Experimental Characterization of Ultra-Wideband Channel Parameter Measurements in an Underground Mine

Hindawi Publishing Corporation Journal of Computer Networks and Communications Volume 2011, Article ID 157596, 7 pages doi:10.1155/2011/157596 Research Article Experimental Characterization of Ultra-Wideband Channel Parameter Measurements in an Underground Mine B. Nkakanou, G. Y. Delisle, and N. Hakem LRTCS-UQAT, 450 3eme Avenue Local 105, Val-d’Or, QC, Canada J9P1S2 Correspondence should be addressed to B. Nkakanou, Received 6 May 2011; Accepted 25 August 2011 Academic Editor: Mohamed El-Tanany Copyright © 2011 B. Nkakanou et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Experimental results for an ultra-wideband (UWB) channel parameters in an underground mining environment over a frequency range of 3 GHz to 10 GHz are reported. The measurements were taken both in LOS and NLOS cases in two different size mine galleries. In the NLOS case, results were acquired for different corridor obstruction angles. The results were obtained during an extensive measurement campaign in the UWB frequency, and the measurement procedure allows both the large- and small-scale parameters such as the path loss exponent, coherence bandwidth, and so forth, to be quantified. The capacity of the UWB channel as a function of the physical depth of the mine gallery has also been recorded for comparison purposes. 1. Introduction Ultra-wideband (UWB) radio is a technology that has attracted a great deal of interest from academia, industry, and global standardization bodies over the recent years. The FCCs are defined as UWB signals having 10 dB bandwidth greater than 25% of their center frequencies of the radiation [1]. Ultra-wideband is a wireless technology that has offered many advantages, mainly the high-speed data transmissions, short-duration pulse, low-power spectral density, and large instantaneous bandwidth. Theses specifications allow coexistence with other existing technologies and enable fine time resolution. Many studies have shown that UWB is a good candidate for short-range multiple-access communications in dense multipath environments [2–4]. The potential of UWB system provides the following features: multiple accesses due to wide transmission bandwidths, accurate position location and ranging, lack of significant multipath fading due to fine delay resolution, and protected communications due to low transmission power. In order to establish a suitable model for the ultrawideband channel behavior which is used when designing WB communications systems to support applications in underground mine environment, it is then important to have a thorough understanding of the propagation channel constraints. In recent years, several measurement campaigns to characterize the mining channel were conducted by the Télébec Underground Communications Research Laboratory (LRTCS) located in the mining area of Val-d’Or, QC, Canada [5, 6]. This laboratory, specialized in complex confined area communication, has at its disposal a unique experimental mine (CANMET-Canadian Centre for Minerals and Energy Technology). Characterization of channel propagation in underground environments has been an area of research since many years, but these studies have been carried out almost exclusively in tunnels. Also, many propagation measurements have been carried out for indoor narrowband propagation channels, and several models have been proposed in the literature [5– 7]. However, due to their restricted measurement bandwidth, they were inappropriate for the UWB systems. Similarly, UWB measurements and characterization of channels in indoor and outdoor environments [8–11] have been also performed in that type of environment. However, despite these various research efforts, there is still a significant lack of information about propagation characteristics of UWB systems in a confined environment. The objectives of this paper are to present measurements and characterization of ultra-wideband (UWB) propagation in an underground mining environment and to detail the experimental procedures and measurement setup used to collect the data. Experimental procedures and locations 2 Journal of Computer Networks and Communications where the measurements were carried out are reported with full detail; then, the postprocessing of the acquired data is explained. Finally, the results pertaining to the signal quality, small-scale effects, large-scale path loss exponents, time dispersion parameters, and capacity are discussed. Some sitespecific trends and observations are described, and channel performances for two types of directive and omnidirectional antennas are compared. The paper is organized as follows. In Section 2, the mining environment and measurement setup are presented. In Section 3, relevant channel parameters are presented based on the measurements. Section 4 presents the conclusions. 1 cm 2. Measurement System x = 10 m Intensive measurements were carried out in underground galleries of a former gold mine at CANMET in Val-d’Or, QC, Canada. The measurements were conducted at two levels (40 m and 70 m) in the mine. The purpose of these measurements was to achieve a characterization of the two propagation channels based on statistical analysis and modelling of the channel’s impulse response. The measurements were taken in both line of sight (LOS) and non-line of sight (NLOS) scenarios. The measurements were taken between 1 m and 10 m in LOS and in NLOS cases at regular interval of 1 m. A description of measurement plan is described in Figure 1. 2.1. Measurement Plan. The goal of the measurements was to investigate the small- and large-scale variations in the statistics of the channel. Large-scale variations are due to high antenna separation changes, one meter, for instance, where small-scale variations indicate changes in statistics when the moving antenna position changes by a few centimeters. The environment mainly consists of very rough walls; the floor is uneven, and there are some puddles of water mainly at level 70. Figure 1 illustrates the map of the gallery with all its adjacent galleries at level 70. At level 70, the dimensions of the mine corridors are approximately 2.5 m in width and 3 m in height (Figure 2). The gallery walls are somewhat discontinuous, and the lengths of the galleries used for the experimentation are approximately 80 meters in length for level 70 and 100 meters at level 40. In NLOS case, measurements at different angles of obstruction were taken. At level 40, the dimensions of the mine corridors are 4 m in width and approximately 5 m in height. This gallery is broader and higher than the one at level 70, and the floor slope is about 15 degrees. 2.2. Measurements. A vector network analyzer (VNA) is measurement equipment which can measure scattering parameters or S-parameters, which gives both the amplitude and phase (...truncated)