Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
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Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 3 WLAN Radio Frequency Design Considerations
Radio Resource Management (Auto-RF)
Dynamic Transmit Power Control
Appropriate AP power levels are essential to maintaining a coverage area, not only to ensure correct (not
maximum) amount of power covering an area, but also to ensure that excessive power is not used, which
would add unnecessary interference to the radiating area. AP power settings are also used to control
network redundancy by helping to ensure real-time failover in the event of the loss of an AP. The WLC
is used to dynamically control the AP transmit power level based on real-time WLAN conditions. In
normal instances, power can be minimized to gain extra capacity and reduce interference among the APs.
RRM attempts to balance APs so that they see their neighbors at -65 dBm. If an AP outage is detected,
power can be automatically increased on surrounding APs to fill the coverage gap created by the loss of
the AP.
maximum) amount of power covering an area, but also to ensure that excessive power is not used, which
would add unnecessary interference to the radiating area. AP power settings are also used to control
network redundancy by helping to ensure real-time failover in the event of the loss of an AP. The WLC
is used to dynamically control the AP transmit power level based on real-time WLAN conditions. In
normal instances, power can be minimized to gain extra capacity and reduce interference among the APs.
RRM attempts to balance APs so that they see their neighbors at -65 dBm. If an AP outage is detected,
power can be automatically increased on surrounding APs to fill the coverage gap created by the loss of
the AP.
RRM algorithms are designed to create the optimal user experience. For example, if the power of an AP
is turned down to Level 4 (where Level 1 = highest and Level 8 = lowest) and the received signal strength
indicator (RSSI) value of a user drops below an acceptable threshold, the AP power is increased to
provide a better experience to that client. When Dynamic Transmit Power Control (DTPC) is enabled,
the access points add channel and transmit power information to beacons. Client devices using DTPC
receive the information and adjust their settings automatically.
is turned down to Level 4 (where Level 1 = highest and Level 8 = lowest) and the received signal strength
indicator (RSSI) value of a user drops below an acceptable threshold, the AP power is increased to
provide a better experience to that client. When Dynamic Transmit Power Control (DTPC) is enabled,
the access points add channel and transmit power information to beacons. Client devices using DTPC
receive the information and adjust their settings automatically.
Coverage Hole Detection and Correction
The coverage hole detection and correction algorithm is aimed at determining coverage holes based on
the quality of client signal levels and then increasing the transmit power of the APs to which those clients
are associated.
the quality of client signal levels and then increasing the transmit power of the APs to which those clients
are associated.
The algorithm determines whether a coverage hole exists when client SNR levels pass below a given
SNR threshold. The SNR threshold is considered on an individual AP basis and based primarily on the
transmit power of each AP.
SNR threshold. The SNR threshold is considered on an individual AP basis and based primarily on the
transmit power of each AP.
When the average SNR of a single client dips below the SNR threshold for at least 60 seconds, this is
seen as an indication that the WLAN client does not have a viable location to which to roam. The AP
transmit power of that client is increased, correcting the coverage hole.
seen as an indication that the WLAN client does not have a viable location to which to roam. The AP
transmit power of that client is increased, correcting the coverage hole.
Client and Network Load Balancing
The IEEE 802.11 standard does not define the process or reasons for client roaming, and therefore it
cannot be easily predicted what clients will do in any given situation. For example, all users in a
conference room can associate with a single AP because of its close proximity, ignoring other APs that
are farther away but with greater free capacity.
cannot be easily predicted what clients will do in any given situation. For example, all users in a
conference room can associate with a single AP because of its close proximity, ignoring other APs that
are farther away but with greater free capacity.
The WLC has a centralized view of client distribution across all APs. This can be used to influence where
new clients attach to the network if there are multiple “good” APs available. If configured, the WLC can
proactively use AP probe responses to guide clients to the most appropriate APs to improve WLAN
performance. This results in a smooth distribution of capacity across an entire wireless network. Keep in
mind that this load balancing is done at client association, not while a client is connected.
new clients attach to the network if there are multiple “good” APs available. If configured, the WLC can
proactively use AP probe responses to guide clients to the most appropriate APs to improve WLAN
performance. This results in a smooth distribution of capacity across an entire wireless network. Keep in
mind that this load balancing is done at client association, not while a client is connected.