State of Microwave Backhaul – Part 2

‘Because We Can’ is the motto when it comes to technology and Chaos events so when cccamp19 came around there were no less than three backup microwave links available to the land based temporary fiber cable to the next POP that rodents find quite attractive. In the first post on the topic I’ve described the first two that bridged a distance over 10 km and offered a bandwidth of 10 Gbit/s. For this post I’ve collected some technical details about the microwave link they had all the way to Berlin which was 57 km away!

57 km, that’s how far you can push technology today if you have a high chimney available and the TV tower in the center of Berlin where the antenna could be installed at a height of around 220m. Using the 18 GHz band and a channel bandwidth of 56 MHz, the maximum line rate in clear weather in the morning was 430 Mbit/s with 1024 QAM modulation and around 380 Mbit/s during the day with 512 QAM. Transmit power was 0.158 mW which resulted in an EIRP with two 90 cm (3 foot) dish antennas that had a gain of 43,5 dBi each of 2.8 kW. Yes, I can imagine how to bridge that distance with such a gain. But just to give you an idea, a mobile phone has 10x this transmit power in the uplink direction! And in terms of reliability the link was still operating at 71 Mbit/s during a severe thunderstorm on one of the days.

And here’s an interview with one of the guys who has set this up in German for further reading.