I have two sine signals with frequencies f1 and f2, and phase p1 and p2.
I modulate the phase of these signals to transmit two symbols simultaneously, chosen from the set [0,1,2,3]. For example, I represent 0 by 45 degrees phase shift, 1 by 90 degrees phase shift, etc.
The signals will pass through an optical communication channel, potentially getting distorted. This means there could be intermodulation products and harmonics.
I plan on using an FFT to determine magnitude and phase changes of the signals. I am hoping to retrieve the symbols from the phase changes I detect using the FFT. I want the magnitude to stay constant while the phase is shifting to transmit the symbols.
The sampling rate I'm working with is 7800 hz. I will potentially have to fit 16 transmission channels (frequencies) below 1500 hz. At any time, two frequencies randomly chosen from the set of 16 frequencies may be present, transmitting symbols as explained above.
Is this going to work, and what are the key issues to keep and mind and to work around? Any practical pointers or references are highly appreciated as I'm a novice in phase modulation and encoding/decoding of information in this fashion.
Thanks for helping! B