# A Non-WSSUS Channel Simulator for V2X Communication Systems
## 1 Introduction  
The worldwide growth of the vehicle fleet has caused high levels of pollution due to inefficient traffic control and increased concerns about the number of deaths and injuries from vehicular accidents. Intelligent transportation systems (ITSs) are a group of technologies that address these problems by managing vehicle operations and assisting drivers with safety and contextual information [1; 2]. ITSs require a wireless communication platform to keep a vehicle connected with other vehicles and with other elements on the road [3; 4; 5; 6; 7; 8; 9; 10]. The technical requirements of this vehicular communicationplatform are more stringent in terms of robustness and latency than those of traditional mobile cellular communications since road safety applications demand a timely transmission and processing of messages that help to bring the driver's awareness to potentially hazardous situations. Such applications aim to decrease the probability of traffic accidents by employing messages that include do-not-pass, emergency-brake, lane change, blind spot, and forward-collision warnings [5]. These warning messages carry information about the position, speed, and acceleration of the transmitting vehicle [4; 5], and they are continuously received by neighbor vehicles over a range of hundreds of meters. These safety applications, therefore, rely on direct communication platforms that enable information exchange over short distances. The dedicated short-range communications (DSRC) systems were the first vehicle-to-everything (V2X) communication technology specifically tailored for ITS applications [3; 4; 5; 6]. Both the Federal Communications Commission of the U.S. Government and the European Telecommunications Standards Institute have allocated frequency bands for DSRC operation in the 5.9 GHz spectrum. In addition, the Institute of Electrical and Electronics Engineers (IEEE) developed an amendment to the 802.11 standard for wireless local area networks (WLANs) to address DSRC in vehicular environments within the 5.9 GHz band. This set of specifications for the physical and medium access control layers of DSRC systems, which is known as the IEEE 802.11p standard [11], specifies the use of orthogonal frequency division multiplexing (OFDM) as the transmission scheme for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications [11]. With these specifications, the V2V and V2I information exchange can be accomplished for relative speeds up to 500 km/h. On the other hand, the Third-Generation Partnership Project (3 GPP) developed adjustments to the specifications of Long-Term Evolution (LTE) networks to enable V2X applications [8; 12]. The device-to-device (D2D) paradigm envisioned in LTE networks supports new use cases related to short-range V2X communications [7; 8; 9; 13]. Since Release 14, V2X data transmission is supported in LTE devices using two complementary modes: conventional network-based communication for interaction with the cloud, which is known as vehicle-to-network (V2N); and direct D2D communications for high-speed and low-latency V2V, V2I, and vehicle-to-pedestrian (V2P) links [14]. The latter mode is defined for short-range V2X communications employing a direct communications interface (PC5), which specifies the use of single carrier frequency division multiple access (SC-FDMA) as the transmission scheme and operates also in the 5.9 GHz ITS band [14]. Furthermore, 3 GPP has also been developing specifications for the upcoming fifth-generation (5G) mobile cellular networks to support V2X communications [15]. This new set of specifications, which started in Release 16, will extend the capabilities of the current LTE-based V2X (LTE-V2X) for new applications, such as autonomous vehicles. In this emerging technology, the 5.9 GHz ITS band is also considered to be exploited for D2D-based V2X applications using the PC5 interface [15].