Function Of Pulse Shape Research Articles

Hybrid mmWave MIMO Systems Under Hardware Impairments and Beam Squint: Channel Model and Dictionary Learning-Aided Configuration

Low overhead channel estimation based on compressive sensing (CS) has been widely investigated for hybrid wideband millimeter wave (mmWave) multiple-input multiple-output (MIMO) systems. The channel sparsifying dictionaries used in prior work are built from ideal array response vectors evaluated on discrete angles of arrival/departure. In addition, these dictionaries are assumed to be the same for all subcarriers, without considering the impacts of hardware impairments and beam squint. In this manuscript, we derive a general channel and signal model that explicitly incorporates the impacts of hardware impairments, practical pulse shaping functions, and beam squint, overcoming the limitations of mmWave MIMO channel and signal models commonly used in previous work. Then, we propose a dictionary learning (DL) algorithm to obtain the sparsifying dictionaries embedding hardware impairments, by considering the effect of beam squint without introducing it into the learning process. We also design a novel CS channel estimation algorithm under beam squint and hardware impairments, where the channel structures at different subcarriers are exploited to enable channel parameter estimation with low complexity and high accuracy. Numerical results demonstrate the effectiveness of the proposed DL and channel estimation strategy when applied to realistic mmWave channels.

Enhancing the Anti-Dispersion Capability of the AO-OFDM System via a Well-Designed Optical Filter at the Transmitter

This paper proposes a novel method to improve the anti-dispersion ability of the all-optical orthogonal frequency division multiplexing (AO-OFDM) system. By replacing the Sinc-shaped filter with a Gauss-shaped filter for sub-carrier generation and inserting a cyclic prefix (CP), the impact of dispersion on the system can be significantly mitigated. Formula derivation and numerical analysis of the pulse-shaping function of the AO-OFDM system in the time domain for each cycle indicated that the pulse-shaping function generated by the Gauss-shaped filter was less affected by the dispersion effect than that of the Sinc-shaped filter. Meanwhile, less inter-carrier crosstalk between carriers was also observed. After carrying out system transmission simulations employing these two different filters, we found that the AO-OFDM system based on the Gauss-shaped filter could greatly improve the anti-dispersion ability compared with the system based on a Sinc-shaped filter. When the parameter settings in both schemes were identical, that is, the number of subcarriers was 32 and the power of a single subcarrier was −13 dBm, the bit error rate (BER) of the system based on the proposed Gauss-shaped filter after 60 km SMF transmission was only 1.596 × 10−3, while the BER of the traditional Sinc-shaped filter based system scheme was as high as 8.545 × 10−2.

Time-Dependent Multistate Switching of Topological Antiferromagnetic Order in Mn3Sn

The manipulation of antiferromagnetic order by means of spin-orbit torques opens unprecedented opportunities to exploit the dynamics of antiferromagnets in spintronic devices. In this work, we investigate the current-induced switching of the magnetic octupole vector in the Weyl antiferromagnet Mn$_3$Sn as a function of pulse shape, field, temperature, and time. We find that the switching behavior can be either bistable or tristable depending on the temporal structure of the current pulses. Time-resolved Hall effect measurements reveal that Mn$_3$Sn switching proceeds via a two-step demagnetization-remagnetization process caused by self-heating over a timescale of tens of ns followed by cooling in the presence of spin-orbit torques. Our results shed light on the switching dynamics of Mn$_3$Sn and prove the existence of extrinsic limits on its switching speed.

Pulsed field induced excitation in impurity doped quantum dot: Interplay with Gaussian white noise

Current study strives to realizing the role of Gaussian white noise (GWN) and external pulsed field (PF) on the time-average excitation rate (TAER) of impurity doped quantum dot (QD). The PF is characterized by a pulse shape function which may be continuous or discontinuous with time. In the present study we invoke sinusoidal and triangular shape functions as continuous ones and regular telegraphic and random telegraphic shape functions as discontinuous ones. GWN links with the system additively and multiplicatively. The study emphasizes on analyzing the role of various physical parameters, application of noise, pathway of application of noise and the attributes of the PF (amplitude, phase, shape and the number of pulses) in designing the TAER profiles. The TAER profiles come out to be comprising of features like persistent rise, persistent fall, maximization (useful for attaining large nonlinear optical response), minimization and saturation (the dynamic freezing).

On the Effect of Compactness of Pulse Shaping Function on Inter-Symbol Interference

In this letter we theoretically and numerically investigate the effectiveness of a compact pulse in terms of producing less inter-symbol interference (ISI) and thus less symbol error rate (SER). We present theoretical equations to express the signal to interference plus noise ratio (SINR) for different levels of ISI as well as theoretical SER in terms of quantified compactness of the pulse. In a single compact form equation, we expressed the relationship that connects all the aforementioned terms with each other and with the spectral efficiency. A well-studied ‘better-than-raised cosine’ (BTRC) pulse shape in quadrature amplitude modulation (QAM) is considered and the performance are compared with standard pulses such as Gaussian and raised cosine pulse shapes. Performance comparison results are presented showing that the BTRC pulse outperforms the conventional pulses in both SNIR and SER metrics.

On the Connection Between Compactness of Pulse Shaping Function and ISI

This letter investigates the effect of compactness of a pulse shaping filter on the inter-symbol interference (ISI) by presenting a theoretical equation which directly expresses the bit error rate (BER) in terms of quantified compactness of the pulse. We numerically compute time-bandwidth product (TBP) of the considered pulses as the measure of compactness. To compute the TBP, we use four definitions of pulse width (i.e., time duration in time domain and bandwidth in frequency domain) including root mean square (RMS), full width at half maximum (FWHM), 99% energy concentration and - 40 dB bounded energy duration. We show that the standard pulses poses different compactness properties based on the defined TBP and the - 40 dB definition is the most effective definition to study ISI versus TBP. We also propose a new pulse which offers the least TBP based on - 40 dB definition among all standard pulses and show that this pulse outperforms these well-known pulses in terms of BER and bandwidth efficiency.

Probabilistic Modeling of Horizontal Wave-in-Deck Loads on a Square Concrete Deck

AbstractThe square concrete deck is being used as an elevated transition piece in offshore structure but has a large exposure area to extreme waves. This study focused on the horizontal wave-in-deck loads on the square concrete deck. Wave flume tests were carried out to investigate the wave-in-deck loads on a specimen of a square concrete deck. Horizontal wave-in-deck loads on the specimen with ten different structural orientations were measured under three nonlinear regular wave trains. A novel analytical model of the horizontal wave-in-deck loads on the square thick deck was proposed by including both impact maxima and pulse shape function. The temporal development of the resultant horizontal wave-in-deck loads was studied from the measured forces through data post-processing. The effects of structural orientation, inundation depth, and the correlation between the rise and decay time were considered based on the experimental data. The marginal distributions of the impact maxima and rise time for the horizontal wave-in-deck loads on the square deck were investigated, and the joint probability model of impact maxima and rise time was finally developed using Plackett copula. The research provides a useful stochastic model in assessing the wave-in-deck loads on the square concrete deck.

An all-digital frequency tunable IR-UWB transmitter with an approximate 15th derivative Gaussian pulse generator

This work presents a new frequency-tunable, OOK–modulated, impulse-radio ultra-wideband (IR-UWB) transmitter, where approximate 15th derivative Gaussian pulses are produced by a monopulse-synthesis pulse generator. The center frequency of our output UWB pulses can be easily adjusted between 4 and 9 GHz by controlling delay time. Thus, the whole UWB frequency band from 3.1 to 10.6 GHz can be covered and utilized. Since the proposed monopulse-synthesis pulse generator already includes a pulse shaping function, RF bandpass filters are not required, thus realizing the extremely low complexity and small circuit area. The proposed IR-UWB transmitter has been implemented and fabricated in a standard 0.18 μm CMOS 1p6m process. The power supply voltage is 1.8 V and the targeted data rate is 31.25 Mbps. Chip measurement results show that the power spectrum density conforms to the FCC spectrum masks, and the peak-to-peak voltage of output UWB pulses is 56 mV. In addition, the core area of the chip is 0.02 mm2, the measured frequency tuning range is 3.1–10.6 GHz, and the measured energy dissipation is only 12.5 pJ/bit. Compared to the state-of-the-art designs in the literature, the chip area and tunable frequency range are improved by at least 33% and 53%, respectively.

ICI Mitigation in OFDM System Using Negative Peak Augmented Raised Cosine Power Pulse

Orthogonal frequency division multiplexing (OFDM) is a digital modulation technique generally which is utilized in modern wireless applications to support high data rates. The carrier frequency offset (CFO), which models the frequency discrepancy between the transmitter and receiver oscillators, gives rise to inter carrier interference (ICI), along with destroying the orthogonality between the OFDM subcarriers. Thus the alleviation of an ICI power is extremely important in an OFDM system. Pulse shaping functions is a standout amongst the most generally utilized solutions with the end goal of lessening the ICI power. In this paper, an Adaptive pulse shaping filter based on the concept of Negative Peak Augmentation is proposed to mitigate the ICI and to enhance the performance of the OFDM system. The simulation results demonstrate the impact of the proposed pulse shaping function and performance investigation in terms of SIR, SNR and BER is carried out to show the superiority of the proposed pulse shaping function.

Performance Enhancement of 5G OFDM Systems Using Modified Raised Cosine Power Pulse

OFDM is a key modulation technology of current wireless communication systems such as 4G LTE/LTE-A. The fifth generation (5G) of wireless cellular networks is required to support a large variety of services such as extreme mobile broadband (xMBB) and novel machine type communication services. In this new scenario, wave-form shaping plays key role to reduce out-of-band (OOB) radiations. So pulse shaping based orthogonal frequency division multiplexing (OFDM) systems are the most promising proposals for 5G wireless cellular networks. These systems are designed on the success of LTE/LTE-A and many other present wireless cellular systems. In this paper, we have proposed a new pulse shaping window called Modified Raised Cosine Power pulse for N-subcarriers OFDM systems that suppresses OOB radiation and reduces peak to average power ratio (PAPR). It has been observed that the inter-carrier interference, signal to interference noise ratio, bit error rate and complementary cumulative distribution function of the PAPR versus threshold PAPR (PAPR0) performances of the OFDM system with proposed pulse shape filter is far better than all recently proposed pulse shaping function.

Theoretical and Experimental Research on Laser-Induced Damage of Fused Silica Optics Due to Stimulated Brillouin Scattering

The damage behavior of fused silica optics induced by stimulated Brillouin scattering (SBS) was studied theoretically and experimentally based on a coupled-wave theory. The SBS-induced damage mechanism was systematically investigated by analyzing the evolutions of the Stokes-light intensity and induced stress as a function of laser pulse shape, thickness, and surface reflectance of the optics. The results show that the SBS-induced damage often occurs on the front surface of the fused silica optics. The Tophat beam has the most effect on an SBS-induced damage, followed by a focused Gaussian pulse. SBS effect is strongly thickness dependent, which is associated with the gain length. The SBS-induced damage can be efficiently suppressed by decreasing the surface reflection of the optics. Good agreements are obtained between the experimental and theoretical results, which strengthen our understanding of the damage mechanism of fused silica and provide a favorable reference for developing high-power laser systems.

Pair Production Induced by Ultrashort and Ultraintense Laser Pulses in Plasmas

The probability of Schwinger pair production is calculated, which is induced by an ultraintense and ultrashort laser pulse propagating in a plasma. The dependence of the probability on the amplitude of the laser pulse and the frequency of plasmas is analyzed. Particularly, the effect of the pulse duration on the probability is discussed, by introducing a pulse-shape function to describe the temporal shape of the laser pulse. The results show that a laser with shorter pulse is more efficient in pair production. The probability of pair production increases when the order of the duration is comparable to the period of a laser.

Estimation of Symbol Timing in Physical-Layer Network Coding With Arrival Time Differences

Network coding on physical-layer shows much interest due to its well-known ability to double the throughput in relay-aided networks. In an asynchronous PNC system, when the nodes are not equally distant from the relay, the path lengths from the nodes to the relay can vary sufficiently to cause the superimposed waveforms to be evidently offset in time. These arrival time differences, also influenced by the discrepancy of node-clocks, can lead to severe performance degradation and must be estimated in practice. To deal with this problem, a novel symbol timing estimator with baud-rate sampling is proposed in this letter, which is based on the a priori knowledge of the pulse-shaping function. Compared with the known techniques with high oversampling factor, the proposed scheme shows the lower complexity advantage with the unit oversampling factor and better mean square error performance when the excess bandwidth factor of the pulse-shaping function is at 0.3.

Stochastic Theory of the Fission Chamber Current Generated by Non-Poissonian Neutrons

The Campbell theorem, relating the variance of the current of a fission chamber (a “filtered Poisson process“) to the intensity of the detection events and to the detector pulse shape, becomes invalid when the neutrons generating the fission chamber current are not independent. Recently, a formalism was developed by the present authors, by which the variance of the detector current can be calculated for detecting neutrons in a subcritical multiplying system, where the detection events are obviously not independent. In the present paper, the previous formalism, which only accounted for prompt neutrons, is generalized to account also for delayed neutrons. A rigorous probabilistic analysis of the detector current was performed by using the same simple, but realistic detector model as in the previous work. The results of the present analysis made it possible to determine the bias of the traditional Campbelling techniques both qualitatively and quantitatively. The results show that the variance still remains proportional to the detection intensity, and is thus suitable for the monitoring of the mean flux, but the calibration factor between the variance and the detection intensity is an involved function of the detector pulse shape and the subcritical reactivity of the system, which diverges for critical systems.

Indirect-drive ablative Richtmyer Meshkov node scaling

The ablation front Rayleigh Taylor hydroinstability growth dispersion curve for indirect-drive implosions has been shown to be dependent on the Richtmyer Meshkov growth during the first shock transit phase. In this paper, a simplified treatment of the first shock ablative Richtmyer-Meshkov (ARM) growth dispersion curve is used to extract differences in ablation front perturbation growth behavior as function of foot pulse shape and ablator material for comparing the merits of various ICF design option.

Stimulated Emission Enhancement Using Shaped Pulses.

Controlling stimulated emission is of importance because it competes with absorption and fluorescence under intense laser excitation. We performed resonant nonlinear optical spectroscopy measurements using femtosecond pulses shaped by π- or π/2-step phase functions and carried out calculations based on density matrix representation to elucidate the experimental results. In addition, we compared enhancements obtained when using other pulse shaping functions (chirp, third-order dispersion, and a time-delayed probe). The light transmitted through the high optical density solution was dominated by an intense stimulated emission feature that was 14 times greater for shaped pulses than for transform limited pulses. Coherent enhancement depending on the frequency, temporal, and phase characteristics of the shaped pulse is responsible for the experimental observations.

Intense-Field Double Detachment of Electrostatically Bound F(-)(NF3)n Cluster Anions.

The interaction of intense laser pulses with size-selected F(-)(NF3)n clusters is experimentally studied. Intense-field double- and multiple-detachment processes in the isolated atomic F(-) anion and in electrostatically bound F(-)(NF3) dimer and F(-)(NF3)2 trimer systems are directly compared. Both dimer and trimer systems are found to exhibit similar enhancement of the highly nonlinear processes, with respect to the atomic system, as reflected in significantly lower saturation intensities. The dependencies of different product channels as a function of laser peak intensity, polarization ellipticity, and laser pulse shape are presented, indicating an efficient nonrescattering mechanism.

A Windowing Technique for Optimal Time-Frequency Concentration and ACI Rejection in OFDM-Based Systems

In this paper, we introduce a windowing technique, which provides optimal time-frequency containment and maximal adjacent channel interference (ACI) rejection for orthogonal frequency-division multiplexing (OFDM)-based systems. Instead of using a single pulse shape function for all subcarriers, multiple functions are considered in order to maximize the time-frequency containment of the OFDM waveform. The main strategy is to concentrate the spectrum of windowing functions into a given bandwidth while achieving maximum suppression in the out-of-band region. This is achieved by employing prolate-based windowing functions which give optimal spectral concentration for time-limited pulse shapes. The windowing functions are designed per-subcarrier basis in order to exploit available concentration band for each subcarrier. In addition, the proposed concept is considered for the receive filtering in the presence of ACI. It is shown that the optimal spectral concentration property also maximizes ACI rejection for OFDM receivers.

Time-Asymmetric and Subcarrier-Specific Pulse Shaping in OFDM-Based Waveforms

In orthogonal frequency-division multiplexing (OFDM) systems, suppressing the out-of-band (OOB) emission with pulse shaping comes with a price. The expense emerges in designing the transition between consecutive symbols. The price can be either the reduction of spectral efficiency (SE) with symbol extension for better transition or the introduction of intersymbol and intercarrier interference (ISI and ICI) due to reduced cyclic prefix (CP) size. In this paper, we propose a time-asymmetric and per-subcarrier (per-SC) pulse-shaping method to minimize the introduced interference without sacrificing SE and OOB performances. Although time-asymmetric pulse reduces the interference due to shortened CP by exploiting the asymmetry in channel delay profile, it causes spectral growth. Thus, the time asymmetry of the pulse-shaping function is gradually increased for the inner SCs that have wider spectral room to the OOB region. A generalized Kaiser window with adjustable time asymmetry is introduced to the provided framework. Theoretical and simulation results showed that the proposed technique achieves superior BER performance while achieving the same level of OOB suppression of pulse shaping and SE of plain OFDM.

Analytical optimal pulse shapes obtained with the aid of genetic algorithms.

We propose a methodology to design optimal pulses for achieving quantum optimal control on molecular systems. Our approach constrains pulse shapes to linear combinations of a fixed number of experimentally relevant pulse functions. Quantum optimal control is obtained by maximizing a multi-target fitness function using genetic algorithms. As a first application of the methodology, we generated an optimal pulse that successfully maximized the yield on a selected dissociation channel of a diatomic molecule. Our pulse is obtained as a linear combination of linearly chirped pulse functions. Data recorded along the evolution of the genetic algorithm contained important information regarding the interplay between radiative and diabatic processes. We performed a principal component analysis on these data to retrieve the most relevant processes along the optimal path. Our proposed methodology could be useful for performing quantum optimal control on more complex systems by employing a wider variety of pulse shape functions.