63 research outputs found
Two Low-Complexity Efficient Beamformers for an IRS- and UAV-Aided Directional Modulation Network
As excellent tools for aiding communication, an intelligent reflecting surface (IRS) and an unmanned aerial vehicle (UAV) can extend the coverage area, remove the blind area, and achieve a dramatic rate improvement. In this paper, we improve the secrecy rate (SR) performance of directional modulation (DM) networks using an IRS and UAV in combination. To fully explore the benefits of the IRS and UAV, two efficient methods are proposed to enhance the SR performance. The first approach computes the confidential message (CM) beamforming vector by maximizing the SR, and the signal-to-leakage-noise ratio (SLNR) method is used to optimize the IRS phase shift matrix (PSM), which is called Max-SR-SLNR. To reduce the computational complexity, the CM, artificial noise (AN) beamforming, and IRS phase shift design are independently designed in the following method. The CM beamforming vector is constructed based on the maximum ratio transmission (MRT) criteria along the channel from Alice-to-IRS, the AN beamforming vector is designed by null-space projection (NSP) on the remaining two channels, and the PSM of the IRS is directly given by the phase alignment (PA) method. This method is called the MRT-NSP-PA. The simulation results show that the SR performance of the Max-SR-SLNR method outperforms the MRT-NSP-PA method in the cases of small-scale and medium-scale IRSs, and the latter approaches the former in performance as the IRS tends to a larger scale
Physical layer security against eavesdropping in the internet of drones (IoD) based communication systems
rones or unmanned aerial vehicles (UAVs) communication technology, which has recently been
thoroughly studied and adopted by 3GPP standard (Release 15) due to its dynamic, flexible, and flying
nature, is expected to be an integral part of future wireless communications and Internet of drones
(IoD) applications. However, due to the unique transmission characteristics and nature of UAV systems
including broadcasting, dominant line of site and poor scattering, providing confidentiality for legitimate
receivers against unintended ones (eavesdroppers) appears to be a challenging goal to achieve in such
scenarios. Besides, the special features of UAVs represented by having limited power (battery-operated)
and precessing (light RAM and CPU capabilities), makes applying complex cryptography approaches
very challenging and inefficient for such systems. This motives the utilization of alternative approaches
enabled by physical layer security (PLS) concept for securing UAV-based systems. Techniques based
on PLS are deemed to be promising due to their ability to provide inherent secrecy that is complexity independent, where no matter what computational processing power the eavesdropper may have, there
is no way to decrypt the PLS algorithms. This work is dedicated to highlight and overview the latest
advances and state of art researches on the field of applying PLS to UAV systems in a unified and
structured manner. Particularity, it discusses and explains the different, possible PLS scenarios and
use cases of UAVs, which are categorized based on how the drone is utilized and employed in the
communication system setup. The main classified categories include the deployment of the flying, mobile
UAV as a 1) base station (BS), 2) user equipment (UE), 2) relay, or 4) jammer. Then, recommendations
and future open research issues are stated and discussed.No sponso
RIS-Aided Cell-Free Massive MIMO Systems for 6G: Fundamentals, System Design, and Applications
An introduction of intelligent interconnectivity for people and things has
posed higher demands and more challenges for sixth-generation (6G) networks,
such as high spectral efficiency and energy efficiency, ultra-low latency, and
ultra-high reliability. Cell-free (CF) massive multiple-input multiple-output
(mMIMO) and reconfigurable intelligent surface (RIS), also called intelligent
reflecting surface (IRS), are two promising technologies for coping with these
unprecedented demands. Given their distinct capabilities, integrating the two
technologies to further enhance wireless network performances has received
great research and development attention. In this paper, we provide a
comprehensive survey of research on RIS-aided CF mMIMO wireless communication
systems. We first introduce system models focusing on system architecture and
application scenarios, channel models, and communication protocols.
Subsequently, we summarize the relevant studies on system operation and
resource allocation, providing in-depth analyses and discussions. Following
this, we present practical challenges faced by RIS-aided CF mMIMO systems,
particularly those introduced by RIS, such as hardware impairments and
electromagnetic interference. We summarize corresponding analyses and solutions
to further facilitate the implementation of RIS-aided CF mMIMO systems.
Furthermore, we explore an interplay between RIS-aided CF mMIMO and other
emerging 6G technologies, such as next-generation multiple-access (NGMA),
simultaneous wireless information and power transfer (SWIPT), and millimeter
wave (mmWave). Finally, we outline several research directions for future
RIS-aided CF mMIMO systems.Comment: 30 pages, 15 figure
RIS-assisted Scheduling for High-Speed Railway Secure Communications
With the rapid development of high-speed railway systems and railway wireless
communication, the application of ultra-wideband millimeter wave band is an
inevitable trend. However, the millimeter wave channel has large propagation
loss and is easy to be blocked. Moreover, there are many problems such as
eavesdropping between the base station (BS) and the train. As an emerging
technology, reconfigurable intelligent surface (RIS) can achieve the effect of
passive beamforming by controlling the propagation of the incident
electromagnetic wave in the desired direction.We propose a RIS-assisted
scheduling scheme for scheduling interrupted transmission and improving quality
of service (QoS).In the propsed scheme, an RIS is deployed between the BS and
multiple mobile relays (MRs). By jointly optimizing the beamforming vector and
the discrete phase shift of the RIS, the constructive interference between
direct link signals and indirect link signals can be achieved, and the channel
capacity of eavesdroppers is guaranteed to be within a controllable range.
Finally, the purpose of maximizing the number of successfully scheduled tasks
and satisfying their QoS requirements can be practically realized. Extensive
simulations demonstrate that the proposed scheme has superior performance
regarding the number of completed tasks and the system secrecy capacity over
four baseline schemes in literature.Comment: 15 pages, 10 figures, to appear in IEEE Transactions on Vehicular
Technolog
Reconfigurable Intelligent Surface Enabled Joint Backscattering and Communication
Reconfigurable intelligent surface (RIS) as an essential topic in the
sixth-generation (6G) communications aims to enhance communication performance
or mitigate undesired transmission. However, the controllability of each
reflecting element on RIS also enables it to act as a passive backscatter
device (BD) and transmit its information to reader devices. In this paper, we
propose a RIS-enabled joint backscattering and communication (JBAC) system,
where the backscatter communication coexists with the primary communication and
occupies no extra spectrum. Specifically, the RIS modifies its reflecting
pattern to act as a passive BD and reflect its own information back to the base
station (BS) in the backscatter communication, while helping the primary
communication from the BS to the users simultaneously. We further present an
iterative active beamforming and reflecting pattern design to maximize the user
average transmission rate of the primary communication and the goodput of the
backscatter communication by solving the formulated multi-objective
optimization problem (MOOP). Numerical results fully uncover the impacts of the
number of reflecting elements and the reflecting patterns on the system
performance, and demonstrate the effectiveness of the proposed scheme.
Important practical implementation remarks have also been discussed.Comment: 11 pages, 8 figures, published to IEEE TV
Signal Processing and Learning for Next Generation Multiple Access in 6G
Wireless communication systems to date primarily rely on the orthogonality of
resources to facilitate the design and implementation, from user access to data
transmission. Emerging applications and scenarios in the sixth generation (6G)
wireless systems will require massive connectivity and transmission of a deluge
of data, which calls for more flexibility in the design concept that goes
beyond orthogonality. Furthermore, recent advances in signal processing and
learning have attracted considerable attention, as they provide promising
approaches to various complex and previously intractable problems of signal
processing in many fields. This article provides an overview of research
efforts to date in the field of signal processing and learning for
next-generation multiple access, with an emphasis on massive random access and
non-orthogonal multiple access. The promising interplay with new technologies
and the challenges in learning-based NGMA are discussed
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