# Deterministic Propagation Modeling for Intelligent Vehicle Communication in Smart Cities
## 1 Introduction
Some of V2I applications reported in the Transit Vehicle-to-Infrastructure (V2I) Assessment Study [16] are: Transit Vehicle-Pedestrian/ Cyclist Crossing Warning, Transit Stop/Station Pedestrian Safety, Transit Vehicle and Center Data Exchange Application, Transit Traveler Information Infrastructure Application, Red Light Violation Warning (RLVW), Left Turn Assist (LTA), Stop Sign Violation Warning (SSVW), Reduced Speed Zone Warning (RSZW), Pedestrian in Signalized Crosswalk Warning (PCW) etc. A proposed application aimed at assisting transit vehicle maneuvers and detours to handle special events at strategic locations to perform dynamic information collection/disemination, is the V2I Portable Infrastructure which features the concept of portable infrastructure such as portable RSUs and signage. The design of accurate propagation models for realistic V2I enabling must take into account some unique characteristics in terms of antenna heights, placement of the RSUs, environment type (e.g., urban, suburban, highway) and specific considerations for small-scale fading due to particular location of antennas [17]. Urban environments are characterized by the combination of different object types such as buildings, vehicles, pedestrians, vegetation etc., as well as their number, size, and density, that have a profound impact on radio propagation [18]. Some propagation impairments such as reflection from, diffraction around and transmission loss through objects (influence of vegetation, building entry loss, cars, trees, pedestrians, etc. ), and external environment, give rise to issues such as Quasi-Line-of-Sight (QLoS), Non-Line-of-Sight (NloS), temporal and spatial variation of path loss and multipath effects from reflected and diffracted components of the wave. The rapid changes in radio propagation conditions are one of the main challenges for channel modelling in vehicular communications. Channel modeling approaches can be roughly classified into four categories [19]: (1) empirical (they require calibration but offer rapid results); (2) stochastic (characterize the channel from a frequency selection perspective); (3) geometry-based stochastic (commonly used for propagation prediction in mobile communication); and (4) deterministic (used in propagation prediction of specific environments). While stochastic and geometry-based stochastic could fail to characterize significant surrounding obstacles (foliage, lamppost, pedestrians, etc.) and V2I empirical tests provide useful insight for specific in situ scenarios [20], the deterministic ray launching simulators are suited for vehicular propagation analysis of large-size scenarios yielding a reasonable tradeoff between accuracy and computational cost. The principle of ray launching approaches is that a consistent number of path rays follows from the transmitter to the receiver over the direct, reflected and diffracted rays. Some current state-of-the art simulators focus mainly on V2V or V2I communications operating in a cellular sense and, although the literature includes many propagation models and channel simulators for V2V systems [21; 22], there is a need for further studies to investigate V2I propagation using 3D deterministic tools in complex environments such as urban ones. In this work, an in-house 3D Ray-Launching (3D-RL) algorithm (hybrid deterministic method) based on Geometrical Optics (GO), Geometrical Theory of Diffraction (GTD) and its extension the Uniform Theory of Diffraction (UTD) has been used to analyze the large-scale and small-scale signal propagation phenomena, which includes the analysis of Doppler Shift and Doppler Spread as time-changing statistics of the V2I channel in a three-dimensional (3D) urban scenario.