802.11N Primer - Understanding Spatial Streams - Cisco Aironet 1700 Deployment Manual

Cisco Aironet Series 3700 Access Point
Figure 53 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 55).
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 55. The MCS values correspond to actual data rates.
Cisco Aironet Series 1700/2700/3700 Access Point Deployment Guide
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