GNSS array receiver faced with overloaded interferences:anti-jamming performance and the incident directions of interferences

Anti-jamming solutions based on antenna arrays enhance the anti-jamming ability and the robustness of global navigation satellite system(GNSS)receiver remarkably.However,the performance of the receiver will deteriorate significantly in the overloaded interferences scenario.We define the overloaded interferences scenario as where the number of interferences is more than or equal to the number of antenna arrays elements.In this paper,the effect mechanism of interferences with different incident directions is found by studying the anti-jamming performance of the adaptive space filter.The theoretical analysis and conclusions,which are first validated through numerical examples,reveal the relationships between the optimal weight vector and the eigenvectors of the input signal autocorrelation matrix,the relationships between the interference cancellation ratio(ICR),the signal to interference and noise power ratio(SINR)of the adaptive space filter output and the number of interferences,the eigenvalues of the input signal autocorrelation matrix.In addition,two simulation experiments are utilized to further corroborate the theoretical findings through soft anti-jamming receiver.The simulation results match well with the theoretical analysis results,thus validating the effect mechanism of overloaded interferences.The simulation results show that,for a four elements circular array,the performance difference is up to 19 dB with different incident directions of interferences.Anti-jamming performance evaluation and jamming deployment optimization can obtain more accurate and efficient results by using the conclusions.

High-order extended coprime array design for direction of arrival estimation

Nonuniform linear arrays,such as coprime array and nested array,have received great attentions because of the increased degrees of freedom(DOFs)and weakened mutual coupling.In this paper,inspired by the existing coprime array,we propose a high-order extended coprime array(HoECA)for improved direction of arrival(DOA)estimation.We first derive the closed-form expressions for the range of consecutive lags.Then,by changing the inter-element spacing of a uniform linear array(ULA),three cases are proposed and discussed.It is indicated that the HoECA can obtain the largest number of consecutive lags when the spacing takes the maximum value.Finally,by comparing it with the other sparse arrays,the optimized HoECA enjoys a larger number of consecutive lags with mitigating mutual coupling.Simulation results are shown to evaluate the superiority of HoECA over the others in terms of DOF,mutual coupling leakage and estimation accuracy.

Reconstruction of time series with missing value using 2D representation-based denoising autoencoder

Time series analysis is a key technology for medical diagnosis,weather forecasting and financial prediction systems.However,missing data frequently occur during data recording,posing a great challenge to data mining tasks.In this study,we propose a novel time series data representation-based denoising autoencoder(DAE)for the reconstruction of missing values.Two data representation methods,namely,recurrence plot(RP)and Gramian angular field(GAF),are used to transform the raw time series to a 2D matrix for establishing the temporal correlations between different time intervals and extracting the structural patterns from the time series.Then an improved DAE is proposed to reconstruct the missing values from the 2D representation of time series.A comprehensive comparison is conducted amongst the different representations on standard datasets.Results show that the 2D representations have a lower reconstruction error than the raw time series,and the RP representation provides the best outcome.This work provides useful insights into the better reconstruction of missing values in time series analysis to considerably improve the reliability of timevarying system.

Radiation pattern analyses of circular aperture antenna to generate radio orbital angular momentum

圆形口径天线近来被认为是在毫米波频段产生具有高功率电磁轨道角动量的自然方式之一。但是,目前的研究并没有给出该种天线的辐射特性分析。本文从理论角度推导了产生轨道角动量的圆形口径天线的辐射特性,并通过仿真实验验证了理论结果的准确性。正交横电模(TE)和横磁模(TM)激励的圆形口径天线的仿真实验表明,TE_(g1)可以产生纯净g–1模态的轨道角动量,更适合在实际应用中使用。本文对该类天线的分析有助于毫米波电磁波涡旋的产生的研究和分析。

Range resolution and sampling frequency trade-off for GPS passive radar

In a global positioning system(GPS)passive radar,a high resolution requires a high sampling frequency,which increases the computational load.Balancing the computational load and the range resolution is challenging.This paper presents a method to trade off the range resolution and the computational load by experimentally determining the optimal sampling frequency through an analysis of multiple sets of GPS satellite data at different sampling frequencies.The test data are used to construct a range resolution-sampling frequency trade-off model using least-squares estimation.The theoretical analysis shows that the experimental data are the best fit using smoothing and nthorder derivative splines.Using field GPS C/A code signal-based GPS radar,the trade-off between the optimal sampling frequency is determined to be in the 20461.25–24553.5 kHz range,which supports a resolution of 43–48 m.Compared with the conventional method,the CPU time is reduced by approximately 50%.

Research on Modulation Signal Denoising Method Based on Improved Variational Mode Decomposition

In order to further analyze the micro-motion modulation signals generated by rotating components and extract micro-motion features,a modulation signal denoising algorithm based on improved variational mode decomposition(VMD)is proposed.To improve the time-frequency performance,this method decomposes the data into narrowband signals and analyzes the internal energy and frequency variations within the signal.Genetic algorithms are used to adaptively optimize the mode number and bandwidth control parameters in the process of VMD.This approach aims to obtain the optimal parameter combination and perform mode decomposition on the micro-motion modulation signal.The optimal mode number and quadratic penalty factor for VMD are determined.Based on the optimal values of the mode number and quadratic penalty factor,the original signal is decomposed using VMD,resulting in optimal mode number intrinsic mode function(IMF)components.The effective modes are then reconstructed with the denoised modes,achieving signal denoising.Through experimental data verification,the proposed algorithm demonstrates effective denoising of modulation signals.In simulation data validation,the algorithm achieves the highest signal-to-noise ratio(SNR)and exhibits the best performance.

Digital Channelization Technology for HF Communication Base on Fast Filter Bank

Channelization typically realized by digital filter banks is an important topic in high frequency(HF) communication and software defined radios(SDR) areas. Channelization has a rigorous requirement for the characteristic of frequency response, e.g., steep transitional band and sharp decay. To address this issue, we investigated the feasibility and implementation of applying fast filter bank(FFB) in channelization in this paper. We analyzed the butterfly structure of FFB similar with fast Fourier transform(FFT), in which prototype sub-filters are cascaded to achieve a low complexity. Hence, it is suitable for designing filter bank with steep transitional band and sharp decay in stop-band. Moreover, we designed a pipelined structure of FFB to achieve a balance between area and performance. Design example shows that FFB has lower computational complexity compared with the other filter banks.

A hypersonic target coherent integration detection algorithm based on Doppler feedback

The traversal search of multi-dimensional parameter during the process of hypersonic target echo signal coherent integration,leads to the problem of large amounts of calculation and poor real-time performance.In view of these problems,a modified polynomial Radon-polynomial Fourier transform(MPRPFT)hypersonic target coherent integration detection algorithm based on Doppler feedback is proposed in this paper.Firstly,the Doppler estimation value of the target is obtained by using the target point information obtained by subsequent non-coherent integration detection.Then,the feedback adjustment of the coherent integration process is performed by using the acquired target Doppler estimation value.Finally,the coherent integration is completed after adjusting the search interval of compensation.The simulation results show that the algorithm can effectively reduce the computational complexity and improve the real-time performance on the basis of the effective coherent integration of hypersonic target echo signals.

UAV flight strategy algorithm based on dynamic programming

Unmanned aerial vehicles(UAVs) may play an important role in data collection and offloading in vast areas deploying wireless sensor networks, and the UAV’s action strategy has a vital influence on achieving applicability and computational complexity. Dynamic programming(DP) has a good application in the path planning of UAV, but there are problems in the applicability of special terrain environment and the complexity of the algorithm.Based on the analysis of DP, this paper proposes a hierarchical directional DP(DDP) algorithm based on direction determination and hierarchical model. We compare our methods with Q-learning and DP algorithm by experiments, and the results show that our method can improve the terrain applicability, meanwhile greatly reduce the computational complexity.

Multiple interferences suppression with space-polarization null-decoupling for polarimetric array

The adaptive digital beamforming technique in the space-polarization domain suppresses the interference with forming the coupling nulls of space and polarization domain.When there is the interference in mainlobe,it will cause serious mainlobe distortion,that the target detection suffers from.To overcome this problem and make radar cope with the complex multiple interferences scenarios,we propose a multiple mainlobe and/or sidelobe interferences suppression method for dual polarization array radar.Specifically,the proposed method consists of a signal preprocessing based on the proposed angle estimation with degree of polarization(DoP),and a filtering criterion based on the proposed linear constraint.The signal preprocessing provides the accurate estimated parameters of the interference,which contributes to the criterion for null-decoupling in the space-polarization domain of mainlobe.The proposed method can reduce the mainlobe distortion in the space-polarization domain while suppressing the multiple mainlobe and/or sidelobe interferences.The effectiveness of the proposed method is verified by simulations.

Fast density peak-based clustering algorithm for multiple extended target tracking

The key challenge of the extended target probability hypothesis density (ET-PHD) filter is to reduce the computational complexity by using a subset to approximate the full set of partitions. In this paper, the influence for the tracking results of different partitions is analyzed, and the form of the most informative partition is obtained. Then, a fast density peak-based clustering (FDPC) partitioning algorithm is applied to the measurement set partitioning. Since only one partition of the measurement set is used, the ET-PHD filter based on FDPC partitioning has lower computational complexity than the other ET-PHD filters. As FDPC partitioning is able to remove the spatially close clutter-generated measurements, the ET-PHD filter based on FDPC partitioning has good tracking performance in the scenario with more clutter-generated measurements. The simulation results show that the proposed algorithm can get the most informative partition and obviously reduce computational burden without losing tracking performance. As the number of clutter-generated measurements increased, the ET-PHD filter based on FDPC partitioning has better tracking performance than other ET-PHD filters. The FDPC algorithm will play an important role in the engineering realization of the multiple extended target tracking filter.

Memristor-based vector neural network architecture

Vector neural network(VNN)is one of the most important methods to process interval data.However,the VNN,which contains a great number of multiply-accumulate(MAC)operations,often adopts pure numerical calculation method,and thus is difficult to be miniaturized for the embedded applications.In this paper,we propose a memristor based vector-type backpropagation(MVTBP)architecture which utilizes memristive arrays to accelerate the MAC operations of interval data.Owing to the unique brain-like synaptic characteristics of memristive devices,e.g.,small size,low power consumption,and high integration density,the proposed architecture can be implemented with low area and power consumption cost and easily applied to embedded systems.The simulation results indicate that the proposed architecture has better identification performance and noise tolerance.When the device precision is 6 bits and the error deviation level(EDL)is 20%,the proposed architecture can achieve an identification rate,which is about 92%higher than that for interval-value testing sample and 81%higher than that for scalar-value testing sample.

A Strategy for Loading Oblique Photogrammetry Models and Multilayer Basemap Data

With the development of drone technology and oblique photogrammetry technology, the acquisition of oblique photogrammetry models and basemap becomes more and more convenient and quickly. The increase in the number of basemap leads to excessively redundant basemap tiles requests in 3D GIS when loading oblique photogrammetry models, which slows down the system. Aiming at improving the speed of running system, this paper proposes a dynamic strategy for loading basemap tiles. Different from existing 3D GIS which loading oblique photogrammetry models and basemap tiles inde-pendently, this strategy dynamically loads basemap tiles depending on different height of view and the range of loaded oblique photogrammetry models. We achieve dynamic loading of basemap tiles by predetermining whether the basemap tiles will be covered by the oblique photogrammetry models. The experimental results show that this strategy can greatly reduce the num-ber of redundant requests from the client to the server while ensuring the user’s visual requirements for the oblique photogrammetric model.

Analysis of GPS P(Y) signal power enhancement based on the observations with a semi-codeless receiver

The Global Position System(GPS)satellites of Block IIR-M and later versions can turn on the signal power enhancement if needed.In recent years,this power enhancement has been triggered several times when the U.S force was involved in local conflicts,which was observed by the monitoring receivers at International GNSS Service(IGS)/international GNSS Monitoring and Assessment System(iGMAS)stations or the high-gain antennas at monitoring ground stations.The specific power enhancement magnitudes with these two observation methods are different.The observations of L1/L2 P(Y)power with a high-gain antenna are accurate,while the observations at IGS/iGMAS stations contain biases.This paper analyses the reasons for the observation biases with monitoring receivers at IGS/iGMAS stations and proposes a method verifying the accurate relation between the observed carrier-to-noise ratio(C/N_(0))data and the real power enhancement magnitudes.When the power enhancement event happens,the observed L1/L2 P(Y)C/N_(0) data at IGS/iGMAS stations can be corrected using the model proposed in this paper.In the analysis,this paper concludes that the power of L1P(Y)increases by about 4.3–5.3 dB and the power of L2P(Y)by about 4.6–5.2 dB in power enhancement events,which matches the designed capability of GPS satellites as well.The results are also verified by the data of high-gain antennas.

Electromagnetic protection strategy using adaptive energy selective mechanism

Electromagnetic spaces face growing threats from both naturally occurring and artificial electromagnetic pulses;however,the current protection methodologies are still far from practical needs.To address this issue,we propose an electromagnetic protection strategy that makes use of an adaptive energy selective mechanism.This strategy,carried out using electromag-netic metamaterials,provides in-band protection to electronic equipment with a high tolerance threshold and fast response.We propose several approaches to further enhance the protective performance of electromagnetic metamaterials.These include reconfigurable designs based on digital circuits and deep learning algorithms,as well as the adoption of nanoscale field-controlled devices made of two-dimensional(2D)phase transition materials and nanoelectromechanical systems.Our study can not only lead to a comprehensive protection sy stem with superior compatibility,but also offer reliable support for maintaining electromagnetic spatial security.

Convenient noncooperative speckle-correlation imaging method

For speckle-correlation-based scattering imaging,an iris is generally used next to the diffuser to magnify the speckle size and enhance the speckle contrast,which limits the light flux and makes the setup cooperative.Here,we experimentally demonstrate a non-iris speckle-correlation imaging method associated with an image resizing process.The experimental results demonstrate that,by estimating an appropriate resizing factor,our method can achieve high-fidelity noncooperative speckle-correlation imaging by digital resizing of the raw captions or on-chip pixel binning without iris.The method opens a new door for noncooperative high-frame-rate speckle-correlation imaging and benefits scattering imaging for dynamic objects hidden behind opaque barriers.

Wearable CNT/Ti_(3)C_(2)T_(x)MXene/PDMS composite strain sensor with enhanced stability for real-time human healthcare monitoring

Strain sensors with good stability are vital to the development of wearable healthcare monitoring systems.However,the design of strain sensor with both duration stability and environmental stability is still a challenge.In this work,we propose an ultra-stable and washable strain sensor by embedding a coupled composite film of carbon nanotube(CNT)and Ti_(3)C_(2)T_(x) MXene into polydimethylsiloxane(PDMS)matrix.The composite strain sensor with embedded microstructure and uneven surface makes it conformal to skin,while the CNT/MXene sensing layer exhibits a resistance sensitive to strain.This sensor shows reliable responses at different frequencies and with long-term cycling durability(over 1,000 cycles).Meanwhile,the CNT/MXene/PDMS composite strain sensor provides the advantages of superior anti-interference to temperature change and water washing.The results demonstrate less than 10%resistance changes as the temperature rises from-20 to 80℃or after sonication in water for 120 min,respectively.The composite sensor is applied to monitor human joint motions,such as bending of finger,wrist and elbow.Moreover,the simultaneous monitoring of the electrocardiogram(ECG)signal and joint movement while riding a sports bicycle is demonstrated,enabling the great potential of the as-fabricated sensor in real-time human healthcare monitoring.

Maximal admissible mode decision delay in terminal guidance

Mode decision-maker is a critical component in the logic-based Integrated Estimation and Guidance(IEG) system. For the best possible estimation and guidance performance, the mode decision delay of the mode decision-maker should be limited to a range as small as possible. This paper presents a numerical method for computing the maximal admissible mode decision delay that varies with time-to-go. Particular attention has been paid to highly maneuvering target interception in terminal guidance. The results of this research offer useful guidelines for the design of the mode decision-maker in IEG systems.

Pusher:an augmented fuzzer based on the connection between input and comparison operand

Coverage based fuzzing is a widespread vulnerability detection technique,and it has exposed many bugs in many real-world programs.However,its attention is to eliminate the testing on the repeated paths,yet it still employs random mutation to generate inputs,which is blind to penetrate complex comparisons in the program.As a result,the testing coverage is limited.Despite some solution proposals are presented,this problem is still partially solved.This paper argues that random mutation is mainly limited by two challenges,the sizable search space and the lack of a useful feedback to direct the search.Then we present an augmented fuzzing technique by addressing these two challenges.First of all,we point out a black relationship between input contents and comparison operands,which is dubbed connection.Second,we present a novel method to collect the comparison operands during execution,which is leveraged to infer the connections.Based on the connections,the fuzzer can learn about which input byte affects on which comparison instruction to establish a smaller search space.Third,the connection provides a useful feedback to direct the search.We resort to a modern metaheuristic algorithm to satisfy this searching requirement.We developed a prototype Pusher and evaluated its performance on several benchmarks and four real-world programs.The experimental results demonstrate that Pusher works better than some other state-of-the-art fuzzers on bug detection,and can achieve a higher testing coverage.Moreover,we take a detailed statistic about the execution overhead in Pusher,and the results indicate that the execution overhead introduced by our approach is within an acceptable scope.

Performance enhancement for antipodal Vivaldi antenna modulated by a high-permittivity metasurface lens

A metasurface unit is designed operating at 2–20 GHz to enhance the gain and radiation performance of an antipodal Vivaldi antenna(AVA).The unit has a simple structure,stable ultra-wideband performance,high permittivity,and can independently modulate two polarization modes electromagnetic waves.We analyze the current distribution on the unit and extract equivalent characteristic parameters to verify the ability of independent modulation on two polarization modes electromagnetic waves.The designed metasurface unit is integrated into the aperture of the AVA and forms the metasurface lens(ML)for guiding the propagation of electromagnetic waves.Two types of ML are proposed and integrated into the AVA to design antennas Ant1 and Ant2.The modulation effect of the lens on the electromagnetic wave is analyzed from the perspective of electric field amplitude and phase,and the final design is obtained.From the optimized design results,the AVA and the proposed Ant2 are fabricated and measured,and the measurement results are in good agreement with the simulation ones.The impedance bandwidth measured by Ant2 basically covers the 2–18 GHz frequency band.Compared with the conventional AVA,the gain of the proposed Ant2 is increased by 0.6–3.7 d B,the sidelobe level is significantly reduced,and the directivity has also been clearly improved.