MIMO Array Calibration in Non-stationary Channels with Residual Surfaces and Slepian Spherical Harmonics

TL;DR

This paper introduces a calibration method for MIMO arrays in non-stationary channels that uses residual surfaces and Slepian spherical harmonics to improve beamforming accuracy and hardware compensation.

Contribution

It presents a novel calibration technique that estimates residual surfaces with spherical harmonics, enabling effective hardware compensation in dynamic environments.

Findings

Achieves beamforming gains close to theoretical optimums

Reduces error in target direction estimation

Enhances null-steering capabilities

Abstract

The fundamental mechanism driving MIMO beamforming is the relative phases of signals departing the transmit array and arriving at the receive array. If a propagation channel affects all transmitted signals equally, the relative phases are a function of the directions of departure and arrival, as well as the transmit and receive hardware. In a non-stationary channel, the amplitudes and phases of arriving signals may vary significantly over time, making it infeasible to directly measure the influence of hardware. In this paper, we present a calibration method for achieving indirect measurement and compensation of hardware influences in non-stationary channels. Our method characterizes the patterns of array elements relative to a reference element and estimates these relative patterns, termed residual surfaces, using a Slepian spherical harmonic basis. Using simulations, we demonstrate that our calibration method achieves beamforming gains that closely match theoretical optimums. Our results also show a reduction in the error in estimating the target direction, lower side lobes, and improve null-steering capabilities.