Search

Word embeddings have gained increasing popularity in the recent years due to the Word2vec library and its extension fastText that uses subword information. In this paper, we aim at improving the execution speed of fastText training on homogeneous multi- and manycore CPUs while maintaining accuracy. We present a novel open-source implementation that flexibly incorporates various algorithmic Variants including negative sample sharing, batched updates. and a byte-pair encoding-based alternative for subword units. We build these novel variants over a fastText implementation that we carefully optimized for the architecture, memory hierarchy, and parallelism of current manycore CPUs. Our experiments on three languages demonstrate 3-20x speed-up in training time at competitive semantic and syntactic accuracy.

There have been many recent advances in the Traffic Signal Control literature that use reinforcement learning, most of which is undertaken using the model-free approach. Approaches in the model-free domain, attempt to learn the value or the policy function directly without attempting to learn the environment transition dynamics. Therefore, training the value function under a specified dynamics fails to differentiate the value updates from the underlying dynamics, making these methods require much larger agent-environment interaction data to generalize over different scenarios. In contrast, approaches that optimize agent actions w.r.t. a learned dynamics model inherently avoid this tight coupling of dynamics and value, allowing for much faster adaptation as traffic scenarios change. For this work on single intersection control, we specifically adopt this latter model-based approach of learning a microscopic simulator model and then apply tree-search techniques to optimize control actions. This approach quickly generalizes to a diverse set of traffic demands, whereas the model-free method performs suboptimally in conditions unseen during training. Another benefit of model-based approaches is the ability to control new intersections with previously unseen topologies, which makes the method transferable in terms of both demand and intersection structure variation. Finally, we observe that pairing these control strategies with the learned model also makes our approach debuggable and explainable, which is a critical requirement for real-world deployment.

We study list-decoding over adversarial channels governed by oblivious adversaries (a.k.a. oblivious Arbitrarily Varying Channels (AVCs)). This type of adversaries aims to maliciously corrupt the communication without knowing the actual transmission from the sender. For any oblivious AVCs potentially with constraints on the sender's transmitted sequence and the adversary's noise sequence, we determine the exact value of the minimum list-size that can support a reliable communication at positive rate. This generalizes a classical result by Hughes (IEEE Transactions on Information Theory, 1997) and answers an open question posed by Sarwate and Gastpar (IEEE Transactions on Information Theory, 2012). A lower bound on the list-decoding capacity (whenever positive) is presented. Under a certain combinatorial conjecture, we also prove a matching upper bound. En route to a tight characterization of the list-decoding capacity, we propose a method for subcode construction towards the resolution of the combinatorial conjecture.

Myopic arbitrarily varying channels (AVCs) are point-to-point communication models in which a channel state is controlled by a malicious adversary (a jammer) who receives side-information about the transmitted codeword via a side- channel (wiretapping) and wishes to maximize the probability of error. Compared to standard "oblivious" AVCs, myopic AVCs can potentially use the side information to launch a more effective attack, lowering the capacity of the channel. In this paper, we define a novel property, myopic symmetrizability, and prove it is a sufficient condition for the capacity of any myopic AVC to be zero. We also study the sufficiently myopic setting, in which, roughly speaking, the jammer’s side information reveals less information on the codeword transmitted than eventually available at the receiver. In this scenario we show that myopic symmetrizability is also a necessary condition for the capacity to equal zero, by providing a novel code construction using non-i.i.d. codebooks. A key technical lemma, interesting in its own right, is an argument showing that for any positive-rate code (whether for myopic AVCs or not) one can identify a corresponding distribution P X,X' that is a convex combination of product distributions, and such that a constant fraction of pairs of codewords have an empirical distribution approximately equaling P X,X' .

We study achievable rates of reliable communication in a power-constrained two-way additive interference channel over the real alphabet where communication is disrupted by a power-constrained jammer. This models the wireless communication scenario where two users Alice and Bob, operating in the full duplex mode, wish to exchange messages with each other in the presence of a jammer, James. Alice and Bob simultaneously transmit their encodings $ \underline{x}_A $ and $\underline{x}_B $ over $ n $ channel uses. It is assumed that James can choose his jamming signal $ \underline{s} $ as a noncausal randomized function of $ \underline{x}_A $ and $ \underline{x}_B $, and the codebooks used by Alice and Bob. Alice and Bob observe $ \underline{x}_A+\underline{x}_B +\underline{s}$, and must recover each others' messages reliably. In this article, we provide upper and lower bounds on the capacity of this channel which match each other and equal $ \frac{1}{2}\log\left(\frac{1}{2} + \mathsf{SNR}\right) $ in the high-$\mathsf{SNR}$ regime (where $\mathsf{SNR}$, signal to noise ratios, is defined as the ratio of the power constraints of the users to the power constraint of the jammer). We give a code construction based on lattice codes, and derive achievable rates for large $\mathsf{SNR}$. We also present upper bounds based on two specific attack strategies for James. Along the way, sumset property of lattices for the achievability and general properties of capacity-achieving codes for memoryless channels for the converse are proved, which might be of independent interest.

In this article, we revisit the classical problem of channel coding and obtain novel results on properties of capacity- achieving codes. Specifically, we give a linear algebraic characterization of the set of capacity-achieving input distributions for discrete memoryless channels. This allows us to characterize the dimension of the manifold on which the capacity-achieving distributions lie. We then proceed by examining empirical properties of capacity-achieving codebooks by showing that the joint-type of k-tuples of codewords in a good code must be close to the k- fold product of the capacity-achieving input distribution. While this conforms with the intuition that all capacity-achieving codes must behave like random capacity-achieving codes, we also show that some properties of random coding ensembles do not hold for all codes. We prove this by showing that there exist pairs of communication problems such that random code ensembles simultaneously attain capacities of both problems, but certain (superposition ensembles) do not.Due to lack of space, several proofs have been omitted but can be found at https://sites.google.com/view/yihan/ [1]

Consider the communication efficient secret sharing problem. A dealer wants to share a secret with $n$ parties such that any $k\leq n$ parties can reconstruct the secret and any $z, Comment: Extended version of a paper submitted to ISIT 2020

The task for handwritten digit recognition has been troublesome due to various variations in writing styles. Therefore, we have tried to create a base for future researches in the area so that the researchers can overcome the existing problems. The existing methods and techniques for handwritten digit recognition were reviewed and understood to analyze the most suitable and best method for digit recognition. A number of 60,000 images were used as training sets of images with pixel size of 28×28. The images/training sets were matched with original image. It was found out after complete analysis and review that classifier ensemble system has the least error rate of just 0.32%. In this paper, review of different methods handwritten digit recognition were observed and analyzed.

We consider the problem of covert communication over continuous-time additive white Gaussian noise (AWGN) channels under spectral mask constraints. In addition to requiring the legitimate receiver to reliably decode, covert communication also requires that the warden is unable to estimate whether or not communication is taking place. The spectral mask at the transmitter restricts excessive radiation beyond the bandwidth of interest. We develop a communication scheme with theoretical guarantees for both covertness and reliability, based on pulse amplitude modulation (PAM) with Binary Phase Shift Keying (BPSK) and root raised cosine (RRC) carrier pulses. Given a fixed time T and a spectral mask with bandwidth parameter W, we show that one can transmit $\mathcal{O}\left( {\sqrt {WT} } \right)$ bits of information covertly and reliably, and our proposed scheme provides a lower bound on the covert capacity.

We study an adversarial communication problem where sender Alice wishes to send a message m to receiver Bob over an arbitrarily varying channel (AVC) controlled by a malicious adversary James. We assume that Alice and Bob share randomness K unknown to James. Using K, Alice first encodes the message m to a codeword X and transmits it over the AVC. James knows the message m, the (randomized) codebook and the codeword X. James then inputs a jamming state S to disrupt communication; we assume a state-deterministic AVC where S completely specifies the channel noise. Bob receives a noisy version Y of codeword X; it outputs a message estimate $\mathop {\hat m}$ using Y and the shared randomness K. We study AVCs, called ‘adversary-weakened’ AVCs here, where the availability of shared randomness strictly improves the optimum throughput or capacity over it than when it is not available; the randomized coding capacity characterizes the largest rate possible when K is unrestricted. In this work, we characterize the exact threshold for the amount of shared randomness K so as to achieve the randomized coding capacity for ‘adversary-weakened’ AVCs.We show that exactly log(n) equiprobable and independent bits of randomness, shared between Alice and Bob and unknown to adversary James, are both necessary and sufficient for achieving randomized coding capacity for ‘adversary-weakened’ AVCs. For sufficiency, our achievability is based on a randomized code construction which uses deterministic list codes along with a polynomial hashing technique which uses the shared randomness. Our converse, which establishes the necessity of log(n) bits of shared randomness, uses a known approach for binary AVCs, and extends it to general ‘adversary-weakened’ AVCs using a notion of confusable codewords.

The difference in capacity formulae between worst-case and average-case channel noise models has been part of information theory since the early days of the field. This paper continues a line of work studying intermediate models in which the channel behavior can depend partially on the transmitted codeword. In particular, we consider a model in which a binary erasure channel (with maximum fraction of erasures p) is controlled by an adversary who can observe the transmitted codeword through an independent and memoryless erasure channel (with erasure probability q). Upper and lower bounds on the capacity are given for two models: a noncausal model, in which the adversary can choose their erasures based on the entire (partially observed) codeword, and a causal model, in which at each time the adversary must choose its erasures based on the current and previously observed codeword bits. The achievable rate for the noncausal case is larger than the Gilbert-Varshamov bound and for some parameter ranges exceeds the linear programming (LP) bound; we also provide a non-trivial outer bound on the capacity. For the causal case, we show the capacity is 1−2p+q for p ≥ q (prior work shows the capacity to equal 1−p when p

We study a general Omniscient Arbitrarily Varying Channel (AVC) problem where Alice wishes to communicate a message to receiver Bob by inputting a length-n vector x to a channel. Jammer James observes x, and as a function of x chooses a state sequence s. Bob observes y (such that channel inputs and outputs are related component-wise as y i = w(x i ,s i ) for some deterministic function w(.,.)) from which he must estimate m with no error. Input and state constraints determine feasible inputs x and s for Alice and James respectively. In this work we characterize when a positive communication rate is possible.We first show that the capacity of any such AVC completely depends upon the relationship between a confusability set, and the set of completely-positive-self-couplings (both are convex sets of certain single-letter probability distributions). Our main result provides essentially matching necessary and sufficient conditions for capacity positivity; we show that the zero-error capacity of an AVC is positive if there are completely-positive-self-couplings outside the confusability set of the given AVC; and that the AVC capacity is zero if all completely-positive-self couplings are in the interior of this confusability set. Our achievability uses a novel code construction based on completely-positive-self-couplings called cloud codes which are strict generalizations of all known Gilbert-Varshamov (GV) type codes. Our converse is based upon Ramsey-theoretic ideas, a generalization of the Plotkin bound leveraging a known result on the duality of completely positive matrices and copositive matrices, and a Fourier-analytic proof of the non-existence of certain sequences of random variables.

The aim of the ESA SnowLab project is to provide a comprehensive multi-frequency, multi-polarisation, multi-temporal dataset of active microwave measurements over snow-covered grounds to investigate the relationship between effective snow- and ground parameters and the resultant signals detected by microwave radar. An important part for the development of microwave models is the microstructural characterisation. This characterisation can only be done by repeated measurements by SnowMicroPen and more completely, but also much more expensive, by X-ray micro-tomography. Within this project we complemented the microwave measurements of Alpine snow in Switzerland with extensive effective snow- and ground parameters and meteorological data. Microwave backscatter measurements were conducted using the 9 – 18 GHz ESA SnowScat instrument and since December 2018 the recently built ESA WBScat instrument. WBScat allows to extend the spectral coverage to 1 – 40 GHz.

This paper presents the design of a robust observer based controller for four-tank coupled system (FTCS) using higher-order sliding-mode control scheme. The FTCS is considered as a multiple-input and multiple-output (MIMO) nonlinear system having significant coupled dynamics. The problem of liquid level control for FTCS is considered to achieve the desired set point. First, a sliding mode observer of higher order has been designed so that the estimated states achieve convergence to the plant states. Based on this observer, a robust controller using super-twisting algorithm has been proposed which can improve the performance of the FTCS. The applicability of this proposed robust controller for FTCS has been illustrated through simulation studies. Finally, a comparison has been made with the existing controller for FTCS to show the efficacy of proposed control scheme.

This paper is focussed on the robust controller design and performance analysis of four tank coupled system (FTCS). The FTCS is a nonlinear system with multiple-input-multiple-output (MIMO) having significant coupled dynamics. The problem of liquid level control for FTCS is considered to achieve the desired set point. First, the nonlinear model of FTCS has been linearized and levels of the tanks are controlled using three different linear control strategies. Further, a robust controller has been proposed to the FTCS nonlinear model to improve the performance using integral sliding mode approach. The robust performance of the proposed controller for FTCS has been illustrated through simulation studies. A comparative analysis has been carried out among all the controllers in the existence of FTCS parametric uncertainty and external disturbances.

Forest fires are a ferocious phenomenon. They require quick action to prevent any damage from happening. Robots can act as great first responders in this regard. In this paper a model of a robot for forest firefighting purposes is presented. The model is tested against static stress loading. The design and simulation for the same has been done in Autodesk’s Fusion 360.

We study a lossy source coding problem for an arbitrarily varying remote source (AVRS) which was proposed in a prior work. An AVRS transmits symbols, each generated in an independent and identically distributed manner, which are sought to be estimated at the decoder. These symbols are remotely generated, and the encoder and decoder observe noise corrupted versions received through a two-output noisy channel. This channel is an arbitrarily varying channel controlled by a jamming adversary. We assume that the adversary knows the coding scheme as well as the source data non-causally, and hence, can employ malicious jamming strategies correlated to them. Our interest lies in studying the rate distortion function for codes with a stochastic encoder, i.e, when the encoder can privately randomize while the decoder is deterministic. We provide upper and lower bounds on this rate distortion function.

We consider the problem of stealth communication over a multipath network in the presence of an active adversary. The multipath network consists of multiple parallel noiseless links, and the adversary is able to eavesdrop and jam a subset of links. We consider two types of jamming - erasure jamming and overwrite jamming. We require the communication to be both stealthy and reliable, i.e., the adversary should be unable to detect whether or not meaningful communication is taking place, while the legitimate receiver should reconstruct any potential messages from the transmitter with high probability simultaneously. We provide inner bounds on the robust stealth capacities under both adversarial erasure and adversarial overwrite jamming.

Group Testing (GT) addresses the problem of identifying a small subset of defective items from a large population, by grouping items into as few test pools as possible. In Adaptive GT (AGT), outcomes of previous tests can influence the makeup of future tests. This scenario has been studied from an information theoretic point of view. Aldridge 2012 showed that in the regime of a few defectives, adaptivity does not help much, as the number of tests required for identification of the set of defectives is essentially the same as for non-adaptive GT. Secure GT considers a scenario where there is an eavesdropper who may observe a fraction $\delta$ of the outcomes, and should not be able to infer the status of the items. In the non-adaptive scenario, the number of tests required is $1/(1-\delta)$ times the number of tests without the secrecy constraint. In this paper, we consider Secure Adaptive GT. Specifically, when an adaptive algorithm has access to a private feedback link of rate $R_{f}$ , we prove that the number of tests required for both correct reconstruction at the legitimate user, with high probability, and negligible mutual information at the eavesdropper is $1/min\{1,1-\delta+R_{f}\}$ times the number of tests required with no secrecy constraint. Thus, unlike non-secure GT, where an adaptive algorithm has only a mild impact, under a security constraint it can significantly boost performance. A key insight is that not only the adaptive link should disregard test results and send keys, these keys should be enhanced through a “secret sharing” scheme before usage.

Dedicated short range communication based electronic toll collection are gaining popularity due to their advantages like spatial and timely distribution of traffic., cashless, server based toll collection, safety regulations, saving of time, fuel and so on. They have been installed in many developed countries like Korea, Japan and are now being installed in India also. DSRC-ETC is based on the backbone of wireless communication network and thus inherits its demerits like signal interference called as Electro Magnetic Interference (EMI) which can cause loss in terms of wrong interpretation of the user's data leading to false payments. In order to remove this, a microwave absorber design has been proposed in this work, which can be easily integrated to the pillars and sidewalls of the toll system. The absorber is based on the filler incorporated polymer composites utilizing grid for frequency selection. Carbon fiber/ epoxy polymer composite being light weight, temperature resistant, chemical resistant, structurally strong fits the requirement of the above application. The grid is based on carbon fibers, thus can be easily incorporated to the existing layers. The absorber is designed for typical ETC specifications that are −11 dB absorption at around center frequency of 5.8 GHz. Thus using this absorber, the ETC system can be made more reliable and user friendly.