无线可见光通信关键技术研究

发布时间：2018-09-09 15:55

【摘要】：无线可见光通信系统是指利用可见光波作为信息的载体进行信号传输的通信系统。该技术方案在提供通信的基本需求以外还具有电磁兼容性良好、无频谱许可要求、改善特定环境下通信质量以及提高信息安全性等优势,因此受到学术界与工业界的广泛关注。室内环境下的无线可见光通信技术使得室内LED光源兼顾通信与照明等功能,扣除照明本身的能耗,用于无线传输的能耗显著低于传统射频无线通信系统。近年来,作为研究热点之一的无线可见光通信技术,已经被更多的研究人员关注。例如,在光波传输机理下无线光通信技术能否逼近传统信道容量；无线光通信中高效调制编码理论研究等。随着LED绿色高效光源的推广普及,室内无线可见光通信技术将会被广泛地应用在无线通信“最后一米”的解决方案中。在这一背景下,无线可见光通信系统的信道模型和容量分析、光电资源配置与优化、高效传输调制与接收研究也必然受到人们的关注。本文针对上述室内环境下的无线可见光通信系统的若干关键技术展开深入研究,具体说来,论文作了以下主要贡献：本论文第二章针对光波传输机理,研究了无线光通信系统的信道容量问题。本章研究首先基于泊松光子信道模型,推导得出脉冲位置调制下的光通信系统的传输容量表达式,进一步研究了泊松信道的容量下界问题；接着本章考虑了系统传输信号的峰值功率约束对信道容量的影响,推导得出平均功率与峰值功率约束条件同时或者分别存在情形下的信道容量上下限,并利用计算机仿真结果表明这些结果的准确性；本章最后针对光正交频分复用技术存在限幅截断的特性,分析了ACO-OFDM与DCO-OFDM系统限幅信号的功率,并分别给出系统的最大可行传输速率的理论推导。本论文第三章研究无线光通信系统的信道均衡问题。本章分析了无线光通信系统中码间干扰的主要来源,针对室内LED光源调制带宽相对较窄的问题提出了分数域均衡的方案,利用信号过采样来提升均衡滤波器抽头的分辨率；接着本章根据理论推导得出的分数域均衡器抽头系数最优解设计了两种均衡算法,分别给出迫零算法与判决反馈算法的滤波器抽头系数解；最后利用计算机仿真结果验证了不同速率下分数域间隔均衡的性能优越性。本论文第四章主要研究了DCO-OFDM发送端优化问题。我们从光正交频分复用调制的原理出发,分别分析了三种光正交频分复用调制的特点。大部分现有研究工作都只考虑到光信号单极性的特点而采用了信号下限幅截断操作。实际上如何抑制高峰均比一直是OFDM传输系统中的一个重要问题。这一章研究采用上下非对称限幅截断的方法,使得发射信号功率满足光源LED的线性工作区域要求。同时为了克服因限幅截断引起系统误码率恶化的问题,我们对DCO-OFDM方案中的偏置电流功率进行优化。本章研究在保证非对称限幅截断满足系统硬件需求的同时最小化所有子载波上的信号限幅失真函数。依据优化准则建立起来的功率控制问题是一个组合优化问题,目标函数是非凸函数。接着本章给出了一个合理的搜索算法对全局最优解进行判定,计算机仿真结果表明合理选择发送端偏置电流功率对于DCO-OFDM系统来说非常必要,也在一定程度上缓解了限幅截断噪声对系统误码率的影响。最后,论文第五章考虑了光正交频分复用方案接收端优化问题。本章利用误差向量幅度值来表征接收端信号的失真水平,并理论推导得出上下限幅截断信号的误差向量幅度。在此基础上,本章给出了最大似然检测接收误比特率的理论值。我们接着给出两种改进型的迭代最大似然检测接收算法：1.通过对残留限幅噪声的迭代估算并对原始估计序列的更新得到最大似然算法的析出信号；2.通过权重因子将限幅噪声高斯白化,使得最大似然估计检测算法满足最优线性估计条件,再通过迭代算法得出接收机析出信号。计算机仿真证实了本章提出的迭代接收算法可以有效地提高系统的性能。
[Abstract]:Wireless visible light communication system is a kind of communication system that uses visible light wave as the carrier of information to transmit signals. This technology scheme has the advantages of good electromagnetic compatibility, no spectrum licensing requirement, improving communication quality and improving information security in a specific environment, besides providing the basic requirements of communication, so it has received academic attention. Wireless visible light communication technology in indoor environment makes the indoor LED light source take into account the functions of communication and lighting, deducting the energy consumption of lighting itself. The energy consumption for wireless transmission is significantly lower than that of traditional radio frequency wireless communication system. More and more researchers pay attention to it. For example, whether the wireless optical communication technology can approach the traditional channel capacity under the optical transmission mechanism; the research of high-efficiency modulation and coding theory in wireless optical communication. In this context, the channel model and capacity analysis, optoelectronic resource allocation and optimization, high-efficiency transmission modulation and reception research of wireless visible light communication systems will inevitably attract people's attention. In general, the main contributions of this paper are as follows: In the second chapter, aiming at the transmission mechanism of light wave, the channel capacity of wireless optical communication system is studied. Firstly, based on the Poisson photon channel model, the expression of the transmission capacity of optical communication system under pulse position modulation is derived, and the capacity of Poisson channel is further studied. Secondly, considering the influence of peak power constraints on channel capacity, the upper and lower limits of channel capacity are deduced when the average power and peak power constraints exist at the same time or respectively, and the computer simulation results show the accuracy of these results. The cross-frequency division multiplexing (OFDM) technology has the characteristic of limiting truncation. The power of limiting signals in ACO-OFDM and DCO-OFDM systems is analyzed, and the theoretical derivation of the maximum feasible transmission rate is given. In the third chapter, the channel equalization problem in wireless optical communication systems is studied. The main sources of ISI in wireless optical communication systems are analyzed. In order to solve the problem of narrow modulation bandwidth of indoor LED light source, a scheme of fractional domain equalization is proposed, which uses signal oversampling to improve the resolution of equalization filter tap. Then two equalization algorithms are designed according to the optimal solution of fractional domain equalizer tap coefficient derived from theory, and zero forcing algorithm and decision are given respectively. The filter tap coefficients of the feedback algorithm are solved. Finally, the performance of fractional-domain interval equalization at different rates is verified by computer simulation results. In the fourth chapter, the optimization problem of DCO-OFDM transmitter is studied. In fact, how to suppress the Peak-to-Average Ratio (PAPR) is always an important problem in OFDM transmission system. In this chapter, the method of upper and lower asymmetric amplitude-limiting truncation is used to make the transmitted signal power satisfy the light source. In order to overcome the deterioration of BER caused by clipping, we optimize the bias current power in the DCO-OFDM scheme. The power control problem established by the optimization criteria is a combinatorial optimization problem with the objective function being non-convex. Then a reasonable search algorithm is given to determine the global optimal solution. The computer simulation results show that it is necessary and necessary to select the bias current power of the transmitter reasonably for the DCO-OFDM system. Finally, in the fifth chapter, the receiver optimization problem of OFDM scheme is considered. In this chapter, the distortion level of the received signal is represented by the amplitude of the error vector, and the amplitude of the error vector of the upper and lower limit truncated signal is deduced theoretically. In this chapter, we give the theoretical value of the maximum likelihood detection receiver bit error rate. We then give two improved iterative maximum likelihood detection receiver algorithms: 1. The resultant signal of the maximum likelihood algorithm is obtained by iteratively estimating the residual limiting noise and updating the original estimation sequence; 2. The limiting noise is high by weighting factor. The whitening makes the maximum likelihood estimation detection algorithm satisfy the optimal linear estimation condition, and then obtains the receiver emitted signal through the iterative algorithm. Computer simulation proves that the iterative receiver algorithm proposed in this chapter can effectively improve the system performance.
【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN929.1

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