Researches On Non-distortional Methods Of Peak-to-Average Power Ratio Reduction In OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is a special kind of multi-carriers transmission technology. It can strongly resist multi-path delay and transmit high-rate data with high bandwidth. However many key problems of OFDM system have not been solved yet, such as sensitivity to frequency offset and high peak-to-average power ratio (PAPR), which limit the wide applications of OFDM. This dissertation focuses on the problem of high PAPR. The signal scrambling technique, which can distortionlessly provide an effective PAPR reduction in OFDM system, are mainly analyzed, including Partial Transmit Sequence (PTS) and Selective Mapping (SLM).First, the basic principle of OFDM, including its key techniques, advantages and disadvantages are analyzed. The definition and distribution of PAPR are introduced. Thereafter some current PAPR reduction methods are summarized.The main problem of PTS is its great complexity in phase factors selection. A suboptimal algorithm was proposed to combat the problem. But the computational complexity of the suboptimal PTS remains highly to some extent. Thus an improved suboptimal PTS method is proposed to further reduce the computational complexity of conventional suboptimal PTS. On the other side, SLM provide a good performance for PAPR reduction, but it may suffer from the high computational complexity of the inverse fast Fourier transforms (IFFT). To lower the complexity of conversion in SLM, a Matrix conversion substitute method is proposed to replace IFFT. The Matrix conversion substitute method can greatly reduce the computation with little loss of PAPR reduction.The Side Information (SI) processing in PTS and SLM is an important research topic. The quality of transmitting and detecting of SI is crucial to the correctly recover of the primary information. Based on the every sub-carrier of OFDM system with Quadrature Phase Shift Keying (QPSK) modulation, a new SI processing method is proposed. The proposed SI processing method can be used in both PTS-OFDM and SLM-OFDM. By rotating the phases of QPSK data, SI can be embedded into the OFDM signals with no loss of frequency efficiency. Subsequently, at the receiver, SI can be easily and correctly detected.