Antenna Impedance Estimation at MIMO Receivers

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.