If you thought 5G wireless was fast at one Gbit/s, how does 40 Gbit/s sound? That's the new wireless data transmission record set by a team of engineers in Germany using integrated solid state mm-wave transceivers. This data transmission rate was demonstrated over a distance of 1 km (0.6 miles) and it is hoped that such links could be used to close gaps between optical networks in rural areas at a fraction of the cost of installing optical fiber.

As internet-enabled services continue to change entertainment media access from wholesale to retail, the demand for faster transmission of larger quantities of data is leaping skyward, eating every new data communication resource we can muster. There is only so much bandwidth that can be accommodated by grabbing a bit of white space here and nibbling away at an amateur radio band there. The only practical path to dramatically larger bandwidth is to migrate into the millimeter-wave bandspace lying above 30 GHz.

The lower end of the mm-wave frequency band is already being used for various forms of large-scale data transmission, with the 60 GHz band now becoming active for Wi-Fi and other consumer data transmission applications – not to mention the tiny, high-precision radars that will someday keep our cars from bumping into each other and enable autonomous vehicles.

Before the end of the decade, it is likely that the 60 GHz band, as well as the other bands below 100 GHz allotted for data transfer, will also run out of room. In response to this situation, considerable attention is currently being paid to the 200–280 GHz band.

As applications move to shorter and shorter wavelengths, they encounter more environmental problems, such as atmospheric attenuation and rain fade. Though at 60 GHz the atmosphere will absorb 3/4 of the RF power for each kilometer of distance, at 240 GHz the same amount of absorption may require tens of kilometers of distance, depending on the humidity. Rain fade, the reduction in effective power caused by the mm-waves scattering from the raindrops, is not a major factor in a slow drizzle, but anything more can greatly restrict the distance over which this band can be used.

As part of the “Millilink” project, researchers from the Fraunhofer Institute for Applied Solid State Physics in Freiburg, Germany, together with the University of Stuttgart and the Karlsruhe Institute of Technology (KIT), developed a 240 GHz transceiver chip that measures only 4 x 1.5 mm. The size of the chip is related to the small circuits and antennas required to work with very short wavelengths. The chip uses a semiconductor technology developed at Fraunhofer that is based on growing circuits on III-V semiconductors, including the high electron mobility transistors that make it possible for the chip to operate up to 300 GHz and beyond.

Radio links have hitherto been unable to match the multi-Gbits/s data transmission rates of multimode optical fibers, but the new German demonstration shows this soon may not be the case. The fast data transmission of the mm-wave radio link leads to bit transparency in data transmission. If you want to use optical fibers to transmit data, but also have to ford a canyon with a radio link, there is no need to compress the signal coming from the optical fiber. It can be fed directly into a radio link, transmitted across the canyon, reconverted into optical data, and then returned into the next section of glass fiber. No reduction in data throughput would result.

The researchers say the demonstration of 40 Gbit/s wireless data transmission rate is just the beginning. “Improving the spectral efficiency by using more complex modulation formats or a combination of several channels, i.e. multiplexing, will help to achieve even higher data rates”, says Jochen Antes of KIT.

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