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  • 1
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    Cross-Layer Design for the Physical, MAC, and Link Layer in Wireless Systems (2008)
    Springer
    Details
    Publication Date: 2008-08-18
    Print ISSN: 1687-6172
    Electronic ISSN: 1687-6180
    Topics: Electrical Engineering, Measurement and Control Technology
    Published by Springer
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    PAPER CURRENT
  • 2
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    Optimizing Satellite Communications With Adaptive and Phased Array Antennas (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: Space Communications, Spacecraft Communications, Command and Tracking
    Type: ESTC 2004; Jun 21, 2004 - Jun 23, 2004; Palo Alto, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Linking Satellites Via Earth "Hot Spots" and the Internet to Form Ad Hoc Constellations (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: As more assets are placed in orbit, opportunities emerge to combine various sets of satellites in temporary constellations to perform collaborative image collections. Often, new operations concepts for a satellite or set of satellites emerge after launch. To the degree with which new space assets can be inexpensively and rapidly integrated into temporary or "ad hoc" constellations, will determine whether these new ideas will be implemented or not. On the Earth Observing 1 (EO-1) satellite, a New Millennium Program mission, a number of experiments were conducted and are being conducted to demonstrate various aspects of an architecture that, when taken as a whole, will enable progressive mission autonomy. In particular, the target architecture will use adaptive ground antenna arrays to form, as close as possible, the equivalent of wireless access points for low earth orbiting satellites. Coupled with various ground and flight software and the Internet. the architecture enables progressive mission autonomy. Thus, new collaborative sensing techniques can be implemented post-launch. This paper will outline the overall operations concept and highlight details of both the research effort being conducted in 〈he area of adaptive antenna arrays and some of the related successful autonomy software that has been implemented using EO-1 and other operational satellites. Keywords: collaborative remote sensing smart antennas, adaptive antenna arrays, sensor webs. ad hoc constellations, mission autonomy and
    Keywords: Space Communications, Spacecraft Communications, Command and Tracking
    Type: SPIE 2004; Nov 08, 2004 - Nov 12, 2004; Honolulu, HI; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Sensor Webs: Autonomous Rapid Response to Monitor Transient Science Events (2005)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: To better understand how physical phenomena, such as volcanic eruptions, evolve over time, multiple sensor observations over the duration of the event are required. Using sensor web approaches that integrate original detections by in-situ sensors and global-coverage, lower-resolution, on-orbit assets with automated rapid response observations from high resolution sensors, more observations of significant events can be made with increased temporal, spatial, and spectral resolution. This paper describes experiments using Earth Observing 1 (EO-1) along with other space and ground assets to implement progressive mission autonomy to identify, locate and image with high resolution instruments phenomena such as wildfires, volcanoes, floods and ice breakup. The software that plans, schedules and controls the various satellite assets are used to form ad hoc constellations which enable collaborative autonomous image collections triggered by transient phenomena. This software is both flight and ground based and works in concert to run all of the required assets cohesively and includes software that is model-based, artificial intelligence software.
    Keywords: Spacecraft Instrumentation and Astrionics
    Type: E-15021 , American Meteorological Society 2005 Conference; Jan 10, 2005 - Jan 13, 2005; San Diego, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    LEO Download Capacity Analysis for a Network of Adaptive Array Ground Stations (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: To lower costs and reduce latency, a network of adaptive array ground stations, distributed across the United States, is considered for the downlink of a polar-orbiting low earth orbiting (LEO) satellite. Assuming the X-band 105 Mbps transmitter of NASA s Earth Observing 1 (EO-1) satellite with a simple line-of-sight propagation model, the average daily download capacity in bits for a network of adaptive array ground stations is compared to that of a single 11 m dish in Poker Flats, Alaska. Each adaptive array ground station is assumed to have multiple steerable antennas, either mechanically steered dishes or phased arrays that are mechanically steered in azimuth and electronically steered in elevation. Phased array technologies that are being developed for this application are the space-fed lens (SFL) and the reflectarray. Optimization of the different boresight directions of the phased arrays within a ground station is shown to significantly increase capacity; for example, this optimization quadruples the capacity for a ground station with eight SFLs. Several networks comprising only two to three ground stations are shown to meet or exceed the capacity of the big dish, Cutting the data rate by half, which saves modem costs and increases the coverage area of each ground station, is shown to increase the average daily capacity of the network for some configurations.
    Keywords: Ground Support Systems and Facilities (Space)
    Type: SERP 2005; Jun 27, 2005 - Jun 30, 2005; Las Vegas, NV; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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