Subject: [NEXTEL-1] Beware the BPL Buzz

From: marcel_rf1 <[email-masked]>
Date: Tue, 03 Aug 2004 00:36:40 -0000

Beware the BPL Buzz
By Peter Coffee
August 2, 2004

The hype around broadband over power lines evades an obvious and 
grave risk: radio interference.

Bad things happen when ideal IT concepts bump into the realities of 
imperfect hardware. This time, I'm talking about the slow-motion 
train wreck of BPL (broadband over power lines), a basically bad idea 
that's now the subject of a newly launched IEEE standard process.

With lots of people wanting its benefits and few people understanding 
its drawbacks, BPL seems likely to gain too much momentum to be 
killed. A win for BPL, though, could be a loss for some valuable 
applications of the radio spectrum - but you'd never know that 
there's a serious risk, or even a controversy, if all you saw was
the 
IEEE's cheerful July 20 announcement of IEEE P1675, "Standard
for 
Broadband over Power Line Hardware."

The IEEE announcement calls the BPL proposition "relatively 
straightforward," saying "A computer-router combination and a
coupler 
take the signal from an optical-fiber cable as it enters a substation 
and imposes it on the electric current. The signal travels over the 
medium-voltage lines, with repeaters placed every 0.5 to 1 mile to 
keep the signal viable. A repeater/router near a residence or 
business extracts the signal off the medium voltage just before the 
transformer and injects it onto the low-voltage wiring on the other 
side of the transformer. The signal is now on all of the low-voltage 
wiring within the structure and can be accessed at any outlet by 
plugging in a modem."

The elephant in the living room prompts my follow-up question:
"Where else is that signal accessible - whether it's wanted
or not?" 
Incredibly, the words "radio" and "interference" are
not even 
mentioned in the IEEE announcement, even though the risk of radio 
interference from BPL is obvious and grave.

BPL proposals place data signals on carrier channels that span a 
broad swath of frequencies.  Those carrier frequencies overlap those 
used by everything from international shortwave broadcasts to 
standard time signals to CB radios (remember those?) to baby monitors 
to the low end of the range of TV channels. Although not 
intentionally radiated, those BPL signals will be traveling on wires 
that can't help but behave to some degree as antennas.

We keep signals confined, on a small scale, by precisely tailoring 
signal paths in chips and on circuit boards. We control them on a 
larger scale by using shielded conductors, or twisted-pair lines that 
cancel stray radiation by combining equal and opposite components.  
And when we need to convey a complex signal at high power levels - 
for example, when feeding a moon-bounce radio antenna array - we 
don't use just an ordinary wire. We use a transmission line, a 
carefully tailored component that matches voltage and current ratios 
between the source and destination and that minimizes stray radiation 
of signals.

Electrical power lines are designed to carry power and are optimized 
for efficiency and safety - not for minimum radiation of high-
bandwidth energy.

The IEEE P1675 announcement speaks about traditional power-system 
priorities and quotes Terrence Burns, chair of the IEEE BPL Standards 
Working Group, as saying, "Power companies face a number of 
issues ... for example, how to assess the performance and safety of 
repeaters/ routers, medium- and low-voltage coupling hardware and 
other equipment before buying. Other issues include how best to put 
this equipment in place and to keep the overall system operating well 
and prevent it from interfering with power delivery. The new standard 
will help them deal with these concerns."

Is radio interference someone else's problem?  To be fair, some
BPL 
proposals do include active measures for detecting and avoiding 
communication interference. I'm sorry to rain on proposers'
various 
parades, but shortwave communications are what we turn to when other 
things aren't working, and I don't like that failures in a
new and 
complex system could put an essential backup system at risk.
"Nearly all electrical utilities are exploring BPL because the 
potential benefits are so substantial," said Burns. Yes, and
there 
would also be "potential benefits" in breaking the second law
of 
thermodynamics, but no one expects to be taken seriously if he or she 
proposes to try. Radio's realities deserve equal respect from the 
proponents of BPL.

Technology Editor Peter Coffee can be reached at peter_coffee @ 
ziffdavis.com.

http://www.eweek.com/article2/0,1759,1630521,00.asp

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