Sub10 Systems: Oxygen absorption makes 60 GHz perfect for backhaul

UK-based startup Sub10 Systems is touting the largely ignored 60 GHz spectrum band as the next big thing in wireless backhaul.

Sub10 touted its wares last week during the Mobile World Congress in Barcelona, where it looked to hook up with major infrastructure vendors and operators that might be interested in its point-to-point millimeter-wave Ethernet bridges, which are designed for "small cell backhaul in an urban environment," said Grant Grafton, Sub10's global sales and marketing director. "This is what every operator is looking for to connect femtos and picos at street level," he said.

Sub10, which is based in Devon, UK, got its name from the fact that wavelengths in the 57-64 GHz band vary from 10 millimeters down to 1 millimeter. Started in 2010, the young company already has a notable backhaul contract win with Orange Austria, which is using 90 of Sub10's line-of-sight (LOS) bridges to support an LTE metrocell deployment in Vienna, linking base stations and points of presence. The deployment was secured via a partnership with Alcatel-Lucent.

Sub10 manufactures two versions of its Liberator-branded terminals, both of which deliver full-duplex data. The V320 offers data rates up to 320 Mbps and delivers LOS connections over distances up to 1 kilometer, while the V1000 offers data rates up to 1 Gbps and LOS coverage up to 800 meters. Each terminal weighs 2.5 kilograms and measures 18 centimeters by 18 centimeter, making the devices quite unobtrusive.

A prime selling point for the 60 GHz band used by Sub10's devices is that it is either license-exempt or lightly licensed in more than 22 countries, including the United States, the UK, China, Germany, Japan, the United Arab Emirates, Australia and New Zealand. Using an unlicensed band for backhaul enables an operator to avoid the time-consuming license application process as well as burdensome license fees.

The millimeter-wave portion of the RF spectrum has been largely unexploited for commercial wireless applications despite the fact that it has impressive performance characteristics. Sub10 says the band enables fiber-optic data transmission speeds because there is 7 GHz of continuous bandwidth available in the band vs. less than 0.3 GHz at other unlicensed bands.

Sub10 also contends that the 60 GHz band's unique characteristics related to oxygen absorption give it interference immunity, high security and high frequency reuse.

At 60 GHz, the oxygen molecule becomes highly absorbent of electromagnetic energy, which weakens the 60 GHz signals over distance, keeping them from overshooting their intended target. This oxygen absorption also reduces link radiation so a 60 GHz link will not interfere with other 60 GHz links operating in the same geographic vicinity, thus enabling higher frequency reuse, said Grafton.

However, the oxygen absorption situation means the maximum operating range for 60 GHz links is influenced by rain, though not by mist, fog, dust or snow. That means the impact of potential rainfall must be accounted for in any 60 GHz backhaul deployment, something Grafton contends is easily addressed because rainfall statistics are well known for locations around the globe.

In addition, Grafton said that because beam width is narrower at 60 GHz than at lower-frequency unlicensed bands, "you get licensed capacity in unlicensed spectrum."

He said Sub10 is also working on point-to-point equipment for 70GHz and 80 GHz E-Band spectrum.

Research firm Maravedis has predicted that the millimeter-wave market would earn more backhaul market share this year. "Small cell backhaul solutions in the 60 GHz are emerging, developing innovative form factors that may not be easily recognized by regular citizens, meaning radios that will go unnoticed," said the firm. Maravedis said suppliers to watch include BridgeWave and Siklu.

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