Ultra-wideband for navigation and communications

Precision coordinated maneuvering of multiple space vehicles would offer significant performance advantages to both commercial and scientific missions by increasing the versatility and potential capabilities of the formation. Ultra-wideband systems can provide centimeter level accuracy ranging measurements over distances of kilometers, using only milliwatts of power from an omni-directional transceiver no bigger than a pager. Using these precise range measurements between the vehicles, it is possible to resolve the relative geometry of the entire formation. The ultra-wideband (UWB) system presented in this work is not RADAR; it is active ranging over a code divisible multiple access (CDMA) communications channel with no carrier frequency. Each transceiver is given a unique pseudo-random noise code, which is broadcast using pulse position modulation (shifting pulses or monocycles forward or backward in time relative to an constant rate pulse train), in a type of call and return scheme to measure time of flight between vehicles. As a byproduct of CDMA encoding, a UWB navigation system could also provide a megabit per second communications channel to each vehicle, providing further savings of power, weight, and cost. A simple ranging experiment has been designed as a proof of concept. The experiment includes bench top equipment for sending and receiving ultrawideband monocycles and post processing algorithms for determining range. To implement the system, it was necessary to design and develop ultra-wideband antennas to efficiently propagate the monocycle pulses with minimal distortion. These antennas were tested in an anechoic chamber constructed for the ranging experiment and data on their characterization is presented in this paper. This paper presents the experimentally derived ranging accuracies and compares them to theoretically derived ranging accuracies for the UWB based measurement. It also provides a characterization of the distortions encountered in the pulse waveform during transmission and reception from our custom antennas. UWB ranging systems offer a robust solution to relative vehicle navigation in a variety of space mission configurations.