ZyXEL Communications ZyAIR B-5000, Руководство пользователя

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ZyAIR B-5000 User’s Guide
Site Planning
A-4
Co-Channel and Adjacent Channel Interference
Co-channel interference results when another RF link is using the same channel frequency.
Adjacent-channel interference results when another RF link is using an adjacent channel frequency.
A spectrum analyzer can be used to determine if there is any strong signals present at the site and determine
how close they are to the desired frequency. The further away from your proposed frequency, the less likely
they are to cause a problem.
Antenna placement and polarization, is the most effective method of reducing this type of interference.
Antennas
Antennas play a key role in reducing the potential for interference. They come in a variety of
configurations that have different performance characteristics in the areas of gain and direction. Antennas
that transmit/receive in all directions are known as
omni-directional , while those that transmit/receive in
one specific direction are categorized as directional .
Antennas are tuned to operate on a specific group of frequencies. The manufacturer also fixes other specific
attributes such as beam width and gain. Antennas should be selected and placed according to your site and
your application.
In general, the larger the antenna, the higher the gain and the larger the mast required. It is best to use the
smallest antenna that will provide sufficient protection from interference and enough signals at the far end
of the link to provide good reception even with fading.
Antenna Characteristics
Frequency
An antenna in the frequency of 2.4GHz (IEEE 802.11b) or 5GHz(IEEE 802.11a) is needed to
communicate efficiently in a wireless LAN.
Radiation Pattern
A radiation pattern is a diagram that allows you to visualize the shape of the antenna’s coverage
area.
Antenna Gain
Antenna gain, measured in dB (decibel), is the increase in coverage within the RF beam width.
Higher antenna gain improves the range of the signal for better communications.
For an indoor site, each 1 dB increase in antenna gain results in a range increase of approximately
2.5%. For an unobstructed outdoor site, each 1dB increase in gain results in a range increase of
approximately 5%. Actual results may vary depending on the network environment.