| 1. |
- Hong, Xuezhi, et al.
(author)
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Linearly interpolated sub-symbol optical phase noise suppression in CO-OFDM system
- 2015
-
In: Optics Express. - 1094-4087. ; 23:4, s. 4691-4702
-
Journal article (peer-reviewed)abstract
- An optical phase noise suppression algorithm, LI-SCPEC, based on phase linear interpolation and sub-symbol processing is proposed for CO-OFDM system. By increasing the temporal resolution of carrier phase tracking through dividing one symbol into several sub-blocks, i.e., sub-symbols, inter-carrier-interference (ICI) mitigation is achieved in the proposed algorithm. Linear interpolation is employed to obtain a reliable temporal reference for sub-symbol phase estimation. The new algorithm, with only a few number of sub-symbols (N-B = 4), can provide a considerably larger laser linewidth tolerance than several other ICI mitigation algorithms as demonstrated by Monte-Carlo simulations. Numerical analysis verifies that the best performance is achieved with an optimal and moderate number of sub-symbols. Complexity analysis shows that the required number of complex-valued multiplications is independent of the number of sub-symbols used in the proposed algorithm. (C) 2015 Optical Society of America
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| 2. |
- Hong, Xuezhi, et al.
(author)
-
Low-complexity linewidth-tolerant time domain sub-symbol optical phase noise suppression in CO-OFDM systems
- 2016
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In: Optics Express. - 1094-4087. ; 24:5, s. 4856-4871
-
Journal article (peer-reviewed)abstract
- Two linewidth-tolerant optical phase noise suppression algorithms, non-decision aided sub-symbol optical phase noise suppression (NDA-SPS) and partial-decision aided sub-symbol optical phase noise suppression (PDA-SPS), based on low-complexity time domain sub-symbol processing are proposed for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. High accuracy carrier phase estimation is achieved in the NDA-SPS algorithm without decision error propagation. Compared with NDA-SPS, partial-decision aided estimation is introduced in PDA-SPS to reduce the pilot-overhead by half, yet only a small performance degradation is induced. The principles and computational complexities of the proposed algorithms are theoretically analyzed. By adopting specially designed comb-type pilot subcarriers, multiplier-free observation-based matrix generation is realized in the proposed algorithms. Computationally intensive discrete Fourier transform (DFT) or inverse DFT (IDFT) operations, which are usually carried out in other high-performance inter-carrier-interference (ICI) mitigation algorithms multiple times, are completely avoided. Compared with several other sub-symbol algorithms, the proposed algorithms with lower complexities offer considerably larger laser linewidth tolerances as demonstrated by Monte-Carlo simulations. Numerical analysis verifies that the optimal performance of PDA-SPS can be achieved with moderate numbers of sub-symbols.
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| 3. |
- Hong, Xiaojian, et al.
(author)
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Low-complexity optical phase noise suppression in CO-OFDM system using recursive principal components elimination
- 2015
-
In: Optics Express. - 1094-4087. ; 23:18, s. 24077-24087
-
Journal article (peer-reviewed)abstract
- A low-complexity optical phase noise suppression approach based on recursive principal components elimination, R-PCE, is proposed and theoretically derived for CO-OFDM systems. Through frequency domain principal components estimation and elimination, signal distortion caused by optical phase noise is mitigated by R-PCE. Since matrix inversion and domain transformation are completely avoided, compared with the case of the orthogonal basis expansion algorithm (L = 3) that offers a similar laser linewidth tolerance, the computational complexities of multiple principal components estimation are drastically reduced in the R-PCE by factors of about 7 and 5 for q = 3 and 4, respectively. The feasibility of optical phase noise suppression with the R-PCE and its decision-aided version (DA-R-PCE) in the QPSK/16QAM CO-OFDM system are demonstrated by Monte-Carlo simulations, which verify that R-PCE with only a few number of principal components q (= 3) provides a significantly larger laser linewidth tolerance than conventional algorithms, including the common phase error compensation algorithm and linear interpolation algorithm. Numerical results show that the optimal performance of R-PCE and DA-R-PCE can be achieved with a moderate q, which is beneficial for low-complexity hardware implementation.
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| 4. |
- Hong, Yuanyuan, et al.
(author)
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A Multi-Floor Arrayed Waveguide Grating Based Architecture with Grid Topology for Datacenter Networks
- 2020
-
In: IEEE Access. - 2169-3536 .- 2169-3536. ; 8, s. 107134-107145
-
Journal article (peer-reviewed)abstract
- This paper proposes a grid topology based passive optical interconnect (POI) architecture that is composed of multiple floors of arrayed waveguide grating routers (AWGRs) to offer high connectivity and scalability for datacenter networks. In the proposed POI signal only needs to pass one AWGR, and thus can avoid the crosstalk accumulation and cascaded filtering effects, which exist in many existing POI architectures based on cascaded AWGRs. Meanwhile, due to high connectivity, the proposed grid topology based POI also has the potential advantage of high reliability. Simulation results validate the network performance. With a proper node degree, the proposed grid topology can achieve acceptable blocking probability. Besides, steady performance is kept when the number of floors increases, indicating good scalability of the proposed POI.
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| 5. |
- Hong, Yuanyuan, et al.
(author)
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Elastic all-optical multi-hop interconnection in data centers with adaptive spectrum allocation
- 2017
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In: Optics Communications. - : Elsevier. - 0030-4018 .- 1873-0310. ; 383, s. 478-484
-
Journal article (peer-reviewed)abstract
- In this paper, a novel flex-grid all-optical interconnect scheme that supports transparent multi-hop connections in data centers is proposed. An inter-rack all-optical multi-hop connection is realized with an optical loop employed at flex-grid wavelength selective switches (WSSs) in an intermediate rack rather than by relaying through optical-electric-optical (O-E-O) conversions. Compared with the conventional O-E-O based approach, the proposed all-optical scheme is able to off-load the traffic at intermediate racks, leading to a reduction of the power consumption and cost. The transmission performance of the proposed flex-grid multi-hop all-optical interconnect scheme with various modulation formats, including both coherently detected and directly detected approaches, are investigated by Monte-Carlo simulations. To enhance the spectrum efficiency (SE), number-of-hop adaptive bandwidth allocation is introduced. Numerical results show that the SE can be improved by up to 33.3% at 40 Gbps, and by up to 25% at 100 Gbps. The impact of parameters, such as targeted bit error rate (BER) level and insertion loss of components, on the transmission performance of the proposed approach are also explored. The results show that the maximum SE improvement of the adaptive approach over the non-adaptive one is enhanced with the decrease of the targeted BER levels and the component insertion loss.
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| 6. |
- Hong, Yuanyuan, et al.
(author)
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Hybrid Routing and Adaptive Spectrum Allocation for Flex-Grid Optical Interconnects
- 2018
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In: Journal of Optical Communications and Networking. - : Optical Society of America. - 1943-0620 .- 1943-0639. ; 10:5, s. 506-514
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Journal article (peer-reviewed)abstract
- A hybrid routing scheme with an adaptive spectrum assignment is proposed for flex-grid all-optical core switch supporting multihop transparent paths in data center networks. Compared with conventional spectrum assignment algorithms (RSA) developed for a multihop network with optical-electric-optical (OEO) conversion in every hop (i.e., RSA for EO) and that devised for an all-optical multihop network (i.e., RSA for AO), the present RSA algorithm provides better utilization of network resources. Being aware of the all-optical bypass path in hopping, the proposed RSA reduces the blocking probability due to lack of bandwidth-tunable transceivers, which is the major reason for blocking for an RSA for the EO. Similar to the RSA for the AO, the proposed RSA is compatible with the number-of-hops adaptive spectrum assignment, which improves spectrum efficiency. On the other hand, the new algorithm enhances connectivity by eliminating the number-of-hops limitation, which severely constrains the performance of RSA for the AO. Simulations for the system are carried out to investigate the performance of the new algorithm. The impacts of various parameters, such as traffic load, ratio of connection requests with different data rates, and resource configuration on the link cost, are studied in terms of network blocking probability (BP). The achievable traffic load of the proposed RSA under varied connection degrees (i.e., the maximum number of ports that one rack has in order to connect to the core switch) and number of racks is also assessed to keep BP no more than 0.1. The results show that the proposed RSA with appropriate cost functions outperforms the EO and AO, which implies that it has the highest scalability.
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| 7. |
- Hong, Yuanyuan, et al.
(author)
-
Neural network-assisted decision-making for adaptive routing strategy in optical datacenter networks
- 2022
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In: Optical Switching and Networking. - : Elsevier BV. - 1573-4277. ; 45
-
Journal article (peer-reviewed)abstract
- To improve the blocking probability (BP) performance and enhance the resource utilization, a correct decision of routing strategy which is most adaptable to the network configuration and traffic dynamics is essential for adaptive routing in optical datacenter networks (DCNs). A neural network (NN)-assisted decision-making scheme is proposed to find the optimal routing strategy in optical DCNs by predicting the BP performance for various candidate routing strategies. The features of an optical DCN architecture (i.e., the rack number N, connection degree D, spectral slot number S and optical transceiver number M) and the traffic pattern (i.e., the ratio of requests of various capacities R, and the load of arriving request) are used as the input to the NN to estimate the optimal routing strategy. A case of two-strategy decision in the transparent optical multi-hop interconnected DCN is studied. Three metrics are defined for performance evaluation, which include (a) the ratio of the load range with wrong decision over the whole load range of interest (i.e., decision error E), (b) the maximum BP loss (BPL) and (c) the resource utilization loss (UL) caused by the wrong decision. Numerical results show that the ratio of error-free cases over tested cases always surpasses 83% and the average values of E, BPL and UL are less than 3.0%, 4.0% and 1.2%, respectively, which implies the high accuracy of the proposed scheme. The results validate the feasibility of the proposed scheme which facilitates the autonomous implementation of adaptive routing in optical DCNs.
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| 8. |
- Hong, Yuanyuan, et al.
(author)
-
Neural network-assisted routing strategy selection for optical datacenter networks
- 2020
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In: Optics InfoBase Conference Papers. - 2162-2701. - 9781943580828
-
Conference paper (peer-reviewed)abstract
- This paper proposes the neural network-assisted routing strategy selection for the optical datacenter networks. Results reveal the high accuracy of strategy selection within the range of interested traffic load, validating feasibility of the proposed scheme.
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| 9. |
- Fei, Chao, et al.
(author)
-
Demonstration of 15-M 7.33-Gb/s 450-nm Underwater Wireless Optical Discrete Multitone Transmission Using Post Nonlinear Equalization
- 2018
-
In: Journal of Lightwave Technology. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0733-8724 .- 1558-2213. ; 36:3, s. 728-734
-
Journal article (peer-reviewed)abstract
- In this paper, we experimentally demonstrate an underwater wireless optical communication (UWOC) system using a 450-nm gallium nitride (GaN) laser and adaptive bit-power loading discrete multitone (DMT). To enhance the system capacity, a post nonlinear equalizer based on the simplified Volterra series is employed at the receiver to mitigate the nonlinear impairments of the UWOC system. By combining the adaptive bit-power loading with nonlinear equalization, 7.33-Gb/s DMT-modulated UWOC under 15-m tap water is achieved at a bit error rate below the 7% hard-decision forward error correction (FEC) limit 3.8 x 10(-3). The electrical signal bandwidth is 1.25 GHz, which corresponds to an electrical spectrum efficiency of similar to 6 bit/s/Hz. The capacity-distance product reaches 109.95 Gb/s-m in a single channel UWOC system with tap water. Compared with the linear equalization case, the system capacity at the FEC limit for 15-m underwater transmission is improved by similar to 18% with the nonlinear equalization. Furthermore, the impact of turbidity on the performance of UWOC system is investigated by measuring the signal-to-noise ratio (SNR) under different suspension concentrations of Al(OH)(3) and Mg(OH)(2). The results show that significant SNR gains (>3 dB for transmission distance up to 11 m) can be obtained by the nonlinear equalization over a wide range of water turbidity levels representing "clear ocean," "coastal ocean," and "harbor water," which demonstrates the robustness of the proposed scheme in various ocean environments.
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| 10. |
- Gong, Yu, et al.
(author)
-
Passive optical interconnects at top of the rack : offering high energy efficiency for datacenters
- 2015
-
In: Optics Express. - 1094-4087. ; 23:6, s. 7957-7970
-
Journal article (peer-reviewed)abstract
- This paper introduces a new concept, namely passive optical interconnect at top of the rack in the datacenter networks, and investigates several architectures, which use only passive optical components to interconnect different servers. In such a manner, the proposed schemes are able to offer higher bandwidth and significantly improve energy efficiency compared to their electronic counterpart that is based on commodity switches. The proposed passive optical interconnect schemes are experimentally demonstrated in order to validate the transmission performance. Besides, an assessment in terms of energy consumption and cost has also been carried out, which shows our proposed concept can significantly outperform the conventional commodity switches on energy efficiency while keeping the cost in the similar level.
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| 11. |
- Gong, Yu, et al.
(author)
-
Passive Optical Interconnects at Top of the Rack for Data Center Networks
- 2014
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In: 2014 INTERNATIONAL CONFERENCE ON OPTICAL NETWORK DESIGN AND MODELING. ; , s. 78-83
-
Conference paper (peer-reviewed)abstract
- Limited scalability of the current commodity switches in terms of capacity and power consumption becomes a bottleneck of the development of data center networks. To solve this problem, optical switches have been proposed to interconnect different servers inside the data centers. However, most of such work has focused on core switches, which handle the communications among different racks inside the data centers as well as interfaces to Internet. In fact intra-rack communications dealing with the traffic inside a single rack in the data centers could also take up a substantial proportion of the total traffic in the data center networks, in particular for cloud computing. With this in mind, this paper proposes novel architectures based on passive optical interconnect at top of the rack (ToR) for data center networks inheriting the advantages of passive optical network (PON) technologies. With reliable and stable passive optical components, intra-rack communications can be realized in an optical domain rather than the conventional electrical switches at ToR. In such a manner, our schemes have a great potential to offer higher bandwidth and reduce power consumption. The transmission performance evaluation carried out by both simulation and experiments has verified the feasibility of the proposed architectures for passive optical interconnects.
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| 12. |
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| 13. |
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| 14. |
- Hong, Xuezhi, et al.
(author)
-
AWG based passive optical interconnects for datacenters
- 2014
-
In: Optics InfoBase Conference Papers. - : OSA - The Optical Society. - 9781943580149
-
Conference paper (peer-reviewed)abstract
- We propose a cascaded arrayed waveguide grating based passive optical interconnect scheme for datacenters, which outperforms various existing architectures in terms of scalability and cabling complexity. Proof-of-concept experiments are carried out.
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| 15. |
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| 16. |
- Hong, Xuezhi, et al.
(author)
-
Passive Optical Interconnects Based on Cascading Wavelength Routing Devices for Datacenters : A Cross-Layer Perspective
- 2017
-
In: Journal of Optical Communications and Networking. - : Optical Society of America. - 1943-0620 .- 1943-0639. ; 9:4, s. C45-C53
-
Journal article (peer-reviewed)abstract
- A general passive optical interconnect (POI) architecture based on cascading wavelength routing devices is proposed for datacenters. An analysis shows that with a proper port configuration, the logic topology of the proposed POI is equivalent to a DCell network, which has rich connectivity, leading to a high fault tolerance. Compared with the existing arrayed waveguide grating (AWG)-based architecture, such as H-LION, the proposed architecture has a higher AWG port utilization and lower cabling complexity that result in better scalability. Meanwhile, an impairment-aware scalability analysis is carried out to estimate the impact of in-band crosstalk on the size of the POI. Furthermore, a cross-layer investigation of the proposed POI provides a guideline to select proper physical-layer implementations, including optical interface structure and design of the transceiver, for acceptable network performance. The numerical results reveal that, with a moderate number of shortest paths K and degrees of node D, (a) the bidirectional optical interface is more suitable for large-scale datacenter networks than the unidirectional one, (b) an array of fixed receivers can be replaced by just a small number of tunable receivers with negligible degradation in network performance, and (c) decreasing 50% of the tuning range of the receivers causes only a minor increase of blocking probability, which demonstrates a good balance between the complexity of the transceiver design and network performance.
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| 17. |
- Jiao, Yuqing, et al.
(author)
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An integrated optical mixer based on SU8 polymer for PDM-QPSK demodulation
- 2011
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In: IEEE Photonics Technology Letters. - 1041-1135. ; 23:20, s. 1490-1492
-
Journal article (peer-reviewed)abstract
- This letter presents the design and fabrication of an optical mixer based on SU8 polymer for the demodulation of polarization division multiplexed-quadrature phase shift keying (PDM-QPSK) signals. The mixer consists of two novel polarization beam splitters (PBSs) and two 4 × 4 multimode interference (MMI) couplers. It is the first polymer-based optical mixer incorporated with PDM functionality. The experimental results show good performances of the mixer.
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| 18. |
- Lu, Yang, et al.
(author)
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Matrix Receiving Scheme Supporting Arbitrary Multiple-Wavelength Reception for Optical Interconnects
- 2017
-
In: European Conference on Optical Communication, ECOC. - : IEEE. - 9781538656242 ; 2017-September
-
Conference paper (peer-reviewed)abstract
- An arbitrary multiple-wavelength reception scheme using only a few fixed-wavelength filters is proposed for optical interconnects. Filter matrices design based on error-control coding theory is devised. The feasibility of the proposed scheme is demonstrated in a four-wavelength reception experiment.
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| 19. |
- Lu, Yang, et al.
(author)
-
Multi-channel collision-free reception for optical interconnects
- 2018
-
In: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 26:10, s. 13214-13222
-
Journal article (peer-reviewed)abstract
- A multi-channel reception scheme that allows each node to receive an arbitrary set of wavelengths simultaneously (i.e., collision-free) is proposed for optical interconnects. The proposed scheme only needs to use a few receivers and fixed-wavelength filters that are designed based on error-control coding theory. Experiments with up to four channel collision-free reception units are carried out to demonstrate the feasibility of the proposed scheme.
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| 20. |
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| 21. |
- Zhang, Guowu, et al.
(author)
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Low-complexity frequency domain nonlinear compensation for OFDM based high-speed visible light communication systems with light emitting diodes
- 2017
-
In: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:4, s. 3780-3794
-
Journal article (peer-reviewed)abstract
- A novel frequency domain nonlinear compensation method, FD-NC, is proposed for orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) system. By tackling the memory nonlinear impairments from light emitting diodes (LEDs) in the frequency domain rather than in the time domain, the proposed method has much lower computational complexity than the conventional time domain Volterra nonlinear compensation method (TD-NC). Both theoretical derivation and experimental investigation of the proposed method in OFDM based VLC systems with four types of commercial LEDs are presented. The results of experiments show that the proposed low-complexity FD-NC method with a moderate truncation factor achieves a performance comparable to that of the TD-NC. The application of FD-NC method in the bit-power loading OFDM VLC system is also experimentally demonstrated. Compared with the linear equalization case, at a bit error rate (BER) of 3.8 x 10(-3) (a), the transmission distance of a 960 Mbps VLC system can be extended from 0.7 m to 1.8 m by the FD-NC, and (b) the achievable system capacity can be enhanced by 18.7%similar to 36.5% for transmission distance in the range of 0.5 m similar to 2 m with the FD-NC. The complexity analysis shows that the required number of real-valued multiplications (RNRM) of the FD-NC is independent of linear or nonlinear memory length. The reduction of RNRM achieved by the FD-NC over the TD-NC becomes more profound for a larger nonlinear memory length or a smaller truncation factor.
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| 22. |
- Zhang, Junwei, et al.
(author)
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Asynchronous multiple access in visible light communication system based on DFT spread OFDM/OQAM
- 2015
-
In: Asia Communications and Photonics Conference, ACPC 2015. - Washington, D.C. : Optical Society of America (OSA). - 9781943580064
-
Conference paper (peer-reviewed)abstract
- A multiuser asynchronous visible light communication system adopting DFT spread (DFS-) OFDM/OQAM is proposed and experimentally demonstrated. Both high spectral locality and low peak-to-average power ratio are achieved with DFTS-OFDM/OQAM, which improves system’s transmission performance.
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| 23. |
- Zhang, Lu, et al.
(author)
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Nonlinearity-aware 200 Gbit/s DMT transmission for C-band short-reach optical interconnects with a single packaged electro-absorption modulated laser
- 2018
-
In: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 43:2, s. 182-185
-
Journal article (peer-reviewed)abstract
- We experimentally demonstrate the transmission of a 200 Gbit/s discrete multitone (DMT) at the soft forward error correction limit in an intensity-modulation direct-detection system with a single C-band packaged distributed feedback laser and traveling-wave electro absorption modulator (DFB-TWEAM), digital-to-analog converter and photodiode. The bit-power loaded DMT signal is transmitted over 1.6 km standard single-mode fiber with a net rate of 166.7 Gbit/s, achieving an effective electrical spectrum efficiency of 4.93 bit/s/Hz. Meanwhile, net rates of 174.2 Gbit/s and 179.5 Gbit/s are also demonstrated over 0.8 km SSMF and in an optical back-to-back case, respectively. The feature of the packaged DFB-TWEAM is presented. The nonlinearity-aware digital signal processing algorithm for channel equalization is mathematically described, which improves the signal-to-noise ratio up to 3.5 dB.
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| 24. |
- Zhang, Zhuo, et al.
(author)
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Demonstration of three‐dimensional indoor visible light positioning with multiple photodiodes and reinforcement learning
- 2020
-
In: Sensors. - : MDPI AG. - 1424-8220. ; 20:22, s. 1-14
-
Journal article (peer-reviewed)abstract
- To provide high‐quality location‐based services in the era of the Internet of Things, visible light positioning (VLP) is considered a promising technology for indoor positioning. In this paper, we study a multi‐photodiodes (multi‐PDs) three‐dimensional (3D) indoor VLP system enhanced by reinforcement learning (RL), which can realize accurate positioning in the 3D space without any off-line training. The basic 3D positioning model is introduced, where without height information of the receiver, the initial height value is first estimated by exploring its relationship with the received signal strength (RSS), and then, the coordinates of the other two dimensions (i.e., X and Y in the horizontal plane) are calculated via trilateration based on the RSS. Two different RL processes, namely RL1 and RL2, are devised to form two methods that further improve horizontal and vertical positioning accuracy, respectively. A combination of RL1 and RL2 as the third proposed method enhances the overall 3D positioning accuracy. The positioning performance of the four presented 3D positioning methods, including the basic model without RL (i.e., Benchmark) and three RL based methods that run on top of the basic model, is evaluated experimentally. Experimental results verify that obviously higher 3D positioning accuracy is achieved by implementing any proposed RL based methods compared with the benchmark. The best performance is obtained when using the third RL based method that runs RL2 and RL1 sequentially. For the testbed that emulates a typical office environment with a height difference between the receiver and the transmitter ranging from 140 cm to 200 cm, an average 3D positioning error of 2.6 cm is reached by the best RL method, demonstrating at least 20% improvement compared to the basic model without performing RL.
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| 25. |
- Zhang, Zhuo, et al.
(author)
-
Iterative point-wise reinforcement learning for highly accurate indoor visible light positioning
- 2019
-
In: Optics Express. - : OPTICAL SOC AMER. - 1094-4087 .- 1094-4087. ; 27:16, s. 22161-22172
-
Journal article (peer-reviewed)abstract
- Iterative point-wise reinforcement learning (IPWRL) is proposed for highly accurate indoor visible light positioning (VLP). By properly updating the height information in an iterative fashion, the IPWRL not only effectively mitigates the impact of non-deterministic noise but also exhibits excellent tolerance to deterministic errors caused by the inaccurate a priori height information. The principle of the IPWRL is explained, and the performance of the IPWRL is experimentally evaluated in a received signal strength (RSS) based VLP system and compared with other positioning algorithms, including the conventional RSS algorithm, the k-nearest neighbors (KNN) algorithm and the PWRL algorithm where iterations exclude. Unlike the supervised machine learning method, e.g., the KNN, whose performance is highly dependent on the training process, the proposed IPWRL does not require training and demonstrates robust positioning performance for the entire tested area. Experimental results also show that when a large height information mismatch occurs, the IPWRL is able to first correct the height information and then offers robust positioning results with a rather low positioning error, while the positioning errors caused by the other algorithms are significantly higher.
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