Bandwidth optomization

Hello eda, I'm glad I can be a part of your community!

I'm posting about methods for optomizing bandwidth. The new KA-SAT satellite runs at 2Mb/s per MHz. The total bandwidth for the satellite is 39Gb/s - a very substantial increase compared to past satellites.

Are all bandwidth optimization technologies based on software and encoding methods? Are they effectively more complex and built variations of things like CTCSS?

Is it possible to transmit frequencies within a frequency so longs as the rf signals are smaller than the original carrier wave? i.e. running a 25MHz, 50MHz, 75MHz, 100MHz, etc. signal within a 125MHz transmitter/receiver.

I'm a little new to this, so feel free to point me to articles/pages/etc.
8)