2,584 research outputs found
Deep Learning Methods for Universal MISO Beamforming
This letter studies deep learning (DL) approaches to optimize beamforming
vectors in downlink multi-user multi-antenna systems that can be universally
applied to arbitrarily given transmit power limitation at a base station. We
exploit the sum power budget as side information so that deep neural networks
(DNNs) can effectively learn the impact of the power constraint in the
beamforming optimization. Consequently, a single training process is sufficient
for the proposed universal DL approach, whereas conventional methods need to
train multiple DNNs for all possible power budget levels. Numerical results
demonstrate the effectiveness of the proposed DL methods over existing schemes.Comment: to appear in IEEE Wireless Communications Letters (5 pages, 3
figures, 2 tables
A Bipartite Graph Neural Network Approach for Scalable Beamforming Optimization
Deep learning (DL) techniques have been intensively studied for the
optimization of multi-user multiple-input single-output (MU-MISO) downlink
systems owing to the capability of handling nonconvex formulations. However,
the fixed computation structure of existing deep neural networks (DNNs) lacks
flexibility with respect to the system size, i.e., the number of antennas or
users. This paper develops a bipartite graph neural network (BGNN) framework, a
scalable DL solution designed for multi-antenna beamforming optimization. The
MU-MISO system is first characterized by a bipartite graph where two disjoint
vertex sets, each of which consists of transmit antennas and users, are
connected via pairwise edges. These vertex interconnection states are modeled
by channel fading coefficients. Thus, a generic beamforming optimization
process is interpreted as a computation task over a weight bipartite graph.
This approach partitions the beamforming optimization procedure into multiple
suboperations dedicated to individual antenna vertices and user vertices.
Separated vertex operations lead to scalable beamforming calculations that are
invariant to the system size. The vertex operations are realized by a group of
DNN modules that collectively form the BGNN architecture. Identical DNNs are
reused at all antennas and users so that the resultant learning structure
becomes flexible to the network size. Component DNNs of the BGNN are trained
jointly over numerous MU-MISO configurations with randomly varying network
sizes. As a result, the trained BGNN can be universally applied to arbitrary
MU-MISO systems. Numerical results validate the advantages of the BGNN
framework over conventional methods.Comment: accepted for publication on IEEE Transactions on Wireless
Communication
Deep Learning Methods for Joint Optimization of Beamforming and Fronthaul Quantization in Cloud Radio Access Networks
Cooperative beamforming across access points (APs) and fronthaul quantization
strategies are essential for cloud radio access network (C-RAN) systems. The
nonconvexity of the C-RAN optimization problems, which is stemmed from per-AP
power and fronthaul capacity constraints, requires high computational
complexity for executing iterative algorithms. To resolve this issue, we
investigate a deep learning approach where the optimization module is replaced
with a well-trained deep neural network (DNN). An efficient learning solution
is proposed which constructs a DNN to produce a low-dimensional representation
of optimal beamforming and quantization strategies. Numerical results validate
the advantages of the proposed learning solution.Comment: accepted for publication on IEEE Wireless Communications Letter
Deleterious effects in reproduction and developmental immunity elicited by pulmonary iron oxide nanoparticles
With the extensive application of iron oxide nanoparticles (FeNPs), attention about their potential risks to human health is also rapidly raising, particularly in sensitive subgroups such as pregnant women and babies. In this study, we a single instilled intratracheally FeNPs (1, 2, and 4 mg/kg) to the male and female parent mice, mated, then assessed reproductive toxicity according to the modified OECD TG 421. During the pre-mating period (14 days), two female parent mice died at 4 mg/kg dose, and the body weight gain dose-dependently decreased in male and female parent mice exposed to FeNPs. Additionally, iron accumulation and the enhanced expression of MHC class II molecules were observed in the ovary and the testis of parent mice exposed to the highest dose of FeNPs, and the total sex ratio (male/female) of the offspring mice increased in the groups exposed to FeNPs. Following, we a single instilled intratracheally to their offspring mice with the same doses and evaluated the immunotoxic response on day 28. The increased mortality and significant hematological- and biochemical- changes were observed in offspring mice exposed at 4 mg/kg dose, especially in female mice. More interestingly, balance of the immune response was shifted to a different direction in male and female offspring mice. Taken together, we conclude that the NOAEL for reproductive and developmental toxicity of FeNPs may be lower than 2 mg/kg, and that female mice may show more sensitive response to FeNPs exposure than male mice. Furthermore, we suggest that further studies are necessary to identify causes of both the alteration in sex ratio of offspring mice and different immune response in male and female offspring mice.
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Real-time observations of TRIP-induced ultrahigh strain hardening in a dual-phase CrMnFeCoNi high-entropy alloy.
Strategies involving metastable phases have been the basis of the design of numerous alloys, yet research on metastable high-entropy alloys is still in its infancy. In dual-phase high-entropy alloys, the combination of local chemical environments and loading-induced crystal structure changes suggests a relationship between deformation mechanisms and chemical atomic distribution, which we examine in here in a Cantor-like Cr20Mn6Fe34Co34Ni6 alloy, comprising both face-centered cubic (fcc) and hexagonal closed packed (hcp) phases. We observe that partial dislocation activities result in stable three-dimensional stacking-fault networks. Additionally, the fraction of the stronger hcp phase progressively increases during plastic deformation by forming at the stacking-fault network boundaries in the fcc phase, serving as the major source of strain hardening. In this context, variations in local chemical composition promote a high density of Lomer-Cottrell locks, which facilitate the construction of the stacking-fault networks to provide nucleation sites for the hcp phase transformation
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