Robust Optical Wireless Link for the Backhaul and Fronthaul of Small Radio Cells

TLDR

The study proposes optical wireless links as a robust outdoor backhaul for small radio cells (WiFi, LTE, 5G) over 20–200 m and explores their evolution toward 5G networks. A mathematical model incorporating impairments was used to design an optimized link, which was then implemented in a prototype using low‑cost optoelectronic components and a 1 Gb/s baseband chipset. Field trials in Berlin over five months showed visibility never dropped below 180 m, with >1 km range 99 % of the time; rate‑adaptive transmission improved availability in fog or sunlight, and the prototype achieved real‑time data rates of 800, 500, and 225 Mb/s over 20, 100, and 215 m links with 2 ms latency at 95 % load.

Abstract

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.