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Fronthaul/C-RAN

Is It Finally Time for Free-Space Optics to Shine?

Just like Superman, free-space optics (FSO) can travel as fast as the speed of light. This optical, wireless line-of-sight technology uses invisible beams of light to provide optical bandwidth connections. FSO is currently being positioned as a possible 5G backhaul and fronthaul solution because it can deliver huge volumes of data at super-fast speeds, without wires.

"We're talking about 20 to 50 Gigabits per user," says Barry Matsumori, CEO of Denver-based FSO company BridgeComm, and a veteran of Qualcomm and SpaceX.

BridgeComm believes its technology is a good option for 5G backhaul because it can work in dense urban areas where spectrum is limited, and its technology can also be used in conjunction with traditional microwave backhaul because it won't cause interference.

The downfall of FSO is that the signal must have line-of-sight; it won't travel through trees, and it doesn't work well when there is dense fog. "FSO's nemesis is small water vapors," Matsumori says. "Propagating through dense fog is hard."

But because 5G requires a lot of cell sites and the distance from the cell site to the base station could be hundreds of feet rather than miles, experts say FSO is a viable 5G backhaul solution. And it also could be a good option for fronthaul, which is the distance between the base station's baseband unit and the remote radio heads that are typically at the top of a tower, because it can support a lot of users and deliver fast speeds. "If operators don't have that type of speed in their fronthaul and backhaul, they will have to throttle speeds," Matsumori says.

One added benefit of FSO is that it has built-in security. Matsumori notes that because FSO is basically a narrow beam of light, it is very difficult to detect and therefore difficult to intercept. BridgeComm believes it has an advantage over other FSO firms because it has developed a transmitter that can provide a one-to-many signal, which means that it can talk to multiple parties and spread the data throughput around.

But BridgeComm isn't the only FSO company that wants to provide 5G backhaul for wireless operators. Santa Clara, California-based Collinear Networks has a proprietary system called CNX that uses free-space optics combined with millimeter-wave spectrum to deliver high-capacity links. The CNX system also uses an intelligent traffic handling system to control the high-capacity links. Collinear says its links can deliver up to 20Gbit/s wireless transport capacity.

In an interview with Light Reading late last year, Abraham Pucheril, Collinear's EVP of sales and product marketing, said that the company is looking closely at markets in Asia and Europe, some of which don't have much fiber. However, the company does believe that the type of capacity needed for 5G will make its wireless transport system very appealing in many markets.

Industry analyst Emmy Johnson with Skylight Research says that 5G could make FSO a possible backhaul solution, but she says that so far there aren't any wireless operators using or even trialing the technology.

Indian operator BSNL, however, said in May that it is considering using FSO for backhaul in the states of Rajasthan and Gujarat. BSNL told ETTelecom that it is currently studying the technology and its potential use.

Optical research firm CIR issued a report in 2019 that predicted that optical networking and cabling for 5G fronthaul and backhaul equipment will reach $4.1 billion in 2021. But the firm didn't specify how much of that $4.1 billion will likely go to FSO. CIR analyst Lawrence Gasman said that FSO may make sense in areas where digging up the ground for new fiber is outrageously expensive. However, he adds that FSO is only a niche solution.

Not a new concept
FSO isn't a new concept. The technology was first developed in the 1960s and several FSO companies in the early 2000s tried to position the technology as a good option for backhaul back when 3G networks were still being deployed.

Terrabeam was a Seattle-based FSO company that launched in 1997 and marketed its technology as a broadband solution and as a backhaul connection for wireless operators in dense urban areas. Terrabeam received more than $575 million in funding from some high-profile financiers, including Lucent Technologies, SoftBank Ventures, Merrill Lynch and Madrona Investments. The company was headed by Dan Hesse, prior to his stint as the CEO of Sprint. However, the company never was able to make its proposition a reality and in 2004 it was sold for $52 million in stock to a Falls Church, Virginia, company called YDI.

— Sue Marek, special to Light Reading. Follow her @suemarek.

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