Advanced Digital Signal Processing Research Articles

Experimental Demonstration of 120-Gb/s Nyquist PAM8-SCFDE for Short-Reach Optical Communication

The limited band of optical and electrical devices in an intensity-modulation direct detection (IM/DD) system is considered to be a major bottleneck that hinders the increase in transmission capacity. Spectrally efficient modulation formats and advanced digital signal processing are key technologies to improving the performance of IM/DD for high-speed short-reach optical systems. In this paper, we propose and experimentally demonstrate a novel Nyquist eight-level, pulse-amplitude, single-carrier modulation with frequency-domain equalization (PAM8-SCFDE). In addition, 40-GBd Nyquist PAM8-SCFDE signals can be successfully transmitted over 2-km standard single-mode fiber or 20-km large effective area fiber based on 10-G-class DAC and photodiode. Therefore, the achieved aggregate data rate is 120 Gb/s, and the measured bit error rate (BER) is under 7% pre-forward-error-correction (FEC) threshold of $3.8\times 10^{-3} $ . Compared with conventional PAM8, this scheme can provide double spectral efficiency and 6-dB receiver sensitivity improvement.

Fiber Nonlinearity Compensation: Commercial Applications and Complexity Analysis

Fiber nonlinearities define the ultimate performance bound for optical communication systems. Todays 100 Gb/s commercial products employ advanced digital signal processing (DSP) algorithms, capable to adequately address linear channel impairments, leaving fiber nonlinearity compensation (NLC) as the next logical step to improve transmission performance, and consequently diminish the need for signal regeneration. Over the last few decades, several techniques have been presented to minimize or mitigate channel nonlinearities, ranging from specialized link designs in direct–detect legacy networks to advanced DSP algorithms in coherent systems. However, specifically in the coherent age, NLC has always been perceived as an extremely complex approach, allowing insignificant gains when practical implementations are considered. In this paper, we focus on the real-world commercial use cases and complexity tradeoffs for NLC, and review several application scenarios, including homogeneous and heterogeneous networks, dispersion unmanaged and dispersion managed link infrastructures, flex-grid networks, and short reach to ultra long-haul transmission applications. We establish that in various practical use cases, NLC may enable substantial performance gains, well beyond conventionally acknowledged bounds.

Effect of Glottal Excitation Interchange in Hindi and Dogri Languages

Voice acoustics is an active area of research which studies speaking voice and has gain popularity due to rapid advancements in digital signal processing. The shape of glottal excitation and the vocal tract may be speaker and language dependent. The objective of this paper is to study the effect of glottal excitation interchange on the quality and intelligibility in Hindi and Dogri languages. For this, recordings of six speakers (3 males and 3 females) were carried out in Dogri and Hindi languages. Cardinal vowels (/a/, /i/, /u/) were extracted from recordings of each speaker. Investigations were carried out by interchanging the glottal excitations corresponding to the vowels in the two languages for each speaker. The analysis of the results showed that interchange of excitation does not provide satisfactory quality of the synthesized speech in terms of identity and clarity of speech. Further, the synthesized speech is perceived as it was spoken in the original language. It was also observed that if any two of the parameters (excitation, gain, vocal tract LPC coefficients) are interchanged, the accent of the original language also changes. It means that minimum two of the three parameters are necessary to interchange for modifying the accent of the language under consideration.

Experimental Investigation on Fiber-Wireless MIMO System With Different LO at W Band

We experimentally demonstrate an optical-wireless transmission system at W band, which can support long-distance wireless transmission and tolerate some frequency difference of the local oscillators (LOs) at the receiver. The generation of millimeter-wave signal is based on the photonic technique by heterodyne mixing of an optical polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signal and an optical LO signal. After 20-km fiber transmission, tens of gigabit-per-second millimeter-wave signals are delivered over multiple-input–multiple-output (MIMO) wireless links by different polarization antennas. Then, analog downconversion is performed before the received signal is demodulated by coherent detection and advanced digital signal processing. Using this system, we experimentally demonstrate the transmission of 18.7-, 29.9-, and 37.4-Gb/s PDM-QPSK wireless signals at W band over 80-, 40-, and 20-m wireless links, respectively, with bit error rate less than the forward error correction threshold of $3.8\times 10^{-3}$ . In addition, we investigate the effect of different frequency LOs on the MIMO system performance, finding that the system can tolerate about 1.25-GHz frequency difference for a 10-Gbaud signal. The proposed system can be suitable for the building-to-building broadband connection, in-building hybrid fiber-wireless access networks, and some scenarios that bridge natural obstacles and difficult-to-access terrain.

Generalized Maximum Likelihood for Cross-Polarization Modulation Effects Compensation

We investigate the mitigation of nonlinearities with advanced digital signal processing focusing in particular on cross-polarization effects. Based on a relaxation of an analytical model derived for cross-polarization effects, this paper proposes a novel compensation method called generalized maximum likelihood. It performs a joint blind channel estimation and symbol detection, and it additionally accounts for the statistical prior distributions of the cross-polarization crosstalk coefficients. This avoids an overestimation of these crosstalk coefficients. A practical method for both fast computations and optimal performance is then presented, which allows nonlinear compensation for high-order modulations. Next, we present Monte-Carlo simulations showing that the proposed algorithm performs close to the theoretical limits. Large performance improvement can be obtained and this is particularly emphasized with higher order modulation such as a 16-ary quadrature amplitude modulation. Finally, using Nyquist pulse shaping and polarization-division multiplexed with a quadrature phase-shift keying modulation, the experiments are shown to be in accordance with the simulations and show up to 0.7 dB improvement in Q-factor for the worst-case samples.

A High Spectral Efficiency Coherent Microwave Photonic Link Employing Both Amplitude and Phase Modulation With Digital Phase Noise Cancellation

A high spectral efficiency coherent microwave photonic link (MPL) supporting amplitude and phase modulation incorporating a digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, a continuous-wave light wave is amplitude- and phase-modulated by two microwave vector signals carried by a microwave carrier at an identical frequency. The modulated optical signal is polarization multiplexed with an unmodulated optical carrier and transmitted over a length of a single-mode fiber (SMF). At the receiver, the optical signal is detected coherently by a coherent receiver to which a local oscillator (LO) laser source is also applied. Through advanced digital signal processing, the microwave vector signals are recovered, and the phase noise introduced by both the transmitter laser source and LO laser source is cancelled. An experiment is performed. The transmission of a 2.5-Gb/s 16-QAM and a 1.25-Gb/s QPSK microwave vector signals both at 2.5 GHz over a 25-km SMF is implemented. The total bit rate of the MPL is 3.75 Gb/s. The transmission performance of the MPL in terms of error vector magnitudes and bit error rates is evaluated.

Real-Time Monitoring System of Microseismic Signal based on Virtual Instrument and Wavelet Analysis

Seismic acquisition and monitoring system can collect, store, analyze and dispose the rock burst seismic waves or the vibration of other objects. This paper utilizes single chip computer technology, virtual instrument technology, sen- sor technology, database management technology, wavelet analysis technology, combining the real condition of the mine microseismic signal to establish a set of mine microseismic signal real time monitoring and warning system. Finish the seismic signals data collection by the single chip microcomputer and its periphery circuit design, meanwhile use the pow- erful graphical programming capabilities and flexible diversify data processing functions of the LabVIEW software, com- bining with advanced digital signal processing technology such as wavelet transform to complete seismic signal acquisi- tion and filtering processing, records and analysis, monitoring and early warning functions which offers evidence for the safety monitoring of underground mine and has a good application prospect.

Low-power-penalty wavelength multicasting for 36 Gbit/s 16-QAM coherent optical signals in a silicon waveguide.

All-optical wavelength multicasting has been experimentally demonstrated for 36 Gbit/s 16-quadrature amplitude modulation signals based on four-wave mixing processes in a silicon waveguide with multiple pumps. In our experiment, dual pumps are injected together with the signal into the waveguide and nine idlers are generated, involving five wavelength multicasting channels. Coherent detection and advanced digital signal processing are employed, and the recovered constellation diagrams of the multicasting idlers show a root-mean-square error vector magnitude degradation as small as 2.74%. The bit error rate (BER) results are measured for these multicasting idlers, and the power penalties are all lower than 0.96 dB at the BER of 3.8×10(-3) (corresponding to the forward error correction threshold).

Active Stateful PCE With Hitless LDPC Code Adaptation [Invited

The path computation element (PCE) architecture was originally proposed with a stateless condition, i.e., considering only network reserved resources during constraint-based path computations. More recently, a stateful architecture was introduced to additionally maintain the state of computed and established label switch paths (LSPs). Furthermore, the PCE architecture evolved to active functionality, enabling the PCE to directly issue recommendations to the network. In this study, we present and discuss several use cases where the active stateful architecture can provide some benefits. They include impairmentaware path computations in the context of multirate optical networks, recovery solutions, global defragmentation, and dynamic LSP adaptations. The latter use case is then specifically demonstrated in a network testbed including a flexigrid optical network operated with a multicarrier 1 Tb/s transmission with coherent detection. Novel advanced digital signal processing (DSP) monitoring functionalities are introduced and experimentally demonstrated. These monitoring functionalities are utilized to trigger a new hitless dynamic adaptation technique operating on the applied low-density parity check (LDPC) transmitted coding. The technique has been successfully demonstrated to increase transmission robustness upon impairment degradation, such that no traffic disruption is experienced. Moreover, to accommodate the LSP coding adaptation, network reconfiguration has been performed, successfully driven by the PCE thanks to the active functionality.

A New Kind of Smart Dual DSP2812 Power Quality Monitor Based on Dedicated Users

Focus on the increasingly prominent problems of power quality of dedicated users, study on solving electric energy problems, especially for harmonic pollution, was essential. This paper to study the method of testing and calculating electric energy index, then designed hardware to monitor and analyze power quality measurement data. The hardware was developed base on dual DSP2812, which was very advanced digital signal processing chip, and the hardware utilized high precision instantaneous synchronous sampling chip MAX1324, extended RAM and FLASH, RS232 communication circuit, high capacity SD card storage circuit, etc. The dual DSP power quality smart meter was tested and applied in dedicated users and its reliability, practicability, availability and accuracy was authenticated. This smart meter also has advantages of easy to carry, low cost, high precision, easy to promote, etc. can effectively meet power quality management of dedicated users.

Real-time blind audio source separation: performance assessment on an advanced digital signal processor

Many on-line blind audio source separation (BASS) algorithms have been presented so far to the scientific community, but only a few of them have been evaluated in terms of their real-time performance. In this paper we consider a well-established BASS method (oriented to voices separation) evaluating its performance in terms of separation quality allowed by a real-time embedded computing implementation, also considering novel and state-of-the-art improvements to the it. To this aim, the algorithm has been implemented and ported for real-time execution onto an advanced low-power digital signal processor targeted for complex-domain applications. The optimized embedded implementation is able to perform up to five iterations of the gradient for any input frame of data, achieving good separation levels (up to 11.8 dB of signal to interference ratio on custom recording in real environments). The proposed solution doubles the performance of a C-optimized version running on a traditional PC processor, achieving a better separation result with lower power requirements.

Metabolite of tryptophan promoting changes in EEG signal and the oxidative status of the brain

Tryptophan is an essential amino acid precursor of neurotransmitter serotonin and triptamine. During its metabolism, indole-3-acetic acid (IAA) is generated; this substance presents both antioxidant and prooxidant effects in different biological systems in addition to hipoglicemic effects. To date, electroencephalography (EEG) has been used to evaluate the temporal effect of several substances in neurotransmission. The goal of this study was to characterize the effect of IAA in the brain by analysing the EEG signal and evaluate the oxidative status by means of biochemical parameters. The EEG was acquired by using a noninvasive method, and the brain electric signal was analysed by advanced digital signal processing techniques to determinate the energy signal filtered in different band frequencies. Furthermore, the oxidative status of the brain was investigated by measuring the activity of antioxidant enzymes and lipid peroxidation as well as blood glucose rates of the animals treated with different doses of IAA. Our results showed the relationship of IAA administration with changes in EEG signals. The oxidative status of the brain was modified by IAA after 14 days of treatment.

Advanced DSP for 400 Gb/s and Beyond Optical Networks

This paper presents a systematic review of several digital signal processing (DSP)-enabled technologies recently proposed and demonstrated for high spectral efficiency (SE) 400 Gb/s-class and beyond optical networks. These include 1) a newly proposed SE-adaptable optical modulation technology-time-domain hybrid quadrature amplitude modulation (QAM), 2) two advanced transmitter side digital spectral shaping technologies-Nyquist signaling (for spectrally-efficient multiplexing) and digital pre-equalization (for improving tolerance toward channel narrowing effects), and 3) a newly proposed training-assisted two-stage carrier phase recovery algorithm that is designed to address the detrimental cyclic phase slipping problem with minimal training overhead. Additionally, this paper presents a novel DSP-based method for mitigation of equalizer-enhanced phase noise impairments. It is shown that performance degradation caused by the interaction between the long-memory chromatic dispersion compensating filter/equalizer and local oscillator laser phase noise can be effectively mitigated by replacing the commonly used fast single-tap phase-rotation-based equalizer (for typical carrier phase recovery) with a fast multi-tap linear equalizer. Finally, brief reviews of two high-SE 400 Gb/s-class WDM transmission experiments employing these advanced DSP algorithms are presented.

Advanced Digital Signal Processing and Coding for Multi-Tb\/s Optical Transport [From the Guest Editors

The articles in this special section aims to highlight diverse recent advances in digital signal processing (DSP)and coding, enabling TbE and multi-TbE optical transport while addressing bandwidth and energy constraints. The addressed topics range from sophisticated modulation and coding schemes to advanced detection schemes. The multi-Tb/s optical transports over either singlemode fibers or few-mode/few-core fibers are also topics covered in this special issue. The main technologies covered by this special issue comprise multiple-input, multiple-output (MIMO) signal processing, advanced multilevel and multidimensional modulation schemes, advanced multiplexing schemes, signal processing for superchannel transmission, advanced DSP for signal detection and equalization, and advanced coding, all aiming at achieving multi-Tb/s optical transports.

Advanced DSP Techniques Enabling High Spectral Efficiency and Flexible Transmissions: Toward elastic optical networks

In this article, we describe advances in digital signal processing (DSP) techniques that enable Tb/s transmission, and software-defined flexible transponders that support adaptive modulation formats and elastic optical networks (EONs).

A high-speed bi-directional visible light communication system based on RGB-LED

In this paper, we propose and experimentally demonstrate a bi-directional indoor communication system based on visible light RGB-LED. Spectrally efficient modulation formats (QAM-OFDM), advanced digital signal processing, pre- and post-equalization are adopted to compensate the severe frequency response of indoor channel. In this system, we utilize red-green-blue Light emitting diodes (LEDs), of which each color can be used to carry different signals. For downlink, the low frequencies of each color are used while for uplink, the high frequencies are used. The overall data rate of downlink and uplink are 1.15-Gb/s and 300-Mb/s. The bit error ratios (BERs) for all channels after 0.7 m indoor delivery are below pre-forward-error-correction (pre-FEC) threshold of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . To the best of our knowledge, this is the highest data rate in bi-directional visible light communication system.

A Low-Power Compact NQR Based Explosive Detection System

Nuclear quadruple resonance (NQR) has been studied for explosive detection for years. Some prototype NQR-based detection systems have been reported, but were all designed from the laboratory perspective, with bulky sizes and high power consumption. To achieve a portable NQR-based detection system for field applications, a low-power compact system utilizing state-of-the-art semiconductor technologies is presented in this paper. Several novel circuits for the key modules are proposed, including a Class-D type power amplifier, a power multiplexing and matching network, a customized IC with integrated analog signal processing chain, and a microcontroller-based logic control unit. An advanced digital signal processor platform is employed for data collecting and processing. The customized IC is fabricated in 0.18 μm CMOS process. Test results on the prototype system show the effectiveness of the proposed solution and low power consumption as 2.12 W in the receiving state. The power efficiency of the proposed transmitting section is higher than 60%.

Ambient noise as the new source for urban engineering seismology and earthquake engineering: a case study from Beijing metropolitan area

In highly populated urban centers, traditional seismic survey sources can no longer be properly applied due to restrictions in modern civilian life styles. The ambient vibration noise, including both microseisms and microtremor, though are generally weak but available anywhere and anytime, can be an ideal supplementary source for conducting seismic surveys for engineering seismology and earthquake engineering. This is fundamentally supported by advanced digital signal processing techniques for effectively extracting the useful information out from the noise. Thus, it can be essentially regarded as a passive seismic method. In this paper we first make a brief survey of the ambient vibration noise, followed by a quick summary of digital signal processing for passive seismic surveys. Then the applications of ambient noise in engineering seismology and earthquake engineering for urban settings are illustrated with examples from Beijing metropolitan area. For engineering seismology the example is the assessment of site effect in a large area via microtremor observations. For earthquake engineering the example is for structural characterization of a typical reinforced concrete high-rise building using background vibration noise. By showing these examples we argue that the ambient noise can be treated as a new source that is economical, practical, and particularly valuable to engineering seismology and earthquake engineering projects for seismic hazard mitigation in urban areas.

A 30 Gb/s full-duplex bi-directional transmission optical wireless-over fiber integration system at W-band

We propose and experimentally demonstrate a full-duplex bi-directional transmission optical wireless-over fiber integration system at W-band (75-100 GHz) with the speed up to 15 Gb/s for both 95.4 GHz link and 88.6 GHz link for the first time. The generation of millimeter-wave (mm-wave) wireless signal is based on the photonic technique by heterodyne mixing of an optical quadrature-phase-shift-keying (QPSK) signal with a free-running light at different wavelength. After 20 km fiber transmission, up to 30 Gb/s mm-wave signal is delivered over 2 m wireless link, and then converted to the optical signal for another 20 km fiber transmission. At the wireless receiver, coherent detection and advanced digital signal processing (DSP) are introduced to improve receiver sensitivity and system performance. With the OSNR of 15 dB, the bit error ratios (BERs) for 10 Gb/s signal transmission at 95.4 GHz and 88.6 GHz are below the forward-error-correction (FEC) threshold of 3.8 × 10(-3) whether post filter is used or not, while the BER for 15 Gb/s QPSK signal employing post filter in the link of 95.4 GHz is 2.9 × 10(-3).

Fast and robust software‐based digital phase‐locked loop for power electronics applications

In this study, a fast and fully software-based algorithm for digital phase-locked loop (PLL) is proposed via a new hybrid approach in software and hardware by using an advanced digital signal processor architecture. The proposed algorithm is robust against line disturbances such as phase-angle jump, voltage sag, third harmonic injection, multi-zero crossing and step change in frequency at the input voltage. Performance and robustness of the proposed method are investigated through experimental studies. Furthermore, it is compared with three different PLL algorithms in detail to show its superiority over existing methods.