2,971 research outputs found
RISnet: A Scalable Approach for Reconfigurable Intelligent Surface Optimization with Partial CSI
The reconfigurable intelligent surface (RIS) is a promising technology that
enables wireless communication systems to achieve improved performance by
intelligently manipulating wireless channels. In this paper, we consider the
sum-rate maximization problem in a downlink multi-user
multi-input-single-output (MISO) channel via space-division multiple access
(SDMA). Two major challenges of this problem are the high dimensionality due to
the large number of RIS elements and the difficulty to obtain the full channel
state information (CSI), which is assumed known in many algorithms proposed in
the literature. Instead, we propose a hybrid machine learning approach using
the weighted minimum mean squared error (WMMSE) precoder at the base station
(BS) and a dedicated neural network (NN) architecture, RISnet, for RIS
configuration. The RISnet has a good scalability to optimize 1296 RIS elements
and requires partial CSI of only 16 RIS elements as input. We show it achieves
a high performance with low requirement for channel estimation for geometric
channel models obtained with ray-tracing simulation. The unsupervised learning
lets the RISnet find an optimized RIS configuration by itself. Numerical
results show that a trained model configures the RIS with low computational
effort, considerably outperforms the baselines, and can work with discrete
phase shifts
Reconfigurable Intelligent Surface for Physical Layer Security in 6G-IoT: Designs, Issues, and Advances
Sixth-generation (6G) networks pose substantial security risks because
confidential information is transmitted over wireless channels with a broadcast
nature, and various attack vectors emerge. Physical layer security (PLS)
exploits the dynamic characteristics of wireless environments to provide secure
communications, while reconfigurable intelligent surfaces (RISs) can facilitate
PLS by controlling wireless transmissions. With RIS-aided PLS, a lightweight
security solution can be designed for low-end Internet of Things (IoT) devices,
depending on the design scenario and communication objective. This article
discusses RIS-aided PLS designs for 6G-IoT networks against eavesdropping and
jamming attacks. The theoretical background and literature review of RIS-aided
PLS are discussed, and design solutions related to resource allocation,
beamforming, artificial noise, and cooperative communication are presented. We
provide simulation results to show the effectiveness of RIS in terms of PLS. In
addition, we examine the research issues and possible solutions for RIS
modeling, channel modeling and estimation, optimization, and machine learning.
Finally, we discuss recent advances, including STAR-RIS and malicious RIS.Comment: Accepted for IEEE Internet of Things Journa
Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays
Massive MIMO (multiple-input multiple-output) is no longer a "wild" or
"promising" concept for future cellular networks - in 2018 it became a reality.
Base stations (BSs) with 64 fully digital transceiver chains were commercially
deployed in several countries, the key ingredients of Massive MIMO have made it
into the 5G standard, the signal processing methods required to achieve
unprecedented spectral efficiency have been developed, and the limitation due
to pilot contamination has been resolved. Even the development of fully digital
Massive MIMO arrays for mmWave frequencies - once viewed prohibitively
complicated and costly - is well underway. In a few years, Massive MIMO with
fully digital transceivers will be a mainstream feature at both sub-6 GHz and
mmWave frequencies. In this paper, we explain how the first chapter of the
Massive MIMO research saga has come to an end, while the story has just begun.
The coming wide-scale deployment of BSs with massive antenna arrays opens the
door to a brand new world where spatial processing capabilities are
omnipresent. In addition to mobile broadband services, the antennas can be used
for other communication applications, such as low-power machine-type or
ultra-reliable communications, as well as non-communication applications such
as radar, sensing and positioning. We outline five new Massive MIMO related
research directions: Extremely large aperture arrays, Holographic Massive MIMO,
Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive
MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin
Alternating Beamforming with Intelligent Reflecting Surface Element Allocation
Intelligent reflecting surface (IRS) has become a promising technology to aid
next generation wireless communication systems. In this paper, we develop an
alternating beamforming technique with a novel concept of IRS element
allocation for multiple-input multiple-output systems when a base station
supports multiple single antenna users aided with a single IRS. Specifically,
we allocate each IRS element separately to each user, thus, in the beamforming
stage allowing the IRS element only consider a single user at a time. In result
to this separation, the complexity is vastly decreased. The proposed
beamforming technique tries to maximize the minimum rate of all users with
minimal complexity. In the numerical results, we show that the proposed
technique is comparable to the convex optimization-based benchmark with
sufficiently less complexity.Comment: 5 pages, 3 figures, submitted to Wireless Communications Letters
(WCL
Generalised Impedance Model of Wireless Links Assisted by Reconfigurable Intelligent Surfaces
We devise an end-to-end communication channel model that describes the
performance of RIS-assisted MIMO wireless links. The model borrows the
impedance (interaction) matrix formalism from the Method of Moments and
provides a physics-based communication model. In configurations where the
transmit and receive antenna arrays are distant from the RIS beyond a
wavelength, a reduced model provides accurate results for arbitrary RIS unit
cell geometry. Importantly, the simplified model configures as a cascaded
channel transfer matrix whose mathematical structure is compliant with widely
accepted, but less accurate, system level RIS models. A numerical validation of
the communication model is presented for the design of binary RIS structures
with scatterers of canonical geometry. Attained results are consistent with
path-loss models: For obstructed line-of-sight between transmitter and
receiver, the channel capacity of the (optimised) RIS-assisted link scales as
, with RIS-receiver distance at fixed transmitter position. Our
results shows that the applicability of communication models based on mutual
impedance matrices is not restricted to canonical minimum scattering RIS unit
cells.Comment: Submitted to IEEE Transactions on Antennas and Propagation; 15 pages,
11 figure
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