in 2003 IT/AV Report
Handicapping the Wireless
By By Neal Weinstock
Wireless LANs are the
epicenter of industry heat. The market research firm In-Stat
reported 8 million WLAN units sold in 2002, and expects
33 million in 2003. That huge increase may be as much about
manufacturers’ wishful thinking as consumer demand.
Nevertheless, wireless chips should continue on a rapid
downward cost curve. The IEEE standards 802.11b, 802.11a
and 802.11g have been approved and widely adopted, with
more iterations coming. Bigger-bandwidth versions of IEEE
802.15 (Bluetooth) and Ultra Wide Band (UWB) are on the
way. But can these standards be put to use for AV?
They must, according
to Duncan Kitchin, wireless LAN architect for Intel. “802.11b
in home networks was driven by broadband internet connection
sharing,” he stated. “802.11a in home networks
will be driven by high bandwidth multimedia streams between
devices in the home.”
Wireless connections would mean greatly faster and easier
AV installations. Wireless video cameras for security, process
control and other industrial uses can be a tremendous productivity
enhancement. For example, in many cities, people are in
the habit of checking traffic webcams before deciding on
their commutation route. Wired webcams involve a not inconsiderable
installation expense. See
website of the New York City Department of Transportation
Real-Time Traffic Camera advisory. There are just 82 digital
still cameras mounted around New York, and only 17 streaming
video cameras. That’s not much over thousands of miles
You Might Never Know
With miles between cameras
aimed at major routes such as the Brooklyn-Queens Expressway,
you’d never really know whether a webcam’s clear-looking
traffic means your drive to the airport will be smooth,
or that there’s a jam-up just before the camera’s
location. If a wireless connection can reduce overall installation
and maintenance costs enough to put up several times the
number of webcams, the benefits will strongly outweigh the
occasional environmental or contention-based interference
causing signal outages.
Wireless before the
days of 802.11 would have meant licensed spectrum, at from
12 to 26GHz depending on the location. Licenses in these
frequencies are costly, and may not be available in a particular
area. Higher-bandwidth systems are also far more power-hungry
than 802.11. Still-image digital cameras and 802.11 may
even be powered by the solar cells that are now ubiquitous
on emergency phones at roadsides.
Although audio takes
up far less bandwidth than video, wireless may happen more
slowly in audio installations, because latency must be tighter
in audio. Glitches in surveillance webcams are OK, but quality
video can’t have latency greater than 25ms. Audio
will sound murky if latency between stereo pairs or other
closely aligned monitors comes in greater than about a tenth
of that, or 2.5ms (though “golden ears” will
insist on much less). Voice-quality audio, such as the payload
in an airport PA system, requires about 20ms latency at
maximum. According to Intersil, the largest supplier of
802.11 chips, 802.11b at 11Mbps can carry up to 10 isochronous
voice channels (at typical voice quality of 44kHz) by using
the standard’s PCF option, with 4 to 6ms latency/channel.
After many years of work on PCF over 802.11b and improved
audio compression codecs, various schemes allow multiple
streams of quality audio over WLAN.
On the Surface
On the surface, carriage
of AV over IEEE 802.11a and 802.11g would seem to be a no-brainer.
Both offer 54Mbps, with effective carriage capacity of a
20 to 30Mbps payload. In comparison, DVD video streams are
6Mbps; theoretically, four or five could be accommodated.
So could a couple of dozen 96k digital audio channels. But
there are limits to the attractiveness of these standards
for real-time media.
According to Intel’s
Kitchin, both the established 802.11a and b standards’
MACs are only about “50% efficient.” That’s
due not only to the collisions, backoff time and acknowledgements
inherent not in Ethernet, but to additional features that
were built into the wireless standard to enhance its ability
to deal with new devices introducing themselves to the cloud.
Other 802.11 devices roaming into the cloud might insist
on network access; a security scheme that denies them access
is easy to deploy, but takes up some signal headroom and
may limit the network’s usefulness for AV apps. Any
other RF emitters nearby may interfere with connections.
Examples include other 802.11 devices, microwave ovens (mainly
affecting 802.11a at 5GHz), 2.4GHz portable phones and Bluetooth
(affecting 802.11b and g at 2.4GHz).
Interference is a bigger
problem in the more populated 2.4GHz spectrum used by 802.11b
and g, a lesser one in the more recently opened 5GHz range
used by 802.11a. But some of the problem at lower frequencies
is a facet of the greater reach they make possible at any
given power. IEEE 802.11a only has about a 50-foot range;
signals in the 2.4GHz range can be trusted for about three
to four times that distance. Less range may be inconvenient,
but it also means that the microwave oven in the commissary
down the hall can’t reach your signal.
Finally, different environmental
objects may scramble any radio signal, depending on the
characteristics of the frequency band. Steel is a big problem
for the 5GHz range, so 802.11a may not work in a high-rise
office building…or it may only work within a single
room there. That’s all you might expect anyway from
802.11a’s 50-foot distance. Masses of concrete can
also pose problems. All of which tends to limit best performance
by these networks to the setting of a home or a small suburban
office or fast-food restaurant.
Kitchin chairs the 802.11e
task group, which expects to enhance the 802.11a standard
by allowing delivery of real-time traffic with the tightest
possible latency. This will imply many choices among a great
number of possible new ways of prioritizing certain traffic
and denying access to other traffic. So, in a year or two,
we will probably get a new 802.11 standard that allows QoS
for multiple streams of real-time AV.
Newer Protocols Spur Action
Major spurs to action
on improvements in 802.11 are the ongoing improvements in
competing protocols. The best known is often called wideband
Bluetooth, or IEEE 802.15.3. The most radical is Ultra Wide
Band. Both offer opportunity to step back, rethink bandwidth
use and QoS for AV, and produce standards that are better
than 802.11. After all, 802.11 includes an accretion of
iterations dating back decades.
802.15.3 is by far the
less radical of the new standards, and much more directly
competitive with 802.11. It aims for up to 55Mbps as far
as 70 meters, and peer-to-peer connectivity with QoS for
AV. It also supports low-power devices and 128-bit encryption.
According to John Barr of Motorola, chairman of the IEEE
802.15.3 Task Group, “Compared to 802.11 at 2.4GHz,
an 802.15.3 2.4GHz PHY system causes less interference because
it occupies a smaller bandwidth and transmits at lower power
If the peer-to-peer
and AV-oriented nature of 802.15.3 sound much like the benefits
of Firewire, that’s intentional. The standard was
inspired by 1394 and can also be used, according to Barr,
as a wireless 1394 replacement, up to that 55Mbps bandwidth
limit. This would not be the first wireless protocol based
on 1394; in Europe, HiperLAN is also known as “wireless
As with 1394, what’s important about 802.15.3 is on
a level above the physical. The 802.15.3 PHY isn’t
much different from 802.11’s. So it should come as
no surprise that the proponents of 802.15.3 are looking
at alternate PHYs, especially UWB.
All other radios today
use limited bandwidth, and modulate frequency or amplitude
within that band. Instead, UWB sends patterns of extremely
short (sub-nanosecond) pulses across vast areas of spectrum.
With frequency ranging from hundreds of thousands to billions
of pulses per second, and using pulse-position modulation,
binary keying and other techniques, UWB achieves strong
signals even at low power. It looks like white noise to
an existing radio receiver, and coexists with it.
The technology was developed
for the US Department of Defense (DoD), and remained classified
until a few years ago. Recently, the Federal Communications
Commission persuaded the DoD to go public with UWB. Commercial
use at low power is now conditionally allowed.
Various spectrum licensees are lobbying against UWB, saying
they fear it may affect their signals. The military, however,
has long been using UWB without affecting those signals.
Manufacturers of existing 802.11 can’t be happy about
UWB, either; it is a disruptive technology that may upset
their apple cart.
The FCC has limited
UWB power spectral density (PSD) to -41.25dBm/MHz. The PSD
limits for the 2.4GHz ISM and 5GHz U-NII bands used by 802.11
and current 802.15.3 are more than 40dB higher per MHz.
Many observers believe that this highly conservative limit
on UWB power will be raised eventually, because interference
with existing communications is a non-issue. Even at such
low power, UWB is capable of carrying 100Mbps or even higher
data rates. UWB is, however, currently limited to short
The leading company
in commercializing UWB, a Virginia start-up backed by Motorola,
Texas Instruments and Cisco Systems called Xtreme Spectrum,
already has a PHY chip that does 25Mbps at 50 meters. They
and the standards working groups have goals of specifying
110Mbps service at 10 meters distance, and 400Mbps at five
That 400Mbps at five
meters high-capacity/short distance rating, if combined
with the 802.15.3 standard in a MAC or link layer sitting
on top of UWB, would coincidentally yield almost the exact
characteristics of IEEE 1394a, without wires. This new hybrid
standard is now known as 802.15.3a.
The Network Effect
Which brings us back
to wireless 1394. HiperLAN was not widely adopt- ed because
802.11 edged it in the market with lower pricing and wider
use. Networking technologies are among the best examples
of the “network effect”; users want to use what
other users are using, so they can connect to more users.
As soon as one among any number of competing technologies
seems to be the more widely used, almost all potential users
Could 802.11 already
have such a head start over 802.15.3a that the game is over
before it starts? Probably not this time. There is a confusing
profusion of 802.11 standards, and they are mostly mutually
incompatible. Manufacturers will have to move rapidly to
provide systems that connect at both 2.4 and 5GHz, and that
easily upgrade to whatever becomes most popular as a future
QoS standard: 802.11e, or g, or maybe something else.
Any consumers stuck
with 802.11b and a lot of interference, or 802.11a where
most of their friends use 802.11b, are likely candidates
to switch to 802.15.3a when they upgrade. Electronics manufacturers
that want to build in high-bandwidth, peer-to-peer connections
to link a camera or loudspeaker will simply choose the best
UWB does, however, face
other significant hurdles. For now, it’s allowed only
in the United States. UWB requires clear proof that it does
not interfere with existing radio at greater power ratings,
and it requires new hardware. 802.11 may yet pull out another
AV installations win
either way, though. As the hardware companies chase their
grail of consumer demand for wireless home AV networking,
they will bring greater labor savings and quicker, safer
installs to all networked AV.