Advanced Compact 5G MIMO Base Station for Sub-6 GHz and Millimeter Wave Frequencies: Practical Implementation in Underground Mines

A novel compact 5G multiple-input-multiple-output (MIMO) base station (5G-BS) is introduced for enhancing communications in underground mine environments. The structure includes four identical mm-wave antenna arrays combined with two sub-6 GHz antennas. The four mm-wave antenna arrays are symmetrically arranged around the central axis and positioned 45° apart from one another, while the sub-6 GHz antennas are symmetrically placed in the top corners of the structure. The design is initially evaluated through laboratory measurements, achieving gains of 4.6 dBi in the sub-6 GHz band and 10.5 dBi in the mm-wave band, with an envelope correlation coefficient (ECC) of less than 0.028. Additionally, the effectiveness of the design is validated through experimental measurements including: path loss, time dispersion and coherence bandwidth along with channel capacity evaluation, which have been conducted in real world underground mine using the proposed base station. Thanks to its simplicity and compact design, the array structure is a strong candidate for underground mine communications, capable of covering quad-band 5G frequencies (700 MHz, 3.5 GHz, 28 GHz, and 38 GHz).