Mm‐waves propagation measurements in underground mine using directional MIMO antennas

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