Watchguard Firebox X15, User Manual

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226 WatchGuard Firebox X Edge
The signal attenuation caused by multi-path reflections is the result
of how you adjust the antenna. When the receiver is moved
½ wavelength, the signal strength changes by as much as 30 dB. To
adjust for this problem, the Firebox X Edge Wireless uses “antenna
receiver diversity.” In this system, the effect of multi-path fading is
decreased through the use of two antennas that are spaced other
than ½ wavelength apart. The Firebox X Edge Wireless automatically
selects the antenna that receives the stronger signal.
Laptop computers usually have one antenna and have signal loss
because of antenna position. Because of this, the Firebox X Edge
can receive signals from the laptop while the laptop does not receive
signals from the Edge.
Channel bandwidth
Channel bandwidth changes when you use different modulations.
Devices compliant with the 802.11b standard use the CCK (11 Mbps,
5.5 Mbps), DQPSK (2 Mbps), and DBPSK (1 Mbps) modulation
schemes. 802.11g devices use OFDM. The Firebox X Edge automati-
cally selects the modulation procedure that gives the lowest Packet
Error Rate (PER). The PER is not allowed to be more than eight per-