基于正交多项式LD通信非线性建模技术的研究Research on Nonlinear ModelingTechnology of LED Communication Based onOrthogonal Polynomial王庆炜Whang Qingwei基于正交多项式LED通信非线性建模技术的研究摘要近年来，被称为“绿色照明”的发光二极管技术正在迅速发展。LED(Light-emitting Diode,发光二极管)通信或可见光通信是一个有前途的领域，并且越来越受到研究的关注。LED是LED通信中非线性的主要来源：通过利用存储多项式和一系列相关补偿措施使得LED非线性建模成功。但是存储多项式系数的估计值存在数值不稳定性，导致建模不准确并且优化非线性性能较差，因此需要对非线性进行有效建模，并通过预失真或后失真技术来优化非线性，以避免通信性能严重下降。本文的主要工作内容如下：通过定性分析和仿真，研究LED通信接收前端的输出噪声与非线性失真情况，指出非线性失真才是制约LED通信中的最主要因素。首先提出了一种基于正交多项式的非线性建模技术，利用带有脉冲幅度调制(PAM)信号的LED通信，寻求有效的LED非线性建模和适当的非线性优化技术，以优化LED通信中的非线性和减少信道中的ISI(Inter-Symbol Interference,码间干扰)失真影响。其次视距LED通信的一个困难在于：多径色散会导致高数据速率下的ISI影响。我们扩展了基于正交多项式的LED建模技术的工作，并考虑了由于LED记忆效应和多径色散导致的LED非线性和ISI失真。提出了一种基于正交多项式技术的LED非线性和复合ISI通道联合估计方法。使得ISI光通道和具有记忆效应的LED非线性可以被共同被估计和优化处理：应用低复杂度的频域均衡来消除由于LED记忆效应和光学ISI信道而造成的失真影响，最后运用后失真器优化无记忆效应的LED非线性：仿真结果表明所提出的技术可以有效地处理LED的非线性和ISI失真效应。关键词：发光二极管(LED)通信；非线性；记忆多项式；正交多项式；符号间干扰(ISI)失真AbstractIn recent years,light-emitting diodes (LEDs)technology,known as"GreenIllumination",is growing rapidly.LED communications,or visible light communicationsis a promising field and is getting more and more research focus.LED is the majorsource of nonlinearity in LED communications,and the nonlinearity needs to bemodelled effectively and thereby mitigated through pre-distortion or post-distortion toavoid severe degradation of communication performance.The primary objectives of this thesis are to develop effective and efficient LEDnonlinearity modelling and proper nonlinearity mitigation as well as signal detectiontechniques to mitigate the nonlinear and inter-symbol interference (ISD)distortions inLED communications.Memory polynomial is often used for LED nonlinearity modelling and mitigation inthe literature.However,the estimation of memory polynomial coefficients suffers fromnumerical instability,resulting in inaccurate modelling and poor performance innonlinearity mitigation.Firstly,we focus on LED nonlinearity modelling and mitigationusing memory polynomials.To solve the above numerical instability problem,wepropose an alternative LED nonlinearity modelling technique based on orthogonalpolynomials.For the first time,we develop a special set of orthogonal polynomial basisfor LED communications with pulse amplitude modulation (PAM)signalling for LEDnonlinear system modeling.Due to the use of the orthogonal polynomials,the new basismatrix for the nonlinear model is quasi-orthogonal,which avoids the numericalinstability problem during the estimation of the polynomial coefficients,and leads tolow complexity and accurate LED nonlinearity modeling.Furthermore,a pre-distorter isemployed to mitigate the LED nonlinearity.Simulations show that the proposedtechnique significantly outperforms the conventional memory polynomial basedtechniques.Secondly,another challenge in indoor LED communications is that multipathdispersion can lead to ISI at high data rates.We extend our work on orthogonalpolynomial based LED modelling technique and consider both the LED nonlinearityand ISI distortions due to LED memory effect and multipath dispersion.A jointestimation approach to LED nonlinearity and composite ISI channel based onorthogonal polynomial technique is proposed.Then,we design a receiver which consistsof three modules,a nonlinearity and composite channel estimator,a frequency domain