Viavi OneExpert CATV 630, Extended Quick Start Manual

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103
OFDM is DYNAMIC with varying subcarriers and LDPC
MER and Level alone don’t tell the whole story
 Profiles and CWE analysis are
important
THINGS TO CHECK:

PLC is working well

NCP is working well

Profile A is working well with some
correctible (in this case running 256
QAM)

Profile B (running 1024 QAM in this case)
is on the edge: 100% correctable CWE
but LDPC is correcting them all!

This makes sense, 1024 QAM level
should be ≥12dBmV and MER > 34 dB




CM Minimum CNR/MER Performance in AWGN
QAM
Modulation
Up to 1 GHz
CNR(dB)
Min P
6AVG
dBmV
4096 41.0 -6
2048 37.0 -9
1024 34.0 -12
512 30.5 -12
256 27.0 -15
128 24.0 -15
64 21.0 -15
16 15.0 -15
Component Tasks Importance CWE expectations and impact
PLC
PHY Link Channel
Contains CRITICAL OFDM signal
decoding information
Critical
Should have 0 Uncorrectable-CWE otherwise OFDM may not
work
NCP
Next CW Pointer
Tells modem which CW are present and
in which profile to find each CW
Critical Should have 0 U-CWE otherwise OFDM may not work
Profile A
Boot profile. ALL 3.1 modems must be
able to use profile A
Critical
U-CWE will cause poor QOE and possibly make OFDM
carrier unusable, forcing data to standard QAM carriers
instead of OFDM
Profile B,C,D
Enable higher modulations for greater
efficiency
High U-CWE will affect bandwidth and overall QOE
