New holography-inspired reconfigurable surface developed for wireless communication

Reconfigurable intelligent surfaces (RIS) are engineered structures comprised of several elements known as ‘meta-atoms,’ which can reshape and control electromagnetic waves in real-time. These surfaces could contribute to the further advancement of wireless communications and localization systems, as they could be used to reliably redirect, strengthen and suppress signals.

In conventional applications of RIS for wireless communication, each meta-atom is controlled by a system known as the ‘base-station,’ which is connected to the surface via electrical cables. While surfaces following this design can attain good results, their reliance on wires and a base station could prevent or limit their real-world deployment.

Researchers at Tsinghua University and Southeast University recently developed a new RIS that controls itself and does not need to be connected to a base station. This new surface, introduced in a paper published in Nature Electronics, draws inspiration from holography, a well-known method to record and reconstruct an object’s light pattern to produce a 3D image of it.

“We wanted to build a truly autonomous reconfigurable intelligent surface (RIS) for wireless communications,” Tie Jun Cui, senior author of the paper, told Tech Xplore. “To achieve autonomy, this RIS system should rely on good but low-cost sensors. The sensors we selected are radio frequency power detectors.”

Frequency power detectors are electronic circuits that measure the strength of an incoming electromagnetic signal. The researchers leveraged these components to measure the distribution of microwave power across their reconfigurable surface.

“Power detectors are only sensitive to the signal amplitude, which is analogous to a hologram that only records amplitude information of a light field,” said Cui. “These hologram-related techniques can help us to build a self-controlled RIS (SC-RIS) to obtain environmental information on its own before serving the communication users.”

How the new surface works

In the team’s RIS design, a base station and a user send coherent radio frequency (RF) signals to the reconfigurable surface. This signal produces an interference pattern with unique characteristics on the surface, via a process that somewhat resembles the creation of holograms.

“If the two sources move slightly, these strips will experience a drastic change,” explained Linglong Dai, the other senior author of the paper. “Therefore, we came up with a very-low-complexity algorithm that retrieves the position based on these strips. Then, we find the algorithm only cares about the amplitude of the interference pattern, so in hardware, the sensor only needs to measure the intensity components.”

Once the reconfigurable surface attains the location of a user, it can alter the reflective phase of each meta-atom. This allows it to guide the signal originating from a base station toward the user, without being physically connected to this station.

Compared to conventional designs, researchers’ design thus significantly reduces the complexity of RIS systems, eliminating the need for control cables.

Heading towards more intelligent wireless communication systems

In initial tests, the team’s RIS was found to perform remarkably well, successfully redirecting received microwave signals. In the future, it could be used to advance wireless infrastructure, broadening its coverage and enabling the optimization of communications in real-time.

“We introduced a novel and low-cost approach for RIS self-control, which enables massive deployment of RISs for future-generation communications,” said Dai. “We anticipate that RISs will act like plug-and-play USB devices that can autonomously serve adjacent users in a radio access network.”

Dai, Cui and their colleagues are currently trying to improve their proposed RIS design and further validate its potential for real-world applications. For instance, they are working on strategies that would allow several surfaces to coordinate their activity to serve multiple users at once.

“These strategies are more complicated, since different users are in different locations, with different data rate requirements and different hardware capabilities,” added Cui and Dai. “To optimize the phase shifts of these multiple SC-RISs, we could adopt decentralized algorithms. This could maximize the quality of service (QoS), while keeping the communication overhead low.”

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