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This study reveals the interests towards the use of directional (D)-multiple-input and multiple-output (MIMO) setup as a potential solution to overcome the severe propagation loss of inherent line of sight (LOS) mm-waves communications in underground mine. To show the advantages of the proposed D-MIMO, two separate measurement campaigns are assessed in a comparative way; the first uses a single-input single-output (SISO), while the second uses a 2 × 2 D-MIMO system. Furthermore, due to the unavoidable blockage of direct LOS in underground mines, the miner's shadowing effects (NLOS-MSE) are investigated. Thus, using both D-SISO and D-MIMO setup, the channel propagation characteristics are extracted and investigated with and without the presence of a miner completely blocking LOS. Under LOS, results show that, besides offering a reliable mm-waves link budget, D-MIMO restrains the average path loss (PL) by more than 4.7 dB, further suppresses the root mean square delay to 1.85 ns and offers an average capacity of 23.3 bits/s/Hz. As a miner completely blocks LOS, the proposed D-MIMO system has shown a greater signal ability to overcome the effects of a miner's body; NLOS-MSE compensation of about 4.3 dB and a capacity gain of 19.6 bits/s/Hz have been achieved over the conventional SISO system. [ABSTRACT FROM AUTHOR]

This study presents a new low-cost multiple-input multiple-output (MIMO) beam-pace technique to increase the overall link capacity of wireless MIMO communications systems in scatter-rich underground mines. This technique is based on generating multiple orthogonal beams for data spatial multiplexing using conformal cylindrical-shape patch arrays. Hence, this study is intended to reveal interests towards the use of conformal MIMO systems for underground mine communications. Two separate 4 × 4 MIMO measurement campaigns are performed and then investigated in a comparative way; the first uses conformal microstrip patch arrays (CMPA), while the second uses conventional planar microstrip patch arrays (PMPA). Based on sweeping-frequency technique (2.35-2.55) GHz, the channel performance is characterised in terms of path loss, fading distribution, capacity and RMS time dispersion parameters. Whether under a line of sight (LOS) or a non-LOS (NLOS) condition, the extracted results confirm the performance priority of CMPA for underground mines communications as they further enhance the propagation characteristics and the capacity gain of the channel; under NLOS, a maximal capacity of 12.95 bits/s/Hz is achieved compared to 9.6 bits/s/Hz obtained using PMPA. For LOS and NLOS cases, maximal capacity boosts of up to 0.43 and 3.35 bits/s/Hz are achieved over PMPA, respectively. [ABSTRACT FROM AUTHOR]