242 research outputs found
Multiple Antenna Techniques for Terahertz Nano-Bio Communication
Using higher frequency bands becomes an essential demand resulting from the explosive wireless traffic needs and the spectrum shortage of the currently used bands. This paper presents an overview on the terahertz technology and its application in the area of multi-input multi-output antenna system and in-vivo nano-communication. In addition, it presents a preliminary study on applying multiple input-single output (MISO) antenna technique to investigate the signal propagation and antenna diversity techniques inside the human skin tissues, which is represented by three layers: stratum corneum (SC), epidermis, and dermis layers, in the terahertz (THz) frequency range (0.8-1.2) THz. The spatial antenna diversity is investigated in this study to understand MISO system performance for two different in-vivo channels resulting from the signal propagation between two transmitting antennas, located at the dermis layer, and one receiving antenna, located at epidermis layer. Three techniques are investigated: selection combining (SC), equal-gain combing (EGC), and maximum-ratio combining (MRC). The initial study indicates that using multiple antenna technique with THz might be not useful for in-vivo nano-communication
MAC-Oriented Programmable Terahertz PHY via Graphene-based Yagi-Uda Antennas
Graphene is enabling a plethora of applications in a wide range of fields due
to its unique electrical, mechanical, and optical properties. In the realm of
wireless communications, graphene shows great promise for the implementation of
miniaturized and tunable antennas in the terahertz band. These unique
advantages open the door to new reconfigurable antenna structures which, in
turn, enable novel communication protocols at different levels of the stack.
This paper explores both aspects by, first, presenting a terahertz
Yagi-Uda-like antenna concept that achieves reconfiguration both in frequency
and beam direction simultaneously. Then, a programmable antenna controller
design is proposed to expose the reconfigurability to the PHY and MAC layers,
and several examples of its applicability are given. The performance and cost
of the proposed scheme is evaluated through full-wave simulations and
comparative analysis, demonstrating reconfigurability at nanosecond granularity
with overheads below 0.02 mm and 0.2 mW.Comment: Accepted for presentation in IEEE WCNC '1
Nanoscale Reconfigurable Intelligent Surface Design and Performance Analysis for Terahertz Communications
Terahertz (THz) communications have been envisioned as a promising enabler to
provide ultra-high data transmission for sixth generation (6G) wireless
networks. To tackle the blockage vulnerability brought by severe attenuation
and poor diffraction of THz waves, a nanoscale reconfigurable intelligent
surface (NRIS) is developed to smartly manipulate the propagation directions of
incident THz waves. In this paper, the electric properties of the graphene are
investigated by revealing the relationship between conductivity and applied
voltages, and then an efficient hardware structure of electrically-controlled
NRIS is designed based on Fabry-Perot resonance model. Particularly, the phase
response of NRIS can be programmed up to 306.82 degrees. To analyze the
hardware performance, we jointly design the passive and active beamforming for
NRIS aided THz communication system. Particularly, an adaptive gradient descent
(A-GD) algorithm is developed to optimize the phase shift matrix of NRIS by
dynamically updating the step size during the iterative process. Finally,
numerical results demonstrate the effectiveness of our designed hardware
architecture as well as the developed algorithm.Comment: 9 pages, 8 figures. arXiv admin note: substantial text overlap with
arXiv:2012.0699
Phase shift optimization algorithm for achievable rate maximization in reconfigurable intelligent surface-assisted THz communications
Terahertz (THz) band communications are considered a crucial technology to support future applications, such as ultra-high bit rate wireless local area networks, in the next generation of wireless communication systems. In this work, we consider an ultra-massive multiple-input multiple-output (UM-MIMO) THz communication system operating in a typical indoor scenario where the direct link between the transmitter and receiver is obstructed due to surrounding obstacles. To help establish communication, we assume the aid of a nearby reconfigurable intelligent surface (RIS) whose phase shifts can be adjusted. To configure the individual phase shifts of the RIS elements, we formulate the problem as a constrained achievable rate maximization. Due to the typical large dimensions of this optimization problem, we apply the accelerated proximal gradient (APG) method, which results in a low complexity algorithm that copes with the non-convex phase shift constraint through simple element-wise normalization. Our numerical results demonstrate the effectiveness of the proposed algorithm even when considering realistic discrete phase shifts’ quantization and imperfect channel knowledge. Furthermore, comparison against existing alternatives reveals improvements between 30% and 120% in terms of range, for a reference rate of 100 Gbps when using the proposed approach with only 81 RIS elements.info:eu-repo/semantics/publishedVersio
Terahertz Communications for 6G and Beyond Wireless Networks: Challenges, Key Advancements, and Opportunities
The unprecedented increase in wireless data traffic, predicted to occur
within the next decade, is motivating academia and industries to look beyond
contemporary wireless standards and conceptualize the sixth-generation (6G)
wireless networks. Among various promising solutions, terahertz (THz)
communications (THzCom) is recognized as a highly promising technology for the
6G and beyond era, due to its unique potential to support terabit-per-second
transmission in emerging applications. This article delves into key areas for
developing end-to-end THzCom systems, focusing on physical, link, and network
layers. Specifically, we discuss the areas of THz spectrum management, THz
antennas and beamforming, and the integration of other 6G-enabling technologies
for THzCom. For each area, we identify the challenges imposed by the unique
properties of the THz band. We then present main advancements and outline
perspective research directions in each area to stimulate future research
efforts for realizing THzCom in 6G and beyond wireless networks.Comment: This work has been submitted to the IEEE for possible publication.
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Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View
The next-generation wireless technologies, commonly referred to as the sixth
generation (6G), are envisioned to support extreme communications capacity and
in particular disruption in the network sensing capabilities. The terahertz
(THz) band is one potential enabler for those due to the enormous unused
frequency bands and the high spatial resolution enabled by both short
wavelengths and bandwidths. Different from earlier surveys, this paper presents
a comprehensive treatment and technology survey on THz communications and
sensing in terms of the advantages, applications, propagation characterization,
channel modeling, measurement campaigns, antennas, transceiver devices,
beamforming, networking, the integration of communications and sensing, and
experimental testbeds. Starting from the motivation and use cases, we survey
the development and historical perspective of THz communications and sensing
with the anticipated 6G requirements. We explore the radio propagation, channel
modeling, and measurements for THz band. The transceiver requirements,
architectures, technological challenges, and approaches together with means to
compensate for the high propagation losses by appropriate antenna and
beamforming solutions. We survey also several system technologies required by
or beneficial for THz systems. The synergistic design of sensing and
communications is explored with depth. Practical trials, demonstrations, and
experiments are also summarized. The paper gives a holistic view of the current
state of the art and highlights the issues and challenges that are open for
further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications
Surveys & Tutorial
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