Cisco Cisco Aironet 1140 Access Point Libro blanco

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In wireless networks, there are typically many coverage holes near the edges of cells where signal strength is too

low for good Wi-Fi performance. Clients encounter these holes as they roam from cell to cell. By reducing the

number and depth of coverage holes, Cisco ClientLink helps ensure more reliable, predictable, and homogeneous

coverage throughout the floorspace. The performance maps in Figures 4 and 5 demonstrate how the maximum

receive data rate at the client improves from the use of ClientLink technology. In this particular example, the signal

improves by 5 dB and the data rate is increased from 24 Mbps to 36 Mbps. Note that typical indoor enterprise

environments are considered Non-Line-of-Sight (NLOS) environments—meaning that the Wi-Fi signal typically

bounces off one or more objects before reaching its destination. Based on both academic analysis

and empirical

measurements, the expected range of improvement using transmit beamforming with two transmit antennas in an

NLOS environment is from 4 to 6.5 dB.

Figure 4. Initial Coverage Map Without ClientLink

Figure 5. Improved Coverage Map With ClientLink

Deployment Guidelines

The following are some guidelines to consider when deploying systems with Cisco ClientLink technology:

●

Although ClientLink increases the SNR and data rates of clients at the edges of the cell, it does not extend

the maximum range of a cell. This is because certain packets that must be heard by all clients (such as

beacons) are sent as broadcasts, which ClientLink cannot optimize. These broadcast packets effectively

become the limiting factor on the cell size. Therefore cell spacing should not be increased when using

ClientLink. In fact, to be conservative, the ClientLink feature can be turned off during a site survey.

●

Because the absolute size of the cell has not been extended, ClientLink presents no issues with an increased

number of hidden nodes. When a packet is sent via ClientLink to a specific client, although the signal is

improved for that client, the signal heard by all other clients is not in general degraded.

Perahia and Stacey, Cambridge University Press, "Next Generation Wireless LANs", p. 338