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Vehicular Ad-hoc Networks for Smart Cities: First International Workshop, 2014



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Author: Anis Laouiti

Publisher: Springer

Genres:

Publish Date: September 9, 2014

ISBN-10: 9812871578

Pages: 93

File Type: PDF

Language: English

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Book Preface

Vehicular ad-hoc network (VANET) is a special type of ad-hoc network that is like mobile ad-hoc network (MANET). It can be utilized to improve vehicle safety, enhance traffic efficiency, and provide infotainment in vehicles. VANET has several distinguishing characteristics that differentiate it from MANET. In VANET, topology is very dynamic because vehicles move at a high speed. Blum and Eskandarian [1] stated that multihop paths in VANET are very short-lived because vehicles move at very high speed, as compared to the MANET. Unlike MANET, the mobility of vehicles is regular and predictable in VANET, and there are no power constraints. Vehicles can be equipped with some positioning systems (GPS and GALILEO), through which vehicles’ position can be predicted. This predictability allows an improvement in link selection. Figure 1 shows the difference between the MANET and VANET. VANETs are considered to be a class of MANET. However, VANETs have some distinguishing characteristics. Some of these characteristics, as discussed by Gillani et al. [2], are high node mobility, high dynamic network topology, enough battery power, sufficient storage capacity, high processing power, and availability of GPS. Due to these characteristics of VANET, the medium access control (MAC) solutions presented for MANET are not suitable for VANET. A MAC solution is required to specify the way the nodes share the underlying channel.

While designing a MAC protocol for VANET, the type of messages should also be considered [3]. As there are three types of priority-based messages in VANET applications, hence the MAC protocol should allocate the channel on the basis of message type. The first type of message is periodic messages which give information about the vehicles’ current status (position, speed, and direction), these messages are usually needed to broadcast. The second type of messages is of an event-driven messages (emergency message usually related to safety) and these messages have high priority. This type of message is very time-critical, so need high transmission rate. The third type of message is informational messages (nonsafety application messages). These messages need prioritized access. In addition to handling the channel access on the basis of message types, a VANET MAC protocol should also consider some other challenges of VANET like its decentralized communication mode (most VANET applications don’t rely on any infrastructure) and unpredictable response and reliability.

This paper presents the MAC layer challenges of VANETs and state-of-the art solutions proposed in literature to meet those challenges. The MAC protocols are classified into three classes depending upon the mechanism they use for channel access.


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