The potential of low-orbit satellites to provide high-speed communications to millions of people worldwide has been limited by the fact that their antenna arrays can only handle one user at a time.
This one-to-one ratio requires companies to launch expensive and complex constellations of many satellites or large individual satellites with many arrays, leading to overcrowded orbits. For example, SpaceX’s Starlink network currently consists of over 6,000 satellites in low-Earth orbit, with plans to launch tens of thousands more.
However, researchers at Princeton Engineering and Yang Ming Chiao Tung University in Taiwan have developed a technique that allows low-orbit satellite antennas to manage signals for multiple users simultaneously, significantly reducing the required hardware.
In their recent publication in IEEE Transactions on Signal Processing, the researchers present a groundbreaking method to overcome the single-user constraint. Their approach leverages antenna arrays to focus radio waves precisely where needed, allowing each beam to carry information such as texts or phone calls.
While terrestrial antenna arrays can handle multiple signals per beam, low-orbit satellites are limited to one signal due to their high speed and constantly changing positions, making it challenging to manage multiple signals effectively.
“For a cell tower to communicate with a car moving 60 miles per hour down the highway, compared to the rate that data is exchanged, the car doesn’t move very much,” said coauthor H. Vincent Poor, the Michael Henry Strater University Professor of Electrical and Computer Engineering at Princeton. “But these satellites are moving very fast to stay up there, so the information about them is changing rapidly.”
The researchers have developed a groundbreaking system that efficiently splits transmissions from a single antenna array into multiple beams without the need for additional hardware. This innovation allows satellites to overcome the limitation of serving only one user per antenna array.
Coauthor Shang-Ho (Lawrence) Tsai, a professor of electrical engineering at Yang Ming Chiao Tung University, likened the approach to emitting two distinct rays from a single flashlight without the need for multiple bulbs. This advancement results in substantial cost and power consumption reduction by requiring only one bulb instead of multiple.
In practical terms, a network with fewer antennas could imply a reduction in the number of satellites, smaller satellites, or both. Tsai explained that a conventional low Earth orbit satellite network covering the United States might require 70 to 80 satellites, but this number could potentially shrink to 16 with this new technique.
Moreover, the new method can be integrated into existing satellites that are already constructed, further underlining the potential to simplify satellite design, as noted by coauthor Poor.
Low-orbit satellites reside in the lower layer of Earth’s atmosphere, between 100 and 1,200 miles from the surface. The increased number of satellites raises the risk of collisions and space debris, which could pose long-term threats. With companies like Amazon and OneWeb launching their own constellations, it’s vital to address these hazards.
While the concept in the paper is theoretical, the potential efficiency gains are significant. The underlying mathematics in this paper are predictive, and the field tests using underground antennas have validated its effectiveness. This innovative approach has the potential to mitigate the risks associated with the growing low-orbit satellite industry.
“The next step is to implement this in a real satellite and launch it into space,” he said.
Journal reference:
- Yan-Yin He, Shang-Ho Tsai, H. Vincent Poor. Physical Beam Sharing for Communications With Multiple Low Earth Orbit Satellites. IEEE Transactions on Signal Processing, 2024; DOI: 10.1109/TSP.2024.3408061