Abstract:
The present invention provides a solution to mistaken location calculations based on multipath effects. The present invention utilizes tags attached to objects that transmit signals at various power levels for reception by sensors stationed throughout a facility. Sensor readings at the various power levels are utilized to determine the location of the tagged object.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The Present application claims priority to U.S. Provisional Patent Application No. 61/165,872, filed on Apr. 1, 2009, and is a continuation-in-part application of U.S. patent application Ser. No. 12/114,740, filed on May 2, 2008, which claims priority to U.S. Provisional Application No. 60/916,737, filed on May 8, 2007, now abandoned. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to wireless tracking systems and methods. More specifically, the present invention relates to a system and method for mitigating multipath errors associated with the wireless tracking of objects by utilizing tags that transmit signals at various power levels. 
     2. Description of the Related Art 
     The ability to quickly determine the location of objects located within a facility is becoming a necessity of life. To the uninformed observer, the placement of transponders, also known as tags, on numerous non-stationary objects whether in an office or home would appear to be an unnecessary use of resources. However, the uninformed observer fails to appreciate the complexity of modern life and the desire for efficiency, whether at the office or home. 
     For example, in a typical hospital there are numerous shifts of employees utilizing the same equipment. When a new shift arrives, the ability to quickly locate medical equipment not only results in a more efficient use of resources, but also can result in averting a medical emergency. Thus, the tracking of medical equipment in a hospital is becoming a standard practice. 
     The tracking of objects in other facilities is rapidly becoming a means of achieving greater efficiency. A typical radio frequency identification system includes at least multiple tagged objects each of which transmits a signal, multiple receivers for receiving the transmissions from the tagged objects, and a processing means for analyzing the transmissions to determine the locations of the tagged objects within a predetermined environment. The tags can also receive signals. 
     Several prior art references discloses various tracking systems. 
     McKee et al., U.S. Pat. No. 6,915,135 discloses a system for determining presence, identity and duration of presence in a given area (a table in a restaurant) of an object (tag attached to a waiter). 
     Lester, U.S. Pat. No. 3,805,265 discloses a location system that uses line-of-sight radiant wave energy for signal transmission. 
     Schwengler U.S. Pat. No. 7,050,819, is directed at the problem of adequate power for a mobile telephone for a two-way communication function or a regeneration function as a node of a mesh network. 
     Christ, U.S. Pat. No. 5,977,913, discloses a radiofrequency system that is utilized within a prison and allows for an individual to be located after an alarm is triggered by the individual. 
     Zodnik, U.S. Patent Publication Number 2004/0147232, discloses wall-mounted (RJ-11 or RJ-45) wireless transceivers configured to only track the location of a self-identified wireless communication device in order to communicate the location of the self-identified wireless communication device to an emergency service such as 911. 
     One exemplary method triangulates the strongest received signals to determine the location of a tagged object. This method is based on the assumption that the receivers with the strongest received signals are the ones located closest to the tagged object. However, such an assumption is sometimes erroneous due to common environmental obstacles. Multipath effects can result in a further located receiver having a stronger received signal from a tagged object than a more proximate receiver to the tagged object, which can result in a mistaken location determination. The prior art has disclosed various means for overcoming multipath effects. 
     Tekinay, U.S. Pat. No. 6,259,894 for a Method For Improved Line-Of-Sight Signal Detection Using RF Model Parameters, discloses a method for reducing time-shift due to multipathing for a RF signal in an RF environment. 
     Close, U.S. Pat. No. 3,869,673 for a Method And Apparatus For Measuring Multipath Distortion, discloses a method for indicating multipath distortion in a received signal. 
     Lennen, U.S. Pat. No. 5,402,450 for a Signal Timing Synchronizer, discloses a method and apparatus for reducing the effects of multipath induced distortions on the accuracy of detecting the time of arrival of a received signal. 
     Fortune et al., U.S. Pat. No. 5,450,615 for a Prediction Of Indoor Electromagnetic Wave Propagation For Wireless Indoor Systems, discloses techniques for predicting RF propagation within a structure. 
     Other prior art references have disclosed the use of varying energy levels. For instance, Nakanishi, U.S. Pat. No. 5,451,847 for a Variable Energy Radio Frequency Quadrupole Linac discloses changing radio frequency energy levels to emitted focused and accelerated beams. 
     Kaewell, Jr. et al., U.S. Pat. No. 7,082,286 for a Path Searcher Using Reconfigurable Correlator Sets discloses producing a path profile for a user based on sorted output energy levels. 
     Fernabdez-Cobaton et al., U.S. Pat. No. 6,697,417 for a System And Method Of Estimating Earliest Arrival Of CDMA Forward And Reverse Link Signals discloses a mobile station receiver that detects the arrival times and energy levels of received signals, and constructs a searcher histogram and a finger histogram associated with each pilot signal. 
     The prior art has yet to resolve mistaken location calculations based on multipath effects for objects tracked within an indoor facility. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a solution to mistaken location calculations based on multipath effects. The present invention utilizes communication devices attached to objects that transmit signals at various power levels for reception by sensors stationed throughout a facility. 
     One aspect of the present invention is a method for determining a real-time location of an object within a facility. The method includes transmitting a first wireless power level signal from a communication device associated with an object. The method also includes transmitting a second wireless power level signal from the communication device associated with the object. In a preferred embodiment, the first and second power level signals are different. In an alternative embodiment, the first and second power level signals are the equal. The method also includes receiving the first wireless power level signal at at least one of a plurality of sensors positioned within an indoor facility and receiving the second wireless power level signal at at least one of a plurality of sensors positioned within a facility. The method also includes calculating a first power level location from the first wireless power level signal utilizing a first location algorithm. The method also includes calculating a second power level location from the second wireless power level signal utilizing a second location algorithm. The method also includes determining a real-time location of the object using the first power level location and the second power level location. 
     Preferably the first location algorithm is a radial basis function algorithm and the second location algorithm is a proximity detection algorithm. Preferably the first power level location and the second power level location are the same location. Preferably the first transmission power level is 1 milli-Watt and the second transmission power level is 0.5 milli-Watt. Preferably the indoor facility is a hospital. Alternatively, the indoor facility is an office, manufacturing plant and similar facilities. The wireless first power level signal is preferably one of light, radiofrequency, sound and magnetic energy. The second wireless power level signal is preferably one of light, radiofrequency, sound and magnetic energy. The first location algorithm and the second location algorithm are preferably a combination of at least two of an RBF algorithm, proximity detection, minimum mean square error calculation, maximum likelihood of calculation, time difference of arrival calculation, time of arrival calculation, spatial diversity algorithm, and angle of arrival calculation. 
     The method further includes associating the object with a second object. The method further includes triggering an event such as commencing a workflow event, transmitting an alert, transmitting a report, logging onto a computer, logging off of a computer, activating a camera, and activating a light. 
     Another aspect of the present invention is a system for determining a real-time location of an object within a facility. The system preferably includes mobile objects, sensors, and a central processor. Alternatively, the system comprises mobile objects, wireless transceivers such as infrared, ultrasound and radiofrequency transceivers, and processors such as computers, servers, microprocessors, mobile phones, personal digital assistants and similar processing devices. Each of the objects includes a communication device which transmits a first wireless power level signal and a second wireless power level signal. The sensors are positioned within the indoor facility, with at least one of the sensors receiving the first wireless power level signal and with at least one of the sensors receiving the second wireless power level signal. The server is in communication with each of the sensors. The server calculates a first power level location of the mobile object from the first wireless power level signal utilizing a first location algorithm, calculates a second power level location of the object from the second wireless power level signal utilizing a second location algorithm, and determines the location of the mobile object. 
     Another aspect of the present invention is a method for determining a real-time location of an object within a facility. The method includes receiving a first wireless power level signal at at least one of a plurality of sensors positioned within a facility. The method also includes receiving a second wireless power level signal at at least one of the plurality of sensors positioned within an indoor facility. The method also includes calculating a first power level location from the first wireless power level signal utilizing a first location algorithm. The method also includes calculating a second power level location from the second wireless power level signal utilizing a second location algorithm. The method also includes determining a real-time location of an object using the first power level location and the second power level location. 
     Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is schematic view of a system for determining a real-time location of an object within a facility. 
         FIG. 2  is a multi-floor view of a facility employing a system for determining a real-time location of an object within a facility. 
         FIG. 3  is a floor plan view of a single floor in a facility employing the system for determining a real-time location of an object within a facility. 
         FIG. 4  is a two-floor view of a facility including a tagged object and sensors of a system for determining a real-time location of an object within a facility. 
         FIG. 5  is a flow chart of a method determining a real-time location of an object within a facility. 
         FIG. 6  is a flow chart of a method determining a real-time location of an object within a facility. 
         FIG. 7  is a block diagram of a communication device employing variable radiofrequency power level transmissions. 
         FIG. 8  is a block diagram of a communication device employing variable light intensity level transmissions. 
         FIG. 9  is a block diagram of a communication device employing variable sound level transmissions. 
         FIG. 10  is a block diagram of a communication device employing variable magnetic energy level transmissions. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-4 , a system for tracking objects within a facility is generally designated  50 . The system  50  is capable of determining real-time location of an object  100  within a facility  70 . The system  50  preferably includes a plurality of sensors  55 , a plurality of bridges  56 , a plurality of communication devices  60  and at least one central processor  65 . One example of the components of the system  50  is disclosed in U.S. Pat. No. 7,197,326, for a Wireless Position Location And Tracking System, which is hereby incorporated by reference in its entirety. A more specific example of the sensors  55  is disclosed in U.S. Pat. No. 7,324,824, for a Plug-In Network Appliance, which is hereby incorporated by reference in its entirety. 
     The system  50  is preferably employed at a facility  70  such as a business office, factory, home, hospital and/or government agency building. The system  50  is utilized to track and locate various objects positioned throughout the facility  70 . The communication devices  60  preferably continuously transmit signals on a predetermined time cycle, and these signals are received by sensors  55  positioned throughout the facility  70 . Alternatively, the tags  60  transmit signals in a random, ad-hoc or dynamic manner, and these signals are received by the sensors  55  positioned throughout the facility  70 . As discussed below, in order to mitigate multipath effects, the communication devices  60  transmit signals at various power levels. The sensors  55  transmit the data from the communication devices  60  to a bridge  56  for transmission to a server  65 . If a sensor  55  is unable to transmit to a bridge  56 , the sensor  55  may transmit to another sensor  55  in a mesh network-like system for eventual transmission to a bridge  56 . In a preferred embodiment, a transmission is sent from a transmission distance of six sensors  55  from a bridge  56 . Alternatively, a transmission is sent from a transmission distance ranging from ten to twenty sensors  55  from a bridge  56 . The central processor  65  preferably continuously receives transmissions from the sensors  55  via the bridges  56  concerning the movement of objects  100  bearing a communication device  60  within the facility  70 . The central processor  65  processes the transmissions from the sensors  55  and calculates a real-time position for each of the objects  100  bearing a communication device  60  within the facility  70 . The real-time location information for each of the objects  100  bearing a communication devices  60  is preferably displayed on an image of a floor plan of the facility  70 , or if the facility  70  has multiple floors, then on the floor plan images of the floors of the facility  70 . The floor plan image may be used with a graphical user interface of a computer, personal digital assistant, or the like so that an individual of the facility  70  is able to quickly locate objects  100  within the facility  70 . 
     As shown in  FIG. 1 , the system  50  utilizes sensors  55  to monitor and identify the real-time position of non-stationary objects bearing or integrated with communication devices  60 . The sensors  55   a - f  preferably wirelessly communicate with each other (shown as double arrow lines) and with a central processor  65  through a wired connection  66  via at least one bridge  56 , such as disclosed in the above-mentioned U.S. Pat. No. 7,324,824 for a Plug-In Network Appliance. The communication devices  60   a - c  transmit signals at various power levels (shown as dashed lines) which are received by the sensors  55   a - e , which then transmit signals to bridges  56  for eventual transmission to a central processor  65 . The central processor  65  is preferably located on-site at the facility  70 . However, the system  50  may also include an off-site central processor  65 , not shown. 
     In a preferred embodiment, each communication device  60  preferably transmits a radio frequency signal of approximately 2.48 GigaHertz (“GHz”). The communication format is preferably IEEE Standard 802.15.4. Alternatively, each communication device  60  transmits an infrared signal or an ultrasound signal. Each communication device  60  preferably transmits at a plurality of transmission power levels, preferably ranging from two to twenty different transmission power levels (energy levels), more preferably from two to ten different transmission power levels, and most preferably two different transmission power levels. Alternatively, the transmission power levels are the same. The number of communication device transmission power levels varies depending on data transmission constraints and time constraints for the system. In one preferred embodiment, the first power level is approximately 1 milli-Watt and the second power level is approximately 0.5 milli-Watt. In a preferred embodiment, the communication device  60  transmits each signal at a different power level before transmitting again at the original power level. Alternatively, the communication device  60  transmits at a sequence of power levels that can be predicted by the sensors  55 , bridges  56  and/or central processor  65 . For example, the communication device  60  transmits a first signal at a first power level and the next signal at a second power level. Those skilled in the pertinent art will recognize that the communication devices  60  may operate at various frequencies and mediums (infrared, ultrasound and others) without departing from the scope and spirit of the present invention. 
     As shown in  FIGS. 2-4 , the facility  70  is depicted as a hospital. The facility  70  has a multitude of floors  75   a - c . An elevator  80  provides access between the various floors  75   a ,  75   b  and  75   c . Each floor  75   a ,  75   b  and  75   c  has a multitude of rooms  90   a - i , with each room  90  accessible through a door  85 . Positioned throughout the facility  70  are sensors  55   a - o  for obtaining readings from communication devices  60   a - d  attached to or integrated into non-stationary objects  100   a ,  100   b  (see  FIGS. 2 and 4 ). A bridge  56  is also shown for receiving transmissions from the sensors  55  for processing by the central processor  65 . 
     As shown in  FIG. 4 , the communication device  60   a  is attached to movable bed  100   a  positioned on an upper floor  75   c . The communication device  60   a  transmits a signal which is received by sensors  55   a ,  55   b  and  55   c . If the signal to sensor  55   c  is the strongest, then an analysis of the readings from the sensors  55   a - c  may place the communication device  60   a , and thus the movable bed  100   a , at position  60 ′ on the lower floor  75   b . This type of faulty reading would likely occur with triangulation. To prevent such a faulty positioning reading, the present invention processes the readings preferably according to a method which eliminates the reading from sensor  55   c  from the location calculation for movable bed  100   a.    
     A method  1000  for determining a real-time location of an object within a facility is illustrated in  FIG. 5 . At block  1001 , a first wireless power level signal is transmitted from a communication device associated with an object. At block  1002 , a second wireless power level signal is transmitted from the communication device associated with the object. At block  1003 , the first wireless power level signal is received at at least one of a plurality of sensors positioned within a facility. At block  1004 , the second wireless power level signal is received at at least one of a plurality of sensors positioned within the facility. The same sensor may receive both the first and second wireless power level signals. At block  1005 , a first power level location is calculated from the first wireless power level signal utilizing a first location algorithm. At block  1006 , a second power level location is calculated from the second wireless power level signal utilizing a second location algorithm. Preferably the first location algorithm is a radial basis function algorithm and the second location algorithm is a proximity detection algorithm. At block  1007 , a real-time location of the object is determined using the first power level location and the second power level location. 
     Another method  2000  for determining a real-time location of an object within a facility is illustrated in  FIG. 6 . At block  2001 , a first wireless power level signal from a communication device is received at at least one of a plurality of sensors positioned within a facility. At block  2002 , a second wireless power level signal from the communication device is received at at least one of a plurality of sensors positioned within the facility. The same sensor may receive both the first and second wireless power level signals. At block  2003 , a first power level location is calculated from the first wireless power level signal utilizing a first location algorithm. At block  2004 , a second power level location is calculated from the second wireless power level signal utilizing a second location algorithm. Preferably the first location algorithm is a radial basis function algorithm and the second location algorithm is a proximity detection algorithm. At block  2005 , a real-time location of the object is determined using the first power level location and the second power level location. 
     A communication device  60  that utilizes different power levels of radiofrequency signals is illustrated in  FIG. 7 . A microcontroller  101  has a software programmable transmit power for modification from transmission to transmission. The transmissions are transmitted through transceiver  103 . A power supply  105  provides power to the device  60 . All of the components are preferably contained within a housing  170 . 
     A communication device  60   a  that utilizes different power levels of light is illustrated in  FIG. 8 . A microcontroller  201  has a software programmable transmit power for modification from transmission to transmission. The transmissions are transmitted through LED  203 , preferably an infrared transceiver. A power supply  205  provides power to the device  60   a . All of the components are preferably contained within a housing  207 . 
     A communication device  60   b  that utilizes different power levels of sound is illustrated in  FIG. 9 . A microcontroller  301  has a software programmable transmit power for modification from transmission to transmission. The transmissions are transmitted through a speaker device  303 , preferably an ultrasound transducer. A power supply  305  provides power to the device  60   b . All of the components are preferably contained within a housing  307 . 
     A communication device  60   c  that utilizes different power levels of magnetic energy is illustrated in  FIG. 10 . A microcontroller  401  has a software programmable transmit power for modification from transmission to transmission. The transmissions are transmitted through a magnetic energy generator  403 , preferably an electromagnetic transceiver. A power supply  405  provides power to the device  60   c . All of the components are preferably contained within a housing  407 . 
     From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes modification and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claim. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims.