Modem
Reference Manual for EL470 IP Satellite Modem
Structured Command
DmMeasEsNoStruct
Header Es/No
estimation
Header Es/No estimat
Location
/Modem/Monitor/Demodulation
Description
This command reads out the concatenation of
DmMeasEsNoSat
and
DmMeasEsNo
. All DVB-S2 demodulators have an integrated Es/No
estimator. Their Es/No estimation is made on the physical layer header
symbols. Because it is done on known BPSK symbols, it is more accurate
(+/- 0.3dB typically in a linear channel) than the DVB-S Eb/No estimation.
But this header estimation has some consequences:
•
It does not take into account some distortions on higher
modulations, especially on 16APSK and 32APSK, due to saturation
in amplifiers working with minimal output back off. BPSK signals are
much less influenced by these non-linear effects of saturation.
•
There are only 90 header symbols/baseband frame of minimum 2K
and maximum 32K symbols. Averaging the noise on many headers
is required to have some stable reading. The header Es/No
estimation is rather slow at lower symbol rates.
•
All non compensated disturbances are measured on the
demodulated header symbols. Saturation and group delay distortion
can cause a large difference compared to the Es/No measured with
a spectrum analyser. This is typically the case with a high group
delay distortion and high Es/No.
•
With the equalizer function enabled, group delay distortions are
better compensated on the NTC/7044 than on the NTC/7062 board
and Es/No indication is more accurate.Remark: The Es/No indication
ranges from -2 dB to + 24 dB.
RMCP
Command
REs
Access
Normal user : R
Expert user : R
SNMP
Table
ntcDevsMod01DemodulatorEntry
Command
ntcDevsMod01DmMeasEsNoStruct
OID
1.3.6.1.4.1.5835.3.1.13.1.50.1.1
Variables
Page
Structured Command
DmEstLinMarStruct
Link Margin Estimate
Link Margin Estimate
Location
/Modem/Monitor/Demodulation
Description
Readout of the indication of the receive margin before reaching the
threshold point of a quasi error free operation (QEF) operation.
In DVB-S, the Eb/No for quasi error free operation is taken from the DVB
standards EN300421 and EN301210. Basically it is the margin in dB that
subtracting the modcod dependenta signal can decrease in Eb/No before
errors will have noticeable effects on the output transport stream.
In DVB-S2, the link margin is derived from the true C/N value, including
both linear and non-linear distortion.
RMCP
Command
Lms
Access
Normal user : R
Expert user : R
SNMP
Table
ntcDevsMod01DemodulatorEntry
Command
ntcDevsMod01DmEstLinMarStruct
version 3.1
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