Synchronization for Multicarrier Systems

Abstract: This thesis has synchronization of Multicarrier systems, more specifically Orthogonal Frequency Division Multiplexing (OFDM) systems, as the main theme. The thesis addresses two areas, the first proposing and analyzing time and frequency estimators for OFDM systems, the second investigating more practical issues around these estimators. The practical part addresses implementation and applies the estimators in an OFDM-based mobile multiuser communication system, one of the proposals for the Universal Mobile Telecommunication System (UMTS/IMT-2000). Estimation of time and frequency offsets is a core issue in synchronizing an OFDM system. We address this issue with a family of new time and frequency offset estimators using the signal redundancy provided by the cyclic prefix. The estimators are all based on the Maximum Likelihood (ML) criterion, but for different system models, e.g., with different channels, with and without pulse shaping, with and without using pilot information, and under different implementational constraints. Furthermore, the design of an OFDM-based multiuser mobile communications system using both time and frequency division multiple access has been attempted. A standardization proposal for UMTS has been developed and submitted, suggesting, among other things, a synchronization method and parameter values describing the time and frequency grid. The work documented here has been performed at Lund Institute of Technology, Luleå University of Technology, Telia Research AB, and the Telecommunications Research Center Vienna (ftw.). Financial support has been received from NUTEK (The Swedish National Board for Industrial and Technical Development), Vetenskapsrådet (The Swedish Research Council), Telia Research AB, and VINNOVA through the Eureka/Medea+ A106 INCA and A110 MIDAS programs.