Thursday, May 11, 2017

Facebook dreams of better network connectivity platforms – Part 2

Preamble

Facebook has a stated goal of reducing the cost of network connectivity by an order of magnitude. To achieve this its labs are playing with millimetre wave wireless, free-space optics and drones in the stratosphere.

Project Aquila takes flight

At this year's F8 conference, Facebook gave an update on the Aquila drone aircraft, which is being assembled in California's Mojave Desert. The Aquila project is cool - pretty much everything about this initiative, from its name to its sleek design, has an aura about it that says 'this is cool', who wouldn't want to be developing a solar-powered drone with the wingspan of a Boeing 737. Using millimetre wave technology onboard Aquila, Facebook has achieved data transmission speeds of up to 36 Gbit/s over a 13 km distance; and using free-space optical links from the aircraft has achieved speeds of 80 Gbit/s over 13 km.

Several media sources reported a technical set-back last year (rumours of a cracked frame) but those are in the past or perhaps not relevant any more. At F8, Facebook said Aquila has progressed and is now ready for field testing. However, here again, one element that seems to be missing is the business case. Just where is this aircraft going to fly and who will pay for it?

As described by Facebook, Aquila will serve regions of the planet with poor or no Internet access. Apparently, this would not include the oceans and seas, nor the polar regions, where such an aircraft might have to hover for months or years before serving even one customer. Satellites already cover much of our planet’s surface and for extremely remote locations this is likely to remain the only option for Internet access. New generations of satellites, include medium earth orbit (MEO) constellations, are coming with improved latency and throughput. So Facebook's Aquila must aim to be better than the satellites.

The aircraft is designed to soar and circle at altitudes up 90,000 feet during the day, slowly descending to 60,000 by the end of the night. The backhaul presumably will be a free-space laser to a ground station below. At such a height, Aquila would be above the weather and above the jet stream. During the day, with an unobscured view of the sun, it would recharge the batteries needed to keep flying at night.

Apart from satellites, the alternative architecture for serving such regions would be conventional base stations mounted on tall masts and connected via fibre, microwave or satellite links. Many vendors are already offering solar-powered versions of these base stations, and there are plenty of case studies of how they have been used successfully in part of Africa, and the advantages over a high-flying drone are obvious: mature technology, fixed towers and known costs, no possibility of dangerous or embarrassing crashes.

One could imagine that the Facebook approach might bring new Internet access possibilities to areas such as the Sahara, the Atacama, over islands in the Indonesian archipelago. But is not clear if Aquila’s onboard radios would be powerful enough to penetrate dense forests, such as in the Amazon or Congo. So, if the best deployment scenario is a desert or island with some humans but insufficient Internet access, why is satellite service not a viable option? The likely answer again is economics. Perhaps the populations living in these regions simply have not had the money to purchase enough smartphones or laptops to make it worthwhile for a carrier to bring service.

A further consideration worth noting is that it may be difficult for an American company to secure permission to have a fleet of drone aircraft circling permanently over a sovereign nation. Intuitively, many people would not feel comfortable with a U.S. drone circling overhead, even if it were delivering faster social media.

Designing a communications platform for emergency deployments

Facebook's connectivity lab is also interested in disaster preparedness. At the F8 keynote, it unveiled Tether-tenna, a helicopter-drone that carries a base station and is connected via fibre and a cable with high-voltage power to a mooring station. The system is designed for rapid deployment after a natural disaster and could provide mobile communications over a wide area. But is it a complex technology that provides minimal benefits (certainly not an order of magnitude) over existing solutions?

The closest equivalent in the real world is the cellular-on-wheels (COWs) segment, which is now commonly used by most mobile operators for extending or amplifying their coverage during special events such as outdoor concerts and football matches. A typical COW is really just a base station mounted on a truck or trailer. After being hauled to the desired location, the units can be put into operation in a matter of minutes, using on-board batteries, diesel generators or attachment to the electrical grid. The units often have telescoping masts that extend 4-5 metres in height.

In comparison to a COW, Facebook's Tether-tenna heli-drone will have a height advantage, perhaps 100 metres over the competitors, enabling it to extend coverage over a greater range. However, the downsides are quite apparent too. Base station weight restrictions on the heli-drone, which also must carry the weight of the tether, will be more limiting than on a mast, and this means that the Tether-tenna will not provide the density of coverage possible via a COW, thereby limiting its potential use cases.

In addition, a crashing heli-drone could do a lot of damage to people or property on the ground, and wind would be a major factor, as would lightning strikes. There is also the possibility of collisions with other drones, airplanes or birds. Therefore ensuring safety might require a human operator to be present when the drone is flying, and insurance costs inevitably would be higher than any of the many varieties of COWs that are already in service.

AT&T has a more elegant name for this gear, preferring to call them Cells on Light Trucks (COLTs). During the recent Coachella 2017 music festival in California, AT&T deployed four COLTs equipped with high-capacity drum set antennae, which offer 30x the capacity of a traditional, single-beam antenna. AT&T reported that the COLTs were instrumental in handling the 40 Tbit/s of data that traversed its network during the multi-day event - the equivalent of 113 million selfies. Data traffic from Coachella was up 37% over last year, according to AT&T. Would a heli-drone make sense for a week-long event such as this?  Probably not, but it's still a cool concept.

All of this raises the question: is a potential business case even considered before a development project gets funded at Facebook?

In conclusion, Facebook is a young company with a big ambition to connect the unconnected. Company execs talk about a ten-year plan to advance its technologies, so they have the time and money to play with multiple approaches that could make a difference. A business case for these three projects may not be apparent now but they could evolve into something serendipitously.

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