Higher layer issues: ad-hoc and sensor networks

Ultra-wide-band (UWB) radio has the potential of allowing simultaneous com- munication of a large number of users at high bit rates. In addition, the high temporal resolution inherent to UWB provides robustness against multipath fading and is particularly attractive for indoor local area network (LAN) applications. UWB is also capable of recovering distance information with great precision. As we will show later in this chapter, distance and position data can lead to better organization of wireless networks, for instance, through better resource management and routing. UWB signals spread, however, over very large bandwidths and overlap with narrowband services. As a consequence, regulatory bodies impose severe limitations on UWB power density in order to avoid interference provoked by UWB onto coexisting narrowband systems. It is therefore necessary to take into account power considerations when designing UWB systems. Throughout this chapter we will show how the distance information made available by the UWB technology can be exploited to achieve low power levels and increase network lifetime in the long term, while providing an adequate network performance (in terms of data throughput) in the short term.