2,311 research outputs found
Artificial-Noise-Aided Physical Layer Phase Challenge-Response Authentication for Practical OFDM Transmission
Recently, we have developed a PHYsical layer Phase Challenge-Response
Authentication Scheme (PHY-PCRAS) for independent multicarrier transmission. In
this paper, we make a further step by proposing a novel artificial-noise-aided
PHY-PCRAS (ANA-PHY-PCRAS) for practical orthogonal frequency division
multiplexing (OFDM) transmission, where the Tikhonov-distributed artificial
noise is introduced to interfere with the phase-modulated key for resisting
potential key-recovery attacks whenever a static channel between two legitimate
users is unfortunately encountered. Then, we address various practical issues
for ANA-PHY-PCRAS with OFDM transmission, including correlation among
subchannels, imperfect carrier and timing recoveries. Among them, we show that
the effect of sampling offset is very significant and a search procedure in the
frequency domain should be incorporated for verification. With practical OFDM
transmission, the number of uncorrelated subchannels is often not sufficient.
Hence, we employ a time-separated approach for allocating enough subchannels
and a modified ANA-PHY-PCRAS is proposed to alleviate the discontinuity of
channel phase at far-separated time slots. Finally, the key equivocation is
derived for the worst case scenario. We conclude that the enhanced security of
ANA-PHY-PCRAS comes from the uncertainty of both the wireless channel and
introduced artificial noise, compared to the traditional challenge-response
authentication scheme implemented at the upper layer.Comment: 33 pages, 13 figures, submitted for possible publicatio
Molecular geometric deep learning
Geometric deep learning (GDL) has demonstrated huge power and enormous
potential in molecular data analysis. However, a great challenge still remains
for highly efficient molecular representations. Currently, covalent-bond-based
molecular graphs are the de facto standard for representing molecular topology
at the atomic level. Here we demonstrate, for the first time, that molecular
graphs constructed only from non-covalent bonds can achieve similar or even
better results than covalent-bond-based models in molecular property
prediction. This demonstrates the great potential of novel molecular
representations beyond the de facto standard of covalent-bond-based molecular
graphs. Based on the finding, we propose molecular geometric deep learning
(Mol-GDL). The essential idea is to incorporate a more general molecular
representation into GDL models. In our Mol-GDL, molecular topology is modeled
as a series of molecular graphs, each focusing on a different scale of atomic
interactions. In this way, both covalent interactions and non-covalent
interactions are incorporated into the molecular representation on an equal
footing. We systematically test Mol-GDL on fourteen commonly-used benchmark
datasets. The results show that our Mol-GDL can achieve a better performance
than state-of-the-art (SOTA) methods. Source code and data are available at
https://github.com/CS-BIO/Mol-GDL
High-responsivity vertical-illumination Si/Ge uni-traveling-carrier photodiodes based on silicon-on-insulator substrate
Si/Ge uni-traveling carrier photodiodes exhibit higher output current when
space-charge effects are overcome and thermal effects are suppressed, which is
highly beneficial for increasing the dynamic range of various microwave
photonic systems and simplifying high-bit-rate digital receivers in different
applications. From the point of view of packaging, detectors with
vertical-illumination configuration can be easily handled by pick-and-place
tools and are a popular choice for making photo-receiver modules. However,
vertical-illumination Si/Ge uni-traveling carrier (UTC) devices suffer from
inter-constraint between high speed and high responsivity. Here, we report a
high responsivity vertical-illumination Si/Ge UTC photodiode based on a
silicon-on-insulator substrate. The maximum absorption efficiency of the
devices was 2.4 times greater than the silicon substrate owing to constructive
interference. The Si/Ge UTC photodiode was successfully fabricated and had a
dominant responsivity at 1550 nm of 0.18 A/W, a 50% improvement even with a 25%
thinner Ge absorption layer.Comment: 5pages,2figure
Dichloridobis[2-(2-furyl)-1-(2-furylmethyl)-1H-benzimidazole-κN 3]cadmium(II)
In the title complex, [CdCl2(C16H12N2O2)2], the CdII ion exhibits site symmetry 2. It shows a distorted tetrahedral coordination defined by two N atoms from symmetry-related 2-(2-furyl)-1-(2-furylmethyl)-1H-benzimidazole ligands and by two symmetry-related Cl atoms. Intramolecular C—H⋯O hydrogen bonds stabilize the molecular configuration. Adjacent molecules are linked through C—H⋯Cl hydrogen bonds into a network structure
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