Low-orbit satellites could soon offer tens of millions of individuals worldwide access to high-speed communications, however the satellites’ potential has been stymied by a technological limitation — their antenna arrays can only manage one user at a time.
The one-to-one ratio signifies that firms must launch either constellations of many satellites, or large individual satellites with many arrays, to offer wide coverage. Each options are expensive, technically complex, and may lead to overcrowded orbits.
For instance, SpaceX went the “constellation” route. Its network, StarLink, currently consists of over 6,000 satellites in low-Earth orbit, over half of which were launched prior to now few years. SpaceX goals to launch tens of 1000’s more in the approaching years.
Now, researchers at Princeton engineering and at Yang Ming Chiao Tung University in Taiwan have invented a way that permits low-orbit satellite antennas to administer signals for multiple users directly, drastically reducing needed hardware.
In a paper published June 27 in IEEE Transactions on Signal Processing, the researchers describe a method to overcome the single-user limit. The strategy builds on a standard technique to strengthen communications by positioning antenna arrays to direct a beam of radio waves precisely where it’s needed. Each beam carries information, like texts or phone calls, in the shape of signals. While antenna arrays on terrestrial platforms equivalent to cell towers can manage many signals per beam, low-orbit satellites can only handle one.
The satellites’ 20,000 miles-per-hour speed and continuously changing positions make it nearly unimaginable to handle multiple signals without jumbling them.
“For a cell tower to speak with a automobile moving 60 miles per hour down the highway, in comparison with the speed that data is exchanged, the automobile doesn’t move very much,” said co-author H. Vincent Poor, the Michael Henry Strater University Professor in Electrical and Computer Engineering at Princeton. “But these satellites are moving very fast to not sleep there, so the knowledge about them is changing rapidly.”
To cope with that limitation, the researchers developed a system to effectively split transmissions from a single antenna array into multiple beams without requiring additional hardware. This permits satellites to beat the limit of a single user per antenna array.
Co-author Shang-Ho (Lawrence) Tsai, professor of electrical engineering at Yang Ming Chiao Tung University, compared the approach to shining two distinctive rays from a flashlight without counting on multiple bulbs. “Now, we only need one bulb,” he said. “This implies an enormous reduction in cost and power consumption.”
A network with fewer antennas could mean fewer satellites, smaller satellites, or each. “A traditional low Earth orbit satellite network might have 70 to 80 satellites to cover the US alone,” Tsai said. “Now, that number may very well be reduced to possibly 16.”
The brand new technique might be incorporated into existing satellites which might be already built, in accordance with Poor. “But a key profit is that you could design a less complicated satellite,” he said.
Impacts in space
Low-orbit satellites reside within the lower layer of Earth’s atmosphere, between 100 and 1,200 miles from the surface. This region of space offers limited real estate. The more objects flying around, the more likely they’re to crash, breaking apart and releasing smaller fragments of debris that may then crash into other objects.
“The priority there is not a lot getting hit by a falling satellite,” Poor said, “But concerning the long-term way forward for the atmosphere, and the orbit being clouded up with space debris causing problems.”
Since the low-orbit satellite industry is gaining traction at a rapid pace, with firms including Amazon and OneWeb deploying their very own satellite constellations to offer web service, the brand new technique has the potential to scale back the danger of those hazards.
Poor said that while this paper is solely theoretical, the efficiency gains are real. “This paper is all mathematics,” he said. “But on this field particularly, theoretical work tends to be very predictive.”
Since publishing the paper, Tsai has gone on to conduct field tests using underground antennas and has shown that the maths does, in actual fact, work. “The subsequent step is to implement this in an actual satellite and launch it into space,” he said.
