As 5G communication technology develops, vehicular communications that require high reliability, low latency, and massive connectivity are drawing increasing interest from those in academia and industry. Due to these developing technologies, vehicular communication is not limited to vehicle components in the forms of Vehicle-to-Vehicle (V2V) or Vehicle-to-Infrastructure (V2I) networks, but has also been extended to connect with others, such as pedestrians and cellular users. Dedicated Short-Range Communications (DSRC) is the conventional vehicular communication standard for Intelligent Transportation Systems (ITS). More recently, the 3rd Generation Partnership Project introduced Cellular-Vehicle-to-Everything (C-V2X), a competitor to DSRC. Meanwhile, the Federal Communications Commission (FCC)issued a Notice of Proposed Rulemaking (NPRM) to consider deploying Unlicensed National Information Infrastructure (U-NII)devices in the ITS band with two interference mitigation approaches: Detect-and-Vacate (DAV)and Re-channelization (Re-CH). With multiple standard options and interference mitigation approaches, numerous regulatory taxonomies can be identified and notification of relevant technical challenges issued. However, these challenges are much broader than the current and future regulatory taxonomies pursued by the different countries involved. Because their plans differ, the technical and regulatory challenges vary. This paper presents a literature survey about the technical challenges, the current and future ITS band usage plans, and the major research testbeds for the U.S., Europe, China, Korea, and Japan. This survey shows that the most likely deployment taxonomies are (1) DSRC, C-V2X, and Wi-Fi with Re-CH; (2) DSRC and C-V2X with interoperation, and (3) C-V2X only. The most difficult technical challenge is the interoperability between the Wi-Fi-like DSRC and 4G LTE-like C-V2X.

Vehicular Ad-hoc Network (VANET) is an emerging technique dedicated to wireless vehicular communication to improve transportation safety by exchanging driving information between vehicles. For safety purposes, vehicles periodically broadcast a safety packet via Vehicle-to-Vehicle (V2V) communication. Accordingly, VANET safety applications demand a reliable exchange of the safety packet with high Packet Delivery Ratio (PDR), acceptable latency, and communication fairness. However, the communication performance significantly degrades due to numerous packet collisions when a large number of vehicles simultaneously access limited channel resources for the safety broadcast. In particular, the problem grows more severe in congested VANETs absent infrastructures since vehicles must control channel access using a self-adaptive scheme without external assistance. Thus, a robust and decentralized channel access protocol for VANETs is required to achieve road safety. In this paper, we propose an intelligent channel access algorithm empowered by cooperative Reinforcement Learning (RL), in which vehicles coordinate the channel access in a fully-decentralized manner. We also consider a proper interaction scheme between vehicles for enhancing the V2V safety broadcast in infrastructure-less congested VANETs. We provide evaluation results with extensive simulations according to various levels of traffic congestion. Simulations confirm the superior performance of the algorithm: the algorithm has a 20% increase in PDR compared to the latest RL-based channel access scheme. Furthermore, the algorithm satisfies the low latency requirement of VANET safety applications as well as both short-term and long-term communication fairness.

Despite the rapid development of wireless technology, there has been little application of the technology to improve railroad crossing safety. We present vehicle-to-railroad channel characterization and dedicated short range communications (DSRC) performance results at railroad crossings in rural and suburban environments. Our results show that an omnidirectional antenna provides slightly better performance in rural conditions. However, a bi-directional antenna increased warning range by more than 200 m in suburban conditions. A proper configuration of the DSRC radio provides reliable warning of an approaching train for cars near a railroad crossing.

Given the interest of researchers for wireless communications in electromagnetic (EM) shadow areas, a magnetic field communication has emerged to overcome RF challenges based on magnetic permeability characteristics. However, magnetic field communication has the demerit of a short communication range. Considering this limitation, we have proposed the GMI sensor-based field receiver to obtain immunity to low-frequency noise and high sensitivity for extension of communication range in previous studies. Further, this paper designs a magnetic field communication system with a GMI sensor-based receiver including a transmitter. Even though the basic concept of magnetic field communication is taken from previous studies, this study conducts the different realization of the system with transmitter system and communication link. Besides, this paper proposes the experiment of magnetic field communication using a GMI sensor-based system to verify its applicability in the practical environment for the first time. Bit error rate (BER), spurious-free dynamic range (SFDR), and random noise are measured with an on-off keying (OOK) communication link to analyze the stability and reliability of the system. The experimental verification and analysis entail the conditions of communication distance and channel medium to mimic practical communication in atmospheric, underwater, and underground environments. A comprehensive analysis of the system design and experimental verification for application in a practical environment show the possibility of the proposed system to realize improved wireless communications in EM shadow areas.

Although wireless technology is available for safety-critical applications, few applications have been used to improve train crossing safety. To prevent potential collisions between trains and vehicles, we present a Dedicated Short-Range Communication (DSRC)-enabled train safety communication system targeting passive crossings. Since our application’s purpose is preventing collisions between trains and vehicles, we present a method to calculate the minimum required warning time for head-to-head collision. We therefore define the best and worst-case scenarios and provide empirical data collected at six operating crossings in the U.S. with numerous system configurations, including modulation scheme, transmission power, antenna type, train speed, and vehicle braking distances. From our measurements, we find that the warning application coverage range is independent of the train speed, that the omnidirectional antenna with high transmission power is the best configuration for our system, and that the communications latency is less than 1 ms on average and around 5 m worst case. We use the radio communication coverage and introduce the safeness level metric to evaluate the suitability of DSRC for collision avoidance. From the measured data, we observe that the DSRC-enabled train safety communication system is feasible for up to 35 mph train speeds which is providing more than 25–30 s to avoid a collision for 25–65 mph vehicle speeds. Higher train speeds are expected to be safe, but additional data over extended distances are needed for a definite conclusion.