Decentralized Environmental Notification Messages Research Articles

LAMP: A latency-aware MAC protocol for joint scheduling of CAM and DENM traffic over 5G-NR sidelink

Cooperative Awareness Messages (CAMs) and Decentralized Environmental Notification Messages (DENMs) are two types of messages used in Intelligent Transport Systems (ITS) for Vehicle-to-Everything (V2X) communication. CAMs are used to periodically exchange the current state of a vehicle with its nearby vehicles and the DENMs are used to aperiodically provide critical and time-sensitive information about current environmental conditions to other vehicles and infrastructure entities. While considerable research has been conducted on the efficient scheduling of CAM and DENM separately or at the network level coexistence, no work has been done to integrate the scheduling of both message types at the granularity of the per-vehicle level. The scheduling of CAM is commonly done through Semi-Persistent Scheduling (SPS). However, no equivalent scheduling algorithm has been developed for the aperiodic and variable-sized DENMs. As a result, there is a need for novel mechanisms that can efficiently prioritize and schedule mixed traffic of CAM and DENM messages. This paper introduces a Quality of Service (QoS) scheduler called LAMP for segregating traffic in the Radio Link Control (RLC) layer for joint sidelink scheduling of CAM and DENM at the vehicular level. The LAMP scheduler is aided with a special resource selection and reservation scheme for mixed traffic scenarios. The groundwork involves an experimental analysis in Network Simulator-3 (NS-3) that uses the New Radio (NR) Vehicle-to-Everything (V2X) module in Mode-2. The simulation findings demonstrate that LAMP could significantly reduce the end-to-end latency of DENM by 89.36% and CAM by 40.2% while also increasing the packet reception rate by 12.1% and 9.74% for CAM and DENM with repetitions, respectively.

Performance comparison based on priority between 802.11p and C-V2X

With the increasing number of vehicles, the issue of traffic safety has become more and more prominent. There is a growing demand for real-time vehicle monitoring and vehicle-to-vehicle communication, which has led to the rapid development of connected car technology. Currently, the two mainstream wireless access technologies that support vehicle-to-everything (V2X) communication are Dedicated Short-Range Communications (DSRC) and Cellular-V2X (C-V2X) or LTE-V2X. This paper aims to compare the performance of these two technologies by studying two types of information, Cooperative Awareness Messages (CAM) and Decentralized Environmental Notification Messages (DENM), as well as the prioritization defined for C-V2X. Additionally, this paper compares the prioritization of 802.11p with different priority levels of C-V2X. Through simulation experiments, it is ultimately proven that 802.11p outperforms C-V2X in terms of latency but is inferior to C-V2X in terms of collision probability.

Emergency Braking With ACC: How Much Does V2V Communication Help?

This letter provides a safety analysis for emergency braking scenarios involving consecutive vehicles. The vehicles use adaptive cruise control (ACC) with a constant-distance policy together with additional vehicle-to-vehicle (V2V) communication for emergency braking. We provide explicit formulas describing how the minimum safe inter-vehicle distance (IVD), for avoiding rear-end collision, can be shortened with the use of decentralized environmental notification messages (DENMs). More precisely, those formulas describe the dependency of such IVDs on V2V communication delay. We further show how these results can be used to compute probabilities of safe braking in the presence of packet losses.

On the design and implementation of an on-board test bed system for V2V road hazard signaling

This paper describes the design, implementation, and testing of an ITS-G5 prototype Road hazard Signaling (RHS) system that is inspired by the concept of crowdsourcing. Our approach enables drivers to interact with a touchscreen onboard interface to send ITS-G5 decentralized environmental notification messages (DENM) in order to warn nearby vehicles against the presence of a hazardous situation. These messages are analyzed, filtered for relevance, and presented to concerned drivers via the Onboard Units (OBUs) so that precautionary measures can be taken. We describe the design and implementation aspects of the proposed system and update the open source cargeo6 implementation of the ITS GeoNetworking protocol stack. We successfully implemented and validated the prototype system using an indoor testbed and carried various performance analysis experiments.

A Discrete-Time Markov Chain Based Comparison of the MAC Layer Performance of C-V2X Mode 4 and IEEE 802.11p

Vehicle-to-vehicle (V2V) communication plays a pivotal role in intelligent transport systems (ITS) with cellular-vehicle to everything (C-V2X) and IEEE 802.11p being the two competing enabling technologies. This paper presents multi-dimensional discrete-time Markov chain (DTMC) based models to study the medium access control (MAC) layer performance of the IEEE 802.11p standard and C-V2X Mode 4, considering periodic cooperative awareness messages (CAMs) and event-driven decentralized environmental notification messages (DENMs). Closed-form solutions for the steady-state probabilities of the models are obtained, which are then utilized to derive expressions for several key performance metrics. Numerical results are provided to draw insights on the performance. In particular, a performance comparison between IEEE 802.11p and C-V2X Mode 4 in terms of the average delay, the collision probability, and the channel utilization is presented. The results show that IEEE 802.11p is superior in terms of average delay, whereas C-V2X Mode 4 excels in collision resolution. The paper also includes design insights on possible future MAC layer performance enhancements of both standards.

Prototype to Increase Crosswalk Safety by Integrating Computer Vision with ITS-G5 Technologies

Human errors are probably the main cause of car accidents, and this type of vehicle is one of the most dangerous forms of transport for people. The danger comes from the fact that on public roads there are simultaneously different types of actors (drivers, pedestrians or cyclists) and many objects that change their position over time, making difficult to predict their immediate movements. The intelligent transport system (ITS-G5) standard specifies the European communication technologies and protocols to assist public road users, providing them with relevant information. The scientific community is developing ITS-G5 applications for various purposes, among which is the increasing of pedestrian safety. This paper describes the developed work to implement an ITS-G5 prototype that aims at the increasing of pedestrian and driver safety in the vicinity of a pedestrian crosswalk by sending ITS-G5 decentralized environmental notification messages (DENM) to the vehicles. These messages are analyzed, and if they are relevant, they are presented to the driver through a car’s onboard infotainment system. This alert allows the driver to take safety precautions to prevent accidents. The implemented prototype was tested in a controlled environment pedestrian crosswalk. The results showed the capacity of the prototype for detecting pedestrians, suitable message sending, the reception and processing on a vehicle onboard unit (OBU) module and its presentation on the car onboard infotainment system.

On Latency and Reliability of Road Hazard Warnings Over the Cellular V2X Sidelink Interface

Decentralized Environmental Notification Messages (DENMs) are generated by a vehicle upon detection of an accident or other hazards on the road, and need to be promptly and reliably transmitted. Delayed or lost messages may have fatal consequences, especially in critical driving situations, such as automated overtake and emergency braking, when vehicles can be very close to each other. In this letter, the DENM latency and reliability performances are characterized over the Cellular Vehicle-to-everything (C-V2X) sidelink (PC5 interface). The conducted study uses analytical tools, among which stochastic geometry, to derive performance results, then validated by simulations. The results are applied to the case of DENMs for emergency electronic brake lights, and helpful insights are provided for this crucial case and for other more general DENM-assisted V2X use cases.

Design of the Emergency Messages Integration for Vehicle to Everything (V2X) Communications of Connected Cars

So far, international standardization of message specifications between V2X(Vehicle to Everything) safety communications are BSM(Basic Safety Message) by US-led SAE and CAM(Cooperative Awareness Message)/DENM(Decentralized Environmental Notification Message) by EU-led ETSI. However, in the emergency situation such as car accidents or road traffic jam, there may be insufficient time to process all messages. In this paper, we propose an integration of emergency messages for V2X communications of connected vehicles in VANETs(Vehicular Ad hoc Networks), To do this, we are using the Mobile Virtual Fence(MVF), which has been preliminarily researched and developed. So we extract and integrate only emergency messages as the fields of similar messages between BSM and CAM/DENM, and apply it to the MVF. If it will be the connected MVFs like connected cars in the future and any traffic accident or traffic jam occurs, the proposed messages will be communicated to each other to avoid the accident. Therefore the proposed integration of emergency messages between BSM and CAM/DENM specification will be contribute to improve the safety and reliability as the unified and integrated emergency messages.

An Improved Dynamic Broadcast Storm Mitigation for VANETs

Research development of recent years has identified the Wireless Access in Vehicular Environment (WAVE) technology as a prominent and efficient candidate for future vehicular communication. Under WAVE standard safety messages are broadcast or exchanged between all involved mobiles at the rate of 1 to 10 Hz. However, in a congested environment, Broadcast Storm (BSt) problem naturally occurs and exhausts the available channel bandwidth thereby rendering exchange and sharing of vital information impossible. In our recent work, the Dynamic Broadcast Storm Mitigation Algorithm (DBSMA) proved to be a good candidate for BSt problem mitigation for Cooperative Awareness Messages (CAMs) only. In the present work, the DBSMA is improved (IDBSMA) to cater for both CAMs and Decentralized Environmental Notification Messages (DENMs). The developed IDBSMA approach was tested under two cases scenario condition and simulation result demonstrated the outperformance of the IDBSMA over the DBSMA algorithm in three dimensions. Firstly, in terms of broadcasting delay, secondly in terms of performance within the preset range and lastly in terms of Reserved Margin Space (RMS) to account for the DENMs messages.

Automatic accident detection with multi-modal alert system implementation for ITS

The rapid technological growth is now providing global opportunities to enable intelligent transportation system (ITS) to tackle road accidents which is considered one of the world's largest public injury prevention problem. For this purpose, eCall is an initiative by European Union (EU) with the purpose to bring rapid assistance to an accident location. This paper1 presents HDy Copilot, an application for automatic accident detection integrated with multimodal alert dissemination, via both eCall and IEEE 802.11p (ITS-G5). The proposed accident detection algorithm receives inputs from the vehicle, via ODB-II, and from the smartphone sensors, namely the accelerometer, the magnetometer and the gyroscope. An Android smartphone is used as human machine interface, so that the driver can configure the application, receive road hazard warnings issued by other vehicles in the vicinity and cancel countdown procedures upon false road vehicle crash detection. The HDy Copilot is developed for Android OS as it provides open source APIs that allow access to its hardware resources. The application is implemented, tested and connected to an IEEE 802.11p based prototype. The generated results show that the application successfully detects collisions, rollovers, performs the eCall along with sending Minimum Set of Data (MSD) and Decentralized Environmental Notification Message (DENM).

Experimental evaluation of CAM and DENM messaging services in vehicular communications

The Cooperative Awareness Basic Service and Decentralized Environmental Notification Basic Service have been standardized by the European Telecommunications Standards Institute (ETSI) to support vehicular safety and traffic efficiency applications needing continuous status information about surrounding vehicles and asynchronous notification of events, respectively. These standard specifications detail not only the packet formats for both the Cooperative Awareness Message (CAM) and Decentralized Environmental Notification Message (DENM), but also the general message dissemination rules. These basic services, also known as facilities, have been developed as part of a set of standards in which both ISO and ETSI describe the Reference Communication Architecture for future Intelligent Transportation Systems (ITS). By using a communications stack that instantiates this reference architecture, this paper puts in practice the usage of both facilities in a real vehicular scenario. This research work details implementation decisions and evaluates the performance of CAM and DENM facilities through a experimental testbed deployed in a semi-urban environment that uses IEEE 802.11p (ETSI G5-compliant), which is a WiFi-like communication technology conceived for vehicular communications. On the one hand, this validation considers the development of two ITS applications using CAM and DENM functionalities for tracking vehicles and disseminating traffic incidences. In this case, CAM and DENM have demonstrated to be able to offer all the necessary functionality for the study case. On the other hand, both facilities have been also validated in a extensive testing campaign in order to analyze the influence in CAM and DENM performance of aspects such as vehicle speed, signal quality or message dissemination rules. In these tests, the line of sight, equipment installation point and hardware capabilities, have been found as key variables in the network performance, while the vehicle speed has implied a slight impact.