Chaotic Pulse Position Modulation Research Articles

Modulated Radio Frequency Stealth Waveforms for Ultra-Wideband Radio Fuzes.

The increasingly complex electromagnetic environment of modern warfare and the proliferation of intelligent jamming threaten to reduce the survival rate of radio fuzes on the battlefield. Radio frequency (RF) stealth technology can fundamentally improve the anti-interception and reconnaissance capabilities of radio fuzes, thereby lessening the probability of them being intercepted, recognized, and jammed by the enemy. In this paper, an RF stealth waveform based on chaotic pulse-position modulation is proposed for ultra-wideband (UWB) radio fuzes. Adding a perturbation signal based on the Tent map ensures that the chaotic sequences have sufficiently long periods despite hardware byte limitations. Measuring the approximate entropy and sequence period shows that the Tent map with the addition of perturbation signals can maintain good randomness under byte constraints, closely approximating the Tent map with ideal precision. Simulations verify that the proposed chaotic mapping used to modulate the pulse position of an ultra-wideband radio fuze signal results in superior detection, anti-interception, and anti-jamming performance.

Numerical analysis of coalescence motion of droplets in oil under CPPM electric field

In this work, the coalescence motion characteristics of two droplets under the chaotic pulse position modulation (CPPM) electric field and the influence of electric field parameters on the coalescence motion of the droplets were studied. The numerical results show that the coalescence motion of the droplets under the action of CPPM electric field is related to the deformation relaxation time. The pulse width mainly affects the droplet movement process, and has little effect on the droplet coalescing time. The electric field strength affects the droplet coalescence efficiency, and the greater the electric field strength, the shorter the droplet coalescing time. This study provides a theoretical basis for the application of CPPM electric field in practice.

Error performance analysis for chaotic pulse width position modulation in free space optical communication system

Abstract In this paper, a pulse time modulation method called chaotic pulse width position modulation (CPWPM) is studied for free space optical communication system. This is a digital modulation technique that combines pulse position modulation and pulse width modulation with chaos. In this scheme, the binary information is carried by both the position and width of the pulses, which are modulated by a chaotic signal. Hence, on a single pulse, two bits of information are encoded, which results in higher bit rates, better privacy, and larger effective bandwidth as compared to chaotic pulse position modulation (CPPM) and chaotic pulse width modulation (CPWM) techniques. Probability of error is investigated for different FSO scenarios, i.e., varying turbulence conditions and link lengths for CPWPM scheme. Finally, the performance of CPWPM-FSO system is compared with a commonly used differential chaos shift keying (DCSK) scheme. CPWPM-FSO system shows comparable results as DCSK-FSO system (for probability of error, P e = 10−4 average signal-to-noise ratio (SNR) required for DCSK and CPWPM scheme is 40 dB and 41 dB, respectively, for same length and system conditions), while data rate is doubled in latter, and this verifies the validity of using CPWPM in FSO communication system.

High anti-interference 3D imaging LIDAR system based on digital chaotic pulse position modulation

High anti-interference 3D imaging LIDAR system based on digital chaotic pulse position modulation

Bifurcation and Entropy Analysis of a Chaotic Spike Oscillator Circuit Based on the S-Switch.

This paper presents a model and experimental study of a chaotic spike oscillator based on a leaky integrate-and-fire (LIF) neuron, which has a switching element with an S-type current-voltage characteristic (S-switch). The oscillator generates spikes of the S-switch in the form of chaotic pulse position modulation driven by the feedback with rate coding instability of LIF neuron. The oscillator model with piecewise function of the S-switch has resistive feedback using a second order filter. The oscillator circuit is built on four operational amplifiers and two field-effect transistors (MOSFETs) that form an S-switch based on a Schmitt trigger, an active RC filter and a matching amplifier. We investigate the bifurcation diagrams of the model and the circuit and calculate the entropy of oscillations. For the analog circuit, the "regular oscillation-chaos" transition is analysed in a series of tests initiated by a step voltage in the matching amplifier. Entropy values are used to estimate the average time for the transition of oscillations to chaos and the degree of signal correlation of the transition mode of different tests. Study results can be applied in various reservoir computing applications, for example, in choosing and configuring the LogNNet network reservoir circuits.

Numerical simulation of dynamic characteristics of droplet in oil under a CPPM electric field

The size of droplets in oil are dynamically changes during demulsification, thereby changing the optimum demulsification electric field frequency. Thus, the constant pulsed electric field cannot meet the requirement of optimum frequency. The variable frequency pulsed electric field can cater to the change in optimum demulsification frequency, and has high demulsification ability. However, the dynamic characteristics of the droplet in oil at the variable frequency pulsed electric field are unclear. Therefore, a chaotic pulse position modulation (CPPM) electric field is considered a type of variable frequency pulsed electric field, where the pulse frequency is chaotic but pulse width and field intensity are constant. The droplet deformation dynamic model under the CPPM electric field is established by applying finite element method. The dynamic and chaotic characteristics of the droplet deformation in oil in this electric field are investigated, and the influence of pulse width and electric field intensity on droplet deformation is discussed. Results show that the deformation of droplet in oil is nonstationary vibration with the action of the CPPM electric field, and its deformation is chaotic vibration. The chaos of droplet deformation decreases with the increase in pulse width, and an optimum pulse width can be found to make the droplet have large deformation ratio and high vibration times. The deformation ratio of droplet can be increased by increasing the electric field intensity, but the droplet are easy to split and the deformation is no longer chaotic at high electric field intensity, and an optimum electric field intensity can be found to make the droplet have large deformation ratio and deformation stability.

FPGA-Based Dual-Pulse Anti-Interference Lidar System Using Digital Chaotic Pulse Position Modulation

We investigated an FPGA-based dual-pulse anti-interference light detection and ranging (LiDAR) system with digital chaotic pulse position modulation (DCPPM). The dual-pulse signal is a periodic pulse pair, in which the first pulse is a periodic pulse, and the second pulse based on DCPPM is a pulse with a random time interval from the first pulse in each period. The real-time generation and detection of the position-modulated dual-pulse are realized by a field-programmable gate array (FPGA). The DCPPM-based dual-pulse lidar system integrates the characteristics of anti-interference, high pulse peak power, and fast measurement. In this letter, the repetition frequency of the dual-pulse signal is 100kHz. There is an initial time interval of 128ns between dual pulses, the step number of random time interval between dual pulses is 0~255, and the step accuracy is 6.4ns. Under a 1.25GSa/s sampling rate of the analog to digital converter (ADC), an accuracy within ±6cm has been obtained. Finally, under 100kHz periodic pulse interference and 100kHz DCPPM-based dual-pulse interference, the probability of correct detection has been counted every 250 measurements (up to 2000 times). The two correct detection probabilities with average values above 99% have been obtained, which are respectively 99.29% and 99.68%. The good anti-interference performance of the proposed lidar system has been verified.

Target Localization and Tracking Using an Ultra-Wideband Chaotic Radar With Wireless Synchronization Command

An ultra-wideband chaotic radar with wireless synchronization command is proposed and experimentally demonstrated for target localization and tracking. This radar uses the wideband chaotic pulse position modulation (CPPM) signal as the probe signal and the radar structure of single-transmitting-dual-receiving. The echo signal scattered from a target is collected by two receivers. The target is located and tracked accurately in two-dimensional space using the signal processing scheme. In particular, the radar receivers can directly generate the CPPM reference signals through a wireless synchronization command, so that the transceivers can be physically separated without cable or optical fiber connection. Experimental results demonstrate the proposed chaotic radar can locate and track the target accurately. A localization error of 11 cm and a detection resolution of 17 cm can be both achieved. Moreover, this radar possesses the excellent immune performance to the external electromagnetic interferences, which makes it suitable in the complex electromagnetic environment caused by the cooperative work of multiple radars.

Performance analysis of spread spectrum techniques for laser remote sensing multiple-input multiple-output systems

Spread spectrum techniques have been implemented in laser remote sensing systems in order to solve the crosstalk problem. The performances of chaotic pulse position modulation (CPPM) as well as orthogonal codes modulation have been compared using correlation analysis and detection probability estimations. Characteristics, such as power efficiency and noise robustness, also have been emphasized. In addition, the experimental results of anticrosstalk and multiple-input multiple-output capabilities of the CPPM have been shown. The results show that the CPPM modulation exhibits excellent performance.

Ultra-Wideband Chaos Life-Detection Radar with Sinusoidal Wave Modulation

We propose and experimentally demonstrate an ultra-wideband (UWB) chaos life-detection radar. The proposed radar transmits a wideband chaotic-pulse-position modulation (CPPM) signal modulated by a single-tone sinusoidal wave. A narrow-band split ring sensor is used to collect the reflected sinusoidal wave, and a lock-in amplifier is utilized to identify frequencies of respiration and heartbeat by detecting the phase change of the sinusoidal echo signal. Meanwhile, human location is realized by correlating the CPPM echo signal with its delayed duplicate and combining the synthetic aperture technology. Experimental results demonstrate that the human target can be located accurately and his vital signs can be detected in a large dynamic range through a 20-cm-thick wall using our radar system. The down-range resolution is 15[Formula: see text]cm, benefiting from the 1-GHz bandwidth of the CPPM signal. The dynamic range for human location is 50[Formula: see text]dB, and the dynamic ranges for heartbeat and respiration detection respectively are 20[Formula: see text]dB and 60[Formula: see text]dB in our radar system. In addition, the bandwidth of the CPPM signal can be adjusted from 620[Formula: see text]MHz to 1.56[Formula: see text]GHz to adapt to different requirements.

Chaos Through-Wall Imaging Radar

We experimentally demonstrate a chaos through-wall imaging radar using ultra-wideband chaotic-pulse-position modulation (CPPM) microwave signal. The CPPM signal based on logistic map with 1-ns pulse width and 1-GHz bandwidth is implemented by a field programmable gate array (FPGA) and then up-converted as the radar transmitting signal. Two-dimensional image of human objects behind obstacles is obtained by correlation method and back projection algorithm. Our experiments successfully perform through-wall imaging for single and multiple human objects through 20-cm thick wall. The down-range resolution of the proposed radar is 15 cm. Furthermore, the anti-jamming properties of the proposed radar in CPPM jamming, linear frequency-modulated jamming, and Gaussian noise jamming environments are demonstrated by electromagnetic simulations using the finite-difference time-domain. The simulation results show the CPPM microwave signal possesses excellent jamming immunity to the noise and radio frequency interference, which makes it perform superbly in multiradar environments.

Ultra-low power anti-crosstalk collision avoidance light detection and ranging using chaotic pulse position modulation approach**Project supported by Tsinghua University Initiative Scientific Research Program, China (Grant No. 2014z21035).

A novel concept of collision avoidance single-photon light detection and ranging (LIDAR) for vehicles has been demonstrated, in which chaotic pulse position modulation is applied on the transmitted laser pulses for robust anti-crosstalk purposes. Besides, single-photon detectors (SPD) and time correlated single photon counting techniques are adapted, to sense the ultra-low power used for the consideration of compact structure and eye safety. Parameters including pulse rate, discrimination threshold, and number of accumulated pulses have been thoroughly analyzed based on the detection requirements, resulting in specified receiver operating characteristics curves. Both simulation and indoor experiments were performed to verify the excellent anti-crosstalk capability of the presented collision avoidance LIDAR despite ultra-low transmitting power.

Laser detection of remote targets applying chaotic pulse position modulation

Chaotic pulse position modulation (CPPM) has been successfully used in robust digital communication for years. We propose to adapt CPPM for laser detection of remote targets to address the issue of noise. Specified in a time-of-flight (TOF) consecutive laser ranging application scenario, the feasibility of laser detection applying CPPM for laser detection is experimentally investigated. The scheme including the adaptive design for laser detection and parameter settings with validation is introduced. Lab-based electrical experiment and a proof-of-concept outdoor TOF experiment are further conducted to verify the feasibility of laser ranging and detection using CPPM through comparison with traditional Lidar detection and other pulse interval patterns. According to experiments and the following analysis, laser ranging using CPPM is feasible and more robust than traditional laser ranging.

Bipolar chaotic pulse position modulation communication system based on cyclic LDPC

To overcome the error propagation and improve the communication efficiency of the chaotic pulse position modulation (CPPM) system, the bipolar chaotic pulse position modulation (BCPPM) communication system is proposed here. In BCPPM, every two-bit data are set as a group. The first bit and the discrete chaotic map determine the position of sent pulse, while the second bit determines the polarity of sent pulse. Each pulse in the channel contains two-bit information, so this scheme improves the communication efficiency. A (255,175) cyclic low-density parity-check code (LDPC) was designed, and its generator matrix and parity check matrix are cycled. Furthermore, the constructed BCPPM communication system is utilized in the cyclic LDPC aiming to mitigate the effect of noise. In the transmitter, it uses the encoder structure of cyclic codes while the min-sum algorithm is deployed to decode in the receiver. The analysis indicates that the proposed system is secure, insensitive to the channel distortion and convenient for multiple access communication. The simulation results show that in the additive white Gaussian noise (AWGN) channel, multipath channel, multiuser model, and hybrid communication environment, the BCPPM system has lower bit error rate (BER) compared with those of the CPPM and chaotic pulse on-off-keying (CPOOK). In addition, using cyclic LDPC codes, the system is more suitable for hardware implementation.

Experimental Study on Conducted EMI Mitigation in SMPS using a Novel Spread Spectrum Technique

Switched mode power supplies (SMPS) are power electronic circuits extensively used in a wide range of applications. High frequency switching operation of SMPS causes electromagnetic emissions and has the potential to interfere with system operation, which in turn has an impact on system performance. This makes electromagnetic compatibility (EMC) an important concern. In this paper, a new and simple spread spectrum technique is proposed by modulating chaotic pulse position modulation (CPPM) and pulse width modulation (PWM). The resulting CPWM is implemented to reduce the conducted EMI in SMPS. The proposed method is found to be effective in reducing conduction EMI. The effectiveness and simplicity of the proposed method on spreading those dominating frequencies is compared to the EMI mitigation technique using an external chaotic generator. Finally, the levels of conductive EMI with standard PWM, CPWM with an external chaos generator and the proposed method are experimentally verified to comply with the CISPR 22A regulations. The results confirm the effectiveness of the proposed method.

An approach for parameter estimation of combined CPPM and LFM radar signal

In this paper, the problem of parameter estimation of the combined radar signal adopting chaotic pulse position modulation (CPPM) and linear frequency modulation (LFM), which can be widely used in electronic countermeasures, is addressed. An approach is proposed to estimate the initial frequency and chirp rate of the combined signal by exploiting the second-order cyclostationarity of the intra-pulse signal. In addition, under the condition of the equal pulse width, the pulse repetition interval (PRI) of the combined signal is predicted using the low-order Volterra adaptive filter. Simulations demonstrate that the proposed cyclic autocorrelation Hough transform (CHT) algorithm is theoretically tolerant to additive white Gaussian noise. When the value of signal noise to ratio (SNR) is less than −4dB, it can still estimate the intra-pulse parameters well. When SNR=−3dB, a good prediction of the PRI sequence can be achieved by the Volterra adaptive filter algorithm, even only 100 training samples.

M×N‐ary chaotic pulse‐width‐position modulation

PurposeThis paper presents and investigates a method named M×N‐ary chaotic pulse‐width‐position modulation (CPWPM) which is based on the combination of M‐ary chaotic pulse‐position modulation (CPPM) and N‐ary chaotic pulse‐width modulation (CPWM) in order to provide a better performance in noise‐affected environments as well as improve significantly bit rate.Design/methodology/approachAnalysis of schemes for modulator and demodulator are presented in detail through describing the schemes of the individual methods and their combination. Theoretical evaluation of bit‐error rate (BER) performance in presence of additive white Gaussian noise (AWGN) is provided. Chaotic behavior with tent map in variation of modulation parameters is also investigated. In order to verify the theoretical analyses, numerical simulations are carried out and their results are reported.FindingsBoth evaluation and simulation results show that when the number of symbols increases, the bit rate is improved significantly but the BER performance is just slightly worse. This makes M×N‐ary CPWPM become an effective method for chaos‐based digital communication.Originality/valueAlthough CPPM, CPWM and M‐ary modulation methods have been described in the literature separately, their combination is presented and investigated for the first time in this paper.

A simple approach of generating CPWM for reducing conducted emission in switched mode power supplies

In this work, the problem of improving the performance of switched mode power supply (SMPS) by reducing the electromagnetic interference (EMI) using simplified chaotic pulse width modulation (CPWM) generation method is addressed. The key is the generation of CPWM by modulating chaotic pulse position modulation (CPPM) and PWM. The advantage of the scheme is the simplicity and the easy implementation in the feedback path of the converter without the need of any huge external chaotic generator circuit. The proposed method is found to be effective in reducing the peak EMI in SMPS. The effectiveness of the proposed method on spreading those dominating frequencies, compared to the conventional PWM scheme is evaluated by spectral analysis. Finally, levels of conductive EMI are experimentally verified to comply with the CISPR 22 regulations.

Improvement of Bit Rate Using M-ary Chaotic Pulse Position Modulation

Recent studies have pointed out that Chaotic Pulse Position Modulation (CPPM) is a very promising method for improving privacy and security in chaos-based digital communication. Especially, CPPM provides better performance than other chaotic modulation methods in noise- and distortion-affected environments. In this paper we present our development of a robust method named M-ary CPPM which is based on the combination of the conventional CPPM and multi-symbol modulation in order to improve the transmission bit rate. The M-ary CPPM signal has a pulse train format in which each pulse is a symbol and the chaotically-varied inter-pulse time interval conveys the binary information of k bits (M = 2k). The analysis and development of modulation and demodulation schemes are presented in detail. Theoretical evaluation of Bit-Error-Rate (BER) performance in the presence of additive white Gaussian noise (AWGN) and the use of AWGN filtering is also provided. The chaotic behavior of the M-ary CPPM is investigated with the variation of modulation parameters. In order to verify the performance of the proposed schemes, numerical simulations were carried out in Simulink and comparison between simulation and theoretical results is reported.

Chaotic Pulse-Position Baseband Modulation for an Ultra-Wideband Transceiver in CMOS

A CMOS impulse radio transceiver that uses chaotic pulse-position modulation for ultra-wideband (UWB) communications is designed. While the conventional direct-sequence spread-spectrum (DSSS) system dither the time delay between impulses by a pseudorandom number generator, chaotic modulation dithering uses a predictable but wideband nonlinear function, resulting in significant improvements in spectral spreading. The nonlinear functions implemented in the transmitter and receiver use a tent map, requiring only a voltage-to-time and time-to-voltage converter. A R-S latch enables the parallel implementation of two consecutive states of the tent map. Due to the predictable nature of the nonlinear mapping functions, receiver synchronization time is achieved in Order (0) time, as opposed to the conventional DSSS correlating receivers. Implemented in a 0.25 μm CMOS technology, the transceiver achieves an average data rate of 25 Mbps and a BER <; 10e-9, while sending 0.4-ns wide UWB baseband impulses.