Research On Synchronization Techniques For SC-FDE In LTE Uplink

Single carrier frequency domain equalization (SC-FDE) is an efficient wireless transmission technology, which can effectively combat against inter-symbol interference (ISI) in high data rate transmission. Using low complexity frequency domain equalization, it can remove time and frequency dispersion caused by multipath fading channels. Compared with OFDM, it has lower peak-to-average power ratio (PAPR), therefore, it is regarded as a good alternative of OFDM, and it has been applied in the uplink of LTE successfully. In SC-FDE system, timing and frequency synchronization techniques are necessary premiss to obtain good equalization performance. So, this paper focuses on the research of these two techniques for SC-FDE system. The following works are completed:Firstly, this paper makes an overview of LTE system, and carries on the comparative analysis between SC-FDE and OFDM, following with the elaboration of SC-FDE fundamental principles. Then theoretical analysis of timing offset and carrier frequency offset is performed, and influence of the two kinds of synchronization problems on SC-FDE is further presented, which shows the necessity to explore synchronization algorithms.Secondly, based on existing classic data-aided synchronization algorithms, this paper points out that the timing metric of Schmidl & Cox algorithm has a plateau, which leads to some uncertainty in timing estimation, and the estimation range is not wide enough. To settle these problems, a data-aided joint timing and frequency synchronization algorithm is presented. The modified algorithm adopts a special training sequence, which not only eliminates the plateau of timing metric, but also suppresses false peaks. Besides, the estimation accuracy is improved while calculation complexity keeps low. According to the theory that integer CFO in the time domain is equal to cyclic shift in the frequency domain, this paper proposes a new method. The new method estimates and compensates fractional CFO first, and then the received sequence is transformed into frequency domain, in which it correlates with local sequence. Then the peak of the correlation function is found, whose index is the cyclic shift, and the index is equal to the integer CFO. The proposed method has higher estimation accuracy in AWGN channels as well as lower SNR circumstances, but the performance is limited in multipath channels. Especially, it is more adaptive in SC-FDE since CFO estimation is performed in frequency domain.Thirdly, a non-data-aided joint timing and frequency synchronization algorithm is proposed, too. This algorithm adopts a UW-based frame structure, which has less degradation in spectrum efficiency. Based on the composite synchronization error information between two consecutiveUWs, timing offset and carrier frequency offset are estimated simultaneously using recursiveweighted least-squares algorithm, which reduces calculation complexity.In conclusion, this paper focuses on the research of synchronization techniques for SC-FDEsystem, and proposes data-aided and non-data-aided algorithms respectively. Performance in LTEchannels is also analyzed. The future research will consider reducing CFO estimation’s dependenceon timing synchronization, and strengthening robustness of the algorithm in multipath fadingchannels. Furthermore, combining synchronization with channel estimation and frequency domianequalization to obtain global optimum is an interesting direction.