106 research outputs found
RIS-Parametrized Rich-Scattering Environments: Physics-Compliant Models, Channel Estimation, and Optimization
The tunability of radio environments with reconfigurable intelligent surfaces
(RISs) enables the paradigm of smart radio environments in which wireless
system engineers are no longer limited to only controlling the radiated signals
but can in addition also optimize the wireless channels. Many practical radio
environments include complex scattering objects, especially indoor and factory
settings. Multipath propagation therein creates seemingly intractable coupling
effects between RIS elements, leading to the following questions: How can a
RIS-parametrized rich-scattering environment be modelled in a physics-compliant
manner? Can the parameters of such a model be estimated for a specific but
unknown experimental environment? And how can the RIS configuration be
optimized given a calibrated physics-compliant model? This chapter summarizes
the current state of the art in this field, highlighting the recently unlocked
potential of frugal physical-model-based open-loop control of RIS-parametrized
rich-scattering radio environments.Comment: 29 pages, 3 figures, author's version of chapter from forthcoming
book "Reconfigurable Metasurfaces for Wireless Communications: Architectures,
Modeling, and Optimization
Efficient Computation of Physics-Compliant Channel Realizations for (Rich-Scattering) RIS-Parametrized Radio Environments
Physics-compliant channel models of RIS-parametrized radio environments
require the inversion of an "interaction matrix" to capture the mutual coupling
between wireless entities (transmitters, receivers, RIS, environmental
scattering objects) due to proximity and reverberation. The computational cost
of this matrix inversion is typically dictated by the environmental scattering
objects in non-trivial radio environments, and scales unfavorably with the
latter's complexity. In addition, many problems of interest in wireless
communications (RIS optimization, fast fading, object or user-equipment
localization, etc.) require the computation of multiple channel realizations.
To overcome the potentially prohibitive computational cost of using
physics-compliant channel models, we i) introduce an isospectral reduction of
the interaction matrix from the canonical basis to an equivalent reduced basis
of primary wireless entities (antennas and RIS), and ii) leverage the fact that
interaction matrices for different channel realizations only differ regarding
RIS configurations and/or some wireless entities' locations.Comment: 12 pages, 1 figure, submitted to an IEEE Journa
Leveraging Chaos for Wave-Based Analog Computation: Demonstration with Indoor Wireless Communication Signals
In sight of fundamental thermal limits on further substantial performance
improvements of modern digital computational processing units, wave-based
analog computation is becoming an enticing alternative. A wave, as it
propagates through a carefully tailored medium, performs the desired
computational operation. Yet, the necessary designs are so intricate that
experimental demonstrations will necessitate further technological advances.
Here, we show that, counterintuitively, the carefully tailored medium can be
replaced with a random medium, subject to an appropriate shaping of the
incident wave front. Using tunable metasurface reflect-arrays, we demonstrate
our concept experimentally in a chaotic microwave cavity. We conclude that
off-the-shelf wireless communication infrastructure in combination with a
simple reflect-array suffices to perform analog computation with Wi-Fi waves
reverberating in a room.Comment: 13 pages including 5 figures + 7 pages Supplemental Materia
A self-adaptive RIS that estimates and shapes fading rich-scattering wireless channels
We present a framework for operating a self-adaptive RIS inside a fading
rich-scattering wireless environment. We model the rich-scattering wireless
channel as being double-parametrized by (i) the RIS, and (ii) dynamic
perturbers (moving objects, etc.). Within each coherence time, first, the
self-adaptive RIS estimates the status of the dynamic perturbers (e.g., the
perturbers' orientations and locations) based on measurements with an auxiliary
wireless channel. Then, second, using a learned surrogate forward model of the
mapping from RIS configuration and perturber status to wireless channel, an
optimized RIS configuration to achieve a desired functionality is obtained. We
demonstrate our technique using a physics-based end-to-end model of
RIS-parametrized communication with adjustable fading (PhysFad) for the example
objective of maximizing the received signal strength indicator. Our results
present a route toward convergence of RIS-empowered localization and sensing
with RIS-empowered channel shaping beyond the simple case of operation in free
space without fading.Comment: 5 pages, 3 figures, submitted to an IEEE Conferenc
Turning Optical Complex Media into Universal Reconfigurable Linear Operators by Wavefront Shaping
Performing linear operations using optical devices is a crucial building
block in many fields ranging from telecommunication to optical analogue
computation and machine learning. For many of these applications, key
requirements are robustness to fabrication inaccuracies and reconfigurability.
Current designs of custom-tailored photonic devices or coherent photonic
circuits only partially satisfy these needs. Here, we propose a way to perform
linear operations by using complex optical media such as multimode fibers or
thin scattering layers as a computational platform driven by wavefront shaping.
Given a large random transmission matrix (TM) representing light propagation in
such a medium, we can extract a desired smaller linear operator by finding
suitable input and output projectors. We discuss fundamental upper bounds on
the size of the linear transformations our approach can achieve and provide an
experimental demonstration. For the latter, first we retrieve the complex
medium's TM with a non-interferometric phase retrieval method. Then, we take
advantage of the large number of degrees of freedom to find input wavefronts
using a Spatial Light Modulator (SLM) that cause the system, composed of the
SLM and the complex medium, to act as a desired complex-valued linear operator
on the optical field. We experimentally build several
complex-valued operators, and are able to switch from one to another at will.
Our technique offers the prospect of reconfigurable, robust and
easy-to-fabricate linear optical analogue computation units
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