Project S03 - Space-Time Signalling for MIMO Reflectometry with Vortex Waves

Principal Investigators: Prof. Dr. Aydin Sezgin, RUB ETIT; Prof. Dr. Daniel Erni, UDE ATE

The goal of this exploratory project is to investigate novel schemes for reliable characterization of textured material (sub-)surfaces. This is done based on the spectral signatures of the backscattered wireless signals, including the Fourier transforms of the second order statistics such as covariance and correlation functions. This is achieved by multiple-input multipleoutput antenna (MIMO) reflectometry as illustrated in Fig.1(a), i.e., utilizing multiple antenna systems in conjunction with radio frequency (RF) vortex waves carrying an orbital angular momentum (OAM). Such vortex beams offer an additional degree of freedom (DoF) with respect to both an increased spectral efficiency (when looking at e.g. advanced wave-based multiplexing schemes) and a potentially increased sensitivity to (sub-)surface features, material properties and form anisotropy in the framework surface material sensing. Both features will be explored in this project while adopting the capabilities of modern signal processing methods (e.g. widely linear signal processing) to advanced RF reflectometry schemes. As a proof of principle, we will start with tailored antenna arrays that support corresponding spatial diversity for OAM emission/detection allowing for three novel measurement concepts: (i) planar arrays for MIMO-based near-field reflectometry, (ii) planar arrays for MIMO-based ellipsometry with oblique incident vortex beam processing, and (iii) a novel ultra-compact ellipsometry setup using normally incident vortex beams of varying OAM mode orders. The vortex beams are then combined with associated signal processing methods such as convex optimization, estimation, transmit waveform and receive filtering design for extracting material/structure characteristics. The following central questions will be addressed:

  • Adaptive material impulse response (aka channel) estimation with joint transmit waveform and receive filtering design considering widely linear signal processing in sub-mm-wave systems,
  • Covariance and correlation estimation of the received signal to extract the material characteristics,
  • Worst-case noise robust antenna array optimization for MIMO reflectometry,
  • Potential and optimality of vortex beam-based RF reflectometry using orbital angular momenta as additional degree-of-freedom for (sub-)surface material sensing applications.

Overall, the project is appealing, as optimal and robust space-time signalling concepts in sub-mm MIMO reflectometry in order to maximize the gain of information have not been addressed properly yet. Consequently, we address the 3rd challenge of the MARIE vision, i.e., to dynamically characterize both surface and subsurface materials.