Unlicensed Millimeter Wave Spectrum

I haven’t seen it talked about a lot, but the FCC has set aside millimeter wave spectrum that can be used by anybody to provide broadband. That means that entities will be able to use the spectrum in rural America in areas that the big cellphone companies are likely to ignore.

The FCC set aside the V band (60 GHz) as unlicensed spectrum. This band provides 14 GHz of contiguous spectrum available for anybody to use. This is an interesting spectrum because it has a few drawbacks. This particular spectrum shares a natural harmonic with oxygen and thus is more likely to be absorbed in an open environment than other bands of millimeter wave spectrum. In practice, this will shorten bandwidth delivery distances a bit for the V band.

The FCC also established the E band (70/80 GHz) for public use. This spectrum will have a few more rules than the 60 GHz spectrum and there are light licensing requirements for the spectrum. These licenses are fairly easy to get for carriers, but it’s not so obvious that anybody else can get the spectrum. The FCC will get involved with interference issues with the spectrum – but the short carriage distances of the spectrum make interference somewhat theoretical.

There are several possible uses for the millimeter wave spectrum. First, it can be focused in a beam and used to deliver 1-2 gigabits of broadband for up to a few miles. There have been 60 GHz radios on the market for several years that operate for point-to-point connections. These are mostly used to beam gigabit broadband in places where that’s cheaper than building fiber, like on college campuses or in downtown highrises.

This spectrum can also be used as hotspots, as is being done by Verizon in cities. In the Verizon application, the millimeter wave spectrum is put on pole-mounted transmitters in downtown areas to deliver data to cellphones as fast as 1 Gbps. This can also be deployed in more traditional hot spots like coffee shops. The problem of using 60 GHz spectrum for this use is that there are almost no devices yet that can receive the signal. This isn’t going to get widespread acceptance until somebody builds this into laptops or develops a cheap dongle. My guess is that cellphone makers will ignore 60 GHz in favor or the licensed bands owned by the cellular providers.

The spectrum could also be used to create wireless fiber-to-the-curb like was demonstrated by Verizon in a few neighborhoods in Sacramento and a few other cities earlier this year. The company is delivering residential broadband at speeds of around 300 Mbps. These two frequency bands are higher than what Verizon is using and so won’t carry as far from the curb to homes, so we’ll have to wait until somebody tests this to see if it’s feasible. The big cost of this business plan will still be the cost of building the fiber to feed the transmitters.

The really interesting use of the spectrum is for indoor hot spots. The spectrum can easily deliver multiple gigabits of speed within a room, and unlike WiFi spectrum won’t go through walls and interfere with neighboring rooms. This spectrum would eliminate many of the problems with WiFi in homes and in apartment buildings – but again, this needs to first be built into laptops, sart TVs and other devices.

Unfortunately, the vendors in the industry are currently focused on developing equipment for the licensed spectrum that the big cellular companies will be using. You can’t blame the vendors for concentrating their efforts in the 24, 28, and 39 GHz ranges before looking at these alternate bands. There is always a bit of a catch 22 when introducing any new spectrum – a vendor needs to make the equipment available before anybody can try it, and vendors won’t make the equipment until they have a proven market.

Electronics for millimeter wave spectrum is not as easily created as equipment in lower frequency bands. For instance, in the lower spectrum bands, software-defined radios can easily change between nearby frequencies with no modification of hardware. However, each band of millimeter wave spectrum has different operating characteristics and specific antenna requirements and it’s not nearly as easy to shift between a 39 GHz radio and a 60 GHz radio – they requirements are different for each.

And that means that equipment vendors will need to enter the market if these spectrum bands are ever going to find widespread public use. Hopefully, vendors will find this worth their while because this is a new WiFi opportunity. Wireless vendors have made their living in the WiFi space and they need to be convinced that they have the same with these widely available spectrum bands. I believe that if some vendor builds indoor multi-gigabit routers and receivers, the users will come.

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.