A refined ray tracing approach for wireless communications inside underground mines and metrorail tunnels

Underground mines and metrorail tunnels represent severe environments for the propagation of waves which is of interest for radio-frequency (RF) mapping and its analysis. Since the EM waves for various operations are frequently in the high-frequency domain, asymptotic ray-theoretic methods are often the most optimal choice for deterministic EM field analysis. Moreover RF field build-up inside a closed cavity like environment is an important aspect and they can be characterized using ray tracing approaches only if their shapes are close to canonical ones like semi circular or cylindrical. The ray tracing tends to become complicated for such concave hybrid enclosure. An accurate surface modeling is required towards refined ray-tracing procedure for predicting the ray-path description for the electromagnetic (EM) field distribution within the structure. In this paper, HF ray tracing techniques are implemented for two different applications such as underground mines and metrorail. The underground mine and metrorail tunnel are considered as a cylindrical tunnel of the required dimensions. Multiple transmitting sources are placed inside the designed concave structures which may be considered as the router positions for wireless LAN applications. A quasi-analytical HF ray-tracing technique is implemented in conjunction with analytical surface modeling. Multiple receivers are placed randomly inside the tunnel as well as in the metrorail and the ray propagation analysis is carried out. Unlike the available ray-tracing packages, that use numerical search methods, a quasi-analytical ray-propagation model is developed to obtain the ray-path details inside the cavity which involves the ray-launching, ray-bunching, and an adaptive cube for ray-reception.