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Robust optical wireless link for the backhaul and fronthaul of small radio cells

: Schulz, D.; Jungnickel, V.; Alexakis, C.; Schlosser, M.; Hilt, J.; Paraskevopoulos, A.; Grobe, L.; Farkas, P.; Freund, R.

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Journal of Lightwave Technology 34 (2016), Nr.6, S.1523-1532
ISSN: 0733-8724
European Commission EC
FP7-ICT; 318600; SODALES
SOftware-Defined Access using Low-Energy Subsystems
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer HHI ()

This paper summarizes recent work on the use of optical wireless links as a robust outdoor backhaul solution for small radio cells, such as WiFi, LTE and 5G, over distances between 20 and 200 m. Results of a 5-month outdoor field trial in Berlin, Germany, indicate that the visibility range was never below 180 m, with more than 1 km in 99% of all times during this period. Rate-adaptive transmission proved to improve the availability remarkably in the occasional presence of fog or sunlight. A mathematical model of the backhaul link including these impairments is presented and implemented to obtain an optimized link design. A prototype was realized, accordingly, using low-cost optoelectronic components and a 1 Gb/s baseband chipset. Gross data rates of 800, 500, and 225 Mb/s have been achieved in real-time operation over 20, 100, and 215 m outdoor link distance, respectively, with 2 ms latency at 95% load. Finally, we discuss further evolution towards 5G mobile networks.