Antenna Impedance Estimation at MIMO Receivers

TL;DR

This paper introduces a real-time method for estimating antenna impedance at MIMO receivers by leveraging training sequences and classical estimation techniques, applicable in various Rayleigh fading channels.

Contribution

It develops a novel estimation framework that uses existing training resources to accurately estimate antenna impedance during operation.

Findings

Closed-form ML estimator derived for i.i.d. fading

Method of moments estimator for correlated channels

Proposed algorithms enable real-time impedance estimation

Abstract

This paper considers antenna impedance estimation based on training sequences at MIMO receivers. The goal is to firstly leverage extensive resources available in most wireless systems for channel estimation to estimate antenna impedance in real-time. We assume the receiver switches its impedance in a predetermined fashion during each training sequence. Based on voltage observation across the load, a classical estimation framework is developed incorporating the Rayleigh fading assumption. We then derive in closed-form a maximum-likelihood (ML) estimator under i.i.d. fading and show this same ML estimator is a method of moments (MM) estimator in correlated channels. Numerical results suggest a fast algorithm, i.e., MLE in i.i.d. fading and the MM estimator in correlated fading, that estimates the unknown antenna impedance in real-time for all Rayleigh fading channels.