Advanced Digital Signal Processing Techniques Research Articles

Implementation of Digital Signal Processor for Pulse Doppler Radar

This paper presents the design and implementation of a digital signal processor (DSP) board, utilizing a TMS320C50 family DSP chip, for pulse-Doppler radar systems. Pulse-Doppler radar systems often encounter challenges such as strong clutter, noise, and jamming in dealing with echoes. To overcome these challenges, advanced digital signal processing techniques are employed. The main objective of this paper is to introduce a cost-effective signal processing solution that significantly enhances the performance of the radar system and brings it up to speed with modern radar technologies. The hardware described in this work can also be effectively utilized for implementing various types of signal processing algorithms. Additionally, as a secondary objective, the paper presents the digital realization of a radar detector. Traditionally, this detector was constructed using an analog Doppler filter bank. However, in this work, it is digitally implemented using N digital filters in place of the analog bank. By utilizing the designed DSP board and implementing the radar detector digitally, this paper demonstrates the potential for improved performance and efficiency in pulse-Doppler radar systems. The advancements made in this work contribute to the development of cost-effective and technologically advanced radar systems. The research results are presented for four different wind conditions, showcasing the effectiveness of the proposed approach. Furthermore, the paper suggests an algorithm that combines parametric and non-parametric techniques and provides a detailed explanation of its implementation. Finally, using the non-parametric technique, the probability of detection curves (PD) are simulated with respect to the signal-to-clutter ratio (SCR) for each wind condition, and the simulation results are depicted and compared. The achievements of this paper include the proposal of an efficient approach for clutter suppression in ground surveillance pulse Doppler radar, the comparison of different clutter suppression algorithms, and the development of an algorithm that combines parametric and non-parametric techniques. The simulation results provide valuable insights into the performance of the proposed algorithms under different wind conditions.

Direct Modulation and Free-Space Transmissions of up to 6 Gbps Multilevel Signals With a 4.65-$\mu$m Quantum Cascade Laser at Room Temperature

A roadmap for future wireless communications is expected to exploit all transmission-suitable spectrum bands, from the microwave to the optical frequencies, to support orders of magnitude faster data transfer with much lower latency than the deployed solutions nowadays. The currently under-exploited mid-infrared (mid-IR) spectrum is an essential building block for such an envisioned all-spectra wireless communication paradigm. Free-space optical (FSO) communications in the mid-IR region have recently attracted great interest due to their intrinsic merits of low propagation loss and high tolerance of atmospheric perturbations. Future development of viable mid-IR FSO transceivers requires a semiconductor source to fulfill the high bandwidth, low energy consumption, and small footprint requirements. In this context, quantum cascade laser (QCL) appears as a promisingtechnological choice. In this work, we present an experimental demonstration of a mid-IR FSO link enabled by a 4.65-μm directly modulated (DM) QCL operating at room temperature. We achieve a transmission data rate of up to 6 Gbps over a 0.5-m link distance. This achievement is enabled by system-level characterization and optimization of transmitter and receiver power level and frequency response and assisted with advanced modulation and digital signal processing (DSP) techniques. This work pushes the QCL-based FSO technology one step closer to practical terrestrial applications, such as the fixed wireless access and the wireless mobile backhaul. Such a QCL-based solution offers a promising way towards the futuristic all-spectra wireless communication paradigm by potentially supporting the whole spectrum from the MIR to the terahertz (THz).

Performance analysis of coherent free‐space optics transmission link using in‐phase quadrature modulator‐based polarization multiplexed‐256‐quadrature amplitude modulation

AbstractA single‐channel high information rate free‐space optics transmission link is presented incorporating in‐phase quadrature modulator‐based polarization multiplexed‐256‐quadarature amplitude modulation scheme. An information rate of 160 Gbit/s with 10 Gbaud symbol rate is achieved for free‐space information transmission. Advanced digital signal processing techniques at the receiver along coherent detection have been used to compensate the losses incurred by the information signal propagating the free‐space media. The transmission performance of the proposed link has been enhanced by using different optical amplifiers, that is, Erbium‐doped fiber amplifier and semiconductor optical amplifier, and their performance has been compared. The link performance is analyzed for required laser line width, launch power requirements, increasing transmission range, increasing beam divergence angle and optical power required at the receiver. Bit error rate and error vector magnitude metrics have been used to analyze the link performance. A maximum transmission of 3.9 km for clear weather atmospheric conditions is achieved. The proposed link has the potential to meet the last‐mile access needs and to provide high‐bandwidth high‐speed information links required for future fifth generation wireless communication and Internet of Things applications.

Recent Progress on Novel DSP Techniques for Mode Division Multiplexing Systems: A Review

This paper provides an overview of latest progress on the novel advanced digital signal processing (DSP) techniques for long-haul mode division multiplexing (MDM) systems with high capacity. Space-division multiplexing (SDM) techniques have been developed for a period to increase the capacity of optical communication system by at least one order of magnitude through MDM techniques using few-mode fibers (FMFs) or multi-core multiplexing (MCM) using multi-core fibers (MCFs). The signals in MDM links are mainly impaired by the linear and nonlinear effects in FMFs, making DSP techniques become necessary to undo these impairments. In this paper, we not only review the advanced multiple-input multiple-output (MIMO) DSP techniques for compensating linear impairments in FMFs, but also enclose the state of the art of novel DSP techniques to deal with nonlinear effects. Firstly, we introduce the MIMO schemes for equalizing modal crosstalk and modal dispersion. Then, we focus on the fast tracking of time-varying (TV) channels in FMF links through frequency-domain (FD) recursive least square (RLS) algorithm. Besides, we also cover the mainstream DSP solutions for mode-dependent loss (MDL) and several possible methods to compensate nonlinearity in FMF. Moreover, artificial intelligence (AI) technologies are also discussed for its high nonlinearity tolerance and may bring a revolution in MDM systems on the process of channel equalization, link monitoring, etc. In the end, a brief conclusion and perspective will be provided.

Advanced Digital Signal Processing Techniques on the Classification of the Heart Sound Signals

Speech processing subject primarily depends on the digital signal processing (DSP) methods, such as convolution, discrete Fourier transform (DFT), fast Fourier transforms (FFT), finite impulse response (FIR) and infinite impulse response (IIR) filters, FFT recursive and non-recursive digital filters, FFT processing, random signal theory, adaptive filters, upsampling and downsampling, etc. Recursive and non-recursive digital filters are primarily deployed to absorb the signal of interest signals and to block the unwanted signals (noise). Broadly, low-pass, high-pass, band-pass, and band-stop filters are implemented for filtering functions. In frequent, the DSP theories can be used for further biomedical engineering domains like biomedical imaging (MRI, ultrasound, CT, X-ray, PET) and genetic signal analysis-cum-processing too. In this article, the experiments such as voiced/unvoiced detection, formants estimation using FFT and spectrograms, pitch estimation and tracking and yes/no sound classification are used. Also, the analysis of normal/abnormal heart sound signals using simple energy computation and the zero-crossing rate and their results are obtained. For the entire study, the Matlab R2018a tool is used to obtain the simulation results. At last, the criticism, feedbacks, comments, reactions from the student are detailed for the exceptional development of the course.

Digital Pre- and Post-Equalization for C-Band 112-Gb/s PAM4 Short-Reach Transport Systems

Insufficient system bandwidth and chromatic dispersion (CD) of fiber are major limitations for high-speed four-level pulse amplitude modulation (PAM4) direct detection systems. In this article, we investigate C-band 112-Gb/s PAM4 optical transport systems over 10-km and 20-km standard single-mode fiber (SSMF) transmission, which suffers from both bandwidth limitation and CD-induced power fading. Advanced digital signal processing techniques are proposed to handle those channel distortions. At the transmitter, a low-complexity $1+\alpha Z^{-1}$ finite impulse response (FIR) filter coarsely pre-compensates system bandwidth without a preliminary channel estimation. At the receiver, a modified feed-forward equalizer and decision feedback equalizer (FFE-DFE) is employed to compensate residual insufficient bandwidth and CD-induced power fading. Moreover, a novel multi-symbols joint decision is proposed for receiver-side FFE-DFE to mitigate symbol error propagation and correct possible previous error symbols. Experimental results show that the proposed pre-equalization technique exhibits a better transmission performance, which reduces bit error ratio (BER) from $3.3\times 10^{-3}$ to $5.5\times 10^{-4}$ for optical back to back transmission. As for 10-km transmission case, FFE-DFE with 5-symbols joint decision achieves a BER of $7.3\times 10^{-5}$ , which is better than the BER of $1.6\times 10^{-4}$ with ideal error-propagation-free FFE-DFE (EPF-FFE-DFE). Furthermore, for 20-km transmission scenario, FFE-DFE with 8-symbols joint decision achieves a BER of $6.0\times 10^{-4}$ , which is also a superior result than the BER of $9.1\times 10^{-4}$ with EPF-FFE-DFE.

26.8-m THz wireless transmission of probabilistic shaping 16-QAM-OFDM signals

Recently, remarkable efforts have been made in developing wireless communication systems at ultrahigh data rates, with radio frequency (RF) carriers in the millimeter wave (30–300 GHz) and/or in the terahertz (THz, >300 GHz) bands. Converged technologies combining both the electronics and the photonics show great potential to provide feasible solutions with superior performance compared to conventional RF technologies. However, technical challenges remain to be overcome in order to support high data rates with considerably feasible wireless distances for practical applications, particularly in the THz region. In this work, we present an experimental demonstration of a single-channel THz radio-over-fiber (RoF) system operating at 350 GHz, achieving beyond 100 Gbit/s data rate over a 10-km fiber plus a >20-m wireless link, without using any THz amplifiers. This achievement is enabled by using an orthogonal frequency division multiplexing signal with a probabilistic-shaped 16-ary quadrature amplitude modulation format, a pair of highly directive Cassegrain antennas, and advanced digital signal processing techniques. This work pushes the THz RoF technology one step closer to ultrahigh-speed indoor wireless applications and serves as an essential segment of the converged fiber-wireless access networks in the beyond 5G era.

Advanced DSP for Coherent Optical Fiber Communication

In this paper, we provide an overview of recent progress on advanced digital signal processing (DSP) techniques for high-capacity long-haul coherent optical fiber transmission systems. Not only the linear impairments existing in optical transmission links need to be compensated, but also, the nonlinear impairments require proper algorithms for mitigation because they become major limiting factors for long-haul large-capacity optical transmission systems. Besides the time domain equalization (TDE), the frequency domain equalization (FDE) DSP also provides a similar performance, with a much-reduced computational complexity. Advanced DSP also plays an important role for the realization of space division multiplexing (SDM). SDM techniques have been developed recently to enhance the system capacity by at least one order of magnitude. Some impressive results have been reported and have outperformed the nonlinear Shannon limit of the single-mode fiber (SMF). SDM introduces the space dimension to the optical fiber communication. The few-mode fiber (FMF) and multi-core fiber (MCF) have been manufactured for novel multiplexing techniques such as mode-division multiplexing (MDM) and multi-core multiplexing (MCM). Each mode or core can be considered as an independent degree of freedom, but unfortunately, signals will suffer serious coupling during the propagation. Multi-input–multi-output (MIMO) DSP can equalize the signal coupling and makes SDM transmission feasible. The machine learning (ML) technique has attracted worldwide attention and has been explored for advanced DSP. In this paper, we firstly introduce the principle and scheme of coherent detection to explain why the DSP techniques can compensate for transmission impairments. Then corresponding technologies related to the DSP, such as nonlinearity compensation, FDE, SDM and ML will be discussed. Relevant techniques will be analyzed, and representational results and experimental verifications will be demonstrated. In the end, a brief conclusion and perspective will be provided.

Physical Layer Strategies to Save Lightpath Regenerators

We investigate the viability of hybrid fiber amplifiers (HFA) and advanced digital signal processing (DSP)-based transceivers in translucent optical networks. We focus on the reduction of optical-electro-optical (OEO) regenerators required to support a 200 Gbps any-to-any traffic. In this paper, two network topologies, Pan-European and USNET, are quantitatively analyzed according to three different upgrade strategies. The first upgrade strategy includes selective placement of HFA in a network using different Raman amplification levels. The second upgrade strategy includes the use of two different DSP techniques of digital backpropagation and probability shaping (PS) at the transceivers. The third upgrade strategy involves a combination of both HFA and DSP techniques in a network. Our results indicate that by using these upgradation strategies, a prominent reduction in OEO regenerators can be obtained, which can lead to full transparency of a network. In the Pan-European topology, improving the equivalent noise figure (ENF) of the optical amplifiers by 5 dB, it is possible to reduce by 74% the amount of required regenerators. Then, by applying advanced DSP techniques like PS, this percentage grows up to 82%. In the USNET topology, by reducing the ENF by 2 dB, it is possible to reach full transparency. By using PS, it is enough to reduce the ENF by just 0.5 dB to reach the same results.

Room Response Equalization—A Review

Room response equalization aims at improving the sound reproduction in rooms by applying advanced digital signal processing techniques to design an equalizer on the basis of one or more measurements of the room response. This topic has been intensively studied in the last 40 years, resulting in a number of effective techniques facing different aspects of the problem. This review paper aims at giving an overview of the existing methods following their historical evolution, and discussing pros and cons of each approach with relation to the room characteristics, as well as instrumental and perceptual measures. The review is concluded by a discussion on emerging topics and new trends.

Meeting ecodesign efficiency requirements: ensuring accuracy in power transformer loss tests via TLM system calibrations

As part of the sustainable energy policies of the european union (EU), the Ecodesign Directive puts efficiency requirements per 1 July, 2015 on medium and large power transformers. This increases the importance of unambiguous measurement of power transformer losses, and thus of the accuracy of the transformer loss measurement (TLM) systems used by power transformer manufacturers for verification of these losses. Higher accuracy measurements not only lead to increased confidence in the product at the customers, but also allows for saving costs by designing transformers close to the loss limits. To support high-quality power transformer loss measurements, van swinden laboratorium (VSL) has developed a reference system for calibration of TLM systems at the best accuracy levels. A significant advantage is that the TLM systems are calibrated as a whole, thereby covering all possible error sources. Using advanced digital signal processing techniques, high currents are generated with adjustable, stable phase with respect to the applied test voltage. Test results show that calibration accuracies of 25 μrad in phase (corresponding to 0.25% in active power at power factor of 0.01) are achieved for test voltages and currents up to 100 kV and 2 kA, respectively – a factor 10 better than typical TLM system specifications.

All Analog Processing of Speckle Affected Self-Mixing Interferometric Signals

Self-mixing (SM) or optical feedback interferometry has been extensively used for high precision displacement and vibration sensing. However, presence of speckle can significantly degrade the SM interferometric signal and cause changes in signal amplitude as well as in the operating optical feedback regime, resulting in reduction in measurement precision. Previously, different advanced digital signal processing techniques have been proposed to undo the effects caused by speckle. However, their complex and computationally heavy nature inhibits their use for real-time, high bandwidth sensing applications. In this regard, an all analog signal processing algorithm has been presented in this paper, which allows real-time processing of speckle affected SM signal while using standard analog circuits. Various simulations indicated that it is able to correctly process speckle affected SM signals having amplitude variation of at least one order and optical feedback parameter $C$ reduction until 0.5. This proposed algorithm has been tested on experimentally acquired speckle affected SM signals and found capable of dealing with variations in optical feedback regime and amplitude modulation of SM signals, in accordance with simulation results. The developed hardware prototype circuit measures a maximum displacement amplitude of 0.4 mm at a maximum target velocity of 8 mm/s for an SM sensor with a laser wavelength of 785 nm as long as $C >0.5$ . The proposed all analog processing could be a significant step toward a robust, low-cost, integrated, real-time SM displacement sensor.

A low-overhead switched-mode Energy saving strategy for OFDMA-PON downstream transmission

Abstract Green networks and energy saving have become important topics of worldwide concern and attracted intensive attention from both academia and industry. As orthogonal frequency division multiplexing access passive optical network (OFDMA-PON) employs more advanced and energy-consuming digital signal processing (DSP) techniques than other PON systems, it is of critical importance to improve the energy efficiency of OFDMA-PONs. In this paper, we propose a switched-mode energy saving strategy with low overhead for OFDMA-PON downstream transmission. By embedding information in the short training sequences (STSs) of the OFDM frame preamble, the STSs serve a twofold purpose: providing time synchronization and carrying the information with regard to the destination of the frame, hence eliminating the need for extra upper-layer control or information exchange between OLT and ONU. As STS is an inherent part of the OFDM frame, the proposed scheme requires little extra overhead in transmission time and hardware cost. The ONU continues the subsequent processing only when it is the intended receiver, while the unintended ONUs drop the frame and stands by to save energy. In order to achieve a tradeoff between energy saving and delay performance, the scheme switches between single-ONU mode and team mode where either a single ONU or a team of ONUs are the targeted receivers. We verify the feasibility of proposed scheme through experiments and evaluate the performance in terms of energy saving and packet delay by simulations. The results indicate that substantial energy can be saved compared with conventional OFDMA-PON systems.

A REVIEW OF VIBRATION MACHINE DIAGNOSTICS BY USING ARTIFICIAL INTELLIGENCE METHODS

In the industry, gears and rolling bearings failures are one of the foremost causes of breakdown in rotating machines, reducing availability time of the production and resulting in costly systems downtime. Therefore, there are growing demands for vibration condition based monitoring of gears and bearings, and any method in order to improve the effectiveness, reliability, and accuracy of the bearing faults diagnosis ought to be evaluated. In order to perform machine diagnosis efficiently, researchers have extensively investigated different advanced digital signal processing techniques and artificial intelligence methods to accurately extract fault characteristics from vibration signals. The main goal of this article is to present the state-of-the-art development in vibration analysis for machine diagnosis based on artificial intelligence methods.

Guest Editorial: Evolutionary Advancements in Wireless Software Defined Radio Systems

The field of wireless communications over the years has been constantly making significant advancements in the domain of Software Defined Radios (SDRs). These reconfigurable radios are also capable to learn from their environment like the spectrum and then undertake rapid decisions based on its selfdefined policies leading to the development of wider range of new applications. Thus, new topics and concepts are not only been investigated in the Digital Signal Processing domain but also in the Cognitive Radio domain for an effective and efficient use of the spectrum. Using such technologies with widely accepted international standards like the Software Communications Architecture (SCA) in military software defined radios also requires that they go through the testing and certification processes. Thus, in this Special Issue of the Springer Journal of Signal Processing Systems, all these topics leading towards the evolution of SDRs are discussed. This Special Issue comprises of three sets containing a total of nine articles. The first set of articles put focus on the various cognitive radio technologies like Dynamic Spectrum Access and Spectrum Sensing. The still existing inefficient use of the spectrum is discussed in various SDR research communities. New and innovative ideas are continuously investigated to use the spectrum in the most efficient way in order to meet the ever growing demands of high data throughput. Use of Cognitive Radios is one such way to achieve it. These radios are able to sense the radio environment in order to identify portions of the spectrum that are unused at a specific time or location and are able to reconfigure themselves. Various algorithms and techniques are being investigated to achieve such results in a dynamic environment. The second set of articles discusses several advanced Digital Signal Processing techniques. All these techniques aim at optimizing operationally relevant criteria. These criteria vary from achieving higher robustness, lower bit error rates, longer communication ranges, and minimal energy consumption to faster deployments. The proofs of the achievements are given either by simulation or by prototype implementation on off-the-shelf low cost hardware. The third set of articles illustrates the importance test and certification of Software Defined Radios in the military domain using internationally accepted standard like the SCA. Standards like the SCA allow waveforms to be ported easily across heterogeneous platforms. It also provides neatly defined interfaces and Application Program Interfaces (APIs) aimed to increase portability and interoperability of radios. In the final phase of the development of SDRs, efficient ways of testing and agencies providing the certification of standards play a significant role. * Marc Adrat marc.adrat@fkie.fraunhofer.de

Design Tradeoffs and Challenges in Practical Coherent Optical Transceiver Implementations

This tutorial discusses the design and ASIC implementation of coherent optical transceivers. Algorithmic and architectural options and tradeoffs between performance and complexity/power dissipation are presented. Particular emphasis is placed on flexible (or reconfigurable) transceivers because of their importance as building blocks of software-defined optical networks. The paper elaborates on some advanced digital signal processing (DSP) techniques such as iterative decoding, which are likely to be applied in future coherent transceivers based on higher order modulations. Complexity and performance of critical DSP blocks such as the forward error correction decoder and the frequency-domain bulk chromatic dispersion equalizer are analyzed in detail. Other important ASIC implementation aspects including physical design, signal and power integrity, and design for testability, are also discussed.

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 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).

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.

Experiment of a Quaternion-Based Extended Kalman Filter with Noise Reduction Technique Using MEMS Sensors for Attitude State Estimation

Position and orientation acquirement is one hot topic in sensor data fusion research and application area. Micro-Electro-mechanical Systems (MEMS) sensor is a kind of low-cost and feasible tool that could measure some movement information, including acceleration and angular rate and so on, while burst noise and outlier signal influence the sensor data for accurate information acquirement and related application analysis. Some advanced digital signal processing techniques could realise the improvement of signal quality. The algorithm of median filter, combined with mean filter, was implemented to output better data for orientation estimation with fewer burst noise and outlier signals. Considering our designed and developed sensor system, including a tri-axis accelerometer, a dual-axis pitch and roll gyroscope and a yaw gyroscope used in this research, the construction of sensor model and a kind of quaternion-based extended Kalman filter (EKF) method and involved formulas for attitude state estimation are described in this paper. The experiment of this quaternion-based EKF with noise reduction processing was implemented using MEMS sensors. Regarding the EKF result of orientation estimation, this paper analyses the reason why the yaw drift generated. The EKF result of orientation estimation proves the feasibility of 2 degrees of freedom for attitude state estimation application.