Ronald Jacksha

RF Propagation in Mines and Tunnels: Extensive measurements for vertically, horizontally, and cross-polarized signals in mines and tunnels.

This article reports measurement results on radiofrequency (RF) propagation in tunnels and mines for vertically, horizontally, and cross-polarized signals. Extensive measurements have been made in concrete tunnels, coal mines with rock dust and shotcrete, with and without conductive mesh, and hard-rock mines. The measurements include power attenuation over distances with and without line of sight (LOS) at four frequencies (455, 915, 2,450, and 5,800 MHz) that are common to underground radios, as well as swept wideband-frequency measurements from 30 MHz to 1 GHz at fixed separation distances to investigate the attenuation behavior as the waveguide cutoff frequency is approached. In addition, power loss associated with radio propagation around a 90? corner was measured for the four frequencies and two polarizations in an operational coal mine.

Modeling RF propagation in tunnels

As mandated by the 2006 Mine Improvement and New Emergency Response (MINER) Act, many underground coal mines have installed UHF radio systems to provide communications between personnel on the surface and underground. In an effort to better understand UHF signal propagation in tunnel environments, we made radio signal attenuation measurements in concrete tunnels at frequencies of 455 MHz, 915 MHz, 2.45 GHz, and 5.8 GHz. In this paper, a ray tracing method is used to model the channel. Although the tunnel has an arched roof, the model describes the propagation behavior very well using a rectangular tunnel with the same width. The measured data verify the ability of the ray tracing model to predict radio frequency propagation at all the four frequencies. In addition, the propagation constants for the different frequencies are investigated and shown to be consistent with the measured values.

Modeling and measurement of the influence of antenna transversal location on tunnel propagation

The ray tracing and modal methods are applied to model the influence of antenna location (within the tunnel cross section) on tunnel propagation. Measurement results in a railroad tunnel are provided to validate the models. Simulation results are shown to agree with measurement results well. Both simulation and measurement results suggest that more receive power can be obtained by placing the transmitter or receiver antenna close to the center location of the tunnel cross section.

Measurement of RF propagation in tunnels

Radio signal propagation in tunnels exhibits significant differences from outdoor or indoor multipath environments (radio signals reflected off walls, floors, or other objects). This research measures the propagation of UHF/SHF radio signals from 455 MHz up to 5.8 GHz in frequency bands commonly used for underground wireless communications and electronic tracking. The paper focuses on the experimental methods used to collect vertically and horizontally polarized signal propagation data in tunnels as a function of separation distance between the transmitter and receiver antennas, and presents measurement results. The data show the dependence of the propagation characteristics on frequency, polarization, and tunnel dimensions.

Modeling and measurement of wireless channels for underground mines

This paper investigates wireless channel modeling for underground mines. The ray tracing and modal methods, which have been widely used for modeling radio propagation in tunnels, are applied to model wireless channels in underground mines. In addition, propagation measurements are taken in an underground hard rock mine at three different frequencies (455 MHz, 915 MHz, and 2.45 GHz). Simulation results based on the ray tracing and modal methods are compared to measurement results and show agreement. Challenges for modeling wireless channels in mines are discussed.

Time Domain and Frequency Domain Deterministic Channel Modeling for Tunnel/Mining Environments

Understanding wireless channels in complex mining environments is critical for designing optimized wireless systems operated in these environments. In this paper, we propose two physics-based, deterministic ultra-wideband (UWB) channel models for characterizing wireless channels in mining/tunnel environments - one in the time domain and the other in the frequency domain. For the time domain model, a general Channel Impulse Response (CIR) is derived and the result is expressed in the classic UWB tapped delay line model. The derived time domain channel model takes into account major propagation controlling factors including tunnel or entry dimensions, frequency, polarization, electrical properties of the four tunnel walls, and transmitter and receiver locations. For the frequency domain model, a complex channel transfer function is derived analytically. Based on the proposed physics-based deterministic channel models, channel parameters such as delay spread, multipath component number, and angular spread are analyzed. It is found that, despite the presence of heavy multipath, both channel delay spread and angular spread for tunnel environments are relatively smaller compared to that of typical indoor environments. The results and findings in this paper have application in the design and deployment of wireless systems in underground mining environments.

Measurement and modeling of radio propagation from a primary tunnel to cross junctions

In this paper, we propose a new model for predicting around-corner coupling loss associated with radio signals propagating from a primary tunnel to cross junctions. The proposed model is based on the classic modal method that has been widely used for predicting power distribution in straight tunnels. The uniform theory of diffraction (UTD) is applied to calculate mode coupling coefficients. Simulation results based on the proposed model are compared to measurement results taken in a concrete tunnel and show good agreement.