Modulation Waveform Research Articles

A High Spatiotemporal Resolution Ultrasonic Ranging Technique With Multiplexing Capability

In this article, a high-performance water-coupled ultrasonic ranging technique is presented. We improved the conventional time-of-flight (ToF) ranging technique based on digital correlation of pseudorandom noise (PRN) waveforms by introducing signal carrier phase shift detection with an I/Q coherent reception method. In this way, the spatial resolution is dominated mainly by the digitization resolution of the analog-to-digital converter (ADC) used in the receiver circuit. Submicrometer resolution is achieved in the entire full-scale-range (FSR) while keeping the ADC sampling rate at the Nyquist sampling limit of the carrier frequency of ranging signal. In this study, we use quadrature amplitude modulation (QAM) waveforms of a set of 1023-bit GPS Gold codes with 8 MHz carrier as a ranging signal. Experiments carried out in a water vessel reveal micrometer-level accuracy and precision for quasi-static and dynamic cases. It is experimentally illustrated that the proposed method is capable of multiplexing. The optimal ranging performance is approached by selecting an appropriate set of systemic technical parameters and ranging signals. This allows to define the figure of merit (FOM) indicating the performance upper bound of such a ranging system.

Zero-Crossing Modulation for Wideband Systems Employing 1-Bit Quantization and Temporal Oversampling: Transceiver Design and Performance Evaluation

Next-generation wireless communications systems are anticipated to utilize the vast amount of available spectrum in the millimeter-wave and sub-terahertz bands above 100 G Hz to meet the ever-increasing demand for higher data rates. However, the analog-to-digital converter (ADC) power consumption is expected to be a major bottleneck if conventional system designs are employed at these frequencies. Instead, shifting the ADC resolution from the amplitude domain to the time domain by employing 1-bit quantization and temporal oversampling w.r.t. the Nyquist rate is expected to be more energy-efficient. Hence, we consider a system employing 1-bit quantization and temporal oversampling at the receiver, which operates on a wideband line-of-sight channel. We present a practical transceiver design for a zero-crossing modulation waveform, which combines faster-than-Nyquist signaling and runlength-limited (RLL) transmit sequences. To this aim, we derive four fixed-length finite-state machine RLL encoders enabling efficient transmit signal construction and soft-demapping at the receiver. Moreover, we propose a soft-output equalizer, which approximates maximum a posteriori RLL symbol detection. We evaluate the system performance in terms of peak-to-average-power ratio, coded block error rate, and a lower bound on the spectral efficiency (SE) w.r.t. a fractional power containment bandwidth. Our numerical results show that SEs of up to 4 bit/s/Hz are achievable with the presented transceiver design.

Rose-Like MoO₃/MoS₂/rGO Low-Temperature Ammonia Sensors Based on Multigas Detection Methods

In order to improve the sensitivity of the pure MoO3 sensor to ammonia and reduce its operating temperature, MoO3/MoS2/rGO was prepared in this work, and the gas-sensitive performance of MoO3/MoS2/rGO was studied. The results of the static gas sensitivity test show that, compared with pure MoO3, MoO3/MoS2/rGO greatly improves the response of the sensor to ammonia at low temperature. Moreover, this article discusses the multigas detection methods by waveform-matched dynamic temperature modulation based on low-temperature gas sensor composites of rose-like MoO3/MoS2/rGO, which is used to solve the shortcoming of poor selectivity of metal–oxide–semiconductor gas sensor. Multigas (including acetone, methanol, ethanol, benzene, toluene, and ammonia) detection methods by waveform-matched dynamic temperature modulation are investigated, in which the experimental results show that the dynamic response curves of the sensor have obvious differences to each gas under different temperature waveform modulations. Temperature modulation waveforms with different periods and variations are investigated, including rectangular wave, triangular wave, and sine wave. This provides a feasible way to improve the selectivity of the sensor. In order to establish and verify the accuracy of the multigas detection model, 100 sets of response curves are selected for each waveform. Finally, the gas-sensing mechanism of gas-sensitive materials to ammonia is analyzed. Preparation of highly sensitive materials, dynamic testing, and gas identification methods can provide the technical basis for the application of gas sensors.

Adaptive filter bank multi-carrier waveform design for joint communication-radar system

We present a transmit power adaptive filter-bank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) waveform for joint communication and radar system. For frequency selective fading channels or frequency sensitive targets, a joint optimization problem is designed by taking both the radar detection performance and communication channel capacity into the objective function under the constraint of limited transmit power. In addition, we derive the power allocation condition where the optimal performance of radar and communication can be achieved simultaneously. Otherwise, the tradeoff between radar and communication performance is necessary by adjusting the weighting factor. The proposed algorithm can realize adaptive transmission where the parameters of the transmitting waveform can be optimally designed for the next pulse by utilizing the measured values of the current signal and the channel state information. Moreover, the feasibility and advantages of FBMC as the radar signal are analyzed from the aspects of average ambiguity function, multipath effect and Doppler shift. Simulation results verify the effectiveness of the proposed scheme. Compared with the equal power allocation, the proposed adaptive transmission power algorithm in this paper shows better performance.

Development of a Non-invasive Deep Brain Stimulator With Precise Positioning and Real-Time Monitoring of Bioimpedance

Methods by which to achieve non-invasive deep brain stimulation via temporally interfering with electric fields have been proposed, but the precision of the positioning of the stimulation and the reliability and stability of the outputs require improvement. In this study, a temporally interfering electrical stimulator was developed based on a neuromodulation technique using the interference modulation waveform produced by several high-frequency electrical stimuli to treat neurodegenerative diseases. The device and auxiliary software constitute a non-invasive neuromodulation system. The technical problems related to the multichannel high-precision output of the device were solved by an analog phase accumulator and a special driving circuit to reduce crosstalk. The function of measuring bioimpedance in real time was integrated into the stimulator to improve effectiveness. Finite element simulation and phantom measurements were performed to find the functional relations among the target coordinates, current ratio, and electrode position in the simplified model. Then, an appropriate approach was proposed to find electrode configurations for desired target locations in a detailed and realistic mouse model. A mouse validation experiment was carried out under the guidance of a simulation, and the reliability and positioning accuracy of temporally interfering electric stimulators were verified. Stimulator improvement and precision positioning solutions promise opportunities for further studies of temporally interfering electrical stimulation.

A Time-Approximation Filter for Direct RF Transmitter

This article presents a highly programmable time-approximation filter (TAF) that can be embedded in a direct RF transmitter architecture. The proposed filter technique approximates the impulse response of a finite impulse response (FIR) filter with a modulated LO waveform, leading to an equivalent RF bandpass filtering during the frequency up-conversion process. The silicon prototype in 65-nm CMOS achieves an error vector magnitude (EVM) performance of -42 dB for a 20-MHz, 256-QAM signal and -43 dB for a 10-MHz, 1024-QAM signal at 2.4 GHz. Due to TAF, the out-of-band noise floor achieves -158 dBc/Hz at a 100-MHz frequency offset.

Processing Continuous Active Sonar Transmissions to Achieve an Arbitrarily Fast Update Rate With Full Instantaneous Bandwidth

A processing technique for continuous active sonar (CAS) that uses linear frequency modulation (LFM) waveforms is presented. LFM CAS employs wideband long-duration LFMs with 100% transmit duty cycle. The received signals are typically processed in sub-bands by forming a sequence of matched-filter replicas that correspond to consecutive segments of the full waveform; this increases the update rate of the sonar at the cost of decreased performance in each sub-band due to the decrease in processing bandwidth and duration (energy). The algorithm presented in this article achieves fast updates by forming a sequence of unique matched-filter replicas through a number of circular shifts to the transmitted LFM, resulting in processing across the frequency jump between pings. This approach allows increased processing duration and bandwidth (up to the full duration/bandwidth of the LFM) at the cost of reduced independence between updates. The circular-shift algorithm is mainly considered in the limit where the full duration and bandwidth of the waveform are exploited to provide partially independent detection and ranging opportunities. The update rate can be arbitrarily chosen independent of processing duration. The algorithm is validated with sonar data from the LCAS15 sea trial.

A variable chirp rate stepped frequency linear frequency modulation waveform designed to approximate wideband non-linear radar waveforms

The non-linear frequency modulation (NLFM) waveform is one of the existing waveforms that can be used in high range resolution radar applications. However, a high sampling frequency and consequently an expensive ADC are required. To overcome this drawback while taking advantage of the features of the NLFM waveform, we suggest approximating the wideband NLFM waveform by a piecewise linear waveform and using it in a stepped frequency (SF) framework. Thus, a variable chirp rate SF-LFM waveform is proposed where SF is combined with a train of LFM pulses having different chirp rates, durations, and bandwidths. In this paper, these parameters are derived from a tangent-based NLFM waveform. At the receiver, a generalized version of the time domain (TD) algorithm is proposed to process the received echoes. Our purpose is to obtain the high range resolution profile (HRRP) whose properties are of the same magnitude orders as those obtained using a tangent-based NLFM waveform. These properties are the peak sidelobe ratio, the integrated sidelobe, and the range resolution. Toward this goal, a multi-objective optimization issue is addressed to deduce the parameters of the proposed waveform by using two types of approaches based on evolutionary algorithms. Their relevance is compared. Our analysis and simulations show that the proposed approaches attain the targeted performance goals with a smaller sampling frequency at the receiver.

NLFM pulse radar for drone detection using predistortion technique

The development of radar technology for the detection of small drones is getting attention of researchers. In this work, the detection of drones using Ku-band radar system has been discussed. We have utilized the advantage of nonlinear frequency modulation (NLFM) waveform for the suppression of range sidelobes. The performance and sensitivity of a radar system can be related with the linearity of system response. Here, we have made an effort to minimize non-linearity in the radar system response by using digital predistortion method. In this method, amplitude weighting coefficients have been calculated based on the received data. We have used FPGA-based transceiver for intermediate frequency (IF) signal generation and data acquisition, along with Ku-band up-down converters. The radar system was first calibrated for desired frequency band using amplitude predistortion method. In this article, experiment results for the detection of single drone and two drones using NLFM pulse signal are presented.

High-Speed Optical Digital-to-Analog Converter Operation of Compact Two-Segment All-Silicon Mach–Zehnder Modulator

An optical digital-to-analog converter (DAC) is a promising solution for the efficient generation of multilevel modulation signals without a high-speed electrical DAC and a large swing linear driver. We report the design and characterization of an all-Si segmented Mach–Zehnder modulator for an optical DAC transmitter. The modulator comprises a forward-biased positive intrinsic negative (PIN) phase shifter integrated with a passive resistance and capacitance (RC) equalizer (PIN-RC) to optimize a tradeoff between modulation efficiency and analog bandwidth. We successfully confirmed an eye diagram of 90-Gbaud NRZ signal owing to a wide 3-dB bandwidth of 43.9 GHz. Additionally, a 70-Gbaud four-level pulse amplitude modulation (PAM4) waveform can be obtained via the optical DAC operation using a lumped segmented modulator because of its broad electro–optic bandwidth and uniform characteristics. A two-segmented modulator has a compact footprint of 300 μm × 600 μm. Error-free performances based on the patterns of the PRBS11 of NRZ signals were obtained at 50–70 Gbaud. The bit-error-rates of 60-Gbaud PAM4 and 70-Gbaud PAM4 were less than the 7% hard and 25.5% soft decision forward error correction limits, respectively. The optical DAC transmitter using an all-Si segmented PIN-RC modulator is suitable for next-generation high-speed multilevel transmitters.

Long Range UAS Mission by LPWAN Communication

One of the key challenges for long range Unmanned Aerial Systems (UAS) is the limitation of the communication capability. Many existing communication technics are conventionally adopted in UAS to improve the quality of the communication such as satellite communication, cellular networks, and relay aircrafts. However, the mentioned solutions often incur several drawbacks including costs, complexity, communication delay, or inefficient power consumption. LoRaWAN is one of the recently emerging communication technics used in the Low Power Wide Area Networks (LPWAN) technology. It has a promising potential to improve the coverage of UAS communication, since it can transmit/receive signals below the noise floor in a very long range with very low energy consumption by using the waveform modulation technique called Chirp Spread Spectrum (CSS). In this paper, we show the potential of LPWAN as the supplementary communication in UAS. The experiment results show that LoRaWAN can maintain the communication capability beyond 80 km where the popular RF device, RFD900x, has lost its ability to communicate at this distance.

Detecting Wireless Steganography With Wavelet Analysis

In wireless communications, information is transmitted through a modulated waveform according to the associated modulation technique. However, there has been growing research to transmit information covertly by modulating waveforms further while pretending to be a normal transmission. Modulation-based wireless steganography techniques cause malicious information leakage without being aware of it by nearby devices. In this letter, we propose a detection scheme based on wavelet analysis with various well-known wavelets (e.g., Haar, Morlet, Shannon) to distinguish effectively between the primary channel and a channel created from the modulation-based technique. Practical experiments show that the proposed scheme can detect the modulation-based techniques at least with 93.25% accuracy under most circumstances.

Estimation of Modulation Parameters of LPI Radar Using Cyclostationary Method

Low Probability of intercept (LPI) radars work on the principle of low peak-power and wide bandwidth. To achieve this, the LPI radars use special type of modulated waveforms which are difficult to intercept. The main tasks of intercept receivers are to detect, estimate and classify LPI signals even in the presence of high noise. Accurate estimation of the modulation parameters also provides information about threat to radar so that necessary counter measures could be initiated against the enemy radars. In the present work, Cyclo-stationary (CS) method is used to estimate the parameters of Polytime coded LPI signals. CS method is efficient for the analysis of periodic waveforms like LPI signals and finds applications in many fields such as array signal processing, estimation of direction of arrival, signal detection. Cyclic auto correlation function and the spectral correlation density function (SCD) which are the basis for CS analysis are computed for all the four types of polytime codes. Generation of all the four types of Polytime codes and computation of SCD coefficients are carried out using MATLAB. From the contour plot of SCD function, the parameters carrier frequency, bandwidth and code rate are measured. It is assumed that the received signal is not corrupted with any noise. The simulation results are compared with the values available in the literature. The maximum error of estimation is well within ± 6% for all the codes in the proposed method whereas the maximum error reported in the literature is 25.7%. Hence the proposed method is better. Since CS method is sensitive to sampling frequency, the analysis is repeated for three different sampling frequencies and in all cases, the estimation error is less than 6%.

Electro-Optic Intensity Modulation in Fe-Doped KTa0.65Nb0.35O3 Crystals

KTa0.65Nb0.35O3 and Fe-doped KTa0.65Nb0.35O3 crystals were grown by the top-seeded solution growth method (TSSG). Fe ion doping significantly improves the electro-optic properties of cubic KTN crystals. We describe their electro-optic modulation theory and experimental research. The electro-optic modulation waveform deduced by theoretical calculation is basically consistent with the waveform measured in the experiment. We observed the attenuation of light modulation under multiple voltage cycles. The modulation curve of the crystal is inconsistent when the crystal voltage is boosting and bucking. Under the same voltage condition, the higher the incident light power, the faster the modulation depth attenuation. In this experiment, the size of the KTN crystal chip is 6 mm × 5 mm × 2 mm. We obtain the effective electro-optic coefficient as s11 − s12 = 1.34 × 10−15 m2/V2; the half-wave voltage near the Curie temperature is 39 V.

Low-rank enhanced convolutional sparse feature detection for accurate diagnosis of gearbox faults

It is a challenge problem to accurately recognize damage distribution pattern for multi-stage industrial gearboxes in filed, due to entangled relationships between strong interferences/noises and complicate transfer path modulations. In this work, a tailored two-stage strategy (LR-CSL) based on low-rank representation and convolutional sparse learning is proposed. Based on the periodic similarity of focused features, a weighted low-rank stage is firstly utilized to suppress strong interferences and noises, which provides a cornerstone to enhance blind deconvolution methods. Then, a convolutional sparse stage is adopted to mitigate the transfer path modulation by enforcing one nonnegative bounded regularizer, which guarantees the reliable recovery of impulsive source envelopes. Lastly, the damage distribution patterns could be reliably confirmed by directly referring to the recovered source envelopes (rather than modulated waveforms) and gearbox dynamics. Comprehensive health evaluations to one 750 kW wind turbine drivetrain are performed blindly and gear surfaces with multiple weak spalling patterns are recognized accurately. Moreover, the spalling fault evolution process is deduced and maintenance guidances are allocated. Further analysis also confirms the first low-rank stage plays a necessary and important role in boosting LR-CSL’s deconvolution capability. Lastly, quantitative evaluations demonstrate that our LR-CSL method achieves a higher diagnostic accuracy than state-of-the-art fault diagnosis techniques.

Enhanced Fault-Tolerant Model Predictive Current Control for a Five-Phase PM Motor With Continued Modulation

To deal with the single-phase open-circuited fault, an enhanced fault-tolerant model predictive current control with continued modulation is proposed in this article. This method includes reconstructing the postfault vector distribution and adopting a multistep vector selection method. In the reconstruction procedure, the transition vectors are generating to realize standard pulsewidth modulation waveforms. Then, the unreachable area can be filled by creating new synthetic vectors. Finally, the vectors with oversized amplitudes are optimized by using null vectors. In order to cover the full modulation area, a multistep vector selection method is used to determine the phase angle and amplitude of the optimal vector. The phase angle can be determined by defining two cost functions and adopting duty cycle modulation technology. The amplitude of the optimal vector can be optimized by utilizing the duty cycle modulation technology again. The oscillation, due to the back electromotive force, is compensated in each step. A thorough experimental evaluation has been conducted to confirm the effectiveness and superiority of the proposed fault-tolerant method.

Hybrid metamaterials enable multifunctional manipulation of mechanical waves on solid-fluid interfaces

Mechanical waves exhibit complex propagations and waveform transitions on the interfaces of different media. By attaching an ultra-thin layer including local resonators on a solid panel, we demonstrate that this ultra-thin layer contains two control paths for solid and air, manipulating elastic and sound waves on the solid–air interface, respectively. Owing to simultaneously breaking the spatial symmetry of the solid panel and adjusting the boundary impedance of the solid–air interface, the proposed ultra-thin layer combines three operating states that are unique to each of the existing mechanical wave metamaterials. Specifically, we observe the “sound state” for intensely reflecting sound waves at the local anti-resonance, the “elastic state” for completely preventing elastic waves at the local resonance, and the “transition state” for totally converting elastic waves into sound waves at the entire monopole-type resonance. Hence, we denote such an ultra-thin layer as the “hybrid metamaterial.” Our work may broaden the way of designing multifunctional materials and devices for manipulating mechanical waves.

Mathematical Characterization and Simulation of LoRa

LoRa is a recently developed physical layer modulation technique characterized by low power consumption and long range communication capabilities. Due to the organic relevance of these features in the Internet of Things, LoRa has gained significant traction in the contemporary telecom industry. LoRa has been rigorously analyzed with regard to its functionalities and applications. However, due to its proprietary nature, precise descriptions of the underlying modulation waveforms are not publicly available. In this paper, we first derive a mathematical characterization of LoRa with regard to its chirp frequency and phase. Our analysis shows that a single matched filter is sufficient to decode all LoRa data symbols. Further, when the output of the matched filter is sampled at a rate equal to the transmission bandwidth, a constant frequency output is produced, which directly corresponds to the transmitted symbol value. For a visual understanding of LoRa, we present detailed simulations of its waveforms at different stages of the communication pipeline. In particular, the error performance simulation clearly demonstrates that LoRa can receive and decode data packets even when the SNR is below 0 dB.

Partly isolated three‐port DC–DC converter based on impedance network

This study proposed a novel partly isolated three port converter (PITPC) based on a quasi-Z source converter for photovoltaic applications. Compared with the conventional quasi-Z source converter, the proposed DC–DC converter has dual input sources and uses the switched capacitors and coupled inductor techniques, helping the converter to gain a high voltage. To achieve the power flow control, the proposed converter uses only three power switches with low voltage stress and it is developed for hybridising photovoltaic panels, rechargeable batteries and isolated loads. For this purpose, the proposed PITPC can be easily reconfigured into dual-input single-output, single-input dual-output and single-input single-output modes; so it can even operate when the photovoltaic panel fails to provide energy to the load. Moreover, the study thoroughly discusses various converter operating modes and provides explanations and necessary relationships for circuit operations. The study also explains the control strategy as well as the pulse width modulation waveforms for the proposed converter. Simulation results from MATLAB/Simulink examine the proposed topology performance. The experimental results confirm the advantages claimed for the proposed converter; the results also show a well-distributed efficiency curve and a peak of 96.3%.

A 1.45 GHz All-Digital Spread Spectrum Clock Generator in 65nm CMOS for Synchronization-Free SoC Applications

The increase of clock frequency in digital circuits exacerbates the electromagnetic interference (EMI) between devices. Spread-spectrum techniques reduce the electromagnetic noise lowering harmonic peaks of the clock signal by means of frequency modulation. In System-on-Chips (SoCs) another requirement in many applications is the coexistence of both modulated and un-modulated clock domains. In these cases, suitable synchronization systems are used to allow data to cross the boundary between spread and un-spread clock domains. In this paper we present a spread-spectrum clock generator (SSCG) able to provide both spreaded and un-spreaded clocks. The spreaded clock has a specially designed modulation profile, allowing at the same time a seamless synchronization-free interface between spreaded and un-spreaded clock domains and a large EMI reduction. The paper presents the derivation of the new highly discontinuous modulation profile (that allows to achieve an EMI reduction up to 15.8dB) and implementation details of an all-digital SSCG able to provide the developed modulation waveform. A test chip has been fabricated in UMC 65nm CMOS technology, using a novel dual-output digitally controlled delay line. The circuit can generate both spread and un-spread clocks (double output mode) or the spread clock alone (single output mode). Area occupation is 0.102mm2, whereas power consumption is 48.5mW in double output mode and 34mW in single output mode.