Multiple-input multiple-output beam-space for high-speed wireless communication in underground mine

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 x 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.