During the initial development of the IEEE 802.11n (11n)
amendment for improving the throughput of wireless LANs, a
lot of excitement existed surrounding the potential higher
throughput (i.e., faster downloads), and increased range (distance)
achievable. However, delays in the development of this
standard (which began in 2003, and is still in the final draft
stages) as well as vendor, customer reluctance to adopt the
pre-11n offerings in the marketplace, have generally slowed
interest in this next-generation technology.
However, there is still much to be excited about. The latest
draft of IEEE 802.11n (Draft 3.0) offers the potential of
throughputs beyond 200 Mbps, based on physical layer
(PHY) data rates up to 600 Mbps. This is achieved through
the use of multiple transmit and receive antennas, referred
to as MIMO (multiple input, multiple output). Using techniques
such as spatial division multiplexing (SDM), transmitter
beamforming, and space-time block coding (STBC), MIMO
is used to increase dramatically throughput over single
antenna systems (by two to four times) or to improve range
of reception, depending on the environment.
This article offers an exposition on the techniques used in
IEEE 802.11n to achieve the above improvements to throughput
and range. First, the current generation WLAN devices
(11a/b/g) are described in terms of the benefits offered to end
users. Next, the evolution of the 11n amendment is discussed,
describing the main proposals given, and illustrating reasons
for the delay in standardization. Then, the changes to the PHY
for 11n are presented. A description of channel modeling with
MIMO is shown, followed by the signal processing techniques
employed, including MIMO channel estimation and detection,
space-time block coding (STBC), and transmitter beamforming.
Simulation results are presented which illustrate the benefits
of these techniques, versus the existing 11a/g structures,
for both throughput and range. Finally, a brief section outlining
considerations for the rapid prototyping of a baseband
design based on the 802.11n PHY is presented. We conclude
with a discussion of the future for 11n, describing the issues
addressed with Drafts 2.0 and 3.0, as well as its place in a
wireless market with WiMAX and Bluetooth.
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