Secrecy Analysis of EGT and MRT Precoders for M -QAM Constellations

This work presents an information theoretical analysis of the intrinsic secrecy of circular and square M-QAM signals when these constellations are precoded with equal gain transmission (EGT) and maximum ratio transmission (MRT) techniques. The main results show that for low order constellations, a significant percentage of the exchanged information is intrinsically protected by the EGT precoder, while in the MRT case, an interesting result shows that the secrecy level doesn't scale with the entropy of the source, and therefore perfect secrecy rate can be achieved asymptotically increasing the constellation order M. Furthermore, the results provided in this work can be used to quantify a minimum entropy value that a shared secret key must have to fully secure the information from an eavesdropper.