OPEN COMMUNICATION
■ FIGURE 2. This is the SiBEAM
WirelessHD module operating at
60 GHz. Note the phased array
antenna on the right. The main beam
uses 36 elements and the other
16 are for return path
communications
and spares.
original fast data stream. With
MIMO, you can really get very high
speeds in limited bandwidth.
At one time, the cost of multiple
transmitters, receivers, and antennas
was prohibitive. Today, the IC
companies put these all on one low
cost chip. For example, one vendor
puts 4 x 4 MIMO on a single
802.11n Wi-Fi chip that can achieve
a data rate of 600 Mbps in a 20
MHz channel. That is excellent. The
technique can extend that speed to
beyond 1 Gbps.
This is the technique used by
chip maker Amimon. The Amimon
chips operate in the unlicensed
spectrum around 5. 8 GHz. That is
the same band used by 802.11a
Wi-Fi. They combine OFDM and a
4 x 5 MIMO (four transmitters and
five receivers and antennas) to
achieve a data rate as high as 3 Gbps
in a 40 MHz channel — more than
enough for uncompressed HD
video. This technique is now a video
transmission standard called Wireless
Home Digital Interface (WHDI).
You can find out more about it at
www.whdi.org or www.amimon.
com. WHDI is already being built
into TV sets, set top boxes, and other
devices line PCs, dongles, and video
games. Look for more in the future as
your home entertainment system
connections go wireless.
Another wireless technology
has emerged to also address the
uncompressed video transmission
problem. It too has become a
standard called WirelessHD. Check
out www.wirelesshd.org for more
details. The first chips were made by
SiBEAM. This technology uses the
unlicensed mm wave band around
60 GHz. With a bandwidth of 7 GHz
to play with, it is relatively easy to
get data rates to well into the gigabit
region. The standard calls for the
use of OFDM and a wide bandwidth
to get data rates to 4 Gbps.
Uncompressed video is a snap. But,
there are issues.
First, the range of a 60 GHz
signal is usually short. In this
application, the range is about 10
meters or a little over 30 feet. That
is typical for video links at home.
The big aggravation at mm wave
frequencies is the reflections that
cause multipath signals that can
interfere with one another and cause
fading. Multipath is the bane of
microwave and mm waves.
Furthermore, mm wave signals do
not pass through objects very well
like lower frequencies do. So, if
your dog should walk between the
transmitter and receiver you will
momentarily block the signal.
Millimeter waves are more like light
waves that are easily blocked as with
your TV infrared (IR) remote control.
SiBEAM has solved this problem
by integrating a phased array antenna
on the chip to implement very
narrow beams of signal and
automatic beam pointing to alleviate
the multipath problem. At 60 GHz,
your typical dipole antenna is only
about 1/16th of an inch long so it is
easy to place several make many on
a single chip. What they did is put a
36 antenna array that automatically
adjusts its directionality to maintain a
radio link under multipath reflections
or beam interruptions. A side benefit
of the phased array is that it is a real
power multiplier.
Focusing a radio wave beam with
an antenna gives the same effect as
raising transmitter power. We call
that effective radiated power (ERP).
A 100 m W signal can be made to
act like a one watt or 10 watt signal
giving greater transmission range and
reliability.
Another effort to achieve above
1 Gbps data rates over wireless is
that of the WiGig Alliance, an
organization devoted to achieving a
worldwide standard for high speed
wireless data in the 60 GHz band.
The IEEE’s continuing efforts with
Wi-Fi may soon produce the
802.11ad standard that is expected
to provide 1 Gbps+ data rates to
extend the Wi-Fi speed limit. Maybe
we don’t generally need that speed
for most operations but we are going
to get it anyway. Isn’t that just the
way of electronics? NV
August 2009 87
