Increased ranging capacity using Ultrawideband direct-path pulse signal strength with dynamic recalibration

Pulsed-RF (aka. Ultrawideband, or UWB) signaling strategies inherently produce separation of multipath reflections from the earliest Line-of-Sight (LOS) signal. Direct waveform scanning in each UWB transceiver allows coarse estimation of distance through relative signal strength measure of the earliest, most direct path pulse. Even with multipath separation this technique suffers from errors due to channel and antenna pattern changes inherent in distributed dynamic localization systems. This problem can be overcome through occasional, as-needed precise two-way Time-of-Flight (TOF) ranging which can provide periodic dynamic recalibration of the Coarse Range Estimate (CRE). CRE error conditions such as Non-Line-of-Sight (NLOS) and signal saturation can be mitigated through real-time direct sampling and analysis of the pulse waveform. In this investigation a recursive model-based Kalman range filter is used to combine the less accurate CRE with very accurate TOF Precision Range Measurements (PRM). In order to support dynamic recalibration a simple periodic “1 out of N” PRM scheduler is compared to a more flexible and capable Range Target Prioritization (RTP) algorithm designed to minimize PRM requirements while maximizing range accuracy in a network environment. The resulting ranging system is much more scalable and suitable for large-scale systems such as distributed ad hoc collision avoidance, safety, and automation networks.