Joint Turbo Frequency Domain Equalization and Carrier Synchronization

In this paper we propose a synchronization method to compensate for the effect of frequency offset and phase noise generated by local oscillator instabilities for a Turbo Frequency Domain Equalizer (TFDE). TFDE is considered as an efficient equalization method which benefits from both good performance of iterative systems and reasonable complexity due to performing equalization in the frequency domain. We propose a joint turbo equalization and synchronization method in which the feedback information, generated iteratively by the decoder, is used for synchronization. As iterations continue, if the feedback information becomes more reliable, the performance of the synchronization method is continually improved. We propose two methods based on different criteria when the system suffers from only frequency offset. We also suggest a method based on Maximum A Posteriori (MAP) criterion in the presence of both frequency offset and phase noise which can be considered as a decision directed phase lock loop. These methods achieve considerable performance improvement with reasonable complexity.