Study For The Key Technique In OFDM Communication System

As an optimum version of the multicarrier transmission scheme, the Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme is a promising candidate for achieving high data rate transmission in mobile environment. Due to the advantages of large data rate with sufficient robustness to wireless channel impalements, high spectral efficiency, immunity to impulse interference and intersymbol interference (ISI), and capability to handle multipath fading, the OFDM and the application of OFDM to high data rate mobile communication system is being investigated widely by many researchers.OFDM has several properties, which make it an attractive modulation scheme for high speed data transmission. However, one major difficulty is its large Peak to Average Power Ratio (PAPR).These large peaks cause saturation in power amplifiers, leading to intermodulation products among the subcarriers and disturbing out of band energy. Therefore, it is highly desirable to reduce the high PAPR, which is an obstacle of utilities of OFDM.In this paper, the main research objective is the study of techniques for reducing the PAPR of an OFDM system. Some significative conclusions are draw from this study. The major contents are listed as below.A short introduction to the principle of OFDM and definition of PAPR, its statistical description are presented. Some PAPR reduction techniques found in literature are introduced, simulated and discussed.Detailed analyses for the μ-law companding technique to reduce the PAPR are implemented in theory. Moreover, an expression for describing the PAPR CCDF after μ-law companding also are derived. As a confirmation of the analytical approach, thesimulation results, performed in MATLABTM environment, are presented and verify the analytical approach. Further, the performances of such OFDM system on AWGN channel are simulated and discussed.Proposing a new method based on the idea of block averaging to reduce the PAPR of OFDM system. Sequentially, two modified version basing on the method are put forward. The simulation results show that the method can reduce the PAPR of OFDM system effectively.