Synchronization and channel estimation in OFDM systems

Abstract: This thesis addresses synchronization and channel estimation in OFDM communication systems. The joint maximum likliehood estimator of symbol time and carrier frequency offsets for OFDM systems using a cyclic prefix is presented. This estimator exploits the redundancy introduced by the prefix and does not require extra pilot information. Signal models, accounting for pulse shaping, channel dispersion, or slowly changing synchronization errors and the associated maximum likliehood estimators are presented. Tracking synchronization of a multiuser OFDM system, which often has been questioned, is feasible using a scheme incorporating the above estimator concept. Furthermore, this thesis analyzes channel estimators based on the discrete Fourier transform. The symbol error rate of systems employing these estimators may experience an irreducible error floor. A novel channel estimation concept using singular-value decomposition of the channel attenuations is presented. These channel estimators, designed with suitably chosen fixed design parameters, combine low-complexity and high performance.