Effectiveness of Implicit Beamforming with Large Number of Antennas Using Calibration Technique in Multi-User MIMO System

Abstract

This paper examines the effectiveness of implicit beamforming (IBF), which enables transmission without channel state information (CSI) feedback in multi-user multiple-input multiple-output (MU-MIMO) systems with a large number of antennas. First, we explain why CSI feedback from terminal stations to the base station produces a very large overhead. A calibration technique is then introduced, which compensates for the difference between the complex amplitudes of the transmitters and receivers to facilitate CSI-feedback-free beamforming; this technique is called IBF. The efficacy of this calibration technique is demonstrated by measuring the amplitude and phase errors obtained using a 16-element array testbed and by performing a channel capacity evaluation. Finally, the throughput under IEEE802.11ac-based massive MIMO transmission, both with and without CSI feedback, is obtained in terms of the medium access control efficiency.

Development of the Phaseless Calibration Algorithm for a Digital Antenna Array

“…Calibration of antenna arrays is in demand in complexes of various purposes. These are multi-user MIMO systems [29,30]; various on-board aviation systems [31,32]; ground and satellite stations [33][34][35][36]; and even floating [37] or rotational platforms [38]. Calibration algorithms are constantly being improved, new ones are appearing, and known methods are being experimentally studied [39][40][41].…”