1,645 research outputs found
Cellular Offloading via Downlink Cache Placement
In this paper, the downlink file transmission within a finite lifetime is
optimized with the assistance of wireless cache nodes. Specifically, the number
of requests within the lifetime of one file is modeled as a Poisson point
process. The base station multicasts files to downlink users and the selected
the cache nodes, so that the cache nodes can help to forward the files in the
next file request. Thus we formulate the downlink transmission as a Markov
decision process with random number of stages, where transmission power and
time on each transmission are the control policy. Due to random number of file
transmissions, we first proposed a revised Bellman's equation, where the
optimal control policy can be derived. In order to address the prohibitively
huge state space, we also introduce a low-complexity sub-optimal solution based
on an linear approximation of the value function. The approximated value
function can be calculated analytically, so that conventional numerical value
iteration can be eliminated. Moreover, the gap between the approximated value
function and the real value function is bounded analytically. It is shown by
simulation that, with the approximated MDP approach, the proposed algorithm can
significantly reduce the resource consumption at the base station.Comment: Submitted for IEEE ICC 201
MDP-Based Scheduling Design for Mobile-Edge Computing Systems with Random User Arrival
In this paper, we investigate the scheduling design of a mobile-edge
computing (MEC) system, where the random arrival of mobile devices with
computation tasks in both spatial and temporal domains is considered. The
binary computation offloading model is adopted. Every task is indivisible and
can be computed at either the mobile device or the MEC server. We formulate the
optimization of task offloading decision, uplink transmission device selection
and power allocation in all the frames as an infinite-horizon Markov decision
process (MDP). Due to the uncertainty in device number and location,
conventional approximate MDP approaches to addressing the curse of
dimensionality cannot be applied. A novel low-complexity sub-optimal solution
framework is then proposed. We first introduce a baseline scheduling policy,
whose value function can be derived analytically. Then, one-step policy
iteration is adopted to obtain a sub-optimal scheduling policy whose
performance can be bounded analytically. Simulation results show that the gain
of the sub-optimal policy over various benchmarks is significant.Comment: 6 pages, 3 figures; accepted by Globecom 2019; title changed to
better describe the work, introduction condensed, typos correcte
A comprehensive analysis of Fermi Gamma-Ray Burst Data: IV. Spectral lag and Its Relation to Ep Evolution
The spectral evolution and spectral lag behavior of 92 bright pulses from 84
gamma-ray bursts (GRBs) observed by the Fermi GBM telescope are studied. These
pulses can be classified into hard-to-soft pulses (H2S, 64/92),
H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We
focus on the relationship between spectral evolution and spectral lags of H2S
and H2S-dominated-tracking pulses. %in hard-to-soft pulses (H2S, 64/92) and
H2S-dominating-tracking (21/92) pulses. The main trend of spectral evolution
(lag behavior) is estimated with
(), where is the peak photon
energy in the radiation spectrum, is the observer time relative to the
beginning of pulse , and is the spectral lag of photons
with energy with respect to the energy band - keV. For H2S and
H2S-dominated-tracking pulses, a weak correlation between
and is found, where is the pulse width. We also study the spectral
lag behavior with peak time of pulses for 30 well-shaped pulses
and estimate the main trend of the spectral lag behavior with . It is found that is correlated with
. We perform simulations under a phenomenological model of spectral
evolution, and find that these correlations are reproduced. We then conclude
that spectral lags are closely related to spectral evolution within the pulse.
The most natural explanation of these observations is that the emission is from
the electrons in the same fluid unit at an emission site moving away from the
central engine, as expected in the models invoking magnetic dissipation in a
moderately-high- outflow.Comment: 58 pages, 11 figures, 3 tables. ApJ in pres
Memory efficient location recommendation through proximity-aware representation
Sequential location recommendation plays a huge role in modern life, which
can enhance user experience, bring more profit to businesses and assist in
government administration. Although methods for location recommendation have
evolved significantly thanks to the development of recommendation systems,
there is still limited utilization of geographic information, along with the
ongoing challenge of addressing data sparsity. In response, we introduce a
Proximity-aware based region representation for Sequential Recommendation (PASR
for short), built upon the Self-Attention Network architecture. We tackle the
sparsity issue through a novel loss function employing importance sampling,
which emphasizes informative negative samples during optimization. Moreover,
PASR enhances the integration of geographic information by employing a
self-attention-based geography encoder to the hierarchical grid and proximity
grid at each GPS point. To further leverage geographic information, we utilize
the proximity-aware negative samplers to enhance the quality of negative
samples. We conducted evaluations using three real-world Location-Based Social
Networking (LBSN) datasets, demonstrating that PASR surpasses state-of-the-art
sequential location recommendation method
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