Cisco Cisco Catalyst 6500 6000 Series Services Maintenance Partition 白皮書
Wireless LAN Design Guide for High Density
Client Environments in Higher Education
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• H = height of the antenna
• A = downtilt angle
• BW = the 3 dB horizontal beamwidth of the antenna
By adjusting the downtilt of the antenna, it is possible to “dial in” ― or add WLAN coverage― to specific areas within the coverage
zone. APs and RF energy operate much like light cast by lighting fixtures. It is possible to light an entire warehouse with a bare
bulb on the ceiling, but the result is low levels of light in some areas. But if there are multiple fixtures, including some with
higher patterns of luminosity to illuminate larger, the result is comprehensive overall lighting. RF is invisible, so measuring the
coverage and adjusting it appropriately requires tools to measure the coverage. For each antenna placement, simply walking
the area below it and adjusting the antenna to change the pattern based on Received Strength Signal Indication (RSSI) levels to
match coverage requirements is generally all that is required at the initial installation. Antennas hear the same as they transmit.
If measuring and adjusting are done carefully, using consistent measurements and tools, good results can be achieved. Any
additional tuning can be managed with power threshold adjustments through RRM. In all cases, a full site survey to compare the
results to the plan is required once all assets are installed.
• A = downtilt angle
• BW = the 3 dB horizontal beamwidth of the antenna
By adjusting the downtilt of the antenna, it is possible to “dial in” ― or add WLAN coverage― to specific areas within the coverage
zone. APs and RF energy operate much like light cast by lighting fixtures. It is possible to light an entire warehouse with a bare
bulb on the ceiling, but the result is low levels of light in some areas. But if there are multiple fixtures, including some with
higher patterns of luminosity to illuminate larger, the result is comprehensive overall lighting. RF is invisible, so measuring the
coverage and adjusting it appropriately requires tools to measure the coverage. For each antenna placement, simply walking
the area below it and adjusting the antenna to change the pattern based on Received Strength Signal Indication (RSSI) levels to
match coverage requirements is generally all that is required at the initial installation. Antennas hear the same as they transmit.
If measuring and adjusting are done carefully, using consistent measurements and tools, good results can be achieved. Any
additional tuning can be managed with power threshold adjustments through RRM. In all cases, a full site survey to compare the
results to the plan is required once all assets are installed.
Directionality in an antenna increases the overall gain and resulting power that will be delivered. Modest gains (4-8 dBi) can be
easily managed by RRM. Some situations, however, require higher gain antennas (10-13- 17 dBi) to achieve a desired coverage
area pattern. It is important to pay attention to the effective isotropic radiated power (EIRP) as this will rise with the antenna gain.
Physically attenuating the transmission line using good quality RF attenuators rated for the spectrum and power may be required.
With TX power set to its minimum (-1 dBm), a 13 dBi antenna will have an EIRP of 12 dBm. If a WLAN design calls for a transmit
power of 4-5 dBm, then a 10 dB attenuator will be needed to put the EIRP back in the tunable range of the AP’s transmit power.
Attenuators will reduce the overall signal level that is on transmit and receive and will thereby reduce the received power of the
clients at the AP. This is not a problem since the approach is to compensate for higher antenna gain.
easily managed by RRM. Some situations, however, require higher gain antennas (10-13- 17 dBi) to achieve a desired coverage
area pattern. It is important to pay attention to the effective isotropic radiated power (EIRP) as this will rise with the antenna gain.
Physically attenuating the transmission line using good quality RF attenuators rated for the spectrum and power may be required.
With TX power set to its minimum (-1 dBm), a 13 dBi antenna will have an EIRP of 12 dBm. If a WLAN design calls for a transmit
power of 4-5 dBm, then a 10 dB attenuator will be needed to put the EIRP back in the tunable range of the AP’s transmit power.
Attenuators will reduce the overall signal level that is on transmit and receive and will thereby reduce the received power of the
clients at the AP. This is not a problem since the approach is to compensate for higher antenna gain.