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  • COMMUNICATIONS AND RADAR  (5)
  • NUMERICAL ANALYSIS  (1)
  • 1
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    A synchronization technique for optical PPM signals (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A technique for maintaining synchronization between optical PPM (pulse-position modulation) pulses and a receiver clock by means of a delay-tracking loop is described and analyzed. The tracking loop is driven by a doubly stochastic Poisson process that contains information about the location of the desired slot boundaries. The slot boundaries are subject to slowly varying random delays that are ultimately tracked by the loop. The concept of fractional rms delay error is introduced to quantify the effects of signal and background induced shot noise on the performance of the delay-tracking loop.
    Keywords: COMMUNICATIONS AND RADAR
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    NASA TECHNICAL REPORTS
  • 2
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    Performance of residual carrier array-feed combining in correlated noise (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: An array feed combining system for the recovery of signal-to-noise ratio (SNR) loss due to antenna reflector deformation has been implemented and is currently being evaluated on the Jet Propulsion Laboratory's 34-meter DSS-13 antenna. In this system, the defocused signal field captured by a focal plane array feed is recovered using real-time signal-processing and signal-combining techniques. The current signal-processing and signal-combining algorithms are optimum under the assumption that the white Gaussian noise processes in the received signals from different array elements are mutually uncorrelated. Experimental data at DSS 13 indicate that these noise processes are indeed mutually correlated. The main result of this article is an analytical derivation of the actual SNR performance of the current suboptimal signal-combining algorithm in this correlated-noise environment. The analysis here shows that the combined signal SNR can either be improved or degraded depending on the relation between the array signal and noise correlation coefficient phases. Further performance improvement will require the development of signal-combining methods that take into account the correlated noises.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 131-147
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Capacity of a multimode direct detection optical communication channel (1981)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The capacity is derived under both peak and average signal power constraints and without a signal bandwidth constraint. A random telegraph wave type signalling scheme of Kabanov is known to achieve capacity provided enough signalling bandwidth is available. In the absence of received background noise, an optimally coded PPM system is shown to achieve capacity with greatly reduced bandwidth as compared to Kabanov signals.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 51-70
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    A synchronization technique for optical PPM signals (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A technique for maintaining synchronization between optical PPM (pulse-position modulation) pulses and a receiver clock by means of a delay-tracking loop is described and analyzed. The tracking loop is driven by a doubly stochastic Poisson process that contains information about the location of the desired slot boundaries. The slot boundaries are subject to slowly varying random delays that are ultimately tracked by the loop. The concept of fractional rms delay error is introduced to quantify the effects of signal and background induced shot noise on the performance of the delay-tracking loop.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 24-31
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Capacity of a direct detection optical communication channel (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The capacity of a free space optical channel using a direct detection receiver is derived under both peak and average signal power constraints and without a signal bandwidth constraint. The addition of instantaneous noiseless feedback from the receiver to the transmitter does not increase the channel capacity. In the absence of received background noise, an optimally coded PPM system is shown to achieve capacity in the limit as signal bandwidth approaches infinity. In the case of large peak to average signal power ratios, an interleaved coding scheme with PPM modulation is shown to have a computational cutoff rate far greater than ordinary coding schemes.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''80; National Telecommunications Conference; Nov 30, 1980 - Dec 04, 1980; Houston, TX
    Format: text
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  • 6
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    Quadratic integer programming for large scale banded matrices (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper is concerned with the integer quadratic program where the variables are constrained to belong to a given set of discrete values. This quadratic integer program is shown to be equivalent to a problem of finding the shortest path in a particular directed graph called a trellis when the matrix is a positive-definite symmetric banded matrix. An efficient procedure for solving this shortest path problem is presented which allows the solution of the integer quadratic program. This method is particularly effective when the half-bandwidth of the matrix is significantly smaller than its dimension.
    Keywords: NUMERICAL ANALYSIS
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