User's Manual

hwc_apstartup.fm
Configuring the Wireless AP
Wireless AP overview
A31003-W1050-U100-2-7619,
March 2008
HiPath Wireless Controller, Access Points and Convergence Software V5 R1 , C20/C2400 User Guide 63
Note: MIMO should not be confused with the Diversity feature. While Diversity
is the use of two antennas to increase the odds that a better radio stream is
received on either of the antennas, MIMO antennas radiate and receive multi-
streams of the same packet to achieve the increased throughput.
The Diversity feature is meant to offset the liability of RF corruption, arising out
of multipath, whereas MIMO converts the liability of multipath to its advantage.
Because the 802.11n AP operates with multiple-antennas, it is capable of picking-
up even the weakest signals from the client devices.
Channel bonding
In addition to MIMO technology, the 802.11n AP makes a number of additional
changes to the radio to increase the effective throughput of the Wireless LAN.
The radios of regular HiPath Wireless APs use radio channel that are 20 MHz
wide. This means that the channels must be spaced at 20 MHz to avoid
interference. The radios of 802.11n AP can use two channels at the same time to
creat a 40 MHz wide channel. By using the two 20 MHz channels in this manner,
the 802.11n AP achieves more than double throughput. The 40-MHz channels in
802.11n are two adjacent 20-MHz channels, bonded together. This technique of
using two channels at the same time is called channel bonding.
Shortened guard interval
The purpose of the guard interval is to introduce immunity to propagation delays,
echoes and reflections of symbols in orthogonal frequency division multiplexing
(OFDM) — a method by which information is transmitted via a radio signal in
Wireless APs.
In OFDM method, the begining of each symbol is preceded by a guard interval.
As long as the echoes fall within this interval, they will not affect the safe decoding
of the actual data, as data is only interpreted outside the guard interval. Longer
guard periods reduce the channel efficiency. The 802.11n AP provides reduced
guard periods, thereby increasing the throughput.
MAC enhancements
The 802.11n AP also has an improved MAC layer protocol that reduces the
overheads (in the MAC layer protocol) and the contention losses. This results in
increased throughput.
The 802.11n AP is available in the following two models:
• Model AP3610 – Six internal antennas