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

Roth, Jeffrey M.; Rauch, Stephen; Reynolds, Brett; Schieler, Curt; Ulmer, Todd G.

doi:10.1117/12.2607413

Cited by 2 publications

(1 citation statement)

References 5 publications

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“…This can be done in-lab by using a relatively fast modulator to attenuate the optical signal from the test transmitter. [7][8][9] To obtain the integration times required to characterize codeword error rate (CWER) performance, it is desirable to be able to synthesize fade vectors to modulate the signal continuously in real time for CWER tests that may run for many hours.…”

Section: Introductionmentioning

confidence: 99%

Statistical analysis of fading power vectors for real-time atmospheric channel emulation

Chahine

Katz

Vyhnalek

et al. 2023

Free-Space Laser Communications XXXV

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The design and testing of a free-space optical communication system requires assessment of the impact of random fluctuations in received power from a laser beam transmitted over an atmospheric channel. A number of methods for generating fading power vectors for in-lab emulation of an atmospheric channel have previously been reported. These techniques include spectral shaping and filtering of a signal from a normally distributed pseudo-random number generator, full wave optics simulations with random phase screens, and pre-recorded measurements from experimental free-space links. In this work, a statistical analysis of atmospheric fading is presented with the goal of producing a practical engineering model suitable for generating synthetic fade vectors in real-time for long-duration receiver testing with channel interleaving. Specifically, a parametric model is developed for turbulence-induced fade on space-to-ground links with large-aperture receivers, including aperture-averaging and the effects of aperture size on the instantaneous coupling efficiency for mode-limited receivers. In particular, we analyze the probability density function and temporal power spectrum for fluctuations of the coupling efficiency for few-mode fibers in a range of turbulence conditions.

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Section: Introductionmentioning

confidence: 99%

Statistical analysis of fading power vectors for real-time atmospheric channel emulation

Chahine

Katz

Vyhnalek

et al. 2023

Free-Space Laser Communications XXXV

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Diversity of repeat-coded waveforms with forward-error correction and interleaving in fading atmospheric channels

Roth,

Rauch,

Schieler

et al. 2024

Laser Communication and Propagation Through the Atmosphere and Oceans XIII

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Interleaving and repeat coding are techniques that provide immunity to channel effects for optical communications links. Interleaving provides robustness at the physical layer of the network stack, at the expense of additional latency. The temporal diversity ratio, L, is defined as the number of statistically-independent fade events experienced by an individual code-word in an interleaved framing structure. L characterizes an interleaver's ability to whiten a channel so forward-error correction codes for mitigating additive white Gaussian noise function effectively. For large L's, an interleaver can tolerate a wide duration of fade dropouts with high latency, while smaller L's improve latency yet suffer more fade-induced power penalties. Repeat coding is another technique that can enhance a channel's resilience to atmospheric fading by sending identical copies of frames. Repeatcoding techniques allow a link to operate at lower signal-to-noise ratios, while still maintaining a fixed slot clock to simplify receiver design. We define Q as the frame replication factor for a repeat-coded waveform.We investigate interleaver performance in different regimes of both L and Q. We develop a model to supplement interleaver dynamics with repeat coding under atmospheric fading, and investigate regimes with different values of fading strength, interleaver diversity L, and repeat-coding Q. An experimental optical modem testbed with a flexible configuration is used to validate the model. We show good agreement between the model and experimental laboratory tests over a wide range of cases studied.

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

Cited by 2 publications

References 5 publications

Statistical analysis of fading power vectors for real-time atmospheric channel emulation

Statistical analysis of fading power vectors for real-time atmospheric channel emulation

Diversity of repeat-coded waveforms with forward-error correction and interleaving in fading atmospheric channels

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