可见光通信OFDM调制技术研究
发布时间：2018-09-10 14:16
【摘要】：基于正交频分复用(OFDM)技术的可见光通信(VLC)系统的主要特点有：首先,可见光通信系统一般采用强度调制／直接检测(IM/DD)的方式,OFDM基带信号必须是正的实信号；其次,发光二极管(LED)的线性动态范围非常有限,如果输入信号的幅度太小,会造成截止失真,而若信号幅度过大,又会引起饱和失真；再次,OFDM系统的峰均比比较高,会严重影响系统的性能。本文基于以上几个方面来开展相关的研究工作。本文主要的研究内容和创新点如下：1.对可见光系统中的OFDM调制技术进行分析与改进。针对VLC系统与射频通信系统的不同特点,研究几种适用于VLC系统的光OFDM调制方式,并比较其性能特点。同时,提出了一种基于Flip-OFDM技术的改进方法,减小了系统噪声的影响,提高系统的误码率性能。2.为了减小LED非线性的影响,提高系统的频谱效率,将振幅移相键控(APSK)与OFDM技术相结合的传输方案(APSK-OFDM)引入VLC系统中。与传统的矩形正交振幅调制(QAM)技术相比,APSK信号的包络起伏比较小,对LED的非线性要求比较低。仿真结果表明,当考虑到LED的非线性特性因素时,APSK-OFDM调制的系统性能要比QAM-OFDM调制好。同时,研究了不同的APSK信号星座图的相对半径与系统误码率性能之间的关系。由于可见光OFDM系统的各子信道的衰落情况各不相同,为了实现系统带宽资源的充分利用,提出将APSK-OFDM调制方案与自适应技术相结合,根据不同子信道状况来合理地分配系统资源,提高VLC系统的整体性能。3.提出降低可见光OFDM系统峰均比的新方法。首先研究了可见光OFDM系统中峰均比的概率分布,为后续研究提供理论基础。然后分析几种降低OFDM系统峰均比的典型方法：压扩法、选择性映射法(SLM)和部分传输序列法(PTS),并仿真分析其性能特点。这些方法的性能各不相同,若仅采用单一的方法往往难以取得理想的效果,需要综合考虑到系统的峰均比性能与系统复杂度等因素的影响。同时,研究VLC系统的光通效率与系统峰均比的关系。为此,本文提出将离散傅里叶变换(DFT)展开分别与SLM方法和PTS方法相结合的联合算法。分析结果表明,在系统的峰均比性能相近的情况下,联合算法的复杂度要远远小于单一算法；同时联合算法也能明显提高系统的光通效率。
[Abstract]:The main features of the visible light communication (VLC) system based on orthogonal frequency division multiplexing (OFDM) are as follows: firstly, the intensity modulation / direct detection (IM/DD) mode is generally adopted in the visible light communication system. The linear dynamic range of (LED) is very limited. If the input signal amplitude is too small, it will cause cut-off distortion, and if the signal amplitude is too large, it will cause saturation distortion. Will seriously affect the performance of the system. This paper based on the above several aspects to carry out the relevant research work. The main contents and innovations of this paper are as follows: 1. The OFDM modulation technology in visible light system is analyzed and improved. According to the different characteristics of VLC system and radio frequency communication system, several optical OFDM modulation modes suitable for VLC system are studied, and their performance characteristics are compared. At the same time, an improved method based on Flip-OFDM technology is proposed to reduce the influence of system noise and improve the BER performance of the system. In order to reduce the influence of LED nonlinearity and improve the spectral efficiency of the system, a transmission scheme (APSK-OFDM), which combines amplitude shift keying (APSK) with OFDM technology, is introduced into the VLC system. Compared with the traditional rectangular quadrature amplitude modulation (QAM) technique, the envelope fluctuation of (QAM) signal is smaller, and the nonlinear requirement of LED is lower. The simulation results show that the system performance of APSK-OFDM modulation is better than that of QAM-OFDM modulation when considering the nonlinear characteristics of LED. At the same time, the relationship between the relative radii of different constellations of APSK signals and the bit error rate (BER) performance of the system is studied. In order to realize the full utilization of the bandwidth resources of the visible OFDM system, a combination of APSK-OFDM modulation scheme and adaptive technology is proposed to reasonably allocate the system resources according to the different subchannel conditions because of the different fading conditions of each sub-channel in the visible light OFDM system, in order to make full use of the bandwidth resources of the system. Improve the overall performance of VLC system. A new method for reducing PAPR of visible OFDM system is proposed. The probability distribution of peak-to-average ratio (PAPR) in a visible OFDM system is studied firstly, which provides a theoretical basis for further research. Then several typical methods to reduce the peak-to-average ratio of OFDM system are analyzed: compression expansion method, selective mapping method (SLM) and partial transmission sequence method (PTS), and their performance characteristics are analyzed by simulation. The performance of these methods is different. If only a single method is used, it is difficult to achieve ideal results, so it is necessary to take into account the influence of the PAPR performance and the complexity of the system. At the same time, the relationship between the optical efficiency and the PAPR of VLC system is studied. In this paper, a joint algorithm combining discrete Fourier transform (DFT) expansion with SLM method and PTS method is proposed. The analysis results show that the complexity of the joint algorithm is much smaller than that of the single algorithm when the PAPR performance of the system is similar, and the joint algorithm can obviously improve the optical efficiency of the system.
【学位授予单位】：解放军信息工程大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.1
本文编号：2234684
[Abstract]:The main features of the visible light communication (VLC) system based on orthogonal frequency division multiplexing (OFDM) are as follows: firstly, the intensity modulation / direct detection (IM/DD) mode is generally adopted in the visible light communication system. The linear dynamic range of (LED) is very limited. If the input signal amplitude is too small, it will cause cut-off distortion, and if the signal amplitude is too large, it will cause saturation distortion. Will seriously affect the performance of the system. This paper based on the above several aspects to carry out the relevant research work. The main contents and innovations of this paper are as follows: 1. The OFDM modulation technology in visible light system is analyzed and improved. According to the different characteristics of VLC system and radio frequency communication system, several optical OFDM modulation modes suitable for VLC system are studied, and their performance characteristics are compared. At the same time, an improved method based on Flip-OFDM technology is proposed to reduce the influence of system noise and improve the BER performance of the system. In order to reduce the influence of LED nonlinearity and improve the spectral efficiency of the system, a transmission scheme (APSK-OFDM), which combines amplitude shift keying (APSK) with OFDM technology, is introduced into the VLC system. Compared with the traditional rectangular quadrature amplitude modulation (QAM) technique, the envelope fluctuation of (QAM) signal is smaller, and the nonlinear requirement of LED is lower. The simulation results show that the system performance of APSK-OFDM modulation is better than that of QAM-OFDM modulation when considering the nonlinear characteristics of LED. At the same time, the relationship between the relative radii of different constellations of APSK signals and the bit error rate (BER) performance of the system is studied. In order to realize the full utilization of the bandwidth resources of the visible OFDM system, a combination of APSK-OFDM modulation scheme and adaptive technology is proposed to reasonably allocate the system resources according to the different subchannel conditions because of the different fading conditions of each sub-channel in the visible light OFDM system, in order to make full use of the bandwidth resources of the system. Improve the overall performance of VLC system. A new method for reducing PAPR of visible OFDM system is proposed. The probability distribution of peak-to-average ratio (PAPR) in a visible OFDM system is studied firstly, which provides a theoretical basis for further research. Then several typical methods to reduce the peak-to-average ratio of OFDM system are analyzed: compression expansion method, selective mapping method (SLM) and partial transmission sequence method (PTS), and their performance characteristics are analyzed by simulation. The performance of these methods is different. If only a single method is used, it is difficult to achieve ideal results, so it is necessary to take into account the influence of the PAPR performance and the complexity of the system. At the same time, the relationship between the optical efficiency and the PAPR of VLC system is studied. In this paper, a joint algorithm combining discrete Fourier transform (DFT) expansion with SLM method and PTS method is proposed. The analysis results show that the complexity of the joint algorithm is much smaller than that of the single algorithm when the PAPR performance of the system is similar, and the joint algorithm can obviously improve the optical efficiency of the system.
【学位授予单位】：解放军信息工程大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.1
【参考文献】
相关期刊论文 前4条
1 张建昆;杨宇;陈弘达;;室内可见光通信调制方法分析[J];中国激光;2011年04期
2 张华;宋正勋;刘冬彦;周晓兵;尹力会;;基于自适应OFDM的可见光通信系统分析[J];长春理工大学学报(自然科学版);2010年01期
3 朱晓东;朱光喜;林沛;;基于线性变换降低OFDM系统中峰均功率比的方法[J];计算机工程与科学;2009年07期
4 刘志新;雷菁;雍玲;;卫星信道中APSK星座的优化设计[J];上海航天;2006年05期
相关硕士学位论文 前1条
1 魏承功;基于白光LED的室内可见光通信系统研究[D];长春理工大学;2008年
，本文编号：2234684
本文链接：https://www.wllwen.com/kejilunwen/wltx/2234684.html
