A RESEARCH TEAM in Germany yesterday claimed to have solved the knotty problem of delivering high-speed digital communications over the "last mile" into homes and businesses located in isolated or rural areas.
The researchers showed off a wireless data bridge that transmits digital information at a record breaking speed of 20Gbit/sec. The data turbo boost was, they explained, achieved by using higher frequencies than those typically used in mobile communications - the wireless bridge operates at 200GHz, two orders of magnitude greater than cell phone frequencies.
"An inexpensive, flexible, and easy-to-implement solution to the 'last mile' problem is the use of wireless technology," said Swen Koenig, a researcher at Karlsruhe Institute of Technology's (KIT) Institute of Photonics and Quantum Electronics.
"Instead of investing in the cost of digging trenches in the ground and deploying ducts for the fibres, data is transmitted via the air-over a high-speed wireless link."
The setup sees the optical fibre infrastructure used up to its ending point and then connected to a wireless gateway. This gateway converts the optical data to electrical millimetre-wave signals that feed an antenna. The transmitting antenna "illuminates" a corresponding receiving antenna. At the receiving point, the electrical signal is directed toward its final destination, either using another wireless channel in a relay technique via copper wire or a coaxial TV cable or with an optical fibre.
A major issue in integrating a wireless link into a fibre optic environment is to ensure that the wireless link supports data rates comparable to those of the optical link - ideally about 100Gbit/sec, according to Igmar Kallfass, a researcher and the project's leader at the Fraunhofer Institute for Applied Solid State Physics IAF, as well as a professor at KIT.
"Besides optoelectronic conversion, no further processing must be involved before the signals reach the antenna. This also holds for the receiving part in a reversed sequence," Kallfass said.
He added that such multi-gigabit wireless transmission demands multi-GHz bandwidths, which are only available at much larger frequencies than mobile communications normally use. Millimeter-wave frequencies - radio frequencies in the range of 30-300GHz - fulfill this need. By comparison, laser light, as used in optical communications, provides bandwidths of many terahertz (THz).
After the first fibre span, the optical signal is received in the first wireless gateway and converted to an electrical signal. The electronic up-converter module is then used to encode the electrical signal onto a radio frequency carrier of 220 GHz. This modulated carrier then feeds the antenna that radiates the data. The antenna of a second wireless gateway receives the signal.
In the first indoor experiment, the wireless transmission distance was limited to 50 centimetres, but this has now been boosted to 20 metres, notes Kallfass.
The team will present its research at the Optical Fiber Communication Conference and Exposition / National Fiber Optic Engineers Conference (http://www.ofcnfoec.org), taking place next month in Los Angeles. µ
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