User Manual

16 Introduction to the Extricom Wireless LAN System
Brief Overview of 802.11n
The following section describes at a high level the main features and terms of 802.11n. It also
outlines which features of the standard are supported by Extricom products at this time. This section
is provided to give customers using Extricom's 802.11n products an overview of 802.11n
technology, and to help them understand what parameters need to be to configured on the Extricom
switch in order to support 802.11n.
802.11n is a member of the 802.11 family of standards; it can function in both the 2.4 GHz and
5GHz bands using OFDM transmission (as with 802.11a and 802.11g). The emphasis in 802.11n
design was mainly on increasing bandwidth, range and performance of the 802.11 protocol itself.
This was largely achieved by using multiple transmitters/receivers (MIMO) and enhancements to
the OFDM PHY and 802.11 MAC layers.
MIMO
Definition: 802.11a/b/g devices used SISO architecture (single input, single output) for transmitter
and receiver paths. 802.11n uses MIMO (Multiple inputs / multiple outputs) architecture. That is,
multiple transmitter and multiple receiver antennas (NxM) are used to support multiple,
simultaneous data streams.
Extricom 802.11n: Extricom Access Points are equipped with three receivers and three
transmitters, so as to make 3x3 MIMO possible. Initially, however, the firmware in the radio chipset
will operate in a 3x2 MIMO configuration. This will be firmware upgradeable when the chipset
manufacturer makes this enhancement available.
Data Streams
Definition: Spatial multiplexing divides data into multiple streams and sends it simultaneously over
multiple paths using the multiple transmitters (antenna) over the channel. These streams are
recombined by the multiple receivers to get the original data.
Extricom 802.11n: Extricom Access Points support two data streams over the 3x3 transmitter/
receivers.
Channel Bonding
Definition: All earlier versions of 802.11 have used 20 MHz wide channels, defined in the 2.4 GHz
and 5 GHz bands. 802.11n- Draft 2.0 specifies operation in the same 20 MHz channels used by
802.11b/g in the 2.4 GHz and 802.11a in the 5 GHz bands, but adds a mode where a full 40-MHz
wide channel can be used. This offers approximately twice the throughput of a 20-MHz channel.
Extricom 802.11n: Extricom products support 20 and 40MHz channels both in 2.4GHz and 5GHz.
Guard Interval
Definition: In OFDM, inter-symbol interference occurs when the delay between different RF paths
to the receiver exceeds the guard interval, causing a reflection of the previous symbol to interfere
with the strong signal from the current symbol: a form of self-interference. 802.11n allows a shorter
guard interval to increase PHY performance.
Extricom 802.11n: Extricom supports configurable guard interval (400 or 800 ns). However, short
guard interval is only supported with 40MHz channel.