3,367 research outputs found
Mobile radio alternative systems study, executive summary
Present day mobile communication technologies, systems and equipment are described from background in evaluating the concepts generated in the study. Average propagation ranges are calculated for terrestrial installations in each of seven physiographic areas of the contiguous states to determine the number of installations that would be required for nationwide coverage. Four system concepts are defined and analyzed to determine how well terrestrial systems can fulfill the requirements at acceptable costs
Guidelines for spaceborne microwave remote sensors
A handbook was developed to provide information and support to the spaceborne remote sensing and frequency management communities: to guide sensor developers in the choice of frequencies; to advise regulators on sensor technology needs and sharing potential; to present sharing analysis models and, through example, methods for determining sensor sharing feasibility; to introduce developers to the regulatory process; to create awareness of proper assignment procedures; to present sensor allocations; and to provide guidelines on the use and limitations of allocated bands. Controlling physical factors and user requirements and the regulatory environment are discussed. Sensor frequency allocation achievable performance and usefulness are reviewed. Procedures for national and international registration, the use of non-allocated bands and steps for obtaining new frequency allocations, and procedures for reporting interference are also discussed
Shuttle/spacelab MMAP/electromagnetic environment experiment phase B definition study
Progress made during the first five months of the Phase B definition study for the MMAP/Electromagnetic Environment Experiment (EEE) was described. An antenna/receiver assembly has been defined and sized for stowing in a three pallet bay area in the shuttle. Six scanning modes for the assembly are analyzed and footprints for various antenna sizes are plotted. Mission profiles have been outlined for a 400 km height, 57 deg inclination angle, circular orbit. Viewing time over 7 geographical areas are listed. Shuttle interfaces have been studied to determine what configuration the antenna assembly must have to be shared with other experiments of the Microwave Multi-Applications Payload (MMAP) and to be stowed in the shuttle bay. Other results reported include a frequency plan, a proposed antenna subsystem design, a proposed receiver design, preliminary outlines of the experiment controls and an analysis of on-board and ground data processing schemes
Future benefits and applications of intelligent on-board processing to VSAT services
The trends and roles of VSAT services in the year 2010 time frame are examined based on an overall network and service model for that period. An estimate of the VSAT traffic is then made and the service and general network requirements are identified. In order to accommodate these traffic needs, four satellite VSAT architectures based on the use of fixed or scanning multibeam antennas in conjunction with IF switching or onboard regeneration and baseband processing are suggested. The performance of each of these architectures is assessed and the key enabling technologies are identified
Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)
Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression
Disaster warning system: Satellite feasibility and comparison with terrestrial systems. Volume 2: Final report
For abstract, see Vol. 1
A cosmic microscope to probe the Universe from Present to Cosmic Dawn - dual-element low-frequency space VLBI observatory
A space-based very long baseline interferometry (VLBI) programme, named as
the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space
working together with giant ground-based telescopes (e.g., Square Kilometre
Array, FAST, Arecibo) to image the low radio frequency Universe with the
purpose of unraveling the compact structure of cosmic constituents including
supermassive black holes and binaries, pulsars, astronomical masers and the
underlying source, and exoplanets amongst others. The operational frequency
bands are 30, 74, 330 and 1670 MHz, supporting broad science areas. The mission
plans to launch two 30-m-diameter radio telescopes into 2,000 km x 90,000 km
elliptical orbits. The two telescopes can work in flexibly diverse modes: (i)
space-ground VLBI. The maximum space-ground baseline length is about 100,000
km; it provides a high-dynamic-range imaging capacity with unprecedented high
resolutions at low frequencies (0.4 mas at 1.67 GHz and 20 mas at 30 MHz)
enabling studies of exoplanets and supermassive black hole binaries (which emit
nanoHz gravitational waves); (ii) space-space single-baseline VLBI. This unique
baseline enables the detection of flaring hydroxyl masers, and more precise
position measurement of pulsars and radio transients at milli-arcsecond level;
(iii) single dish mode, where each telescope can be used to monitor transient
bursts and rapidly trigger follow-up VLBI observations. The large space
telescope will also contribute in measuring and constraining the total angular
power spectrum from the Epoch of Reionization. In short, the Cosmic Microscope
offers astronomers the opportunity to conduct novel, frontier science.Comment: Accepted for publication in Chinese Journal of Space Science, 10
pages, 2 figure
- …