Bikash Kumar Dey

University of Kalyani

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Vinod M. Prabhakaran

Tata Institute of Fundamental Research

Sidharth Jaggi

University of Bristol

Jithin Ravi

Indian Institute of Technology Bombay

Michael Langberg

University at Buffalo, State University of New York

Amitalok J. Budkuley

Indian Institute of Technology Kharagpur

Mayank Bakshi

Arizona State University

Neha Sangwan

University of California, San Diego

Tapashi G. Roy

University of Chittagong

Sibi Raj B. Pillai

Indian Institute of Technology Bombay

S.K.S. Hazari

University of Chittagong

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Institute of Electrical and Electronics Engineers

University of Maryland, College Park

University of Toronto

Monash University

Cornell University

Rutgers, The State University of New Jersey

Indian Institute of Technology Bombay

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New York University

University of California, Los Angeles

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Distributed Rate Adaptation and Power Control in Fading Multiple Access Channels

IEEE Transactions on Information Theory (2015)

Sreejith Sreekumar Bikash Kumar Dey Sibi Raj B. Pillai

Traditionally, the capacity region of a coherent fading multiple access channel (MAC) is analyzed in two popular contexts. In the first, a centralized system with full channel state information at the transmitters (CSITs) is assumed, and the transmit power and data-rate can be jointly chosen for every fading vector realization. On the other hand, in fast-fading links with distributed CSIT, the lack of full CSI is compensated by performing ergodic averaging over sufficiently many channel realizations. Notice that the distributed CSI may necessitate decentralized power-control for optimal data-transfer. Apart from these two models, the case of slow-fading links and distributed CSIT, though relevant to many systems, has received much less attention. In this paper, a block-fading additive white Gaussian noise MAC with full CSI at the receiver and distributed CSI at the transmitters is considered. The links undergo independent fading, but otherwise have arbitrary fading distributions. The channel statistics and respective long-term average transmit powers are known to all parties. We first consider the case where each encoder has knowledge only of its own link quality, and not of others. For this model, we compute the adaptive capacity region, i.e., the collection of average rate-tuples under blockwise coding/decoding such that the rate-tuple for every fading realization is inside the instantaneous MAC capacity region. The key step in our solution is an optimal rate allocation function for any given set of distributed power control laws at the transmitters. This also allows us to structurally characterize the optimal power control for a wide class of fading models. Further extensions are also proposed for the case where each encoder has additional partial CSI about the other links.

Channel state information

Transmitter power output

Fading distribution

10.1109/tit.2015.2463271

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Citations (15)

On existence of good self-dual quasi-cyclic codes

Bikash Kumar Dey

This paper describes the existence of good self-dual quasicyclic codes. In this paper, with the assumption that there are infinite primes p for which 2 is primitive, we prove that there exist classes of self-dual 2p-quasicyclic codes and Type II 8p-quasicyclic codes of length respectively 2p/sup 2/ and 8p/sup 2/ which asymptotically meet the Gilbert-Varshamov bound.

10.1109/isit.2004.1365220

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On the oblivious transfer capacity of the degraded wiretapped binary erasure channel

2022 IEEE International Symposium on Information Theory (ISIT) (2015)

Manoj K. Mishra Bikash Kumar Dey Vinod M. Prabhakaran Suhas Diggavi

We study oblivious transfer (OT) between Alice and Bob in the presence of an eavesdropper Eve over a degraded wiretapped binary erasure channel from Alice to Bob and Eve. In addition to the privacy goals of oblivious transfer between Alice and Bob, we require privacy of Alice and Bob's private data from Eve. In previous work we derived the OT capacity (in the honest-but-curious model) of the wiretapped binary independent erasure channel where the erasure processes of Bob and Eve are independent. Here we derive a lower bound on the OT capacity in the same secrecy model when the wiretapped binary erasure channel is degraded in favour of Bob.

Erasure

Binary erasure channel

Alice and Bob

Binary symmetric channel

Oblivious transfer

10.1109/isit.2015.7282639

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The benefit of a 1-bit jump-start, and the necessity of stochastic encoding, in jamming channels

arXiv (Cornell University) (2016)

Bikash Kumar Dey Sidharth Jaggi Michael Langberg Anand D. Sarwate

We consider the problem of communicating a message $m$ in the presence of a malicious jamming adversary (Calvin), who can erase an arbitrary set of up to $pn$ bits, out of $n$ transmitted bits $(x_1,\ldots,x_n)$. The capacity of such a channel when Calvin is exactly causal, i.e. Calvin's decision of whether or not to erase bit $x_i$ depends on his observations $(x_1,\ldots,x_i)$ was recently characterized to be $1-2p$. In this work we show two (perhaps) surprising phenomena. Firstly, we demonstrate via a novel code construction that if Calvin is delayed by even a single bit, i.e. Calvin's decision of whether or not to erase bit $x_i$ depends only on $(x_1,\ldots,x_{i-1})$ (and is independent of the "current bit" $x_i$) then the capacity increases to $1-p$ when the encoder is allowed to be stochastic. Secondly, we show via a novel jamming strategy for Calvin that, in the single-bit-delay setting, if the encoding is deterministic (i.e. the transmitted codeword is a deterministic function of the message $m$) then no rate asymptotically larger than $1-2p$ is possible with vanishing probability of error, hence stochastic encoding (using private randomness at the encoder) is essential to achieve the capacity of $1-p$ against a one-bit-delayed Calvin.

Bit (key)

Code (set theory)

10.48550/arxiv.1602.02384

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Citations (3)

CCDC 235880: Experimental Crystal Structure Determination

The Cambridge Structural Database (2005)

Tapashi G. Roy S.K.S. Hazari Bikash Kumar Dey H.A. Miah C. Bader

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

10.5517/cc7xg1m

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Computationally Efficient Codes for Strongly Dobrushin-Stambler Nonsymmetrizable Oblivious AVCs

2022 IEEE International Symposium on Information Theory (ISIT) (2024)

Bikash Kumar Dey Sidharth Jaggi Michael Langberg Anand D. Sarwate Yang Zhang

10.1109/isit57864.2024.10619362

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Blind Adaptive Weighted Aggregation Scheme for Event Detection in Multihop Wireless Sensor Networks

Wireless Personal Communications (2010)

Bhushan Jagyasi Deepthi Chander U.B. Desai S. N. Merchant Bikash Kumar Dey

Fusion center

Robustness

10.1007/s11277-010-0123-4

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On the sum capacity of multiaccess block-fading channels with individual side information

Yash Deshpande Sibi Raj B. Pillai Bikash Kumar Dey

We consider the problem of finding optimal, fair and distributed power-rate strategies to achieve the sum capacity of the Gaussian multiple-access block-fading channel. The transmitters have access to only their own fading coefficients, while the receiver has access to all of the fading coefficients. We propose a distributed strategy called the `midpoint' strategy which is optimal when the system cannot tolerate outage. In addition, we demonstrate a successive decoding scheme that can achieve this maximal sum-rate. In presence of outage, we show that the strategies based on a single threshold are suboptimal.

Channel state information

Fading distribution

10.1109/itw.2011.6089524

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Citations (13)

Power controlled adaptive sum-capacity in the presence of distributed CSI

International Symposium on Information Theory and its Applications (2012)

Krishnamoorthy Iyer Sibi Raj B. Pillai Bikash Kumar Dey

We consider a distributed MAC setting with block-wise flat fading links and full receiver CSI (channel state information). Each user has individual CSI (knowledge of its own fading coefficient) and is unaware of the link quality of other links. Outage is not allowed in any communication block. In this distributed set up, throughput optimal power-rate allocation strategies are of interest. The average sum-throughput is also known as power controlled adaptive sum-capacity in literature, an open-problem for several interesting fading models like Rayleigh fading. Part of this problem was recently solved for the case where the users have identical power constraints and fading statistics. We extend this result in two directions. 1) We find the power controlled adaptive sum-capacity when the users have different average power constraints and identical channel statistics, and propose bounds when the channel statistics are different. 2) We analyze the impact of finite-rate additional CSI on the fading coefficients of the other links, and compute the optimal throughput in some interesting cases.

Channel state information

Fading distribution

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Private Index Coding

arXiv (Cornell University) (2020)

Varun Narayanan Jithin Ravi Vivek Kumar Mishra Bikash Kumar Dey Nikhil Karamchandani

We study the fundamental problem of index coding under an additional privacy constraint that requires each receiver to learn nothing more about the collection of messages beyond its demanded messages from the server and what is available to it as side information. To enable such private communication, we allow the use of a collection of independent secret keys, each of which is shared amongst a subset of users and is known to the server. The goal is to study properties of the key access structures which make the problem feasible and then design encoding and decoding schemes efficient in the size of the server transmission as well as the sizes of the secret keys. We call this the private index coding problem. We begin by characterizing the key access structures that make private index coding feasible. We also give conditions to check if a given linear scheme is a valid private index code. For up to three users, we characterize the rate region of feasible server transmission and key rates, and show that all feasible rates can be achieved using scalar linear coding and time sharing; we also show that scalar linear codes are sub-optimal for four receivers. The outer bounds used in the case of three users are extended to arbitrary number of users and seen as a generalized version of the well-known polymatroidal bounds for the standard non-private index coding. We also show that the presence of common randomness and private randomness does not change the rate region. Furthermore, we study the case where no keys are shared among the users and provide some necessary and sufficient conditions for feasibility in this setting under a weaker notion of privacy. If the server has the ability to multicast to any subset of users, we demonstrate how this flexibility can be used to provide privacy and characterize the minimum number of server multicasts required.

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