9500 MXC User Manual
3DB 23063 ADAA - Rev 004 July 2007 Vol. IV-7-21
• "If the RSL value is within range, but the SNR is low, then the transmit power
is increased until the SNR is within the specified range.
• ATPC power changes can occur at a rate of 6 dB/second to provide
compensation for rapid fading conditions.
• ATPC will fail to maintain the remote target threshold settings if the fading
condition is severe enough to require more local transmit power than set as the
maximum TX power, or if the power level required is beyond the capability of
the transmitter.
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
ATP C.
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