Optimization of Antenna Placement in Distributed MIMO Systems for Underground Mines

Low angular spread of propagation environments and small interelement spacing within mobile terminals are two main factors degrading the capacity of multiple-input-multiple-output (MIMO) systems. This is particularly more evident in underground tunnels and mines that have lower angular spread compared to conventional environments. In such environments where colocated MIMO (C-MIMO) systems may not perform properly, we have shown that for access-point-to-mobile communications with limited and fixed antenna spacing at the mobile end, capacity close to that of an independent and identically distributed Rayleigh channel is achievable by employing distributed MIMO (D-MIMO) systems. To find and optimize C-MIMO and D-MIMO average capacities, we employed the waveguide-multimode model and particle-swarm-optimization method. We found that D-MIMO systems show desirable performance while significantly outperforming C-MIMO configurations. Nevertheless, D-MIMO desirable performance depends on the antennas' placement and is achievable for optimized locations. Based on the results, by uniformly distributing D-MIMO antennas along the tunnel axis and optimizing the transverse location of antennas afterward, suitable performance can be achieved. This paper is concluded by providing implications for D-MIMO antenna deployment in underground mines.