# A Non-WSSUS Channel Simulator for V2X Communication Systems
## 1 Introduction
Despite recent technological and standardization advances, vehicular communications still present important challenges due to the propagation environment and the station's high mobility [16; 17; 18]. For this reason, the development of simulation tools that lend themselves to the design, testing, and optimization of V2X communication systems has become a crucial research area. These simulation tools must reproduce the propagation conditions that are observed in vehicular wireless channels to allow the identification of factors that affect the performance of the communication system. Such propagation conditions are simulated following reference channel models that consider particular aspects of the propagation environment, such as multipath interactions, small-scale fading, and shadowing [16; 17]. Nonetheless, the applicability of the simulation tools should not be restricted to a particular environment. In fact, a flexible channel simulator allows gaining insight into different communication environments and also supports realistic application-related scenarios, e.g., for collision avoidance [16]. The flexibility of the simulator might also enable emulating data transmission under different protocols, such that one can evaluate the system performance considering various sets of specifications for V2X communication technologies. A variety of channel simulators has been proposed for vehicular communications. Some of them are based on the wide sense stationary uncorrelated scattering (WSSUS) assumption that is often invoked for the simulation of traditional fixed-to-mobile (F2M) cellular communication channels [19; 20; 21]. However, recent empirical findings have demonstrated that the WSSUS condition [22] is not satisfied in vehicular environments [23; 24; 25]. For this reason, several non-WSSUS V2V channel simulators have also been developed in the literature [26; 27; 28; 29]. Some of these non-WSSUS channel simulators take as input the geometric structure and physical properties of the propagation environment and follow the principles of ray tracing simulation to compute the channel impulse response (CIR). These simulators provide a good approximation to the response of real-world channels, but they require a high amount of computational resources to reproduce the propagation conditions by considering the physical properties and the location of interfering objects (IOs). Therefore, these tools are not easily scalable to support system-level simulations that allow the evaluation of the system's performance. Time-delay filter models are another approach to simulate the vehicular channel [27; 28; 29]. In this approach, both the amplitude and phase of each filter coefficient are modeled using a correlation matrix. Nonetheless, these simulators are not straightforward to reconfigure to different scenarios of interest. This paper presents a non-WSSUS V2X channel simulator for the performance evaluation of V2X communication systems. Such a simulator is based on the combination of the Monte Carlo and sum-of-cisoids (SOC) principles [30]. This tool is intended for V2X communication systems based on multicarrier techniques where the information is transmitted in frames, such as the DSRC and cellular-based V2X (C-V2X) systems. The simulator is based on a reference V2X channel model that allows velocity variations and non-linear trajectories of the mobile stations (MSs) [31]. Furthermore, this reference model provides information about the time and frequency (TF) correlation properties of non-WSSUS channels under arbitrary isotropic and non-isotropic scattering conditions. To exemplify the practical value of the proposed simulator, we present a bit error rate (BER) performance analysis of two channel estimation techniques that are considered for IEEE 802.11p transceivers: the least squares (LS) estimator, and the spectral temporal averaging (STA) technique [32]. Our results show that the performance of the LS estimator decreases whenever the relative speed of the MSs or the frame length increases.