Secrecy Rate of Adaptive Modulation Techniques in Flat-Fading Channels

In this paper, we analyze the Secrecy Rate of Adaptive Modulation transmission systems over flat-fading time-varying channels. The scenario considered consists of a transmitter communicating with a legitimate receiver in the presence of an eavesdropper. Expressions for the Mutual Information (MI) between the transmitter and the legitimate receiver and between the transmitter and the eavesdropper are presented. In addition, the Secrecy Rate is evaluated as the difference between the legitimate receiver MI and the eavesdropper MI. Unlike others studies that are based on a water-filling approach, here the MI expressions are obtained from the classical MI definition considering some assumptions usually adopted in the wireless communication systems context, and they are expressed in terms of important parameters of an adaptive modulation scheme.