I guess I could see that working on Cable, part time, on some channels but not all channels, all the time, providing like ya say they upgrade / maintain their old systems properly. I am sure an Adaptive approach would work well for them. Meaning, changing the modulation and coding scheme on the fly based on the specific channel conditions. Much like is done today on Satellite with DVB-S2 ACM/VCM. Should be much easier to implement on cable since they already have an uplink path that could be used to provide the necessary feedback.
FWIW, was playin around with cable tuning just the other day. And many channels come in at 40 dB snr now, and that's with some less than desirable splitting going on in the house. But at the same time there may be a channel(s) adjacent to a 40 dB'er that are only at 29 dB or so.
So, it seems to vary quite a bit here from one channel to the next.
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