Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
3-25
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 3 WLAN Radio Frequency Design Considerations
Manually Fine-Tuning WLAN Coverage
Manually Fine-Tuning WLAN Coverage
A number of factors can affect the WLAN coverage, as follows:
•
Channel and data rate selection
•
Overlapping WLAN coverage for location management, voice, or data-only
•
Power level
•
Antenna choice (omni-directional, or directional antenna)
For a given data rate and location, the WLAN designer may alter power levels and/or elect to use a
different antenna, to effect changes to the coverage area and/or coverage shape. Altering power levels
or channel selection can be done manually as described below, or the Cisco Wireless Controller can do
this automatically via the Radio Resource Management (RRM) algorithms, also referred to as Auto-RF.
Cisco recommends the use of Radio Resource Management (RRM) to control the power level and
channel, keeping in mind that the channel changing algorithm is highly dampened so that only a very
disruptive (and persistent) interference source would cause a change to the channel topology, which in
turn would cause clients to reassociate and any voice calls to be dropped. Changes in AP power do not
impact clients. (See
different antenna, to effect changes to the coverage area and/or coverage shape. Altering power levels
or channel selection can be done manually as described below, or the Cisco Wireless Controller can do
this automatically via the Radio Resource Management (RRM) algorithms, also referred to as Auto-RF.
Cisco recommends the use of Radio Resource Management (RRM) to control the power level and
channel, keeping in mind that the channel changing algorithm is highly dampened so that only a very
disruptive (and persistent) interference source would cause a change to the channel topology, which in
turn would cause clients to reassociate and any voice calls to be dropped. Changes in AP power do not
impact clients. (See
for more details).
Channel and Data Rate Selection
Channel selection depends on the frequencies that are permitted for a particular region. For example, the
North American and ETSI 2.4 GHz channel sets permit allocation of three nonoverlapping channels: 1,
6, and 11 while the 5 GHz channel set permits 23 channels.
North American and ETSI 2.4 GHz channel sets permit allocation of three nonoverlapping channels: 1,
6, and 11 while the 5 GHz channel set permits 23 channels.
The channels should be allocated to the coverage cells as follows:
•
Overlapping cells should use nonoverlapping channels.
•
Where channels must be re-used in multiple cells, those cells should have minimal overlap with each
other.
other.
shows this pattern. In 802.11a deployments, adjacent channels should be avoided
as overlapping cells.
Recommendations for Channel Selection
Channel selection can be done manually, as described below.