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Here, the beamforming design for multiuser multiple-input and multiple-output (MIMO) downlink transmission aided by an intelligent reflecting surface (IRS) with discrete phase shifts is studied. The authors deduce a minimum signal-to-interference-plus-noise-ratio (SINR) maximization fairness problem with the transmit beamformer, the receive beamformer and IRS phase shifts as optimization variables, which is generally NP-hard. Hence, an alternating optimization algorithm based on the gradient extrapolated majorizationminimization (GEMM) approach is employed to solve the above problem. Specifically, when the transmit beamformer and reflective phase shift are fixed, the authors give an optimal closed expression for the receive beamformer. Then, the receive beamformer is fixed, and the minimum SINR maximization problem at the transmitter is transformed into a power minimization problem. Finally, under the zero-forcing (ZF) transmitter beamformer, the GEMM algorithm is used to optimize the reflective phase shift. Simulation results show that by comparing to existing methods, the proposed GEMM algorithm can almost achieve the same performance with lower complexity.

A surface wave exciter adapting to different-diameter lines for single power line communications is proposed in this article. A side-feeding structure is designed which enables surface wave communication on existing power lines without any damage. The proposed surface wave exciter is mainly composed of a horn, two symmetrical feeding structures, a separable feeding ring, and a separable short-circuit metal ring. In order to avoid high order modes caused by insufficient excitation of side-feeding structure, two-port feeding structure is proposed. Meanwhile, the impedance matching of the exciter is improved.The exciter is designed to adapt to several lines with different diameters by using the separable feeding ring and short-circuit metal ring. Two prototypes for the proposed design are fabricated and tested. The measured results indicated that the input reflection coefficients (S 11 ) are less than −10 dB and the efficiencies are better than 30% in the Sub-6 GHz wireless communications.Moreover, a single power line communication system, which uses surface wave to transmit signal, is set up and tested. The transmission loss and the throughput are investigated to further prove the reliability of single power line surface wave communications. K E Y W O R D S power line, power line communications, surface wave, surface wave exciter