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Connected and fully automated vehicles are expected to revolutionize our mobility in the near future on a global scale, by significantly improving road safety, traffic efficiency, and traveling experience. Enhanced vehicular applications, such as cooperative sensing and maneuvering or vehicle platooning, heavily rely on direct connectivity among vehicles, which is enabled by sidelink communications. In order to set the ground for the core contribution of this paper, we first analyze the main streams of the cellular-vehicle-to-everything (C-V2X) technology evolution within the Third Generation Partnership Project (3GPP), with focus on the sidelink air interface. Then, we provide a comprehensive survey of the related literature, which is classified and critically dissected, considering both the Long-Term Evolution-based solutions and the 5G New Radio-based latest advancements that promise substantial improvements in terms of latency and reliability. The wide literature review is used as a basis to finally identify further challenges and perspectives, which may shape the C-V2X sidelink developments in the next-generation vehicles beyond 5G.

Connectivity and automation are increasingly getting importance in the automotive industry, which is observing a radical change from vehicles driven by humans to fully automated and remotely controlled ones. The test and validation of all the related devices and applications is thus becoming a crucial aspect; this is raising the interest on hardware-in-the-loop (HiL) platforms which reduce the need for complicated field trials, thus limiting the costs and delay added to the process. With reference to the test and validation of vehicle-to-everything (V2X) communications aspects, and assuming either sidelink LTE/5GV2X or IEEE 802.11p/bd technologies, in this work we focus on the real-time HiL simulation of the information exchanged by one vehicle under test and the surrounding, simulated, objects. Such exchange must be reproduced in a time-efficient manner, with elaborations done fast enough to allow testing the applications in real-time. More precisely, we discuss the simulation of nonideal positioning and channel propagation taking into account current impairments. We also provide details on optimization solutions that allowed us to trade-off minor loss in accuracy with a significant reduction of the computation time burden, reaching up to more than one order of magnitude speed increase in our experiments., The 2021 IEEE 93rd Vehicular Technology Conference: VTC2021-Spring

Recent advancements in vehicle-to-everything (V2X) communications have greatly increased the flexibility of the physical (PHY) and medium access control (MAC) layers. This increases the complexity when investigating the system from a network perspective to evaluate the performance of the supported applications. Such flexibility, in fact, needs to be taken into account through a cross-layer approach, which might lead to challenging evaluation processes. As an accurate simulation of the signals appears unfeasible, a typical solution is to rely on simple models for incorporating the PHY layer of the supported technologies based on off-line measurements or accurate link-level simulations. Such data are, however, limited to a subset of possible configurations, and extending them to others is costly when not even impossible. The goal of this paper is to develop a new approach for modeling the PHY layer of V2X communications that can be extended to a wide range of configurations without leading to extensive measurement or simulation campaigns at the link layer. In particular, given a scenario and starting from results in terms of the packet error rate (PER) vs. signal-to-interference-plus-noise ratio (SINR) related to a subset of possible configurations, we first approximated the curves with step functions characterized by a given SINR threshold, and we then derived one parameter, called implementation loss, that was used to obtain the SINR threshold and evaluate the network performance under any configuration in the same scenario. The proposed methodology, leading to a good trade-off among the complexity, generality, and accuracy of the performance evaluation process, was validated through extensive simulations with both IEEE 802.11p and LTE-V2X sidelink technologies in various scenarios. The results first show that the curves can be effectively approximated by using an SINR threshold, with a value corresponding to 0.5 PER, and then demonstrate that the network-level outputs derived from the proposed approach are very close to those obtained with complete curves, despite not being restricted to a few possible configurations.

In this article, we present CarLink, a new simulation platform with hardware-in-the-loop (HiL), designed and implemented to reduce the time spent on field tests through the emulation of a complex vehicular scenario in a controlled laboratory environment. Specifically, CarLink can simulate a generic traffic scenario and let each vehicle in it communicate with a vehicle under test (VUT), which is actually physically available HiL and equipped with long- and short-range wireless communication capabilities. Communication between simulated vehicles and the VUT is provided by an external management unit (EMU) that integrates the virtual world with the physical one. The architecture is also designed to allow the integration of advanced driver assistance systems (ADAS) testing for the validation of future connected and automated vehicles.

In the last few years, two technologies have been developed to enable direct exchange of information between vehicles. These technologies, currently seen as alternatives, are ITS-G5, as commonly referred in Europe, and sidelink LTE-vehicle-to-everything (LTE-V2X) (one of the solutions of the so-called cellular-V2X, C-V2X). For this reason, the attention has been mostly concentrated on comparing them and remarking their strengths and weaknesses to motivate a choice. Differently, in this work we focus on a scenario where both are used in the same area and using the same frequency channels, without the assistance from any infrastructure. Our results show that under co-channel coexistence the range of ITS-G5 is severely degraded, while impact on LTE-V2X is marginal. Additionally, a mitigation method where the CAM data generation is constrained to periodical intervals is shown to reduce the impact of co-channel coexistence, with less degradation on ITS-G5 performance and even improvement for LTE-V2X.

Vehicles are increasingly becoming connected and short-range wireless communications promise to introduce a radical change in the drivers' behaviors. Among the main use cases, the intersection management is surely one of those that could mostly impact on both traffic safety and efficiency. In this work, we consider an intersection collision warning application and exploit an hardware-in-the-loop (HIL) platform to verify the impact on the risk of accidents as well as the average time to travel a given distance. Besides including real ITS-G5 compliant message exchanges, the platform also includes a channel emulator with real signals. Results show that the risk of collisions can be drastically reduced, with an overall trade-off between safety and traffic efficiency. At the same time, it is shown that the presence of real channel conditions cannot guarantee the same condition of zero-risk as with ideal channel propagation, remarking the importance of channel conditions and signal processing.

In the latest years, 3GPP has added short range cellular-vehicle-to-anything (C-V2X) to the features of LTE and 5G in order to make vehicles, roadside devices, and vulnerable users directly exchange information using the same chipset as for classical long range connections. C-V2X is based on the use of advanced physical layer techniques and orthogonal resources, and one of the main aspects affecting its performance is the way resources are allocated. Allocations can be either managed by the network or in a distributed way, directly by the nodes. The latter case, called Mode 4, is defined to manage those situations where the network cannot be involved in the scheduling process, for example due to a lack of coverage, but could also be adopted in order to reduce the processing burden of eNodeB. An algorithm, defined in the standards, makes nodes sense the medium and identify the best time-frequency combination to allocate their messages. Focusing on C-V2V Mode 4, in this work we analyze the parameters of the algorithm designed by 3GPP and their impact on the system performance. Through simulations in different large scale scenarios, we show that modifying some parameters have negligible effect, that the proper choice of others can indeed improve the quality of service, and that a group of parameters allows to trade-off reliability with update delay. The provided results can also be exploited to guide future work.

To improve safety on the roads, next-generation vehicles will be equipped with short-range communication technologies. Many applications enabled by such communication will be based on a continuous broadcast of information about the own status from each vehicle to the neighborhood, often referred as cooperative awareness or beaconing. Although the only standardized technology allowing direct vehicle-to-vehicle (V2V) communication has been IEEE 802.11p until now, the latest release of long-term evolution (LTE) included advanced device-to-device features designed for the vehicular environment (LTE-V2V) making it a suitable alternative to IEEE 802.11p. Advantages and drawbacks are being considered for both technologies, and which one will be implemented is still under debate. The aim of this paper is thus to provide an insight into the performance of both technologies for cooperative awareness and to compare them. The investigation is performed analytically through the implementation of novel models for both IEEE 802.11p and LTE-V2V able to address the same scenario, with consistent settings and focusing on the same output metrics. The proposed models take into account several aspects that are often neglected by related works, such as hidden terminals and capture effect in IEEE 802.11p, the impact of imperfect knowledge of vehicles position on the resource allocation in LTE-V2V, and the various modulation and coding scheme combinations that are available in both technologies. Results show that LTE-V2V allows us to maintain the required quality of service at even double or more the distance than IEEE 802.11p in moderate traffic conditions. However, due to the half-duplex nature of devices and the structure of LTE frames, it shows lower capacity than IEEE 802.11p if short distances and very high vehicle density are targeted.

In this paper, we consider a multi-user scenario where an arbitrary number of sources transmit their messages to the intended destinations by means of relays in a decode-and-forward two-hop mechanism. To minimize the interference generated in the scenario, two opportunistic relay selection mechanisms are proposed and investigated. The performance of the two selection mechanisms is analytically evaluated, in terms of outage probability and average achievable rate, under the assumption that relay nodes are distributed according to a Poisson point process. Asymptotical analysis is also presented for infinite node density. Numerical results show that the selection of the relays has a significant impact on the amount of interference generated and a suitable choice can improve the overall performance.

Future connected and automated vehicles (CAVs) will rely not only on their own sensors, but also on surround vehicles sensors, continuously exchanging information on the perceived environment and drivers' intentions. In addition, the amount of information coming from both the environment through the communication systems and the onboard advanced driver assistance systems (ADAS) is incredibly increasing and must be managed and fused. This is posing new challenges to be faced by the underlying communication technologies, since they will have to sustain higher throughput often with lower latency in a highly dynamic environment. In this paper we discuss the main characteristics of the actual wireless access technologies and the efforts under discussions at international level to satisfy the incoming new requirements and allow safe and efficient applications. Specifically, we start discussing IEEE 802.11p and Cellular-V2X (C-V2X) technologies and the roadmap of their evolution, then we go inside the new requirements, especially in terms of capacity and latency, and we discuss solutions coming from complementary technologies, such as mmwaves and terahertz communications, also considering the use of reconfigurable meta surfaces.

The third generation partnership project (3GPP) has issued specifications for the autonomous assignment of radio resources by vehicles on the sidelink of the cellular-vehicle-to-everything (C-V2X) technology. It is based on a sensing mechanism for resource selection and a semi-persistent scheduling for resource reservation to periodic safety messages. Imperfect sensing due to hidden terminals and to half-duplex on board transceivers may result in the selection of interfered resources for successive message transmissions. As a consequence of the lost packets, involved vehicles may become blind to the presence of other vehicles in their vicinity even for many seconds, with threats to the road safety. In this paper, we define these events as wireless blind spot s (WBSs) and characterize their probability to occur. We propose an enhancement to the autonomous mode in order to reduce the WBS duration and demonstrate the benefits of the proposal against the legacy mode, both analytically in a simplified scenario and through simulations in a highway environment.

Current vehicular communication technologies were designed for a so-called phase 1, where cars needed to advise of their presence. Several projects, research activities and field tests have proved their effectiveness to this scope. But entering the phase 2, where awareness needs to be improved with non-connected objects and vulnerable road users, and even more with phases 3 and 4, where also coordination is foreseen, the spectrum scarcity becomes a critical issue. In this work, we provide an overview of various 5G and beyond solutions currently under investigation that will be needed to tackle the challenge. We first recall the undergoing activities at the access layer aimed to satisfy capacity and bandwidth demands. We then discuss the role that emerging networking paradigms can play to improve vehicular data dissemination, while preventing congestion and better exploiting resources. Finally, we give a look into edge computing and machine learning techniques that will be determinant to efficiently process and mine the massive amounts of sensor data.

Vehicles will be equipped with short-range wireless technologies with the aim to improve safety and traffic efficiency. Novel applications are thus being implemented for future cars and trucks, and one of the main issues is how to conduct tests and optimizations in an effective way, limiting the need to perform costly and time consuming experiments on the road. To cope with this issue, we have implemented a simulator with hardware-in-the-loop (HIL), called TRUDI, where the hardware and the implemented applications are tested in the laboratory by injecting virtual positions of the vehicles with the support of a traffic simulator. TRUDI acts as a man-in-the-middle between the communication module and the application itself, making it possible to perform tests with the real devices and providing as an output a system ready for the road. Using TRUDI, it is possible to check the application with a few vehicles and real wireless devices or many vehicles using simulated communication components before moving to experiments on the road. As an example use case, an application for the intersection management is presented, where the driver is warned of the presence and speed of other vehicles approaching the same junction.

The Cellular Vehicle-to-Everything (C-V2X) radio access technology has been specified by the Third Generation Partnership Project (3GPP) in Releases 14 and 15, with special focus on enabling direct communication between vehicles, over the sidelink PC5 interface. More recently, 3GPP has launched the New Radio (NR) standardization activity for the first phase of fifth generation (5G) systems and is ready to enhance C-V2X in several ways under the 5G NR Release 16. 5G NR V2X will encompass flexible numerologies and agile frame structure, higher frequency spectrum, novel and more sophisticated multiple access techniques that well answer the quest for high capacity, ultra-low latency and high reliability of the cooperative automated driving use cases. In this paper, we investigate the impact of the NR flexible numerology, i.e., scalable Transmission Time Interval (TTI) duration and sub-carrier spacing (SCS), on the C-V2X autonomous access mode, according to which vehicles self-allocate resources for transmission. Whereas it is well known that shorter TTI and larger SCS facilitate latency reduction, they have also the potential to mitigate the interference generated by in-band emissions, by better spreading transmissions in the time-frequency domain. Achieved simulation results show that the investigated NR features provide several improvements in terms of message reliability and timeliness when compared to the legacy C-V2X solution.

The cellular Vehicle-to-Everything (C-V2X) radio access technology, specified by the Third Generation Partnership Project (3GPP), enables direct communications between vehicles, using the sidelink radio resources over the PC5 interface. In C-V2X Mode 4, a vehicle autonomously selects the resources and keeps them for consecutive transmissions before a resource reselection is triggered, according to a sensing-based semi-persistent scheduling mechanism. A wrong estimation of the resource occupancy status may lead to persistent packet losses, due to collisions with simultaneous transmissions from other vehicles. In this paper, we propose to provide vehicles with on-board full-duplex transceivers and harness this capability (i) to make the sensing phase more accurate, (ii) to make a more informed resource reselection decision, and (iii) to enhance packet decoding while transmitting. Achieved simulation results show that the proposal provides several improvements in terms of packet transmission reliability and timeliness when compared against the legacy C-V2X Mode 4.

The revolution of cooperative connected and automated vehicles is about to begin and a key milestone is the introduction of short range wireless communications between cars. Given the tremendous expected market growth, two different technologies have been standardized by international companies and consortia, namely IEEE 802.11p, out for nearly a decade, and short range cellular-vehicle-to-anything (C-V2X), of recent definition. In both cases, evolutions are under discussion. The former is only decentralized and based on a sensing before transmitting access, while the latter is based on orthogonal resources that can be also managed by an infrastructure. Although studies have been conducted to highlight advantages and drawbacks of both, doubts still remain. In this work, with a reference to the literature and the aid of large scale simulations in realistic urban and highway scenarios, we provide an insight in such a comparison, also trying to isolate the contribution of the physical and medium access control layers.

The correct and prompt definition of priorities at intersections is one of the key issues for vehicular safety and efficient traffic management. Traffic lights currently control only a limited number of intersections and increasing their number is clearly infeasible due to the high costs of deployment and maintenance. A new solution will be possible in a near future, when vehicles will be equipped with wireless technologies. Their capability of communicating and coordinating to each other will create the conditions for the implementation of a virtual traffic light (VTL) architecture, where priorities are autonomously defined by the involved vehicles. With this scenario in mind, we describe a novel VTL algorithm aiming at defining the priorities of the intersections in a distributed and controlled way. Besides the algorithm description, the main related issues are thoroughly discussed. In addition, a real implementation is detailed and the validation of the algorithm is provided. The testbed, based on the IEEE 802.11p short range wireless technology, has been reproduced in a controlled laboratory environment and in a field trial with equipped vehicles. (C) 2016 Elsevier B.V. All rights reserved.

The paper investigates the transmission characteristics of a low power device, named micro.sp©, patented by STE Industries, to be used for Internet of Things (IoT) applications where battery duration is a critical aspect and the transmitted information is organized in messages composed by a limited number of bits. The technical characteristics of micro. $\text{sp}^{\bigcirc\!\!\!\!\!\text{C}}$ are compared with those of Bluetooth low energy (BLE) devices, which appears as the main competing short range wireless technology. Experimental results show that micro $\text{sp}^{\bigcirc\!\!\!\!\!\text{C}}$ can be considered an enabling technology for the implementation of very low consumption short-range devices (according to ETSI definition). To give some examples, measurements have revealed that assuming to transmit few bytes every 30 seconds, a micro.sp© device can work for more than 30 years with the same coin battery, more than double the time of the BLE devices.

Vehicles will soon be connected and will be interacting directly with each other and with the road infrastructure, bringing substantial benefits in terms of safety and traffic efficiency. The past decade has seen the development of different wireless access technologies for vehicle-to-everything (V2X) communications and an extensive set of related use cases have been drafted, each with its own requirements. In this paper, focusing on short-range communications, we analyze the technical and economic motivations that are driving the development of new road users' connectivity, discussing the international intentions to mandate on board devices for V2X communication. We also go in depth with the enabling wireless access technologies, from IEEE 802.11p to short-range Cellular-V2X and other complementary technologies, such as visible light communication (VLC) and millimeterWaves, up to hybrid communication and 5G. We conclude our survey with some performance comparison in urban realistic scenarios, underlying that the choice of the future enabling technology is not so easy to predict and mostly depends on mandatory laws at the international level.

The use of vehicles as sensors is a new paradigm to enable an efficient environment monitoring and an improved traffic management. In most cases, the sensed information must be collected at a remote control center and one of the most challenging aspects is the uplink acquisition of data from vehicles, which is presently performed through cellular networks. With the objective to offload cellular networks, in this paper we propose and discuss the adoption of the WAVE/IEEE 802.11p protocols, which represent the state of the art for short range vehicle-to-vehicle and vehicle-to-roadside communications. More specifically, we discuss the system design and assess the cellular resource saving that can be obtained in urban scenarios through the deployment of WAVE/IEEE 802.11p devices on the vehicles and roadside units, evaluating the impact of the percentage of equipped vehicles, of the number of deployed road side units, and of the adopted routing protocol. Results, obtained through an integrated simulation platform taking both realistic vehicular environments and wireless network communication aspects into account, show that the deployment of few road side units and the use of low complexity routing protocols leads to a significant reduction of cellular resource occupation, even approaching 100% with a high density of equipped vehicles.

International audience; On the path to zero fatalities on the roadways, all vehicles have to periodically broadcast cooperative awareness messages (CAMs) in a timely and reliable manner, even in areas of high traffic density. The carrier senses multiple access with collision avoidance (CSMA/CA) scheme of IEEE 802.11, the de-facto standard for vehicular communications, is known to offer no reliability to broadcast packets that cannot be acknowledged, and to poorly perform at high network load due to collisions and interference. In this paper, an enhanced CSMA/CA protocol is analyzed for vehicular networks, which improves the CAM timeliness and reliability by leveraging full-duplex (FD) transceivers on board. FD devices can listen to the channel while transmitting, thus making collision detection viable. A FD vehicle can detect a CAM collision while sending, promptly abort the packet and retransmit it later. Results achieved through an analytical model under mathematically tractable assumptions, and through extensive system-level simulations in a complex urban environment, show the effectiveness of the protocol to cope with direct collisions, especially in high traffic areas, paving the way towards the realization of cooperative automated driving.

Crowd sensing is a powerful tool to map and predict interests and events. In the future, it could be boosted by an increasing number of connected vehicles sharing information and intentions. This will be made available by on board wireless connected devices able to continuously communicate with other vehicles and with the environment. Among the enabling technologies, visible light communication (VLC) represents a low cost solution in the short term. In spite of the fact that vehicular communications cannot rely on the sole VLC due to the limitation provided by the light which allows communications in visibility only, VLC can however be considered to complement other wireless communication technologies which could be overloaded in dense scenarios. In this paper we evaluate the performance of VLC connected vehicles when urban crowd sensing is addressed and we compare the performance of sole vehicular visible light networks with that of VLC as a complementary technology of IEEE 802.11p. Results, obtained through a realistic simulation tool taking into account both the roadmap constraints and the technologies protocols, help to understand when VLC provides the major improvement in terms of delivered data varying the number and position of RSUs and the FOV of the receiver.

Report del progetto v2X secondo anno

Progetto V2X, terzo deliverable del secondo anno

Vehicle-to-everything (V2X) communication will be the key technology to improve safety on the road. In particular, the cooperative awareness service will give vehicles the capacity of being aware of the neighborhood through the periodic dissemination of beacon messages, carrying mobility information. Applications like these need a wireless technology able to provide high reliability and low latency. In this context, Cellular-V2X based on long term evolution (LTE) Release 14 is a promising candidate. Objective of this work is to focus on LTE Sidelink mode 3, where resources reserved to direct links are managed by the network and to propose a resource scheduling algorithm based on the knowledge, with different levels of accuracy, of the positions of the vehicles at the network side. Through simulations, carried out in realistic highway and urban scenarios, we compare the proposed solution with a benchmark algorithm based on the concept of reuse distance and we demonstrate that the new solution, other than always offering the highest performance in terms of packet reception ratio and latency, does not require the fine tuning of any parameter.

rapprto del progetto v2X, secondo deliverable secondo anno

Direct connectivity between vehicles will let a variety of new applications become a reality, from safety to traffic management and infotainment. Different wireless access technologies can enable this kind of connections, from mobile-fi IEEE 802.11p in the US and ETSI G5 in Europe, to the more recent 3GPP long term evolution (LTE) for vehicle-to-vehicle (V2V) communications. To integrate the capabilities and performance of these radio access technologies, light emitting diodes (LEDs) operating in the front and rear vehicles' lights, can introduce a further degree of connectivity through the so called visible light communication (VLC), by setting up direct links between vehicles in visibility and between vehicles and the road side (such as traffic lights and variable message panels). This paper investigates the performance of vehicular visible light networks (VVLNs) in terms of message delivery rate when full-duplex (FD) capabilities are exploited. Specifically, instead of considering carrier sensing multiple access with collision avoidance (CSMA/CA) as foreseen by the IEEE 802.15.7 standard for VLC, we here propose a CSMA with collision detection (CSMA/CD) protocol exploiting the reverse link made available by the concurrent use of LEDs as transmitters and photodiodes as receivers for an immediate feedback during decoding. Results show an increase of up to 10% in the delivered data thanks to FD in realistic urban scenarios and give guidelines to network designers.

For automotive safety applications, vehicles directly exchange periodic beacons that contain status information such as position, speed, acceleration, etc., and the application layer issues warnings if a hazardous situation is detected. The update rate of these beacons should be high enough to allow the application to swiftly react to prevent accidents and current recommendations provide fixed values for different safety use cases. This approach is sub-optimal since wireless resources might be used when not necessary, e.g., when cars are queuing at a traffic light, and the proposals made for variable beacon periodicity (BP) typically do not take into account the safety aspect or are strictly related to the access technology in use. This paper presents a new algorithm called beaconing adaptation for safety enhancement (BASE) that adapts the BP to minimize the amount of radio resources used by the safety application without breaching safety requirements. BASE is access technology agnostic and focuses on common traffic and traveling conditions (not on particular crossroads, overtaking, etc.), and the results presented in this paper show how it allows for substantial capacity gains in a highway collision-avoidance scenario.

Resource allocation is a challenging issue in multiuser wireless systems. Since users are not all in the same conditions and do not achieve the same performance given the same amount of resources, resource allocation must typically deal with the following two conflicting objectives: on the one hand, the overall performance should be maximized, tending to prioritize few users in better conditions, and on the other hand, fairness among users should be maximized, consequently reducing the overall performance. Identifying the compromise that is somehow optimum is all but simple and this aspect is normally worsened by the absence of a curve describing how the maximum performance varies changing the accepted level of fairness. To cover this gap, in this paper, we propose a unified and general mathematical formulation of the optimal performance versus fairness tradeoff in multiuser wireless communication systems. Differently from the existing literature, our approach is based on the generalized Lagrange method and adopts general definitions for both performance and fairness. Besides the exact solving equations describing how the maximum performance varies with fairness, we also derive a simpler lower bound with reduced computational cost. Example results are provided for two case studies, respectively, concerning linear and logarithmic dependence of performance on resources.

Safety enhancement is the main objective to pursue through the exploitation of connected vehicles. To this aim, the exchange of periodic beacon messages through vehicle-to-vehicle (V2V) communications is essential to guarantee a timely and reliable alert, whatever is the targeted safety application. In this paper, we focus on beaconing in vehicular networks and we evaluate the reliability of beacons exchange between vehicles in realistic urban scenarios. Specifically, IEEE 802.11p, which is the actual standard de facto for vehicular communications, is considered as radio access technology and the impact of distance and obstacles on beacons reliability is evaluated. Results obtained through detailed simulations highlight the high impact of distance and obstacles, to be carefully taken into account in the application design.

Il documento descrive l'analisi dei terminali di interesse per il progetto V2X