Earlier this year, Stanford University researchers created a full-duplex radio that allowed wireless signals to be sent and received simultaneously, thereby doubling the speed of existing networks. Using the same approach, researchers at Rice University have now developed similar full-duplex technology that would effectively double the throughput on mobile networks without the addition of any extra towers.
Currently, mobile phones use two different frequencies to provide two-way communications - one to send transmissions and another to receive. This is because the strength of the transmission drowns out any incoming signal on the same frequency. While it was long thought impossible to overcome this problem, in 2010 Ashutosh Sabharwal, professor of electrical and computer engineering at Rice, and colleagues Melissa Duarte and Chris Dick, published a paper showing that full-duplex was possible.
The trick lay in canceling out the transmitted signal at the source so an incoming signal on the same frequency could still be heard. Like the Stanford approach, the technology developed by the Rice researchers achieves this by employing an extra antenna at the source.
"We send two signals such that they cancel each other at the receiving antenna - the device ears," Sabharwal said. "The canceling effect is purely local, so the other node can still hear what we're sending."
Many modern wireless communications standards, including 802.11n, 4G, LTE, WiMAX and HSPA+, use multiple antennas at both the transmitter and receiver to improve communications performance. This is called multiple-input and multiple-output, or MIMO, and this provided the researchers with a way to implement their full-duplex technology that is low cost and wouldn't require complex new radio hardware.
"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," said Sabharwal. "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 years."
The full-duplex technology is set to be rolled into Rice's "wireless open-access research platform," or WARP. This 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. Stanford researchers actually used WARP in developing their full-duplex technology and Sabharwal says that adding full-duplex to WARP will allow other researchers to start innovating on top if Rice's breakthrough.
"There are groups that are already using WARP and our open-source software to compete with us," he said. "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."
The Rice University team has already gone one step further by achieving asynchronous full-duplex, which means one node can start receiving a signal when it's in the middle of transmitting. Sabharwal says his team is the first to demonstrate this technology, which would allow mobile carriers to further maximize traffic on their networks.