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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Next generation communications satellites: Multiple access and network studies

Following an overview of issues involved in the choice of promising system architectures for efficient communication with multiple small inexpensive Earth stations serving hetergeneous user populations, performance evaluation via analysis and simulation for six SS/TDMA (satellite-switched/time-division multiple access) system architectures is discussed. These configurations are chosen to exemplify the essential alternatives available in system design. Although the performance evaluation analyses are of fairly general applicability, whenever possible they are considered in the context of NASA's 30/20 GHz studies. Packet switched systems are considered, with the assumption that only a part of transponder capacit is devoted to packets, the integration of circuit and packet switched traffic being reserved for further study. Three types of station access are distinguished: fixed (FA), demand (DA), and random access (RA). Similarly, switching in the satellite can be assigned on a fixed (FS) or demand (DS) basis, or replaced by a buffered store-and-forward system (SF) onboard the satellite. Since not all access/switching combinations are practical, six systems are analyzed in detail: three FS SYSTEMS, FA/FS, DA/ES, RA/FS; one DS system, DA/DS; and two SF systems, FA/SF, DA/SF. Results are presented primarily in terms of delay-throughput characteristics.

Stern, T. E.↗
NASA NTRS1986

Mobile satellite communications technology - A summary of NASA activities

Studies in recent years indicate that future high-capacity mobile satellite systems are viable only if certain high-risk enabling technologies are developed. Accordingly, NASA has structured an advanced technology development program aimed at efficient utilization of orbit, spectrum, and power. Over the last two years, studies have concentrated on developing concepts and identifying cost drivers and other issues associated with the major technical areas of emphasis: vehicle antennas, speech compression, bandwidth-efficient digital modems, network architecture, mobile satellite channel characterization, and selected space segment technology. The program is now entering the next phase - breadboarding, development, and field experimentation.

Dutzi, E. J.↗
NASA NTRS2004

Optimizing Satellite Communications With Adaptive and Phased Array Antennas

A new adaptive antenna array architecture for low-earth-orbiting satellite ground stations is being investigated. These ground stations are intended to have no moving parts and could potentially be operated in populated areas, where terrestrial interference is likely. The architecture includes multiple, moderately directive phased arrays. The phased arrays, each steered in the approximate direction of the satellite, are adaptively combined to enhance the Signal-to-Noise and Interference-Ratio (SNIR) of the desired satellite. The size of each phased array is to be traded-off with the number of phased arrays, to optimize cost, while meeting a bit-error-rate threshold. Also, two phased array architectures are being prototyped: a spacefed lens array and a reflect-array. If two co-channel satellites are in the field of view of the phased arrays, then multi-user detection techniques may enable simultaneous demodulation of the satellite signals, also known as Space Division Multiple Access (SDMA). We report on Phase I of the project, in which fixed directional elements are adaptively combined in a prototype to demodulate the S-band downlink of the EO-1 satellite, which is part of the New Millennium Program at NASA.

Ingram, Mary Ann↗
NASA NTRS1988

Speech coding at 4800 bps for mobile satellite communications

A speech compression project has recently been completed to develop a speech coding algorithm suitable for operation in a mobile satellite environment aimed at providing telephone quality natural speech at 4.8 kbps. The work has resulted in two alternative techniques which achieve reasonably good communications quality at 4.8 kbps while tolerating vehicle noise and rather severe channel impairments. The algorithms are embodied in a compact self-contained prototype consisting of two AT and T 32-bit floating-point DSP32 digital signal processors (DSP). A Motorola 68HC11 microcomputer chip serves as the board controller and interface handler. On a wirewrapped card, the prototype's circuit footprint amounts to only 200 sq cm, and consumes about 9 watts of power.

Gersho, Allen↗
NASA NTRS1988

Assessment of satellite communications quality study. Addendum 1: Impact of propagation delay on data transmission

The single factor that irrevocably distinguishes geostationary satellite telephony transmission from terrestrial transmission is the greater propagation delay over satellite links. This difference has always provoked vigorous debate over the impact of delay on the subscribers using services incorporating satellite links. The issue is addressed from a variety of directions including human factors studies, laboratory subjective tests that evaluate delay with and without echo, and field tests that obtain data on the opinion of subscribers regarding the quality of service of operational circuits in both national U.S. domestic and international trans-Atlantic network. The tests involved the use of both echo suppressors and echo cancellers.

Campanella, S. J.↗
NASA NTRS1974

Shuttle station, and satellite communications program

A parametric approach is developed to analyze and evaluate the performance of any link or links of a satellite relay system. The approach factors into the calculations the constraints of coherent radio frequency interference, multipath, and equipment design. The report is divided into three sections dealing with Spread Spectrum Techniques (Section 1), Power Budget Calculations (Section 2), and Required Capabilities and Design Factors for Tracking and Data Relay Systems TDRS (Section 3).

Lawsine, L.↗
NASA NTRS1983

Beam forming networks for mm-wave satellite communications

Technology features of a beam forming network (BFN) employing ferrite devices to provide multiple beam antenna pattern control for satellites used in telecommunications are described. The BFN produces the phase and amplitude distribution for each horn in an antenna array, with the number of horns in the array being equal to the number of outputs in the BFN. One configuration involves microwave switches and permits illumination of a single feed horn at a time using ferrite latching circulators that function by reversing the circulation direction. A more flexible version, yielding a variable amplitude distribution across the feed horn array to accommodate changing traffic patterns or serving a TDMA system, includes the capability of forming nulls in the system with a variable phase shifter in the input ports. The antenna scan angles in phased arrays can be limited to 8 deg from center. Acceptable insertion losses have been demonstrated in BFN with hundreds of ports and switching rates as high as 10 kHz.

Sharon, T. E.↗
NASA NTRS1988

High efficiency, long life traveling wave tubes for future communications satellites

Electron beam devices, primarily traveling wave tubes (TWTs), have been used as the power amplifiers in almost all space communications and data transmission systems. Based on the technology that is presently available and the expected success of current research efforts, it is reasonable to predict the development of a new class of microwave TWTs with efficiencies in excess of 60 percent and lifetimes of at least 10 years. Because of this rapid advance of technology, the TWT is expected to remain the dominant device for power amplifiers in space.

Dayton, James A., Jr.↗
NASA NTRS1988

High efficiency, long life traveling wave tubes for future communications satellites

Electron beam devices, primarily traveling wave tubes (TWTs), have been used as the power amplifiers in almost all space communications and data transmission systems. Based on the technology that is presently available and the expected success of current research efforts, it is reasonable to predict the development of a new class of microwave TWTs with efficiencies in excess of 60 percent and lifetimes of at least ten years. Because of this rapid advance of technology, the TWT is expected to remain the dominant device for power amplifiers in space.

Dayton, J. A., Jr.↗
NASA NTRS1972

Propulsion requirements for communications satellites.

The concept of characteristics thrust is introduced herein as a means of classifying propulsion system tasks related particularly to geosynchronous communications spacecraft. Approximate analytical models are developed to permit estimation of characteristic thrust for injection error corrections, orbit angle re-location, north-south station keeping, east-west station keeping, spin axis precession control, attitude rate damping, and orbit raising applications. Performance assessment factors are then outlined in terms of characteristic power, characteristic weight, and characteristic volume envelope, which are related to the characteristic thrust. Finally, selected performance curves are shown for power as a function of spacecraft weight, including the influence of duty cycle on north-south station keeping, a 90 degree orbit angle re-location in 14 days, and finally comparison of orbit raising tasks from low and intermediate orbits to a final geosynchronous station. Power requirements range from less than 75 watts for north-south station keeping on small payloads up to greater than 15 KW for a 180 day orbit raising mission including a 28.5 degree plane change.

Isley, W. C.↗
NASA NTRS1988

Pilot-aided modulation for narrow-band satellite communications

This paper discusses a number of tone-aided modulation techniques which have been studied as part of the Mobile Satellite Experiment (MSAT-X) Program. In all instances tone(s) are inserted into data-free portions of the transmit spectrum and used by the receiver to sense the amplitude and frequency/phase distortions introduced by the channel. The receiver then uses this information in a feedforward manner to lessen the effect of the distortions on the data detection performance. Particular techniques discussed are the Tone Calibration Technique (TCT), the Dual Tone Calibrated Technique (DTCT), Transparent Tone-In-Band (TTIB), and Dual-Tone Single Sideband (DTSSB).

Saulnier, Gary J.↗
NASA NTRS1995

Hand-held terminal antennas for personal satellite communications

This paper deals with two hand-held antenna types operating with geostationary and medium earth orbit (GEO and MEO) satellite systems. They could be applied to the low earth orbit (LEO) and highly elliptical orbit (HEO) systems respectively doing the appropriate frequency scale designs. The first one is a lambda/2 (1/2 turn) quadrifilar helix (quasi-hemispherical coverage), and the second one is a self-diplexed antenna made of a circular patch and a short-circuited ring patch in stacked configuration (zenithal coverage).

Caballero, J. E.↗
NASA NTRS1978

Delta launch Canadian communications satellite Telesat-D (Anik-B)

Telesat-D (Anik-B) is the first of a series of three (Telesat-D, -E, -F) second generation satellites developed for Telesat/Canada. These second generation satellites will replace three first generation HS-333 satellites (Telesat-A, -B, -C) developed for Telesat/CNADA AND LAUNCHED BY Delta 2914 vehicles in 1972, 1973, and 1975 and successfully placed in orbit as Anik-A1, -A2, -A3. The Telesat-D(Anik-B) satellite will be place in sync-transfer orbit by a Delta 3914 launch vehicle, currently scheduled for launch on December 15, 1978. The Telesat-E and -F(Anik-C1 and -C2) missions are scheduled for launch on the Space Shuttle in 1981 to replace the function of the Anik-A2 and -A3 (Telesat-B, and -C) satellites. The Anik-B will provide point-to-point voice, TV, and data communications traffic to Canada's ten provinces.

Source record↗
NASA NTRS1983

Intelsat communications satellite scheduled for launch

To be placed into a highly elliptical transfer orbit by the Atlas Centaur (AC-61) launch vehicle, the INTELSAT V-F satellite has 12,000 voice circuits and 2 color television channels and incorporates a maritime communication system for ship to shore communications. The stages of the launch vehicle and the launch operations are described. A table shows the launch sequence.

Source record↗
NASA NTRS1983

The 30 GHz communications satellite low noise receiver

A Ka-band low noise front end in proof of concept (POC) model form for ultimate spaceborne communications receiver deployment was developed. The low noise receiver consists of a 27.5 to 30.0 GHz image enhanced mixer integrated with a 3.7 to 6.2 GHz FET low noise IF amplifier and driven by a self contained 23.8 GHz phase locked local oscillator source. The measured level of receiver performance over the 27.3 to 30.0 GHz RF/3.7 to 6.2 GHz IF band includes 5.5 to 6.5 dB (typ) SSB noise figure, 20.5 + or - 1.5 dB conversion gain and +23 dBm minimum third order two tone intermodulation output intercept point.

Steffek, L. J.↗
NASA NTRS1992

Advances in MMIC technology for communications satellites

This paper discusses NASA Lewis Research Center's program for development of monolithic microwave integrated circuits (MMIC) for application in space communications. Emphasis will be on the improved performance in power amplifiers and low noise receivers which has been made possible by the development of new semiconductor materials and devices. Possible applications of high temperature superconductivity for space communications will also be presented.

Leonard, Regis F.↗
NASA NTRS1978

Millimeter wave communication satellite concepts

Methodology has been developed for identifying viable and appropriate technologies for future NASA millimeter wave research as based upon the technical requirements of potential space communication services. Applicability of the methodology has been verified through its use with two conceptual communications systems. The subsystem cost and weight models are the appropriate level of detail for this study. Application of the methodology to the detailed design of a satellite system would require further model refinement.

Holland, L. D.↗