I. Introduction
The radio wave propagation environment needs to be accurately predicted when designing and selecting base stations for mobile communication systems to achieve high-speed communication. Empirical and deterministic models are two typical methods used to predict radio wave propagation [1]. The empirical model is obtained by statistically processing and formulating the measurement data, whose examples include the Okumura-Hata model [2] and the Walfisch-Ikegami model [3], [4]. On the other hand, a deterministic model is used to estimate radio propagation characteristics on the basis of electromagnetic field theory, such as the finite-difference time-domain (FDTD) method [5] and ray tracing method [6], [7].