FREE MOBILE CLOUD
COMPUTING CONCEPTS - TRAINING_MODULES_WITH_TONS_OF_VIDEOS
Post by Paul Sanderson with Beverly Hills IT Pros
Corporations are beginning to use wireless LANs
to carry voice and video, increasing the need for speed, capacity and reliability. But because WLANs share a finite allocation
of frequency spectrum, without increased spectral efficiency they will consume all the available frequency channels and interfere
with one another - becoming victims of their own success.
Multiple Input Multiple Output is a smart antenna technique that increases speed, range, reliability and
spectral efficiency for wireless systems. Given the demands that applications are placing on WLANs, MIMO chipsets will figure prominently in new access points and network interface cards.
MIMO
is one technology being considered for 802.11n, a standard
for next-generation 802.11 that boosts throughput to 100M bit/sec. In the meantime, proprietary MIMO technology improves performance
of existing 802.11a/b/g networks.
A
conventional radio uses one antenna to transmit a datastream. A typical smart antenna radio, on the other hand, uses multiple
antennas. This design helps combat distortion and interference. Examples of multiple-antenna techniques include switched antenna
diversity selection, radio-frequency beam forming, digital beam forming and adaptive diversity combining.
These smart antenna techniques are one-dimensional,
whereas MIMO is multi-dimensional. It builds on one-dimensional smart antenna technology by simultaneously transmitting multiple
datastreams through the same channel, which increases wireless capacity.
You can think of conventional radio transmission as
traveling on a one-lane highway. The speed limit governs the maximum allowable flow of traffic through that lane. Compared
with conventional radios, one-dimensional smart antenna systems help move traffic through that lane faster and more reliably
so that it travels at a rate closer to the speed limit. MIMO helps traffic move at the speed limit and opens more lanes. The
rate of traffic flow is multiplied by the number of lanes that are opened.
During the 1990s, Stanford University researchers Greg
Raleigh and VK Jones showed that a characteristic of radio transmission called multipath, which had previously been considered
an impairment to radio transmission, is actually a gift of nature. Multipath occurs when signals sent from a transmitter reflect
off objects in the environment and take multiple paths to the receiver.
The researchers showed that multipath
can be exploited to multiplicatively increase the capacity of a radio system.
mimo flow
tablet-holder
mimo
tablet-holder
If each multipath
route could be treated as a separate channel, it would be as if each route were a separate virtual wire. A channel with multipath
then would be like a bundle of virtual wires.
To exploit the benefits the virtual wires offer, MIMO uses multiple, spatially separated
antennas. MIMO encodes a high-speed datastream across multiple antennas. Each antenna carries a separate, lower-speed stream.
Multipath virtual wires are utilized to send the lower-speed streams simultaneously.
But wireless
is not as well behaved as a bundle of wires. Each signal transmitted in a multipath environment travels multiple routes. This
makes a wireless system act like a bundle of wires with a great deal of leakage between them, causing transmitted signals
to jumble together. The MIMO receiver uses mathematical algorithms to unravel and recover the transmitted signals.
