A Shoe to Shoe RF Ranging Sensor for Aiding Inertial Navigation

An RF ranging sensor based on time-interleaved Dual Frequency Continuous Wave (DFCW) radar is proposed to measure the absolute distance between two shoes to aid a dead reckoning system for pedestrian navigation. Conventional single frequency Continuous Wave (CW) radar provides accurate but ambiguous range measurement, while DFCW techniques are employed to find the approximate range of the target and to remove the ambiguity of the single frequency CW radar. The two frequencies in the proposed DFCW radar work in a Time division Duplexing (TDD) manner so that they can share the same transceiver hardware. Such a composite DFCW/CW system can be implemented with a simple direct conversion receiver which is desirable for applications such as pedestrian navigation where compact and low power consumption devices are required. The feasibility of the proposed sensor is demonstrated by a sensor prototype based on Commercial Off The Shelf (COTS) components in a practical environment. An absolute accuracy (RMS) of 0.92 mm has been achieved for a maximum test range of 600 mm. The results show that the proposed ranging sensor is promising for measuring the distance in short range applications.