TABLE OF CONTENTS There are a number of error sources that may seriously degrade the accuracy of the range estimation. Before getting into different ranging algorithms and fundamental bounds, some of those error sources will be briefly overviewed in this section.
Multipath propagation introduces challenges for UWB ranging due to a large number of MPCs and relatively long excess delays compared to the transmitted pulse duration. In the absence of multipath propagation, estimation of the arrival time of a signal is relatively easy: the cross-correlation of the received signal with a local template [3] is obtained, and the TOA is given by the correlation peak (see Section 5.5.1 for details).
In practice, reflections from scatterers in an environment arrive at a receiver as replicas of the transmitted signal with various attenuation levels and delays. As discussed in Chapter 3, the maximum excess delay of the received multipath signal can be on the order of a hundred nanoseconds, and the strongest MPC may arrive much later than the first path. For such a signal, the TOA is no longer given by the correlation peak, and first path detection algorithms are required. In typical UWB channels, the first path may be considerably weaker than the strongest component (see Fig. 5.2), and it may arrive several tens of nanoseconds earlier than the strongest [100]. As illustrated in various simple scenarios in Fig. 5.3, the first path may be weaker than the later paths...
