Barker Code Research Articles

Airborne sparse flight array SAR 3D imaging based on compressed sensing in frequency domain

In airborne array synthetic aperture radar (SAR), the three-dimensional (3D) imaging performance and cross-track resolution depends on the length of the equivalent array. In this paper, Barker sequence criterion is used for sparse flight sampling of airborne array SAR, in order to obtain high cross-track resolution in as few times of flights as possible. Under each flight, the imaging algorithm of back projection (BP) and the data extraction method based on modified uniformly redundant arrays (MURAs) are utilized to obtain complex 3D image pairs. To solve the side-lobe noise in images, the interferometry between each image pair is implemented, and compressed sensing (CS) reconstruction is adopted in the frequency domain. Furthermore, to restore the geometrical relationship between each flight, the phase information corresponding to negative MURA is compensated on each single-pass image reconstructed by CS. Finally, by coherent accumulation of each complex image, the high resolution in cross-track direction is obtained. Simulations and experiments in X-band verify the availability.

Accurate Estimation of LPI Radar Pulse Train Parameters via Change Point Detection

Estimating the time of arrival (TOA), pulse width (PW), and pulse repetition interval (PRI) is critical for identifying the low probability of intercept (LPI) radar signals as it is common in electronic warfare (EW) to experience a pulse train being received. To determine these parameters, we need to differentiate between pulse and noise in a pulse train. However, separating the LPI radar pulse train into pulse and noise is challenging owing to its characteristics and modulation scheme. Therefore, we propose a method to accurately estimate TOA, PW, and PRI using change point detection, which can effectively classify the pulse train into pulse and noise. The main contributions of this study are as follows. First, a denoising method robust to various modulation schemes is introduced. Second, an algorithm capable of estimating the parameters without considering the threshold calculation is presented. Moreover, most prior studies have entailed parameter estimations for a single pulse. In contrast, we focus on estimating parameters when a pulse train is intercepted and generating superior results even in the signal-to-noise ratio under 0 dB. We present experiments performed on the following eight modulation schemes: linear frequency modulation, Costas, Barker, Frank, P1, P2, P3, and P4 codes. Furthermore, we compare the proposed method with the wavelet-based method, which has received much attention in EW. The results demonstrate that the proposed method outperforms the conventional approaches.

Defect detection of GFRP laminates by barker code modulation excitation infrared thermal imaging

During the preparation and service of GFRP laminates, due to the influence of manufacturing process, it is easy to produce debonding defect. This paper expounds the basic principle and test process of infrared nondestructive testing, which using the barker code modulation of the thermal wave to identify the GFRP laminate debonding defect. Through the establishment of infrared thermal imaging testing system, this paper studies its detection effect on defects with different diameter, depth and diameter-to-depth ratio, processes the image sequence by using principal component analysis (PCA) and discrete Fourier transform (DFT) algorithms, and finally calculates and compares the processed signal-to-noise ratio (SNR). The results show that Barker code modulated thermal wave infrared detection can detect the debonding defects of GFRP laminates. Among them, the detection effect of 13-bit Barker coded modulation excitation is better, and the image processed by DFT has better recognition effect.

DESAIN SIMULASI UNJUK KERJA BARKER CODE PADA KANAL FREQUENCY SELECTIVE FADING

The signal that arrives at the receiving end is the sum of the various transmissions passed by the signal (multipath) which is influenced by the channel so that there is signal interference. Many innovations have been made so that the received signal can have high security, one of which is spread spectrum with a dual access scheme to increase the ability of many spectrum users in a limited number without disturbing one another. This simulation was tested with the aim of spreading the spectrum with different code lengths for the same bit length of information, and observed from the change in the BER value obtained from the MATLAB 2018a simulation results to find out how the barker code performance on the frequency selective fading channel on a single user. The analysis of this research is obtained from the simulation results in the form of a graph that shows the BER value compared to Eb/No. The BER value shown by the barker code performance on the flat fading channel, which is compared based on the existing flat theory, shows the graph trend and the BER value generated from the simulation is close to the theoretical flat BER value. The performance of the barker code on the frequency selective fading channel is carried out by varying the number of multipath components 7, 5, and 3. The simulation results show that multipath 3 is the best with the smallest bit error value compared to multipath 7 and 5. Barker code performance is strongly influenced by the number of multipath components, the more the number of multipath components, the more performance of the barker code bit error, and vice versa.

Multi-band microwave signals generation based on a photonic sampling with a flexible ultra-short pulse source.

We propose and experimentally demonstrate a photonic sampling-enabled multi-band microwave signals generation scheme. The intermediate-frequency input signal is up-converted to high frequency output signals in multiple frequency bands, after being optically sampled by an ultra-short optical pulse train and subsequently being detected by a photodetector (PD). The ultra-short pulse source, realized by using an electro-optic modulation-based time lens with the chirp compensation, can be flexibly adjusted to enhance the performance of multi-band frequency up-conversion. In the experiment, after optimizing the optical ultra-short pulse source with a repetition frequency of 8 GHz, ten phase-coded up-converted microwave signals with a 13-bit Barker code were successfully generated within a frequency range from 7 GHz to 41 GHz. The power fluctuation among the generated microwave signals in multi-band is measured to be 5.9 dB. The experiment results indicate that, our proposed scheme can realize the multi-band up-conversion with a high fidelity.

Polyphase codes for multiplexed acoustic signalling and sensing on pipes

Transmission of acoustic signals between distributed sensor nodes may be useful for status monitoring of elongated structures such as pipelines. In principle, coded signals can be used in an asynchronous multiplexed system, provided the signals are distinguishable. However, multimode effects complicate signal propagation, so any such codes should be short. A search for polyphase code families with properties suitable for acoustic code division multiple access is presented. Algorithms for reduction of search space to allow use of a laptop for code discovery are described. Short codes of base 6 are shown to outperform codes of bases 2, 3, 4 and sets suitable for systems with 2 and 3 users are identified. The codes have similar properties to Barker codes but larger sidelobes. Their use is demonstrated by simulation and experiment at kHz frequencies using an air-filled copper pipe, an electromagnetic acoustic transducer (EMAT) and a microphone designed to excite and detect the mode. Low loss propagation over 25 m is achieved with a 20 kHz carrier. Excellent agreement between experiment and theory is demonstrated, with performance limited by transducer bandwidth.

Development of the Sanya Incoherent Scatter Radar and Preliminary Results

AbstractLed by the Institute of Geology and Geophysics, Chinese Academy of Sciences, we have built a brand‐new modular active digital phased array, with all solid‐state transmission and digital receiving incoherent scatter radar (ISR) in Sanya (18.3°N, 109.6°E), a station in low latitude China called Sanya ISR (SYISR) since 2015. The development of SYISR involved the indoor design and development of key components, an outdoor prototype test, and the production and debugging of the entire array. The unique features of SYISR include a single‐channel directly connected T/R unit and antenna, a radar array monitoring and calibration network, environmental adaptability design and open architecture. The entire radar has 4,096 channels and 5,930 modules in total. All the technical indices, mainly including a >2 MW peak power, a 43 dBi antenna gain and a <120 K noise temperature, either meet or are superior to the designed value through an independent evaluation. Waveforms of single pulse, linear frequency modulation, Barker code, long pulse and alternating code have been implemented to meet multiple purposes. Four observational modes for ionospheric experiments, including zenith stare, perpendicular to geomagnetic field, meridian scan, and all sky scan, have been developed. We have implemented time domain decoding, frequency domain decoding, and statistical inversion methods in calculating the autocorrelation function and power spectra in signal processing. The preliminary experimental results on ionospheric parameters, plasma lines, irregularities and hard targets are reasonable and encouraging, which greatly enhances our confidence in achieving our scientific goals in the future.

Almost perfect sequence modulated multiplexing ion mobility spectrometry.

Multiplexing ion mobility spectrometry with multiple ion injection pulses was used to achieve a high duty cycle and thus improve the signal-to-noise (S/N) ratio while maintaining high resolving power compared with the traditional single-pulse signal averaging method. Historically, an ion mobility spectrum was reconstructed by various multiplexing methods including Fourier transform ion mobility spectrometry (FT-IMS), Hadamard transform ion mobility spectrometry (HT-IMS), and linear frequency modulation correlation ion mobility spectrometry (LFM-CIMS) sequence or Barker code. To achieve an artifact-free multiplexing ion mobility spectrum, an almost perfect sequence (APS) with correlation technique was proposed to modulate the Bradbury-Nielson ion gate and was compared with FT-IMS, HT-IMS, LFM-IMS, and the traditional single-pulse signal averaging method. Experimental results showed that there are no artifact peaks in the APS-IMS spectra except an inverted mirror peak, and the S/N ratio was improved 5-8 times with a repetition time of 40-60 ms, corresponding to the improvement in the duty cycle. With the same duty cycle and similar acquisition time, APS-IMS showed a higher S/N ratio than HT-IMS for its unique autocorrelation response. The APS-IMS technique offered a higher duty cycle and relatively shorter modulation period compared with reported multiplexing methods and is suitable to track rapidly changing signals without losing information and adding extra transformation artifact peaks.

A Novel Methodology for Spectrally Efficient FMCW Radar Systems

In this letter, we present a novel scheme that compresses the transmit bandwidth of frequency modulated continuous wave (FMCW) radar signal by making use of Barker codes and frequency shifts. The proposed system achieves bandwidth compression where the frequency of the signal is modulated over time using one of the Barker code sequences. Therefore, the changes in the slope of the signal are controlled by Barker codes. To avoid ghost targets, small frequency steps are added at the point of discontinuities. The proposed scheme achieves proportionally superior bandwidth compression at a cost of slightly degraded range resolution. The results are validated by implementation of the scheme on hardware and measuring the bandwidth on a spectrum analyzer. Finally, we jointly optimize spectral efficiency and range resolution to determine the optimal length of the Barker sequence. The resulting flexible design is a huge boost to the applicability of existing FMCW radar systems.

Image quality improvement of magneto-acousto-electrical tomography with Barker coded excitation

Magneto-acousto-electrical tomography (MAET) combines the advantages of the high resolution of ultrasound imaging and the high contrast of electrical impedance tomography for imaging the conductivity of tissues. The traditional MAET uses a short pulse as the excitation waveform, and the amplitude of the MAE signal for a single acquisition is very weak. Thus, the multiple-acquisition mode for averaging was adopted to reduce the system noise while significantly increasing the data acquisition time. In this study, a coded-based MAET method was proposed to improve the image quality of MAET. We theoretically derived the principle of the coded-based MAET and analyzed the performance of different pulse compression techniques. The 13-bit Barker code was selected, and phantoms of different shapes and conductivity were used to verify the proposed method experimentally. Finally, in vitro experiment was conducted to investigate the performance of the proposed method in tissue level application. The experimental results show that the proposed method can significantly improve image quality and speed up the imaging time.

Application of pulse compression technique in metal materials cracks detection with LF-EMATs

ABSTRACT To address the problem of low signal-to-noise ratio (SNR) and poor spatial resolution of cracks detection of the angled SV wave electromagnetic acoustic transducer (EMAT), pulse compression technique (PCT) and line-focusing technique are introduced into the angled SV wave EMAT. A finite element (FE) model of the line-focusing (LF) EMAT detection process based on the Barker code excitation was established, and the effects of the design parameters of magnet and meander-line coil (MLC) on the main lobe amplitude and width of the defect echo after pulse compression were analysed. The optimal combination of LF-EMAT design parameters and excitation parameters was obtained, and it was compared with the traditional angled SV wave EMAT and the tone-burst excitation method by experimental measurements. The results shows that compared with angled SV wave EMAT with tone-burst excitation, LF-EMAT can improve the SNR by 14.9 dB with no synchronous average and be processed by PCT. The SNR from LF-EMAT with PCT is10 dB at 1.5 mm lift-off, while the SNR of the angled SV wave EMAT with tone-burst excitation is less than 0 dB at 1 mm lift-off. When the Barker code PCT is applied to the LF-EMAT detection, we can achieve the purpose of increasing EMAT lift-off and reducing the synchronous averages to meet the demand of online, rapid, and high-temperature detection.

Detection and Parameter Estimation Analysis of Binary Shift Keying Signals in High Noise Environments.

In this paper, a new method for detecting and estimating the parameters of a binary phase shift keying (BPSK) signal, based on a cross-correlation function, is proposed. The proposed method consists of two stages. The first stage is used to detect or estimate a signal carrier frequency, and the second stage is used to estimate its pulse width or symbol rate. Firstly, the proposed method is investigated by use of a simulated BPSK signal in the form of Barker Codes 7, 11, and 13 in the MATLAB environment. Based on the simulation results, the functionality of this method is verified using a real-time BPSK signal generated by an E8267C generator. This is described in the second part of this paper. The experimental test results confirm that the proposed method is able to detect and estimate the parameters of all BPSK signals with

Micro-crack defects detection of semiconductor Si-wafers based on Barker code laser infrared thermography

Micro-crack defects are easy to form in the semiconductor Si-wafer surface during the production process, which finally effect the quality of silicon based microelectronic products. In order to ensure the quality and performance of products, it is important and necessary to carry out nondestructive testing (NDT) for Si-wafers. This paper experimentally investigates the performance of the Barker code laser infrared thermography (BCLIT) technique for the semiconductor Si-wafer defect detection, using an optical infrared thermography set-up in transmission method. The thermal wave signal response of the laser to the Barker code modulation waveform is collected by an infrared camera, which was stored as image sequences. Then the detectability was studied according to processed results via the Total Harmonic Distortion (THD) algorithm from obtained image sequence. In addition, linear frequency modulation thermal wave imaging (LFMTWI) technique was used to compare and analyze the performance of BCLIT. Experiments performed on the Si-wafer under the low power density condition indicate that the higher of the excitation power and the wider of the crack width, the better the detection effect. Furthermore, the performance of BCLIT is better than the traditional LFMTWI with all cases in evaluation index result of signal-to-noise ratio (SNR). The research results show that the BCLIT technique significantly improve SNR and defect detectability, and it can be used for the semiconductor Si-wafers micro-crack defects detection even under low power density excitation.

Modified Pulse Sequences Based on Barker Codes

The article considers an approach to the modification of manipulative impulse sequences based on Barker codes. It is proposed to change the structure of the encoded pulses by the duration of the elementary message, taking into account the change in the duty cycle of their repetition while maintaining the total average energy. Numerical relations are obtained that determine the spectral and temporal parameters for a seven-element pulse sequence, with an increase in the pulse repetition rate by two and three times. Numerical values are calculated that determine the ratio of the duration of the peaks of the cross-correlation functions between the modified and canonical forms of pulse sequences. Reasonable estimates are presented that characterize the increase in the resolution of the peaks of the cross-correlation functions by 4.43 times in the transition to the proposed modified structure of the pulse sequence.

Hybrid Coded Excitation of the Torsional Guided Wave Mode T(0,1) for Oil and Gas Pipeline Inspection

Ultrasonic guided wave testing is an essential technique in non-destructive testing for structural integrity of oil and gas pipelines. This technique, based on the pulse-echo method, is often used for the long-range detection of pipelines at any location. However, guided waves suffer from high attenuation when they propagate in attenuative material structures and multiple wave modes due to the excitation, which reduces the power of echo signals and induces corruption caused by coherent noise. In this paper, a developed hybrid coded excitation method that uses the convolution of a Barker code and Golay code pair is proposed and applied for an ultrasonic guided wave testing system to excite the torsional guided wave mode T(0,1) in a steel pipe. The proposed method combines the advantages of these two coding methods and increases the flexibility of code lengths. The performance is evaluated by signal to noise ratio and peak sidelobe level of the processed signal. Both theoretical simulations and experiments have investigated using the proposed codes composed of Barker codes and Golay code pairs of different lengths and combinations. The experimental results show the significant improvement of the signal to noise ratio and the peak sidelobe level due to the proposed hybrid code usage for the excitation of guided waves. The values are further improved to around 32 dB and around −24 dB, respectively. Overall, the proposed hybrid coded method for improving the echo SNR can benefit from guided wave testing to reduce coherent and random noise levels and many other potential applications.

Photonic generation of frequency-tunable biphase and quadriphase coded pulse signals without background interference enabled by vector modulation and balanced detection.

An approach to generating frequency-tunable biphase and quadriphase coded pulse signals without background interference based on a polarization division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM) is presented and demonstrated. Two ternary baseband code sequences are separately encoded into a pair of orthogonal optical carriers by exploiting a polyphase encoder on the basis of the principle of vector modulation, which in turn can be mapped to the phase shifts of the generated phase coded waveforms after the balanced detection. The frequency tunability can also be achieved by controlling the bias voltage of the associated modulator, so that the carrier frequency can be tuned to either fundamental or doubled frequency. Additionally, by designing different phase codes, the generated pulse signals can be conveniently switched between the quadriphase and biphase coding waveforms. The major advantage of the proposed approach is that four phase shifts can be obtained by simply adjusting the polarity of the ternary code sequences, overcoming the power-dependent limitation of the previous work. A proof-of-principle experiment is conducted to assess the feasibility of the proposed approach built on the Barker code and Frank code phase coded pulse signals generation. Experimental results show the phase coded pulse signals at 12 and 24 GHz carrier frequency are well behaved in terms of peak-to-sidelobe ratio (PSR), range-Doppler coupling and Doppler tolerance.

Moon Imaging Technique and Experiments Based on Sanya Incoherent Scatter Radar

This article introduces the experiment design for Moon imaging based on Sanya incoherent scatter radar (SYISR) and algorithm research in data processing. The peak power of SYISR is 2 MW. The transmitted frequency used for Moon imaging experiments is 430 MHz. We conducted Moon imaging experiments using two types of waveforms, 13-bit Barker code, and linear frequency modulation (LFM) chirp. Considering both resolution and signal-to-noise ratio (SNR), the use of an LFM chirp with a bandwidth of 0.3 MHz and a pulsewidth of 2 ms can give higher SNR and resolution for Moon imaging using SYISR. Several key techniques were applied in the experiment design and data processing: 1) for the reliability of the imaging algorithm, the range-Doppler imaging algorithm commonly used in synthetic aperture imaging was applied; 2) to avoid the sidelobe effect of the 13-bit Barker code matched filter, a sidelobe-free filter was used; and 3) to mitigate the problem of “north–south ambiguity,” mosaic imaging of the Doppler northern and southern hemispheres of the nearside of the Moon was adopted. Two types of imaging results are obtained: mosaic images of the northern and southern hemispheres of the Moon and local regional images. The results demonstrate the feasibility and reliability of Moon imaging based on SYISR, which enables potential further lunar geology investigations in the future.

Экспериментальное исследование двумерного подавления помех в активном радаре на базе адаптивной антенной решетки для случая короткой выборки

The paper analyzes an experiment on two-dimensional (in azimuth and elevation) noise suppression in an active radar in the decimeter wavelength range. The radar includes an adaptive antenna array, the canvas of which has a rectangular topology. As jammers, a continuous tone generator is used, as well as a phase-shift keyed signal generator – a Barker code of length 11. In both cases, the interference can be considered narrowband. As a useful signal (reflected from the target), a Barker code of length 11, generated by the simulator, was used. The noise suppression was carried out by the power vector method, as well as by the method of direct inversion of the noise correlation matrix. The case of a short sample when evaluating the correlation matrix is considered separately, as the most interesting for practice in conditions of limited computing resources of digital signal processors. A set of scenarios is considered both in azimuth and in elevation. In all scenarios, there was one interference and one useful signal. For each of them, the estimation of losses in relation to signal-tonoise, the interference suppression coefficient was performed, and the directivity diagrams of the adaptive antenna array were formed. The processing of the experimental data showed the high efficiency of the power vector method. In all scenarios, interference is suppressed almost to the level of thermal noise.

Symbol synchronization method of radio engineering systems using additional Barker code sequences

Symbol synchronization method of radio engineering systems using additional Barker code sequences

Image Quality Improvement of Magneto-Acousto-Electrical Tomography with Barker Coded Excitation

Image Quality Improvement of Magneto-Acousto-Electrical Tomography with Barker Coded Excitation