14
TANDBERG
FieldView Administrator Guide
D14098.02 June 2008
Wireless Coverage
Range achievable over the 802.11b/g WLAN interface can vary from hundreds
of meters under near ideal conditions down to much shorter distances under
challenging conditions. Coverage area can vary dramatically depending on a
variety of factors, including:
Topography
•
Walls, dividers, windows, ceilings, floors, etc.
•
Radio-reflective materials (may cause attenuation and/or multi-path
•
reflections)
Interference and noise
•
Access point and antenna mounting location
•
Antenna type and orientation
•
TANDBERG FieldView Device orientation
•
Network traffic
•
Number of connected devices
•
Effect of Topography on Coverage
Fig. 3-2 shows an aerial view of a simple floor plan with a single access point
(denoted as AP). The dark blue shaded area indicates the coverage pattern
that the access point provides for this site. The building’s walls and dividers act
as attenuators for the signal, shaping the coverage pattern as shown.
Signal to Noise Ratio
Achievable range is directly related to the quality of the signal received by
the TANDBERG FieldView Device. The quality is a factor of the radio signal
strength, which is affected by attenuators such as the topographic features
listed above and the air itself, and the interference and noise level.
As the noise level approaches the level of the desired received signal, the
quality will suffer. To increase usable range, noise must be kept to a minimum
and signal strength must be used to overcome the remaining noise level (there
is always some level of background noise). The usual measure of signal quality
is Signal-to–Noise Ratio (SNR) which is illustrated in Fig. 3-3 with a simplified
signal.
The TANDBERG FieldView Device provides received signal strength and
SNR information that can be used to assist with range determination and
troubleshoot problems. A more rigorous method of ensuring proper coverage
across a facility is done using a site survey, as discussed in the section
Site
Survey
.
Other Factors Affecting Coverage
Range further depends on the configuration of the video and audio settings. In
general, higher bit rate settings will lower the range achieved before noticeable
artifacts occur.
In practice, range will vary widely with the factors discussed. The TANDBERG
FieldView Device has been tested and found to work satisfactorily at a distance
of over 200 meters with a 1 Mbps video stream under near-ideal conditions
(outdoors, line of sight, no obstructions, access point mounted at 8 feet, no
nearby 2.4 GHz interference sources). At the other extreme, combinations of
interference and topographic factors can limit range to a fraction of the ideal.
Coverage problems can usually be resolved by assuring proper access point
placement and/or adding additional access points.
Fig. 3-2 Wireless Coverage Map (Aerial
View).
Fig. 3-3 Signal to Noise Ratio (SNR).
Fig. 3-4 Wireless Cell Layout.
Chapter 3
