6G mobile communications Increased data rate in mobile communication with 3D reflectors

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The next generation of wireless communication not only requires more bandwidth at higher frequencies—it also needs a bit more time. Researchers at Cornell University have now developed a corresponding chip: delay instead of phase delay.

*Henning Wriedt is a freelance specialist author.

Researchers from Cornell University in the US have developed a semiconductor chip that adds the necessary time delay so that signals sent over multiple arrays can align at a single point in space. This approach is intended to enable ever smaller devices to work with the higher frequencies required for future 6G communication.

The majority of current wireless communication, such as 5G phones, operates at frequencies below 6 GHz. However, technology companies have set a goal to develop a new wave of 6G mobile communication that utilizes frequencies over 20 GHz. Here, a larger bandwidth is available. This means that more data can be transmitted at a higher speed. 6G is expected to be 100 times faster than 5G.

However, as data losses due to the environment are greater at higher frequencies, the way the data is transmitted is of great importance. Instead of a single transmitter and a single receiver, most 5G and 6G transmitting stations use so-called phased array antennas. These are phase-controlled group antennas with strong directionality, which achieve the bundling of radiation energy through the arrangement and interconnection of individual radiators.

"Each frequency in the communication band goes through different time delays," explains doctoral student Bal Govind. "The problem we're addressing is decades old - it's about transmitting high bandwidth data in a cost-effective way so that the signals of all frequencies arrive at the right time in the right place."

"It's not just about developing something with sufficient delay, but something with sufficient delay where you still have a signal at the end," says Professor Alyssa Apsel in Cornell Engineering. "The trick is that we have managed to do this without enormous losses."

This time delay has so far been created by phase shift circuits, which can only process a certain amount of data. This is a special problem with broadband signals, where the highest and lowest frequencies can fall out of phase, blurring the signal. A phenomenon known as "beam squint". Integrating time delay circuits into a tiny chip that fits into a smartphone is no easy task.

CMOS chip with reflectors instead of wires

"Most time delays are literally constructed with a long wire with which one can delay a signal from point A to point B. And this delay has to be tuneable so that we can redirect the beam to different places. We want it to be reconfigurable," says Apsel.

Govind worked with postdoc Thomas Tapen to develop a complementary metal-oxide-semiconductor (CMOS) that can set a time delay over an ultra-wide bandwidth of 14 GHz with a phase resolution of up to one degree.

Govind: "Since the goal of our design was to accommodate as many of these delay elements as possible, we imagined what it would be like to wrap the signal path in three-dimensional waveguides and bounce signals off them to cause a delay, instead of running wave-length wires laterally across the chip."

The team developed a series of these 3D reflectors, which strung together form a "tuneable transmission line".

The resulting integrated circuit requires 0.13 mm² space and is therefore smaller than phase shifters. However, it nearly doubles the channel capacity - that is the data rate—of conventional wireless arrays. By increasing the projected data rate, the chip could provide faster service and bring more data to mobile users.

"The big problem with phased array antennas is the trade-off between trying to make these things small enough to fit on a chip, and maintaining efficiency," says Apsel. "The answer that most of the industry has agreed on is, 'Well, we can't make a time delay, so we'll make a phase delay.' And that fundamentally limits the amount of information you can transmit and receive. It's just accepted as such."

"I think one of our most important innovations is really the question: Do you have to build it like this?" says Apsel. "If we can increase the channel capacity tenfold by changing a component, that's an interesting shift in communication."

The team's work titled "Ultra-Compact Quasi-True-Time-Delay for Boosting Wireless Channel-Capacity" was published in the journal "Nature". The lead author is doctoral student Bal Govind, co-author Thomas Tapen.(kr)

Link: Article in Nature: DOI 10.1038