星座图扩展法降低OFDM系统PAPR的研究

发布时间：2018-04-24 20:38

本文选题：正交频分复用 + 峰均功率比　；参考：《太原理工大学》2017年硕士论文

【摘要】：随着社会的快速发展,人们对文字、图像、语音、视频的数据传输速率及可靠性提出了更高的要求。正交频分复用(OFDM)技术因其具有频谱利用率高、抗多径衰落及抗符号间干扰(ISI)能力强等优点,成为无线通信系统中一种非常有吸引力的技术。然而,OFDM技术因其采用多载波进行调制,导致系统的峰均功率比(PAPR)较高,这在一定程度上影响了OFDM技术的进一步应用及推广。因而,如何有效优化PAPR性能成为OFDM技术中一项重要的研究课题。本文针对这一课题,开展了基于星座图扩展法(ACE)降低PAPR的研究,具体的工作如下:(1)介绍了目前降低OFDM系统PAPR值的三大方法:信号预畸变类方法,编码类方法,以及概率类方法。通过理论分析和模拟仿真评估了三类技术的优缺点,结果表明概率类技术是最有潜力优化OFDM系统PAPR性能的方法。(2)对概率类方法中的ACE算法进行了论述,重点介绍了ACE的三种具体可实现算法:ACE凸集映射法(ACE-POCS),ACE智能梯度投影法(ACE-SGP),预失真ACE法(ACE-BD)。针对三种算法在优化PAPR性能的同时,带来高复杂度问题,本文基于最小二乘逼近法(LSA)提出了ACE-POCS的改进算法——LSA-ACE-POCS。LSA-ACE-POCS算法的主要思想是利用LSA方法得到削波信号最佳加权因子?,促使削波信号以较快地速度接近原始噪声。仿真结果表明,与ACE-POCS算法相比,LSA-ACE-POCS算法在不恶化系统误码率(BER)性能的情况下,经过一次迭代过程中就可达到传统算法经过多次迭代后的PAPR优化效果,显著降低了计算复杂度。因此,LSA-ACE-POCS改进算法在降低PAPR方面具有一定的竞争力。(3)考虑将ACE-POCS算法与部分传输序列(PTS)算法联合起来降低PAPR。根据两种算法不同的联合方式,提出了PTS-ACE-POCS、交织ACE-POCS-PTS(Interlaced ACE-POCS-PTS)、半对半ACE-POCS-PTS(Half-to-Half ACE-POCS-PTS)、以及ACE-POCS-PTS四种联合算法。通过PAPR降低程度,所需计算复杂度,以及BER性能三方面对四种组合算法进行仿真分析,结果表明ACE-POCS-PTS算法是性能最优的。另外,通过对ACE-POCS-PTS算法的性能进一步仿真分析发现:当OFDM系统采用较大子载波数目,较低阶MQAM调制方式时,ACE-POCS-PTS算法对于优化PAPR性能是个很有吸引力的选择。
[Abstract]:With the rapid development of society, people demand higher data transmission rate and reliability of text, image, voice and video. Orthogonal Frequency Division Multiplexing (OFDM) technology has become an attractive technology in wireless communication systems because of its high spectral efficiency, strong anti-multipath fading and anti-ISI capability. However, because of its multi-carrier modulation, the PAPR of the system is higher, which to some extent affects the further application and popularization of OFDM technology. Therefore, how to effectively optimize PAPR performance has become an important research topic in OFDM technology. In this paper, the research of reducing PAPR based on the constellation map extension method is carried out. The main work is as follows: 1) three methods to reduce the PAPR value of OFDM system are introduced: signal predistortion class method, coding class method and probability class method. The advantages and disadvantages of the three kinds of techniques are evaluated by theoretical analysis and simulation. The results show that probabilistic class technique is the most promising method to optimize the PAPR performance of OFDM system. (2) the ACE algorithm in probabilistic class method is discussed. In this paper, three specific implementable algorithms of ACE are introduced, namely: ACE-POCSS mapping method and ACE-SGPG method, and predistortion ACE method. In order to solve the problem of high complexity while optimizing the PAPR performance of the three algorithms, This paper presents an improved ACE-POCS algorithm based on the least square approximation (LSA). The main idea of the LSA-ACE-POCS.LSA-ACE-POCS algorithm is to obtain the optimal weighting factor of the clipping signal by using the LSA method, and to promote the clipping signal to approach the original noise at a faster speed. Simulation results show that compared with the ACE-POCS algorithm, the LSA-ACE-POCs algorithm can achieve the PAPR optimization effect of the traditional algorithm after multiple iterations without deteriorating the performance of the system bit error rate (BER). The computational complexity is significantly reduced. Therefore, the improved LSA-ACE-POCs algorithm is competitive in reducing PAPR. We consider combining the ACE-POCS algorithm with the partial transmission sequence (ACE-POCS) algorithm to reduce the PAPR. According to the different joint methods of the two algorithms, four joint algorithms of PTS-ACE-POCSs, interleaved ACE-POCS-PTS(Interlaced ACE-POCS-PTSs, half-to-semi- ACE-POCS-PTSs, and ACE-POCS-PTS are proposed. Four combined algorithms are simulated from three aspects of PAPR reduction, computational complexity and BER performance. The results show that the ACE-POCS-PTS algorithm is the best. In addition, through the further simulation analysis of the ACE-POCS-PTS algorithm, it is found that the ACE-POCS-PTS algorithm is an attractive choice for optimizing the PAPR performance when the OFDM system adopts a large number of sub-carriers and a lower order MQAM modulation mode.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.53

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