SIMULATION AND ANALYSIS OF A PASSIVE UPLINK-TRIGGERED LTE JAMMER USING PLL FREQUENCY CONTROL

In the paper the application of nonlinear and non-recursive Newton Type estimation numerical algorithm for voltage and current spectra estimation during off-nominal frequency condition and severe signal distortions is presented. The algorithm is not sensitive to power system frequency changes and voltage and current amplitude distortions. It is an important improvement with regard to the commonly utilized approaches based on e.g. Discrete Fourier transform, or other approaches derived in spectral domain. The unknown frequency is simultaneously measured (estimated) with the spectrum of the input signal. The algorithm is tested using voltages and currents obtained from the ATP-EMTP simulation program, using Simulink model and in laboratory conditions. In the first test, a typical MV network example is used. By this, a motor start and a short circuit followed with the current transformers saturation transients are particularly analyzed. The purpose of Simulink test is to compare the NTA algorithm with FFT. Laboratory test consists of connecting a synchronous generator to the network, when synchronization is not ideal and severe disturbance of generator currents and voltages occur.

While spatial structured light based free space optical communication provides high-bandwidth communication with broad application prospect, severe signal distortion caused by optical scattering from ambient microparticles in the atmosphere can lead to data degradation. A deep-learning-based adaptive demodulator has been demonstrated to resolve the information encoded in the severely distorted channel, but the high generalization ability for different scattering always requires prohibitive costs on data preparation and reiterative training. Here, we demonstrate a meta-learning-based auto-encoder demodulator, which learns from prior theoretical knowledge, and then training with only three realistic samples per class can rectify and recognize transmission distortion. By employing such a demodulator to hybrid vector beams, high fidelity communication can be established, and data costs are reduced when faced with different scattering channels. In a proof-of-principle experiment, an image with 256 gray values is transmitted under severe scattering with an error ratio of less than 0.05%. Our work opens the door to high-fidelity optical communication in random media environments.

The clock signals are required integrity over the system, it is desirable that all clock signals are distributed with a uniform delay. The backward crosstalk among the sections of a serpentine delay line accumulates to appear as a laddering wave in the receiving waveform. This occurrence results in severe signal distortion. The lossy effect of thin-film serpentine delay line has been investigated with both simulation and experiment approaches. The test microstrip ser- pentine line was made on silicon substrate; the TDT measurement results have been verified with those obtained by the SPICE simulation. Due to the effect of the resistive line, the laddering waves in lossy serpentine were depressed.

Beamforming with multiple microphones is essential for Automatic Speech Recognition (ASR) in earbuds, cell phones, and smart speakers. Although fixed delay-and-sum (DAS) beamforming is simple to implement, it only suppresses noise from a fixed direction of arrival (DoA) [1]; hence, it is ineffective in real varying noise conditions. Reference [2] implements ultra-low-power keyword spotting (KWS) with noise suppression, but the lack of an ADC and beamforming limit practical application. On the other hand, adaptive beamforming (ABF) actively adjusts nulls to suppress varying noise sources. Adaptive beamforming with a trained DNN is promising [3] but requires extensive training data and high power consumption and is not applicable for battery-operated systems. Conventional adaptive beamforming [4 – 5] (Fig. 32.5.1) adaptively reduces noise and interference in the output of a fixed DAS beamformer. Although conventional ABF is effective and compact, it is hampered by: 1) high DSP power consumption due to high ADC sampling rate and the need for complex calculations, especially in the blocking matrix (BM); 2) target signal direction errors in DAS cause severe signal distortion; and 3) worst-case input-SNR design causes high ADC and DSP power regardless of actual signal conditions.

An algorithm for adaptive pulse signal shaping is proposed for the tag response signal with large fluctuations of radio frequency identification (RFID) tag test systems, which has not been addressed in the literature for the scenario. To verify the proposed algorithm, an experimental platform implemented with a field programmable gate array (FPGA) is set up based on National Instruments. The experimental results show that the algorithm is sufficient for correcting the RFID tag response pulse signal even for the signal with severe signal distortion.

When cochannel interference covers less than 100% of the spectral band of a signal, that interference can be totally spectrally excised without total excision of the signal. But severe signal distortion can result. When the signal is cyclostationary, some degree of signal restoration can be achieved by exploiting the spectral redundancy exhibited by such signals. For example, perfect reconstruction is theoretically possible for a BPSK signal with 100% excess bandwidth after 75% spectral excision. Several signal and interference scenarios are considered and the degree of signal restoration, after spectral excision, that is attainable using an adaptive FIR frequency-shift filter, is determined by computer simulation.

The frequency variance of antenna characteristics may result in severe signal distortion in an ultra wideband communications system. We identify the antenna parameters important in the context of propagation and channel modelling, and analyse their variation with frequency. The group delay, VSWR, impedance and radiation pattern of omni-directional UWB antennas are studied over a range of frequencies. We propose a spatio-spectral normalisation scheme to isolate the effect of the antenna from the channel, which can be useful in channel measurements. We anticipate that higher SNR can be obtained with the proposed angular compensation technique.

The shape of an ultrasound pulse that is reflected by a specular reflector will be distorted because of differences in the length of the path traveled by the acoustical waves between different points on the transducer surface to different points on the reflector surface. This effect can be studied by calculating the radiation coupling function for the combination of a transducer and a reflector. The calculation is performed with a numerical method, basically a modification of ray models used in the calculation of heat transfer by radiation. The signal distortion can be described as a linear filtering process. Its transfer function elucidates the distortion of an emitted waveform. By way of example, the transfer function is calculated for various positions and diameters of a cylindrical reflector in front of a focused transducer. It appears that severe signal distortions can be expected in practical situations.

Oil debris sensors can provide important machine health information by detecting metallic particles in lubricating oil. However, the debris signal generated by the sensor is often contaminated by background noise, thereby leading to misleading detection results. Though some methods have been proposed to detect particle existence by noise reduction, they often cause severe signal distortion and hence the volume of the debris cannot be accurately estimated. This paper presents an integral enhanced empirical mode decomposition (EMD) and correlated reconstruction (CR) approach to extract particle signature with minimal distortion. The integral transform is used to boost the detectability of the weak signature and suppress the high-frequency noise. EMD with a mode cell thresholding strategy is then adopted to remove the trend components caused by the integral transform and further purify the integral enhanced signal. The trend components of decomposed intrinsic-mode functions (IMFs) are identified and removed using a high-pass filter with variable cutoff frequency. Some of the de-trended IMFs are selected based on a synthesized correlation coefficient to reconstruct the particle signature with minimal distortion. It should be also pointed out that the only pre-specified parameter in the proposed method is the level of de-trending accuracy, and no other parameters are needed to be pre-selected for its execution. The proposed approach is validated using both simulated and experimental data. The results show that the proposed method can effectively extract weak particle signatures from noisy data mixtures.

The backward crosstalk among the sections of a serpentine delay line accumulates to appear as a laddering wave in the receiving waveform. This occurrence results in severe signal distortion and timing skew of the clock signal. The layout of double layer serpentine delay line can reduced crosstalk between lines. The waveform of double layer serpentine delay line has been investigated with simulation approach. The results obtained by the SPICE simulation shown that the laddering waves in double layer serpentine were retarded. Although a laddering wave still exist but the penalty of the delay time incurred by the crosstalk is depressed.

Electroencephalogram (EEG) plays an important role in brain disease diagnosis and research of brain-computer interface (BCI). However, the measurements of EEG are often exposed to strong interference of power line artifact (PLA). Digital notch filters (DNFs) can be applied to remove the PLA effectively, but it also results in severe signal distortions in the time domain. To address this problem, spectrum correction (SC) based methods can be utilized. These methods estimate harmonic parameters of the PLA such that compensation signals are produced to remove the noise. In order to ensure high accuracy during harmonic parameter estimations, a novel approach is proposed in this paper. This novel approach is based on the combination of sparse representation (SR) and SC. It can deeply mine the information of PLA in the frequency domain. Firstly, a ratio-based spectrum correction (RBSC) using rectangular window is employed to make rough estimation of the harmonic parameters of PLA. Secondly, the two spectral line closest to the estimated frequency are calculated. Thirdly, the two spectral lines with high amplitudes can be utilized as input of RBSC to make finer estimations of the harmonic parameters. Finally, a compensation signal, based on the extracted harmonic parameters, is generated to suppress PLA. Numerical simulations and actual EEG signals with PLA were used to evaluate the effectiveness of the improved approach. It is verified that this approach can effectively suppress the PLA without distorting the time-domain waveform of the EEG signal.

A so-called completely automated public Turing test to tell computers and humans apart (CAPTCHA) represents a challenge-response test that is widely used on the Internet to distinguish human users from fraudulent computer programs, often referred to as bots. To enable access for visually impaired users, most Web sites utilize audio CAPTCHAs in addition to a conventional image-based scheme. Recent research has shown that most currently available audio CAPTCHAs are insecure, as they can be broken by means of machine learning at relatively low costs. Moreover, most audio CAPTCHAs suffer from low human success rates that arise from severe signal distortions. This article proposes two different audio CAPTCHA schemes that systematically exploit differences between humans and computers in terms of auditory perception and language understanding, yielding a better trade-off between usability and security as compared to currently available schemes. Furthermore, we provide an elaborate analysis of Google’s prominent reCAPTCHA that serves as a baseline setting when evaluating our proposed CAPTCHA designs.

Generally, wireless systems suffer from Carrier Frequency Offsets (CFO), which results either from the receiver's oscillator's impairments or Doppler shifts. The frequency offset between transmitter and receiver local oscillator is a main drawback of OFDM systems. A frequency drift in the receiver's oscillator would result in a frequency offset in the received signal, this offset consists of two parts: a Fine offset, as a fraction of OFDM subcarrier spacing, and a Coarse offset that is equal to an integer multiple of the subcarrier spacing. Coarse offsets results in two problems; firstly, the modulation symbols are located on the wrong frequency bins, secondly, the pilots used for channel estimation are misplaced leading to a faulty channel estimate and severe signal distortion by the Equalizer. Fine Offsets result in a loss of orthogonality and thus ICI (Inter-Carrier Interference), as the frequency bin of a certain modulation symbol would contain some information about the neighboring symbol bin.

This paper presents a method for determining the probability of rare events, in particular for probability density function (pdf) and bit error rate (BER) estimation. The derivation of the method is based on the presumption that the pdf is a member of a family of distributions very often named as the generalized exponential (GE) class of distributions. Based on high reliability estimations obtained in short simulation/measurement times, the low probably events are estimated accurately by extrapolation. The suggested method can be applied to some distributions that are different from GE distributions, such as noncentral chi-square distributions, to extrapolate to low probability events, with some extrapolation error. It can also be applied to BER estimation. The method is in particular helpful for estimating channels suffering from both severe signal distortion causing undesired intersymbol interference (ISI) of several symbols, and from severe noise. Such conditions prevail, for example, in metro and long haul high-speed optical fiber communication systems. So the method may be implemented in particular in maximum-likelihood sequence estimation (MLSE) optical receivers using nonparametric channel model estimation. A special use of the extrapolation method is explained for practical systems using trellis branch metrics derived from the estimated pdf to decode the transmitted sequence of symbols.

In mobile underwater acoustic (UWA) communications, the Doppler effect causes severe signal distortion, which leads to carrier frequency shift and compresses/broadens the signal length. This situation has a more severe impact on communication performance in the case of low signal-to-noise ratio and variable-speed movement. This paper proposes a non-data-aided Doppler estimation method for M-ary spread spectrum UWA communication systems in mobile scenarios. The receiver uses the spread spectrum codes dedicated to transmitting signals with different frequency offsets as local reference signals. Correlation operations are performed symbol by symbol with the received signal. The decoding and Doppler estimation of the present symbol are achieved by searching the correlation maximum in the code domain and frequency domain. The length of the current symbol is corrected for the next symbol synchronization using the estimated Doppler coefficient. To optimize the process of Doppler estimation and symbol synchronization, a heuristic search method is used. By adjusting the Doppler factor search step size, setting the threshold value, and using the Doppler factor estimation of the previous symbol, the search range can be significantly reduced and the computational complexity decreased. The Fisher-Yates shuffle algorithm is used to traverse the search range to ensure reliability of the results. Simulation results show that enlarging the frequency-domain search step size in some degree does not affect the decoding accuracy. On 15 May 2021, a shallow-water mobile UWA spread spectrum communication experiment was conducted in Weihai, China. The horizontal distance between the transmitter and the receiver is 3.7–4.0 km, and the communication rate is 41.96 bits per second. The transmitting ship moves at a speed of 0–3 m/s, and the bit error rate (BER) is lower than 1e−3, which is better than that of the sliding correlation despreading method with average Doppler compensation.