Ofdm System Based On Fractional Fourier Transform, The Papr Reduction Algorithms Research

Orthogonal Frequency Division Multiplexing(OFDM) is a kind of multicarrier digital modulation technique. OFDM has become a popular technique in various high-speed wireless data transmission system since 1990s. Now it has become the key problem in research of beyond 3G.Traditional multicarrier techniques based on FFT perform a frequency domain decomposition of a channel characterized by frequency selective distortion in a plurality of subchannels that are affected by frequency flat distortion. The distortion in each independent subchannel can then be easily compensated by simple gain and phase adjustments. However, when the channel is doubly selective (that is, time-frequency-selective), as it usually happens in the rapidly fading wireless channel, this traditional methodology fails. The OFDM system based on IFRFT and FRFT employs orthogonal signal bases of the chirp type, so the subchannel carrier frequencies are time varying and ideally decompose the frequency distortion of the channel perfectly at any instant in time, then the performance of the system is enhanced. But one of the main implementation disadvantages of the OFDM system based on FRFT is the high peak to average power ratio (PAPR).In this thesis , the problem of PAPR in the OFDM system based on FRFT is discussed. First the function of PAPR in the OFDM system based on FRFT is achieved. The density of the signal power is different in different fractional domain, at the same time the FRFT is unitary transformation, the average power of the signal is same, so the PAPR of the signal isn't same in different fractional domain. simulation shows in optional fractional domain the performance of the PAPR is better than the traditional system. Then the Selected Mapping(SLM) is employed to lower the PAPR of this system,. Compared with the system based on FFT, simulation results show good efficiency of proposed algorithm when calculation is done in the optimal fractional domain. At last, Partial Transmit Sequence(PTS) is employed to lower the PAPR. Compared with the system based on FFT, simulation results show good efficiency of the PTS algorithm when calculation is done in the optimal fractional...