Aerohive Networks Aerohive AP141, Hardware Reference Manual

Page: 73 / 111

Chapter 7 The AP340 Platform
72 Aerohive
Figure 5 Directional antenna patterns
Omnidirectional Antennas
You typically orient omnidirectional antennas vertically, positioning them on all devices in the same
direction. Omnidirectional antennas create coverage areas that can be toroidal (doughnut-shaped) or
cardioid (heart- or plum-shaped), broadcasting to the sides much more effectively than up or down (see
Figure 6 ). In general, this is good for most office environments because you have large flat floors. However, it
can be a problem in environments with high ceilings.
Figure 6 Omnidirectional antenna radiation patterns
MIMO
MIMO (Multiple In, Multiple Out) is a major WLAN advancement introduced in the IEEE 802.11n standard in
which multiple RF links are formed on the same channel between the transmitter and receiver
simultaneously. To accomplish this, the transmitter separates a single data stream into multiple spatial
streams, one for each RF chain (an a various digital signal processing modules linked to the
antenna). The transmit antennas at the end of each RF chain then transmit their spatial streams. The
recipient’s receive antennas obtain streams from all the transmit antennas. In fact, due to multipath, they
receive multiple streams from each transmit antenna. The receive antennas pass the spatial streams to the
digital signal processors in their RF chains, which take the best data from all the spatial streams and
reassemble them into a single data stream once again (see Figure 7 on page 73 ).
Higher gain
Lower gain
(Bird’s eye view)
Patch
antennas
Higher gain
Toroidal pattern Cardioid pattern