You have a lot of amplifiers! With that said, there is no formula. Many operators are in North America are migrating to short runs of amplifiers. The terminology is often called Fiber Node + # of amplifiers or Node + 4. In many cases is it is not uncommon to see no more than four amplifiers after the fiber node and a number of operators are even migrating to Node + 1. Why? Because when you have so few actives on your return plant, you end up with very few upstream impairments. further you end up with fewer subscribers per port. Clearly this does not scale in rural areas where you will need many more actives, but it should give you a sense of what is becoming common.

So when you have 24 amps in cascade and an SNR of <30dB, this is not surprising. You have a lot of opportunities for ingress and other plant noise, group delay, etc. to get in. I would recommend that if at all possible you segment your plant with some fiber nodes and you should see your SNR improve.

-Brady

The idea sounds good, but does not work in application. By moving to a higher-order constellation, it is possible to transmit more bits per symbol. However, if the mean energy of the constellation is to remain the same (by way of making a fair comparison), the points must be closer together and are thus more susceptible to noise and other corruption; this results in a higher bit error rate and so higher-order QAM can deliver more data less reliably than lower-order QAM, for constant mean constellation energy.

For 64- and 256-QAM, you are confined to 6 and 8 bits per block, respectively. That fundamentally limits your data throughput. I also added a document to the Library for your reference on QAM in a digital cable plant. You might find it interesting. Check it out here.

-Brady

Currently the DOCSIS specification states that a minimum of four (4) upstream channels can be bonded. So the implication is that more than four can be bonded. I don’t know of any system that is currently doing more than four, in fact few are actually truly doing four upstream bonded channels – its just getting traction now.

-Brady

Here is my question, can the US be improved with the new standard to define more “bits” in a block ? instead of having 8-bit for 256-QAM, how about pump up to 16-bit per block ? would this technically be possible ?

Thanks,
Jim Chen
951-907-3210 (cell)