Информационное Руководство для Cisco Cisco WT2750 Multipoint Broadband Wireless System
Q. How can I check to determine if there is interference?
Check whether the problem is continuous or intermittent. Interference usually occurs
intermittently, or else you would have noticed the interference when the link was first
commissioned.
intermittently, or else you would have noticed the interference when the link was first
commissioned.
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Check whether the receive−signal level is proper at both ends. This measurement
reflects the receipt of both desired and undesired (interference) signals.
reflects the receipt of both desired and undesired (interference) signals.
An interference problem can newly manifest in a system with a history of reliable
operation, yet the source of interference may have been there all along. This is
possible, when some other problem affects the outdoor system (see above) and
degrades the receive signal levels, and thus allows the interferer to cause a link
quality problem. The interferer degrades the signal−to−noise ratio in this case,
because the interferer is also just noise as far as your system is concerned. In such
cases, the newly−degraded receive−signal level allows an already existing interferer
to cause problems.
operation, yet the source of interference may have been there all along. This is
possible, when some other problem affects the outdoor system (see above) and
degrades the receive signal levels, and thus allows the interferer to cause a link
quality problem. The interferer degrades the signal−to−noise ratio in this case,
because the interferer is also just noise as far as your system is concerned. In such
cases, the newly−degraded receive−signal level allows an already existing interferer
to cause problems.
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If the received−signal indication (RSSI) is correct and you suspect interference,
measure the signal−to−interference+noise ratio (SINR) at each end of the system.
measure the signal−to−interference+noise ratio (SINR) at each end of the system.
You can plot and track this parameter (as well as RSS) as a function of time with the
help of the radio histogram feature set. In this way, you can track these two
parameters simultaneously and correlate them with observations of the degraded
performance. If, for example, the RSS always remains steadily good, and SINR
exhibits periods of abnormally poor readings, check the link performance (such as
error rate) during those periods of poor SINR. If there is a correlation, the link
experiences interference. When the RSSI is good at both ends, interference is
intermittent.
help of the radio histogram feature set. In this way, you can track these two
parameters simultaneously and correlate them with observations of the degraded
performance. If, for example, the RSS always remains steadily good, and SINR
exhibits periods of abnormally poor readings, check the link performance (such as
error rate) during those periods of poor SINR. If there is a correlation, the link
experiences interference. When the RSSI is good at both ends, interference is
intermittent.
♦
Use a spectrum analyzer to diagnose interference. The spectrum analyzer shows an
image of the frequency band, and shows interfering signals on or near your
frequency. The toughest cases involve intermittent interferers because such interferers
can appear infrequently and randomly. For these cases you must have a spectrum
analyzer that can capture the images over time, so that you can verify infrequent and
random interferers.
image of the frequency band, and shows interfering signals on or near your
frequency. The toughest cases involve intermittent interferers because such interferers
can appear infrequently and randomly. For these cases you must have a spectrum
analyzer that can capture the images over time, so that you can verify infrequent and
random interferers.
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Q. What must I do when I confirm that I have an interference problem?
A. Locate the source of the interference. In order to do so, look around at both ends of your
link. Do you see any other antennas or related equipment? If you identify other nearby radio
equipment, try to learn:
link. Do you see any other antennas or related equipment? If you identify other nearby radio
equipment, try to learn:
Who operates it
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Who owns it
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What frequency or frequencies it operates on
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With how much power does this other equipment transmit
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What kind or type of antenna polarization is in use
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See if you can contact the owner or operator of this other equipment to find out:
What are the hours of operation?
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Will they work with you to confirm if their equipment is indeed the source of your
problem? Diplomacy helps here.
problem? Diplomacy helps here.
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When you have confirmed the type and location (and other details) of the interfering radio
equipment, you can figure out a solution. Start with your antennas.
equipment, you can figure out a solution. Start with your antennas.