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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Bandwidth efficient trellis-coded modulation with prescribed decoding delay - new interpretations and results

Motivated by previous work of Li and Rimoldi for obtaining bandwidth efficient TCM signals with finite decoding delay, we present an alternative representation for their encoder/signal mapper transmitter structure which merely consists of a single filter having an input equal to the equivalent of the inoput data bits in their implementation.

trellis coding bandwidth efficient modulation digi↗
NASA NTRS1996

(abstract) MCD3 - A Constraint Length 15 Viterbi Decoder

JPL is responsible for many space missions, as part of NASA's continuing unmanned exploration of the solar system. Signals from spacecraft at planetary distances arrive at Earth with poor S/N ratio. To reduce errors, the signals are encoded with an inner code of Viterbi encoding. One of the key parameters of Viterbi encoding is the constraint length. Previous space missions have used a constraint length of 7. Newer missions use 15, to give a considerably improved error correction ability. However, the complexity of the Viterbi decoder is increased so as to be 256 times more complex.

communications↗
NASA NTRS2005

Memory-efficient decoding of LDPC codes

We present a low-complexity quantization scheme for the implementation of regular (3,6) LDPC codes. The quantization parameters are optimized to maximize the mutual information between the source and the quantized messages. Using this non-uniform quantized belief propagation algorithm, we have simulated that an optimized 3-bit quantizer operates with 0.2dB implementation loss relative to a floating point decoder, and an optimized 4-bit quantizer operates less than 0.1dB quantization loss.

Low-Density-Parity-Check (LDPC)↗
NASA NTRS1998

Pre-coding method and apparatus for multiple source or time-shifted single source data and corresponding inverse post-decoding method and apparatus

A pre-coding method and device for improving data compression performance by removing correlation between a first original data set and a second original data set, each having M members, respectively. The pre-coding method produces a compression-efficiency-enhancing double-difference data set. The method and device produce a double-difference data set, i.e., an adjacent-delta calculation performed on a cross-delta data set or a cross-delta calculation performed on two adjacent-delta data sets, from either one of (1) two adjacent spectral bands coming from two discrete sources, respectively, or (2) two time-shifted data sets coming from a single source. The resulting double-difference data set is then coded using either a distortionless data encoding scheme (entropy encoding) or a lossy data compression scheme. Also, a post-decoding method and device for recovering a second original data set having been represented by such a double-difference data set.

Yeh, Pen-Shu↗
NASA NTRS1997

Pre-coding method and apparatus for multiple source or time-shifted single source data and corresponding inverse post-decoding method and apparatus

A pre-coding method and device for improving data compression performance by removing correlation between a first original data set and a second original data set, each having M members, respectively. The pre-coding method produces a compression-efficiency-enhancing double-difference data set. The method and device produce a double-difference data set, i.e., an adjacent-delta calculation performed on a cross-delta data set or a cross-delta calculation performed on two adjacent-delta data sets, from either one of (1) two adjacent spectral bands coming from two discrete sources, respectively, or (2) two time-shifted data sets coming from a single source. The resulting double-difference data set is then coded using either a distortionless data encoding scheme (entropy encoding) or a lossy data compression scheme. Also, a post-decoding method and device for recovering a second original data set having been represented by such a double-difference data set.

Yeh, Pen-Shu↗
NASA NTRS1997

Maximum a posteriori decoder for digital communications

A system and method for decoding by identification of the most likely phase coded signal corresponding to received data. The present invention has particular application to communication with signals that experience spurious random phase perturbations. The generalized estimator-correlator uses a maximum a posteriori (MAP) estimator to generate phase estimates for correlation with incoming data samples and for correlation with mean phases indicative of unique hypothesized signals. The result is a MAP likelihood statistic for each hypothesized transmission, wherein the highest value statistic identifies the transmitted signal.

Altes, Richard A.↗
NASA NTRS2011

Coding for Parallel Links to Maximize the Expected Value of Decodable Messages

When multiple parallel communication links are available, it is useful to consider link-utilization strategies that provide tradeoffs between reliability and throughput. Interesting cases arise when there are three or more available links. Under the model considered, the links have known probabilities of being in working order, and each link has a known capacity. The sender has a number of messages to send to the receiver. Each message has a size and a value (i.e., a worth or priority). Messages may be divided into pieces arbitrarily, and the value of each piece is proportional to its size. The goal is to choose combinations of messages to send on the links so that the expected value of the messages decodable by the receiver is maximized. There are three parts to the innovation: (1) Applying coding to parallel links under the model; (2) Linear programming formulation for finding the optimal combinations of messages to send on the links; and (3) Algorithms for assisting in finding feasible combinations of messages, as support for the linear programming formulation. There are similarities between this innovation and methods developed in the field of network coding. However, network coding has generally been concerned with either maximizing throughput in a fixed network, or robust communication of a fixed volume of data. In contrast, under this model, the throughput is expected to vary depending on the state of the network. Examples of error-correcting codes that are useful under this model but which are not needed under previous models have been found. This model can represent either a one-shot communication attempt, or a stream of communications. Under the one-shot model, message sizes and link capacities are quantities of information (e.g., measured in bits), while under the communications stream model, message sizes and link capacities are information rates (e.g., measured in bits/second). This work has the potential to increase the value of data returned from spacecraft under certain conditions.

Klimesh, Matthew A.↗
NASA NTRS2018

Systems and Methods for Transmitting Data Using Parallel Decode Capacity Optimized Symbol Constellations

Transmitters are described that use non-uniformly spaced symbol constellations that have increased capacity compared to conventional constellations. In many embodiments, a transmitter includes a coder configured to receive bits and output encoded bits, a mapper configured to map said encoded bits to symbols in a non-uniform symbol constellation selected from a plurality of symbol constellations, and a modulator configured to generate a signal for transmission via the communication channel using symbols generated by the mapper. In a variety of embodiments, wherein the non-uniform symbol constellation comprises a set of non-uniformly spaced constellation points, and the location points in the non-uniform symbol constellation are chosen to optimize parallel decode capacity of the non-uniform symbol constellation subject to at least one optimization constraint. In many embodiments, the non-uniform symbol constellation is a quadrature amplitude modulation constellation or a phase shift keyed constellation.

Barsoum, Maged F.↗
DOE OSTI2025

MSU IETC LSTM Ethernet Decode (AN EDGE)

This research explores the ability of machine learning to perform signal separation of an Ethernet style encoded, full-duplex communication. Typical signal separation currently requires an active tap of the communication line, followed by a recombination and retransmission of the data. The purpose of this research is to study a passive approach to data acquisition from a full-duplex signal. The machine learning model used in this research is a long-short-term memory recurrent neural network (LSTM-RNN). The results show that the LSTM was largely successful in recreating the transmission signal from the measured data points, though the separated signals have not yet been tested using a decoding method.

Full Duplex Signals↗
NASA NTRS1994

Enhanced Decoding for the Galileo Low-Gain Antenna Mission

Due to a malfunctioning high-gain antenna, the Galileo spacecraft is transmitting all its data through a low-gain antenna, and the data rate will seldom exceed 100 bits per second during its two-year tour of Jupiter's satellites.

decoder Viterbi decoder Reed-Solomon baseline codi↗
NASA NTRS2001

Improving turbo-like codes using iterative decoder analysis

The density evolution method is used to analyze the performance and optimize the structure of parallel and serial turbo codes, and generalized serial concatenations of mixtures of different outer and inner codes. Design examples are given for mixture codes.

turbo codes iterative decoding↗