Research On The Peak-to-Average Power Ratio Reduction Techniques For OFDM Systems

Orthogonal frequency division multiplexing (OFDM) technology has become the key technology of the fourth generation of mobile communication due to its bandwidth efficiency and good immunity to multipath fading and impulse noise. Because an OFDM signal is the sum of many independent signals modulated onto subchannels of equal bandwidth, the OFDM signal has very high peak power when many sub-carrier phases are same or approximate, which demands that some parts of system have large linear region or else the high peak signal going through a power amplifier may cause the nonlinear distortion. So how to reduce the high peak-to-average power ratio of OFDM signal is the important issue. According to the problem, the thesis focuses on the reducing the PAPR for OFDM systems. The content is organized as follows:Firstly, the dissertation briefly introduces the history of OFDM technology, application in communication system and key technologies of OFDM system. Analyze the reason why the system has high peak-to-average power ratio. The definition and distribution of PAPR are also presented in detail. Summarize the three kinds of PAPR reducing techniques and compare the performances of each algorithm.Secondly, the dissertation studies clipping method to reduce the high peak-to-average power ratio. One problem of traditional clipping is peak regrowth due to the filtering for the clipped signal. To suppress the peak regrowth, the Clipping and Filtering method and the repeated CAF method are proposed. The simulation results prove that the RCAF method significantly reduces the PAPR and peak regrowth. Then the mechanism of peak regrowth is described and the deep clipping method is proposed to reduce the peak regrowth effectively without iteration. The deep clipping method achieves significant reduction of peak regrowth that is equivalent to that by four times repeated CAF. To improve the BER performance of system, an iterative estimation and cancellation of clipping non-linear distortion scheme is studied and simulated.Thirdly, the typical methods using probability technology to reduce the PAPR are analyzed. The main drawbacks of traditional SLM method are the high complexity and need to transmit the side information. To solve these problems, some improved methods are proposed. By choosing the excellent signal sequences before IFFT, improved SLM method can achieve the approximate performance with fewer IFFT operations. Furthermore, the dissertation studies dummy sequences insertion method, which needn't transmit the side information. An improved DSI method is put forward to reduce PAPR by introducing sub-block division thought. We insert scramble bit into signal sequences equably. The simulation results showed that the improved DSI method is more effective than traditional DSI method with same operations.