Pseudo-random Modulation Research Articles

Digital pseudo-random modulation: a key to EMI reduction in EVS boost converters

Digital pseudo-random modulation: a key to EMI reduction in EVS boost converters

Sub-Nyquist SAR Imaging and Error Correction Via an Optimization-Based Algorithm.

Sub-Nyquist synthetic aperture radar (SAR) based on pseudo-random time-space modulation has been proposed to increase the swath width while preserving the azimuthal resolution. Due to the sub-Nyquist sampling, the scene can be recovered by an optimization-based algorithm. However, these methods suffer from some issues, e.g., manually tuning difficulty and the pre-definition of optimization parameters, and a low signal-noise ratio (SNR) resistance. To address these issues, a reweighted optimization algorithm, named pseudo-ℒ0-norm optimization algorithm, is proposed for the sub-Nyquist SAR system in this paper. A modified regularization model is first built by applying the scene prior information to nearly acquire the number of nonzero elements based on Bayesian estimation, and then this model is solved by the Cauchy-Newton method. Additionally, an error correction method combined with our proposed pseudo-ℒ0-norm optimization algorithm is also present to eliminate defocusing in the motion-induced model. Finally, experiments with simulated signals and strip-map TerraSAR-X images are carried out to demonstrate the effectiveness and superiority of our proposed algorithm.

3.05 kW, 13.7 GHz linewidth fiber amplifier based on PRBS phase modulation for SBS suppression

In this paper, we establish a multi-stage fiber amplifier with pseudo-random binary sequence (PRBS) phase modulation. The stimulated Brillouin gain spectra of the main amplifier with both the unmodulated and pseudo-random binary sequence phase modulated configuration are measured (with corresponding output power), and the stimulated Brillouin scattering (SBS) threshold is investigated experimentally and theoretically. The pseudo-random binary sequence phase modulation parameters are optimized by theoretical simulation. With a two-stage preamplifier chain and a counter-pumping main amplifier stage, a maximum 3.05 kW output power with a slope efficiency of 85.9% is obtained experimentally. The central wavelength of the fiber amplifier is 1050 nm, associated with a full-width at half-maximum linewidth of 13.7 GHz. The stimulated Brillouin scattering reflectivity is below 0.01% at 3.05 kW at 13.7 GHz, which indicates that stimulated Brillouin scattering can be suppressed efficiently at this power and linewidth level.

Pseudorandom modulation continuous-wave narrowband sodium temperature and wind lidar

Abstract. We report the first pseudorandom modulation continuous-wave (PMCW) narrowband sodium temperature and wind lidar developed at the University of Science and Technology of China (USTC). The laser system uses a 1178 nm diode seed laser and a fiber Raman amplifier with a fiber-coupled acousto-optic frequency shifter (AOFS) to generate a narrowband 589.158 nm light with an output power of 1.5 W at three frequencies of v0, v+, and v−. Based on an innovative technique and algorithm, the main beam and the residual beam modulated by electro-optic modulator (EOM) with M pseudorandom sequence code (M-code) are separately directed to the vertical and eastward directions. The three-frequency light is designed in timing with the multiple-period 127-bit M-code groups. The uncertainties of the temperature and wind with the vertical and temporal resolutions of 1 km and 30 min under clear-sky conditions are estimated to be 5.0 K and 10 m s−1, respectively, at the sodium peak. The temperature and wind results are in good agreement with those observed by satellite and nearby ground-based meteor radar, demonstrating the reliability of the PMCW narrowband sodium lidar system for measuring the mesopause region's temperature and wind.

Pseudo-random time modulation technique for neutron diffraction instruments on compact accelerator-driven neutron sources

Time modulation methods are routinely used on neutron scattering time-of-flight instruments, which exploit the time structure of neutron pulses for energy determination. In the past, complex time modulation methods were proposed, either to maximize the neutron flux which can be used, or to increase the energy resolution of the measurements. In this article, we explore the possibilities offered by such methods and in particular random modulation using statistical choppers to improve the performances of the DIoGENE scattering instrument installed around the IPHI-neutron CANS source at Saclay. We conclude that when the source is operated in continuous mode, the implementation of a statistical chopper is very efficient to perform either metallurgical studies such as strain scanning or phase transition studies. Random modulation techniques may be easily and efficiently implemented because the high capacity of modern computers enables high-speed data processing from large surface pixelated detectors.

A 2 kW, 8 GHz-Linewidth Yb-Doped Polarization-Maintained Fiber Laser with Quasi-Flat-Top Pseudo Random Binary Sequence Phase Modulation for SBS Suppression.

We demonstrated a narrow-linewidth high-power Yb-doped polarization-maintaining (PM) fiber laser with near-diffraction-limited beam. The laser system consisted of a phase-modulated single-frequency seed source and four-stage amplifiers in the master oscillator power amplifier configuration. A quasi-flat-top pseudo random binary sequence (PRBS) phase-modulated single-frequency laser with a linewidth of 8 GHz was injected into the amplifiers for suppressing stimulated Brillouin scattering. The quasi-flat-top PRBS signal was readily generated from the conventional PRBS signal. The maximum output power was 2.01 kW with polarization extinction ratio (PER) of ~15 dB. The beam quality (M2) was less than 1.3 over the power scaling range.

High-density and broad band optical frequency combs generated by pseudo-random phase modulation of optically injected gain-switched semiconductor lasers

We have demonstrated optical frequency combs (OFCs) featuring low and continuously tunable line spacing in the kilohertz range. The OFCs are generated by pulsed gain-switching of optically injected commercial semiconductor lasers emitting at around 1.55 μm. After generation, the OFCs are efficiently densified by pseudo-random-binary-sequence phase modulation. The case of an OFC generated by gain-switching at a repetition rate of 1 GHz has been numerically and experimentally analyzed and the conditions for optimal densification have been found. In this case, the comb has been densified by a factor of 2047 and exhibits a 90 GHz flat and broad spectrum consisting of more than 184,000 spectral lines, separated 488 kHz. Although this densification factor is not the largest that can be achieved with the method, it is more than 100 times larger than previously reported factors for gain-switching OFCs. These results open prospects for the use of potentially integrable gain-switching OFCs in applications requiring sub-megahertz line spacing.

Network authentication by close-loop synchronized chaotic lasers

We numerically study a new hardware method for network authentication, using a pair of chaotic lasers subject to the same optical injection from a third chaotic laser, in a close-loop configuration. One laser is in the secure environment, the other is in the unsecure environment, and if their parameters are matched (i.e., they are ‘twins’), in suitable operating conditions they synchronize and generate the same pseudo-random amplitude modulation. Access to the secure environment is authorized only if the two responses are found equal. As in other schemes based on Physical Unclonable Functions (PUFs), security relies on unavoidable small differences between nominally identical but physically separate devices: due to the strong sensitivity of chaos to laser parameter dispersion, finding a suitable laser to synchronize is a very difficult task for the Adversary, while the laser of the Authorized user can be selected as a twin of the one in the secure environment.

Shaping of converter interference for error rate reduction in PLC based smart metering systems

Smart metering systems often utilize Power Line Communication (PLC) for bidirectional data exchange between smart energy meters and data concentrators. Electromagnetic interference generated by power electronic converters have been found as a main cause of communication errors in PLC data transmission. In this paper novel, modified pseudo-random pulse width modulation technique was developed to significantly reduce PLC frame error rate caused by interference generated by power electronic converters. Moreover, cyber–physical system has been presented as a case study providing high flexibility in controlling the switching rate of change of the modulation. As a general contribution, in the paper has been proposed the concept of electromagnetic interference noise shaping to broaden the possibility of preventing and mitigating non-compatibility scenarios between power electronic converters and telecommunications devices. The experimental results might be useful for system integrators involved in assurance of electromagnetic compatibility of power electronic interfaces and PLC based smart metering systems.

APPLICATION OF DETERMINATED NOISE IN A RADIO COMMUNICATION SYSTEM WITH DIGITAL MODULATION

The article describes a communication system with digital pseudo-random modulation. The system is one of the variants of spread spectrum radio communication systems. This communication system uses deterministic noise as the spreading sequence. The noise immunity of the considered communication system can be changed by scaling the spreading factor — the length of the modulation symbol. By increasing the spreading factor, not only an increase in the noise immunity of the system is achieved, but also the possibility of separating subscribers simultaneously operating in a common frequency band. It has been established that for communication systems with digital pseudo-random modulation, the length of the modulation symbol (the value of the spreading factor) and the number of subscribers to be separated are related by a quadratic dependence.

A proposal of structure and control overcoming conducted electromagnetic interference in a buck converter

This paper describes modelling a step-down chopper designed for a photovoltaic application to study its performance of electromagnetic compatibility (EMC) in conducted mode. The EMC measurements attended at this stage have shown that the buck converter is a harmful device for its electromagnetic environment. Indeed, the fast-switching operation leads to higher levels of conducted and radiated electromagnetic interference (EMI) and subsequently facilitates the electromagnetic coupling with the surrounding environment. In this sense, we present a new proposal of structure and control based on a combination of two techniques, namely pseudo-random modulation and soft switching, thus minimizing the conducted electromagnetic emissions at the source. The usefulness of this new strategy, evaluated through a comparative study, lies in its efficiency compared to the classical PWM method, allowing both to reduce the rise of current and voltage gradients and spread the electromagnetic spectrum over a wide frequency range. The simulation results prove that a significant gain in EMC has been reached.

Impact of Pseudo-Random Modulation on Measured Conducted EMI

This paper demonstrates that using conventional frequency scanning methods for the evaluation of conducted electromagnetic interference generated by DC/DC converters can give misleading results when pseudo-random modulation is used as part of the converter control scheme. The paper therefore proposes that the resolution bandwidth of the super heterodyne EMI test receiver used for measurements and the dwell time should be adjusted to match the control parameters of the random modulation scheme. The use of different values for resolution bandwidth and dwell time is demonstrated and measurements for random and fixed modulation schemes are compared.

Effective Brillouin Gain Spectra Broadening for SBS Suppression Based on Pseudo Random Bit Sequence Phase Modulation in Fiber System

We describe stimulated Brillouin scattering process in a fiber system with light field phase modulated by lowpass filtered and amplified pseudo random bit sequence (PRBS) using localized nonfluctuating source model. The effective Brillouin gain spectra and the ratio of normalized Stimulated Brillouin Scattering (SBS) threshold to RMS optical linewidth is used to characterize the SBS suppression capability of the PRBS phase modulation. The normalized effective Brillouin gain spectra for different modulation parameters are calculated to exhibit the Brillouin gain broadening process. Based on the theoretical model, we find that the SBS threshold reaches a maximum for the ratio of cutoff frequency to clock rate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r_c</i> = 0.53 and RMS modulation depth <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k_rms</i> = 0.55 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</i> for PRBS9. An effective Brillouin gain spectrum measurement setup is established, and the theoretical predictions are verified by the experiment.

A 1.2-Mpixel Indirect Time-of-Flight Image Sensor With 4-Tap 3.5-μm Pixels for Peak Current Mitigation and Multi-User Interference Cancellation

A 1.2-Mpixel indirect time-of-flight (ToF) CMOS image sensor is presented to lower peak current and to cancel out multi-user interference. The proposed 4-tap 3.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> demodulation pixel is optimally designed to improve quantum efficiency (QE) and demodulation contrast (DC). A new “multiple-interleaving” scheme is proposed to reduce the peak current and self-compensate fixed-pattern phase noise (FPPN) with the minimal side effect of DC imbalance. To cancel out interference from the other ToF sensors, a multi-user interference cancellation (MUIC) scheme based on pseudorandom modulation is adopted. From the measurement results, we achieve a high QE of 38% at 940 nm and a high DC of 96% and 80% at 100- and 200-MHz modulation frequencies, respectively. With the superior pixel performance, the depth noise of <0.92% and <0.3% is achieved at the full and 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 binning modes, respectively. The multiple-interleaving scheme suppresses the peak current to less than 0.9 A and removes the column FPPN with constant DC for the whole pixel array. The proposed MUIC proves that at least two interferers can be successfully rejected. The sensor chip is fabricated in a two-stack process with 65 nm for the top die and 65 nm for the bottom die.

Pseudo-random modulation continuous-wave lidar for the measurements of mesopause region sodium density.

The sodium fluorescence lidar utilizes a 589 nm narrowband pulse laser system to measure mesopause region atomic sodium density, atmospheric temperature, and wind. However, this system is complicated and unstable. The continuous-wave (CW) sodium laser system can achieve ultra-narrow bandwidth, all-solid-state, and small compact size, as such it is extremely valuable for mobile, aircraft, and space-borne applications. In this study, we developed the first pseudo-random modulated CW (PMCW) sodium lidar by using an electro-optic modulated narrowband 589 nm CW laser with an output power of ∼1.2W. A pseudorandom M-sequence-code with a length of 127 is used to achieve altitude information by modulating laser and then decoding photon signals. Also, a biaxial structure with 9 m separation between the optical axes of the transmitter and receiver is designed to suppress the strong near-ground signals, which are crucial for improving the signal-to-noise ratio (SNR) of the PMCW lidar system. Nighttime measurements on December 2-4, 2019 show that the SNR at sodium layer peak is more than 10, corresponding to a statistical uncertainty of less than 10% in sodium density with temporal and spatial resolutions of 5 min and 1.05 km respectively. The comparison of vertical profiles of sodium density simultaneously observed by PMCW lidar and collocated pulse lidar shows good agreement.

Оценка соотношения между длиной коррелятора и числом абонентов в системе связи с цифровой псевдослучайной модуляцией

This article examines one of the options for implementing a communication system with pseudo-random digital modulation. For such systems the spreading factor (the signal base) is an important parameter. This work contains the results of operability study for the system in multi-user radio channel. During numerical simulation it was established how the correlator length depends on the number of users simultaneously working in the common frequency band. It is shown that this dependence has a quadratic character.

Blind parameter estimation of pseudo-random binary code-linear frequency modulation signal based on Duffing oscillator at low SNR* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61973037 and 61673066).

Conventional parameter estimation methods for pseudo-random binary code-linear frequency modulation (PRBC-LFM) signals require prior knowledge, are computationally complex, and exhibit poor performance at low signal-to-noise ratios (SNRs). To overcome these problems, a blind parameter estimation method based on a Duffing oscillator array is proposed. A new relationship formula among the state of the Duffing oscillator, the pseudo-random sequence of the PRBC-LFM signal, and the frequency difference between the PRBC-LFM signal and the periodic driving force signal of the Duffing oscillator is derived, providing the theoretical basis for blind parameter estimation. Methods based on amplitude method, short-time Fourier transform method, and power spectrum entropy method are used to binarize the output of the Duffing oscillator array, and their performance is compared. The pseudo-random sequence is estimated using Duffing oscillator array synchronization, and the carrier frequency parameters are obtained by the relational expressions and characteristics of the difference frequency. Simulation results show that this blind estimation method overcomes limitations in prior knowledge and maintains good parameter estimation performance up to an SNR of –35 dB.

Binary-Sequence Frequency Hopping Communication Method Based on Pseudo-Random Linear Frequency Modulation

To improve the signal detection performance of binary-sequence frequency hopping communication when the complementary channel is jammed, a binary-sequence frequency hopping communication system based on pseudo-random liner frequency modulation (LFM) is proposed. The transmitting end uses the chirp signal to carry out the in-band spread spectrum of the binary-sequence frequency hopping signal, and then sends it out through the radio frequency front end. At the receiving end, the received signal is dehopped and processed by fractional Fourier transform. The source information is obtained by sampling decision. Firstly, a binary-sequence frequency hopping system model based on pseudo-random LFM is constructed. Secondly, the bit error rate expression of anti-partial band jamming and follower jamming under the Rice channel is derived. The results show that this method has at least 5 dB performance gain than binary sequence frequency hopping for different parameter settings under partial band jamming and follower jamming, and the anti-jamming performance is significantly better than the conventional frequency hopping communication.

Time and phase synchronization in communication system with a digital pseudo-random modulation

The paper is concerned a model of a digital communication system where the samples of white Gaussian noise with zero mean and dispersion σ2are used as a modulated (carrier) low-frequency signal. Methods of the digital-phase modulation are used in a system for transmission of information message. The communication technology reminds CDMA (Code Division Multiple Access). However, a key of feature of this system is that digital samples of white Gaussian noise are used to increase the spectrum of the information message instead of traditional Walsh-Hadamard binary sequences. In this system the repeat period of the pseudo-random sequence values is specified by the parameter and can be equal to the time (duration) of several information symbols contrast to CDMA, in which the duration of repetition period equals to the duration of modulating symbol. On the one hand, the solution allows you to increase the confidentiality of the transmitted message and more evenly expand its frequency spectrum as compared with the existing of CDMA methods. On the other hand, scientists face two significant scientific tasks that make the work meaningful. First, it is necessary to ensure the synchronous operation of pseudo-random sequence generators in the receiving and transmitting devices. Secondly, it is necessary to define a phase shift amount of the frequency-change oscillator in receiving device. Both problems are the result of the asynchronous starting of the receiver. A control signal is used to solve these problems in the radio communication system which is transmitted simultaneously with an information message. So the result of modulator work is the sum of both information and control modulated signals. The proposed methods and algorithms provide the coherent signal processing with the digital pseudorandom modulation in the receive path of communication channel. The paper is a course of early research studies and it contains a detailed mathematical description of modulation and demodulation signals in the communication system with the digital pseudorandom modulation. The numerical model of the system is described in MatLab language. All numerical experiments were carryout in a mathematical computing system of MatLab.

A Highly Sensitive Deep-Sea In-Situ Turbidity Sensor With Spectrum Optimization Modulation-Demodulation Method

This paper focuses on the design and development of a high sensitivity, low-power consumption deep-sea in-situ turbidity sensor with low-cost electronic design. A pseudo-random sequence modulation is applied to the amplitude measurement of the light diffuse radiation for the first time. This method can improve the detection sensitivity of turbidity sensors without increasing LED light intensity or building complex optical path structures in deep-sea application scenarios. The stability and anti-interference ability of the sensor has also been improved. To meet field requirements of deep-sea and long term detection, we also designed a light-scattering path and watertight mechanical structure. The limit of detection of the sensor was improved to 0.0036 FTU with a concentration range of 0 to 20 FTU and an R-square of 0.9991. The sensor has low power consumption with a supply current of 18.9 mA in operation mode and 25.4 μA in sleep mode. The bottom lander experiments in South China Sea indicated that the sensors successfully completed in-situ measurement tasks and can detect small changes in turbidity. The maximum dive depth reaches 3,413 meters. Thus, the experimental results show that the specifications of our turbidity sensor are comparable to those of commercial in-situ turbidity sensor products at these turbidity levels. The results also show that the PRS modulation method can be applied to weak optical signal detection with different optical principles.