Radio device could double speed of wireless networks

A new device that can send and receive radio signals at the same time could double the speed of wireless internet networks.

Existing devices can only receive radio-frequency signals when they are not sending them because the outgoing transmission drowns out the much weaker incoming signal.

But researchers at Stanford University in California have developed a way of filtering out the outgoing signal, leaving the device to transmit and receive at the same time.

This creates the possibility of simultaneous two-way communication over short-range radios such as walkie-talkies, which typically require users to take turns talking.

It could also improve the speed of wireless communication devices, which normally spend around half their time transmitting data and so lose downloading speed.

Mobile phones use a workaround system to allow users to talk at the same time but it is expensive and less feasible for wireless internet networks.

Stanford’s device works by sending out a second signal that cancels out the first when received by the input antenna.

The second signal is the same as the first but is transmitted from a point that is further away from the receiver by half the signal’s wavelength.

Two signals offset by half a wavelength create something called ‘destructive interference’ where their inverted wave patterns effectively cancel each other out.

The device was developed by three engineering graduate students, Jung Il Choi, Mayank Jain and Kannan Srinivasan, with help from assistant professors Philip Levis and Sachin Katti.

They have developed a basic prototype device and are now looking to commercialise it by improving its efficiency to increase the strength of the transmissions and the distances over which they work.

‘It turns out that the system has a few points of engineering precision, where the more precise you make a component, the better the cancellation can be,’ Levis told The Engineer.

‘In the current design, there are three such points: how well the amplitude of the two signals is matched; how precisely the two signals are out of phase; and noise in the circuitry.’

The equipment used is relatively simple and the team hope that as it is improved, the device would need less complex software to operate, making it suitable to include it in wireless network technology and even mobile phones.

‘It turns out doubling capacity, while nice, is not the greatest benefit, as there are existing approaches to double capacity when you have multiple antennas [called Multiple Input Multiple Output, or MIMO],’ said Levis.

‘But there are some unique advantages full duplex provides and we think these might be the most compelling advantages.’