无线光接入网关键技术研究
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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。
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 .
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。
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 .
引文
1、 吴承治，光接入网工程，人民邮电出版社，1998年5月
2、 邱 昆，光纤通信导论，电子科技大学出版社，1995年1月
3、 原 荣， 光纤通信网络，电子工业出版社，199年2月
4、 吴健等，随机介质中的光传播理论，成都电讯工程学院出版社，1988年10月
5、 Isaac I. Kim, Bruce McArth, Comparison of laser beam propagation at 785nm and 1550nm in fog and haze for optical wireless communications, SPIE 4214,2001
6、 P.F.Szajowski, G.. Nykolak, 2.4Km Free Space Communication 1550nm Transmission Link Operating at 2.5Gb/s -Experimental result. SPIE 3532，1998
7、 Alastair D.McAulay and Jianghui Li, Improving bandwidth for line-of sight optical wireless in turbulent air ,SPIE 3850,1999
8、 Anthomy Acampora，A hybrid approach for universal broadband access using small radio cells interconnected by free space optical links，IEEE，1998
9、 Penny Polak-Dingel, Long-term fading statistics mersurement of an atmospheric optical communication channel, SPIE 3850, 1999
10、陈顺生，天线原理，东南大学出版社，1989年10月
11、J.H.Franz, V.K.Jain 著，徐宏杰，何珺等译，光通信器件与系统，电子工业出版社，2002年4月
12、李贤、徐铭、邓兴成，高背景条件下的信号接收技术，电子科技大 学学报，1998年10月
13、周晓迈、熊兆飞、黄铁侠，改善脉冲时间扩展激光PPM信道上通信性能的新方法，电子学报，1994年10月
14、周晓迈、陈文革，背景光噪声下的直接检测光PPM编码系统的性能研究，电信科学，1994年12月
15、周晓迈、陈文革，脉冲扩展激光PPM信道上的解调研究，华中理工大学学报，1995年10月
16、jinlong,Zhang, Modulation Analysis for Outdoor Application of Optical
Wireless Communication, IEEE,2000
17、 Hyuncheol Park and John.R.Barry, Modulation analysis for wireless infrared communications ,IEEE,1995
18、A.Gameriro and R.Alves, Coding technique for Wireless Infrared Communcation, SPIE 3532,1998
19.、R.A.Mullen,K.T.Celmer,etc, Wireless Optic Protection Fiber via Sonnet Ring Closure, SPIE 4214, 2001
20、.P.Dodley,D.M.Britz, Free Space Optical Technology and Distribution Archirtecture for Broadband Metro And Local Service, SPIE 4214, 2001
21、 刘敏、魏玲，MATLAB通信仿真与工程应用，国防工业出版社，2001年1月
22、R.m.gagliardi,S.karp著，陈根祥等译，光通信技术与应用，电子工业出版社，1998年4月
23、H.Ppark,J.R.Barry,Performance of multiple pulse position modulation on multipath channel, IEE,December 1996.
24、曹志刚，钱亚生著，现代通信原理，清华大学出版社，1992年8月第一版
25、High-speed power-efficient indoor wireless infrared communication using code combining .I，
2、 邱 昆，光纤通信导论，电子科技大学出版社，1995年1月
3、 原 荣， 光纤通信网络，电子工业出版社，199年2月
4、 吴健等，随机介质中的光传播理论，成都电讯工程学院出版社，1988年10月
5、 Isaac I. Kim, Bruce McArth, Comparison of laser beam propagation at 785nm and 1550nm in fog and haze for optical wireless communications, SPIE 4214,2001
6、 P.F.Szajowski, G.. Nykolak, 2.4Km Free Space Communication 1550nm Transmission Link Operating at 2.5Gb/s -Experimental result. SPIE 3532，1998
7、 Alastair D.McAulay and Jianghui Li, Improving bandwidth for line-of sight optical wireless in turbulent air ,SPIE 3850,1999
8、 Anthomy Acampora，A hybrid approach for universal broadband access using small radio cells interconnected by free space optical links，IEEE，1998
9、 Penny Polak-Dingel, Long-term fading statistics mersurement of an atmospheric optical communication channel, SPIE 3850, 1999
10、陈顺生，天线原理，东南大学出版社，1989年10月
11、J.H.Franz, V.K.Jain 著，徐宏杰，何珺等译，光通信器件与系统，电子工业出版社，2002年4月
12、李贤、徐铭、邓兴成，高背景条件下的信号接收技术，电子科技大 学学报，1998年10月
13、周晓迈、熊兆飞、黄铁侠，改善脉冲时间扩展激光PPM信道上通信性能的新方法，电子学报，1994年10月
14、周晓迈、陈文革，背景光噪声下的直接检测光PPM编码系统的性能研究，电信科学，1994年12月
15、周晓迈、陈文革，脉冲扩展激光PPM信道上的解调研究，华中理工大学学报，1995年10月
16、jinlong,Zhang, Modulation Analysis for Outdoor Application of Optical
Wireless Communication, IEEE,2000
17、 Hyuncheol Park and John.R.Barry, Modulation analysis for wireless infrared communications ,IEEE,1995
18、A.Gameriro and R.Alves, Coding technique for Wireless Infrared Communcation, SPIE 3532,1998
19.、R.A.Mullen,K.T.Celmer,etc, Wireless Optic Protection Fiber via Sonnet Ring Closure, SPIE 4214, 2001
20、.P.Dodley,D.M.Britz, Free Space Optical Technology and Distribution Archirtecture for Broadband Metro And Local Service, SPIE 4214, 2001
21、 刘敏、魏玲，MATLAB通信仿真与工程应用，国防工业出版社，2001年1月
22、R.m.gagliardi,S.karp著，陈根祥等译，光通信技术与应用，电子工业出版社，1998年4月
23、H.Ppark,J.R.Barry,Performance of multiple pulse position modulation on multipath channel, IEE,December 1996.
24、曹志刚，钱亚生著，现代通信原理，清华大学出版社，1992年8月第一版
25、High-speed power-efficient indoor wireless infrared communication using code combining .I，