Carrier in Carrier Tech. Information wanted.

I have learnt of a new technology on satellite modems called the Carrier-In-Carrier. I understand a modem like ComTech QX can use a single frequency for its Rx and Tx, therefore cutting bandwidth cost to half! Can anyone better explain the technology behind this innovation and any other implication this development has or will have in present or future.

Ime

The carrier in carrier technique does not cut bandwidth costs in half.

If you buy 1 MHz of bandwidth you get allocated a proportional amount of power (dBW).

To get the best capacity (in bit/s) out of that resource you need to use up all of the 1 MHz bandwidth and all of the power simultaneously.   If you use less than 1 MHz you will get less bit/s.  If you use less than the allocated power you will get less bit/s.  So aim to operate a carrier (or multiple carriers) that fully utilise what you have paid for.  You can put two equal height (half bandwidth) carriers side by side or put two full width, but half power, carriers on top of one another.  If you choose the last option you need the special carrier-in-carrier modems to cancel out the mutual interference effect, by subtracting a delayed copy of the transmit signal from the received signal.

Turbo FEC code gives significant improvement over other FEC methods and is therefore the obvious choice, but you must adjust your FEC coding ratio and choice of modulation method to fully exploit the purchased resource.  Larger dishes will result in lower bit/s cost.

Best regards, Eric.