| Having a set of characteristics such as robustness against frequency-selective fading channels, high bandwidth efficiency, and expandability, OFDM ( Orthogonal Frequency Division Multiplexing)has been proposed to be a potential candidate for the next generation mobile communication systems. However, a major drawback of OFDM signals is their high Peak-to-Average Power Ratio (PAPR). So, how to effectively reduce the PAPR of input OFDM signal of the amplifier is the important issue, which needs to be addressed in OFDM systems. According the problems mentioned above, this dissertation focuses on the reducing the PAPR algorithms design for OFDM systems.First, several characteristics of wireless communications fading channel and various effects of radio propagations are analyzed in detail. Small-scale fading of mobile radio channel is specifically discussed. Effect of Doppler frequency shift on mobile channel is also presented. The thesis introduces the principle of OFDM and the key techniques of OFDM (the synchronism technology, the estimation of the signal channel, reduce the PAPR technology and the signal channel coding).The definition of PAPR, its statistical description are presented. Some PAPR reduction techniques found in literature are introduced, simulated and discussed.Secondly, we introduce the principle of clipping- filtering and its advantages and disadvantage; we also introduces a new method based on the analysis of the traditional idea of compressing and expanding to reduce the PAPR of OFDM system. Sequentially, a modified version basing on the method are put forward and is simulated. The simulation results show that the method can reduce the PAPR of OFDM system effectively with moderate function, simple method and strong practicality.Finally, the thesis introduces signal no-aberration method to reduce the Peak-to-average Power ration. Signals scrambling techniques are analyzed and compared comprehensively,including Selective Map Ping(SLM) and Partial Transmit Sequences(PTS). After analysis and comparison, this paper pointed out that we should selects the suitable algorithm according to specific request to reduce the Peak-to-average Power ratio, then system's overall performance can be best. |
