Digitalna predizobličenja za radio-frekvencijska pojačala snage

master's thesis

• Title (english): Digital predistortion in radio-frequency power amplifiers
• Author: Matej Osonjački
• Mentor: Tomislav Suligoj (mentor)
• Committee member: Tomislav Suligoj (predsjednik povjerenstva)
• Committee member: Dubravko Babić (član povjerenstva)
• Committee member: Goran Molnar (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; Zagreb
• Defense date and country: 2020-07-10, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Computing
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Electrical Engineering

Abstract

Iako neizostavan dio komunikacijskih sustava, pojačalo je kritičan element koji unosi nelinearnosti u sustav u obliku neželjenih komponenti u spektru koje se ne mogu ukloniti filtriranjem jer se nalaze na frekvenciji ulaznog signala. Te komponente uzrokuju neispravnu demodulaciju i potencijalno neispravno dekodiranje signala, a rješavaju se pred-distorzijom signala. Kako se zadnjih godina digitalni dio odašiljača (ali i prijemnika) pomaknuo prema izlaznom pojačalu (ulazu u prijemnik), tako i digitalna pred-distorzija dobiva prednost pred analognom. Glavni cilj pred-distorzije je predizobličiti ulazni signal kako bi on ostao linearan prolaskom kroz nelinearno pojačalo. Za to je bilo potrebno promatrati izlazni i ulazni signal te na temelju njihove usporedbe dobiti funkcije koje su osnova modeliranja sustava za digitalnu pred-distorziju RF signala. Osnovna podjela je bezmemorijske i memorijske modele, a memorijski su opsežniji i bolji jer obuhvaćaju i utjecaj prošlih komponenata signala na trenutnu. Uz linearnost, za komunikacijske sustave najbitnija je efikasnost. Bilo je potrebno postići linearan prijenos signala uz što manju disipaciju snage. To je postignuto praćenjem ovojnice signala i njezinom upotrebom u modulatoru napajanja RF pojačala snage. Bitno je bilo vremenski uskladiti RF granu s granom u kojoj se nalazi modulator napajanja kako ne bi došlo do dodatnih nepoželjnih distorzija te je bilo bitno naći optimum između zahtjeva za linearnošću i efikasnošću. Primjenom navedenih algoritama postignuta su vrlo dobra poboljšanja oba tražena parametra.

Abstract (english)

Power amplifier is crtitical part of communication system which disrupts system linearity by adding unwanted frequency components into signal spectrum. Those components are responsible for incorrect demodulation which could cause wrong information extraction on receiver. Digital predistortion is the main tool for fixing this problem. The objective of digital predistortion use was to to predistort signal so it becomes linear after passing through power amplifier. Analysis of output and input was important for extrapolation of AM/AM and AM/PM characteristics of power amplifier. Based on those characteristics memory or memoryless model for digital predistortion algorithm is chosen. Memory ploynomials are more precise because they include signal history into power amplifier modeling giving more extensive and more precise model. Apart from linearity, efficiency is the most important parameter of communication system. Envelope tracking method for efficiency enhacement was used for power supply modulation. Time alignment between RF and power supply branches was crucial because without it new distortions would be added into signal. Optimum between linearity and efficiency was found by combining those algorithms.

• Keywords: digitalna predizobličenja; pojačala snage; radio-frekvencijska; memorijski sustavi; bezmemorijski sustavi; memorijski polinomi; linearnost; efikasnost; praćenje ovojnice; komunikacijski sustavi; QAM
• Keywords (english): digital predistortion; power amplifiers; radio-frequency; systems with memory; memoryless systems; memory polynomials; linearity; efficiency; envelope tracking; communication systems; QAM
• Language: croatian
• URN:NBN: urn:nbn:hr:168:914490
• Study programme: Title: Electrical Engineering and Information Technology; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka elektrotehnike i informacijske tehnologije (magistar/magistra inženjer/inženjerka elektrotehnike i informacijske tehnologije)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Closed access
• Created on: 2023-01-13 13:23:00