128,247 research outputs found
High Energy Physics Forum for Computational Excellence: Working Group Reports (I. Applications Software II. Software Libraries and Tools III. Systems)
Computing plays an essential role in all aspects of high energy physics. As
computational technology evolves rapidly in new directions, and data throughput
and volume continue to follow a steep trend-line, it is important for the HEP
community to develop an effective response to a series of expected challenges.
In order to help shape the desired response, the HEP Forum for Computational
Excellence (HEP-FCE) initiated a roadmap planning activity with two key
overlapping drivers -- 1) software effectiveness, and 2) infrastructure and
expertise advancement. The HEP-FCE formed three working groups, 1) Applications
Software, 2) Software Libraries and Tools, and 3) Systems (including systems
software), to provide an overview of the current status of HEP computing and to
present findings and opportunities for the desired HEP computational roadmap.
The final versions of the reports are combined in this document, and are
presented along with introductory material.Comment: 72 page
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
ASCR/HEP Exascale Requirements Review Report
This draft report summarizes and details the findings, results, and
recommendations derived from the ASCR/HEP Exascale Requirements Review meeting
held in June, 2015. The main conclusions are as follows. 1) Larger, more
capable computing and data facilities are needed to support HEP science goals
in all three frontiers: Energy, Intensity, and Cosmic. The expected scale of
the demand at the 2025 timescale is at least two orders of magnitude -- and in
some cases greater -- than that available currently. 2) The growth rate of data
produced by simulations is overwhelming the current ability, of both facilities
and researchers, to store and analyze it. Additional resources and new
techniques for data analysis are urgently needed. 3) Data rates and volumes
from HEP experimental facilities are also straining the ability to store and
analyze large and complex data volumes. Appropriately configured
leadership-class facilities can play a transformational role in enabling
scientific discovery from these datasets. 4) A close integration of HPC
simulation and data analysis will aid greatly in interpreting results from HEP
experiments. Such an integration will minimize data movement and facilitate
interdependent workflows. 5) Long-range planning between HEP and ASCR will be
required to meet HEP's research needs. To best use ASCR HPC resources the
experimental HEP program needs a) an established long-term plan for access to
ASCR computational and data resources, b) an ability to map workflows onto HPC
resources, c) the ability for ASCR facilities to accommodate workflows run by
collaborations that can have thousands of individual members, d) to transition
codes to the next-generation HPC platforms that will be available at ASCR
facilities, e) to build up and train a workforce capable of developing and
using simulations and analysis to support HEP scientific research on
next-generation systems.Comment: 77 pages, 13 Figures; draft report, subject to further revisio
Storage codes -- coding rate and repair locality
The {\em repair locality} of a distributed storage code is the maximum number
of nodes that ever needs to be contacted during the repair of a failed node.
Having small repair locality is desirable, since it is proportional to the
number of disk accesses during repair. However, recent publications show that
small repair locality comes with a penalty in terms of code distance or storage
overhead if exact repair is required.
Here, we first review some of the main results on storage codes under various
repair regimes and discuss the recent work on possible
(information-theoretical) trade-offs between repair locality and other code
parameters like storage overhead and code distance, under the exact repair
regime.
Then we present some new information theoretical lower bounds on the storage
overhead as a function of the repair locality, valid for all common coding and
repair models. In particular, we show that if each of the nodes in a
distributed storage system has storage capacity \ga and if, at any time, a
failed node can be {\em functionally} repaired by contacting {\em some} set of
nodes (which may depend on the actual state of the system) and downloading
an amount \gb of data from each, then in the extreme cases where \ga=\gb or
\ga = r\gb, the maximal coding rate is at most or 1/2, respectively
(that is, the excess storage overhead is at least or 1, respectively).Comment: Accepted for publication in ICNC'13, San Diego, US
Exact Optimized-cost Repair in Multi-hop Distributed Storage Networks
The problem of exact repair of a failed node in multi-hop networked
distributed storage systems is considered. Contrary to the most of the current
studies which model the repair process by the direct links from surviving nodes
to the new node, the repair is modeled by considering the multi-hop network
structure, and taking into account that there might not exist direct links from
all the surviving nodes to the new node. In the repair problem of these
systems, surviving nodes may cooperate to transmit the repair traffic to the
new node. In this setting, we define the total number of packets transmitted
between nodes as repair-cost. A lower bound of the repaircost can thus be found
by cut-set bound analysis. In this paper, we show that the lower bound of the
repair-cost is achievable for the exact repair of MDS codes in tandem and grid
networks, thus resulting in the minimum-cost exact MDS codes. Further, two
suboptimal (achievable) bounds for the large scale grid networks are proposed.Comment: (To appear in ICC 2014
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