Showing papers by "Bell Labs published in 1976"

The rate-distortion function for source coding with side information at the decoder

Abstract: Let \{(X_{k}, Y_{k}) \}^{ \infty}_{k=1} be a sequence of independent drawings of a pair of dependent random variables X, Y . Let us say that X takes values in the finite set \cal X . It is desired to encode the sequence \{X_{k}\} in blocks of length n into a binary stream of rate R , which can in turn be decoded as a sequence \{ \hat{X}_{k} \} , where \hat{X}_{k} \in \hat{ \cal X} , the reproduction alphabet. The average distortion level is (1/n) \sum^{n}_{k=1} E[D(X_{k},\hat{X}_{k})] , where D(x,\hat{x}) \geq 0, x \in {\cal X}, \hat{x} \in \hat{ \cal X} , is a preassigned distortion measure. The special assumption made here is that the decoder has access to the side information \{Y_{k}\} . In this paper we determine the quantity R \ast (d) , defined as the infimum ofrates R such that (with \varepsilon > 0 arbitrarily small and with suitably large n )communication is possible in the above setting at an average distortion level (as defined above) not exceeding d + \varepsilon . The main result is that R \ast (d) = \inf [I(X;Z) - I(Y;Z)] , where the infimum is with respect to all auxiliary random variables Z (which take values in a finite set \cal Z ) that satisfy: i) Y,Z conditionally independent given X ; ii) there exists a function f: {\cal Y} \times {\cal Z} \rightarrow \hat{ \cal X} , such that E[D(X,f(Y,Z))] \leq d . Let R_{X | Y}(d) be the rate-distortion function which results when the encoder as well as the decoder has access to the side information \{ Y_{k} \} . In nearly all cases it is shown that when d > 0 then R \ast(d) > R_{X|Y} (d) , so that knowledge of the side information at the encoder permits transmission of the \{X_{k}\} at a given distortion level using a smaller transmission rate. This is in contrast to the situation treated by Slepian and Wolf [5] where, for arbitrarily accurate reproduction of \{X_{k}\} , i.e., d = \varepsilon for any \varepsilon >0 , knowledge of the side information at the encoder does not allow a reduction of the transmission rate.

The Complexity of Flowshop and Jobshop Scheduling

Abstract: NP-complete problems form an extensive equivalence class of combinatorial problems for which no nonenumerative algorithms are known. Our first result shows that determining a shortest-length schedule in an m-machine flowshop is NP-complete for m ≥ 3. For m = 2, there is an efficient algorithm for finding such schedules. The second result shows that determining a minimum mean-flow-time schedule in an m-machine flowshop is NP-complete for every m ≥ 2. Finally we show that the shortest-length schedule problem for an m-machine jobshop is NP-complete for every m ≥ 2. Our results are strong in that they hold whether the problem size is measured by number of tasks, number of bits required to express the task lengths, or by the sum of the task lengths.

Electromigration in thin aluminum films on titanium nitride

Abstract: The aluminum electromigration drift velocity was measured at the temperature range 250–400 °C. A threshold current density was found inversely proportional to the stripe length. An activation energy of 0.65 eV was found for the drift velocity. The occurrence of the threshold is explained by opposing chemical gradients created by the atom pile‐up and depletion at the stripe ends. The threshold may explain several observations reported previously. The threshold is increased by decreasing the temperature or by enclosing the aluminum in silicon nitride. Virtually no electromigration is seen for very short aluminum stripes even at current densities above 106 A/cm2.

A Method for Simulating Stable Random Variables

Abstract: A new algorithm is presented for simulating stable random variables on a digital computer for arbitrary characteristic exponent α(0 < α ≤ 2) and skewness parameter β(-1 ≤ β ≤ 1). The algorithm involves a nonlinear transformation of two independent uniform random variables into one stable random variable. This stable random variable is a continuous function of each of the uniform random variables, and of α and a modified skewness parameter β' throughout their respective permissible ranges.

A comparative performance study of several pitch detection algorithms

Abstract: A comparative performance study of seven pitch detection algorithms was conducted. A speech data base, consisting of eight utterances spoken by three males, three females, and one child was constructed. Telephone, close talking microphone, and wideband recordings were made of each of the utterances. For each of the utterances in the data base; a "standard" pitch contour was semiautomatically measured using a highly sophisticated interactive pitch detection program. The "standard" pitch contour was then compared with the pitch contour that was obtained from each of the seven programmed pitch detectors. The algorithms used in this study were 1) a center clipping, infinite-peak clipping, modified autocorrelation method (AUTOC), 2) the cepstral method (CEP), 3) the simplified inverse filtering technique (SIFT) method, 4) the parallel processing time-domain method (PPROC), 5) the data reduction method (DARD), 6) a spectral flattening linear predictive coding (LPC) method, and 7) the average magnitude difference function (AMDF) method. A set of measurements was made on the pitch contours to quantify the various types of errors which occur in each of the above methods. Included among the error measurements were the average and standard deviation of the error in pitch period during voiced regions, the number of gross errors in the pitch period, and the average number of voiced-unvoiced classification errors. For each of the error measurements, the individual pitch detectors could be rank ordered as a measure of their relative performance as a function of recording condition, and pitch range of the various speakers. Performance scores are presented for each of the seven pitch detectors based on each of the categories of error.

Pseudo-random sequences and arrays

Abstract: Binary sequences of length n = 2m- 1 whose autocorrelation function is either 1 or -1/n have been known for a long time, and are called pseudo-random (or PN) sequences, or maximal-length shift-register sequences. Two-dimensional arrays of area n = 2lm- 1 with the same property have rcently been found by several authors. This paper gives a simple description of such sequences and arrays and their many nice properties.

Timing Recovery in Digital Synchronous Data Receivers

Abstract: A new class of fast-converging timing recovery methods for synchronous digital data receivers is investigated. Starting with a worst-case timing offset, convergence with random binary data will typically occur within 10-20 symbols. The input signal is sampled at the baud rate; these samples are then processed to derive a suitable control signal to adjust the timing phase. A general method is outlined to obtain near-minimum-variance estimates of the timing offset with respect to a given steady-state sampling criterion. Although we make certain independence assumptions between successive samples and postulate ideal decisions to obtain convenient analytical results, our simulations with a decision-directed reference and baud-to-baud adjustments yield very similar results. Convergence is exponential, and for small loop gains the residual jitter is proportional and convergence time is inversely proportional to the loop gain. The proposed algorithms are simple and economic to implement. They apply to binary or multilevel PAM signals as well as to partial response signals.

Differential Gain and Bistability Using a Sodium-Filled Fabry-Perot Interferometer

Abstract: Differential gain and large hysteresis have been seen in the transmission of a Fabry-Perot interferometer containing Na vapor irradiated by light from a cw dye laser. Non-linear dispersion, neglected in earlier work, dominates over nonlinear absorption in Na. The apparatus uses only optical inputs and outputs. Similar apparatus may be useful as an optical amplifier, memory element, clipper, and limiter.

Mixed-valence compounds

Abstract: In a number of rare-earth compounds, the atomic-like $f$ levels and the wide $s\ensuremath{-}d$ band coexist at the Fermi level. Such compounds are being referred to as mixed-valence compounds. These compounds have a variety of unique thermal and magnetic properties. In this article, we review some salient experimental results in such compounds and discuss a theoretical framework in which they may be understood. Special emphasis is given to the Samarium chalcogenides, on which extensive experimental results are available. The review is not meant to be a comprehensive survey of theoretical and experimental results. Rather it reflects the interests of the author. The hope is that the basic unresolved issues in the theory of mixed-valence compounds are pointed out so as to stimulate further experimental and theoretical work.

Curvature loss formula for optical fibers

Abstract: The loss formula for optical fibers with constant radius of curvature of their axes is derived by expressing the field outside of the fiber in terms of a superposition of cylindrical outgoing waves. The expansion coefficients are determined by matching the superposition field to the field of the fiber along a cylindrical surface that is tangential to the outer perimeter of the curved fiber. This method is a direct extension of my derivation of the curvature-loss formula for slab guides.

Thermopower in the correlated hopping regime

Abstract: The high-temperature limit for the thermopower of a system of interacting localized carriers is governed entirely by the entropy change per added carrier. The calculation of this quantity reduces to a simple combinatorial problem dependent only on the density of carriers and the interactions stronger than the thermal energy. We have thus been able to generalize the Heikes formula to include several cases of interacting Fermi systems with spin.

Switched directional couplers with alternating &#916;&#914;

Abstract: Coupled waveguide structures with sections of alternating phase mismatch are proposed as switched directional coupler configurations in which complete conversion of light from one guide to the other can be achieved by an electrical adjustment. These structures can be used to make electrooptic switches and amplitude modulators in integrated optics form with improved conversion and on-off ratios. Couplers with 2, 3, 4, and N sections of alternating phase mismatch are analyzed, and diagrams describing their switching characteristics are given.

On bandwidth

Abstract: It is easy to argue that real signals must be bandlimited. It is also easy to argue that they cannot be so. This paper presents one possible resolution of this seeming paradox. A philosophical discussion of the role of mathematical models in the exact sciences is given and a new formulation of the 2 WT theorem is presented. The paper is a written version of the second Shannon Lecture given at the 1974 International Symposium on Information Theory. An appendix giving proof of the 2 WT theorem has been added.

A pattern recognition approach to voiced-unvoiced-silence classification with applications to speech recognition

Abstract: In speech analysis, the voiced-unvoiced decision is usually performed in conjunction with pitch analysis The linking of voiced-unvoiced (V-UV) decision to pitch analysis not only results in unnecessary complexity, but makes it difficult to classify short speech segments which are less than a few pitch periods in duration In this paper, we describe a pattern recognition approach for deciding whether a given segment of a speech signal should be classified as voiced speech, unvoiced speech, or silence, based on measurements made on the signal In this method, five different measurements are made on the speech segment to be classified The measured parameters are the zero-crossing rate, the speech energy, the correlation between adjacent speech samples, the first predictor coefficient from a 12-pole linear predictive coding (LPC) analysis, and the energy in the prediction error The speech segment is assigned to a particular class based on a minimum-distance rule obtained under the assumption that the measured parameters are distributed according to the multidimensional Gaussian probability density function The means and covariances for the Gaussian distribution are determined from manually classified speech data included in a training set The method has been found to provide reliable classification with speech segments as short as 10 ms and has been used for both speech analysis-synthesis and recognition applications A simple nonlinear smoothing algorithm is described to provide a smooth 3-level contour of an utterance for use in speech recognition applications Quantitative results and several examples illustrating the performance of the method are included in the paper

Electronic properties and superlattice formation in the semimetal TiSe 2

Abstract: Neutron-diffraction studies of ${\mathrm{TiSe}}_{2}$ show that a second-order structural phase transition occurs at ${T}_{0}=202$ K involving transverse atomic displacements with wave vector $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}=(\frac{1}{2},0,\frac{1}{2})$. The electronic transport properties of the most nearly stoichiometric crystals show that ${\mathrm{TiSe}}_{2}$ is a semimetal with ${n}_{e}={n}_{h}={10}^{20}$/${\mathrm{cm}}^{3}$. Small impurity concentrations or deviations from stoichiometry reduce ${n}_{h}$, increase ${n}_{e}$, and suppress the phase transition. This reduction together with the observed displacement pattern lead us to speculate that the transition is driven by an electron-hole coupling.

Automatic recognition of speakers from their voices

Abstract: This paper presents a survey of automatic speaker recognition techniques. The paper indudes a discussion of the speaker-dependent properties of the speech signal, methods for selecting an efficient set of speech measurements, results of experimental studies illustrating the performance of various methods of speaker recognition, and a comparision of the performance of automatic methods with that of human listeners. Both text-dependent as well as text-independent speaker-recognition techniques are discussed.

A “DOGLEG” channel router

Abstract: This paper presents an algorithm for interconnecting two sets of terminals across an intervening channel. It is assumed that the routing is done on two distinct levels with all horizontal paths being assigned to one level and all vertical paths to the other. Connections between the levels are made through contact windows. A single net may result in many horizontal and vertical segments. Experimental results indicate that this algorithm is very successful in routing channels that contain severe constraints. Usually, the routing is accomplished within one track of the mathematical lower bound. The routing algorithm presented here was developed as part of LTX, a computer-aided design system for integrated circuit layout and was implemented on an HP-2100 minicomputer. A typical channel (300 terminals, 100 nets) can be routed in less than 5 seconds. Routing results are presented both for polycell chips under development at Bell Laboratories and for examples that exist in the published literature. For the latter, reductions of 10% in the wiring area were typical.

Language perception of 2-month-old infants shows effects of both innate mechanisms and experience

Abstract: VOICING differences distinguish two or more stop consonants in nearly all the world's languages. It has been found1 that voicing distinctions for stops in word-initial postion can usually be characterised by differences in voice onset time (VOT), where VOT is defined as the time between the stop release burst and the onset of vocal cord vibration (Voicing). For example, the English phonemes /p/ and /b/ differ in this way; voicing follows release in /p/, while voicing is approximately simultaneous with release in /b/.

GaAs lower conduction-band minima: Ordering and properties

Abstract: Synchrotron-radiation Schottky-barrier electroreflectance spectra from the $\mathrm{Ga} 3{d}^{V}$ core levels to the lower $s{p}^{3}$ conduction band have shown that the ${L}_{6}^{C}$ lower conduction-band minima are located 170 \ifmmode\pm\else\textpm\fi{} 30 meV in energy below the ${X}_{6}^{C}$ minima in GaAs. Here, we investigate the implications of this ordering, which is opposite to that commonly accepted as correct. We find that, without exception, the results of previous experiments that apparently supported the opposite ordering can be reinterpreted within the ${\ensuremath{\Gamma}}_{6}^{C}\ensuremath{-}{L}_{6}^{C}\ensuremath{-}{X}_{6}^{C}$ model. By performing a line-shape analysis, we resolve an apparent discrepancy between intraconduction band absorption measurements of the ${X}_{6}^{C}\ensuremath{-}{\ensuremath{\Gamma}}_{6}^{C}$ energy separation. By comparing these optical results with other modulation spectroscopic ($s{p}^{3}$ valence-conduction-band electroreflectance, high-precision reflectance) data, combining these with the results of photoemission, transport (high pressure and high temperature), semiconductor alloy, and luminescence measurements, nonlocal pseudopotential calculations $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}$ theory, the rigid-valence-band hypothesis, and using the systematics of other tetrahedrally bonded semiconductors with temperature and pressure, we obtain a set of consistent parameters describing the ${\ensuremath{\Gamma}}_{6}^{C}$, ${L}_{6}^{C}$, and ${X}_{6}^{C}$ lower conduction-band minima of GaAs. This model resolves the former contradictions in the apparent indirect threshold energy as determined previously by photoemission, transport, and optical measurements. Previous photoemission data for cesiated GaAs show clearly after structure reassignment that hot electrons thermalize in the ${L}_{6}^{C}$ minima. This implies that Gunn oscillator operation in GaAs involves the ${L}_{6}^{C}$, and not ${X}_{6}^{C}$, conduction-band minima. We obtain the variation of these minima with composition, $x$, in the $\mathrm{Ga}{\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}$ alloy series, and show that the increase in binding energy of the N isoelectronic trap with increasing As fraction in this series is in qualitative agreement with the prediction of a two-level model wherein a Koster-Slater isoelectronic trap potential interacts with the densities of states of both ${L}_{6}^{C}$ and ${X}_{6}^{C}$. These results have clear implications for the theory of operation of light-emitting diodes of GaAs and its alloys.

Perceived dimensions of interpersonal relations.

Abstract: A questionnaire study was conducted to discover the fundamental dimensions underlying people's perceptions of interpersonal relations. In the sections of the questionnaire relevant to this report, 87 subjects rated 20 of their own interpersonal relations (e.g., between you and your spouse) and 25 typical, or role, relations (e.g., between husband and wife) on numerous bipolar scales. A multidimensional scaling analysis of the data revealed four dimensions, which were interpreted as cooperative and friendly versus competitive and hostile, equal versus unequal, intense versus superficial, and socioemotional and informal versus task-oriented and formal. The relative importance of these dimensions varied systematically across various subgroups based on biographical characteristics of the subjects. The four dimensions were compared to those from studies of personality, person perception, and individual behavior in interpersonal situations. The stability of the dimensions suggests that they should provide a valuable framework for future research on interpersonal relations and communication.

Antisymmetric taper of distributed feedback lasers

Abstract: In a distributed feedback (DFB) laser with spatial index modulation, an antisymmetric taper of the feedback parameter, k , removes the threshold degeneracy, which is characteristic of uniform structures, and leads to one mode of particularly low threshold. Exact solutions are presented for the special case of an antisymmetric step of k . An approximate perturbation method is developed which gives simple expressions for the threshold gains, and external Q 's of some tapered distributed feedback structures. The method is tested against two exact solutions, the uniform, and the stepped- k DFB laser. It is shown that the threshold of the stepped- k DFB laser is the lowest of any structure with an antisymmetric taper and a prescribed maximum value of |k| .

The Complexity of Near-Optimal Graph Coloring

Abstract: Graph coloring problems, in which one would like to color the vertices of a given graph with a small number of colors so that no two adjacent vertices receive the same color, arise in many applications, including various scheduling and partitioning problems. In this paper the complexity and performance of algorithms which construct such colorings are investigated. For a graph G, let k(G) denote the minimum possible number of colors required to color G and, for any graph coloring algorithm A, let A(G) denote the number of colors used by A when applied to G. Since the graph coloring problem is known to be “NP-complete,” it is considered unlikely that any efficient algorithm can guarantee A(G) = k(G) for all input graphs. In this paper it is proved that even coming close to khgr;(G) with a fast algorithm is hard. Specifically, it is shown that if for some constant r d there exists a polynomial-time algorithm A which guarantees A(G) ≤ r·k(G) + d, then there also exists a polynomial-time algorithm A which guarantees A(G) = k(G).

Software tools

Abstract: Building on the work of others is the only way to make substantial progress in any field. Yet computer programming continues as a cottage industry because programmers insist on reinventing programs for each new application, instead of using what already exists. We must encourage a way of packaging programs so that they can be perceived as standard tools, each performing its specialized task sufficiently well and interfacing to other tools so conveniently that programmers seldom feel any need to make their own version from scratch.In this paper we show how programmers can view substantial parts of what they do as tool building and tool using. By studying some specific examples of general purpose tools, we show how programs can be packaged as tools, so other programmers will use them in preference to building their own. We also comment on the sort of programming environment which seems most hospitable to the development and use of tools.

Meaning, Memory Structure, and Mental Processes

Abstract: Although people experience little difficulty in recognizing printed words and comprehending sentences, they cannot do it instantaneously. Experimental psychologists have recently measured the speed of these mental processes by applying a reaction-time method. The method provides new data concerning the organization and retrieval of familiar semantic information in human memory. It has been found that close relations between the meanings of words help people to recognize and pronounce the words faster, especially when the words are hard to see because of visual distortions. Close relations between word meanings also facilitate the comprehension of some sentences, as indicated by how long a person takes to decide whether the sentences are true or false. The facilitation is not universal, however. When the relation between the meanings of two words must be analyzed carefully, their proximity may actually inhibit mental processing. These results, along with additional findings, support the hypothesis that human memory includes a semantic network that represents various categories of objects at distinct locations linked to specify their relations with each other. The memory structure probably influences a number of different mental processes that use it. One possible access route to the network is through a set of detectors designed to accumulate sensory information and signal the presence of particular words. There also appear to be processes for searching and comparing pieces of knowledge after a person finds the memory locations of designated categories. Further research using the reaction-time method may provide a more detailed inventory of what facts are retrieved directly from memory and what are computed from other stored information (36).