31 research outputs found
Harmonic Retrieval of CFO and Frame Misalignment for OFDM-based Inter-Satellite Links
As dense low Earth orbit (LEO) constellations are being planned, the need for
accurate synchronization schemes in high-speed environments remains a
challenging problem to tackle. To further improve synchronization accuracy in
channeling environments, which can also be applied in the LEO networks, we
present a new method for estimating the carrier frequency offset (CFO) and
frame misalignment in orthogonal frequency division multiplexing (OFDM) based
inter-satellite links. The proposed method requires the transmission of pilot
symbols to exploit 2-D estimation of signal parameters via rotational
invariance techniques (ESPRIT) and estimate the CFO and the frame misalignment.
The Cramer-Rao lower bounds (CRLB) of the joint estimation of the CFO and frame
misalignment are also derived. Numerical results show that the difference
between the proposed method and the state-of-art method is less than 5dB at its
worse.Comment: 5 pages, 2 figures, to be published in 2021 17th International
Symposium on Wireless Communication Systems (ISWCS
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
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
Performance of limited feedback secure MISO systems in temporally correlated channels
25th Signal Processing and Communications Applications Conference, SIU 2017; Antalya; Turkey; 15 May 2017 through 18 May 2017Bu çalışmada, zamanla ilintili kanallarda çoklu anten iletimi ile güvenli haberleşme problemi göz önüne alınmıştır. Güvenlik kapasitesinde kazanç elde etmek için vericide hedeflenen alıcının kablosuz kanal durum bilgisi gereklidir. Bu çalışmada, güvenli çoklu antenli sistemler için kablosuz kanalın zamanda ilintisini kullanan diferansiyel kod kitapçığı içeren bir geri besleme linki sunulmuştur. Farklı kanal ilinti değerleri için güvenlik kapasite performansı gösterilmiştir.We consider the problem of secure communication with multiple antenna transmission in temporally correlated channels. In order to achieve a secrecy gain, a channel state information of the intended receiver at the transmitter is required. In this work, we present a limited feedback link by employing differential codebook which utilizes the temporal correlation properties of the wireless channels for a secure multi-antenna system. The secrecy performances are shown for different channel correlations.TUBITAK (114E626
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
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