Secure Communication for MISO Secrecy Channel With Multiple Multiantenna Eavesdroppers Having Finite Alphabet Inputs

This paper considers secure transmission design for multiple-input-single-output multiple multi-antenna eavesdroppers networks with finite alphabet inputs. To improve the achievable secrecy rate, the joint optimization of beamforming vector and transmitting power is studied. We transform the multi-variable problem into a single-variable problem, and then derive the beamforming vector and the transmitting power using one-dimensional search method. Specially, the secure transmission designs in the extremely signal-to-noise ratio (SNR) regime are investigated. In the low SNR regime, the problem of beamforming design is transformed into a semi-definite programming problem, which can be handled by interior-point-based methods, and the optimal transmitting power is obtained. Besides, two different secure schemes, which are zero-force beamforming scheme and joint beamforming and jamming scheme, are proposed to increase the achievable secrecy rate at high SNR. Numerical results demonstrate that the proposed schemes significantly improve the secrecy performance of the system.