Tomoharu YOKOTA     Kazuhiko ASAKA     Hideki MATSUMOTO
Tsuyoshi YAMAGUCHI     Chiharu KASAI

Introduction     Configuration of study system Weather dependency of the Link Quality of the Free Space Optical Transmission System Simulation of optical propagation characteristics Conclusion

Outline

This study was finished according to the commission of TAO (Telecommunications Advancement Organization of Japan) and we will appreciate for the support of TAO.

In this study, the relation between the link quality of the Free Space Optical Transmission System and the weather data was verified by the logical analysis and the experiment, and the weather dependency decrease plan (the mutual supplementation with the radio wave) was verified. Moreover the study was intended for the purpose that the Free Space Optical Transmission System is verified to be effective for the construction of the broadband network and the guideline for the construction of the access network is proposed.

As the result, the Free Space Optical Transmission System was verified to have the high quality equivalent to the Cable System.

1 Introduction

Recently the Free Space Optical Transmission System is worthy of note because it is suitable for the wide-band and economical communication system, and effective for the LAN network connection, the access network of the broadband internet and the backup link of optical fiber and communication operator.

But the following problem is indicated. "The Free Space Optical Transmission System seems that it is weak against the influence of rain, fog and scintillation. But the relation between the weather condition and the link quality is not sufficiently clear and the link design for the actual operation is difficult."

In this report, the relation between the link quality and the meteorological data of the Free Space Optical Transmission System and the Radio Wave System is verified by the logical analysis and the experiment, and the weather dependency decrease plan (the mutual supplementation with the radio wave) is verified. For this purpose, the Free Space Optical Transmission System is setup between two buildings 1.2km apart to measure the transmission quality, and the weather & visibility meter is setup to measure the weather condition and the visibility in order to get the basic data of the meteorological information and the transmission quality. The relation between the weather condition and the propagation loss of the Free Space Optical Transmission System is analyzed by computer simulation and is verified theoretically.

Conclusively the link quality of the Free Space Optical Transmission System is indicated clearly and the system design to improve the link quality is reported.

2 Configuration of study system

Figure 2-1  System Configuration of the Study of Optical Propagation Characteristics

For the study of the relation between the link quality of the Free Space Optical Transmission System and the meteorological data, the following data were obtained by the weather & visibility meter, the Free Space Optical Transmission System, the Radio Wave System and the measuring equipments

�@	Meteorological data : visibility, weather, rainfall and others
�A	Bit error rate of the Free Space Optical Transmission System
�B	Reception light power of the Free Space Optical Transmission System
�C	Transmission quality data of the Radio Wave System : packet loss, transmission and reception power, retry number

The equipments were setup at the buildings of Koito Industries (Takanawa, Tokyo) and Canon Sales (Mita, Tokyo) 1.2km apart. System configuration is shown in Figure 2-1.

The Free Space Optical Transmission System 「SIL155M/L1500」 manufactured by Showa Electric Wire & Cable has the maximum transmission speed 155Mbps and the transmission distance 1500m, and has four emission beams of emission angle 2mrad and four reception parts (lens and receive element). In this experiment, the received beam of one lens is led to optical power meter through optical fiber for the light power measurement and the other three beams are used for bit error rate measurement. Wave length is 841.4nm and 853.4nm. The Radio Wave System 「CiscoAironet AIR-BRI340」 is based on IEEE802.11b of radio wave LAN standard and has the transmission speed 11Mbps.

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