Patent Document

[0001]    This application claims the benefit of and is a continuation of U.S. application Ser. No. 10/936,130, entitled “Local Area Network Assisted Positioning,” filed on Sep. 7, 2004, which claims the benefit of and is a continuation in part of U.S. application Ser. No. 10/877,205, entitled “Method and Apparatus for Wireless Network Hybrid Positioning,” filed on Jun. 25, 2004, which claims the benefit of U.S. Provisional Application Ser. No. 60/483,094, entitled “Method and Apparatus for Wireless Network Hybrid Positioning,” filed on Jun. 27, 2003; and U.S. application Ser. No. 10/936,130 also claims the benefit of and is a continuation in part of US PCT Application Serial No. PCT/US04/20920, entitled “Method and Apparatus for Wireless Network Hybrid Positioning,” filed on 28 Jun. 2004, which claims priority to U.S. Provisional Application Ser. No. 60/483,094, entitled “Method and Apparatus for Wireless Network Hybrid Positioning,” filed on Jun. 27, 2003. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates in general to automated location determination and, more specifically, but not by way of limitation, to determining a location of a wireless device. 
         [0003]    There is an ever growing desire to know geographic position of various mobile devices. For example, cellular phone operators are trying to comply with requirements to locate handsets for emergency purposes. Once position is known, emergency personnel can be dispatched to aid resolving the emergency. Knowing geographic location serves many other purposes such as geographic-tied advertising, child supervision, automated parolee supervision, reverse 911, fleet vehicle tracking, etc. 
         [0004]    Conventional location techniques have difficulty accurately resolving location in certain situations. Satellite-based location systems suffer from inaccuracies when a clear view the sky is unavailable. Terrestrial-based systems require communication with several base stations that serve as known references during trilateration, but in some scenarios, since these systems were primarily designed for communication purposes there are not enough geographically dispersed base stations within communication range of the mobile device. Even when communication is possible to multiple base stations, multi-path induced inaccuracies can degrade the ability to resolve an accurate location. 
         [0005]    Conventional location techniques have a wireless phone interacting with base stations associated with the service to which the wireless phone is subscribed. An almanac of base stations indicates to the wireless phone where the base stations are located. On most occasions, at least couple of base stations are visible to the wireless phone. 
         [0006]    Cellular phones often have limited memory to store additional information. Base stations are constantly being added, removed or relocated in a cellular phone network. Almanacs of base stations are occasionally sent to cellular phones to aid in determining location. To communicate and store a large almanac is impractical on some cellular phones. 
       SUMMARY 
       [0007]    A method and system that allow resolving the location of a wireless device are disclosed. Resolving the location in one embodiment relies upon accessing at least one cooperative base station and at least one uncooperative base station. The cooperative base station provides an almanac of base stations that are likely to be near the wireless device. Both cooperative and uncooperative base stations within range can be used to determine the location of the wireless device. The uncooperative base station is not generally available to the wireless device, but can be used to determine distance to the wireless device. An attempt by the wireless device to transport data or voice on the uncooperative base station may or may not be thwarted by the uncooperative base station. 
         [0008]    In one embodiment, the population of base stations is reduced to produce a tailored almanac of base stations. The tailored almanac includes information to uniquely identify each base station, and may include location information for the base stations. 
         [0009]    In another embodiment, any number of different base station types can be used. The base station could be a cellular phone base station, a wireless local area network, a wireless wide area network, a satellite, a terrestrial location beacon, or any other device that can wirelessly communicate in some mode with the wireless device in a manner that allows unique identification of the device and a distance measurement. 
         [0010]    In a variety of other embodiments the general location of the wireless device is determined in different ways. Various embodiments might use the location function integral to the phone, the current cooperative base station and a presumed cell footprint, a number of base stations to find an overlapping cell footprint, a number of cooperative base stations to trilaterate the position, base stations and satellites to trilaterate the position, and/or one or more cooperative base stations that can determine range and angle. Different wireless devices have different capabilities, as do base stations, such that there could be a number of approaches used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0011]    The features, objects, and advantages of embodiments of the disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like elements bear like reference numerals. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
           [0012]      FIGS. 1A ,  1 B and  1 C are a block diagrams of embodiments of a location determination system; 
           [0013]      FIGS. 2A and 2B  are diagrams of embodiments of a single-cell location system; 
           [0014]      FIGS. 3A and 3B  are diagrams of embodiments of a cell sector location system; 
           [0015]      FIG. 4  is a diagram of an embodiment of an overlapping cell location system; 
           [0016]      FIG. 5  is a diagram of an embodiment of a trilateration cell system; 
           [0017]      FIG. 6  is a diagram of an embodiment of a hybrid trilateration system; 
           [0018]      FIG. 7  is a diagram of an embodiment of an angular ranging system; 
           [0019]      FIG. 8  is a flow diagram of an embodiment of a process for locating a position of a wireless device that has native location functions; 
           [0020]      FIG. 9  is a flow diagram of another embodiment of a process for locating a position of a wireless device that has limited location functions; 
           [0021]      FIG. 10  is a diagram of an embodiment of system that gathers location information from uncooperative base stations; 
           [0022]      FIG. 11  is a flow diagram of an embodiment of a process for gathering location information from base stations; and 
           [0023]      FIG. 12  is a diagram of another embodiment of system that gathers location information from uncooperative base stations. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring initially to  FIG. 1A , a block diagram of an embodiment of a location determination system  100 - 1  is shown. The location determination system  100  allows wireless devices  120  to find their geographic location or be located by remote entities by using satellites  152  (e.g., GLONASS, GPS, Galileo, EGNOS, Globalstar, IRIDIUM) and/or base stations  112 , 124  (e.g., cellular phone base station, a wireless local area network, a wireless wide area network, satellite phone, satellite Internet, or any other device that can be uniquely recognized and communicate with the wireless device  120 ). Cooperative base stations  112  are coupled to an almanac processor  122  by way of a wide area network (WAN)  110  in this embodiment, but other embodiments could use a local area network (LAN). The almanac processor  122  accesses a base station database  144  to tailor or customize an almanac according to the estimated location of the wireless device  120 . 
         [0025]    A wireless device  120  can communicate with any number of devices to provide location information. In this embodiment, the wireless device  120  is a cellular phone that may have any number or combination of communication modes (e.g., GSM, CDMA, TDMA, WCDMA, OFDM, GPRS, EV-DO, WiFi, Bluetooth, WiMAX, 802.xx, UWB, satellite, etc.) to transfer voice and/or data with cellular, satellite, wireless data, and/or mesh networks by way of their base stations  112 , 124 . The wireless device  120  in other embodiments could be a tracking device, a child or parolee monitor, navigational device, wireless pager, wireless computer, PDA, asset tag, etc. 
         [0026]    The supported communication modes for each wireless device  120  are stored in a device capability database  140  that includes information to help in determining an uncertainty factor for each location or distance measurement made by a particular wireless device  120  operating in any number of communication modes. 
         [0027]    This embodiment shows cooperative base stations  112 , uncooperative base stations  124  and a satellite location beacon  152  that could each have different communication modes. For example, cellular base stations  112 , 124  might support TDMA and GSM, a satellite base station might support only CDMA, or another satellite base station might support only TDMA. 
         [0028]    Base stations  112 , 124  are defined herein to allow some sort of data and/or voice transport. Base stations  112 , 124  are often affiliated with some entity (e.g., cellular or WiFi service provider) such that only subscribers or subscribers to another system with a roaming agreement can communicate with the base station  112 , 124  to pass data and/or voice traffic. The base stations  112 , 124  may be connected to a WAN or LAN to get a tailored almanac, but only cooperative base stations  112  provide a tailored almanac. The various base stations  112 , 124  may have any number of or combination of communication modes (e.g., GSM, CDMA, TDMA, WCDMA, OFDM, GPRS, EV-DO, WiFi, Bluetooth, WiMAX, 802.xx, UWB, satellite, etc.) to transfer voice and/or data with cellular, satellite, wireless data, and/or mesh networks. 
         [0029]    There are cooperative and uncooperative base stations  112 , 124 . An cooperative base station  112  is one that allows data and/or voice communication with the wireless device  120 . In one example, voice communication can be supported by Voice over IP (VoIP). Uncooperative base stations  124  may not allow data and/or voice traffic, but do provide information useful in determining a location of the wireless device. Uncooperative base stations  124  provide some type of identifier and can often be used for ranging, which is a process where the distance between the base station  124  and the wireless device  120  is determined. The identifier in the case of a WiFi base station  124 , for example, includes a station identifier and MAC address. Also, some uncooperative base stations  124  allow ranging measurements, received signal strength indications and beacon signaling capabilities that can all be used to determine distance. 
         [0030]    The base station database  144  stores the identifier information that can be used to uniquely identify each base station in that class of base stations. For example, each WiFi base station could include a MAC address as identifier information. As another example, a CDMA base station identifier could include SID, NID and Base ID or SID, MSC ID and Base ID. Characteristics of the base station  112 , 124  could be used in uniquely identifying the base station  112 , 124 . For example, if two base stations had the same station identifier, but only one supported a particular communication standard, the two could be uniquely identified. Typically, a wireless device  120  would support a subset of the various communication modes. Also stored in the base station database  144  is location information that is determined for each base station  112 , 124  by performing surveys of the area with the wireless devices. 
         [0031]    In one embodiment, wireless devices  120  can be used to determine the location of each base station  112 , 124 , thereafter the location is reported back to the almanac processor  112 . The location information from various wireless devices  120  for each base station  112 , 124  is aggregated by the almanac processor  112  to update the base station database. As more location data points are gathered, they are weighted according to the accuracy of the location information provided by the wireless device  120  and used to resolve the location of the base station with ever increasing accuracy. The accuracy of each wireless device  120  could be stored in the device capability database  140 , which could have different accuracies for the various ways that a wireless device  120  could gather the information. Any uncertainty that the wireless device  120  could have in knowing its location could also be reflected in the accuracy weighting for the base station database  144 . 
         [0032]    Various types of location beacons could be used by the wireless device  120  to aid in the location determination. This embodiment uses a satellite location beacon  152 , but pseudolites and terrestrial beacon systems such as LORAN could also be used. The more location references, generally, the better the location of the wireless device  120  can be determined. 
         [0033]    This embodiment shows the almanac processor  122  separate from the cooperative base stations  112 , but each cooperative base station  112  or a class of cooperative base stations  112  could have an almanac processor  112  and/or databases  140 , 144  in other embodiments. Some embodiments could integrate the almanac processor  122  into the wireless device  120 . The base station and/or device capability databases  144 , 140  could also be in the wireless device  120  and updated periodically. 
         [0034]    Referring next to  FIG. 1B , another embodiment of the location determination system  100 - 2  is shown. In some embodiments, the base station database  144  is centrally located, but the base station database  144  is distributed regionally or in portions relevant to each cooperative base station  112  or a class of cooperative base stations  112  as a local almanac  158  in the present embodiment. For example, a first base station  112 - 1 , may store a portion of the base station database  114  for its footprint and all adjacent base station footprints in a first local almanac  158 - 1 . As another example, the first local almanac  158 - 1  may contain the base station database for all or select set of CDMA base stations. In yet another example, the first almanac  158 - 1  may not be geographically organized but contain the base stations which are part of a particular service provider network. As the centrally-located base station database  144  is updated, those changes are propagated to the various local almanacs  158  that might use the new information. 
         [0035]    This embodiment does not use a satellite location beacon  152  or other type of location beacon, but has one or more communication satellites base stations  154  for use in voice and/or data communication. This embodiment of the communication satellite base station  154  could, but does not, have a local almanac  158  and/or databases  140 , 144 . The communication satellite base station  154  relies upon the almanac processor  122  to produce tailored almanacs. A satellite ground station  160  communicates with the almanac processor  122  by way of the WAN  110 . 
         [0036]    Referring next to  FIG. 1C , yet another embodiment of the location determination system  100 - 3  is shown. In this embodiment, a cooperative base station  112  is coupled to a local area network (LAN) that is coupled to an almanac processor  122  and device capability and base station databases  140 , 144 . The information in the device capability and base station databases  140 , 144  could be periodically updated or reconciled with remote master versions of these databases using a WAN or the like. The satellite base station  154  in this embodiment also includes an almanac processor  122  and device capability and base station databases  140 , 144 , even though that level of detail is not shown in the figure. 
         [0037]    With reference to  FIGS. 2A and 2B , diagrams of embodiments of a single-cell location system  200  are shown. A cooperative base station  112  has a cell footprint  204  in which it can communicate with the wireless device  120 .  FIG. 2A  shows the uncooperative wireless base station  124  within that cell footprint  204 . 
         [0038]    On occasion, the wireless device  120  is barely within the cell footprint  204  to communicate with the cooperative base station  112 , but has the ability to communicate with uncooperative base stations  124  outside this cell footprint as shown in  FIG. 2B . A cell buffer zone  208  would include uncooperative base stations  124  outside the range of the cooperative base station  112 , but possibly within range of a wireless device  120  within range of the cooperative base station  112 . An uncooperative base station footprint  212  is shown for a base station  124  outside the cell footprint, but within communication range of the wireless device  120 . Including this base station  124  in the cell buffer zone  208  accommodates this scenario. 
         [0039]    In this embodiment, the wireless device  120  is in communication range of a single cooperative base station  112 . In the cell footprint  204  of the cooperative base station  112 , there are eleven uncooperative base stations  124 . The cell buffer zone  208  has two more uncooperative base stations  124 . When the almanac processor  122  receives a request for a tailored almanac, information for the thirteen possible uncooperative base stations are included. 
         [0040]    In one embodiment, the cooperative base station  112  may determine a range to the wireless device  120  and the almanac processor  122  could cull the list of thirteen to those that might fall within an annular ring around the cooperative base station  112 . The ring would be as thick as the range of the wireless device  120  when talking to the various uncooperative base stations  124  in a particular mode plus some error factor from determining the range to the cooperative base station  112 . For example, the wireless device  120  may have a range from the cooperative base station  112  of fifty measurement units with an error factor of ten percent. In one communication mode, the range from the wireless device  120  is fifteen units. In this example, the annular ring would begin at a radius of thirty and extend to seventy measurement units. Any base station  112 , 124  understanding that communication mode and within that annular footprint would be included in the tailored almanac. Of course, if the annular ring extended beyond the cell buffer zone  208  the radius of the ring would be curtailed appropriately. 
         [0041]    As the wireless device  120  may have different modes of communication to the various types of base stations, the thickness could be different for each type of base station communication mode. Further, the wireless device  120  may receive almanac information on other cooperative base stations  112  that the wireless device  120  was unaware of. 
         [0042]    In another embodiment, the almanac processor  122  might cull the number of base stations  112 , 124  included in the tailored almanac. In some cases, the density of base stations  112 , 124  is so great that including additional base stations  112 , 124  that are in close proximity would be of little aid in resolving the location of the wireless device  120 . 
         [0043]    In some embodiments, the almanac processor  122  might exclude base stations  112 , 124  that don&#39;t have any way to uniquely identify them. For example, if two base stations had the same station identifier and did not provide any other codes to uniquely identify them, they both could be excluded from the tailored almanac. Often times, other identifiers in the communication protocol can be combined with identifiers to create a unique identifier that distinguishes the base stations  112 , 124 . In some cases, two or more base stations  112 , 124  that cannot be uniquely identified are so geographically separate that a unique identifier can be formulated by knowing the geographic location of interest such that they could still be used. Only one would be included in any tailored almanac. 
         [0044]    Referring next to  FIGS. 3A and 3B , diagrams of embodiments of a cell sector location system  300  are shown. This embodiment has six cell sectors  304  for a cooperative base station  112 , but other embodiments could have any number of cell sectors. The wireless devices  120  in the cell footprint  204  are divided among the cell sectors  304  such that the base station  112  knows which cell sector(s)  304  communicates with a particular wireless device  120 . The cell sector(s) that might have the wireless device  120  are forwarded to the almanac processor  122 . Any base stations  112 , 124  within the cell sector(s)  304  are forwarded to the cooperative base station  112  for relay to the wireless device  120 . 
         [0045]    In the embodiment of  FIG. 3A , a single cell sector  304  can communicate with the wireless device  120 . The almanac processor  122  would include those base stations  112 ,  124  in that sector  304  along with those in a sector buffer zone  308 . The embodiment of  FIG. 3B  shows the wireless device  120  close to the edge between two cell sectors  304  such that both can receive communication. The almanac processor  122  could provide the base stations  112 , 124  in those two cell sectors  304  and a sector(s) buffer zone  308  around them to any wireless device  120  within or nearby that area. 
         [0046]    With reference to  FIG. 4 , a diagram of an embodiment of an overlapping cell location system  400  is shown. In this embodiment, two cooperative base stations  112  can communicate with the wireless device  120  such that the overlap in the cell footprints  204  is presumed to be the location of the wireless device  120 . The almanac processor  122  would query the device capability and base station databases  140 , 144  to determine how to tailor an almanac for this overlapping region  404 . A portion of the cell buffer zone  208  that overlaps the cell buffer zone  208  of the other cell footprint  204  and cell buffer zone  208  (and vice-versa) would also be analyzed for base stations  112 , 124  to include in any tailored almanac. 
         [0047]    Referring next to  FIG. 5 , a diagram of an embodiment of a trilateration cell system  500  is shown. In this embodiment, the wireless device  120  can communicate with three or more cooperative base stations  112 - 1 , 112 - 2 , 112 - 3  that are geographically separate. A general location of the wireless device  120  is determined by analyzing ranging information gathered by or from a number of cooperative base stations  112 . Time of arrival (TOA) readings from one cooperative base station  112  reduces the general location to a ring around that base station  112 . Two cooperative base stations  112  generating time difference of arrival (TDOA) ranging readings reduce the location to a hyperbole. Three or more can resolve the general location even further. In this embodiment, time of arrival and/or time difference of arrival measurements are used in the trilateration process. 
         [0048]    However small the area becomes, a buffer around that area is determined to compensate for the error in the determination and address the range of the wireless device  120  to base stations  112 , 124 . The almanac processor  122  gathers information for the base stations  112 , 124  likely to be in communication range for each communication mode supported by the wireless device  120 . 
         [0049]    With reference to  FIG. 6 , a diagram of an embodiment of a hybrid trilateration system  600  is shown. This embodiment shows trilateration with different types of communication modes. The wireless device  120  receives ranging information from a satellite location beacon  152  and communicates with two cooperative base stations  112 - 1 , 112 - 2 . Between the three  152 , 112 - 1 , 112 - 2 , the general location can be trilaterated and forwarded to one of the cooperative base stations  112  in exchange for a tailored almanac. 
         [0050]    Referring next to  FIG. 7 , a diagram of an embodiment of an angular ranging system  700  is shown. The cooperative base stations  112  in this embodiment can estimate the angle of arrival (AoA) and distance to the wireless device. This ability allows determining a general location with a single cooperative base station  112 . Where the cooperative base station  112  can only determine AoA and not range, two cooperative base stations  112 - 1 , 112 - 2  can determine a general location. 
         [0051]    The above embodiments do not rely upon uncooperative base stations  124  to find an initial location estimate, but request a tailored almanac from cooperative base stations  112  for refined location estimations. Some embodiments could report the base stations  112 , 124  and location beacons seen and any ranging estimates to those as part of a location request. The almanac processor  112  could take this information and determine a location using the device capability, mode of operation and base station databases  140 , 144 . In this embodiment, the initial gathering of location information is done without the benefit of a tailored almanac. Where the almanac processor  122  determines a more accurate location is required, a tailored almanac could be produced that indicates additional base stations  112 , 124  that are likely within range of the wireless device  120 . 
         [0052]    With reference to  FIG. 8 , a flow diagram of an embodiment of a process for locating a position of a wireless device  120  that has native location functions  800  is shown. The wireless device  120  could trilaterate to cooperative base stations  112  or satellite or ground location beacons to determine a general location in step  804 . In step  808 , the wireless device  120  reports the location estimate and requests a tailored almanac. Some wireless devices may store a base almanac of base stations  112 , 124  that is updated as new tailored almanacs are received. 
         [0053]    In this embodiment, the location estimate could be further refined outside the wireless device in step  812 . For example, the cooperative base station  112  may have some location information from time of arrival or time difference of arrival. The general location is forwarded to the almanac processor  112 . In step  816 , the almanac processor  112  tailors an almanac by finding all base stations  112 , 124  that might be close enough to use in determining a location of the wireless device  120 . This takes into account all the modes of communication of the wireless device  120  that are compatible with the various base stations  112 , 124 , the likely range in those modes, and the likely location of the wireless device  120 . That tailored almanac is sent over the WAN  110  to the cooperative base station  112  and relayed to the wireless device in step  820 . 
         [0054]    In step  824 , further location information is gathered by the wireless device  120 . This location information uses the tailored almanac and could involve uncooperative base stations  124  as well as cooperative base stations  112 . In this embodiment, the wireless device  120  analyzes the location information to refine the location estimate in step  828 . The location estimate is reported to an cooperative base station in step  832 . During the process of determining a location, the wireless device  120  may have location information for the base stations  112 , 124  in the tailored almanac or those not in the almanac yet. In step  836 , this location information together with the almanac-related information such as the identifications of the observed base stations is reported to an cooperative base station  112  and forwarded to the almanac processor  122  for updating the base station database  144 . 
         [0055]    Referring next to  FIG. 9 , a flow diagram of another embodiment of a process  900  for locating a position of a wireless device  120  that has limited location functions is shown. Some wireless devices have limited ability to independently determine their location. This embodiment relies on other parts of the location determination system  100  to analyze location information. In step  908 , the wireless device  120  requests a tailored almanac. The location is estimated by the various cooperative base stations  112  in step  912 . 
         [0056]    That location estimate is passed to the almanac processor  122  for tailoring of almanac information in step  816 . In step  820 , the tailored almanac is sent to the wireless device  120 . Step  824  gathers further location information using the tailored almanac to find uncooperative base stations  124 . In step  916 , the gathered location information is forwarded to the cooperative base station  112 . Step  928  refines the location estimate using the location information. The refinement may be performed in the cooperative base station  112 , the almanac processor  122  or any other location in communication with the cooperative base station  112 . Any additional information gathered by the wireless device  120  is forwarded to the almanac processor  122  to refine the base station database  144 . 
         [0057]    With reference to  FIG. 10 , a diagram of an embodiment of system  1000  that gathers location information from uncooperative base stations  124  is shown. Once the tailored almanac is received by the wireless device  120 , it attempts to locate those base stations listed in the almanac. Shown in the embodiment of  FIG. 10  is a dual-mode wireless device  120  that supports two communication modes. One communication mode has a first footprint  1012 - 1  and the second has a larger footprint  1012 - 2 . The tailored almanac would have all base stations  112 , 124  in the first footprint  1012 - 1  that use the first communication mode and all base stations  112 , 124  in the second footprint  1012 - 2  that use the second communication mode. 
         [0058]    In some embodiments, the almanac processor could perform a motion estimation for the wireless device  120  such that footprints  1012  are adjusted for the likely position of the wireless device  120  when the tailored almanac would be used. Other embodiments, could just expand the footprint according the likely speed or maximum speed of the wireless device  120  should it travel in any direction. In yet other embodiments, a history of handoffs between various base stations can be used to tailor the almanac information. 
         [0059]    Referring next to  FIG. 11 , a flow diagram of an embodiment of a process  1100  for gathering location information from base stations  112 , 124  is shown. The process  1100  begins in step  1104  where the wireless device  120  checks for base stations  112 , 124  in the tailored almanac. This could be done by randomly choosing base stations in the almanac  112 , 124 . In some embodiments, the base stations  112 , 124  could be pre-randomized so that the wireless device  120  could take them in order. 
         [0060]    In another embodiment, the almanac processor  122  could choose another scheme for organizing the base stations  112 , 124  to quickly find one. For example, they may be organized by communication mode and footprint  1012  size. The footprint of the almanac is more quickly covered by using communication modes with larger range. 
         [0061]    Once one base station  112 , 124  in the almanac is found in step  1108 , it may be possible to exclude some of the base stations  112 , 124  in the almanac. After running through the various base stations  112 , 124  to find those in range of the wireless device  120 , the distance to each is estimated in step  1112 . 
         [0062]    Uncooperative base stations  124  still give some information even though data communication is not possible. They will identify themselves, which indicates the wireless device  120  is close enough to communicate. Some uncooperative base stations  124  will indicate signal strength of a received signal. Other uncooperative base stations  124  will acknowledge a message and that propagation time can be correlated to a distance traveled. The signal strength of a signal from the uncooperative base station  124  can intimate distance when the initial or expected signal strength can be determined. 
         [0063]    In some embodiments, the wireless device  120  gathers information on base stations  112 , 124  not included in the almanac in step  1116 . Often the base stations  112 , 124  self identify themselves. If resources are available, in step  1120  ranging may be performed to the unlisted base stations  112 , 124  for later report-back to the almanac processor. In other embodiments, the footprint of the base station or the overlaps of more than one footprint can be analyzed to determine the general location of the wireless device  120 . 
         [0064]    With reference to  FIG. 12 , a diagram of another embodiment of system  1200  that gathers location information from uncooperative base stations  124  is shown. The depicted uncooperative base stations  124  are those identified in a tailored almanac as likely to be in communication range. In this embodiment, three uncooperative base stations  124 - 1 , 124 - 4 , 124 - 5  operate in a first communication mode with first communication footprints  1212 - 1 ,  1212 - 4 , 1212 - 5 ; two uncooperative base stations  124 - 2 , 124 - 6  operate in a second communication mode with second communication footprints  1212 - 2 , 1212 - 6 ; and one uncooperative base station  124 - 3  operates in a third communication mode with a third communication footprint  1212 - 3 . The current position of the wireless device  120  only allows communication with three uncooperative base stations  124 - 2 , 124 - 3 , 124 - 4 . Even without ranging measurements, this can narrow down the location of the wireless device  120 , but with ranging measurements, a very precise location can be determined. 
         [0065]    The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Technology Category: g