In this paper, we propose a multihop broadcast protocol for dissemination of time-critical emergency messages (EMs) in vehicular ad hoc networks (VANETs), where the IEEE 802.11p technology is used for communication among the nodes. The proposed trinary partitioned black-burst-based broadcast protocol (3P3B) consists of two primary mechanisms. First, a mini distributed interframe space (DIFS) in a medium access control (MAC) sublayer is introduced to give the time-critical EMs a higher access priority to the communication channel compared with other messages. Second, a trinary partitioning is designed to iteratively partition the communication range into small sectors. The trinary partitioning mechanism allows the farthest possible vehicle in the farthest sector from the sender node to perform forwarding to increase the dissemination speed by reducing the number of forwarding hops. In addition, 3P3B reduces the contention period jitter, which is independent of the density of vehicles, resulting in a more stable contention period. Analytical models are proposed for performance evaluation in conjunction with simulation-based performance analysis. The results demonstrate that 3P3B outperforms benchmarks of the existing broadcast protocols in VANETs in terms of the average message dissemination speed, message progress, communication delay, and packet delivery ratio

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Communication technology for vehicles has become an important topic for research. IEEE standards including IEEE 802.11p and IEEE P1609.1-4 have emerged to provide a framework for intervehicular communication (IVC). However, due to particular characteristics of IVC, such as high mobility, unstable connectivity, and network partitioning, information routing becomes inevitably challenging. This article reviews the recent research progress to highlight research challenges in vehicular routing protocol as a guideline for future development of IVC applications. The article focuses on the IEEE DSRC/WAVE standard. The state of the art in IVC routing protocols is surveyed, and open issues for further research are highlighted in the article

Abstract-Environmental problems, such as pollutions, become more intensive every year. One of the major causes is a higher fuel consumption and CO 2 emission. In year 2009, 23 percent of CO 2 emission globally comes from land transportation systems, which is equal to 7,000 million tons of CO 2 . This large amount of pollution gas must be reduced to slow down global environmental problems. Reduction of fuel consumption and CO 2 emission in land transportation systems, which will have immediate positive economical and environmental impacts, has become an important part of green technology to alleviate global warming due to human activities. Intelligent Transportation Systems (ITS), which aims at applications of Information and Communication Technology (ICT) in the transportation systems, has offered unique opportunities for the green ITS. This article aims to provide a survey of the latest published applications as well as the envisaged technical challenges in this research area.Index Terms-Green technology, traffic light-to-vehicle communication, TLVC, fuel consumption, CO 2 emission, intelligent transportation system, Green ITS, vehicular communications I. INTRODUCTION VIRONMENTAL problems become a serious concern for the mankind. Huge amount of pollution is released every year due to the growth of world economics, resulting in the global warming problem. There are several attempts to alleviate the global warming, such as uses of alternative natural energy; solar, wind, and water energy. However, the investment of natural energy production is very high and gives low return rate for industries. As a result, this approach is not yet achieved.According to statistics, more than 30,000 million tons of CO 2 is emitted each year [1]. As shown in Fig. 1a, North America is the number one continent of fuel consumption and C. Suthaputchakun is a PhD student of Electronic Engineering Department, University of Surrey, Guildford, Surrey, GU2 7XH, UK, on leave from Bangkok University, Bangkok, 12120, Thailand. (e-mail: c.suthaputchakun@surrey.ac.uk) Z. Sun is a professor of Electronic Engineering Department, University of Surrey, Guildford, Surrey, GU2 7XH, UK. (e-mail: z.sun@surrey.ac.uk) M. Dianati is a lecturer/RCUK academic fellow

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In this paper, we study the use of IEEE 802.11e for priority based messaging in Military Inter-Vehicle Communications (IVC). In the battlefield, messages generated by military vehicles (i.e., urgent combat related messages, warning messages) have different priorities which have different performance requirements in terms of delay and reliability. The message priorities are assigned based on the urgency of the message. For example, combat related messages will have the highest priority which is reflected in the lowest delay and highest reliability. We investigate the use of IEEE 802.11e to provide such priority based service differentiation. We examine a number of parameters' setting in the IEEE 802.11e Enhanced Distribution Coordination Access (EDCA) that will meet military vehicular communication requirements for different types of messages. OPNET based simulation studies are conducted to compare the protocol performance for each priority in terms of average delay as well as the percentage of dropped data. The results show that using proper parameters' setting for 802.11e will result in an efficient solution for IVC that supports different priority messaging.

communication technologies [1][2][3][4][5]. Several applications have been proposed for vehicular networks based on these standards [6][7][8][9][10][11]. In [6][7], the use of road-map information for ground vehicles tracking is proposed to enhance vehicles' position prediction. In contrast to vehicle detection and tracking, papers [8][9] promote autonomous car navigation using road profile recognition along with a support from GPS. In [10], vehicular remote tolling services are proposed based on communication through vehicular network standards. Apart from these applications, there are many vehicular applications concerning safety. Due to the nature of wireless communications, implementation of any protocols in VANETs poses a number of challenges including: broadcast storm problem, the hidden terminal problem, and frequent interruptions of connections when the underlying network is sparse. In addition, provision of different QoS levels for different broadcast applications is a non-trivial problem. Lack of infrastructure support adds the complexity of the broadcast protocols due to high volume of signaling overhead among the communication peers. High level of media access control (MAC) layer collisions can also have adverse impacts on the efficiency of the protocol due to hidden terminal problem.Here we summarize the key issues. Most of the existing broadcast protocols in the literature focus on how to select an efficient message forwarder to reduce broadcast delay and optimise network resource usage. To this end, there are some existing techniques, such as black-burst in Urban Multi-hop Broadcast (UMB) [12], contention window in Smart Broadcast (SB) [13], and binary partitioning in Binary-Partition-Assisted Broadcast (BPAB) [14]. These techniques aim to address the challenges broadcasting in ad-hoc networks. However, these solutions are not optimised for sparse networks, where there are frequent interruptions to the connectivity of the network. To address these shortcomings, authors in [18] and [19] propose Distributed Vehicular Broadcast (DV-CAST) [18] and Beaconless Broadcast (BL-CAST) protocols [19] respectively. These solutions demonstrate good performance in term of reliability even when the network is frequently disconnected. However, as DV-CAST operations are based on knowledge of the local topology information, the protocol needs periodic exchange of information among the vehicles. This incurs additional overhead and communication bandwidth resources especially in a large VANET with large numbers of vehicles in the network. BL-CAST, in contrast, takes the network overhead into consideration and operates without additional information exchange between vehicles. Nonetheless, no handshake mechanism is implemented in BL-CAST. As a consequence, this protocol is vulnerable to hidden terminal problem. In addition, the QoS provisions for different applications are not feasible in these aforementioned solutions.Therefore, this paper proposes a multi-hop broadcast protocol namely Trinary Partition Black Burst...