On the Wireless Channel Characteristics of Outdoor-to-Indoor LTE Small Cells

We demonstrate a ray tracing framework to extract the three dimensional (3D) channel parameters as input to stochastic models in studying small cell environments, and investigate the dependency of the channel parameters on environmental characteristics, antenna patterns and frequency. We focus on Long Term Evolution (LTE) small cells, taking as reference outdoor small cells deployments providing services to indoor users. We present measurement results proving the feasibility of outdoor deployment of small cells for indoor coverage and validate the ray tracing framework with the available measurements. Many stochastic channel models treat the channel parameters in two dimensions and ignore the variation in the elevation plane. They are designed to capture the characteristics of macrocellular networks, where LTE base stations (eNBs) are placed hundreds of meters away from each other. In contrast, small cells are deployed much more closely to each other. The performance of small cells is highly dependent on 3D antenna patterns, the environment specific characteristics such as 3D geometry of the buildings, materials used for building construction and their specific propagation properties at different frequencies. Therefore, the site specific modeling of channel parameters in three dimensions is quintessential for small cell environments. We demonstrate ray tracing as an efficient technique to extract the 3D site-specific channel parameters pertaining to small cell environments, and to calibrate the stochastic models used with site specific channel parameters.