ANALYZING BAND LIMITED VOLTERRA SERIES FOR BROADBAND SIGNALS

Abstract

Theiincreaseiinitheidemandifor high data rates has led to theideployment of wider bandwidthsiandicomplexiwaveformsiiniwirelessicommunicationisystems.iMulticarrieri wave-forms such asiorthogonalifrequencyidivision multiplexing (OFDM) employed in modern systemsiare veryisensitive to theitransmitterichaininonidealities dueitoitheir high peak-to-average-power-ratio (PAPR) characteristic. Theyiare therefore affected by nonlinearitransmitter componentsiparticularly the poweriamplifier (PA). Moreover, toienhance poweriefficiency, PAs typicallyioperate nearisaturation regioniand hence becomeimore nonlinear. Power efficiency is highly desirableiespeciallyiin batteryipowerediand portableidevices asiwell as in base stations. Henceithere is aiclear need foriefficient linearization algorithmsiwhich improve poweriefficiencyiwhile maintainingihigh spectral efficiency. Digitalipredistortion (DPD) has been recognized as one of the mostieffective methodsi in mitigating PA nonlinearidistortions. Theimethod involvesithe applicationiof inverse PA nonlinearifunctioniupstreamiof theiPA suchithat the overall systemioutput hasia linear ampli-fication. The computationiofitheinonlinearityiprofile and theiinversioniof theiPAifunction are particularly difficultiandicomplicated especially when involving wideband radio access waveforms, ianditherefore memory effects, which areibeingiemployed inimodern communi-cation systems, suchias iniLong TermiEvolution/Advanced (LTE/LTE-A). Inirecentitechnical literature, different approachesiwhich focusion the linearizationiof specific frequency bands or sub-bandsionly haveibeen developedito alleviate thisiproblem, thereby reducingithe complexity of DPD. Inithisithesis, weiinvestigate and analyzeiband-limited digital predistortionitechnique iniwhich a band-limiting function isiinserted into theigeneral Volterraioperators in theiDPD modelito control theisignal bandwidthiunder modeling, whichilogicallyitransforms theigeneral Volterra series-basedimodel intoia band-limited version. Iniorderitoivalidate thisiidea, ia high-poweriLDMOSiDoherty PA excitedibyivarious wideband signals, iincludingi100-MHz long-termievolutioniadvanced signals, was tested. Experimentaliresultsishowedithatiexcellentilinearizationiperformanceicanibeiobtainedibyiemp-loyingitheiproposed approach. Furthermore, ithis techniqueican be applied toiotherilinear-in-parameter models.iInifutureiultra-widebandisystems, thisitechniqueicanisignificantly improve system performance and reduce DPD implementation cost.