Hi Guys,
I'm a bit clueless (background of networking guy rather than RF cable guy, 0's and 1's make more sense to me..) how to interpret this if-mib-31 value, CL mib says:
docsIf31CmUsOfdmaChanTxPower OBJECT-TYPE
SYNTAX TenthdBmV
UNITS "dBmV"
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This attribute represents the operational transmit power for
the associated OFDMA upstream channel."
::= { docsIf31CmUsOfdmaChanEntry 10 }
for CM's having this value at 199, transmit power on a SC-QAM is ~56dBmv, OFDMA power of 130 complies with SC-QAM transmit power of ~40dBmv
Seems to be this value is the value calculated back into power over 1.6MHz, probably has something to do with the total channel power over the whole ofdma block but i'd like to know how this refers to the power on SC-QAMs, just a bit more familiar to that..
Anybody? Thanks in adv!
a value of 199 on this value correlates to 49.75 dBmV (199 / 4 = 49.75)
SC-Qams are measured in whatever channel width they are, so if your SC-QAM was 6.4 MHz wide, your OFDMA power should be 6 db different due to the widths the channel was measured at, and if it was 3.2 Mhz wide your OFDMA should be 3 db different.
So I suspect based on your numbers you are using 6.4 MHz wide channels because:
56 dBmV on a 6.4 MHz channel should roughly correlate to 50 dBmV on an OFDMA channel
40 dBmV on a 6.4 MHz channel should roughly correlate to 34 dBmV on an OFDMA channel
you had 199 for a correlation with a SC-QAM channel which is 49.75 dBmV
and you had 132 for a correlation with a SC-QAM channel which is 33 dBmV
Which pretty well tracks.
Looks like you have a very old MIB file:
Name: docsIf31CmUsOfdmaChanTxPower
Type: OBJECT-TYPE
OID: 1.3.6.1.4.1.4491.2.1.28.1.13.1.10
Full path: iso(1).org(3).dod(6).internet(1).private(4).enterprises(1).cableLabs(4491).clabProject(2).clabProjDocsis(1).docsIf31Mib(28).docsIf31MibObjects(1).docsIf31CmUsOfdmaChanTable(13).docsIf31CmUsOfdmaChanEntry(1).docsIf31CmUsOfdmaChanTxPower(10)
Module: DOCS-IF31-MIB
Numerical syntax: Gauge (32 bit)
Base syntax: Unsigned32
Composed syntax: Unsigned32
Status: current
Max access: read-only [r--]
Units: QuarterdBmV
Description: This attribute represents the operational transmit power for
the associated OFDMA upstream channel.The CM reports its Target
Power, P1.6r_n as described in [PHYv3.1]. Valid values for this
object are 68 to (213 + (4*(Pmax - 65 dBmV))), since 68 quarter dBmV
represents the lowest Tx power value 17 dBmV and 213 represents the
nearest quarter dBmV to the highest Tx power value 53.2 dBmV.
Ah, makes sense, this description looks a bit different, just found out i used the 2016 one.. Not too smart I'd say.
Thanks for this one!