280 research outputs found
Multiple Access in Aerial Networks: From Orthogonal and Non-Orthogonal to Rate-Splitting
Recently, interest on the utilization of unmanned aerial vehicles (UAVs) has
aroused. Specifically, UAVs can be used in cellular networks as aerial users
for delivery, surveillance, rescue search, or as an aerial base station (aBS)
for communication with ground users in remote uncovered areas or in dense
environments requiring prompt high capacity. Aiming to satisfy the high
requirements of wireless aerial networks, several multiple access techniques
have been investigated. In particular, space-division multiple access(SDMA) and
power-domain non-orthogonal multiple access (NOMA) present promising
multiplexing gains for aerial downlink and uplink. Nevertheless, these gains
are limited as they depend on the conditions of the environment. Hence, a
generalized scheme has been recently proposed, called rate-splitting multiple
access (RSMA), which is capable of achieving better spectral efficiency gains
compared to SDMA and NOMA. In this paper, we present a comprehensive survey of
key multiple access technologies adopted for aerial networks, where aBSs are
deployed to serve ground users. Since there have been only sporadic results
reported on the use of RSMA in aerial systems, we aim to extend the discussion
on this topic by modelling and analyzing the weighted sum-rate performance of a
two-user downlink network served by an RSMA-based aBS. Finally, related open
issues and future research directions are exposed.Comment: 16 pages, 6 figures, submitted to IEEE Journa
Wideband User Grouping for Uplink Multiuser mmWave MIMO Systems With Hybrid Combining
[Abstract]
Analog-digital hybrid precoding and combining schemes constitute an interesting approach to millimeter-wave (mmWave) multiple-input multiple-output (MIMO) systems due to the low hardware complexity and/or low power required for its deployment. However, the design of the hybrid precoders and combiners of a wideband multiuser (MU) mmWave MIMO system is challenging because the signal processing in the analog domain is constrained to be frequency flat. Furthermore, the number of radio frequency (RF) chains limits the number of individual streams that a common base station (BS) can simultaneously serve. This work jointly addresses the user scheduling, the user precoder design, and the BS hybrid combining design for the uplink of wideband MU mmWave MIMO systems. On the one hand, user precoding and BS hybrid combining are jointly designed to minimize the impact of having frequency-flat RF components. On the other hand, a number of users larger than the number of RF chains are served at the BS by employing a distributed quantizer linear coding (DQLC)-based non-orthogonal multiple access (NOMA) scheme. The use of this encoding strategy also allows exploiting the spatial correlation between the source information. Simulation results show remarkable performance gains of the proposed approaches for wideband mmWave MIMO hardware-constrained systems.10.13039/501100010801-Xunta de Galicia (Grant Number: ED431C 2020/15)
10.13039/501100010801-Centro de Investigación de Galicia CITIC (Grant Number: ED431G2019/01)
10.13039/501100011033-Agencia Estatal de Investigación of Spain (Grant Number: RED2018-102668-T and PID2019-104958RB-C42)
European Regional Development Funds (ERDF) of the EU (ERDF Galicia 2014-2020 & AEI/ERDF programs, UE)
Predoctoral (Grant Number: BES-2017-081955)Xunta de Galicia; ED431C 2020/15Xunta de Galicia; ED431G2019/0
State of the Art, Taxonomy, and Open Issues on Cognitive Radio Networks with NOMA
The explosive growth of mobile devices and the rapid increase of wideband
wireless services call for advanced communication techniques that can achieve
high spectral efficiency and meet the massive connectivity requirement.
Cognitive radio (CR) and non-orthogonal multiple access (NOMA) are envisioned
to be important solutions for the fifth generation wireless networks.
Integrating NOMA techniques into CR networks (CRNs) has the tremendous
potential to improve spectral efficiency and increase the system capacity.
However, there are many technical challenges due to the severe interference
caused by using NOMA. Many efforts have been made to facilitate the application
of NOMA into CRNs and to investigate the performance of CRNs with NOMA. This
article aims to survey the latest research results along this direction. A
taxonomy is devised to categorize the literature based on operation paradigms,
enabling techniques, design objectives and optimization characteristics.
Moreover, the key challenges are outlined to provide guidelines for the domain
researchers and designers to realize CRNs with NOMA. Finally, the open issues
are discussed.Comment: This paper has been accepted by IEEE Wireless Communications
Magazine. Pages 16, Figures
A Tutorial on Nonorthogonal Multiple Access for 5G and Beyond
Today's wireless networks allocate radio resources to users based on the
orthogonal multiple access (OMA) principle. However, as the number of users
increases, OMA based approaches may not meet the stringent emerging
requirements including very high spectral efficiency, very low latency, and
massive device connectivity. Nonorthogonal multiple access (NOMA) principle
emerges as a solution to improve the spectral efficiency while allowing some
degree of multiple access interference at receivers. In this tutorial style
paper, we target providing a unified model for NOMA, including uplink and
downlink transmissions, along with the extensions tomultiple inputmultiple
output and cooperative communication scenarios. Through numerical examples, we
compare the performances of OMA and NOMA networks. Implementation aspects and
open issues are also detailed.Comment: 25 pages, 10 figure
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