Patent Publication Number: US-7590720-B2

Title: Systems and methods for locating geographical regions of mobile computer users

Description:
RELATED APPLICATIONS 
   This is a continuation application of and priority is claimed to co-pending U.S. patent application having Ser. No. 09/760,180, with a filing date of Jan. 12, 2001, for “Systems and Methods for Locating Mobile Computer Users in a Wireless Network” of Paramvir Bahl. This co-pending United States patent Application is commonly assigned herewith and is hereby incorporated herein by reference for all that it discloses. 

   BACKGROUND OF THE INVENTION 
   The proliferation of lightweight, portable computing devices and high-speed wireless local area networks (LANs) has enabled users to remain connected and be able to compute while on the move inside buildings and on campus areas around buildings. This new paradigm has given birth to a new class of applications that are “location aware.” The goal of mobile computing in many instances is to enable a user to interact effectively with his or her physical surroundings. One example of such an interaction is to track physical locations of network users, particularly mobile users. Doing so allows one network user to query the network for a location of another network user and to receive a reasonably accurate response. 
   One component of these systems is the actual tracking system, which determines the user&#39;s location. The Global Positioning System (GPS) is one example of a technology, which enables the creation of inexpensive and portable systems that can help locate and track users. GPS systems currently are used to provide direction to drivers through an in-vehicle system; provide location and tracking information for marine navigation; and allow shipping companies to locate and track individual shipments. However, the GPS system relies on an unobstructed view of several satellites, making its use for tracking users who are indoors ineffective. 
   To overcome this obstacle, alternate technologies have been developed to locate and track users or objects in an indoor environment. One such system uses tags placed on the items that are to be tracked. In an electronic sense, the tags can be either active or passive, and they communicate with base stations. The base stations are physically linked together through a wired or wireless network. Each tag transmits a unique code to identify itself. The location of the tag can thereby be determined to be in the vicinity of the base station with which the tag last communicated. 
   Such tag-based tracking and location systems require a significant installation of specialized base stations. A tag-based system can only determine the location of the tags as being “near” a particular base station. As a result, a large number of base stations must be installed to achieve a sufficiently high resolution. Furthermore, obtrusive tags have to be placed on every item that is to be tracked or located, and in the case of infrared tags, the system operates only when there is a line of sight between the tag and a base station. For these reasons, tag-based systems have shown very limited success. 
   Another technology has been developed which uses radio frequency transmissions from base stations and mobile units to track the location of mobile units. This technology is described in U.S. patent application Ser. No. 09/513,155, entitled “Using a Derived Table of Signal Strength Data to Locate and Track a User In a Wireless Network”, and in U.S. patent application Ser. No. 09/513,355, entitled “Locating and Tracking a User in a Wireless Network Through Environmentally Profiled Data.” 
   In this system, a Wireless Local Area Network (WLAN) is utilized for locating and tracking users. A WLAN consists of base stations connected to a wired network, and mobile devices that are “connected” to the WLAN through radio frequency signals with the base stations. The signal sensing ability of both the base station and the mobile device are used to determine the location of the mobile device, and thus the location of the user of the mobile device. In particular, the strength of the signals received from several base stations is measured by the mobile device. The mobile device then compares the signal strength from each of the base stations to a pre-computed table containing the base stations&#39; signal strength at various known locations of the mobile device. From this comparison, the mobile device determines its location. Alternatively, the signal strength from the mobile device can be measured at a number of base stations. This signal strength is then compared by a central computer to a pre-computed table containing the mobile computer&#39;s signal strength at the base stations for various known locations. From this table, the central computer determines the location of the mobile computer. 
   Although the mobile computer can identify its location using this system, a problem remains as to how one user, say User A, who is logged onto a network on a fixed or mobile computer can locate another mobile computer or, more likely, the person using the mobile computer, say User B. This problem has been solved for finding stationary users, since the requesting user, User A, can simply determine the location of a network access point to which the stationary user&#39;s, User B&#39;s, computer is connected and use that location to infer his or her location. But since, by definition, a mobile user can be physically located virtually anywhere within the coverage of the network, the problem becomes significantly more difficult to solve. 
   Yet another problem exists when one user is logged onto more than one computer in a network. Current systems and methods don&#39;t allow for distinguishing between the computers to identify where the user may be physically located. 
   SUMMARY OF THE INVENTION 
   Systems and methods are described that enable a network user to query the network for the location of another network user, particularly a mobile user. If the mobile user is logged onto more than one computer on the network, the requesting user can determine which of the computers the mobile user is currently using. 
   The mobile user periodically updates a local server database with the location coordinates of the mobile user and the time at which each update is received. A user name identifying the mobile user is associated with the location and time of update. 
   When another user wants to find the mobile user, the other user invokes a location manager to search a server database for a user name identifying the user. If the last update from the mobile user was made within a certain threshold of the query, the last known location stored on the server is immediately sent to the other user as the current location of the mobile user. This option requires very little overhead. 
   If the last update from the mobile user was made a while ago (i.e., outside the threshold), then the system invokes a location tracking service to determine the mobile user&#39;s location. By including periodic updates to the server, the user&#39;s computer enables the location manager to locate users using their computers even when they are not mobile and when they are not wirelessly connected. 
   The mobile computer is also configured to transmit an “active” signal if the mobile computer has been used within a specified time period. For example, if the mobile computer has been actively used within the two minutes prior to the latest update, the active signal is transmitted together with the location (and other) information. Therefore, when a user is logged onto multiple machines, it is possible to determine on which machine the user was most recently active. The location of the active machine is deemed to be the location of the user. 
   Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative implementations, which proceeds with reference to the accompanying figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the various methods and arrangements of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a block diagram generally illustrating an exemplary computer system on which the present invention resides. 
       FIG. 2  is a block diagram of a wireless network system including a server and three mobile computers. 
       FIG. 3  is a flow diagram of client-side operations in a method for locating a mobile user within a wireless network. 
       FIG. 4  is a flow diagram of server-side operations in a method for locating a mobile user within a wireless network. 
   

   DETAILED DESCRIPTION 
   The invention is illustrated in the drawings as being implemented in a suitable computing environment. Although not required, the invention will be described in the general context of computer-executable instructions, such as program modules, to be executed by a personal computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, including hand-held devices, multi-processor systems, microprocessor based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. The invention may also be practice in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
   With reference to  FIG. 1 , an exemplary wireless network system  100  for implementing the invention includes a general purpose computing device in the form of a conventional mobile personal computer  120 , including a processing unit  121 , a system memory  122 , and a system bus  123  that couples various system components including the system memory to the processing unit  121 . The system bus  123  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The system memory includes read only memory (ROM)  124  and random access memory (RAM)  125 . A basic input/output system (BIOS)  126 , containing the basic routines that help to transfer information between elements within the mobile personal computer  120 , such as during start-up, is stored in ROM  124 . The mobile personal computer  120  further includes a hard disk drive  127  for reading from and writing to a hard disk  160 , a floppy disk drive  128  for reading from or writing to a removable magnetic disk  129 , and an optical disk drive  130  for reading from or writing to a removable optical disk  131  such as a CD ROM or other optical media. 
   The hard disk drive  127 , floppy disk drive  128 , and optical disk drive  130  are connected to the system bus  123  by a hard disk drive interface  132 , a floppy disk drive interface  133 , and an optical disk driver interface  134 , respectively. The drives and their associated computer-readable media provide non-volatile storage of computer-readable instructions, data structures, program modules and other data for the mobile personal computer  120 . Although the exemplary environment described herein employs a hard disk  160 , a removable magnetic disk  129 , and a removable optical disk  131 , it will be appreciated by those skilled in the art that other types of computer-readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks, Bernoulli cartridges, random access memories, read only memories, and the like may also be used in the exemplary operating environment. 
   A number of program modules may be stored on the hard disk  160 , magnetic disk  129 , optical disk  131 , ROM  124  or RAM  125 , including an operating system  135 , one or more application programs  136 , other program modules  137 , and a program data  138 . A user may enter commands and information into the mobile personal computer  120  through input devices such as a keyboard  140  and a pointing device  142 . Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  21  through a serial port interface  146  that is coupled to the system bus, but may be connected by other interfaces, such a parallel port, game port or universal serial bus (USB). A monitor  147  or other type of display device is also connected to the system bus  123  via an interface, such as a video adapter  148 . In addition to the monitor, personal computers typically include other peripheral output devices, not shown, such as speakers and printers. 
   The mobile personal computer  120  may operate in a networked environment using logical connections to one or more remote computers, such as a server  149 . The remote server  149  may be another type of remote computer, such as another personal computer, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the mobile personal computer  120 , although only a memory storage device  150  has been illustrated in  FIG. 1 . The logical connections depicted in  FIG. 1  include a Wireless Local Area Network (WLAN)  151  and a wide area network (WAN)  152 . Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet. 
   When used in a WLAN networking environment, the mobile personal computer  120  is connected to the local network  151  through a wireless network interface or adapter  153 . The wireless interface  153  transmits packets wirelessly to a base station  161 . The base station  161  can then retransmit the packets, either through a wired or wireless network to the remote server  149 . When used in a WAN networking environment, the personal computer  120  typically includes a modem  154  or other means for establishing communications over the WAN  152 . The modem  154 , which may be internal or external, is connected to the system bus  123  via the serial port interface  146 . In a networked environment, program modules depicted relative to the mobile personal computer  120 , or portions thereof, may be stored in the remote memory storage device. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. 
     FIG. 1  also shows several fixed network resources, such as a printer  162 , a scanner  164  and a copier  166 . Information about the fixed resources  162 ,  164 ,  166  is contained in a resource database  168  stored in the memory storage device  150 . Information contained included information regarding location of each fixed resource and properties of each fixed resource. It is noted that, while only a few fixed resources are shown, any number of fixed resources may be logically or directly connected to the remote server  149 . Other resources are not necessarily connected to the remote server  149 . Though not shown or discussed in the present example, other examples of fixed resources include an office, files, documents, e-mail addresses, databases, users, distributed components, and the like. 
   The memory storage device  150  also includes a user database  170  that stores information about users connected to the network  100 . Such information includes, but is not limited to, user name, last known location, time of last location update and an activity indicator. This information will be discussed in greater detail below. 
   In the description that follows, the invention will be described with reference to acts and symbolic representations of operations that are performed by one or more computers, unless indicated otherwise. As such, it will be understood that such acts and operations, which are at times referred to as being computer-executed, include the manipulation by the processing unit of the computer of electrical signals representing data in a structured form. This manipulation transforms the data or maintains it at locations in the memory system of the computer, which reconfigures or otherwise alters the operation of the computer in a manner will understood by those skilled in the art. The data structures where data is maintained are physical locations of the memory that have particular properties defined by the format of the data. However, while the invention is described in the foregoing context, it is not meant to be limiting as those of skill in the art will appreciate that various acts and operations described hereinafter may also be implemented in hardware. 
     FIG. 2  depicts a wireless network system  200  similar to the system  100  shown in  FIG. 1  but shown, in part, in greater detail. The wireless network system  200  includes a server  202  having memory  204  in which a user database  206  is stored. The user database  206  includes records having various fields. A user field  208  stores an identifier associated with a particular user of the system  200 . Such an identifier is commonly referred to as a user name. A last known location field  210  stores a location of a computing unit determined and transmitted to the server  202  by the computing unit. The location stored in the last known location field  210  may be described in terms of absolute coordinates (latitude, longitude and/or altitude), coordinates relative to a known, fixed location (x meters, y meters from the front door of Building A), or a geographical unit (Room  2216 , Conference Room A, etc.). Alternatively, the location may be the location of a network node, or access point, to which the computing unit is connected. 
   A time field  212  stores a time at which the last known location was transmitted. An active field  214  is included in the user database  206  and contains an indicator to indicate if the computing unit associated with a particular active field  214  was in use for a specific period of time prior to the transmission of the location information. For example, if a computing unit has not received any actuations by a user for, say, three minutes before a location update is transmitted to the server  202 , a value of the active field  214  will indicate that the computing unit is not active. If, on the other hand, the computing unit was in use at the time the location update was transmitted to the server  202 , the value of the active field  214  will indicate that the computing unit is active. The implications of the active field  214  and its indications will be discussed in greater detail, below. 
   The user database  206  also contains an OK field  215 . The OK field  215  is used to store a list of users that a user identified in the user field  208  has authorized to receive the identified user&#39;s location. Initially, the OK field  215  is set to a default that allows any requesting user to find out where the identified user (the user identified in the user field  208 ) is located. However, the identified user may update the OK field  215  so that only those user authorized by the identified user can locate the identified user. 
   The server  202  is connected to a wireless access point  216 . The wireless access point  216  may or may not be integrated into the server  202  itself. The wireless access point  216 , as the name implies, serves as a reception point for wireless transmissions directed to the server  202 . The server  202  may also be connected to a wired network  218 , though this is not required if the network  200  is strictly for wireless users. 
   Several mobile computers are shown in communication with the wireless access point  216  of the network  200 . Mobile A  218  is a mobile computer that is a part of the wireless network  200 . Mobile B  220  and Mobile C  222  are, likewise, connected within the wireless network  200 . It is noted that, although only three mobile computers are shown in  FIG. 2 , the wireless network  200  can comprise virtually any number of mobile computers, limited only by the physical constraints of the system. 
   Mobile A  218  includes memory  224  and a wireless network interface  226 , which is used to communicate with the wireless access point  216  to access the wireless network  200 . Mobile A  218  also includes a clock  228  that provides a time stamp for location transmissions from Mobile A  218 . The memory  224  of Mobile A  218  stores a location manager  230 , network communication protocol(s)  232  used by Mobile A  218  to communicate with the wireless network  200 , and a location tracking service  234 , which is configured to identify a location of Mobile A  218  upon request. Whenever the location manager  230  requires the location of Mobile A  218 , it queries the location tracking service  234 . The location tracking service  234  places the mobile&#39;s wireless network hardware in promiscuous receive mode so that it can receive beacons from all nearby base stations. Using the signal strength of the beacon packets with an appropriate, previously established radio map of the area or building, Mobile A  218  calculates its position. Alternatively, the location tracking service  234  in Mobile A  218  may simply query its wireless network interface  226  to determine the address of the wireless access point  216  to which it is connected. It may then either transmit this address to the server  202  which does a look up to determine the location of the wireless access point  216  or the Mobile A  218  may itself determine the location of the wireless access point  216  using a map of the area or building and transmit that location to the server  202 . This location is then considered by the server  202  as the location of the Mobile A  218  and stored in the last known location  210  field. 
   In some implementations, it may be desirable to encrypt the location information before it is transmitted to the server  202 . For instance, if a user of Mobile A  218  does not want users outside the system to determine the location of Mobile A  218 , then the location data can be encrypted prior to transmitting the location data to the server  202 . Also, a feature is described below, wherein a user of Mobile A  218  can identify users that are authorized to determine the location of Mobile A  218 . In that case, it is important to encrypt the location information so only the authorized users can determine the location of Mobile A  218 . 
   Although the location tracking service  234  is described as utilizing a radio frequency (RF) system that determines the location of Mobile A  218  by detecting RF signals transmitted from a number of base stations, it is noted that the location tracking service  234  may use any available method to identify the location of Mobile A  218 , such as a GPS system, an IR-based system, a tag-based system, etc. 
   Mobile B  220  includes a location manager  236  and Mobile C  222  includes a location manager  238 . Location manager  236  of Mobile B  220  and location manager  238  of Mobile C  222  are similar to location manager  230  of Mobile A  218 , even though the only functionality described herein for location managers  236 ,  238  is a function that requests the location of Mobile A  218 . These and other elements shown in  FIG. 2  will be discussed in greater detail, below, with reference to  FIG. 3  and  FIG. 4 . 
     FIG. 3  is a flow chart depicting client-side operations in a method for locating a mobile user in a wireless network. At block  300 , Mobile A  218  determines its location from analysis of various radio frequency signal transmitted from known locations. The location may be determined in absolute (latitude, longitude, altitude) coordinates or in coordinates relative to a known absolute location (x meters, y meters from front door of Building A). If the wireless network system information is organized in a directory structure that associates a geographical region with each directory level (state, county, city, building, office, etc.), the location may be determined as a geographical unit, e.g., office  2216 , Building A, etc. Such a geographically based information management system is described in U.S. patent application Ser. No. 09/766,505, entitled “Information Management and Processing In a Wireless Network.” 
   Mobile A  218  then determines a system time at step  302 . This is accomplished by accessing the system time of the server  202  to which Mobile A  218  is connected. 
   At block  304 , Mobile A  218  determines if a user has been active on Mobile A  218  for a specified time period prior to the location determination block  300 . For instance, if the specified time period is two minutes, then Mobile A  218  is deemed to be active if a user operation has occurred in the two minutes prior to the determination block  300 . If so (“Yes” branch, block  304 ), then a user name of a user on Mobile A  218 , is transmitted to the server  202  together with the location coordinates, the time of the location determination, and an active signal indicating that Mobile A  218  is active (block  306 ). If the user has not operated Mobile A  218  during the specified time period (“No” branch, block  304 ), the active signal is not transmitted. In that case, only the user name, location coordinates and time of the location determination are transmitted to the server  202  at block  308 . When the active signal is received at the server  202 , the server  202  indicates in the user database  206  that Mobile A  218  is active. Contemporaneously therewith, the server  202  clears any other active signal that may be present for a computer used by the user logged onto Mobile A  218 , since only one computer can be active for a user at any given time. 
   In an alternative implementation, Mobile A  218  does not periodically update its location with the server  202 . This may be preferable in a situation where a user of Mobile A  218  wishes to conserve battery power or network bandwidth. In such an implementation, Mobile A  218  initially registers with the server  202  when Mobile A  218  becomes active. Thereafter, Mobile A  218  only updates its location when it receives a request to do so from the server  202 . The server  202  makes such a request in the event that it receives a request from another user to locate Mobile A  218 . 
     FIG. 4  is a flow chart depicting server-side operations in a method for locating a mobile user in a wireless network. At block  400 , the server  202  receives a request from a computing unit (such as Mobile B  220  or Mobile C  222 ) for a location of a specific user. For the present discussion, assume that Mobile C  222  submits a request to the server  202  for the location of “Victor,” who is logged onto the network on Mobile A  218 . Also assume that “Victor” is a unique user name. When the request for “Victor” is received, the server  202  searches for any entry in the user database  206  having “Victor” in the user field  208 . If “Victor” is not found in the user database  206  (“No” branch, block  402 ), a “User Not Found” message is sent to Mobile C  222  at block  404 . 
   If “Victor” is found in the user database  206  (“Yes” branch, block  402 ), then the server  202  continues to search the user field  208  of the user database  206  for other “Victor” entries at block  406 . If at least one other “Victor” entry is found (“Yes” branch, block  406 ), the server locates the “Victor” entry that indicates an “active” status in the active field  214  (block  408 ). Block  408  is not performed if no other “Victor” entry is found. 
   At block  410 , a time differential is calculated by finding the difference between the time of the last location update (time field  212 ) and a current time. The time differential is compared to a pre-defined threshold at block  412 . If the time differential is within the threshold (“Yes” branch, block  412 ), then the location stored in the last known location field  210  of the user database  206  is deemed to be the location of “Victor,” the user of Mobile A  218  (block  418 ). If the time differential is greater than the threshold (“No” branch, block  412 ), then a signal is transmitted to the location manager  230  of Mobile A  218  requesting a location update, which causes the location manager  230  to invoke the location tracking service  234  at block  414  to determine the current location of Mobile A  218 . The current location information is then transmitted to the server  202  at block  416 , where it is stored in the user database  206 . Then, at block  418 , the current location (which is now stored in the last known location field  210 ) is deemed to be the location of the user, “Victor.” 
   It is noted that the systems and methods described herein may also be utilized to located fixed system users as well. In such a case, a location tracking service in a fixed computing resource can determine the address of its own network interface card and send that address to the network server. The network server can then look up the appropriate database to determine the name of the machine which contains this network card and its location. In this way, a user&#39;s location can be determined from the location of the computing resource, the user&#39;s name and the user&#39;s “active” status. 
   Conclusion 
   The described implementations advantageously provide for an effective way to locate a mobile user in a wireless network, even if the mobile user is logged into more than one computer. Other advantages will be apparent to those of skill in the art. 
   Although the invention has been described in language specific to structural features and/or methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps are disclosed as preferred forms of implementing the claimed invention.