Showing papers on "Offset (computer science) published in 1997"

ML estimation of time and frequency offset in OFDM systems

Abstract: We present the joint maximum likelihood (ML) symbol-time and carrier-frequency offset estimator in orthogonal frequency-division multiplexing (OFDM) systems. Redundant information contained within the cyclic prefix enables this estimation without additional pilots. Simulations show that the frequency estimator may be used in a tracking mode and the time estimator in an acquisition mode.

Timing and frequency synchronization of OFDM signals

Abstract: A method and apparatus achieves rapid timing synchronization, carrier frequency synchronization, and sampling rate synchronization of a receiver to an orthogonal frequency division multiplexed (OFDM) signal. The method uses two OFDM training symbols to obtain full synchronization in less than two data frames. A first OFDM training symbol has only even-numbered sub-carriers, and substantially no odd-numbered sub-carriers, an arrangement that results in half-symbol symmetry. A second OFDM training symbol has even-numbered sub-carriers differentially modulated relative to those of the first OFDM training symbol by a predetermined sequence. Synchronization is achieved by computing metrics which utilize the unique properties of these two OFDM training symbols. Timing synchronization is determined by computing a timing metric which recognizes the half-symbol symmetry of the first OPDM training symbol. Carrier frequency offset estimation is performed in using the timing metric as well as a carrier frequency offset metric which peaks at the correct value of carrier frequency offset. Sampling rate offset estimation is performed by evaluating the slope of the locus of points of phase rotation due to sampling rate offset as a function of sub-carrier frequency number.

Monolithic magnetic Hall sensor using dynamic quadrature offset cancellation

Abstract: The offset voltage and its temperature drift and production spread, which generally degrades the zero-level stability and reproducibility of magnetic Hall sensors, can be reduced using a single Hall plate and switching means for periodic permutation of the supply and output contact pairs. The present work describes a chopper-based 5-V monolithic linear Hall sensor with a /spl plusmn/0.1 T full scale where this dynamic plate offset cancellation technique has been employed together with a cost-effective signal conditioner. The device was integrated using a 2-/spl mu/m conventional BiCMOS process and the final chip, measuring 15/spl times/1.5 mm/sup 2/, shows, after packaging in a 3-pin plastic package, a residual offset with a production spread and a temperature-induced drift five to ten times smaller than in currently used multiplate dc quadrature cancellation approaches. The device does not require external components and provides an output free of HF residues.

A high efficiency carrier estimator for OFDM communications

Abstract: In OFDM communications, the loss of orthogonality due to carrier offset must be compensated before DFT-based demodulation can be performed. We present two blind carrier offset estimation algorithms by exploiting the intrinsic structure information of OFDM signals. Both algorithms offer the accuracy of super resolution subspace methods, viz., MUSIC and ESPRIT, without involving computationally intensive subspace decompositions. Adaptation rules for implementation of one of the proposed algorithm are provided. Also derived is the Cramer-Rao bound of the carrier offset estimates with which the performance of the new algorithms is evaluated.

Comparing offset curve approximation methods

Abstract: Offset curves have diverse engineering applications, spurring extensive research on various offset techniques. In a paper on offset curve approximation (Lee et al., 1996), we suggested a new approach based on approximating the offset circle instead of the offset curve itself. To demonstrate the effectiveness of this approach, we compared it extensively with previous methods. To our surprise, Tiller and Hanson's (1984) simple method outperforms other methods for offsetting (piecewise) quadratic curves, even though its performance is not as good for high degree curves. The experimental results revealed other interesting facts, too. Had these details been reported several years ago, we believe offset approximation research might have developed somewhat differently. This article is intended to fill an important gap in the literature. We conducted qualitative as well as quantitative comparisons employing various contemporary offset approximation methods for freeform curves in the plane. We measured the efficiency of the offset approximation in terms of the number of control points generated while making the approximations within a prescribed tolerance.

Offset optics for use with optical heads

Abstract: An optical head (107) is provided for transmission of light between a source (101) and a storage location (107) along an optical path that includes at least one offset optical element.

Fast similarity search in the presence of longitudinal scaling in time series databases

Abstract: The problem of finding patterns of interest in time series databases (query by content) is an important one, with applications in virtually every field of science. A variety of approaches have been suggested. These approaches are robust to noise, offset translation, and amplitude scaling to varying degrees. However, they are all extremely sensitive to scaling in the time axis (longitudinal scaling). We present a method for similarity search that is robust to scaling in the time axis, in addition to noise, offset translation, and amplitude scaling. The method has been tested on medical, financial, space telemetry and artificial data. Furthermore the method is exceptionally fast, with the predicted 2 to 4 orders of magnitude speedup actually observed. The method uses a piecewise linear representation of the original data. We also introduce a new algorithm which both decides the optimal number of linear segments to use, and produces the actual linear representation.

Data encoding method and apparatus for outputting encoded data at a designated time

Abstract: There occurs an output timing lag between audio and video, for example, in case of building a system. Excessive frame skipping, etc. occurs. Prior to comparing a PTS and an SCR of MPEG within an apparatus, an offset value is added to the value of PTS. A minus offset value is used for a fast decode process. Offset values are written into an audio offset value register etc. by a host CPU. A value obtained by adding PTS and an offset value and an internal clock SSC depending on an SCR are compared by an adder-subtracter. If comparison shows the decode process is still fast, a decision controller instructs, for example, display of the same frame twice.

Die-cavity pocketing via cutting simulation

Abstract: For die-cavity pocketing, the cavity volume is sliced into a number of cutting-layers by horizontal cutting-planes, and each layer is pocket-machined using the contour-parallel offset method in which the tool-paths are obtained by repeatedly offsetting the boundary-pocketing curve. The major challenges in die-cavity pocketing include: 1) finding a method for obtaining the boundary-pocketing curve, 2) generating evenly spaced contour-parallel offset toolpaths, 3) detecting and removing uncut-regions, and 4) estimating chip-loads for an adaptive feed control. No systematic solution for these problems has been offered in the literature, except the curve offsetting methods for computing contour-parallel offset curves. Presented in the article is a straightforward approach to die-cavity pocketing, in which all the four challenges are handled successfully by using the existing cutting-simulation methods.

Outer-vehicle monitoring device

Abstract: PROBLEM TO BE SOLVED: To reduce data processing amounts, and to surely recognize a remote three- dimensional object by effectively using the information of the already detected three- dimensional object. SOLUTION: A distance picture from an image processor 20 is read in a computer 30 for processing a picture, the presence or absence of a three-dimensional object and distance data of are calculated for each block of the distance picture, the present position of the three-dimensional object which is detected by the previous recognizing processing is estimated, and an area surrounding the estimated position of this three- dimensional object is set. Then, the distance data in this area are extracted and grouped, those in which the distance of each block is adjacent are gathered as a group, and the group is divided at a part where the lining direction of the data is largely changed for each group. Afterwards, the groups are reunited from the mutual position relation of each group, one three-dimensional object is recognized as the combination of an object and a side wall, and a parameter such as the position and back and forth and right and left moving speed of the three-dimensional object is calculated. Thus, the calculation processing is reduced, and the stability of the recognized result of the remote three-dimensional object whose stability has some problems in a conventional way is improved. COPYRIGHT: (C)1998,JPO

Vision-based lateral control of vehicles

Abstract: We describe the problem of automated steering using computer vision, focusing the analysis and design on appropriate lateral controllers. We investigate various static feedback strategies where the measurements obtained from vision, namely offset from the center line at some lookahead distance and the angle between the road tangent and the orientation of the vehicle at some lookahead distance, are directly used for control. Within this setting we explore the role of lookahead, its relation to the vision processing delay, the longitudinal velocity and road geometry. Results from ongoing experiments with our autonomous vehicle system are presented along with simulation results.

Design and stability analysis of a lane following controller

Abstract: This paper considers the design and stability analysis of a steering controller. The objective of the controller is to steer a ground vehicle along a reference line located in the middle of the lane to be followed. We define an arbitrary look-ahead point located on the local longitudinal axis of the vehicle. The distance between the look-ahead point and the reference line is called the look-ahead offset. During perfect lane tracking, the ratio of the steer angle to the look-ahead offset is independent of the curve radius under reasonable approximations. That ratio is computed in terms of the vehicle speed and various vehicle parameters. Then, a constant controller is designed to achieve that ratio at steady state. The controller is a continuous function of the vehicle speed. The only information processed by the controller is the look-ahead offset, which can be measured using a radar-based or a vision-based sensor. Using Routh-Hurwitz analysis, we analytically prove that the closed-loop system is stable. Given any range of longitudinal speeds, there exists a sufficiently large look-ahead distance ensuring the closed-loop stability for all speeds in that speed range. For a particular set of parameter variations, it is also shown that choosing the look-ahead distance large enough guarantees the robustness of closed-loop stability, Various simulation results demonstrating the performance of the controller are included.

Optical disc and optical disc driving apparatus

Abstract: An optical disc using a single-spiral land and groove track format enabling accurate tracking offset correction and reliable detection of the transition point between a land track and a groove track, and a driving apparatus therefor, are disclosed. Four physical address areas PID1, PID2, PID3, and PID4 are recorded to a header aera such that PID1 and PID2 are offset one-half track pitch toward the outside circumference of the disc from the groove track center, and PID3 and PID4 are offset one-half track pitch toward the inside circumference of the disc from the groove track center, and the physical address areas PID1 - PID4 can be detected by means of a difference signal in the radial direction. The single frequency pattern area VFO at the beginning of each PID is lengthened by PID1 and PID3, thereby enabling tracking offset correction using a sum signal, and detection of the land-groove transition point using a difference signal obtained from the PID offset.

Garbage collection system and method for locating root set pointers in method activation records

Abstract: In an object oriented computer system, a root set of object references includes object references stored in the computer system's registers, as well as object references stored in activation records in the program stack. Whenever a method is invoked, a corresponding activation record is stored on the program stack. The activation record includes the invocation address for the method called as well as parameters passed to the called method. A class loader, which loads object classes into memory, determines the locations of the object references in the activation records associated with each method in a loaded object class. A list of offset values for each method activation record is stored by the class loader in a hash table data structure at a location in the hash table data structure determined by hashing the unique invocation address assigned to the method. At the beginning of each garbage collection cycle, a root set locator procedure processes each activation record in the program stack by applying a hash function to the invocation address in the activation record to determine where in the hash table data structure to locate the object reference offsets for that activation record. Using the located object reference offsets, each of the object references in the activation record is added to a root set list. The number of processor cycles required to locate and copy all the object references in activation records in the program stack is a linear function of the number of such object references.

Method for display time stamping and synchronization of multiple video object planes

Abstract: A method of encoding a local time base embedded in the compressed data is disclosed. The local time base is encoded in two parts. The first part has a modulo time base that indicates the specific interval in the reference time base and the second part has a time base increment relative to the reference time. Two forms of time base increment is used to allow for the possibility of different encoding order and displaying order. A mechanism for the synchronization of multiple compressed streams with local time base is also described. A time base offset mechanism is also used to allow finer granularity synchronization of the multiple compressed streams.

Method and digital receiver for receiving orthogonal frequency-division multiplexed signals

Abstract: A digital receiver uses a local oscillator to down-convert an orthogonal frequency-division multiplexed signal that has been modulated by differential phase-shift keying, and performs further processing to obtain a differentially demodulated array of phase values. According to a first aspect of the invention, the digital receiver detects a carrier offset, applies a corresponding phase correction to the values in the array, then shifts the entire array by an amount corresponding to the carrier offset. As a result, the local oscillator need be tuned only in a frequency range equal to the subcarrier spacing. According to a second aspect of the invention, the local oscillator is tuned within a range equal to the subcarrier spacing multiplied by a certain integer, the array is shifted by a multiple of this integer, and the phase correction is eliminated.

Cellular TDMA base station receiver with dynamic DC offset correction

Abstract: A receiver (10) corrects for dynamic DC offsets by utilizing an open loop predictive DC offset correction stage (18) to respond instantly to changes in AGC settings on a timeslot by timeslot basis. The receiver has an AC coupled baseband receiver and has memory (22) for storing calibration offset data (24 and 26) representing a calibration offset voltage value for each automatic gain control (AGC) state determined relative to a known reference value. The predictive DC offset stage (18) predicts a predictive DC offset correction value (74 and 76) for a selected timeslot using stored calibration offset data (24 and 26) and an average of stored calibration offset data corresponding to AGC states for all timeslots in a given frame.

The Optimal Tax Rate for Capital Income is Negative

Abstract: We examine the problem of optimal taxation in a dynamic economy with imperfectly competitive markets. We find that the optimal tax system will tend to provide subsidies for the purchase of capital goods to offset gaps between price and marginal cost. The average tax on capital income will be negative, even if pure profits are not taxed away and even if the alternative distortionary taxes have an infinite efficiency cost. These arguments hold even if it is necessary to tax consumption goods which also sell above marginal cost; the difference is that capital goods are intermediate goods and consumption goods are final goods. Since observed markups are greater for equipment than for construction, this analysis justifies the Investment Tax Credit's discrimination in favor of equipment over structures.

Linearizing offset cancelling white balancing and gamma correcting analog to digital converter for active pixel sensor imagers with self calibrating and self adjusting properties

Abstract: A novel analogue to digital (A/D) converter semiconductor integrated circuit intended for digitizing signals generated by a physical stimulus sensing electronic apparatus, and more particularly, for digitizing signals generated by an array of photo-integrator circuits of an active pixel sensor (APS) imaging device. The A/D converter is a modified single slope integration type, wherein the reference ramp signal exhibits predetermined nonlinearity and offset. The nonlinearity and offset of the reference ramp signal track the nonlinearity and offset components in the signal being digitized, the latter being nonlinearity and offset components contributed by sources appearing in advance of the A/D conversion point in the signal acquisition and processing path of a digital camera system. In particular, the ramp generator for an A/D converter intended for an APS imaging array is partly a replica of the active photo-integrator circuit used in the APS pixel array fabricated on the same semiconductor substrate as the APS array. The ramp generator differs from a photo-integrator in that it produces output by responding to input provided by a current source rather than a photo-sensing device. As the ramp generator and the signal path nonlinearities and offsets track regardless of manufacturing variations and variations in operating conditions, the A/D conversion process successfully linearizes and removes offsets from the signal path, self calibrating against manufacturing variations and self adjusting against variations in operating conditions. The A/D converter further provides white balancing and gamma correction functionality for APS imager cameras. White balancing is performed by using different valued current sources in the ramp generators providing A/D conversion reference ramp for each different color in the color space sampled by the APS array. Gamma correction is performed by clocking the counter of the A/D converter with a clock frequency varying with time. The A/D converter replaces costly and technically less effective digital signal processing (DSP) means which were previously required.

Double-Hall sensor with self-compensated offset

Abstract: A novel Double-Hall sensor is reported with a signal offset compensated by design It consists of two single Hall devices sharing the same active area The sensor detects the magnetic induction perpendicular to the chip surface The sensor signal is given by the difference of the Hall voltages of the two single devices They have almost equal offsets but magnetic responses of opposite sign due to structure symmetry This simple self-compensation efficiently reduces the offset to values below 2 mT at room temperature The thermal offset drift is lower than 11 /spl mu/T//spl deg/C The small-sized Double-Hall sensor requires only one voltage source and one differential amplifier for operation Therefore, the implementation of an accurate and inexpensive magnetic sensor microsystem with high cutoff frequency is straightforward

Method for the reception of multicarrier signals and related apparatus

Abstract: There are various methods for terrestrial transmission of digital multicarrier broadcast signals, having modulation types like OFDM, QPSK and QAM. A main concern in connection with such systems is synchronisation in case a receiver is switched on or tuned to another channel. Present receiver tuning concepts are based on the assumption that an acceptable number only of fixed center frequencies exists. Now, some broadcasters and national organisations are considering a lot of exceptions or, in general, additional large offset frequency positions in order to reduce the influence from and to other services in the same or neighbouring frequency sections. This will increase the amount of fixed channel numbers to be tuned and subsequently the size of the receiver memory and the scanning time for the entire set of frequencies. According to the invention, the time needed by the receiver to reach a given tuning point with adequate accuracy and to exclude the possibility that there is a system-compliant signal is reduced significantly by a special evaluation (EV2) of correlation values. After such decision the receiver can go ahead to the next tuning point. If, however, a system-compliant signal has been found - even with an offset - the multicarrier signal is further decoded in the normal way. The conformity check can also be carried out in the subsequent normal reception.

Fingerprint-reading system with integrated heating resistors

Abstract: A fingerprint-reading system including a sensor on which a finger, whose imprint is to be read, is pressed. The sensor has an active surface of elements sensitive to variations in temperature and integrated heating resistors that create a transient variation in the temperature of the sensitive elements thereby to generate temporary charges in each element when pressed by a finger. The charges are output in synchronism with creation of the transient variations in the temperature of the sensitive elements to provide stable images of the fingerprint which may be motionless. The output of the sensor enables real-time display of the fingerprint images and processing of authentication data. The heating resistor enables the sensor to produce stable images of a fingerprint by producing an internal excitation to offset the tendency of electrical charges, induced by variations of the physical temperature of the finger, from disappearing because the temperature of the finger has reached equilibrium.

Common angle imaging with offset plane waves

Abstract: Migration is commonly used as a wavefield focussing tool in the study of the variation of reflection amplitude with offset (AVO), or with angle of incidence at reflectors. Migrations are typically applied to common offset or common incident angle sections. In many processing systems, common angle sections are formed by simple l-d transformations from offset to angle of common midpoint (CMP) gathers based on ray tracing. In this paper, we provide a wave-equation framework for migrating common incidence angle sections that have been formed from Radon transforms over offset in CMP gathers. Radon transformation of the scalar wave equation results in an independent wave equation for each offset plane wave. The offset plane wave equation is nearly equivalent to the zero offset wave equation, except for an additional term related to dip in the midpoint direction, and to offset ray parameter (angle of incidence at the surface). Within this framework, finite difference, pseudo-spectral, and Kirchhoff migrations for common angle sections can be easily adapted from existing algorithms. The availability of a wave equation for common angle sections allows rigorous and efficient application of wave equation techniques for AVO studies and complex structural imaging problems.

Vehicle equipment rack

Abstract: A vehicle equipment rack that includes first, second and third rotatably interconnected members. The second and third members rotate between a first position in which all three members are aligned and a second position in which the second and third members are angularly offset from the first member. The second and third members may also angularly offset from one another when the second and third members are in the second position. The vehicle equipment rack may also include a drive train operatively connected between the second and third members. The drive train is configured to rotate one of these moveable members upon rotation of the moveable member.

System and method for PN offset index planning in a digital CDMA cellular network

Abstract: A system optimally assigns pseudo-noise (PN) offsets in a cellular network that includes several sectors. The system sets parameters for the cellular network, determines potential interference between each of the sectors and mobile units in the cellular network based on the set parameters, and identifies constraints for each of the sectors based on the determined potential interference. The system then approximates a highest co-offset protection value for successful PN offset assignments based on the determined potential interference and the identified constraints, and selectively adjusts a sector co-offset protection value using the approximated highest co-offset protection value as a starting point to obtain optimum PN offset assignments.

An Analog Integrated Circuit for Continuous-Time Gain andOffset Calibration of Sensor Arrays

Abstract: Parameter variations cause unavoidable nonuniformities in Infra-Red Focal Plane Arrays and other integrated sensors. Since these nonuniformities change slowly with time, calibrating sensors one-time only is not suitable–much more frequent calibration is required. We have developed an algorithm that continually calibrates an array of sensors that contain gain and offset variations. This algorithm has been mapped to analog hardware and designed and fabricated with a 2um CMOS technology. Measured results from the chip show that the system achieves invariance to gain and offset variations of the input signal.

Optical disc having oscillating lands and grooves

Abstract: In an optical disc, an ID field contains a plurality of address information, and is preliminarily recorded in convex and concave signals, and is composed of two sets offset by about 1/2 track pitch toward the internal or external track direction adjacent to the guide track, an information recording field is composed of grooves and lands oscillating at a single frequency in the radial direction, and the grooves and lands alternate in every revolution of the guide track. When w bits of information are included in one period of oscillation, an information unrecorded field between the ID field and information recording field is arranged to have a length of w/10 bits or more and/or w bits or less, and therefore, when recording continuous information data such as video data, it is possible to record continuously by generating a clock securely from the oscillating signal, and moreover, the format efficiency is improved, so that a format of a larger capacity is achieved.

Tuning system for achieving quick acquisition times for a digital satellite receiver

Abstract: The RF signals received from the LNB and the corresponding IF signal produced by the tuner may be offset in frequency due to reasons other than a frequency drift of the oscillator of the LNB, such as satellite transponder frequency adjustments made by the satellite transmission system. A tuner (9) includes a local oscillator (911) controlled by a controller. The controller (a) controls the frequency of the local oscillator (911); (b) stores digital nominal frequency representative words for respective ones of RF signals received; (c) stores digital offset representative words for respective ones of the RF signals; (d) determines a frequency offset of said carrier signal after a RF signal has been tuned; (e) updates all of the digital offset representative words in accordance with the frequency offset of the carrier; (f) derives the tuning representative word for an RF signal selected to be tuned by combining said nominal frequency representative word for the RF signal selected to be tuned with the previously updated offset representative word for the RF signal selected to be tuned; and (g) updates the respective digital offset representative word for an individual RF signal presently being tuned if correct tuning is not achieved with the previously updated offset representative word.