【作者】 肖江南；

【导师】 陈林；

【作者基本信息】 湖南大学 ， 计算机应用技术， 2013， 博士

【摘要】 随着光传输系统中信号传输速率的提高和传输距离的增加,光传输链路中色度色散、偏振模色散以及光纤非线性效应等因素严重影响传输系统的性能。本论文基于这样的考虑,对高速长距离光纤传输系统中的信号进行处理。利用OFDM技术频谱利用率高、抗色散能力强和传输容量大等优势,把OFDM技术与无线系统结合形成光载无线(ROF)通信系统,实现光纤跟无线无缝结合,但相对无线传输,ROF系统的传输速率和传输距离提高了很多。与直接检测相比,相干检测系统的优势在于具有更高的接收灵敏度和频谱利用率,可以提高中继传输距离。但在相干检测传输系统中,两个激光器的频率不同步造成接收信号星座图旋转和偏移,而且激光器线宽引起的相位噪声对传输系统都会造成严重影响。因此,为了提高光纤传输系统的性能,本文对光纤传输系统中影响系统性能的若干问题进入了深入探讨和研究,理论分析和实验验证了提高光纤传输系统性能的几个关键技术。对以后的光纤传输系统的发展具有理论和实用价值。本论文主要工作和取得的成果为如下几个部分：第一、针对高PAPR的OOFDM信号对光传输系统中电器件、光器件以及光纤非线性效应的影响,提出了两个降低OOFDM信号PAPR方法。一个是Hadamard转换结合压扩变换技术,另一个是FE-Nyquist脉冲成型技术。Hadamard转换结合压扩变换技术降低OOFDM信号PAPR技术,主要是利用了Hadamard是非正弦正交变换,转换过程中没有复杂的乘法运算,而且可以改变信号的非周期自相关性。而压扩转换技术主要对OFDM信号中小幅度信号进行放大,而对大幅度信号进行压缩,从而降低OFDM信号的PAPR。FE-Nyquist脉冲成型技术降低OOFDM信号PAPR主要是利用FE-Nyquist矩阵具有正交性,OFDM信号与FE-Nyquist矩阵乘积后的数据序列具有一定的相关性,从而使OFDM信号各子载波之间具有一定的相关性,这样降低OFDM信号相位相同情况出现的概率,从而降低OFDM信号的PAPR。第二、使用LDPC编码级联TCM编码调制技术提高OFDM-ROF系统性能。讲述了ROF系统的优势和各部分的功能。理论分析了LDPC编码和TCM编码调制技术的编译码原理和结构,利用TCM不降低信号频带利用率和不降低功率利用率,还能获得系统编码增益等优势,可以解决系统频带利用率不足问题。实验搭建了60GHz光载毫米波系统。实验结果验证了LDPC-TCM编码调制技术能很好的提高OFDM-ROF系统性能。第三、针对传统均衡技术把均衡部分和译码部分分离带来的不足,使用Turbo迭代均衡技术,该技术使Turbo均衡中的均衡器具有处理输入先验信息与输出后验信息的功能,Turbo中的均衡器与Turbo译码器进行信息交换,降低Turbo编码技术的算法复杂度。为了减少偏振复用系统中偏振模色散和偏振串扰对传输系统的干扰影响和均衡技术算法复杂度,本文提出基于MIMO-CMA迭代均衡技术,该技术能有效降低偏振模色散和偏振串扰的影响,通过实验验证了MIMO-CMA迭代均衡技术能提高偏振复用CO-OFDM系统性能,而且该均衡技术的算法复杂度较低。第四、针对相干检测系统中由于本振光与信号光频率不同步和激光器线宽带来的信号相位旋转和相位噪声等影响,本文提出了基于八阶统计量盲相位估计结合最大似然相位估计方法来提高单载波系统中信号相位估计精度,减少相位估计算法复杂度。理论分析了八阶统计盲相位估计和最大似然相位估计方法原理,以及各自的优缺点。实验验证了该级联相位估计方法能提高单载波系统中信号相位估计精度和减少相位估计计算量,说明该方法能有效降低激光器线宽对信号的影响。更多还原

【Abstract】 With the increasing of transmission distance and rate, the fiber chromatic-dispersion, polarization-mode-dispersion and nonlinear-effect will seriously affect the performance of transmission systems. To solve this problem, the paper focuses on the high efficient signal processing in high-rate and long-haul fiber-optics communication systems. We have explored the OFDM radio-over-fiber system which the advantage of high spectral efficiency, high-capacity and strong dispersion resistance of OFDM signal to realize seamless integration of the wireless and fiber communication system. Comparing to the direct-detection systems, the coherent-detection systems have higher receiving sensitivity and capacity, and can promote transmission distance. However, in coherent-detection systems, the two transceivers lasers’frequency is not possible the same, this will lead to the rotation and shifting of the constellation. Also, the phase noise of the lasers will damage the transmission system. Therefore, to promote the performance of the fiber transmission system, this paper involves some related key technical problems. The paper includes the following parts:First, we propose two methods including the Hadamard transforming with companding and the FE-Nyquist pulse sharping technique to reduce the PAPR of OFDM signal to diminish the nonlinear effect of electrical and optical device. The Hadamard transforming technique with companding takes the advantage of the nonsinusoidal orthogonal transforming without complex multiply operation, so as to reduce the signal correlation. The companding transforming which amplify the small amplitude signals and compress the large amplitude signal is used at the OOFDM transmitter to reduce the signal PAPR. The Hadamard transforming technique also takes the advantage of orthogonality FE-Nyquist matrix. The product of OFDM signal and the FE-Nyquist matrix has certain correlation, and this enhance the correlation of the sub-carriers of the OFDM signal so as to reduce the OFDM signal’s PAPR.Second, we employ the LDPC coding in catenation with TCM coding to promote the performance of OFDM-ROF system performance. We analyze the function and advantage of ROF system. And also we make an introduction of the LDPC and TCM coding, theoretically analyze the LDPC and TCM coding and decoding principle and structure. The TCM coding can get obvious coding gain without decrease system bandwidth and power utilization. We build a60GHz OFDM-ROF experimental system and verify that the LDPC-TCM coding can promote its performance.Third, to overcome the shortcoming of the traditional equalization and decoding technology, we employ the Turbo iterative equalization technology. The technology enables the Turbo equalizer input a priori information and output posterior information, exchange of information with the Turbo decoder and reduce Turbo coding algorithm complexity. To reduce interference of the polarization mode disper-sion and polarization crosstalk in polarization division multiplexing transmission system, we propose a low-complexity MIMO-CMA iterative equalization technology which is experimentally verified.Finally, to solve the problem of signal phase rotation and phase noise due to the frequency out-of-sync lasers and the laser linewidth in coherent detection systems, we propose an8-order blind phase estimation algorithm which is combined with max-likelihood method to enhance the accuracy of single-carrier phase estimation and reduce the algorithm complexity. We make a theoretical analysis of the estimation principle of8-order statistical blind phase estimation and the max-likelihood method, also with their merits and drawbacks. The proposed algorithm is also experimentally verified. The experiment shows that this method can reduce the influence of spectral linewidth of laser signal. And the method is simple, has the merit of real-time coherent detection of single carrier system.更多还原