【作者】 王丽娟；

【导师】 季策；

【作者基本信息】 东北大学 ， 电子与通信工程（专业学位）， 2015， 硕士

【摘要】 正交频分复用(OFDM)是一种多载波调制技术,具有较高的频谱利用率和良好的抗多径衰落能力,但OFDM技术具有较高的峰均功率比(PAPR),会降低系统性能。因此,如何降低OFDM的峰均功率比是亟需解决的问题。本文主要对降低OFDM系统峰均功率比的技术进行了研究,包括以下几个方面:首先,从OFDM技术的背景及发展历史开始,简单介绍了 OFDM的基本原理及其优缺点,分析了 OFDM系统的PAPR的定义及分布,对降低PAPR的三大类方法做了简单的总结,并且重点对选择性映射算法做了详细的介绍分析。针对SLM算法在降低OFDM系统PAPR的过程中需要进行多次IFFT运算导致系统复杂度上升的缺点,本文将引入顺序选择固定相位序列的思想,根据系统预设的PAPR值,按照相位序列的顺序依次选取相位序列对信号进行处理,直到满足系统要求为止。该算法在保证降低OFDM系统PAPR效果的情况下,有效降低了 IFFT运算的次数,降低了系统的复杂度。通过在选择性映射算法中引入交叉熵(CE),可以得到最优的相位序列,从而使SLM算法降低OFDM系统PAPR的效果达到最优。然而,在CE-SLM算法实现的过程中,需要经过多次迭代运算,增加了算法的复杂度。针对这一问题,本文在CE-SLM算法中引入一个快速收敛因子,在保持与CE-SLM算法降低PAPR效果一致的情况下,降低了得到最优相位序列所需的迭代次数,最终使得算法的复杂度得到有效降低。传统限幅算法实现简单,并且具有较好的降低PAPR效果,但是由于该算法对信号的直接截取而导致系统的误码率上升。针对这一问题,本文将CE算法引入传统限幅算法中,即当信号峰值超过系统要求时,运用CE算法产生并逐次优化相位序列,直到信号满足系统要求为止。改进算法在保证限幅算法降低PAPR效果的同时,不引入非线性失真,有效的解决了传统限幅算法导致系统误码率上升的缺点。最后,对完成的工作进行了总结,并对未来研究方向进行了展望。更多还原

【Abstract】 Orthogonal Frequency Division Multiplexing(OFDM)is a kind of multi-carrier transmission technology,it has high spectrum efficiency and good anti-multipath performance,but the Peak-to-Average Power Ratio(PAPR)of the OFDM system is very high,and it will reduce the performance of the system.So we need to solve the high PAPR of the OFDM system urgently.This paper will give the research on the techniques for OFDM Peak-to-Average Power Ratio reduction,and it mainly includes the following respects:Firstly,this paper starts from the background and development of the OFDM technology,makes a simple introduction of the principle of OFDM and its advantages and disadvantages,then studies the definition and distribution of the PAPR of OFDM system,and makes a summary of three kinds of methods of reducing PAPR,finally Selective Mapping(SLM)is discussed in detail.SLM requires many times IFFT operation in the process of reducing PAPR of OFDM system,this will make system complexity increasing.In order to solve this problem,this paper will introduce the idea of selecting the fixed phase sequence according to the order.Firstly setting the PAPR that the system can accept,then choosing the phase sequence one by one according to the order of the phase sequence until the PAPR of the OFDM signal meets system requirements.Under the condition of keeping the effects of reducing PAPR of OFDM system,this algorithm reduces the number of IFFT operation effectively,so it can reduce the complexity of the system.SLM algorithm uses Cross Entropy(CE)algorithm to get the most optimal phase sequence so that SLM can make the effect of PAPR Reduction achieve optimum.However,it needs too many times iterative computations,so it will increase the complexity of the algorithm.In order to solve this problem,a fast convergence factor was introduced in the CE-SLM algorithm to reduce times of iterative computations to get the most optimal phase sequence.This algorithm reduces the iterative times of getting the optimal phase sequence under the condition of having the same effect of reducing PAPR with the CE-SLM algorithm,eventually reducing the complexity of the algorithm effectively.Clipping algorithm is easy to realize and has a good effect on reducing PAPR of the OFDM system,but it will rise the error rate of the system because of it makes the signal directly intercept.To solve this drawback of clipping technique,this paper introduces CE to clipping algorithm,when the peak of signal is greater than the system allows,applying the CE algorithm to optimize the phase sequence used in SLM algorithm until the PAPR of the signal meets system requirements.The improved algorithm keep the same effect of reducing PAPR of OFDM system with the clipping algorithm,it doesn’t introduce nonlinear distortion and effectively solves the drawbacks that the clipping algorithm make the error rate of the system rise.Finally,making a summary of the work has been done,and looking forward to the direction for future research.更多还原