A

Access (Network)

Networks can be considered to have two responsibilities; one is to provide access and the other is to provide transport for data or voice.

Access Link

In a node-based system, the first link, which is from the miner's handheld radio to a node, is through the air and is called the access link.

Access Node

The node providing the service to the miner.

Accuracy

The measure of error in the miner's reported location.

Active Tag

A tag that contains its own source of power for transmitting identification information.

Ad Hoc Network

A wireless ad hoc network is a decentralized wireless network. The network is ad hoc because each node is willing to forward data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity.

Air Interface

See Access Link.

Alternate Communications Path

A communications path that may be used to continue communications in the event that a primary path is blocked. A communications cable routed through a borehole is an alternate communications path.

Amplitude

For an electromagnetic or radio wave, amplitude refers to the maximum value of the periodically varying wave.

Analog Signal

A signal whose amplitude varies continuously in time. See Digital Signal.

Attenuation

The reduction of a signal's amplitude or power.

Availability

The probability that a system is operating properly when it is needed (i.e., the probability that the system has not failed or is not undergoing repair when it needs to be used).

B

Backbone System

A system that ties together several diverse systems and provides a common path for the transfer of communications or data. A leaky feeder is a common type of backbone system.

Backhaul

The communications path from an access node to the surface.

Backhaul Link

The connection between nodes.

Backup System

A system that may be deployed in the event that a primary system fails. For example, an Medium Frequency system may be used as a backup in the event of leaky feeder failure.

Band

A specific range of frequencies in the electromagnetic spectrum.

Bi-Directional

A communications system that passes information in both directions along its connected paths.

Bit

A binary digit equal to either a 0 or 1.

Bridge

A device that provides interoperability between different technologies.

Bridge Nodes

A node within a communications system that also acts as a bridge. See Bridge.

Bridge Repeater

A repeater within a communications system that also acts as a bridge. See Bridge.

Byte

A byte is an ordered collection of bits (0's and 1's). Although there is no standard, typically there are 8 bits per byte. See Bit.

C

Capacity (Communications System)

The information carrying ability of a communications system.

Capacity (Tracking System)

The maximum number of people a tracking system can monitor in its coverage area.

Carrier Frequency

The nominal frequency of a radio transmission. See Frequency.

Channel Capacity

The upper bound on the amount of information that can be reliably transmitted over a communications channel.

Compressed Voice

Audio (voice) that has been encoded so as to reduce the number of bits required for storage or transmission.

Constrained Mesh Network

A network where the allowable backhaul links that form the network topology must be pre-programmed into each node.

Coverage

Refers to the region or area in which radio-based communications services are available.

D

Dead Reckoning

The process of predicting and fixing position by course, speed, and distance traveled.

Digital Router Or Router

A networking device whose software and hardware are usually tailored to the tasks of routing and forwarding information. For example, on the Internet, information is directed to various paths by routers.

Digital Signal

A signal in which the intensity maintains a constant amplitude for some period of time and then abruptly changes to another constant level where the different levels represent the binary digits 0 or 1. See Analog Signal.

Discrete Antenna

An localized arrangement of conductors to radiate or receive electromagnetic waves such as a whip or dipole.

Distributed Antenna

A dispersed antenna such as a leaky feeder cable when used in connection to a coal mine communications system.

Downlink

Pertaining to the transmission path from the base station to a mobile station.

Dual Independent Communications Path

Communications paths to the surface that do not depend on or transgress a common set of entries. Generally this means that the two paths out of the mine differ in direction from the mine by at least 90 degrees.

E

Electromagnetic Compatibility

The condition which prevails when electronic/electrical systems or equipment are performing their individually designed functions without causing/suffering unacceptable EMI degradation to/from other equipment in the same environment.

Electromagnetic Energy

The energy carried by an electromagnetic wave.

Electromagnetic Environment (EME)

The radiated or conducted EM emission levels, in various frequency ranges that may be encountered by a system when performing its designed functions.

Electromagnetic Interference (EMI)

Electromagnetic energy which causes a malfunction in an electronic/electrical system or equipment, or interferes with its reception or processing of a desired signal. EMI may result from intentional and proper operation of equipment, or it may be unintentionally generated. EMI can be categorized as mild, medium, or severe, depending on the reaction of the victim equipment.

Electromagnetic Spectrum (EM)

A range of electromagnetic radiation frequencies. The term is normally used when referring to the frequencies as a group.

Electromagnetic Wave

A form of radiated energy that travels in waves that are a combination of electric and magnetic fields.

Explosion-Proof Enclosure

Explosion-proof enclosures must meet three criteria. First, it must be an enclosure that is rugged in construction and suitable for use in mining applications; second, the enclosure has a minimum structural yield pressure of at least 150 psig, without significant permanent distortion; third, there shall be no visible luminous flames or ignitions of a combustible methane-air atmosphere surrounding the enclosure during explosion testing.

F

Frequency

For an electromagnetic or radio wave, frequency refers to the number of oscillations per second, measured in Hertz. See Hertz.

Full Mesh

A mesh arrangement in which every node is connected to every other node.

Fully Wireless

See Through-the-Earth System, TTE.

H

Hard-Wired System

A communications system requiring physical wired connections between devices to operate.

Hardened System

A system in which protective measures have been taken to ensure the system's survivability. An example is enclosing a leaky feeder cable in a PVC pipe and burying it in a trench to enhance protection against roof falls.

Hardening

Increasing strength and ruggedness of system components to provide protection from damage.

Hardwired

Connected by physical wiring or cabling.

Hertz

A unit of measure equivalent to cycles per second.

Hop

An intermediate network connection consisting of a leg from one router to another router over which a packet travels to reach its destination.

I

Inertial Navigation

A navigation aid that uses a computer and motion sensors (accelerometers and gyroscopes) to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references. See Dead Reckoning.

Inertial Tracking

A tracking system that uses inertial navigation.

Infrastructure

All fixed location equipment within the mine and in entries to the mine.

Interference

Stray electromagnetic energy (radiated, coupled, conducted, or induced) that causes undesirable or unacceptable responses, interruptions, malfunctions, or degradation of performance in a subsystem or equipment.

Intermodulation Interference

EMI caused by the mixing, in a nonlinear junction, of two or more signals. The mixing process creates new signals at frequencies that are sums and differences of integral multiples of the original signals.

Internet Protocol

A particular prescription or method used for communicating data across a packet-switched network.

Interoperability

The ability of different communications systems to communicate with one another.

Interrogate

Refers to the initial RF signal transmitted by an RFID tag reader to a tag, which begins the transfer of information between the two devices.

Intrinsically Safe

Describes electrical equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal opertions to cause ignition of an atmospheric mixture of methane in its most easily ignited concentration.

IP Address

An Internet Protocol (IP) address is a numerical identification (logical address) that is assigned to devices participating in a computer network utilizing the Internet Protocol for communication between its nodes. Although IP addresses are stored as binary numbers, they are usually displayed in human-readable notations, such as 208.77.188.166.

L

Latency

The time delay suffered by packets of information as they hop from node to node in a mesh network. More generally, the time it takes information to travel from one point to another in a communications network.

Leaky Feeder

A communications device also known as "leaky coax," which assists wireless transmission. A coaxial cable that has been modified to allow signals traveling within it to leak out over its entire length.

Line-of-Sight (LOS)

An unobstructed straight-line path between a transmitter and receiver.

Link Budget

The quantitative result of an evaluation of the factors that contribute to RF power gain or loss in establishing a communications link between two components.

Local Area Network (LAN)

A data communications system that lies within a limited spatial area, has a specific user group, has a specific topology, and is not a public switched telecommunications network, but may be connected to one.

M

MAC Address

In computer networking, a Media Access Control address (MAC address) is a quasi-unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification.

Medium Frequency (MF) System

Communications systems that operate in the range of 300-3000 KHz. MF systems have been shown to work well in tunnels where there are metallic structures such as power lines and pipes. The signals can couple onto conductors and travel long distances.

Mesh Network

A communications system where every node is connected to every other node and consequently has built in redundancy. In underground mines, this connectivity may be limited by the mine's geometry and cost considerations.

Mesh or Node-Based System

A communications system which relies on multiple individual devices to establish a communications path.

Mesh Point

Another term for node in a node-based communications network.

Modulator

A device by which analog or digital information is converted to signals at RF frequencies suitable for transmission.

N

Network

A system containing any combination of interconnected communications equipment used to transmit or receive information.

Node

A point of connection into a communications network.

Node-Based Tracking

A tracking system using node-based communications nodes to determine radio location.

Noise

A received signal consists of the transmitted signal plus additional undesirable voltage or current distortions, usually considered random, which tend to obscure the transmitted signal. All noise is interference, but not all interference is considered noise.

Noise Figure (NF)

The ratio of actual output noise to that which would remain if the device itself did not introduce noise. NF is a number by which the performance of a radio receiver can be specified.

P

Partial Mesh

A mesh arrangement in which every node is connected to multiple other nodes.

Passive Tag

A tag that does not contain its own source of power (battery).

Peer To Peer Communications

A communications system in which every handset can communicate with every other handset without the aid of the infrastructure in the mine.

Permissible

Refers to electrically operated equipment designed, constructed, and installed to ensure that such equipment will not cause a mine explosion or mine fire and, to the greatest extent possible, other accidents when used inby the last open crosscut of an entry.

Physical Communications Link

The path connecting one transmitter and one receiver through the interconnecting transmission media.

Point of Presence

An artificial demarcation point or interface point between communications entities.

Propagation

The process whereby an EM wave travels through a surrounding medium, losing energy as it travels.

Protocol

The set of standard rules for data representation, signaling, authentication, and error detection required to send information over a communications channel.

R

Radio

A device used by individuals for voice or text communications.

Radio Frequency

The range of frequencies within which radio waves are typically transmitted, roughly 3 kHz to about 300 GHz.

Radio Frequency Interference (RFI)

An unwanted disturbance that affects an electrical circuit due to electromagnetic radiation emitted from an external source. See also the definition for EMI.

Reader

A tracking system component that interrogates a tag.

Received Signal Strength Indicator (RSSI)

RSSI is a technique in which the strength of the RF signal received is used to determine the distance of the transmitter from the receiver.

Receiver

An electrical device designed to receive electromagnetic energy.

Redundancy

Redundancy involves the duplication of system functions to ensure that those functions will survive some level of damage to the system; in the context of communications systems, it is used to describe a system that can maintain communications with the surface when a single communication path is disrupted.

Redundant System

A system other than the normal operations system, designed to provide communications with the surface when the normal operations path is disrupted. A redundant system may be installed in a separate entry from the normal operating system provided that a failure in the normal operations system or path does not affect the redundant system or path.

Reliability (Basic)

Basic reliability is a measure of a system's ability to perform its functions without the need for repairs or adjustments. Basic reliability accounts for the time a system or component would be expected to operate without adjustments or repairs and only considers the reliability of the individual components; it does account for the arrangement of components (series versus parallel, for example).

Reliability (Operational)

The probability that a system can perform and complete its functions satisfactorily. The series or parallel arrangement of components is accounted for in this probability. For example, a redundant design reduces single points of failure and therefore raises the likelihood of the system completing its specified functions, raising the operational reliability.

Repeater

A device placed at intervals in a communications path to receive a signal and then re-transmit at a higher power than received.

Resolution

Tracking system resolution is the smallest change in a miner's location that can be detected or displayed.

Reverse RFID

An RFID system where the locations of tag and reader are reversed; the tags are located at fixed, known positions within the mine and each miner wears an RFID reader.

RFID

A system that uses radio waves to communicate identification information between a tag and a reader. In a coal mine tracking system, the tag is worn by the miner and readers are placed throughout the mine.

S

Scan Rate

The frequency with which a tracking system updates location data.

Secondary System

Secondary communications systems operate in non-conventional frequency bands, use large antennas that are best suited for fixed locations or portable applications, and do not have sufficient throughput for general operations. Examples are TTE or MF systems. (MF may perform as a primary system for a small mine.)

Self-Healing Mesh Architecture

A mesh network that automatically reconfigures itself if a node fails so that the maximum possible connectivity is maintained.

SHF System

System operating in the Super High Frequency range (3 GHz to 30 GHz).

Signal Propagation Characteristics

A technical description of the effects of the environment on the communications signal as it travels between devices.

Signal-to-Noise Ratio (SNR)

The ratio of a signal power to the noise power corrupting the signal. In less technical terms, signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise.

Single Communications Path Areas

Areas that do not have dual independent communications paths.

Spectrum

A range of electromagnetic waves.

Survivability

The measure of a system's ability to remain operational after an accident.

System

The working combination of communications or tracking components.

T

Tag

A component in an electronic location systems that transmits unique identification information via radio waves.

Thermal Noise

The electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage.

Thermal Runaway

A destructive process experienced by lithium chemistry batteries in which there is a chemical reaction producing a rapid increase in temperature leading to an intense fire and possibly an explosion.

Through-the-Earth System, TTE

A communications system that does not rely on any devices, wires, or structures between the transmitter and receiver.

Time Difference of Arrival (TDOA)

A tracking system method based on the propagation time between a tag and a reader.

Tracking Reporting Area

The area where the system is capable of receiving an active reading from the miner's tracking device.

Transceiver

A device that functions as both transmitter and receiver.

Transmission Line

A material structure forming a continuous conducting path from one place to another, directing the transmission of electromagnetic energy with a relatively low loss. The term transmission line includes essentially all types of cables. Examples are telephone lines, power cables, twin lead, coaxial cables, and other similar items.

Transmission Medium

The intervening substance through which electromagnetic waves travel.

Transmitter

An electrical device designed to radiate electromagnetic energy.

Two-Way Communications

The ability of the miner's handset to receive and transmit information.

U

UHF System

A system operating in the Ultra High Frequency range (300 to 3000 MHz).

Untethered

A device is considered untethered if there are no cables or wires connected to the device, i.e., cordless.

Uplink

Pertaining to the transmission path from a mobile station to the base station.

V

VHF system

A system operating in the Very High Frequency range (30 to 300 MHz).

W

Wave Length

The distance between two consecutive peaks of a wave.

Wi-Fi

Wireless Fidelity. The Wi-Fi Alliance (organization) owns the Wi-Fi (registered trademark) term and specifically defines Wi-Fi as any "wireless local area network (WLAN) products based on the IEEE 802.11 standards."

Wire Plant

The collection of conductors in a mine.

Wired System

Used to refer to systems whose components are connected using wires, cables, or fiber-optics. See also hardwired.

Wireless (Communications System)

A system that operates locally without wires.

Wireless Access Point (WAP)

In computer networking, a wireless access point (WAP) is a device that allows wireless communications devices to connect to a wireless network using Wi-Fi, Bluetooth, or related standards. The WAP usually connects to a wired network, and can relay data from wireless devices.

Wireless Local Area Network (WLAN)

A network in which the mobile user can connect to a local area network through a wireless connection. See Local Area Network (LAN).

Z

ZigBee

A specification for a suite of high level communications protocols using small, low-power digital radios based on the IEEE 802.15.4-2006 standard for wireless personal area networks (WPANs), such as wireless headphones connecting with cell phones via short-range radio.

Zone-Based RFID

See RFID.