Some Invariance Properties of the Wide-Band Ambiguity Function
Some invarianceproperties of the wide-bandambiguity function R. A. Altes ESL Incorporated,Sunnyvale, California 94086 (Received 10 December 1971) Certainchanges in pulseshape do not affectthe resolutioncapability of a sonarsystem. These changes can be expressedas mathematical transformations that leave invariant important properties of thewide-band am- biguityfunction. Such transformations provide a largenumber of signaland filter functions, all of whichsatisfy a givenrange-Doppler resolution requirement. The sonardesigner can then choose the signaland filter that bestsatisfy other system constraints (e.g., ease of signalgeneration and filter synthesis,clutter suppression capability, and peak power). SubjectClassification: 15.2, 15.3. INTRODUCTION by examiningthe relativemagnitude of When echoesare detectedby meansof a correlation oo 2 process,the capabilitiesof a sonarsystem can be de- scribedin termsof the wide-bandcross-ambiguity func- Ix•,(•,•; 3,•)12= (3g)•f• tion. Although this function dependsupon the sonar signal-filterpair, there are transformationsof signal = s• (2) and filter that will not affect certain propertiesof the f• u(t)u*Es(t+r)3dt2, ambiguityfunction. Such transformationssuggest the existenceof alter- where s=3/•, r=•(•--•). Again, s>0. If s=l and native waveformsthat will satisfya particularrange- r=0, i.e., if •=3 and ?= •, I x•l • assumesits maximum Doppler resolutionrequirement. Having found alter- possiblevalue for a given signalenergy. The function natives, the designercan then choosethe signal and Ix•(r,s) l 2 is called the wide-bandauto-ambiguity filter that best satisfyother systemconstraints2 function; I x•,(r,s) I • is the wide-bandcross-ambiguity function. Invariance transformations are also important to the studyof animalecholocation. Dolphins, for example, The auto-ambiguityfunction is an important special are capable of using a bewilderingvariety of echo- case of the cross-ambiguityfunction and corresponds location waveforms.
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