# Experimental Demonstration of MmWave Vehicle-to-Vehicle Communications Using IEEE 802.11 ad
## 1 Introduction  
Various 5G wireless technologies were standardized and developed by academia and industries related to the field of telecommunications, and are now ready to be deployed with several key features such as enhanced mobile broadband (eMBB), ultra reliable low latency communications (URLLC), etc. A new radio for the 5G wireless networks is expected to use various radio frequencies, above or below 6 GHz. As compared to the 28, 60, and 73 GHz spectrum, the frequencies near the 3 GHz spectrum receive considerable attention from service providers because the millimeter Wave (mmWave) suffers from significant pathloss and link blockage caused by obstacles (e.g., buildings, vehicles and human beings) owing to severe penetration loss and reflection. However, it is advantageous to still consider the mmWave spectrum to obtain several hundred mega-hertz (MHz) of bandwidth because of the scarcity of spectrumbelow 6 GHz. Thus, measurement campaigns and demonstrations of mmWave communications have been conducted in real testbeds [1; 2; 3]. Subsequently, mmWave channel models are established based on these measurement results [4; 5; 6; 7]. The 5G era has reserved the development of various applications and services for the near future as they require gigabit data rate, fast response (less than 1 ms for end-to-end delay), and massive connections. One such interesting application is vehicular communication for autonomous driving and in-vehicle infotainment. Autonomous driving systems primarily rely on sensor devices equipped on vehicles, such as LiDAR, near-medium range radar, long-range radar (LRR) and cameras. However, communications between vehicles or a vehicle and an infrastructure such as a road-side unit (RSU) are essential to control a fleet of vehicles to avoid chain-reaction crashes instead of controlling individual cars. Moreover, an autonomous vehicle has rich data, such as high-resolution video (e.g., UHD 4K) from dash cameras, which can be used to improve vehicle control precisely. For instance, the curvature recognition of the road in front of the vehicle can be improved from 30 m to 50 m in distance ahead if using 2 MP instead of 0.3 MP data [8]. In the last decade, dedicated short-range communications (DSRC) and IEEE 802.11p/wireless access in vehicular environment (WAVE) standards have guided vehicle-to-vehicle (V2V) communications, which enables vehicles to exchange safety messages to alarm or notify vehicle status and infotainment data using a 10 MHz bandwidth channel that supports up to 27 Mbps data rate. Further, the third generation partnership program (3 GPP) introduced long-term evolution (LTE) based vehicle to infrastructure (V2I) communication and device-to-device (D2D) communication for the V2V communication. However, neither technologies is sufficient to transmit the increasing sensor data of future smart cars. Accordingly, 3 GPP [9] is developing a new standard applying the 5G radio (e.g., mmWave) to vehicular communications in Release 19. Recently, various academic studies on mmWave-based vehicle-to-everything (V2X) communications were conducted. Practical mmWave vehicular testbeds have been built to evaluate the performance of V2I or V2V [10; 11]. Moreover, the channel models of the V2X communications are exploited in [12; 13; 14; 15] and several ideas to reduce beam alignment and training overhead are proposed in [16; 17; 18; 19]. The problems of mmWave beam alignment and width selection to reduce interference among vehicles are solved by a distributed algorithm in [20; 21; 22]. [PERSON] [8] proposed a channel assignment algorithm for mmWave V2V beams to avoid reciprocal beam interference. The IEEE 802.11 ad standard, also known as the Wireless Gigabit Alliance (WiGig), which specifies the physical and link layers for mmWave communications, was released approximately a decade ago to provide a gigabit connection between proximate devices. The WiGig uses a 60 GHz mmWave spectrum and supports more than 4 Gbps data rate with 2 GHz channel bandwidth.