Directly-modulated laser (DML) is widely employed in intensity modulation and direct detection (IMDD) system due to its low cost and high output power. However, the corresponding frequency chirp is ...regarded as one of the main disadvantages for its application in passive optical networks (PONs). In this paper, we theoretically analyze the frequency response evolution of DML based system under different chirp and dispersion conditions, proving that the system bandwidth can be improved by interactions between negative dispersion and DML chirp. Based on this concept, we experimentally demonstrated downstream 50 Gb/s PAM4 signal transmission over 20 km single-mode fiber (SMF) access based on the 10 Gb/s DML operating at 1310 nm and avalanche photodiode (APD). A dispersion-shifted fiber (DSF) providing -150 ps/nm dispersion at 1310 nm in the optical line terminal (OLT) is used to pre-equalize the frequency response of bandwidth-limited directly modulated signals in the optical domain. Thanks to our proposed dispersion-supported equalization (DSE) technique, the system bandwidth can be improved by 5 GHz. Feed-forward equalization (FFE), decision feedback equalization (DFE) and Volterra filter are employed to evaluate the signal performance improvement, respectively. By evaluating the receiver sensitivity, the DSE combined with FFE scheme shows 2 dB improvement than the complex Volterra algorithm, indicating its potential to reduce the complexity of digital signal processing (DSP) and therefore a lower cost and power consumption in PON.
Predicting Grades Meier, Yannick; Jie Xu; Atan, Onur ...
IEEE transactions on signal processing,
02/2016, Letnik:
64, Številka:
4
Journal Article
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To increase efficacy in traditional classroom courses as well as in Massive Open Online Courses (MOOCs), automated systems supporting the instructor are needed. One important problem is to ...automatically detect students that are going to do poorly in a course early enough to be able to take remedial actions. Existing grade prediction systems focus on maximizing the accuracy of the prediction while overseeing the importance of issuing timely and personalized predictions. This paper proposes an algorithm that predicts the final grade of each student in a class. It issues a prediction for each student individually, when the expected accuracy of the prediction is sufficient. The algorithm learns online what is the optimal prediction and time to issue a prediction based on past history of students' performance in a course. We derive a confidence estimate for the prediction accuracy and demonstrate the performance of our algorithm on a dataset obtained based on the performance of approximately 700 UCLA undergraduate students who have taken an introductory digital signal processing over the past seven years. We demonstrate that for 85% of the students we can predict with 76% accuracy whether they are going do well or poorly in the class after the fourth course week. Using data obtained from a pilot course, our methodology suggests that it is effective to perform early in-class assessments such as quizzes, which result in timely performance prediction for each student, thereby enabling timely interventions by the instructor (at the student or class level) when necessary.
Research in graph signal processing (GSP) aims to develop tools for processing data defined on irregular graph domains. In this paper, we first provide an overview of core ideas in GSP and their ...connection to conventional digital signal processing, along with a brief historical perspective to highlight how concepts recently developed in GSP build on top of prior research in other areas. We then summarize recent advances in developing basic GSP tools, including methods for sampling, filtering, or graph learning. Next, we review progress in several application areas using GSP, including processing and analysis of sensor network data, biological data, and applications to image processing and machine learning.
Based on the two polarization-division-multiplexing jointed intensity modulation and direction detection (2×PDM-IM/DD) system, the performance of the simplified receiver is studied for alternative ...intensity modulation formats such as PAM-4, CAP-16 and DMT. At bit rate up to ∼2×112-Gbit/s, compared with the single polarization signal, experimental results show that the power penalty of 2×PDM-PAM-4, CAP-16 and DMT is ∼0.8-dB, 1.2-dB and 1.3-dB (back-to-back) at 7% forward error correction (FEC) threshold, respectively. The transmission (i.e. 25-km non-zero dispersion shift fiber) penalty is 1.8-dB, 1.4-dB and 1.7-dB for the corresponding modulation formats. Furthermore, the comparative analysis of the simplified receiver among the three modulation formats is carried out.
•Performance of the simplified receiver is studied for 2×PDM-PAM, CAP and DMT signals•At bit rate of 2×112-Gbit/s, power penalty is acceptable for the three modulation formats•Compare to single polarization penalty of 2×PDM-PAM4, CAP16 and DMT is ∼0.8, 1.2, 1.3dB•Power penalty after 25-km NZDSF is 1.8, 1.4 and 1.7dB for 2×PDM-PAM4, CAP16 and DMT
In this paper, we discuss building blocks that enable the exploitation of optical capacities beyond 100 Gb/s. Optical networks will benefit from more flexibility and agility in their network ...elements, especially from coherent transceivers. To achieve capacities of 400 Gb/s and more, coherent transceivers will operate at higher symbol rates. This will be made possible with higher bandwidth components using new electro-optic technologies implemented with indium phosphide and silicon photonics. Digital signal processing will benefit from new algorithms. Multi-dimensional modulation, of which some formats are already in existence in current flexible coherent transceivers, will provide improved tolerance to noise and fiber nonlinearities. Constellation shaping will further improve these tolerances while allowing a finer granularity in the selection of capacity. Frequency-division multiplexing will also provide improved tolerance to the nonlinear characteristics of fibers. Algorithms with reduced computation complexity will allow the implementation, at speeds, of direct pre-compensation of nonlinear propagation effects. Advancement in forward error correction will shrink the performance gap with Shannon's limit. At the network control and management level, new tools are being developed to achieve a more efficient utilization of networks. This will also allow for network virtualization, orchestration, and management. Finally, FlexEthernet and FlexOTN will be put in place to allow network operators to optimize capacity in their optical transport networks without manual changes to the client hardware.
The recently developed digital coherent receiver enables us to employ a variety of spectrally efficient modulation formats such as <inline-formula><tex-math>M</tex-math></inline-formula>-ary ...phase-shift keying and quadrature-amplitude modulation. Moreover, in the digital domain, we can equalize all linear transmission impairments such as group-velocity dispersion and polarization-mode dispersion of transmission fibers, because coherent detection preserves the phase information of the optical signal. This paper reviews the history of research and development related to coherent optical communications and describes the principle of coherent detection, including its quantum-noise characteristics. In addition, it discusses the role of digital signal processing in mitigating linear transmission impairments, estimating the carrier phase, and tracking the state of polarization of the signal in coherent receivers.
This work introduces the ±CIM SRAM macro having the unique capability of performing in-memory multiply-and-accumulate computation with signed inputs and signed weights. This uniquely enables the ...execution of a broad set of workloads, ranging from storage, subsequent signal processing, and pre-conditioning or feature extraction to final convolutional neural network (CNN) computations. The ability to handle arbitrary input/weight sign in any operand within the same array and the same access cycle enables true end-to-end data locality, preserving the inherent benefits of in-memory computing along the entire signal chain. The proposed broad-purpose computing SRAM is based on a commercial 8T dual-port bitcell, and its simplicity allows the enhanced periphery to be pitch-matched with the array, making it amenable for automated design via memory compilers. The ±CIM pipelined architecture allows concurrent read/write and compute operations, avoiding the traditional memory unavailability in compute mode for improved throughput and easier system integration. A 40-nm test chip demonstrating the ±CIM architecture with adjustable input/weight precision exhibits an energy efficiency up to 41 TOPS/W, at an area (energy) overhead of 38% (25%) and negligible performance overhead compared to a compiled SRAM baseline. The sub-LSB computation mean-squared error associated with mismatch (0.38 LSB) and temporal noise (0.62 LSB) confirms the inherent robustness of the architecture. When used for neural network tasks (LeNet-5 and VGG), the accuracy drop is kept between 0.3% and 3.4%, compared to a double-precision software implementation. As an example of digital signal processing (DSP) workload, a frequency-domain feature extractor for voice activity detection keeps the accuracy drop lower than 3.8%.
The coherent transmission technology using digital signal processing and advanced modulation formats, is bringing networks closer to the theoretical capacity limit of optical fibres, the Shannon ...limit. The in-phase/quadrature electro-optic modulator that encodes information on both the amplitude and the phase of light, is one of the underpinning devices for the coherent transmission technology. Ideally, such modulator should feature a low loss, low drive voltage, large bandwidth, low chirp and compact footprint. However, these requirements have been only met on separate occasions. Here, we demonstrate integrated thin-film lithium niobate in-phase/quadrature modulators that fulfil these requirements simultaneously. The presented devices exhibit greatly improved overall performance (half-wave voltage, bandwidth and optical loss) over traditional lithium niobate counterparts, and support modulation data rate up to 320 Gbit s
. Our devices pave new routes for future high-speed, energy-efficient, and cost-effective communication networks.
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