The Terragraph technology was originally intended as a way to bring street-level WiFi to high-density urban downtowns. Facebook looked around the globe and saw many large cities that lack basic broadband infrastructure – it’s nearly impossible to fund fiber in third world urban centers. The Terragraph technology uses 60 GHz bandwidth and the 802.11ay standard – this technology combination was originally called AirGig.
Using 60GHz and 801.11ay together is an interesting choice for an outdoor application. On a broadcast basis (hotspot) this frequency only carries between 35 and 100 feet depending upon humidity and other factors. The original intended use of the AirGig was as an indoor gigabit wireless network for offices. The 60 GHz spectrum won’t pass through anything, so it was intended to be a wireless gigabit link within a single room. 60 GHz faces problems as an outdoor technology since the frequency is absorbed by both oxygen and water vapor. But numerous countries have released 60Ghz as unlicensed spectrum, making it available without costly spectrum licenses, and the channels are large enough to still be able to deliver bandwidth even with the physical limitations.
It turns out that a focused beam of 60 GHz spectrum will carry up to about 250 meters when used as backhaul. The urban Terragraph network planned to mount 60 GHz units on downtowns poles and buildings. These units would act as both hotspots and to create a backhaul mesh network between units. This is similar to the WiFi networks we saw being tried in a few US cities almost twenty years ago. The biggest downside to the urban idea is the lack of cheap handsets that can use this frequency.
Facebook took a right turn on the urban idea and completed a trial of the technology deployed in a different network design. Last May Facebook worked with Deutsche Telekom to deploy a fixed Terragraph network in Mikebuda, Hungary. This is a small town of about 150 homes covering 0.4 square kilometers – about 100 acres. This is drastically different than a dense urban deployment with a far lower housing density than US suburbs – this is similar to many small rural towns in the US with large lots, and empty spaces between homes. The only current broadband in the town was about 100 DSL customers.
In a fixed mesh network every unit deployed is part of the mesh network each unit can deliver bandwidth into that home as well as bounce signal to the next home. In Mikebuda the two companies decided that the ideal network would be to serve 50 homes (not sure why they couldn’t serve all 100 of the DSL customers). The network is delivering about 650 Mbps to each home, although each home is limited to about 350 Mbps due to the limitations of the 802.11ac WiFi routers inside the home. This is a big improvement over the 50 Mbps DSL that is being replaced.
The wireless mesh network is quick to install and the network was up and running to homes within two weeks. The mesh network configures itself and can instantly reroute and heal to replace a bad mesh unit. The biggest local drawback is the need for pure line-of-sight since 60 GHz can’t tolerate any foliage or other impediments, and tree trimming was needed to make this work.
Facebook envisions this fixed deployment as a way to bring bandwidth to the many smaller towns that surround most cities. However, they admit in the third world that the limitation will be for backhaul bandwidth since the third world doesn’t typically have much middle mile fiber outside of cities – so figuring out how to get the bandwidth to the small towns is a bigger challenge than serving the homes within a town. Even in the US, the cost of bandwidth to reach a small town is often the limiting factor on affordably building a broadband solution. In the US this will be a direct competitor to 5G for serving small towns. The Terragraph technology has the advantage of using unlicensed spectrum, but ISPs are going to worry about the squirrelly nature of 60 GHz spectrum.
Assuming that Facebook can find a way to standardize the equipment and get it into mass production, then this is another interesting wireless technology to consider. Current point-to-multipoint wireless network don’t work as well in small towns as they do in rural areas, and this might provide a different way for a WISP to serve a small town. In the third world, however, the limiting factor for many of the candidate markets will be getting backhaul bandwidth to the towns.