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Mine Alsan

Publications and source records attributed to Mine Alsan.

11 recordsLinked to original sources
arXiv2018

The Symmetric Convex Ordering: A Novel Partial Order for B-DMCs Ordering the Information Sets of Polar Codes

In this paper, we propose a novel partial order for binary discrete memoryless channels that we call the symmetric convex ordering. We show that Arıkan's polar transform preserves 'symmetric convex orders'. Furthermore, we show that while for symmetric channels this ordering turns out to be equivalent to the stochastic degradation ordering already known to order the information sets of polar codes, a strictly weaker partial order is obtained when at least one of the channels is asymmetric. In between, we also discuss two tools which can be useful for verifying this ordering: a criterion known as the cut criterion and channel symmetrization. Finally, we discuss potential applications of the results to polar coding over non-stationary channels.

cs.IT↗
arXiv2018

Channel capacity of polar coding with a given polar mismatched successive cancellation decoder

Arıkan's polar coding, is by now a well studied technique that allows achieving the symmetric capacity of binary input memoryless channels with low complexity encoding and decoding, provided that the polar decoding architecture is used and the decoding metric is matched to the true channel. In this paper, we analyze communication rates that are achievable when the polar coding/decoding architecture is used with the decoder using an incorrect model of the channel. We define the `polar mismatched capacity' as an analogue of the classical mismatched capacity, give an expression for it, and derive bounds on it.

cs.IT↗
arXiv2018

Lower Bounds on the Bayes Risk of the Bayesian BTL Model with Applications to Comparison Graphs

We consider the problem of aggregating pairwise comparisons to obtain a consensus ranking order over a collection of objects. We use the popular Bradley-Terry-Luce (BTL) model which allows us to probabilistically describe pairwise comparisons between objects. In particular, we employ the Bayesian BTL model which allows for meaningful prior assumptions and to cope with situations where the number of objects is large and the number of comparisons between some objects is small or even zero. For the conventional Bayesian BTL model, we derive information-theoretic lower bounds on the Bayes risk of estimators for norm-based distortion functions. We compare the information-theoretic lower bound with the Bayesian Cramér-Rao lower bound we derive for the case when the Bayes risk is the mean squared error. We illustrate the utility of the bounds through simulations by comparing them with the error performance of an expectation-maximization based inference algorithm proposed for the Bayesian BTL model. We draw parallels between pairwise comparisons in the BTL model and inter-player games represented as edges in a comparison graph and analyze the effect of various graph structures on the lower bounds. We also extend the information-theoretic and Bayesian Cramér-Rao lower bounds to the more general Bayesian BTL model which takes into account home-field advantage.

cs.IT↗
arXiv2014

Re-proving Channel Polarization Theorems: An Extremality and Robustness Analysis

The general subject considered in this thesis is a recently discovered coding technique, polar coding, which is used to construct a class of error correction codes with unique properties. In his ground-breaking work, Arıkan proved that this class of codes, called polar codes, achieve the symmetric capacity --- the mutual information evaluated at the uniform input distribution ---of any stationary binary discrete memoryless channel with low complexity encoders and decoders requiring in the order of $O(N\log N)$ operations in the block-length $N$. This discovery settled the long standing open problem left by Shannon of finding low complexity codes achieving the channel capacity. Polar coding settled an open problem in information theory, yet opened plenty of challenging problems that need to be addressed. A significant part of this thesis is dedicated to advancing the knowledge about this technique in two directions. The first one provides a better understanding of polar coding by generalizing some of the existing results and discussing their implications, and the second one studies the robustness of the theory over communication models introducing various forms of uncertainty or variations into the probabilistic model of the channel.

cs.IT↗
arXiv2013

Extremality for Gallager's Reliability Function $E_0$

We describe certain extremalities for Gallager's $E_0$ function evaluated under the uniform input distribution for binary input discrete memoryless channels. The results characterize the extremality of the $E_0(ρ)$ curves of the binary erasure channel and the binary symmetric channel among all the $E_0(ρ)$ curves that can be generated by the class of binary discrete memoryless channels whose $E_0(ρ)$ curves pass through a given point $(ρ_0, e_0)$, for some $ρ_0 > -1$.

cs.IT↗
arXiv2013

Conditions for Robustness of Polar Codes in the Presence of Channel Mismatch

A challenging problem related to the design of polar codes is "robustness against channel parameter variations" as stated in Arıkan's original work. In this paper, we describe how the problem of robust polar code design can be viewed as a mismatch decoding problem. We propose conditions which ensure a polar encoder/decoder designed for a mismatched B-DMC can be used to communicate reliably. In particular, the analysis shows that the original polar code construction method is robust over the class of binary symmetric channels.

cs.IT↗
arXiv2013

Properties of the Polarization Transformations for the Likelihood Ratios of Symmetric B-DMCs

In this paper we investigate, starting with a symmetric B-DMC, the evolution of various probabilities of the likelihood ratios of the synthetic channels created by the recursive application of the basic polarization transformations. The analysis provides a new perspective into the theory of channel polarization initiated by Arıkan and helps us to address a problem related to approximating the computations of the likelihood ratios of the synthetic channels.

cs.IT↗
arXiv2013

Extremality Properties for the Basic Polarization Transformations

We study the extremality of the BEC and the BSC for Gallager's reliability function $E_0$ evaluated under the uniform input distribution for binary input DMCs from the aspect of channel polarization. In particular, we show that amongst all B-DMCs of a given $E_0(ρ)$ value, for a fixed $ρ\geq 0$, the BEC and BSC are extremal in the evolution of $E_0$ under the one-step polarization transformations.

cs.IT↗