ABSTRACT
How to transmit information quickly and reliably is important in modern
communication systems. The frequency resource is limited. So except new modulation
techniques to improve frequency utilization. Orthogonal frequency division
multiplexing (OFDM) is one of the expecting techniques required.
However, one of the demerits against OFDM system is that OFDM is highly
sensitive to synchronization errors. How to obtain correct OFDM symbol timing and
carrier frequency is highly critical to OFDM systems. In digital OFDM receiver, the
clock frequency synchronization of sampling is also important.
The synchronization schemes in OFDM systems are studied in this thesis,
including time synchronization and frequency offset estimation. The main contributions
of thesis include:
1: Based on the research of the influence of timing offset and carrier frequency
offset to OFDM system, the existing synchronization schemes for OFDM systems are
analyzed systemically.
2: A special training sequence of central symmetry is proposed, it is compared with
sequence composed of identical blocks.
3: A new frame synchronization scheme for OFDM systems is proposed. In this
scheme, Simplified estimators have low computational complexity and high estimation
accuracy.
4: New carrier frequency offset estimation scheme for OFDM system is proposed.
The carrier frequency offset estimation includes acquisition and tracking. Computer
simulation illustrates the superior performance of the proposed scheme with regard to
estimation accuracy in both AWGN channel and multi-path channel.
5: We design the synchronization scheme and analyze the performance of the
synchronization system in DAB system. The proposed method can greatly reduce the
resource usage.
Key Words: wireless communication, orthogonal frequency division
multiplexing, frame synchronization, frequency offset estimation,
maximum likelihood estimation, digital audio broadcasting.
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