A portable UWB to GPS emission simulator

Abstract

Due to the low power of GPS signals, GPS ranging applications are sensitive to any signals emitted in the GPS band. Ultra Wide Band (UWB) emitter devices, however, have been approved by the Federal Communication Commission (FCC) to emit at specified, maximum noise-like and tone levels. These emissions are across the GPS band and are specified per UWB device rather than an aggregate effect. These levels were approved in a report and order in February 2002 for the use of UWB devices in commercial and federal bands. This report and order constitutes a modification to the Part 15 emission limits that places UWB technology in the same regulatory category as microwave ovens and computer monitors. Due to the great interest in UWB technology, there has been considerable interest in raising the allowable levels. However, an increase in the UWB emission level limit could further degrade GPS operation. There are many applications where the received GPS signal power level is significantly lower than the ambient GPS signal power level, such as indoors, behind foliage or operation during deep multipath fading in urban environments. Under such conditions, any interference can harmfully degrade the GPS service. In particular, the potential widespread proliferation of UWB devices will significantly raise the noise floor that a receiver sees which can severely degrade GPS operations critical to myriad applications such as E911, precision ranging and automobile navigation. In order to demonstrate the impact of UWB devices under a range of practical operating conditions, a portable UWB emission simulator has been designed, calibrated and demonstrated. This emitter transmits a calibrated, adjustable noise spectrum across the GPS band that conforms to the maximum, noise-like emission specification regulating UWB emitters in the FCC's Part 15 limit. The device thereby assesses the potential impact of UWB emitters below, at, or above this limit. The work describes the design and testing of this calibrated emitter and the implications of these results on the specification of maximum UWB signal levels in the GPS bands. In particular, the paper also describes the results of GPS receiver measurements in the presence of this noise-like UWB emission simulator, which can simulate the aggregate effect of multiple UWB emitters in the GPS band, through an effective aggregate UWB power level.