22 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
Exploring deep learning for adaptive energy detection threshold determination: A multistage approach
The concept of spectrum sensing has emerged as a fundamental solution to address the growing demand for accessing the limited resources of wireless communications networks. This paper introduces a straightforward yet efficient approach that incorporates multiple stages that are based on deep learning (DL) techniques to mitigate Radio Frequency (RF) impairments and estimate the transmitted signal using the time domain representation of received signal samples. The proposed method involves calculating the energies of the estimated transmitted signal samples and received signal samples and estimating the energy of the noise using these estimates. Subsequently, the received signal energy and the estimated noise energy, adjusted by a correction factor (k), are employed in binary hypothesis testing to determine the occupancy of the wireless channel under investigation. The proposed system demonstrates encouraging outcomes by effectively mitigating RF impairments, such as carrier frequency offset (CFO), phase offset, and additive white Gaussian noise (AWGN), to a considerable degree. As a result, it enables accurate estimation of the transmitted signal from the received signal, with 3.85% false alarm and 3.06% missed detection rates, underscoring the system’s capability to adaptively determine a decision threshold for energy detection.European Union’s H2020 Framework Programm
On the traffic offloading in Wi-Fi supported heterogeneous wireless networks
Heterogeneous small cell networks (HetSNet) comprise several low power, low cost (SBSa), (D2D) enabled links wireless-fidelity (Wi-Fi) access points (APs) to support the existing macrocell infrastructure, decrease over the air signaling and energy consumption, and increase network capacity, data rate and coverage. This paper presents an active user dependent path loss (PL) based traffic offloading (TO) strategy for HetSNets and a comparative study on two techniques to offload the traffic from macrocell to (SBSs) for indoor environments: PL and signal-to-interference ratio (SIR) based strategies. To quantify the improvements, the PL based strategy against the SIR based strategy is compared while considering various macrocell and (SBS) coverage areas and traffic–types. On the other hand, offloading in a dense urban setting may result in overcrowding the (SBSs). Therefore, hybrid traffic–type driven offloading technologies such as (WiFi) and (D2D) were proposed to en route the delay tolerant applications through (WiFi) (APs) and (D2D) links. It is necessary to illustrate the impact of daily user traffic profile, (SBSs) access schemes and traffic–type while deciding how much of the traffic should be offloaded to (SBSs). In this context, (AUPF) is introduced to account for the population of active small cells which depends on the variable traffic load due to the active users
Reconfigurable Intelligent Surfaces in Action for Non-Terrestrial Networks
Next-generation communication technology will be fueled on the cooperation of
terrestrial networks with nonterrestrial networks (NTNs) that contain
mega-constellations of high-altitude platform stations and low-Earth orbit
satellites. On the other hand, humanity has embarked on a long road to
establish new habitats on other planets. This deems the cooperation of NTNs
with deep space networks (DSNs) necessary. In this regard, we propose the use
of reconfigurable intelligent surfaces (RISs) to improve and escalate this
collaboration owing to the fact that they perfectly match with the size,
weight, and power restrictions of the operational environment of space. A
comprehensive framework of RIS-assisted non-terrestrial and interplanetary
communications is presented by pinpointing challenges, use cases, and open
issues. Furthermore, the performance of RIS-assisted NTNs under environmental
effects such as solar scintillation and satellite drag is discussed through
simulation results.Comment: 7 pages, 6 figure
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
Measurement Based Statistical Channel Characterization of Air-to-Ground Path Loss Model at 446 MHz for Narrow-Band Signals in Low Altitude UAVs
Powered by the advances in microelectronics technologies, unmanned aerial
vehicles (UAVs) provide a vast variety of services ranging from surveillance to
delivery in both military and civilian domains. It is clear that a successful
operation in those services relies heavily on wireless communication
technologies. Even though wireless communication techniques could be considered
to reach a certain level of maturity, wireless communication links including
UAVs should be regarded in a different way due to the peculiar characteristics
of UAVs such as agility in 3D spatial domain and versatility in modes of
operation. Such mobility characteristics in a vast variety of environmental
diversity render links including UAVs different from those in traditional,
terrestrial mobility scenarios. Furthermore, UAVs are critical instruments for
network operators in order to provide basic voice and short messaging services
for narrow band communication in and around disaster areas. It is obvious that
such widespread use of UAVs under different scenarios and environments requires
a better understanding the behavior of the communication links that include
UAVs. Therefore, in this study, details of a measurement campaign designed to
collect data for large-scale propagation characterization of air-to-ground
links operated by UAVs at 446MHz under narrowband assumption are given. Data
collection, post-processing, and measurement results are provided.Comment: This work is accepted to 2020 IEEE 91st Vehicular Technology
Conference: VTC2020-Spring on January 11, 202
Channel Estimation for Full-Duplex RIS-assisted HAPS Backhauling with Graph Attention Networks
In this paper, graph attention network (GAT) is firstly utilized for the
channel estimation. In accordance with the 6G expectations, we consider a
high-altitude platform station (HAPS) mounted reconfigurable intelligent
surface-assisted two-way communications and obtain a low overhead and a high
normalized mean square error performance. The performance of the proposed
method is investigated on the two-way backhauling link over the RIS-integrated
HAPS. The simulation results denote that the GAT estimator overperforms the
least square in full-duplex channel estimation. Contrary to the previously
introduced methods, GAT at one of the nodes can separately estimate the
cascaded channel coefficients. Thus, there is no need to use time-division
duplex mode during pilot signaling in full-duplex communication. Moreover, it
is shown that the GAT estimator is robust to hardware imperfections and changes
in small-scale fading characteristics even if the training data do not include
all these variations.Comment: This paper has been accepted for the presentation in IEEE ICC'202
Spectrum Sensing and Signal Identification with Deep Learning based on Spectral Correlation Function
Spectrum sensing is one of the means of utilizing the scarce source of
wireless spectrum efficiently. In this paper, a convolutional neural network
(CNN) model employing spectral correlation function which is an effective
characterization of cyclostationarity property, is proposed for wireless
spectrum sensing and signal identification. The proposed method classifies
wireless signals without a priori information and it is implemented in two
different settings entitled CASE1 and CASE2. In CASE1, signals are jointly
sensed and classified. In CASE2, sensing and classification are conducted in a
sequential manner. In contrary to the classical spectrum sensing techniques,
the proposed CNN method does not require a statistical decision process and
does not need to know the distinct features of signals beforehand.
Implementation of the method on the measured overthe-air real-world signals in
cellular bands indicates important performance gains when compared to the
signal classifying deep learning networks available in the literature and
against classical sensing methods. Even though the implementation herein is
over cellular signals, the proposed approach can be extended to the detection
and classification of any signal that exhibits cyclostationary features.
Finally, the measurement-based dataset which is utilized to validate the method
is shared for the purposes of reproduction of the results and further research
and development
Statistical channel modeling for short range line-of-sight terahertz communication
Underutilized spectrum constitutes a major concern in wireless communications especially in the presence of legacy systems and the prolific need for high-capacity applications as well as consumer expectations. From this perspective, Terahertz frequencies provide a new paradigm shift in wireless communications since they have been left unexplored until recently. Such a vast frequency spectrum region extending all the way up to visible light and beyond points out significant opportunities from dramatic data rates on the order of tens of Gbps to a variety of inherent security and privacy mechanisms, and techniques that are not available in the traditional systems. Thus, in this paper, we investigate statistical parameters for short-range line- of-sight channels of Terahertz communication. Short-range measurement campaign within the interval of [3cm, 20cm] are carried out between 275GHz to 325GHz range. Path loss model is examined for different frequencies and distances to provide the insight regarding the effect of the operating frequency. Measurement results are provided with relevant discussions and future directions