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  • COMMUNICATIONS AND RADAR  (3)
  • 2020-2022
  • 2005-2009
  • 1990-1994  (3)
  • 1
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    Baseline antenna design for space exploration initiative (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A key element of the future NASA Space Exploration Initiative (SEI) mission is the lunar and Mars telecommunication system. This system will provide voice, image, and data transmission to monitor unmanned missions to conduct experiments, and to provide radiometric data for navigation. In the later half of 1991, a study was conducted on antennas for the Mars Exploration Communication. Six antenna configurations were examined: three reflector and three phased array. The conclusion was that due to wide-angle scan requirement, and multiple simultaneous tracking beams, phased arrays are more suitable. For most part, this report studies phased array antenna designs for two different applications for Space Exploration Initiative. It also studies one design for a tri-reflector type antenna. These antennas will be based on a Mars orbiting satellite.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-196298 , NAS 1.26:196298
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    A constrained joint source/channel coder design and vector quantization of nonstationary sources (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The emergence of broadband ISDN as the network for the future brings with it the promise of integration of all proposed services in a flexible environment. In order to achieve this flexibility, asynchronous transfer mode (ATM) has been proposed as the transfer technique. During this period a study was conducted on the bridging of network transmission performance and video coding. The successful transmission of variable bit rate video over ATM networks relies on the interaction between the video coding algorithm and the ATM networks. Two aspects of networks that determine the efficiency of video transmission are the resource allocation algorithm and the congestion control algorithm. These are explained in this report. Vector quantization (VQ) is one of the more popular compression techniques to appear in the last twenty years. Numerous compression techniques, which incorporate VQ, have been proposed. While the LBG VQ provides excellent compression, there are also several drawbacks to the use of the LBG quantizers including search complexity and memory requirements, and a mismatch between the codebook and the inputs. The latter mainly stems from the fact that the VQ is generally designed for a specific rate and a specific class of inputs. In this work, an adaptive technique is proposed for vector quantization of images and video sequences. This technique is an extension of the recursively indexed scalar quantization (RISQ) algorithm.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-195145 , NAS 1.26:195145
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Development and evaluation of packet video schemes (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Reflecting the two tasks proposed for the current year, namely a feasibility study of simulating the NASA network, and a study of progressive transmission schemes, are presented. The view of the NASA network, gleaned from the various technical reports made available to use, is provided. Also included is a brief overview of how the current simulator could be modified to accomplish the goal of simulating the NASA network. As the material in this section would be the basis for the actual simulation, it is important to make sure that it is an accurate reflection of the requirements on the simulator. Brief descriptions of the set of progressive transmission algorithms selected for the study are contained. The results available in the literature were obtained under a variety of different assumptions, not all of which are stated. As such, the only way to compare the efficiency and the implementational complexity of the various algorithms is to simulate them.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-187690 , NAS 1.26:187690
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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