| 1. |
- Ding, Jiazheng, et al.
(författare)
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Intra-Channel Nonlinearity Mitigation in Optical Fiber Transmission Systems Using Perturbation-Based Neural Network
- 2022
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 40:21, s. 7106-7116
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a perturbation-based neural network (P-NN) scheme with an embedded bidirectional long short-term memory (biLSTM) layer is investigated to compensate for the Kerr fiber nonlinearity in optical fiber communication systems. Numerical simulations have been carried out in a 32-Gbaud dual-polarization 16-ary quadrature amplitude modulation (DP-16QAM) transmission system. It is shown that this P-NN equalizer can achieve signal-to-noise ratio improvements of similar to 1.37 dB and similar to 0.80 dB, compared to the use of a linear equalizer and a single step per span (StPS) digital back propagation (DBP) scheme, respectively. The P-NN equalizer requires lower computational complexity and can effectively compensate for intra-channel nonlinearity. Meanwhile, the performance of P-NN is more robust to the distortion caused by equalization enhanced phase noise (EEPN). Furthermore, it is also found that there exists a tradeoff between the choice of modulation format and the nonlinear equalization schemes for a given transmission distance.
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| 2. |
- Hou, Jianshen, et al.
(författare)
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Rewiring carbon flux in Escherichia coli using a bifunctional molecular switch
- 2020
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Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176 .- 1096-7184. ; 61, s. 47-57
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Tidskriftsartikel (refereegranskat)abstract
- The unbalanced distribution of carbon flux in microbial cell factories can lead to inefficient production and poor cell growth. Uncoupling cell growth and chemical synthesis can therefore improve microbial cell factory efficiency. Such uncoupling, which requires precise manipulation of carbon fluxes, can be achieved by up-regulating or down-regulating the expression of enzymes of various pathways. In this study, a dynamic turn-off switch (dTFS) and a dynamic turn-on switch (dTNS) were constructed using growth phase-dependent promoters and degrons. By combining the dTFS and dTNS, a bifunctional molecular switch that could orthogonally regulate two target proteins was introduced. This bifunctional molecular switch was used to uncouple cell growth from shikimic acid and D-glucaric acid synthesis, resulting in the production of 14.33 g/L shikimic acid and the highest reported productivity of D-glucaric acid (0.0325 g/L/h) in Escherichia coli MG1655. This proved that the bifunctional molecular switch could rewire carbon fluxes by controlling target protein abundance.
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| 3. |
- Hu, Wenxiu, et al.
(författare)
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High-Dimensional Feature Based Non-Coherent Detection for Multi-Intensity Modulated Ultraviolet Communications
- 2022
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 40:7, s. 1879-1887
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet communication (UVC) has been regarded as a promising supplement for overloaded conventional wireless communications. One challenge lies in the communication deterioration caused by the UV-photon scattering induced intersymbol-interference (ISI), which will be even worse when encountering multilevel pulse amplitude modulation (multi-PAM) symbols. To address this ISI, traditional coherent detection methods (e.g., maximum-likelihood sequence detection, MLSD) require high computational complexities for UV channel estimation and sequential detection space formation, thereby making them less attractive. Current non-coherent detection, which simply combines the ISI-insensitive UV signal features (e.g., the rising edge) into a one-dimensional (1D) metric, cannot guarantee reliable communication accuracy. In this work, a novel high-dimensional (HD) non-coherent detection scheme is proposed, leveraging a HD construction of the ISI-insensitive UV signal features. By doing so, we transform the ISI caused sequential detection into an ISI-released HD detection framework, which avoids complex channel estimation and sequential detection space computation. Then, to compute the detection surface, a UV feature based unsupervised learning approach is designed. We deduce the theoretical bit error rate (BER), and prove that the proposed HI) non-coherent detection method has a lower BER than that of the current 1D non-coherent scheme. Simulation results validate our results, and more importantly, demonstrate a BER that approaches that of the state-of-the-art coherent MLSD (<1 dB in SNR at BER = 4.5 x 10(-8), the 7% overhead forward-error-correction limit), and also a reduction of computational complexity by at least two orders of magnitude.
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| 4. |
- Hu, Wenxiu, et al.
(författare)
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Non-Coherent Detection for Ultraviolet Communications With Inter-Symbol Interference
- 2020
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 38:17, s. 4699-4707
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Tidskriftsartikel (refereegranskat)abstract
- Ultraviolet communication (UVC) serves as a promising supplement to share the responsibility for the overloads in conventional wireless communication systems. One difficulty lies in how to address the inter-symbol-interference (ISI) from the strong scattering nature and the time-varying channel response. This is more challenging for the energy-constrained scenarios (e.g., underwater UV), as existing coherent schemes (i.e., requiring exact channel information for signal detection) become less attractive given the computational and storaging complexity for repeated time-varying channel estimation and statistical signal detection. In this work, a novel non-coherent paradigm is proposed, via the exploration of the UV signal features that are insensitive to the ISI. By optimally weighting and combining the extracted features to minimize the bit error rate (BER), the optimally-weighted non-coherent detection (OWNCD) is proposed, which converts the signal detection with ISI into a binary detection framework, with a heuristic weight updating approach for time-varying channel. As such, the proposed OWNCD avoids the complex channel estimation and guarantees the detection accuracy. Compared to the state-of-the-art coherent maximum likelihood sequence detection (MLSD) in the cases of static and time-varying channel response, the proposed OWNCD can gain similar to 1 dB and similar to 8 dB in signal-to-noise-ratio (SNR) at the 7% overhead forward-error-correction (FEC) limit (BER of 4.5 x 10(-3)), respectively, and can also reduce the computational complexity by 4 order of magnitude.
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| 5. |
- Hu, Wenxiu, et al.
(författare)
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Tapping Eavesdropper Designs Against Physical Layer Secret Key in Point-to-Point Fiber Communications
- 2023
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Ingår i: Journal of Lightwave Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8724 .- 1558-2213. ; 41:5, s. 1406-1414
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Tidskriftsartikel (refereegranskat)abstract
- With the growing demand for service access and data transmission, security issues in optical fiber systems have become increasingly important and the subject of increased research. Physical layer secret key generation (PL-SKG), which leverages the random but common channel properties at legitimate parties, has been shown to be a secure, low-cost, and easily deployed technique as opposed to computational-based cryptography, quantum, and chaos key methods that rely on precise equipment. However, the eavesdropper (Eve) potential for current PL-SKG in fiber communications has been overlooked by most studies to date. Unlike wireless communications, where the randomness comes from the spatial multi-paths that cannot be all captured by Eves, in fiber communications, all the randomness (from transmitted random pilots or channel randomness) is contained in the signals transmitted inside the fiber. This, therefore, enables a tapping Eve to reconstruct the common features of legitimate users from its received signals, and further decrypt the featured-based secret keys. To implement this idea, we designed two Eve schemes against polarization mode distortion (PMD) based PL-SKG and the two-way cross multiplication based PL-SKG. The simulation results show that our proposed Eves can successfully reconstruct the legitimate common feature and the secret key relied upon, leading to secret key rate (SKR) reductions of between three and four orders of magnitude in the PL-SKG schemes studied. As a result, we reveal and demonstrate a novel eavesdropping potential to provide challenges for current physical layer secret key designs. We hope to provide more insightful vision and critical evaluation on the design of new physical layer secret key schemes in optical fiber links, to provide more comprehensively secure, and intelligent optical networks.
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