【作者】 王东；

【导师】 张英海；

【作者基本信息】 北京邮电大学 ， 电子科学与技术， 2013， 博士

【摘要】 随着网络的发展和通信需求的提高,未来的接入网不仅需要满足用户的高带宽需求,而且需要给用户提供灵活多样的接入方式(高速有线接入和灵活的宽带无线接入)。在无源光接入网(PON)中同时传输无线和有线的信号,可以将无线接入的灵活性和有线接入的大容量和高稳定性相结合,提高服务的综合性,具有很高的研究价值。但是,现有的PON与移动网络融合接入存在带宽容量不足、系统结构复杂、带宽资源分配冲突等问题。为解决以上问题,本论文提出基于光正交频分复用(OFDM)的PON与无线接入信号(LTE, WiFi和60GHz-ROF)的异构融合接入模型,实现光与无线的异构融合接入。目前该技术的研究还有难点需要克服：如,下行融合信号的生成及交调干扰的抑制；光OFDM信号的高峰均比(PAPR)抑制和融合信号在光纤中传输时色散效应和噪声影响的消除问题等。从解决以上问题的角度出发,本论文围绕基于光OFDM的光与无线异构融合接入技术展开深入研究,具体工作和创新如下：1)对OFDM-PON技术展开深入研究。分别构建了时分复用(TDM)和波分复用(WDM)与OFDM-PON的混合接入系统架构模型,并进行了性能分析和网络资源分配方式的研究；采用理论分析、仿真计算和实验研究相结合的方法研究了基于外调制的OFDM-PON系统的性能；研究了OFDM-PON的下行载波重利用技术,节省上行传输所需激光光源,最大限度简化用户端结构的同时实现全双工通信。2)论文提出了基于光OFDM的PON与无线接入主流信号LTE, WiFi和60GHz-ROF的异构融合接入模型,使得不同接入方式的接入信号同时在光纤中传输,实现光与无线的异构融合接入：对于OFDM-PON与LTE和WiFi的异构融合模型,论文提出采用中频混频技术使得无线信号的工作频带与有线信号的传输频带远离布里渊散射等非线性效应的易发条件,抑制接收端光电转换时的交调干扰；对于OFDM-PON与60GHz-ROF的信号融合模型,论文提出采用马赫曾德光调制器组结合光学外调制技术生成融合下行信号,简化系统结构,实现光与无线的融合接入。设计生成的有线／无线融合信号通过光调制器调制到光域生成下行光信号,论文对基于马赫曾德调制器的多业务信号调制机制进行了数学建模和分析,优化选用合适的调制深度,使融合信号工作在调制器的线性区域,有效抑制了下行光信号中的无用边带。3)针对光OFDM系统中的高峰均比(PAPR)抑制问题,本论文提出采用压扩参数可控的双曲正切函数对信号进行压扩处理。算法在双曲正切函数中引入两个可控参数,分别控制压扩信号的最大压缩幅值和压扩的非线性程度,使得小信号得到放大,大信号得到压缩,从而有效降低信号的PAPR。仿真结果显示所提算法对PAPR的抑制作用和误码率性能都优于μ律。4)针对光OFDM接入系统中的信道估计问题,本论文提出了一种基于导频的信道估计算法。算法只在光OFDM信号的前半部分子载波中插入导频,利用后补偿的方法结合光纤信道色散效应与子载波频率的对应关系,最终实现了导频数目少,计算复杂度低的信道估计,有效抵抗了传输中色散和相位噪声的影响。相关的性能仿真结果显示,实现了40Gb/s的下行信号接入,且所提算法的误码率性能要高于其他基于LS准则的信道估计算法。本论文从网络架构模型和性能提升算法的角度出发,采用数学建模、仿真计算以及实验研究相结合的方法对基于光OFDM的光与无线融合接入技术展开研究。以上所提技术可简化远端用户接收结构,降低系统成本,提高系统传输性能和频谱效率,增大系统覆盖区域和接入方式的灵活性,最终实现光与无线异构融合的泛在信息接入。更多还原

【Abstract】 With the increasing demand of the communication bandwidth, the future access network should provide not only enough bandwidth, but also various access methods (wired and wireless access). It is significant to research on the heterogeneous integration access technique of passive optical network (PON) and wireless communications which can combine the flexible mobility of the wireless communications and the high-capacity of the wired communication. However, there are some drawbacks in the existing integration network, such as, deficient bandwidth, complexity system structure, and bandwidth distribution conflict. Based on the study of orthogonal frequency division multiplexing (OFDM), novel PON architecture which can simultaneously support various services, such as LTE, wifi and60GHz-radio-over-fiber (ROF) is proposed in this dissertation. However, there are still some challenges, such as, bandwidth distribution scheme, high peak to average power ratio (PAPR) suppression and channel estimation. In order to solve those problems, in-depth research about the heterogeneous integration access technique of optical wired/wireless services based on optical OFDM are made in this dissertation. The detailed works are as follows:(1) Some in-depth studies of the time division multiplexing OFDM-PON and wavelength division multiplexing OFDM-PON, which include system models, performance analysis and network resource allocation, are done with the combined method of theoretical analysis, simulation and experiment. Downlink carrier re-use technology is researched to save the uplink light source and simplify the ONU structure. (2) Based on the above study of OFDM-PON, novel PON architecture which can simultaneously support heterogeneous services such as PON, LTE, WiFi and60GHz-ROF is presented. Intermedium frequency (IF) mixing technology is utilized to make the operation band of OFDM-PON, LTE and WiFi away from the Brillouin scattering effects. Meanwhile, a Mach Zehnder modulator (MZM) group combined with the optical external modulation technique are applied to generate high-quality downlink OFDM-PON-ROF integration signals. The generated wired/wireless heterogeneous signals are modulated into optical domain through optical modulator. In order to generate high quality heterogeneous signals which have no useless signal-band, the mathematical model of MZM is analyzed. Then, suitable modulation depth which could make the integration signals work in the linear region of the optical modulator and reduce the useless signal-band in the downstream signal highly, is optimized.(3) Now, how to suppress the PAPR in optical OFDM access system is still a challenge. Nonlinear companding transform is an effective technique to reduce the PAPR in optical OFDM transmission system. A novel companding scheme, which is based on the modified hyperbolic tangent (MHT) transform, is presented in this dissertation. The MHT scheme can enlarge the small signals and compress the large signals while keeping the average power invariant through two companding parameters. Numerical mathematical models of PAPR have been analyzed. Simulation results show that large PAPR reduction was achieved and offered better bit error rate (BER) performance than the famous μ law.(4) Inspired by nonlinear post-compensation algorithms, a channel estimation algorithm which can highly resist dispersion and phase noise in the optical OFDM system is presented. The proposed scheme is pilot-aided in which just a little number of pilots is inserted in the first half part of the subcarriers and high spectral efficiency is achieved. The fiber dispersion and the phase noise are resisted with the combined method of post-compensation and the relationship between the OFDM subcarriers and the fiber channel mathematic model. Numerical mathematic models have been analyzed. Simulation results show that the presented scheme achieved40Gbit/s data transmission and the BER performance of the proposed algorithm is better than other LS channel estimation algorithms.This dissertation focuss on the heterogeneous intergration access of optical wired/wireless services with the combining method of mathematic model analysis, simulation and experiment.Those above research technologies can highly simplify the remote receiving structure, reduce the cost of transmission, improve the access flexibility and achieve ubiquitous information access. The research in this dissertation will play an important role in the next generation information highway.更多还原