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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

MAVEN Relay Operations Concept

The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission will launch in late 2013 and following a 10 month cruise to Mars, will study the upper atmosphere of the planet. In addition to the science instruments, the MAVEN spacecraft is equipped with an Electra UHF transceiver to support relay communication with landed assets. This paper describes how UHF relay service is provisioned by MAVEN. The discussion includes a description of the Electra payload, the process by which relay activities are coordinated and accounted for, the process of a typical relay session, including uplink and downlink, as well as special commands to calibrate and verify relay performance. The operational processes for providing these services are inherited largely from prior Mars missions and take advantage of existing infrastructure and lessons learned from those missions. Preliminary data volume return capabilities using adaptive data rates and low-density parity check channel coding are presented.

Electra↗
NASA NTRS1994

Decoder Synchronization for Deep Space Missions

The Consultative committee for Space Data STandards (CCSDS) recommends that space communication links employ a concatenated error-correcting channel-coding system in which the inner code is a convolutional (7, 2/2) code and the outer code is a (255,223) Reed-Solomon code.

Decoder↗
NASA NTRS2020

The Use of the CCSDS Unified Space Data Link Protocol on All Space Links

NASA is actively pursuing the development of data link layer protocols for the human space program with the added intent of infusing the key capabilities of efficient space link security, support for inter-networking, and compatible operational modes with Optical Communications. There seems to be two divergent technical approaches on how to provide these capabilities: one associated with the use of a fixed length Protocol Data Unit (PDU) i.e., a fixed length transfer frame, and the other advocating the use of a variable length transfer frame. The objective of this paper is to evaluate the pros and cons of these two approaches within the context of existing Consultative Committee for Space Data Systems (CCSDS) Space Data Link Protocols and Channel Coding Recommendations for all space links: space to ground (return) link, ground to space (forward) link and space to space (proximity) links.

Kazz, Greg J↗
NASA NTRS1993

A simulation study of the performance of the NASA (2,1,6) convolutional code on RFI/burst channels

In an earlier report, the LINKABIT Corporation studied the performance of the (2,1,6) convolutional code on the radio frequency interference (RFI)/burst channel using analytical methods. Using an R(sub 0) analysis, the report concluded that channel interleaving was essential to achieving reliable performance. In this report, Monte Carlo simulation techniques are used to study the performance of the convolutional code on the RFI/burst channel in more depth. The basic system model under consideration is shown. The convolutional code is the NASA standard code with generators g(exp 1) = 1+D(exp 2)+D(exp 3)+D(exp 5)+D(exp 6) and g(exp 2) = 1+D+D(exp 2)+D(exp 3)+D(exp 6) and d(sub free) = 10. The channel interleaver is of the convolutional or periodic type. The binary output of the channel interleaver is transmitted across the channel using binary phase shift keying (BPSK) modulation. The transmitted symbols are corrupted by an RFI/burst channel consisting of a combination of additive white Gaussian noise (AWGN) and RFI pulses. At the receiver, a soft-decision Viterbi decoder with no quantization and variable truncation length is used to decode the deinterleaved sequence.

Perez, Lance C.↗
NASA NTRS1999

Punctured Parallel and Serial Concatenated Convolutional Codes for BPSK/QPSK Channels

As available bandwidth for communication applications becomes scarce, bandwidth-efficient modulation and coding schemes become ever important. Since their discovery in 1993, turbo codes (parallel concatenated convolutional codes) have been the center of the attention in the coding community because of their bit error rate performance near the Shannon limit. Serial concatenated convolutional codes have also been shown to be as powerful as turbo codes. In this dissertation, we introduce algorithms for designing bandwidth-efficient rate r = k/(k + 1),k = 2, 3,..., 16, parallel and rate 3/4, 7/8, and 15/16 serial concatenated convolutional codes via puncturing for BPSK/QPSK (Binary Phase Shift Keying/Quadrature Phase Shift Keying) channels. Both parallel and serial concatenated convolutional codes have initially, steep bit error rate versus signal-to-noise ratio slope (called the -"cliff region"). However, this steep slope changes to a moderate slope with increasing signal-to-noise ratio, where the slope is characterized by the weight spectrum of the code. The region after the cliff region is called the "error rate floor" which dominates the behavior of these codes in moderate to high signal-to-noise ratios. Our goal is to design high rate parallel and serial concatenated convolutional codes while minimizing the error rate floor effect. The design algorithm includes an interleaver enhancement procedure and finds the polynomial sets (only for parallel concatenated convolutional codes) and the puncturing schemes that achieve the lowest bit error rate performance around the floor for the code rates of interest.

Acikel, Omer Fatih↗
NASA NTRS1982

Demodulation of PPM for Reed-Solomon coded optical space channel

The paper proposes a delta-max demodulator for Reed-Solomon coded M-ary PPM modulation over optical (laser) channels including satellite-to-satellite and deep-space-vehicle-to-relay-satellite communications. This demodulator is compared with the threshold demodulator currently in use, and the two demodulators are shown to have identical performance in the absence of background noise. The delta-max demodulator is found to outperform the threshold demodulator as the intensity of background noise increases.

Divsalar, D.↗
NASA NTRS1990

New 16-PSK trellis codes for fading channels

Growth in satellite mobile communications leads to increasing requirements for high data rate transmission that can be met by more efficient modulation schemes (M greater than 8). The 16-PSK trellis coded modulation technique is a very promising solution. A class of new 16-PSK trellis codes with improved error rate are designed based on the criteria on fading channels.

Du, Jun↗
NASA NTRS1979

Coding for optical channels

In a previous paper Pierce considered the problem of optical communication from a novel viewpoint, and concluded that performance will likely be limited by issues of coding complexity rather than by thermal noise. This paper reviews the model proposed by Pierce and presents some results on the analysis and design of codes for this application.

Baumert, L. D.↗
NASA NTRS2006

Protograph LDPC Codes for the Erasure Channel

This viewgraph presentation reviews the use of protograph Low Density Parity Check (LDPC) codes for erasure channels. A protograph is a Tanner graph with a relatively small number of nodes. A "copy-and-permute" operation can be applied to the protograph to obtain larger derived graphs of various sizes. For very high code rates and short block sizes, a low asymptotic threshold criterion is not the best approach to designing LDPC codes. Simple protographs with much regularity and low maximum node degrees appear to be the best choices Quantized-rateless protograph LDPC codes can be built by careful design of the protograph such that multiple puncturing patterns will still permit message passing decoding to proceed

long erasure codes↗
NASA NTRS1993

Worldwide survey of direct-to-listener digital audio delivery systems development since WARC-1992

Each country was allocated frequency band(s) for direct-to-listener digital audio broadcasting at WARC-92. These allocations were near 1500, 2300, and 2600 MHz. In addition, some countries are encouraging the development of digital audio broadcasting services for terrestrial delivery only in the VHF bands (at frequencies from roughly 50 to 300 MHz) and in the medium-wave broadcasting band (AM band) (from roughly 0.5 to 1.7 MHz). The development activity increase was explosive. Current development, as of February 1993, as it is known to the author is summarized. The information given includes the following characteristics, as appropriate, for each planned system: coverage areas, audio quality, number of audio channels, delivery via satellite/terrestrial or both, carrier frequency bands, modulation methods, source coding, and channel coding. Most proponents claim that they will be operational in 3 or 4 years.

Messer, Dion D.↗
NASA NTRS2006

Protograph LDPC Codes Over Burst Erasure Channels

In this paper we design high rate protograph based LDPC codes suitable for binary erasure channels. To simplify the encoder and decoder implementation for high data rate transmission, the structure of codes are based on protographs and circulants. These LDPC codes can improve data link and network layer protocols in support of communication networks. Two classes of codes were designed. One class is designed for large block sizes with an iterative decoding threshold that approaches capacity of binary erasure channels. The other class is designed for short block sizes based on maximizing minimum stopping set size. For high code rates and short blocks the second class outperforms the first class.

protgraph based codes↗
NASA NTRS1987

Trellis-Coded Modulation for Fading Channels

In proposed communication system, digital signals transmitted efficiently over fading channel by combination of trellis coding and multiple-phase-shift keying with addition of asymmetry to signal set. Coding and modulation schemes not designed separately as in previous systems but integrated to yield bandwidth-efficient modulation and forward-error-correction coding. Helps to satisfy need for reliable high-quality transmission of voice and data between land-mobile units via satellites, where limitations of power and bandwidth imposed simultaneously. Also applicable to ionospheric communications between fixed or mobile units.

Simon, Marvin K.↗
NASA NTRS1980

Performance of convolutionally coded unbalanced QPSK systems

An evaluation is presented of the performance of three representative convolutionally coded unbalanced quadri-phase-shift-keying (UQPSK) systems in the presence of noisy carrier reference and crosstalk. The use of a coded UQPSK system for transmitting two telemetry data streams with different rates and different powers has been proposed for the Venus Orbiting Imaging Radar mission. Analytical expressions for bit error rates in the presence of a noisy carrier phase reference are derived for three representative cases: (1) I and Q channels are coded independently; (2) I channel is coded, Q channel is uncoded; and (3) I and Q channels are coded by a common 1/2 code. For rate 1/2 convolutional codes, QPSK modulation can be used to reduce the bandwidth requirement.

Divsalar, D.↗