Research On The Reduction Of Peak To Average Power Ratio In SLM OFDM Systems

OFDM has been often used in mobile communication systems, because of its high bandwidth efficiency, inherent resistance to multichannel fading and Inter-symbol interference. However, it also has some bottlenecks; for example, high Peak-to-average power ratio will bring about high requirements to the linear region of the power amplifier. If the dynamic range of the amplifier cannot satisfy the variation of the signals, signal distortion will occur; resulting in the destruction of orthogonality of the sub channels, and the performance of the system will deteriorate. To enlarge the range of linear region of the amplifier will help to solve the problem, which, however, is costly.Therefore, PAPR of OFDM should be reduced. Thus we focus on the research of the PAPR reduction in the OFDM system. Usually there are three ways of reducing the PAPR: Pre-distortion, coding and probability method. We focus on the selective mapping among the probability methods.Since the SLM method needs extra U-1 alternative IFFT computing, bring about high computational complexity, so great attention has been paid to the IFFT computing. The computing of SLM IFFT is divided into two parts; this method will reduce the computation complexity while remaining almost the same performance as the conventional method.A modified chaotic sequence is used in the SLM to reduce the PAPR in OFDM system. Chaotic sequences have the priority of good autocorrelation, good cross correlation, and easy to be generated, thus making their performance quite good. Whereas, due to the impact of limited precision the autocorrelation function will have a peak value periodically. So, some measures such as the segment method are used to modify the sequences. Then the modified sequences are used in the SLM system, their performance is better than the common phase sequences.