Aviat Networks ECLIPSE EDGE, Руководство пользователя

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42 Aviat Networks
Chapter 4. Eclipse Edge Configuration and Diagnostics
Interference and ATPC
It is possible for a radio to have a good receive signal (high RSL), but poor residual
BER performance (poor SNR), such as can occur when there is co/adjacent
interference. SNR is therefore also used as a factor in ATPC operation, preventing bit
errors occurring due to link fade beyond the point where Forward Error Correction
(FEC) is able to recover errored blocks.
• The ATPC process calculates the SNR based on the signal level derived from the
demodulator and uses this information to maintain the SNR by adjusting the Tx
power at the local terminal.
• The transmit power at the local terminal is increased when the SNR at the remote
terminal falls to the SNR calculated for an RSL 6dB above the 10
-6
threshold. The dB
value will vary slightly, depending on the ODU/modulation combination.
RSL and SNR Interoperation
The ATPC algorithm uses both RSL and SNR inputs to set remote Tx power.
• An above-range RSL will initiate a reduction in remote Tx power.
• When both RSL and SNR are within range, no ATPC action is taken.
• When the RSL is within range but the SNR is below range, SNR will initiate an
increase in remote Tx power.
With low levels of interference ATPC can, depending on the settings and the degree
of interference, optimize the remote Tx power. But with high levels of interference
ATPC action will not be effective.
Check for interference by muting the Tx at the far end and checking RSSI/RSL at the
local end. Where there is a measurable RSL under this condition, do not use ATPC.
Note that the RSSI (RSL) filter has a nominal 56 MHz bandwidth, which means that
depending on the channel bandwidth used, multiple adjacent channels can be
included within the filter passband
1
. Normally this will not cause a problem as
antenna discrimination (beamwidth) and good frequency planning should exclude co
and adjacent channel RSL interferers.
NOTE:
Do not use ATPC where there is a measurable RSL when the
remote-end Tx is muted.
NOTE:
Where ATPC is configured, its operation should be monitored for a
period after installation to ensure it is providing the expected
benefits under the prevailing path conditions. Where indicated,
ATPC settings should be optimized, or in situations of frequent, fast
and high fading it may be best to disable ATPC.
1
RSSI filter bandwidth is not a function of, nor does it affect receiver adjacent channel C/I performance. Eclipse
complies with relevant ETSI and FCC co and adjacent channel requirements.