Asaf Cohen's home page

Asaf Cohen

1200 East California Blvd
M/C 136-93
116-B Moore
Pasadena, California 91125
Phone: (626) 395 - 2219
soofsoof@caltech.edu

tahoe

Last update: 4/6/09.

Short Bio; Research Interests; Current Research; Publications; Dissertations; Recent talks/posters; Pictures;

Short Bio: I am currently a postdoc at Caltech, working with Prof. Michelle Effros on problems in network information theory. The projects are part of the ITMANET-FLoWS (Fundamental Limits of Wireless Systems) research. I received my B.Sc., M.Sc., and Ph.D. in electrical engineering from the Technion - I.I.T., supervised by Prof. Neri Merhav and Prof. Tsachy Weissman.

Research Interests:

Network source coding. Networks with side information. Simple representations for network solutions.
Prediction and sequential decision making. Source coding. Statistical signal processing. Filtering and denoising.
Coding theory. Performance analysis of codes.

Current Research:

On Networks with Side Information (with Salman Avestimehr and Michelle Effros; preprints available upon request)

Abstract: Consider the problem of lossless source coding for networks with side information. This model captures scenarios where the network capacity is insufficient to describe the source to its intended destinations, yet, it can still be delivered without loss provided there is sufficient capacity from a helper. The problem of source coding with side information has numerous applications, from sensor networks, where transmission occurs through nodes which may have correlated data, to multimedia networks, where intermediate nodes may have, for example, a lower-resolution version of the required information.

While several spacial cases of this problem have been addressed in the current literature (e.g., the three-node network of Ahlswede and Korner), the general problem remains unsolved. In this work, we derive inner and outer bounds on the rate region and describe sufficient conditions for the tightness of these bounds. Our approach demonstrates how strategies intended for small canonical problems, combined with network coding, can tackle complex networks, while still inheriting the desirable properties of the building blocks used. Furthermore, due to the complexity of solving large networks, it is highly desirable to identify the key parameters which dictate their rate region. This work substantially extends the network scenarios for which maxflow-mincut analysis is know to describe the rate region in full. Finally, in this work we open a new connection between networking and successive refinement of information.

Linearly Representable Entropy Vectors and their Relation to Network Coding Solutions (with Michelle Effros, Salman Avestimehr and Ralf Koetter; see ITMANET poster)

Abstract: In this work, we address the following question: “When can we guarantee the optimality of linear coding at all internal nodes of a network?” While sufficient conditions for linear coding throughout the network are known, it is not clear whether relaxing the linearity constraints at the terminal nodes can result in simpler operations at the internal nodes. We present a novel method to analyze the space of network solutions using the constraints resulting from the network topology, and we identify sufficient conditions for an optimal linear solution at all internal nodes. These conditions are also sufficient to characterize the rate region only in terms of Shannon information inequalities and to describe the rate region as a cone hull of random vectors over a finite alphabet, independently of any block length.

Journal Publications:

A. Cohen, M. Effros, S. Avestimehr and R. Koetter, ``Linearly Representable Entropy Vectors and their Relation to Network Coding Solutions,” in preparation (preprints available upon request).

A. Cohen, S. Avestimehr, and M. Effros, ``Networks with Side Information,” in preparation (preprints available upon request).

A. Cohen, T. Weissman, and N. Merhav, ``Universal Scanning and Sequential Decision Making for Multi-Dimensional Data, Part II: the Noisy Case,” IEEE Trans. Inform. Theory, vol. 54, no. 12, pp. 5609-5631, December 2008.

A. Cohen, N. Merhav, and T. Weissman, ``Scanning and Sequential Decision Making for Multi-Dimensional Data - Part I: the Noiseless Case,” IEEE Trans. Inform. Theory, vol. 53, no. 9, pp. 3001-3020, September 2007.

A. Cohen and N. Merhav, ``Lower bounds on the error probability of block codes based on improvements on de Caen's inequality,” IEEE Trans. Inform. Theory, vol. 50, no. 2, pp. 290-310, February 2004.

Conference Publications:

A. Cohen, M. Effros, S. Avestimehr and R. Koetter, ``Linearly Representable Entropy Vectors and their Relation to Network Coding Solutions,” submitted to IEEE Information Theory Workshop, Taormina, Sicily, October 2009 (preprints available upon request).

A. Cohen, S. Avestimehr and M. Effros, ``On Networks With Side Information," accepted to IEEE Int. Symp. on Information Theory, June-July 2009 (preprints available upon request).

A. Cohen, N. Merhav, and T. Weissman, ``Scanning, Filtering and Prediction for Random Fields Corrupted by Gaussian Noise,” Proc. IEEE Int. Symp. on Information Theory, pp. 691-695, Nice, France, June 2007.

A. Cohen, N. Merhav, and T. Weissman, ``Scanning and sequential decision making for multi-dimensional data,” Proc. Information Theory and Applications Workshop, pp. 101-110, San Diego, California, January 2007 (invited).

A. Cohen, N. Merhav, and T. Weissman, ``Universal Scanning of Mixing Random Fields and the Performance of the Peano-Hilbert Scan,” IEEE 24^th Convention of Electrical and Electronics Engineering, Eilat, Israel, November 2006 ( student paper award).

A. Cohen, N. Merhav, and T. Weissman, ``Universal scanning and sequential decision making for multi-dimensional data,” Proc. IEEE Int. Symp. on Information Theory, pp. 431-435, Seattle, Washington, July 2006.

A. Cohen and N. Merhav, ``New lower bounds on the error probability for signals over an AWGN channel,” Proc. IEEE Int. Symp. on Information Theory, pp. 10, Yokohama, Japan, June-July 2003.

A. Cohen and N. Merhav, ``New lower bounds on the error probability of a given block code,” Proc. of the 22^nd Convention of Electrical and Electronics Engineers in Israel, pp. 138, Tel-Aviv, Israel, December 2002.

Dissertations:

A. Cohen, ``Topics in Scanning of Multidimensional Data," Ph.D. dissertation, Technion-Israel Inst. Technol., Haifa, Israel, 2007.
A. Cohen, ``Lower Bounds on the Error Probability of a Given Block Code," Ms.c. thesis, Technion-Israel Inst. Technol., Haifa, Israel, 2002.

Recent talks/posters:

``On Networks with Side Information," ITMANET meeting, Stanford, March 2009.
``Networks with Side Information," Caltech, February 2009.
``On Linear Representation for Network Solutions," ITMANET meeting, Washington, September 2008.
``Scanning and Sequential Decision Making for Multidimensional Data," CMI Retreat, La Canada, CA, October 2007.

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