- Ramy Ali (Ph.D. Student)
- Mohammad T. Hussein (Ph.D. Student)
- Farzin Haddadpour

The goal of my research group is to obtain engineering insights into practical problems by formulating and studying appropriate theoretical models. We study problems that arise in information theory and coding theory, and those that lie in the intersection of information theory and theory of distributed computing. I provide here high-level summaries of some facets of our research. For a list of publications, click here.

## Distributed Systems

In modern data storage systems such as data centers, the data is stored in a distributed storage system with multiple servers. In such systems, it is important that the data is available to the user, even though the system components could be unreliable, specifically that the servers could fail. Classical coding theory provides several powerful techniques to design such failure tolerance with a small overhead in terms of storage footprint. In modern data storage systems, there are often additional requirements in several applications that lead to interesting research directions. Some of our work is summarized below.### Information Theory for Consistent Distributed Storage

A common requirement of modern distributed data storage systems, especially in applications to databases and distributed computing systems, is the following property known as consistency: when the data is being constantly updated, a client that reads from the system should obtain the latest version of the data. The design of algorithms for consistent distributed storage has been studied extensively in distributed computing theory, and forms the building block of numerous key-value store services. The goal of our work is to use ideas of information theory and coding theory to understand the storage cost of consistent distributed storage systems. This project involves the use of ideas from information theory, and theory of distributed systems.

Zhiying Wang, Viveck Cadambe, Multi-version Coding for Distributed Storage, Extended version of our papers that appeared in Proceedings of IEEE International Symposium on Information Theory (ISIT) 2014 and the 2014 Allerton Conference on Communications, Control and Computing.

### Repair Efficient Erasure Codes

It is of interest in storage systems that when a server has failed, or is unavailable for some other reason (e.g., when it is away for an upgrade), the data be reconstructed as efficiently as possible from the other available servers. In my research, I have studied code design for reconstruction of data by incurring a small cost of repair, both in terms of access and bandwidth. Some related publications are listed.

Viveck R. Cadambe, Syed A. Jafar, Hamed Maleki, Kannan Ramchandran, Changho Suh, Asymptotic Interference Alignment for Optimal Repair of MDS Codes in Distributed Data Storage, IEEE Transactions on Information Theory, May 2013

Viveck R. Cadambe, Arya Mazumdar An Upper Bound on the Size of Locally Recoverable Codes, IEEE International Symposium on Network Coding (Netcod), Jun, 2013.

## Wireless Communications

It is well known that interference between devices that communicate over the same spectrum is the primary bottleneck of data speeds in modern wireless communication systems. Much of my research in wireless communications has involved the study of*interference alignment*

*-*a promising technique to manages interference in wireless communication systems. In my doctoral work, I developed and studied interference alignment for various communication scenarios. In my postdoctoral stint, I am exploring the use of lattice codes for wireless systems, in particular, their usefulness for interference alignment. Some sample publications are listed below.

Viveck R Cadambe, Syed A Jafar, Interference Alignment on the Degrees of Freedom of the K user Interference Channel, IEEE Transactions on Information Theory, Aug 2008.