792 research outputs found
OFDM over IEEE 802.11b hardware for telemedical applications
Using a wireless Local Area Network (WLAN) to transmit live high-quality video suitable for a telemedical application presents many challenges, including ensuring sufficient Quality of Service (QoS) for the end-user to be able to make an accurate diagnosis. One of the many problems that exist when developing such a system is the multipath effect caused by the reflections of the transmitted signals on various surfaces including walls, floors, furniture and people. This degrades the signal quality and reduces the amount of available bandwidth and, thus, the quality of the image. Presently, most of Europe is using the IEEE 802.11b hardware for such applications. As an alternative to the existing modulation of 802.11b, Orthogonal Frequency Division Multiplexing (OFDM) is investigated, especially for use inside hospitals. The advantages of using this modulation over IEEE 802.11b hardware for a telemedicine application are examined by means of simulation using three different simulation packages
Transmitting Data Through Reconfigurable Intelligent Surface: A Spatial Sigma-Delta Modulation Approach
Transmitting data using the phases on reconfigurable intelligent surfaces
(RIS) is a promising solution for future energy-efficient communication
systems. Recent work showed that a virtual phased massive multiuser
multiple-input-multiple-out (MIMO) transmitter can be formed using only one
active antenna and a large passive RIS. In this paper, we are interested in
using such a system to perform MIMO downlink precoding. In this context, we may
not be able to apply conventional MIMO precoding schemes, such as the simple
zero-forcing (ZF) scheme, and we typically need to design the phase signals by
solving optimization problems with constant modulus constraints or with
discrete phase constraints, which pose challenges with high computational
complexities. In this work, we propose an alternative approach based on
Sigma-Delta () modulation, which is classically famous for its
noise-shaping ability. Specifically, first-order modulation is
applied in the spatial domain to handle phase quantization in generating
constant envelope signals. Under some mild assumptions, the proposed phased
modulator allows us to use the ZF scheme to synthesize the RIS
reflection phases with negligible complexity. The proposed approach is
empirically shown to achieve comparable bit error rate performance to the
unquantized ZF scheme
Frequency-Mixing Intelligent Reflecting Surfaces for Nonlinear Wireless Propagation
We introduce the concept of frequency-mixing intelligent reflecting surface
(FMx-IRS), where the elements of the surface continuously change the phases of
the incident signals. In this way, the FMx-IRS acts as a frequency mixer and
makes the propagation environment nonlinear, thereby introducing new
frequencies. We study the basic features of the proposed concept and
demonstrate its advantages that stem from the novel type of control over the
wireless propagation. The channel decoupling feature and the correlation
between reflected channels are elaborated for the architecture, and are
validated by the simulations.Comment: 5 pages, 4 figur
Design of Reconfigurable Intelligent Surfaces for Wireless Communication: A Review
Existing literature reviews predominantly focus on the theoretical aspects of
reconfigurable intelligent surfaces (RISs), such as algorithms and models,
while neglecting a thorough examination of the associated hardware components.
To bridge this gap, this research paper presents a comprehensive overview of
the hardware structure of RISs. The paper provides a classification of RIS cell
designs and prototype systems, offering insights into the diverse
configurations and functionalities. Moreover, the study explores potential
future directions for RIS development. Notably, a novel RIS prototype design is
introduced, which integrates seamlessly with a communication system for
performance evaluation through signal gain and image formation experiments. The
results demonstrate the significant potential of RISs in enhancing
communication quality within signal blind zones and facilitating effective
radio wave imaging
Physical Layer Authentication Using Intelligent Reflective Surfaces
The Intelligent Reflective Surface (IRS) is one of the key technologies that will increase the coverage of cellular networks and enhance their performance at a low cost. Moreover, the IRS will improve the performance of the Channel-based Physical layer Authentication security mechanism. In this thesis, we propose an authentication scheme that takes advantage of the presence of the IRS in the IRS-assisted multiple input multiple output (MIMO) system to improve the security performance of the system. The proposed cascaded channel estimation authentication scheme has been developed and compared with a systematic channel estimation authentication scheme. We consider a non-line of sight communication between the transmitter and the receiver through the IRS. We will also demonstrate the efficiency of the proposed scheme by comparing it with one of the commonly used schemes. Moreover, we will formulate the optimal attack strategies to test the security of the proposed scheme. The performance of the proposed scheme is evaluated, and the numerical results show the merit of the proposed approach that can be adopted as a Physical layer authentication mechanism.The Intelligent Reflective Surface (IRS) is one of the key technologies that will increase the coverage of cellular networks and enhance their performance at a low cost. Moreover, the IRS will improve the performance of the Channel-based Physical layer Authentication security mechanism. In this thesis, we propose an authentication scheme that takes advantage of the presence of the IRS in the IRS-assisted multiple input multiple output (MIMO) system to improve the security performance of the system. The proposed cascaded channel estimation authentication scheme has been developed and compared with a systematic channel estimation authentication scheme. We consider a non-line of sight communication between the transmitter and the receiver through the IRS. We will also demonstrate the efficiency of the proposed scheme by comparing it with one of the commonly used schemes. Moreover, we will formulate the optimal attack strategies to test the security of the proposed scheme. The performance of the proposed scheme is evaluated, and the numerical results show the merit of the proposed approach that can be adopted as a Physical layer authentication mechanism
Active Reconfigurable Intelligent Surface Aided Wireless Communications
Reconfigurable Intelligent Surface (RIS) is a promising solution to
reconfigure the wireless environment in a controllable way. To compensate for
the double-fading attenuation in the RIS-aided link, a large number of passive
reflecting elements (REs) are conventionally deployed at the RIS, resulting in
large surface size and considerable circuit power consumption. In this paper,
we propose a new type of RIS, called active RIS, where each RE is assisted by
active loads (negative resistance), that reflect and amplify the incident
signal instead of only reflecting it with the adjustable phase shift as in the
case of a passive RIS. Therefore, for a given power budget at the RIS, a
strengthened RIS-aided link can be achieved by increasing the number of active
REs as well as amplifying the incident signal. We consider the use of an active
RIS to a single input multiple output (SIMO) system. {However, it would
unintentionally amplify the RIS-correlated noise, and thus the proposed system
has to balance the conflict between the received signal power maximization and
the RIS-correlated noise minimization at the receiver. To achieve this goal, it
has to optimize the reflecting coefficient matrix at the RIS and the receive
beamforming at the receiver.} An alternating optimization algorithm is proposed
to solve the problem. Specifically, the receive beamforming is obtained with a
closed-form solution based on linear minimum-mean-square-error (MMSE)
criterion, while the reflecting coefficient matrix is obtained by solving a
series of sequential convex approximation (SCA) problems. Simulation results
show that the proposed active RIS-aided system could achieve better performance
over the conventional passive RIS-aided system with the same power budget
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