May 27, 2003
HPWREN Expands into the Licensed Spectrum
Utilizing license-exempt 5.8GHz radios for its 45Mbps wireless backbone has served HPWREN well for the past three years. However, the network occasionally experiences interferences from unknown origins as well as weather-related performance degradations.
"Based on observed patterns, some interferences appear to originate from high-powered and non-point-to-point-link sources while other performance impacts seem to be related to weather - where especially in good weather the signal on long links often deteriorates," explains HPWREN principal investigator Hans-Werner Braun. "A more general concern is that the utilization of the 5.8GHz spectrum is increasing, with lower cost radios entering the market, that often 'litter' with wide-beam antennas used for point-to-point links. The increasing reliance by various applications led us to rethink the kind of radios to use for some critical and occasionally marginal links, and to opt for FCC-licensed radios instead, which yield some degree of spectrum protection - while also allowing for higher directional energy emanating from tight-beam antennas."
The initial link using licensed technology is an HPWREN link from the San Diego Supercomputer Center at UC San Diego to Mount Woodson near Ramona. This HPWREN backbone link now uses Stratex DXR700 type radios, with six-foot antennas. Prior to this change, the link had shown significant interference patterns at times.
Jim Hale and Bud Hale conducted preliminary work and participated in the installation for HPWREN's first licensed link installation. Additional assistance was provided by Mark VanScoy and Pablo Bryant of the San Diego State University's Field Station Programs and Todd Hansen of UC San Diego's ROADNet project.
An additional link to be converted, between Mount Soledad and a mountain top near Fallbrook, is HPWREN's most troublesome backbone link, which often experiences weather-related errors - sometimes as much as 45 dB receive signal level swings.
"Since its early stages, HPWREN has been using 45Mbps full-duplex radios in the license-exempt 5.8GHz spectrum for the backbone links, as well as for some of the high-performance access links," says Braun. "Because we started seeing quite a number of conflicts in the 5.8GHz band - due to interference and weather - we applied for FCC licenses to operate some of our backbone links in the licensed spectrum."
2.4GHz license-exempt spread-spectrum antennas and radios continue to be used for several HPWREN access links, such as the Tribal Digital Village Network (TDVNet). Meanwhile, 5.8GHz radios are used for many HPWREN high-speed access links - including the Mount Laguna Observatory, Palomar Observatory, and the Santa Margarita Ecological Reserve.
Please refer to http://hpwren.ucsd.edu/Photos/20030508/ for images regarding the recent HPWREN licensed link installation.
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