Mobility in Wireless Sensor Networks

CONTENTS 14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380 14.2 Sensor Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381

14.2.1 Uncontrolled Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383 14.2.2 Controlled Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384 14.2.3 Mobility-Control Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384

14.3 Sink Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 14.3.1 Why to Move the Sink? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387

14.3.1.1 Data Gathering in Sparsely Populated Networks . . . . . . . . . . . . . 387 14.3.1.2 Load Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 14.3.1.3 Shortening the Communication Paths . . . . . . . . . . . . . . . . . . . . . . . 388

14.3.2 Random Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389 14.3.3 Predictable Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 14.3.4 Controlled Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392 14.3.5 Adaptive Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

14.4 Virtual Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 14.5 Consequences of Sensor or Sink Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401

14.5.1 Medium Access Control (MAC) Solutions with Mobile Nodes . . . . . . . . . 401 14.5.2 Routing and Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402

14.6 Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 14.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406

Both sensor and sink mobility in wireless sensor networks (WSNs) can have several advantages when compared to static setups. Mobile sensors can be used to eliminate coverage holes, can follow the monitored events, or can concentrate on interesting areas of the monitored region, to supply more detailed measurements where needed. On the other hand, mobile sink nodes can move close to areas where some event is reported (reducing thus the communication distances), can move close to isolated sensors and collect data if multi-hop transmission is not possible, or can balance the load on the relaying sensors and thus the energy consumption in the network. In this chapter, we will discuss in detail the different solutions for sensor and sink mobility, their advantages and drawbacks, and outline the impact they might have on issues such as Medium Access Control (MAC) or routing.