Facebook has managed to transmit data at nearly 20 Gbps between two Southern California towers during testing of a key technology for its plans to deliver internet service to rural areas using drones.
The tests were carried out earlier this year and used frequencies in the so-called E-band, a group of millimeter wave frequencies between 60 and 90 GHz.
These signals are capable of transmitting high-bandwidth data, but are susceptible to attenuation by distance, weather conditions, and obstacles. They are therefore generally used for short-range point-to-point transmissions.
Facebook used a 60 centimeter dish to send data over a 13 kilometer link between Malibu and Woodland Hills.
This test initially recorded data between 100 Mbps and 3 Gbps and allowed engineers to collect transmission data on clear days and during clouds, fog, high winds and rain, Facebook said in a blog post. Thursday.
For testing, Facebook ended up integrating several of its own microwave transmission components into the system, which used a 1.2-meter dish at the receiving end.
The signal received by the dish would drop in half if misdirected by just 0.2 degrees, so accuracy was essential.
To achieve the data rate of up to 20 Gbps, the dish had to be almost perfect: an accuracy of more than 0.07 degrees. In perspective, that’s the equivalent of a baseball pitcher hitting a quarterback, Facebook said.
The distance achieved is significant and already useful for point-to-point links that could transmit high-speed Internet signals over land.
But that’s not far enough to be used as a backhaul link for the company’s envisioned drone internet service.
Facebook’s Aquila drones will provide internet access to remote areas at altitudes between 60,000 and 90,000 feet, or about 18 to 27 kilometers. Since the drones will not always be above the ground station, the link distance could be longer.
For the drone service, Facebook will need to increase the range to between 30 and 50 kilometers and increase the bandwidth to 30 Gbps, the company said.
The next step in California testing is a ground-to-air system that will transmit data to a Cessna aircraft with an onboard data transceiver.
Testing of a system capable of establishing a 20 Gbps data link with the aircraft at an altitude of up to 20,000 feet (six kilometers) has already begun. In 2017, Facebook plans to increase the speed to 40 Gbps both to and from the plane.
“We still have several technical and connectivity challenges to resolve before the technology is fully ready to roll out,” Facebook said.
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