Key Technologies Of Wireless Optical Access Network

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 .