39 research outputs found
Lossy Compression with Near-uniform Encoder Outputs
It is well known that lossless compression of a discrete memoryless source
with near-uniform encoder output is possible at a rate above its entropy if and
only if the encoder is randomized. This work focuses on deriving conditions for
near-uniform encoder output(s) in the Wyner-Ziv and the distributed lossy
compression problems. We show that in the Wyner-Ziv problem, near-uniform
encoder output and operation close to the WZ-rate limit is simultaneously
possible, whereas in the distributed lossy compression problem, jointly
near-uniform outputs is achievable in the interior of the distributed lossy
compression rate region if the sources share non-trivial G\'{a}cs-K\"{o}rner
common information.Comment: Submitted to the 2016 IEEE International Symposium on Information
Theory (11 Pages, 3 Figures
Applications of graph-based codes in networks: analysis of capacity and design of improved algorithms
The conception of turbo codes by Berrou et al. has created a renewed interest in modern graph-based codes. Several encouraging results that have come to light since then have fortified the role these codes shall play as potential solutions for present and future communication problems.
This work focuses on both practical and theoretical aspects of graph-based codes. The
thesis can be broadly categorized into three parts. The first part of the thesis focuses on
the design of practical graph-based codes of short lengths. While both low-density parity-check
codes and rateless codes have been shown to be asymptotically optimal under the message-passing (MP) decoder, the performance of short-length codes from these families under MP decoding is starkly sub-optimal. This work first addresses the
structural characterization of stopping sets to understand this sub-optimality. Using this
characterization, a novel improved decoder that offers several orders of magnitude improvement in bit-error rates is introduced. Next, a novel scheme for the design of a good rate-compatible family of punctured codes is proposed.
The second part of the thesis aims at establishing these codes as a good tool to develop
reliable, energy-efficient and low-latency data dissemination schemes in networks. The problems of broadcasting in wireless multihop networks and that of unicast in delay-tolerant networks are investigated. In both cases, rateless coding is seen to offer an elegant means of achieving the goals of the chosen communication protocols. It was noticed that the ratelessness and the randomness in encoding process make this scheme
specifically suited to such network applications.
The final part of the thesis investigates an application of a specific class of codes called
network codes to finite-buffer wired networks. This part of the work aims at establishing a framework for the theoretical study and understanding of finite-buffer networks. The
proposed Markov chain-based method extends existing results to develop an iterative
Markov chain-based technique for general acyclic wired networks. The framework not only estimates the capacity of such networks, but also provides a means to monitor network traffic and packet drop rates on various links of the network.Ph.D.Committee Chair: Fekri, Faramarz; Committee Member: Li, Ye; Committee Member: McLaughlin, Steven; Committee Member: Sivakumar, Raghupathy; Committee Member: Tetali, Prasa
Strong Coordination over Multi-hop Line Networks
We analyze the problem of strong coordination over a multi-hop line network
in which the node initiating the coordination is a terminal network node. We
assume that each node has access to a certain amount of randomness that is
local to the node, and that the nodes share some common randomness, which are
used together with explicit hop-by-hop communication to achieve strong
coordination. We derive the trade-offs among the required rates of
communication on the network links, the rates of local randomness available to
network nodes, and the rate of common randomness to realize strong
coordination. We present an achievable coding scheme built using multiple
layers of channel resolvability codes, and establish several settings in which
this scheme is proven to offer the best possible trade-offs.Comment: 35 pages, 9 Figures, 4 Tables. A part of this work were published in
the 2015 IEEE Information Theory Workshop, and a part was accepted for
publication in the 50th Annual Conference on Information Sciences and System
Asymptotically Unambitious Artificial General Intelligence
General intelligence, the ability to solve arbitrary solvable problems, is
supposed by many to be artificially constructible. Narrow intelligence, the
ability to solve a given particularly difficult problem, has seen impressive
recent development. Notable examples include self-driving cars, Go engines,
image classifiers, and translators. Artificial General Intelligence (AGI)
presents dangers that narrow intelligence does not: if something smarter than
us across every domain were indifferent to our concerns, it would be an
existential threat to humanity, just as we threaten many species despite no ill
will. Even the theory of how to maintain the alignment of an AGI's goals with
our own has proven highly elusive. We present the first algorithm we are aware
of for asymptotically unambitious AGI, where "unambitiousness" includes not
seeking arbitrary power. Thus, we identify an exception to the Instrumental
Convergence Thesis, which is roughly that by default, an AGI would seek power,
including over us.Comment: 9 pages with 5 figures; 10 page Appendix with 2 figure
Strong Coordination over Noisy Channels: Is Separation Sufficient?
We study the problem of strong coordination of actions of two agents and
that communicate over a noisy communication channel such that the actions
follow a given joint probability distribution. We propose two novel schemes for
this noisy strong coordination problem, and derive inner bounds for the
underlying strong coordination capacity region. The first scheme is a joint
coordination-channel coding scheme that utilizes the randomness provided by the
communication channel to reduce the local randomness required in generating the
action sequence at agent . The second scheme exploits separate coordination
and channel coding where local randomness is extracted from the channel after
decoding. Finally, we present an example in which the joint scheme is able to
outperform the separate scheme in terms of coordination rate.Comment: 9 pages, 4 figures. An extended version of a paper accepted for the
IEEE International Symposium on Information Theory (ISIT), 201
Strong Coordination over Noisy Channels: Is Separation Sufficient?
We study the problem of strong coordination of actions of two agents and
that communicate over a noisy communication channel such that the actions
follow a given joint probability distribution. We propose two novel schemes for
this noisy strong coordination problem, and derive inner bounds for the
underlying strong coordination capacity region. The first scheme is a joint
coordination-channel coding scheme that utilizes the randomness provided by the
communication channel to reduce the local randomness required in generating the
action sequence at agent . The second scheme exploits separate coordination
and channel coding where local randomness is extracted from the channel after
decoding. Finally, we present an example in which the joint scheme is able to
outperform the separate scheme in terms of coordination rate.Comment: 9 pages, 4 figures. An extended version of a paper accepted for the
IEEE International Symposium on Information Theory (ISIT), 201
Coding Schemes for Achieving Strong Secrecy at Negligible Cost
We study the problem of achieving strong secrecy over wiretap channels at
negligible cost, in the sense of maintaining the overall communication rate of
the same channel without secrecy constraints. Specifically, we propose and
analyze two source-channel coding architectures, in which secrecy is achieved
by multiplexing public and confidential messages. In both cases, our main
contribution is to show that secrecy can be achieved without compromising
communication rate and by requiring only randomness of asymptotically vanishing
rate. Our first source-channel coding architecture relies on a modified wiretap
channel code, in which randomization is performed using the output of a source
code. In contrast, our second architecture relies on a standard wiretap code
combined with a modified source code termed uniform compression code, in which
a small shared secret seed is used to enhance the uniformity of the source code
output. We carry out a detailed analysis of uniform compression codes and
characterize the optimal size of the shared seed.Comment: 15 pages, two-column, 5 figures, accepted to IEEE Transactions on
Information Theor