189 research outputs found
Selective Combining for Hybrid Cooperative Networks
In this study, we consider the selective combining in hybrid cooperative
networks (SCHCNs scheme) with one source node, one destination node and
relay nodes. In the SCHCN scheme, each relay first adaptively chooses between
amplify-and-forward protocol and decode-and-forward protocol on a per frame
basis by examining the error-detecting code result, and () relays will be selected to forward their received signals to the
destination. We first develop a signal-to-noise ratio (SNR) threshold-based
frame error rate (FER) approximation model. Then, the theoretical FER
expressions for the SCHCN scheme are derived by utilizing the proposed SNR
threshold-based FER approximation model. The analytical FER expressions are
validated through simulation results.Comment: 27 pages, 8 figures, IET Communications, 201
Grasping Strategy in Space Robot Capturing Floating Target
AbstractWhen the space robot captures a floating target, contact impact occurs inevitably and frequently between the manipulator hand and the target, which seriously impacts the position and attitude of the robot and grasping security. “Dynamic grasping area” is introduced to describe the collision process of manipulator grasping target, and grasping area control equation is established. By analyzing the impact of grasping control parameters, base and target mass on the grasping process and combining the life experience, it is found that if the product of speed control parameter and dB adjustment parameter is close to but smaller than the minimum grasping speed, collision impact in the grasping process could be reduced greatly, and then an ideal grasping strategy is proposed. Simulation results indicate that during the same period, the strategy grasping is superior to the accelerating grasping, in that the amplitude of impact force is reduced to 20%, and the attitude control torque is reduced to 15%, and the impact on the robot is eliminated significantly. The results would have important academic value and engineering significance
Efficient Modeling of Surrogates to Improve Multi-source High-dimensional Biobank Studies
Surrogate variables in electronic health records (EHR) and biobank data play
an important role in biomedical studies due to the scarcity or absence of
chart-reviewed gold standard labels. We develop a novel approach named SASH for
{\bf S}urrogate-{\bf A}ssisted and data-{\bf S}hielding {\bf H}igh-dimensional
integrative regression. It is a semi-supervised approach that efficiently
leverages sizable unlabeled samples with error-prone EHR surrogate outcomes
from multiple local sites, to improve the learning accuracy of the small
gold-labeled data. {To facilitate stable and efficient knowledge extraction
from the surrogates, our method first obtains a preliminary supervised
estimator, and then uses it to assist training a regularized single index model
(SIM) for the surrogates. Interestingly, through a chain of convex and properly
penalized sparse regressions that approximate the SIM loss with
bias-correction, our method avoids the local minima issue of the SIM training,
and fully eliminates the impact of the preliminary estimator's large error. In
addition, it protects individual-level information through
summary-statistics-based data aggregation across the local sites, leveraging a
similar idea of bias-corrected approximation for SIM.} Through simulation
studies, we demonstrate that our method outperforms existing approaches on
finite samples. Finally, we apply our method to develop a high dimensional
genetic risk model for type II diabetes using large-scale data sets from UK and
Mass General Brigham biobanks, where only a small fraction of subjects in one
site has been labeled via chart reviewing
Doubly Robust Augmented Model Accuracy Transfer Inference with High Dimensional Features
Due to label scarcity and covariate shift happening frequently in real-world
studies, transfer learning has become an essential technique to train models
generalizable to some target populations using existing labeled source data.
Most existing transfer learning research has been focused on model estimation,
while there is a paucity of literature on transfer inference for model accuracy
despite its importance. We propose a novel oubly obust
ugmented odel ccuracy ransfer
nferene (DRAMATIC) method for point and interval
estimation of commonly used classification performance measures in an unlabeled
target population using labeled source data. Specifically, DRAMATIC derives and
evaluates the risk model for a binary response against some low dimensional
predictors on the target population, leveraging from source
data only and high dimensional adjustment features from both the
source and target data. The proposed estimators are doubly robust in the sense
that they are consistent when at least one model is correctly
specified and certain model sparsity assumptions hold. Simulation results
demonstrate that the point estimation have negligible bias and the confidence
intervals derived by DRAMATIC attain satisfactory empirical coverage levels. We
further illustrate the utility of our method to transfer the genetic risk
prediction model and its accuracy evaluation for type II diabetes across two
patient cohorts in Mass General Brigham (MGB) collected using different
sampling mechanisms and at different time points
Performance Analysis of Hybrid Relay Selection in Cooperative Wireless Systems
The hybrid relay selection (HRS) scheme, which adaptively chooses
amplify-and-forward (AF) and decode-and-forward (DF) protocols, is very
effective to achieve robust performance in wireless networks. This paper
analyzes the frame error rate (FER) of the HRS scheme in general cooperative
wireless networks without and with utilizing error control coding at the source
node. We first develop an improved signal-to-noise ratio (SNR) threshold-based
FER approximation model. Then, we derive an analytical average FER expression
as well as an asymptotic expression at high SNR for the HRS scheme and
generalize to other relaying schemes. Simulation results are in excellent
agreement with the theoretical analysis, which validates the derived FER
expressions.Comment: IEEE Transactions on Communications, 201
On the Characterization of a Class of Fisher-Consistent Loss Functions and Its Application to Boosting
Accurate classification of categorical outcomes is essential in a wide range of applications. Due to computational issues with minimizing the empirical 0/1 loss, Fisher consistent losses have been proposed as viable proxies. However, even with smooth losses, direct minimization remains a daunting task. To approximate such a minimizer, various boosting algorithms have been suggested. For example, with exponential loss, the AdaBoost algorithm (Freund and Schapire, 1995) is widely used for two-class problems and has been extended to the multi-class setting (Zhu et al., 2009). Alternative loss functions, such as the logistic and the hinge losses, and their corresponding boosting algorithms have also been proposed (Zou et al., 2008; Wang, 2012). In this paper we demonstrate that a broad class of losses, including non-convex functions, achieve Fisher consistency, and in addition can be used for explicit estimation of the conditional class probabilities. Furthermore, we provide a generic boosting algorithm that is not loss-specific. Extensive simulation results suggest that the proposed boosting algorithms could outperform existing methods with properly chosen losses and bags of weak learners.Statistic
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