Remember everytime you change QAM to a larger QAM you loose attenuation by 3db in the return
Attenuation does not change does it? I think that the S/N requirement changes.
S/N must be be 3 dB better for each higher order of modulation.
All versions of DOCSIS specify that 64-level or 256-level QAM (64-QAM or 256-QAM) be used for modulation of downstream data, and QPSK or 16-level QAM (16-QAM) be used for upstream modulation. DOCSIS 2.0 and 3.0 also specify 32-QAM, 64-QAM and 128-QAM also be available for upstream use. So if you are already doing 2.0, your 3.0 should work OK.
With Docsis 3.0, if you use upstream channel bonding, (which is really still under development for the upstream), well your reverse spectrum should be clean enough to eat off of.
It can be done, but only with a lot of work and constant vigilance. If your company does
not have a very good leakage program, along with good preventive maintenance,
then good luck to you.
As far as 29 and 26 taps are concerned, yeah, we don't use em anymore either.
When cable modems first came out (even before docsis) the outputs were only
40 dB. You couldn't get back through with 30, 29, 27, and 26 taps in line, or with
DC-12's or DC-16's in line. Now that cable modem outputs are 55 to 60 dB, we have
added DC-12's back in our design parameters, but still use them sparingly.
Keep your noise low and your upstream CPE levels in the high 40's to real low 50's.