Multipath - Cisco 9971 Deployment Manual

Transmit Power
Due to the potential of elevated multipath in rugged environments, the transmit power of the access point and Cisco Unified
IP Phone 9971 should also be restricted. This is more important if planning to deploy 2.4 GHz in a rugged environment.
If using auto transmit power, the access point transmit power can be configured to use a specified range (maximum and
minimum power levels) to prevent the access point from transmitting too hot as well as too weak (e.g. 5 GHz maximum of
16 dBm and minimum of 11 dBm).
The Cisco Unified IP Phone 9971 will utilize the access point's current transmit power setting to determine what transmit
power it uses for transmitted frames when DTPC is enabled in the access point's configuration.
Fast Roaming
It is recommended to utilize CCKM for fast roaming. Enabling CCKM also reduces the number of frames in the handshake
when roaming to only two frames. Reducing the number of frames during a roam, increases the chances of roam success.
When using 802.1x authentication, it is important to use the recommended EAPOL key settings. See the WLAN
Controller Advanced EAP Settings section in Configuring the Cisco Unified Wireless LAN Controller and Access
Points for more information.
Quality of Service (QoS)
Need to ensure that DSCP values are preserved throughout the wired network, so that Cisco Unified Wireless LAN
Controller and access points can set the WMM UP tag for voice and call control frames correctly.
Beamforming
If using Cisco 802.11n access points, then Beamforming (ClientLink) should be enabled, which can help with client
reception.
See the Beamforming (ClientLink) section in Configuring the Cisco Unified Wireless LAN Controller and Access
Points for more information.

Multipath

Multipath occurs when RF signals take multiple paths from a source to a destination.
A part of the signal goes to the destination while another part bounces off an obstruction, then goes on to the destination. As a
result, part of the signal encounters delay and travels a longer path to the destination, which creates signal energy loss.
When the different waveforms combine, they cause distortion and affect the decoding capability of the receiver, as the signal
quality is poor.
Multipath can exist in environments where there are reflective surfaces (e.g. metal, glass, etc.). Avoid mounting access points
on these surfaces.
Below is a list of multipath effects:
Data Corruption
Occurs when multipath is so severe that the receiver is unable to detect the transmitted information.
Signal Nulling
Occurs when the reflected waves arrive exactly out of phase with the main signal and cancel the main signal completely.
Increased Signal Amplitude
Occurs when the reflected waves arrive in phase with the main signal and add on to the main signal thereby increasing the
signal strength.
Decreased Signal Amplitude
Occurs when the reflected waves arrive out of phase to some extent with the main signal thereby reducing the signal
amplitude.
Cisco Unified IP Phone 9971 Wireless LAN Deployment Guide
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