When fiber optics won't do

San Francisco opts for high-speed wireless links to monitor remote sites

San Francisco's wireless backhaul requires uninterrupted sight lines.

Much of downtown San Francisco is wired with fiber-optic cable to serve the broadband needs of city agencies. But not every arm of every agency is so lucky.


The Public Works Department runs
water-pumping stations throughout the
city and county, nowhere near the fiber
ring. For maintenance and homeland security
reasons, San Francisco wanted realtime
video monitoring at every station, but
the old data lines'typically T1s or multiple
T1s'weren't enough to get the job done.


The T1s were 'pretty expensive and pretty
slow, relative to new technologies,' said
John Eaton of San Francisco-based Xtech
LLC, which was hired to help solve the
bandwidth problem. 'But pump stations
are miles away from the fiber ring, and
running fiber out to a station would be
hundreds of thousands of dollars, minimum.'


Instead, the city decided to use highspeed
wireless links from GigaBeam Corp.
of Herndon, Va. The company's GigaBeam
WiFiber is a point-to-point radio technology
designed to connect facilities at 1.25
Gbps in each direction, said John Krzywicki,
a GigaBeam vice president. Often,
the radios are used to link data centers, or
when it comes to remote sites, to provide
backhaul connectivity.


GigaBeam WiFiber products operate in
the 71-GHz to 76-GHz and 81-GHz to 86-
GHz radio spectrum bands, the frequency
spectrum authorized by the Federal Communications
Commission for wireless,
point-to-point commercial use. Typically,
the links run between three-quarters of a
mile to roughly two miles, depending on atmospheric
conditions. In dry air, the link
can travel 10 miles, officials said.


In San Francisco's case, the bandwidth delivers
network connectivity to each pump
station. Once there, the department uses
prestandard IEEE 802.16 WiMax and
802.11 WiFi technology to divvy up the
bandwidth among video cameras and other
systems. San Francisco has seven links or
nodes connecting the pump stations. Each
node has a WiMax transmitter that sends
a single broadcast to the cameras and
computers that manage pumps, valves,
reservoirs, dams and other waterworks.


'This is a WiMax application that's being
backhauled by GigaBeam,' Krzywicki said.


San Francisco officials plan to beef up
the wireless system to serve other needs.


'The deployment will allow us to take
advantage of the throughput capacity and
cost-effective bandwidth of the WiFiber
links for additional applications, including
geographic information system mapping,
VOIP and general backhaul of data,' said
Hans Loffeld, IT director of the San Francisco
Public Utilities Commission.


GigaBeam's technology differs from
WiMax in that it's designed only for pointto-
point connections.


'That characteristic of one radio being
able to go out to many different receivers is
very valuable, but what it does is break
down the bandwidth into smaller increments,'
Krzywicki said. 'Our radios only go
point to point and get a gigabit's worth of
bandwidth instead of increments of 1 to 2
megabits at a time.'


In San Francisco, the biggest challenge
was actually ensuring sight lines from node
to node. 'The general design, doing your
measurements and getting the coordinates
is actually the hardest part,' Eaton said.
'The physical installation of the radios is
pretty straightforward; it only takes an
hour or two to bring up a link.'


To run fiber along the same routes could
have cost up to $1 million a mile, Krzywicki
said. It cost San Francisco less than
$50,000 a mile to go wireless.


'It's a way to get fiber's performance and
reliability, without having to spend the
kind of money it takes to run fiber half a
mile to two miles,' Eaton said.


Doug Beizer is a staff writer for GCN' sister publication Washington Technology.

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