Nguyen, Huan Cong

English

En af tidens vigtigste protokoller for kanaladgang i fremtidens trådløse bred-båndsnetværk er orthogonal frequency division multiplexing (OFDMA). I OFDMA grupperes de til rådighed værende kanaler i såkaldte sub-kanaler som tildeles samtidige brugere.  Det er essentielt at bibeholde orthogonaliteten af disse sub-kanaler med henblik på at undgå interferens imellem sub-kanalerne (ICI) og som følge heraf undgå interferens imellem brugerne (MUI).Orthogonaliteten imellem sub-kanalerne er relativt let at opretholde i retningen mod brugeren (downlink), hvorimod det er væsentligt sværere i retningen fra brugeren (uplink).  I uplink er det modtagne signal en sum af signalerne fra de forskellige brugere, hver med et individuel offset fra den nominelle bærefrekvens (CFO) som følge af oscillator ustabilitet og/eller Dopplerforskydning.  Konventionelle metoder til korrektion for CFO i downlink'en er designet til enkeltbrugersystemer og er derfor ikke i stand til at korrigere multiple CFO'er i uplink'en.M{\aa}let for denne afhandling er at give praktiske løsninger til synkroniseringsproblemerne som opstår i uplink'en af OFDMA-baserede trådløse bredbåndssystemer.  Adskillige data-assisterede CFO estimeringsalgoritmer foreslås til at opnå nøjagtige estimater af de multiple CFO'er i forskellige scenarier.  Derudover introduceres nye metoder som på baggrund af CFO estimaterne afhjælper den selv- og krydsinterferens som skyldes multiple CFO'er, dvs. MUI.  Resultaterne af evalueringer viser at de foreslåede metoder fungerer bedre end eksisterende metoder i litteraturen ved sammenlignelig eller endda lavere kompleksitet.he Orthogonal Frequency Division Multiple Access (OFDMA) has recently emerged as one of the prime multiple access schemes for the future broadband wireless networks. In OFDMA, available subcarriers are grouped into subchannels, which are assigned to different users operating simultaneously. Preserving the orthogonality among these subchannels is essential, as it prevents the inter-carrier interference (ICI), which consequently eliminates multi-user interference (MUI).While the orthogonality among subchannels can be maintained relatively easily in the downlink, keeping the orthogonality in the uplink is much more difficult. In the uplink, the received signal is the sum of multiple signals coming from different users, each experiences a independent carrier frequency offset (CFO) due  to oscillator instability and / or Doppler shift. Conventional CFO correction method used in the downlink are designed for single-user system, and therefore are not able to correct multiple CFOs in the uplink. The aim of this thesis is to provide practical solutions  for the synchronization issues occurring in the uplink of the OFDMA-based broadband wireless systems.  Several data-aided CFO estimation algorithms are  proposed to achieve accurate measurements of the multiple  CFOs in different scenarios. Once the estimates are available, novel MUI cancellation schemes are introduced to mitigate the self- and cross-interference occurring due to multiple CFOs. Evaluation results show that the proposed schemes outperform the  existing techniques in literature with comparableor even lower additional complexity.</p

    Aalborg UniversitetSynchronization for the uplink of OFDMA-based SystemNguyen, Huan CongPublication date:2008Document VersionPublisher's PDF, also known as Version of recordLink to publication from Aalborg UniversityCitation for published version (APA):Nguyen, H. C. (2008). Synchronization for the uplink of OFDMA-based System. Aalborg Universitetscenter.Institut for Elektroniske Systemer. Afdeling for Kommunikationsteknologi. RapportGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: November 28, 2020Supervisors: Prof. Dr. Ramjee Prasad, Aalborg University, Denmark Assoc. Prof. Dr. Elisabeth de Carvalho The Assessment Committee: Prof. Dr. Enrico Del Re, Department of Electronic and TelecOIIlmunicatioIls (DE'!'), University of Florence, Italy Dr. ,"Verner Mohr, Nokia Siemens Networks GmbH & Co. KG, Munich, Ger­many Prof. Dr. Preben Mogensen, Department of Electronic Systems, Aalborg Uni­versity, Denmark Committee Chairman: Prof. Dr. Preben Mogcnfien, Department of Electronic Systems, Aalborg Univer­sity, Denmark l\tloderator: Prof. B0rge Lindberg, Department of Electronic Systems, Aalborg University, Denmark ISSN 0908-1224 ISBN 87 -92078-44-3 Copyright 2008 by Huan Cong Nguyen All rights reserved. No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the author. 

Synchronization for the uplink of OFDMA-based System

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Synchronization for the uplink of OFDMA-based System

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