133 research outputs found
On the physical layer security characteristics for MIMO-SVD techniques for SC-FDE schemes
partially supported by the FCT -Fundacao para a Ciencia e Tecnologia and Instituto de Telecomunicacoes under projects UID/EEA/50008/2019.
PES3N POCI-01-0145-FEDER-030629.Multi-Input, Multi-Output (MIMO) techniques are seeing widespread usage in wireless communication systems due to their large capacity gains. On the other hand, security is a concern of any wireless system, which can make schemes that implement physical layer security key in assuring secure communications. In this paper, we study the physical layer security issues of MIMO with Singular Value Decomposition (SVD) schemes, employed along with Single-Carrier with Frequency-Domain Equalization (SC-FDE) techniques. More concretely. the security potential against an unintended eavesdropper is analysed, and it is shown that the higher the distance between the eavesdropper and the transmitter or receiver, the higher the secrecy rate. In addition, in a scenario where there is Line of Sight (LOS) between all users, it is shown that the secrecy rate can be even higher than in the previous scenario. Therefore, MIMO-SVD schemes combined with SC-FDE can be an efficient option for highly secure MIMO communications.publishersversionpublishe
High Performance Single Carrier Schemes for Massive MIMO Systems
As the demands for faster and cheaper telecommunication systems continue to grow,
so to do the demands for more efficient and secure systems. There have been several
solutions proposed, with the most commonly accepted ones employing Massive Multiple
Input, Multiple Output (mMIMO), featuring large arrays of antennas. The downside of
these systems lies mainly in the need for computationally heavy channel equalization
algorithms and the high hardware requirements, namely due to the need of many Power
Amplifiers (PAs), Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters
(DACs). This work analyses receivers that can handle these downsides, beginning with the
low complexity equalization receivers Maximal-Ratio Detector (MRD) and Equal-Gain
Detector (EGD), that can lower the equalization’s computation time. Then a Singular
Value Decomposition (SVD) receiver is studied, with a proposed interleaving scheme to
allow for equal performance on all streams, combined with a scheme for estimating and
cancelling the non-linear distortion to reduce the impact of cheaper and more powerefficient
PAs. These receivers are then improved with the introduction of an error correcting
convolutional code. Lastly, it is demonstrated that the SVD receiver can be appealing
as a solution for Physical Layer Security (PLS) in mMIMO systems
Simultaneous Wireless Information and Power Transfer in 5G communication
Green communication technology is expected to be widely adopted in future generation
networks to improve energy efficiency and reliability of wireless communication network.
Among the green communication technologies,simultaneous wireless information and
power transfer (SWIPT) is adopted for its flexible energy harvesting technology through
the radio frequency (RF) signa lthati sused for information transmission. Even though
existing SWIPT techniques are flexible and adoptable for the wireless communication
networks, the power and time resources of the signal need to be shared between infor-
mation transmission and RF energy harvesting, and this compromises the quality of the
signal. Therefore,SWIP Ttechniques need to be designed to allow an efficient resource
allocation for communication and energy harvesting.
The goal oft his thesisis to design SWIP Ttechniques that allow efficient,reliable and
secure joint communications and power transference. A problem associated to SWIPT
techniques combined with multi carrier signals is that the increased power requirements
inherent to energy harvesting purposes can exacerbate nonlinear distortion effects at the
transmitter. Therefore, we evaluate nonlinear distortion and present feasible solutions to
mitigate the impact of nonlinear distortion effects on the performance.Another goal of
the thesisis to take advantage of the energy harvesting signals in SWIP Ttechniques for
channel estimation and security purposes.Theperformance of these SWIPT techniques is
evaluated analytically, and those results are validated by simulations. It is shownthatthe
proposed SWIPT schemes can have excellent performance, out performing conventional
SWIPT schemes.Espera-se que aschamadas tecnologiasde green communications sejam amplamente ado-
tadas em futuras redes de comunicação sem fios para melhorar a sua eficiência energética
a fiabilidade.Entre estas,encontram-se as tecnologias SWIPT (Simultaneous Wireless
Information and Power Transference), nas quais um sinal radio é usado para transferir
simultaneamente potência e informações.Embora as técnicas SWIPT existentes sejam fle-
xíveis e adequadas para as redes de comunicações sem fios, os recursos de energia e tempo
do sinal precisam ser compartilhados entre a transmissão de informações e de energia, o
que pode comprometer a qualidade do sinal. Deste modo,as técnicas SWIPT precisam ser
projetadas para permitir uma alocação eficiente de recursos para comunicação e recolha
de energia.
O objetivo desta tese é desenvolver técnicas SWIPT que permitam transferência de
energia e comunicações eficientes,fiáveis e seguras.Um problema associado às técnicas
SWIPT combinadas com sinais multi-portadora são as dificuldades de amplificação ine-
rentes à combinação de sinais de transmissão de energia com sinais de transferência de
dados, que podem exacerbar os efeitos de distorção não-linear nos sinais transmitidos.
Deste modo, um dos objectivos desta tese é avaliar o impacto da distorção não-linear em
sinais SWIPT, e apresentar soluções viáveis para mitigar os efeitos da distorção não-linear
no desempenho da transmissão de dados.Outro objetivo da tese é aproveitar as vantagens
dos sinais de transferência de energia em técnicas SWIPT para efeitos de estimação de
canal e segurança na comunicação.Os desempenhos dessas técnicas SWIPT são avaliados
analiticamente,sendo os respectivos resultados validados por simulações.É mostrado que
os esquemas SWIPT propostos podem ter excelente desempenho, superando esquemas
SWIPT convencionais
Deep Reinforcement Learning for Multi-user Massive MIMO with Channel Aging
The design of beamforming for downlink multi-user massive multi-input
multi-output (MIMO) relies on accurate downlink channel state information (CSI)
at the transmitter (CSIT). In fact, it is difficult for the base station (BS)
to obtain perfect CSIT due to user mobility, latency/feedback delay (between
downlink data transmission and CSI acquisition). Hence, robust beamforming
under imperfect CSIT is needed. In this paper, considering multiple antennas at
all nodes (base station and user terminals), we develop a multi-agent deep
reinforcement learning (DRL) framework for massive MIMO under imperfect CSIT,
where the transmit and receive beamforming are jointly designed to maximize the
average information rate of all users. Leveraging this DRL-based framework,
interference management is explored and three DRL-based schemes, namely the
distributed-learning-distributed-processing scheme,
partial-distributed-learning-distributed-processing, and
central-learning-distributed-processing scheme, are proposed and analyzed. This
paper \textrm{1)} highlights the fact that the DRL-based strategies outperform
the random action-chosen strategy and the delay-sensitive strategy named as
sample-and-hold (SAH) approach, and achieved over 90 of the information
rate of two selected benchmarks with lower complexity: the zero-forcing
channel-inversion (ZF-CI) with perfect CSIT and the Greedy Beam Selection
strategy, \textrm{2)} demonstrates the inherent robustness of the proposed
designs in the presence of user mobility.Comment: submitted for publicatio
Evaluation of Beamforming Algorithms for Massive MIMO
Massive MIMO relay system is an expansion of the Multiple-Input-Multiple-Output (MIMO) which enabled multiple users and antennas to communicate with each other for data sharing. A relay system with multiple antenna system has an advantage over simple MIMO system as it interconnects base station and users with each other for sharing of information and both BS and users are independent of many antennas. High data rate applications such as Machine-to-Machine communication and wireless sensor networks are experiencing transmit power loss, channel capacity and mismanagement of data. The demand for the Massive MIMO relay system is opening a door for ultra-high latency wireless network applications in case of saving transmit power and transmission of accurate information over the wireless networks.
Due to the loss in transmit power and mismanagement of information over wireless networks, it is difficult to get better performance. Different approaches were made to optimize the overall transmit power of communication systems. One of the approaches was explained in this thesis work. The focus of the thesis is the use of beamforming algorithms named as Maximum Ratio Combining (MRC) and Zero-Forcing (ZF) to maximize the overall capacity of the MIMO system. These algorithms were evaluated on different scenarios to handle the performance and behavior with different network conditions. Various use cases were used for analyzing the beamforming algorithms. The performance of both algorithms was observed by considering the scenarios such as varying the transmit and receive antenna’s size and modulation schemes. Singular Value Decomposition (SVD) Method was used at the main MIMO channel to optimize the channel capacity. SVD divides the MIMO channel into different subchannels and optimizes the channel capacity of individual channels.
The summary of results showed that MRC and ZF in the CP-OFDM environment when the number of RX antennas increased then they gave better BER performance as compared to the single antenna system. On the other hand, with higher modulation schemes efficiency was not good but with lower modulation scheme performance was satisfactory
Interference Exploitation via Symbol-Level Precoding: Overview, State-of-the-Art and Future Directions
Interference is traditionally viewed as a performance limiting factor in wireless communication systems, which is to be minimized or mitigated. Nevertheless, a recent line of work has shown that by manipulating the interfering signals such that they add up constructively at the receiver side, known interference can be made beneficial and further improve the system performance in a variety of wireless scenarios, achieved by symbol-level precoding (SLP). This paper aims to provide a tutorial on interference exploitation techniques from the perspective of precoding design in a multi-antenna wireless communication system, by beginning with the classification of constructive interference (CI) and destructive interference (DI). The definition for CI is presented and the corresponding mathematical characterization is formulated for popular modulation types, based on which optimization-based precoding techniques are discussed. In addition, the extension of CI precoding to other application scenarios as well as for hardware efficiency is also described. Proof-of-concept testbeds are demonstrated for the potential practical implementation of CI precoding, and finally a list of open problems and practical challenges are presented to inspire and motivate further research directions in this area
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