Pulse shaping and signal modulation techniques to improve the multipath and noise performance of narrowband precision RF ranging

Systems that provide precise range or position typically depend on an accurate measurement of the phase of an RF carrier and/or the phase of a modulating code. Noise and interference degrade the accuracy and reliability of the phase measurement. This paper investigates ways to improve the range accuracy and the ambiguity resolution of local-area, narrowband RF ranging systems in the presence of Gaussian noise and multipath interference. The methods examined were based on our intuition that the system would be more resistant to interference and noise if the available bandwidth was used more completely. The RF signal spectrum was modified by three methods: shaping the modulated pulses of the RF carrier, using multiple carriers, and encoding the RF carrier with a PN code. Studies were conducted with Matlab simulations. Pulse shaping improved the immunity to noise and the range ambiguity. Multipath was best handled by encoding the carrier.