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Backscatter Radio at Gigabit Speeds

RFID's faster cousin could lead to high-speed, low-power data transfer

2 min read
mmWave backscatter communicator flexible prototype with an integrated pHEMT transistor front-end and patch antenna array.
Millimeter wave backscatter communicator flexible prototype with an integrated pHEMT transistor front-end and patch antenna array

Correction (26 June 2021): A previous version of this article incorrectly stated the present research was led by a team at Nokia Bell Labs. (One of the study’s authors is now employed there.) Rather, it was Georgia Tech and Heriot-Watt University scientists who conducted the present research 

Backscatter radios encode data in reflected signals to offer wireless communications that consume as little energy as possible—but they can be limited by poor data rates. Now Georgia Tech and Heriot-Watt University scientists have developed backscatter radios capable of gigabit speeds, for potential use in the emerging Internet of Things and other devices, a new study finds.

Whereas conventional radios generate their own signals, backscatter radios transmit data by making tiny changes to reflected signals. This approach requires a minimal number of active components, promising simple low-cost battery-free operations.

However, the low frequencies that backscatter radios often employ and the strategies they use to encode data in reflected signals typically limit their data rates. For example, radio-frequency identification (RFID) tags, which often employ backscatter radios at sub-gigahertz frequencies, transmit data at only kilobits per second rates. At the 2.4 gigahertz frequency often used by WiFi and Bluetooth, backscatter is generally limited to hundreds of megabits per second.

Now scientists have developed a backscatter radio operating at millimeter-wave frequencies of 24 to 28 gigahertz, the kind used in upcoming 5G cell phones. The new device is capable of data rates of 2 gigabits per second over distances of 0.5 meters, consuming just 0.17 picojoules per bit. This means it requires thousands of times less power than standard radios—whereas commonly used millimeter-wave radio components consume 600 to 700 milliwatts of power, the new device uses roughly 0.5 milliwatts.

The new device consists of an antenna array and a single high-frequency transistor. The transistor can apply a voltage or not to make the antenna respectively either receive or reflect incoming signals.

The high-frequency radio waves the new device works with allow it to transmit data at similarly high rates. The researchers also implemented more complex data-encoding strategies than often used with backscatter radio to help support high data rates.

However, the millimeter-wavelength radio signals this new device works with are easily absorbed by the air, walls and many other obstacles. The scientists tuned the composition and geometry of their antenna and transistor to help account for and minimize these losses.

More complex data-encoding schemes can increase data rates, “although the distance of communication will decrease,” says study co-author Spyridon Daskalakis, an electrical and computer engineer at Herriot-Watt University in Edinburgh, Scotland. “So we can get 10 gigabits per second, but the distance will be centimeters, or you can go for lower data rates but greater distances.”

Potential applications for the new device include those for high data rates over short distances and low power. “For example, you can imagine transferring lots of photos from your phone by placing it close to a reader and transmitting gigabytes of data in just seconds,” Daskalakis says. “You might also imagine this helping to transmit data within cars.”

The single transistor at the core of the backscatter radio is simple enough to manufacture using inkjet printing of silver nanoparticle inks on flexible polymer backings, drastically reducing fabrication costs and the amount of time needed to prototype new devices, the researchers say.

The scientists detailed their findings online this month in the journal Nature Electronics.

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Metamaterials Could Solve One of 6G’s Big Problems

There’s plenty of bandwidth available if we use reconfigurable intelligent surfaces

12 min read
An illustration depicting cellphone users at street level in a city, with wireless signals reaching them via reflecting surfaces.

Ground level in a typical urban canyon, shielded by tall buildings, will be inaccessible to some 6G frequencies. Deft placement of reconfigurable intelligent surfaces [yellow] will enable the signals to pervade these areas.

Chris Philpot

For all the tumultuous revolution in wireless technology over the past several decades, there have been a couple of constants. One is the overcrowding of radio bands, and the other is the move to escape that congestion by exploiting higher and higher frequencies. And today, as engineers roll out 5G and plan for 6G wireless, they find themselves at a crossroads: After years of designing superefficient transmitters and receivers, and of compensating for the signal losses at the end points of a radio channel, they’re beginning to realize that they are approaching the practical limits of transmitter and receiver efficiency. From now on, to get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a host of factors, many of them random and therefore unpredictable?

Perhaps the most promising solution, right now, is to use reconfigurable intelligent surfaces. These are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties, such as its amplitude, phase, and polarization, as the wave is reflected or refracted by the surface. So as the waves fall on such a surface, it can alter the incident waves’ direction so as to strengthen the channel. In fact, these metasurfaces can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the repeater concept.

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