Testing and Research on Interference to GPS from UWB Transmitters

Ultra-Wideband (UWB) signal transmission is a potentially promising technology that is defined by a large fractional bandwidth. Most UWB systems are based on very short pulses of radio frequency energy. UWB technology has potential in a variety of applications, including communication and ranging, and is expected to see increased civil use in the future. Since signals from GPS satellites have very low power levels (−130 dBm or −160 dBW [1]) near the surface of the earth, potential interference from UWB to GPS receivers (and corresponding GPS-based systems such as aeronautical safety-critical flight systems) is a serious concern. Research and testing of this possible interference source is necessary because GPS has a pivotal role in so many critical systems that the public depends upon for its safety and welfare. In interference testing, pseudorange measurement accuracy is the primary metric of choice for aviation receivers. The most demanding applications, such as aircraft precision approach, require one-sigma pseudorange errors of 15 centimeters or less [2,3]. Acquisition time is the metric of choice for land users, as emergency vehicles may need to quickly acquire the GPS signal after signal loss due to buildings, tunnels, or other obstructions. These users need to acquire the GPS signals and develop new position estimates before the vehicle moves behind the next obstruction. The majority of the tests described in this paper measured UWB impact on the accuracy and loss-of-lock performance of a high-grade GPS aviation receiver. A smaller test set measured UWB impact on the loss-of-lock performance for two different receivers: the original aviation receiver as well as a low-cost OEM receiver. This OEM receiver is similar to the ones that will find application in cell phones and therefore will deliver E-911 location information in accord with the FCC mandate for such service. Finally, an additional test set was designed to measure UWB impact on the signal acquisition performance of a third receiver, which was a high-grade, general-purpose GPS receiver. In all tests, the UWB interference impact relative to broadband-noise was measured. These tests are crafted to provide input to a separate process that considers the operational scenarios that might place UWB and GPS equipment in proximity to each other. Other key factors were also examined such as antenna manipulation and spectrum whitening.