| Orthogonal Frequency Division Multiplexing (OFDM) technology can resist the multipath fading effectively, realize the high speed data transmission and has a high spectral efficiency. OFDM has become the key technology of the fourth generation of mobile communication. The major defect of OFDM system is high peak-to-average power ratio (PAPR), which makes intermodulation distortion and deteriorates the performance of the OFDM systems. How to reduce the PAPR of OFDM signal effectively is urgently waits to be solved. This dissertation focuses on reducing the PAPR algorithms design for OFDM systems. The content is as follows:First, in the dissertation, design criteria for phase sequences in Selected Mapping(SLM) is proposed. SLM is an important scheme which has good performance and with no distortion. Phase sequence is a crucial problem of SLM. Designing and choosing good performance phase sequences can enhance the performance without extra complexity. Interpretational criteria is very important. The phase sequences which have smaller aperiodic autocorrelation and crosscorrelation function have better performance in SLM. The phase-controlled sequences and chaotic sequences are applied in SLM based on the interpretational criteria. The simulation results prove that the performance of these two sequences is better than performance of traditional Shapiro-Rudin, Walsh sequences.Second, we present a new dummy sequences insertion (DSI) scheme. DSI method is more effective than block encoding and needn't any supplementary information. The compensation sequences are inserted at the end of signal sequences in traditional DSI scheme, which need many times operation to satisfy the system request. By introducing sub-block division thought, we insert scramble bit into signal sequences equably. This method is more effective than traditional DSI with same operations.Third, the simplification method of SLM is proposed. The high complexity is the main drawback of SLM. By choosing the excellent signal sequences before IFFT, improved scheme can achieve the approximate performance of traditional SLM with fewer IFFT operations. In order to avoid complex sequence correlate operation, scrambling and optimal are operated in binary sequences before modulation. The simulation results prove that improved SLM scheme can achieve the approximate performance of traditional SLM using only 25%-50% IFFT operations. The complexity of SLM can be reduced greatly.Finally, the realization principle and the factors which influence the performance of PTS are studied in this dissertation. We carry on comparative analysis to SLM and PTS schemes reasonably. Iterative shifting linear searching method and the method based on dual tree are studied. These methods can reduce the complexity greatly with little performance losing. |
