Preliminary Assessment of Interference Between Ultra-Wideband Transmitters and the Global Positioning System: A Cooperative Study

摘要

Ultra-wideband (UWB) technologies are used today for a wide variety of precise position-determination and radar-imaging applications. Soon, UWB devices will be deployed for wireless communications. UWB operation is based on transmission of very short impulses of radio energy, generally at low power, whose characteristic spectrum signature extends across a wide range of radio frequencies. Because such signals have a great deal of information redundancy and frequency diversity, they are particularly well suited for use in environments where multipath distortion is likely or where fine-resolution ranging is paramount. UWB signals can be coded so that multiple UWB users can coexist, without harmful interference, in close proximity. Unlicensed UWB signals will have relatively low power spectrum density and generally will cause little or no interference to existing radio systems. However, any effects of UWB transmissions on the Global Positioning System (GPS) represent a particularly critical test of UWB spectrum-sharing. GPS is a special case because there are now more than 10 million direct users of GPS throughout the world and many of the applications are vital for safety of the public and of property, particularly aircraft flight and approach control. GPS is particularly sensitive to interference because it is a space-to-earth signal system, and the satellite signals are received at a level of only -164 dBW. Because GPS is such a life-critical technology, Interval Research Corporation and Stanford University embarked on collaborative tests of UWB/GPS interference. The first goal was to establish the general magnitude of any interference so as to guide further investigations. This paper describes the design of the first tests and reports preliminary results. In particular, it reports on how different UWB signal characteristics, not just peak power, determine some of the potential for harmful interaction.