Abstract:
A plurality of wireless devices can obtain location related information from members of a plurality of location anchors located throughout a region being monitored. The devices can each send probes to the location anchors. The anchors which receive a probe can each respond with a signal carrying at least an anchor address. Each of the devices can process the respective received signal to establish a distance parameter, and, can forward the address and the distance parameter to a displaced location estimating engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/683,056 filed Aug. 14, 2012, entitled, “System and Method for Improved Location System Accuracy”. The &#39;056 application is hereby incorporated herein by reference. 
    
    
     FIELD 
     The application pertains to systems and methods for establishing locations of mobile wireless devices, such as gas detectors, radiation detectors or the like, in a region being monitored. More particularly, the application pertains to such systems and methods wherein the mobile devices obtain location indicating information from fixed location anchors and forward that information to a location establishing engine. 
     BACKGROUND 
     Portable gas detectors which can be used to monitor one or more conditions in a region of interest can wirelessly communicate with a Wi-Fi based network of access points. Each of the access points of the network can provide IEEE 802.11 access service. The members of the network can forward detector generated information as to gas concentrations and detector location indicating information to a location manager which can incorporate a location determining engine. 
     Systems of the type described above have been disclosed in US Patent Application Publication 2011/0161885 published Jun. 30, 2011, application Ser. No. 12/695,736 filed Jan. 28, 2010, entitled “WIRELESS LOCATION-BASED SYSTEM AND METHOD FOR DETECTING HAZARDOUS AND NON-HAZARDOUS CONDITIONS, and US Patent Application Publication 2011/0161044 published Jun. 30, 2011, application Ser. No. 12/959,250 filed Dec. 2, 2010, entitled “WIRELESS LOCATION-BASED SYSTEM FOR DETECTING HAZARDOUS CONDITIONS. The above two published applications, 0161885 and 0161044 are both assigned to the Assignee hereof and are hereby incorporated by reference. 
     Wi-Fi based wireless location system accuracy is known to exhibit a probability distribution of location error when attempting to estimate the location of a mobile device. For example, the empirical data suggests the average location estimate may be accurate to within 35% of the average wireless local area network (WLAN) access point (AP) spacing when estimated using received signal strength indication (RSSI) information. However some applications may require more accuracy than would be provided by the WLAN infrastructure. Thus in order to provide adequate location system accuracy in a typical WLAN system, it may be necessary to deploy additional access points beyond those necessary for WLAN coverage. Installation of these additional access points may be expensive in terms of material cost of additional APs and also either installation cost of backhaul communications wiring e.g. for Ethernet or material cost of additional radios in the APs to provide equivalent wireless back haul communications. A lower cost solution to improve location accuracy would be desirable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a system which embodies a detector locating system in accordance herewith; 
         FIG. 2  illustrates a block diagram of a detector usable in the system of  FIG. 1 ; and 
         FIG. 3  illustrates a block diagram of a location anchor usable in the system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     While disclosed embodiments can take many different forms, specific embodiments hereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles hereof, as well as the best mode of practicing same, and is not intended to limit the claims hereof to the specific embodiment illustrated. 
     In embodiments hereof, the mobile devices, also interchangeably referred to herein as detectors, transmit probes into portions of a region being monitored. Location anchors distributed in the region which receive the probes can each transmit at least a location indicating address that can be read by the receiving mobile device. The mobile device can then make signal strength measurements of responses from members of a plurality of location anchors L distributed in a region being monitored. Alternately, round trip time-of-flight measurements can be made of an interval between the time of the request and time of the response. The address and signal strength (RSSI), or, time-of-flight information can be transmitted from the mobile device to a location manager which can then estimate the location of the device in the region. 
     Because it is the mobile devices that communicate with the location manager, and not the location anchors, the location anchors advantageously each have a lower total installed cost, that is lower cost inclusive of installation cost and materials cost, than a corresponding access point would have since they need not provide back-haul communications. The elimination of back-haul communications equipment offers an opportunity to save (installed) cost at each anchor location. Hence more location anchors can be provided, at the same or lesser cost, for improved location accuracy. 
     For example, in the location anchors, there is no need for Ethernet port electronics or Ethernet wire installation (for back haul communications). Alternatively to avoid having to install Ethernet wiring the access points may utilize an additional back haul radio. The location anchors in the present embodiments do not need back haul radios. So the relative total installed cost for a location anchor can be reduced as compared to an access point 
       FIG. 1  illustrates aspects of a wireless regional monitoring system  10  installed in a region R 1 . Access points AP provide wireless local area network service throughout the region R 1  via backhaul wires  20  or via a wireless backhaul link  21  to the location manager  24 . Members of a plurality of relatively low cost location anchors, L are distributed throughout the region R 1 . The anchors L can provide responses R to wireless probes P received from mobile devices, or units, for example gas detectors D . . . Dn, moving through the region R 1  by transmitting, at least location anchor address data which is related to the location of the respective location anchor L. 
     The detectors Di, upon receiving the responses R to the probes P from the anchors L, can read the address of the responding location anchor and can measure the associated RSSI or time-of-flight of the response R. The results of such measurements, along with address information for the respective location anchor, can then be forwarded via one of the APs to the Location Manager which makes estimates of the position of the respective devices, such as detectors D. The dotted line  26  indicates the relay of this measurement information from the detector D via one of the APs to the location manager  24 . Advantageously, the location anchors L exhibit a lower total installed cost than the APs as the location anchors need not support Ethernet electronics or connectors and need not be wired for Ethernet backhaul communications nor contain additional backhaul radios. 
     In yet another aspect, the detectors, such as detector Di can communicate directly with the location manager  24  provided it supports an internal AP or e.g. Wi-Fi Direct functionality. It will also be understood that other forms of communications between the detectors, such as detector Di, and the Location Manager  24  come within the spirit and scope of the invention. 
       FIG. 2  illustrates a block diagram of an exemplary mobile unit, such as the detector Di. Detector Di includes a housing  30  which can be carried on or about the person of someone working in or moving through the region R 1 . Housing  30  can carry one or more ambient condition sensors, S 1 , S 2  . . . Sn responsive for example to gas, smoke, temperature, radiation, or the like all without limitation. 
     Control circuits  32 , carried by housing  30 , are coupled to the one or more sensors Si, and to a transceiver  34 . Transceiver  34  can be implemented as an RF transceiver, for example, and without limitation. The control circuits can be implemented, at least in part, by a programmable processor  32   a  which executes pre-stored instructions in a storage unit  32   b . Housing  30  can also carry an audio/visual output device  36  with operator controls  36   a.    
     It will be understood that the detector Di can communicate via transceiver  34  with the location anchors L in the region R 1 . Based on responses from the location anchors L, detector Di can in turn communicate wirelessly with the location manager  24 , directly or via access points AP, without limitation, as discussed above. 
       FIG. 3  illustrates a block diagram of an exemplary location anchor, such as one of the anchors L. Anchor L includes a housing  40  which carries control circuits  42  coupled to a transceiver  44 . Transceiver  44  can be implemented as an RF transceiver, for example, and without limitation. 
     It is an important aspect of the embodiment  10  disclosed in  FIGS. 1-3  that the transceiver  44  need only be capable of communicating with the detectors, such as the detector Di in the region R 1 . The detector Di communicates with the location manager  24 , via circuitry not located in the location anchors, namely transceiver  34  and not transceiver  44 . These communications are apart from the operation of the location anchors L, and take place, either via an access point, AP or via a direct link to the location manager. As a result, the structure of the location anchors L is simplified. No Ethernet communications circuits, or back haul radios, need be installed in the anchors L. Hence, to reduce location error, numerous anchors L can be installed throughout the region R 1 , at a reduced expense compared to a similar number of access points AP. 
     In summary, location anchors may respond to probes from respective mobile devices such that the mobile devices may measure the RSSI of the respective response, or time-of-flight from transmission of the probe to receipt of a response from a respective anchor. The mobile devices may then report the measured RSSI from location anchors, or time-of-flight to a location manager where estimated positions of the respective mobile devices may be determined. The location anchors can also identify themselves, by providing address information, which the mobile devices can forward to the location manager. 
     In embodiments hereof, total installed cost for the additional location anchors may be reduced as compared to the equivalent total installed cost of the same number of access points. This reduction is due to eliminating the back-haul communications equipment required by an access point. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims. 
     Further, logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from the described embodiments.