论文总字数：26994字

摘 要

基于发光二极管（Light Emitting Diode, LED）的可见光通信（Visible Light Communication, VLC）技术是当今世界学者研究的热门课题之一。学者不断地研究VLC中信号的调制与传输方式以获得更高的传输速率以及更好的抗噪性能。多载波技术以其高速传输、抗多径干扰和对频谱灵活应用的优点，被广泛应用于VLC系统中。

首先，本文对可见光通信系统的原理、特点和发展情况做了简单介绍。同时介绍了正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术和正交振幅调制(Quadrature Amplitude Modulation, QAM)的概念。接着着重介绍了两种VLC中的OFDM技术:直流偏置光正交频分复用(Direct Current Optical Orthogonal Frequency Division Multiplexing, DCO-OFDM)和非对称截断光正交频分复用(Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing, ACO-OFDM)。

接着详细介绍了翻转正交频分复用(Flip Orthogonal Frequency Division Multiplexing, Flip-OFDM)方案，给出了Flip-OFDM信号的产生过程，以及两种接收机设计方案。分别在加性高斯白噪声(Additive White Gaussian Noise, AWGN)信道和多径信道下对两种方案做仿真，通过比较误比特率(Bit Error Ratio, BER)曲线，证明迭代型接收机的性能要优于传统型接收机。

文章还介绍了增强型单极正交频分复用(enhanced Unipolar Orthogonal Frequency Division Multiplexing, eU-OFDM)方案，给出了eU-OFDM信号的产生过程，以及传统的接收机方案。通过利用eU-OFDM方案的帧结构特点，设计出新的接收机方案。分析了两种接收机方案分别在AWGN信道和多径信道下的仿真BER曲线。得到新的接收机方案性明显优于传统接收机的结论。

文章最后提出了一种基于Flip-OFDM的新调制方案，该方案在频谱效率上优于Flip-OFDM，并且对其分别在AWGN和多径信道下进行仿真和性能分析。

关键词：可见光通信；多载波技术；正交频分复用；频谱效率

ABSTRACT

Visible light communication (VLC) is based on white light LED, and it’s one of the most popular technologies in the world today. In order to obtain higher transmission rate, and has better noise immunity, scholars proposed many modulation and transmission schemes for VLC. Among those schemes, multi-carrier technology is widely used in VLC which supports high-speed transmission, and is capable of combating multipath interference and using spectrum flexibly.

Firstly, this article introduces principles, characteristics and development of VLC system, and also gives some introduction on the technology of Orthogonal Frequency Division Multiplexing (OFDM) and quadrature amplitude modulation (QAM). Then, it introduces two kinds of OFDM technology in VLC: direct current biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM).

Then Flip-OFDM scheme is introduced. The process of Flip-OFDM signal generation is given, as well as two receivers are designed. Respectively, two receivers’ simulations are performed in additive white Gaussian noise (AWGN) channel and multipath channel. By comparing the bit error rate (BER) curves, it is proved that the iterative receiver performs better than the traditional receiver.

After that, this paper introduces the enhanced Unipolar Orthogonal Frequency Division Multiplexing (eU-OFDM) scheme, and gives process of eU-OFDM signal generation, and the traditional receiver. By using the characteristic of the frame structure of the eU-OFDM scheme, a new receiver is designed. Simulations of the two receivers are made in both AWGN channel and multipath channel, which draws the conclusion that the performance of the new receiver is better than that of the traditional receiver.

Finally, this paper proposes a new modulation scheme, which is based on Flip-OFDM. The spectral efficiency of the proposed one is better than that of Flip-OFDM. Based on it, the simulations are made both in AWGN channel and multipath channel to analysis its performance.

Key Words: Visible light communication, multi-carrier technology, OFDM, spectral efficiency

目录

摘 要 I

ABSTRACT II

第一章 绪 论 1

1.1 可见光通信概述 1

1.2 VLC国内外研究现状 2

1.2.1 VLC的发展 2

1.2.2 VLC的研究内容 3

1.3 多载波技术 4

1.3.1 多载波技术简述 4

1.3.2 OFDM技术发展及基本原理 4

1.4 VLC中的OFDM技术 5

1.4.1 DCO-OFDM 5

1.4.2 ACO-OFDM 6

1.5 QAM调制 6

1.6 课题研究意义 7

1.7 本文研究内容 7

第二章 Flip-OFDM 8

2.1 Flip-OFDM的产生过程 8

2.2 Flip-OFDM信号的接收机算法 9

2.2.1 传统Flip-OFDM接收算法 9

2.2.2 迭代型Flip-OFDM接收算法 10

2.3 仿真及性能分析 14

2.4 本章小结 15

第三章 eU-OFDM 16

3.1 eU-OFDM的调制过程 16

3.2 传统的eU-OFDM接收算法 17

3.3 改进eU-OFDM接收算法 18

3.4 性能分析及仿真 19

3.4.1 频谱效率 19

3.4.2 功率效率 20

3.4.3 仿真及其分析 22

3.5 本章小结 23

第四章 改进Flip-OFDM 24

4.1 调制过程 24

4.2 接收机算法 26

4.3 性能分析及仿真 26

4.3.1 频谱效率 26

4.3.2 仿真及分析 27

4.4 本章小结 29

第五章 全文总结与展望 30

5.1 全文工作总结 30

5.2 进一步研究方向 31

致谢 32

参考文献 33

第一章 绪 论

1.1 可见光通信概述

可见光通信（Visible Light Communication, VLC）是一种指使用可见光波频段的光作为信息传输媒质，直接在空气等介质传输信息的通信方式。发光二极管（Light Emitting Diode, LED）是一种绿色环保光源，其被视作下一代主要的照明器材。和其他常见的照明器材比起来，它不但具备绿色环保、功耗低、尺寸小、价格低廉和使用时间长的优点，还具备很好的调制性能和很强的响应灵敏度。随着人们不断发掘LED等的特性，VLC也随之发展起来。现在，已经可以做到短距离高速通信^【1】。这种利用LED灯发光特点对消息进行调制和传输的通信方法，通信速率在理论上可达数百兆每秒。因其具有部署灵活，信息容量大和环保安全的特点，使人们对它有着极大的兴趣，近几年发展的也非常迅速。

VLC系统根据部署位置主要分为两种：室内可见光通信系统和室外可见光通信系统，两者主要在通信信道上有着不同的特点：室内可见光信道为室内大气路径，传输距离较小，且由于散射带来的信号衰减影响较小^【15】。室外可见光信道为室外大气路径，传输距离长，且信号散射严重。室内可见光通信系统由个人计算机，移动终端和LED灯构成。可以实现无线光通信。室外可见光通信系统主要是在智能交通领域的应用。

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