Communications in the observation limited regime

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 141-145).We consider the design of communications systems when the principal cost is observing the channel, as opposed to transmit energy per bit or spectral efficiency. This is motivated by energy constrained communications devices where sampling the signal, rather than transmitting or processing it, dominates energy consumption. We show that sequentially observing samples with the maximum a posteriori entropy can reduce observation costs by close to an order of magnitude using a (24,12) Golay code. This is the highest performance reported over the binary input AWGN channel, with or without feedback, for this blocklength. Sampling signal energy, rather than amplitude, lowers circuit complexity and power dissipation significantly, but makes synchronization harder. We show that while the distance function of this non-linear coding problem is intractable in general, it is Euclidean at vanishing SNRs, and root Euclidean at large SNRs. We present sequences that maximize the error exponent at low SNRs under the peak power constraint, and under all SNRs under an average power constraint. Some of our new sequences are an order of magnitude shorter than those used by the 802.15.4a standard.(cont.) In joint work with P. Mercier and D. Daly, we demonstrate the first energy sampling wireless modem capable of synchronizing to within a ns, while sampling energy at only 32 Msamples per second, and using no high speed clocks. We show that traditional, minimum distance classifiers may be highly sensitive to parameter estimation errors, and propose robust, computationally efficient alternatives. We challenge the prevailing notion that energy samplers must accurately shift phase to synchronize with high precision.by Manish Bhardwaj.Ph.D

Hoeffding Races--model selection for MRI classification

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (leaves 58-61).by Oded Maron.M.S

Construction of nonlinear filter algorithms using the saddlepoint approximation

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 75-76).In this thesis we propose the use of the saddlepoint method to construct nonlinear filtering algorithms. To our knowledge, while the saddlepoint approximation has been used very successfully in the statistics literature (as an example the saddlepoint method provides a simple, highly accurate approximation to the density of the maximum likelihood estimator of a non-random parameter given a set of measurements), its potential for use in the dynamic setting of the nonlinear filtering problem has yet to be realized. This is probably because the assumptions on the form of the integrand that is typical in the asymptotic analysis literature do not necessarily hold in the filtering context. We show that the assumptions typical in asymptotic analysis (and which are directly applicable in statistical inference since the statistics applications usually involve estimating the density of a function of a sequence of random variables) can be modified in a way that is still relevant in the nonlinear filtering context while still preserving a property of the saddlepoint approximation that has made it very useful in statistical inference, namely, that the shape of the desired density is accurately approximated. As a result, the approximation can be used to calculate estimates of the mean and confidence intervals and also serves as an excellent choice of proposal density for particle filtering. We will show how to construct filtering algorithms based on the saddle point approximation.by Esosa O. Amayo.M.Eng

Noise tolerant algorithms for learning and searching

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.Includes bibliographical references (p. 109-112).by Javed Alexander Aslam.Ph.D

Composing after computers : the application of computational metaphors to musical thought

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1987.Bibliography: leaves [121]-125. "Discography and scores": leaf 126.by Gregory Mark Gargarian.M.S

A functional model of similarity

In the first chapters, the prevalent conception of the nature of similarity is shown to be too narrow, and the argument is developed that models of similarity must encompass both analytic and synthetic components. Some general problems of measurement and the testing of psychological models are also discussed.A review of the philosophical treatment of the concept of similarity is made in order to understand the origins of the models found in the present psychological literature. These are then analysed in terms of their implicit object representations and cognitive processes. The distinction between the'class inclusion' and 'distance relation' models of similarity is shown tobe qualitative in nature, and to correspond to the analytic-synthetic distinction in terms of cognitive process.A functional model of the psychological processes and object representations involved in similarity judgements is then proposed. The fundamental idea involved in this model is that the global properties of referents are synthetically evaluated in terms of their contextual relations, whilst an analytic 'pattern matching' of local properties is made. Various theoretical aspects of the model are examined experimentally, and its general applicability is indicated in a series of applied studies.The scope of the argument is finally broadened to encompass a development of Torgerson's (196.5) conception of the nature of the dimensions resulting from MDS analysis. Dimensions may be considered as 'virtual' artifacts of the experimental task and the individual's conception of it. This possibility allows the methodology to escape the dominating influence of its psychophysical tradition, and become a conceptually deeper tool for cognitive psychology

Quantum state discrimination with bosonic channels and Gaussian states

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 161-166).Discriminating between quantum states is an indispensable part of quantum information theory. This thesis investigates state discrimination of continuous quantum variables, focusing on bosonic communication channels and Gaussian states. The specific state discrimination problems studied are (a) quantum illumination and (b) optimal measurements for decoding bosonic channels. Quantum illumination is a technique for detection and imaging which uses entanglement between a probe and an ancilla to enhance sensitivity. I shall show how entanglement can help with the discrimination between two noisy and lossy bosonic channels, one in which a target reflects back a small part of the probe light, and the other in which all probe light is lost. This enhancement is obtained even though the channels are entanglement-breaking. The main result of this study is that, under optimum detection in the asymptotic limit of many detection trials, 6 dB of improvement in the error exponent can be achieved by using an entangled state as compared to a classical state. In the study of optimal measurements for decoding bosonic channels, I shall present an alternative measurement to the pretty-good measurement for attaining the classical capacity of the lossy bosonic channel given product coherent-state inputs. This new measurement has the feature that, at each step of the measurement, only projective measurements are needed. The measurement is a sequential one: the number of steps required is exponential in the code length, and the error rate of this measurement goes to zero in the limit of large code length. Although not physically practical in itself, this new measurement has a simple physical interpretation in terms of collective energy measurements, and may give rise to an implementation of an optimal measurement for lossy bosonic channels. The two problems studied in my thesis are examples of how state discrimination can be useful in solving problems by using quantum mechanical properties such as entanglement and entangling measurements.by Si Hui Tan.Ph.D