Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
C H A P T E R
9-1
Enterprise Mobility 4.1 Design Guide
OL-14435-01
9
VoWLAN Design Recommendations
This chapter provides additional design considerations when deploying voice over WLAN (VoWLAN)
solutions. WLAN configuration specifics may vary depending on the VoWLAN devices being used and
the WLAN design. This chapter provides more details about key RF and site survey considerations that
are generally applicable to VoWLAN deployments, which were introduced in
solutions. WLAN configuration specifics may vary depending on the VoWLAN devices being used and
the WLAN design. This chapter provides more details about key RF and site survey considerations that
are generally applicable to VoWLAN deployments, which were introduced in
Antenna Considerations
The more demanding network requirements of VoWLAN impacts WLAN planning at all levels, down to
the choice of antenna. Key antenna considerations are as follows:
the choice of antenna. Key antenna considerations are as follows:
•
Access point (AP) antenna selection
•
Antenna placement
•
Handset antenna characteristics
AP Antenna Selection
Cisco recommends a diversity ceiling-mount antenna for voice applications. Ceiling mounted antennas
offer a quick and easy installation. More importantly, they place the radiating portion of the antenna in
open space, which allows the most efficient signal propagation and reception. Cisco recommends that
all antennas be placed 1 to 2 wavelengths from highly reflective surfaces such as metal. The 2.4 GHz
wave is 4.92 inches (12.5 cm) and the 5 GHz is 2.36 inches (6 cm). The separation of one or more
wavelengths between the antenna and reflective surfaces allows the AP radio a better opportunity to
receive a transmission, and reduces the creation of nulls when the radio transmits. Orthogonal
frequency-division multiplexing (OFDM) used by 11g and 11a helps to mitigate problems with
reflections, nulls, and multipath; however, good antenna placement and the use of appropriate antenna
types provide a superior solution. The ceiling tile itself is a good absorber of signals transmitted into the
area above the ceiling and reflected back into the coverage area.
offer a quick and easy installation. More importantly, they place the radiating portion of the antenna in
open space, which allows the most efficient signal propagation and reception. Cisco recommends that
all antennas be placed 1 to 2 wavelengths from highly reflective surfaces such as metal. The 2.4 GHz
wave is 4.92 inches (12.5 cm) and the 5 GHz is 2.36 inches (6 cm). The separation of one or more
wavelengths between the antenna and reflective surfaces allows the AP radio a better opportunity to
receive a transmission, and reduces the creation of nulls when the radio transmits. Orthogonal
frequency-division multiplexing (OFDM) used by 11g and 11a helps to mitigate problems with
reflections, nulls, and multipath; however, good antenna placement and the use of appropriate antenna
types provide a superior solution. The ceiling tile itself is a good absorber of signals transmitted into the
area above the ceiling and reflected back into the coverage area.
Antennas come in many types and form factors; no single type or module of antenna is best for all
applications and locations. For additional information on the performance of various antenna types, and
the part numbers of Cisco Aironet antennas, see the Cisco Aironet antenna guide at the following URL:
applications and locations. For additional information on the performance of various antenna types, and
the part numbers of Cisco Aironet antennas, see the Cisco Aironet antenna guide at the following URL: