I have implemented a QPSK modulator and demodulator using classic text-book examples: Square Root Raised Cosine Impulse shaping and Matched Filtering.
The problem is that I've been told that I could only used square waves for the modulation instead of sine waves on the emitter side (only +/-Vmod) and this really degrades the performance of the communication.
After further investigation it seems that the root cause of the lack of performance is not really the use of square wave but the change of impulse shaping/matched filtering implied by it.
Basically my question is the following: Using only +/-Vmod (and 0V if necessary) on the emitter side, am I wrong in assuming that the best case scenario is using a Rectangular Impulse Shaping with the according Matched Filter or is there some other combination that could provide better results?
If you have any ideas or links I could learn from don't hesitate! I'm struggling because I don't know if my reasoning is wrong or if its my implementation.