Facebook Takes a Stab at Wireless Broadband

Facebook has been exploring two technologies in its labs that they hope will make broadband more accessible for the many communities around the world that have poor or zero broadband. The technology I’m discussing today is Terragraph which uses an outdoor 60 GHz network to deliver broadband. The other is Project ARIES which is an attempt to beef up the throughput on low-bandwidth cellular networks.

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.

New WiFi Technologies

Wi-FiThere are some interesting breakthroughs coming out in WiFi that will change how we use the frequency.

First, a group of student engineers at the University of Washington have released a report that may enable the use of WiFi as the primary method of communicating with Internet of Things devices.

The primary shortcoming of current WiFi technology for IoT is that it is power-hungry. A typical current WiFi transmission between two devices requires a radio at both ends of the transmission path along with a baseband chip that is used to encode the data onto the radio wave. Because the WiFi spectrum is expected to always be busy and have interference, the typical WiFi transmission requires several hundreds of milliwatts of power at each end of the transmission path in order to have a strong enough signal to distinguish it from the background noise from other WiFi signals. And that means that a typical WiFi router is a big user of power in a home.

It is the need for big power that has made it impractical to consider WiFi as the technology for talking to large numbers of tiny IoT sensors in the environment. There is no practical way to power such devices.

The student engineers invented a new type of hardware that uses 10,000 times less power than a traditional WiFi device. They are calling the technology ‘passive WiFi’. The technology uses only one WiFi router in the system that send out signals to the many IoT sensors. Those sensors then mirror the signal back to the transmitting device. In doing so the sensors transmit their current status back to the original router using almost no power – 10 to 50 microwatts. The technique involved takes advantage of what is called frequency backscatter and the whole process uses only a fraction of the full WiFi spectrum.

This technique has a lot of promise. Up until now the best option for talking to small sensors has been Bluetooth. But WiFi spectrum is almost 1,000 times more efficient than Bluetooth and also can include security features that aren’t possible with Bluetooth.

In another breakthrough, Samsung has developed WiFi that can deliver up to 4.6 gigabit speeds using the 60 GHz spectrum. This is the spectrum that is often referred to as millimeter wave radio. Samsung’s breakthrough not only takes advantage of this higher frequency, but the company has also made a breakthrough that allows a data transfer rate that is almost 10 times faster than current WiFi.

This technology means that soon we will have to talk differently about different pieces of the WiFi spectrum. The term ‘WiFi’ is a set of standards that can be applied to many different slices of frequency, but different frequencies have very different operating characteristics.

The 60 GHz frequency cannot pass through walls or almost anything else, and that means that it is going to be used to make very fast wireless data connections within a room. Further, this frequency dissipates very quickly with distance and its effective range is only a few meters, meaning that this frequency will not be usable for outdoor hotspots. It’s a one-room application only. This technology presupposes that a room utilizing it will be connected to fiber.

The antenna array needed for 60 GHz is very different than that used for traditional WiFi and so I am expecting it will be many years before we see too many devices designed to use both regular WiFi and 60 GHz spectrum. It’s more likely until the higher spectrum is widely used that there will be a dongle receiver that you could connect to a laptop or other device.

I would expect the early market for this technology to be applications that need a lot of bandwidth but that don’t lend themselves easily to running fiber. That might mean future virtual reality or augmented reality headsets and systems, factory floors to connect to equipment or in crowded hospital emergency rooms. There are not that many applications today that need more bandwidth than can be supplied by normal WIFi, so expect this to be initially used for those applications that do. But over time there will be more and more real world applications that need more bandwidth and this will be another tool to deliver bandwidth over short distance.