2,926 research outputs found
Efficient Downlink Channel Reconstruction for FDD Multi-Antenna Systems
In this paper, we propose an efficient downlink channel reconstruction scheme
for a frequency-division-duplex multi-antenna system by utilizing uplink
channel state information combined with limited feedback. Based on the spatial
reciprocity in a wireless channel, the downlink channel is reconstructed by
using frequency-independent parameters. We first estimate the gains, delays,
and angles during uplink sounding. The gains are then refined through downlink
training and sent back to the base station (BS). With limited overhead, the
refinement can substantially improve the accuracy of the downlink channel
reconstruction. The BS can then reconstruct the downlink channel with the
uplink-estimated delays and angles and the downlink-refined gains. We also
introduce and extend the Newtonized orthogonal matching pursuit (NOMP)
algorithm to detect the delays and gains in a multi-antenna multi-subcarrier
condition. The results of our analysis show that the extended NOMP algorithm
achieves high estimation accuracy. Simulations and over-the-air tests are
performed to assess the performance of the efficient downlink channel
reconstruction scheme. The results show that the reconstructed channel is close
to the practical channel and that the accuracy is enhanced when the number of
BS antennas increases, thereby highlighting that the promising application of
the proposed scheme in large-scale antenna array systems
QCD radiative correction to color-octet inclusive production at B Factories
In nonrelativistic Quantum Chromodynamics (NRQCD), we study the
next-to-leading order (NLO) QCD radiative correction to the color-octet
inclusive production at B Factories. Compared with the leading-order
(LO) result, the NLO QCD corrections are found to enhance the short-distance
coefficients in the color-octet production by a factor of about 1.9. Moreover, the
peak at the endpoint in the energy distribution predicted at LO can be
smeared by the NLO corrections, but the major color-octet contribution still
comes from the large energy region of . By fitting the latest data of
observed by Belle, we
find that the values of color-octet matrix elements are much smaller than
expected earlier by using the naive velocity scaling rules or extracted from
fitting experimental data with LO calculations. As the most stringent
constraint by setting the color-singlet contribution to be zero in
, we get an upper limit of the
color-octet matrix element, at NLO in .Comment: 18 pages, 8 figure
Functional characterization of intracellular ion channels with the endolysosomal patch-clamp technique
Functional characterization of intracellular ion channels with the endolysosomal patch-clamp technique
FDD Massive MIMO Based on Efficient Downlink Channel Reconstruction
Massive multiple-input multiple-output (MIMO) systems deploying a large
number of antennas at the base station considerably increase the spectrum
efficiency by serving multiple users simultaneously without causing severe
interference. However, the advantage relies on the availability of the downlink
channel state information (CSI) of multiple users, which is still a challenge
in frequency-division-duplex transmission systems. This paper aims to solve
this problem by developing a full transceiver framework that includes downlink
channel training (or estimation), CSI feedback, and channel reconstruction
schemes. Our framework provides accurate reconstruction results for multiple
users with small amounts of training and feedback overhead. Specifically, we
first develop an enhanced Newtonized orthogonal matching pursuit (eNOMP)
algorithm to extract the frequency-independent parameters (i.e., downtilts,
azimuths, and delays) from the uplink. Then, by leveraging the information from
these frequency-independent parameters, we develop an efficient downlink
training scheme to estimate the downlink channel gains for multiple users. This
training scheme offers an acceptable estimation error rate of the gains with a
limited pilot amount. Numerical results verify the precision of the eNOMP
algorithm and demonstrate that the sum-rate performance of the system using the
reconstructed downlink channel can approach that of the system using perfect
CSI
MegDet: A Large Mini-Batch Object Detector
The improvements in recent CNN-based object detection works, from R-CNN [11],
Fast/Faster R-CNN [10, 31] to recent Mask R-CNN [14] and RetinaNet [24], mainly
come from new network, new framework, or novel loss design. But mini-batch
size, a key factor in the training, has not been well studied. In this paper,
we propose a Large MiniBatch Object Detector (MegDet) to enable the training
with much larger mini-batch size than before (e.g. from 16 to 256), so that we
can effectively utilize multiple GPUs (up to 128 in our experiments) to
significantly shorten the training time. Technically, we suggest a learning
rate policy and Cross-GPU Batch Normalization, which together allow us to
successfully train a large mini-batch detector in much less time (e.g., from 33
hours to 4 hours), and achieve even better accuracy. The MegDet is the backbone
of our submission (mmAP 52.5%) to COCO 2017 Challenge, where we won the 1st
place of Detection task
Robust Affinity Propagation using Preference Estimation
Affinity propagation is a novel unsupervised learning algorithm for exemplar-based clustering without the priori
knowledge of the number of clusters (NC). In this article, the influence of the “preference” on the accuracy of
AP output is addressed. We present a robust AP clustering method, which estimates what preference value could
possibly yield an optimal clustering result. To demonstrate the performance promotion, we apply the robust AP
on picture clustering, using local SIFT, global MPEG-7 CLD, and the proposed preference as the input of AP.
The experimental results show that over 40% enhancement of ARI accuracy for several image datasets
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