Improving physical-layer security using APSK constellations with finite-alphabet inputs

Physical-layer security could efficiently prevent wiretapping for wireless communication from the information-theoretic perspective. However, most related works in this area are based on the assumption of Gaussian inputs, which are impractical for a practical communication system. In this paper, we study the physical-layer security with finite-alphabet inputs, wherein amplitude phase shift keying (APSK) constellation is considered to improve the achievable secrecy rate performance. It is concluded that the secrecy rate can be improved by using APSK, comparing to its quadrature amplitude modulation (QAM) counterpart, which is verified by both the minimum mean square error (MMSE) theoretic derivation and simulation results. A specific strategy of selecting constellation orders for secure communication is also presented.