Vehicular Ad-hoc Networks for Smart Cities

Vehicular ad-hoc network (VANET) is a special form of mobile ad-hoc network (MANET) in which vehicles communicate with each other by creating an ad-hoc network. Before the deployment of VANET, it is necessary to address some important issues of VANET, specially concerning about architecture, routing, mobility, and security. Medium access control (MAC) protocols specify the way in which nodes share the underlying channel. As no standard exists for VANET, the research community has previously used IEEE 802.11a and 802.11b as the MAC layer access technologies. In this paper, we have discussed that the main challenge for VANET safety applications is to design an efficient MAC, so that all safety-related messages can be sent on time and such a protocol should be reliable because human lives are involved in the case of VANET. First, the challenges and requirements of a medium access protocol for VANET are discussed and then a survey of MAC solutions available in the literature to deal with these challenges in VANET is presented.

Research in vehicular ad-hoc networks (VANETs) have attracted a lot of attention in the recent years as emerging wireless technologies have opened up the way to many new exciting applications. VANETs are highly dynamic wireless networks that are designed to support vehicular safety, traffic management, and user-oriented applications. Each vehicle can exchange information to inform other vehicles about the current status or a dangerous situation such as an accident. Detecting and sending information about such situations requires a reliable broadcast service between vehicles, thus increasing the need for an efficient medium access control (MAC) protocol. In this paper, we propose ASAS, an Adaptive Slot Assignment Strategy, which takes advantage of bandwidth spatial reuse and reduces intra-cluster and inter-cluster message collisions without having to use an expensive spectrum and complex mechanisms such as CDMA or FDMA. Cluster heads (CHs) which are elected among the vehicles are then responsible for assigning time slots to the other vehicles in their clusters. The evaluation results show the interest of ASAS in terms of slot reuse and collision rates in different speed conditions.

Vehicular ad-hoc networks (VANETs) have been a hot research topic in academia and industry with respect to safety of drivers and entertainment applications. Many MAC layer protocols have defined in research. The IEEE 802.11p is one of the popular carrier sense multiple access (CSMA)-based MAC layer protocol for VANET and is successfully used for safety applications. However, IEEE 802.11p is less efficient for bandwidth hungry and delay-sensitive applications as there is significant fixed overhead of channel access, the inter-frame spaces, and acknowledgments of each frame transmitted. In this paper, an aggregation mechanism, named Vehicular MAC protocol data unit (V-MPDU) with block acknowledgment as an extension of the existing IEEE 802.11p is proposed. The proposed aggregation technique collects frames against each destined node and wraps each frame in a single IEEE 802.11p header. Moreover, it permits each of the aggregated data frames to acknowledge individually or re-transmit in case of any transmission error. Hence, it improves the channel access mechanism in terms of efficiency as multiple frames transmit in single transmission opportunity, which ultimately reduce number of potential collisions and re-transmissions as well. Further, effective bandwidth automatically improves.

The need for safety and comfort in vehicular environments has led to a lot of research in vehicular ad-hoc networks (VANET), ranging from vehicle to vehicle (V2V) and vehicle to infrastructure (V2I) communications to security. As regards the latter aspect, mostly the focus has been on resorting to public key infrastructure (PKI) and its related concepts. Moreover, methods used to detect the most feared security attacks are based almost exclusively on the use of physical characteristics as well as PKI concepts or both. However with emerging technologies that enable connecting a vehicle to external resources, VANET is evolving, thus inheriting security threats that are common place in conventional IT systems. Therefore, as it is shown in the paper, VANET security must go beyond cryptographic-centric mechanisms that are commonly used for providing data security in wireless environment.

In recent years, the VANET has received a greater attention among researchers in academia and industry due to its potential safety application and nonsafety application. Malicious users are one of the types of attackers in VANET and create the security problems. Confidentiality, integrity and availability (CIA) are major components of security goals. The increasing research interest, potential applications, and security problem in VANET lead to the needs to review the attacks on security goals. In this paper, the aim is to present the survey of attacks on security goals and to describe in details the nature of attacks and the behaviour of attackers through different scenarios in the network. The paper also provides a better understanding of security goals and finally it provides an analysis and classifies the attacks on the basis of security goals into different threat levels that can help in the implementation of VANET in real life.

The use of vehicular ad-hoc network (VANET) has been increasing immensely over the past few years. VANET has played a very important role in safety issues on roads. There are many routing protocols in VANET, out of which broadcasting protocol is used more frequently for sharing, traffic, weather and emergency, road conditions among vehicles and delivering advertisements and announcements. Several types of broadcasting protocols have been proposed, out of which DV-CAST protocol and edge aware epidemic protocol (EAEP) are two such types that have come into force recently. It is said that these two protocols can be of great use later but their performances are yet to be explored in different scenarios. So in this paper the performance of DV-CAST protocol and EAEP are discussed, in well-connected and totally disconnected highway and city scenarios respectively, and a conclusion was reached about which protocol works better in different scenarios. The evaluation includes the measurements of the parameters such as packet drop and throughput. NCTUns 6.0 was used as the network simulator. NCTUns is a high fidelity and extensible network simulator and emulator which helps to simulate complex scenarios. The challenges and future perspectives of broadcasting protocols are also discussed in this paper. This work helps the researchers, who are currently working on other routing protocols in VANET, to come to a decision about the best routing protocols that are to be used in different scenarios.

On highways, each vehicle uses periodic 1-hop broadcast messages to advertise its position and other information so that vehicles in the vicinity and those which are hops away can find the advertising vehicle for information exchange. During destination discovery, a vehicle issues broadcast messages, which travel hop by hop in search of destination. We argue that since periodic 1-hop messages are sent on regular intervals, so these can be manipulated in such an intelligent way that routing protocols may not need to execute broadcast destination discovery procedure. The continuous periodic HELLO broadcast mechanism can assist the routing protocol in this regard. The proposed ZoomOut HELLO (ZOH) technique introduces a neighbour-cum-forwarding (NF) table. In this scheme, periodic ZOH mechanism will populate the NF table, while the forwarding mechanism will use it. We introduce the concepts of Front and Behind relatives, which are selected out of 1-hop neighbours based on the typed HELLO messages exchanged between 1-hop neighbours. ZOH is a broadcast suppression technique and implicitly provides chain of relatives in the front and behind direction of each vehicle. A routing protocol can therefore use this chain. We have developed analytical model for ad-hoc on-demand distance vector (AODV), preferred group broadcast (PGB), reliable opportunistic broadcast (R-OB-VAN) and ZoomOut HELLO, and implemented them in MATLAB. The results show that ZoomOut HELLO generates least number of RREQ rebroadcast messages and has minimum network delay due to RREQ messages.

The fading environment plays a critical role for vehicular communication. High fading environments lead to high data losses, which seriously affect the communication of safety applications in vehicular ad-hoc networkings (VANETs). Rician and Rayleigh fading models are considered to be realistic fading models for vehicular communication. This paper contributes in two aspects specifically for safety applications (a) Evaluation of Rician and Rayleigh fading for vehicular environment (b) It proposes a suitable combination of data rate and transmission power (Tx) that will minimize fading effects caused by Rician and Rayleigh fading. NCTUns is used to simulate vehicles with a safety application protocol called wave short message protocol (WSMP). By using appropriate combination of these parameters, significant improvements have been observed in throughput.