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Re: 2.4 GHz Cordless Phones



Here is an interesting article oin this topic from a recent Wall Street Journal:

> Date: Mon, 8 Jan 2001 11:35:57 -0800
> MIME-Version: 1.0
> From today's Wall Street Journal
>
> Raft of New Wireless Technologies Could Lead to Airwave Gridlock
> By JARED SANDBERG
> Staff Reporter of THE WALL STREET JOURNAL
>
> For months it was driving Howard McCollister nuts.  The 50-year-old
> surgeon from Deerwood, Minn., had equipped his kids' Apple
> laptops with wireless antennas called the AirPort.  The doodads allow the
> McCollister siblings to connect to the Internet without a direct phone
> line.  Instead, they receive their Internet link through the air, via a
> small radio transmitter connected to a phone. The setup ended arguments
> "about one or  the other hogging the phone line," says Dr. McCollister.
>
> But the wireless link kept blinking out, and Dr. McCollister couldn't
> figure out what was wrong. He upgraded the software and
> pored over online discussion groups without any luck.
>
> Finally, a friend who is an Apple dealer asked if he had a cordless phone
> that transmits its calls at 2.4 gigahertz and Dr. McCollister had his
> breakthrough. Two months earlier, he had bought two of the phones for his
> kids. It turned out they were creating interference that scotched the
> computer connection. Confirming the problem, he found a document on
> Apple's Web site that lists things ranging from 2.4 gigahertz phones to
> microwave ovens as potential sources of interference.
>
> Brace for mid-air collisions. The high-tech industry is hyping a raft of
> new technologies that use the airwaves to link personal computers, Palm
> hand-held devices and other gadgets to the Internet and corporate
> networks, as well as to each other. Executives say such wireless
> connections herald a new era of anywhere, anytime computing.
>
> But these technologies communicate in the increasingly crowded 2.4
> gigahertz band of the radio spectrum, potentially clogging
> the airwaves like planes over LaGuardia. Developed to liberate people from
> their desks and the linguine knots of cables emerging from their
> computers, some wireless technologies could create airborne entanglements
> that increase the complexity of computing, instead of reducing it.
>
> "New technology is always more complex at first," says Forrester Research
> analyst Galen Schreck. "We promise something that
> is going to be magical, something that will configure itself, but that
> doesn't emerge until later into the game."
>
> The wireless technologies come in several flavors.  One is called Wi-Fi,
> which also goes by the technical name 802.11b, and is used by Apple.
> [(Note:  this insert reference is from Wired News, Nov 16, 2000--see full
> reference in e-mail below)  Time Domain executives demonstrated a 10 Mbps
> wireless network, which is based on the company's first generation UWB
> chip, called the PulsON. The second generation PulsON chip, which goes
> into production at the end of the year, transmits data at 40 Mbps -- four
> times the speed of 802.11, a popular wireless networking standard.]
>
> It is aimed at allowing machines inside houses to communicate at high
> speeds and share Internet connections. A similar technology used by other
> companies is dubbed HomeRF. Lastly, there's a nascent technology called
> Bluetooth that is intended to allow hand-held computers, cellphones,
> pagers, laptops and computer peripherals such as printers to communicate
> with each other at distances of up to 30 feet. That way, for instance, you
> could zap a phone number from your cellphone to a friend's Palm.
>
> Typically, interference occurs when two radio signals using the same
> frequency collide, corrupting both. The receiving antenna simply can't
> pick out the correct signal and it must be retransmitted, resulting in a
> loss of speed.
>
> Yet the Federal Communications Commission knew such interference was the
> likely outcome when it set aside the 2.4 gigahertz spectrum for such uses.
> Unlike most areas of the radio spectrum, which are licensed for specific
> applications such as TV signals or cellphones, the 2.4 gigahertz band was
> designed as a sort of innovation zone, where technology companies and
> cash-strapped entrepreneurs could test new wireless devices without first
> seeking a costly government license.
>
> The band has been swamped in recent years by communications companies
> using it for data networking, resulting in a free-for-all of radio
> signals. Yet the FCC considers such interference to be the price of doing
> business in the band. Engineers must build wireless systems robust enough
> to coexist with such "noise."
>
> "Every one of these devices has a label on it that says they can cause
> interference and must accept interference," says
> Julius Knapp, chief of the policy division in the FCC's engineering
> office. He says most products should work fine. But, he adds, "If you
> really require high reliability, that's really not what this band was set
> up for."
>
> Some industry engineers say there's little to worry about. Sure, there
> will be some collisions, but wireless technology is constantly improving.
> For example, in the early days of cordless phones users sometimes could
> hear their neighbor's conversations, while baby monitors could pick up
> signals from the infant next door.
>
> Anticipating interference, most newer wireless systems use "spread
> spectrum" technologies, in which the signal hops within a small band of
> frequencies at lightening speeds, or changes the pattern of transmissions,
> to reduce the impact of warring signals. Spread spectrum technology,
> originally conceived during World War II by actress Hedy Lamarr to thwart
> eavesdropping, essentially prevents the kind of accidental snooping of the
> past.
>
> Because most of these new wireless devices operate at relatively short
> ranges, any interference should be confined to a localized area. What's
> more, most of the anticipated uses won't require a constant connection to
> the network, so they won't always be sending out a signal that could cause
> interference. For example, when a user is browsing the Web from a wireless
> laptop, the computer doesn't need to keep a constant connection to the
> wireless Internet link.
>
> Bluetooth is aimed at connecting gadgets when they are near each other.
> For example, a user may point to a phone number on the screen of
> Bluetooth-enabled Palm; the Palm would then wake up a cellphone in the
> user's briefcase, which would allow the user to communicate through a
> wireless Bluetooth headphone.
>
> When there is a signal overlap, the technologies are designed to "degrade
> gracefully" and retransmit any lost data, engineers say. "There's no doubt
> that because they share the same spectrum, they're going to collide," says
> Tod Sizer, a researcher at Lucent Technologies Inc.'s Bell Labs and the
> chairman of the Bluetooth Coexistence committee. But Mr. Sizer is
> optimistic that equipment makers will devise fixes that will prevent users
> from noticing the interference.
>
> Yet technology has proven time and again that anticipating its use can be
> a tricky. A few weeks ago, Sony Corp. unveiled a television set in Japan
> called the Airboard. Resembling the screen of a laptop computer, it uses
> Wi-Fi to allow consumers to roam their homes while watching the tube.
> Networking giant 3Com Corp. has a radio, dubbed the Kerbango, that the
> company says will use Wi-Fi to deliver Net-based wireless music. And at
> San Francisco's 3Com Park, hand-held computers using Wi-Fi are being
> deployed to allow 49ers football fans to chat by typing and to call up
> player statistics.
>
> These are just the kinds of data-intensive applications, often requiring a
> constant connection, in which interference could pose problems. Suddenly,
> there could be a hiccup in a TV picture or a pause in a song.
>
> Similarly, no one predicted that Wi-Fi would be used as an instrument for
> techno-ideologues. Some people in cities such as San Francisco and London
> are putting antennas on their rooftops to link their in-home wireless
> systems, in effect creating neighborhood networks. That allows them to
> share their Internet connections or resources such as digital music files
> stored on their home PCs. Anyone with a $150 wireless Wi-Fi card can join
> in over the air.
>
> Matt Westervelt, a 28-year-old system administrator for Real Networks
> Inc., has been working since July on a home-grown wireless network in the
> Seattle area. With some of the same grass-roots idealism that gave rise to
> the Internet, Mr. Westervelt is hoping to free people from the grip of
> Internet services and their monthly fees, as well as the government and
> its regulators. "We're in control of it," he says. "We're not leasing
> someone else's network."
>
> Governments may not stop these networks, but buildings, street lamps and
> wet trees might. Outdoor usage of Wi-Fi is particularly prone to
> interference, including from some street lamps that emit radiation. And as
> more neighbors use the network, the potential for interference
> multiplies.
>
> Some fans of these public-access wireless networks even envision them
> being used for voice calls, totally cutting out the phone
> system. But wireless guru Harvie Branscomb says that anyone trying to
> offer phone service over such networks won't get the kind of quality of
> traditional cellular networks. "They probably never will," says Mr.
> Branscomb, who was contracted five years ago by a Sun Microsystems Inc.
> executive to build one of the first public-access wireless networks, in
> Aspen, Colo.
>
> Most users are more concerned about garden-variety interference involving
> the new wireless networks. The most problematic collisions will occur
> when, say, two Bluetooth devices are communicating near a laptop that is
> connected to a somewhat distant Wi-Fi transmitter. Under this scenario,
> the Bluetooth devices could cause problems for the laptop as it tries to
> communicate with
> the wireless network.
>
> "Then the performance degradation is almost catastrophic," says Manpreet
> Khaira, founder of wireless start-up Mobilian Corp.
> He says customer-service centers of companies that sell these devices "are
> going to be overloaded" with complaints.
>
> Now, companies such as Mobilian and Intersil Corp. are trying to create
> transmitters that will co-exist peacefully. Standards bodies that
> determine requirements for the technologies also are calling for
> suggestions to solve the problem. Stephen Schellhammer, a senior director
> at Symbol Technologies Inc. and head of such a standards group, is
> optimistic. Still, he's aware that the technologies are being used in ways
> no one would have originally conceived. "No one can predict everything,"
> he says.


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