2,670 research outputs found
On Randomized Memoryless Algorithms for the Weighted -server Problem
The weighted -server problem is a generalization of the -server problem
in which the cost of moving a server of weight through a distance
is . The weighted server problem on uniform spaces models
caching where caches have different write costs. We prove tight bounds on the
performance of randomized memoryless algorithms for this problem on uniform
metric spaces. We prove that there is an -competitive memoryless
algorithm for this problem, where ;
. On the other hand we also prove that no randomized memoryless
algorithm can have competitive ratio better than .
To prove the upper bound of we develop a framework to bound from
above the competitive ratio of any randomized memoryless algorithm for this
problem. The key technical contribution is a method for working with potential
functions defined implicitly as the solution of a linear system. The result is
robust in the sense that a small change in the probabilities used by the
algorithm results in a small change in the upper bound on the competitive
ratio. The above result has two important implications. Firstly this yields an
-competitive memoryless algorithm for the weighted -server problem
on uniform spaces. This is the first competitive algorithm for which is
memoryless. Secondly, this helps us prove that the Harmonic algorithm, which
chooses probabilities in inverse proportion to weights, has a competitive ratio
of .Comment: Published at the 54th Annual IEEE Symposium on Foundations of
Computer Science (FOCS 2013
Construction and commissioning of a technological prototype of a high-granularity semi-digital hadronic calorimeter
A large prototype of 1.3m3 was designed and built as a demonstrator of the
semi-digital hadronic calorimeter (SDHCAL) concept proposed for the future ILC
experiments. The prototype is a sampling hadronic calorimeter of 48 units. Each
unit is built of an active layer made of 1m2 Glass Resistive Plate
Chamber(GRPC) detector placed inside a cassette whose walls are made of
stainless steel. The cassette contains also the electronics used to read out
the GRPC detector. The lateral granularity of the active layer is provided by
the electronics pick-up pads of 1cm2 each. The cassettes are inserted into a
self-supporting mechanical structure built also of stainless steel plates
which, with the cassettes walls, play the role of the absorber. The prototype
was designed to be very compact and important efforts were made to minimize the
number of services cables to optimize the efficiency of the Particle Flow
Algorithm techniques to be used in the future ILC experiments. The different
components of the SDHCAL prototype were studied individually and strict
criteria were applied for the final selection of these components. Basic
calibration procedures were performed after the prototype assembling. The
prototype is the first of a series of new-generation detectors equipped with a
power-pulsing mode intended to reduce the power consumption of this highly
granular detector. A dedicated acquisition system was developed to deal with
the output of more than 440000 electronics channels in both trigger and
triggerless modes. After its completion in 2011, the prototype was commissioned
using cosmic rays and particles beams at CERN.Comment: 49 pages, 41 figure
Signal Processing for Caching Networks and Non-volatile Memories
The recent information explosion has created a pressing need for faster and more reliable data storage and transmission schemes. This thesis focuses on two systems: caching networks and non-volatile storage systems. It proposes network protocols to improve the efficiency of information delivery and signal processing schemes to reduce errors at the physical layer as well. This thesis first investigates caching and delivery strategies for content delivery networks. Caching has been investigated as a useful technique to reduce the network burden by prefetching some contents during oË™-peak hours. Coded caching [1] proposed by Maddah-Ali and Niesen is the foundation of our algorithms and it has been shown to be a useful technique which can reduce peak traffic rates by encoding transmissions so that different users can extract different information from the same packet. Content delivery networks store information distributed across multiple servers, so as to balance the load and avoid unrecoverable losses in case of node or disk failures. On one hand, distributed storage limits the capability of combining content from different servers into a single message, causing performance losses in coded caching schemes. But, on the other hand, the inherent redundancy existing in distributed storage systems can be used to improve the performance of those schemes through parallelism. This thesis proposes a scheme combining distributed storage of the content in multiple servers and an efficient coded caching algorithm for delivery to the users. This scheme is shown to reduce the peak transmission rate below that of state-of-the-art algorithms
Memoryless Algorithms for the Generalized -server Problem on Uniform Metrics
We consider the generalized -server problem on uniform metrics. We study
the power of memoryless algorithms and show tight bounds of on
their competitive ratio. In particular we show that the \textit{Harmonic
Algorithm} achieves this competitive ratio and provide matching lower bounds.
This improves the doubly-exponential bound of Chiplunkar and
Vishwanathan for the more general setting of uniform metrics with different
weights
Ad hoc IoT approach for monitoring parking control process
The purpose of this research is to develop a collaborative approach to control the parking in a city using IoT (Internet of Things). This approach is based on Bluetooth Low Energy (BLE) beacons to control the parking process without having to investment in sensors. Parking violations can be easily detected through the proposed collaborative process among user's mobile devices. A reward mechanism incentives users' participation. This approach uses an ad hoc network of users who send information to a central system regarding georeferenced beacon information. Comparing with previous payments associated with a vehicle, the approach can identify parking violations, e.g. parking without associated payment.info:eu-repo/semantics/publishedVersio
The Incremental Constraint of k-Server
Online algorithms are characterized by operating on an input sequence revealed over time versus a single static input. Instead of generating a single solution, they produce a sequence of incremental solutions corresponding to the input seen so far. An online algorithm's ignorance of future inputs limits its ability to produce optimal solutions. The incremental nature of its solutions is also an obstacle. The two factors can be differentiated by examining the corresponding incremental algorithm, which has knowledge of future inputs, but must still provide a competitive solution at each step.
In this thesis, the lower bound of the incremental constraint of k-server is shown to be to 2
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