1,578 research outputs found
Reconfigurable Intelligent Surface Aided NOMA Networks
Reconfigurable intelligent surfaces (RISs) constitute a promising performance
enhancement for next-generation (NG) wireless networks in terms of enhancing
both their spectrum efficiency (SE) and energy efficiency (EE). We conceive a
system for serving paired power-domain non-orthogonal multiple access (NOMA)
users by designing the passive beamforming weights at the RISs. In an effort to
evaluate the network performance, we first derive the best-case and worst-case
of new channel statistics for characterizing the effective channel gains. Then,
we derive the best-case and worst-case of our closed-form expressions derived
both for the outage probability and for the ergodic rate of the prioritized
user. For gleaning further insights, we investigate both the diversity orders
of the outage probability and the high-signal-to-noise (SNR) slopes of the
ergodic rate. We also derive both the SE and EE of the proposed network. Our
analytical results demonstrate that the base station (BS)-user links have
almost no impact on the diversity orders attained when the number of RISs is
high enough. Numerical results are provided for confirming that: i) the
high-SNR slope of the RIS-aided network is one; ii) the proposed RIS-aided NOMA
network has superior network performance compared to its orthogonal
counterpart.Comment: arXiv admin note: text overlap with arXiv:1910.0095
Reconfigurable Intelligent Surface-Empowered MIMO Systems
Reconfigurable intelligent surface (RIS)-assisted communications appear as a
promising candidate for future wireless systems due to its attractive
advantages in terms of implementation cost and end-to-end system performance.
In this paper, two new multiple-input multiple-output (MIMO) system designs
using RISs are presented to enhance the performance and boost the spectral
efficiency of state-of-the-art MIMO communication systems. Vertical Bell Labs
layered space-time (VBLAST) and Alamouti's schemes have been considered in this
study and RIS-based simple transceiver architectures are proposed. For the
VBLAST-based new system, an RIS is used to enhance the performance of the
nulling and canceling-based sub-optimal detection procedure as well as to
noticeably boost the spectral efficiency by conveying extra bits through the
adjustment of the phases of the RIS elements. In addition, RIS elements have
been utilized in order to redesign Alamouti's scheme with a single radio
frequency (RF) signal generator at the transmitter side and to enhance its bit
error rate (BER) performance. Monte Carlo simulations are provided to show the
effectiveness of our system designs and it has been shown that they outperform
the reference schemes in terms of BER performance and spectral efficiency.Comment: To appear in IEEE SYSTEMS JOURNAL, 9 pages, 6 figures, and 1 tabl
Increased Multiplexing Gain with Reconfigurable Surfaces: Simultaneous Channel Orthogonalization and Information Embedding
Reconfigurable surface (RS) has been shown to be an effective solution for
improving wireless communication links in general multi-user multiple-input
multiple-output (MU-MIMO) setting. Current research efforts have been largely
directed towards the study of reconfigurable intelligent surface (RIS), which
corresponds to an RS made of passive reconfigurable elements with only phase
shifting capabilities. RIS constitutes a cost- and energy- efficient solution
for increased beamforming gain since it allows to generate constructive
interference towards desired directions, e.g., towards a base station (BS).
However, in many situations, multiplexing gain may have greater impact on the
achievable transmission rates and number of simultaneously connected devices,
while RIS has only been able to achieve minor improvements in this aspect.
Recent work has proposed the use of alternative RS technologies, namely
amplitude-reconfigurable intelligent surface (ARIS) and fully-reconfigurable
intelligent surface (FRIS), to achieve perfect orthogonalization of MU-MIMO
channels, thus allowing for maximum multiplexing gain at reduced complexity. In
this work we consider the use of ARIS and FRIS for simultaneously
orthogonalizing a MU-MIMO channel, while embedding extra information in the
orthogonalized channel. We show that the resulting achievable rates allow for
full exploitation of the degrees of freedom in a MU-MIMO system with excess of
BS antennas.Comment: 6 pages, 2 figures, accepted at IEEE GLOBECOM 202
Active Reconfigurable Intelligent Surface Aided Wireless Communications
Reconfigurable Intelligent Surface (RIS) is a promising solution to
reconfigure the wireless environment in a controllable way. To compensate for
the double-fading attenuation in the RIS-aided link, a large number of passive
reflecting elements (REs) are conventionally deployed at the RIS, resulting in
large surface size and considerable circuit power consumption. In this paper,
we propose a new type of RIS, called active RIS, where each RE is assisted by
active loads (negative resistance), that reflect and amplify the incident
signal instead of only reflecting it with the adjustable phase shift as in the
case of a passive RIS. Therefore, for a given power budget at the RIS, a
strengthened RIS-aided link can be achieved by increasing the number of active
REs as well as amplifying the incident signal. We consider the use of an active
RIS to a single input multiple output (SIMO) system. {However, it would
unintentionally amplify the RIS-correlated noise, and thus the proposed system
has to balance the conflict between the received signal power maximization and
the RIS-correlated noise minimization at the receiver. To achieve this goal, it
has to optimize the reflecting coefficient matrix at the RIS and the receive
beamforming at the receiver.} An alternating optimization algorithm is proposed
to solve the problem. Specifically, the receive beamforming is obtained with a
closed-form solution based on linear minimum-mean-square-error (MMSE)
criterion, while the reflecting coefficient matrix is obtained by solving a
series of sequential convex approximation (SCA) problems. Simulation results
show that the proposed active RIS-aided system could achieve better performance
over the conventional passive RIS-aided system with the same power budget
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