Proof of Concept: Local TX Real-Time Phase Calibration in MIMO Systems

TL;DR

This paper introduces and validates a simple real-time phase calibration method for MIMO systems, enhancing beamforming accuracy and enabling coherent transmission on SDR platforms.

Contribution

It presents a novel local phase calibration technique for digital arrays, comparing instantaneous and smoothed approaches for real-time synchronization.

Findings

Both calibration methods effectively improve phase coherence.

Achieved RMS jitter between 2.1 ps and 124 fs across SDR models.

Enables practical implementation of advanced MIMO techniques.

Abstract

Channel measurements in MIMO systems hinge on precise synchronization. While methods for time and frequency synchronization are well established, maintaining real-time phase coherence remains an open requirement for many MIMO systems. Phase coherence in MIMO systems is crucial for beamforming in digital arrays and enables precise parameter estimates such as Angle-of-Arrival/Departure. This work presents and validates a simple local real-time phase calibration method for a digital array. We compare two different approaches, instantaneous and smoothed calibration, to determine the optimal interval between synchronization procedures. To quantitatively assess calibration performance, we use two metrics: the average beamforming power loss and the RMS cycle-to-cycle jitter. Our results indicate that both approaches for phase calibration are effective and yield RMS of jitter in the 2.1 ps to 124 fs range for different SDR models. This level of precision enables coherent transmission on commonly available SDR platforms, allowing investigation on advanced MIMO techniques and transmit beamforming in practical testbeds.