50 research outputs found
Nature of Oil Price Shocks and Monetary Policy
We investigate the nature of oil price shocks to the Korean economy in recent years and find that the recent hike in oil price is induced by the increase in oil demand in contrast to the previous years when oil price run-up is mostly from supply disruptions. We also study how monetary responses to oil price shocks affect economic stability and find that an accommodative policy yields more stable outcomes.
HARQ Buffer Management: An Information-Theoretic View
A key practical constraint on the design of Hybrid automatic repeat request
(HARQ) schemes is the size of the on-chip buffer that is available at the
receiver to store previously received packets. In fact, in modern wireless
standards such as LTE and LTE-A, the HARQ buffer size is one of the main
drivers of the modem area and power consumption. This has recently highlighted
the importance of HARQ buffer management, that is, of the use of buffer-aware
transmission schemes and of advanced compression policies for the storage of
received data. This work investigates HARQ buffer management by leveraging
information-theoretic achievability arguments based on random coding.
Specifically, standard HARQ schemes, namely Type-I, Chase Combining and
Incremental Redundancy, are first studied under the assumption of a
finite-capacity HARQ buffer by considering both coded modulation, via Gaussian
signaling, and Bit Interleaved Coded Modulation (BICM). The analysis sheds
light on the impact of different compression strategies, namely the
conventional compression log-likelihood ratios and the direct digitization of
baseband signals, on the throughput. Then, coding strategies based on layered
modulation and optimized coding blocklength are investigated, highlighting the
benefits of HARQ buffer-aware transmission schemes. The optimization of
baseband compression for multiple-antenna links is also studied, demonstrating
the optimality of a transform coding approach.Comment: submitted to IEEE International Symposium on Information Theory
(ISIT) 2015. 29 pages, 12 figures, submitted to journal publicatio
NeFL: Nested Federated Learning for Heterogeneous Clients
Federated learning (FL) is a promising approach in distributed learning
keeping privacy. However, during the training pipeline of FL, slow or incapable
clients (i.e., stragglers) slow down the total training time and degrade
performance. System heterogeneity, including heterogeneous computing and
network bandwidth, has been addressed to mitigate the impact of stragglers.
Previous studies split models to tackle the issue, but with less
degree-of-freedom in terms of model architecture. We propose nested federated
learning (NeFL), a generalized framework that efficiently divides a model into
submodels using both depthwise and widthwise scaling. NeFL is implemented by
interpreting models as solving ordinary differential equations (ODEs) with
adaptive step sizes. To address the inconsistency that arises when training
multiple submodels with different architecture, we decouple a few parameters.
NeFL enables resource-constrained clients to effectively join the FL pipeline
and the model to be trained with a larger amount of data. Through a series of
experiments, we demonstrate that NeFL leads to significant gains, especially
for the worst-case submodel (e.g., 8.33 improvement on CIFAR-10). Furthermore,
we demonstrate NeFL aligns with recent studies in FL.Comment: 21 page
Large thickness dependence of the carrier mobility in a transparent oxide semiconductor, La-doped BaSnO3
We report herein that the carrier mobility of the 2%-La-doped BaSnO3 (LBSO)
films on (001) SrTiO3 and (001) MgO substrates strongly depends on the
thickness whereas it is unrelated to the lattice mismatch (+5.4% for SrTiO3,
-2.3% for MgO). Although we observed large differences in the lattice
parameters, the lateral grain size (~85 nm for SrTiO3, ~20 nm for MgO), the
surface morphology and the density of misfit dislocations, the mobility
increased almost simultaneously with the thickness in both cases and saturated
at ~100 cm2 V-1 s-1, together with the approaching to the nominal carrier
concentration (=[2% La3+]), clearly indicating that the behavior of mobility
depends on the film thickness. The present results would be beneficial to
understand the behavior of mobility and fruitful to further enhance the
mobility of LBSO films.Comment: 15 pages, including 4 figure
Buffer layer-less fabrication of high-mobility transparent oxide semiconductor, La-doped BaSnO3
Transparent oxide semiconductors (TOSs) showing both high visible
transparency and high electron mobility have attracted great attention towards
the realization of advanced optoelectronic devices. La-doped BaSnO3 (LBSO) is
one of the most promising TOSs because its single crystal exhibits a high
electron mobility. However, in the LBSO films, it is very hard to obtain high
mobility due to the threading dislocations, which are originated from the
lattice mismatch between the film and the substrate. Therefore, many
researchers have tried to improve the mobility by inserting a buffer layer.
While the buffer layers increased the electron mobilities, this approach leaves
much to be desired since it involves a two-step film fabrication process and
the enhanced mobility values are still significantly lower than single crystal
values. We show herein that the electron mobility of LBSO films can be improved
without inserting any buffer layers if the films are grown under highly
oxidative ozone (O3) atmospheres. The O3 environments relaxed the LBSO lattice
and reduced the formation of Sn2+ states, which are known to suppress the
electron mobility in LBSO. The resultant O3-LBSO films showed improved mobility
values up to 115 cm2 V-1 s-1, which is among the highest in LBSO films on
SrTiO3 substrates and comparable to LBSO films with buffer layers.Comment: 16 pages including 5 figure
On-chip Brillouin lasers based on 10 million-Q chalcogenide resonators without direct etch process
We present a new device platform which defines on-chip chalcogenide waveguide/resonators without directly etching chalcogenide. Using our platform, we have demonstrated chalcogenide ring resonators with record high Q-factor exceeding 1.1x107 which is 10 times larger than previous record on on-chip chalcogenide resonators. A ring cavity is designed and fabricated for Stimulated Brillouin lasing on our platform. Thanks to the high-Q factor, Brillouin lasing with threshold power of 1 mW is demonstrated. This value is more than an order of magnitude improvement than previous world record for on-chip chalcogenide Brillouin lasers. We also developed an efficient and flexible method for resonator waveguide coupling with our device platform. Coupling between a resonator and a waveguide can be varied from under coupled region to over-coupled regio