Cisco 10-ft Low Loss Cable AIR-CAB010LL-N= Manual De Usuario
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AIR-CAB010LL-N=
Reference Guide
© 2009 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
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Figure 4. Multipath Distortion
You can relate this to a common occurrence in your car. As you pull up to a stop, you may notice
static on the radio. But as you move forward a few inches or feet, the station starts to come in
more clearly. By rolling forward, you move the antenna slightly, out of the point where the multiple
signals converge.
A diversity antenna system can be compared to a switch that selects one antenna or another,
never both at the same time. The radio in receive mode will continually switch between antennas
listening for a valid radio packet. After the beginning sync of a valid packet is heard, the radio will
evaluate the sync signal of the packet on one antenna, then switch to the other antenna and
evaluate. Then the radio will select the best antenna and use only that antenna for the remaining
portion of that packet.
On transmit, the radio will select the same antenna it used the last time it communicated to
that given radio. If a packet fails, it will switch to the other antenna and retry the packet.
One caution with diversity, it is not designed for using two antennas covering two different
coverage cells. The problem in using it this way is that, if antenna no. 1 is communicating to device
no. 1 while device no. 2 (which is in the antenna no. 2 cell) tries to communicate, antenna no. 2 is
not connected (due to the position of the switch), and the communication fails. Diversity antennas
should cover the same area from only a slightly different location.
With the introduction of the latest DS physical layer chips, and the use of diversity antenna
systems, DS systems have equaled or surpassed FH in handling multipath interference. While the
introduction of WBFH does increase the bandwidth of FH systems, it drastically affects the ability
to handle multipath issues, further reducing its range compared to present DS systems in high RF
reflective sites.
Wireless LAN Design
Before the physical environment is examined, it is critical to identify the mobility of the application,
the means for coverage, and system redundancy. An application such as point-to-point, which
connects two or more stationary users, may be best served by a directional antenna, while mobile
users will generally require a number of omnidirectional micro cells. These individual micro cells
can be linked together through the wired LAN infrastructure or by using the wireless repeater
functionality built into every Cisco Aironet Access Point. All Cisco Aironet Wireless LAN products
are designed to support complex multicell environments transparently through the patented Cisco
MicroCellular Architecture.