The Aerospace Corporation

Optodyne, Inc.

California Institute of Technology

The United States of America As Represented by the Administrator of the

Charles C Wang

Dean Jeffrey Sklar

Tien M Nguyen

Patrick Lawrence Smith

Hen-Geul Yeh

Lan Xu

James Yoh

Tsun-Yee Yan

Diana M Johnson

William Rafferty

Joe S Zhou

Khaled I Dessouky

Samuel Lim

Unjeng Cheng

An nth root transformation is used for generating near Gaussian metrics from non-Gaussian metrics for input into a conventional turbo decoder that is based on the assumption that the input sequence to the decoder has a Gaussian distribution. The nth root transformation transforms channel non-Gaussian statistics to near Gaussian statistics for use with conventional turbo decoding for improved noncoherent communications over a non-Gaussian channel, such as a fading channel. For a differential coherent PSK waveform, where the channel statistics of a demodulator are non-Gaussian, for example, in the presence of fading, the nth root transformation is used to transform the non-Gaussian statistics to near Gaussian statistics for generating near Gaussian metrics, for improved PSK communications.

Turbo decoding system using nth root metrics for non-Gaussian communication channels

Hierarchical modulation preferably uses a 16-ary quadrature amplitude modulation (QAM) modulator with a convolutional encoder that combine to effectively provide unequal protection to two different segments of streaming input data, with improved power efficiency with the same bandwidth efficiency, by encoding the first segment as coded data as LSBs as the second segment remains uncoded as uncoded MSBs, with the MSBs used for QAM constellation modest reliability interquadrant demodulation and detection, and with the LSBs used for low reliability intraquadrant detection, but with the LSBs subject to convolutional encoding and decoding rendering the LSBs with high reliability detection, such that, the two segments have unequal coding and modulation for providing unequal levels of reliability detection.

Unequal hierarchical communications modulation method

A parallel orthogonal frequency division multiplexed (OFDM) communications system includes a transmitter and receiver, the transmitter having a parallel fast Fourier transform (FFT) module operating in parallel to a conventional inverse fast Fourier transform (IFFT) module for providing respective orthogonal outputs received by the receiver. The receiver has a parallel IFFT module and a conventional FFT module for providing respective orthogonal outputs. The respective orthogonal outputs are combined to form a composite signal that provides improved insensitivity to relative frequency offsets and Doppler frequency offsets. The parallel FFT and IFFT modules in the OFDM communication system provides improved signal diversity and performance in the presence of relative frequency offsets and Doppler frequency offsets, and provides improved tracking capability for the receiver with backward compatibility.

Parallel orthogonal frequency division multiplexed communication system

A turbo coded communication system includes a gray scale mapper in a transmitter for generating a symbol constellation of modulated signals points that can be separated by boundary lines in the constellation space into bitwise groups of zero bits and one bits where the shortest distance from a boundary line to received value in the constellation space indicates the bitwise soft metrics that is computed using a set of bitwise soft metric equations are a function of a minimum angle using closed form algebraic equations in turbo decoding receiver. In the case of phase shift keying (PSK) modulation, the bit boundary lines are predetermined by a minimum angle in the constellation space for a specified M-ary modulation, so that, the soft metric equations are only a function of the received signal value for providing efficient computation of the bitwise soft metric.

M-Ary phase shift keying (PSK) bit-boundary turbo coded system

A turbo coded communication system includes a gray scale mapper in a transmitter for generating a symbol constellation of modulated signals points that can be separated by boundary lines in the constellation space into bitwise groups of zero bits and one bits where the shortest distance from a boundary line to received value in the constellation space indicates the bitwise soft metrics that is computed using a set of bitwise soft metric equations are a function of the minimum distance using closed form algebraic equations in turbo decoding receiver. In the case of quadrature amplitude modulation (QAM), the bit boundary lines are predetermined by a minimum distance in the constellation space for a specified M-ary modulation, so that, the soft metric equations are only a function of the received signal value for providing efficient computation of the bitwise soft metric.

M-Ary quadrature amplitude modulation (QAM) bit-boundary turbo coded system

Turbo decoding system using NTH root metrics for non-Gaussian communication channels

The degree to which a rotating object like a machine tool spindle undesirably wobbles in directions both transverse and parallel to its axis of rotation is measured preferably by providing a laser beam or other beam energy source which directs the beam toward a beam reflecting surface, most advantageously a curved surface, like a spherical or cylindrical surface. The reflecting surface is most advantageously formed by a spherical body mounted for adjustment in a plane perpendicular to the rotating axis involved, so that the center of the curved surface can be positioned as close as possible to the axis involved before error measurements are taken. In such case, the distance the beam traverses between the beam source and the point on the curved surface struck by the beam is a measure of the degree to which the spindle undesirably wobbles in directions both transverse to and parallel to the spindle axis. The beam source and the beam traverse distance measuring means can be a commercially available laser head which by use of focussing means, if needed, returns the reflected beam to the laser head which is designed to produce beam traverse distance measurement data.

Method and apparatus for measuring displacement or motion error

An adaptive predistorter system receives and predistorts an input signal so as to linearize the output signal of a nonlinear high power amplifier amplifying the predistorted input signal using closed-loop feedback of the output signal in complex form at baseband so as to adaptively change the amount of the predistortion of the input signal in the presence of high power amplifier changing characteristics.

High power amplifier predistorter system

A method of obtaining by use of a laser measuring apparatus position measurement error information of a body to be moved under computer control in a volumetric space along paths having designated measuring points for position error evaluation or correction. The method in a preferred form includes the steps of directing a laser beam in a given direction in said space and placing a laser beam reflector on the body to be moved in directions non-parallel to said direction, the reflector being sufficiently large that it will receive and reflect said directed laser beam back to said apparatus for actual reflector distance measurement along the beam path as said body is so moved. Then, with the computer of said system moving said body along said non-parallel paths measuring and recording with said apparatus the actual positions of said reflector along said beam path as the body reaches said various measuring points. The actual reflector position measurements are compared with the ideal reflector measurements and from the reflector position error so determined the body position error components at said measuring points are computed.

Vector measurement for coordinate measuring machine

The degree of accuracy a machine tool or the like is moved along a given path is determined by a unique preferably laser beam directing measuring system directing simultaneously or in sequence a laser beam parallel to the orthogonal axes of the two or three dimensional space in which the spindle or other object is to be moved in a path which can diverge appreciably in directions other than the directions of these axes. The beam directing means includes means which provides a measure of the actual positions the object has at various sampling times relative to the axis along which the beam is directed. This actual path position data is compared to the desired path position data used to program the object moving machine to determine the path position error at the sampling times involved.

Tool path measurement

The turbo coding system combines: a) repetitive turbo encoder bit partitioning and decoder bit deletion; with b) error-floor mitigating encoder non-flushing the second constituent encoder with the second a-posteriori probability (APP) decoder starting backward recursion from any possible states as a powerful improvement to conventional turbo coding. The repetitive turbo encoding process repeats the bits of the systematic root sequence and appends flushing sequence prior to interleaving and encoding by the second constituent turbo encoder for providing an interleaved repetitive second encoded output for turbo decoding. The error-floor mitigating turbo encoding process does not flush the second constituent encoder to the zero ending state so that turbo decoding forward recursion may be end in any possible state and backward recursion may start from any possible state to avoid potential mismatches between the forward and backward recursions. The modified a posterior probability second decoder initializes the beginning state metric of the backward recursion with the ending state metric of the forward recursion. The two processes provide significant bit error rate improvement. Iterative decoding provides iterative results that are subject to majority voting selection for improved estimations of the decoded systematic data sequence.

Error-floor mitigated and repetitive turbo coding communication system

The turbo encoding process does not flush tail bits of the second constituent encoder at the end of a block systematic data so that this second constituent encoder is not placed in a known zero ending state but placed in any possible ending state from which backward recursion starts at all possible beginning states during decoding to estimate the systematic data while avoiding potential mismatches between the forward and backward recursions during decoding, and between the systematic and second parity-check tail bits during decoding. The modified a posterior probability second decoder implements the backward recursion starting from all possible states. Significant bit error rate improvement is had without a significant error floor in the range of interest. Iterative decoding provides iterative results that are subject to majority voting selection for improved estimations of the decoded systematic data sequence.

Error-floor mitigating turbo code communication method

The turbo encoding process repeats the bits of the systematic data and appends the flushing tail bits prior to interleaving and encoding by the second constituent turbo encoder for providing an interleaved repetitive second encoded output for turbo decoding as a repetitive turbo code method to reduce the error floor of turbo coding. Preferably, the repetitive systematic string is also encoded by the first encoder and is transmitted providing repetitive transmitted first encoded sequence and a repetitive transmitted systematic sequence from the turbo encoder. The turbo decoder operates on three repetitive sequences and perform bit deletion among r repetitive systematic bits after conventional turbo decoding. The repetitive sequences may also be subjected to encoder puncturing and decoder bit insertion as an alternative enhancement.

Repetitive turbo coding communication method

A satellite communications system includes an orbiting communications satellite for relaying communications to and from a plurality of ground stations, and a network management center for making connections via the satellite between the ground stations in response to connection requests received via the satellite from the ground stations, the network management center being configured to provide both open-end service and closed-end service. The network management center of one embodiment is configured to provides both types of service according to a predefined channel access protocol that enables the ground stations to request the type of service desired. The channel access protocol may be configured to adaptively allocate channels to open-end service and closed-end service according to changes in the traffic pattern and include a free-access tree algorithm that coordinates collision resolution among the ground stations.

Land-mobile satellite communication system

A Michelson-type self-aligning interferometer utilizes a laser to produce an output beam of light that is split into signal and reference beams. The signal beam is directed through a Bragg-cell, for heterodyne detection, and a beam expander, for facilitating target acquisition, toward a retroreflector located on a target body. The signal beam is thereby reflected back through the beam expander and Bragg-cell toward the resonance mirror of the laser, and is now shifted in frequency by 2.OMEGA.. The returning signal beam remains co-linear with the output beam since it returns over the same path and through the same optical elements, especially the laser resonance mirror. Thus, the interferometer can accommodate a significant amount of component misalignment without loss of operation. The signal beam, once reflected from the resonance mirror of the laser and partially reflected by the beam splitter, is co-linear with the reference beam. The signal beam and reference beam are directed into a detector to produce an electrical signal. A frequency divider and a phase demodulator extract the phase of the electrical signal through heterodyne detection, the phase being proportional to the position of the retroreflector and, hence, the target body.

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Arcadia, CA, United States of America

Charles C Wang