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Automated driving is now possible in diverse road and traffic conditions. However, there are still situations that automated vehicles cannot handle safely and efficiently. In this case, a Transition of Control (ToC) is necessary so that the driver takes control of the driving. Executing a ToC requires the driver to get full situation awareness of the driving environment. If the driver fails to get back the control in a limited time, a Minimum Risk Maneuver (MRM) is executed to bring the vehicle into a safe state (e.g., decelerating to full stop). The execution of ToCs requires some time and can cause traffic disruption and safety risks that increase if several vehicles execute ToCs/MRMs at similar times and in the same area. This study proposes to use novel C-ITS traffic management measures where the infrastructure exploits V2X communications to assist Connected and Automated Vehicles (CAVs) in the execution of ToCs. The infrastructure can suggest a spatial distribution of ToCs, and inform vehicles of the locations where they could execute a safe stop in case of MRM. This paper reports the first field operational tests that validate the feasibility and quantify the benefits of the proposed infrastructure-assisted ToC and MRM management. The paper also presents the CAV and roadside infrastructure prototypes implemented and used in the trials. The conducted field trials demonstrate that infrastructure-assisted traffic management solutions can reduce safety risks and traffic disruptions. [ABSTRACT FROM AUTHOR]

The critical nature of vehicular communications requires their extensive testing and evaluation. Analytical models can represent an attractive and cost-effective approach for such evaluation if they can adequately model all underlying effects that impact the performance of vehicular communications. Several analytical models have been proposed to date to model vehicular communications based on the IEEE 802.11p (or DSRC) standard. However, existing models normally model in detail the MAC (Medium Access Control), and generally simplify the propagation and interference effects. This reduces their value as an alternative to evaluate the performance of vehicular communications. This paper addresses this gap, and presents new analytical models that accurately model the performance of vehicle-to-vehicle communications based on the IEEE 802.11p standard. The models jointly account for a detailed modeling of the propagation and interference effects, as well as the impact of the hidden terminal problem. The model quantifies the PDR (Packet Delivery Ratio) as a function of the distance between transmitter and receiver. The paper also presents new analytical models to quantify the probability of the four different types of packet errors in IEEE 802.11p. In addition, the paper presents the first analytical model capable to accurately estimate the Channel Busy Ratio (CBR) metric even under high channel load levels. All the analytical models are validated by means of simulation for a wide range of parameters, including traffic densities, packet transmission frequencies, transmission power levels, data rates and packet sizes. An implementation of the models is provided openly to facilitate their use by the community. [ABSTRACT FROM AUTHOR]

Future connected and automated driving applications can require larger bandwidth and higher data rates than currently supported by sub-6GHz V2X technologies (e.g., DSRC, ITS-G5 or C-V2X). This has triggered interest in developing mmWave vehicular communications. However, solutions are necessary to solve the challenges resulting from the use of high-frequency bands and the high mobility of vehicles. This article contributes to this active research area by proposing a sub- 6GHz assisted mmWave MAC that decouples the mmWave data and control planes. The proposal offloads mmWave MAC control functions to a sub-6GHz V2X technology. This approach improves the operation of the MAC as the control functions benefit from the longer range, and the broadcast and omnidirectional transmissions of sub-6GHz V2X technologies. This study demonstrates that the proposed sub-6GHz assisted mmWave MAC reduces the control overhead and delay, and increases the spatial sharing compared to mmWave communications using a configuration of IEEE 802.11ad tailored to vehicular networks. The proposed MAC is here evaluated for V2V communications using 802.11p for the control plane and 802.11ad for the data plane, although it can be adapted to other technologies such as C-V2X and 5G NR-V2X. [ABSTRACT FROM AUTHOR]

Cellular operators are facing considerable capacity and energy-efficiency challenges as cellular data traffic keeps rising. Several studies have shown that multihop cellular networks (MCNs) could help tackle these challenges through the integration of device-to-device (D2D) and cellular communications. This article demonstrates that significant energy- efficiency gains can be achieved when MCNs jointly exploit opportunistic networking and the traffic delay-tolerance characteristics of relevant mobile data services. [ABSTRACT FROM PUBLISHER]

Future wireless networks are expected to provide high bandwidth multimedia services in extended areas with homogeneous quality of service levels. Conventional cellular architectures might not be able to satisfy these requirements due to the effect of surrounding obstacles and the signal attenuation with distance, in particular under non-line-of-sight propagation conditions. Recent studies have investigated the potential of multihop cellular networks (MCNs) to overcome the traditional cellular architecture limitations through the integration of cellular and ad hoc networking technologies. However, these studies are generally analytical or simulation-based. On the other hand, this article reports the first experimental field tests, which validate and quantify the benefits MCNs using mobile relays can provide over traditional cellular systems. [ABSTRACT FROM PUBLISHER]