Space–Time Line Code for Enhancing Physical Layer Security of Multiuser MIMO Uplink Transmission

In this article, we investigate a secure uplink multiple-input multiple-output communication system, in which the multiple users transmit information to a legitimate access point (AP) when a passive eavesdropper exists. A secure multiple access method is proposed for single-antenna users by employing space-time line codes (STLCs), which enables noncoherent detection at the legitimate AP without channel state information (CSI) and achieves full spatial diversity. While extending the secure STLC scheme from the single-antenna to two-antenna users by combining the STLC with artificial noise (AN) injection, we design a low-complexity AN signals with the optimal power control scheme. The proposed AN is ensured to be eliminated after STLC decoding at the legitimate AP, while sustained in eavesdropper's received signals as interference. Theoretical sum secrecy rates are derived by considering time-varying fading channels with the uncertainty of CSI at the users, and the numerical results verify that the proposed STLC schemes outperform the existing secure transmission schemes in terms of the sum secrecy rate.