Research On PAPR Reduction And Synchronization In OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) has high spectral efficiency and is an effective transmission scheme for counteracting multipath fading. As a multi-carrier modulation technique, OFDM has high Peak-to-Average Power Ratio (PAPR) and is also very sensitive to synchronization error, and solving these problems are meaningful.This paper focuses on PAPR reduction and synchronization algorithms in OFDM systems profoundly. The main creativities are as following:(1) This thesis proposed an improved PTS method, which using the cyclic shift feature of FFT to generate more alternative signals to overcome the disadvantage of high computational complexity in traditional PTS algorithm. In MATLAB simulation, the improved method searches the phase factor combinations meeting the system conditions without an exhaustive searching over all allowed phase factor combinations in traditional PTS, which can simplify the computational complexity further. Simulation results show that the improved PTS method can reduce PAPR in a lower complexity than traditional methods.(2) Based on those synchronization methods for OFDM in wireless channel, this thesis proposed an improved joint timing and frequency synchronization estimation algorithm. At first step, the improved algorithm takes the coarse timing and fractional frequency offset estimation using the characteristics of repeated sequences in accordance with SC algorithm; then, the estimated fractional frequency offset is compensated to eliminate its impacts on system performance; later, a more precise timing and integer frequency offset estimation for OFDM signals is done by the synchronization algorithm based on orthogonal sequences. MATLAB simulation show that the improved algorithm can get high accuracy for both frequency offset estimation and timing estimation.Finally, some conclusion to the whole dissertation is given, and the further research plans are pointed out.The high PAPR and synchronization problems are common problems in multi-carrier communication technology. The research in this thesis can be applied in other multi-carrier communication systems, such as OFDMA and WiMAX.