Wireless networks can greatly facilitate the communication in underground mines and road/subway tunnels, where the propagation characteristics of electromagnetic (EM) waves are significantly different from those in terrestrial environments. According to the structure of underground mines and road tunnels, two types of channel models can be utilized, namely, tunnel and room/pillar channel models. However, there exists no theoretical model for room-and-pillar channel in underground mines to date, and current existing tunnel channel models do not provide an analytical solution for both near and far regions of the sources. In this paper, the multimode model is proposed, which provides an analytical expression for the received power and the power delay profile at any position in a tunnel.Moreover, the multimode model is extended to characterize the room-and-pillar channel in the underground mines after combining it with the shadow fading model. The theoretical models are validated by experimental measurements. Based on the proposed channel models, the effects of various factors on the signal propagation are analyzed. The factors include: the operating frequency, the size of the tunnel or underground mine room, the antenna position and polarization, and the electrical parameters.

https://www.researchgate.net/profile/Ian_Akyildiz/publication/224142283_Channel_modeling_and_analysis_for_wireless_networks_in_underground_mines_and_road_tunnels/links/54086b710cf2bba34c285fe1.pdf

Channel modeling and analysis for wireless networks in underground mines and road tunnels

Mining and mineral exploration play important roles in the global economy. In mining operations, communication systems play vital roles in ensuring personnel safety, enhancing operational efficiency and process optimization. Over the period 1920-2012, this article surveys the evolution of wireless communications in underground mines, the developments of the underlying technology, and progress in understanding and modeling the underground wireless propagation channel. Current and future trends in technology, applications and propagation modeling are also identified. About ninety relevant references have been reviewed that consider: 1) the emergence of technology and applications, 2) analytical, numerical and measurement-based propagation modeling techniques, and 3) implications of the physical environment, antenna placement and radiation characteristics on wireless communication system design. Affected systems include narrowband, wideband/ultra-wideband (UWB) and multiple-antenna systems. The paper concludes by identifying open areas of research.

A Survey of Wireless Communications and Propagation Modeling in Underground Mines

After a recent series of unfortunate underground mining disasters, the vital importance of communications for underground mining is underlined one more time. Establishing reliable communication is a very difficult task for underground mining due to the extreme environmental conditions. Until now, no single communication system exists which can solve all of the problems and difficulties encountered in underground mine communications. However, combining research with previous experiences might help existing systems improve, if not completely solve all of the problems. In this survey, underground mine communication is investigated. Major issues which underground mine communication systems must take into account are discussed. Communication types, methods, and their significance are presented.

Underground Mine Communications: A Survey

Results are presented on wideband radio propagation measurements and statistical modeling at 2.4 GHz and 5.8 GHz in real underground mine tunnels. This peculiar type of confined environment is characterized by very rough surfaces and a frequent absence of a line-of-sight between transmitting and receiving antennas. The resulting propagation characteristics differ from those frequently encountered in more typical indoor environments such as offices and corridors. Indeed, the rms delay spread shows little or no correlation with respect to transmitter-receiver distance and, in addition, no impulse response path arrival clustering effect is observed. However, the path amplitude distribution does tend to follow a Rice distribution in the line-of-sight case, and a Rayleigh distribution otherwise.

Radio Wave Characterization and Modeling in Underground Mine Tunnels

This paper presents comprehensive experimental results obtained from narrowband and wideband radio-channel measurements in an underground mine with narrow veins at 2.4 GHz. From continuous-wave (CW) measurement data, large-scale distance-power curves and path-loss exponents of the environment are determined. Other relevant parameters, such as the mean excess delay, the maximum excess delay, the root-mean-square (rms) delay spread, and the coherence bandwidth are extracted from the wideband-measurement data. Results show a propagation behavior that is specific for these underground environments with rough surfaces. The rms delay spread does not follow a dual-slope relation with respect to distance, as in environments with smooth surfaces. Moreover, the dependence of the rms delay spread on the bidimensional position of the user is found to be very significant. For the majority of locations, the rms delay-spread values are less than 60 ns.

Radio-channel characterization of an underground mine at 2.4 GHz

For ptI seeibid vol46, no9, p1328, (1998)The uniform theory of diffraction (UTD) developed in part 1 is used to predict narrow- and wide-band propagation characteristics in tunnels at 900- and 1800-MHz Narrow-band propagation characteristics is shown in the spatial domain and wide-band propagation in the time domain In empty straight-tunnel environments, propagation exhibits a break-point phenomenon and has very short time delay spread In empty curved or branched tunnel environments, propagation suffers higher loss Vehicles cause additional propagation loss and larger varying time delay spread in tunnels The measured results have validated the accuracy of the theoretical model and provided important information on narrow-band and wide-band propagation characteristics in empty, branched and obstructed tunnels

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R.G. Kouyoumjian

Papers

Ray-optical prediction of radio-wave propagation characteristics in tunnel environments. 2. Analysis and measurements