无线光接入网关键技术研究

【作者】 陈旭；

【导师】 邱琪； 刘炎焱；

【作者基本信息】 电子科技大学 ， 光学， 2003， 硕士

【摘要】 随着光纤通信技术的发展，2.5G-10Gbps的光纤干线正在不断的向用户延伸，但由于成本和光纤敷设工程上的难道，只有很少的用户直接和光纤干线相连，通常光纤只延伸到了路边、小区；另一方面，许多用户内部的局域网也具有很高的传输速率，一般为100Mbps甚至1Gbps的以太网。但是光纤干线和局域网间接入系统却是传统的铜缆、ADSL、同轴电缆等，传输速率都在10Mbps以下。所以光纤和局域网间“最后一公里”的接入成为解决宽带传输的瓶颈问题。结合光传输媒质的特点、采用无线的接入手段，无线光接入网是解决“最后一公里”问题经济合理的较佳方案。本文阐述了无线光接入网的各项技术。首先在总体上比较了一些传统接入网和无线光接入网。接着介绍无线光传输的大气信道的特点，着重分析大气的散射、吸收和湍流效应对光传输的影响。在第三章介绍无线光接入系统的光收发单元，采用多孔径卡塞格伦式的收发天线对消除减小大气湍流影响有较大作用，针对大气信道的特点无线光系统收发单元在光源、光探测器、前置放大电路上存在许多有别于光纤通信的技术，同时还阐述了光接收机包括背景噪声的噪声机制和接收灵敏度、误码率等指标，最后给出了一个整个传送链路的功率预算。第四章是对无线光接入的调制解调和编码技术的分析，也是本文的重点，比较了PPM调制和OOK调制的带宽和功率利用率、硬判决解调和最大似然解调对系统性能的改善，以及采用RS纠错码对系统性能的改善。第五章是针对由于无线光链路用微波作为备用链路或者无线光链路作为光纤环路的备用链路的网络拓扑介绍。最后在第六章对本文进行总结。更多还原

【Abstract】 With the development of the Fiber communication, very high speed fiber optic backbone has being closed to the customer, but few customers has connected to fiber backbone directly. On the other hand, many customers are running some high speed network within their LAN, such as fast Ethernet (100Mbps), or Gigabit Ethernet (1.0Gbps). But between the LAN and backbone is provided by much lower bandwidth technologies available through the existing copper wire, ADSL, cable modem, and the "last mile" (between the LAN and fiber backbone) problem has become a bottle-neck in the wideband transmission. Considering the advantage of optic , using the wireless mode, optical wireless access network is a better method to solve the "last mile" problem.In this thesis, we focused on the main key technology of the wireless optical access network. At first, we compare the wireless optical access with other access network in general. Then we introduce the character of the atmosphere channel , which we emphasized on the atmosphere scatter, absorption and scintillation’s effect on the laser beam. In chapter Ⅲ,we explain why we used Cassegrain telescope to collect the optical signal at first, then the lightsource, detector, front amplifier used in optical communication has been compared to that of fiber communication ,the noise including shot noise, thermal noise and background light noise has been explained here for analysis the SNR and BER in the next section. chapter Ⅳis the most important part in this paper, we used Pulse Position Modulation (PPM) and maxim-likelihood demodulation to increase the power efficiency ,improve the BER ,also we used RS(Reed-Solomon) code to correct the bunched bit error because of the atmosphere scintillation .with the PPM modulation /ML demodulation method and RS code, the performance of the system improved to a new stage. Based on the former parts, what are the topology of a wireless optical access network ? how can a wireless optical access network connect to the backbone network and customer’s LAN? These are the main topics of chapter Ⅴ. Chapter Ⅵ summarized the main work in this paper, and some problem that have not been solved was bring foreword .更多还原