689 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 (RIS) Aided Multi-User Networks: Interplay Between NOMA and RIS
This article focuses on the exploitation of reconfigurable intelligent
surfaces (RISs) in multi-user networks employing orthogonal multiple access
(OMA) or non-orthogonal multiple access (NOMA), with an emphasis on
investigating the interplay between NOMA and RIS. Depending on whether the RIS
reflection coefficients can be adjusted only once or multiple times during one
transmission, we distinguish between static and dynamic RIS configurations. In
particular, the capacity region of RIS aided single-antenna NOMA networks is
characterized and compared with the OMA rate region from an
information-theoretic perspective, revealing that the dynamic RIS configuration
is capacity-achieving. Then, the impact of the RIS deployment location on the
performance of different multiple access schemes is investigated, which reveals
that asymmetric and symmetric deployment strategies are preferable for NOMA and
OMA, respectively. Furthermore, for RIS aided multiple-antenna NOMA networks,
three novel joint active and passive beamformer designs are proposed based on
both beamformer based and cluster based strategies. Finally, open research
problems for RIS-NOMA networks are highlighted.Comment: 13 pages, 6 figure
IRS-assisted UAV Communications: A Comprehensive Review
Intelligent reflecting surface (IRS) can smartly adjust the wavefronts in
terms of phase, frequency, amplitude and polarization via passive reflections
and without any need of radio frequency (RF) chains. It is envisaged as an
emerging technology which can change wireless communication to improve both
energy and spectrum efficiencies with low energy consumption and low cost. It
can intelligently configure the wireless channels through a massive number of
cost effective passive reflecting elements to improve the system performance.
Similarly, unmanned aerial vehicle (UAV) communication has gained a viable
attention due to flexible deployment, high mobility and ease of integration
with several technologies. However, UAV communication is prone to security
issues and obstructions in real-time applications. Recently, it is foreseen
that UAV and IRS both can integrate together to attain unparalleled
capabilities in difficult scenarios. Both technologies can ensure improved
performance through proactively altering the wireless propagation using smart
signal reflections and maneuver control in three dimensional (3D) space. IRS
can be integrated in both aerial and terrene environments to reap the benefits
of smart reflections. This study briefly discusses UAV communication, IRS and
focuses on IRS-assisted UAC communications. It surveys the existing literature
on this emerging research topic and highlights several promising technologies
which can be implemented in IRS-assisted UAV communication. This study also
presents several application scenarios and open research challenges. This study
goes one step further to elaborate research opportunities to design and
optimize wireless systems with low energy footprint and at low cost. Finally,
we shed some light on future research aspects for IRS-assisted UAV
communication
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