New world record in wireless data transmission

Researchers of the Fraunhofer Institute for Applied Solid State Physics and the Karlsruhe Institute for Technology have achieved the wireless transmission of 40 Gbps at 240 GHz over a distance of one kilometre. Their most recent demonstration sets a new world record and ties in seamlessly with the capacity of optical fibre transmission. In the future, such radio links will be able to close gaps in providing broadband internet by supplementing the network in rural areas and places which are difficult to access.

Digital, mobile and networked - changing media usage habits of modern society require the faster transmission of increasing volumes of data. Compared to the European standard, Germany lags behind in the expansion of the fibre-optic network, according to statistics from the FTTH Council Europe. Deploying new fibre-optic cables is expensive and difficult when there are natural or urban obstacles such as rivers or traffic junctions. Broadband radio links can help to overcome such critical areas, thereby facilitating the expansion of the network infrastructures. In rural areas they can be a cost effective and flexible alternative to ‘fibre to the home’.

Researchers have now set a new world record in wireless data transmission: For the first time, fully integrated electronic transmitters and receivers have been developed for a frequency of 240 GHz, which allows the transmission of data rates of up to 40 Gbps. This equals the transmission of a complete DVD in under a second, or 2400 ADSL internet connections. Distances of over one kilometre have already been covered by using a long-range demonstrator, which the Karlsruhe Institute of Technology set up between two skyscrapers as part of the Millilink project.

“We have managed to develop a radio link based on active electronic circuits, which enables similarly high data rates as in fibre-optic systems, therefore allowing seamless integration of the radio link,” says Prof Ingmar Kallfass, who coordinated the project at Fraunhofer IAF within the scope of a Shared Professorship between IAF and KIT. Since 2013, Kallfass has been with the University of Stuttgart, where he continues to lead the project.

Using the high-frequency range between 200 and 280 GHz not only enables the fast transmission of large volumes of data, but also results in very compact technical assembly. Since the size of electronic circuits and antennae scales with frequency/wavelength, the transmitter and receiver chip only measures 4 x 1.5 mm². The semiconductor technology developed at Fraunhofer IAF, based on transistors with high electron mobility (HEMT), makes it possible to use the frequency between 200 and 280 GHz with active transmitters and receivers in the form of compact, integrated circuits. The atmosphere shows low attenuation in this frequency range, which enables broadband directional radio links.

“This makes our radio link easier to install compared to free-space optical systems for data transmission. It also shows better robustness in poor weather conditions such as fog or rain,” explains Jochen Antes of KIT.

Up to now, radio links were not able to directly transmit the data rates of glass fibre. This might change in the future, as the test set-up of the project shows. Such a high-performance system would also have the advantage of the so-called bit transparency, ie, the signal of a glass fibre could be fed directly and without energy-consuming transcoding into a radio link. It could then be transmitted and redirected into a glass fibre. The record data from the test set-up is only the beginning.

“Improving the spectral efficiency by using more complex modulation formats or a combination of several channels (multiplexing) will help to achieve even higher data rates,” says Antes.

The Federal Ministry of Education and Research (BMBF) supports the Millilink project with a total of €2 million of funding within the support measure “Next-generation broadband access networks”. Apart from the two research institutes Fraunhofer IAF and KIT, the project involves the industrial partners Siemens AG, Kathrein KG und Radiometer Physics GmbH. The aim of the project is integrating radio links into broadband optical communication networks in order to provide rural areas with access to fast internet. Other possible applications are indoor wireless local area networks (WLAN), wireless personal area networks (WPAN) as well as intra-machine and board-to-board communication.