Researchers at Cornell University have developed a new type of radio-on-a-chip that could mean cheaper, more flexible wireless systems. Smartphone makers could, for example, use the technology to make a single model of each phone that works anywhere in the world.
Single-chip radios have become a popular choice for communications hardware in the last decade because most characteristics of the radio are determined through software, not discrete hardware components. For this reason, they are often referred to as software-defined radios.
But software can only do so much. In many transceiver devices -- ones that transmit and receive -- an array of filters is needed to protect the sensitive receiver circuity from signals being transmitted. Those signals can be up to a billion times more powerful that the ones being received, so without the filters, the radio would be overwhelmed and useless.
In cellphones, the radio transmits and receives simultaneously on different frequencies. This allows you to listen and speak at the same time without having to take turns and say "over" each time you finish.
The Cornell researchers have figured out a way to generate the transmit signal that allows it to be canceled out on the receive side. That way, hardware filters aren't needed.
"The reason why it works is a unique design," said Alyssa Apsel, a professor at Cornell and member of the team that developed the technology. The radio generates several signals that in one direction combine to produce the desired transmit signal. In the other direction they cancel each out, thus doing the job of a filter.
The new design could make software radios cheaper, but that's secondary to a bigger advance.
"We can enable this function at any frequency, just by tuning some parameters," said Apsel. "So we can make a radio that is truly reconfigurable, changed on the fly to spectrum in your location."
That's becoming more important as the airwaves get more crammed with wireless signals.
A couple of decades ago, a cellphone that covered three frequency bands would have worked pretty much anywhere in the world, but the latest LTE technology is available for more than 30 different bands.
Things are likely to get more complicated as demand for spectrum leads more countries to make band assignments specific to their needs. So a radio that can quickly be reprogrammed for a particular region could be useful.
The radio developed at Cornell covers frequencies from 300MHz to 5GHz, which encompasses many active communications bands, including those for cellphones, Wi-Fi, amateur radio, emergency services and some fixed wireless broadband and satellite communications.
They've managed to attain 25dB of isolation between the transmit and receive signals so far. Apsel said hardware filters will typically isolate from 20dB to 40dB, but the researchers aren't done yet. She's confident of achieving 50dB isolation or more.
The research was detailed in a paper, “A wideband fully integrated software-defined transceiver for FDD and TDD operation,” published online in the Institute of Electrical and Electronics Engineers’ Journal of Solid-State Circuits on January 27, 2017. Apsel worked with Cornell professor Alyosha Molnar.
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