Hardware Autopsy
and is then transmitted in parallel through
several transmitting antennas. The receiver
is also equipped with an array of anten-
nas and acquires these multiple streams as
superimposed “images,” not independent
signals. Keep in mind, however, that sig-
nal scattering (caused by environmental
obstacles) could leave each signal with a
slightly different profi le: One stream might
lack defi nition at a certain point in the trans-
mission (which would normally be perceived
as a drop-out that could disrupt or negate
the validity of the data stream), while another
might be very well defi ned at that same point
(but lacking somewhere else).
That’s when the signal processing fi rm-
ware comes into play on the receiving side. It
identifi es the various substreams, compares
the scattering effects, and creates a single
valid signal from them. Finesse at this point
is, of course, crucial. In validating the multiple
streams, the strongest signal is fi rst extracted
from the group. Theoretically, that should be
the most reliable one, but it’s also the source of
the most noise on top of the remaining signals.
Once that’s out of the way, the process contin-
ues through the rest of the streams, repeating
down to the weakest signal. (Remember, it’s
not all magic. These signals can be differenti-
ated from each other thanks to the differences
created by multipath propagation.)
In theory, much of which has been proven in
practice, the more multipath propagation effects
that occur, the more accurate the fi nal signal will
be, because more points of comparison can be
made between the multiple streams. In other
words, the more a signal is scattered, the more
likely it is that multipath effects will cause differ-
ent differences in that signal, which, when com-
pared with each other, will result in one cohesive
signal when processed.MIMO IN THE REAL WORLD
As you might suspect, one result of MIMO
technology is more reliable transmissions, but
that is only one result. The other is increased
range. In case you’re forming the question
“Huh?” on your lips after reading that, consider
what’s happening. Multipath signal propaga-
tion normally leads to truncated distances: The
scattering effect causes the signal to fade into
oblivion. MIMO won’t have unlimited range,
but because the technology uses interference
to regenerate the signal, the point where you
lose signal moves further from the transmitter.
A degraded signal is problematic for a typical
antenna and receiver, but a signal needs to be
nearly nonexistent for MIMO to stop working.
You’ve probably already identifi ed the
“weak” point in MIMO technology: signal
processing. Not only is the original transmis-
sion divided at the starting point, it must alsor&dBREAKING DOWN TECH —PRESENT AND FUTURE
NOVEMBER 2005 MA XIMUMPC 59
White Paper: MIMO Technology
CHASSIS
The sticker on the chassis contains the usual technical yadda yadda, but
take a moment before you install the drive to jot down the drive’s model and
serial numbers and file them somewhere accessible. That way you won’t
have to pry open your case if you need to contact technical support later.SPINDLE
Optical drives require extremely precise control
over the speed of disc rotation. That’s why
optical drive spindles are attached directly to
the motor, instead of being driven by a belt
as with the platter of a record player.
The close proximity of the motor to
the laser pickup introduces
vibration, however, which some
manufacturers minimize
by using motors with
fluid bearings.CLAMP
The clamp rests on the
unprinted inner hub of
optical media for additional
stabilization. Big whoop,
right? Well, if you were a
polycarbonate disc spin-
ning at 10,000rpm millime-
ters above a plastic tray,
we think you’d take all the
stabilization you could get!LASER PICKUP ASSEMBLY
The pickup assembly is a little throne
where the laser squats beneath a system of lenses,
shining a laser on the underside of optical discs to
read the “pits” and “lands” stamped on the disc.
These pits and lands are the physical manifestation
of the digital ones and zeroes that make up your
data. Some players and burners use two separate
lasers for CD and DVD work, while others use a
single laser that is capable of modulating its wave-
length between both formats.Anatomy of an Optical Drive
From CD-ROMs to double-layer DVD burners, optical drives pack some wicked technology
in those ugly little metal enclosures. And let’s face it: Everybody loves lasers!ACTUATOR
If you’ve ever watched the flat,
stiff ribbon of an inkjet printer yank
the printer head back and forth across
the page, you’ve got a good idea of how
the actuator in an optical drive works. It’s
attached to the laser pickup assembly, which
is in turn mounted to lubricated rails that run
parallel to the sides of the drive. The actuator
moves the pickup assembly quickly back and
forth beneath the spinning disc, reading the
data before it’s reconstituted into Word docu-
ments, video clips, or pictures of humiliated
cats wearing fake antlers on Christmas Eve.