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Topologi control in wireles ad hoc and sensor network - Santi P.

Santi P. Topologi control in wireles ad hoc and sensor network - Wiley publishing , 2005. - 282 p.
ISBN-10 0-470-09453-2
Download (direct link): topologycontess2005.pdf
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Concerning message complexity, XTC can be classified as a lightweight protocol, since its computation requires exchanging 2n messages (under the assumption that link quality is measured using received signal strength).
In case the link quality-based order coincides with the neighbor order based on Euclidean distance, GXTC satisfies some additional property. In particular, in (Wattenhofer and Zollinger 2004), it is proved that GXTC has logical node degree at most 6, it is planar, and that it is a subgraph of the RNG. More particularly, it is shown that if the node placement is such that no node has two or more neighbors at the same distance (as it is likely the case in presence of random node distribution), GXTC is exactly the RNG. Thus, the algorithm reported in Figure 12.6 can be considered a distributed implementation of the computation of the RNG, as it is the DistRNG protocol of Figure 11.7. Note that a notable feature of XTC as compared to DistRNG is that it does not require directional information, which is typically provided using expensive directional antennas.
Summarizing, the XTC protocol
- computes a topology that contains only bidirectional links;
- preserves worst-case connectivity;
- is lightweight;
- in case the link quality-based order coincides with the distance-based order, the XTC protocol
- produces a planar topology with logical node degree at most 6;
- produces a subgraph of the RNG.
13
Dealing with Node Mobility
In the previous chapters, we have presented several distributed topology control (TC) protocols, based on different approaches (location-based, direction-based, and neighbor-based TC). When describing the protocols and analyzing their properties, we implicitly assumed that the network nodes were stationary. Indeed, node mobility is a prominent feature of ad hoc networks: in most application scenarios, the wireless devices that form the network, or at least a significant percentage of them, are mobile. This is the case, for instance, of ad hoc networks used to deliver traffic information (here, vehicles can be seen as network nodes), or to provide ubiquitous Internet access (here, portable devices carried by humans can be used to increase service coverage), or in the delivery of location-aware information (as in the previous example, humans carrying a wireless device can be seen as network nodes). In some cases, node mobility is present in wireless sensor networks also: for instance, if sensors are deployed on the surface of the ocean to monitor, say, the water temperature, we can expect that they are carried around by ocean flows.
So, it seems that current literature on TC has ignored one of the most important features of ad hoc and sensor networks, that is, node mobility. Is this fact true? As we shall see, the answer to this question is ‘in part, yes’: although some TC techniques explicitly designed for mobile networks have been introduced, many fundamental issues related to applying TC in mobile networks have not been addressed yet.
Leaving the discussion of open research issues related to the application of TC in mobile networks to Chapter 15, in this chapter we review the current state of the art on this topic. We start by revisiting the design guidelines discussed in Chapter 9 in the context of mobile networks. Then, we discuss the effect of node mobility on the value of the CNN, which, as we have seen in the previous chapter, is a fundamental network parameter in neighbor-based TC. In the last section, we present some of the TC protocols (or reconfiguration procedures of known protocols) that have been proposed in the literature to deal with node mobility.
Topology Control in Wireless Ad Hoc and Sensor Networks P. Santi
© 2005 John Wiley & Sons, Ltd
144
DEALING WITH NODE MOBILITY
13.1 TC Design Guidelines with Mobility
As we have discussed in Chapter 9, a TC protocol should be designed according to several guidelines, which we summarize below:
1. fully distributed and asynchronous implementation;
2. construct the topology using only local information;
3. build a topology that preserves the original network connectivity (at least w.h.p.) using only bidirectional links;
4. construct a topology with small physical node degree;
5. use relatively ‘low-quality’ information to build the topology.
Let us consider these design guidelines in the context of mobile networks. A first comment is about what we mean by mobile network. It is clear that different types of node mobility may occur in ad hoc networks, ranging from highly mobile networks (e.g. vehicular ad hoc networks, where node velocity can be above 100 km/h), to networks in which node mobility is extremely low (say, if a sensor network is used to monitor the movement of turtles). Since the latter type of mobility is well approximated by stationary networks, in this chapter we are concerned with networks in which node mobility is at least moderate. In other words, we want to discuss what changes in the picture that we have drawn in Chapters 9-12 when the assumption that node positions do not change during the execution of the TC protocol and for a certain period of time after its execution is dropped.
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