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On One-Bit Quantization [article]

Sourbh Bhadane, Aaron B. Wagner
2022 arXiv   pre-print
We consider the one-bit quantizer that minimizes the mean squared error for a source living in a real Hilbert space. The optimal quantizer is a projection followed by a thresholding operation, and we provide methods for identifying the optimal direction along which to project. As an application of our methods, we characterize the optimal one-bit quantizer for a continuous-time random process that exhibits low-dimensional structure. We numerically show that this optimal quantizer is found by a
more » ... ural-network-based compressor trained via stochastic gradient descent.
arXiv:2202.05292v1 fatcat:duduz2b4arhmrhlx6ribookruu

Estimating Entropy of Distributions in Constant Space [article]

Jayadev Acharya, Sourbh Bhadane, Piotr Indyk, Ziteng Sun
2019 arXiv   pre-print
We consider the task of estimating the entropy of k-ary distributions from samples in the streaming model, where space is limited. Our main contribution is an algorithm that requires O(k log (1/ε)^2/ε^3) samples and a constant O(1) memory words of space and outputs a ±ε estimate of H(p). Without space limitations, the sample complexity has been established as S(k,ε)=Θ(k/εlog k+log^2 k/ε^2), which is sub-linear in the domain size k, and the current algorithms that achieve optimal sample
more » ... y also require nearly-linear space in k. Our algorithm partitions [0,1] into intervals and estimates the entropy contribution of probability values in each interval. The intervals are designed to trade off the bias and variance of these estimates.
arXiv:1911.07976v1 fatcat:yom3mxqtsbgo7dwudqdwxqohha

Do Neural Networks Compress Manifolds Optimally? [article]

Sourbh Bhadane, Aaron B. Wagner, Johannes Ballé
2022 arXiv   pre-print
Artificial Neural-Network-based (ANN-based) lossy compressors have recently obtained striking results on several sources. Their success may be ascribed to an ability to identify the structure of low-dimensional manifolds in high-dimensional ambient spaces. Indeed, prior work has shown that ANN-based compressors can achieve the optimal entropy-distortion curve for some such sources. In contrast, we determine the optimal entropy-distortion tradeoffs for two low-dimensional manifolds with circular
more » ... structure and show that state-of-the-art ANN-based compressors fail to optimally compress the sources, especially at high rates.
arXiv:2205.08518v1 fatcat:rh7mel342fdyjixq2fs5od2kpi

Irregular Recovery and Unequal Locality for Locally Recoverable Codes with Availability [article]

Sourbh Bhadane, Andrew Thangaraj
2017 arXiv   pre-print
Bhadane and A. Thangaraj are with the Department of Electrical Engineering, Indian Institute of Technology Madras, Chennai 60036, India.  ... 
arXiv:1705.05005v1 fatcat:yq2mqk6apvfgddjaas7uwgn4wa

Principal Bit Analysis: Autoencoding with Schur-Concave Loss [article]

Sourbh Bhadane, Aaron B. Wagner, Jayadev Acharya
2021 arXiv   pre-print
We consider a linear autoencoder in which the latent variables are quantized, or corrupted by noise, and the constraint is Schur-concave in the set of latent variances. Although finding the optimal encoder/decoder pair for this setup is a nonconvex optimization problem, we show that decomposing the source into its principal components is optimal. If the constraint is strictly Schur-concave and the empirical covariance matrix has only simple eigenvalues, then any optimal encoder/decoder must
more » ... mpose the source in this way. As one application, we consider a strictly Schur-concave constraint that estimates the number of bits needed to represent the latent variables under fixed-rate encoding, a setup that we call Principal Bit Analysis (PBA). This yields a practical, general-purpose, fixed-rate compressor that outperforms existing algorithms. As a second application, we show that a prototypical autoencoder-based variable-rate compressor is guaranteed to decompose the source into its principal components.
arXiv:2106.02796v2 fatcat:2tnsrzummncktoyg7quu77igd4

IITMSAT Communications System : A LeanSat Design Approach [article]

Akshay Gulati, Shubham Chavan, Joseph Samuel, Sampoornam Srinivasan, Pradeep Shekhar, Akshat Dave, Aditya Sant, Sourbh Bhadane, Mayug Maniparambil, Vishnu Prasad Sivasankarakurup, Dhanalakshmi Durairaj, David Koilpillai, Harishankar Ramachandran
2017 arXiv   pre-print
IITMSAT is a student-built nano satellite mission of Indian Institute of Technology Madras, Chennai, India. The objective is to study the precipitation of high energy electrons and protons from Van-Allen radiation belts to lower altitude of 600-900 km due to resonance interaction with low frequency EM waves. The unique communications system design of IITMSAT evolves from the challenging downlink data requirement of 1 MB per day in the UHF band posed by the mission and the satellite's payload,
more » ... EED (Space based Proton and Electron Energy Detector). To ensure continuous downlink data stream in the short Low earth Orbit passes, a robust physical layer protocol was designed to counter time-varying aspects of a Space-Earth telecom link. For the on-board communications system, two types of design alternatives exist for each module. The first option is a custom design wherein a module is developed from scratch using discrete components.The other option is an integrated design wherein an electronics COTS module can be directly plugged into the subsystem. This module is evaluated by carrying out vibration and thermal tests. If an integrated module is low-cost and meets the design requirements, it is preferred over a custom design. In order to carry out performance tests under simulated link conditions, an RF attenuation test setup was designed that can work at extreme temperatures. Burn-In tests for 72 hours at ambient and extreme temperatures were carried out. Integrated tests indicate all IITMSAT design requirements have been met. Hence a robust communications system has been validated. The time taken for development of on-board telecom and GS was less than a year and was achieved at a low cost which agrees to a LeanSat approach.
arXiv:1711.01145v1 fatcat:q3icfyo7lrevjnccvqltnvveqa

Social Distancing Has Merely Stabilized COVID-19 in the US [article]

Aaron B. Wagner, Elaine L. Hill, Sean E. Ryan, Ziteng Sun, Grace Deng, Sourbh Bhadane, Victor Hernandez Martinez, Peter Wu, Dongmei Li, Ajay Anand, Jayadev Acharya, David S. Matteson
2020 medRxiv   pre-print
Social distancing measures, with varying degrees of restriction, have been imposed around the world in order to stem the spread of COVID-19. In this work we analyze the effect of current social distancing measures in the United States. We quantify the reduction in doubling rate, by state, that is associated with social distancing. We find that social distancing is associated with a statistically-significant reduction in the doubling rate for all but three states. At the same time, we do not
more » ... significant evidence that social distancing has resulted in a reduction in the number of daily confirmed cases. Instead, social distancing has merely stabilized the spread of the disease. We provide an illustration of our findings for each state, including point estimates of the effective reproduction number, R, both with and without social distancing. We also discuss the policy implications of our findings.
doi:10.1101/2020.04.27.20081836 fatcat:jqyki6eyqfh7lozjhbc4u3nyou

Social distancing merely stabilized COVID‐19 in the US

Aaron B. Wagner, Elaine L. Hill, Sean E. Ryan, Ziteng Sun, Grace Deng, Sourbh Bhadane, Victor Hernandez Martinez, Peter Wu, Dongmei Li, Ajay Anand, Jayadev Acharya, David S. Matteson
2020 Stat  
Social distancing measures have been imposed across the US in order to stem the spread of COVID-19. We quantify the reduction in doubling rate, by state, that is associated with this intervention. Using the earlier of K-12 school closures and restaurant closures, by state, to define the start of the intervention, and considering daily confirmed cases through April 23rd, 2020, we find that social distancing is associated with a statistically-significant (p < 0.01) reduction in the doubling rate
more » ... or all states except for Nebraska, North Dakota, and South Dakota, when controlling for false discovery, with the doubling rate averaged across the states falling from 0.302 (0.285, 0.320) days-1 to 0.010 (-0.007, 0.028) days-1. However, we do not find that social distancing has made the spread subcritical. Instead, social distancing has merely stabilized the spread of the disease. We provide an illustration of our findings for each state, including estimates of the effective reproduction number, R, both with and without social distancing. We also discuss the policy implications of our findings.
doi:10.1002/sta4.302 pmid:32837718 pmcid:PMC7404665 fatcat:6ejsg57dknbmvmins2upy25mnq

Design and implementation of a robust downlink communication system for nanosatellites

Jagdish Mevada, Joseph Samuel, Sourbh Bhadane, Akshay K. Gulati, R. D. Koilpillai
2015 2015 International Conference on Space Science and Communication (IconSpace)  
The design of a robust downlink communication system for nanosatellites in UHF amateur radio band involves many challenges like radio spectrum constraints, time-varying Doppler, clock drifts and synchronization in a LEO satellite channel. This paper presents the system designed and implemented for IITMSAT, a student satellite project at IIT Madras, which successfully overcomes these challenges using a robust physical layer design implemented on a generic Software Defined Radio platform. The
more » ... ormance of the proposed design is verified through simulations as well as hardware. The communication system gives a good performance which is only about 1 dB away from theory.
doi:10.1109/iconspace.2015.7283827 fatcat:up5qcdilybekdhiiuyr55wcdxm