arXiv subjects

Nematollah Iri

Publications and source records attributed to Nematollah Iri.

4 recordsLinked to original sources

arXiv2022

Universal Variable-to-Fixed Length Lossy Compression at Finite Blocklengths

We consider universal variable-to-fixed length compression of memoryless sources with a fidelity criterion. We design a dictionary codebook over the reproduction alphabet which is used to parse the source stream. Once a source subsequence is within a specified distortion of a dictionary codeword, the index of the codeword is emitted as the reproduced string. Our proposed dictionary consists of coverings of type classes in the boundary of transition from low to high empirical lossy rate. We derive the asymptotics of the ε-coding rate (up to the third-order term) of our coding scheme for large enough dictionaries.

cs.IT↗

arXiv2020

Type Size Code for Compressing Erdös-Rényi Graphs

We consider universal source coding of unlabeled graphs which are commonly referred to as graphical structures. We adopt an Erdös-Rényi model to generate the random graphical structures. We propose a variant of the previously introduced Type Size code, where type classes are characterized based on the number of edges of the graphical structures. The proposed scheme sorts the graphical structures based on the size of their type classes and assigns binary sequences to them in this order. The $ε$-coding rate of the Type Size code (up to the third-order term) for compressing graphical structures is derived.

cs.IT↗

arXiv2017

Fundamental Limits of Universal Variable-to-Fixed Length Coding of Parametric Sources

Universal variable-to-fixed (V-F) length coding of $d$-dimensional exponential family of distributions is considered. We propose an achievable scheme consisting of a dictionary, used to parse the source output stream, making use of the previously-introduced notion of quantized types. The quantized type class of a sequence is based on partitioning the space of minimal sufficient statistics into cuboids. Our proposed dictionary consists of sequences in the boundaries of transition from low to high quantized type class size. We derive the asymptotics of the $ε$-coding rate of our coding scheme for large enough dictionaries. In particular, we show that the third-order coding rate of our scheme is $H\frac{d}{2}\frac{\log\log M}{\log M}$, where $H$ is the entropy of the source and $M$ is the dictionary size. We further provide a converse, showing that this rate is optimal up to the third-order term.

cs.IT↗

arXiv2016

Fine Asymptotics for Universal One-to-One Compression of Parametric Sources

Universal source coding at short blocklengths is considered for an exponential family of distributions. The \emph{Type Size} code has previously been shown to be optimal up to the third-order rate for universal compression of all memoryless sources over finite alphabets. The Type Size code assigns sequences ordered based on their type class sizes to binary strings ordered lexicographically. To generalize this type class approach for parametric sources, a natural scheme is to define two sequences to be in the same type class if and only if they are equiprobable under any model in the parametric class. This natural approach, however, is shown to be suboptimal. A variation of the Type Size code is introduced, where type classes are defined based on neighborhoods of minimal sufficient statistics. Asymptotics of the overflow rate of this variation are derived and a converse result establishes its optimality up to the third-order term. These results are derived for parametric families of $i.i.d.$ sources as well as Markov sources.

cs.IT↗