Coordinate descent

Electronic engineering

Engineering

Telecommunications

Transmitter power output

Channel (broadcasting)

Mathematics

Beamforming

Mathematical optimization

Transmitter

Semidefinite programming

Computer science

Base station

Algorithm

Computer network

Transmission (telecommunications)

Secure transmission

IEEE Wireless Communications Letters

This letter focuses on the secure transmission for an intelligent reflecting surface (IRS)-assisted millimeter-wave (mmWave) and terahertz (THz) system, in which a base station (BS) communicates with its destination via an IRS, in the presence of a passive eavesdropper. To maximize the system secrecy rate, the transmit beamforming at the BS and the reflecting matrix at the IRS are jointly optimized with transmit power and discrete phase-shift constraints. It is first proved that the beamforming design is independent of the phase shift design under the rank-one channel assumption. The formulated non-convex problem is then converted into two subproblems, which are solved alternatively. Specifically, the closed-form solution of transmit beamforming at the BS is derived, and the semidefinite programming (SDP)-based method and element-wise block coordinate descent (BCD)-based method are proposed to design the reflecting matrix. The complexity of our proposed methods is analyzed theoretically. Simulation results reveal that the proposed IRS-assisted secure strategy can significantly boost the secrecy rate performance, regardless of eavesdropper's locations (near or blocking the confidential beam).

Secure Transmission for Intelligent Reflecting Surface-Assisted mmWave and Terahertz Systems