A
team of researchers in Germany has created a new way to overcome many
of the issues associated with bringing high-speed digital communications
across challenging terrain and into remote areas, commonly referred to
as the “last mile” problem. The researchers developed a record-speed
wireless data bridge that transmits digital information much faster than
today’s state-of-the-art systems.
These
unprecedented speeds, up to 20 billion bits of data per second, were
achieved by using higher frequencies than those typically used in mobile
communications—the wireless bridge operates at 200 GHz (two
orders of magnitude greater than cell phone frequencies).
The
team will present their research at the Optical Fiber Communication
Conference and Exposition/National Fiber Optic Engineers Conference
(OFC/NFOEC), taking place March 4-8 at the Los Angeles Convention
Center.
“An
inexpensive, flexible, and easy-to-implement solution to the ‘last
mile’ problem is the use of wireless technology,” explains Swen Koenig, a
researcher at Karlsruhe Institute of Technology’s (KIT) Institute of
Photonics and Quantum Electronics, who will present the findings at
OFC/NFOEC. “Instead of investing in the cost of digging trenches in the
ground and deploying ducts for the fibers, data is transmitted via the
air—over a high-speed wireless link.”
In
this type of setup, the optical fiber infrastructure is used up to its
ending point and then connected to a wireless gateway. This gateway
converts the optical data to electrical millimeter-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 fiber. Wireless links also serve as a bridging element
in fiber optic networks, if obstacles and difficult-to-access terrain
such as lakes, valleys, or construction sites are in its pathway.
“The
challenge in integrating a wireless link into a fiber optic environment
is to ensure that the wireless link supports data rates comparable to
those of the optical link—ideally about 100 Gbit/s—and that it’s transparent to the data,” notes 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.”
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
30-300 GHz—fulfill this need. By comparison, laser light, as used in
optical communications, provides bandwidths of many terahertz (THz).
Indeed,
free-space optical point-to-point links that use laser light for data
communication between two optical gateways are already commercially
available. However, free space optical links don’t work or only work
with limited quality and stability under adverse atmospheric conditions
such as fog, rain, and dust. In contrast, a wireless link at
millimeter-wave frequencies remains operational under such conditions.
“For
our experiment, we use state-of-the-art electronic up- and
down-converter modules developed at the Fraunhofer IAF. Previously,
wireless data transmission at frequencies greater than 200 GHz with
electronic up- and down-converters was virtually unexplored,” Kallfass
says.
After
the first fiber 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
our first indoor experiment, the wireless transmission distance was
limited to 50 cm, which we’ve now increased to 20 m,”
notes Kallfass. “The second wireless gateway performs the inverse
operation of the first gateway by an electronic down-converter module.
Eventually, the electrical signal is again encoded onto laser light and
transmitted over the second fiber span.”
This
experiment was carried out within the framework of the MILLILINK
project led by the Fraunhofer IAF and funded by the German Federal
Ministry of Research and Education. Other partners include: KIT, Siemens
Corporate Research and Technologies, Kathrein, and Radiometer Physics.
The consortium is supported by Deutsche Telekom and Telent.
Koenig’s
presentation at OFC/NFOEC, titled “High-speed wireless bridge at 220
GHz connecting two fiber-optic links each spanning up to 20 km,” will
take place Monday, March 5 at 1:30 p.m. in the Los Angeles Convention
Center.
Optical Fiber Communication Conference and Exposition/National Fiber Optic Engineers Conference
