Abstract:
System and method for enabling a wireless computing device to continuously determine its position includes a wireless computing device and a wireless positioning system substantially collocated therewith. The wireless positioning system has a first positioning mode in which it communicates with a wireless positioning network to enable the geographic location of the computing device to be determined upon reception of signals from the positioning network and a second positioning mode in which it enables the geographic location of the wireless computing device to be determined upon reception of signals from one or more of the wireless beacons and analysis of the signals in light of positional information about wireless beacons contained in a database. The wireless positioning system switches between the positioning modes depending on reception of signals from the wireless positioning network.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority under 35 U.S.C. §119(e) of U.S. provisional patent application Ser. No. 60/649,180 filed Feb. 3, 2005, the specification of which is incorporated by reference herein. 

   FIELD OF THE INVENTION 
   The present invention relates generally to a system and method for enabling a wireless computing device to determine its position using a wireless positioning network, e.g., a satellite-based positioning system, irrespective of the reception of positioning signals from the wireless positioning network by the computing device. 
   The present invention also relates to a system and method for passively building a database of wireless beacons by means of wireless computing devices equipped with positioning systems and disseminating the database to other computing devices. 
   The present invention also relates to a system and method ascertaining the geographical locations of wireless computing devices based on a database of wireless beacons and a system and method for creating the database of wireless beacons. 
   BACKGROUND OF THE INVENTION 
   As portable wireless computing devices proliferate, there is a growing demand to continuously and accurately know the geographic location of the computing devices. There are basically two different ways to determine the geographic locations of a computing device, either using a wireless positioning network such the GPS system or using a database of wireless beacons and determining position using this database. 
   The first technique suffers from the difficulty in continuously obtaining signals, e.g., from a network of satellite, to enable the position of the computing device to be determined. It is recognized that such difficulties commonly arise in enclosed areas and confined areas, such as in areas with a large concentration of tall buildings and in tunnels. 
   The second technique requires the creation of a database of wireless beacons, and the computing device to be within range of a plurality of such wireless beacons. In the absence of wireless beacons within range, the position of the computing device cannot be determined. 
   For the second technique, several systems are being used to enable wireless computing devices to determine their position. One such system is Place Lab. Place Lab is software providing low-cost, easy-to-use device positioning for location-enhanced computing applications. The Place Lab approach is to allow wireless computing devices such as notebook computers, PDAs and cell phones, to locate themselves by listening for radio beacons such as 802.11 access points, GSM cell phone towers, and fixed Bluetooth devices that exist in the surrounding environment. These beacons all have essentially unique identifications, for example, a MAC address. The devices compute their own location by hearing one or more IDs, looking up the associated beacons&#39; positions in a stored map, and estimating their own position referenced to the beacons&#39; positions. Additional information about Place Lab is found in: Place Lab: Device Positioning Using Radio Beacons in the Wild, by Anthony LaMarca et al., Pervasive 2005, Munich, Germany; Challenge: Ubiquitous Location-Aware Computing and the “Place Lab” Initiative, by Bill N. Schilit et al., Proceedings of The First ACM International Workshop on Wireless Mobile Applications and Services on WLAN (WMASH 2003), San Diego, Calif. September 2003; A Case Study in Building Layered DHT Applications, by Yatin Chawathe et al., January 2005; Accuracy Characterization for Metropolitan-scale Wi-Fi Localization, by Yu-Chung Cheng et al., Proceedings of Mobisys 2005, January 2005; Social Disclosure of Place: From Location Technology to Communication Practices, by Ian Smith et al., Pervasive 2005, Munich, Germany; and Privacy and Security in the Location-enhanced World Wide Web, by Jason I. Hong et al., Proceedings of Ubicomp 2003, Seattle, Wash. October 2003. 
   Another positioning system is that of Skyhook Wireless which uses a database of known Wi-Fi access points to calculate the precise location of any Wi-Fi enabled device. For this system, known Wi-Fi networks are mapped, e.g., by having hired drivers travel every street in a neighborhood, and a user&#39;s location is calculated based on the Wi-Fi networks the Wi-Fi enabled device detects at a given moment using proprietary software. If the device can identify three networks, it can determine its position, e.g., using triangulation. The more networks the device detects simultaneously, the more accurate the locational fix. 
   It would be desirable to provide a single positioning system for a wireless computing device which is capable of continuously determining the position of the wireless computing device using both a wireless positioning network and a database of wireless beacons to enable optimum positional determination. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a new system and method for enabling a wireless computing device to determine its position using a wireless and/or satellite-based positioning system irrespective of the reception of positioning signals therefrom by the computing device. 
   It is yet another object of the present invention to provide a new system and method for geographically locating wireless computing devices using signals broadcast by wireless beacons. 
   It is still another object of the present invention to provide a new system and method for passively building a database of wireless beacons by means of wireless computing devices equipped with positioning systems and disseminating the database to other computing devices. 
   Still another object of the present invention is to provide a new system and method ascertaining the geographical locations of wireless computing devices based on a database of wireless beacons and a system and method for creating the database of wireless beacons. 
   In order to achieve one of the above objects and others, a system for enabling a wireless computing device to continuously determine its position in accordance with the invention includes a wireless computing device and a wireless positioning system substantially collocated therewith. The wireless positioning system has a first positioning mode in which it communicates with a wireless positioning network to enable the geographic location of the wireless computing device to be determined upon reception of signals from the wireless positioning network and a second positioning mode in which it enables the geographic location of the wireless computing device to be determined upon reception of signals from one or more of the wireless beacons and analysis of the signals in light of positional information about wireless beacons contained in a database. The wireless positioning system switches between the first and second positioning modes to obtain a determination of its geographic location depending on reception of signals from the wireless positioning network. Since the locational information in the first positioning mode, i.e., that from the wireless positioning network, is more accurate, when such information is available it is used and when unavailable, a database-derived location is provided. The switch may be implemented as a software-switch. 
   In the second positioning mode, the wireless beacons provide identification information which is associated with data about the strength of a signal therefrom and received by the wireless computing device. This identification and signal strength data is input into a calculation algorithm which determines the geographic location of the wireless computing device therefrom, the identification information being used to obtain positional information about the wireless beacons which is contained in the database. 
   To create the database, particularly constructed wireless computing devices are used. Specifically, the wireless computing devices is provided with a scanner arranged to communicate with the wireless positioning network to enable its geographic location to be determined upon reception of signals from the wireless positioning network, for example, coupled to a GPS device. The scanner then obtains positional information about itself and identification and signal strength information about wireless beacons in order to derive the geographic location of the wireless beacons for inclusion in the database, using a calculation algorithm. In particular, software in the scanner analyzes the strength of signals received from the wireless beacons at a plurality of different positions of the scanner and applies an algorithm to determine the position of the wireless beacons therefrom. 
   A method for enabling a wireless computing device to continuously determine its position in accordance with the invention involves coupling the wireless computing device to a wireless positioning network to enable the geographic location of the wireless computing device to be determined upon reception of signals from the wireless positioning network, providing a database of identification and positional information about wireless beacons and enabling the geographic position of the wireless computing device to be continuously determined by obtaining a position signal derived from the signals from the wireless positioning network upon reception thereof and in the absence of reception of usable signals from the wireless positioning network, deriving a position signal from reception of signals from wireless beacons detected by the wireless computing device and analysis of the received signals using the database. The database is constructed by obtaining identification and signal strength data about each wireless beacon at a plurality of locations at which a signal from that wireless beacon is being received and applying an algorithm to determine positional information about the wireless beacons based on the signal strength data. 
   A method for administering a database of wireless beacons in accordance with the invention entails maintaining a central database of wireless beacons, providing the central database to a plurality of wireless computing devices, enabling each wireless computing device to determine identification and positional information about wireless beacons not contained in the central database, periodically forwarding the identification and positional information about wireless beacons not contained in the central database from the wireless computing devices to the central database, updating the central database to include the forwarded identification and positional information, and periodically directing the updates of the central database to the plurality of wireless computing devices. Each wireless computing device can be designed to determine identification and positional information about wireless beacons as described above with respect to use of the scanner. 
   A related embodiment of the invention is a system for enabling a wireless computing device to continuously determine its position in which a central database is provided containing identification and positional information about wireless beacons and receives identification and positional information about wireless beacons not previously contained therein and generates database updates based thereon. Wireless computing devices each include a local database containing positional information about wireless beacons and wirelessly communicate with the central database to receive the database updates and add the database updates to the local database. A wireless positioning system is substantially collocated with each wireless computing device and enable the geographic location of the wireless computing device to be determined upon reception of signals from at least one wireless beacon and analysis of the signals in light of the positional information about wireless beacons contained in the local database. This location determination can be performed in any of the ways described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like elements, and wherein: 
       FIG. 1  is a schematic of a general concept used in the invention for enabling position of a wireless computing device to be determined. 
       FIG. 2  is a schematic showing a scanner used to create a database of wireless beacons in accordance with the invention. 
       FIG. 3  is an illustration of multiple scanner readings obtained to create the database of wireless beacons. 
       FIG. 4  is a flowchart showing the mapping of wireless beacons from the scanner readings. 
       FIG. 5  is a flowchart showing the determination of the position of a computing device based on instantaneously received signals from wireless beacons and the database thereof. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIG. 1 , to provide a system and method for enabling a wireless computing device to determine its position using a wireless and/or satellite-based positioning system irrespective of the reception of positioning signals therefrom by the computing device, each computing device  10  is coupled to a wireless or satellite-based positioning systems such as a GPS device  12  such that the computing device  10  and GPS device  12  are effectively collocated. Using positional data provided by the GPS device  12  and data about wireless beacons, Wi-Fi access points, cell phone towers or other comparable systems (hereinafter referred to as beacons) within reception range of the computing device  10 , the computing device  10  creates a database of wireless beacons within a wireless positioning system  14  including the geographic location of each beacon (the exact manner in which such a database is formed is described below). 
   A software switch  16  is interposed between the GPS device  12  and the computing device  10  to vary the manner in which a determination by the computing device  10  of its position is made. Specifically, when the GPS device  12  receives an accurate positioning signal, switch  16  would allow this GPS signal to be directed to the computing device  10  so that the computing device would consider its position that determined by the GPS signal. On the other hand, when the GPS device  12  is unable to provide an accurate GPS signal, switch  16  would allow a positioning signal derived from the wireless positioning system  14 , and based on input from the computing device  10  at that time, to be directed to the computing device  10  and the computing device  10  would consider its position that indicated by this positioning signal. 
   Switch  16  would operate to revert back to allowing a GPS signal from GPS device  12  to be directed to computing device  10  once GPS device  12  provides an accurate GPS signal. Accuracy of the GPs signal can be made in a manner known to those skilled in the art. 
   Accordingly, the computing device  10  would be able to continuously know its position even in the absence of an accurate GPS signal. The computing device  10  could be designed to indicate the source of its positioning signal, e.g., an icon on a screen thereof could indicate either a satellite-derived signal (a signal from GPS device  12 ) or a database-derived signal (a positioning signal from wireless positioning system  14 ). 
   Although represented as separate elements in  FIG. 1 , this is for the purposes of explanation only and it should be understood that computing device  10  can include wireless positioning system  14  and switch  16  can be software implemented in the computing device  10 . Moreover, GPS device  12  can also be incorporated into the computing device  10  so that a single hand-held or portable unit could include the entire system in accordance with this embodiment of the invention. 
   The database of wireless beacons in wireless positioning system  14  can be considered a map which associates the fixed physical location of each wireless beacon, i.e., where they are geographically located, with a unique or semi-unique identification code of each wireless beacon. The location of each beacon can be expressed, for example, by latitude and longitude, or possibly by another coordinate system. 
   Construction of such a map may be accomplished in a variety of ways, the simplest but most labor intensive being to place a positioning device, e.g., a GPS device, at the same location of each wireless beacon to thereby obtain the physical location of the wireless beacon from the GPS device. This however is highly impractical in view of the constant addition of wireless beacons and the manpower that would be required. 
   A preferred and far simpler method would be to collect data about each wireless beacon based on information about the strength of a signal provided by each wireless beacon at a plurality of locations at which a signal from that wireless beacon is being received. Basically, the geographic location of each wireless beacon is determined based on analysis of the signal strength provided by that wireless beacon as a function of geographic location. 
   To enable such an analysis, a scanner  18  is equipped or collocated with a GPS device  20  and during movement of the scanner  18 , a series of readings consisting of the position of the scanner  18 , obtained using the GPS device  20 , and the strength of the signal received at this position are obtained from a wireless beacon (see  FIG. 2 ). The scanner  18  may be a hand-held computing device such as a PDA or cell phone including a processor having software  22  designed to analyze the signal received via an antenna  24  from every single beacon at different positions and estimate a geographic location thereof. A series of readings for each beacon will be stored in a database  26 . Thus, if multiple beacons are being mapped, there will be multiple series of readings. 
   Referring to  FIG. 3 , these readings will look like a series of data sets designated (Xi, Yi, Si) where Xi and Yi are the latitude and longitude, respectively, of the position of the scanner  18  and Si is the strength of a signal received at this position from wireless beacon  28 . With the scanner  18  at position P 1 , a reading of (X 1 ,Y 1 ,S 1 ) is obtained, with the scanner  18  at position P 2 , a reading of (X 2 ,Y 2 ,S 2 ) is obtained and with the scanner  18  at position P 3 , a reading of (X 3 ,Y 3 ,S 3 ) is obtained. 
   Each series of readings, i.e., the readings obtained from each individual beacon  28 , recorded by the scanner  18  may be stored in the scanner&#39;s memory. To obtain an estimated position of each beacon, the series of readings relating only to that beacon is input to a calculation algorithm  30  that processes the readings to provide as output, an estimated position of the beacon  28  (see  FIG. 4 ). If multiple series of readings are input to the algorithm, then the position of all of the beacons  28  from which readings were obtained will be output. 
   Note that at each position of the scanner  18 , multiple readings can be obtained, one for each beacon  28  in reception range of the scanner  18 . These readings can be stored with an identification of the beacon  28  so that the readings can later be combined with other readings from the same beacon  28  in order to determine the location of the beacon  28 . 
   Different calculation algorithms  30  can be used in the invention to process each series of readings into the position of the beacon  28 . These include Centroid, triangulation, Newton and the like. An exemplifying calculation algorithm  30 , namely the Centroid algorithm, is described below. Generally, regardless of which algorithm  30  is used, approximately the same estimated position of the beacon  28  will be obtained and thus, the invention is not limited to use of any particular algorithm. 
   It is important to bear in mind that scanner  18  can be and typically is the same as computing device  10  (in which case, GPS device  20  is the same as GPS device  12 , the software  22  and database  26  would be part of the wireless positioning system  14  and antenna  24  would be part of the wireless computing device  10 ). This embodiment will be considered hereinafter. In this case, computing device  10  would not only create and/or update the database  26  of wireless beacons in the wireless positioning system  14  via operation of the scanning software  22  (when GPS signals from GPS device  12 ,  20  are available) but would also use the same database  26  of wireless beacons it is updating to determine its position in the absence of an accurate GPS signal from the GPS device  12 ,  20  (when GPS signals from GPS device  12 ,  20  are not available). Thus, when GPS signals are available and switch  16  is allowing the GPS signal from the GPS device  12 ,  20  to be directed to the computing device  10 , computing device  10  is working as scanner  18  to scan the area around the computing device  10  to determine the presence of (unmapped) wireless beacons and obtain geographic positional information about these unmapped wireless beacons for inclusion in the database  26  of wireless beacons resident in the wireless positioning system  14 . 
   After the estimated position of the beacons is obtained, the final step in creating the database  26  of wireless beacons in wireless positioning system  14  is to store the positions of the beacons  28  in a database in a manner in which the position of the beacon is associated with an identification code. For example, the position of each beacon  28  can be stored in the database  26  in the form (Id, X, Y) where Id is a unique identification associated with or referencing the beacon  28  and X, Y are the latitude and longitude coordinates, respectively, of the beacon  28  as determined in the manner described above. 
   The database creation step continues whenever a GPS signal is available and the position of the scanner  18  has changed. Thus, when the scanner  18  is the same as computing device  10 , movement of the computing device  10  in the presence of a GPS signal from GPS device  12 ,  20  can results in continuous updating of the database  26  of wireless beacons in wireless positioning system  14 . 
   In the exemplifying use described above with respect to  FIG. 1 , the database  26  of wireless beacons in wireless positioning system  14  is used only when a GPS signal from GPS device  12 ,  20  is unavailable. At this time, it is necessary to input data into the database  26  to determine the position of the computing device  10 . 
   With reference to  FIG. 5 , determining the position of the computing device  10  using the database  26  of wireless beacons in wireless positioning system  14  entails querying a receiver unit of the computing device  10 , i.e., a network adapter or cell antenna  24 , to find out which wireless beacon(s)  28  are “visible” and what is the strength of the signal received by the receiver from each wireless beacon  28 . Visible beacons  28  are those from which the receiver receives a signal. 
   From the antenna  24 , the computing device  10  will obtain a series of readings each containing the unique identification associated with or referencing one of visible wireless beacons  28  and the strength of the signal from that wireless beacon  28 . This series of readings can be expressed in the form of (Id, Si) where Id is the unique identification of the wireless beacon  28  and Si is the signal strength. 
   The computing device  10  then submits this information to database  26  in wireless positioning system  14  which contains the geographic location of the wireless beacons  28  in association with their identification. Using the data contained in the database  26 , the corresponding, estimated geographic location of the wireless beacon  28  is obtained based on its identification contained in the information and is associated with the signal strength. 
   After the location of the visible beacon(s)  28  associated with the antenna  24  is known, a series of (Xi, Yi, Si) records is provided to the calculation algorithm  30  to estimate the position of the antenna  24 , i.e., the position of the computing device  10 . 
   As described above, a calculation algorithm  30  is used to determine the position of a wireless beacon  28  when creating the database  26  of wireless beacons and also to determine the position of the computing device  10  in the absence of a GPS signal from GPS device  12 ,  20 . 
   When determining the position of a wireless beacon  28  in the mapping mode from the series of readings (Xi,Yi,Si) to determine the position (X,Y) of the wireless beacon  28 , the Centroid calculating algorithm averages the latitudes and longitudes recorded and adds the signal strength squared as a weight:
 
 X =( S 1 2   *X 1 +S 2 2   *X 2 + . . . +Sn   2   *X 2)/( S 1 2   +S 12 2   + . . . +Sn   2 )
 
 Y =( S 1 2   *Y 1 +S 2 2   *Y 2 + . . . +Sn   2   *Y 2)/( S 1 2   +S 12 2   +. . . +Sn   2 )
 
where X and Y are the estimated position of the beacon  28  and the Si, Xi, Yi the information recorded by the scanner  18 .
 
   When estimating the position of the computing device  10  using the same formula, Xi, Yi would be the coordinates of the wireless beacons  28  referenced in the database  26  and Si would be the strength of the signal received from those same wireless beacons  28 . 
   Applying the database mapping technique described above using scanner  18 , when incorporated into the wireless computing device  10  with a common GPS device  12 , it becomes possible to create a collaborative database. That is, a database which is continually being updated with data about new wireless beacons can be formed. Scanner  18  obtains identification and signal strength data about new, unmapped wireless beacons when the GPS device  12  receives accurate positioning signals and determines the position of the unmapped wireless beacons for inclusion in the database of wireless beacons in the wireless positioning system  14  which is used when accurate GPS signals from GPS device are not available. The same positional information about previously unmapped wireless beacons being directed to the database in the wireless positioning system  14  can also be directed to a central monitoring or administration facility which is charged with the responsibility for providing an accurate database of wireless beacons. The positional information can be forwarded to this facility periodically, such as every 24 hours. In conjunction with an upload of positional information about new wireless beacons, positional information about new wireless beacons obtained from other wireless computing devices  10  can be downloaded from the facility. 
   The central facility thereby oversees collection of individual contributions to the database, one from each participating (collective) wireless computing device, and disseminates the collection of the individual contributions to all wireless computing devices using the same positioning technique. It must be understood that not all wireless computing devices  10  will be equipped with a scanner  18  in which case, only some wireless computing devices would contribute positional information to the central facility but all wireless computing devices would preferably receive the update of positional information. Since the uploading of the positional information from the wireless computing devices to the central facility and downloading of the positional information from the central facility to the wireless computing devices may be done without involvement of the user, the central and individual databases of wireless beacons can therefore be passively created, updated and disseminated. 
   While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.