96 Chapter IV RF Ranging Methods and Performance Limits for Sensor Localization Steven Lanzisera University of California, Berkeley, USA Kristofer S.J. Pister University of California, Berkeley, USA Copyright © 2009, IGI Global, distributing in print or electronic forms without written permission of IGI Global is prohibited. AbsTRAcT Localization or geolocation of wireless sensors usually requires accurate estimates of the distance between nodes in the network. RF ranging techniques can provide these estimates through a variety of methods some of which are well suited to wireless sensor networks. Noise and multipath channels fundamentally limit the accuracy of range estimation, and a number of other implementation related phenomena further impact accuracy. This chapter explores these effects and selected mitigation techniques in the context of low power wireless systems. INTRODUcTION In this chapter we will discuss techniques for estimating the range between wireless sensor nodes using radio frequency (RF) measurements. Localization is a two part process that can roughly be divided into a phase where the relationships between nodes are estimated (range or angle) and a phase where these relationships are used to estimate locations of the devices. RF ranging, one of the options for the frst phase, will be the topic of this chapter. In particular, RF time of fight methods where RF propagation time is estimated will be considered in depth. Other ranging methods (ultrasonic, sonic, light) have been proposed and tested but they are all limited from widespread adoption. Ultrasonic and sonic signals have