it the Flipper
Multi-rate, ultra-short laser pulses -- with wavelets shaped like
the sonar image of a dolphin's chirp -- are faster than lightning
and zip through clouds, fog and adverse weather conditions, carrying
huge amounts of digital information.
Using these laser pulses in optical
wireless communication could find applications ranging from
wireless exchanges between air and ground vehicles on the
battlefield to short links between college campus buildings, say Penn State University (PSU)
"The new Penn State approach embeds data in ultra-short pulses of
laser light, shaped as wavelets, and then transmits the wavelets at
various rates," said PSU spokesperson Barbara Hale.
Known as "Meyer's Type," the wavelets used by the Penn State team
look like the sonar images of dolphin
Sending information on the backs of digital dolphins swimming at
different rates through the stratosphere may trump traditional
The dolphin-emulating wavelets minimize bandwidth waste and, as
ultra-short pulses, are less likely to interact with rain or fog
that could degrade the signal.
"The multi-rate approach offers many advantages," said Mohsen
Kavehrad, the W. L. Weiss professor of electrical engineering and
director of the Penn State Center
for Information and Communications Technology Research. "For
example, lower-rate signals can get through clouds or fog when high
rate signals can't. By sending the same message at several different
rates, one of them can probably get through."
Kavehrad and his team have shown that the multi-rate approach
achieves an average bit rate higher than conventional optical
wireless links operating at 2.5 Gigabits per second (Gbps).
It also provides an increased level of communication reliability
by maintaining a minimum of one active link throughout varying
Windows and Wavelets
Optical wireless systems -- also known as free-space optics (FSO)
-- carry voice, video and data information on line-of-sight,
point-to-point laser beams.
Inclement conditions, however, can hamper traditional outdoor FSO
systems, which have been used for over 30 years. Bad weather and
other obstructions often prevent the transmitter and receiver from
"seeing" each other.
But clouds and fog often clear abruptly, providing brief windows
for transmission, Kavehrad told NewsFactor. The ability to get
through these little windows makes pulsed delivery of wavelets
better suited to FSO.
"The wavelets are easy to generate," said PSU research team
member Belal Hamzeh. "We use holography to generate and separate the
wavelets. You just generate the mother wavelet and then the others
can be generated as a fraction of the transmission bit rate of the
mother. They can all co-exist in the channel without interference."
Kavehrad and Hamzeh described the system November 1st at the Military Communications conference
in Monterey, California.