Assistant Professor
Department of Electrical Engineering - Systems
University of Southern California
dimakis at usc [dot] edu
532 EEB, 3740 McClintock Ave., (Mail Code 2560)
University of Southern California
Los Angeles, CA 90089-2560
Assistant Professor
Department of Electrical Engineering - Systems
University of Southern California
dimakis at usc [dot] edu
532 EEB, 3740 McClintock Ave., (Mail Code 2560)
University of Southern California
Los Angeles, CA 90089-2560
Interests |
Publications |
Links |
Resume|
Bio Sketch |
Teaching
Selected Publications on:
Distributed Storage
Gossip and Message Passing Algorithmss
Coding Theory and Linear Programming decoding
Game theory
Statistical Signal Processing
I am interested in communications, signal processing and networking.
In particular, coding for distributed storage, message passing algorithms and distributed inference, network coding and sparse graph codes.
I received my PhD at the
Wireless Foundations lab in the EECS department, UC Berkeley
and my undergraduate studies in Electrical and Computer Engineering department
National Technical Univerisity of Athens in 2003.
During the summer of 2006 I was with the labs of Martin Vetterli and
Patrick Thiran at
Ecole Polytechnique Federale de Lausanne
During the summer of 2007 I was with the
Communication and Collaboration Systems group at
Microsoft Research and worked with Yunnan Wu on coding for storage in Data Centers.
During 2008 I was a postdoctoral scholar at the
Center for the Mathematics of Information at Caltech.
Research Publications
What's new:
Coding for Distributed Storage
"Reducing Repair Traffic for Erasure Coding-based Storage via Interference Alignment"
(new)
Y. Wu and A. G. Dimakis, ISIT 2009
.
Slides from a survey talk on distributed storage
Summarizes the interference alignment technique and regenerating codes
(email me for powerpoint version)
(Preliminary versions appeared in Infocom 2007 and Allerton 2007)
Data centers and sensor networks require reliable information storage
over individually unreliable nodes.
Storing a file using an erasure code, in fragments spread across nodes, requires less redundancy than simple replication for the same level of reliability.
However, since fragments must be periodically replaced as nodes fail, a key question is how to generate a new encoded fragment in a distributed way while
transferring as little data as possible across the network.
For an erasure coded system, a common practice to repair from a node failure is for a new node to download
subsets of data stored at a number of surviving nodes, reconstruct a lost coded block using the downloaded data,
and store it at the new node. We show that this procedure is sub-optimal. We introduce the notion of regenerating
codes, which allow a new node to download functions of the stored data from the surviving nodes. We show that
regenerating codes can significantly reduce the repair bandwidth. Further, we show that there is a fundamental tradeoff
between storage and repair bandwidth which we theoretically characterize using flow arguments on an appropriately
constructed graph. By invoking constructive results in network coding, we introduce regenerating codes that can
achieve any point in this optimal tradeoff.
"Distributed storage allocation problems"
(new)
D. Leong, A. G. Dimakis, T. Ho, Workshop on Network Coding theory and Applications
(NetCod) 2009.
"On the delay of network coding over line networks"
(new)
T. Dikaliotis, A. G. Dimakis, T. Ho, M. Effros, ISIT 2009.
We extend Geographic gossip by allowing all the nodes on a
random path to be averaged and show how this path averaging
can be implemented with minimal complexity in a sensor network
if sensors have location information.
The main result is that Geographic Gossip with path averaging converges
using a number of messages linear in the number of nodes,
which improves by a sqrt(n) factor over geographic gossip and is order-optimal.
Gossip (or average Consensus) algorithms, are simple randomized message-passing
algorithms that can be used to compute global functions of data distributed
over a network with minimal coordination.
The proposed gossip algorithm (Geographic Gossip) uses geographic informationto
dramatically improve the convergence time, hence minimizing the number of
communicated messages.
(preliminary version appeared
ISIT 2006).
Slides for Facet Guessing decoding
We study how the structure of the interaction graph affects the Nash equilibria of the resulting game. In particular, for a fixed interaction graph, we are interested if there exist Nash equilibria which arise when random utility tables are assigned to the players. We provide conditions for the structure of the graph under which equilibria are likely to exist and complementary conditions which make the existence of equilibria highly unlikely. Our results have immediate implications for many deterministic graphs and generalize known results for games on the complete graph. In particular, our results imply that the probability that bounded degree graphs have Nash equilibria is exponentially small in the size of the graph and yield a simple algorithm that finds small non-existence certificates for a large family of graphs. In order to obtain a refined characterization of the degree of connectivity associated with the existence of equilibria, we study the model in the random graph setting. In particular, we look at the case where the interaction graph is drawn from the Erdos-Renyi, G(n,p), model where each edge is present independently with probability p. For this model we establish a double phase transition for the existence of pure Nash equilibria as a function of the average degree p n consistent with the non-monotone behavior of the model. We show that when the average degree satisfies n p > (2 + Omega(1)) log n, the number of pure Nash equilibria follows a Poisson distribution with parameter 1. When 1/n << n p < (0.5 -Omega(1)) log n pure Nash equilibria fail to exist with high probability. Finally, when n p << 1/n a pure Nash equilibrium exists with high probability.
My undergraduate thesis was supervised by Prof. Maragos. We proposed a nonlinear model for time-varying resonances where the instantaneous phase of a sinusoidal oscillation is a self-similar stochastic process. We have theoretically derived the second order statistics of the modulated process for a very general class of Self-similar processes that include Fractional Brownian Motion and Fractional Stable Levy Motion as special cases. We have also applied these ideas to data from fricative phonemes and demonstrated their applicability for speech modelling.
(Copyright belongs to the publisher in most cases. The author/authors assert copyright in all other cases.)
Artistic attempts
I was the Webmaster of the IEEE Student branch in National Technical University of Athens (NTUA). Visit the
site .
Fun upper bounds: My Erdos Number is less than or equal to 3:
(Paul Erdos-> Noga Alon-> Richard Karp-> myself)
No known finite upper bounds on my Bacon number exist.