Xiaolin Qiao

Real-Valued MUSIC for Efficient Direction Estimation With Arbitrary Array Geometries

Most of the existing methods for direction-of-arrival (DOA) estimation are based on numerical characteristics behind the entire array output covariance matrix (AOCM). Since the AOCM is generally a complex matrix, those approaches require tremendous complex computations accordingly. This paper addresses the problem of DOA estimation with real-valued computations by considering the real part of AOCM (R-AOCM) and the imaginary part of AOCM (I-AOCM) separately. It is shown that the null space of R-AOCM and that of I-AOCM are the same subspace, which coincides with the intersection of the original noise subspace and its conjugate subspace. Using such a mathematical fact, a novel real-valued MUSIC (RV-MUSIC) estimator with a real-valued subspace decomposition on only R-ACOM (or I-AOCM) instead of the entire ACOM is derived. Compared with most state-of-the-art unitary algorithms suitable for only centro-symmetric arrays (CSAs), the proposed technique can be used with arbitrary array geometries. Unlike conventional MUSIC with exhaustive spectral search, RV-MUSIC involves a limited search over only half of the total angular field-of-view with a real-valued noise subspace, and hence reduces the complexity by 75%. Theoretical performance analysis on the mean square error (MSE) and numerical simulations demonstrate that RV-MUSIC shows a very close accuracy to the standard MUSIC.

Studies of the variations of the first Schumann resonance frequency during the solar flare on 7 March 2012

The ELF measurements at the YS station in China during the X5.4 solar flare on 7 March 2012 are examined. The first modal Schumann resonance (SR) frequencies of the horizontal magnetic field components were found to increase by 0.1–0.2 Hz during the X-ray burst. During the enhancement of the proton flux, the first modal frequency of the east-west magnetic field component decreases by approximately 0.6 Hz at most, while the variation in the north-south magnetic field component is less well defined. The mechanisms of the variations are simulated with a finite difference time domain technique by modeling the perturbed conductivity profile in the day-night asymmetric Earth-ionosphere cavity and modeling the global lightning source with the raw flash data measured by satellites. The simulated varying trends of the SR frequencies observed near the ground with the altitudes of the conductivity perturbations are nearly the same as those previously reported and are interpreted by the two characteristic height model first proposed by Greifinger and Greifinger. It is concluded that the SR frequencies increase for enhanced conductivity above the altitude of 60–70 km because of the lowered magnetic height and decrease for enhanced conductivity below this altitude due to the lowered electric height. This finding can explain the opposite behaviors of the SR frequencies during X-ray bursts and strong solar proton events (SPEs). The simulation model in this work proved to be effective, with the simulated shifts in the values of SR frequencies during X-ray bursts and SPEs being close to the practical measurements.

SS-based sketch recognition for graphics of traffic accident

To improve the efficiency of drawing the graphic symbols of the scene of traffic accident, a SS-based sketch recognition technology is introduced into the identification of traffic sketches. While four basic cartography factors, including straight line, polyline, circle and arc, are put forward to partition the intricate sketch into the combination of multi-strokes, according to the basic characteristic of the graphics. Online sketch recognition can reveal latent primitive shapes and show the regularized shape on screen immediately through feature recognition, shape fitting and regularization. After the primitive stroke are grouped according to the spatial relationships, the users intention is caught and suggested through computing their similarity with the predefined templates both in partial structures as well as in overall configuration. Practical application proves the proposed method both effective and efficient.

A Kind of Signal Processing Method for the Polarization Phased Array Radar

This paper discusses a kind of polarization phased array radar system and its signal processing method. The polarization signal processing technology is introduced to improve the detection performance and anti-jamming ability of the radars. In order to achieve the performance of low probability of intercept (LPI) for the transmitted signal, the linear frequency modulation (LFM) is adopted inside each pulse and the frequency coded technology is adopted among pulses. The radar system can received the scatted signal of the target through dual polarization channels simultaneously and the polarization information of the target scatted signal can be obtained. In signal processing, the polarization parameter estimation and polarization detection technology are used. The basic structure of the polarization phased array radar is introduced, and the specific LFM pulse compression and polarization detection method are discussed. The analysis results in this paper can provide a reference for the design of the polarization phased array radar. theory is utilized in the analysis of targets polarization scattering characteristic in the wide-band polarimetric case, a new conception of polarization spectrum is presented and targets signature processing and recognition are investigated on the basis of polarization spectrum. In (5), the relationship between targets scattering energy and the incident polarization is derived on the great circle track on the Poincare Sphere. Considering the wideband measurement condition, the conception of energy spectrum in the polarization domain is defined. On the basis of energy spectrum, the polarization features of five kinds of airplane targets are extracted in the wide-band and polarimetric case, and satisfactory recognition results are achieved. In (6), based on the wideband polarization radar system, the concept of the polarization-frequency stability is defined, and polarization features are extracted in accordance with the dynamic distribution information of the polarization state on the Poincare sphere. On this basis, the identification of five kinds of aircrafts is investigated. The results show that this method to identify airborne targets is very effective. From above, we discuss a kind of dual polarization phased array radar system and proposed a kind of radar transmitted signal waveform, which adopts LFM signal inside each pulse and frequency coded signal among pulses, and polarization information processing technology is used to improve the target detection performance. The proposed signal processing method is helpful to improve the anti-jamming ability of the radar systems.

Design and implementation of an antenna measurement system for the mono-pulse radar

The mono-pulse radars have been widely used in many fields such as target tracking because they have high angle measurement accuracy and good anti-jamming ability. It is important to research, develop and measure the mono-pulse radar antennas. This paper design a kind of mono-pulse antenna measurement system based on turning table, step motor controller, vector network analyzer and the Visual Basic development environment. The antenna measurement system has two channels to acquire and analyze data, then the sum and difference directional pattern of the antenna can be measured fast and accurately. Based on the theorem of the mono-pulse antenna measurement system, this paper introduces the system hardware structure and the software implementation scheme in detail. Finally, some basic practical measurements were done and the experiment measurement results indicate that the system can basically satisfy the design requirements.

A new corner matching algorithm based on gradient

In this paper, a novel corner matching algorithm is presented. Gradient operator in Harris corner detector is directly used to compute the similarity between corners. Then initial matches are obtained. The algorithm is contrasted with normalized cross-correlation. Its computational complexity is reduced and matching speed is improved effectively because this method only adopts the addition and subtraction operations. Experiments on several real images test the matching speed, the matching precision and matching rate of the algorithm. The results demonstrate that the algorithm not only have higher speed but also get higher matching precision and correct matching rate. Even though the stereo image pairs have brightness differences, it still performs rather well.

Acquisition and Processing for the Signal of Miniature Mass Spectrometer

A kind of miniature mass spectrometer is designed. It is portable and can be used for field detecting. Signal acquisition and processing is accomplished to obtain mass spectrum. Mathane and methyl salicylate are tested in this platform. The instrument currently can provide mass/charge range of approximately 10~150, while the RF power is only 0.7W.

A Method for Rapid Matching Based on Second Order Partial Derivative

Our goal is to enhance matching speed which is important for image engineering. Second Partial Derivative operator in Harris corner detector is directly used to compute the similarity between corners. Then initial matches are obtained. The algorithm is contrasted with normalized cross-correlation and method based on horizontal and vertical gradient. Its computational complexity is reduced and matching speed is improved effectively because this method only adopts the addition and subtraction operations. Experiments on several real images test the matching speed, the matching precision and matching rate of the algorithm. The results demonstrate that the algorithm not only have higher speed but also get higher matching precision and correct matching rate. Even though the stereo image pairs have brightness differences, it still performs rather well.

An improved polarization and DOA estimation algorithm

In order to reduce the computation complexity during the multi-dimension iterative search of the MUSIC algorithm used to estimate the polarization and DOA of incident signal, an improved algorithm for estimating the polarization and DOA is proposed based on a polarization sensitive uniform array. Firstly, the polarization and DOA of the incident signal are coarsely estimated by a beam forming method based on FFT operation, then the traditional MUSIC algorithm is adapted to get the multi-dimension iterative search. By this method, the searching area for the multi-dimension full space is reduced to a smaller size, and the computation complexity is effectively reduced. The availability of the algorithm has been verified by the simulation.

Joint DOA and polarization estimation for unequal power sources based on reconstructed noise subspace

In most literature about joint direction of arrival (DOA) and polarization estimation, the case that sources possess different power levels is seldom discussed. However, this case exists widely in practical applications, especially in passive radar systems. In this paper, we propose a joint DOA and polarization estimation method for unequal power sources based on the reconstructed noise subspace. The invariance property of noise subspace (IPNS) to power of sources has been proved an effective method to estimate DOA of unequal power sources. We develop the IPNS method for joint DOA and polarization estimation based on a dual polarized array. Moreover, we propose an improved IPNS method based on the reconstructed noise subspace, which has higher resolution probability than the IPNS method. It is theoretically proved that the IPNS to power of sources is still valid when the eigenvalues of the noise subspace are changed artificially. Simulation results show that the resolution probability of the proposed method is enhanced compared with the methods based on the IPNS and the polarimetric multiple signal classification (MUSIC) method. Meanwhile, the proposed method has approximately the same estimation accuracy as the IPNS method for the weak source.