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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Modulation Classification of Satellite Communication Signals Using Cumulants and Neural Networks

National Aeronautics and Space Administration (NASA)'s future communication architecture is evaluating cognitive technologies and increased system intelligence. These technologies are expected to reduce the operational complexity of the network, increase science data return, and reduce interference to self and others. In order to increase situational awareness, signal classification algorithms could be applied to identify users and distinguish sources of interference. A significant amount of previous work has been done in the area of automatic signal classification for military and commercial applications. As a preliminary step, we seek to develop a system with the ability to discern signals typically encountered in satellite communication. Proposed is an automatic modulation classifier which utilizes higher order statistics (cumulants) and an estimate of the signal-to-noise ratio. These features are extracted from baseband symbols and then processed by a neural network for classification. The modulation types considered are phase-shift keying (PSK), amplitude and phase-shift keying (APSK),and quadrature amplitude modulation (QAM). Physical layer properties specific to the Digital Video Broadcasting - Satellite- Second Generation (DVB-S2) standard, such as pilots and variable ring ratios, are also considered. This paper will provide simulation results of a candidate modulation classifier, and performance will be evaluated over a range of signal-to-noise ratios, frequency offsets, and nonlinear amplifier distortions.

Signal Classification↗
NASA NTRS1984

Test results for 27.5- to 30-GHz communications satellite receivers

Five proof of concept receivers are tested. The receivers operate in the 27.5 to 30 GHz uplink band for communications satellites and produce an output at C band. Receiver requirements and test results are given. Test methods are discussed and results are compared with the contractor's test results.

Conroy, M. J.↗
NASA NTRS1991

A Code Phase Division Multiple Access (CPDMA) technique for VSAT satellite communications

A reference concept and implementation relevant to the application of Code Phase Division Multiple Access (CPDMA) to a high capacity satellite communication system providing 16 Kbps single hop channels between Very Small Aperture Terminals (VSAT's) is described. The description includes a potential implementation of an onboard CPDMA bulk demodulator/converter utilizing programmable charge coupled device (CCD) technology projected to be available in the early 1990's. A high level description of the system architecture and operations, identification of key functional and performance requirements of the system elements, and analysis results of end-to-end system performance relative to key figures of merit such as spectral efficiency are also provided.

Bruno, R.↗
NASA NTRS1990

A spread-spectrum modem using constant envelope BPSK for a mobile satellite communications terminal

This paper describes a 5-kilobit/s spread spectrum modem with a 1.275 mega-Hz chip rate for mobile satellite communications. We used a Viterbi decoder with a coding gain of 7.8 dB at a BER of 10(exp -5) to decrease the required receiver power. This reduces the cost of communication services. The spread spectrum technique makes the modem immune to terrestrial radio signals and keeps it from causing interference in terrestrial radio systems. A class C power amplifier reduces the modem's power consumption. To avoid nonlinear distortion caused by the amplifier, the envelope of the input signal is kept constant by adding quadrature channel signal to the BPSK signal. To simulate the worst case, we measured the modem's output spectrum using a limiting amplifier instead of the class C amplifier, and found that 99 percent of the spectral power was confined to the specified 2.55 mega-Hz bandwidth.

Iizuka, N.↗
NASA NTRS1974

Multiple beam communicating satellites with remote beam steering and beam shaping

Multiple beam phased arrays are shown to enhance the performance of several anticipated geostationary communications satellite programs because of the greater efficiency and flexibility of the phased array. It is shown that the efficiency of arrays can be significantly greater than corresponding multiple feed dishes and that the problems of crossover loss and performance degradation with parts failures are thereby avoided. On an open loop basis, it is shown that a multiple beam array can provide higher EIRP over a coverage area. On a closed loop basis, it is shown that an adaptive array can provide nulling of unwanted signals while simultaneously providing gain in the direction of a desired signal.

Sielman, P. F.↗
NASA NTRS1983

A figure of merit for competing communications satellite designs

Trends in launch schedules, weights, power, and space segment costs per transponder year for Intelsats and North American domsats (domestic communications satellites) are discussed. The Intelsat system currently services 25,000 point to point telephone links at any one moment, and a $3 billion order has been placed for Intelsat VIs, which feature 36,000 telephone circuits each. The Intelsat VI spacecraft will weigh 1670 kg in orbit, a continuance of the trend to heavier satellites, while the domsats will stay at 650 kg due to launch vehicle limitations. Direct television broadcast satellites are being designed for receive only (R/O) earth stations, with each satellite capable of servicing 50,000 individual ground stations. Competition is growing for C and Ku band satellite transponders for DBS, with costs $350,000 each. No standardized design has yet emerged.

Lovell, R. R.↗
NASA NTRS1992

Circuit-switch architecture for a 30/20-GHz FDMA/TDM geostationary satellite communications network

A circuit switching architecture is described for a 30/20 GHz frequency division, multiple access uplink/time division multiplexed downlink (FDMA/TDM) geostationary satellite communications network. Critical subsystems and problem areas are identified and addressed. Work was concentrated primarily on the space segment; however, the ground segment was considered concurrently to ensure cost efficiency and realistic operational constraints.

Ivancic, William D.↗
NASA NTRS1992

Circuit-switch architecture for a 30/20-GHz FDMA/TDM geostationary satellite communications network

A circuit-switching architecture is described for a 30/20-GHz frequency-division, multiple-access uplink/time-division-multiplexed downlink (FDMA/TDM) geostationary satellite communications network. Critical subsystems and problem areas are identified and addressed. Work was concentrated primarily on the space segment; however, the ground segment was considered concurrently to ensure cost efficiency and realistic operational constraints.

Ivancic, William D.↗
NASA NTRS1988

An overview of the OmniTRACS: The first operational mobile Ku-band satellite communications

The service features of the OmniTRACS system developed by Omninet Communications Services of Los Angeles, California are described. This system is the first operational mobile Ku-band satellite communications system that provides two-way messaging and position determination and reporting services to mobile users on a nationwide basis. The system uses existing Ku-band satellites under a secondary international allocation for mobile satellite services.

Salmasi, Allen↗
NASA NTRS1979

Concepts for 18/30 GHz satellite communication system study. Executive summary

An examination of a multiplicity of interconnected parameters ranging from specific technology details to total system economic costs for satellite communication systems at the 18/30 GHz transmission bands are presented. It was determined that K sub A band systems can incur a small communications outage during very heavy rainfall periods and that reducing the outage to zero would lead to prohibitive system costs. On the other hand, the economics of scale, ie, one spacecraft accommodating 2.5 GHz of bandwidth coupled with multiple beam frequency reuse, leads to very low costs for those users who can tolerate the 5 to 50 hours per year of downtime. A multiple frequency band satellite network can provide the ultimate optimized match to the consumer performance/economics demands.

Baker, M.↗
NASA NTRSDate not supplied

Development and Ground Demonstration of a Satellite Communication Terminal for Future Space Missions

As commercial companies continue to develop communication services and infrastructure in near-Earth orbit, NASA is actively pursuing commercially-led satellite communications for future missions. Many of these commercial services are offered in the K/Ka-band, ranging from 17 to 31 GHz, covering spectrum allocated to commercial networks, military, and civilian government space operations, and can be tailored to support orbiting spacecraft. A key enabling technology needed for this vision is a multi-frequency (wideband), multi-waveform user terminal which can operate over multiple services. This presentation discusses the work undertaken at NASA’s Glenn Research Center to develop a RF user spacecraft terminal. Specifications and design considerations that support interoperability will be discussed as well as off the shelf technology gaps. Furthermore, simulation and benchtop testing results will be discussed as well as details of the initial successful over-the-air demonstrations using NASA, Inmarsat, and SES services.

Radio↗
NASA NTRS1980

NASA's program in communication satellites

It is noted that NASA is currently proceeding with a revitalized R&D program aimed at the development and demonstration of advanced communication satellite system concepts and the related enabling technologies. The paper reviews the important elements of this program thrust, the approach NASA is taking to assure proper involvement of both the system supplier industry and the service supplier industry and the specific technology focus in the near term. Finally, highlights of the current NASA and industry activities related to opening up the 30/20 GHz frequency band for both commercial and military use are presented.

Sivo, J. N.↗