802.11N Primer - Understanding Spatial Streams - Cisco Aironet 3700 Series Deployment Manual

Cisco Aironet Series 3700 Access Point
Figure 54 Example of a High Gain Antenna AIR-ANT2480V-N with its Cover Removed
A high gain antenna may have a null or dead spot directly underneath it because the antenna element is
often much longer with less metal surface area available to conduct the radio wave if you are located
directly underneath it. However, the further away you are from the antenna the more surface is available
and so the better it performs.

802.11n Primer - Understanding Spatial Streams

For a video on understanding the fundamentals of Spatial Streams refer to the following URL:
http://www.cisco.com/en/US/netsol/ns767/index.html
MIMO which refers to a radio system that has multiple separate receive and transmit paths, is at the heart
of 802.11n. MIMO systems are described using the number of transmitters and receivers in the system.
For example, "two by one" or 2x1 refers to a system with two transmitters and one receiver (Figure 56).
Spatial streams, the act of transmitting information out of more than one antenna port concurrently,
require that the APs have at least two or more transmitters and support elements of 802.11n, e.g., support
of multiple spatial streams.
In the 802.11a/b/g days, data rates were actual Mbps rates, such as 2, 11, 54 Mbps and so on, and was
done with one transmitter. In the case of the AP 3500 series, it has two transmitters per band so it
supports 802.11n data rates of up to 300 Mbps using two spatial streams.
With 802.11n, the different data rates are called Modulation and Coding Scheme (MCS) index value, and
the value also defines how many streams are used. The AP 3500 supports up to 300 Mbps MCS rate 15
when configured with a bonded channel and short guard interval (GI). Refer to Figure 56. The MCS
values correspond to actual data rates.
Cisco Aironet Series 2700/3700 Access Points Deployment Guide
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