Configuration of multiple input multiple output antenna arrays for wireless communications in underground mines

In recent years, the underground mining community has begun to embrace standards-based short-range wireless communications technology as a key part of their strategy for enhancing the safety and productivity of their operations. Here, we show how the significant differences between wireless propagation in conventional surface environments and underground mines affect the design of modern wireless communications systems based upon multiple-input multiple-output (MIMO) antenna array technology. In order to achieve this goal, we have employed a variety of approaches to characterize wireless propagation (and MIMO-based wireless system performance) in underground environments representative of those found in modern hard rock mines, including: 1) field measurements collected using a custom-designed channel sounder in both a building service tunnel at the University of British Columbia and an underground lead-zinc mine at Myra Falls, BC, 2) simulations based upon ray-tracing in representative environments and 3) theoretical models based upon waveguide mode expansion in representative environments. We have used the results obtained: 1) to determine the reduction in the angular spread of multipath signals that arrive at the receiver in an underground mine compared to that observed in conventional surface environments and the manner in which it decreases with increasing transmitter-receiver separation and 2) to show that the antenna elements in MIMO antenna arrays used in underground environments must therefore be separated by several wavelengths (rather than the customary half-wavelength used in surface environments) in order to achieve acceptable performance. Further, the separation between the antennas must increase as the transmitter-receiver separation increases, higher order modes attenuate and, as a consequence, angular spread decreases. Other outcomes of this work include: 1) demonstration that the power azimuth spectrum (PAS) in underground mine environments can be modeled by a Gaussian distribution and 2) development of a novel technique based upon particle swarm optimization (PSO) for assessing and optimizing the performance of distributed-MIMO antenna systems in underground mine environments.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat