Vehicular Safety Communications Research Articles

A Semi-Markov Process Model for Performance Evaluation of DSRC Vehicular Safety Communication

In this study, a new semi-Markov process (SMP)-based model is devised to evaluate the IEEE 802.11p enhanced distributed channel access (EDCA) broadcast performance for vehicular safety communication. Differing from the existing SMP analytical models, the proposed model takes the virtual collision among various prioritized access categories (ACs) inside each vehicle into consideration. Moreover, in contrast to the Markov chain-based models, our model is simpler but with approximate accuracy. Concretely, we first capture the behavior of each AC’s backoff entity using SMP. Then, the parameters of interest in the vehicular ad hoc network (VANET) such as packet transmission probability, conditional collision probability, and saturation throughput are derived. Finally, via MATLAB simulations, we demonstrate that the newly developed model achieves comparable accuracy in calculating these output parameters while its complexity and computation time is around one-tenth of that of the Markov chain-based models. Therefore, the proposed model is more suitable for real-time performance analysis of IEEE 802.11p EDCA safety communication in a freeway scenario.

Performance analysis of cooperative communications at road intersections using stochastic geometry tools

Vehicular safety communications (VSCs) provide relevant solutions to avoid congestion and road accidents, more particularly at road intersections since these areas are more prone to accidents. In this context, one of the main impairments that can affect the performance of VSCs is interference. In this paper, we study the performance of cooperative transmissions at intersections in presence of interference for VSCs. We use tools from stochastic geometry, and model interferer vehicles locations as a Poisson point process. First, we calculate the outage probability for a direct transmission when the receiving nodes can be on the road (as vehicles), or outside the road (as infrastructures). Then, we analyze the outage probability performance of a cooperative transmission scheme. The analysis takes into account two dimensions: the decoding strategy at the receiving nodes, and the vehicles mobility. We determine the optimal relay position under different traffic densities and for different vehicles mobility models. We also show that the outage probability does not improve after the number of infrastructure relays reach a threshold value. Finally, we show that the outage probability performance of VSCs is higher at intersections than on highways. We validate our analytical results by Monte-Carlo simulations.

Performance Analysis of DSRC-Based Vehicular Safety Communication in Imperfect Channels

Vehicle-to-vehicle (V2V) communication empowers vehicles to share information by broadcasting basic and critical safety messages. Dedicated short-range communication (DSRC), the medium access control (MAC) layer of which utilizes the IEEE 802.11p protocol, is a promising candidate technology for vehicular communication. Safety applications usually demand safety message dissemination to be prompt and reliable. To satisfy these strict requirements, the MAC layer of vehicular safety communication tends to adopt Distributed Coordination Function (DCF) or single-class Enhanced Distributed Channel Access (EDCA) without request-to-send/clear-to-send (RTS/CTS), acknowledgment (ACK) and retransmission mechanisms as the access scheme. As far as we know, although many numerical models have been provided to understand the IEEE 802.11 DCF performance, there is no precise model that examines the performance of vehicular safety communication exploiting such an access scheme in imperfect channels with different incoming traffic loads. In this paper, we settle this problem by developing an analytical model where the impacts of various incoming traffic loads, packet length distribution, hidden terminal effects, node mobility, the MAC layer queuing system, and the faulty radio channels are all included which no one has done this before. The experimental and numerical results reveal that the constructed model can exactly forecast the vehicular network performance of packet delay, delivery rate, and reception rate under different traffic and channel circumstances.

Balancing Power and Rate Control for Improved Congestion Control in Cellular V2X Communication Environments

The Society of Automotive Engineers (SAE) J2945/1 standard prescribes a wireless channel congestion control algorithm for periodic Basic Safety Messages (BSMs) in vehicular safety communication. The algorithm is designed to work with the Dedicated Short Range Communication (DSRC) technology as the radio interface, and utilizes transmit (Tx) power control and rate control elements for the periodic BSM transmissions, which are supposed to work in a complementary manner. An equivalent standard is being made for the cellular vehicle-to-everything (C-V2X) communication environment, and it is expected that the J2945/1 congestion control algorithm will be reused. Unfortunately, we find that when transplanted to the C-V2X communication environment, the J2945/1 algorithm exhibits a poor balance between the two control elements under congestion. Specifically, the Tx rate control is pushed to its limit much earlier than the Tx power control. We believe that this is due to the new relation formed between the respective inputs to the control elements, channel busy ratio (CBR) and the vehicle density (VD), induced by the different radio technology used in the C-V2X communication. The consequence of the unbalanced control dynamics is the degraded update delay of neighboring vehicles' kinematics due to the over-exerted rate control, which potentially undermines the driving safety. In this paper, we propose to adjust the rate control function to react to congestion in a more relaxed manner so that the power control contributes more actively to the overall congestion control. With the re-balancing between the control elements, we show that the update delay improves, where larger improvements are obtained in closer, more safety-critical distances from the BSM transmitter. We believe that in future efforts to define the standard congestion control algorithm for the C-V2X environment, the balanced control aspect as explored in this paper should be considered in the design phase.

Improving Information Age in SAE J2945 Congestion-Controlled Beaconing

The Society of Automotive Engineers J2945 standard prescribes a wireless channel congestion control algorithm for basic safety messages in vehicular safety communication. The algorithm utilizes transmit (Tx) power and rate controls, but we find that the Tx power control hardly engages in most practical vehicular traffic densities. We explain the cause and propose an alternative way to utilize both the control mechanisms. Specifically, we suggest that the Tx power control be first exerted to its limit, followed by the Tx rate control coping with further congestion. We show that the proposed alternative not only addresses the inadequate power control issue but also leads to better information age performance for vehicles in the most safety-critical distances.

A Stochastic Geometry Approach to the Modeling of DSRC for Vehicular Safety Communication

Vehicle-to-vehicle safety communications based on the dedicated short-range communication technology have the potential to enable a set of applications that help avoid traffic accidents. The performance of these applications, largely affected by the reliability of communication links, stringently ties back to the MAC and PHY layer design, which has been standardized as IEEE 802.11p. The link reliabilities depend on the signal-to-interference-plus-noise ratio (SINR), which, in turn, depends on the locations and transmit power values of the transmitting nodes. Hence, an accurate network model needs to take into account the network geometry. For such geometric models, however, there is a lack of mathematical understanding of the characteristics and performance of IEEE 802.11p. Important questions such as the scalability performance of IEEE 802.11p have to be answered by simulations, which can be very time consuming and provide limited insights to future protocol design. In this paper, we investigate the performance of IEEE 802.11p by proposing a novel mathematical model based on queuing theory and stochastic geometry. In particular, we extend the Matérn hard-core type-II process with a discrete and nonuniform distribution, which is used to derive the temporal states of backoff counters. By doing so, concurrent transmissions from nodes within the carrier sensing ranges of each other are taken into account, leading to a more accurate approximation to real network dynamics. A comparison with Network Simulator 2 (ns2) simulations shows that our model achieves a good approximation in networks with different densities.

On improving delay performance of IEEE 802.11p vehicular safety communication

In this work, we present the design of an efficient Deterministic medium Access DA for Dedicated Short-Range Communication DSRC vehicular safety communication over IEEE 802.11p, called Vehicular DA VDA. VDA supports two types of safety services emergency and routine safety messages with different priorities and strict requirements on delay, especially for emergency safety messages. VDA processes both types of safety messages to maintain a balance between two conflicting requirements: reducing chances of packets collisions and lowering the transmission delay. VDA allows vehicles to access the wireless medium at selected times with a lower contention than it would otherwise be possible within two-hop neighbourhood with the classical 802.11p EDCA or DCF schemes. Besides, we propose an improvement of VDA called Dynamic VDA opportunities Re-assignment DVR to avoid network performance degradation caused by interference outside the two-hops. Particularly, our scheme provides an efficient adaptive adjustment of the Contention Free Period CFP duration to establish a priority between emergency and routine messages. Simulations show that the VDA scheme, used with 802.11p, clearly outperforms 802.11p alone in high-offered load conditions while bounding the transmission delay of safety messages. Furthermore, beyond two-hops, DVR is able to efficiently tackle the interference phenomenon by reducing losses and delays of safety applications.

Design of an Integration Platform for V2X Wireless Communications and Positioning Supporting C-ITS Safety Applications

In this paper, an integrated inter-vehicles wireless communications and positioning system supporting alternate positioning techniques is proposed to meet the requirements of safety applications of Cooperative Intelligent Transportation Systems (C-ITS). Recent advances have repeatedly demonstrated that road safety problems can be to a large extent addressed via a range of technologies including wireless communications and positioning in vehicular environments. The novel communication stack utilizing a dedicated frequency spectrum (e.g. at 5.9 GHz band), known as Dedicated Short-Range Communications (DSRC), has been particularly designed for Wireless Access in Vehicular Environments (WAVE) to support safety applications in highly dynamic environments. Global Navigation Satellite Systems (GNSS) is another essential enabler to support safety on rail and roads. Although current vehicle navigation systems such as single frequency Global Positioning System (GPS) receivers can provide route guidance with 5-10 meters (road-level) position accuracy, positioning systems utilized in C-ITS must provide position solutions with lane-level and even in-lane-level accuracies based on the requirements of safety applications. This article reviews the issues and technical approaches that are involved in designing a vehicular safety communications and positioning architecture; it also provides technological solutions to further improve vehicular safety by integrating the DSRC and GNSS-based positioning technologies.

An Interacting Stochastic Models Approach for the Performance Evaluation of DSRC Vehicular Safety Communication

In this paper, an analytic model is proposed for the performance evaluation of vehicular safety related services in the dedicated short range communications (DSRC) system on highways. The generation and service of safety messages in each vehicle is modeled by a generalized M/G/1 queue. The overall model is a set of interacting M/G/1 queues, one queue for each vehicle. The interaction is that the server is shared as it is the contention medium. To make the model scalable, we use semi-Markov process (SMP) model to capture the shared server's behavior from one tagged vehicle's perspective, where the medium contention and back off behavior for this vehicle and influences from other vehicles are considered. Furthermore, this SMP interacts with the tagged vehicle's own M/G/1 queue through fixed-point iteration. The proof for the existence, uniqueness and convergence of the fixed point is provided. Based on the fixed-point solution, performance indices including mean transmission delay, packet delivery ratio (PDR), and packet reception ratio (PRR) are derived. Analytic-numeric results are verified through extensive simulations under various network parameters. Compared with the existing models, the proposed SMP model facilitates the impact analysis of hidden terminal problem on the PDR and PRR computation in a more precise manner.

Design and Analysis of a Robust Broadcast Scheme for VANET Safety-Related Services

IEEE- and ASTM-adopted dedicated short-range communications (DSRC) standards are key enabling technologies for the next generation of vehicular safety communications. Vehicle-safety-related communication services, which require reliable and fast message delivery, usually demand broadcast communications in vehicular ad hoc networks (VANETs). In this paper, we propose and justify a distributive cross-layer scheme for the design of the control channel in DSRC with three levels of broadcast services that are critical to most potential vehicle-safety-related applications. The new scheme for enhancing broadcast reliability includes preemptive priority in safety services, dynamic receiver-oriented packet repetitions for one-hop emergency warning message dissemination, a multifrequency busy tone and minislot within the distributed interframe space (DIFS) in IEEE 802.11, and robust distance-based relay selection for multihop broadcast of emergency notification messages. Compared with a current draft of IEEE 802.11p and other schemes for DSRC safety-related services, the scheme proposed in this paper is more robust and scalable and easy to implement. Additionally, we investigate the reliability and performance of the proposed broadcast scheme for DSRC VANET safety-related services on the highway analytically and by simulations. The analytic model accounts for the impact of the hidden terminal problem, the fading channel conditions, varied message arrival intervals, and the backoff counter process on reliability and performance.

Performance and Reliability of DSRC Vehicular Safety Communication: A Formal Analysis

IEEE- and ASTM-adopted dedicated short range communications (DSRC) standard toward 802.11p is a key enabling technology for the next generation of vehicular safety communication. Broadcasting of safety messages is one of the fundamental services in DSRC. There have been numerous publications addressing design and analysis of such broadcast ad hoc system based on the simulations. For the first time, an analytical model is proposed in this paper to evaluate performance and reliability of IEEE 802.11a-based vehicle-to-vehicle (V2V) safety-related broadcast services in DSRC system on highway. The proposed model takes two safety services with different priorities, nonsaturated message arrival, hidden terminal problem, fading transmission channel, transmission range, IEEE 802.11 backoff counter process, and highly mobile vehicles on highway into account. Based on the solutions to the proposed analytic model, closed-form expressions of channel throughput, transmission delay, and packet reception rates are derived. From the obtained numerical results under various offered traffic and network parameters, new insights and enhancement suggestions are given.

Design of 5.9 ghz dsrc-based vehicular safety communication

The automotive industry is moving aggressively in the direction of advanced active safety. Dedicated short-range communication (DSRC) is a key enabling technology for the next generation of communication-based safety applications. One aspect of vehicular safety communication is the routine broadcast of messages among all equipped vehicles. Therefore, channel congestion control and broadcast performance improvement are of particular concern and need to be addressed in the overall protocol design. Furthermore, the explicit multichannel nature of DSRC necessitates a concurrent multichannel operational scheme for safety and non-safety applications. This article provides an overview of DSRC based vehicular safety communications and proposes a coherent set of protocols to address these requirements