latitude and longitude can be written into the tag when it is deployed. 
     The result is that by proximity to a particular tag individual  44  can establish his or her position relative to the bread crumb tags whose positions have been established through a dead reckoning track or inertial navigation. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.