Improving confidentiality is a main concern in most 5 wireless transmission systems. Traditionally, confidentiality is 6 guaranteed by means of encryption, where transmitted data are 7 encrypted prior to transmission and only the intended receiver(s) 8 can decrypt them. However, encryption/decryption process involves high complexity and heavy signalling in the key distribution/agreement protocols. Thus, aiming toward overcoming complexity, physical-layer security has been proposed as a promising candidate to improve confidentiality against eavesdroppers by
exploiting physical-layer techniques. In this paper, we propose a physical-layer security scheme that adapts the modulation type
based on the channel phase in order to secure the transmitted data. Moreover, the phase of the transmitted signal is adjusted in order to improve the immunity against eavesdroppers. The proposed scheme has been designed to achieve high robustness against channel estimation errors. The performance of the proposed scheme is evaluated through analysis and simulations in order to demonstrate the significant improvement in the confidentiality.