Ohad Elishco - CS-Lecture
Wednesday, 15.1.2020, 10:30
Advisor: Department of Electrical Engineering, University of Maryland at College Park
We are living in the era of massive data. Some estimate that more than 90% of the worlds
data was generated in recent years. This large amount of data comes with technological
challenges such as: distributed storage systems, synchronization issues, density
constraints, power constraints and more.
The talk will be partitioned into two, independent parts in which some solutions to those
challenges will be discussed. Specifically, we will touch upon dynamical distributed
storage systems, and Polya string models.
In the first part of the talk we will discuss dynamical distributed storage. In
distributed storage systems the data is partitioned and the parts are saved in several
storage units, each part per unit. The storage units are unreliable and prone to failures.
Upon such failure, the system repairs the failed unit using the information stored in
other units. This repair process incurs in-network traffic. The problem of node repair
based on erasure coding for distributed storage aims at optimizing the tradeoff of
in-network traffic and storage overhead. The existing body of works focuses on the failure
of a unit (or several units) and the ensuing reconstruction process, but puts less
emphasis on the time evolution of the entire network and the inherent stochastic nature of
unit failures. In the talk, we will present a dynamical version of distributed storage
systems and will build upon the so called fixed cost model, suggested by Akhlaghi et al.
in 2010. We will estimate the increment of the file size that can be reliably stored over
In the second part of the talk we will discuss Polya string models. A motivating
application for studying those models comes from in-vivo DNA-based storage systems. In
those systems information is stored inside a living organism in order to be read from its
decedents. Unfortunately, due to the DNA replication process, this information is prone to
many kinds of errors, including insertions, deletions, and duplication errors. In the talk
we will cover the case of duplication errors and specifically will focus on
end-duplications. The end-duplication model assumes that at each step, a bit from the
sequence is chosen uniformly at random, copied, and placed at the end of the sequence.
Thus, at each step the length of the sequence is increased. We will present the entropy
rate of the end-duplication model and of the noisy end-duplication (in which the bit that
is placed at the end is passed through a binary channel).
Ohad Elishco is a post-doctoral researcher at the department of electrical engineering,
University of Maryland at College Park. He received his B.Sc. in mathematics
and his B.Sc. in electrical engineering in 2012 from Ben-Gurion University of the Negev,
Israel; the M.Sc. and Ph.D degrees in electrical engineering from Ben-Gurion University if
the Negev, Israel, in 2013, 2017 respectively. Between 2017-2018 he was a post-doctoral
researcher in the department of electrical engineering, Massachusetts institute of
technology. His research interests include coding theory and dynamical systems.