69,126 research outputs found
A Communication Model for Large Intelligent Surfaces
The purpose of this paper is to introduce a communication model for Large
Intelligent Surfaces (LIS). A LIS is modelled as a collection of tiny closely
spaced antenna elements. Due to the proximity of the elements, mutual coupling
arises. An optimal transmitter design depends on the mutual coupling matrix.
For single user communication, the optimal transmitter uses the inverse of the
mutual coupling matrix in a filter matched to the channel vector. We give the
expression of the mutual coupling for two types of planar arrays. The
conditioning number of the mutual coupling matrix is unbounded as the antenna
element density increases, so only the dominant values can be inverted within
reasonable computation. The directivity is partial but still significant
compared to the conventional gain. When the spacing between elements becomes
small (smaller than half a wavelength), the directivity surpasses the
conventional directivity equal to the number of antennas, as well as the gain
obtained when modelling the surface as continuous. The gain is theoretically
unbounded as the element density increases for a constant aperture.Comment: 6 pages, 7 figures; typos correcte
Multiuser MIMO with Large Intelligent Surfaces: Communication Model and Transmit Design
This paper proposes a communication model for multiuser multiple-input
multiple-output (MIMO) systems based on large intelligent surfaces (LIS), where
the LIS is modeled as a collection of tightly packed antenna elements. The LIS
system is first represented in a circuital way, obtaining expressions for the
radiated and received powers, as well as for the coupling between the distinct
elements. Then, this circuital model is used to characterize the channel in a
line-of-sight propagation scenario, rendering the basis for the analysis and
design of MIMO systems. Due to the particular properties of LIS, the model
accounts for superdirectivity and mutual coupling effects along with near field
propagation, necessary in those situations where the array dimension becomes
very large. Finally, with the proposed model, the matched filter transmitter
and the weighted minimum mean square error precoding are derived under both
realistic constraints: limited radiated power and maximum ohmic losses.Comment: 6 pages, 3 figures; This paper is submitted to IEEE International
Conference on Communications (ICC) 202
Reconfigurable Intelligent Surfaces for Wireless Communications: Principles, Challenges, and Opportunities
Recently there has been a flurry of research on the use of reconfigurable
intelligent surfaces (RIS) in wireless networks to create smart radio
environments. In a smart radio environment, surfaces are capable of
manipulating the propagation of incident electromagnetic waves in a
programmable manner to actively alter the channel realization, which turns the
wireless channel into a controllable system block that can be optimized to
improve overall system performance. In this article, we provide a tutorial
overview of reconfigurable intelligent surfaces (RIS) for wireless
communications. We describe the working principles of reconfigurable
intelligent surfaces (RIS) and elaborate on different candidate implementations
using metasurfaces and reflectarrays. We discuss the channel models suitable
for both implementations and examine the feasibility of obtaining accurate
channel estimates. Furthermore, we discuss the aspects that differentiate RIS
optimization from precoding for traditional MIMO arrays highlighting both the
arising challenges and the potential opportunities associated with this
emerging technology. Finally, we present numerical results to illustrate the
power of an RIS in shaping the key properties of a MIMO channel.Comment: to appear in the IEEE Transactions on Cognitive Communications and
Networking (TCCN
- …