WO2012154153A1 - Wireless network compass - Google Patents

Abstract

A system and method for providing navigational direction toward an exit portal or some other point of refuge in an underground mine or other passageway for the benefit of a user carrying a wireless mesh network mobile radio unit. The system provides visual, audible or tactile indication, or a combination of such indications, of navigational direction when beset by emergency conditions including but not limited to reduction of visibility by smoke, airborne particulates such as coal dust or other dust, or fog or other vapor. The system uses properties of data incorporated in digital radio network message packets and measurements of signal strength to determine whether the bearer is moving toward or away from an exit portal or other point of refuge.

Description

WIRELESS NETWORK COMPASS

TECHNICAL FIELD

[0001] The present invention relates to a system and method for adding navigation capability to a wireless voice and data communication system. The wireless system is designed for use in underground and above-ground hazardous areas for dispatch, remote supervision, and tracking of personnel, as well as monitoring, asset control, and management of wireless sensors and equipment. More specifically, the navigation methodology and apparatus employs unique features of a reliable wireless ad hoc mesh network architecture and protocol to support navigation during normal and emergency operation.

BACKGROUND OF THE INVENTION

[0002] Robust and reliable communications are critical for both normal operations and in the event of an emergency in underground and hazardous work areas such as coal mines to determine the conditions of personnel, environment and equipment. The Mine Improvement and New Emergency Response Act of 2006, also known as the 2006 MINER Act, amended the Federal Mine Safety and Health Act of 1977 by mandating that underground coal mine operators must provide for post accident communication between underground and surface personnel via a wireless two-way medium. The 2006 MINER Act also required an electronic tracking system in order for surface personnel to determine the location of any person trapped underground.

[0003] Methods of wireless communications developed for use above ground are generally not effective in mines, tunnels and other underground facilities due to the environment and limited radio wave propagation. Therefore, other methods and devices have been developed in an attempt to fill this void.

[0004] Prior art for emergency guidance in underground mines includes lifelines deployed in passages (tunnels commonly known as entries or crosscuts) designated as primary or secondary escapeways. Lifelines are ropes usually fastened to the ceiling and affixed at intervals with mechanical shapes providing tactile indication of the direction toward the exit, emergency oxygen supply caches, and shelters built at strategic locations in the hazardous area. Primary and secondary escapeways are further marked by color-coded markers affixed at periodic intervals in the respective passage. A disadvantage of such prior art lifelines and marking of escape passages in underground mines is that they are subject to damage and may be rendered unusable by events causing emergency conditions in underground mines, including fires and explosions, roof collapse of an escapeway, with smoke and dust limiting visibility to a few feet.

[0005] Other prior art methods and apparatus using transmissions from

geosynchronous global positioning system ("GPS") satellites and terrestrial transmitters for navigation by persons afoot or in vehicles are rendered ineffective in underground locations and in the interior of above ground structures because the radio signals do not penetrate sufficiently.

[0006] Still other prior art methods and apparatus based on use of a magnetic compass to determine a bearing and heading are often difficult to use or unusable for low- visibility navigation in mines where the floor plans are often complex and cover large distances. In these cases, the bearing to an egress portal is not direct, and the heading to a shelter may change numerous times en route. Lacking a view of the destination, the user of a magnetic compass cannot establish a bearing from which to pursue a heading.

[0007] Different prior art methods for navigation rely on dead-reckoning techniques to guide a user to egress and are dependent on recording of gyroscope and other inertial- sensor devices from which a path of ingress can be reconstructed. However, in emergency conditions in hazardous locations such as underground mines, the path of ingress may not be the preferred path of egress.

[0008] However, the prior art does include disclosure of an intrinsically safe, low cost, wireless ad hoc mesh network with battery backup which has been approved by the Mine Safety and Health Administration for deployment in hazardous environments as a complete wireless communication network supporting communications and tracking. Details of the approved network are disclosed in the following patent applications: PCT/US09/37753 filed March 20, 2009; and PCT/US09/37755 filed March 20, 2009. Other wireless networks which share some of the aspects of the approved network are disclosed in U.S. patent no. 7,119,676 issued Oct 10, 2006 and U.S. appl'n serial no. 11/687,030 filed March 16, 2007. All of the aforementioned U.S. patents and published patent applications are incorporated by reference as if fully set forth herein. This wireless network includes mesh network routers that operate below ground with access points above ground that connect to external networks to provide dispatch, collaborative detection, location, assessment, and tracking during emergency events as well as normal operation. The radio communication system implementation provides data and voice communications among personnel and data communications among network nodes, sensors, computers, machinery, and other industrial equipment located either underground in mines or other underground passages, or located above ground inside and outside of buildings and other structures. Such a system operates both from line power sources and, when so-equipped, for long periods of time from battery power, so that emergency events causing or mandating shutdown of line power feeding facilities do not interrupt operation of the radio network

[0009] This radio communication system sends all messages digitally, including voice and data messages coded as sequences of binary numbers, enabling partitioning of messages into segments for transmission and later reassembling of the segments into the original contiguous messages. This arrangement enables alternation between transmit and receive operation at appointed times ("time-division duplex" or TDD) in synchrony with neighboring fixed and mobile radio nodes ("digital radio communication system") and allows sharing of a limited bandwidth and limited number of channel frequencies among a large number of fixed and mobile network nodes ("time-division multiple access" or TDMA).

[0010] Moreover, this digital radio communication system is capable of autonomous network formation at power-up or entry of a powered-up fixed or mobile node in radio range of other active network nodes. This system is also capable of autonomous network reformation since nodes remain active after failure of one or more network nodes.

[0011] In addition, this digital radio communication system derives information from radio signals otherwise used for network maintenance and uses such information for determining location and movement ("tracking") of bearers of mobile radio nodes in the hazardous area for display on computer equipment located away from the hazardous area.

[0012] Furthermore, this digital radio communication system is responsive to user messages with low latency and supports network maintenance by sending messages partitioned into short segments ("packets") using frequent radio transmissions separated in time by intervals ranging from small fractions of a second to a few seconds depending on the number of packets required to send the complete message and on the number and priority of other messages awaiting transmission at neighboring network nodes. All packets have information categories in common including the originating transmitter identity, the intended recipient identity, the message type and length, the priority, and error checking codes in addition to any payload content. [0013] Another feature of this digital radio communication system is that it employs one or more methods of avoiding excessive congestion of network traffic channels, such methods including but not limited to a parameter known as "Time To Live" (TTL) assigned as a positive integer number enclosed with radio network transmission packets by the node originating the message. TTL denotes the maximum number of times that the message may be retransmitted by other nodes progressively receiving and relaying the message through a network.

[0014] An additional aspect of this digital radio communication system is its inclusion of information providing unique and substantially permanent identification of the originating radio node within every message packet as it is first transmitted and preserved with the message as it is successively retransmitted through the network by other nodes.

[0015] In yet a further feature of this digital radio communication system, it employs one or more methods of measuring signal quality including but not limited to "Received Signal Strength Indicator" (RSSI) in which radio frequency (RF) energy gathered by the antenna of the radio receiver of a network node, which energy originates from the radio transmitter emission of a signal configured for compatible communication within said network, is evaluated by the receiver to generate a numeric value of the power dissipated by the signal at the antenna input to the receiver. Because radio signal strength can vary significantly due to constructive (reinforcing) and destructive (attenuating) multipath interference when a receiver moves even only a small distance, prior art has demonstrated various numerical techniques for averaging successive RSSI measurements to identify consistent values and short-term trends in its values.

[0016] What has not been provided by this digital radio communication system, is an easy-to-use, dependable device and method for enabling personnel located in an underground mine or in a contiguous above-ground area receiving coverage from such a radio system, either on foot or in a vehicle, to navigate safely from inside the mine to an exit point from the mine or delineated radio coverage area and/or to a point of refuge within the mine or area.

SUMMARY OF THE INVENTION

[0017] This invention relates to a wireless mesh system and method normally used for communicating message packets between nodes in the system but also capable of providing navigational direction assistance toward an entry portal or some other point of refuge in an underground mine or other area to a user carrying a wireless mesh network mobile radio unit ("mobile node"). The system is comprised of a computer server located outside of the area, at least one gateway node (GWN) outside of the area which is in communications contact with the server, a plurality of fixed mesh node radios (FMNR) dispersed throughout the area at a known distance from the entry portal each of which can communicate with at least one other GWN or FMNR and at least one mobile mesh network radio (MMNR) node incorporating a direction indicator, each MMNR being in communications contact with at least one FMNR and/or another MMNR. Each of the nodes incorporates a microprocessor and nonvolatile data storage. Each FMNR is identified by a sequentially increasing number, a portal proximity number (PPN) indicating its relative distance ranking from the entry portal relative to all other FMNRs in the system with a higher number indicating a greater distance. Each FMNR is further identified by a time-to-live (TTL) integer stored in memory which represents the number of times a message originating with a GWN has been received and retransmitted by other FMNRs before it is received by the subject FMNR wherein each FMNR may only received and transmit the same GWN- originated message one time.

[0018] When operation of the system is initiated, a decision is made whether to respond to navigation requests by relying solely on PPN numbers or solely on TTL integers or by employing both PPN numbers and TTL integers. When a request for navigational assistance is requested by an MMNR, a determination is made whether the requesting MMNR is receiving message packets from more than one other node. If not, the sole node is identified and the RSSI of each received packet is measured and, for those RSSI values which are not anomalous, chronologically ordered. If the RSSI value of a currently received packet is higher than that of previously received packets, a direction indicator is activated to confirm to the user that movement is correct. Otherwise, the direction indicator alerts the user to incorrect direction of movement. If packets are being received from more than one node, identifying information, including PPN numbers, for the node sending the most recently received packet as well as for all other nodes within communications range is retrieved. If PPN-based navigation has been selected, retrieving the PPN and chronological RSSI values for each node from which packets can be received and comparing them. The direction indicator provides a confirmation of correct movement if the RSSI value of a selected node is increasing while the RSSI from other nodes is decreasing. The direction indicator alerts the user of incorrect movement direction if the RSSI of the selected node is decreasing over time while the RSSI of other nodes has been increasing. If TTL-based navigation has been selected, relevant information, including TTL values, is extracted from message packets originating from a GWN. The TTL values for all such received packets are compared. If the packet from the node with the highest TTL value also shows increasing RSSI values over time while RSSI values associated with packets received from other nodes are decreasing, the direction indicator is activated to confirm to the user that movement is correct. Otherwise, the direction indicator alerts the user to incorrect direction of movement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The foregoing and other objects, aspects, functional concepts, and advantages of the invention described herein are better understood by reference to the drawings, in which:

FIG. 1 is a schematic diagram of a typical underground mine in which various digital wireless network nodes are installed and/or operative.

FIG. 2 is a schematic diagram of part of an underground mine in which both fixed and mobile nodes have been placed showing both the Portal Proximity Numbers (PPN) assigned to each fixed node and acceptable and unacceptable egress paths for each mobile node.

FIG. 3 is a schematic diagram of part of an underground mine in which both fixed and mobile nodes have been placed showing Portal Proximity Numbers assigned to each fixed node, TTL values and acceptable and unacceptable egress paths for each mobile node.

FIG. 4 is a schematic diagram showing only the PPN and TTL relationships between the first three fixed nodes closest to a mine portal and two mobile nodes among the fixed nodes.

FIG. 5 is a graphical representation of received signal strength (RSSI) at a mobile mesh network radio (MMNR) as it moves away from a gateway node (GWN) towards a first fixed mesh network radio (FMNR).

FIG. 6 is a graphical representation of RSSI at an MMNR as it moves away from a first FMNR and towards a second FMNR.

FIG. 7A is a flowchart demonstrating implementation and use of the navigation method according to the principles of this invention.

FIG. 7B is a continuation of the flowchart of FIG. 7A.

FIG. 7C is a continuation of the flowchart of FIG. 7B.

DETAILED DESCRIPTION OF THE INVENTION

[0020] This invention relates to a method and apparatus ("Wireless Network

Compass") for using existing network parameters to define a new parameter of digital radio network operation to determine the progress of a mobile radio toward or away from a reliable path to an exit portal or refuge/shelter under all conditions including poor visibility and absence of legacy directional aids.

[0021] FIG. 1 illustrates in schematic form an example of part of a typical underground mine 10 in which a digital wireless mesh network of the type described above has been installed in excavated spaces. There are multiple unexcavated spaces 15 which may either be spaced-apart pillar type forms having a typical dimension of 40 to 80 feet on each side or in larger, irregular spaces. The network includes a plurality of fixed radio nodes deployed to meet regulatory requirements for tracking coverage in entries designated as primary and secondary escapeways and for providing wireless signal connectivity to above- ground computer equipment outside the mine. Fresh air enters the mine from an air intake portal 20 and circulates through the excavated spaces in the directions indicated by arrows 25 along primary escapeways 30. Vehicles and personnel on foot also enter the mine through portal 20. The excavated mine area also typically provides a belt portal 35 for conveyor belt pathways 40 which may also be used as secondary escapeways. Air exhausts from the mine in the directions indicated by arrows 45 towards exhaust fan 50. Air flow both into and out of mine 10 is typically guided along intended paths by means of non-structural stopping walls 52. A predetermined number of fixed mesh network radio (FMNR) nodes 55 are dispersed both inside mine 10 and outside of the mine at air intake portal 20. The FMNRs are non- mobile network radios each of which incorporate at least a microprocessor and a separate nonvolatile memory. Each FMNR 55 must be positioned so as to enable radio

communication with at least one other FMNR 55 and normally with two or more FMNRs 55. In addition, gateway nodes (GWN) 60 are provided outside of mine 10 near air intake portal 20 and near belt portal 35. Gateway nodes 60 are the same as FMNR nodes but include a hardwire data connection to an external server computer.

[0022] Mine users on foot carry a mobile mesh network radio (MMNR) 65 which is equipped with software required to determine the direction toward the nearest FMNR 55 deployed along a primary or secondary escapeway, using the methods explained with regard to Fig. 2, Fig. 3 and Fig. 4. Similarly, vehicles operating inside the mine are equipped with the same or analogous MMNR 65 for the same purpose.

[0023] In a preferred embodiment, each FMNR 55 is assigned a Portal Proximity Number (PPN) which is inserted as a parameter into the administrative header portion of each packet transmitted by that FMNR. The assignment is typically accomplished in a wireless manner by a gateway server computer located outside mine 10 using an SNMP-like protocol for remotely reading and revising current configuration parameters of each FMNR 55 operating at its deployed underground location and/or for installing updated software. In an alternative embodiment, a PPN may be assigned to each GWN 60 or FMNR 55 directly by persons responsible for managing the network directly rather than relying on network software. Such assignments can be accomplished using a hard- wire digital connection to the gateway server or other computer such as may be used to set configuration parameters or install software updates either at a manufacturing site or above-ground at mine 10 prior to deployment of each node into or around mine 10. The assigned PPN for each FMNR 55 is stored in nonvolatile memory of that FMNR. PPN can be assigned to each FNMR 55 based on its proximity to a portal, such as air intake portal 20, using the following principles:

(a) Gateway Nodes (GWN) 60 and FMNRs 55 deployed at or outside any portal will be assigned the lowest PPN, a numeric value such as 1 or 1.1.

(b) The remaining FMNRs 55 deployed underground will be assigned PPNs with higher numeric values for increasing relative distance from a portal. For example, an FMNR 500 feet from the primary escapeway portal might have a PPN= 3 and an FMNR 570 feet from the secondary escapeway portal might be assigned a PPN=5, the number 5 chosen larger than 3 because 570 feet is larger than 500 feet. Another FMNR located 1500 feet from the secondary escapeway portal might be assigned PPN=6, again, the number 6 chosen as greater than 5 because 1500 feet is greater than 570 feet. And an FMNR located 2000 feet from the primary escapeway portal might then be assigned PPN=8, and so on. FMNRs 55 which are equidistant from a portal will have the same PPN.

[0024] FIG. 2 illustrates in schematic form a portion of a mine 10 in which a PPN has been assigned to each FMNR 55. The assigned PPN is the number shown within each of the FMNRs 55. Fixed nodes physically closer to portal 20 have a lower PPN than those further away from portal 20. Note that, since they are equidistant from the portal, there are two FMNRs 55 with the PPN of 4. For each MMNR 65 shown in FIG. 2, acceptable destination paths based on reaching that FMNR 55 with which communications are possible with a low detection error rate and which has the lowest PPN are shown by solid lines, while unacceptable paths towards other communicating FMNRs 55 are indicated by dashed lines. PPNs are assigned to support an escape scenario where personnel navigating a hazardous condition may be required to cross between one escapeway and another, as well as to continue on one escapeway. Simultaneous radio reception of FMNRs located on both escapeways renders unambiguous indication of the direction to the portal. MMNR 65 seeking an egress need only direct movement of a user toward an FMNR 55 labeled with the lowest PPN it can receive with a low detection error rate. Thus, an MMNR 65 need not pass a closer FMNR 55 before it begins guiding the user toward a farther FMNR 55 having a lower PPN.

[0025] The bit error rate, or the packet error rate, is continuously monitored by this system in any of a number of ways known in the art. An acceptable error rate is a

configurable parameter which may be set or changed prior to or while using the system. A node may have a low PPN but a high error rate because, for example, of a mine roof collapse occluding the mine entry representing the primary path of its radio signal propagation and also therefore the presumptive path of escape. In that case the method of this invention would favor indicating to the user that a preferable avenue of movement is towards another node with a lower PPN than the last node passed, but possibly higher than the PPN of the node with the signal indicated as unreliable due to its measured error rate.

[0026] An optional additional parameter may also be implemented in the method and apparatus of this invention. A Time-To-Live (TTL) integer parameter is generated and included in each data packet transmitted by every GWN 60, every FMNR 55 and every MMNR 65 in the wireless mesh network. TTL begins as a maximum number set as an administrative option for each node originating messages. Each TTL is reduced by 1 each time another node retransmits a message to neighbor nodes within radio range.

Consequently, the higher the TTL in a packet received from a node at or outside a portal, such as air intake portal 20, the closer the sending radio transceiver is to that portal. FIG. 3 illustrates in schematic form a portion of mine 10 in which a plurality of FMNRs 55 and MMNRs 65 are positioned and shows how TTL parameters are generated based on transmissions between nodes. As in FIG. 2, assigned PPNs are the numbers shown within each of the FMNRs 55. In FIG. 3, GWN 60 has been assigned a TTL number of 40 which thereby becomes the maximum TTL number for packets originated by GWN 60 in this arrangement of nodes. When GWN 60 transmits a packet, the packet is received first by MMNR 80 and then by FMNR 85. A TTL parameter value of 40 accompanies the packet. FMNR 85 decrements the TTL value by one (i.e. to 39 in this example) and retransmits the received packet together with the new TTL value to nodes with which it is in communication, in this case including MMNR 90 and FMNR 95. The TTL value is again decremented by one at FMNR 95, and the packet is then transmitted together with the new TTL value of 38 to the nodes with which FMNR 95 can communicate, including MMNR 100, FMNR 105, FMNR 110 and MMNR 115. Each node is able to track packets which it has already received by means of duplicate filter software resident in each FNMR so that retransmission of a packet previously received and retransmitted is blocked. This process continues until either a TTL value of 1 is reached or all FMNR nodes in the network have received the packet originally transmitted by GWN 60. Normally, only fixed nodes (FMNRs and GWNs) retransmit packets received from other nodes. However, MMNRs can act as an ad hoc relay for other MMNRs when the latter are out of range of any fixed nodes. In FIG. 3, the dotted line indicates transmittal of packets between nodes with the TTL value appearing as a number adjacent each dotted line segment.

[0027] TTL parameters provide an additional way in which FMNRs can determine and self-assign their own PPN numbers. Proximity to the portal 20 can be inferred by the relative value of TTL in two or more successive retransmissions of the same packet with GWN 60 origin identity by two neighboring FMNRs in mine 10. Each FMNR sends to, and receives from, neighboring FMNRs with which it can communicate neighbor reports which are existing operational maintenance transmissions enabling network formation, repair and handoff of mobile nodes. Each FMNR culls TTL data from retransmissions by neighboring FMNRs of GWN node packets. Information from the neighbor reports and the culled TTL data enable each FMNR over time to determine and self-assign its own PPN. In summary, the RSSI, TTL and the PPN of all packets received by that FMNR are culled and stored in that FMNR's nonvolatile memory. The programming in the microprocessor of each FMNR enables it to recognize in packet administrative headers a valid range of assigned PPN values and the state wherein a PPN value has not yet been established for the FMNR transmitting said packet. If the originating node for a packet is identified as a GWN, the TTL, RSSI and the PPN associated with the packet received first at the node is compared to the TTL, RSSI and PPN associated with subsequently received retransmissions of that first received packet from any other node. If the TTL of the first received packet is higher than the TTL of subsequently received retransmissions of the first received packet, and if a valid PPN exists in the first received packet, but a PPN is unassigned or is a higher value in the subsequently received retransmissions of the first received packet, and if the FMNR can ascertain its own relative proximity to the navigation destination among the nodes emitting transmissions and retransmissions by analysis of RSSI values measured for the received packets and analysis of RSSI values measured and reported by the transmitting nodes for each other, a PPN value is assigned which is larger than the PPN associated with the first received packet but smaller than any PPN values that may already be assigned in the retransmitting nodes. In the example depicted in FIG. 3, MMNR 80 and FMNR 85 receive GWN 60 transmissions including parameter transmissions indicating a maximum TTL of 40 and a minimum PPN=1, as would be configured by default for the GWN by virtue of its having hardware capable of TCPIP. FMNR 85 retransmits the GWN 60 packets with the TTL decremented by 1 (i.e. 39 = 40-1), then hears its neighbor FMNR 95, the second FMNR located farther into the mine, retransmit the GWN 60 packet again with the original TTL decremented by 1 more integer (i.e., 38 = 39-1, total decrement = 2). From GWN neighbor reports, FMNR 85 knows GWN 60 cannot hear (is out of radio range of) FMNR 95, or if in range, it learns from the GWN 60 neighbor reports and FMNR 95 neighbor reports that it receives a much stronger signal strength (RSSI) from both GWN 60 and FMNR 95 than GWN 60 and FMNR 95 receive from each other. Therefore FMNR 85 concludes that it is physically between GWN 60 (at the portal) and FMNR 95, and FMNR 85 assigns itself a PPN incremented by one from the next outby node, in this case GWN 60. Thus, FMNR 85 has learned its physical order of proximity to portal 20 within the network, represented as PPN=1+1=2. The self-assignment of PPNs by FMNRs progresses from the portal inby, since an FMNR can only be sure of the lowest PPN it can self-assign after it hears an outby FMNR transmit packets with a PPN value. The success of this process mediated by such an algorithm in software is dependent on a standard practice deployment of FMNRs in the network, such that every FMNR is in radio range of at least one other FMNR; if an FMNR only hears 1 other FMNR, the second FMNR is required to be closer to the GWN/portal. Normally each FMNR will be in range of 2 or more other FMNRs; of the other FMNRs, at least one will be closer to the GWN/portal, and the remaining FMNRs will be either equidistant or farther away. The process of fixed nodes (FMNRs) recognizing proximity to the portal as described above depends on using only the TTL value from packets for which the packet header identifies the originator

(creator) as a GWN, in the case of FIG. 3 as GWN 60. The farther away a packet travels from GWN 60, the more times the packet will be retransmitted, and thus the lower will be its TTL, and the higher should be the PPN of FMNRs retransmitting the packet. Therefore, based on the combined TTL and PPN parameter values calculated as just explained, the solid lines in FIG. 3 represent acceptable destination paths when seeking egress from mine 10 by seeking to move towards nodes with lower PPNs, while the dashed lines show unacceptable destination paths when seeking egress from mine 10 since such paths do not lead to nodes having lower PPNs.

[0028] Each MMNR may be optionally programmed to use only the TTL parameter from GWN packets, or the PPN parameter for all FMNR packets, or both parameters in conjunction to verify the reliability of directional determinations and/or to enable more frequent updates of sensory direction indicators, as discussed below, for the user. If the MMNR uses the TTL value transmitted or retransmitted in GWN packets, the MMNR is configured to store the network ID of the GWN in its long-term microprocessor memory so that it can compare and identify received packets as originating from the GWN, outside the portal.

[0029] An MMNR may also be optionally programmed to store the unique network identity of certain special fixed nodes deployed within a mine in order to improve navigation near emergency shelters and oxygen caches in underground mines, such that the MMNR renders a distinct special notification to its user when RSSI from the special fixed node is high, alerting the user to the proximity of the special facility.

[0030] In one alternative embodiment, the MMNR may store in its memory a record of all fixed nodes in the network labeled by node identity paired with respective PPN and/or with the TTL used by GWNs and FMNRs in, respectively, transmitting or retransmitting packets originated by GWNs. Such a record of FMNRs may be introduced into the MMNR by several mechanisms including but not limited to:

(a) programming or, when network nodes are replaced, redeployed, or otherwise reconfigured, reprogramming using network communications ("over-the-air programming"); or

(b) programming through wired connection at initialization of service or through configuration update capability incorporated into an MMNR battery charging device; or

(c) self -programming whereby the MMNR learns and records the identities, logical channels used, and PPN and/or retransmitted GWN TTL of each fixed node in the order it encounters the radio signals from said nodes as the user proceeds into an underground mine or other expanse for which the network provides communication coverage.

[0031] In a preferred embodiment, the MMNR maintains a table stored in its microprocessor memory, containing the unique ID of each node from which it is currently able to receive paired with the PPN of the respective node, the TTL of GWN packets received from the respective node, and at least two vintages of some variant of rolling average of RSSI calculation measured from recent packets received from the respective node. The rolling average is calculated as an arithmetic or geometric average and the individual RSSI values used in the average may be weighted equally or weighted according to age for the calculation. The time span represented by the sequence of RSSI measurements used in the rolling average is long enough, such as 1 to 30 seconds, to avoid erroneous guidance to the user due to short-term RF propagation variation. The time between the two successive RSSI average calculations is short enough, such as 0.5 to 2 seconds, to provide frequent updates to indicate whether the user is on a desirable escape path or has momentarily digressed to an unfavorable path. Since various digital radio systems may transmit tens to hundreds of packets in each second, there are a range of viable methods for choosing the span and interval of RSSI values from which to create the updates. The following table illustrates an example where RSSI for each packet at intervals of 100 milliseconds are used in a 1.0 second running average (an average of 10 sequential packet values) as a basis to update indication to the user every 0.5 seconds. Among the packet RSSI values can be seen some values representative of the unusually weak signals regularly observed by mobile receivers due to destructive fading. A long enough sample sequence used as input to an arithmetic average or other window function smoothes these fade values of RSSI to enable usefully reliable inference of the trend of signal strength.

Table 1

[0032] FIG. 4 illustrates in schematic form a small portion of mine 10 in which only the first three nodes closest to a mine portal 20 and two mobile nodes among the three fixed nodes are shown together with the applicable PPNs for each fixed node shown within each node and the altered TTL generated at each FMNR node shown as a label on the dotted line(s) exiting each node. FIG. 5 is a graph illustrating RSSI as received at MMNR 80. The line labeled GWN 60 shows the progressive decline in Received Signal Strength (RSSI) at MMNR 80 as measured on the left Y axis as MMNR 80 moves away from GWN 60 and the distance between those nodes increases. FIG. 5 also illustrates with the lines labeled FMNR 85 and FMNR 95 how the RSSI at MMNR 80 progressively increases as MMNR 80 approaches closer to FMNR 85 and FMNR 95. Thus, FIG. 5 demonstrates that, if a more recent RSSI value is higher than an earlier RSSI value for a certain fixed node, and if the fixed node always transmits at a constant power level, the MMNR at which the RSSI is measured is approaching that fixed node. FIG. 6 is a graph illustrating RSSI as received at MMNR 90. The line labeled FMNR 85 shows that the RSSI of a signal transmitted by FMNR 85 and received by MMNR 90, as measured on the left Y axis, progressively decreases as MMNR 90 moves away from FMNR 85 and towards FMNR 95. Similarly, the line in FIG. 6 labeled FMNR 95 shows how the RSSI of the signal received at MMNR 90 from FMNR 95 progressively increases as MMNR 90 moves towards FMNR 95. Thus, FIG. 6 demonstrates that, if the recently measured RSSI value is lower than the older RSSI value for transmissions from a given fixed node, the MMNR is moving away from that fixed node.

[0033] The general rule governing navigation by an MMNR to a portal by the most direct route is that a mobile unit is assured of moving toward a portal when the RSSI is increasing for the fixed node signal with the lowest PPN and the highest TTL of GWN packets received; and/or the RSSI is decreasing for the fixed node signal with the second lowest PPN and the second highest GWN packet TTL.

[0034] The derivation of user indication from combinations of RSSI trend and neighboring fixed node attributes (PPN or retransmitted GWN TTL) is summarized in the following series of scenario tables. In each scenario, 1 or 2 nodes are listed with a hypothetical pair of RSSI measurements, "old" (earlier/prior reading) and "new" (most recent reading). The RSSI trend is the relative change from old to new: increasing RSSI indicating movement closer to the labeled node, or decreasing RSSI indicating movement away from the labeled node.

[0035] In Table 2, only PPN is used for the determination. Node A has a lower PPN than Node B, indicating that Node A is closer to the portal (such as portal 20) than Node B. The RSSI data indicates the MMNR is moving closer to Node A and farther from Node B, and the display affirms the user' s direction of movement. TABLE 2

[0036] In Table 3, only TTL received in GWN-originated packets is used for the determination. Node B has a lower TTL than Node A, indicating that Node A is closer to the portal than Node B. The RSSI data indicates the MMNR is moving closer to Node A and farther from Node B, and the display affirms the user's direction of movement.

TABLE 3

[0037] In Table 4, both TTL received in GWN-originated packets and PPN for neighboring fixed nodes are used for the determination. Node B has a higher TTL and lower PPN than Node A, indicating that Node B is closer to the portal than Node A. However, the RSSI data indicates the MMNR is moving closer to Node A and farther from Node B, and the display warns the user that direction of movement is away from the portal.

TABLE 4

[0038] In Table 5, both TTL received in GWN-originated packets and PPN for neighboring fixed nodes are used for the determination. Node A has a higher TTL and lower PPN than Node B, indicating that Node A is closer to the portal than Node B. The RSSI data for Node A indicates the MMNR is moving closer to node A and in possible contradiction, the RSSI for Node B indicates the MMNR is moving toward Node B. However, the RSSI values for Node B are determined to be too weak for reliable trend assessment, and the data for Node B is ignored for the current display update, which affirms the user' s direction of movement.

TABLE 5

[0039] In Table 6, only one node, Node C, is in reception range of the MMNR, and any PPN and GWN TTL values decoded from Node C are not used by the MMNR. The RSSI trend calculation for Node C indicates the user is moving toward it and the MMNR directional display is updated to affirm the user's direction of movement.

TABLE 6

[0040] In the Table 7, only one node, Node C, is in reception range of the MMNR, and any PPN and GWN TTL values decoded from Node C are not used by the MMNR. The RSSI trend calculation for Node C indicates the user is moving away from it and the MMNR directional display is updated to warn the user.

TABLE 7

[0041] If the MMNR receives a signal from only 1 fixed node, the embedded microprocessor algorithm uses the trend of RSSI data for signals received from that fixed node to direct the user toward that node, since this guidance is most likely to bring the user in reception range of other fixed nodes, and also to improve the tracking of the user as viewed at the network management computer outside the hazardous area. Note that although a strong RSSI usually is associated with a low error rate, there are exceptions to that general rule which is why digital radio systems may monitor both RSSI and error rates. These two values may be used as variables either independently or in conjunction by node-embedded software to control internode behavior.

[0042] In the preferred embodiment, the MMNR provides a means for the user to activate or deactivate the operation of the navigation guidance function, so that distraction of the indication to the user and any additional power consumption from the MMNR battery are not a burden during non-emergency conditions. In an alternate embodiment, the MMNR provides the directional function whenever it is powered on. In yet another embodiment, the directional guidance function in MMNR units is activated by reception of a network signal indicating an emergency condition, originating either from an MMNR or from a network management entity such as a gateway server computer outside the hazardous area.

[0043] Alternative options for user indication apparatus to be incorporated into an

MMNR within the scope of this invention include but are not limited to one or more of the following, all requiring and providing perceptibility in conditions of poor visibility:

Brightly colored light such as a light-emitting diode (LED) display with one color for affirmation of direction of movement ("affirmation") and a different color for warning of wrong direction of movement ("warning"); or Bright light source flashing in one pattern to indicate affirmation and flashing in a readily discernable different pattern to indicate warning; or

A vibrating alerter operating in one pattern of pulsing to indicate affirmation and operating in an easily distinguished different pattern to indicate warning; or

An audible ringer tone or tone modulation pattern to indicate affirmation and a recognizably different tone or tone modulation pattern to indicate warning; or

An audible recorded or synthesized human voice instruction providing affirmation or warning as to the advisability of the current direction of movement; or

A back-lighted symbol on an MMNR LCD screen such as a green arrow to indicate affirmation and a distinctly different symbol appearing on the MMNR LCD, such as a red "X", to indicate warning.

[0044] FIG. 7A, FIG. 7B and FIG. 7C are flowcharts presenting in block diagram form the method for using the navigation method and apparatus disclosed herein within an underground mine or other delineated deployment area of the wireless network, having at least one entrance or otherwise designated point of egress, and all undamaged nodes transmitting at a constant power level. Referring now to FIG. 7A, at 700, all nodes are positioned with their respective distances away from the mine entrance measured and recorded. All GWNs are placed outside of or at a mine entrance, and all FMNRs are usually placed within the mine. The distance of all nodes away from the mine entrance is measured and recorded at 705. All the nodes are then configured at 710. In the preferred embodiment, configuration from a GWN server computer includes wirelessly reading and altering parameters at each FMNR at its underground location, loading appropriate and/or updated software into the GWN, FMNR and each MMNR to be used within the mine and configuring each MMNR to store the network ID of the GWN in its long-term microprocessor memory and, if desired, the network ID of special fixed nodes deployed near emergency shelters and oxygen caches in the mine. Parameters may include one or more of assignment of acceptable bit error rates, a minimum acceptable RSSI level, the lowest PPN number to be assigned to the GWN and the PPN number to be assigned to each FMNR. A decision is made at 712 whether or not configure and use navigation in the deployed system. If not, navigation configuration is bypassed and normal operation of transmitting and receiving is initiated at 740. If navigation configuration is intended, then a decision is made at 715 whether to configure the system for PPN or TTL navigation. If PPN is chosen, then at 720 PPN values are set for all fixed-node transmitters in the system. After configuring PPN, there is a decision at 725 as to whether configuration for TTL navigation is also intended. TTL is always checked for a non-navigation, operational reason, as follows. If a packet from any node is not addressed to the fixed node receiving it, the TTL test determines whether that fixed node must retransmit that packet. Thus, absent errors in a packet, enabling an MMNR to read the originating node label and the TTL of the packet enables one way to implement this invention in an existing system without modifying the preexisting packet format. If after configuring PPN, the decision to use TTL is then made at 725 and consequently at 727 reception of TTL is enabled for all mobile nodes used in the system. Whether or not TTL was selected for use after PPN was first configured, the process of configuration is complete at 735. If after first deciding to configure navigation at 712, a choice is then made to configure for TTL navigation at 715, the process proceeds to 730 where reception of TTL is enabled for all mobile nodes used in the system. After configuring TTL navigation at 730, a decision is made at 732 whether to configure PPN navigation in addition. If PPN navigation is then to be configured, at 734 PPN values are assigned to all fixed-node transmitters in the system. Whether or not PPN was selected for use after TTL was first configured, the process of configuring navigation is complete at 735. Navigation configuration data including PPN data and TTL data, whichever options were selected, are stored in the nonvolatile memory of the GWN, the FMNRs and, if desired, the MMNRs. Normal network packet

communications, including transmission and reception, begin at 740 and continue, as shown in FIG. 7B, at 745. Normal communications includes sending packets of data from one node to another, each packet including a header identifying the node from which the packet originated, the node to have most recently retransmitted the packet and the PPN of that most recently retransmitting node. For each packet transmitted from one node to another at 750, treatment of the received packet differs depending on whether it is received by an MMNR at 755 or an FMNR at 760. In both cases, at 765 and 770 respectively, that packet's RSSI and bit error rate (BER) are measured and stored in the respective node. Also in both cases, the bit error rate is tested against the assigned parameter for acceptable bit error rates, respectively at 775 and 780. If the bit error rate is too high, the packet is discarded at 785 and 790, respectively, and the process continues at 745. If the BER is acceptable and the receiving node is an FMNR, a decision is made at 795 whether this is the first time that the incoming packet has been received by this node. If it is not, the packet is discarded at 800 and normal network packet communications continue at 745. If so, the packet is tested at 805 to determine whether or not the TTL associated with the packet is greater than 1. If not, the packet is discarded at 810 and the process continues at 745. If so, the receiving node retransmits the packet at 815 with the associated TTL decremented by 1 and normal network packet communications continue at 745. If the BER is acceptable and the receiving node is an MMNR, the receiving node checks whether the incoming packet is received directly from a fixed node (i.e., an FMNR or GWN), or is relayed from an FMNR or GWN by an MMNR at 820. If the packet fails all these source conditions, any non-navigation disposition mandated by instructions in the node's microprocessor as warranted by the packet type and content, such as playing encoded voice audio or an alert sound or displaying a text message or retransmitting or discarding the packet, is executed at 825 and the process continues at 745. If the packet received by the MMNR was transmitted by a fixed node or by an MMNR acting as a relay for a fixed node, the receiving node extracts data, including, as available, transmitting node identity, TTL and PPN values from the incoming packet and stores that data locally at 830. Any additional disposition mandated by instructions in the node's microprocessor as warranted by the packet type and content, such as playing encoded voice audio or an alert sound or displaying a text message or retransmitting or discarding the packet, is then executed at 832. Whether or not an emergency navigation function has been activated by an MMNR, as determined at 835, normal network packet communications will continue at 745.

[0045] However, if the navigation function has been activated, the process continues as shown in FIG. 7C. If at any time the navigation function is disabled at the MMNR, as determined at 840, the network operation continues only normal transmission and reception at 842, the process also referenced in FIG. 7B. If the navigation function has not been disabled, the process continues to determine whether the activated MMNR is receiving packets from only one other node, as determined at 844. If not, the microprocessor in that MMNR is programmed to extract the pertinent packet data and measure the RSSI value associated with each incoming packet from the node currently heard at 845 so as to create a chronologically ordered history of RSSI values for the signals received from the node at 845. The earlier and current RSSI data for the currently heard node are compared at 850.

Numerical processing pursuant to a decision algorithm to detect and dispose of possibly anomalous or apparently spurious values of RSSI is performed at 853. If the current RSSI is not higher than the previous RSSI, as determined at 855, then an indicator associated with each MMNR is activated at 860 to warn the MMNR user that the current direction of movement is not in the direction of the single received node and the process continues at 840. But, if the current RSSI is higher than the recent but earlier RSSI, the indicator is activated at 865 to confirm to the user that the direction of movement is correct. If a portal is reached, as determined at 870, the MMNR user can exit the mine or other delineated deployment area of the wireless network, and the emergency navigation process ends. Otherwise, the process continues at 840. If the activating MMNR can receive packets from more than one other node, as determined at 844, the MMNR retrieves PPN/TTL/RSSI data to the extent available for the node sending the most recently received data packet as well as similar data for each other such communicating node currently in radio reception range at 875. The navigation process then follows one of three mutually non-exclusive modes according to how the MMNR was programmed at 735. In the first mode, beginning at 880, only PPN values, fixed-node transmitter identifier labels, and RSSI values from each packet are used for navigation. In the second mode, beginning at 892, only GWN-originated TTL as identified by the originator identifier label and RSSI values from each packet are to be used for navigation. In the third mode, both PPN and GWN-originated TTL, along with node transmitter identifier and originator identifier labels and RSSI values for each packet, are used for navigation, and the MMNR microprocessor executes both paths starting at 880 and 892. If the PPN method is to be used, as determined at 880, the chronological trend of RSSI values is evaluated for the fixed node (FMNR or GWN) currently in range for radio reception with the lowest PPN at 882. Also, the chronological trends of RSSI values for fixed nodes in receiving range with higher PPNs are evaluated at 884. If the chronological trend indicates RSSI is increasing with time for the node with the lowest PPN, it indicates that the user is moving closer to that node, and thus closer to the point of egress of the mine or other wireless-network deployed area. Similarly, if the chronological trend indicates RSSI is decreasing with time for the nodes with PPN higher than the lowest PPN in range of radio reception, it likewise indicates that the user is moving toward the portal. The converse cases indicate that the user is moving away from the portal. A decision algorithm is used at 885 to resolve the directional implication of the RSSI trends for the multitude of fixed nodes currently in range of radio reception, resulting in a determination at 890 as to whether the user is moving toward or away from the point of egress. If the TTL method is to be used, as determined at 892, the chronological trend of recent RSSI values is evaluated for the fixed node currently in range for radio reception with the highest GWN-originated TTL at 894. Also, the chronological trends of recent RSSI values for fixed nodes in receiving range with lower GWN-originated TTL are evaluated at 896. Similarly to the PPN process, the TTL process uses a decision algorithm at 898 to resolve the directional implication of the RSSI trends for the multitude of fixed nodes currently in range of radio reception, resulting in a determination at 900 as to whether the user is moving toward or away from the point of egress. In both the TTL and PPN methods, it is only necessary that RSSI for most non-selected nodes be decreasing over time as it is possible that RSSI for a few non-selected nodes may actually be transitionally increasing. The important factor in this situation is that the RSSI for the selected node be increasing. In the event that both PPN and TTL modes are enabled for navigation, the separate PPN and TTL evaluation processes proceed as described independently and in tandem. Whether PPN-only, TTL-only, or both PPN and TTL evaluations are executed, the separate directional determinations are reconciled using an indicator resolution algorithm at 905, which passes through single-mode results and reconciles contradictions between simultaneous dual-mode results. The output of the indicator resolution algorithm is applied as a final decision at 910. If the consensus of the RSSI trends and reconciliation algorithm(s) is that the MMNR user is moving toward the point of egress, the indicator in the MMNR is activated to prompt the user at 915 to continue to move in the direction of the currently- received node nearest the point of egress. In the event a portal of the mine (or other wireless mesh network-deployed area) is reached, as determined at 870, the user can exit the mine. If the portal is not reached, the user can continue to seek navigation guidance by returning to 840. If the consensus of the RSSI trends and reconciliation algorithm(s) is that the MMNR user is moving away from a point of egress, the indicator in the MMNR is activated at 920 to warn the user that the present direction of movement leads away from a mine portal, and processing returns to 840 to retrieve further packets until a portal is reached and the user may successfully exit the mine or other wireless mesh network-deployed area from which an MMNR user seeks egress.

[0046] While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. In addition, many

modifications may be made to adapt the teaching of the present invention to a particular situation without departing from its central scope. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed as the best mode

contemplated for carrying out the present invention, but that the present invention include all embodiments falling within the scope of the appended claims.

Claims

CLAIMS What is claimed is:

1. A method based on a wireless mesh radio network for navigating from within an area having restricted wireless communication capability to a target point which may be an entry portal, a point of refuge or shelter or a location of emergency supplies, the area including a plurality of stationary fixed mesh network node (FMNR) transceivers located throughout the space at known locations and known distances from the entry portal, each having a programmable microprocessor and a nonvolatile data storage capability, such that each FMNR is able to communicate with at least one other FMNR, and at least one programmable, microprocessor-controlled mobile mesh network radio (MMNR) transceiver node having a nonvolatile data storage capability, a navigation function programmed therein and a direction indicator, each user of the area being provided access to an MMNR, there being at least one gateway node (GWN) transceiver having a microprocessor and a nonvolatile data storage capability located outside of the area close to an entry portal which communicates with a server computer having a data storage capacity, the server computer having stored therein an administratively selectable highest Time-to-Live (TTL) integer, an administratively selectable lowest Proximity Portal Number (PPN) number and an acceptable bit error rate (BER) as well as a preferred navigation type to be used chosen from among PPN-based, TTL-based or both, comprising:

preparing the network to respond to a navigation request from an MMNR by, in part, assigning a unique PPN number and TTL integer to each FMNR and GWN and associating a unique identifier label with each GWN and each FMNR;

determining whether a navigation request has been activated by an MMNR,

if not, returning to preparing,

if so, further determining if the activating MMNR is receiving packets from more than one node,

if not,

extracting an identifier label from the received packet, measuring RSSI for each received packet,

creating a chronologically ordered history of RSSI values for packets received from the one node at the activating MMNR,

comparing the RSSI data for earlier and currently heard packets received from the one node,

detecting and disposing of anomalous RSSI values should there be any,

still further determining if the RSSI of the currently received signal is higher than the RSSI of the previously received signal,

if so,

further activating the direction indicator associated with the activating MMNR to confirm to the user that the direction of movement is correct,

checking if the target point has been reached, if so, exiting the area and ending the process,

if not, returning to further determining; if not,

yet further activating the direction indicator associated with the activating MMNR to alert the user that the direction of movement is incorrect,

if so,

retrieving identifier label, PPN, TTL and RSSI values to the extent available for the node sending the most recently received data packet at the activating MMNR and for each other node currently in radio reception range of the activating MMNR,

if PPN-type navigation has been selected,

further extracting PPN values, fixed node transmitter identifier labels, and chronological RSSI values from each received packet,

comparing PPN values associated with all received packets, selecting the node having the lowest PPN value and examining chronological RSSI data for the selected node, further comparing chronological RSSI values associated with each other node from which packets can be received, if the RSSI value of the selected node has been increasing over time and if the RSSI values of other received nodes have been decreasing over time, yet further activating the direction indicator associated with the activating MMNR to confirm to the user that the direction of movement is correct,

checking if the target point has been reached, if so, exiting the area and ending the process,

if not, returning to further determining; if the RSSI of the selected node has been decreasing over time and if the RSSI of other received nodes has been increasing over time,

yet further activating the direction indicator associated with the activating MMNR to alert the user that the direction of movement is incorrect, and

returning to determining;

if TTL-type navigation has been selected,

further extracting TTL values, fixed node transmitter identifier labels, and chronological RSSI values from each received packet having an identifier label indicating that the packet originated with a GWN,

comparing TTL values associated with all received packets having an identifier label indicating that the packet originated with a GWN, selecting the node having the highest TTL value and examining chronological RSSI data for the selected node,

further comparing chronological RSSI values associated with each other node from which packets can be received, if the RSSI value of the selected node has been increasing over time and, if the RSSI values of most other received nodes have been decreasing over time,

yet further activating the direction indicator associated with the activating MMNR to confirm to the user that the direction of movement is correct,

checking if the target point has been reached, if so, exiting the area and ending the process,

if not, returning to further determining; if the RSSI of the selected node has been decreasing over time and if the RSSI of other received nodes has been increasing over time,

yet further activating the direction indicator associated with the activating MMNR to alert the user that the direction of movement is incorrect, and returning to determining.

2. The method of claim 1 wherein preparing further comprises:

configuring all nodes in the network;

choosing which type of navigation is desired from amongst PPN-based, TTL-based or both PPN-based and TTL-based;

if PPN-based is chosen, assigning second a PPN to each FMNR in the network and storing PPN data in the nonvolatile data storage of all nodes in the network;

if TTL-based is chosen, enabling TTL reception for each MMNR and storing TTL data in the nonvolatile data storage of all nodes in the network;

commencing normal network communications operations between nodes in the network by sending packets of data from one node to another, each packet including a header identifying the node from which the packet originated, the node to have most recently retransmitted the packet and the PPN of that most recently retransmitting node;

measuring and storing the received signal strength (RSSI) of each received packet at the receiving node;

further measuring and storing the BER of each received packet at the receiving node and discarding any packet for which the BER is above the acceptable BER;

if the receiving node is an FMNR or GWN,

determining whether this is the first time that the particular packet has been received;

if not, discarding the packet,

if so, determining whether the TTL integer assigned to the packet is greater than 1,

if not, discarding the packet, if so, decrementing the TTL integer, retransmitting the packet and returning to commencing;

if the receiving node is an MMNR,

determining whether the received packet was sent from an FMNR or GWN or MMNR acting as a relay for an FMNR,

if not, executing instructions contained within the node's microprocessor as warranted by the packet type and content and returning to commencing; and

if so, extracting from the packet header and storing in the nonvolatile memory of the receiving node the transmitting node's identifier label and the PPN and TTL associated with the transmitting node and then executing instructions contained within the node's microprocessor as warranted by the packet type and content.

3. The method of claim 1 wherein a navigation request may be activated by an MMNR user or upon reception of a network signal generated either by another MMNR or the server computer.

4. The method of claim 2 wherein configuring further comprises

wirelessly reading and altering parameters at each FMNR;

loading into and updating software at each node, as required; storing GWN identifier labels in each MMNR;

optionally separately identifying and storing FMNR identifier labels for any FMNR located at or near a refuge, shelter or location of emergency supplies;

propagating an acceptable bit error rate and a minimum acceptable RSSI to all FMNRs and MMNRs in the network;

enabling each FMNR to track packets which it has received and to block retransmission of previously transmitted packets; and

assigning first the lowest PPN to the GWN and to any FMNR located outside the area and the highest TTL to the GWN.

5. The method of claim 4 wherein assigning second a PPN further comprises:

associating each FMNR in the system with a portal proximity number (PPN) sequentially increased by a positive numeric value according to the distance of that FMNR from the entry portal relative to the distance from the entry portal of all other

FMNRs in the system with a higher numeric value indicating a greater distance, wherein the FMNR nearest the entry portal and inside the area is assigned a PPN equal to the lowest PPN plus a positive numeric value and wherein further FMNRs equidistant from the entry portal are assigned the same PPN.

6. The method of claim 5 wherein assigning second a PPN may be performed automatically by software in a GWN or directly by users of the system.

7. The method of claim 4 wherein enabling TTL reception for each MMNR further comprises:

associating the highest TTL with any packet originating at a GWN and inserting that TTL in an administrative header of that packet; and

each time that that packet is received and retransmitted by another node, decrementing the TTL associated with that packet and reinserting the resulting TTL in the administrative header of the retransmitted packet.

8. The method of claim 7 wherein assigning second a PPN further comprises:

monitoring and storing in the nonvolatile data storage of the receiving FMNR of the RSSI, TTL and the PPN of all packets received by that FMNR, each FMNR having a means established in the programming of its microprocessor and nonvolatile memory by which to recognize in packet administrative headers a valid range of assigned PPN values and the state wherein a PPN value has not yet been established for the FMNR transmitting said packet;

if the originating node for a packet is identified as a GWN,

comparing the TTL, RSSI and the PPN associated with the packet received first at a node to the TTL, RSSI and PPN associated with subsequently received retransmissions of that first received packet from any other node; and

if the TTL of the first received packet is higher than the TTL of subsequently received retransmissions of the first received packet, and if a valid PPN exists in the first received packet, but PPN is unassigned or is a higher value in the subsequently received retransmissions of the first received packet, and if the FMNR can ascertain its own relative proximity to the navigation destination among the nodes emitting transmissions and retransmissions by analysis of RSSI values measured for the received packets and analysis of RSSI values measured and reported by the transmitting nodes for each other, assigning a PPN value larger than the PPN associated with the first received packet but smaller than any PPN values that may already be assigned in the retransmitting nodes.

9. The method of claim 4 wherein if FMNR nodes located near a refuge, shelter or location of emergency supplies are separately identified and such location is a target point, implementing an additional distinctive signal in the direction indicator to notify an MMNR user of proximity to such a target point.

10. The method of claim 1 wherein each said MMNR is optionally programmed to contain within its memory any or all of the following:

the identity of all FMNRs and GWNs in the system paired with their respective PPN and/or the TTL used by GWNs and FMNRs in, respectively, transmitting or retransmitting packets originated by GWNs; and

a table containing the unique identifier label of each node from which it is currently able to receive paired with the respective PPN and TTL of each such node and a rolling average of RSSI values measured from recent packets received from each transmitting node.

11. A wireless mesh communications system for enabling navigation from a point inside of an area in which wireless communication is partially limited to a target point which may be an entry portal into the area, a point of refuge or shelter or a location of emergency supplies comprising:

a computer server located outside of the area having a data storage capability;

at least one gateway node (GWN) transceiver connected to and communicating with said server, each said GWN being located at or near an entry portal and each GWN having a microprocessor and a nonvolatile data storage capability;

a plurality of fixed mesh node radio (FMNR) transceivers dispersed throughout the area at known distances from the entry portal and at fixed locations from which each FMNR can communicate with at least one other FMNR and at least one FMNR can communicate with at least one of said GWN, each said FMNR having a microprocessor and a nonvolatile data storage capability and each FMNR being identified by a sequentially increasing portal proximity number (PPN) stored in its nonvolatile memory indicating its relative distance ranking from the entry portal relative to all other FMNRs in the system with a higher number indicating a greater distance; and

at least one mobile mesh network radio (MMNR) transceiver node incorporating a direction indicator, each said MMNR being in wireless contact with at least one said FMNR and/or another said MMNR and each said MMNR having a microprocessor and a nonvolatile data storage capability.

12. The system of claim 11 wherein each FMNR is further identified by a time to live integer (TTL) stored in its nonvolatile memory representing the number of times a message originating with a said GWN has been received and retransmitted by other said FMNRs before being received by the subject FMNR wherein each FMNR may only receive and retransmit the same GWN-originated message one time.

13. The system of claim 12 wherein the lowest PPN and the highest TTL are linked to at least one said GWN.

14. The system of claim 11 wherein each GWN is hard- wired to said computer server.

15. The system of claim 11 wherein the direction indicator in each said MMNR is implemented with one or more features selected from the group consisting of colored lights with one or more colors, flashing lights, physical vibrator, audible tone generator which may be modulated, synthesized human voice, "X"s and checkmarks, an LED display or an LCD screen.