Outdoor Measurements Using an Optical Wireless Link for Fixed-Access Applications

In this paper, results are presented from a long-term outdoor field trial using a rate-adaptive, LED-based optical wireless link over 100 m rooftop-to-rooftop distance. The optical link is installed in parallel to a 60 GHz link, enabling a direct comparison of both technologies for the same conditions by logging signal-to-noise ratios, data rates, and weather conditions. A model for the optical link has been developed for performance prediction based on weather data. Besides studying particular weather events, an analysis was conducted for the whole statistics. Results indicate that availability of the optical link was higher than 99.99%, despite severe weather conditions due to fog, rain, and snow. Although both links offer several hundred megabit per second, the optical link has a higher data rate 99.8% of the time while the 60 GHz link has a more consistent performance. Correlation is weak in bad weather conditions, e.g., if the SNR is low for the 60 GHz link due to heavy rain, the SNR in the optical link is high as the fog is light at the same time. Further measurements verify low latencies in the millisecond to sub-millisecond range for the optical link. Results indicate that the optical link is a promising low-cost solution for fixed access applications such as the replacement of fiber on the last 100 m to the end user, also denoted as wireless-to-the-home, and as a backhaul for Wi-Fi and small mobile radio cells.