2,041 research outputs found
A Holistic Investigation on Terahertz Propagation and Channel Modeling Toward Vertical Heterogeneous Networks
User-centric and low latency communications can be enabled not only by small
cells but also through ubiquitous connectivity. Recently, the vertical
heterogeneous network (V-HetNet) architecture is proposed to backhaul/fronthaul
a large number of small cells. Like an orchestra, the V-HetNet is a polyphony
of different communication ensembles, including geostationary orbit (GEO), and
low-earth orbit (LEO) satellites (e.g., CubeSats), and networked flying
platforms (NFPs) along with terrestrial communication links. In this study, we
propose the Terahertz (THz) communications to enable the elements of V-HetNets
to function in harmony. As THz links offer a large bandwidth, leading to
ultra-high data rates, it is suitable for backhauling and fronthauling small
cells. Furthermore, THz communications can support numerous applications from
inter-satellite links to in-vivo nanonetworks. However, to savor this harmony,
we need accurate channel models. In this paper, the insights obtained through
our measurement campaigns are highlighted, to reveal the true potential of THz
communications in V-HetNets.Comment: It has been accepted for the publication in IEEE Communications
Magazin
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
Mathematical modeling of ultra wideband in vivo radio channel
This paper proposes a novel mathematical model for an in vivo radio channel at ultra-wideband frequencies (3.1–10.6 GHz), which can be used as a reference model for in vivo channel response without performing intensive experiments or simulations. The statistics of error prediction between experimental and proposed model is RMSE = 5.29, which show the high accuracy of the proposed model. Also, the proposed model was applied to the blind data, and the statistics of error prediction is RMSE = 7.76, which also shows a reasonable accuracy of the model. This model will save the time and cost on simulations and experiments, and will help in designing an accurate link budget calculation for a future enhanced system for ultra-wideband body-centric wireless systems
Modeling and Analysis of sub-Terahertz Communication Channel via Mixture of Gamma Distribution
With the recent developments on opening the terahertz (THz) spectrum for
experimental purposes by the Federal Communications Commission, transceivers
operating in the range of 0.1THz-10THz, which are known as THz bands, will
enable ultra-high throughput wireless communications. However, actual
implementation of the high-speed and high-reliability THz band communication
systems should start with providing extensive knowledge in regards to the
propagation channel characteristics. Considering the huge bandwidth and the
rapid changes in the characteristics of THz wireless channels, ray tracing and
one-shot statistical modeling are not adequate to define an accurate channel
model. In this work, we propose Gamma mixture-based channel modeling for the
THz band via the expectation-maximization (EM) algorithm. First, maximum
likelihood estimation (MLE) is applied to characterize the Gamma mixture model
parameters, and then EM algorithm is used to compute MLEs of the unknown
parameters of the measurement data. The accuracy of the proposed model is
investigated by using the Weighted relative mean difference (WMRD) error
metrics, Kullback-Leibler (KL)-divergence, and Kolmogorov-Smirnov test to show
the difference between the proposed model and the actual probability density
functions (PDFs) that are obtained via the designed test environment. According
to WMRD error metrics, KL-divergence, and KS test results, PDFs generated by
the mixture of Gamma distributions fit the actual histogram of the measurement
data. It is shown that instead of taking pseudo-average characteristics of
sub-bands in the wideband, using the mixture models allows for determining
channel parameters more precisely.Comment: This paper has been accepted for publication in IEEE Transactions on
Vehicular Technolog
Terahertz Wireless Channels: A Holistic Survey on Measurement, Modeling, and Analysis
Terahertz (0.1-10 THz) communications are envisioned as a key technology for
sixth generation (6G) wireless systems. The study of underlying THz wireless
propagation channels provides the foundations for the development of reliable
THz communication systems and their applications. This article provides a
comprehensive overview of the study of THz wireless channels. First, the three
most popular THz channel measurement methodologies, namely, frequency-domain
channel measurement based on a vector network analyzer (VNA), time-domain
channel measurement based on sliding correlation, and time-domain channel
measurement based on THz pulses from time-domain spectroscopy (THz-TDS), are
introduced and compared. Current channel measurement systems and measurement
campaigns are reviewed. Then, existing channel modeling methodologies are
categorized into deterministic, stochastic, and hybrid approaches.
State-of-the-art THz channel models are analyzed, and the channel simulators
that are based on them are introduced. Next, an in-depth review of channel
characteristics in the THz band is presented. Finally, open problems and future
research directions for research studies on THz wireless channels for 6G are
elaborated.Comment: to appear in IEEE Communications Surveys and Tutorial
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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