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DOE OSTI2025

Evidence for triaxial shape coexistence in 74 Ge

The deformation properties of the low-lying states in 74 Ge have been investigated using multistep Coulomb excitation. The measurements were carried out with the advanced 𝛾-ray tracking array, GRETINA, and the CHICO2 particle detector. A comprehensive set of 𝐸⁢2 transition and diagonal matrix elements was deduced following an analysis with the semiclassical coupled-channels code GOSIA. The data were compared with results of calculations carried out within the framework of the generalized triaxial rotor model as well as with the configuration interaction shell model and the symmetric rotor model. Results from calculations with covariant density functional theory were used to construct a five-dimensional collective Hamiltonian for further comparisons with the data. Collectively, the calculations provide an accurate reproduction of the experimental matrix elements and further support an understanding in terms of the coexistence of two axially asymmetric shapes. In conclusion, this leads to an overall interpretation of the underlying structure of 74 Ge requiring triaxiality, as is also the case in the neighboring even-mass Ge isotopes.

59 ≤ A ≤ 89↗

NASA NTRS1975

College curriculum-sharing via CTS

Domestic communication satellites and video compression techniques will increase communication channel capacity and reduce cost of video transmission. NASA Ames Research Center, Stanford University and Carleton University are participants in an experiment to develop, demonstrate, and evaluate college course sharing techniques via satellite using video compression. The universities will exchange televised seminar and lecture courses via CTS. The experiment features real-time video compression with channel coding and quadra-phase modulation for reducing transmission bandwidth and power requirements. Evaluation plans and preliminary results of Carleton surveys on student attitudes to televised teaching are presented. Policy implications for the U.S. and Canada are outlined.

Hudson, H. E.↗

NASA NTRS1977

Advanced imaging communication system

Key elements of system are imaging and nonimaging sensors, data compressor/decompressor, interleaved Reed-Solomon block coder, convolutional-encoded/Viterbi-decoded telemetry channel, and Reed-Solomon decoding. Data compression provides efficient representation of sensor data, and channel coding improves reliability of data transmission.

Hilbert, E. E.↗

NASA NTRS1975

Digital TV processing system

Two digital video data compression systems directly applicable to the Space Shuttle TV Communication System were described: (1) For the uplink, a low rate monochrome data compressor is used. The compression is achieved by using a motion detection technique in the Hadamard domain. To transform the variable source rate into a fixed rate, an adaptive rate buffer is provided. (2) For the downlink, a color data compressor is considered. The compression is achieved first by intra-color transformation of the original signal vector, into a vector which has lower information entropy. Then two-dimensional data compression techniques are applied to the Hadamard transformed components of this last vector. Mathematical models and data reliability analyses were also provided for the above video data compression techniques transmitted over a channel encoded Gaussian channel. It was shown that substantial gains can be achieved by the combination of video source and channel coding.

Source record↗

NASA NTRS1975

An advanced imaging communication system for planetary exploration

An advanced imaging communication system (AICS) for planetary exploration is presented. The system offers 'end-to-end' information rate improvements of 3 to 5 times over existing systems in addition to extensive user flexibility to adapt his rate/fidelity priorities to fit a particular mission. AICS contains two major system elements. The first is a concatenated Reed-Solomon/Viterbi coded channel. This provides a powerful, yet practical, solution to the usual 'error vulnerability' problem associated with compressed data. The second major element is an extremely adaptive image data compression algorithm called RM2. The details of this algorithm as presently simulated are discussed in considerable detail. Used in conjunction with the virtually error free performance of the Reed-Solomon/Viterbi channel the stated AICS advantages are obtained.

Rice, R. F.↗

NASA NTRS1983

The impact of mismatch on the performance of coded narrow-band FM with limiter/discriminator detection

An examination of the impact of mismatch on the performance of convolutionally encoded/Viterbi decoded narrow-band FM with limiter/discriminator detection is presented. Attention was given to the potential gain available by the combination of this type of system in terms of hard and soft decision decoding. Soft decision decoding was demonstrated to offer only approximately 0.3 dB better performance than hard decision coding. It was also shown, through a technique involving the number of clicks occurring in each detection interval, that both soft and hard decision decoding bit error probability performance could be improved. It is concluded that the mismatch between the coding channel and the decoding metric of the Viterbi algorithm is responsible for reducing the difference between hard and soft decoding metrics.

Simon, M. K.↗

NASA NTRS1985

Standards for space data systems

NASA has chaired the Consultative Committee for Space Data Systems (CCSDS) for the past four years. During that time, a top-level, end-to-end reference model for space data sytems has been developed that identifies the functions anad services which must be provided by space data systems, and defines the interfaces between major functional elements. A group of definitions for standard protocols has been derived by analyzing these interfaces, and a set of detailed guidelines for space data system standards is in the final stages of negotiation among member CCSDS agencies. Two guidelines that address packet telemetry and channel coding have been approved and are being incorporated into the internal standards of member agencies. Others (packet telecommand, time code, standards data format unit) are in review within CCSDS technical panels and will soon be submitted for approval. These guidelines provide a mechanism for significant cost savings in the implementation of space data systems by allowing reuse of hardware and software for different payloads and for missions, and by enabling the substitution of new technology/higher performance elements at key points in the data system without causing major perturbations in the remainder of the system.

Connell, E. B.↗

NASA NTRS1986

A new method for frame synchronization

A frame synchronization method based on an examination of the shortest bit length containing all error bursts is introduced. It is shown that the new method is more reliable and efficient than the commonly used one based on counting the number of errors for the convolutionally coded channel.

Shahshahani, M.↗

NASA NTRS1987

Digital modulation for an aeronautical mobile satellite system

A review is provided of radio technology, particularly signal modulation, in a satellite-based aeronautical communication system. The propagation environment is examined, and a generic signal-detection strategy is established. The following are then covered: signal bandwidth and carrier modulation; power performance; error detection and block coding; channel spacing; the modulator and demodulator; and coarse frequency error detection.

Davarian, F.↗

NASA NTRS1990

Application of CCSDS packet telemetry recommendations by JPL

The Consultative Committee for Space Data Systems (CCSDS) has adopted three Recommendations dealing with telemetry for conventional missions: Packet Telemetry, Telemetry Channel Coding and Time Code Formats. The currently flying JPL spacecraft were designed prior to the adoption of these Recommendations. Future JPL missions will be compatible, as will the Deep Space Network and Space Flight Operations Center. This paper discusses ways in which application of the Recommendations causes or allows functions to be done differently from previous JPL projects, including the impact on timing and on telemetry adaptability.

Moyd, K. I.↗

NASA NTRS1991

Use of residual redundancy in the design of joint source/channel coders

A technique for providing error protection without the additional overhead required for channel coding is developed, starting from the premise that, during source coder design, for the sake of simplicity or due to imperfect knowledge, assumptions have to be made about the source which are often incorrect. This results in residual redundancy at the output of the source coder. The residual redundancy can then be used to provide error protection in much the same way as the insertion of redundancy in convolutional coding provides error protection. To show the validity of this approach, it is applied to image coding using differential pulse code modulation (DPCM). Substantial performance gains are obtained, in terms of both objective and subjective measures.

Sayood, Khalid↗

NASA NTRS1990

MSAT voice modulation considerations

The challenge for Mobile satellite (MSAT) voice services is to provide near toll quality voice to the user, while minimizing the power and bandwidth resources of the satellite. The options for MSAT voice can be put into one of two groups: Analog and Digital. Analog, nominally narrowband single sideband techniques, have a shown robustness to the fading and shadowing environment. Digital techniques, a combination of low rate vocoders and bandwidth efficient modems, show the promise of enhanced fidelity, as well as easier networking to the emerging digital world. The problems and tradeoffs to designers are many, especially in the digital case. Processor speed vs. cost and MET power requirements, channel coding, bandwidth efficiency vs. power efficiency etc. While the list looks daunting, in fact an acceptable solution is well within the technology. The objectives are reviewed that the MSAT voice service must meet, along with the options that are seen for the future.

Bossler, Dan↗

NASA NTRS1992

Deep space communications technology thrusts

The paper discusses the technology thrusts that are currently being developed for deep space missions as well as the expected dividends of these thrusts during the 1990's and beyond. Particular attention is given to Ka-band (32 GHz) development, channel coding, source coding, and optical communications. The ongoing development described here attempts to meet the telecommunications demands of future missions by stressing cooperative developments between ground networks and flight projects in order to optimize NASA's overall investment in solar system investment.

Yuen, Joseph H.↗

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 (7,1/2) code and the outer code is a (255,223) Reed-Solomon code. The traditional implementation is to perform the node synchronization for the Viterbi decoder and the frame synchronization for the Reed-Solomon decoder as separate, sequential operations. This article discusses a unified synchronization technique that is required for deep space missions that have data rates and signal-to-noise ratios (SNR's) that are extremely low. This technique combines frame synchronization in the bit and symbol domains and traditional accumulated-metric growth techniques to establish a joint frame and node synchronization. A variation on this technique is used for the Galileo spacecraft on its Jupiter-bound mission.

Statman, J. I.↗

NASA NTRS1994

System considerations for efficient communication and storage of MSTI image data

The Ballistic Missile Defense Organization has been developing the capability to evaluate one or more high-rate sensor/hardware combinations by incorporating them as payloads on a series of Miniature Seeker Technology Insertion (MSTI) flights. This publication represents the final report of a 1993 study to analyze the potential impact f data compression and of related communication system technologies on post-MSTI 3 flights. Lossless compression is considered alone and in conjunction with various spatial editing modes. Additionally, JPEG and Fractal algorithms are examined in order to bound the potential gains from the use of lossy compression. but lossless compression is clearly shown to better fit the goals of the MSTI investigations. Lossless compression factors of between 2:1 and 6:1 would provide significant benefits to both on-board mass memory and the downlink. for on-board mass memory, the savings could range from $5 million to $9 million. Such benefits should be possible by direct application of recently developed NASA VLSI microcircuits. It is shown that further downlink enhancements of 2:1 to 3:1 should be feasible thorough use of practical modifications to the existing modulation system and incorporation of Reed-Solomon channel coding. The latter enhancement could also be achieved by applying recently developed VLSI microcircuits.

Rice, Robert F.↗

NASA NTRS1995

Joint Synchronization Of Viterbi And Reed-Solomon Decoders

Synchronization times reduced to reduce loss of data. Scheme for decoding received doubly encoded binary-data signal provides for joint synchronization of two decoders. Applies to concatenated error-correcting channel coding communication system in which, at transmitter, data first encoded by interleaved Reed-Solomon code (block code), then by convolutional code.

Statman, Joseph I.↗

NASA NTRS1997

The Implications of Encoder/Modulator/ Phased Array Designs for Future Broadband LEO Communications

In this paper we summarize the effects of modulation and channel coding on the design of wide angle scan, broadband, phased army antennas. In the paper we perform several trade studies. First, we investigate the amplifier back-off requirement as a function of variability of modulation envelope. Specifically, we contrast constant and non-constant envelope modulations, as well as single and multiple carrier schemes. Additionally, we address the issues an(f concerns of using pulse shaping filters with the above modulation types. Second, we quantify the effects of beam steering on the quality of data, recovery using selected modulation techniques. In particular, we show that the frequency response of the array introduces intersymbol interference for broadband signals and that the mode of operation for the beam steering controller may introduce additional burst or random errors. Finally, we show that the encoder/modulator design must be performed in conjunction with the phased array antenna design.

Vanderaar, Mark↗

NASA NTRS2010

High-Performance CCSDS AOS Protocol Implementation in FPGA

The Consultative Committee for Space Data Systems (CCSDS) Advanced Orbiting Systems (AOS) space data link protocol provides a framing layer between channel coding such as LDPC (low-density parity-check) and higher-layer link multiplexing protocols such as CCSDS Encapsulation Service, which is described in the following article. Recent advancement in RF modem technology has allowed multi-megabit transmission over space links. With this increase in data rate, the CCSDS AOS protocol implementation needs to be optimized to both reduce energy consumption and operate at a high rate.

Clare, Loren P.↗