# Interference Analysis for Vehicle-to-Vehicle Communications at 28 GHz
## 1 Introduction  
In recent years, vehicle-to-everything (V2X) communication has gained huge interest due to its ability to improve road safety and reduce the number of accidents [1]. The V2X communications generally refer to the exchange of information among different intelligent transportation systems (ITS) such as traffic safety, automated driving, and infotainment. It can be further subdivided into vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-person (V2P) and vehicle-to-network (V2N) communication. Many efforts have been carried out to enable vehicular communication and the first of them was to allocate a dedicated 75 MHz spectrum by the United States Federal Communications Commission (FCC) [2] and 30  MHz by European Telecommunications Standards Institute (ETSI) [3] at 5.9 GHz.  
Several communication technologies have already been developed to operate in 5.9 GHz band such as IEEE 802.11p [4] and Long-Term Evolution (LTE)-V2V [5]. However, the available spectrum is not enough for emerging V2X applications where high data rates are required, such as sharing cameras and Light Detection and Ranging(LIDARs) information [6; 7; 8]. Therefore, to offload traffic millimeter wave bands (mmWave), where more bandwidth is available, is being considered [6]. Many measurement campaigns have been carried out in the framework of some European Projects such asDRIVE and PROMETHEUS [9] at mmWave. In this perspective, various requirements and use-cases are being considered with reference to both highway and urban applications [10]. In an urban scenario, vehicles can exchange information with the infrastructure and can collect data from other vehicles to generate information regarding traffic congestion and parking reservations, etc. [11].  
The mmWave spectrum offers several advantages. First, large available channel bandwidth (e.g., 400 MHz per channel as defined in 5G New Radio (NR)) [12; 13]. Second, due to smaller wavelengths at mmWave frequencies, it is possible to design a large number of antennas; therefore, directional beamforming is possible to boost the received signal power and reduce the impact of out-of-cell interference [14]. A large number of antennas enable the use of multiple-input multiple-output (MIMO) communication which further improves spectral efficiency. Overall higher network capacity is expected in the mm-wave band [15; 16].  
However, the mmWave band suffers from high path loss due to the higher order of frequencies which reduces the coverage area. Moreover, the Doppler shift is directly proportional to the carrier frequency and speed of the moving vehicle [17]. Doppler shift introduces inter-carrier-interference (ICI) in OFDM systems which could be potential limitations in enabling V2V communication [18]. In addition, signals at higher frequencies cannot penetrate from most solid materials such as walls. As a result, the movement of reflectors and obstacles, or even the orientation of UE can cause the channel to appear and disappear [19; 20; 21]. The wireless channel behavior at mmWave is totally different from the lower bands; hence, dedicated approaches are required to model the performance of a communication system.