A TPSAS-Based TSDD Hybrid Precoding Algorithm for FD-MIMO Systems

Cost-effective hybrid precoding has been attracting extensive attention for millimeter wave full-dimension multiple input multiple output (FD-MIMO) green communication systems. To enhance beamforming flexibility and energy efficiency (EE) while obtaining satisfactory spectral efficiency (SE), this paper introduces an adaptive fully-connected subarrays structure with two-layer shared phase shifters (TPSAS) and proposes a TPSAS-based two-stage double dimensional hybrid precoding (TSDDHP) algorithm. Firstly, the TPSAS structure is given to reduce hardware complexity while attractively making full use of the vertical and horizontal dimensions information. Then, to achieve TPSAS-based energy-efficient and flexible hybrid precoding, the TSDDHP algorithm is developed to obtain digital and analog precoders for point-to-point (PTP) and multi-user (MU) scenarios. For PTP scenario, the vertical analog precoder, the horizontal analog precoder, and the digital precoder are acquired by the equivalent quadratic function, properties of dual norm and unitarily invariant norm, respectively. For MU scenario, a linear zero-forcing approach and an equivalent quadratic function are used to gain the digital, the vertical and horizontal analog precoders, respectively. Theoretical analyses and simulation results verify that the proposed scheme is superior to others in terms of beamforming flexibility and EE while acquiring satisfactory SE with lower computation complexity.