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The electromagnetic spectrum is getting crowded, as more and more technologies tap into frequencies in the gigahertz and tens of gigahertz range. This means that future wireless technologies such as 6G may need to operate even farther up the frequency scale—100 gigahertz and above. And that could lead to some problems. Satellites needed to keep tabs on climate change and other scientific infrastructure already operate in those bands, and they’re not used to having to share. Fortunately, some solutions are in the works.
“It is critical to avoid any harm on remote weather sensing and radio astronomy users, as they support key operations for our society,” explains Michele Polese, a principal research scientist at the Institute for the Wireless Internet of Things (WIoT) at Northeastern University, in Boston. “Therefore, any technology that could be considered for a transition toward shared spectrum will have to be carefully designed and evaluated before being considered for adoption.”
In 2020, Polese and his colleagues demonstrated the first spectrum-sharing system for frequencies above 100 GHz.
Polese and his colleagues propose several solutions, such as time sharing, spatial sharing, and signal-level sharing between technologies, that could help save satellite signals and deal with interference more broadly. First, they note that because higher frequencies allow for larger bandwidth during communications, this could help shorten the time needed for transmissions, thus potentially enabling more refined and flexible time-sharing strategies among users. Essentially, some technologies could take turns tapping into a certain frequency range.
In this case, emerging technologies will need to be designed to coexist and share the spectrum. The authors point out that this may be more challenging to implement quickly in satellites and for telescopes, which require more long-term planning and implementation. However, as telecommunications quickly evolve and future networks like 6G are planned, there’s an opportunity to embed the hardware and software designs to facilitate sharing of the electromagnetic spectrum.
“Spectrum-sharing solutions discussed today can be integrated into tomorrow’s standards and technologies, embedding coexistence and spectrum sharing in the protocol stack, rather than layering it on top as an afterthought,” says Polese.
One factor that may help facilitate the sharing of the spectrum above 100 GHz is that these signals are highly directional, so they can be spatially manipulated so as not to interfere with one another, thereby decreasing the chances of overlap. In their study, Polese and his colleagues describe a way to emit high-frequency telecommunications signals using an “inverse pyramidal” antenna-array design. The antenna helps keep signals close to Earth’s surface and avoids impinging on the remote-sensing satellites that track the climate and weather changes orbiting above.
Polese and his colleagues operate several experimental test-beds at Northeastern University to evaluate spectrum sharing, including Colosseum, for frequencies below 6 GHz, and the TeraNova platform for above 100 GHz, led by Josep Jornet.
In 2020, the team demonstrated for the first time a spectrum-sharing system above 100 GHz, capable of hopping between different frequency bands to avoid interfering with sensing satellites. In this scenario, using a dual-band backhaul link, the wireless system operated on two frequency bands. Whenever a satellite using one of the frequencies for sensing was in sight, the system automatically switched to the other frequency.
The Northeastern team will continue to study ways to find solutions between frequency-sharing technologies. Moving forward, Polese says, “we are focusing on modeling radio-frequency interference [RFI] with large-scale wireless network models, and understanding the theoretical limits and relationship between the design parameters of 6G networks and the RFI at the satellite interface.”
Polese and his colleagues reviewed the interference problem and potential solutions in Proceedings of the IEEE.
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