The days of waiting for smartphones to upload video may be numbered. Rice University
engineering researchers have made a breakthrough that could allow wireless
phone companies to double throughput on their networks without adding a single
Rice’s new “full-duplex” technology allows wireless devices like
cell phones and electronic tablets to both “talk” and
“listen” to wireless cell towers on the same frequency—something that
requires two frequencies today.
“Our solution requires minimal new hardware, both for mobile devices
and for networks, which is why we’ve attracted the attention of just about
every wireless company in the world,” says Ashutosh Sabharwal, professor
of electrical and computer engineering at Rice. “The bigger change will be
developing new wireless standards for full-duplex. I expect people may start
seeing this when carriers upgrade to 4.5G or 5G networks in just a few
In 2010, Sabharwal and Rice colleagues Melissa Duarte and Chris Dick
published the first paper showing that full-duplex was possible. That set off a
worldwide race to demonstrate that the technology could actually be used in a
real network. This summer (2011), Sabharwal and Rice’s Achaleshwar Sahai and
Gaurav Patel set new performance records with a real-time demo of the
technology that produced signal quality at least 10 times better than any
previously published result.
“We showed that our approach could support higher throughput and better
link reliability than anything else that’s been demonstrated, which is a plus
for wireless carriers,” Sabharwal says. “On the device side, we’ve
shown that we can add full duplex as an additional mode on existing hardware.
Device makers love this because real estate inside mobile devices is at a
premium, and it means they don’t have to add new hardware that only supports
To explain why full-duplex wireless was long thought impossible for wireless
networks, Sabharwal uses the analogy of two people standing far apart inside an
otherwise empty arena. If each shouts to the other at the same time, neither
can hear what the other is saying. The easy solution is to have only one person
speak at a time, and that’s what happens on two-way radios where only one
person may speak at a given time. Cell phones achieve two-way communications by
using two different frequencies to send and listen.
Rice’s team overcame the full-duplex hurdle by employing an extra antenna
and some computing tricks. In the shouting analogy, the result is that the shouter
cannot hear himself, and therefore hears the only other sound in the arena—the
person shouting from far away.
“We send two signals such that they cancel each other at the receiving
antenna—the device ears,” Sabharwal says. “The canceling effect is
purely local, so the other node can still hear what we’re sending.”
He says the cancellation idea is relatively simple in theory and had been
proposed some time ago. But no one had figured a way to implement the idea at
low cost and without requiring complex new radio hardware.
“We repurposed antenna technology called MIMO, which are common in today’s
devices,” Sabharwal says. “MIMO stands for ‘multiple-input
multiple-output’ and it uses several antennas to improve overall performance.
We took advantage of the multiple antennas for our full-duplex scheme, which is
the main reason why all wireless carriers are very comfortable with our
Sabharwal said Rice is planning to roll its full-duplex innovations into its
“wireless open-access research platform,” or WARP. WARP is a
collection of programmable processors, transmitters, and other gadgets that
make it possible for wireless researchers to test new ideas without building
new hardware for each test. Sabharwal says adding full-duplex to WARP will
allow other researchers to start innovating on top of Rice’s breakthrough.
“There are groups that are already using WARP and our open-source software
to compete with us,” he says. “This is great because our vision for
the WARP project is to enable never-before-possible research and to allow
anyone to innovate freely with minimal startup effort.”
Sabharwal’s team has gone one step further and achieved asynchronous
full-duplex too—that is one wireless node can start receiving a signal while
it’s in the midst of transmitting. Asynchronous transmission is import for
carriers wishing to maximize traffic on their networks, and Rice’s team is the
first to demonstrate the technology.
“We’ve also developed a preliminary theory that explains why our system
is working the way that it is,” Sabharwal says. “That’s also
important for carriers and device makers, because engineers aren’t likely to
implement something like this without a clear understanding of fundamental