A novel nonlinear secure transmission design for MU-MISO systems with limited feedback

We study transceiver design for secure communication of multiuser multi-antenna systems with assistant of a cooperative helper. There is an external multiple-antenna eavesdropper trying to obtain the confidential messages. Due to the finite-rate constraint of feedback channels, only quantized channel state information of the legitimate users is available at the transmitter and the helper. A nonlinear precoding strategy using Tomlinson Harashima precoding at the legitimate transmitter and a null-space beamforming scheme at the helper are proposed based on the quantized channel state information. Assuming a genie-aided perfect successive interference cancelation at Eve, we obtain closed-form expressions of the performance bounds for the achievable ergodic rate of each legitimate user and the ergodic secrecy sum rate. Numerical results illustrate that our proposed nonlinear-precoded strategy outperforms linear precoding scheme.