可見光通信OFDM調(diào)制技術(shù)研究
發(fā)布時間：2018-09-10 14:16
【摘要】：基于正交頻分復用(OFDM)技術(shù)的可見光通信(VLC)系統(tǒng)的主要特點有：首先,可見光通信系統(tǒng)一般采用強度調(diào)制／直接檢測(IM/DD)的方式,OFDM基帶信號必須是正的實信號；其次,發(fā)光二極管(LED)的線性動態(tài)范圍非常有限,如果輸入信號的幅度太小,會造成截止失真,而若信號幅度過大,又會引起飽和失真；再次,OFDM系統(tǒng)的峰均比比較高,會嚴重影響系統(tǒng)的性能。本文基于以上幾個方面來開展相關的研究工作。本文主要的研究內(nèi)容和創(chuàng)新點如下：1.對可見光系統(tǒng)中的OFDM調(diào)制技術(shù)進行分析與改進。針對VLC系統(tǒng)與射頻通信系統(tǒng)的不同特點,研究幾種適用于VLC系統(tǒng)的光OFDM調(diào)制方式,并比較其性能特點。同時,提出了一種基于Flip-OFDM技術(shù)的改進方法,減小了系統(tǒng)噪聲的影響,提高系統(tǒng)的誤碼率性能。2.為了減小LED非線性的影響,提高系統(tǒng)的頻譜效率,將振幅移相鍵控(APSK)與OFDM技術(shù)相結(jié)合的傳輸方案(APSK-OFDM)引入VLC系統(tǒng)中。與傳統(tǒng)的矩形正交振幅調(diào)制(QAM)技術(shù)相比,APSK信號的包絡起伏比較小,對LED的非線性要求比較低。仿真結(jié)果表明,當考慮到LED的非線性特性因素時,APSK-OFDM調(diào)制的系統(tǒng)性能要比QAM-OFDM調(diào)制好。同時,研究了不同的APSK信號星座圖的相對半徑與系統(tǒng)誤碼率性能之間的關系。由于可見光OFDM系統(tǒng)的各子信道的衰落情況各不相同,為了實現(xiàn)系統(tǒng)帶寬資源的充分利用,提出將APSK-OFDM調(diào)制方案與自適應技術(shù)相結(jié)合,根據(jù)不同子信道狀況來合理地分配系統(tǒng)資源,提高VLC系統(tǒng)的整體性能。3.提出降低可見光OFDM系統(tǒng)峰均比的新方法。首先研究了可見光OFDM系統(tǒng)中峰均比的概率分布,為后續(xù)研究提供理論基礎。然后分析幾種降低OFDM系統(tǒng)峰均比的典型方法：壓擴法、選擇性映射法(SLM)和部分傳輸序列法(PTS),并仿真分析其性能特點。這些方法的性能各不相同,若僅采用單一的方法往往難以取得理想的效果,需要綜合考慮到系統(tǒng)的峰均比性能與系統(tǒng)復雜度等因素的影響。同時,研究VLC系統(tǒng)的光通效率與系統(tǒng)峰均比的關系。為此,本文提出將離散傅里葉變換(DFT)展開分別與SLM方法和PTS方法相結(jié)合的聯(lián)合算法。分析結(jié)果表明,在系統(tǒng)的峰均比性能相近的情況下,聯(lián)合算法的復雜度要遠遠小于單一算法；同時聯(lián)合算法也能明顯提高系統(tǒng)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.
【學位授予單位】：解放軍信息工程大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN929.1
本文編號：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.
【學位授予單位】：解放軍信息工程大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN929.1
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