Mr. Brett Reynolds Profile

Brett Reynolds

at MIT Lincoln Lab.

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Publications (3)

Proceedings Article | 12 March 2024 Presentation + Paper

Implementing and testing generalized pointing, acquisition, and tracking for a space-based adaptive communications node (Space-BACN)

Todd Ulmer, Brett Reynolds, John Moores, Mike Butterfield, Gregory Kuperman

Proceedings Volume 12877, 128770O (2024) https://doi.org/10.1117/12.3009620

KEYWORDS: Acquisition tracking and pointing, Beam divergence, Standards development, Optical testing, Transmitters, Free space optical communications

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Proceedings Article | 4 March 2022 Presentation + Paper

Forward error correction and interleaving performance for lasercom terminals in fading channels

Jeffrey Roth, Stephen Rauch, Brett Reynolds, Curt Schieler, Todd Ulmer

Proceedings Volume 11993, 1199307 (2022) https://doi.org/10.1117/12.2607413

KEYWORDS: Receivers, Forward error correction, Scintillation, Channel projecting optics, Transmitters, Performance modeling, Electro optics, Digital electronics, Variable optical attenuators, Telecommunications

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Interleaving is a well-known technique utilizing temporal diversity to mitigate burst errors in a communications link. Interleaving provides robustness at the physical layer of the network stack, at the expense of an increase in latency. An important parameter used in characterizing interleaver performance is the temporal diversity L, defined as the number of statistically independent fade events experienced by an individual codeword. This temporal diversity L characterizes the interleaver’s ability to whiten a channel so that forward error correction codes designed to mitigate additive white Gaussian noise function effectively. For large values of L, the interleaver is effectively “infinite”, and deeper interleaving produces no additional benefit. As L is decreased, the power penalty grows, and increasingly more average power must be transmitted to ensure error-free decoding at the receiver. Here we investigate interleaver performance in the regime where L is decreasing and the interleaver is not effectively infinite. Our goals are to (1) determine the regime where the interleaver is no longer effectively infinite, and (2) characterize the power penalty as a function of L to understand how the performance degrades as L is reduced. A theoretical model is presented that allows us to investigate interleaver performance in the presence of weak, moderate, and strong turbulence (scintillation indices of 0.2, 0.5, and 1.0, respectively). The model results show a gradual increase in penalty for reduced L for the weak-fading conditions. The moderate and strong fading conditions show similar dependence, with significant penalties over 3 dB developing as L drops below 100, and these penalties grow more rapidly when L drops below 10. We show close agreement to these models with experiments using a fiber-based, optical modem. This optical modem utilizes rate-1/2 coding together with a variable interleaver delay spanning three octaves. The optical data signal is transmitted through a fade emulator that applies the same fade profiles used in the theoretical model. This faded signal is sent to an optical-to-electrical receiver, and then into a digital electronics unit that processes the electrical signal to assess the coded communications performance.

Proceedings Article | 4 March 2019 Presentation + Paper

Variable, two-color acquisition beam for free-space laser communication terminals

Jeffrey Roth, Shankararaman Ramakrishnan, Robert Murphy, Alicia Volpicell, Stephen Rauch, Michael Andrle, Alexander King, Brett Reynolds, John Taylor, Ronald Parenti, John Chang, Todd Ulmer

Proceedings Volume 10910, 109100Q (2019) https://doi.org/10.1117/12.2513964

KEYWORDS: Acquisition tracking and pointing, Transmitters, Optical amplifiers, Signal attenuation, Free space optical communications, Receivers, Telecommunications, Optical communications, Beam shaping, Atmospheric scintillation, Beam mode converters

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