Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
3-11
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 3 WLAN Radio Frequency Design Considerations
Planning for RF Deployment
Effective Isotropic Radiated Power
Although transmitted power based on the radio setting is rated in either dBm or milliwatts, the maximum
energy density coming from an antenna from a complete system is measured as effective isotropic
radiated power (EIRP), which is a summation of the dB values of the various components. EIRP is the
value that regulatory agencies, such as the FCC or ETSI, use to determine and measure power limits,
expressed in terms of maximum energy density within the first Fresnel of the radiating antenna. EIRP is
calculated by adding the transmitter power (in dBm) to antenna gain (in dBi) and subtracting any cable
losses (in dB). For example, if you have a Cisco Aironet bridge connected to a solid dish antenna by a
50 foot length of coaxial cable, plugging in the numbers gives the following:
energy density coming from an antenna from a complete system is measured as effective isotropic
radiated power (EIRP), which is a summation of the dB values of the various components. EIRP is the
value that regulatory agencies, such as the FCC or ETSI, use to determine and measure power limits,
expressed in terms of maximum energy density within the first Fresnel of the radiating antenna. EIRP is
calculated by adding the transmitter power (in dBm) to antenna gain (in dBi) and subtracting any cable
losses (in dB). For example, if you have a Cisco Aironet bridge connected to a solid dish antenna by a
50 foot length of coaxial cable, plugging in the numbers gives the following:
•
Bridge—20 dBm
•
50 Foot Cable—3.3 dBm (negative because of cable loss)
•
Dish Antenna—21 dBi
•
EIRP—37.7dBm
For more information, see the following URL:
Planning for RF Deployment
Many of the RF-design considerations are interdependent or implementation-dependent. As a result,
there is no “one-size-fits-all” template for the majority of requirements and environments.
there is no “one-size-fits-all” template for the majority of requirements and environments.
Cisco Wireless Control System (WCS) provides integrated RF prediction tools that can be used to create
a detailed wireless LAN design, including LWAPP AP placement, configuration, and
performance/coverage estimates. IT staff can import real floor plans into Cisco WCS and assign RF
characteristics to various building components to increase design accuracy.
a detailed wireless LAN design, including LWAPP AP placement, configuration, and
performance/coverage estimates. IT staff can import real floor plans into Cisco WCS and assign RF
characteristics to various building components to increase design accuracy.
Graphical heat maps help IT staff visualize anticipated wireless LAN behavior for easier planning and
faster rollout. WCS also supports irregular shaped buildings by offering drawing tools to help
organizations easily design and support WLAN deployments in such buildings.
faster rollout. WCS also supports irregular shaped buildings by offering drawing tools to help
organizations easily design and support WLAN deployments in such buildings.
shows an
example of the planning tool.