2/2013

Full-duplex technology for more efficient data transmission

Mikko Valkama

Researchers at TUT and Aalto University are developing a full-duplex radio that allows data to be sent and received simultaneously on the same frequency. The technology has the potential to double the throughput of wireless communication systems.  

“Many engineering professionals, in particular radio frequency (RF) engineers, doubt that full-duplex technology will ever be functional, let alone cost-effective,” says Professor Mikko Valkama from the Department of Electronics and Communications Engineering at TUT.

Valkama and Professor Risto Wichman from Aalto University represent the opposite school of thought and are convinced that their research groups will succeed in building a fully functional full-duplex radio and wireless communication system prototype. The groups consist of 2-3 researchers in both universities.   

“It won’t be easy. We need to overcome major technical hurdles in the field of antenna design, radio frequency circuits and digital signal processing,” admits Mikko Valkama.

Current technology wastes bandwidth

Nowadays, when mobile phones and base stations send and receive information – such as speech or data – they either transmit signals over separate channels or take turns transmitting over a shared channel so fast that it is, in principle, undetectable to a human observer. The scarcity of the radio frequency spectrum limits the number of simultaneous connections, or, for example, the data rate of any individual connection, as transmission resources need to be split between transmitting and receiving. Such limitation can, in principle, be overcome with full-duplex technology.   

The major practical problem of full-duplex technology is the interference between incoming and outgoing signals. For example, when a mobile phone sends a signal to a base station, the strength of the signal is around +20 dBm (decibels relative to a milliwatt), i.e. approximately 100 milliwatts. This may not sound like much, but it greatly exceeds the strength of the signal that the phone receives from the base station.

“Incoming signals may be as weak as -90 or -100 dBm. Thus, outgoing signals are easily a billion times more powerful, or even more,” compares Valkama.

If the signals are transmitted and received on the same frequency, the incoming signal is blocked out – unless specific isolation, cancellation and enhancement methods are developed and deployed.

The research groups headed by Valkama and Wichman are set to address this issue by developing separate receiving and transmitting antennas, attenuating the outgoing signal before it reaches the sensitive receiver chain circuits, and using additional analog/RF and digital signal processing solutions to eliminate any remaining interference.

Another goal is to explore the system- and network-level benefits of different scenarios and identify the most effective approach for radio resource management in systems deploying full-duplex capable radios.

Collaboration with Finnish and international partners

Two parallel research projects have been launched to overcome the challenges of full-duplex radio. One is funded by the Academy of Finland and the other by Tekes. In addition, the projects are connected to DIGILE Ltd, the Finnish Strategic Centre for Science, Technology and Innovation in the field of ICT, and industrial partners.   

“If we succeed, the first applications could become commercially available before the end of this decade,” estimates Valkama. They will most likely be small-cell devices similar to WLAN/WiFi networks.

 

Text: Martti Tammisto
Photo: Marjaana Malkamäki

 
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