Research On Technology Of Peak-to-average Power Ratio Reduction In OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is a parallel transmission scheme of multi-carriers modulation. It transmits information through orthogonal sub-carriers with high utilization of frequency spectrum and good capability of countering multi-path interference. However, the high peak-to-average power ratio is one of the main drawbacks of OFDM, which restricts the development of OFDM technology. This thesis mainly focuses on the analysis to the effective PAPR reduction algorithms and the main contents are as follows:Firstly, the thesis elaborates the principle of OFDM system and its key techniques. After that, the PAPR reduction techniques for OFDM system are studied. Then, the active constellation extension (ACE) technique and Selective Mapping (SLM) are discussed in detail.Secondly, in the analysis to reduce the PAPR by using the ACE algorithm, a union algorithm for PAPR reduction, which is combined with modified ACE-SGP algorithm and adaptive clipping algorithm, is proposed in this thesis. In order to reduce PAPR, the main idea of this algorithm is adjusting the size of clipping level by using adaptive strategy, and then using a novel the step size in each iterative calculation. The simulation results show that the union algorithm can not only reduce the PAPR effectively, improved the convergence speed significantly and realize the compromise among the amount of computation, BER and PAPR reduction, but also without side information and any processing at the receiver end, simple and practical.This thesis also analyzes the performance of the SLM, the computational complexity of this method is very high, but also need to transfer large amounts of side information. To solve this problem, this thesis proposes an improved algorithm for low complexity based on chaotic sequence. The algorithm by introducing chaotic sequence and iteration to generate the phase factor, thus achieve the purpose of reducing redundant information. Transmission signals can be divided into two groups and to get two groups of the minimum of the PAPR by using the SLM, then merge the two groups of signal transmission. Simulation shows that the improved algorithm can not only reduce the computational complexity, reduce the side information transmission, improve the utilization of bandwidth of the system, but also can reduce PAPR effectively.Finally, the work has been done is summarized, at the same time for the future technology development trend, puts forward a proposal for the next step research work.