124 research outputs found
Sparse Message Passing Based Preamble Estimation for Crowded M2M Communications
Due to the massive number of devices in the M2M communication era, new
challenges have been brought to the existing random-access (RA) mechanism, such
as severe preamble collisions and resource block (RB) wastes. To address these
problems, a novel sparse message passing (SMP) algorithm is proposed, based on
a factor graph on which Bernoulli messages are updated. The SMP enables an
accurate estimation on the activity of the devices and the identity of the
preamble chosen by each active device. Aided by the estimation, the RB
efficiency for the uplink data transmission can be improved, especially among
the collided devices. In addition, an analytical tool is derived to analyze the
iterative evolution and convergence of the SMP algorithm. Finally, numerical
simulations are provided to verify the validity of our analytical results and
the significant improvement of the proposed SMP on estimation error rate even
when preamble collision occurs.Comment: submitted to ICC 2018 with 6 pages and 4 figure
A Calibration Method for Wide Field Multicolor Photometric System
The purpose of this paper is to present a method to self-calibrate the
spectral energy distribution (SED) of objects in a survey based on the fitting
of an SED library to the observed multi-color photometry. We adopt for
illustrative purposes the Vilnius (Strizyz and Sviderskiene 1972) and Gunn &
Stryker (1983) SED libraries. The self-calibration technique can improve the
quality of observations which are not taken under perfectly photometric
conditions. The more passbands used for the photometry, the better the results.
This technique has been applied to the BATC 15-passband CCD survey.Comment: LateX file, 1 PS file, submitted to PASP number 99-025 The English
has been improved and some mistakes have been correcte
User Activity Detection and Channel Estimation for Grant-Free Random Access in LEO Satellite-Enabled Internet-of-Things
With recent advances on the dense low-earth orbit (LEO) constellation, LEO
satellite network has become one promising solution to providing global
coverage for Internet-of-Things (IoT) services. Confronted with the sporadic
transmission from randomly activated IoT devices, we consider the random access
(RA) mechanism, and propose a grant-free RA (GF-RA) scheme to reduce the access
delay to the mobile LEO satellites. A Bernoulli-Rician message passing with
expectation maximization (BR-MP-EM) algorithm is proposed for this
terrestrial-satellite GF-RA system to address the user activity detection (UAD)
and channel estimation (CE) problem. This BR-MP-EM algorithm is divided into
two stages. In the inner iterations, the Bernoulli messages and Rician messages
are updated for the joint UAD and CE problem. Based on the output of the inner
iterations, the expectation maximization (EM) method is employed in the outer
iterations to update the hyper-parameters related to the channel impairments.
Finally, simulation results show the UAD and CE accuracy of the proposed
BR-MP-EM algorithm, as well as the robustness against the channel impairments.Comment: 14 pages, 9 figures, accepted by Internet of Things Journa
Optical Photometry of Type II-P Supernova 2004dj in NGC 2403
We present photometric data of the type II-P supernova (SN) 2004dj in NGC
2403. The multicolor light curves cover the SN from 60 to 200 days after
explosion, and are measured with a set of intermediate-band filters that have
the advantage of tracing the strength variations of some spectral features. The
light curves show a flat evolution in the middle of the plateau phase, then
decline exponentially at the late times, with a rate of 0.100.03 mag (10
days) in most of the filters. In the nebular phase, the spectral energy
distribution (SED) of SN 2004dj shows a steady increase in the flux near 6600
\AA and 8500 \AA, which may correspond to the emission lines of H and
Ca II near-IR triplet, respectively. The photometric behavior suggests that SN
2004dj is a normal SN II-P. Compared with the light curves of another typical
SN II-P 1999em, we estimate the explosion date to be June 1021 UT, 2004
(JD 245316721) for SN 2004dj. We also estimate the ejected nickel mass
during the explosion to be = 0.023 0.005
from two different methods, which is typical for a SN II-P. We derive the
explosion energy erg, the ejecta
mass , and the initial radius for the presupernova star of SN 2004dj,
which are consistent with other typical SNe II-P.Comment: 15 pages, 9 figures, accepted for publication in A
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