Picture This: Cutting the Cord
Jul 1, 2004 12:00 PM,
By Jeff Sauer
The InFocus LiteShow interface with the LP600 projector.
If you’ve been following the projector industry, especially personal
travel-size models, you probably know that “wireless” is
one of the day’s hottest features. It’s not hard to understand why if
you imagine road warrior presenters attempting to tactfully carry on a
conversation, set a proper mood for their pitch, and remain cool all
while fumbling with setup and cables between their projector and
notebook computer. Booting up and starting the show is potentially a
lot more elegant and is a lot of what wireless offers.
It’s no surprise, then, that several projector manufacturers have
come out with wireless interfaces between computers and projectors.
These generally consist of an 802.11b, or WiFi, PC Card in the computer
talking to, most often, another PC Card inserted into a slot in the
projector (though there are a few unique solutions out there).
WIRELESS SOLUTIONS
For example, InFocus’s LiteShow interface plugs directly in to the
projector’s M1-DA connector. It’s an intuitive solution because that’s
where the VGA cable would otherwise attach were you to traditionally
tether the projector and computer together. About the size of a small
cell phone, the LiteShow module is a little larger than a PC Card, but
building the 802.11b receiver into an external module allows InFocus to
use it with smaller travel projectors than those needing to house a PC
Card slot. The LiteShow is an InFocus product that first and foremost
augments the company’s products, but it is not an exclusive solution
and can work with other projectors that use the same M1-DA connector.
However, though there are a few others, M1-DA — equipped
projectors are a strong minority in the market.
OTC Wireless, on the other hand, makes a product called the WiJet,
which is similar to the LiteShow except that it features a standard
15-pin RGB port instead of the M1-DA connector. The WiJet is also an
external unit rather than a PC Card that would go into a slot, and it
uses 802.11b as the communications protocol.
Of course, if you have followed the trend toward wireless
connections, you probably also know that these 802.11b interfaces come
with something of a performance penalty. Images tend to be a little
softer. Color range sometimes isn’t quite as full. But most obviously,
latency causes projected images to appear as much as three to four
seconds after they would appear on a local monitor, such as on the
notebook’s built-in display. Mouse movements typically show very
little, if any, perceivable delay, and adding bullet points to
PowerPoint slides generally happens within a second. However, advancing
entire slides and especially opening new windows on the desktop can
take from one to four seconds to appear, and that can be a little
disconcerting to a presenter.
What’s more, though 802.11b can reach up to 11 Mbps — more
bandwidth than the average DVD movie — it is not yet an effective
solution for video content. Indeed, some early 802.11b wireless
solutions simply choked when trying to play motion video. The reasons
are twofold: first, actual 802.11b throughput tends to be only around 4
to 5 Mbps; and second, the type of compression used to send a
potentially enormous amount of onscreen data to the projector is not as
efficient as the native MPEG format of DVD video.
MPEG-2 needs to compress “only” 30 frames/60 fields of
720-by-480 images every second compared with much of the higher
resolutions and refresh rates of most computer displays. MPEG also uses
highly optimized temporal compression with bidirectional motion
estimation and motion prediction algorithms to do it. Typical wireless
projector solutions tend to use Vector Quantization compression, which
can be efficient on the larger blocks of identical colors that
generally appear on a computer screen (like the white background of
this page or the blue background of a PowerPoint slide). However, this
compression method is far less effective with the constant interframe
and intraframe variations that are the norm in video. Yes, wireless
projector solutions do leverage temporal compression, sending, for
example, only the area of mouse movements rather than the entire
screen, but it is not as advanced as that of MPEG.
BETTER BIT RATES
What if those wireless solutions could move more data? It would be
no surprise that performance would improve. At least a couple wireless
companies are doing just that.
Avocent Technology LongView Wireless Extender
Avocent Technology, best know for its KVM switches, offers the
LongView Wireless Extender ($995), a transmitter unit that has both a
local monitor out and a wireless antenna bundled with a receiver unit
for a remote display. (A similar, newly announced AutoView Wireless
product adds one-to-many KVM switches.) It uses standard 15-pin ports
to connect the computer, the local monitor, and the remote display, so
it’s a little like the aforementioned WiJet, though it also sends
wireless keyboard and mouse data. However, instead of 802.11b, Avocent
has built the unit around the much higher bandwidth 802.11a standard.
That standard uses the underused 5 GHz frequency band rather than the
increasingly crowded 2.4 GHz band of 802.11b.With 54 Mbps (about 27 Mbps actual) of headroom rather than just 11
Mbps, the LongView Wireless Extender has a lot more data to play with
than 802.11b solutions. The result is almost no visible latency (less
than one second for even dramatic onscreen changes) on computer source
material and a lot better performance with motion video.Admittedly, motion video quality is still not what you’d get from a
cabled solution, because Avocent must still recompress the analog RGB
data coming from the computer in order to send it wirelessly to the
receiver, even if the video started as MPEG-2. That’s a compromise but
one that allows the LongView Wireless Extender to function with
straightforward computer data, motion video, or, as it often is the
case, a combination of data and video or other moving images. For
example, a presentation might have video in a window of a PowerPoint
slide. Or perhaps a digital signage application might have an
information scrolling ticker at the bottom of the screen or switch back
and forth between video and data. That sort of application is likely
one of the uses that Pioneer Electronics and Avocent have in mind for
the recently announced LongView module that will slide into a Pioneer
plasma monitor expansion slot, thus creating an effective
“wireless plasma.”OTC Wireless, by contrast, is about to ship another WiJet product,
the WiJet.Video ($799), which uses a standard PC Card in the source
computer that can effectively separate the Windows screen information
for any MPEG video that might be playing in a window or at full screen.
Similar to how Windows uses Active X controls to map motion video over
a section (or all of) the desktop, OTC’s WiJet software (installed on
the source computer) sends native MPEG video over a different WiFi
channel or port than the Windows VGA data. The WiJet device then
reassembles the VGA and video data again on the remote display side,
overlaying the video in the appropriate section of the screen. Using
that approach means the video does not go through a cycle of being
uncompressed and recompressed, thus reducing likely cascading artifacts
and maintaining image quality.Unlike the other WiJet hardware, the WiJet.Video uses the 802.11g
protocol, which achieves a similar 54 Mbps theoretical bandwidth to
802.11a and an actual bandwidth of between 20 and 27 Mbps, depending on
traffic (802.11g uses the same 2.4 GHZ as 802.11b). The WiJet.Video
receiver includes an MPEG decode chip to allow the video to be
displayed either on a data display or through a separate composite
output (S-video or component with an adapter) to a video monitor,
albeit without Windows desktop information.LOOK MA, NO CABLESAll of these wireless solutions show that cutting the cord and
eliminating the tether between the computer and the display have great
appeal. Whether it’s that hypothetical road warrior, a digital signage
application, or just a clearer installation without unsightly cables,
no one likes to be tied down.Jeff Sauerwrites the “Picture This” column
for Sound & Video Contractor and is a
contributing editor for Video Systems. He’s a video producer, an
industry consultant, and director of the Desktop Video Group, a video
and computer products testing lab in Cambridge, Massachusetts. He can
be reached at[email protected].
