The need of a medium access control (MAC) protocol for an efficient broadcast service is of great importance to support the high-priority safety applications in vehicular ad hoc networks (VANETs). This paper introduces VeMAC, a novel multichannel TDMA MAC protocol proposed specifically for a VANET scenario. The VeMAC supports efficient one-hop and multihop broadcast services on the control channel by using implicit acknowledgments and eliminating the hidden terminal problem. The protocol reduces transmission collisions due to node mobility on the control channel by assigning disjoint sets of time slots to vehicles moving in opposite directions and to road side units. Analysis and simulation results in highway and city scenarios are presented to evaluate the performance of VeMAC and compare it with ADHOC MAC, an existing TDMA MAC protocol for VANETs. It is shown that, due to its ability to decrease the rate of transmission collisions, the VeMAC protocol can provide significantly higher throughput on the control channel than ADHOC MAC.

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VeMAC: A TDMA-Based MAC Protocol for Reliable Broadcast in VANETs

To make transportation safer, more efficient, and less harmful to the environment, traffic telematics services are currently being intensely investigated and developed. Such services require dependable wireless vehicle-to-infrastructure and vehicle-to-vehicle communications providing robust connectivity at moderate data rates. The development of such dependable vehicular communication systems and standards requires accurate models of the propagation channel in all relevant environments and scenarios. Key characteristics of vehicular channels are shadowing by other vehicles, high Doppler shifts, and inherent nonstationarity. All have major impact on the data packet transmission reliability and latency. This paper provides an overview of the existing vehicular channel measurements in a variety of important environments, and the observed channel characteristics (such as delay spreads and Doppler spreads) therein. We briefly discuss the available vehicular channel models and their respective merits and deficiencies. Finally, we discuss the implications for wireless system design with a strong focus on IEEE 802.11p. On the road towards a dependable vehicular network, room for improvements in coverage, reliability, scalability, and delay are highlighted, calling for evolutionary improvements in the IEEE 802.11p standard. Multiple antennas at the onboard units and roadside units are recommended to exploit spatial diversity for increased diversity and reliability. Evolutionary improvements in the physical (PHY) and medium access control (MAC) layers are required to yield dependable systems. Extensive references are provided.

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Vehicular Channel Characterization and Its Implications for Wireless System Design and Performance

Various wireless communication systems exist, which enable a wide range of applications and use cases in the vehicular environment. These applications can be grouped into three types, namely, road safety, traffic efficiency, and infotainment, each with its own set of functional and performance requirements. In pursuance of assisting drivers to travel safely and comfortably, several of these requirements have to be met simultaneously. While the coexistence of multiple radio access technologies brings immense opportunities towards meeting most of the vehicular networking application requirements, it is equally important and challenging to identify the strength and weaknesses of each technology and understand which technology is more suitable for the given networking scenario. In this paper, we evaluate two of the most viable communication standards, Institute of Electrical and Electronics Engineers (IEEE) 802.11p and long-term evolution (LTE) by 3rd Generation Partnership Project for vehicular networking. A detailed performance evaluation study of the standards is given for a variety of parameter settings such as beacon transmission frequency, vehicle density, and vehicle average speed. Both standards are compared in terms of delay, reliability, scalability, and mobility support in the context of various application requirements. Furthermore, through extensive simulation-based study, we validated the effectiveness of both standards to handle different application requirements and share insight for further research directions. The results indicate that IEEE 802.11p offers acceptable performance for sparse network topologies with limited mobility support. On the other hand, LTE meets most of the application requirements in terms of reliability, scalability, and mobility support; however, it is challenging to obtain stringent delay requirements in the presence of higher cellular network traffic load.

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LTE and IEEE 802.11p for vehicular networking: a performance evaluation

This paper summarizes the state of the art in connected vehicles—from the need for vehicle data and applications thereof, to enabling technologies, challenges, and identified opportunities. Connectivity is increasing around the world and its expansion to vehicles is no exception. With improvements in connectivity, sensing, and computation, the future will see vehicles used as development platforms capable of generating rich data, acting based on inference, and effecting great change in transportation, the human-vehicle dynamic, the environment, and the economy. Connected vehicle technologies have already been used to improve fleet safety and efficiency, with emerging technologies additionally allowing data to be used to inform aspects of vehicle design, ownership, and use. While the demand for connected vehicles and its enabling technology has progressed significantly in recent years, there remain challenges to connected and collaborative vehicle application deployment before the full potential of connected cars may be realized. From extensibility and scalability to privacy and security, this paper informs the reader about key enabling technologies, opportunities, and challenges in the connected vehicle landscape.

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A Survey of the Connected Vehicle Landscape—Architectures, Enabling Technologies, Applications, and Development Areas

This report is to present the research of Wireless Access for Vehicular Environments (WAVE). It introduces the basic technologies used in this standard, also proposes some limitations and applications of this criteria. Based on this, this report focuses on two limitations: real-time communication constraints and unfairness dedication of channel with using distributed coordination function on Medium Access Control (MAC) layer. Some ideas for improving these limitations are raised with the results of simulations. For the real-time problem, a Time Division Multiple Access (TDMA) MAC layer is studied and evaluated. For the unfairness dedication of channel problem, a priority is given to each node of different speed to achieve a dynamic contention window size. The result of simulation shows this method efficiently improves this limitation. Keywords— IEEE 802.11p, IEEE P1609, WAVE, MAC, RSU,

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Editorial: wireless access in vehicular environments

In order to provide Dedicated Short Range Communication (DSRC) for future vehicle-to-vehicle (V2V) communication the IEEE is currently working on the IEEE 802.11p Wireless Access in Vehicular Environments (WAVE) standard. The standard shall provide a multi-channel DSRC solution with high performance for multiple application types to be used in future Vehicular Ad Hoc Networks (VANETs). We provide a performance evaluation of the standard, considering collision probability, throughput and delay, using simulations and analytical means. WAVE can prioritize messages, however, in dense and high load scenarios the the troughput is decreases while the delay is increasing significantly.

S. Eichler

Papers

Performance Evaluation of the IEEE 802.11p WAVE Communication Standard