Abstract:
An intrinsically safe accurate location information network for personnel and assets in underground mines, including wireless access points and subnetwork controllers, active wireless locator/messenger tags, network controller(s), and enterprise servers running application control software. The wireless access points are installed in mine entries and crosscuts and track the active wireless locator/messenger tags. The active tags may be worn by mine personnel or installed in mining equipment. The network subsystems form relay networks that wirelessly carry telemetry and control data without the need to penetrate the earth. The subsystems determine the location of persons and assets underground and monitor safety-related information, which can be used for disaster avoidance, early warning of impending disaster, and improved rescue effectiveness. .

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/806,919, filed Jul. 10, 2006 (Jul. 10, 2006). 
     
    
     SEQUENCE LISTING 
       [0002]    Not applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0003]    Not applicable. 
       REFERENCE TO A MICROFICHE APPENDIX 
       [0004]    Not applicable. 
       BACKGROUND INFORMATION AND DISCUSSION OF RELATED ART 
       [0005]    1. Field of the Invention 
         [0006]    The present invention relates generally to wireless communication systems, and more particularly to a system for use in deep underground mines to track and monitor personnel and equipment, and to provide wireless two-way communications for day-to-day miner safety enhancement and for rescue operations. 
         [0007]    2. Discussion of Related Art 
         [0008]    There are numerous risks inherent in underground mining operations: fire, cave-in, methane or coal-dust explosion, flooding, asphyxiation, and so forth. When miners are trapped, the success of rescue operations depends upon the rapidity and the efficiency of the rescue response. Both would be greatly enhanced if mining operators implemented a suitable underground communications and personnel tracking system. 
         [0009]    There are numerous difficulties in using the current location-finding devices in an underground environment. GPS technology simply does not work. GPS satellites transmit low power radio signals, denominated L 1  and L 2 . The L 1  frequency is for civilian GPS systems and operates at 1575.42 MHZ in the UHF band. However, the signals are line-of-sight, and though they can pass through clouds and generally transparent materials, they will not penetrate solid objects such as buildings and earth. 
         [0010]    Moreover, there are numerous challenges in using wireless communications generally for underground use. Until the present, there has not existed a wireless communication system capable of functioning as a backhaul method in underground environments. And it is difficult to use radio frequency propagation devices in underground environments as the basis for an accurate location algorithm because underground environments tend to block signals, cause multipath fading, co-interference, hardware/package degradation, environmental damage due to dust, water, and the like. Further, there are difficulties in implementing large-scale distributed wireless networks and hybrid wired/wireless networks in underground environments, especially given the generally linear and labyrinthine configurations of most tunnel and mine structures, and due to the presence of signal blocking machinery. Moreover, there are the challenges in achieving the following objectives: (1) acceptable “location update rate” performances with large-scale mine footprints having a large number of miners across low bandwidth backhaul networks (e.g. existing long-haul RS485 at 2400 bps); (2) providing a system requiring only a low power demand suitable for all-battery operation in some areas; (3) adequate fault-tolerance for a solution aimed at protecting/saving human life, especially where the deployment environment is harsh and hazardous; and (4) sufficient portability and rapid deployment characteristics needed in emergency rescue scenarios. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention has been developed to answer the needs set out in the Mine Improvement and New Emergency Response Act of 2006 (MINER Act), S. 2803 [109 th ], signed by President George W. Bush on Jun. 15, 2006. The MINER Act of 2006 requires, in pertinent part, that each mine operator develop and implement an accident response plan within 60 days of the enactment of the Act. Among the plan requirements, mine operators must implement a two-way wireless communications and tracking system. The requirements for post accident communications include redundant means of communication with the surface for trapped miners and others underground, such as secondary telephone or equivalent two-way communication. The requirements for post-accident tracking entail that mine operators adopt a system consistent with commercially available technology and any applicable physical constraints of the mine that allows for above-ground personnel to ascertain the current and/or immediately pre-accident location of all underground personnel. The system must be reliable and serviceable in a post-accident setting. 
         [0012]    In addition the present invention has been designed to meet the requirements of Title 30, Code of Federal Regulations, relating to the interconnection of Mine Health and Safety Administration (MSHA) evaluated mine-wide monitoring systems and MSHA approved longwall mining systems. It is particularly adapted to meet the requirements of 30 CFR Part 18, relating to the need to reduce the risk of fire and explosion hazards in mine environments, and is intended for favorable evaluation of intrinsic safety under MSHA Program Circular PC-4003. 
         [0013]    The system of the present invention meets the requirements of the MINER Act of 2006 and 30 CFR by providing an intrinsically safe accurate location information system for personnel and assets in underground mines. The system enables two-way communications of emergency information across a wide underground coverage area. In summary terms, the system consists of wireless access points and subnetwork controllers, active wireless locator/messenger tags, network controller(s), and optional enterprise servers running application control software. The wireless access points are installed in the entries and crosscuts of underground mines to track the active transponder devices and to make emergency communications available to miners. The active tags are wearable by personnel entering and exiting mines. Likewise, they can be attached to the equipment moving into, used throughout, and exiting mines. 
         [0014]    The system of the present invention utilizes completely un-tethered wireless peer-to-peer radio/computer subsystems, such as Zigbee nodes, in underground tunnels in the mining  environment to form robust relay networks that wirelessly carry telemetry and control data without the need to penetrate the earth. While ZigBee nodes are preferred, other and future high level communication protocols are contemplated, as long as they are devised for use with compact low-power digital radios based on a standard accepted for wireless personal area networks (WPANs), and having a long battery life and secure networking. 
         [0015]    The peer-to-peer radio/computer subsystems and networks of the inventive system are engineered to determine the location of persons and assets underground, using characteristics of standard routing/relay machinery in innovative ways, but also using some entirely novel methodologies. 
         [0016]    The present invention makes it technically possible and economically feasible to monitor an array of safety-related information which can be quickly acted upon to save lives. These advantages arise from several features of the invention, including: (a) the invention allows for monitoring for unsafe conditions, thus facilitating proactive avoidance of some disasters; (b) the invention allows for early warning of some impending disasters so that workers can escape safely; and the invention allows for vastly improved rescue effectiveness in those unfortunate situations where avoidance or escape is not possible. This latter advantage arises because when using the present invention, trapped or imperiled workers can be readily located in the aftermath of an incident, and this allows authorities to quickly provide appropriate assistance and/or rescue. Secondarily, the present invention enables a host of other mine monitoring/management functions which help improve operational effectiveness at the mines and thereby enhance the general market acceptance of the invention. 
         [0017]    The wireless mine monitoring and rescue communications system of the present invention also uses a set of permanently mounted tags in fixed locations throughout the mine as calibrators and self-test devices to enhance the reliability of the system. The system software logs the status and communications of all active tags along with their physical location. The system also self-monitors health-check parameters that contribute to a continuous self-assessment of network status. When predetermined thresholds are reached, the system automatically takes corrective action, triggers alarms as appropriate, issues trouble alerts, and otherwise manages the network and all connected devices. 
         [0018]    The inventive system is designed for high fault-tolerance in the particularly harsh environments of coal mines. The system incorporates several types of redundancy and fail-over capability as a means of maximizing up-time even in the face of many accident and disaster scenarios. Indeed, mine accidents should have no appreciable adverse affect on the operation of the inventive system. Even in the event of a worst-case collapse or explosion that destroys a portion of the network, most of the system will continue to operate normally. Hypothetical fault analysis shows that at least 90% of the mine-wide network will likely remain operational in even the most severe situations. This continuing operation allows the communications personnel tracking to continue in the post-accident time period, across all but the most severely damaged sections. Even if a sub-part of the network becomes inoperative in a disaster, the damaged portion can have its functionality effectively replaced, either by automatic self-healing of the wireless network, or by a rescue team entering that area with a portable “rapid deployment” version of the system (to replace a failed subnet, for example). 
         [0019]    An additional feature of the present invention allows a rescue team to use a handheld “location sniffer” in a standalone hand-carried mode to rapidly find people in the affected area. In rescue scenarios, this location sniffer is able to detect and identify beacon signals from a miner many hundreds of feet away, depending on tunnel conditions. 
         [0020]    The present invention can also collect wireless sensor data on many other kinds of safety related information, such as atmospheric conditions (methane, CO, etc), temperature, water levels and the like. It employs extensible architectures that facilitate the incorporation of future developments, improvements, and enhancements, such as monitoring of miner biometrics, and/or enhanced short-message two-way communications. 
         [0021]    The system of the present invention is intended for use with both regular mine operation and emergency situations. The following features are notable: 
         [0022]    Network Redundancy: The backbone wireless subnetworks (each called a “subnet”) can be laid out as either standard self-healing networks or in double redundant topology. The network topology is configurable by the network-planner or installer before the installation. Nominally each subnet consists of 25 wireless access points (WAPs) which cover approximately 5000 linear feet of tunnel entry and crosscut per subnet. This may be easily increased in size and scope (“up-scaled”) to service a mine of any size. 
         [0023]    Miner Location Time: In even the largest mines, the inventive tracking and communications system can determine the location of every single miner every 30 seconds. Under presently developed configurations, up to 65,000 uniquely identifiable tags can be used in any one mine. 
         [0024]    Networks Configurations for Special Circumstances: In certain environments, such as in congested lifts or mine train stations where a large number of miners collect in relatively small spaces, special subnet controllers may be programmed into a “high speed sweep” mode. In this mode the locations of dozens or even hundreds of miners can be determined every few seconds. 
         [0025]    Battery Backup: Wireless Access Points utilized in the present invention are typically powered using hybrid battery-plus-wired-power methods (with battery backup), though they can be can be configured in some areas for all-battery operation (as indicated by portability needs, economic considerations, and other factors). Both options are suitably engineered for safety in the harsh and hazardous mine environment. 
         [0026]    Portability and Ease of Installation: A rapid deployment all-battery version of the inventive system may be deployed for special circumstances where there is a need to heal a worst-case post-accident failure of some part of the system network. 
         [0027]    Scalability Using Added Subnets: Each location subnet generally includes 25 access points plus a subnet controller, installed in approximately 5000 feet of tunnel. Each subnet can handle up to a few hundred miners in the immediate vicinity at any given time. Subnets can be added and inter-connected to cover any mine size and any practical number of miners. Backhaul methods include RS485 or DX-V-Bus as standard, but support for leaky feeder, fiber, cable, ethernet, Wifi, and CANBus backhauls can also be arranged according to the specific characteristics and size of the target mine. 
         [0028]    The inventive system may be used slightly differently in the three contemplated applications: 
         [0029]    Regular Operation: The system records miner location and status information, and communicates alert information. It also continuously self-monitors the entire network for proper functioning. The user interface is highly powerful, yet designed to be highly intuitive so as to make actionable safety information entirely intelligible at all times. The standard user interface in the present invention is accessible via any standard client-based web-browser. Views are organized to provide data in the most simple and effective manner possible. The highest level and simplest view of location data, for example, is via “tag” symbols populating a graphical mine map. Where relevant, drill-down into progressively higher levels of detail is provided via simple point-and-click actions with a mouse. Advanced administrator functions are also provided for system managers. While system software and above-ground IT infrastructure is generally hosted and managed at the mine site, aggregations of data from multiple mines can be optionally provided offsite, with the data accessed and the system managed remotely over the Internet via subscription service. The latter may be an attractive option for some large mine operators. 
         [0030]    Post Emergency “Backup” Operation: When a catastrophic emergency arises, or when ventilation falters or fails, or when main power is interrupted, all wireless access points and subnet controllers in the inventive system operate in an “intrinsically safe mode” and draw power from their integral backup batteries. This ensures that 100% of the system is safe to operate in any post-accident scenario. Specific system subnetworks can be deployed in permissible areas, and others less expensively in the normally fresh-air areas, but all configurations provide 100% intrinsically safe operation in the post-accident or post-ventilation-failure scenarios when an entire mine would be considered hazardous. 
         [0031]    The inventive system self-monitors and will report the status of all access points before, during, and after a disaster event. In a worst-case disaster scenarios, where parts of the network service may be interrupted or destroyed, the system will attempt to automatically self-heal (using state-of-the-art methods such as “failed node hop-over”, “adoption of orphaned nodes”, and “ring fault repair”. If parts of the network are unable to self-heal, then the zones with unconnected access points will remain initially inoperable but will nonetheless indicate the areas of the most serious disruption so that they can be repaired or their inoperability mitigated by manual human intervention (rescuers/searchers using the repair subnet or “location sniffer” for example). 
         [0032]    The system captures the immediate pre-accident location and status of all personnel and subsequently tracks any movement of personnel in the areas of the system network that remain operational. Even in the event of a worst-case accident, it is calculated that 90% of the system network will remain operational and allow two-communications and tracking of people as they make their way to safety or otherwise respond to the event. 
         [0033]    Emergency Rescue Operation: In this scenario part of the system is damaged due to worst-case mine collapse or explosion. When this occurs, a rescue team can bring in the rapid-deployment portable subnet, comprising battery-operated wireless access points, to restore and repair system tracking capability in the affected zone. The system is able to differentiate the portable access points from the pre-installed access points, and will adopt the new subnet appropriately. Additionally, or alternatively, a portable hand-carried “location sniffer” can be used to quickly detect the location of people in affected areas of the mine where normal service may have been interrupted. Additionally, a separate portable rapid-deployment network of all-battery-powered nodes can be deployed by the rescue team over a couple miles of tunnel distance, and operated in “RescueComm or ReachComm” mode, to provide full-roaming voice services and data services for the rescue team during the rescue operation. 
       OBJECTS AND ADVANTAGES 
       [0034]    It is therefore a principal object of the present invention to provide a wireless mine tracking, monitoring, control, and rescue communications system that includes self-monitoring of all wireless infrastructure, with some over-the-air or over-the-wire reconfiguration/reprogramming, which also guarantees high reliability and low maintenance cost. 
         [0035]    It is another object of the present invention to provide a real-time display of link quality on a digital link quality meter within the node being deployed to ensure that deployments of peer-to-peer radio links are robust in difficult and variable tunnel environments, around corners, where obstructions exist, and the like. This is especially critical in rapid deployment scenarios. 
         [0036]    Still another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that includes remotely aware and remotely actuated, “bounce power” hard reset capability for each subnet, thus yielding high fault-tolerance and high uptime through rapid remote response to hardware or software failures. 
         [0037]    Yet another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has support for 100% battery-only operation, or hybrid battery-plus-wired-power operation of underground networks. 
         [0038]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has a distributed computing architecture for high-speed data acquisition and control over huge mine/tunnel topologies. 
         [0039]    An even further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that includes flexible architecture that easily integrates into a broadband backhaul, such as fiber, ethernet, and the like. 
         [0040]    Yet another object of the present invention to provide a wireless mine monitoring/control and rescue communications system that provides safe underground battery-change methodology for unsafe explosive atmospheres in mines. 
         [0041]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that includes networking architecture designed to be fault-tolerant against hardware and system failures, specific self-healing and fail-over methods, along with use of “ring” architectures. 
         [0042]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has networking architecture designed to be disaster tolerant (against cave-ins, explosions, and so forth). 
         [0043]    Another object is to provide peer-to-peer routing algorithms modified to add “RSSI/LQI threshold” as a hop candidate “qualifier”, thus ensuring that only robust links are used in dynamic routing. 
         [0044]    Another object of the present invention to provide a wireless mine monitoring/control and rescue communications system that includes use of a motion detector, and/or tilt sensor as a “shutoff mechanism”, in addition to optimized sleep-beacon-sleep processes, to aid in the battery life/efficiency of the mobile location transponders. 
         [0045]    Yet another object of the present invention to provide a wireless mine monitoring/control and rescue communications system that includes portable “rapid deployment subnet” options for rescue use in locating rescuers and miners. 
         [0046]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that features a portable rapid deployment rescue communications system to carry voice and data services. 
         [0047]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that offers adjunct wireless integration of rescuers&#39; walkie talkie systems that enables bi-directional connection of a rescue team “cluster of rescuers” to the surface, so that they have un-tethered communication to and from the surface. 
         [0048]    Still another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has a handheld “miner location sniffer” option for rescue use in locating miners or victims, especially in the case where tunnel cave-ins or explosions have destroyed part of the normal location system network. 
         [0049]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that utilizes battery-frugal, wireless, and “location-aware” sensors that can be placed within the underground wireless networking infrastructure. This enables a host of such sensor types, including mine atmosphere, mine environmental condition, miner biometrics, miner location, asset location, and many others. This also includes the adjunct wireless and battery operated sensors which allow monitoring of critical environmental and safety parameters during rescue operations. 
         [0050]    A further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has numerous battery-frugal and wireless actuator devices enabled—such as miner paging, turn-on fan/turn-off equipment, sound alarm, direct evacuation, and so forth. 
         [0051]    A still further object of the present invention is to provide a new and improved wireless mine monitoring/control and rescue communications system that has an LCD display-based paging and/or short message communications service enabled by the bi-directional wireless infrastructure, and un-tethered communications for mining personnel (bi-directional). 
         [0052]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has a “panic button” built in to the mobile location transponder. This allows an injured miner, or one otherwise needing to summon emergency assistance, to do so with the simple push of a button. The system software is immediately aware of both the location and identity of the miner, as well as his need for assistance, and issues alarms and signals accordingly. 
         [0053]    Yet another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that provides un-tethered voice-message service (short messages) from the miner to the surface via an inexpensive messaging appliance. 
         [0054]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that provides each miner&#39;s helmet with  integral alarm message indicators (LEDs). 
         [0055]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that includes miniature long-life location transponders for worn by miners or affixed to equipment and other assets. 
         [0056]    Yet another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that includes methods for high speed location tracking and determination for a large numbers of miners in highly congested areas, as well as a novel browser-based graphical user interface allowing simple drag-and-drop of wireless location infrastructure symbols upon representative mine maps for intuitive rendering of location info (node relative), miner identity, status, and the like. 
         [0057]    Still another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has a user interface including drill-down from the highest country-wide level to the lowest sensor level, as well as automated alarming, real-time trend graphing of parameters, and trouble dispatch. 
         [0058]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that addresses common RF propagation problems in underground tunnels, including absorptive loss effects, multipath, other constructive/destructive interference effects, waveguide effects, tunnel bend effects, and blockages. 
         [0059]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has RF propagation problems properly characterized and understood for use in proximity to and around long-wall mining machinery. 
         [0060]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that includes high-accuracy location algorithms utilizing RF vector-gradient, physical-tunnel-boundary knowledge, automated RF self-calibration of individual transponder ID and specific wearer characteristics, human movement heuristics, probabilistic triangulation based on various RF propagation parameters, and various filtering and historical smoothing methods. 
         [0061]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that utilizes autonomous and distributed computing methods such as “tag-table build, push, wipe” for rapid re-discovery/updating of the location of thousands of miners/assets in even huge mines every 30 seconds. 
         [0062]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that addresses RF propagation effects for propagation through mine-safe plastic packages/enclosures. 
         [0063]    Yet another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that uses an innovative method for traversing RF-blocking barriers, such as steel ventilation control doors, using an “antenna-coupled joiner cable.” 
         [0064]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that provides a method of safety enhancement by checking miners into and out of the mine using a cross-check of the detected mobile location transponder ID against a barcode reader at the check-in station. 
         [0065]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that includes methods of automated daily health-check-monitoring, of all mobile location transponders, using processes which run on the existing wireless infrastructure network. 
         [0066]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that has support for both turnkey self-hosted installations, and subscription service business models. 
         [0067]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that is capable of peer-to-peer radio relay in tunnels, thus allowing non-earth-penetrating wireless networking. 
         [0068]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that is easy, quick, and economical to install because wireless battery operated sensors and wireless networking nodes can simply be set in place and do not need wiring infrastructure for power or communications. 
         [0069]    A still further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that offers bi-directional networking/data-communications for both into-mine and out-of-mine movement of messages. This feature is not possible with RFID technologies. 
         [0070]    Still another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that is highly accurate in providing miner location services (2-25 meters), compared with a crude zonal accuracy of 200-10,000 meters. 
         [0071]    A further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that provides whole mine updating of the location of hundreds or thousands of miners within 30 seconds. 
         [0072]    Still a further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that is tamper-proof by being automatically self-aware of the status and locations of all elements of the system. 
         [0073]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that utilizes heuristics, filtering, time averaging, calibration, use of human movement and tunnel boundary data, in addition to statistical analysis of RF parametrics, thus allowing for a much more accurate location estimate than provided in prior technology. 
         [0074]    A further object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that provides support for both subscription service hosting, as well as for turnkey self-hosted businesses, which reduces economic barriers to entry for many cash poor mine owners. 
         [0075]    Another object of the present invention is to provide a wireless mine monitoring/control and rescue communications system that is self-calibrating. 
         [0076]    Possible uses for the present invention include: miner location; mine monitoring and control, including asset location services; rescue team assistance in locating victims of mine disasters or other mishaps; monitoring underground nuclear waste storage facilities; monitoring and control of trains, subways and/or their tunnel environments/processes; locating inmates and guards in a prison environment; asset location/monitoring of any type in below-ground or above-ground environments; indoor location services of any type, enabling the kinds of applications indoors that GPS enables outdoors; SCADA systems of any type; automatic meter reading; industrial monitoring and control; and Homeland Security and Border Patrol. 
         [0077]    Other novel features which are characteristic of the invention, as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings, in which preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration and description only and are not intended as a definition of the limits of the invention. The various features of novelty that characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. The invention does not reside in any one of these features taken alone, but rather in the particular combination of all of its structures for the functions specified. 
         [0078]    There has thus been broadly outlined the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form additional subject matter of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based readily may be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES  
         [0079]    The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
           [0080]      FIG. 1  is a schematic diagram providing an overview of the wireless coal mine safety communications system of the present invention; 
           [0081]      FIG. 2  is a schematic diagram showing the rescue communications and voice/data intercom system employed in the present invention; 
           [0082]      FIGS. 3A through 3F  comprise electronic schematic diagrams of the various operational elements of the radio transceiver module utilized in the present invention; 
           [0083]      FIG. 4  is a schematic diagram of a emergency location sniffer; 
           [0084]      FIG. 5  is a schematic diagram of a self-healing hop-over concept; 
           [0085]      FIG. 6  is a schematic diagram of a roaming tail hand-over structure; 
           [0086]      FIGS. 7A and 7B  are schematic diagrams showing the RF propagation range and self-healing fault tolerance of the present invention; 
           [0087]      FIG. 8  is a schematic view of a rugged intrinsically safe enclosure for safe underground battery change; 
           [0088]      FIG. 9  is a schematic block diagram showing the typical communications hierarchy of the preferred embodiment of the inventive system; 
           [0089]      FIG. 10  is a schematic block diagram showing the power distribution system of the present invention; 
           [0090]      FIG. 11  is a schematic block diagram showing an isolated supply power distribution for system subnet controllers where any associated component is installed in a normally hazardous area; and 
           [0091]      FIG. 12  is a schematic block diagram showing a non isolated supply power distribution for system subnet controllers where all associated components are installed in fresh air areas. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0092]    The following detailed description of the invention is best understood by referring to the included drawings wherein like items are labeled with like reference designators. 
         [0093]    Referring first to  FIG. 1 , which a schematic block diagram providing an overview of the wireless coal mine safety communications system of the present invention, it will be seen that a computer/transceiver/vocoder  101  is linked to a storage system database  102  which can be internal to computer/transceiver/vocoder  101  or externally linked to computer  101 . Computer  101  operates under the control of custom software  103 . 
         [0094]    Custom software  103  includes instructions for controlling each bi-directional network communications link  107  (used for communications with a subnet made up of one or more wireless peer-to-peer radio/computer subsystems  104 ), as well as bi-directional communications link  108  (used for communications with one or more portable bi-directional pager/short-message device  106 ). Additionally, custom software  103  contains instructions to control Internet connections made via a RescueComm/ReachComm tail,  109 , which is a computer/transceiver/voice applicant used by a rescuer to access the system of  FIG. 2 . In this way, custom software  103  provides a graphical user interface to remotely located Internet browsers operating on such access devices as a personal computer  105  or other network capable access device. Custom software  103  also includes instructions for controlling read/write access to data contained in storage system database  102 . 
         [0095]    While performing the functions related to system communications, custom software  103  also provides a graphical user interface that allows users to view, in real time, system attributes and performance metrics, as well as the location and status of system components (including mobile components, such as the wireless peer-to-peer radio/computer subsystems (wireless access points or “WAPs”)  104 , and mobile location transponders,  202  in  FIG. 2 , worn by personnel). In this way, an individual person can monitor the entire network status along with the locations of each network node and mobile asset. This information can be visibly overlaid on a geographic map representation of the entire network, showing, for instance, the physical layout of mine tunnels and the locations of miners within each tunnel. 
         [0096]    Myriad data types may be handled by the custom software, though the principal types included for tracking and communications in a standard package include: Tag ID (miner #), Name, Access Rights, Time Stamp, Miner Location, Asset Location, Emergency Status, Tag Health, Network Health, Battery Condition, Alarm Conditions, Alert Conditions, Specified Thresholds, and various System Administration Settings. Optional data types may be included as desired and needed in custom installations and as requested by the mine operator. Data is presented in various views depending on the data type (examples including graphical maps or table views), but data can also be easily exported to other applications for integration into legacy systems. 
         [0097]    Referring next to  FIG. 2 , we see a schematic block diagram of the rescue communications and voice/data intercom system employed in the present invention. In this diagram, computer  101  is located inside command center  203  and communicates directly and wirelessly with one or more wireless peer-to-peer radio/computer subsystem  104  via a bi-directional network communications link  107 . One wireless peer-to-peer radio/computer subsystem  104  can be configured to work with others to create a self-healing daisy-chained and/or peer-to-multiple peer wireless subnet. A single link between computer  101  and one instance of wireless peer-to-peer radio/computer subsystem  104  via a bi-directional network communications link  107  is all that is necessary for computer  101  to be made available to all instances of wireless peer-to-peer radio/computer subsystem  104  that are wirelessly linked into the same subnet via their own bi-directional network communications link  107 . 
         [0098]    Note that wireless peer-to-peer radio/computer subsystem  104  can be stationary (as a semi-permanently placed network node/sensor/controller) or mobile (mounted on a vehicle or attached to a person). 
         [0099]    In the preferred embodiment, each wireless peer-to-peer subsystem includes a subnet controller and a plurality of wireless access points (described more fully in connection with  FIGS. 9-12 ). The subnet created when multiple instances of wireless peer-to-peer radio/computer subsystem  104  are semi-permanently installed and placed into communication with one another is a self-healing network with the ability to communicate with mobile and non-mobile instances of wireless peer-to-peer radio/computer subsystem  104  from each installed instance (placement) of a wireless peer-to-peer radio/computer subsystem  104 . This means that as a rescuer travels along the path where instances of wireless peer-to-peer radio/computer subsystem  104  have been installed, the rescuer is able to maintain continuous voice and data communications to/from computer/transceiver/vocoder  109  to/from computer/transceiver/vocoder  101 . 
         [0100]    Due to the portable wireless, battery-powered operation of wireless peer-to-peer radio/computer subsystem  104 , the wireless access points of the system can be easily walked to a convenient appropriate location and installed very quickly. This makes emergency rapid deployment of one or more subnets possible without the need to spend time wiring and providing power to multiple network node devices. In this way, for instance, in a mine rescue emergency, computer  101  can be placed in communication with a first instance of a wireless peer-to-peer radio/computer subsystem  104 , and from the beginning location of this first instance, a chain of other individual instances of wireless peer-to-peer radio/computer subsystem  104  can be rapidly and easily deployed along the way as rescuers proceed toward the emergency location. Two way voice communications are made through head-set transceiver unit  109  which has a bi-directional communication link  107   a  with the subsystem  104 . These elements allow rescuers to maintain real time two-way communications with personnel at command center  203 . Additionally, as each wireless peer-to-peer radio/computer subsystem  104  is placed, a location map develops automatically due to the location-awareness of wireless peer-to-peer radio/computer subsystem  104 . 
         [0101]    Also shown in  FIG. 2  is the sensor array  201  optionally in communication with radio frequency transceiver module (mobile location transponders)  202 . Miners and rescuers can wear this transponder device as they work in a mine. Radio frequency transceiver module  202  communicates with any instance of wireless peer-to-peer radio/computer subsystem  104  (or with any instance of a handheld location sniffer, as described in  FIG. 4 ) via its own bi-directional network communications link  107 . Radio frequency transceiver module  202  has an internal processor that enables location awareness through analysis of the received signal strength indication (RSSI) of received radio frequency signals generated by nearby instances of wireless peer-to-peer radio/computer subsystem  104 . Since each instance of wireless peer-to-peer radio/computer subsystem  104  includes a self-identifying set of symbols in transmissions, radio frequency transceiver module  202  is aware of the unique identity of each instance of wireless peer-to-peer radio/computer subsystem  104  with which it communicates. 
         [0102]    When in communication with an instance of wireless peer-to-peer radio/computer subsystem  104 , radio transceiver module  202  can send data messages back to, and receive data messages from, computer  101  via the subnet consisting of the one or more instances of wireless peer-to-peer radio/computer subsystem  104 . When connected to sensor array  201 , radio transceiver module  202  can pass the information collected by sensor array  201  back to computer  101  in real time as necessary. 
         [0103]    In a preferred embodiment of the transceiver module  202  worn by mine personnel, the devices are powered by a lithium ion wafer battery with a nominal battery life of two years. In keeping with the inherently safe design standards implemented in much of the instant invention, the batteries can be replaced only by technicians. The transponder beacon interval is every 5 seconds at a transmit frequency/modulation/power of 2.4 GHz-DSSS-1 milliwatt peak, and 1 microwatts average. The typical range for communications and tracking with such devices is approximately 300 feet, with a 500 feet maximum. Alert signals may be of four types, all initiated with a button press, and include: (1) extreme emergency; (2) minor emergency: (3) non-emergency checkout to remote area; and (4) cancel. In its current configuration, the transponder is 2×3.6×0.9 inches in a rugged polycarbonate and silicone rubber enclosure. It may be mounted in several ways with appropriate mounting apparatus on a miner&#39;s belt, helmet, pocket, breather, fanny pack, and the like, according to the preferences of the miner and the mine operator. 
         [0104]    Further, in the preferred embodiment, the wireless access points of the wireless peer-to-peer subsystem are powered by DC 7-24VDC wired power primary (for fresh air area installations), and DC 7-12VDC isolated supply (I.S.) wired power primary (for permissible areas), having a DC 3.6-4.0VDC I.S. lithium battery (backup battery) DC 3.6-4.0 VDC I.S. lithium/caplamp untethered option. The power connection is a 12 AWG 2-conductor twisted pair MSHA, and operation continues uninterrupted for 48-96 hours after disconnect. The data/communications connection is 100% wireless. It has a transmit frequency/modulation/power of 2.4 GHz-DSSS-50 milliwatt. The antenna is a built-in chip antenna that transmits through the wireless access enclosure. The data type is packet data with a transmission rate of 250 kbit/second, and a range for peer-to-peer network communications of greater than 500 feet, though the wireless access points are normally spaced no more than 150-200 feet to ensure strong link budget and “hop-over of one failed node.” In such a configuration, the location accuracy in “defined” coverage areas (i.e., within the entry or crosscut where a subnet is deployed) is +/−1 node spacing (200 feet typical) with 95% degree of confidence. The location accuracy in “supplemental” coverage areas (i.e., those outside of the entry/crosscut where a subnet is deployed) ensures that a location is known to be within 500 feet of any node(s) that “heard” the miner&#39;s beacon, again with 95% degree of confidence. The wireless access points provide seven types of alert signals using a high intensity strobe disposed on the apparatus housing, including: (1) flashing red, signifying extreme danger and calling for immediate evacuation; (2) solid red, signifying danger and requiring that personnel prepare for evasive action and call; (3) flashing yellow, calling for someone to acknowledge a miner&#39;s extreme alert; (4) solid yellow, calling for someone to acknowledge a miner&#39;s minor alert; (5) flashing green, signifying all is well, return to normal operations; (6) solid green (quick)—acknowledging a checkout; and (7) solid green (long), calling for someone to contact the mine office or dispatcher. The preferred housing is currently 6.3×10.2×4.2 inches, and fabricated from fiberglass reinforced polycarbonate. The mounting is a chain mounting with a uni-strut for affixing the housing to roof bolts or plates or wire mesh. 
         [0105]    Referring next to  FIGS. 3A-F , electronic schematic diagrams of radio transceiver module  202  are shown. Referring first to  FIGS. 3A through 3C , it can be seen that hybrid integrated circuit (IC) U 301  is a combination radio frequency transceiver and micro controller used to communicate wirelessly with external compatible devices. IC U 301  uses as its antenna a specially dimensioned printed circuit board ‘pad’ to which pin  9  (Ant Out) is directly connected when IC U 301  is mounted on the circuit board. 
         [0106]    Circuit ground for IC U 301  is provided through pins  25 ,  26 ,  37  and  38 . RF ground is provided through pins  1  through  8  and pin  10 , as well as pins  52  through  57  and  60  through  62 . Analog ground is provided through pins  37 ,  38  and  50 . 
         [0107]    Pins  11 - 23 ,  29 ,  30 ,  41 - 45 ,  47  and  59  of IC U 301  are not used. Pins  24 ,  27 ,  28 ,  29 ,  32 - 36 ,  39 ,  41  and  48  of IC U 301  are used only during the initial commissioning of the module (when programming the processor and configuring the module settings). Connectors J 303  and J 301  are where these pins are connected. Connectors J 303  and J 301  are used to connect external control and power systems to the module during the initial commissioning process. 
         [0108]    Referring now to  FIG. 3F , radio transceiver module  202  has an alert signal trigger capability through switches S 301  and S 302 . When both of these momentary-on switches are pressed simultaneously, the voltage from the VCC source is made available through resistor R 303  to the top of capacitor C 303 , thus charging the capacitor to full voltage. Capacitor C 303  is used to “memorize” the fact that the alert signal switches (S 301  and S 302 ) have been pressed by the miner. In effect this capacitor forms a sample-and-hold function, with the capacitor voltage being read by the high-impedance 12-bit ADC on board IC U 301  via the connection between the top of capacitor C 303  and pin  49  (ADC1_IN) of IC U 1 . The “cancel alert” function is invoked by rapidly discharging capacitor C 303  to ground through R 304  by pressing momentary-on switch S 303 . 
         [0109]    When a miner carrying transceiver module  202  has an emergency, the alert signal can be triggered by simultaneously pressing switches S 301  and S 302 . When both of these momentary-on switches are pressed simultaneously, the logic contained in IC U 301  recognizes the condition. This is because the voltage at pin  49  (ADC1_IN) is raised to the level of VCC, and this condition is measured by the internally integrated analog-to-digital converter of IC U 301 . When the internally integrated micro controller of IC U 301  polls the analog-to-digital converter (this is regularly done at very short intervals), the high voltage condition is reported back to the micro controller, thus making the logic in the micro controller aware of the condition. Once the micro controller is aware of this condition, it automatically causes IC U 301  to make a radio frequency transmission that contains data that uniquely identifies the transceiver module  202  that is transmitting, as well as data indicating that there is an emergency related to this miner and the location of the miner. The emergency transmission is received by the nearest wireless peer-to-peer radio/computer subsystem  104 , which (via the wireless data subnet consisting of multiple instances of wireless peer-to-peer radio/computer subsystem  104  as seen in  FIG. 2  along with computer  101  as seen in  FIG. 1 ) passes the message back to computer  101 . This allows users monitoring mine conditions at computer  101  to see immediately that the miner has an emergency, and where the miner is located. Because each individual instance of transceiver module  202  has a unique digital identity, it is possible for a mapping to occur in computer  101  that links each individual instance of transceiver module  202  with the name and function of the miner who is carrying it. If the miner realizes that the emergency transmission was unintentionally triggered, or that there is no actual emergency, pressing the “cancel alert” button switch S 303  will cause a rapid reduction in the voltage at pin  49  (ADC1_IN), which is detected by the internal components of IC U 1  (as described above). This causes IC U 1  to immediately make a radio frequency transmission that contains an “emergency cancelled” data message, along with the unique identity of the instance of transceiver module  202  that made the transmission. When this message reaches computer  101  (via the wireless subnet described in  FIG. 2 ), computer  101  informs those monitoring the mine status that the emergency alert has been cancelled. 
         [0110]    Referring next to  FIG. 3D , Pin  51  (VCC) of IC U 301  is connected to the VCC/BATT+ power source (+3.6 VDC) provided by batteries B 301  and B 302  operating in parallel with double redundant blocking diodes, D 303 , D 304 , and D 305 , D 306 , to protect against back-loading EMF from one battery into the other. Optional relay LS 301 , when used, provides a magnetically operated ‘Off’ switch that can be used to automatically turn the unit off when the unit is placed on a magnetic surface. 
         [0111]    Now referring to  FIG. 3E , a sleep cycle battery conditioner circuit is shown, comprising power conditioning capacitors C 305  and C 306  and zener diodes D 301 , D 302 , and D 307 . Together, these components stabilize power spikes that occur when IC U 1  “awakens” and makes a very brief radio frequency transmission (“beacon on”) before retuning to “sleep” mode. Power conditioning capacitors C 305  and C 306  are necessary to decouple the batteries from the brief higher energy demand of the “beacon on” interval (the few milliseconds when IC U 301  transmits radio frequency signals. Triple shunt zener diodes D 301 , D 302 , and D 307 , keep the voltage across capacitors C 305  and C 306  below 4.3V, even in the case of unlikely buildup of static charge. 
         [0112]    Pin  46  of U 301  is connected to one side of inductor L 301 , and the other side of inductor L 301  is connected to the top of zener diodes D 301 , D 302  and D 307  (and thereby, the VCC/BATT+ power source (+3.6 VDC) provided by batteries B 1  and B 2 ). Capacitors C 301  and C 302  filter audio and radio frequency components from the DC power arriving at pin  46  of IC U 301 . 
         [0113]    Referring next to  FIG. 4 , there is shown a schematic block diagram of an emergency location sniffer. In this diagram, it can be seen that a CPU board  401  acts as a master controller that receives its direct-current (DC) power from battery pack  402  via switch  403 . CPU board  401  communicates with external systems via RS-232 interface  404 . CPU board  401  communicates with LCD panel  405  via a first USB interface  409 . CPU board  401  communicates with head node board  406  via a second USB interface  409 . 
         [0114]    Still referring to  FIG. 4 , head node board  406  has a radio frequency transceiver that uses an externally mounted antenna with which to receive and transmit radio frequency signals. Head node board  406  sends digitized representations of the RSSI of received signals to CPU board  401  via USB interface  409 . When uses as a miner location ‘sniffer’ (as in the case of a mine rescue operation), the transceiver of head node board  406  sends to CPU board  401  the RSSI of the received signal being transmitted by a radio frequency transceiver module  202  (carried on the person of a miner). Along with this information, head node board  406  sends to CPU board  401  the binary data modulated onto the radio frequency signal transmitted by radio frequency transceiver module  202 , including the unique digital identity of the transmitting instance of radio frequency transceiver module  202 . 
         [0115]    Upon receiving the information provided by head node board  406 , CPU board  401  displays on LCD panel  405  the unique identity of each transmitting instance of radio frequency transceiver module  202 , as well as its RSSI. 
         [0116]    Head node board  406  also provides the user with indications of the status of the DC power, as well transmit and receive data activity through a set of labeled light-emitting diodes (LEDs)  406   a ,  406   b , mounted so as to be externally viewable on the surface of the chassis containing head node board  406 . Additional externally viewable LEDs are provided (controlled by head node board  406 ) that indicate a status condition that is received as part of a data message transmitted by radio frequency transceiver module  202 . The meaning of each status condition is user-definable. 
         [0117]    In this configuration and feature set, the emergency location sniffer shown in  FIG. 4  can be used to locate a missing miner who is carrying (or is nearby a) radio frequency transceiver module  202 . 
         [0118]    Now referring to  FIG. 5 , there is shown a schematic diagram of a self-healing hop-over concept. In this diagram, instance B of wireless peer-to-peer radio/computer subsystem  104   b  is in communication with instance C of wireless peer-to-peer radio/computer subsystem  104   c  via a bi-directional network communications link  107 . Similarly, instance C of wireless peer-to-peer radio/computer subsystem  104   c  is in communication with instance D of wireless peer-to-peer radio/computer subsystem  104   d  via a bi-directional network communications link  107 . Additionally, instance D of wireless peer-to-peer radio/computer subsystem  104   d  is in communication with instance E of wireless peer-to-peer radio/computer subsystem  104   e  via a bi-directional network communications link  107 . All instances of wireless peer-to-peer radio/computer subsystem  104   b - 104   e  are located inside the earth tunnel bounded by tunnel wall  501 . 
         [0119]    Referring still to  FIG. 5 , it can be seen that, if instance D of wireless peer-to-peer radio/computer subsystem  104   d  fails, instances C and E of wireless peer-to-peer radio/computer subsystem,  104   c  and  104   e , respectively, recognize the loss of signal from instance D, and then begin immediately to communicate wirelessly with one another directly via a bi-directional network communications link  107 . This hop-over link recovery technique is possible due to the intelligence built into the wireless peer-to-peer radio/computer subsystem  104 . 
         [0120]    Now referring to  FIG. 6 , a schematic diagram of a roaming tail hand-over structure is shown. In this diagram, instance B of wireless peer-to-peer radio/computer subsystem  104   b  is in communication with instance C of wireless peer-to-peer radio/computer subsystem  104   c  via a bi-directional network communications link  107 . Similarly, instance C of wireless peer-to-peer radio/computer subsystem  104   c  is in communication with instance D of wireless peer-to-peer radio/computer subsystem  104   d  via a bi-directional network communications link  107 . Additionally, instance D of wireless peer-to-peer radio/computer subsystem  104   d  is in communication with instance E of wireless peer-to-peer radio/computer subsystem  104   e  via a bi-directional network communications link  107 . Again, all instances of wireless peer-to-peer radio/computer subsystem  104   b - 104   e  are located inside the longwall mine earth tunnel bounded by tunnel wall  501 . Radio frequency transceiver module  202  is in motion, located somewhere between instances C and D,  104   c  and  104   d , respectively, of wireless peer-to-peer radio/computer subsystem. Radio frequency transceiver module  202  is initially in communication with instance C of wireless peer-to-peer radio/computer subsystem  104   c  via bi-directional network communications link  107   c.    
         [0121]    Still referring to  FIG. 6 , it can be seen that instance C of wireless peer-to-peer radio/computer subsystem,  104   c , will see a reduction in the signal strength of signals transmitted by radio frequency transceiver module  202  as the module moves away from instance C,  104   c , and towards instance D,  104   d , of wireless peer-to-peer radio/computer subsystem. Inversely, instance D,  104   d , of wireless peer-to-peer radio/computer subsystem will see an increase in the signal strength of signals transmitted by radio frequency transceiver module  202  as the module moves away from instance C and towards instance D. Because instances C and D of wireless peer-to-peer radio/computer subsystem,  104   c  and  104   d , are in direct communication with one another via a bi-directional network communications link  107 , they are able to negotiate a hand-over of the communications with radio frequency transceiver module  202  to instance D of wireless peer-to-peer radio/computer subsystem when the quality (signal strength) of bi-directional network communications link  107   d  exceeds the quality of bi-directional network communications link  107   c.    
         [0122]    Referring next to  FIGS. 7A and 7B , there are shown schematic diagrams of the RF propagation range and self-healing fault-tolerance of the present invention. In these diagrams, a wireless daisy-chained network  701  having plurality of wireless nodes A through G (each an instance of the above-described wireless peer-to-peer radio/computer subsystem  104 ). Nodes A through G of daisy-chained network  701  are physically and geographically separated from one another by a distance of approximately 100 meters, and are positioned along a generally straight line of a total distance of approximately 600 meters. Similarly, daisy-chained network  706  is configured with nodes A through G spaced at approximately 100 meters from one another, and further includes network node H positioned between nodes B and C. 
         [0123]    If node G is assumed to be the transmitting unit under consideration, it can be seen that when node G of daisy-chained network  701  transmits at a power level of −18 dBm (16 microwatts), the usable-quality signal has a range that reaches to a location just past node F. When node G transmits at a power level of −12 dBm (63 microwatts), the usable-quality signal has a range that reaches a location just past node D. When node G transmits at a power level of −6 dBm (250 microwatts), the usable-quality signal reaches just past node C. When node G transmits at a power level of 0 dBm (1 milliwatt), the usable-quality signal reaches just past node B. Thus, it can be seen that by increasing its radio frequency power output level in a controlled manner, an instance of wireless peer-to-peer radio/computer subsystem  104  can extend its reach to more distant network nodes if necessary to automatically recover from the loss of one or more nearby network nodes. Similarly, by reducing its radio frequency power output level in a controlled manner, an instance of wireless peer-to-peer radio/computer subsystem can contract its reach to limit it to only the nearest network nodes to automatically handle the return to operation of one or more nearby network nodes. This automatic self-healing of the network is particularly important in a mineshaft environment where a fire or cave-in could damage one or more of the network nodes. When such an event occurs, there is little or no time for network repair and configuration activities (nor is it likely that a network repair person is going to be on location at the right time with the right equipment and tools for the troubleshooting and repair job). 
         [0124]    Referring to  FIG. 7B , it can be seen that when node H of daisy-chained network  706  transmits at a power level of −24 dBm (4 microwatts), the usable-quality signal reaches just past nodes B and C. This shows that an intermediate node (H) can be placed into a location between two other nodes, and it will automatically adjust its transmitted radio frequency power to a level that reaches just beyond the nearest neighboring network nodes (thereby increasing overall network traffic capacity without increasing radio interference by transmitting beyond the necessary distance). 
         [0125]    Now referring to  FIG. 8 , a diagram of a preferred embodiment of a rugged, intrinsically safe (IS) enclosure for safe underground battery change for a preferred embodiment of the wireless peer-to-peer radio/computer subsystem  104 , shown here assembled for hanging from a coal mine ceiling  801 . Bolt  803  attaches roof plate  802  to coal ceiling  801 . Roof plate  802  is slightly flanged to make it easy to force the top (horizontal) portion of L-shaped hanger  804  between the top surface of roof plate  802  and coal ceiling  801 , thereby securing hanger  804  to coal ceiling  801 . 
         [0126]    Hanger  804  has a hook on its bottom end that hooks through hanging eye  805 , which in turn is welded directly to the top center of metal top end cap  807 . Surrounding, and extending above hanging eye  805 , pipe coupler  806  is welded to the top of top end cap  807 . On the inside of the lower portion of top end cap  807  are a set of female pipe threads (not shown) that mate to the male pipe threads helically encircling pipe nipple  808 . Mounted inside top end cap  807  is rechargeable battery  819 . The negative terminal of rechargeable battery  819  is electrically connected to the metal surface of top end cap  807 . When the IS enclosure is assembled, top end cap  807  is screwed onto the top of metal pipe nipple  808  using the mating pipe threads so that the negative terminal of rechargeable battery  819  is electrically connected to pipe nipple  808 . 
         [0127]    Pipe nipple  808  has contact mounting bracket  810  secured to its inside by mounting bolt  809 . Contact mounting bracket  810  extends from the inside wall of pipe nipple  808  to just past the horizontal center of the inside of pipe nipple  808 . Mounting bracket  810  is made of a non-electrically-conducting material. Electrical contact  817  (made of electrically conductive material, typically a metal) is secured into position and passes through mounting bracket  810 . 
         [0128]    Electrical contact  817  is dimensioned such that when secured into position and extending through mounting bracket  810 , it does not extend past the top or bottom of pipe nipple  808 . Extending downward from electrical contact, and electrically connected to electrical contact  817 , springy metal contact  816  is dimensioned to reach only far enough to make contact with the electrical terminal on the top of radio frequency transceiver/logic module  820  when the pipe threads on the outside of the bottom of pipe nipple  808  have already engaged with the pipe threads on the inside of the top of bottom end cap  811 . When the IS enclosure is assembled, metal bottom end cap  811  is screwed onto the bottom of pipe nipple  808 . This brings the negative terminal of rechargeable battery  819  into electrical connection with the metal surface of bottom end cap  811 . 
         [0129]    Radio frequency transceiver/logic module  820  is mounted in the base or bottom inside of bottom end cap  811 . The electrical ground (negative power input terminal) of radio frequency transceiver/logic module  820  is connected to the metal surface of bottom end cap  811 . Disposed atop radio frequency transceiver/logic module  820  is an electrical terminal for receiving the DC power from the positive terminal of rechargeable battery  819 . When the IS enclosure is assembled, the power from the positive terminal of rechargeable battery  819  passes through springy metal contact  818 , electrical contact  817 , springy metal contact  816 , and finally to the electrical terminal located on the top of radio frequency transceiver/logic module  820 . In this manner, radio frequency transceiver/logic module  820  receives its operating electrical power. 
         [0130]    Radio frequency transceiver/logic module  820  is electrically connected to antenna  812  via coaxial transmission line  815 . Antenna  812  is mounted in the bottom center of bottom end cap  811 , with its radiating element extending downward to the outside of bottom end cap  811 . The radio frequency transceiver of radio frequency transceiver/logic module  820  uses antenna  812  for radio communications with other compatible radio devices. 
         [0131]    The logic component of radio frequency transceiver/logic module  820  controls the data network communications functions of the module, allowing the module to interlink with other similar modules and automatically self-configure for operation in a peer-to-peer or peer-to-multi-peer network architecture. 
         [0132]    The logic component may also communicates with a gas sensor  813 , receiving sensor output and passing a representation of that output to external systems (such as computer  101  seen in  FIG. 1 ). Gas sensor  813  is preferably mounted on the inside of bottom end cap  811 , which includes opening placing gas sensor into fluid communication with the outside (ambient mine) environment and allowing gases to pass into contact with gas sensor  813  for analysis. A seal around gas sensor  813  prevents potentially damaging gases from leaking past gas sensor  813  and into the interior of the IS enclosure. Gas sensor  813  is in communication with radio frequency transceiver/logic module  820  via communications link wire  814 . 
         [0133]    When the need arises to open and then reassemble the IS enclosure to change rechargeable battery  819 , it is necessary for safety to prevent any electrical spark from being exposed to the mine environment. To prevent this, a springy metal contact  818  is connected electrically to the positive contact of rechargeable battery  819 . Springy metal contact  818  extends downward from rechargeable battery  819  to a distance that will allow contact with electrical contact  817  only after pipe nipple  808  has already begun threading itself into the interior threads of top end cap  807  during the reassembly of the enclosure. Since top end cap  807  and pipe nipple  808  are both electrically conductive, once thread mating is established, an electrical shield is produced that surrounds the point of contact between springy metal contact  818  and electrical contact  817 , thereby preventing any possible spark from being exposed to the mine environment when contact is finally made between springy metal contact  818  and electrical contact  817 . 
         [0134]    When the need arises to open and then reassemble the IS enclosure to access radio frequency transceiver/logic module  820 , it is also necessary for safety to prevent any electrical spark from being exposed to the mine environment. To prevent this, springy metal contact  816  is connected electrically to electrical contact  817  and extends downward from electrical contact  817  a distance that allows for contact with the electrical terminal located on the top of radio frequency transceiver/logic module  820  only after pipe nipple  808  has already begun threading itself into the interior threads of bottom end cap  811  during reassembly of the enclosure. Since bottom end cap  811  and pipe nipple  808  are each electrically conductive, once thread mating commences, an electrical shield is produced that surrounds the point of contact between springy metal contact  816  and the electrical terminal located on the top of radio frequency transceiver/logic module  820 , thereby preventing any possible spark from being exposed to the mine environment when contact is finally made between springy metal contact  816  and the electrical terminal located on the top of radio frequency transceiver/logic module  820 . 
         [0135]    Referring next to  FIG. 9 , it will be seen that the typical communications hierarchy  900  of the preferred embodiment of the inventive system includes an optional server/aggregator  902 , which can be located anywhere in the world, and which has a broadband connection  904  with at least one location network controller  906   a  located at a first mine site. The server  902  may be in communication other network controllers  906   b  at other mine sites. In turn, the location network controllers are in communication with one or more location subnet controllers  908 , the interconnection including an MSHA barrier  910  at the surface ports when conditions call for such safeguards. The connection is preferably made via RS485 cable or DX-V-bus  912 . The subnet controllers are also in communication with one another, either wired or wireless  914 . 
         [0136]    Still referring to  FIG. 9 , each subnet controller  908  has a 100% wireless communication link  916  with a plurality of wireless access points  918 , creating a subnet system (element  104 , as described in  FIGS. 1-8 ). In turn, each wireless access point is in wireless communication with mobile location transponders  920  ( 202  in  FIGS. 1-8 ), which are worn by mine personnel. 
         [0137]    Next referring to  FIG. 10  the power distribution system  930  for the inventive system is shown. Where the installation is in normally fresh areas, standard 120VAC  940  is provided to the location network controllers  906   a - b,  and mine power 100-250VAC  942  is provided to the subnet controllers  908  as permitted. The wireless access points  918  are provided with 24VDC  944  through the subnet controllers  908 , and include 48 hour battery backup and optional 100% battery power. The mobile location transponders  920  are 100% battery powered by non-rechargeable sealed Li-ion wafer cell batteries. 
         [0138]      FIG. 11  shows a non-isolated supply power distribution  950  for system subnet controllers  908  where the associated components are installed in a normally fresh air area. It will be seen that the chains of wireless access points  918  are provided with non-isolated 24VDC power via field wires  944 , preferably Carolprene MSHA (black jacket) 12AWG/2 unshielded twisted pairs. The power to the wireless access points dies by default when main power  942  is shut down. 
         [0139]    In the preferred embodiment, the subnet controller units  908  are enclosed in a 24×24×10 inch housing  952  and weigh approximately 200 lb fully assembled, or 300 lb on a pedestal with a terminal block. The housing package is EXd coal-dust and methane explosion-proof and flameproof pressure vessel and includes floor mount apparatus. When required the housing is a Class 1 Division 1 housing; otherwise it is a NEMA 4 Division 2 standard enclosure. The main power supply  942  in an intrinsically safe option is a 90-250VAC in 9.5VDC-IS@ 1A with 4 channels out to the field wires  944 ; in a non-intrinsically safe option the power supply is 24VDC@4A output. The backup battery type is a UPS rechargeable, with standard 12 hour backup operation. The operation temperature range is 0 to 85 C, with a storage temperature range of −20 to 85 C. The housing includes LED indicators for Power ON, RX/TX, and Status 1, 2, 3. The interface to the WAPs, mobile tags, and wireless network is 100% over-the-air wireless at 2.4 GHz. The interface to the backbone network in the intrinsically safe option is an RS485 or DX-V-Bus standard backbone data bus  954 , though ethernet, fiber-optic, leaky feeder, and other options can be accommodated. MSHA approved IS barriers  956  are provided where required in hazardous environments. The subnet controller CPU  955  runs on a Linux platform, though other generally secure operating systems may be employed and are inherently contemplated in the present disclosure. The subnet controller unit includes a master radio transceiver  958  and antenna  960  for wireless communications with both wireless access points and with the location network controller 
         [0140]      FIG. 12  shows an isolated supply power distribution  970  for system subnet controllers  908  where any associated component may be installed in normally hazardous areas. All elements are essentially identical to the power distribution in a non-isolated system, but here power to the wireless access points  918  is divided and isolated by a plurality of isolated power supplies  948  into 9.5VDC field wire runs  946  and provided by MSHA (blue jacket) 12AWG/3 unshielded twisted pairs with two conductors permitted for ground returns for reduced resistance. 
         [0141]    Thus by this explanation, along with reference to the included figures, the necessary elements, features and functions of the present invention are disclosed. However, while there is provided herein a full and complete disclosure of the preferred embodiments of this invention, it is not desired to limit the invention to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like. 
         [0142]    Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which are defined by the claims herein.