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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Advanced satellite communication system

The objective of this research program was to develop an innovative advanced satellite receiver/demodulator utilizing surface acoustic wave (SAW) chirp transform processor and coherent BPSK demodulation. The algorithm of this SAW chirp Fourier transformer is of the Convolve - Multiply - Convolve (CMC) type, utilizing off-the-shelf reflective array compressor (RAC) chirp filters. This satellite receiver, if fully developed, was intended to be used as an on-board multichannel communications repeater. The Advanced Communications Receiver consists of four units: (1) CMC processor, (2) single sideband modulator, (3) demodulator, and (4) chirp waveform generator and individual channel processors. The input signal is composed of multiple user transmission frequencies operating independently from remotely located ground terminals. This signal is Fourier transformed by the CMC Processor into a unique time slot for each user frequency. The CMC processor is driven by a waveform generator through a single sideband (SSB) modulator. The output of the coherent demodulator is composed of positive and negative pulses, which are the envelopes of the chirp transform processor output. These pulses correspond to the data symbols. Following the demodulator, a logic circuit reconstructs the pulses into data, which are subsequently differentially decoded to form the transmitted data. The coherent demodulation and detection of BPSK signals derived from a CMC chirp transform processor were experimentally demonstrated and bit error rate (BER) testing was performed. To assess the feasibility of such advanced receiver, the results were compared with the theoretical analysis and plotted for an average BER as a function of signal-to-noise ratio. Another goal of this SBIR program was the development of a commercial product. The commercial product developed was an arbitrary waveform generator. The successful sales have begun with the delivery of the first arbitrary waveform generator.

Staples, Edward J.↗
NASA NTRS2010

Spacecraft Multiple Array Communication System Performance Analysis

The Communication Systems Simulation Laboratory (CSSL) at the NASA Johnson Space Center is tasked to perform spacecraft and ground network communication system simulations, design validation, and performance verification. The CSSL has developed simulation tools that model spacecraft communication systems and the space and ground environment in which the tools operate. In this paper, a spacecraft communication system with multiple arrays is simulated. Multiple array combined technique is used to increase the radio frequency coverage and data rate performance. The technique is to achieve phase coherence among the phased arrays to combine the signals at the targeting receiver constructively. There are many technical challenges in spacecraft integration with a high transmit power communication system. The array combining technique can improve the communication system data rate and coverage performances without increasing the system transmit power requirements. Example simulation results indicate significant performance improvement can be achieved with phase coherence implementation.

Hwu, Shian U.↗
NASA NTRS1981

Radio-wave propagation for space communications systems

The most recent information on the effects of Earth's atmosphere on space communications systems is reviewed. The design and reliable operation of satellite systems that provide the many applications in space which rely on the transmission of radio waves for communications and scientific purposes are dependent on the propagation characteristics of the transmission path. The presence of atmospheric gases, clouds, fog, precipitation, and turbulence causes uncontrolled variations in the signal characteristics. These variations can result in a reduction of the quality and reliability of the transmitted information. Models and other techniques are used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz have been reviewed. Particular emphasis has been placed on the effects of precipitation on the Earth/space path, including rain attenuation, and ice particle depolarization. Other factors are sky noise, antenna gain degradation, scintillations, and bandwidth coherence. Each of the various propagation factors has an effect on design criteria for communications systems. These criteria include link reliability, power margins, noise contribution, modulation and polarization factors, channel cross talk, error rate, and bandwidth limitations.

Ippolito, L. J.↗
NASA NTRSDate not supplied

Recent on-Orbit Results and Arq Performance Analysis for the Tbird 200-Gbps Mission

The TeraByte Infrared Delivery (TBIRD) mission has successfully demonstrated 200-Gbps laser communication downlinks from a 6U CubeSat in low-Earth orbit (LEO) and has delivered up to 4.8 terabytes (TB) error-free in a 5-minute pass. In total 65 passes have been performed since launch in May 2022, with 25 of those passes conducted in April-May 2023. The TBIRD space and ground terminals leverage commercial fiber-coupled coherent transceivers along with a custom Automatic Repeat reQuest (ARQ) protocol to ensure error-free communication through the atmospheric fading channel. This paper presents data throughput results from the on-orbit passes and an analysis of the ARQ system operation that shows that near-optimal performance was achieved. We also present results from Doppler compensation experiments that led to an increase in the data volume transferred per pass.

Tbird↗
NASA NTRSDate not supplied

Recent On-Orbit Results and ARQ Performance Analysis for the TBIRD 200-Gbps Mission

The TeraByte Infrared Delivery (TBIRD) mission has successfully demonstrated 200-Gbps laser communication downlinks from a 6U CubeSat in low-Earth orbit (LEO) and has delivered up to 4.8 terabytes (TB) error-free in a 5-minute pass. In total, 65 passes have been performed since launch in May 2022, with 22 of those passes conducted in April-May 2023. The TBIRD space and ground terminals leverage commercial fiber-coupled coherent transceivers along with a custom Automatic Repeat reQuest (ARQ) protocol to ensure error-free communication through the atmospheric fading channel. This paper presents data throughput results from the on-orbit passes and an analysis of the ARQ system operation that shows that near-optimal performance was achieved. Results from Doppler compensation experiments that increased the data volume per pass are also presented.

optical↗
NASA NTRS1986

Reduced-Bandwidth Coding for Mobile Communication

Fade-resistant mobile systems use power and spectrum efficiently. Transmission system employs tone-calibrated technique (TCT). Residual carrier used in technique to reduce fading-induced effects and coherently demodulate received signal. TCT potentially efficient in use of power and of frequency spectrum. Coding technique, intended for residual-carrier transmission system, alleviates fading and spectrum crowding that hamper mobile communications.

Davarian, F.↗
NASA NTRS1976

Design criteria for noncoherent Gaussian channels with MFSK signaling and coding

This paper presents data and criteria to assess and guide the design of modems for coded noncoherent communication systems subject to practical system constraints of power, bandwidth, noise spectral density, coherence time, and number of orthogonal signals M. Three basic receiver types are analyzed for the noncoherent multifrequency-shift keying (MFSK) additive white Gaussian noise channel: hard decision, unquantized (optimum), and quantized (soft decision). Channel capacity and computational cutoff rate are computed for each type and presented as functions of the predetection signal-to-noise ratio and the number of orthogonal signals. This relates the channel constraints of power, bandwidth, coherence time, and noise power to the optimum choice of signal duration and signal number.

Butman, S. A.↗
NASA NTRS1993

Diversity reception for advanced multi-satellite networks: A CDMA approach

Diversity reception for Synchronous CDMA (S-CDMA) is introduced and analyzed. A Gaussian co-channel synchronous and asynchronous interference approximation is derived to evaluate the effects on the system bit error rate. Numerical results are provided for a simple mobile communication system where the signals transmitted by two distinct satellites in visibility are coherently combined by a three fingers Rake receiver. A second example showing performance of an integrated ground/satellite single frequency network for digital audio broadcasting is presented. Results show the capacity advantage of utilizing S-CDMA in combination with diversity reception.

Colzi, E.↗
NASA NTRS2013

Human-in-the-Loop Operations over Time Delay: NASA Analog Missions Lessons Learned

Teams at NASA have conducted studies of time-delayed communications as it effects human exploration. In October 2012, the Advanced Exploration Systems (AES) Analog Missions project conducted a Technical Interchange Meeting (TIM) with the primary stakeholders to share information and experiences of studying time delay, to build a coherent picture of how studies are covering the problem domain, and to determine possible forward plans (including how to best communicate study results and lessons learned, how to inform future studies and mission plans, and how to drive potential development efforts). This initial meeting s participants included personnel from multiple NASA centers (HQ, JSC, KSC, ARC, and JPL), academia, and ESA. It included all of the known studies, analog missions, and tests of time delayed communications dating back to the Apollo missions including NASA Extreme Environment Mission Operations (NEEMO), Desert Research and Technology Studies (DRATS/RATS), International Space Station Test-bed for Analog Research (ISTAR), Pavilion Lake Research Project (PLRP), Mars 520, JPL Mars Orbiters/Rovers, Advanced Mission Operations (AMO), Devon Island analog missions, and Apollo experiences. Additionally, the meeting attempted to capture all of the various functional perspectives via presentations by disciplines including mission operations (flight director and mission planning), communications, crew, Capcom, Extra-Vehicular Activity (EVA), Behavioral Health and Performance (BHP), Medical/Surgeon, Science, Education and Public Outreach (EPO), and data management. The paper summarizes the descriptions and results from each of the activities discussed at the TIM and includes several recommendations captured in the meeting for dealing with time delay in human exploration along with recommendations for future development and studies to address this issue.

Rader, Steven N.↗
NASA NTRS2003

Quantum detection of coherent-state signals in the presence of noise

A general method for solving an important class of quantum detection problems will be presented and evaluated. The quantum theory for detecting pure states for communications purposes has been developed over two decades ago, however the mixed state problem representing signal plus noise states has received little attention due to its great complexity. Here we develop a practical model for solving the mixed-state problem using a discrete approximation to the coherent-state representation of signal plus noise density operators.

Quantum communication quantum detection↗
NASA NTRS1994

Optical Heterodyne With Lower Phase Noise

Proposed improvement enhances utility of optical-heterodyne apparatus used to generate radio signal at chosen frequency between 1 and 1,000 GHz. Two lasers injection-locked to third, mode-locked laser. Beat-frequency heterodyne output contains much less phase noise if generated from outputs of two independent lasers, and phase-coherent with reference signal. Potential applications include phased-array radar, fiber-optic communication systems, fiber-optic stabilized oscillators, and other applications involving conversions between optical and millimeter-wave signals.

Logan, Ronald T.↗
NASA NTRS1975

Coherence properties of wideband satellite signals caused by ionospheric scintillation

Radio scintillation on satellite signals caused by small-scale irregularities in F-region ionospheric electron density can be an important limitation on earth-satellite communication and navigation systems. Scintillation imposes distortion in both amplitude and phase on wideband signals. In the present work, the shallow-modulated phase screen theory is developed in terms of coherence bandwidth including a model based on a turbulent-like power-law description of the irregularities. The model results usually show a greater coherence bandwidth in the signal phase than in the signal amplitude. Therefore, systems that require phase coherence over a large bandwidth should be less affected than those requiring amplitude coherence.

Rufenach, C. L.↗
NASA NTRS1993

Transmission over EHF mobile satellite channels

Land mobile satellite communications at Ka-band (30/20 GHz) are attracting an increasing interest among researchers because of the frequency band availability and the possibility of small earth station designs. However, communications at the Ka-band pose significant challenges in the system designs due to severe channel impairments. Because only very limited experimental data for mobile applications at Ka-band is available, this paper studies the channel characteristics based on experimental data at L-band (1.6/1.5 GHz) and the use of frequency scaling. The land mobile satellite communication channel at Ka-band is modelled as log-normal Rayleigh fading channel. The first and second-order statistics of the fading channel are studied. The performance of a coherent BPSK system over the fading channel at L-band and K-band is evaluated theoretically and validated by computer simulations. Conclusions on the communication channel characteristics and system performance at L-band and Ka-band are presented.

Zhuang, W.↗
NASA NTRS1970

Block-coded communications

Theory for block-coded telemetry systems is useful in testing performance of one- and two-way, phase-coherent telemetry systems when double-conversion, superheterodyne, phase-locked receiver, preceded by bandpass limiter is used to track carrier.

Lindsey, W. C.↗
NASA NTRS2017

Path Profiles of Cn2 Derived from Radiometer Temperature Measurements and Geometrical Ray Tracing

Atmospheric turbulence has significant impairments on the operation of Free-Space Optical (FSO) communication systems, in particular temporal and spatial intensity fluctuations at the receiving aperture resulting in power surges and fades, changes in angle of arrival, spatial coherence degradation, etc. The refractive index structure parameter Cn2 is a statistical measure of the strength of turbulence in the atmosphere and is highly dependent upon vertical height. Therefore to understand atmospheric turbulence effects on vertical FSO communication links such as space-to-ground links, it is necessary to specify Cn2 profiles along the atmospheric propagation path. To avoid the limitations on the applicability of classical approaches, propagation simulation through geometrical ray tracing is applied. This is achieved by considering the atmosphere along the optical propagation path as a spatial distribution of spherical bubbles with varying relative refractive index deviations representing turbulent eddies. The relative deviations of the refractive index are statistically determined from altitude-dependent and time-varying temperature fluctuations, as measured by a microwave profiling radiometer. For each representative atmosphere ray paths are analyzed using geometrical optics, which is particularly advantageous in situations of strong turbulence where there is severe wavefront distortion and discontinuity. The refractive index structure parameter is then determined as a function of height and time.

Atmospheric turbulence↗
NASA NTRS1985

Semiconductor Laser Phased Array

Oscillations synchronized and modulated individually for beam steering. Phased array of GaAs infrared lasers put out powerful electronically-steerable coherent beam. Fabricated as integrated circuit on GaAs chip, new device particularly suited to optical communications, optical data processing and optical detection and ranging systems.

Katz, J.↗