is an upcoming
amendment to the IEEE
802.11-2007 wireless networking
standard to significantly improve network throughput over previous
standards, such as 802.11b
and 802.11g,
with a significant increase in the maximum raw, OSI
physical layer (PHY)
data rate from 54 Mbit/s to a maximum of 600 Mbit/s. The current state
of the art supports a PHY rate of 450 Mbit/s, with the use of 3 spatial
streams at a channel width of 40 MHz.[1]
Depending on the environment, this may translate into a user throughput
(TCP/IP) of 110 Mbit/s.
The 802.11n task group has completed their work
and the amendment is expected to be approved by IEEE-SA RevCom
in September 2009,[2]
followed by publication in November.
IEEE 802.11n builds on previous
802.11 standards
by adding multiple-input
multiple-output (MIMO) and 40 MHz operation to the physical
(PHY) layer, and frame aggregation to the
MAC layer.
MIMO uses multiple transmitter and receiver
antennas to improve the
system performance. MIMO is a technology which uses multiple antennas
to coherently resolve more information than possible using a single
antenna. Two important benefits it provides to 802.11n are antenna
diversity and spatial multiplexing.
MIMO technology relies on multipath signals.
Multipath signals are
the reflected signals arriving at the receiver some time after the line
of sight (LOS) signal transmission has been received. In a non-MIMO
based 802.11a/b/g network, multipath signals were perceived as
interference degrading a receiver's ability to recover the message
information in the signal. MIMO uses the multipath signal's diversity
to increase a receiver's ability to recover the message information
from the signal.
Another ability MIMO technology provides is
Spatial Division
Multiplexing (SDM). SDM spatially multiplexes multiple independent data
streams, transferred simultaneously within one spectral channel of
bandwidth. MIMO SDM can significantly increase data throughput as the
number of resolved spatial data streams is increased. Each spatial
stream requires a discrete antenna at both the transmitter and the
receiver. In addition, MIMO technology requires a separate radio
frequency chain and analog-to-digital converter for each MIMO antenna
which translates to higher implementation costs compared to non-MIMO
systems.
40 MHz channels is another feature incorporated
into 802.11n
which
uses doubles the 20 MHz channel width from 20Mhz in previous 802.11
PHYs to transmit data. This allows for a doubling of the PHY data rate
over a single 20 MHz channel. It can be enabled in the 5 GHz mode, or
within the 2.4 GHz if there is knowledge that it will not interfere
with any other 802.11 or non-802.11 (such as Bluetooth) system using
those same frequencies.[3]
References:
- ^ a
Intel Ultimate N Wifi Link 5300 Product Brief
(PDF)
- ^
http://www.pcmag.com/article2/0,2817,2350483,00.asp
- ^
https://mentor.ieee.org/802.11/dcn/09/11-09-0576-03-000n-sp2-40mhz-coexistence-cids-presentation.ppt
source - IEEE
802.11n. (2009, August 11). In Wikipedia, The Free Encyclopedia.
Retrieved August 15, 2009, from http://en.wikipedia.org/wiki/802.11n