Near-Ground Propagation Channel Modeling and Analysis in Underground Mining Environment at 2.4 GHz

This paper presents a detailed measurement and performance analysis of near-ground propagation channels in an underground mine for both Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) scenarios. The analysis is derived from channel measurements conducted at a frequency of 2.4 GHz with a bandwidth of 200 MHz, utilizing four different combinations of transmitter-receiver (Tx-Rx) antenna heights ranging from 10 cm to 120 cm. Key channel characteristics such as large-scale path loss, time dispersion, and coherence bandwidth are reported and evaluated. The study suggests that a multi-slope (four-slope) path loss model is more effective in predicting path loss across various propagation segments in the mining environment. The path loss coefficient (n) and shadowing variance $(\sigma)$ show significant sensitivity to both the Tx-Rx distance and the heights of the Tx-Rx antennas, while the root mean square delay spread $(\tau _{\mathrm { rms}})$ and coherence bandwidth (BC) are less affected by these variables. Moreover, distinct path loss patterns are observed for each combination of Tx-Rx antenna heights, resulting in varying signal attenuation levels. The identification of an optimal height for minimizing signal loss is thus required. These observations provide valuable and crucial insights into the near-ground propagation characteristics within the intricate and scattering-rich conditions of underground mines.