7

Other Challenges and Security Aspects

Wireless communications create further challenges that impact on networking protocols and algorithms in any layer. These additional issues arise mainly because of factors such as mobility and scalability. Localization, synchronization, addressing, data aggregation and querying, coverage, mobility and resource management are all additional challenges faced by untethered communications and we will review these topics in this chapter.

7.1 Localization and Positioning

Localization (Bulusu et al., 2000; Doherty et al., 2001; Savvides et al., 2001; Erdogan et al., 2003; Niculescu and Nath, 2003; Patwari et al., 2003) is one of the key issues in ad hoc networks, and especially in sensor networks because sensed data is almost meaningless without associating it with location data in many applications. Moreover, localization may be needed for some tasks such as spatial addressing of nodes and geographical routing. Like many other aspects related to ad hoc networks, the required level of localization accuracy differs from one application to another. For example, it may be enough to indicate in which room the measurement is made in one application. On the other hand, an accuracy level down to centimeters may be required in another application.

The first option for node localization is the global positioning system (GPS). However, GPS is not always a viable option for ad hoc networks. Nodes may be located in places where signals coming from satellites ...

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