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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Standard-M mobile satellite terminal employing electronic beam squint tracking

In recent years, extensive experience has been built up at the University of Bristol in the use of the Electronic Beam Squint (EBS) tracking technique, applied to large earth station facilities. The current interest in land mobile satellite terminals, using small tracking antennas, has prompted the investigation of the applicability of the EBS technique to this environment. The development of an L-band mechanically steered vehicle antenna is presented. A description of the antenna is followed by a detailed investigation of the tracking environment and its implications on the error detection capability of the system. Finally, the overall hardware configuration is described along with plans for future work.

Hawkins, G. J.↗
NASA NTRS1990

Performance of a family of omni and steered antennas for mobile satellite applications

The design and performance of a family of vehicle antennas developed at JPL in support of an emerging US Mobile Satellite Service (MSS) system are described. Test results of the antennas are presented. Trends for future development are addressed. Recommendations on design approaches for vehicle antennas of the first generation MSS are discussed.

Woo, K.↗
NASA NTRS1990

An ANSERLIN array for mobile satellite applications

Design, analysis, construction, and test of linear arrays of ANSERLIN (annular sector, radiating line) elements are reported and discussed. Due to feeding simplicity and easy construction as well as good CP performance, a planar array composed of a number of such linear arrays each producing a shaped beam tilted in elevation, is a good candidate as a vehicle-mounted mechanically steered antenna for mobile satellite applications. A single level construction technique was developed that makes this type of array very cost competitive with other low-profile arrays. An asymmetric 19.5 inch long four-element array was fabricated and tested with reasonable performance. A smaller five-element symmetric array (16 inch long) was also designed and tested capable of operating in either sense of circular polarization. Efforts were made to successfully reduce this effect.

Colomb, F. Y.↗
NASA NTRS1990

Aeronautical mobile satellite service: Air traffic control applications

Canada's history both in aviation and in satellite communications development spans several decades. The introduction of aeronautical mobile satellite communications will serve our requirements for airspace management in areas not served by line-of-sight radio and radar facilities. The ensuing improvements in air safety and operating efficiency are eagerly awaited by the aviation community.

Sim, Dave↗
NASA NTRS1990

Considerations of digital phase modulation for narrowband satellite mobile communication

The Inmarsat-M system for mobile satellite communication is specified as a frequency division multiple access (FDMA) system, applying Offset Quadrature Phase Shift Keying (QPSK) for transmitting 8 kbit/sec in 10 kHz user channel bandwidth. We consider Digital Phase Modulation (DPM) as an alternative modulation format for INMARSAT-M. DPM is similar to Continuous Phase Modulation (CPM) except that DPM has a finite memory in the premodular filter with a continuous varying modulation index. It is shown that DPM with 64 states in the VA obtains a lower bit error rate (BER). Results for a 5 kHz system, with the same 8 kbit/sec transmitted bitstream, is also presented.

Grythe, Knut↗
NASA NTRS1990

Analogue and digital linear modulation techniques for mobile satellite

The choice of modulation format for a mobile satellite service is complex. The subjective performance is summarized of candidate schemes and voice coder technologies. It is shown that good performance can be achieved with both analogue and digital voice systems, although the analogue system gives superior performance in fading. The results highlight the need for flexibility in the choice of signaling format. Linear transceiver technology capable of using many forms of narrowband modulation is described.

Whitmarsh, W. J.↗
NASA NTRS1990

A new coherent demodulation technique for land-mobile satellite communications

An advanced coherent demodulation technique is described for land mobile satellite (LMS) communications. The proposed technique features a combined narrow/wind band dual open loop carrier phase estimator, which is effectively able to compensate the fast carrier phase fluctuation by fading with sacrificing a phase slip rate. Also included is the realization of quick carrier and clock reacquisition after shadowing by taking open loop structure. Its bit error rate (BER) performance is superior to that of existing detection schemes, showing a BER of 1 x 10(exp -2) at 6.3 dB E sub b/N sub o over the Rician channel with 10 dB C/M and 200 Hz (1/16 modulation rate) fading pitch f sub d for QPSK. The proposed scheme consists of a fast response carrier recovery and a quick bit timing recovery with an interpolation. An experimental terminal model was developed to evaluate its performance at fading conditions. The results are quite satisfactory, giving prospects for future LMS applications.

Yoshida, Shousei↗
NASA NTRS1990

Performance of a low data rate speech codec for land-mobile satellite communications

In an effort to foster the development of new technologies for the emerging land mobile satellite communications services, JPL funded two development contracts in 1984: one to the Univ. of Calif., Santa Barbara and the other to the Georgia Inst. of Technology, to develop algorithms and real time hardware for near toll quality speech compression at 4800 bits per second. Both universities have developed and delivered speech codecs to JPL, and the UCSB codec was extensively tested by JPL in a variety of experimental setups. The basic UCSB speech codec algorithms and the test results of the various experiments performed with this codec are presented.

Gersho, Allen↗
NASA NTRS1990

USDA Forest Service mobile satellite communications applications

The airborne IR signal processing system being developed will require the use of mobile satellite communications to achieve its full capability and improvement in delivery timeliness of processed IR data to the Fire Staff. There are numerous other beneficial uses, both during wildland fire management operations or in daily routine tasks, which will also benefit from the availability of reliable communications from remote areas.

Warren, John R.↗
NASA NTRS1992

Ge's Mobile, Coherent Doppler Lidar Test/Ealuation Facilities

The primary objective of this independent research and development (IR and D) program in support of the Laser Atmospheric Wind Sounder (LAWS) program is to develop and evaluate technologies with direct applications to spaceborne laser wind sensing, and to develop system level engineering experience in designing, operating, and modeling a coherent Doppler lidar. GE is developing a mobile, ground based coherent Doppler lidar as an end-to-end system level test facility to evaluate applicable technologies, verify system level performance issues, perform instrument calibration, and validate end-to-end system performance model predictions. Here, the primary focus is on a description of the ground based lidar system and the performance during the initial shakedown operation after system integration.

Sroga, J. T.↗
NASA NTRS1991

Proceedings of the Workshop on Advanced Network and Technology Concepts for Mobile, Micro, and Personal Communications

The Workshop on Advanced Network and Technology Concepts for Mobile, Micro, and Personal Communications was held at NASA's JPL Laboratory on 30-31 May 1991. It provided a forum for reviewing the development of advanced network and technology concepts for turn-of-the-century telecommunications. The workshop was organized into three main categories: (1) Satellite-Based Networks (L-band, C-band, Ku-band, and Ka-band); (2) Terrestrial-Based Networks (cellular, CT2, PCN, GSM, and other networks); and (3) Hybrid Satellite/Terrestrial Networks. The proceedings contain presentation papers from each of the above categories.

Paul, Lori↗
NASA NTRS1991

Direct broadcast satellite-radio: Portable and mobile reception trade-offs

There has been considerable international effort in the areas of system studies, system development, and regulatory work for a Direct Broadcast Satellite Radio (DBS-R). An important milestone will be the 1992 World Radio Administrative Conference (WARC 1992) consideration of frequency allocation in the 500 - 3000 MHz range for such a service. There is an interagency agreement between Voice of America and the National Aeronautics and Space Administration for a coordinated program in DBS-R. This program includes seven tasks: systems tradeoff studies, propagation measurements, satellite experiment and demonstration, receiver development, market studies, regulatory studies, and WARC preparations. The findings of ongoing work under the first task, systems tradeoff studies, are discussed. Topics covered include digital bit rate and audio quality, propagation considerations and link margin estimates for portable reception, link margin estimates for mobile reception, coverage, and satellite size and cost estimates for a regional DBS-R coverage example.

Golshan, Nasser↗
NASA NTRS1991

Determination of C1-C4 alkanes by ion mobility spectrometry

Results are presented from a comparison between two ion-mobility-spectrometer (IMS) methods of sample ionisation: a conventional IMS with very dry helium and an IMS using metastable helium ionization. As one of the tests, a mixture of several hydrocarbons expected to be the components of Titan's atmosphere (made of ethane, ethylene, acetylene, propane, n-butane, isobutane, and propyne in concentrations from 20 to 200 ppm) was analyzed by both methods. Results from the dry-He IMS showed that the dry-helium approach was more adequate for the analysis of these gases than the metastable-helium IMS approach. In the metastable-He approach, in which several versions of He ionization reaction were tested, the spectra produced were not as clear as the conventional IMS spectra, due to the fact that the strong electric field introduced in the reaction region to generate metastable helium affected the gating, resolution, and collection of the ions.

Kojiro, Daniel R.↗
NASA NTRS1991

Space batteries for mobile battlefield power applications

A review of space power systems was undertaken to identify advanced space batteries for mobile applications. State-of-the-art systems are described. The technology issues that need to be addressed in order to bring these systems along and meet the needs of the user are discussed. Future research directions are examined.

O'Donnell, Patricia M.↗
NASA NTRS1992

Direct broadcast satellite-audio, portable and mobile reception tradeoffs

This paper reports on the findings of a systems tradeoffs study on direct broadcast satellite-radio (DBS-R). Based on emerging advanced subband and transform audio coding systems, four ranges of bit rates: 16-32 kbps, 48-64 kbps, 96-128 kbps and 196-256 kbps are identified for DBS-R. The corresponding grades of audio quality will be subjectively comparable to AM broadcasting, monophonic FM, stereophonic FM, and CD quality audio, respectively. The satellite EIRP's needed for mobile DBS-R reception in suburban areas are sufficient for portable reception in most single family houses when allowance is made for the higher G/T of portable table-top receivers. As an example, the variation of the space segment cost as a function of frequency, audio quality, coverage capacity, and beam size is explored for a typical DBS-R system.

Golshan, Nasser↗
NASA NTRS1991

Preliminary design of a mobile lunar power supply

A preliminary design for a Stirling isotope power system for use as a mobile lunar power supply is presented. Performance and mass of the components required for the system are estimated. These estimates are based on power requirements and the operating environment. Optimization routines are used to determine minimum mass operational points. Shielding for the isotope system is given as a function of the allowed dose, distance from the source, and the time spent near the source. The technologies used in the power conversion and radiator systems are taken from research in the Civil Space Technology Initiative (CSTI) program.

Schmitz, Paul C.↗
NASA NTRS1992

A communication protocol for mobile satellite systems affected by rain attenuation

A communication protocol is described that has been developed as part of a K/Ka-band mobile terminal breadboard system to be demonstrated through NASA's Advanced Communications Technology Satellite (ACTS) in 1993. The protocol is aimed at providing the means for enhancing link availability and continuity by supporting real-time data rate selection and changes during rain events. Particular attention is given to the system architecture; types of links, connections, and packets; the protocol procedures; and design rationales.

Lay, Norman↗
NASA NTRS1992

Mobilization of the platinum group elements by low-temperature fluids: Implications for mineralization and the iridium controversy

Geochemical investigations on the widely dispersed Late Proterozoic Acraman impact ejecta horizon and its host marine shales in the Adelaide Geosyncline provide strong evidence for low-temperature mobilization of the platinum group elements (PGE), including Ir. The ejecta horizon was formed when the middle Proterozoic dacitic volcanics in the Gawler Ranges, central South Australia, were impacted by a very large (ca. 4 km) meteorite. The resulting structure, now represented by Lake Acraman, is Australia's largest meteorite impact structure. Debris from the impact was blasted for many hundreds of kilometers, some falling into the shallow sea of the Adelaide Geosyncline, some 300 km to the east of the impact site.

Dowling, Kim↗