Research On Peak-to-Average Power Ratio Reduction Of OFDM System

Orthogonal frequency division multiplexing (OFDM) is a special multi-carrier transmission technology. Owing to the high spectrum efficiency, robustness to multi-path fading, great simplification of channel equalization and fast digital implementation with Fast Fourier Transform (FFT), OFDM is becoming one common technology in the high-speed communication.However, many key problems of an OFDM system have not been solved yet, such as sensitivity of frequency offset and high peak-to-average power ratio (PAPR), which limit the wide applications of OFDM technique. This thesis mainly focuses on the techniques of PAPR reduction. And MATLAB is used to achieve simulation.Firstly, the principle, key techniques, advantages and disadvantages of OFDM technology are analyzed in the thesis. And a basic OFDM system is simulated by using MATLAB. Secondly, the definition and distribution of PAPR are introduced, and three kinds of techniques to reduce the PAPR are summarized. The principles of various techniques are analyzed separately. The representative techniques are simulated, whose advantages and disadvantages are analyzed according to the simulation results.A modified Selective Mapping (SLM) method is proposed in this thesis, based on the particular study of signal scrambling techniques, including Selective Mapping and Partial Transmit Sequences (PTS). The core of modified method is choosing a vector with low PAPR in each coset of a linear block codes as its coset leader, instead of the weight vector in conventional SLM method. And a sequence with the lowest PAPR is chose to transmit according to a new decision criterion. The key idea of the decision criterion is that how to choose a sequence by the sequence itself. The modified SLM method is simulated using MATLAB. The simulation results show that the modified SLM method has good performance in PAPR reduction, and it has almost equal performance to the conventional method. On the other hand, it reduces the complexity of the system.In a word, the modified SLM method is better than the conventional one.