High reliable optical wireless links for the last mile access

Abstract

In the last couple of years the need for higher data rates and more bandwidth has arisen. This development will continue in the next couple of decades and allegorizes a challenge for the future next generation networks. Taking this into account the end-user will need higher data rates, getting theoretical access to the full available bandwidth of the backbone delivered to the home. Free space optics (FSO) is an excellent supplement to conventional radio links and fiber optics, capable of handling point-to-point and point-to-multipoint connections. On the one hand-side FSO is a broadband wireless solution for the "last mile" connectivity in metropolitan networks, on the other hand-side FSO can be used to interlink locations within one local area network. In the last years different types of cost-effective systems were developed and realized at the Institute of Broadband Communication of Graz University of Technology (TU Graz). The first type was based on a modular concept using available standard components allowing demonstrations at a data rate of 2 times 10 Mbit/s for short distances up to 300 m at a specific power margin of 25 dB/km. Later the units were improved to allow a data rate of 100 Mbit/s, higher data rates are currently under development. The reliability and availability of a FSO-link is mainly determined by the local atmospheric conditions, in free space the transmitted light is reflected, refracted or absorbed by objects, rain, fog, wind or sun. All these parameters directly influence the quality of a FSO-link and indirectly affect the quality of an access network. Many FSO-installations (permanent and nomadic use) have been set-up in the area of Styria by TU Graz and cooperation partners. In this contribution we will show some practical installations for different events, including the latest permanent installation, which was started in the summer of 2007 together with the municipality of Dobl, a small suburb of Graz, and the ML11 GmbH, an IT-company. Within this cooperation the elementary school of Dobl was connected to the Internet via FSO. The FSO-units were successfully installed and the setup is now used to explore the influence of weather on the FSO-link in the area of Graz.