Verint Video Intelligence Solutions
115
Nextiva S4200 Series User Guide
Interference from External Sources
The 2.4 and 5 GHz frequency bands are license-free bands. this absence of frequency
coordination can result in interference between various systems. For instance, if a link with
an RF line of sight is subject to excessive video delay and very low frame rate (or possibly
breakdown of video images), it could be due to interference. Fortunately, you have ways of
adapting your setup to avoid interference:
Change the frequency channel until you find a clean one.
Replacing the integrated antenna with an external one producing a higher gain can
significantly lower the interference from other radio systems and reduce the number of
signals that are picked up. Consider replacing the antenna if switching channels does
not correct the problem or if all channels must be used to colocate several systems.
If installing an external antenna, choose horizontal polarization. Most external devices
operating in the 2.4 or 5 GHz band use vertical polarization, as well as the integrated
antennas in the Nextiva wireless devices. Using a different polarization can give a good
isolation to external interferences caused by vertically polarized devices.
There should not be any interference in the 4.9 GHz band, since it is a licensed band with
usage limited to public safety.
Interference from Nextiva Devices
Wireless interference can occur between colocated wireless cells using adjacent frequency
channels (for example, channels 149 and 153 in the 5 GHz band, or channels 1 and 6 in the
2.4 GHz band). The symptoms are lower throughput than expected or many CRC errors and
communication retries; the number of CRC errors and retries is displayed in the command
line interface of the device (Advanced > Communication Status and Statistics > Wireless
Communication Throughput). A typical interference case is when many devices are installed
on the same roof or share the same pole. Therefore, it is preferable to avoid using adjacent
channels.
Even second adjacent channels can cause wireless interference.
If your setup requires the use of adjacent channels, follow these guidelines:
1. Separate as much as possible the devices from each other. See page 120 for the
minimum distances to respect.
2. Vary antenna polarization. The integrated antenna uses vertical polarization, so when
installing external antennas, select horizontal polarization. By reversing polarization,
you improve the wireless cell isolation. If wireless cells share the same roof or pole,
alternate antenna polarization.
3. Perform a site survey to determine exactly which devices are causing interference. For
the procedure, see page 116.
4. Decrease the tx power of the wireless links that have a good RF margin (15 dB or
more). This way, the interference generated by the device is reduced.
Note: All the devices in a wireless cell must have the same polarization.
