Constant envelope precoding for secure millimeter-wave wireless communication

This paper exploits the potential of large antenna arrays to develop a secure millimeter wave (mmwave) transmission scheme. To reduce the peak-to-average power ratio (PAPR), the idea of constant envelope precoding (CEP) is introduced to improve the power efficiency of power amplifiers. In the CEP scheme, only phase variation of each antenna is used to form the desired signal at the target receiver, while the sum power of noise-free signals received by all eavesdroppers is minimized for secure transmission. A nonconvex optimization problem is formulated with equality and unit modulus constraints. To tackle the nonconvex constraints, the augmented Lagrangian penalty method is employed to address the challenging problem. An efficient iterative algorithm is further proposed to tackle the problem of precoder design. Simulation results confirm the effectiveness and superiority of the proposed CEP secure transmission scheme.