Training-aided joint frame and frequency synchronization for free space optical communication signals with low OSNR

Cheng, Qian; Cui, Sheng; Zhou, Keji; Liu, Deming

doi:10.1016/j.optcom.2020.126046

Cited by 7 publications

(6 citation statements)

References 11 publications

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“…The proposed algorithm is compared with a TS-based joint processing algorithm in [19] for the overall complexity of FS and FOE in Table II. In this case, the complexity of the FS algorithm considers only the computation of 𝐶 𝑚 (𝑑) , while assuming a sliding window M times (M is generally the length of the entire training cycle of symbols without setting a threshold).…”

Section: Complexity Analysis and Comparisonmentioning

confidence: 99%

“…The TS-based FOE algorithm [18], [19] uses the TS to remove the modulated phase of the received signal and avoids the 4th power operation that is commonly employed in blind estimation algorithms. As a result, its complexity is lower and the estimation range is wider.…”

Section: Introductionmentioning

confidence: 99%

“…Another critical issue in the TS-based approach is accurately locating the starting point of the TS to estimate the frequency offset correctly. Although an algorithm for joint frame and frequency synchronization has been proposed in [19], it does not perform well with a short number of training symbols for FOE. Therefore, developing a generalized FOE scheme that is highly performant, low complexity, and supports multiple formats remains a challenging task.…”

Section: Introductionmentioning

confidence: 99%

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Carrier FOE Scheme Based on FSTS in Spatial Diversity PM Coherent FSO Communication

Wang

Tang

2023

IEEE Photonics J.

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The efficient and cost-effective suppression of atmospheric turbulence effects in free-space optical (FSO) communication poses a significant challenge. To address this challenge, a carrier frequency offset estimation (FOE) scheme based on frame-synchronous training sequence (FSTS) is proposed, which can be applied to spatial diversity polarization multiplexing (PM) coherent FSO communication system. The proposed scheme integrates the functions of frame synchronization (FS) and FOE by designing distinct training sequences for the X and Y polarizations. Specifically, the FOE scheme achieves high accuracy, wide range, low complexity, and multi-format versatility while maintaining FS accuracy. Simulation results for PM 4/16-quadrature amplitude modulation (QAM) demonstrate the feasibility and generality of the proposed scheme. Moreover, when combined with the spatial diversity reception under strong and weak turbulence conditions, the proposed algorithm exhibits higher receiver sensitivity compared to the conventional training sequence (TS)-based FOE algorithm. The advantages of this scheme make it highly promising for high-speed coherent FSO communications across multiple modulation formats.

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Section: Complexity Analysis and Comparisonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Carrier FOE Scheme Based on FSTS in Spatial Diversity PM Coherent FSO Communication

Wang

Tang

2023

IEEE Photonics J.

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“…nn SS + consisting of the same symbol sequences to be added must be estimated first, so that the OPO can be compensated before the coherent addition. The OPO estimation can be realized blindly or with the help of pilot symbols and frame synchronization algorithms able to locate them under very lower OSNR [23], [24]. To average out the error induced by the large ASE noise, the OPO can be estimated by the following equations [23] …”

Section: Phase Alignment Error and Combining Lossmentioning

confidence: 99%

Toward Practical Temporal Diversity Coherent Combining Based Variable Data-Rate Free Space Optical Communication Systems

Cui

Chen

et al. 2022

IEEE Access

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Free-space optical communication (FSOC) systems with variable data-rates can support different missions with different transmission distances and ensure reliable transmission in periods of unfavorable weather conditions. The temporal diversity coherent combining (TDCC) technique can adjust the data-rate in a very large range using a software-defined manner by taking advantage of the digital coherent receivers able to recover the signal field. In this paper, we investigate the relationships between the computational complexity, optical phase alignment error, combining loss (CL) and data-rate for the TDCCbased variable data-rate coherent optical receiver. We also propose a method to minimize the computational complexity while achieving the expected output optical signal-to-noise ratio (OSNR) and the highest datarate for an arbitrary input OSNR. Numerical simulations and experiments are carried out to validate the analytical expressions and proposed methods. The results provide an efficient tool and useful guidelines for the design of low computation complexity TDCC-based variable data-rate FSOC systems. INDEX TERMSTemporal diversity coherent combining, free-space optical communication, variable data rate, phase alignment, combining loss.

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“…The interested reader is referred to Refs. [9], [18] and [19] for further details of the time alignment algorithms. In previous work, we only studied the equal gain combining (EGC) based digital phase alignment [17].…”

Section: Introductionmentioning

confidence: 99%

Toward Practical Digital Phase Alignment for Coherent Beam Combining in Multi-Aperture Free Space Coherent Optical Receivers

Rao

Cui

et al. 2020

IEEE Access

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In free space optical communication systems, multi-aperture coherent optical receivers based on digital coherent beam combining (D-CBC) technique can provide exceptionally high sensitivity and are more robust to the atmosphere turbulence compared with the single aperture receivers with the same collection area. D-CBC relies on the digital phase alignment algorithm (PAA) to align the different versions of signals in phase. However, due to the limited working frequency and space of the digital signal processing (DSP) circuits, the main obstacle to realizing real-time phase alignment of multiple high-speed optical signals is the computation complexity. Therefore, we need to minimize the computation complexity while guaranteeing a satisfactory performance. In this paper, we investigate the relationship between the computation complexity and the combining loss (CL) for both maximum ratio combining (MRC) and equal gain combining (EGC) based D-CBC. Universal analytical expressions are deduced that allow easy minimization of the computation complexity for both MRC and EGC based receivers according to the prescribed CL and input optical signal-to-noise ratios (OSNRs). The analytical expressions are validated by extensive numerical simulations. It is demonstrated that the computation complexity is mainly determined by the quality of the signal with a larger OSNR in MRC, while it is determined by the overall quality of the signals in EGC. When EGC is replaced with MRC, the computation complexity can be reduced by more than 55% at the same CL when the OSNR difference between the signals to be combined is above 10dB. The maximum computation complexity increases exponentially with decreasing input OSNR lower limit and the smaller the CL, the steeper the slope. Furthermore, when the prescribed CL is relaxed from 0.1 to 0.5dB, the maximum computation complexity can be reduced by about 80%. The results provide useful guidelines toward practical phase alignment on a real-time platform.INDEX TERMS Multi-aperture receiver, free-space optical communication, phase alignment, digital coherent combining, equal gain combing, maximum ratio combining, combining loss

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Training-aided joint frame and frequency synchronization for free space optical communication signals with low OSNR

Cited by 7 publications

References 11 publications

Carrier FOE Scheme Based on FSTS in Spatial Diversity PM Coherent FSO Communication

Carrier FOE Scheme Based on FSTS in Spatial Diversity PM Coherent FSO Communication

Toward Practical Temporal Diversity Coherent Combining Based Variable Data-Rate Free Space Optical Communication Systems

Toward Practical Digital Phase Alignment for Coherent Beam Combining in Multi-Aperture Free Space Coherent Optical Receivers

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