About Ieee 802.11G/B Wireless; Noise Level - Watchguard Firebox X15 User Manual

About IEEE 802.11g/b Wireless

In general, RF power and signal bandwidth create a maximum limit
on the rate that data can be sent on a wireless connection. The
equation below calculates the maximum data rate:
ChannelCapacity
This equation shows that the channel capacity (bits/s) is set by:
• Channel bandwidth: 11 Mbits/s for 802.11b and 54 MBits/s for
802.11g
• Signal strength: 15 dBm transmitted by the Firebox X Edge
Wireless
• Noise level: Set by the environmental conditions and the design
of the receiver.
The maximum data rate cannot be more than the channel capacity.

Noise level

Channel capacity is decreased by increasing the noise level in the
frequency range of the system. The noise level is set by many fac-
tors. First, it is affected by background noise caused by the ambient
temperature of the atmosphere at the frequency range of the sys-
tem. Also, the operating temperature of the components of the
802.11 g/b receiver creates noise. The primary cause of interference
is transmitters that use the same frequency range:
• Cordless phones
• An 802.11b device set to use adjacent channels. We recommend
that you set three channels between each adjacent wireless
access points (e.g. 1, 5, and 9 or 2, 6, and 10).
• Microwave ovens
• Sodium-type lighting systems (fusion lamps)
• Arc welders (broadband spark-gap transmitters)
• Blue-Tooth transmitters (A Blue-Tooth transmitter operates at a
lower power level than an 802.11b device. To cause
interference, the Blue-Tooth transmitter must be very near to an
802.11b receiver.)
• Industrial, scientific, and medical equipment that can also
operate in this frequency range.
224
= ChannelBandwidth
⎛
1 + SignalStrength
×
---------------------------------------------------------------------- -
log
⎝
2
NoiseLevel
WatchGuard Firebox X Edge
⎞
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