Inter-pulse Interference Research Articles

Интервально-импульсная модуляция сверхширокополосных хаотических радиоимпульсов: теория и эксперимент

An approach to reduce the negative impact of multipath signal propagation (interpulse interference) in a wireless communication channel has been proposed. Pulse-interval modulation of chaotic radio pulses allows to increase the time interval between pulses without reducing the average bitrate. The possibility of using this method in ultra-wideband microwave channels with multipath propagation is demonstrated. The noise immunity of the AWGN channel has been studied. An experimental implementation of the method is described.

Improved Detection Schemes for Non-coherent Pulse-Position Modulation.

Energy-detection (ED) pulse-position modulation (PPM) receivers exhibit poor performance and low rates. Coherent receivers do not have such problems but their complexity is unacceptable. We propose two detection schemes to increase the performance of non-coherent PPM receivers. Unlike the ED-PPM receiver, the first proposed receiver cubes the absolute value of the received signal before demodulation and achieves a considerable performance gain. This gain is obtained because the absolute-value cubing (AVC) operation reduces the effect of low-SNR samples and increases the effect of high-SNR samples on the decision statistic. To further increase energy efficiency and rate of the non-coherent PPM receivers at almost the same complexity, we use the weighted-transmitted reference (WTR) system instead of the ED-based receiver. The WTR system has adequate robustness to weight coefficients and integration interval variations. To generalize the AVC concept to the WTR-PPM receiver, the reference pulse is first passed through a polarity-invariant squaring (PIS) operation and then is correlated with the data pulses. In this paper, the performance of different receivers employing the binary PPM (BPPM) is investigated at data rates of 2.08 and 9.1 Mbps over in-vehicle channels in the presence of noise, inter-block interference, inter-pulse interference, and inter-symbol interference (ISI). Simulations show that the proposed AVC-BPPM receiver outperforms the ED-based one in the absence of ISI and offers the same performance in the presence of strong ISI, the WTR-BPPM system considerably outperforms the ED-BPPM system (especially at high rates), and the proposed PIS-based WTR-BPPM system considerably outperforms the conventional WTR-BPPM system.

Photonic Generation of 30 GHz Bandwidth Stepped-Frequency Signals for Radar Applications

Wideband microwave signals with high time-frequency linearity for high-resolution radar applications can be optically generated using high-speed electronic waveform generators. Frequency-shifting modulation in an optical cavity provides an attractive approach to generate broadband microwave signals with reduced complexity requiring only MHz-level electronics. However, the in-loop signal instability and inter-pulse interference usually cause amplitude fluctuations, leading to limited signal-to-noise ratio and signal bandwidth. Here, we overcome these challenges and demonstrate, for the first time, the photonic generation of 30-GHz-wide stepped-frequency (SF) signals with 100 MHz frequency steps defined by an MHz-level electrical oscillator. We achieved this performance by mitigating the in-loop polarization scrambling and inter-pulse interference using a polarization-maintaining cavity and a high-extinction optical switch. This allows stable consecutive acousto-optic frequency-shifting modulation that significantly improves the signal-to-noise ratio. While achieving a bandwidth surpassing the state-of-the-art demonstrations based on wideband electronics, our approach alleviates the necessity for high-speed signal generators or wideband tunable lasers. To exemplify the utility, we systematically evaluate the signal quality and show its applications in radar imaging compared to those using electrical waveform generators.

Direct-Sequence Ultrasonic Wideband Technology for Intra-Body Communications

This letter proposes a direct-sequence ultrasonic wideband (DS-UsWB) for intra-body communications (IBCs). The DS technology superimposed channel coding is proposed to enable simultaneous multi-node communications in body area networks (BANs). We simulate the channel impulse response model in a human arm by $k$ -Wave, and analyze the chip duration and pulse duration requirements to avoid an inter-symbol interference (ISI) and an inter-pulse interference (IPI) for the DS-UsWB. We then derive the closed-form formulations for data rate and bit error rate (BER) for the DS-UsWB system. Simulation results verify our theoretical analysis, and show that the proposed DS-UsWB system performance is better than the existing ultrasonic wideband (UsWB) system.

Joint Symbol and ToA Estimation for Iterative Transmitted Reference Pulse Cluster UWB System

In the impulse radio ultra-wideband (UWB) literature, a transmitted reference pulse cluster (TRPC)-based non-coherent receiver is proposed to avoid the requirement of a wideband analog delay-line-based receiver. However, the TRPC receiver is effected by inter-pulse interference (IPI) and reduced energy transmission efficiency due to the transmission of reference pulses. In this paper, we propose an iterative TRPC (ITRPC) receiver to improve the performance of a conventional TRPC receiver by considering a blockwise data symbol detection. The ITRPC receiver estimates a new reference signal from the data pulses of the block. The estimated new reference signal in the ITRPC receiver reduces the effect of noise and IPI, which results in the improved performance. Furthermore, the single reference pulse either in a frame or a whole data symbol block is transmitted in the proposed ITRPC structure, which enhances the data rate and energy transmission efficiency of the system. The performance of the ITRPC receiver is analyzed for the binary-phase-shift-keying-modulated UWB system in standard IEEE 802.15.4a channels in the presence of additive white Gaussian noise.

Method of Blind Detection of Ultrawideband Chaotic Radio Pulses on the Background of Interpulse Interference

The problem of blind detection of ultrawideband (UWB) microwave chaotic radio pulses transmitted via a multipath propagation channel has been considered. Based on the results of measurements of the UWB chaotic radio pulse propagation in a real wireless channel, a method of their detection not subject to the influence of interpulse interference is proposed.

Diffraction at a Time Grating in the Dynamical Sauter-Schwinger Process

The Sauter-Schwinger pair creation from the quantum vacuum driven by a sequence of identical time-dependent electric-field pulses is considered. We show the appearance of intra- and inter-pulse interference structures in momentum distributions of produced pairs. These structures are interpreted in terms of the eigenvalues of the time-evolution operator for an arbitrary eigenmode of the fermionic field. We demonstrate a nearly perfect coherence of inter-pulse structures, which is due to nonadiabatic transitions at avoided crossings of the phases defining the time evolution operator. As we also show, this nearly perfect coherent enhancement can be accidentally lost.

Ultra-wideband chaotic radio pulse reception in the case of inter-pulse interference

The problem of receiving ultra-wideband (UWB) chaotic radio pulses of microwave band that passed through a multipath channel is considered. Based on measurements of UWB chaotic radio pulse propagation through a real wireless channel, a method for reception is proposed that is not affected by interpulse interference.

Способ слепого обнаружения сверхширокополосных хаотических радиоимпульсов на фоне межимпульсной интерференции

The blind detection of ultra-wideband (UWB) chaotic radio pulses of microwave band in multipath channel is considered. Based on the measurement results of propagation of UWB chaotic radio pulses in a real wireless channel, a method for their detection is proposed that is not affected by interpulse interference.

Diffraction at a time grating in electron-positron pair creation from the vacuum

The Sauter-Schwinger process of electron-positron pair creation from vacuum, driven by a sequence of time-dependent electric-field pulses, is studied in the framework of quantum-field theoretical approach. As demonstrated by our numerical results, the probability distributions of produced pairs exhibit intra- and inter-pulse interference structures. We show that such structures can be observed beyond the regime of applicability of the WKB theory, which was the focus of earlier investigations. Going beyond these developments, we perform the analysis of the time-evolution operator for an arbitrary eigenmode of the fermionic field. This shows that a perfect coherent enhancement of the inter-pulse peaks can never be reached. A nearly perfect coherence, on the other hand, is due to nonadiabatic transitions at avoided crossings of the phases defining the unitary time evolution. This analysis allows us to determine the conditions under which the nearly perfect coherence is lost.

Interpulse interference of electron emission from an atom irradiated by sinusoidally phase-modulated pulse**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403300), the National Natural Science Foundation of China (Grants Nos. 11774129, 11274141, 11627807, 11604119, and 11534004), and the Jilin Provincial Research Foundation for Basic Research, China (Grant No. 20170101153JC).

We theoretically investigate the photoelectron emission from an atom irradiated by an amplitude modulated sinusoidally phase-modulated pulse through solving the time-dependent Schrödinger equation in the momentum space. By controlling the phase amplitude of the pulse in the frequency domain, it can be found that the photoelectron spectra appear as explicit interference phenomena, which originated from the interference between the directly ionized electron and the ionization of the pre-excited atom from different subpulses.

FTN multicarrier transmission based on tight Gabor frames

A multicarrier signal can be synthesized thanks to a symbol sequence and a Gabor family (i.e., a regularly time–frequency shifted version of a generator pulse). In this article, we consider the case where the signaling density is increased such that inter-pulse interference is unavoidable.Over an additive white Gaussian noise channel, we show that the signal-to-interference-plus-noise ratio is maximized when the transmitter and the receiver use the same tight Gabor frame. What is more, we give practical efficient realization schemes and show how to build tight frames based on usual generators. Theoretical and simulated bit-error probability are given for a non-coded system using quadrature amplitude modulations. Such a characterization is then used to predict the convergence of a coded system using low-density parity-check codes. We also study the robustness of such a system to errors on the received bits in an interference cancellation context.

Analysis of a FTN Multicarrier System: Interference Mitigation Based on Tight Gabor Frames

Cognitive radio applications require flexible waveforms to overcome several challenges such as opportunistic spectrum allocation and white spaces utilization. In this context, multicarrier modulations generalizing traditional cyclic-prefix orthogonal frequency-division multiplexing are particularly justified to fit time-frequency characteristics of the channel while improving spectral efficiency.In our theoretical framework, a multicarrier signal is described as a Gabor family the coefficients of which are the symbols to be transmitted and the generators are the time-frequency shifted pulse shapes to be used. In this article, we consider the case where non-rectangular pulse shapes are used with a signaling density increased such that inter-pulse interference is unavoidable. Such an interference is minimized when the Gabor family used is a tight frame. We show that, in this case, interference can be approximated as an additive Gaussian noise. This allows us to compute theoretical and simulated bit-error-probability for a non-coded system using a quadrature phase-shift keying constellation. Such a characterization is then used in order to predict the convergence of a coded system using low-density parity check codes. We also study the robustness of such a system to errors on the received bits in an interference cancellation context.

Analysis of Ultrawideband Pulse Distortion Due to Lossy Dielectric Walls and Indoor Channel Models

Ultrawideband (UWB) communication channels cause pulse distortion and result in many multipath components arriving at the receiver in clusters. In this paper, the effects of lossy dielectric walls on UWB pulses are analyzed. The frequency-dependent parameters of commonly used building materials are used to analyze the effects of multiple reflections and transmissions, material distortion, and interpulse interference on the UWB pulse waveform. The possibility of polarization-dependent distortion is discussed. Various thicknesses of walls and angles of incidence are considered. The distortion due to each effect is quantified in terms of maximum correlation coefficients (MCCs). The overall effect of the wall is modeled as a tapped-delay-line filter based on the MCC. The results are used to specify the multicluster structure of UWB channel models for indoor communication.

Weighted Symbol Decision for Transmitted Reference Impulse Radio Ultra-Wideband Receiver by Modifying Hadamard Matrix

The UWB technique is employed in this study to exclude unusual multipath components by introducing a modified Hadamard matrix. Within the concept of this approach, IPI is totally removed and the S/N is improved. The successful UWB developments were always challenged by some external factors such as noise, interference and wrong multipath components. The challenges were treated by several researchers and, in many occasions, success was achieved in improving the data rate. The basic objectives of the improvement include removing the inter-pulse interference, distinguishing the wrong multipath components and to achieve high accuracy. Transmitted reference impulse radio ultra-wideband is only one of these techniques where it is aimed to have better detection and estimation. The analogue signals are digitalized -a crucial step that significantly pushed transmitted reference impulse radio ultra-wide to a new frontier. The basic element of this study is to digitalize the output quantities of integrable data by using analogue-to-digital convertor. The other element of this study is to modify the Hadamard matrix in transmitter and receiver to achieve total removal of inter-pulse interference. As a result, the estimation and the decision were enhanced and, on other side, a reduction in signal-to-noise ratio by amount ranges from 7.12% to about 14.42% at the receiver compared to the previous modification (modified hoped single delay). Other achievements were performed by targeting inter-pulse interference total removal and the wrong multipath error was altered which led to high accuracy, better information and less simple error rate.

Continuous spectra in high-harmonic generation driven by multicycle laser pulses

We present observations of the emission of XUV continua in the 20-37 eV region by high harmonic generation (HHG) with $4$-$7\ \mathrm{fs}$ pulses focused onto a Kr gas jet. The underlying mechanism relies on coherent control of the relative delays and phases between individually generated attosecond pulse, achievable by adjusting the chirp of the driving pulses and the interaction geometry. Under adequate negative chirp and phase matching conditions, the resulting interpulse interference yields a continuum XUV spectrum, which is due to both microscopic and macroscopic (propagation) contributions. This technique opens the route for modifying the phase of individual attosecond pulses and for the coherent synthesis of XUV continua from multicycle driving laser pulses without the need of an isolated attosecond burst.

Method for Bandwidth Efficiency Increasing of M-ary PPM Transmitted-Reference UWB Communication Systems

One of the main drawbacks of conventional transmitted reference (TR) ultra-wideband systems is the fact that time delay between the reference and the data pulse has to be at least equal to channel delay spread, in order to avoid inter-pulse interference (IPI). This requirement drastically limits the achievable data rate of conventional TR systems based on M-ary pulse position modulation (PPM). In this paper, the new method for M-ary TR PPM scheme bandwidth efficiency increasing is proposed. In the proposed method the orthogonal codes are used such that only the pulses which can cause IPI are coded. Usage of such type of coding allows the reduction of time delay between the reference and the data pulse, whereas IPI is avoided. The proposed method achieves higher bandwidth efficiency than the conventional TR PPM method for the similar BEP performance level. Furthermore, the results show that an additional increase in bandwidth efficiency can be achieved by using higher modulation levels. Additionally, the analysis on tradeoffs between the BEP performance, bandwidth reduction and system costs is given in this paper.

Optimal Receiver Scheme for Transmitted-Reference Ultra-Wideband System in Coal Mine

An average Transmitted-Reference (TR) receiver scheme based on orthogonal codes is proposed for improving the bit error rate (BER) performance and the transmitting rate of Ultra-wideband (UWB) TR receiver systems in coal mine. Orthogonal codes are used for modulating the reference pulses and the data pulses in each frame of every bit. Since the orthogonality of the two codes, the inter-pulse interference (IPI) is greatly reduced. Then the decoding reference pulses and the data pulses are averaged in a frame, which decreases the noise in the reference pulses and the data pulses. Finally, I demonstrate this optimal receiver scheme by the simulation in the coal mine roadway ultra-wideband channel model. Detailed simulation experiments are presented to validate the effectiveness of this proposed method. The experimental results show that this method can not only efficiently reduce the noise interference in receiving signals, but also can provide higher transmission rate, which make UWB signal receiving in coal mines more accurately. Index Terms—Coal mine, Ultra-wideband, Transmitted- Reference receiver, bit error rate

All-optical DAC using counter-propagating optical and electrical pulses in a Mach-Zehnder modulator.

A novel method of converting binary-level electrical pulses into multi-level optical pulses using only a conventional traveling-wave optical modulator is presented. The method provides low inter-pulse interference due to the counter-propagating pulses, low amplitude noise, and a timing jitter determined chiefly by the quality of the optical pulse source. The method only requires one electrical drive per modulator and provides low-jitter variable-amplitude optical pulses that are suitable for shaping into a wide variety of modulation formats using a programmable optical filter.

Visualization of high-order dispersion for compression of few-cycle pulses

We present a visually intuitive method for higher-order dispersion compensation based on multi-photon interpulse interference pulse scans. The dispersion values obtained from these scans are fed back as a correction to an acousto-optical programmable dispersive filter to compensate residual higher-order dispersions up to fifth order. This method is applied to the dispersion management of a non-collinear optical parametric chirped-pulse amplifier. A grism-pair stretcher is designed based on a global dispersion balance which provides a large stretching factor and supports a spectral bandwidth of up to 320 nm. It is implemented in a two-stage three-pass non-collinear optical parametric chirped-pulse amplifier and stretches 6-fs seed pulses to about 80 ps from 700 to 1,000 nm. The amplified pulses are compressed by material dispersion. Pulses of less than 10-fs duration with a pulse energy of 125 μJ are obtained at 20-kHz repetition rate.