基于正交频分复用的可见光通信非线性信道均衡机制研究

The visible light communication combines indoor illumination and communication, which has become research hotspot in recent years. However, in the visible light communication systems, obvious nonlinear characteristic has been observed for LED transmitter. When the OFDM signal is loaded on the LED, the LED nonlinearity will produce crosstalk for OFDM subcarriers, which will introduce In-band and out-band noise for OFDM signal spectrum. As a result, system performance deteriorates as the nonlinearity expands. Therefore, how to establish a nonlinear model for LED and eliminate the crosstalk of the LED nonlinearity according to the characteristics of OFDM is a major challenge for modulation techniques of visible light communications. In this project, we focus on the LED nonlinearity, and develop a nonlinear model for LED to eliminate noise for the nonlinear channel. A simplified LED nonlinear model is proposed in frequency domain, which can reduce calculation complexity. A self-adaption scheme of hybrid time-frequency domain equalization is presented to mitigate the LED nonlinearity for OFDM systems Based on the nonlinear model. Based on the research achievements, a high-speed visible light communication over longer distances can be achieved.

可见光通信技术融合了室内照明和通信技术，成为近几年来研究的热点。然而，在可见光通信系统中，发射端LED往往是具有较强的非线性特性。如果把OFDM信号加载在LED上时，非线性效应会使得OFDM各子载波产生串扰。这会使得OFDM信号频谱的带宽内部和带宽外部都引入噪声，从而导致系统性能恶化。因此，如何根据OFDM的自身特点，来建立LED非线性模型，消除非线性串扰，就是当前可见光调制技术所面临的主要挑战。因此，本项目以LED的非线性效应为研究对象，对LED的非线性模型和非线性信道均衡问题进行深入研究。提出一个基于频域的LED非线性简化模型，降低了计算复杂度；基于这个模型，提出使用自适应时-频域联合均衡机制来彻底消除OFDM系统中的非线性。综合两方面的研究，可以实现高速、长距离的可见光通信。

在可见光通信系统中，发射端LED往往是具有较强的非线性特性。非线性效应会造成正交频分复用（OFDM）中各子载波产生串扰，使得OFDM信号频谱的带宽内部和带宽外部都引入噪声，从而导致系统性能恶化。因此，本项目对基于OFDM可见光通信系统的非线性干扰和非线性信道均衡问题进行深入研究。.解决LED非线性问题相关研究成果包括：提出了基于对称恢复的非对称切除OFDM（ACO-OFDM）解调方法，来缓解LED的非线性干扰；提出了一个基于计算机视觉的智能信道估计方法和模型，来消除混合信道（大气和水下）的非线性干扰；提出了基于单个快速傅里叶变换的ACO-OFDM（LACO-OFDM）解调方法，来缓解LACO-OFDM系统内的非线性干扰；提出了对偶最大似然检测方法，来提升LACO-OFDM系统在非线性信道下的性能。.解决非线性信道均衡相关研究成果包括：提出了混合时-频域的数字预畸变均衡方法，来消除OFDM系统的带内和带外非线性噪声；提出了基于深度神经网络的信道均衡方法来消除LED非线性干扰；提出了预失真技术来消除分层LACO-OFDM系统内的非线性干扰。.通过对上述两个问题的研究，取得一系列成果，解决了LED非线性干扰和非线性信道均衡问题，为高速率、长距离的可见光传输提供理论基础和技术支撑。