可见光通信具有频谱资源丰富、应用场景多样、无电磁干扰等优点，成为近年来的研究热点，然而现有的可见光通信技术还面临着各种各样的挑战。本文围绕“高谱效OFDM的可见光通信”这一中心，以分层非对称限幅光正交频分复用（Layered Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing，LACO-OFDM）方式为研究对象，在自适应调制、调光控制、干扰抑制、能效优化等方面进行研究，主要有以下工作：首先，针对不同环境下的自适应调制问题，面向LACO-OFDM中子载波资源和功耗之间的折中问题，提出一种可变层数的自适应LACO-OFDM调制策略，以在不同环境下均能实现高频谱效率。该策略综合考虑应用环境和系统复杂度等要求，研究在电功率或光功率受限的条件下，LACO-OFDM中的传输数据率与层数之间的关系，通过最大化数据率得到不同噪声条件下的近似最优层数，得出自适应的LACO-OFDM层数分配方案。其次，针对照明和通信的双重需求，提出一种基于混合LACO-OFDM的调光控制方法。该方法将正负两种高谱效的OFDM信号添加不同的直流偏置后进行时分复用，通过调整两种信号比例和缩放因子，实现不同的调光水平。该方法可以充分利用LED动态范围，在较宽的调光范围内实现稳定且较高的传输速率，同时解调复杂度较现有方案简单，在实现调光控制的同时提供高谱效的通信方案。再次，针对层间干扰问题，考虑将层间干扰在发射端进行预失真消除，提出一种基于部分预失真的自适应高谱效调制技术。该方法同时考虑误差传播和功耗两方面问题，通过部分预失真操作消除部分层之间的信号干扰，在适当增加预失真信号功率的前提下还能进一步提高通信性能，同时平衡发射端和接收端的复杂度差异，实现不同环境下的灵活传输方案。最后，针对能效优化问题，对基于OFDM的可见光通信调制技术进行分析，提出一种能效与谱效折中的调制方案选择策略。根据可见光通信信道的模型，分析每种调制方式的传输数据速率和LED的电功率，给出能量效率和频谱效率之间关系的理论公式，研究直流偏置、功率分配、层数等参数对于谱效能效性能的影响。在实际应用中，需在能耗要求下保证通信质量，自适应地选择最佳传输方案。
Visible light communication (VLC), with its advantages of rich spectrum resources, various application scenarios, and no electromagnetic interference, has drawn significant attention in recent years. However, the existing VLC technology also faces various challenges. This thesis focuses on the topic of "Visible Light Communication Based on OFDM with High Spectral Efficiency ", and studies the layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) scheme in terms of adaptive modulation, dimming control, interference suppression, and energy efficiency optimization. The main contributions are as follows:Firstly, focusing on the issue of adaptive modulation under different environments, an adaptive LACO-OFDM scheme with variable layers is proposed to make a tradeoff between subcarrier resources and power consumption, which can obtain high spectral efficiency. The proposed strategy takes the application environment, computational complexity and other requirements into consideration. With constrained power, the relationship between the transmission data rate and the layer number in LACO-OFDM is investigated. The near optimal number of layers under different noise scenarios can be obtained by maximizing the data rate, resulting in an adaptive layer number allocation for LACO-OFDM.Secondly, a dimming control scheme with high spectral efficiency for visible light communication based on hybrid LACO-OFDM is proposed to realize lighting and communication simultaneously. Different DC biases are added to the positive and negative OFDM signals with high spectral efficiency and the two kinds of signals are mixed by time division multiplexing for transmission. The proportions of the two signals and scaling factors are adjusted to achieve different dimming levels. The proposed scheme can make full use of the dynamic range of power of light emitting diodes (LEDs) and acquire a wide illumination range with a relatively stable and high data rate. The demodulation process of the proposed strategy is simpler than that of the existing schemes. The method can realize communication with high spectral efficiency while achieving dimming control.Thirdly, aiming at the inter-layer interference, an adaptive modulation scheme based on partially pre-distorted LACO-OFDM is proposed in this thesis by eliminating the inter-layer interference at the transmitter. Both the error propagation and power consumption are taken into consideration. The process of partial pre-distortion can eliminate the inter-layer interference of specific layers, which can improve the communication performance with suitable power consumption. The difference of the computational complexities at the transmitter and the receiver can be balanced, realizing a flexible transmission scheme in different environments.Finally, for the optimization of energy efficiency, the OFDM-based modulation schemes for visible light communication are analyzed, resulting in an adaptive modulation strategy that makes a tradeoff between energy efficiency and spectral efficiency. The data rate and electrical LEDs are analyzed based on the channel model of the visible light communication, which can help formulate the theoretical expressions of the spectral efficiency and the energy efficiency. The influences of the DC biases, the power allocation, and the layer number are also investigated in the thesis. For practical application, it is necessary to ensure the communication quality under the requirements of power consumption, thus the modulation scheme can be selected adaptively.
