Researchers from the Fraunhofer Institute for Applied Solid State Physics and the Karlsruhe Institute for Technology have achieved wireless transmission of 40 Gbit/s at 240 GHz over a distance of one kilometer. Their latest demonstration sets a new world record and fits perfectly into fiber optic transmission capacity. In the future, these radio links will fill the gaps in high-speed Internet provision by supplementing the network in rural areas and hard-to-reach places.
Digital, mobile and networked – the changing media usage habits of modern society require faster transmission of increasing volumes of data. Compared to the European standard, Germany is lagging behind in the expansion of the fiber optic network, according to statistics from the FTTH Council Europe. Deploying new fiber optic cables is expensive and difficult when there are natural or urban obstacles such as rivers or road junctions. Broadband radio links can help overcome these critical areas, facilitating the expansion of network infrastructures. In rural areas, they can be a cost-effective and flexible alternative to ‘fiber to the home’.
Researchers have now set a new world record for wireless data transmission: For the first time, fully integrated electronic transmitters and receivers have been developed for a frequency of 240 GHz, which enables the transmission of data rates of up to at 40 Gbps. That’s equivalent to transmitting a full DVD in less than a second or 2400 DSL16000 Internet connections. Distances of more than one kilometer have already been covered with a long-range demonstrator, which the Karlsruhe Institute of Technology has installed between two skyscrapers as part of the “Millilink” project. “We have succeeded in developing a radio link based on active electronic circuits, which allows data rates as high as in fiber optic systems, thus enabling seamless integration of the radio link”, says Professor Ingmar Kallfass, who coordinated the project at the Fraunhofer IAF under a joint chair between IAF and KIT. Since 2013, Kallfass has been at the University of Stuttgart, where he continues to lead the project.
High frequencies enable fast data transmission
The use of the high frequency range between 200 and 280 GHz not only allows the fast transmission of large data volumes, but also results in a very compact technical package. Since the size of electronic circuits and antennas scale with frequency/wavelength, the transmitter and receiver chip is only 4 x 1.5 mm². The semiconductor technology developed at the Fraunhofer IAF, based on high carrier mobility transistors (HEMT), allows the frequency between 200 and 280 GHz to be used with active transmitters and receivers in the form of compact integrated circuits. The atmosphere exhibits low attenuation in this frequency range, allowing wideband 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 bad weather conditions such as fog or rain,” says Jochen Antes of KIT.
Until now, radio links have not been able to directly transmit the data rates of fiberglass. This may change in the future, as shown in the project’s test configuration. Such a high-performance system would also have the advantage of so-called bit transparency, i.e. the signal from a glass fiber could be fed directly and without power-consuming transcoding into a radio link. It could then be transmitted and redirected into a fiberglass. The test configuration record data is just the beginning. “Improving spectral efficiency by using more complex modulation formats or combining multiple channels, i.e. multiplexing, will help achieve even higher data rates,” says Antes. This could give further impetus to the expansion of the broadband network. Perhaps then Germany will no longer occupy the lower ranks compared to the rest of Europe.
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Material provided by Karlsruhe Institute of Technology. Note: Content may be edited for style and length.
