How to interconnect for Massive MIMO Self-Calibration?

TL;DR

This paper investigates optimal interconnection strategies for self-calibration in massive MIMO base stations, revealing conditions under which star or daisy chain configurations are preferable, supported by theoretical and numerical analysis.

Contribution

It identifies the optimal interconnection strategies for internal self-calibration in massive MIMO systems, comparing star and daisy chain configurations under different resource constraints.

Findings

Star interconnection is optimal with equal measurements.

Daisy chain outperforms star with equal time resources.

Numerical results confirm theoretical analysis.

Abstract

In time-division duplexing (TDD) systems, massive multiple-input multiple-output (MIMO) relies on the channel reciprocity to obtain the downlink (DL) channel state information (CSI) with the acquired uplink (UL) CSI at the base station (BS). However, the mismatches in the radio frequency (RF) analog circuits at different antennas at the BS break the end-to-end UL and DL channel reciprocity. To restore the channel reciprocity, it is necessary to calibrate all the antennas at the BS. This paper addresses the interconnection strategy for the internal self-calibration at the BS where different antennas are interconnected via hardware transmission lines. Specifically, the paper reveals the optimality of the star interconnection and the daisy chain interconnection respectively. From the results, we see the star interconnection is the optimal interconnection strategy when the BS are given the same number of measurements. On the other hand, the daisy chain interconnection outperforms the star interconnection when the same amount of time resources are consumed. Numerical results corroborate our theoretical analyses.