Connectivity-aware Medium Access Control in platoon-based Vehicular Ad Hoc Networks

Various ongoing research efforts in Vehicular Ad hoc Network (VANET) related to safety and non-safety applications have been published in academia and industry. One of the main areas in VANET that is still lacking of significant research contributions is toward designing reliable Medium Access Control (MAC) protocols. Existing surveys on MAC protocols in VANET mostly discuss general MAC methods, that include contention-based and contention-free MAC protocols. A hybrid MAC protocol that adopts both contention-based and contention-free MAC, proposed to enhance the network performance in VANET, is fruitful to be explored further. Hence, a survey of hybrid MAC protocols for VANET is presented in this paper. The benefits and limitations of the existing hybrid MAC protocols are discussed based on their classification to provide some insights into the recent advancement of high-performance MAC protocols for vehicular networks. Finally, some open research issues are highlighted as part of future research directions that need further investigations.

The IEEE 1609.4 [1] is a MAC extension of IEEE 802.11p [2] to support multi-channel operations. However, the IEEE 1609.4 does not allow nodes to exchange non-safety messages during the CCH interval. This paper proposes a Vehicular Enhanced Multi-channel MAC protocol (VEMMAC) for Vehicular Ad hoc Networks (VANETs). The VEMMAC adopts the IEEE 1609.4 with alternating sequences of the Control Channel (CCH) interval and the Service Channel (SCH) interval. Different from the IEEE 1609.4, the VEMMAC allows nodes to transmit non-safety messages during CCH interval and broadcast safety messages twice with each in the CCH and SCH interval. Our proposal can utilize the channel resources more efficiently than the IEEE 1609.4. The simulation results show that the proposed VEMMAC protocol achieves higher throughput for service data and is more reliable for safety messages broadcast than other protocols.

Highly dynamic geographical topology, two-direction mobility, and varying traffic density can lead to fairness issues in Vehicular Ad-hoc Networks (VANETs). The Medium Access Control (MAC) protocol plays a vital role in sharing the common wireless channel efficiently between vehicles in a VANET system. However, ensuring fairness between vehicles can be a challenge in designing MAC protocols for VANET systems. The existing protocol, IEEE 802.11 DCF, ensures that the packet transmission rate for a particular vehicle is directly proportional to the amount of time a vehicle spends within a service area, but it does not guarantee that faster vehicles will be able to send the minimum number of packets. Other existing MAC protocols based on IEEE 802.11 are able to provide a minimum amount of data transmission regardless of velocity, but are unable to provide an amount of data transmission that is more proportionate to the time a vehicle spends in the service area. To address the above limitations, we propose a Speed Aware Fairness Enabled MAC (SAFE-MAC) protocol that calculates the residence time of a vehicle in a service area by using mobility metrics such as position, direction, and speed to synthesize the transmission probability of each individual vehicle with respect to its residence time. This is achieved by dynamically altering the values of parameters such as minimum contention window, maximum backoff stage, and retransmission limit in the MAC protocol. We then develop an analytical model to compare the performance of our proposed protocol with contemporary MAC protocols. Numerical analysis results show that our proposed protocol significantly improves fairness among the speed-varying vehicles in VANET.

Rapid development and deployment of vehicular ad-hoc networks (VANETs) require an efficient and scalable media access control (MAC) protocol to support high-priority safety applications. To meet the requirements, researchers have proposed many distributed TDMA-based MAC protocols for VANET in recent years. Despite the superior performance shown in the simulations, few of the proposed protocols have been evaluated in the real-world environment. However, according to the measurement-based works, the extremely unstable wireless communication of VANETs in the real world challenges the performance of the MAC protocols. Hence it may deteriorate if the protocol is implemented in real vehicles. In this paper, we design and implement a real-time testbed for distributed TDMA-based MAC protocols in VANETs. The testbed utilizes the collaboration of hardware (FPGA) and software (Linux) to handle the high-priority and low-priority tasks, and high-accuracy GPS receiver for time synchronization. Results of the measurements show that the transmission delay of the high-priority packets is bounded and the TDMA access is functional.

Vehicular Ad Hoc Networks (VANETs) and their diverse applications experience growing interest in both academic and industry. Different types of traffic packets delivered through vehicle-to-vehicle and vehicle-to-infrastructure communications are intended to improve passenger safety and comfort. In this paper, we propose a multiple priority supported Medium Access Control (MAC) protocol for VANETs based on the time slotted p-persistent channel access mechanism. The protocol differentiates the services packets into multi-priority on the Control Channel (CCH). Theoretical analysis based on Markov model is presented to optimize the transmission probabilities of the packets with different priorities, as well as the adjustable intervals of the CCH and the Services Channels (SCHs). Both analytical results and simulation experiments show that the proposed MAC protocol is able to ensure the prioritized transmission of the safety packets and also achieve optimal system performance with respect to saturated throughput.

The current medium access control (MAC) protocol of the wireless access in vehicular environments (WAVE) system is based on IEEE 802.11 distributed coordination function (DCF) and enhanced distributed channel access (EDCA), which have drawbacks in supporting throughput-sensitive non-safety applications in vehicular ad-hoc network (VANET). In order to address the problem, we propose a novel MAC protocol, namely vehicular MESH network (VMESH), which is specifically designed for the control channel (CCH) and multiple service channels (SCHs) structure of WAVE. A synchronized and distributed beaconing scheme is employed in the VMESH protocol for the purposes of neighborhood awareness and dynamic resource reservation on SCHs. The advantages of the VMESH protocol in supporting the throughput-sensitive non-safety applications in VANET are shown through the theoretical analysis comparing to the current WAVE MAC.

IEEE 802.11p is a communication protocol which is extended by IEEE 802.11 standard, mainly used in Vehicular Ad-Hoc Networks (VANETs). VANETs generally include the Service Channel (SCH) and Control Channel (CCH). In the traditional 802.11p protocol, the length ratio between CCH and SCHs is fixed. This paper presents a variable SCH interval(VSI) multichannel medium access control (MAC) scheme under the non-saturated channel. Under this scheme, we can control the length of CCH interval and SCH interval. This paper uses three-dimensional Markov chain model to calculate the delay of WAVE service announcement (WSA) frame. We propose a VSI MAC calculation model under unsaturated condition to achieve the maximum throughput. The simulation results indicate that the proposed scheme can help VANETs increase the unsaturated throughput of SCHs and lower the transmission delay of data frames obviously.

In vehicular ad hoc networks (VANETs), the medium access control (MAC) protocol is of great importance to provide time-critical safety applications. Contemporary multihop broadcast protocols in VANETs usually choose the farthest node in broadcast range as the forwarder to reduce the number of forwarding hops. However, in this paper, we demonstrate that the farthest forwarder may experience large contention delay in case of high vehicle density. We propose an IEEE 802.11-based multihop broadcast protocol VDF to address the issue of emergency message dissemination. To achieve the tradeoff between contention delay and forwarding hops, VDF adaptably chooses the forwarder according to the vehicle density. Simulation results show that, due to its ability to decrease the transmission collisions, the proposed protocol can provide significantly lower broadcast delay.

Intelligent Transportation Systems (ITS) is an integrated approach being developed to exchange relevant information to increase the safety and efficiency of the road transportation systems. Vehicular Ad hoc Network (VANET), a variant of mobile ad hoc networks (MANET), is a core component of ITS. Performance of this smart ITS mainly owes to the design of efficient routing protocols in VANETs. Distinct features of VANETs like unsteady connectivity, high mobility and partitioning of the network have made routing of the information in VANETs difficult and challenging, hence dictating the development of efficient routing protocols. The computation of the best route measures the performance of communication whereas routing protocols takes care of communication & routing of the data. Provision of smart communication, necessitates the analysis of routing protocols in VANET. Accordingly in this paper we have reviewed various types of existing routing protocols in VANET, listing their advantages and disadvantages. Lastly possible inclinations of forthcoming research linked to VANET routing are discussed.

Contention-based medium access control (MAC) protocols for vehicular ad hoc networks (VANETs), such as IEEE 802.11p, have been revealed inefficient performance due to merging collisions, hidden terminal problems, poor resource utilization, and inconsistency in various traffic scenarios. This paper proposes a novel clustering-based contention-free MAC (CC-MAC) protocol to handle intra-cluster and inter-cluster transmission collision problems in VANETs. A cluster head (CH) assigns the time slots to the cluster members depending on their traffic demands. Inter-cluster interference among vehicles is minimized by comparing the relative offset time and reducing access delay during the slot allocation. Furthermore, a TDMA-based predetermined scheme is proposed to improve resource utilization for both control channel and service channels, and merging collisions are resolved by disjointed slot assignment. Hidden terminal problem is resolved by detecting slot assignment identification on gateway vehicles regarding the direction of the vehicle’s mobility. Simulation results show that the proposed protocol outperforms the IEEE 802.11p, STCM, and optimized CB-MAC protocols in both highway and urban traffic scenarios in terms of normalized throughput, packet delivery ratio and average end-to-end delay.

Vehicular ad hoc networks (VANETs) present an intriguing platform for several applications on e.g., intelligent transportation system (ITS) and infotainment applications aspire to be the main pattern of communication among vehicles while travelling. This can significantly impact on the amount of data exchanged by vehicles, increasing the contention on communication links and thus, degrading the quality of service of these applications. So, discrimination of data becomes imperative and forwarding critical information on suitable routes becomes decisive. Hence, a quality of service (QoS)-driven mechanism is needed to handle and assign network resources according to the stringent application data traffic demands. But, VANETs high node mobility and frequent link failure, stuck a big challenge in implementing an effective policy to meet and enforce these QoS requirements. A promising way to tackle this issue is to enforce QoS at the network layer, since it is the crucial point in VANETs’ communication. So, over the years, many QoS-aware routing protocols were specifically conceived for VANETs. In this paper, we present a comprehensive survey of QoS-aware routing protocols in VANETs’ literature. We examined the protocols based on their ability to support ITS infotainment services, their multi-constraint path problem (MCP), protocol’s functionality and weakness, objectives and design challenges. This way, we outline future directions for VANETs QoS-aware protocol research.

International audience

The emergence of the Internet of Things (IoT) is gradually changing people’s lives and is widely used in various fields. Wireless body area networks (WBAN) and vehicular ad-hoc networks (VANET) are typical examples of IoT applications. In both environments, an attacker can tamper, intercept, and eavesdrop on data transmitted in the public channel. Therefore, it is necessary to design authentication and key agreement (AKA) protocols to protect the communication of entities. Recently, Wu et al. proposed a novel AKA protocol in WBAN. Jagriti et al. proposed an anonymous AKA protocol in VANET. In this paper, we analyse of Wu et al.’s protocol and Jagriti et al.’s protocol, respectively. Unfortunately, we find that Wu et al.’s protocol cannot resist sensor node capture attacks, and Jagriti et al.’s protocol cannot resist session key disclosure attacks, on board unit (OBU) capture attacks, and man-in-the-middle attacks. Finally, we propose some suggestions for the two protocols.

VANET (Vehicular Ad-hoc Network) is an ad-hoc wireless network which nodes are composed by mostly moving vehicles and infrastructure communications or access points along the road. It integrates adhoc networking, cellular technology, wireless LAN and other technologies, which include GPS(Global Positioning System), digital mapping, sensing technologies and advanced information processing tools to support Intelligent Traffic Systems (ITS). VANET is developed mainly to improve road safety and to increase the traffic efficiency. It is designed to support the exchange of warning messages among the vehicles to increase the passenger safety and other information related to VANET applications and services . To achieve these goals, there are several issues that should be addressed. One of these challenges is designing reliable and efficient Medium Access Control (MAC) protocol for VANET. Due to VANET’s distinguishing characteristics, such as high mobility of the nodes, dynamic network topology, enough battery power, high processing power, etc, the MAC protocols designed for MANET (Mobile Ad-hoc Network) are not suitable for VANET. The research community has been working to develop MAC protocols appropriate for this ad-hoc network by proposing new design or modifying the existing one.In this paper, the VANET’s architecture, characteristics, applications and standard are discussed and then a comprehensive study of several MAC protocols available in the literature is presented.

Past few decades have witnessed large increase in number of vehicles on roads due to which the traffic safety needs have also become complex and hence necessary to be taken care of. Vehicular ad hoc networks (VANETs) are becoming an asset for achieving all these goals. VANETs provide applications like driver assistance, passenger comfort and vehicle safety. Apart from its general characteristics due to the dynamic nature of road environments and traffic patterns, communication linkage among vehicles in VANETs suffers breakage problem hence requires a very reliable routing protocol. To manage the communication efficiently many routing protocols are already available for MANETs which can be further used for routing and communication among vehicles in VANETs, but characteristics of these two networks (VANET and MANET) are very different, so there is requirement to enhance these MANET routing protocols so that those can be used in VANETs. When we use some existing routing protocols in VANET then number of link breakage are surprisingly high because mobility is higher in VANETs as compared to MANETs. So this paper presents advanced version of an existing MANET routing protocol for better performance in VANET environment. The new routing protocol has removed problem of large number of routing error messages which was existing in AODV routing protocol. Protocol proposed in this paper has better results as compared to AODV and paper has also shown results of simulation and also elaborated the findings.