Optimization of Massive Full-Dimensional MIMO for Positioning and Communication

TL;DR

This paper explores optimizing massive FD-MIMO base stations for simultaneous high-rate data communication and 3D positioning, addressing challenges like imperfect CSI and limited ADC/DAC resolution with novel beamforming algorithms.

Contribution

It introduces low-complexity Kronecker beamforming solutions that effectively balance communication and positioning performance under practical hardware constraints.

Findings

Proposed algorithms achieve near-optimal performance for both tasks.

Kronecker beamforming offers a low-complexity alternative with limited performance loss.

Numerical results confirm effectiveness under realistic hardware limitations.

Abstract

Massive Full-Dimensional multiple-input multiple-output (FD-MIMO) base stations (BSs) have the potential to bring multiplexing and coverage gains by means of three-dimensional (3D) beamforming. Key technical challenges for their deployment include the presence of limited-resolution front ends and the acquisition of channel state information (CSI) at the BSs. This paper investigates the use of FD-MIMO BSs to provide simultaneously high-rate data communication and mobile 3D positioning in the downlink. The analysis concentrates on the problem of beamforming design by accounting for imperfect CSI acquisition via Time Division Duplex (TDD)-based training and for the finite resolution of analog-to-digital converter (ADC) and digital-to-analog converter (DAC) at the BSs. Both \textit{unstructured beamforming} and a low-complexity \textit{Kronecker beamforming} solution are considered, where for the latter the beamforming vectors are decomposed into separate azimuth and elevation components. The proposed algorithmic solutions are based on Bussgang theorem, rank-relaxation and successive convex approximation (SCA) methods. Comprehensive numerical results demonstrate that the proposed schemes can effectively cater to both data communication and positioning services, providing only minor performance degradations as compared to the more conventional cases in which either function is implemented. Moreover, the proposed low-complexity Kronecker beamforming solutions are seen to guarantee a limited performance loss in the presence of a large number of BS antennas.