The objective of this chapter is to discuss data dissemination in vehicular networks in detail. We concentrate essentially on network-layer and application-layer protocols, which are often discussed and developed as a single protocol above the respective access technologies. The key objective is to achieve information exchange between any two vehicles, from one vehicle to all neighboring ones, from one vehicle to infrastructure components, from infrastructure to one or all neighboring vehicles, and dissemination from a vehicle to all those that are interested in the content.

We start by looking at ad-hoc routing protocols that were suggested in the early days of vehicular networks. Having identified their limitations, we explore alternatives, starting with geographic routing and geocast as communication primitives, and then exploring one of the most promising domains in the scope of vehicular networks: beaconing or one-hop broadcasting. In this framework, this chapter details the basic principles underlying such inter-vehicle communication (IVC) approaches, namely unicast, local broadcast, anycast, and multicast communication principles as used in vehicular networks. We of course investigate the current state of the standardization efforts, primarily focusing on the European Telecommunications Standards Institute (ETSI) standardization towards cooperative awareness messages (CAMs) and decentralized environmental notification messages (DENMs) as well as the ETSI GeoNetworking initiative. Furthermore, we explore options for exploiting available infrastructure such as roadside units (RSUs) or even parked vehicles to provide access to some backbone network or to help spread information among the vehicles. We conclude this chapter with a discussion of delay/disruption-tolerant network (DTN) approaches and the use of concepts known from Internet-based peer-to-peer networks.

This chapter is organized as follows.

1. • Ad-hoc routing (Section 5.1) – We start by exploring classical mobile ad-hoc network (MANET) routing algorithms in detail, because some basic knowledge of ad-hoc routing is needed in order to understand the more sophisticated vehicular ad-hoc network (VANET) routing options. In this section, we also discuss the applicability of MANET routing to VANETs as well as the specific challenges resulting from the underlying mobility pattern and delay constraints for vehicular safety applications.

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The wireless technology multimedia sensor network (WMSN) is a multidisciplinary technology. Researchers from diverse fields such as wireless and ad-hoc sensor networks, multimedia, distributed signal processing, control theory, and embedded systems have contributed new ideas to innovate real-life applications. Advances in embedded electronics and MEMS have resulted in greater processing power per unit size of the sensor nodes in such a way that today it is possible to bring them together in a more powerful, complex, and compact manner. With the increased processing power, it is now able to capture and process complex multimedia data such as video, audio, and images. For example, with the help of new sensing technologies, it is possible to provide proper images and audio-visual feeds in different surveillance applications, in addition to the scalar parameters of environment. The easy availability of inexpensive miniaturized hardware such as cameras and microphones, the advancements in distributed signal processing, and multimedia source coding allow much richer sampling of the environment than traditional WSNs. This trend opened up new opportunities for protocol designers to propose effective and energy-efficient solutions of the existing problems [1–62].

Network applications

Applications of WMSNs introduce new multimedia features in addition to the general capabilities of WSNs, to enrich them in terms of monitoring. Along with enhancing the existing sensor network applications, WMSNs use various multimedia-specific ideas to pioneer new opportunities in this field. We classify these applications of WMSNs into several categories and explain them briefly in this chapter.

Wireless sensor networks (WSNs) exhibit an “autocratic” operational policy with minimal human intervention. So, such networks must be self-configurable to maintain their autonomy. The requisitions of WSN-specific applications are quenched by temporal cooperation and coordination among the sensor nodes. Naturally, these nodes are expected to perpetuate a healthy intra-network infrastructure. However, they are power constrained with a bounded communication range and low computational ability. Hence, issues related to network infrastructure should be dynamically handled with efficacy.

Topology is a vital aspect of WSNs that needs attention for both network and fault management. In this chapter, we focus on two aspects of topology: (a) topology management, and (b) topology control.

Topology management is the process of deriving a simple graph of node connectivity by determining the inter-nodal links and virtual relationships for efficient operations within a network contour. Topology management aims at conserving the energy of the nodes and consequently extending the lifetime of the network with parallel maintenance of network connectivity.

Topology control of a WSN is a measure of the degree of network coverage and internode connectivity. Topology management and control might appear analogous. However, these two aspects are distinct, and so is their categorization, which we will discuss in this chapter.

Communication between vehicles (and between vehicles and available infrastructure) is the topic of this chapter. Essentially, we give a basic introduction to inter-vehicle communication (IVC) identifying the key concepts in the safety as well as in the non-safety application domains. For this, we derive all the relevant communication concepts and solutions for those applications and, most importantly, identify the requirements such as maximum delays, minimum dissemination range, or minimum data rates. Furthermore, we present an overview on the possible communication paradigms, such as whether information is to be exchanged without the help of any available infrastructure or whether infrastructure elements – roadside units (RSUs), parked vehicles, or even widely deployed cellular networks – can be used for the information exchange.

The scope of this chapter is to introduce IVC as an active research field. The main motivation is to become familiar with the field to a level that helps one to understanding the fundamental concepts and their limitations. All the communication principles outlined will be studied in greater detail in the following chapters.

This chapter is organized as follows.

1. • Applications (Section 3.1) – In this section, we introduce the field starting with typical applications for IVC. We will show that the scope and character of these applications vary widely, which complicates the development of common and generalized IVC protocols.

2. • Requirements and components (Section 3.2) – Starting from knowledge about IVC applications, we derive requirements on IVC solutions and study metrics to assess their effectiveness. In a second part, we introduce all the communication entities involved and possible mechanisms for information exchange.

3. • Concepts for inter-vehicle communication (Section 3.3) – This section can be regarded as the main part of this chapter. We broadly study all the communication principles and protocols that have been considered for IVC. This overview explains why the different protocols have been studied and what their main advantages and disadvantages are.

4. • Fundamental limits (Section 3.4) – We conclude this chapter by discussing fundamental limits for IVC.

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Wireless sensor networks (WSNs) have fascinated both the research and development communities. Applications of WSNs have mushroomed in both civilian and military domains. The growth of wireless sensor networks was originally motivated by military applications; however, WSNs are now used in all kinds of civilian and industrial applications [1–20]. Currently, the overwhelming majority of WSNs measure scalar tangible phenomena such as humidity, pressure, temperature, movement, and pollutants. Typically, most WSNs are built for delay-tolerant and low-bandwidth applications. Hence, most research efforts have concentrated on this latter paradigm, which is often called terrestrial sensor networks. In any WSN application the main challenge is the lifetime of the network. A WSN structure includes a gateway that offers wireless connectivity back to the wired/fixed network.

In nearly all applications of the WSNs, they are used to monitor certain physical processes. They are deployed for measuring the temperature, air pressure, radiation of the human body, chemical reactions, movement of objects, vitals of the body, and so on. By doing this we can recover some important information of the boundaries that are often called edges. To keep track of the edge of a physical development, the recognition of a boundary is imperative. The issue of discovering the boundary is considered to be the first step for resolving the edge detection. In digital processing there are many methods for identifying the edge; however, they are not easy to implement in the WSNs’ environment since the sensor nodes are not equally spaced like pixels, and because of limited computational power and memory [3–6].

Wireless sensor networks (WSNs) use the same medium (which is the air) for wireless transmission that the nodes in a wireless local area network use. In order for nodes in a local area network to communicate properly, standard access protocols like IEEE 802.11, IEEE 802.15.4, and ZigBee, are available. However, these and other protocols cannot be directly applied to the wireless sensor area networks. The major difference is that, unlike the devices participating in local area networks, sensors are equipped with a small source of power (usually a battery), which drains very quickly. In addition, sensor nodes have limited resources of memory and computational power. Hence, there is a need to design new protocols for medium access control (MAC). This chapter investigates some of the major MAC protocols available [1–7].

Medium access control in wireless networks

There exists a very good set of standard protocols for wired and wireless area networks, which are proven to operate efficiently. There are many reasons for not using the wired and traditional wireless MAC protocols for WSNs. The standard protocols in wired local area networks use the well-known carrier sense multiple access with collision detection (CSMA/CD) scheme for individual stations to access the medium. This protocol, the IEEE 802.3, is known as Ethernet [1–46]. In this scheme, each station senses a medium for a random amount of time. If no activity is detected it starts its own transmission. If it detects any activity in the medium it defers its transmission until the activity ceases. If it senses a collision of packets from different nodes in the networks it backs off a random exponential amount of time and then starts contending for transmission using the backoff exponential algorithm. Slotted ALOHA networks traditionally use a time division multiple access (TDMA) scheme [9–10]. In this scheme, the time is divided into an equal number of slots such that a node is allowed to transmit only in its allotted slot. Here, the disadvantage is that a node is allowed to transmit if and only if it owns the slot; otherwise it has to listen to the medium for the data intended for it. Therefore, if the node has no data to send the bandwidth is simply wasted because there will be no activity for the amount of slot time allotted to a node with no data.

Radio access technologies like WiFi, IEEE 802.11p, and LTE form the basis of any communication stack, and the choice of technology heavily influences application performance. They are the topic of this chapter.

In general, two families of radio access technologies can be differentiated: those based on cellular networks and those based on short-range radio. Traditionally, these two families were conceptually vastly different. Cellular networks relied on central coordination, whereas short-range radio operated in a fully distributed fashion. Cellular networks used licensed spectrum, whereas short-range radio had to make do with unlicensed spectrum. These differentiations are no longer strictly true. Cellular networks are slowly moving towards (some) distributed control, while short-range radio, particularly for inter-vehicle communication (IVC), is profitting from infrastructure support and central services. Further, short-range radio for IVC can now rely on allocated dedicated spectrum. A new trend further blends licensed and unlicensed spectrum into spectrum that has primary users, which can access the spectrum with absolute priority, but one also allows its white spaces to be filled by non-primary users.

We will take a detailed look at the concepts and the underlying principles of representative radio access technologies from both families, always with a focus on their use in vehicular networks.

This chapter is organized as follows.

1. • Cellular networks (Section 4.1) – We start by following the evolution of the Third Generation Partnership Project (3GPP) family of cellular networks: from GSM, via UMTS, to LTE, with a perspective on future technologies. We will always be considering both halves of a cellular network, that is, the air interface and the radio access network (RAN), as well as the core network.

2. • Short-range radio technologies (Section 4.2) – We then turn towards a classical short-range radio technology, following the evolution of IEEE 802.11 wireless LAN (WLAN) and its many extensions. We discuss one extension in particular detail: IEEE 802.11p, which extended WLAN for use in vehicular networks. Lastly, we discuss efforts building on WLAN to provide a complete IVC protocol suite.

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