813 research outputs found
Increasing Availability in Distributed Storage Systems via Clustering
We introduce the Fixed Cluster Repair System (FCRS) as a novel architecture
for Distributed Storage Systems (DSS), achieving a small repair bandwidth while
guaranteeing a high availability. Specifically we partition the set of servers
in a DSS into clusters and allow a failed server to choose any cluster
other than its own as its repair group. Thereby, we guarantee an availability
of . We characterize the repair bandwidth vs. storage trade-off for the
FCRS under functional repair and show that the minimum repair bandwidth can be
improved by an asymptotic multiplicative factor of compared to the state
of the art coding techniques that guarantee the same availability. We further
introduce Cubic Codes designed to minimize the repair bandwidth of the FCRS
under the exact repair model. We prove an asymptotic multiplicative improvement
of in the minimum repair bandwidth compared to the existing exact repair
coding techniques that achieve the same availability. We show that Cubic Codes
are information-theoretically optimal for the FCRS with and complete
clusters. Furthermore, under the repair-by-transfer model, Cubic Codes are
optimal irrespective of the number of clusters
Users Caching Two Files: An Improved Achievable Rate
Caching is an approach to smoothen the variability of traffic over time.
Recently it has been proved that the local memories at the users can be
exploited for reducing the peak traffic in a much more efficient way than
previously believed. In this work we improve upon the existing results and
introduce a novel caching strategy that takes advantage of simultaneous coded
placement and coded delivery in order to decrease the worst case achievable
rate with files and users. We will show that for any cache size
our scheme outperforms the state of the art
Compute-and-Forward: Finding the Best Equation
Compute-and-Forward is an emerging technique to deal with interference. It
allows the receiver to decode a suitably chosen integer linear combination of
the transmitted messages. The integer coefficients should be adapted to the
channel fading state. Optimizing these coefficients is a Shortest Lattice
Vector (SLV) problem. In general, the SLV problem is known to be prohibitively
complex. In this paper, we show that the particular SLV instance resulting from
the Compute-and-Forward problem can be solved in low polynomial complexity and
give an explicit deterministic algorithm that is guaranteed to find the optimal
solution.Comment: Paper presented at 52nd Allerton Conference, October 201
GDSP: A Graphical Perspective on the Distributed Storage Systems
The classical distributed storage problem can be modeled by a k-uniform {\it
complete} hyper-graph where vertices represent servers and hyper-edges
represent users. Hence each hyper-edge should be able to recover the full file
using only the memories of the vertices associated with it. This paper
considers the generalization of this problem to {\it arbitrary} hyper-graphs
and to the case of multiple files, where each user is only interested in one, a
problem we will refer to as the graphical distributed storage problem (GDSP).
Specifically, we make progress in the analysis of minimum-storage codes for two
main subproblems of the GDSP which extend the classical model in two
independent directions: the case of an arbitrary graph with multiple files, and
the case of an arbitrary hyper-graph with a single file
New Shortest Lattice Vector Problems of Polynomial Complexity
The Shortest Lattice Vector (SLV) problem is in general hard to solve, except
for special cases (such as root lattices and lattices for which an obtuse
superbase is known). In this paper, we present a new class of SLV problems that
can be solved efficiently. Specifically, if for an -dimensional lattice, a
Gram matrix is known that can be written as the difference of a diagonal matrix
and a positive semidefinite matrix of rank (for some constant ), we show
that the SLV problem can be reduced to a -dimensional optimization problem
with countably many candidate points. Moreover, we show that the number of
candidate points is bounded by a polynomial function of the ratio of the
smallest diagonal element and the smallest eigenvalue of the Gram matrix.
Hence, as long as this ratio is upper bounded by a polynomial function of ,
the corresponding SLV problem can be solved in polynomial complexity. Our
investigations are motivated by the emergence of such lattices in the field of
Network Information Theory. Further applications may exist in other areas.Comment: 13 page
Virtual Reality of Fantasy Travel Utopia
Virtual reality can be considered as one of the most influential technologies of the human future. Architecture as human life container is the most important platform for this technology. In order to understand outlook of virtual reality in architecture it is necessary to get familiar with this technology and its evolution. Many years ago, intervention of virtuality and reality was an impossible dream in the human mind. But when Jason Lanier, American scientist, announced realization of this dream, a new horizon was opened to the human. Although this technology initially was regarded mostly as fun and computer games, over the time, the virtual reality technology has become one of the controversial issues in art and science world. At first, non-immersive virtual reality came to existence and despite of evolution in human special imaginations, created challenges for the human in 3D world. However, after a while, immersive virtual reality made it possible to experience every spatial imagination foe the human. Architecture science was no exception in experiencing changes due to close relationship with special imaginations. Meanwhile, possibility of confronting the space designed in human scale, possibility for movement in the designed space as well as possibility for observing changes in different scales with lowest costs were changes in architecture world. But what which can fundamentally change future of architecture is combination of virtual reality and augmented reality, which allows the full integration of virtuality and reality
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