基于HACO-OFDM的室内可见光通信PAPR抑制技术研究

发布时间：2018-05-10 21:07

本文选题：可见光通信 + HACO-OFDM　；参考：《兰州交通大学》2017年硕士论文

【摘要】：随着移动互联网技术的迅速发展而无线接入网频谱资源日趋耗尽,传统接入网技术正面临越来越大的挑战。当今世界正在呼唤一种能拓宽频谱资源、绿色节能、可移动的新型接入方式。在此背景下,可见光通信技术应运而生。可见光通信技术采用白光LED作为光源,利用LED灯光承载的高速明暗闪烁的信号来传输信息,适用于各种室内接入场景。它在满足照明的同时实现通信功能,具有无电磁辐射、高度保密性的优势,是近年来无线通信领域研究的热点问题之一。然而,LED有限的调制带宽严重限制了可见光通信的传输速率,成为了制约可见光通信发展的瓶颈。解决方法是采用频谱效率高、调制效果好的正交频分复用OFDM技术。根据可见光通信的特点,有学者提出了ACO-OFDM调制方式,但是该调制方式具有频谱效率低的缺陷。同时,可见光通信中的OFDM同样面临着信号峰值平均功率比(PAPR)过高的缺陷,高PAPR的信号在可见光通信的非线性器件中传输会引起严重失真。因此OFDM应用于可见光通信中,必须对其信号的高PAPR特性进行抑制。针对这些问题,论文进行了相关的研究,主要工作如下:一、针对ACO-OFDM调制系统有用数据只在奇数子载波上传输,偶数子载波闲置,导致频谱效率低的缺陷,改进一种混合调制方案。在原来的ACO-OFDM调制中偶数子载波上采用CAP调制。通过比较可以发现,改进后的混合调制方案能够在不过多增加系统复杂度的情况下提高频谱利用率。二、针对直接限幅法的不足,研究利用TR算法进行改进。对输入的OFDM信号进行预处理,经过TR矢量和输入信号的循环迭代叠加,抵消了部分输入OFDM信号的高峰值,之后再进行限幅滤波处理。仿真结果表明,在相同的CCDF值下,改进后的TR-Clipping算法相比于直接限幅法具有更佳的PAPR抑制效果三、针对传统PTS技术计算复杂度太高和传输边带信息造成PAPR二次升高的缺陷,研究使用预设阈值和二进制搜索因子作为搜索集合进行优化改进。通过比较可以发现,改进算法是一种次优迭代算法,由于减少了IFFT运算次数其计算复杂度低于原来的PTS算法。
[Abstract]:With the rapid development of mobile Internet technology, wireless access network spectrum resources are increasingly depleted, the traditional access network technology is facing more and more challenges. Nowadays, the world is calling for a new type of access which can broaden the spectrum resources, save energy and move. Under this background, visible light communication technology emerges as the times require. The visible light communication technology uses white light LED as the light source and uses the high speed light and dark flashing signal carried by the LED light to transmit the information, which is suitable for various indoor access scenes. It has the advantages of no electromagnetic radiation and high confidentiality. It is one of the hot issues in the field of wireless communication in recent years. However, the limited modulation bandwidth of LED seriously limits the transmission rate of visible light communication and becomes the bottleneck of the development of visible light communication. The solution is to adopt orthogonal Frequency Division Multiplexing (OFDM) technology with high spectral efficiency and good modulation effect. According to the characteristics of visible light communication, some scholars have proposed a ACO-OFDM modulation scheme, but the modulation mode has the defect of low spectral efficiency. At the same time, the OFDM in visible light communication also faces the defect of high peak-to-average power ratio (PAPR). The signal with high PAPR will cause serious distortion in the nonlinear devices of visible light communication. Therefore, when OFDM is used in visible light communication, the high PAPR characteristic of its signal must be suppressed. In order to solve these problems, the main work of this paper is as follows: first, the useful data of ACO-OFDM modulation system is transmitted only on odd subcarriers, and even subcarriers are idle, which leads to the low spectral efficiency. Improve a hybrid modulation scheme. In the original ACO-OFDM modulation, CAP modulation is used on even number subcarriers. It is found that the improved hybrid modulation scheme can improve the spectral efficiency without increasing the complexity of the system. Secondly, aiming at the deficiency of direct limiting method, the tr algorithm is studied and improved. The input OFDM signal is preprocessed, and the tr vector and the input signal are overlapped iteratively, which cancels the high peak value of some input OFDM signals, and then carries on the amplitude limiting filtering processing. The simulation results show that under the same CCDF value, the improved TR-Clipping algorithm has better PAPR suppression effect than the direct limiting method. In view of the disadvantages of the high computational complexity of traditional PTS technology and the secondary increase of PAPR caused by the transmission of sideband information, the simulation results show that the improved TR-Clipping algorithm has better PAPR suppression effect than the direct limiting method. In this paper, the predefined threshold and binary search factor are used as search set to optimize and improve. By comparison, it is found that the improved algorithm is a suboptimal iterative algorithm, and the complexity of the improved algorithm is lower than that of the original PTS algorithm because of reducing the number of IFFT operations.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.1

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