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Intelligent Machines

Simple Circuit Could Double Cell-Phone Data Speeds

A circuit that lets a radio send and receive data simultaneously over the same frequency could supercharge wireless data transfer.

Demand for wireless bandwidth is growing rapidly.

A relatively simple circuit invented by researchers at the University of Texas could let smartphones and other wireless devices send and receive data twice as fast as they do now.

This circuit could allow cell phones and other devices to double their data bandwidth.

The circuit makes it possible for a radio to send and receive signals on the same channel simultaneously – something known as “full-duplex” communications. That should translate to a doubling of the rate at which information can be moved around wirelessly.

Today’s radios must send and receive at different times to avoid drowning out incoming signals with their own transmissions. As a smartphone accesses the Internet via a cell tower, for example, its radio flips back and forth between sending and receiving, similar way to the way two people having a conversation take turns to speak and listen.

The new circuit, known as a circulator, can isolate signals coming into a device from those it is sending out, acting as a kind of selective filter in between a device’s antenna and its radio circuitry. Circulators are already a crucial part of radar systems, but until now they have always been built using strong magnets made from rare earth metals, making them bulky and unsuited to the circuit boards inside devices such as laptops and smartphones.

The new circuit design avoids magnets, and uses only conventional circuit components. “It’s very cheap, compact, and light,” says Andrea Alù, the associate professor who led the work. “It’s ideal for a cell phone.”

The two-centimeter-wide device could easily be miniaturized and added to existing devices with little modification to the design. “This is just a standalone piece of hardware you put behind your antenna.”

Alù’s circulator design looks, and functions, like a traffic circle with three “roads,” in the form of wires, leading into it. Signals can travel into, or out of, the circle via any of those wires. But components called resonators spaced around that circle force signals to travel around it only in a clockwise direction.

When a wireless device’s antenna is connected to one of the wires leading into the circle, it isolates signals that have just been received from those the device has generated for transmission itself. The new design is described by Alù and colleagues in a paper in the journal Nature Physics.

“This is definitely a significant research development,” says Philip Levis, an associate professor at Stanford. “It’s a very new way to look at a very old problem, and has some very good results.” However Levis notes that work remains to be done to convert the lab-bench breakthrough into something practical for the crucial frequency bands used for Wi-Fi, cellular, and other communications.

Alù says that his circulator can easily be adjusted to work at a wide range of frequencies, and that he is exploring options for commercializing the design. The circuit could, for instance, help simplify and improve technology being tested by some U.S. and European cellular carriers that uses a combination of software and hardware to allow full-duplex radio links (see “The Clever Circuit That Doubles Bandwidth”).

Joel Brand, vice president for product management at startup Kumu Networks, which developed that technology, says the new device could indeed be useful. “We would be happy to take advantage of it,” he says. 

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