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  • 1
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    Terabit free-space data transmission employing orbital angular momentum multiplexing (2012)
    Springer Nature
    Details
    Publication Date: 2012-06-24
    Print ISSN: 1749-4885
    Electronic ISSN: 1749-4893
    Topics: Physics
    Published by Springer Nature
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    PAPER CURRENT
  • 2
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    An Overview of Optical Communication for Deep Space: Issues, Challenges, Solutions (2012)
    In:  Other Sources
    Details
    Publication Date: 2018-06-11
    Description: No abstract available
    Keywords: Communications and Radar
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Bounded-Angle Iterative Decoding of LDPC Codes (2009)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: Bounded-angle iterative decoding is a modified version of conventional iterative decoding, conceived as a means of reducing undetected-error rates for short low-density parity-check (LDPC) codes. For a given code, bounded-angle iterative decoding can be implemented by means of a simple modification of the decoder algorithm, without redesigning the code. Bounded-angle iterative decoding is based on a representation of received words and code words as vectors in an n-dimensional Euclidean space (where n is an integer).
    Keywords: Mathematical and Computer Sciences (General)
    Type: NASA Tech Briefs, April 2009; 19
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    The Dolinar Receiver in an Information Theoretic Framework (2011)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Optical communication at the quantum limit requires that measurements on the optical field be maximally informative, but devising physical measurements that accomplish this objective has proven challenging. The Dolinar receiver exemplifies a rare instance of success in distinguishing between two coherent states: an adaptive local oscillator is mixed with the signal prior to photodetection, which yields an error probability that meets the Helstrom lower bound with equality. Here we apply the same local-oscillator-based architecture with aninformation-theoretic optimization criterion. We begin with analysis of this receiver in a general framework for an arbitrary coherent-state modulation alphabet, and then we concentrate on two relevant examples. First, we study a binary antipodal alphabet and show that the Dolinar receiver's feedback function not only minimizes the probability of error, but also maximizes the mutual information. Next, we study ternary modulation consistingof antipodal coherent states and the vacuum state. We derive an analytic expression for a near-optimal local oscillator feedback function, and, via simulation, we determine its photon information efficiency (PIE). We provide the PIE versus dimensional information efficiency (DIE) trade-off curve and show that this modulation and the our receiver combination performs universally better than (generalized) on-off keying plus photoncounting, although, the advantage asymptotically vanishes as the bits-per-photon diverges towards infinity.
    Keywords: Optics; Communications and Radar; Cybernetics, Artificial Intelligence and Robotics
    Type: SPIE Optics and Photonics 2011; Aug 21, 2011 - Aug 25, 2011; San Diego, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Approaching the Ultimate Limits of Communication Efficiency with a Photon-Counting Detector (2012)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Coherent states achieve the Holevo capacity of a pure-loss channel when paired with an optimal measurement, but a physical realization of this measurement is as of yet unknown, and it is also likely to be of high complexity. In this paper, we focus on the photon-counting measurement and study the photon and dimensional efficiencies attainable with modulations over classical- and nonclassical-state alphabets. We first review the state-of-the-art coherent on-off-keying (OOK) with a photoncounting measurement, illustrating its asymptotic inefficiency relative to the Holevo limit. We show that a commonly made Poisson approximation in thermal noise leads to unbounded photon information efficiencies, violating the conjectured Holevo limit. We analyze two binary-modulation architectures that improve upon the dimensional versus photon efficiency tradeoff achievable with conventional OOK. We show that at high photon efficiency these architectures achieve an efficiency tradeoff that differs from the best possible tradeoff--determined by the Holevo capacity--by only a constant factor. The first architecture we analyze is a coherent-state transmitter that relies on feedback from the receiver to control the transmitted energy. The second architecture uses a single-photon number-state source.
    Keywords: Communications and Radar
    Type: IEEE International Symposium on Information Theory (ISIT''12); Jul 01, 2012 - Jul 06, 2012; Cambridge, MA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    On Approaching the Ultimate Limits of Communication Using a Photon-Counting Detector (2012)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Coherent states achieve the Holevo capacity of a pure-loss channel when paired with an optimal measurement, but a physical realization of this measurement scheme is as of yet unknown, and it is also likely to be of high complexity. In this paper, we focus on the photon-counting measurement and study the photon and dimensional efficiencies attainable with modulations over classical- and nonclassical-state alphabets. We analyze two binary modulation architectures that improve upon the dimensional versus photon efficiency tradeoff achievable with the state-of-the-art coherent-state on-off keying modulation. We show that at high photon efficiency these architectures achieve an efficiency tradeoff that differs from the best possible tradeoff--determined by the Holevo capacity--by only a constant factor. The first architecture we analyze is a coherent-state transmitter that relies on feedback from the receiver to control the transmitted energy. The second architecture uses a single-photon number-state source.
    Keywords: Communications and Radar
    Type: SPIE Photonics West; Jan 21, 2012 - Jan 26, 2012; San Francisco, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Limits on Achievable Dimensional and Photon Efficiencies with Intensity-Modulation and Photon-Counting Due to Non-Ideal Photon-Counter Behavior (2012)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An ideal intensity-modulated photon-counting channel can achieve unbounded photon information efficiencies (PIEs). However, a number of limitations of a physical system limit the practically achievable PIE. In this paper, we discuss several of these limitations and illustrate their impact on the channel. We show that, for the Poisson channel, noise does not strictly bound PIE, although there is an effective limit, as the dimensional information efficiency goes as e[overline] e PIE beyond a threshold PIE. Since the Holevo limit is bounded in the presence of noise, this illustrates that the Poisson approximation is invalid at large PIE for any number of noise modes. We show that a finite transmitter extinction ratio bounds the achievable PIE to a maximum that is logarithmic in the extinction ratio. We show how detector jitter limits the ability to mitigate noise in the PPM signaling framework. We illustrate a method to model detector blocking when the number of detectors is large, and illustrate mitigation of blocking with spatial spreading and altering. Finally, we illustrate the design of a high photon efficiency system using state-of-the-art photo-detectors and taking all these effects into account.
    Keywords: Optics
    Type: SPIE Photonics West; Jan 21, 2012 - Jan 26, 2012; San Francisco, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Serial turbo trellis coded modulation using a serially concatenated coder (2010)
    In:  CASI
    Details
    Publication Date: 2019-08-26
    Description: Serial concatenated trellis coded modulation (SCTCM) includes an outer coder, an interleaver, a recursive inner coder and a mapping element. The outer coder receives data to be coded and produces outer coded data. The interleaver permutes the outer coded data to produce interleaved data. The recursive inner coder codes the interleaved data to produce inner coded data. The mapping element maps the inner coded data to a symbol. The recursive inner coder has a structure which facilitates iterative decoding of the symbols at a decoder system. The recursive inner coder and the mapping element are selected to maximize the effective free Euclidean distance of a trellis coded modulator formed from the recursive inner coder and the mapping element. The decoder system includes a demodulation unit, an inner SISO (soft-input soft-output) decoder, a deinterleaver, an outer SISO decoder, and an interleaver.
    Keywords: Electronics and Electrical Engineering
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Encoders for block-circulant LDPC codes (2009)
    In:  CASI
    Details
    Publication Date: 2019-08-26
    Description: Methods and apparatus to encode message input symbols in accordance with an accumulate-repeat-accumulate code with repetition three or four are disclosed. Block circulant matrices are used. A first method and apparatus make use of the block-circulant structure of the parity check matrix. A second method and apparatus use block-circulant generator matrices.
    Keywords: Computer Programming and Software
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    NASA TECHNICAL REPORTS
  • 10
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    Iterative Demodulation and Decoding of Non-Square QAM (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: It has been shown that a non-square (NS) 2(sup 2n+1)-ary (where n is a positive integer) quadrature amplitude modulation [(NS)2(sup 2n+1)-QAM] has inherent memory that can be exploited to obtain coding gains. Moreover, it should not be necessary to build new hardware to realize these gains. The present scheme is a product of theoretical calculations directed toward reducing the computational complexity of decoding coded 2(sup 2n+1)-QAM. In the general case of 2(sup 2n+1)-QAM, the signal constellation is not square and it is impossible to have independent in-phase (I) and quadrature-phase (Q) mapping and demapping. However, independent I and Q mapping and demapping are desirable for reducing the complexity of computing the log likelihood ratio (LLR) between a bit and a received symbol (such computations are essential operations in iterative decoding). This is because in modulation schemes that include independent I and Q mapping and demapping, each bit of a signal point is involved in only one-dimensional mapping and demapping. As a result, the computation of the LLR is equivalent to that of a one-dimensional pulse amplitude modulation (PAM) system. Therefore, it is desirable to find a signal constellation that enables independent I and Q mapping and demapping for 2(sup 2n+1)-QAM.
    Keywords: Man/System Technology and Life Support
    Type: NPO-40308 , NASA Tech Briefs, September 2004; 9
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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