Radio Science Bulletin 313 - June 2005 - URSI

Definition and Classification ofUltra-Wideband Signalsand DevicesF. SabathE.L. MokoleS.N. SamaddarAbstractOne commonly used way to classify signals anddevices is based on frequency coverage or bandwidth.Three somewhat similar, but significantly different, ultrawideband(UWB) classification schemes from the openliterature are presented. These classification schemes differin how they define bandwidth and categorization criteria. Acomparison of the categorization criteria associated withthe three schemes is followed by the authors’ presentationof a partially codified classification scheme that merges theexisting schemes so that the merged scheme partially satisfiesthe criteria of each individual scheme. The second half ofthe article focuses on a detailed discussion of several of thenumerous bandwidth definitions in the literature. Theinconsistencies inherent in the three classification schemesare illustrated by applying six of the bandwidth definitionsto four test signals, and comparing the results. The articleconcludes by suggesting further topics of discussion thatcould result in a common bandwidth definition and auniform classification scheme.1. IntroductionThe last fifteen years have witnessed increased interestin ultra-wideband (UWB) systems, particularly in the areasof radar, communications, electromagnetic interference,and high-power directed energy. Since 1996, the significantdevelopment of UWB communications systems in thecommercial sector has led to a definition of UWB by the USFederal Communications Commission (FCC). In attemptingto characterize UWB systems in a meaningful way,researchers in each diverse area have formulated their ownpreferred definitions of bandwidth and UWB technologiesthat reflect the specific needs and viewpoints of theirrespective communities. Unfortunately, these definitionsare not mutually consistent, which has created discourseabout establishing universal UWB definitions and standards.To motivate further intercommunity discussion, this papercompares three UWB classification schemes for sixdefinitions of bandwidth. For each bandwidth definition,the inconsistencies, advantages, and disadvantagesassociated with the three UWB definitions are illustrated byapplying these definitions to four ideal real-valuedwaveforms.According to the panel jointly formed by the USOffice of the Secretary of Defense and the Defense AdvancedResearch Projects Agency (OSD/DARPA) [1], a UWBradar system has a bandwidth that is considerably greaterthan that usually associated with conventional radar and, byextrapolation, with communications and other high-powerelectromagnetic systems. To discuss the meaning of UWBat a sufficient depth, a more precise UWB definition,general enough to be useful for the various techniques thatare employed to achieve extremely wide bandwidth, isdesirable: this requires a common definition of bandwidth.Currently, at least three groups within the engineering andscientific communities (the OSD/DARPA panel, the USFCC [2], and the International Electrotechnical Commission(IEC) [3]) have articulated definitions for UWB systemsand signals. Each group has attempted to define a measureof the width, B, of a spectral density, and appropriateclassification criteria by using this spectral measure, tocategorize signals and systems in a meaningful way. Theinconsistencies among these non-coincident definitions,influenced by the differing needs and viewpoints of therespective communities, are discussed in Sections 2 and 3.From an engineering perspective, a single unifyingdefinition of UWB may be desirable but may not beadvisable, because it may not be possible to combine thevarious device and signal definitions of UWB into onecohesive, consistent definition. Nonetheless, careful analysesand discussions should be conducted before definitions ofUWB are established and inserted into the standards of thevarious technical communities. To avoid the confusion andmisunderstanding that currently exist, each definition ofF. Sabath is a member of the Electromagnetic EffectsBranch, Federal Armed Forces Research Institute forProtective Technologies and NBC-Protection,Humboldstrasse, 29623 Munster, Germany;E-mail: Frank.Sabath@ieee.org.E. L. Mokole is a member of the Radar Division, US NavalResearch Laboratory, 4555 Overlook Avenue SW,Washington, DC 20375, USA;E-mail: mokole@radar.nrl.navy.mil.S. N. Samaddar is a consultant for SFA, Inc., 9315 LargoDrive West, Suite 200, Largo, MD 20774, USA.12TheRadio Science Bulletin No 313 (June, 2005)