117 research outputs found
Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites
Satellite Communication systems are a promising solution to extend and
complement terrestrial networks in unserved or under-served areas. This aspect
is reflected by recent commercial and standardisation endeavours. In
particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G,
Non-Terrestrial Networks aimed at deploying satellite systems either as a
stand-alone solution or as an integration to terrestrial networks in mobile
broadband and machine-type communication scenarios. However, typical satellite
channel impairments, as large path losses, delays, and Doppler shifts, pose
severe challenges to the realisation of a satellite-based NR network. In this
paper, based on the architecture options currently being discussed in the
standardisation fora, we discuss and assess the impact of the satellite channel
characteristics on the physical and Medium Access Control layers, both in terms
of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB)
and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis
shows that the main technical challenges are related to the PHY/MAC procedures,
in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic
Repeat reQuest (HARQ) and, depending on the considered service and
architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201
Dynamic RF Chain Selection for Energy Efficient and Low Complexity Hybrid Beamforming in Millimeter Wave MIMO Systems
This paper proposes a novel architecture with a framework that dynamically activates the optimal number of radio frequency (RF) chains used to implement hybrid beamforming in a millimeter wave (mmWave) multiple-input and multiple-output (MIMO) system. We use fractional programming to solve an energy efficiency maximization problem and exploit the Dinkelbach method (DM)-based framework to optimize the number of active RF chains and data streams. This solution is updated dynamically based on the current channel conditions, where the analog/digital (A/D) hybrid precoder and combiner matrices at the transmitter and the receiver, respectively, are designed using a codebook-based fast approximation solution called gradient pursuit (GP). The GP algorithm shows less run time and complexity while compared to the state-of-the-art orthogonal matching pursuit (OMP) solution. The energy and spectral efficiency performance of the proposed framework is compared with the existing state-of-the-art solutions, such as the brute force (BF), the digital beamformer, and the analog beamformer. The codebook-free approaches to design the precoders and combiners, such as alternating direction method of multipliers (ADMMs) and singular value decomposition (SVD)-based solution are also shown to be incorporated into the proposed framework to achieve better energy efficiency performance
Multi-Antenna Data-Driven Eavesdropping Attacks and Symbol-Level Precoding Countermeasures
In this work, we consider secure communications in wireless multi-user (MU)
multiple-input single-output (MISO) systems with channel coding in the presence
of a multi-antenna eavesdropper (Eve). In this setting, we exploit machine
learning (ML) tools to design soft and hard decoding schemes by using precoded
pilot symbols as training data. In this context, we propose ML frameworks for
decoders that allow an Eve to determine the transmitted message with high
accuracy. We thereby show that MU-MISO systems are vulnerable to such
eavesdropping attacks even when relatively secure transmission techniques are
employed, such as symbol-level precoding (SLP). To counteract this attack, we
propose two novel SLP-based schemes that increase the bit-error rate at Eve by
impeding the learning process. We design these two security-enhanced schemes to
meet different requirements regarding complexity, security, and power
consumption. Simulation results validate both the ML-based eavesdropping
attacks as well as the countermeasures, and show that the gain in security is
achieved without affecting the decoding performance at the intended users.Comment: Submitted to the IEEE Transactions on Information Forensics and
Securit
Reconfigurable Intelligent Surfaces for Smart Cities: Research Challenges and Opportunities
The concept of Smart Cities has been introduced as a way to benefit from the
digitization of various ecosystems at a city level. To support this concept,
future communication networks need to be carefully designed with respect to the
city infrastructure and utilization of resources. Recently, the idea of 'smart'
environment, which takes advantage of the infrastructure for better performance
of wireless networks, has been proposed. This idea is aligned with the recent
advances in design of reconfigurable intelligent surfaces (RISs), which are
planar structures with the capability to reflect impinging electromagnetic
waves toward preferred directions. Thus, RISs are expected to provide the
necessary flexibility for the design of the 'smart' communication environment,
which can be optimally shaped to enable cost- and energy-efficient signal
transmissions where needed. Upon deployment of RISs, the ecosystem of the Smart
Cities would become even more controllable and adaptable, which would
subsequently ease the implementation of future communication networks in urban
areas and boost the interconnection among private households and public
services. In this paper, we describe our vision of the application of RISs in
future Smart Cities. In particular, the research challenges and opportunities
are addressed. The contribution paves the road to a systematic design of
RIS-assisted communication networks for Smart Cities in the years to come.Comment: Submitted for possible publication in IEEE Open Journal of the
Communications Societ
Scalable cell-free massive MIMO systems with hardware impairments
© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This is the accepted manuscript version of a conference paper which has been published in final form at https://doi.org/10.1109/PIMRC48278.2020.9217151Despite the deleterious effect of hardware impairments (HWIs) on wireless systems, most prior works in cell-free (CF) massive multiple-input-multiple-output (mMIMO) systems have not accounted for their impact. In particular, the effect of phase noise (PN) has not been investigated at all in CF systems. Moreover, there is no work investigating HWIs in scalable CF (SCF) mMIMO systems, encountering the prohibitively demanding fronthaul requirements of large networks with many users. Hence, we derive the uplink spectral efficiency (SE) under HWIs with minimum mean-squared error (MMSE) combining in closed-form by means of the deterministic equivalent (DE) analysis. Notably, previous works, accounted for MMSE decoding, studied the corresponding SE only by means of simulations. Numerical results illustrate the performance loss due to HWIs and result in insightful conclusions
Performance of Joint Symbol Level Precoding and RIS Phase Shift Design in the Finite Block Length Regime with Constellation Rotation
In this paper, we tackle the problem of joint symbol level precoding (SLP)
and reconfigurable intelligent surface (RIS) phase shift design with
constellation rotation in the finite block length regime. We aim to increase
energy efficiency by minimizing the total transmit power while satisfying the
quality of service constraints. The total power consumption can be
significantly minimized through the exploitation of multiuser interference by
symbol level precoding and by the intelligent manipulation of the propagation
environment using reconfigurable intelligent surfaces. In addition, the
constellation rotation per user contributes to energy efficiency by aligning
the symbol phases of the users, thus improving the utilization of constructive
interference. The formulated power minimization problem is non-convex and
correspondingly difficult to solve directly. Hence, we employ an alternating
optimization algorithm to tackle the joint optimization of SLP and RIS phase
shift design. The optimal phase of each user's constellation rotation is
obtained via an exhaustive search algorithm. Through Monte-Carlo simulation
results, we demonstrate that the proposed solution yields substantial power
minimization as compared to conventional SLP, zero forcing precoding with RIS
as well as the benchmark schemes without RIS.Comment: 6 pages,4 figures. This paper has been accepted by IEEE International
Symposium on Personal, Indoor and Mobile Radio Communication
Perpetual Reconfigurable Intelligent Surfaces Through In-Band Energy Harvesting: Architectures, Protocols, and Challenges
Reconfigurable intelligent surfaces (RISs) are considered to be a key enabler
of highly energy-efficient 6G and beyond networks. This property arises from
the absence of power amplifiers in the structure, in contrast to active nodes,
such as small cells and relays. However, still an amount of power is required
for their operation. To improve their energy efficiency further, we propose the
notion of perpetual RISs, which secure the power needed to supply their
functionalities through wireless energy harvesting of the impinging transmitted
electromagnetic signals. Towards this, we initially explain the rationale
behind such RIS capability and proceed with the presentation of the main RIS
controller architecture that can realize this vision under an in-band energy
harvesting consideration. Furthermore, we present a typical energy-harvesting
architecture followed by two harvesting protocols. Subsequently, we study the
performance of the two protocols under a typical communications scenario.
Finally, we elaborate on the main research challenges governing the realization
of large-scale networks with perpetual RISs.Comment: 7 pages, 8 figure
Integration of Backscatter Communication with Multi-cell NOMA: A Spectral Efficiency Optimization under Imperfect SIC
Future wireless networks are expected to connect large-scale low-powered
communication devices using the available spectrum resources. Backscatter
communications (BC) is an emerging technology towards battery-free transmission
in future wireless networks by leveraging ambient radio frequency (RF) waves
that enable communications among wireless devices. Non-orthogonal multiple
access (NOMA) has recently drawn significant attention due to its high spectral
efficiency. The combination of these two technologies can play an important
role in the development of future networks. This paper proposes a new
optimization approach to enhance the spectral efficiency of nonorthogonal
multiple access (NOMA)-BC network. Our framework simultaneously optimizes the
power allocation of base station and reflection coefficient (RC) of the
backscatter device in each cell under the assumption of imperfect signal
decoding. The problem of spectral efficiency maximization is coupled on power
and RC which is challenging to solve. To make this problem tractable, we first
decouple it into two subproblems and then apply the decomposition method and
Karush-Kuhn-Tucker conditions to obtain the efficient solution. Numerical
results show the performance of the proposed NOMA-BC network over the pure NOMA
network without BC.Comment: 5 pages, 4 figure
Time-and unit-cell splitting comparison for the autonomous operation of reconfigurable intelligent surfaces
In this work, we analytically compare the performance of the time-and unit cell-splitting protocols for satisfying the energy needs of reconfigurable intelligent surfaces (RISs) through wireless energy harvesting from information signals. We first compute the RIS energy consumption per frame for both protocols and subsequently formulate an optimization problem that maximizes the average rate under the constraint of meeting the RIS long-term energy consumption demands. Analytical solutions to the optimal allocation of resources that involve a single integral are provided for both protocols in the case of random transmitter-RIS links that are subject to Rician or Nakagami-m fading distributions. Moreover, closed-form solutions are provided for the case of deterministic transmitter-RIS links. In addition, increasing and decreasing monotonic trends are revealed, based on analysis, for the ratio of the achievable rates of the presented protocols with respect to the RIS energy consumption. Finally, numerical results validate the analytical findings and reveal that the unit cell-splitting protocol exhibits a notably higher average rate performance compared with its time-splitting counterpart throughout the feasible range of RIS energy consumption values. However, this comes at a cost of a notably reduced signal-to-noise ratio as the RIS energy demands increase.This work has been supported by the Luxembourg National Research Fund (FNR)-RISOTTI Project, ref. 14773976.Peer ReviewedPostprint (published version
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