4,448 research outputs found
Joint Transceiver Design for Dual-Functional Full-Duplex Relay Aided Radar-Communication Systems
Driven by the demand for massive and accurate sensing data to achieve wireless network intelligence under a limited available spectrum, the coexistence between radar and communication systems has attracted public attention. In this paper, we investigate a novel dual-functional full-duplex relay aided radar-communication system where the phased-array radar is employed at the amplify-and-forward (AF) relay. A joint transceiver design is proposed to maximize the minimum signal-to-interference-plus-noise ratio (SINR) among all detection directions at the radar receiver under communication quality-of-service and total energy constraints. The formulated optimization problem is particularly challenging due to the highly nonconvex objective function and constraints. Based on the problem structure, we equivalently decompose it into the radar-energy and relay-energy minimization problems under SINR requirements. To solve the radar-energy minimization problem, we propose a low-complexity algorithm based on the alternating direction method of multipliers to optimize the radar transmit power and receiver. The relay-energy minimization problem can be simplified into an equivalent quadratic programming problem by introducing an insightful unitary matrix. Then, the closed-form expression for the AF relay beamforming matrix can be derived, which is jointly determined by the channel condition of relay communication and the detection direction of the radar. After that, we introduce the overall transceiver design algorithm to the original problem and discuss its optimality and computational complexity. Simulation results verify that the proposed algorithm significantly outperforms other benchmark algorithms
Spectral and Energy Efficiency of Uplink D2D Underlaid Massive MIMO Cellular Networks
CCBY One of key 5G scenarios is that device-to-device (D2D) and massive multiple-input multiple-output (MIMO) will be co-existed. However, interference in the uplink D2D underlaid massive MIMO cellular networks needs to be coordinated, due to the vast cellular and D2D transmissions. To this end, this paper introduces a spatially dynamic power control solution for mitigating the cellular-to-D2D and D2D-to-cellular interference. In particular, the proposed D2D power control policy is rather flexible including the special cases of no D2D links or using maximum transmit power. Under the considered power control, an analytical approach is developed to evaluate the spectral efficiency (SE) and energy efficiency (EE) in such networks. Thus, the exact expressions of SE for a cellular user or D2D transmitter are derived, which quantify the impacts of key system parameters such as massive MIMO antennas and D2D density. Moreover, the D2D scale properties are obtained, which provide the sufficient conditions for achieving the anticipated SE. Numerical results corroborate our analysis and show that the proposed power control solution can efficiently mitigate interference between the cellular and D2D tier. The results demonstrate that there exists the optimal D2D density for maximizing the area SE of D2D tier. In addition, the achievable EE of a cellular user can be comparable to that of a D2D user
Robust Target Positioning for Reconfigurable Intelligent Surface Assisted MIMO Radar Systems
The direction of arrival (DOA) based multiple-input multiple-output (MIMO) radar technique has been widely utilized for ubiquitous positioning due to its advantage of simple implementability. On the other hand, reconfigurable intelligent surface (RIS) has received considerable attention, which can be deployed on the walls and objects to strengthen the positioning performance. However, RIS is usually not equipped with a perception module, which results in the tremendous challenge for RIS-assisted positioning. To tackle this challenge, this paper propose the fundamental problem of DOA-based target positioning in RIS-assisted MIMO radar system. Unlike conventional DOA estimation systems, the beneficial role of RIS is investigated in MIMO radar system, where a nonconvex promoting function is exploited to estimate DOA task. By adjusting the reflecting elements of the RIS, the proximal projection iterative strategy is developed to obtain the feasible solution. Both theoretical analysis and simulation results illustrate that the proposed scheme can achieve remarkable positioning performance and shed light on the benefits offered by the adoption of the RIS in terms of positioning performance
Childhood secondhand smoke exposure and pregnancy loss in never smokers: The Guangzhou Biobank Cohort Study
published_or_final_versio
The influence of anti-cyclic citrullinated peptide on anticentromere antibody-positive rheumatoid arthritis patients
Effectiveness of varenicline and counseling for smoking cessation in an observational cohort study in China
published_or_final_versio
Effectiveness of additional follow-up telephone counseling in a smoking cessation clinic in Beijing and predictors of quitting among Chinese male smokers
published_or_final_versio
Dynamic service placement for mobile micro-clouds with predicted future costs
Mobile micro-clouds are promising for enabling performance-critical cloud applications. However, one challenge therein is the dynamics at the network edge. In this paper, we study how to place service instances to cope with these dynamics, where multiple users and service instances coexist in the system. Our goal is to find the optimal placement (configuration) of instances to minimize the average cost overtime, leveraging the ability of predicting future cost parameters with known accuracy. We first propose an offline algorithm that solves for the optimal configuration in a specific look-ahead time-window. Then, we propose an online approximation algorithm with polynomial time-complexity to find the placement in real-time whenever an instance arrives. We analytically show that the online algorithm is 0(1)-competitive for a broad family of cost functions. Afterwards, the impact of prediction errors is considered and a method for finding the optimal look-ahead window size is proposed, which minimizes an upper bound of the average actual cost. The effectiveness of the proposed approach is evaluated by simulations with both synthetic and real-world (San Francisco taxi) usermobility traces. The theoretical methodology used in this paper can potentially be applied to a larger class of dynamic resource allocation problems
Density diagnostics derIVed from the O IV and S IV intercombination lines observed by IRIS
The intensity of the \oiv~2s 2p P-2s2p P and \siv~3
s 3p P- 3s 3p P intercombination lines around
1400~\AA~observed with the \textit{Interface Region Imaging Spectrograph}
(IRIS) provide a useful tool to diagnose the electron number density
() in the solar transition region plasma. We measure the electron
number density in a variety of solar features observed by IRIS, including an
active region (AR) loop, plage and brightening, and the ribbon of the
22-June-2015 M 6.5 class flare. By using the emissivity ratios of \oiv\ and
\siv\ lines, we find that our observations are consistent with the emitting
plasma being near isothermal (log[K] 5) and iso-density
( ~10 cm) in the AR loop. Moreover, high
electron number densities ( ~10 cm) are
obtained during the impulsive phase of the flare by using the \siv\ line ratio.
We note that the \siv\ lines provide a higher range of density sensitivity than
the \oiv\ lines. Finally, we investigate the effects of high densities
( 10 cm) on the ionization balance. In
particular, the fractional ion abundances are found to be shifted towards lower
temperatures for high densities compared to the low density case. We also
explored the effects of a non-Maxwellian electron distribution on our
diagnostic method.VP acknowledges support from the Isaac Newton Studentship, the Cambridge Trust, the IRIS team at Harvard-Smithsonian Centre for Astrophysics and the RS Newton Alumni Programme. GDZ and HEM acknowledge support from the STFC and the RS Newton Alumni Programme. JD acknowledges support from the RS Newton Alumni Programme. JD also acknowledges support from the Grant No. P209/12/1652 of the Grant Agency of the Czech Republic. AG acknowledges the in house research support provided by the Science and Technology Facilities Council. KR is supported by contract 8100002705 from Lockheed-Martin to SAO. IRIS is a NASA small explorer mission developed and operated by LMSAL with mission operations executed at NASA Ames Research Center and major contributions to downlink communications funded by the Norwegian Space Center (NSC, Norway) through an ESA PRODEX contract. AIA data are courtesy of NASA/SDO and the respective science teams. CHIANTI is a collaborative project involving researchers at the universities of Cambridge (UK), George Mason and Michigan (USA). ADAS is a project managed at the University of Strathclyde (UK) and funded through memberships universities and astrophysics and fusion laboratories in Europe and worldwide.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by EDP Sciences
CASED: Curriculum Adaptive Sampling for Extreme Data Imbalance
We introduce CASED, a novel curriculum sampling algorithm that facilitates
the optimization of deep learning segmentation or detection models on data sets
with extreme class imbalance. We evaluate the CASED learning framework on the
task of lung nodule detection in chest CT. In contrast to two-stage solutions,
wherein nodule candidates are first proposed by a segmentation model and
refined by a second detection stage, CASED improves the training of deep nodule
segmentation models (e.g. UNet) to the point where state of the art results are
achieved using only a trivial detection stage. CASED improves the optimization
of deep segmentation models by allowing them to first learn how to distinguish
nodules from their immediate surroundings, while continuously adding a greater
proportion of difficult-to-classify global context, until uniformly sampling
from the empirical data distribution. Using CASED during training yields a
minimalist proposal to the lung nodule detection problem that tops the LUNA16
nodule detection benchmark with an average sensitivity score of 88.35%.
Furthermore, we find that models trained using CASED are robust to nodule
annotation quality by showing that comparable results can be achieved when only
a point and radius for each ground truth nodule are provided during training.
Finally, the CASED learning framework makes no assumptions with regard to
imaging modality or segmentation target and should generalize to other medical
imaging problems where class imbalance is a persistent problem.Comment: 20th International Conference on Medical Image Computing and Computer
Assisted Intervention 201
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